bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical role of the C‐terminal segment in the maturation and export to the cell surface of the homopentameric α7–5HT3A receptor
Authors: Pons S. , Sallette J. , Bourgeois J. P. , Taly A. , Changeux J. P. , Devillers‐Thiéry A.
Published: September 2004

Many neurological pathologies are related to misfolded proteins. During folding and assembly in the endoplasmic reticulum, the nicotinic acetylcholine receptor (nAChR) subunits undergo several conformational changes to acquire the ability to bind ligands. After folding and maturation, by mechanisms largely unknown, receptors are exported to the cell surface. We investigated the maturational role of the extracellular C‐terminal segment located at the boundary between the extracellular and the transmembrane domains. In the functional chimeric α7–5HT3A receptor used as a model system, amino acids from the C‐terminal segment were successively deleted or mutated. Upon progressive shortening of the peptide we observed less and less α‐bungarotoxin binding sites until no sites could be detected when the entire peptide had been deleted (chimera Del 5). Protein synthesis and pentameric assembly were not altered. In Del 5 transfected cells, pentameric receptors present in the endoplasmic reticulum were not detected on the cell surface where Del 5 proteins appeared as patches. With the Del 5 chimera, export of proteins to the cell surface diminished to about half that of wild‐type. We propose that the C‐terminal segment plays a double role: (i) through an interaction between the penultimate tyrosine residue of the C‐terminal segment and the Cys loop of the N‐terminal domain, it locks the receptor in a mature α‐bungarotoxin binding conformation; (ii) this mature conformation, in turn, masks a retention signal present in the first transmembrane segment allowing properly assembled and matured receptors to escape to the cell surface.
The role of the magnocellular pathway in serial deployment of visual attention
Authors: Cheng Alicia , Eysel Ulf T. , Vidyasagar Trichur R.
Published: September 2004

Normal human visual function often demands detection of a target among a number of other objects cluttering the scene, such as when searching for a known face in a crowd. In these and similar tasks, the search performed is a serial one, with an attentional spotlight scanning the objects of the scene. We have investigated whether one of the afferent channels in vision, the colour‐blind magnocellular pathway, is essential in such serial searches. We did this by using items that were isoluminant with the background but of a different colour, for which the magnocellular cells would be blind. The search in these conditions required much longer reaction times than when even a very small luminance contrast (2%) was added to the items. Because such luminance contrasts can be detected only by magnocellular cells and not by neurons of the other channels (parvocellular and koniocellular), the magnocellular pathway appears vitally important for serial search. In contrast, in a feature search task, which does not require allocation of attentional resources, the search was as efficient with isoluminance as when luminance contrast was added to the items.
Axon‐dominant localization of cell‐surface cholesterol in cultured hippocampal neurons and its disappearance in Niemann–Pick type C model cells
Authors: Tashiro Yuichi , Yamazaki Tsuneo , Shimada Yukiko , Ohno‐Iwashita Yoshiko , Okamoto Koichi
Published: September 2004

There is growing evidence showing the important role of cholesterol in maintaining neuronal function. In particular, much attention has been paid to the role of the cholesterol‐rich microdomains called lipid rafts. However, the cholesterol distribution on neurons is not clear. Here, we investigated localization of cholesterol in cultured rat hippocampal neurons, using filipin and a novel cholesterol‐binding reagent BCθ. In our culture system, BCθ detects only cell‐surface cholesterol, whereas filipin stains both intracellular and cell‐surface cholesterol. BCθ staining appeared visible in a maturation‐dependent manner and showed axon‐dominant distribution of cell‐surface cholesterol in fully matured neurons. A part of this cholesterol on axons was resistant to detergents at 4 °C, and thus might be involved in lipid rafts. Interestingly, Niemann–Pick type C model neurons induced by class 2 amphiphiles lost the cell‐surface but not the intracellular cholesterol staining. Niemann–Pick type C disease is caused by the disruption of intracellular cholesterol transport and is known to induce neurodegeneration in brains accompanied by formation of neurofibrillary tangles. Our observations suggest the important role of cell‐surface cholesterol in maintaining a functional axonal membrane and indicate that the observed defect in axonal surface cholesterol might lead to neurodegeneration.
Adenosine A2A receptors are involved in physical dependence and place conditioning induced by THC
Authors: Soria Guadalupe , Castañé Anna , Berrendero Fernando , Ledent Catherine , Parmentier Marc , Maldonado Rafael , Valverde Olga
Published: September 2004

