bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term spatial memory in rats with hippocampal lesions
Authors: Ramos Juan M. J.
Published: March 2003

In animal models of human amnesia, using lesion methods, it has been difficult to establish the role played by the hippocampus in the formation of long‐term spatial knowledge. For example, lesions sustained after acquisition have generally produced a flat retrograde amnesia for spatial information. These results have not made it possible to dissociate the participation of the hippocampus in retrieval/performance processes from its participation in consolidation/retention. The present study was designed to investigate if electrolytic hippocampal lesions made before training lead to a deficit in the long‐term retention of spatial knowledge when the rats show equal performance levels during the acquisition. Results show that lesioned rats learn a place response just as well as the control rats when, during the training, an intramaze cue orients the animal in its navigation towards the goal arm. One day after reaching criterion, lesioned and control rats remember the task perfectly during a transfer test in which the intramaze signal used previously is not present. However, 24 days later, the hippocampal animals manifest a profound deficit in the retention of the spatial information. When the spatial task learned during the acquisition phase requires only the use of a guidance strategy, control and lesioned animals show the same level of performance during the training phase and the same degree of retention during the retraining phase 24 days after criterion. Taken together, these results suggest that the hippocampus plays a crucial role in long‐term retention of allocentric spatial information.
Localization of the glutamate–aspartate transporter, GLAST, in rat taste buds
Authors: Lawton D. Maxwell , Furness David N. , Lindemann Bernd , Hackney Carole M.
Published: March 2003

A number of putative neurotransmitter substances have been found in vertebrate taste buds. Amongst these glutamate has been localized in fibres innervating the buds and uptake of glutamate has been shown to occur into receptor cells. It is therefore possible that, in common with other sensory systems, glutamate is a neurotransmitter in taste buds. In the inner ear and retina of mammals, the membranes of supporting cells have been shown to contain the glial glutamate transporter GLAST. In the brain, this protein is involved in glutamate re‐uptake into glial cells where the glutamate is converted into glutamine for recycling into glutamatergic terminals. In this study, the presence of GLAST has been investigated in taste buds in the rat vallate papilla and its distribution compared with that of glutamine to determine whether there are cells in this system that play a glia‐like role in glutamate handling. Immunofluorescent labelling showed that a subset of cells in the taste bud contains GLAST. Immunogold labelling indicated that it occurs in the plasma membranes of supporting cells, especially on the fine cytoplasmic processes of dark cells towards the basal region of the bud. A protein of molecular mass similar to that of cerebellar GLAST was detected in immunoblots of excised papillae. Double labelling and semiquantitative analysis of glutamine and GLAST immunoreactivity showed that the GLAST‐positive cells have a higher level of cytoplasmic glutamine than the adjacent cells. It is proposed that these GLAST‐positive cells play a glia‐like role in the uptake of glutamate following its release at synapses within the taste bud although the precise location of the latter remains uncertain. The GLAST‐positive cells may also be involved in its subsequent conversion to glutamine in a glutamate/glutamine cycle similar to that described in the brain.
O2‐sensing after carotid chemodenervation: hypoxic ventilatory responsiveness and upregulation of tyrosine hydroxylase mRNA in brainstem catecholaminergic cells
Authors: Roux Jean‐Christophe , Pequignot Jean‐Marc , Dumas Sylvie , Pascual Olivier , Ghilini Ginette , Pequignot Jacqueline , Mallet Jacques , Denavit‐Saubié Monique
Published: March 2003

Ventilatory responses to acute and long‐term hypoxia are classically triggered by carotid chemoreceptors. The chemosensory inputs are carried within the carotid sinus nerve to the nucleus tractus solitarius and the brainstem respiratory centres. To investigate whether hypoxia acts directly on brainstem neurons or secondarily via carotid body inputs, we tested the ventilatory responses to acute and long‐term hypoxia in rats with bilaterally transected carotid sinus nerves and in sham‐operated rats. Because brainstem catecholaminergic neurons are part of the chemoreflex pathway, the ventilatory response to hypoxia was studied in association with the expression of tyrosine hydroxylase (TH). TH mRNA levels were assessed in the brainstem by in situ hybridization and hypoxic ventilatory responses were measured in vivo by plethysmography. After long‐term hypoxia, TH mRNA levels in the nucleus tractus solitarius and ventrolateral medulla increased similarly in chemodenervated and sham‐operated rats. Ventilatory acclimatization to hypoxia developed in chemodenervated rats, but to a lesser extent than in sham‐operated rats. Ventilatory response to acute hypoxia, which was initially low in chemodenervated rats, was fully restored within 21 days in long‐term hypoxic rats, as well as in normoxic animals which do not overexpress TH. Therefore, activation of brainstem catecholaminergic neurons and ventilatory adjustments to hypoxia occurred independently of carotid chemosensory inputs. O2‐sensing mechanisms unmasked by carotid chemodenervation triggered two ventilatory adjustments: (i) a partial acclimatization to long‐term hypoxia associated with TH upregulation; (ii) a complete restoration of acute hypoxic responsivity independent of TH upregulation.
Simultaneous movements of upper and lower limbs are coordinated by motor representations that are shared by both limbs: a PET study
Authors: Ehrsson H. Henrik , Naito Eiichi , Geyer Stefan , Amunts Katrin , Zilles Karl , Forssberg Hans , Roland Per E.
Published: March 2003

