bluuebunny/crossref_metadata_2025 huggingface dataset:
Timecourse of object‐related neural activity in the primate prefrontal cortex during a short‐term memory task
Authors: Rainer Gregor , Miller Earl K.
Published: March 2003

We studied the timecourse of neural activity in the primate (Macacca mulatta) prefrontal (PF) cortex during an object delayed‐matching‐to‐sample (DMS) task. To assess the effects of experience on this timecourse, we conducted the task using both novel and highly familiar objects. In addition, noise patterns containing no task‐relevant information were used as samples on some trials. Comparison of average PF ensemble activity relative to baseline activity generated by objects and noise patterns revealed three distinct activity periods. (i) Sample onset elicited a transient sensory visual response. In this sensory period, novel objects elicited stronger average ensemble activity than both familiar objects and noise patterns. (ii) An intermediate period of elevated activity followed, which began before sample offset, and continued well into the delay period. In the intermediate period, activity was elevated for noise patterns and novel objects, but near baseline for familiar objects. (iii) Finally, after average ensemble activity reached baseline activity at the end of the intermediate period, a reactivation period occurred late in the delay. Experience had little effect during reactivation, where activity was elevated for both novel and familiar objects compared to noise patterns. We show that the ensemble average resembles the activity timecourse of many single prefrontal neurons. These results suggest that PF delay activity does not merely maintain recent sensory input, but is subject to more complex experience‐dependent dynamics. This has implications for how delay activity is generated and maintained.
Neural cells from primary human striatal xenografts migrate extensively in the adult rat CNS
Authors: Hurelbrink Carrie B. , Armstrong Richard J. E. , Dunnett Stephen B. , Rosser Anne E. , Barker Roger A.
Published: March 2003

Primary neural cells do not appear to migrate significantly following transplantation into the adult rodent CNS, which is in contrast to expanded neural precursor cells where migration is well‐documented. However, most transplant studies of primary neural tissue have been performed in an allograft situation in which it is difficult to identify graft‐derived cells. We have, therefore, used a xenograft paradigm to investigate the potential for cells derived from grafts of primary human fetal striatal tissue (gestational age of 66–72 days) to migrate following intrastriatal transplantation in an athymic adult rat model of Huntington's disease. The use of an antibody specific to human nuclear antigen enabled clear identification of graft‐derived cells within the host brain, and specific neural phenotypes were determined using human‐specific tau for neurons, glial fibrillary acidic protein for mature astrocytes and Ki67 for proliferative cells. At 6 weeks, the graft mass was very dense with a high proliferative index, few cells had migrated away from the graft, and the cells that had differentiated both within and away from the graft were mainly neurons. In contrast, at 6 months, the graft core was dispersed significantly more and a large number of graft‐derived cells had migrated throughout the brain as far rostral as the olfactory bulb and as caudal as the substantia nigra. Cells had differentiated into both neurons and astrocytes and the level of proliferation was significantly lower within the graft. These results demonstrate that primary neural xenografts contain proliferative cells that possess the ability to migrate and differentiate into both neurons and astrocytes, and suggest that these cells could contribute to normal graft function. This property may be a consequence of the xenograft situation and could potentially be exploited to provide the opportunity to target regions of distant pathology in neurodegenerative diseases using xenotransplantation of embryonic neural tissue.
Effect of halothane on neuronal excitation in the superficial dorsal horn of rat spinal cord slices: evidence for a presynaptic action
Authors: Asai Tatsuya , Kusudo Kei , Ikeda Hiroshi , Takenoshita Makoto , Murase Kazuyuki
Published: March 2003

The action of the volatile anaesthetic halothane on optically recorded neuronal excitation in juvenile rat spinal cord slices was investigated. Prolonged neuronal excitation lasting ≈ 100 ms was evoked in the superficial dorsal horn after single‐pulse dorsal root stimulation that activated both A‐ and C‐fibres. Halothane depressed the neuronal excitation in a concentration‐dependent manner (IC50 0.21 mm, Imax 28%). In Ca2+‐free solution, dorsal root stimulation induced excitation with a short duration of several tens of milliseconds, in which the excitation of the postsynaptic component was largely eliminated. Under these conditions, halothane also depressed the excitation concentration‐dependently (IC50 0.46 mm, Imax 60%). Most of the suppression occurred within 5 min of halothane application, and the effect of halothane was fully reversible upon washout of the anaesthetic. Application of bicuculline and strychnine or picrotoxin, or reduction of extracellular Cl– concentration ([Cl–]o), had no effect on halothane inhibition. Applications of K+ channel blockers tetraethyl ammonium, 4‐aminopyridine, Cs+ or Ba2+ either had no effect or augmented the inhibitory effect of halothane. On the other hand, the degree of inhibition by halothane was found to be dependent on [K+]o; the higher [K+]o, the larger the depression. In addition, decreases in [Na+]o and [Mg2+]o reduced the excitation similar to that of halothane treatment, and the degree of halothane inhibition became larger with lower [Mg2+]o. These results lead to a hypothesis that halothane suppresses the excitation of presynaptic elements by inhibiting presynaptic Na+ channels by shifting the steady‐state inactivation curve in the hyperpolarizing direction.
Adenosine depresses a Ca2+‐independent step in transmitter exocytosis at frog motor nerve terminals
Authors: Huang Shu‐Ming , Kitamura Atsuko , Akita Tenpei , Narita Kazuhiko , Kuba Kenji
Published: March 2003