A2A adenosine and CB1 cannabinoid receptors are highly expressed in the central nervous system, where they modulate numerous physiological processes including adaptive responses to drugs of abuse. Both purinergic and cannabinoid systems interact with dopamine neurotransmission (through A2A and CB1 receptors, respectively). Changes in dopamine neurotransmission play an important role in addictive‐related behaviours. In this study, we investigated the contribution of A2A adenosine receptors in several behavioural responses of Δ9‐tetrahydrocannabinol (THC) related to its addictive properties, including tolerance, physical dependence and motivational effects. For this purpose, we first investigated acute THC responses in mice lacking A2A adenosine receptors. Antinociception, hypolocomotion and hypothermia induced by acute THC administration remained unaffected in mutant mice. Chronic THC treatment developed similar tolerance to these acute effects in wild‐type and A2A‐knockout mice. However, differences in the body weight pattern were found between genotypes during such chronic treatment. Interestingly, the somatic manifestations of SR141716A‐precipitated THC withdrawal were significantly attenuated in mutant mice. The motivational responses of THC were also evaluated by using the place‐conditioning paradigm. A significant reduction of THC‐induced rewarding and aversive effects was found in mice lacking A2A adenosine receptors in comparison with wild‐type littermates. Binding studies revealed that these behavioural changes were not associated with any modification in the distribution and/or functional activity of CB1 receptors in knockout mice. Therefore, this study shows, for the first time, a specific involvement of A2A receptors in the addictive‐related properties of cannabinoids.
Behavioural correlates of an altered balance between synaptic and extrasynaptic GABAAergic inhibition in a mouse model
Authors: Sinkkonen Saku T. , Vekovischeva Olga Y. , Möykkynen Tommi , Ogris Waltraud , Sieghart Werner , Wisden William , Korpi Esa R.
Published: September 2004

GABAA receptors mediate fast phasic inhibitory postsynaptic potentials and participate in slower tonic extrasynaptic inhibition. Thy1α6 mice with ectopic forebrain expression of GABAA receptor α6 subunits exhibit increased extrasynaptic GABAA receptor‐mediated background conductance and reduced synaptic GABAA receptor currents in hippocampal CA1 neurons [W. Wisden et al. (2002) Neuropharmacology 43, 530–549]. Here we demonstrate that isolated CA1 neurons of these mice showed furosemide‐sensitivity of GABA‐evoked currents, confirming the functional expression of α6 subunit. In addition, receptor autoradiography of the CA1 region of Thy1α6 brain sections revealed pharmacological features that are unique for α6βγ2 and α6β receptors. The existence of atypical α6β receptors was confirmed after completely eliminating GABAA receptors containing γ1, γ2, γ3 or δ subunits using serial immunoaffinity chromatography on subunit‐specific GABAA receptor antibodies. Behaviourally, the Thy1α6 mice showed normal features with slightly enhanced startle reflex and struggle‐escape behaviours. However, they were more sensitive to GABAA antagonists DMCM (shorter latency to writhing clonus) and picrotoxinin (shorter latency to generalized convulsions). Tiagabine, an antiepileptic GABA‐uptake inhibitor that increases brain GABA levels, delayed picrotoxinin‐induced convulsions at a low dose of 3.2 mg/kg in Thy1α6 mice, but not in control mice; however, the overall effect of higher tiagabine doses on the convulsion latency remained smaller in the Thy1α6 mice. Altered balance between extrasynaptic and synaptic receptors thus affects seizure sensitivity to GABAergic convulsants. Importantly, the increased extrasynaptic inhibition, even when facilitated in the presence of tiagabine, was not able fully to counteract enhanced seizure induction by GABAA antagonists.
Astroglial processes show spontaneous motility at active synaptic terminals in situ
Authors: Hirrlinger Johannes , Hülsmann Swen , Kirchhoff Frank
Published: September 2004

Within the tripartite structure of vertebrate synapses, enwrapping astroglial processes regulate synaptic transmission by transmitter uptake and by direct transmitter release. We applied confocal and two‐photon laser scanning microscopy to acutely isolated slices prepared from the brainstem of transgenic TgN(GFAP‐EGFP) mice. In transversal sections fluorescently labelled astrocytes are evenly distributed throughout the tissue. Astroglial processes contacted neuronal somata and enwrapped active synaptic terminals as visualized using FM1‐43 staining in situ. Here, at these synaptic regions astroglial process endings displayed a high degree of dynamic morphological changes. Two defined modes of spontaneous motility could be distinguished: (i) gliding of thin lamellipodia‐like membrane protrusions along neuronal surfaces and (ii) transient extensions of filopodia‐like processes into the neuronal environment. Our observations highlight the active role of astrocytes in direct modulation of synaptic transmission.
Managing Work and Care: A Difficult Challenge for Immigrant Families
Authors: Wall Karin , José José São
Published: September 2004