The purpose of this study was to examine the cerebral control of simultaneous movements of the upper and lower limbs. We examined two hypotheses on how the brain coordinates movement: (i) by the involvement of motor representations shared by both limbs; or (ii) by the engagement of specific neural populations. We used positron emission tomography to measure the relative cerebral blood flow in healthy subjects performing isolated cyclic flexion–extension movements of the wrist and ankle (i.e. movements of wrist or ankle alone), and simultaneous movements of the wrist and ankle (a rest condition was also included). The simultaneous movements were performed in the same directions (iso‐directional) and in opposite directions (antidirectional). There was no difference in the brain activity between these two patterns of coordination. In several motor‐related areas (e.g. the contralateral ventral premotor area, the dorsal premotor area, the supplementary motor area, the parietal operculum and the posterior parietal cortex), the representation of the isolated wrist movement overlapped with the representation of the isolated ankle movement. Importantly, the simultaneous movements activated the same set of motor‐related regions that were active during the isolated movements. In the contralateral ventral premotor cortex, dorsal premotor cortex and parietal operculum, there was less activity during the simultaneous movements than for the sum of the activity for the two isolated movements (interaction analysis). Indeed, in the ventral premotor cortex and parietal operculum, the activity was practically identical regardless whether only the wrist, only the ankle, or both the wrist and the ankle were moved. Taken together, these findings suggest that interlimb coordination is mediated by motor representations shared by both limbs, rather than being mediated by specific additional neural populations.
Induction of neuronal death by α‐synuclein
Authors: Saha Anirban R. , Ninkina Natalia N. , Hanger Diane P. , Anderton Brian H. , Davies Alun M. , Buchman Vladimir L.
Published: March 2003

The molecular and cellular mechanisms underlying neuronal loss in neurodegenerative diseases are unclear. It is generally thought that aggregation of mutated, abnormally modified or abnormally folded proteins leads to the accumulation of extracellular, intracellular or intranuclear deposits that severely compromise cell physiology, leading to the death of the affected neurons. However, there is growing evidence that neuronal apoptosis in the absence of obvious pathological deposits could have a serious impact on the pathogenesis of neurodegenerative diseases. α‐Synuclein has been implicated in aetiology and pathogenesis of certain neurodegenerative diseases, although the precise role of this protein in neurodegeneration is uncertain. The normal functions of α‐synuclein and other members of the synuclein family in the development and function of the nervous system also remain elusive. Here we show that overexpression of wild‐type and mutant forms of α‐synuclein in cultured neurons, but not the closely related persyn (γ‐synuclein), causes apoptosis. These findings suggest that abnormalities of α‐synuclein metabolism could lead to the neuronal loss occurring in certain forms of neurodegeneration before the formation of characteristic pathological lesions.
Constitutive overactivation of protein kinase C in guinea pig brain increases α‐secretory APP processing without decreasing β‐amyloid generation
Authors: Roßner Steffen , Beck Mike , Stahl Tobias , Mendla Klaus , Schliebs Reinhard , Bigl Volker
Published: March 2003

Whilst it is generally accepted that the activation of protein kinase C (PKC) increases amyloid precursor protein (APP) secretion in vitro, the role of PKC in the regulation of APP processing and β‐amyloid generation in vivo is still not well understood. In order to address this question, we established the animal model of neocortical microencephalopathy in guinea pigs caused by in utero treatment with methylazoxymethanol acetate, a DNA‐methylating substance that eliminates proliferating cells of neuroepithelial origin. The induction of this neocortical malformation is accompanied by constitutive overactivation of PKC in the neocortex of the offspring. In the cortical and hippocampal tissues of juvenile microencephalic guinea pigs (postnatal day 30), we observed significant increases in basal (by 58% and 74%, respectively,) and phorbol ester‐stimulated PKC enzyme activity (by 47% and 71%) as compared to age‐matched control animals. In the same cortical/hippocampal preparations of methylazoxymethanol‐treated animals, there was increased α‐secretion of APP by 35% and 30% as measured by Western blot analysis using the antibody 6E10, whilst total APP secretion as well as APP mRNA expression remained unaltered. This upregulation of APP α‐secretion was limited to brain areas that displayed elevated PKC activity. However, constitutive overactivation of neocortical PKC did not affect the generation of β‐amyloid peptides 1–40 or 1–42 as measured by ELISA, suggesting that only the α‐secretase pathway of APP processing is affected by chronic PKC overactivation in vivo.
SHORT COMMUNICATIONFetal striatal transplants reinstate the electrophysiological response of pallidal neurons to systemic apomorphine challenge in rats with excitotoxic striatal lesions
Authors: Nakao N. , Nakai K. , Itakura T.
Published: March 2003

Previous studies with single‐unit recording and 2‐[14C]deoxyglucose quantitative autoradiography have shown that systemic administration of apomorphine increases the functional activity of pallidal neurons, and that the enhancement in the globus pallidus (GP) activity is abolished by striatal lesions. The present study employing electrophysiological techniques tested whether embryonic striatal tissue implanted in the excitotoxically damaged striatum of rats may affect the lesion‐induced alteration in the neuronal response of GP to apomorphine. Systemically administered apomorphine significantly increased spontaneously firing rates of GP cells. The blockade of dopamine receptors with haloperidol reversed the increased rate to baseline levels. Quinolinate‐induced striatal lesions attenuated the rate‐increasing effect of apomorphine. Embryonic striatal grafts placed in the lesioned striatum restored the response of GP cells to systemic apomorphine. The graft‐mediated restoration of the GP neuron response to apomorphine were accompanied by an improvement in the motor asymmetry induced by this drug. Considering previous anatomical data to demonstrate extensive innervation of the GP by embryonic striatal grafts, the present results suggest that the grafts reconstruct the functional striatopallidal pathway which is capable of transmitting apomorphine‐induced changes in the neuronal activity.
Differential effects of neurotrophins on ocular dominance plasticity in developing and adult cat visual cortex
Authors: Galuske Ralf A. W. , Kim Dae‐Shik , Castrén Eero , Singer Wolf
Published: March 2003