The depressant action of adenosine on acetylcholine release at frog motor nerve terminals was studied by intracellular recording and Ca2+‐imaging techniques. Adenosine (200 µm) quickly and reversibly decreased the amplitude and quantal content of end‐plate potentials (EPPs) with no change in quantal size in a low‐Ca2+, high‐Mg2+ solution, and EPP amplitude in normal Ringer containing d‐tubocurarine. Likewise, adenosine (200 µm) reduced miniature EPP (MEPP) frequency, but not amplitude, in a high‐K+ (6 mm) solution. Adenosine (40–200 µm), however, did not affect single or repetitive impulse(s)‐induced rises in Ca2+ in the nerve terminals or its basal level. Adenosine (100–200 µm) reduced the Ca2+‐independent enhancement of MEPP frequency caused by hypertonicity. EPPs induced by tetanic stimulation (33 Hz) in Ringer with d‐tubocurarine initially increased in amplitude within 10 stimuli and then declined to the minimum. Adenosine (200 µm) decreased EPP amplitude in the initial phase of the tetanus, but enhanced it in the middle phase, thus prolonging the decay of EPP amplitude. The total sum of these EPPs, reflecting the readily releasable pool of vesicles and its refilling, however, was not changed. The results suggest that adenosine inhibits a Ca2+‐independent step of transmitter exocytosis at frog motor nerve terminals.
Expression of BCL‐2 via adeno‐associated virus vectors rescues thalamic neurons after visual cortex lesion in the adult rat
Authors: Caleo Matteo , Cenni Maria Cristina , Costa Mario , Menna Elisabetta , Zentilin Lorena , Giadrossi Sara , Giacca Mauro , Maffei Lamberto
Published: March 2003

Lesions of the mammalian visual cortex cause the retrograde degeneration of the thalamic neurons projecting to the damaged cortex. The proto‐oncogene bcl‐2 is known to inhibit neuronal apoptosis induced by a variety of noxious stimuli and preserve the functional integrity of the injured cells. Here we have tested whether the overexpression of bcl‐2 via adeno‐associated virus (AAV) vectors is able to protect the neurons in the lateral geniculate nucleus after visual cortex ablation in adult rats. Recombinant AAV vectors encoding Bcl‐2 (AAV‐Bcl‐2) or green fluorescent protein (AAV‐GFP) as a control were stereotaxically injected into the geniculate. Three weeks after vector injection, the ipsilateral visual cortex was removed by aspiration, and cell survival was assessed 2 weeks later. We found that 20% of the geniculate neurons were transduced by the Bcl‐2 vector. These cells were completely protected from death following cortical ablation. Delivery of AAV‐GFP transduced an identical number of geniculate neurons but had no effect on cell survival after lesion. The total number of surviving geniculate neurons was found to be significantly higher in animals injected with AAV‐Bcl‐2 than in rats injected with AAV‐GFP or in control lesioned rats. These data indicate that Bcl‐2 gene therapy with AAV vectors represents an effective treatment to promote neuronal survival after central nervous system insults.
Classical eyeblink conditioning in decerebrate guinea pigs
Authors: Kotani Sadaharu , Kawahara Shigenori , Kirino Yutaka
Published: March 2003

A decerebrate guinea pig preparation was used to test the hypothesis that brainstem–cerebellar circuitry is sufficient for classical delay eyeblink conditioning. Delay conditioning was carried out using a tone conditioned stimulus (CS) paired with a co‐terminating, periorbital shock unconditioned stimulus (US). Decerebrate animals readily acquired the conditioned response (CR), while pseudoconditioning yielded no signs of learning. When a longer tone CS was used, the learning became slower. These CRs were adaptive and appropriately timed relative to the US. Subsequent CS‐alone trials caused extinction of the CR. These characteristics of the eyeblink conditioning were similar to those reported previously in various species, suggesting that the cerebellum and brainstem are sufficient for this type of learning.
Neuronal activity in the monkey motor thalamus during bicuculline‐induced dystonia
Authors: Macia F. , Escola L. , Guehl D. , Michelet Th. , Bioulac B. , Burbaud P.
Published: March 2003

Recent data suggest that a decreased basal ganglia output may occur in dystonia, resulting in an increased thalamic drive to the mesial premotor cortex. In a previous work we found that injection of the GABAA antagonist bicuculline into the rostral motor thalamus induced contralateral dystonic postures, whereas myoclonic jerks were frequent after injection into the caudal motor thalamus. In the present study, we performed electrophysiological recordings in the rostral and caudal parts of the ventrolateral thalamus of two cynomolgus monkeys before and after bicuculline injections or saline injections. Discharge frequencies of thalamic neurons were increased after bicuculline injections vs. controls. Their discharge pattern was more bursty in the caudal part in which bursts of neuronal activity were correlated with myoclonic jerks. After bicuculline injection, neurons responded more frequently and less selectively to passive limb movements in both parts of the motor thalamus. Conversely, the response to microstimulation increased after bicuculline injection, particularly in the caudal part. Our data show that acute bicuculline‐induced dystonia is associated with a reversible overactivity and disorganization of neuronal activity in the motor thalamus. Such a phenomenon might induce an overspreading of cortical activity leading to dystonia. We postulate that the distinct clinical syndromes observed after bicuculline injections into the rostral and caudal motor thalamus are due to differences both in the neuronal circuitry within each thalamic nucleus and in segregated cortical projections.
Increased hypothalamic expression of prolactin in lactation: involvement in behavioural and neuroendocrine stress responses
Authors: Torner Luz , Toschi Nicola , Nava Gabriel , Clapp Carmen , Neumann Inga D.
Published: March 2003

