Internet-administered cognitive behavior therapy for health problems: a systematic review

Cognitive-behavioral interventions are the most extensively researched form of psychological treatment and are increasingly offered through the Internet. Internet-based interventions may save therapist time, reduce waiting-lists, cut traveling time, and reach populations with health problems who can not easily access other more traditional forms of treatments. We conducted a systematic review of twelve randomized controlled or comparative trials. Studies were identified through systematic searches in major bibliographical databases. Three studies focused on patients suffering from pain, three on headache, and six on other health problems. The effects found for Internet interventions targeting pain were comparable to the effects found for face-to-face treatments, and the same was true for interventions aimed at headache. The other interventions also showed some effects, although effects differed across target conditions. Internet-delivered cognitive-behavioral interventions are a promising addition and complement to existing treatments. The Internet will most likely assume a major role in the future delivery of cognitive-behavioral interventions to patients with health problems.
Introduction
Cognitive-behavioral interventions are probably the most extensively researched form of psychological treatment (Butler et al. 2006). Cognitive-behavioral interventions are aimed at challenging negative automatic thoughts and dysfunctional underlying beliefs, and at changing behavioral patterns which are related to the problem being targeted in the therapy. More than 300 published controlled outcome studies, and probably many more, have examined the effects of cognitive-behavioral therapy (CBT) for a wide range of disorders and health problems, ranging from mental health disorders, such as depression (Hollon et al. 2002), anxiety disorders (Barlow 2002), schizophrenia (Pilling et al. 2002), to health conditions such as chronic pain (Morley et al. 1999), sleep problems (Morin et al. 1999), headache (Holroyd 2002), cancer (Moorey and Greer 2002) and many others. Most of these studies have shown that CBT has positive effects on these and several other health conditions. CBT is not only the most extensively researched form of psychotherapy, but also the most widely applied type of psychotherapy (Norcross et al. 2005), and certainly the most widely applied ‘evidence-based’ type of psychological therapy.
CBT is increasingly offered through the Internet. Internet-based interventions may have several advantages over other more traditional forms of delivery. They may save therapist time, reduce waiting-lists, allow patients to work at their own pace, abolish the need to schedule appointments with a therapist, save traveling time, reduce the stigma of going to a psychologist or therapist, and facilitate help for the hard-of-hearing as self-help treatments typically work with visual rather than auditory information (Marks et al. 2007). Furthermore, Internet-delivered self-help may be programmed to enhance patients’ motivation by presenting a wide range of attractive audiovisual information with voices giving instructions in whichever gender, age, accent, language and perhaps game format the client prefers. It can also quickly and automatically report patient progress and self-ratings.
Internet-based interventions may reach populations with health problems, who can not be reached with other more traditional forms of treatments. For example, a considerable proportion of the patients with mental disorders are not reached with traditional forms of treatment (Bijl and Ravelli 2000) because of the stigma associated with mental disorder, prejudices about therapists, lack of willingness to talk to a stranger about personal problems, or because of physical obstacles like walking problems or long distances. For patients with somatic conditions there may be barriers to seek psychological treatment. Internet-guided interventions may reach a segment of this population who cannot be reached through traditional interventions.
Internet-based psychological interventions for many health problems are commonly based on CBT techniques. One reason is that the effects of CBT have been shown in numerous trials. Another reason why CBT is often used in internet-interventions is that these techniques lend themselves to be operationalized in text. CBT interventions can very well be converted into a structured format, with psychoeducation, homework assignments and registration exercises presented via web pages (Ritterband et al. 2006).
Delivering CBT through the Internet does not, however, only have advantages. An online programme may not be suitable for technophobic patients and illiterates, nor can it answer all the possible questions users may ask; it can not detect subtle nonverbal and verbal clues to clients’ misunderstandings; it may encourage clients to cherry-pick from a range of homework options presented; and not all clients find communicating via computers acceptable (Marks et al. 2007). However, subtle text nuances may be detected and somewhat surprisingly, Internet interventions has been found to generate good working alliance between the patient and the therapist (Knaevelsrud and Maercker 2006).
Furthermore, it is not yet very clear whether CBT interventions which have been proven to be effective when delivered in traditional format, are also effective when delivered through the internet. Recent studies, however, indicate that this might be the case for at least some patients and some conditions (Carlbring et al. 2005).
Whether or not an internet-based CBT is effective should be examined in randomized controlled trials, and can obviously not be based on the effects of traditionally delivered CBT (e.g., individual or group format). Since the Internet has become available to the broad public in many Western countries, several trials have examined the effects of cognitive behavioral interventions in randomized trials. In a recent meta-analysis, we examined the effects of internet-based treatments for depression and anxiety disorders, and found that these interventions had large effects (Cohen’s d = 1.00) compared to control conditions, when some kind of guidance was given to the patients receiving the treatment (Spek et al. 2007). This latter observation was also confirmed in a recent review in which a correlation of rho = .75, P < .005 was obtained between amount of contact spent with clients and the effect size (Palmqvist et al. 2007). These large effect sizes suggest that Internet-administered CBT is as effective as face-to-face CBT, and that the format in which CBT is delivered may not be related to the effect sizes found. It is not known, however, whether Internet-administered CBT is also equally effective when other health problems are targeted.
In the current study, we will present the results of a systematic review of Internet-delivered CBT for health problems. In the review, we aim to establish for which health problems Internet-based CBT has been developed, and examined in randomized controlled or comparative trials, and whether these interventions were effective. We also examine the target groups and contents of these intervention, as well the quality of the studies.
Methods
Search strategy and selection of studies
Studies were traced through several methods. First, we conducted a comprehensive literature search in bibliographical databases (from 1966 to February 2007). We examined 1,608 abstracts in Pubmed (295 abstracts), Psycinfo (109), Embase (330) and the Cochrane Central Register of Controlled Trials (374). In order to find unpublished studies, we also searched Digital Dissertations (500 abstracts). We searched these databases by combining terms indicative of effect studies (randomized trials, controlled trials, clinical trials) and Internet (both keywords and text words). Second, we examined the references of earlier reviews of Internet-based interventions (Griffiths et al. 2006; Wantland et al. 2004), and we reviewed the reference lists of retrieved papers.
Studies were included if they met the following criteria: (a) randomized controlled or comparative trials (b) examining interventions that were conducted through the Internet (at least 50% of the intervention), (c) based on CBT techniques, (d) aimed at behavior change (e) in patients with an existing disorder or health problem. We excluded studies aimed at mental disorders, because another recent systematic review was published about these studies (Spek et al. 2007). We also excluded studies focusing on lifestyle (smoking, obesity, exercise, nutrition), because the character of these interventions differs strongly because the focus of these interventions is typically preventative.
Quality assessment
There are at least 25 scales available to assess the validity and quality of randomized controlled trials (Higgins and Green 2005). There is no evidence, however, that these scales provide more reliable assessments of validity. We preferred therefore to use a simple approach for assessing the validity of the studies, as suggested in the Cochrane Handbook (Higgins and Green 2005).
In this context, the validity of a study can be defined as the extent to which its design and conduct are likely to prevent systematic errors (Moher 1995). Variation in validity can explain variation in the results of the studies included in a systematic review and may result in an erroneous conclusions that an intervention is effective if the less rigorous studies are biased toward overestimating an intervention’s effectiveness (Higgins and Green 2005).
We assessed the validity of the studies using four basic criteria: allocation to conditions is conducted by an independent (third) party; adequacy of random allocation concealment to respondents; blinding of assessors of outcomes; and completeness of follow-up data.
Analyses
We examined the characteristics of the target populations, the interventions, and the design of the included studies.