In the present study we examine the influence of neurotrophins on experience‐dependent synaptic rearrangement in developing and adult visual cortex. Brain‐derived neurotrophic factor (BDNF) or nerve growth factor (NGF) was continuously infused into cortical area 18, and the functional architecture of the cortex was examined by use of optical and electrophysiological recording techniques. In kittens, BDNF infusion during monocular deprivation (MD) reversed the normally occurring ocular dominance (OD) shift towards the non‐deprived eye so that the deprived eye dominated the BDNF‐treated cortex after MD. Under conditions of equal activation of thalamocortical synapses, i.e. when animals were either subject to binocular deprivation (BD) or reared without deprivation, BDNF infusion did not disrupt binocularity of cortical units, but reversed the natural OD bias towards the contralateral eye in favour of the ipsilateral eye. In addition, BDNF treatment in kittens led to a loss of the orientation selectivity of cortical units irrespective of rearing conditions. In adult animals, BDNF influenced neither OD distributions nor orientation selectivity. The effect of NGF was markedly different. It was ineffective in kittens but in adult animals it caused a shift of OD towards the deprived eye when MD was combined with NGF infusion. However, in this case orientation selectivity was preserved. Thus, both neurotrophins have profound activity‐ and age‐dependent effects on the functional architecture of the visual cortex. Moreover, our results indicate that simple substitution of neurotrophins in excess is unlikely to compensate for deprivation effects by preserving or restoring the normal functional architecture of the cortex.
Suppression of c‐fos induction in the nucleus accumbens prevents acquisition but not expression of morphine‐conditioned place preference
Authors: Tolliver Bryan K. , Sganga Michael W. , Sharp Frank R.
Published: March 2003

The c‐fos immediate‐early gene is induced by morphine and other drugs of abuse in the nucleus accumbens (NAc), a mesolimbic region implicated in drug abuse and reward. This study examined the role of c‐fos in the acquisition and expression of the conditioned place paradigm (CPP) in the rat by suppressing Fos protein expression with c‐fos antisense oligodeoxynucleotides (ODNs). CPP was completely prevented by c‐fos antisense ODN infused bilaterally into the NAc prior to each systemic morphine injection, whereas sense and missense NAc injections had no effect on CPP. NAc administration of c‐fos antisense ODN after the last systemic morphine conditioning session did not affect the expression of morphine‐CPP. These results suggest that c‐fos expression in NAc is necessary for the acquisition but not expression of morphine‐CPP, and they have important implications for understanding conditioned behaviours and drug craving and addiction.
Spatiotemporal expression of noncatalytic TrkC NC2 isoform during early and late CNS neurogenesis: a comparative study with TrkC catalytic and p75NTR receptors
Authors: Menn Bénédicte , Timsit Serge , Represa Alfonso , Mateos Stéphanie , Calothy Georges , Lamballe Fabienne
Published: March 2003

The TrkC subfamily of primary high‐affinity neurotrophin‐3 receptors is composed of catalytic (kinase‐containing; TrkC K) and noncatalytic (TrkC NC) isoforms generated by alternative splicing. We previously reported the presence of the mouse noncatalytic TrkC NC2 isoform in regions of neuronal differentiation [Menn, B., Timsit, S., Calothy, G. & Lamballe, F. (1998) J. Comp. Neurol., 401, 47–64]. In order to gain insight into specific roles for TrkC NC2 receptors during CNS neurogenesis, we compared its distribution with that of its catalytic counterparts and the p75NTR receptor in in vivo and in vitro model systems of early and late neuronal differentiation. We found that TrkC NC2 expression coincided with the exit of neuronal progenitors from the cell cycle and was maintained in differentiated cerebellar neurons. We also showed that, whilst TrkC K receptors were expressed both in mitotic and postmitotic cells, TrkC NC2 was present only in differentiating neural stem cell progeny, suggesting its involvement in neuronal and glial cell differentiation. During neuritogenesis of primary neocortical neurons, both TrkC isoforms as well as p75NTR were located in axonal and dendritic processes. However, whilst these various receptors were present in the same neuronal compartments, TrkC NC2 distribution was specifically restricted to distinct areas of extending neurites. Taken together, these findings suggest that spatiotemporal localization of the noncatalytic receptor could account for specific local effects of neurotrophin‐3.
The extracellular matrix molecule tenascin‐R and its HNK‐1 carbohydrate modulate perisomatic inhibition and long‐term potentiation in the CA1 region of the hippocampus
Authors: Saghatelyan Armen K. , Gorissen Silke , Albert Martine , Hertlein Birgit , Schachner Melitta , Dityatev Alexander
Published: March 2003