Prolactin (PRL) has recently been shown to exert an anxiolytic effect in male and virgin female rats, as well as an inhibitory tone on hypothalamic‐pituitary‐adrenal (HPA) axis activity. Reduced emotional and neuroendocrine stress responses have been described in lactation, a time of high blood PRL levels. Here we tested brain PRL‐receptor (PRL‐R)‐mediated effects on anxiety, maternal behaviour, HPA axis and oxytocin stress responses in lactating rats. Chronic intracerebroventricular (i.c.v.) infusion of antisense oligonucleotides against the long form of the PRL‐R (AS; osmotic minipump, 0.5 µg/0.5 µL/h) in order to downregulate brain PRL‐R expression increased the anxiety‐related behaviour on the elevated plus maze (P < 0.01) compared with mixed bases‐ and vehicle‐treated rats. Also, PRL‐R AS treatment impaired maternal behaviour (P < 0.05), whereas physiological parameters of lactation (weight gain of the litter, number of milk ejection reflexes during a 20‐min suckling period) were not affected. PRL‐R AS treatment further evoked an increase (P < 0.05) in the stress‐induced adrenocorticotropin release, demonstrating an inhibitory role of PRL on HPA axis responses in lactation. Inhibition of stress responses of the oxytocin system by brain PRL was evidenced by higher stress‐induced (P < 0.05) plasma oxytocin concentration in PRL‐R AS‐treated lactating rats and, in contrast, decreased stress‐induced oxytocin release (P < 0.01) in chronic i.c.v. ovine PRL‐treated (1 µg/0.5 µL/h) virgin rats. Finally, an increased expression of the hypothalamic PRL gene was seen by RT‐PCR in pregnancy and lactation, suggesting an activated state of the brain PRL system during the peripartum period. In summary, activation of the brain PRL system in the peripartum period significantly contributes to emotional and neuroendocrine adaptations, including downregulation of the responsiveness of the HPA axis and oxytocin systems to stressors seen at this time.
Functional glycine receptors are expressed by postnatal nestin‐positive neural stem/progenitor cells
Authors: Nguyen Laurent , Malgrange Brigitte , Belachew Shibeshih , Rogister Bernard , Rocher Véronique , Moonen Gustave , Rigo Jean‐Michel
Published: March 2003

Multipotent neural stem and progenitor cells (NS/PCs) are well‐established cell subpopulations occurring in the developing, and also in the mature mammalian nervous systems. Trophic and transcription factors are currently the main signals known to influence the development and the commitment of NS/PCs and their progeny. However, recent studies suggest that neurotransmitters could also contribute to neural development. In that respect, rodent‐cultured embryonic NS/PCs have been reported to express functional neurotransmitter receptors. No similar investigation has, however, been made in postnatal and/or in adult rodent brain stem cells. In this study, using RT‐PCR and immunocytochemical methods, we show that α1‐, α2‐ and β‐subunit mRNAs and α‐subunit proteins of the glycine ionotropic receptor are expressed by 80.5 ± 0.9% of postnatal rat striatum‐derived, nestin‐positive cells within cultured neurospheres. Whole‐cell patch‐clamp experiments further demonstrated that glycine triggers in 33.5% of these cells currents that can be reversibly blocked by strychnine and picrotoxin. This demonstrates that NS/PCs express functional glycine receptors, the consequence(s) of their activation remaining unknown.
Quantification and localization of PEGylated polycyanoacrylate nanoparticles in brain and spinal cord during experimental allergic encephalomyelitis in the rat
Authors: Calvo Pilar , Gouritin Bruno , Villarroya Henri , Eclancher Françoise , Giannavola Claudia , Klein Christophe , Andreux Jean P. , Couvreur Patrick
Published: March 2003

Under healthy conditions, the blood–brain barrier (BBB) limits the passage of solutes and cells from the blood to the CNS. During neurological diseases, BBB permeability increases dramatically and it has been hypothesized that drug carrier systems such as polymeric nanoparticles could cross the BBB and penetrate into the CNS. PEGylated polyalkylcyanoacrylate nanoparticles (long‐circulating carrier) are one such system and have been investigated during experimental allergic encephalomyelitis (EAE). Brain and spinal cord concentrations of [14C]‐radiolabelled PEGylated polyalkylcyanoacrylate nanoparticles were compared with another blood long‐circulating carrier (poloxamine 908‐coated polyalkylcyanoacrylate nanoparticles) and with conventional non‐long‐circulating polyalkylcyanoacrylate nanoparticles. The microscopic localization of fluorescent nanoparticles in the CNS was also investigated in order to further understand the mechanism by which the particles penetrate the BBB. The results demonstrate that the concentration of PEGylated nanoparticles in the CNS, especially in white matter, is greatly increased in comparison to conventional non‐PEGylated nanoparticles. In addition, this increase was significantly higher in pathological situations where BBB permeability is augmented and/or macrophages have infiltrated. Passive diffusion and macrophage uptake in inflammatory lesions seems to be the mechanism underlying such particles' brain penetration. Based on their long‐circulating properties in blood and on their surface characteristics that allow cell interactions, PEGylated nanoparticles penetrated into CNS to a larger extent than all the other formulations tested. Thus, PEGylated polycyanoacrylate nanoparticles are proposed here as a new brain delivery system for neuroinflammatory diseases.
Neuronal populations in primary motor cortex encode bimanual arm movements
Authors: Steinberg O. , Donchin O. , Gribova A. , De Oliveira S. Cardoso , Bergman H. , Vaadia E.
Published: March 2003