This paper explores the strategies used by immigrant families to reconcile work and care for young children in Finland, France, Italy and Portugal. Drawing upon interviews with couples or lone parents who have children below age ten, it shows that immigrant families rely on a diversity of work/care strategies. These strategies include extensive delegation of care (mostly to formal or non‐familial informal care), negotiation of care within the nuclear family (both partners sharing the care responsibilities as well as older child care), mother‐centredness (mothers cutting back on working hours), child negligence (leaving children alone) and the superimposition of care upon work (taking children to work). Almost all immigrant families, but especially first‐generation ones, suffer from the absence of close kin networks to support childcare, strong pressure to work and from work (long or atypical hours) and various integration problems such as social isolation, lack of information on services, and problems with housing. However, our findings show that migration patterns, among other factors, have a significant impact on work/care strategies. Highly qualified “professional migration” is more associated with extensive paid delegation (often private and high‐cost), “marriage migration” with mother‐centredness, and “unskilled worker migration” with low‐cost solutions supplemented by workplace care, older child care and negligence. First‐generation unskilled worker migrant families are more exposed to occupational and residential segregation, atypical working hours, low earnings and difficulties in managing work and care for young children. Findings point to the still weak regulatory function of the different welfare states in the protection of these families.
Work and Care Strategies of European Families: Similarities or National Differences?
Authors: Larsen Trine P.
Published: September 2004

This paper examines the work and care strategies chosen by full‐time working families with children in Finland, Italy, Portugal and the UK. It asks whether European families in different countries, facing the same problems of balancing employment and childcare responsibilities, respond to their situations in similar ways. An increase in dual‐earner families where both parents work full‐time represents a general employment trend in today's Europe. Also, within families with children, such employment patterns are now more common than they were previously. National differences may therefore not any longer be as marked as often indicated by country‐based surveys. The qualitative data from the SOCCARE Project offer a way to examine this issue. The focal point of the paper is to make a comparative analysis of couples in similar work and care situations. Using their working hours as the common denominator, this paper analyses their daily childcare arrangements and how these are impacted by gender roles, working schedules, flexibility of workplace, income levels, parents’ educational background and availability of care facilities. The paper concludes that European families’ work and care strategies have many similarities whereby national differences may not be as marked as often indicated by contemporary research.
Caregiving in Transition in Southern Europe: Neither Complete Altruists nor Free‐riders
Authors: Simoni Simonetta , Trifiletti Rossana
Published: September 2004

In the framework of the SOCCARE Project, focusing on families dealing with a double front of care for children and frail elderly people, similarities can be found in Italy, France and Portugal beyond their different welfare regimes. The comparison of family histories and caregiving strategies, by the methodology of case‐matching, gives an interesting overview of the relationship between the debate on social care and that on the intergenerational contract. The paper aims to understand which are the available combinations of family, informal and institutional resources making a heavy burden of care “acceptable and still normal”: this focuses both typical situations of each country and common features through the countries. The results show how changes in the representations of obligation and duty in the intergenerational pact produce different outcomes and demands in welfare systems. The analysis of shifting boundaries between the public and private spheres in care provides useful policy recommendations, aimed at improving choices and “sustainable” responsibilities of individuals, families and social networks. Sustainable policies seem to be more dependent on family and structural types and resources of networks than on different welfare and services support.
Bayesian Binary Segmentation Procedure for Detecting Streakiness in Sports
Authors: Yang Tae Young
Published: September 2004

When an individual player or team enjoys periods of good form, and when these occur, is a widely observed phenomenon typically called ‘streakiness’. It is interesting to assess which team is a streaky team, or who is a streaky player in sports. Such competitors might have a large number of successes during some periods and few or no successes during other periods. Thus, their success rate is not constant over time. We provide a Bayesian binary segmentation procedure for locating changepoints and the associated success rates simultaneously for these competitors. The procedure is based on a series of nested hypothesis tests each using the Bayes factor or the Bayesian information criterion. At each stage, we only need to compare a model with one changepoint with a model based on a constant success rate. Thus, the method circumvents the computational complexity that we would normally face in problems with an unknown number of changepoints. We apply the procedure to data corresponding to sports teams and players from basketball, golf and baseball.
A Comparison of Univariate and Multivariate Multilevel Models for Repeated Measures of use of Antenatal Care in Uttar Pradesh
Authors: Griffiths Paula L. , Brown James J. , Smith Peter W. F.
Published: September 2004

We compare two different multilevel modelling approaches to the analysis of repeated measures data to assess the effect of mother level characteristics on women’s use of prenatal care services in Uttar Pradesh, India. We apply univariate multilevel models to our data and find that the model assumptions are severely violated and the parameter estimates are not stable, particularly for the mother level random effect. To overcome this we apply a multivariate multilevel model. The correlation structure shows that, once the decision has been made regarding use of antenatal care by the mother for her first observed birth in the data, she does not tend to change this decision for higher order births.
The Sensitivity of Estimates of the Change in Population Behaviour to Realistic Changes in Bias in Repeated Surveys
Authors: Copas Andrew J. , Farewell Vern T. , Mercer Catherine H. , Yao Guiqing
Published: September 2004