Perisomatic inhibition of pyramidal cells regulates efferent signalling from the hippocampus. The striking presence of HNK‐1, a carbohydrate expressed by neural adhesion molecules, on perisomatic interneurons and around somata of CA1 pyramidal neurons led us to apply monoclonal HNK‐1 antibodies to acute murine hippocampal slices. Injection of these antibodies decreased GABAA receptor‐mediated perisomatic inhibitory postsynaptic currents (pIPSCs) but did not affect dendritic IPSCs or excitatory postsynaptic currents. The decrease in the mean amplitude of evoked pIPSCs by HNK‐1 antibodies was accompanied by an increase in the coefficient of variation of pIPSC amplitude, number of failures and changes in frequency but not amplitude of miniature IPSCs, suggesting that HNK‐1 antibodies reduced efficacy of evoked GABA release. HNK‐1 antibodies did not affect pIPSCs in knock‐out mice deficient in the extracellular matrix molecule tenascin‐R which carries the HNK‐1 carbohydrate as analysed by immunoblotting in synaptosomal fractions prepared from the CA1 region of the hippocampus. For control, HNK‐1 antibody was applied to acute sections of mice deficient in the neural cell adhesion molecule NCAM, another potential carrier of HNK‐1, and resulted in decrease of pIPSCs as observed in wild‐type mice. Reduction in perisomatic inhibition is expected to promote induction of long‐term potentiation (LTP) by increasing the level of depolarization during theta‐burst stimulation. Indeed, LTP was increased by HNK‐1 antibody applied before stimulation. Moreover, LTP was reduced by an HNK‐1 peptide mimic, but not control peptide. These results provide first evidence that tenascin‐R and its associated HNK‐1 carbohydrate modulate perisomatic inhibition and synaptic plasticity in the hippocampus.
Cannabinoids inhibit hippocampal GABAergic transmission and network oscillations
Authors: Hájos N. , Katona I. , Naiem S. S. , Mackie K. , Ledent C. , Mody I. , Freund T. F.
Published: March 2003

Using a new antibody developed against the C‐terminus of the cannabinoid receptor (CB1), the immunostaining in the hippocampus revealed additional axon terminals relative to the pattern reported previously with an N‐terminus antibody. Due to a greater sensitivity of this antibody, a large proportion of boutons in the dendritic layers displaying symmetrical (GABAergic) synapses were also strongly immunoreactive for CB1 receptors, as were axon terminals of perisomatic inhibitory cells containing cholecystokinin. Asymmetrical (glutamatergic) synapses, however, were always negative for CB1. To investigate the effect of presynaptic CB1 receptor activation on hippocampal inhibition, we recorded inhibitory postsynaptic currents (IPSCs) from principal cells. Bath application of CB1 receptor agonists (WIN55,212‐2 and CP55,940) suppressed IPSCs evoked by local electrical stimulation, which could be prevented or reversed by the CB1 receptor antagonist SR141716A. Action potential‐driven IPSCs, evoked by pharmacological stimulation of a subset of interneurons, were also decreased by CB1 receptor activation. We also examined the effects of CB1 receptor agonists on Ca2+‐independent miniature IPSCs (mIPSC). Both agonists were without significant effect on the frequency or amplitude of mIPSCs. Synchronous gamma oscillations induced by kainic acid in the CA3 region of hippocampal slices were reversibly reduced in amplitude by the CB1 receptor agonist CP 55,940, which is consistent with an action on IPSCs. We used CB1–/– knock‐out mice to confirm the specificity of the antibody and of the agonist (WIN55,212‐2) action. We conclude that activation of presynaptic CB1 receptors decreases Ca2+‐dependent GABA release, and thereby reduces the power of hippocampal network oscillations.
Prostaglandin E2‐induced sensitization of bradykinin‐evoked responses in rat dorsal root ganglion neurons is mediated by cAMP‐dependent protein kinase A
Authors: Smith Jacqueline A. M. , Davis Clare L. , Burgess Gillian M.
Published: March 2003

Primary cultures of neonatal rat dorsal root ganglion (DRG) neurons were used to examine the mechanisms underlying both the direct activation and the sensitization of sensory neurons by prostanoids. Prostaglandin E2 (PGE2) elevated cytosolic calcium concentration ([Ca2+]i) in a subpopulation of small (< 19 μm) diameter, capsaicin‐sensitive DRG neurons. PGE2 also stimulated substance P (SP) release from DRG cultures. In contrast to bradykinin, PGE2 did not stimulate phosphoinositidase C (PIC) and the PGE2‐evoked increase in [Ca2+]i was dependent on extracellular calcium. Pre‐treatment with PGE2 potentiated bradykinin‐evoked increases in [Ca2+]i in small diameter neurons and increased the number of cells that responded to low concentrations of bradykinin. A similar effect was seen with prostaglandin I2 (PGI2) but not prostaglandin F2α (PGF2α). PGE2 pretreatment also potentiated bradykinin‐evoked release of SP, inducing a leftward shift in the bradykinin concentration–response curve and an increase in the maximum response. PGE2 stimulated adenylyl cyclase activity in DRG cultures, at concentrations and times consistent with those required to observe both the direct and sensitizing effects of the prostanoid on [Ca2+]i responses. Furthermore, the direct and sensitizing effects of PGE2, on both [Ca2+]i responses and SP release, were mimicked by the membrane permeant cAMP analogue dibutyryl cAMP and inhibited by H89, an inhibitor of cAMP‐dependent protein kinase A (PKA). These observations are consistent with the hypothesis that both direct activation and sensitization of sensory neurons by prostanoids, such as PGE2, are mediated by PKA‐dependent phosphorylation mechanisms.
GDNF enhances the synaptic efficacy of dopaminergic neurons in culture
Authors: Bourque Marie‐Josée , Trudeau Louis‐Eric
Published: March 2003