Previous studies have shown that activity of neuronal populations in the primary motor cortex (MI), processed by the population vector method, faithfully predicts upcoming movements. In our previous studies we found that single neurons responded differently during movements of one arm vs. combined movements of the two arms. It was, therefore, not clear whether the population vector approach could produce reliable movement predictions also for bimanual movements. This study tests this question by comparing the predictive quality of population vectors for unimanual and bimanual arm movements. We designed a bimanual motor task that requires coordinated movements of the two arms, in which each arm may move in eight directions, and recorded single unit activity in the MI of two rhesus (Macaca mulatta) monkeys during the performance of unimanual and bimanual arm movements. We analysed the activity of 212 MI cells from both hemispheres and found that, despite bimanual related activity, the directional tuning and preferred directions of most cells were preserved in unimanual and bimanual movements. We demonstrate that population vectors, constructed from the activity of MI cells, predict accurately the direction of movement both for unimanual and for bimanual movements even when the two arms move simultaneously in different directions.
MOR‐1‐immunoreactive neurons in the dorsal horn of the rat spinal cord: evidence for nonsynaptic innervation by substance P‐containing primary afferents and for selective activation by noxious thermal stimuli
Authors: Spike R. C. , Puskár Z. , Sakamoto H. , Stewart W. , Watt C. , Todd A. J.
Published: March 2003

A direct action of μ‐opioid agonists on neurons in the spinal dorsal horn is thought to contribute to opiate‐induced analgesia. In this study we have investigated neurons that express the μ‐opioid receptor MOR‐1 in rat spinal cord to provide further evidence about their role in nociceptive processing. MOR‐1‐immunoreactive cells were largely restricted to lamina II, where they comprised approximately 10% of the neuronal population. The cells received few contacts from nonpeptidergic unmyelinated afferents, but many from substance P‐containing afferents. However, electron microscopy revealed that most of these contacts were not associated with synapses. None of the MOR‐1 cells in lamina II expressed the neurokinin 1 receptor; however, the μ‐selective opioid peptide endomorphin‐2 was present in the majority (62–82%) of substance P axons that contacted them.

    Noxious thermal stimulation of the foot induced c‐Fos expression in approximately 15% of MOR‐1 cells in the medial third of the ipsilateral dorsal horn at mid‐lumbar level. However, following pinching of the foot or intraplantar injection of formalin very few MOR‐1 cells expressed c‐Fos, and for intraplantar formalin injection this result was not altered significantly by pretreatment with systemic naloxone.

    Although these findings indicate that at least some of the neurons in lamina II with MOR‐1 are activated by noxious thermal stimulation, the results do not support the hypothesis that the cells have a role in transmitting nociceptive information following acute mechanical or chemical noxious stimuli.
Response properties of neurons in the core of the central nucleus of the inferior colliculus of the barn owl
Authors: Wagner Hermann , Mazer James A. , Von Campenhausen Mark
Published: March 2003

The central nucleus of the inferior colliculus (ICC) is particularly important for the processing of interaural time differences (ITDs). In the barn owl, neuronal best frequencies in a subnucleus of the ICC, the ICCcore, span the animal's entire hearing range (≈ 200–10 000 Hz). This means that low‐frequency ITD‐sensitive ICCcore neurons in the owl can be directly compared to ITD‐sensitive mammalian ICC neurons with similar best frequencies as well as to the high‐frequency ITD‐sensitive neurons usually studied in owls. This report represents a first attempt to systematically describe important physiological properties of ICCcore neurons in the barn owl, with particular attention to the low‐frequency region (< 2 kHz). Responses were obtained from 133 neurons or small clusters of neurons; recording sites were confirmed by histological reconstruction of electrode tracks based on electrolytic lesions. Iso‐intensity frequency response functions were typically ≈ 1 octave wide in the low‐frequency range and ≈ 1/3 octave wide in the high‐frequency range. Most neurons were ITD‐tuned; both noise and pure tone stimuli yielded periodic ITD tuning curves with several equivalent response maxima. In most cases ITD tuning curves had a response peak within the barn owl's physiological ITD range. ITD tuning widths were inversely correlated with neuronal best frequency. None of the ICCcore neurons studied were sensitive to interaural level differences. Monaural inputs to ICCcore cells were typically binaurally balanced, i.e. they exhibited similar response thresholds, dynamic ranges, slopes and saturation levels, for both left and right ear monaural stimulation.
Focal application of neutralizing antibodies to soluble neurotrophic factors reduces collateral axonal branching after peripheral nerve lesion
Authors: Streppel M. , Azzolin N. , Dohm S. , Guntinas‐Lichius O. , Haas C. , Grothe C. , Wevers A. , Neiss W. F. , Angelov D. N.
Published: March 2003