The first British National Survey of Sexual Attitudes and Lifestyles (NATSAL) was conducted in 1990–1991 and the second in 1999–2001. When surveys are repeated, the changes in population parameters are of interest and are generally estimated from a comparison of the data between surveys. However, since all surveys may be subject to bias, such comparisons may partly reflect a change in bias. Typically limited external data are available to estimate the change in bias directly. However, one approach, which is often possible, is to define in each survey a sample of participants who are eligible for both surveys, and then to compare the reporting of selected events that occurred before the earlier survey time point. A difference in reporting suggests a change in overall survey bias between time points, although other explanations are possible. In NATSAL, changes in bias are likely to be similar for groups of sexual experiences. The grouping of experiences allows the information that is derived from the selected events to be incorporated into inference concerning population changes in other sexual experiences. We use generalized estimating equations, which incorporate weighting for differential probabilities of sampling and non-response in a relatively straightforward manner. The results, combined with estimates of the change in reporting, are used to derive minimum established population changes, based on NATSAL data. For some key population parameters, the change in reporting is seen to be consistent with a change in bias alone. Recommendations are made for the design of future surveys.
Modelling the Evolution of Distributions: An Application to Major League Baseball
Authors: Koop Gary
Published: September 2004

We develop Bayesian techniques for modelling the evolution of entire distributions over time and apply them to the distribution of team performance in Major League baseball for the period 1901–2000. Such models offer insight into many key issues (e.g. competitive balance) in a way that regression-based models cannot. The models involve discretizing the distribution and then modelling the evolution of the bins over time through transition probability matrices. We allow for these matrices to vary over time and across teams. We find that, with one exception, the transition probability matrices (and, hence, competitive balance) have been remarkably constant across time and over teams. The one exception is the Yankees, who have outperformed all other teams.
Rationality and Judgment
Authors: Siegel Harvey
Published: September 2004

Abstract: Philosophical/epistemic theories of rationality differ over the role of judgment in rational argumentation. According to the “classical model” of rationality, rational justification is a matter of conformity with explicit rules or principles. Critics of the classical model, such as Harold Brown and Trudy Govier, argue that the model is subject to insuperable difficulties. They propose, instead, that rationality be understood, ultimately, in terms of judgment rather than rules. In this article I respond to Brown's and Govier's criticisms of the classical model, and to the “judgment model” they propose in its place. I argue that that model is unable both to distinguish between rational and irrational judgment and to avoid recourse to rules, and is therefore inadequate as an account of rationality, critical thinking, or argument appraisal. More positively, I argue that an adequate account of rationality must include a place for both rules and judgment.
Reductionism and Antireductionism: Rights and Wrongs
Authors: Jones Todd
Published: September 2004

Abstract:Scholars are divided as to whether reduction should be a central strategy for understanding the world. While reductive analysis is the standard mode of explanation in many areas of science and everyday life, many scholars consider reductionism a sign of “intellectual naïveté and backwardness.” This article makes three points about the proper status of antireductionism: First, reduction is, in fact, a centrally important epistemic strategy. Second, reduction to physics is always possible for all causal properties. Third, there are, nevertheless, reasons why we want science to discover properties and explanations other than reductive physical ones.
The Smuggler's Fallacy
Authors: Ferguson Kenneth G.
Published: September 2004

Abstract: David Hume has warned us not to endeavor to derive an “ought” from an “is” (1990, 469–70), reprimanding those who attempt to draw value judgments from empirical facts. But Judith Jarvis Thomson refuses to accept that values and facts are logically disjoint in this manner, primarily because of her worry that such a partition of our moral values from the “facts” will place a grave limitation on any ethical system, namely, that its claims apparently cannot be proven. Consequently, Thomson is on the lookout for some provably true facts that can be used, contra Hume, to draw conclusions about moral values. Thomson begins by rejecting all generalist conceptions of the good (specifically, the utilitarian's identification of the good with pleasure) and proceeds to fracture the good into various kinds of “goodness in a way,” hoping to produce by this disintegration some moral facts that can be used to set ethics on an objective foundation. But I will argue that Thomson's so‐called objective facts are actually nothing but disguised moral claims, and that in attempting to sidestep the classic fallacy identified by Hume, she has blundered into another pitfall—the Smuggler's Fallacy, the offense of concealing her moral conclusions inside the premises of her argument.
Narrative Unity as a Condition of Personhood
Authors: Christman John
Published: September 2004

Abstract: In this article I critically discuss a claim made by several writers in philosophy and the social sciences that for an individual to count as a person, a single personality, or the subject of a life, the experiences of the subject in question must take a narrative form. I argue that narrativity is a misleading and, in some ways of understanding it, implausible condition of what it is that adds unity to personhood and personality. I pursue this critique by considering canonical accounts of narrativity in philosophy and literary studies. I consider those connections between events that must hold for the sequence to be considered a narrative: causal, teleological, and thematic connections. I argue that for each of these, the condition that experiential sequences (for a given subject) must have this structure is empty: any life sequence that is reflected upon in an interpretive spirit can meet it. What the condition of narrativity amounts to, then, is the more basic requirement that the person must be able to look upon the factors and events of her life with a certain interpretive reflection, whether or not those factors and events have any particular narrative unity in a traditional sense.
The Role of a Facilitator in a Community of Philosophical Inquiry
Authors: Kennedy David
Published: September 2004