Glial cell line‐derived neurotrophic factor (GDNF) is known to promote the survival and differentiation of dopaminergic neurons of the midbrain. GDNF also causes an enhancement of dopamine release by a mechanism which is presently unclear. Using isolated dopaminergic neurons of the rat ventral tegmental area in culture, we have tested the hypothesis that GDNF regulates the establishment and functional properties of synaptic terminals. Previous studies have shown that single dopaminergic neurons in culture can co‐release glutamate in addition to dopamine, leading to the generation of a fast excitatory autaptic current via glutamate receptors. Using excitatory autaptic currents as an assay for the activity of synapses established by identified dopaminergic neurons, we found that chronically applied GDNF produced a threefold increase in the amplitude of excitatory autaptic currents. This action was specific for dopaminergic neurons because GDNF had no such effect on ventral tegmental area GABAergic neurons. The enhancement of excitatory autaptic current amplitude caused by GDNF was accompanied by an increase in the frequency of spontaneous miniature excitatory autaptic currents. These observations confirmed a presynaptic locus of change. We identified synaptic terminals by using synapsin‐1 immunofluorescence. In single tyrosine hydroxylase‐positive neurons, the number of synapsin‐positive puncta which represent putative synaptic terminals was found to be approximately doubled in GDNF‐treated cells at 5, 10 and 15 days in culture. The number of such morphologically identified terminals in isolated GABAergic neurons was unchanged by GDNF. These results suggest that one mechanism through which GDNF may enhance dopamine release is through promoting the establishment of new functional synaptic terminals.
Dopamine control of striatal gene expression during development: relevance to knockout mice for the dopamine transporter
Authors: Fauchey Valérie , Jaber Mohamed , Bloch Bertrand , Le Moine Catherine
Published: March 2003

The aim of this study was to determine at which developmental stage and how dopamine regulates the expression of striatal dopamine receptor and neuropeptide mRNAs. For this, we studied the expression of these mRNAs, in relation to dopamine innervation, in normal mice from gestational day 13 (G13) to adult. Particularly, we investigated the adaptive changes in the expression of these markers in mice lacking the dopamine transporter during development. We detected tyrosine hydroxylase, by immunohistochemistry, in the ventral mesencephalon and the striatal anlage in both genotypes at G13, whereas the dopamine transporter appeared in the striatum of normal mice at G14. By in situ hybridization, we detected striatal dopamine D1, D2, D3 receptor, and substance P mRNAs at G13, preproenkephalin A mRNA at G14 and dynorphin mRNA at G17 in normal mice. Although the time of initial detection and the distribution were not affected in mutant mice, quantitative changes were observed. Indeed, D1 and D2 receptor as well as preproenkephalin A mRNA levels were decreased from G14 on, and dynorphin mRNA level was increased from G17 on. In contrast, substance P mRNA level was unaffected. Our data demonstrate that the influence of dopamine on striatal neurons occurs early during the development of the mesostriatal system as quantitative changes appeared in mutant mice as soon as G14. These findings bring new insights to the critical influence of dopamine on the expression of striatal dopamine receptor and neuropeptide mRNAs during development, and suggest that mesostriatal dopamine transmission functions from G14 on.
Impaired cholinergic function in cell lines derived from the cerebral cortex of normal and trisomy 16 mice
Authors: Allen David D. , Martín José , Arriagada Christian , Cárdenas Ana María , Rapoport Stanley I. , Caviedes Raúl , Caviedes Pablo
Published: March 2003

Murine trisomy 16 is an animal model of human Down's syndrome. We have successfully established permanently growing cell lines from the cerebral cortex of normal and trisomy 16 foetal mice using an original procedure. These lines, named CNh (derived from a normal animal) and CTb (derived from a trisomic foetus), express neuronal markers. Considering that Down's syndrome exhibits cholinergic deficits, we examined cholinergic function in these lines, using incorporation of [3H]‐choline and fractional release studies. After 1, 3 and 5 min of [3H]‐choline incubation, CTb cell uptake was lower by ∼ 50% compared to controls. Hemicholinium‐3 significantly reduced the incorporation of [3H]‐choline in both CNh and CTb cells at high concentration (10 μm), suggesting high‐affinity choline transport. However, CTb cells exhibited greater sensitivity to the blocker. For fractional release experiments, the cells were stimulated by K+ depolarization, glutamate or nicotine. When depolarized, CTb cells showed a 68% reduction in fractional release of [3H]‐acetylcholine compared to CNh cell line, and a 45% reduction when stimulated by nicotine. Interestingly, glutamate induced similar levels of release in both cell types. The results indicate the existence of cholinergic dysfunction in CTb cells when compared to CNh, similar to that reported for primary cultures of trisomy 16 brain tissue (Fiedler et al. 1994, Brain Res., 658, 27–32). Thus, the CTb cell line may serve as a model for the study of Down's syndrome pathophysiology.
Pindolol excites dopaminergic and adrenergic neurons, and inhibits serotonergic neurons, by activation of 5‐HT1Areceptors
Authors: Lejeune F. , Millan M. J.
Published: March 2003