A major reason for the insufficient recovery of function after motor nerve injury are the numerous axonal branches which often re‐innervate muscles with completely different functions. We hypothesized that a neutralization of diffusable neurotrophic factors at the lesion site in rats could reduce the branching of transected axons. Following analysis of local protein expression by immunocytochemistry and by in situ hybridization, we transected the facial nerve trunk of adult rats and inserted both ends into a silicon tube containing (i) collagen gel with neutralizing concentrations of antibodies to NGF, BDNF, bFGF, IGF‐I, CNTF and GDNF; (ii) five‐fold higher concentrations of the antibodies and (iii) combination of antibodies. Two months later, retrograde labelling was used to estimate the portion of motoneurons the axons of which had branched and projected into three major branches of the facial trunk. After control entubulation in collagen gel containing non‐immune mouse IgG 85% of all motoneurons projecting along the zygomatic branch sprouted and sent at least one twin axon to the buccal and/or marginal‐mandibular branches of the facial nerve. Neutralizing concentrations of anti‐NGF, anti‐BDNF and anti‐IGF‐I significantly reduced sprouting. The most pronounced effect was achieved after application of anti‐BDNF, which reduced the portion of branched neurons to 18%. All effects after a single application of antibodies were concentration‐dependent and superior to those observed after combined treatment. This first report on improved quality of reinnervation by antibody‐therapy implies that, in rats, the post‐transectional collateral axonal branching can be reduced without obvious harmful effects on neuronal survival and axonal elongation.
Protein kinase C‐mediated translocation of secretory vesicles to plasma membrane and enhancement of neurotransmitter release from PC12 cells
Authors: Shoji‐Kasai Yoko , Itakura Makoto , Kataoka Masakazu , Yamamori Saori , Takahashi Masami
Published: March 2003

In order to elucidate the molecular mechanism of phorbol ester‐induced potentiation of neurotransmitter release, changes in the subcellular distribution of secretory vesicles were studied in PC12 cells. Dopamine (DA) and acetylcholine containing vesicles were selectively labelled by expressing green fluorescent protein‐conjugated vesicular monoamine transporter and vesicular acetylcholine transporter, respectively. In the resting state, these vesicles were distributed throughout the cytoplasm. Phorbol‐12‐myristate‐13‐acetate (PMA), but not the inactive analogue 4α‐PMA, induced a redistribution of both types of secretory vesicles near the plasma membrane, and this change was abolished by a protein kinase C (PKC) inhibitor, bisindolylmaleimide I (BIS). PMA also induced a marked enhancement of depolarization‐induced DA release and phosphorylation of SNAP‐25 at Ser187. BIS completely inhibited PMA‐induced SNAP‐25 phosphorylation but suppressed PMA‐induced enhancement of DA release only partially. These results suggest that PMA enhances neurotransmitter release from PC12 cells by both PKC‐dependent and PKC‐independent mechanisms, and PKC enhances neurotransmitter release by recruiting secretory vesicles to the plasma membrane.
Projections from the parahippocampal region to the prefrontal cortex in the rat: evidence of multiple pathways
Authors: Delatour B. , Witter M. P.
Published: March 2003

The purpose of the present study was to investigate, by means of anterograde tracing methods, the detailed organization of the parahippocampal–prefrontal projections in the rat brain. Efferents from the perirhinal cortex were found to terminate principally in both the ventromedial (prelimbic and infralimbic cortices) and lateral (agranular insular cortex) regions of the prefrontal cortex. Terminal fields were observed mainly in the superficial layers of the prefrontal cortex. Projections arising from the dorsolateral entorhinal cortex, which borders the perirhinal cortex along its ventral extent, were similarly directed to the ventromedial and lateral prefrontal cortices but also encompassed other frontal areas (dorsomedial and orbital prefrontal regions). Terminal fields of entorhinal projections were also found in the superficial layers of the prefrontal cortex. A third pathway, taking its source in the post‐rhinal cortex, presented striking topographical differences with the two other output systems. Hence, post‐rhinal efferences terminated only in the ventrolateral orbital area. The results indicate that two main routes originate from the parahippocampal region to reach the prefrontal cortex. One pathway involves the rostral and lateral portions of the parahippocampal region (perirhinal and dorsolateral entorhinal cortices), and the other relies on its most caudal region, the post‐rhinal cortex. The presence of such different multiple parahippocampal–prefrontal pathways may have functional relevance for learning and memory processes.
Influence of cue‐conditioning on acquisition, maintenance and relapse of cocaine intravenous self‐administration
Authors: Deroche‐Gamonet Véronique , Piat Frédéric , Le Moal Michel , Piazza Pier Vincenzo
Published: March 2003

Conditioning theories propose that, through a Pavlovian associative process, discrete stimuli acquire the ability to elicit neural states involved in the maintenance and relapse of a drug‐taking behaviour. Experimental evidence indicates that drug‐related cues play a role in relapse, however, their influence on the development and maintenance of drug self‐administration has been poorly investigated. In this report, we analysed the effects of a drug‐associated cue light on acquisition, maintenance and reinstatement of intravenous cocaine self‐administration. The results show that a cocaine‐associated cue light can act as an incentive in absence of the drug, but does not directly modify drug‐reinforcing effects. Contingent and non‐contingent presentations of a cocaine‐associated cue light reinstated an extinguished self‐administration behaviour. However, regardless of whether or not a cue light was associated with cocaine infusions, rats acquire cocaine intravenous self‐administration reaching the same levels of intake. Furthermore, after self‐administration has been acquired in presence of the cue light, the omission of the cue light or its non‐contingent presentation did not modify rat behaviour. In conclusion, our work shows that cocaine‐associated explicit cues do not directly interfere with the reinforcing effects of the drug.
Frontal theta activity in humans increases with memory load in a working memory task
Authors: Jensen Ole , Tesche Claudia D.
Published: March 2003