Abstract: Community of philosophical inquiry (CPI) is a way of practicing philosophy in a group that is characterized by conversation; that creates its discussion agenda from questions posed by the conversants as a response to some stimulus (whether text or some other media); and that includes discussion of specific philosophers or philosophical traditions, if at all, only in order to develop its own ideas about the concepts under discussion. The epistemological conviction of community of philosophical inquiry is that communal dialogue, facilitated by a philosophically educated person, recapitulates and reconstructs the major elements—and even the positions or claims—of the tradition, in one form or another, through the distributed thinking characteristic of dialogical discourse. The pedagogical locus of control of CPI is the group as a whole, which is understood as potentially self‐regulating through a process of ongoing dialectical transformation. The role of the facilitator is to act, among other things, from the Socratic “position of ignorance” as a bridge between concepts and arguments and as a trigger for conceptual system transformation.
Earning Their Keep and Keeping What They Earn: A Critique of Organizing Strategies for South Asian Women in the Informal Sector
Authors: Baruah Bipasha
Published: September 2004

It is now widely understood that the needs of women workers in the informal sector are not met by the conservative practices of labour organizations and trade unions. While the contribution of women to the economies of developing countries is critical, women rarely find employment in the regulated unionized sectors of these countries, and are found instead in overwhelming numbers in the sector that is variously termed ‘unorganized’, ‘unprotected’, ‘unregistered’ or ‘informal.’ This article addresses the situation of women in the informal economy in South Asia. The author explores the major challenges and opportunities facing women in their efforts to organize and mobilize for change. She also provides a critical analysis of the different types of interventions adopted by the state and civil society organizations in South Asia to empower women in the informal sector. The author concludes with an attempt to identify the mix of interventions and strategies most needed for different social, political and economic circumstances.
The Impact of Human Factors on Ab Initio Pilot Training
Authors: Davey Caroline L.
Published: September 2004

This article examines critically the power effects of a branch of psychology called Human Factors within the context of commercial aviation. A review of the aviation literature highlights the significance of Human Factors and its relevance to the recruitment and training of ab initio pilots. However, research in the field is criticized for failing to account for existing power relations and the potential effects of a new discursive format. This article uses the concept of discourse associated with Michel Foucault to analyse empirical data from interviews with individuals involved in ab initio pilot training at a European flying college. The analysis illustrates how staff at the training college use the rhetoric of Human Factors to enhance their own contribution and status, without fundamentally changing existing practices. Although this reinforces existing power relations, the Human Factors discourse also potentially empowers a different set of management employees. By illustrating the conflicting values and interests of two sets of managers and trainers at the college, the article is able to demonstrate the negative effects of the new discursive format on male ab initio pilots. It also discusses attitudes to female pilots, contributing to the debate about the ability of management discourses to promote gender equality within commercial organizations.
Governance of Higher Education in Britain: The Significance of the Research Assessment Exercises for the Funding Council Model
Authors: Tapper Ted , Salter Brian
Published: September 2004

This article uses the political struggles that have enveloped the research assessment exercises (RAEs) to interpret the UK's current funding council model of governance. Ironically, the apparently widespread improvement in the research performance of British universities, as demonstrated by RAE 2001, has made it more difficult to distribute research income selectively, which was supposedly the central objective of the whole evaluative process. Whilst enhanced research ratings may be seen as a cause for celebration in the universities, the failure to anticipate this outcome and, more significantly, to plan for its financial implications is seen in political circles as a failure of higher education management. The article explores the alternative models of governance that are likely to emerge as a consequence of this crisis and, in particular, whether the funding councils can have much freedom of action, given the tighter political control of policy goals and their critical dependence upon the academic profession for the conduct of the evaluative process.
A Challenge to Established Assessment Practice
Authors: Elton Lewis
Published: September 2004

The article looks back 35 years to a challenge on examination practices, based on common assumptions at the time. It notes that many – although not all – of these assumptions are still accepted in much of current practice, although some have been examined by researchers and found wanting extensively in the intervening time. The particular assumptions investigated relate to the distribution, recording and use of examination results, the demand for uniformity of treatment, the comparability of degrees, the assessment of imponderables and the use and value of external examiners.
Intraischaemic hypothermia reduces free radical production and protects against ischaemic insults in cultured hippocampal slices
Authors: McManus Terence , Sadgrove Matthew , Pringle Ashley K. , Chad John E. , Sundstrom Lars E.
Published: September 2004