We also examined which main outcome measures were used for each study, and we calculated standardized effect sizes for each of the main outcome measures. These effect sizes (d) were calculated by subtracting (at post-test) the average score of the control group (Mc) from the average score of the experimental group (Me) and dividing the result by the average of the standard deviations of the experimental and control group (SDec). An effect size of 0.5 thus indicates that the mean of the experimental group is half a standard deviation larger than the mean of the control group. Effect sizes of 0.8 can be assumed to be large, while effect sizes of 0.5 are moderate, and effect sizes of 0.2 are small (Cohen 1988).
When sufficient effect sizes were available (at least three effect sizes examining the same outcome measure in the same health problem), we calculated pooled mean effect sizes. For these analyses, we used the computer program Comprehensive Meta-analysis (version 2.2.021), developed for support in meta-analysis. As we expected considerable heterogeneity, we decided to calculate mean effect sizes with the random effects model. In the random effects model, it is assumed that the included studies are drawn from ‘populations’ of studies that differ from each other systematically.
In these analyses, we tested whether there are genuine differences underlying the results of the studies (heterogeneity), or whether the variation in findings is compatible with chance alone (homogeneity; Higgins et al. 2003). As an indicator of homogeneity, we calculated the Q-statistic. We also calculated the I2-statistic which is an indicator of heterogeneity in percentages as well. A value of 0% indicates no observed heterogeneity, and larger values show increasing heterogeneity, with 25% as low, 50% as moderate, and 75% as high heterogeneity (Higgins et al. 2003).
Results
Included studies
A total of 61 papers which possibly met our inclusion criteria were retrieved. Twelve studies (13 papers; two papers were published about the same study) met our inclusion criteria. The other studies were excluded because they did not examine a cognitive-behavioral intervention (30 papers), because they were not a randomized controlled or comparative trial (11 papers), or because they did not examine an Internet-based intervention (7 papers). Selected characteristics of the target groups, the intervention, and the general design of the twelve included studies are presented in Table 1.
Table 1Selected characteristics of Internet-based cognitive behavioral interventions for health problemsParticipantsIntervention and conditionsStudyHealth conditionRecruitmentWomen (%)Age group (M)Conditions NInterventionContactPeriodMeasurementsDropout (%)CountryAndersson et al. 2003HeadacheCommunity8218–59 (40)1. I-CBT + telephone24Psychoeducation, applied relaxation; problem solving; cognitive restructuringE-mail (at request)6 weeksPre, post32Sweden2. I-CBT20Weekly telephone callsDevineni and Blanchard 2005Tension-type, migraine-only or mixed headache Community83NR (42)1. I-CBT39Progressive muscle relaxation + cognitive stress coping therapy (tension-type), or autogenic training + PMR (migraine/mixed)No therapist contact4 weeksPre, post38US2. Waiting-list47Ström et al. 2000 [33]Recurrent headacheCommunity68≥ 18 (37)1. I-CBT51Psychoeducation, applied relaxation; problem solving; cognitive restructuringE-mail (at request)6 weeksPre, post61Sweden2. Waiting-list51Brattberg 2006Chronic pain + burn-out in patients on long-term sick leave Community9018–65 (47)1. I-CBT30Films + texts; psychoeducation + cognitive self-treatment (changing, coping with shame and guilt, depression, identity, etc.)Real live introduction meeting + weekly online sessions20 weeksPre, post, 1 year8Sweden2. Waiting-list30Buhrman et al. 2004Chronic back pain Community6318–65 (45)1. I-CBT25Applied relaxation; physical exercise, coping strategiesE-mail (at request) weekly telephone calls8 weeksPre, post, 3 months8Sweden2. Waiting-list32Hicks et al. 2006Pediatric recurrent pain/headacheCommunity649–16 (12)1. I-CBT25Psychoeduation; relaxation; cognitive restructuringE-mail contact (5 times) + telephone contact (3 times)7 weeksPre, post, 3 months21Canada2. Waiting-list22Andersson et al. 2002TinnitusCommunity4718–70 (48)1. I-CBT53Psychoeducation; applied relaxation; positive imagery; advice on noise sensitivity; cognitive restructuring; behavioral sleep management.Weekly report on progress, weekly encouraging e-mail 6 weeksPre, post, 1 year41Sweden2. Waiting-list64Hopps et al. 2003People with physical disabilities who feel lonelyCommunity53≥ 18 (34)1. I-CBT11Psychoeducation on communication; self-observation, role-playing, confrontation, positive verbalizations; social skills and assertiveness.Weekly sessions on the Internet12 weeksPre, post, 4 months14Canada2. Waiting-list11Lorig et al. 2006Chronic diseases (heart, lung, or type 2 diabetes)Community71≥ 18 (57)1. I-CBT457Exercise programs; relaxation; cognitive restructuring; psychoeducation; physician-patient communication; healthy eating; fatigue management; problem solving Web-based bulletin board discussion groups (trained peer moderators)6 weeksPre, post, 1 year18US2. Care-as-Usual501Owen et al. 2005Early-stage breast cancerClinical100NR (52)1. I-CBT32Psychoeducation; coping advice for common physical symptoms such as pain and fatigue; structured coping-skills training exercisesBulletin board for asynchronous group discussion12 weeksPre, post15US2. Waiting-list30Ström et al. 2004InsomniaCommunity65≥ 18 (44) 1. I-CBT54Psychoeducation; sleep restriction, stimulus control, cognitive restructuringE-mail (at request)5 weeksPre, post24Sweden2. Waiting-list55Wade et al. 2006Pediatric brain injuryClinical385–16 (11)1. I-CBT20Problem solving; communication; behavior management skills; Videocontact with therapist14 weeksPre, post2US2. I-information20Abbreviations: I-CBT: Internet-CBT; NR: not reported
In the twelve included studies, a total of 1,704 patients participated, 841 in the Internet-CBT conditions, and 863 in the control conditions (mean number of respondents per study: 142; standard deviation: 258.7). More than half of these 1,704 patients (56%) participated in one study (Lorig et al. 2006). In none of the other studies was the number of patients per condition larger than 64.
Eleven studies compared an Internet-based CBT intervention to a control condition, while one study compared two types of Internet-based CBT to each other (one with and one without weekly telephone calls). Nine of the eleven controlled studies used a waiting list control group, while one study used a care-as-usual control group, and the other one used an information control group. In all studies, participants were randomized to one of two conditions. In none of the studies was Internet-based CBT compared to a face-to-face intervention of another treatment. Six studies only presented pre-post data, while the other six also had a follow-up measurement (mean length of follow-up in these six studies was 7.67 months; standard deviation 4.76).
Six studies were conducted in Sweden, four in the United States, and two in Canada. All included studies were conducted in the year 2000 or later (one in 2000 and another one in 2002, two in 2003, in 2004, and in 2005, and four in 2006).
The quality of studies varied. Three of the twelve studies reported that allocation to conditions was conducted by an independent party. Concealment of random allocation to respondents was not possible in any of the studies, while blinding of assessors was reported in none of the studies. Drop-out numbers ranged from 2% to 61%. In only one of the studies intention-to-treat analyses were conducted (Hicks et al. 2006; the other studies were limited to completers-only analyses).
The target populations
Three studies focused on patients suffering from pain, three on headache, and six on other health problems (tinnitus; physical disabilities; chronic diseases; breast cancer; insomnia; and pediatric brain injury). In ten of the twelve studies, patients were recruited through announcements on websites, referrals, and community recruitment. In the other two studies patients were recruited through screening of clinical samples. Ten studies were aimed at adults, two at children. None of the interventions were aimed at older adults, although three studies allowed older adults (≥70 years) to participate. The other studies on adults only included younger adults for participation or did not report that they used an age limit.