Recent theoretical work has suggested that brain oscillations in the theta band are involved in active maintenance and recall of working memory representations. To test this theoretical framework we recorded neuromagnetic responses from 10 subjects performing the Sternberg task. Subjects were required to retain a list of 1, 3, 5 or 7 visually presented digits during a 3‐s retention period. During the retention period we observed ongoing frontal theta activity in the 7–8.5‐Hz band recorded by sensors over frontal brain areas. The activity in the theta band increased parametrically with the number of items retained in working memory. A time–frequency analysis revealed that the task‐dependent theta was present during the retention period and during memory scanning. Following the memory task the theta activity was reduced. These results suggest that theta oscillations generated in frontal brain regions play an active role in memory maintenance.
Enhanced motivation to self‐administer cocaine is predicted by self‐grooming behaviour and relates to dopamine release in the rat medial prefrontal cortex and amygdala
Authors: Homberg Judith R. , Van Den Akker Margot , Raasø Halfdan S. , Wardeh George , Binnekade Rob , Schoffelmeer Anton N. M. , De Vries Taco J.
Published: March 2003

Rats, like humans, show strong individual differences in their response to anxiogenic and stressful stimuli. In the present study we evaluated whether differences in stress‐induced self‐grooming behaviour may predict an individual's vulnerability to engage in drug self‐administration behaviour. From a population of Wistar rats, the lower and upper quartile with respect to time spent self‐grooming on an elevated plus maze (EPM) were selected and trained to intravenously self‐administer cocaine under fixed and progressive ratio schedules of reinforcement. High grooming (HG) rats reached considerably higher breakpoints than low grooming (LG) rats but showed no differences in acquisition rate and dose–response relationships. Further, EPM exposure elicited higher anxiety levels and enhanced plasma corticosterone secretion in HG rats. In addition, HG rats did not display enhanced novelty‐seeking and still spent more time self‐grooming during an EPM re‐test following the cocaine self‐administration procedure, indicating that stress‐induced self‐grooming is a stable behavioural trait marker. Neurochemically, electrically evoked [3H]dopamine release in vitro was profoundly lower in brain slices from the substantia nigra, medial prefrontal cortex and amygdala of naive HG rats as compared to LG rats, whereas no differences were found in the nucleus accumbens shell and core, the ventral tegmental area and caudate putamen. In conclusion, stress‐induced self‐grooming specifically predicts enhanced motivation to self‐administer cocaine rather than sensitivity to its reinforcing effects. Responsiveness of dopaminergic nerve terminals in the medial prefrontal cortex and amygdala may represent pre‐existing underlying factors.
Partial regeneration and long‐term survival of rat retinal ganglion cells after optic nerve crush is accompanied by altered expression, phosphorylation and distribution of cytoskeletal proteins
Authors: Dieterich Daniela C. , Trivedi Niraj , Engelmann Ralf , Gundelfinger Eckart D. , Gordon‐Weeks Phillip R. , Kreutz Michael R.
Published: March 2003

In a screen to identify genes that are expressed differentially in the retina after partial optic nerve crush, we identified MAP1B as an up‐regulated transcript. Western blot analysis of inner retina protein preparations confirmed changes in the protein composition of the microtubule‐associated cytoskeleton of crushed vs. uncrushed nerve. MAP1B immunoreactivity and transcript levels were elevated for two weeks after crush. Immunostaining and Western blots with monoclonal antibodies directed against developmentally regulated phosphorylation sites on MAP1B revealed a gradient of MAP1B phosphorylation from the proximal optic nerve stump to the soma of retinal ganglion cells. Most interestingly, using antibodies directed against developmentally regulated phosphorylation sites on MAP1B, we observed that a significant number of crushed optic nerve axons develop MAP1B‐immunopositive growth cones, which cross the crush site and migrate along the distal nerve fragment. In parallel, an abnormal distribution of highly phosphorylated neurofilament protein (pNF‐H) in the cell soma and dendrites of presumably axotomized retinal ganglion cells was observed following partial nerve crush. This redistribution is present for the period between day 7 and 28 postcrush and is not seen in cells that stay connected to the superior colliculus. Axotomized ganglion cells, which contain pNF‐H in soma and dendrites appear to have been disconnected from the colliculus at an early stage but survive axonal trauma for long periods.
Cysteine‐string protein in inner hair cells of the organ of Corti: synaptic expression and upregulation at the onset of hearing
Authors: Eybalin Michel , Renard Nicole , Aure Frédérique , Safieddine Saaid
Published: March 2003

Cysteine‐string protein is a vesicle‐associated protein that plays a vital function in neurotransmitter release. We have studied its expression and regulation during cochlear maturation. Both the mRNA and the protein were found in primary auditory neurons and the sensory inner hair cells. More importantly, cysteine‐string protein was localized on synaptic vesicles associated with the synaptic ribbon in inner hair cells and with presynaptic differentiations in lateral and medial olivocochlear terminals — the cell bodies of which lie in the auditory brainstem. No cysteine‐string protein was expressed by the sensory outer hair cells suggesting that the distinct functions of the two cochlear hair cell types imply different mechanisms of neurotransmitter release. In developmental studies in the rat, we observed that cysteine‐string protein was present beneath the inner hair cells at birth and beneath outer hair cells by postnatal day 2 only. We found no expression in the inner hair cells before about postnatal day 12, which corresponds to the period during which the first cochlear action potentials could be recorded. In conclusion, the close association of cysteine‐string protein with synaptic vesicles tethered to synaptic ribbons in inner hair cells and its synchronized expression with the appearance and maturation of the cochlear potentials strongly suggest that this protein plays a fundamental role in sound‐evoked glutamate release by inner hair cells. This also suggests that this role may be common to ribbon synapses and conventional central nervous system synapses.
Properties of LTD and LTP of retinocollicular synaptic transmission in the developing rat superior colliculus
Authors: Lo Fu‐Sun , Mize R. Ranney
Published: March 2003