Pindolol accelerates the clinical actions of selective serotonin reuptake inhibitors (SSRIs) in man, and modulates extracellular levels of monoamines in corticolimbic structures in rats. Herein, we examined its influence upon electrical activity of serotonergic, dopaminergic and adrenergic perikarya in the dorsal raphe nucleus (DRN), ventral tegmental area (VTA) and locus coeruleus (LC) of anaesthetized rats. In analogy to the serotonin1A(5‐HT1A) agonist, 8‐OH‐DPAT (−100%), pindolol dose‐dependently (0.063– 1.0 mg/kg) decreased (−70%) the firing rate of serotonergic neurons. The inhibitory action of pindolol was abolished by the selective 5‐HT1Aantagonist, WAY‐100,635 (0.031 mg/kg). In contrast, 8‐OH‐DPAT (+26%) and pindolol (0.25–4.0 mg/kg, +60%) dose‐dependently increased the firing rate of dopaminergic cells. Of 57 neurons recorded (pindolol, 2.0 mg/kg), 36 (63%) were excited, 11 (19%) were unaffected and 10 (18%) were inhibited. This variable influence could be attributed to regularly firing neurons in the parabrachial subdivision, inasmuch as all neurons in the paranigral subnucleus were excited. The facilitation of firing by pindolol was accompanied by an increase in burst firing throughout the VTA. Both the increases in burst firing and in firing rate were reversed by WAY‐100,635 (0.031 mg/kg). Finally, the electrical activity of adrenergic neurons was dose‐dependently enhanced by 8‐OH‐DPAT and pindolol (+99% and +83%, respectively). WAY‐100,635 reversed this excitation and, itself, inhibited the activity of adrenergic neurons. In conclusion, via engagement of 5‐HT1Areceptors, pindolol inhibits serotonergic, and activates dopaminergic and adrenergic, neurons in anaesthetized rats. Such actions may contribute to its influence upon mood, both alone and in association with antidepressant agents.
Involvement of the human frontal eye field and multiple parietal areas in covert visual selection during conjunction search
Authors: Donner Tobias , Kettermann Andreas , Diesch Eugen , Ostendorf Florian , Villringer Arno , Brandt Stephan A.
Published: March 2003

Searching for a target object in a cluttered visual scene requires active visual attention if the target differs from distractors not by elementary visual features but rather by a feature conjunction. We used functional magnetic resonance imaging (fMRI) in human subjects to investigate the functional neuroanatomy of attentional mechanisms employed during conjunction search. In the experimental condition, subjects searched for a target defined by a conjunction of colour and orientation. In the baseline condition, subjects searched for a uniquely coloured target, regardless of its orientation. Eye movement recordings outside the scanner verified subjects' ability to maintain fixation during search. Reaction times indicated that the experimental condition was attentionally more demanding than the baseline condition. Differential activations between conditions were therefore ascribed to top‐down modulation of neural activity. The frontal eye field, the ventral precentral sulcus and the following posterior parietal regions were consistently activated: (i) the postcentral sulcus; (ii) the posterior; and (iii) the anterior part of the intraparietal sulcus; and (iv) the junction of the intraparietal with the transverse occipital sulcus. Parietal regions were spatially distinct and displayed differential amplitudes of signal increase with a maximal amplitude in the posterior intraparietal sulcus. Less consistent activation was found in the lateral fusiform gyrus. These results suggest an involvement of the human frontal eye field in covert visual selection of potential targets during search. These results also provide evidence for a subdivision of posterior parietal cortex in multiple areas participating in covert visual selection, with a major contribution of the posterior intraparietal sulcus.
Glucocorticoid enhancement of memory consolidation in the rat is blocked by muscarinic receptor antagonism in the basolateral amygdala
Authors: Power Ann E. , Roozendaal Benno , McGaugh James L.
Published: March 2003

Glucocorticoid‐induced memory enhancement is known to depend on β‐adrenoceptor activation in the basolateral amygdala (BLA). Additionally, inactivation of muscarinic cholinergic receptors in the rat amygdala blocks memory enhancement induced by concurrent β‐adrenergic activation. Together, these findings suggest that glucocorticoid‐induced modulation of memory consolidation requires cholinergic as well as adrenergic activation in the BLA. Two experiments investigated this issue. The first experiment examined whether blockade of muscarinic cholinergic receptors in the BLA with atropine alters the memory‐enhancing effects of the systemically administered glucocorticoid dexamethasone. Dexamethasone (0.3, 1.0 or 3.0 mg/kg, s.c.) administered to rats immediately after inhibitory avoidance training produced dose‐dependent enhancement of 48‐h retention. Concurrent bilateral infusions of the muscarinic cholinergic antagonist atropine (0.5 μg in 0.2 μL per side) into the BLA blocked the memory enhancement. The second experiment investigated whether the BLA is a locus of interaction between glucocorticoid and muscarinic activation. The specific glucocorticoid receptor (GR or type II) agonist RU 28362 (1.0, 3.0 or 10 ng) was infused into the BLA either alone or together with atropine immediately after training. The GR agonist produced dose‐dependent memory enhancement and atropine blocked the memory enhancement. These findings indicate that muscarinic cholinergic activation within the BLA is critical for enabling glucocorticoid enhancement of memory consolidation and that enhancement of memory induced by GR activation in the BLA requires cholinergic activation within the BLA.
Role of the GABAA receptor γ2 subunit in the development of gonadotropin‐releasing hormone neurons in vivo
Authors: Simonian Sharon X. , Skynner Michael J. , Sieghart Werner , Essrich Christian , Luscher Bernhard , Herbison Allan E.
Published: March 2003