Hypothermia has been demonstrated to be an effective neuroprotective strategy in a number of models of ischaemic and excitotoxic neurodegeneration in vitro and in vivo. Reduced glutamate release and free radical production have been postulated as potential mechanisms underlying this effect but no definitive mechanism has yet been reported. In the current study, we have used oxygen–glucose deprivation in organotypic hippocampal slice cultures as an in vitro model of cerebral ischaemia. When assessed by propidium iodide fluorescence, reducing the temperature during oxygen–glucose deprivation to 31–33°C was significantly neuroprotective but this effect was lost if the initiation of hypothermia was delayed until the post‐insult recovery period. The neuroprotective effects of hypothermia were associated with a significant decrease in both nitric oxide production, as assessed by 3‐amino‐4‐aminomethyl‐2′,7′‐difluorofluorescein fluorescence, and superoxide formation. Further, hypothermia significantly attenuated NMDA‐induced nitric oxide formation in the absence of hypoxia/hypoglycaemia. We conclude that the neuroprotective effects of hypothermia are mediated through a reduction in nitric oxide and superoxide formation and that this effect is likely to be downstream of NMDA receptor activation.
Co‐transplantation of carotid body and ventral mesencephalic cells as an alternative approach towards functional restoration in 6‐hydroxydopamine‐lesioned rats: implications for Parkinson's disease
Authors: Shukla S. , Agrawal A. K. , Chaturvedi R. K. , Seth K. , Srivastava N. , Sinha C. , Shukla Y. , Khanna V. K. , Seth P. K.
Published: September 2004

Exogenous administration of various neurotrophic factors has been shown to protect neurons in animal model of Parkinson's disease (PD). Several attempts are being made to search a tissue source simultaneously expressing many of these neurotrophic factors. Carotid body (CB) contains oxygen‐sensitive glomus cells rich in dopamine (DA) and expresses glial cell line‐derived neurotrophic factor, brain‐derived neurotrophic factor and neurotrophin‐3. We have attempted to study the functional restoration following co‐transplantation of CB cells and ventral mesencephalic cells (VMC) in a 6‐hydroxydopamine‐lesioned rat model of PD. A significant recovery (p < 0.001) in d‐amphetamine‐induced circling behavior (80%) and spontaneous locomotor activity (85%) was evident in co‐transplanted animals at 12 weeks post‐transplantation as compared to lesioned animals. Similarly, a significant (p < 0.001) restoration was observed in DA‐D2 receptor binding (77%), striatal DA (87%) and 3,4‐dihydroxyphenylacetic acid (DOPAC) (85%) levels and nigral DA (75%) and DOPAC (74%) levels. Functional recovery was accompanied by tyrosine hydroxylase (TH) expression and quantification of TH‐positive cells by image analysis revealed a significant restoration in TH‐immunoreactive (IR) fiber density in striatum, as well as TH‐IR neurons in substantia nigra pars compacta in co‐transplanted animals over VMC‐transplanted animals. The result suggests that co‐transplantation of CB cells along with VMC provides better and long‐term functional restoration in the rat model of PD, possibly by supporting the survival of newly grafted cells as well as remaining host DA neurons.
Involvement of cytochrome P450 2E1 in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐induced mouse model of Parkinson's disease
Authors: Vaglini Francesca , Pardini Carla , Viaggi Cristina , Bartoli Cristina , Dinucci Dinuccio , Corsini Giovanni Umberto
Published: September 2004

Elucidation of the biochemical steps leading to the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced degeneration of the nigrostriatal dopamine (DA) pathway has provided new clues to the pathophysiology of Parkinson's disease. In line with the enhancement of MPTP toxicity by diethyldithiocarbamate (DDC), here we demonstrate how other cytochrome P450 (CYP) 2E1 inhibitors, such as diallyl sulphide (DAS) and phenylethylisothiocyanate (PIC), also potentiate the selective DA neurone degeneration in C57/bl mice. In addition, we show that CYP 2E1 is present in the brain and in the basal ganglia of this mouse strain, as measured by RT–PCR, western blot analysis and immunohistochemistry. A kinetic analysis of MPTP and its metabolites, by means of the microdialysis technique in the striatum, indicates that no detoxification metabolic pathway is affected by any of these inhibitors. This does not rule out, however, that an undetected detoxification pathway involving CYP 2E1 is operating. In order to provide direct evidence for this isozyme involvement, CYP 2E1 knockout mice were challenged with MPTP or the combined treatment. Here we show that these transgenic mice have a low sensitivity to MPTP alone, similar to their wild‐type counterparts, suggesting that it is likely that transgenic mice compensate for the missing enzyme. However, DDC pretreatment completely fails to enhance MPTP toxicity in CYP 2E1 knockout mice, whereas this enhancement is regularly present in wild‐type animals. This study indicates that the occurrence of CYP 2E1 in C57/bl mouse brain is relevant to MPTP toxicity, and suggests that this isozyme may have a detoxificant role related to the efflux transporter of the toxin.
Identification of tyrosine hydroxylase as a physiological substrate for Cdk5
Authors: Kansy Janice W. , Daubner S. Colette , Nishi Akinori , Sotogaku Naoki , Lloyd Michael D. , Nguyen Chan , Lu Lin , Haycock John W. , Hope Bruce T. , Fitzpatrick Paul F. , Bibb James A.
Published: September 2004