The developing retinocollicular pathway undergoes synaptic refinement in order to form the precise retinotopic pattern seen in adults. To study the mechanisms which underlie refinement, we investigated long‐term changes in retinocollicular transmission in rats aged P0–P25. Field potentials (FPs) in the superior colliculus (SC) were evoked by stimulation of optic tract fibers in an in vitro isolated brainstem preparation. High intensity stimulation induced long‐term depression (LTD) in the SC after both low (1000 stimuli at 1 Hz) and higher (1000 stimuli at 50 Hz) frequency stimulation. The induction of LTD was independent of activation of NMDA and GABAA receptors, because d‐APV (100 µM) and bicuculline (10 µM) did not block LTD. Induction of LTD was dependent upon activation of l‐type Ca2+ channels as 10 µM nitrendipine, an l‐type Ca2+ channel blocker, significantly decreased the magnitude of LTD. LTD was down‐regulated during development. LTD magnitude was greatest in rats aged P0–P9 and significantly less in rats aged P10–P25. Long‐term potentiation (LTP) was induced by low intensity stimulation and only after high frequency tetanus (1000 stimuli at 50 Hz). LTP was NMDA receptor dependent because d‐APV (100 μM) completely abolished it. LTP induction was also blocked by the l‐type Ca2+ channel blocker nitrendipine. The magnitude of LTP first increased with age, being significantly greater at P7–P13 than at P0–3 and then decreased at P23–25. In summary, both LTD and LTP are present during retinocollicular pathway refinement, but have different transmitter and ionic mechanisms and time courses of expression.
Increased vulnerability to kainate‐induced seizures in utrophin‐knockout mice
Authors: Knuesel Irene , Riban Véronique , Zuellig Richard A. , Schaub Marcus C. , Grady R. Mark , Sanes Joshua R. , Fritschy Jean‐Marc
Published: March 2003

Utrophin, the autosomal homologue of dystrophin, the Duchenne muscular dystrophy gene product, is a cytoskeletal protein found in many tissues. In muscle fibers, the level and localization of utrophin depend on their state of differentiation and innervation. Transgenic overexpression of utrophin prevents degeneration of dystrophin‐deficient muscle fibers. In brain, in addition to its enrichment in blood vessels, utrophin is associated primarily with the plasma membrane of large sensory and motor brainstem neurons, suggesting a contribution to their structural stability. Here, we examined the role of utrophin for long‐term survival of dentate granule cells, which become markedly hypertrophic in a mouse model of temporal lobe epilepsy. This morphogenetic change is induced several weeks after a unilateral intrahippocampal injection of kainic acid (KA), while mice experience chronic focal seizures. Using in situ hybridization and immunohistochemistry, we show that dispersion and hypertrophy of granule cells in KA‐treated wildtype mice are accompanied by a strong and long‐lasting expression of utrophin in somata and proximal dendrites. Utrophin knockout mice had a normal hippocampal cytoarchitecture but were more sensitive to KA‐induced excitotoxicity, as shown by increased mortality and faster progression of the lesion. At 6 weeks post‐KA, the numerical density of granule cells and thickness of the granule cell layer were significantly reduced ipsilaterally in mutant mice, indicating a profound reduction in total cell number in the absence of utrophin. These findings suggest that utrophin contributes to protect CNS neurons against pathological insults, in particular, stimuli leading to massive neuronal hypertrophy.
PACAP protects cerebellar granule neurons against oxidative stress‐induced apoptosis
Authors: Vaudry D. , Pamantung T. F. , Basille M. , Rousselle C. , Fournier A. , Vaudry H. , Beauvillain J. C. , Gonzalez B. J.
Published: March 2003

Oxidative stress, resulting from accumulation of reactive oxygen species, plays a critical role in neuronal cell death associated with neurodegenerative diseases and stroke. In the present study, we have investigated the potential neuroprotective effect of pituitary adenylate cyclase‐activating polypeptide (PACAP) on oxidative stress‐induced apoptosis. Incubation of cerebellar granule cells with PACAP inhibited hydrogen peroxide‐evoked cell death in a concentration‐dependent manner. The effect of PACAP on granule cell survival was not mimicked by vasoactive intestinal polypeptide and was blocked by the antagonist PACAP6‐38. The protective action of PACAP upon hydrogen peroxide‐induced neuronal cell death was abolished by the MAP‐kinase kinase (MEK) inhibitor U0126 and mimicked by the caspase‐3 inhibitor Z‐DEVD‐FMK. PACAP markedly inhibited hydrogen peroxide‐evoked caspase‐3 activation and DNA fragmentation. Taken together, these data indicate that PACAP, acting through PACAP receptor type 1, exerts a potent protective effect against neuronal degeneration induced by hydrogen peroxide. The anti‐apoptotic effect of PACAP is mediated through the MAP‐kinase pathway and can be accounted for by inhibition of caspase‐3 activation resulting from oxidative stress.
Downregulation of P2X3 receptor‐dependent sensory functions in A/J inbred mouse strain
Authors: Tsuda Makoto , Shigemoto‐Mogami Yukari , Ueno Shinya , Koizumi Schuichi , Ueda Hiroshi , Iwanaga Toshihiko , Inoue Kazuhide
Published: March 2003