The interventions
The character of the interventions differed from each other. One group of interventions consisted of self-help materials on the Internet, with supporting e-mails or telephone calls (5 studies). In two studies the intervention consisted of self-help materials on the Internet, but without the supporting e-mails or calls. In the other studies, the core of the intervention consists of online contact between a therapist or moderator and the patients (individual or in groups). Most interventions contained psychoeducation on the specific problem, and different CBT modules such as cognitive restructuring, relaxation techniques, and social skills training. The duration of the interventions ranged between 4 and 20 weeks.
Effects of the interventions
The effects of the interventions on the main outcomes of each included study at post-test are presented in Table 2.
Table 2Main outcomes of studies on Internet-based cognitive behavioral interventions for health problemsHealth conditionComparisonMain outcomeEffect size95% CIPainBrattberg 2006Chronic pain and burnoutRehabilitation course versus waiting list controlFunctional limitations0.48−0.03–0.99Buhrman et al. 2004Chronic back painInternet-guided self-help versus waiting list controlCoping with pain0.790.22–1.36Hicks et al. 2006 BPediatric recurrent pain/headacheInternet-guided self-help versus waiting list controlPain0.47−0.24–1.18POOLED0.58a0.25–0.92HeadacheAndersson et al. 2003HeadacheInternet self-help with support versus self-help onlyHeadache0.38−0.35–1.11Devineni and Blanchard 2005Chronic headacheInternet self-help versus waiting list controlHeadache0.560.13–0.99Ström et al. 2000Recurrent headacheInternet self-help versus waiting list controlHeadache0.19−0.40–0.78OtherAndersson et al. 2002TinnitusInternet CBT versus waiting list controlDistress from tinnitus0.26−0.23–0.75Hopps et al. 2003Physical disabilitiesGoal-oriented CBT chat-group teletherapy versus waiting list controlLoneliness0.46−0.45–1.37Lorig et al. 2006Chronic diseases Online CBT workshops versus care-as-usualHealth indicators (only 1 year FU)0.10−0.04–0.24Owen et al. 2005Early-stage breast cancerOnline CBT coping group versus waiting list controlHealth-related quality of life0.22−0.32–0.76Ström et al. 2004InsomniaInternet CBT versus waiting list controlWade et al. 2006Pediatric brain injuryOnline family problem solving therapy versus Internet resources Parental mental health0.700.05–1.35aPooled with the random effects model; Z = 3.40, P < 0.001; Q = 0.75, n.s.; I2 = 0
We pooled the three studies in which Internet-based CBT for pain was compared to control groups. The mean effect size on the main outcome measure was 0.58 (95% CI: 0.25–0.92; P < 0.001), indicating a moderate to large effect of the interventions compared to the control groups at post-test. Heterogeneity was very low (Q = 0.75, n.s.; I2 = 0).
There were also three studies on headache, however one did not use a true control group (but compared two active interventions to each other). Therefore we did not pool the results of these studies. The effect sizes of these interventions were small (d = 0.19; Ström et al. 2000) to moderate (d = 56; Devineni et al. 2005).
The effect sizes of the other studies were in the small to moderate range, varying from small (d = 0.10) for health indicators in chronic diseases at one-year follow-up, to somewhat larger for health-related quality of life in breast cancer patients (d = 0.22) and from tinnitus sufferers (d = 0.26), to moderate (loneliness in patients with physical disabilities; d = 0.46) and large (parental mental health in pediatric brain injury; d = 0.70). Most effect sizes did not significantly differ from zero because of the small sample sizes in the majority of the studies.
Discussion
This systematic review of controlled and comparative studies of Internet-based CBT for health problems showed that this field is developing fast. Since 2000, twelve randomized studies have examined interventions for pain, headache, and several other health problems. Half of these trials were published in 2005 and 2006, and it can be expected that the number of trials will rise sharply in the next few years. Overall, findings are promising but effects are slightly below the effect sizes found for Internet-delivered CBT for anxiety and depression (Spek et al. 2007).
Although several health problems were targeted in these Internet-based studies, there are gaps in the literature in terms of treatments for health problems which have been found to improve by means of CBT. For example, several studies have examined the effects of CBT for chronic fatigue syndrome (Knoop et al. 2007), fibromyalgia (Garcia et al. 2006), incontinence (Garley and Unwin 2006), or multiple sclerosis (Thomas et al. 2006), but these have not yet been transformed into a web based intervention, although trials found positive effects of face-to-face CBT for these problems. Because the promising results of earlier studies, and because of the benefits of Internet-based interventions, we can expect development of new programs for these conditions in the future.
Our review does not cover the whole field of internet interventions. While we focused on CBT for existing health problems, several other studies have examined CBT for mental health problems (Spek et al. 2007), on internet-based preventive interventions aimed at a healthy lifestyle (weight loss, smoking, exercise; e.g., Swartz et al. 2006; Muñoz et al. 2006; Oenema et al. 2001; Tate et al. 2006), and interventions using non-CBT methods (McMahon et al. 2005; Edwards et al. 2006; Gray et al. 2000). However, as was shown in this review, research on CBT interventions has been growing fast in the past few years. Because CBT interventions are very well suited to be used through the internet, it can be expected that research in this area will continue to grow further in the next years.
The included studies do not yet allow us to draw definite conclusions about whether CBT through the Internet are as effective as face-to-face interventions. For most health problems we found only one study examining the effects of an Internet-based CBT study. In fact, it was only for pain and headache did we find more than one studies. However, the effects found for Internet-based interventions aimed at pain are comparable to the effects found for face-to-face treatments for pain (Morley et al. 1999), and the same is most likely true for the Internet-interventions aimed at headache (Bogaards and ter Kuile 1994). The other interventions also found some effects, although some effects were stronger than others. It does seem clear, however, that Internet-based CBT can have significant effects on some of the health problems described in this review. For at least one of the conditions—tinnitus—an effectiveness study has been published showing better results then the first controlled efficacy trial (Kaldo-Sandström et al. 2004).
It has been suggested self-help interventions be used as one of the first steps in stepped-care programs (Scogin et al. 2003). Perhaps Internet-based interventions which are used in healthcare settings should also be placed within these stepped-care frameworks. In these cases, additional care is available if the Internet-based intervention does not reduce the problem of a patient sufficiently. On the other hand, Internet interventions can develop as well, and might at least for some patients be more suitable than face to face CBT. As many health conditions such as chronic pain and cancer require a multidisciplinary team approach for optimal treatment, we assume that future Internet interventions will take advantage of this possibility.
There is no consensus yet among researchers about the way CBT should be presented on the Internet, although standards are emerging. Most interventions used a guided self-help format in which the treatment protocol is presented on the Internet and the patient works it through more or less independently. The patients are supported by brief contacts with therapists through e-mail or telephone. However, other studies use a more traditional format in that the patients go online at the same time as the therapist and have a more or less regular treatment session. Group treatments can also be delivered in such a way.
Another difference between interventions concerns the additional elements on the Internet, apart from CBT. Some interventions have combined the cognitive behavioral interventions with other components, such as psychoeducation, films and texts to read, and a forum for users of the website. Other interventions do not provide such extras.
Our review showed up several other important limitations of the current research in this area. First, most studies used waiting list control groups, and only very few used a care-as-usual or another control group. Subjects in waiting list control groups probably do not take constructive action to reduce their problems themselves during the waiting period, because they are expecting professional help in the future. This may result in an overestimation of the effects of an intervention, because there may be less spontaneous recovery.
Second, most studies recruited participants through the community and through other websites. This is not a problem for interventions that target the general population. But when such an intervention is effective this does not automatically mean that it is also effective in clinical settings. Subjects who are responding to community recruitment are probably very motivated which may improve their results compared to subjects who receive treatment.
Third, none of the twelve identified trials compared Internet-based treatments to face-to-face or other treatments. This is, however, an important issue, because only direct comparisons can give evidence about the comparative effects of Internet-based treatments compared to more traditional treatments and the type of patients who can benefit from it.