We have employed transgenic mouse models to examine the functional significance of the γ2 subunit of the GABAA (γ‐aminobutyric acid) receptor to the correct development of gonadotropin‐releasing hormone (GnRH) neurons in vivo. In the first experiment, the expression of γ2 subunit protein by the GnRH phenotype was determined using transgenic mice in which GnRH gene sequences direct the expression of the LacZ reporter to the nucleus of the GnRH neurons. This greatly facilitates the immunocytochemical identification of non‐nuclear‐located antigens within GnRH neurons and revealed that ∼ 25% of juvenile GnRH neurons were immunoreactive for the γ2 subunit and that this increased to 40% in pubertal mice. In the second experiment, GnRH mRNA expression was examined in the brains of γ2 subunit knockout mice (γ20/0) and their wild‐type (γ2+/+) littermates at embryonic day 15 and postnatal days (P) 0 and 11–16 using in situ hybridization. The distribution and numbers of cells expressing GnRH mRNA in γ2+/+ and γ20/0 mice were not found to differ at any age. However, the GnRH mRNA content of medial septal cells was significantly lower in γ20/0 compared with γ2+/+ mice at P11–16 (P < 0.05) and the same trend was observed for preoptic area neurons. These results demonstrate that while the γ2 subunit of the GABAA receptor is expressed by postnatal GnRH neurons, their embryonic development does not require a functional γ2 subunit. In contrast, postnatal GnRH mRNA expression was found to be dependent upon signalling through the GABAA receptor.
Neuronal, astroglial and microglial cytokine expression after an excitotoxic lesion in the immature rat brain
Authors: Acarin Laia , González Berta , Castellano Bernardo
Published: March 2003

Cytokines are important intercellular messengers involved in neuron–glia interactions and in the microglial‐astroglial crosstalk, modulating the glial response to brain injury and the lesion outcome. In this study, excitotoxic lesions were induced by the injection of N‐methyl‐d‐aspartate in postnatal day 9 rats, and the cytokines interleukin‐1 beta (IL‐1β), interleukin‐6 (IL‐6), tumour necrosis factor alpha (TNFα) and transforming growth factor beta 1 (TGF‐β1) analysed by ELISA and/or immunohistochemistry. Moreover, cytokine‐expressing glial cells were identified by means of double labelling with glial fibrillary acidic protein or tomato lectin binding. Our results show that both neurons and glia were capable of cytokine expression following different patterns in the excitotoxically damaged area vs. the nondegenerating surrounding grey matter (SGM). Excitotoxically damaged neurons showed upregulation of IL‐6 and downregulation of TNFα and TGF‐β1 before they degenerated. Moreover, in the SGM, an increased expression of neuronal IL‐6, TNFα and TGF‐β1 was observed. A subpopulation of microglial cells, located in the SGM and showing IL‐1β and TNFα expression, were the earliest glial cells producing cytokines, at 2–10 h postinjection. Later on, cytokine‐positive glial cells were found within the excitotoxically damaged area and the adjacent white matter: some reactive astrocytes expressed TNFα and IL‐6, and microglia/macrophages showed mild IL‐1β and TGF‐β1. Finally, the expression of all cytokines was observed in the glial scar. As discussed, this pattern of cytokine production suggests their implication in the evolution of excitotoxic neuronal damage and the associated glial response.
Attempted endogenous tissue repair following experimental spinal cord injury in the rat: involvement of cell adhesion molecules L1 and NCAM?
Authors: Brook Gary A. , Houweling Diane A. , Gieling Roben G. , Hermanns Thomas , Joosten Elbert A. J. , Bär Dop P. R. , Gispen Willem‐Hendrik , Schmitt Andreas B. , Leprince P. , Noth Johannes , Nacimiento Wilhelm
Published: March 2003

It is widely accepted that the devastating consequences of spinal cord injury are due to the failure of lesioned CNS axons to regenerate. The current study of the spontaneous tissue repair processes following dorsal hemisection of the adult rat spinal cord demonstrates a phase of rapid and substantial nerve fibre in‐growth into the lesion that was derived largely from both rostral and caudal spinal tissues. The response was characterized by increasing numbers of axons traversing the clearly defined interface between the lesion and the adjacent intact spinal cord, beginning by 5 days post operation (p.o.). Having penetrated the lesion, axons became associated with a framework of NGFr‐positive non‐neuronal cells (Schwann cells and leptomeningeal cells). Surprisingly few of these axons were derived from CGRP‐ or SP‐immunoreactive dorsal root ganglion neurons. At the longest survival time (56 days p.o.), there was a marked shift in the overall orientation of fibres from a largely rostro‐caudal to a dorso‐ventral axis. Attempts to identify which recognition molecules may be important for these re‐organizational processes during attempted tissue repair demonstrated the widespread and intense expression of the cell adhesion molecules (CAM) L1 and N‐CAM. Double immunofluorescence suggested that both Schwann cells and leptomeningeal cells contributed to the pattern of CAM expression associated with the cellular framework within the lesion.
Schizophrenia: glutathione deficit in cerebrospinal fluid and prefrontal cortex in vivo
Authors: Do K. Q. , Trabesinger A. H. , Kirsten‐Krüger M. , Lauer C. J. , Dydak U. , Hell D. , Holsboer F. , Boesiger P. , Cuénod M.
Published: March 2003