There is large variability in the various pain responses including those to tissue injury among inbred mouse strains. However, the determinant factors for the strain‐specific differences remain unknown. The P2X3 sensory‐specific ATP‐gated channel has been implicated as a damage‐sensing molecule that evokes a pain sensation by receiving endogenous ATP from injured tissue. In this study, to clarify the contribution of the sensory P2X3 signalling to strain‐specific differences in tissue injury pain, we examined whether the P2X3‐mediated in vivo and in vitro responses in dorsal root ganglion (DRG) neurons are changed in the A/J inbred mouse strain, which is known to be resistant to tissue injury pain caused by formalin. Here we found that A/J mice exhibited a low magnitude of nocifensive behaviour induced by the P2X agonist α,β‐methylene ATP (αβmeATP) into the hindpaw compared with C57BL/6 J mice. This behaviour was blocked by P2X3 antisense oligodeoxynucleotides. The low magnitude of the in vivo pain sensation could be observed similarly in the in vitro response; the increase in the intracellular Ca2+ increase by αβmeATP in capsaicin‐sensitive DRG neurons from A/J mice was significantly lower than that from C57BL/6 J mice. In A/J DRG neurons the P2X3 protein level was significantly lower compared with C57BL/6 J DRG neurons. The change in P2X3 protein was selective because P2X2 protein was expressed equally in both strains. The present study suggests that the downregulation of sensory P2X3 could be one of the molecular predispositions to low sensitivity to tissue injury pain in the A/J inbred mouse strain.
Expression and immunohistochemical localization of heparan sulphate proteoglycan N‐syndecan in the migratory pathway from the rat olfactory placode
Authors: Toba Yoko , Horie Masao , Sango Kazunori , Tokashiki Akiko , Matsui Fumiko , Oohira Atsuhiko , Kawano Hitoshi
Published: March 2003

N‐syndecan, a membrane‐bound heparan sulphate proteoglycan, is abundantly present in the developing nervous system and thought to play important roles in the neurite outgrowth. In the present study, we examined the distribution of N‐syndecan in the migratory route from the rat olfactory placode using immunohistochemistry and in situ hybridization. At embryonic day 15, both heparan sulphate and N‐syndecan immunoreactivities were localized in and around the migrating cell clusters, which contained luteinizing hormone‐releasing hormone (LHRH) and calbindin D‐28k. Immunoreactivity for other glycosaminoglycan chains, such as chondroitin and keratan sulphate, and core proteins of the chondroitin sulphate proteoglycan, neurocan and phosphacan, were barely detected in the migratory pathway from the olfactory placode. By in situ hybridization histochemistry, N‐syndecan mRNA was localized in virtually all of migrating neurons as well as in cells of the olfactory epithelium and the vomeronasal organ. N‐syndecan immunoreactivity surrounded cells migrating along the vomeronasal nerves that were immunoreactive for neural cell adhesion molecules, NCAM, L1 and TAG‐1. Considering that NCAM is implicated in the migratory process of LHRH neurons and specifically binds to heparan sulphate, it is likely that a heterophilic interaction between NCAM and N‐syndecan participates in the neuronal migration from the rat olfactory placode.
Second phase of formalin‐induced excitation of spinal dorsal horn neurons in spinalized rats is reversed by sciatic nerve block
Authors: Pitcher Graham M. , Henry James L.
Published: March 2003

Considerable debate persists concerning peripheral vs. central mechanisms underlying the second phase of the nociceptive response in the formalin test in the rat. To gain insight into the neurophysiological basis of this pain, we investigated the effects of block of afferent nerve conduction during the second phase of formalin‐evoked excitation of single nociceptive neurons recorded extracellularly from rat spinal dorsal horn segments (L3−4) in pentobarbital‐anaesthetized, male Sprague–Dawley rats. Rats were spinally transected (T9) to examine exclusively peripheral and spinal nociceptive processing. In six control rats, hind paw intraplantar formalin injection (50 µL, 2.5%) induced the typical biphasic increase in the discharge rate of the six wide dynamic range neurons tested. This response consisted of a relatively brief immediate phase (approximately 5 min), followed by decreased firing. An ensuing second phase of elevated discharge began approximately 35 min after injection and persisted to at least 80 min. In this control group, 0.9% saline was applied to the exposed ipsilateral sciatic nerve after onset of the second phase (40 min after formalin injection). In a group of six test rats, application of 2% lidocaine instead of saline reversed the second phase of excitation in all six wide dynamic range neurons examined. When the firing rate was normalized to that at 40 min (100%), the time of saline or lidocaine administration, the rate at 50 min was 120 ± 7.5% in the saline‐treated group and 31 ± 7.4% in the lidocaine‐treated group; following lidocaine treatment firing rate remained markedly less than that before administration throughout the remainder of the recording. It is concluded that: (i) spinal mechanisms alone are not sufficient for induction and maintenance of second phase increased discharge of spinal nociceptive dorsal horn neurons; (ii) descending influences via supraspinal inputs are not causal in the development and maintenance of second phase increased discharge and (iii) tonic input from afferent neurons during the second phase plays a primary and essential role in generating and sustaining the second phase of elevated discharge of dorsal horn neurons and, thus, presumably the second phase of nociceptive scores in the formalin test. The data in this study reveal how much of an altered synaptically elicited response in the spinal dorsal horn can be attributed to postsynaptic plastic changes vs. how much can be simply due to increased synaptic input. The present results are important not only in the context of the formalin test but also in the context of other models related to inflammatory pain and neuropathic pain.