bluuebunny/crossref_metadata_2025_split huggingface dataset:
Excitatory Amino Acid Receptors Participate in Synaptic Transmission of Visual Responses in the Superficial Layers of the Cat Superior Colliculus
Authors: Binns K. E. , Salt T. E. 
Published: April 2006

AbstractThe contribution of NMDA and non‐NMDA receptors to visual synaptic transmission in the superficial layers of the superior colliculus of the cat has been studied using extracellular recording and iontophoretic techniques. Neuronal responses to natural visual stimulation and the ejection of NMDA and AMPA were observed in the absence and presence of the antagonists CNQX, CPP and AP5. CNQX routinely reduced the responses to visual stimulation at ejection currents which selectively blocked the responses to AMPA but not those to NMDA. Agonist selective ejection currents of CPP and AP5 also reduced visual responses of most SC neurons, but there was a substantial majority whose visual responses were resistant to these antagonists. Neurons with CPP/AP5 resistant visual responses were more commonly found 750–1000 μm from the dorsal surface of the SC. The data indicate that, while non‐NMDA receptors are heavily involved in visual synaptic transmission in the superficial SC, the involvement of NMDA receptors varies with recording depth.
Regulation of Ciliary Neurotrophic Factor in Cultured Rat Hippocampal Astrocytes
Authors: Rudge John S. , Morrissey Donna , Lindsay Ronald M. , Pasnikowski Elizabeth M. 
Published: April 2006

AbstractCiliary neurotrophic factor (CNTF) is a pleiotrophic cytokine which is detectable only at very low levels in the intact adult rat CNS, but following an aspirative lesion to the dorsal hippocampus and overlying cortex, CNTF mRNA levels are dramatically up‐regulated in reactive astrocytes. In cultured rat hippocampal astrocytes, CNTF mRNA levels are high, similar to the levels in reactive astrocytes in vivo, but are strongly suppressed after administration of isoproterenol and forskolin, which stimulate the production of intracellular cyclic AMP, induce marked morphological change in the astrocytes and up‐regulate glial fibrillary acidic protein mRNA and nerve growth factor mRNA in these cells. Following a single administration of forskolin to cultured astrocytes, suppression of CNTF mRNA was sustained for up to 7 days. A similar down‐regulation was observed with the endogenous adrenergic agonists noradrenaline and adrenaline as well as, to a lesser extent, dopamine and adenosine. Down‐regulation of CNTF mRNA resulted in a gradual reduction in the level of CNTF protein within the astrocytes. A single addition of forskolin or isoproterenol resulted in a drop in CNTF protein levels to 29 and 52% of control levels respectively after 9 days in vitro, although the rate of turnover of CNTF remained the same. Down‐regulation of CNTF mRNA in cultured hippocampal astrocytes by adenylyl cyclase activation was quite specific, as a wide range of growth factors, cytokines and neurotransmitters had little or no effect upon CNTF mRNA levels.
Effects of Apomorphine and L‐Methionine Sulphoximine on the Release of Excitatory Amino Acid Neurotransmitters and Glutamine in the Striatum of the Conscious Rat
Authors: Exposito Inmaculada , Sanz Belén , Porras Alberto , Mora Francisco 
Published: April 2006

AbstractThe effects of apomorphine, a D1‐, D2‐dopamine receptor agonist, on the extracellular concentrations of excitatory amino acids, glutamic and aspartic acids, and on that of their precursor, glutamine, were investigated using an intracerebral perfusion system. Apomorphine produced a concentration‐related rise in glutamic acid concentration in cerebral perfusates (P < 0.01) whereas only the highest concentration of apomorphine (3 × 10‐3μg/μl) increased the concentration of aspartic acid (P < 0.05). These effects were seen in the sample taken at the same time as the apomorphine injection. The rise in glutamine concentration (P < 0.01) produced by apomorphine continued for 10 min beyond perfusion with apomorphine. These effects were attenuated by previous injections of a D1‐, D2‐dopamine receptor blocker. To investigate further the release of glutamine, the glutamine synthetase inhibitor L‐methionine sulphoximine (MSO) was injected intracerebrally before apomorphine perfusion. After MSO pre‐injection, the extracellular concentration of glutamine decreased (P < 0.01) to near zero concentrations. In MSO‐treated animals, apomorphine did not induce the release of glutamic acid, aspartic acid or glutamine. These results indicate a role for dopamine in the release of excitatory amino acids and glutamine in the neostriatum of the rat. A possible volumetric interaction between dopamine and glutamic acid as well as the hypothesis of a striato‐pallido‐thalamo‐cortico‐striatal feedback loop are discussed.
Reciprocal Connections of the Motor Neocortical Area with the Contralateral Thalamus in the Hedgehog (Erinaceus europaeus) Brain
Authors: Dinopoulos A. 
Published: April 2006