Fourth, most studies were aimed at adults. Only two studies were aimed at children and adolescents, while these groups are probably the most familiar with the Internet. None of the studies were specifically aimed at older adults, while they suffer most from health conditions.
Future research should focus on these limitations of current research. More studies are needed with care-as-usual or other control groups, clinical recruitment strategies, comparisons with face-to-face treatments, and children or older adults as target populations. More research is also needed to examine how CBT should be presented on the Internet, and to examine reasons and solutions to the relatively high drop-out rates in several studies. Finally, it is also important to study how Internet-administered CBT can be integrated in stepped-care models of care.
This review has several limitations. First, the number of included studies is still very small. And the number of studies examining specific health problems is too small to integrate the results of these studies statistically into a meta-analysis. Second, the quality of the included studies is not optimal. Third, the drop-out rates reported are high in some studies. This is a concern for this type of intervention, as patients can very easily withdraw from the intervention. Remarkably, the studies in which more traditional therapies (live sessions with therapists) are delivered through the Internet have the lowest drop-out rates.
Despite these limitations, however, there is no doubt that the number of studies in this area will increase considerably in the next few years, while the promising results of the studies in this review indicate that the Internet will assume a major role in the delivery of CBT to patients with health problems.

internet
cognitive behavior therapy
systematic review
pain
headache
migraine


The distal fascicle of the anterior inferior tibiofibular ligament as a cause of tibiotalar impingement syndrome: a current concepts review

Impingement syndromes of the ankle involve either osseous or soft tissue impingement and can be anterior, anterolateral, or posterior. Ankle impingement syndromes are painful conditions caused by the friction of joint tissues, which are both the cause and the effect of altered joint biomechanics. The distal fascicle of the anterior inferior tibiofibular ligament (AITFL) is possible cause of anterior impingement. The objective of this article was to review the literature concerning the anatomy, pathogenesis, symptoms and treatment of the AITFL impingement and finally to formulate treatment recommendations. The AITFL starts from the distal tibia, 5 mm in average above the articular surface, and descends obliquely between the adjacent margins of the tibia and fibula, anterior to the syndesmosis to the anterior aspect of the lateral malleolus. The incidence of the accessory fascicle differs very widely in the several studies. The presence of the distal fascicle of the AITFL and also the contact with the anterolateral talus is probably a normal finding. It may become pathological, due to anatomical variations and/or anterolateral instability of the ankle resulting from an anterior talofibular ligament injury. When observed during an ankle arthroscopy, the surgeon should look for the criteria described to decide whether it is pathological and considering resection of the distal fascicle. The presence of the AITFL and the contact with the talus is a normal finding. An impingement of the AITFL can result from an anatomical variant or anteroposterior instability of the ankle. The diagnosis of ligamentous impingement in the anterior aspect of the ankle should be considered in patients who have chronic ankle pain in the anterolateral aspect of the ankle after an inversion injury and have a stable ankle, normal plain radiographs, and isolated point tenderness on the anterolateral aspect of the talar dome and in the anteroinferior tibiofibular ligament. The impingement syndrome can be treated arthroscopically.
Introduction
Impingement syndromes of the ankle involve either osseous or soft tissue impingement and can be anterior, anterolateral, or posterior [5, 25]. Ankle impingement syndromes are painful conditions caused by the friction of joint tissues, which are both the cause and the effect of altered joint biomechanics [14]. The leading causes of impingement lesions are post-traumatic ankle injuries, usually ankle sprains, resulting in chronic ankle pain [33]. According to the ISAKOS definition, anterior ankle impingement is a pain syndrome characterised by anterior ankle pain on activity. Recurrent dorsiflexion is often the cause. On investigation, there is pain on palpation at the antero/medial and/or anterolateral aspect of the ankle joint. Some swelling and/or limitations of dorsiflexion are present [32]. The first reported impingement syndromes about the ankle have evolved osseous impingement and generally have been noted in athletes whose sports necessitated sudden acceleration, jumping, and extremes of dorsiflexion or plantar flexion. Impingement of the ankle was first described in the English language literature by Morris [20], in 1943, in five patients who had what he called the athlete’s ankle. This was later called footballer’s ankle in the report of McMurray [18].
Soft tissue impingement of the ankle is a common cause of chronic ankle pain that usually arises at the lateral and/or anterolateral compartment of the ankle joint following an inversion injury [8]. It is estimated that approximately 3% of ankle sprains may lead to anterolateral impingement [32]. Three types of intra-articular soft tissue lesions that lead to these complaints have been described: the meniscoid lesion, synovitis, and the distal fascicle of the anterior inferior tibiofibular ligament (AITFL) [4, 6, 8, 9, 12, 16, 19, 28]. The formation of tibiotalar spurs due to repetitive capsule traction therefore does not seem plausible reason for anterior ankle impingement [29].
Impinging soft tissue pathology in the ankle was first described by Wolin et al. as a “meniscoid mass or lesion” [34]. They described the lesion as a membrane shaped hyalinised scar tissue obstructing the lateral talofibular articulation in nine patients with persistent symptoms over the anterolateral corner of the ankle after an inversion trauma [34]. Some authors thought this lesion was formed from the torn ends of the anterior tibiofibular ligament [3, 21]. However there was no ligamentous tissue found on histologic examination of this lesion [9]. Guhl thought the lesion was of synovial origin [11]. Irritation of the joint by bleeding and a torn capsule or a torn anterior tibiofibular ligament are thought to be the underlying factors for developing post-traumatic synovitis in the ankle [17] which in unstable ankles may lead to formation of fibrosis and granulation tissue. Although synovitis and the meniscoid lesion have been referred frequently, impingement by a separated fascicle of the AITFL is a relatively new and unknown pathology. Bassett et al. [4] were the first who reported a ligamentous etiology of impingement of the anterior aspect of the ankle. The presence of the so-called accessory AITFL, as described by Nikolopoulos was confirmed by them [21]. However they called this accessory ligament, the distal fascicle of the normal AITFL [4]. The distal part of the fascicle rubs against the talus, and that this causes pain at the ankle [1, 2, 4, 8, 12, 22].
The objective of this article was to review the literature concerning the anatomy, pathogenesis, symptoms and treatment of the AITFL impingement and finally to formulate treatment recommendations.
Anatomy of the anterior inferior tibiofibular ligament
The distal tibiofibular joint was classically described as a syndesmosis between the rough, triangular surface on the medial and distal aspect of the fibular shaft and the fibular notch of the distal end of the tibia. The tibiofibular syndesmosis is established by three ligaments: the interosseous ligament, the posterior inferior tibiofibular ligament, and the AITFL [7, 10, 15, 24, 26].
The AITFL is a flat band becoming thicker from superior to inferior [24]. The ligament starts from the distal tibia, 5 mm in average above the articular surface, and descends obliquely between the adjacent margins of the tibia and fibula, anterior to the syndesmosis to the anterior aspect of the lateral malleolus [7, 22]. Its length ranges from 12 to 20 mm [4, 22]; its thickness, from 1 to 3 mm [4, 22]; and its width ranges from 7 to 12 mm at the fibular insertion and 9 to 22 mm at the tibial insertion [22]. This ligament is the weakest of the syndesmotic ligaments and is the first to yield to forces that promote an external rotation of the fibula around its longitudinal axis [15]. Resection of the accessory ligament did not disturb the stability of the syndesmosis, a finding that was in accordance with the results reported by Rasmussen et al. which suggests that mobility is minimally influenced by isolated cutting of the AITFL [23].