Cyclin‐dependent kinase 5 (Cdk5) is emerging as a neuronal protein kinase involved in multiple aspects of neurotransmission in both post‐ and presynaptic compartments. Within the reward/motor circuitry of the basal ganglia, Cdk5 regulates dopamine neurotransmission via phosphorylation of the postsynaptic signal transduction pathway integrator, DARPP‐32 (dopamine‐ and cyclic AMP‐regulated phosphoprotein, Mr 32 000). Cdk5 has also been implicated in regulating various steps in the presynaptic vesicle cycle. Here we report that Cdk5 phosphorylates tyrosine hydroxylase (TH), the key enzyme for synthesis of dopamine. Using phosphopeptide mapping, site‐directed mutagenesis, and phosphorylation state‐specific antibodies, the site was identified as Ser31, a previously defined extracellular signal‐regulated kinases 1/2 (ERK1/2) site. The phosphorylation of Ser31 by Cdk5 versus ERK1/2 was investigated in intact mouse striatal tissue using a pharmacological approach. The results indicated that Cdk5 phosphorylates TH directly and also regulates ERK1/2‐dependent phosphorylation of TH through the phosphorylation of mitogen‐activated protein kinase kinase 1 (MEK1). Finally, phospho‐Ser31 TH levels were increased in dopaminergic neurons of rats trained to chronically self‐administer cocaine. These results demonstrate direct and indirect regulation of the phosphorylation state of a Cdk5/ERK1/2 site on TH and suggest a role for these pathways in the neuroadaptive changes associated with chronic cocaine exposure.
Cystamine increases l‐cysteine levels in Huntington's disease transgenic mouse brain and in a PC12 model of polyglutamine aggregation
Authors: Fox Jonathan H. , Barber David S. , Singh Bhupinder , Zucker Birgit , Swindell Mary K. , Norflus Fran , Buzescu Rodica , Chopra Raman , Ferrante Robert J. , Kazantsev Aleksey , Hersch Steven M.
Published: September 2004

Cystamine, a small disulfide‐containing chemical, is neuroprotective in a transgenic mouse and a Drosophila model of Huntington's disease (HD) and decreases huntingtin aggregates in an in vitro model of HD. The mechanism of action of cystamine in these models is widely thought to involve inhibition of transglutaminase mediated cross‐linking of mutant huntingtin in the process of aggregate formation/stabilization. In this study we show that cystamine, both in vitro and in a transgenic mouse model of HD (R6/2), increases levels of the cellular antioxidant l‐cysteine. Several oxidative stress markers increase in HD brain. We provide further evidence of oxidative stress in mouse HD by demonstrating compensatory responses in R6/2 HD brains. We found age‐dependent increases in forebrain glutathione (GSH), and increased levels of transcripts coding for proteins involved in GSH synthesis and detoxification pathways, as revealed by quantitative PCR analysis. Given the general importance of oxidative stress as a mediator of neurodegeneration we propose that an increase in brain l‐cysteine levels could be protective in HD. Furthermore, cystamine was dramatically protective against 3‐nitropropionic acid‐induced striatal injury in mice. We suggest that cystamine's neuroprotective effect in HD transgenic mice results from pleiotropic effects that include transglutaminase inhibition and antioxidant activity.
Overexpression of α‐synuclein in rat substantia nigra results in loss of dopaminergic neurons, phosphorylation of α‐synuclein and activation of caspase‐9: resemblance to pathogenetic changes in Parkinson's disease
Authors: Yamada Masanori , Iwatsubo Takeshi , Mizuno Yoshikuni , Mochizuki Hideki
Published: September 2004

To elucidate the role of α‐synuclein in the pathogenesis of Parkinson's disease, both human α‐synuclein transgenic mice and targeted overexpression of human α‐synuclein in rat substantia nigra using viral vector‐based methods have been studied, however, little is known about the pathogenetic changes of dopaminergic neuron loss. Therefore, it is necessary to address whether the pathogenetic changes in brains with Parkinson's disease are recapitulated in these models. Here, we used the recombinant adeno‐associated viral (rAAV) vector system for human α‐synuclein gene transfer to rat substantia nigra and observed approximately 50% loss of dopaminergic neurons at 13 weeks after infection, which was comparably slower than the progression of neurodegeneration reported in other studies. In the slower progression of neurodegeneration, we identified several important features in common with the pathogenesis of Parkinson's disease, such as phosphorylation of α‐synuclein at Ser129 and activation of caspase‐9. Both findings were also evident in cortical tissues overexpressing α‐synuclein via rAAV. Our results indicate that overexpression of α‐synuclein via rAAV apparently recapitulates several important features of brains with Parkinson's disease and dementia with Lewy bodies, and thus α‐synucleinopathy described here is likely to be an ideal model for the study of the pathogenesis of Parkinson's disease and dementia with Lewy bodies.
Gene knockout of amyloid precursor protein and amyloid precursor‐like protein‐2 increases cellular copper levels in primary mouse cortical neurons and embryonic fibroblasts
Authors: Bellingham Shayne A. , Ciccotosto Giuseppe D. , Needham B. Elise , Fodero Lisa R. , White Anthony R. , Masters Colin L. , Cappai Roberto , Camakaris James
Published: September 2004