AbstractHorseradish peroxidase unilateral injections in various neocortical areas (prefrontal, somatosensory, auditory, visual) of the hedgehog (Erinaceus europaeus) brain resulted in labelling of nuclei in the ipsilateral thalamus known from studies in other species and in the hedgehog to project to these areas. However, injections in the motor area resulted in retrograde and anterograde labelling of nuclei in both the ipsilateral and contralateral thalamus. These nuclei included the ventral lateral nucleus (VL), the intralaminar nuclei (ILN), the mediodorsal nucleus (MD) and midline nuclei. Large unilateral injections located mainly laterally in the thalamus labelled cells, contralaterally, in the ventral lateral geniculate nucleus, the intergeniculate leaflet and the reticular nucleus of the thalamus but never in VL, ILN and MD. The present results confirm previously described bilateral thalamocortical projections from the VL to the somatosensorimotor area in this species (Regidor and Divac, Brain Behav. Evol., 39, 265–269, 1992) and in addition demonstrate that (i) bilateral thalamocortical projections are established preferentially with the motor area, (ii) several nuclei are involved in such connections, (iii) these connections are reciprocal and topographically organized, and (iv) labelling in the contralateral thalamus observed in the present study is not a result of transneuronal transport of the tracer through thalamothalamic connections. This organization is unique among mammals and supports previous anatomical and electrophysiological findings, on the basis of which it has been suggested that the hedgehog retains a primitive character in neocortical and thalamic evolution.
Exposure to Kainic Acid Mimics the Effects of Axotomy in Cerebellar Purkinje Cells of the Adult Rat
Authors: Rossi Ferdinando , Borsello Tiziana , Strata Piergiorgio 
Published: April 2006

AbstractWe have investigated the long‐term structural changes which affect Purkinje cells exposed to a single dose of kainic acid. Following intraparenchymal injection of the excitotoxin in the cerebellar cortex (1 μ1 of a 1 mg/ml solution), Purkinje cells which survived within the lesioned area or close to its edges showed remarkable axonal abnormalities, involving the formation of torpedoes, hypertrophy of recurrent collaterals and atrophy of the corticofugal portion of the axon. In addition, their dendritic trees were often affected by conspicuous regressive alterations. The climbing fibres contacting these Purkinje cells were characterized by thick perisomatic plexuses, whereas their peridendritic branches were atrophic. The dendrites innervated by such atrophic olivary arbours were studded with huge numbers of newly formed spines. These alterations were already present a few days after kainic acid administration and persisted for the total period of observation of 6 months after the lesion. The remarkable similarity between the abnormalities of Purkinje cells exposed to kainic acid and those observed after axotomy indicates that in these two conditions common mechanisms determine analogous long‐lasting modifications in the affected neurons. It is proposed that kainic acid‐induced intracellular calcium overload disrupts cytoskeletal components and impairs axonal transport, thus depriving the affected Purkinje cells of retrograde trophic influences from their target neurons. As a consequence the affected neurons undergo long‐lasting regressive modifications and compensatory remodelling phenomena.
Increased Expression of the Growth‐associated Protein GAP‐43 in the Myelin‐free Rat Spinal Cord
Authors: Kapfhammer Josef P. , Schwab Martin E. 
Published: April 2006