Nikolopoulos et al. studied 24 cadaveric ankles to describe the anatomy of the AITFL [22]. In five ankles the AITFL appeared to consist of two layers, one superficial and one deep, which were separated by a thin fibrofatty septum [22, 24]. However, the total thickness of these two layers did not exceed the average thickness of the AITFL in the rest of the specimens [22]. In five ankles, the articulated surfaces of the distal tibia and fibula that formed the syndesmosis were covered by articular cartilage and were surrounded by synovial bursa [22]. A completely separate accessory anteroinferior tibiofibular ligament was present in 22 ankles (Fig. 1). Nikolopoulos was the first to describe this accessory ligament [21]. However the results of his study were never published in English literature [26]. Nikolopoulos believed that this anatomical structure represents a separate ligament rather than a distal component of the AITFL [21]. The fact that there was clearly a fibrofatty septum that separates the AITFL from the accessory fascicle, similar to the one that covered the intermediate space between the interosseous and the anterior or the interosseous and the posterior tibiofibular ligaments, suggested that this fascicle could probably be considered an independent accessory ligament [22]. Some other authors described this accessory ligament as a complete separate distal fascicle of the AITFL [4, 15, 26].
Fig. 1The distal fascicle in relation to the anterior inferior tibiofibular ligament
Ray and Kriz [24] founded in 10 of the 46 specimens an accessory ligament. This ligament was parallel and distal to the AITFL. The fibres of the accessory ligament descended obliquely from the lateral, anterior, and distal borders of the tibia to the anteromedial aspect of the lateral malleolus, approximating the fibular insertion of the anterior talofibular ligament (ATFL).
Its length ranges from 17 to 22 mm, its thickness from 1 to 2 mm, and its width from 3 to 5 mm. The maximum, minimum, mean, and standard deviation for the length, width, gap, and angle of declination for the inferior fibre bundle are provided in Table 1. The ligament was not covered by synovial tissue, ran deeper than the AITFL and was described as being intra-articular, although how this was determined was not stated by the authors. The accessory ligament crossed the superior lateral margin of the ankle joint. The accessory ligament was separated from the AITFL by a distinct fibrofatty septum. The ligament could even be divided in two, three, or more fascicles, increasing in length from superior to inferior [24].
Table 1Characteristics of the inferior fascicle of the AITFL [24]MaximumMinimumMeanLigament length (cm)3.42.12.6 ± 0.3Ligament width (cm)1.30.20.4 ± 0.2Gap (cm)0.50.10.2 ± 0.1Declination angle (deg)155.0121.5136.3 ± 7.4
The incidence of the accessory fascicle differs very widely in the several studies (21–92%) [2, 4, 22, 24]. The discrepancies in the incidence between the several studies were probably due to the different definitions of a separate fascicle. Ray and Kriz did not consider it a separate fascicle if any digitations were present between the fascicle and the main body of the AITFL [24]. The incidence was up to 92%, which implied that the ligament may be considered as a normal finding. Vessels from the anterior peroneal artery penetrate through the interlaminar spaces [26]. It is not uncommon to have branches from the anterior tibial artery or peroneal artery or a branch arising from the anastomosis between these two arteries pass between these fascicles [11]. The most inferior fibres of the ligament merged at their fibular attachment with the origin of the ATFL [24].
Ray and Kriz [24] studied 23 cadaveric ankles. A classification scheme was designed to categorise the anatomical variations observed in the AITFL (Table 2).
Table 2AITFL classification system [24]Type 1Multiple fascicles (more than three) with or without small gaps between adjacent fascicles  1AThe inferior fascicle is separated from the rest of the ligament by a gap and possesses its own distinct proximal and distal attachments  1BThe inferior fascicle is not completely separated from the rest of the ligament by a gap. Either its proximal or its distal attachment is continuous with the rest of the ligament  1CMultiple fascicles without gaps intervening between themType 2Three fascicles or less. A distinct inferior fascicle with both its proximal and distal attachments separate from the rest of the ligament. The inferior fascicle is separated completely from the main portion of the ligament by a gapType 3Three fascicles or less. A distinct inferior fascicle with either its proximal or its distal attachment continuous with the rest of the ligament. A gap does not completely separate the inferior fascicle from the rest of the ligamentType 4Three fascicles or less. The lower portion of the ligament possesses an inferior fascicle with both its proximal and distal attachments for the rest of the ligamentType 5Three fascicles or less. A ligament with no separations or gaps within its structure. It may or may not possess a fascicular arrangement
Pathomechanism of the impingement syndrome
It should be stressed that most studies were carried out in vitro and do not take muscular tonus and the effects of weightbearing into consideration, we performed a review of the pathomechanism of the impingement syndrome caused by the distal fascicle of the AITFL.
Bassett et al. correlated the presence of this accessory ligament with pain from impingement in the anterolateral aspect of the ankle in patients with a history of inversion sprains [4]. They postulated that the post-traumatic anterolateral hyperlaxity, due to an injured ATFL, resulted in anterior extrusion of the talar dome with dorsiflexion, which now contacted the inferior fascicle of the AITFL with more pressure and friction [4]. This in turn might set up an environment favouring ligamentous impingement of the anterior aspect of the ankle [4].
Akseki et al. stated that the variations in width, length, and obliquity of the fascicle may be related to the pathological behaviour of the fascicle [2]. Mean width and length of the fascicle with bending during dorsiflexion and dorsiflexion-eversion were significantly higher than the fascicle without bending. Therefore this wider and longer fascicles had more potential to become pathological than thinner ones. They also conclude that if the fibular insertion point is far from the joint level, the fascicle has more potential to become pathological. These findings might be useful during arthroscopic procedures of the ankle.
During dorsiflexion of the ankle the posterior shift of the anterior talus below the tibial plafond in ATFL intact cases was observed. Following incision of the ATFL this posterior shift of the talus was not observed; the talus remained in an anterior position and thus in contact with the fascicle [2]. Lesion of the ATFL led to bending of the fascicle with dorsiflexion and dorsiflexion-inversion in the specimens which the bending sign was negative. Lesion of the ATFL led also to contact between the talus and the fascicle in the ankles which showed no contact previously [2]. After sectioning the ATFL the anteroposterior laxity of the ankle increases especially in dorsiflexion [4, 13].
In 89.3% of the cases contact was observed between the ATFL and the anterolateral corner of the talus [2]. This contact may be normal in some of the cases. Contact was observed at an average of 12° of dorsiflexion of the ankle [4]. Bending of the accessory ligament, indicating further tensioning of its ligamentous bands caused by impingement of the talus, this was noted in an extent of dorsiflexion that varied from 5° to 10° (average 7°) [22]. Maximum dorsiflexion of the foot relieved the contact between the ligament and the superolateral corner of the talus [22]. In other studies the contact was also observed in neutral position [2, 24].
In one study the contact between the fascicle and talar dome was observed throughout the whole range of motion of the ankle [1]. They called this the “arthroscopic impingement test,” and it was positive in all of the cases with AITFL impingement they have studied [1]. Contact between the accessory fascicle and the talus was also observed during eversion of the foot, being more prominent when the foot was placed in a dorsiflexion-eversion position [22]. No interaction of the accessory ligament with the talus was noted during ankle plantar flexion [22].
In 82.9% of the cases with AITFL impingement Ray and Kriz [24] found an anterior abraded articular region of the talus. Akseki et al. [2] found this in 17% of the cases. In the study of Basset et al. [4] 71% of the patients, had an area of abraded articular cartilage on the anterolateral surface of the talar dome. There is no clarity if this abraded cartilage region is an anatomical variant of the talus or a pathological remodelling of the bone due to true ligamentous impingement [4].
On base of these studies we conclude that anterolateral hyperlaxity results in anterior extrusion of the talar dome with dorsiflexion, which contacts the inferior fascicle of the AITFL with more pressure and friction. This hyperlaxity was most likely due to an injured ATFL. Wider and longer fascicles and a fibular insertion point far from the joint level have more potential to become pathological. Often contact between the AITFL and the superolateral corner of the talus and an abraded region of the cartilage of the talus can be observed during arthroscopy.