Schizophrenia is a major psychiatric disease, which affects the centre of the personality, with severe problems of perception, cognition as well as affective and social behaviour. In cerebrospinal fluid of drug‐free schizophrenic patients, a significant decrease in the level of total glutathione (GSH) by 27% (P < 0.05) was observed as compared to controls, in keeping with the reported reduced level of its metabolite γ‐glutamylglutamine. With a new non‐invasive proton magnetic resonance spectroscopy methodology, GSH level in medial prefrontal cortex of schizophrenic patients was found to be 52% (P = 0.0012) lower than in controls. GSH plays a fundamental role in protecting cells from damage by reactive oxygen species generated among others by the metabolism of dopamine. A deficit in GSH would lead to degenerative processes in the surrounding of dopaminergic terminals resulting in loss of connectivity. GSH also potentiates the N‐methyl‐d‐aspartate (NMDA) receptor response to glutamate, an effect presumably reduced by a GSH deficit, leading to a situation similar to the application of phencyclidine (PCP). Thus, a GSH hypothesis might integrate many established biological aspects of schizophrenia.
Developmental regulation of neurogenesis in the pluripotent human embryonal carcinoma cell line NTERA‐2
Authors: Przyborski S. A. , Morton I. E. , Wood A. , Andrews P. W.
Published: March 2003

Embryonal carcinoma (EC) cells provide a caricature of pluripotent embryonic stem (ES) cells and may be used as surrogates for investigating the mechanisms that regulate cell differentiation during embryonic development. NTERA‐2 is a human EC cell line that differentiates in response to retinoic acid yielding cells that include terminally differentiated neurons. The expression of genes known to be involved in the formation of the vertebrate nervous system was examined during retinoic acid‐induced NTERA‐2 differentiation. Differentiation of these human EC cells into neurons could be divided into three sequential phases. During phase 1, in the first week of differentiation, hath1 mRNA showed a small transient increase that correlated with the rapid accumulation of nestin message, a marker of neuroprogenitors. Transcripts of nestin were quickly downregulated during phase 2 as expression of neuroD1, characteristic of neuroprogenitors exiting the cell cycle, was induced. A neural cell surface antigen, detected by the monoclonal antibody A2B5, was expressed by cells exiting the cell cycle, correlating with the expression of neuroD1 as the cells became post‐mitotic. Markers of mature neural cells (e.g. synaptophysin and neuron‐specific enolase) were subsequently increased during phase 3 and were maintained. This regulated pattern of gene expression and commitment to the neural lineage indicates that differentiation of NTERA‐2 neurons in vitro follows a similar pathway to that observed by neural ectodermal precursors during vertebrate neurogenesis in vivo.
Maternal deprivation affects behaviour from youth to senescence: amplification of individual differences in spatial learning and memory in senescent Brown Norway rats
Authors: Oitzl Melly S. , Workel Judith O. , Fluttert Marc , Frösch Fawzia , De Kloet E. Ron
Published: March 2003

Previous studies have shown that deprivation of the infant rat from maternal care has pronounced effects on the stress system during ontogeny. Here we test the hypothesis that 24 h of maternal deprivation at postnatal day 3 will cause persistent changes in behaviour. Spatial learning and memory of male Brown Norway rats deprived as infants were observed in the Morris water maze at 3, 12, 24 and 30–32 months of age (young, adult, aged, senescent). Their nondeprived mother‐reared littermates served as controls. (i) With increasing age, water maze performance declined in deprived and nondeprived groups. However, once the task was learned the animals maintained their good performance during retest at later ages. (ii) Maternal deprivation delayed acquisition until adulthood and caused at every age a higher degree of persistent behaviour as judged from the performance of deprived rats' free swim trials and reversal trials. (iii) At senescence the mean performance in the water maze did not differ between the groups. Instead, the individual performance was strikingly different within each group. Senescent deprived rats were either nonimpaired or impaired with only a few animals showing an intermediate performance. Thus, a large group of animals (≈ 40%) ages successfully as they are resistant to the effect of maternal deprivation. In contrast, the majority of the control animals displayed intermediate performance. Taken together, maternal deprivation has life‐long consequences for behaviour and culminates at senescence in amplification of individual differences in learning ability rather than in a generalized deterioration of cognitive functions.
Representation of accuracy in the dorsal premotor cortex
Authors: Gomez Jose E. , Fu Qinggong , Flament Didier , Ebner Timothy J.
Published: March 2003

The endpoint accuracy of a reaching movement strongly affects kinematics, particularly during the final phases of movement. However, where and how accuracy is represented in the central nervous system remains unknown. In this study, the discharge of 150 neurons located primarily in the dorsal premotor cortex (PMd), were recorded from monkeys performing an instructed delay, centre‐out reaching task in which movement direction and target size were systematically varied. Linear regression analyses were used to assess the dependence of movement kinematics and cell discharge on target direction, size and tangential velocity (i.e. speed). The speed and timing of the movement were dependent on both direction and target size. Initially direction was the dominant predictor whilst target size became more important as the hand reached the target. A temporal multiple linear regression analysis found significant correlations with target size in 99 of 150 cells. The discharge of 134 cells was directionally tuned and 83 cells modulated with mean speed. Significant correlations of discharge with target size occurred throughout the task as did correlations with direction. However, correlations with direction preferentially occurred early in the task, prior to movement onset, whilst correlations with target size tended to occur late, well after movement onset. This temporal dependency of the firing in relationship to target direction and size mirrored that observed for the kinematics. We conclude that the discharge of PMd cells is highly correlated with the accuracy requirement of the movement. The timing of the correlations suggest that accuracy information is available for the planning and for the on‐line control of endpoint accuracy.