Alzheimer's disease is characterised by the accumulation of amyloid‐β peptide, which is cleaved from the copper‐binding amyloid‐β precursor protein. Recent in vivo and in vitro studies have illustrated the importance of copper in Alzheimer's disease neuropathogenesis and suggested a role for amyloid‐β precursor protein and amyloid‐β in copper homeostasis. Amyloid‐β precursor protein is a member of a multigene family, including amyloid precursor‐like proteins‐1 and ‐2. The copper‐binding domain is similar among amyloid‐β precursor protein family members, suggesting an overall conservation in its function or activity. Here, we demonstrate that double knockout of amyloid‐β precursor protein and amyloid precursor‐like protein‐2 expression results in significant increases in copper accumulation in mouse primary cortical neurons and embryonic fibroblasts. In contrast, over‐expression of amyloid‐β precursor protein in transgenic mice results in significantly reduced copper levels in primary cortical neurons. These findings provide cellular neuronal evidence for the role of amyloid‐β precursor protein in copper homeostasis and support the existing hypothesis that amyloid‐β precursor protein and amyloid precursor‐like protein‐2 are copper‐binding proteins with functionally interchangeable roles in copper homeostasis.
Alterations of CaMKII after hypoxia‐ischemia during brain development
Authors: Tang Kaixiong , Liu Chunli , Kuluz John , Hu Bingren
Published: September 2004

Transient brain hypoxia‐ischemia (HI) in neonates leads to delayed neuronal death and long‐term neurological deficits. However, the underlying mechanisms are incompletely understood. Calcium‐calmodulin‐dependent protein kinase II (CaMKII) is one of the most abundant protein kinases in neurons and plays crucial roles in synaptic development and plasticity. This study used a neonatal brain HI model to investigate whether and how CaMKII was altered after HI and how the changes were affected by brain development. Expression of CaMKII was markedly up‐regulated during brain development. After HI, CaMKII was totally and permanently depleted from the cytosol and concomitantly deposited into a Triton‐insoluble fraction in neurons that were undergoing delayed neuronal death. Autophosphorylation of CaMKII‐Thr286 transiently increased at 30 min of reperfusion and declined thereafter. All these changes were mild in P7 pups but more dramatic in P26 rats, consistent with the development‐dependent CaMKII expression in neurons. The results suggest that long‐term CaMKII depletion from the cytosolic fraction and deposition into the Triton‐insoluble fraction may disable synaptic development, damage synaptic plasticity, and contribute to delayed neuronal death and long‐term synaptic deficits after transient HI.
NMDA receptor activation results in PKA‐ and ERK‐dependent Mnk1 activation and increased eIF4E phosphorylation in hippocampal area CA1
Authors: Banko Jessica L. , Hou Lingfei , Klann Eric
Published: September 2004

Protein synthesis is essential for the stabilization of glutamate receptor‐dependent forms of long‐lasting hippocampal synaptic plasticity and for the consolidation of memory, but the signal transduction mechanisms that regulate translation factors during these processes are not well understood. As a first step towards understanding how translation is activated during synaptic plasticity, we investigated how the eukaryotic initiation factor 4E (eIF4E), a rate‐limiting mRNA cap‐binding protein, and its kinase, Mnk1, are regulated by protein kinase C (PKC), cAMP‐dependent protein kinase (PKA) andN‐methyl‐d‐aspartate (NMDA) receptor activation in hippocampal area CA1. We found that treatment of mouse hippocampal slices with either phorbol ester, to activate PKC, or forskolin, to activate PKA, resulted in activation of Mnk1 and increased eIF4E phosphorylation that was dependent on extracellular signal‐regulated kinase (ERK). Similarly, brief treatment of hippocampal slices with NMDA resulted in activation of Mnk1 and increased phosphorylation of eIF4E. The NMDA‐induced activation of Mnk1 and increased phosphorylation of eIF4E were dependent on PKA and ERK, but not PKC, and were present in synaptoneurosome preparations. Immunohistochemical analysis revealed that the PKA‐ and ERK‐dependent increases in Mnk1 activation induced by NMDA also occured in dendrites. These findings identify a specific regulatory pathway that can couple NMDA receptor activation to translation initiation factors in the hippocampus, and may represent a mechanism for triggering dendritic protein synthesis during long‐term potentiation and long‐term memory formation.
Mitochondrial uncoupling as a potential therapeutic target in acute central nervous system injury
Authors: Maragos William F. , Korde Amit S.
Published: September 2004

Mitochondrial dysfunction, resulting from the disruption of calcium homeostasis and the generation of toxic reactive oxygen species, is a central process leading to neuronal injury and death following acute CNS insults. Interventions aimed at preventing disturbances in mitochondrial function have therefore become targets of intense investigation. Mitochondrial uncoupling is a condition in which electron transport is disconnected from the production of ATP. As a consequence, there is a decrease in the mitochondrial membrane potential, which can temporarily decrease calcium influx and attenuate free radical formation. The potential use of pharmacological agents with uncoupling properties may provide a novel therapeutic approach for the treatment of acute neuronal injury.