Diagnosis
The diagnosis of ligamentous impingement in the anterior aspect of the ankle should be considered in patients who have chronic ankle pain in the anterolateral aspect of the ankle after an inversion sprain and who have a stable ankle, normal plain radiographs, and isolated point tenderness on the anterolateral aspect of the talar dome and in the anteroinferior tibiofibular ligament [4]. A popping sensation and aggravation of pain with dorsiflexion and eversion were noted [2, 4]. This audible popping is usually not seen in other causes of impingement of the anterior aspect of the ankle [4]. Pain in the beginning of plantarflexion-inversion may alert the physician for an impinging AITFL [2].
It is usually impossible to distinguish the source of pain in patients with both instability and impingement. So if the patient complains of giving way and frequent sprains, the surgeon may choose a reconstructive procedure [1]. But it should be noted that a painful lesion in the joint (synovitis, meniscoid lesion, or an impinging fascicle of the AITFL) may cause reflex sprains [1]. This process may confuse decision making in this type of combined pathology. The differential diagnosis for pain in the lateral aspect of the ankle after an inversion sprain includes osteochondral fracture, instability of the lateral aspect of the ankle, synovitis or rupture of the peroneal tendon, and ligamentous impingement in the anterior aspect of the ankle, with the latter being the least common [4].
Treatment
Patients should be treated conservatively after an inversion sprain of the ankle for at least 6 months before operative intervention is considered [5]. This is with the exception of patients with an osteochondral fracture. Akseki et al. observed that conservative management with physical therapy, NSAIDs and bracing in patients with instability symptoms, for a period of 3 months, failed in all 21 patients [1].
Not every patient with chronic ankle instability needs a reconstructive procedure [1]. If the history, physical examination, and other diagnostic tests suggest impingement in addition to instability, arthroscopic debridement of the soft tissue lesion may be all that is needed [1. In cases with an area of abraded articular cartilage on the anterolateral surface of the talar dome, further debridement of this region was required [4]. At long-term follow-up arthroscopic excision of soft tissue overgrowth and osteophytes proved to be an effective way of treating anterior impingement of the ankle in patients who had no narrowing of the joint space [30]. Patients with less than 2 years of ankle pain before surgery for anterior ankle impingement showed significant better scores in pain, swelling, ability to work, and engagement in sports [31].
The decision to perform an arthroscopy of the ankle is typically based on the patient’s history and physical examination [9, 19, 28]. Arthroscopically resection of the distal fascicle of the AITFL should be considered when there (Fig. 2): (1) is contact between the AITFL and the talus was prominent also in the beginning of plantarflexion-inversion of the ankle, (2) is increased contact between the talus and the ligament and this continued until maximum dorsiflexion with abrasion of the articular cartilage (the surgeon should remember that this finding may be normal), (3) bending of the fascicle on the anterolateral edge of the talus with dorsiflexion and dorsiflexion-inversion, (4) is a distally inserting fascicle on the fibula, close to the origin of the ATFL on the fibula. This finding may be missed if the distraction is preserved throughout the procedure [2, 24]. For this reason, temporarily relieving distraction is advised, when a distal fascicle is seen during arthroscopy [2, 22].
Fig. 2There is contact between the distal fascicle of AITFL and the talus in dorsiflexion with bending of this fascicle
Only three studies reported on the results of the treatment of AITFL impingement [1, 4, 12]. Akseki et al. [1] arthroscopically resected the distal fascicle of the AITFL in 21 patients with chronic ankle pain after an ankle sprain. During the procedure an impinging distal fascicle of the AITFL was found in all cases. Following anterolateral synovectomie, the fascicle was excised. At an average follow-up of 3 years good to excellent results were obtained in 17 patients. Nineteen patients were satisfied with the procedure and 17 patients returned to previous level of activity. Two patients who had mild laxity were graded as poor because neuromas of the terminal branches of the superficial peroneal nerve. These patients became asymptomatic after an injection of steroids.
Bassett et al. [4] treated seven patients who had talar impingement by an AITFL and they were followed for a mean of 39 months. Two patients had arthroscopy and five had an arthrotomy. In all patients, a thickened distal fascicle of the AITFL was resected. Five patients also needed debridement of an area of abraded hyaline cartilage on the anterolateral aspect of the talar dome at the point where the distal fascicle made contact. Post-operative management consisted of 2–4 days of immobilisation, followed by progressive weightbearing. Four patients reported no pain in their ankle or limitation in activity, and the results were considered to be excellent. Two patients reported improvement, with only occasional pain related to overuse, and the result was considered good. The last patient had been followed for only 6 months with excellent results.
Horner and Liu [12] treated nine athletes with anterolateral ankle pain during and following athletic activities without history of ankle injury. After 3 months conservative management each patient was explored arthroscopically. Patients’ outcomes were rated subjectively and objectively based on the UCLA ankle scoring system. Pathological characteristics were easily identifiable through arthroscopy. The structure may be resected during this procedure without sacrificing the stability of the ankle joint. They report that good to excellent results can be expected from this procedure including in the highest level of athleticism at an average follow-up of 18 months.
The decision to perform an arthroscopy of the ankle is typically based on the patient’s history and physical examination. When an impinging distal fascicle of the AITFL and an abraded anterolateral region of the talus were observed during an ankle arthroscopy, the surgeon should look for the criteria described above to decide whether it is pathological and needs to be resected.
Conclusion
Because of the lack of evidence only preliminary conclusions can be drawn. The AITFL started from the distal tibia, 5 mm in average above the articular surface, and descended obliquely between the adjacent margins of the tibia and fibula, anterior to the syndesmosis to the anterior aspect of the lateral malleolus. The incidence of the accessory fascicle differs very widely in the several studies. The presence of the distal fascicle of the AITFL and also the contact with the anterolateral talus is probably a normal finding. It may become pathological, however, due to anatomical variations and/or anterolateral instability of the ankle resulting from an ATFL injury. When observed during an ankle arthroscopy, the surgeon should look for the criteria described to decide whether it is pathological and considering resection of the distal fascicle.

anterior inferior tibiofibular ligament
impingement syndrome
ankle
accessory fascicle


Adenosine A2A receptors modulate BDNF both in normal conditions and in experimental models of Huntington’s disease

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, enhances synaptic transmission and regulates neuronal proliferation and survival. Functional interactions between adenosine A2A receptors (A2ARs) and BDNF have been recently reported. In this article, we report some recent findings from our group showing that A2ARs regulate both BDNF functions and levels in the brain. Whereas BDNF (10 ng/ml) increased the slope of excitatory postsynaptic field potentials (fEPSPs) in hippocampal slices from wild-type (WT) mice, it was completely ineffective in slices taken from A2AR knock-out (KO) mice. Furthermore, enzyme immunoassay studies showed a significant reduction in hippocampal BDNF levels in A2AR KO vs. WT mice. Having found an even marked reduction in the striatum of A2AR KO mice, and as both BDNF and A2ARs have been implicated in the pathogenesis of Huntington’s disease (HD), an inherited striatal neurodegenerative disease, we then evaluated whether the pharmacological blockade of A2ARs could influence striatal levels of BDNF in an experimental model of HD-like striatal degeneration (quinolinic acid-lesioned rats) and in a transgenic mice model of HD (R6/2 mice). In both QA-lesioned rats and early symptomatic R6/2 mice (8 weeks), the systemic administration of the A2AR antagonist SCH58261 significantly reduced striatal BDNF levels. These results indicate that the presence and the tonic activation of A2ARs are necessary to allow BDNF-induced potentiation of synaptic transmission and to sustain a normal BDNF tone. The possible functional consequences of reducing striatal BDNF levels in HD models need further investigation.
Introduction
Brain-derived neurotrophic factor (BDNF) is an endogenous glycoprotein belonging to neurotrophins, a family of signalling molecules that play a key role in regulating neuronal proliferation, differentiation and survival [1–3]. Among the neurotrophins, BDNF has the widest distribution in the central nervous system [4, 5]. In the adult hippocampus, BDNF is critically involved in the regulation of synaptic plasticity [6] and facilitates long-term potentiation (LTP) [7–10; see 11 for review]. Most biological effects of BDNF are mediated by the tyrosine kinase receptor TrkB. Both BDNF and its receptors are highly expressed in the hippocampus, and the activation state of the complex BDNF/TrkB appears critical for modulating synaptic efficacy [12] and the response to excitotoxic injury [13, 14].
In hippocampal neurones, adenosine has been reported to transactivate TrkB receptors, an effect involving the A2A receptor subtype (A2ARs) [15]. Furthermore, Diogenes et al. [16] reported that A2ARs facilitate the excitatory action of BDNF on hippocampal synaptic transmission.
Besides its involvement in hippocampal functions, BDNF is also very important for the survival of striatal neurons and the activity of corticostriatal synapses [17]. Impairment in BDNF function is though to play a major role in Huntington’s disease (HD), an inherited neurodegenerative disease caused by a mutation in the protein huntingtin and characterised by marked striatal degeneration (see [18] for review). Specifically, it has been shown that the activity of BDNF depends on the presence of normal huntingtin [19–21]. In vitro and in vivo data showed that wild-type huntingtin, but not the mutant protein, stimulates cortical BDNF production by acting at the level of Bdnf gene transcription [20, 21]. At the corticostriatal synapse, BDNF controls glutamate release and its exogenous administration allows striatal neurons to survive excitotoxin-induced neurodegeneration [22].
Mounting evidence also indicates an involvement of striatal A2A receptors in HD (see [23] and [24] for reviews). First, A2ARs are mainly localised on the neurons that degenerate early in HD [25]. Second, A2ARs and underlying signalling systems undergo profound changes in cellular and animal models of HD (see [24] for review). Thus, not only A2ARs seem to regulate BDNF functions in the brain, but both BDNF and A2ARs seem to be implicated in HD.
In this article we report and critically discuss some recent findings on the following issues obtained by our group: (1) the regulatory role exerted by hippocampal A2ARs on BDNF functions and levels as revealed by studies performed in A2AR KO mice, and (2) the effects of A2AR blockade on striatal BDNF levels in experimental models of HD or HD-like striatal degeneration.
In hippocampal slices from wild-type mice, the facilitatory effects exerted by BDNF on synaptic transmission require the endogenous activation of A2AR
In hippocampal slices from wild-type (WT) mice (400-μm thick, see [26] for a detailed methodological description), BDNF (10 ng/ml over 30 min) induced a long-lasting increase in the slope of field excitatory postsynaptic potential (fEPSP) recorded in the CA1 area (Fig. 1). This effect was abolished not only by the inhibitor of Trk phosphorylation K-252a, but also by the selective adenosine A2A antagonists ZM241385 and SCH58261 (Tebano et al., manuscript in preparation). The effects of A2ARs seem to involve the cyclic adenosine monophosphate/protein kinase A (cAMP-PKA) pathway, the main transduction mechanism operated by A2ARs, as the selective PKA inhibitor KT 5720 abolished the excitatory action of BDNF (Tebano et al., manuscript in preparation).
Fig. 1Brain-derived neurotrophic factor (BDNF) facilitates synaptic transmission in hippocampal slices from wild-type (WT) but not A2A receptor (R) knock-out (KO) mice. In hippocampal slices from WT mice, BDNF (10 ng/ml) induces an increase of the excitatory postsynaptic field potentials (fEPSP) slope, whereas a lower concentration (5 ng/ml) is ineffective. BDNF (5, 10 and 20 ng/ml) was totally ineffective in hippocampal slices from A2AR KO mice. *P < 0.05 vs. baseline (paired t test)
The finding that BDNF enhances synaptic transmission in mice hippocampal slices confirms and strengthens previous data on the acute synaptic effects of BDNF at adult central synapses [17, 27]. Although the mechanisms responsible for such synaptic effects are not completely understood, they do not seem to be related to the neuroprotective ability of BDNF. That the above functions of BDNF recognise different molecular mechanisms is indicated by the fact that ligand-induced TrB translocation into lipid rafts is required for short-term synaptic modulation, but not neuronal survival, by BDNF [28]. Whatever the mechanisms, the blocking effect of ZM241385 and SCH58261 suggests that A2ARs have to be tonically activated by endogenous adenosine to manifest BDNF effects. To further explore the apparently “permissive” role of adenosine A2ARs on the synaptic effects of BDNF, A2AR KO mice were used.
BDNF is no longer able to facilitate synaptic transmission in hippocampal slices from A2A KO mice
A2AR KO mice (A2AR-/-) were generated, as previously described [29]. In hippocampal slices from A2AR KO mice, BDNF was no longer able to increase the fEPSP slope (Tebano et al., manuscript in preparation). As shown in Fig. 1, none of the tested concentrations of BDNF (5, 10 and 20 ng/ml) potentiated the synaptic response in slices from A2AR KO mice. Since the effectiveness of BDNF may depend on the proper expression of its receptors, we compared the levels of TrkB protein in WT and A2A KO mice by Western blotting. By using primary anti-TrkB antibody (Bioscience), we found that the levels of full-length TrkB isoforms were very similar in hippocampal extracts from WT and A2AR KO mice (Tebano et al., manuscript in preparation). Thus, the loss of BDNF activity observed in A2AR KO mice is not associated with a reduced density of TrkB receptors.
BDNF protein levels are significantly reduced in the brain of A2AR KO vs. WT mice
The BDNF protein levels were then measured on hippocampal extracts from A2AR KO and WT mice using the BDNF immunoassay system [enzyme-linked immunosorbent assay (ELISA) kit; Promega]. Interestingly, hippocampal BDNF levels were significantly lower in the A2AR KO mice compared with the WT littermates. As shown in Fig. 2, such an effect was not confined to the hippocampus, as a significant loss of BDNF levels was observed also in the striatum of A2A KO vs. WT mice.
Fig. 2Brain-derived neurotrophic factor (BDNF) levels are significantly reduced in the hippocampus and striatum of A2A receptor (R) knock-out (KO) mice. BDNF concentration was significantly reduced in extracts of hippocampal and striatal tissues prepared from A2AR mice compared with wild-type WT mice. The amount of BDNF (total) is expressed as pg/mg of wet tissue [means ± standard error of the mean (SEM) from five mice/group]. *P < 0.05 vs. WT
This result indicates that the presence of A2ARs is required to maintain normal BDNF levels in the brain. Although the mechanism by which A2ARs regulate BDNF is yet undetermined, it is worth mentioning that the cAMP-PKA pathway (the main transduction system operated by A2ARs) has been implicated not only in “gating” BDNF functions [30], but also in modulating BDNF gene transcription [31] and release [32]. Furthermore, Kolarow et al. [33] showed that the PKA inhibitor Rp-cAMP significantly inhibited and delayed BDNF secretion in hippocampal neurons. Interestingly, the endogenous state of activation of A2ARs seems to be adequate to sustain a normal BDNF tone in WT mice, as no increase in the hippocampal levels of BDNF were observed in WT mice treated with a single (0.5 mg/kg i.p sacrifice 24 h later) or with repeated (0.5 mg/kg per day over 5 days) doses of the A2A agonist CGS 21680.
On their whole, the experiments performed in A2A KO mice indicate that A2ARs are essential for the tone and synaptic activity of BDNF. It should be noted, however, that the stimulation or the blockade of A2ARs can induce effects very different from those achieved after stimulation or blockade of the BDNF/TRkB system. For instance, whereas BDNF is thought to play an important role in memory processes [34, 35], adenosine A2ARs seem to negatively influence them. Indeed, an improvement in spatial memory has been reported in A2AR KO mice [36], whereas working memory was impaired in rats overexpressing A2ARs [37]. Another consideration that apparently weakens the importance of the A2AR/BDNF interaction is that A2ARs and TrkB Rs undergo opposite age-related changes in the hippocampus [38]. According to the authors’ interpretation, however, the relationship between age-related changes in the density of TrkB and A2AR receptors does play a role in the modulation of BDNF effects, thus even reinforcing the hypothesis of a close functional interplay between A2ARs and BDNF.
A2ARs regulate striatal BDNF levels in experimental models of HD or HD-like striatal degeneration
Two different models of HD were used: the quinolinic-acid (QA)-lesioned rats (pathogenetic model of HD-like striatal degeneration, [39]) and transgenic R6/2 mice (genetic HD model, [40]). For the method of QA-induced striatal lesions, see [41]. Briefly, QA (180 nmol/1 μl) was unilaterally injected in the striatum of anaesthetised rats, whereas vehicle [1 μl phosphate-buffered saline (PBS)] was injected in the other side. SCH58261 was administered at the doses of 0.01 and 1 mg/kg i.p. 20 min before QA lesion. The levels of BDNF were measured 24 h after surgery. As shown in Fig. 3, BDNF levels were significantly increased in the QA-lesioned vs. the control side. In animals pretreated with both doses of SCH58261 the rise in striatal BDNF was completely prevented. Worthy of note, SCH58261 markedly reduced BDNF levels in the control (vehicle-injected) side also (Fig. 3). As the early rise in BDNF levels most probably reflects a compensatory mechanism following QA injection, one can consider that SCH58261 may worsen QA effects by preventing BDNF increase. Previous studies have, however, demonstrated that this is not the case. We found, indeed, that whereas SCH58261 exerted very clear neuroprotective effects towards QA at 0.01 mg/kg i.p., it was no longer neuroprotective when administered at 1 mg/kg [39]. The finding that SCH58261 reduces BDNF levels irrespective of the dose (neuroprotective or non-neuroprotective) indicates that early changes in the striatal BDNF levels do not seem to correlate with the clinical and neuropathological outcome in the QA model.
Fig. 3The A2A receptor (R)-antagonist SCH58261 reduces striatal brain-derived neurotrophic factor (BDNF) levels in control and quinolinic-acid (QA)-lesioned rats. QA (180 nmol/1 μl) was unilaterally injected in the striatum of anaesthetised rats, whereas vehicle [1 μl phosphate-buffered saline (PBS)] was injected in the other side. SCH58261 was administered at the doses of 0.01 and 1 mg/kg i.p., 20 min before QA lesion. The levels of free mature BDNF were measured 24 h after surgery. BDNF levels were significantly increased in the QA-lesioned vs. the control side. In animals pretreated with both doses of SCH58261, the rise in striatal BDNF was completely prevented. N 5/group. °P < 0.05 vs. PBS. *P < 0.05 vs. corresponding vehicle
R6/2 HD mice may represent a more suitable model to evaluate whether A2AR antagonists have a worsening influence through the reduction of striatal BDNF levels. Indeed, the administration of BDNF has been reported to have beneficial effects in transgenic models of HD [42, 43]. Considering that in the transgenic mice the neurodegenerative process progressively takes place over several weeks, to ascertain whether A2AR blockade could influence striatal BDNF levels, we decided to treat R6/2 mice chronically with SCH58261. The drug was administered at the dose of 0.01 mg/kg per day i.p. over 1 or 3 weeks starting from the fifth week of age. Another group of R6/2 mice was treated with vehicle over 3 weeks. BDNF levels were then assayed at the beginning of the symptomatic phase (8 weeks of age). Three groups of age-matched WT littermates were used as controls and treated in the same way described as above. As shown in Fig. 4, BDNF protein levels were not reduced, and showed instead a nonsignificant tendency to increase, in the striatum of early symptomatic R6/2 vs. WT mice. This finding was unexpected, as a significant decrease in BDNF mRNA has been recently reported in the striatum of R6/2 mice of the same age [43]. Although we have not explored the mechanisms responsible for such a discrepancy, a dissociation between the levels of BDNF protein and mRNA has already been observed in the brains of transgenic R6/1 HD mice [44]. Another reason for which one would expect a reduction in BDNF levels in the striatum of R6/2 mice is that a marked reduction in the expression of A2ARs (which, as mentioned above, are very important to maintain normal BDNF levels) was reported in these mice [45]. More recently, however, the A2AR-stimulated adenylyl cyclase, the A2AR density, and their affinity for the agonist CGS21680 were found unchanged in the striatum of clearly symptomatic R6/2 mice [46].
Fig. 4The A2A receptor (R)-antagonist SCH58261 reduces striatal brain-derived neurotrophic factor (BDNF) levels in R6/2 HD mice SCH58261 was administered at the dose of 0.01 mg/kg per day i.p. over 1 or 3 weeks starting from the fifth week of age. Free mature BDNF levels were then assayed at the beginning of the symptomatic phase (8 weeks of age). Three groups of age-matched wild-type (WT) littermates were used as controls and treated in the same way as described above. Both schedules (1 and 3 weeks) of SCH treatment significantly reduced BDNF levels in the striatum of either R6/2 and WT mice. N  4–7/group. *P < 0.05 vs. corresponding control group (two-tailed unpaired t test)
As for the influence of A2AR blockade, both schedules (1 and 3 weeks) of SCH treatment significantly reduced BDNF levels in the striatum of either R6/2 and WT mice (Fig. 4). Again, however, such an effect does not necessarily imply a negative influence of SCH58261 on HD mice. Indeed, in recent experiments, we found that SCH treatment (0.01 mg/kg per day i.p. between the 5th and the 6th weeks of age) exerted some beneficial effects, namely, normalisation of emotional behaviour and restoration of a normal sensitivity to NMDA in corticostriatal slices (Domenici et al., manuscript in preparation). Thus, although the pharmacological blockade of A2ARs significantly reduces striatal BDNF levels in experimental models of HD or HD-like neurodegeneration, this does not seem to have a negative impact on the course of the disease. Of course, it is still possible that reducing BDNF levels at other time points of the pathological process has a much marked influence on the disease. This issue, as well as the evaluation of BDNF protein changes at different stages of the disease, will be the object of future studies.
Conclusions
Over the last several years, BDNF has emerged not only as a potent neuromodulator but also as a substance exerting fast excitatory actions in neurons, controlling resting membrane potential, neuronal excitability and synaptic transmission and participating in the induction of long-term changes in synaptic transmission [47]. In agreement with the recent evidence that A2ARs play a major role in regulating BDNF functions [16, 48], data reported in this article indicate that the presence and tonic activation of A2ARs are necessary to allow BDNF-induced potentiation of synaptic transmission. As for the mechanisms responsible for the permissive effects of A2ARs, data indicate an involvement of the cAMP-PKA pathway, the main transduction mechanism operated by A2ARs. The finding of reduced BDNF levels in the brain of A2AR KO mice indicates that A2ARs are critical not only to allow the synaptic effects of BDNF but also to maintain normal BDNF levels. Findings also point out that A2ARs tonically regulate BDNF levels in different areas of the brain, irrespective of their levels of expression. The tonic effect exerted by A2ARs in the regulation of BDNF levels is also evident in experimental models of HD (R6/2 mice) and of HD-like striatal degeneration (QA lesion in rats).
Given that BDNF delivery has beneficial effects in models of HD [42, 43], the possible functional consequences of reducing striatal BDNF levels in those models need to be clarified. In particular, further investigations on trophic factors and associated signal pathways are warranted before A2AR antagonists can be considered as a suitable therapeutic approach to HD [24].

adenosine a2a receptors
huntington’s disease
synaptic transmission
bdnf levels
striatum
hippocampus