AbstractIn the normal central nervous system (CNS) the regional expression of the growth‐associated protein GAP43 is complementary to the pattern of myelination. This has led us to suspect that myelin‐associated neurite growth inhibitors might contribute to the suppression of GAP‐43 expression by suppressing sprouting and plastic changes of synaptic terminals in myelinated CNS areas. In order to study the relationship between myelination and GAP‐43 expression more directly, we experimentally prevented myelination of the lumbar spinal cord of rats through neonatal X‐irradiation. The GAP‐43 protein expression in myelin‐free spinal cords was analysed by immunohistochemistry and immunoblotting and compared to age‐matched normal spinal cords. We found that in the absence of myelination, GAP‐43 expression is strongly increased in the spinal cord of 4‐week‐old rats. GAP‐43 was most strongly expressed in descending fibre tracts, where expression in the normal spinal cord is very low. In grey matter the typical regional pattern of GAP‐43 expression did not develop; instead GAP‐43 expression was high in all regions of the spinal cord. The overall pattern of myelination and GAP‐43 expression in the myelin‐free cord resembled that of early postnatal stages. This indicates that the regional down‐regulation of GAP‐43 expression during normal postnatal development did not occur in the myelin‐free areas. Our results support the hypothesis that neurite growth inhibitors from oligodendrocytes and CNS myelin suppress sprouting and plastic changes of synaptic terminals in the normal CNS and are thereby involved in regulating the stability of neural connections.
Rostrocaudal Subregional Differences in the Response of Enkephalin, Dynorphin and Substance P Synthesis in Rat Nucleus Accumbens to Dopamine Depletion
Authors: Voorn Pieter , Docter Gerrit J. , Jongen‐Rêlo Ana L. , Jonker Allert Jan 
Published: April 2006

AbstractQuantitative in situ hybridization histochemistry was used to examine the effects of unilateral 6–hydroxydopamine lesions of the ascending dopaminergic fibres on levels of mRNA encoding the neuropeptides enkephalin, dynorphin and substance P in subregions of the nucleus accumbens. The nucleus accumbens was divided into quadrants and changes in mRNA were measured along the rostrocaudal extent of the nucleus. Two weeks after the lesion an increase was found in enkephalin mRNA in the lesioned side compared to the non‐lesioned side, whereas a decrease was observed for dynorphin and substance P mRNA. The changes in mRNA levels differed from quadrant to quadrant and were not uniformly distributed along the rostrocaudal axis. Both types of changes, i.e. increase and decrease, were much higher in rostral parts of the nucleus than in caudal parts, indicating regional differences in the effects of blockade of the dopaminergic neurotransmission. The lesion‐induced increases and decreases in mRNA levels occurred in both the shell and the core subregions of the nucleus accumbens and were not specifically related to either of these areas. Factors are discussed that may contribute to the rostrocaudal gradient in the changes of enkephalin, substance P and dynorphin mRNA levels. On the basis of their afferent and efferent connections, the rostral and caudal parts of the nucleus accumbens are considered to be involved in different functions. The present results suggest that dopamine depletion may affect these functions in a differential manner.
The Effects of Archistriatal Lesions on One‐trial Passive Avoidance Learning in the Chick
Authors: Lowndes M. , Davies D. C. 
Published: April 2006

AbstractThe avian archistriatum, part of which may be homologous with the mammalian amygdala, has been implicated in fear and avoidance behaviour. There is also evidence to suggest its involvement in learning. One‐trial passive avoidance learning (PAL) has been used extensively to study memory formation in the chick. Young chicks will peck spontaneously at a small, visually conspicuous bead. If the bead has been coated with an aversive substance, the chicks show a disgust response and learn in a single trial not to peck a similar bead on subsequent presentation. Successful acquisition of this one‐trial PAL task involves the formation of a learned association between the bead and a noxious taste, followed by the expression of an avoidance response. In view of the possible involvement of the archistriatum in avoidance and learning behaviour, its role in one‐trial PAL was investigated by ablation. Bilateral electrolytic lesions of the entire archistriatum prevented the acquisition of the one‐trial PAL task. Neither bilateral lesions of the lateral cerebral area nor sham operation affected learning. The impairment of one‐trial PAL caused by archistriatal lesions was not due to effects on the visual or motor components of pecking behaviour. The archistriatum could therefore be directly involved in memory formation. It could also be involved in the organization of avoidance behaviour associated with the task, or it could form part of a circuit linking two other forebrain regions previously implicated in one‐trial PAL, the intermediate part of the medial hyperstriatum ventrale and the lobus parolfactorius.
Positive Feedback between Acetylcholine and the Neurotrophins Nerve Growth Factor and Brain‐derived Neurotrophic Factor in the Rat Hippocampus
Authors: Knipper Marlies , da Penha Berzaghi Maria , Blöchl Andrea , Breer Heinz , Thoenen Hans , Lindholm Dan 
Published: April 2006

AbstractIn the rat hippocampus, nerve growth factor (NGF) and brain‐derived neurotrophic factor (BDNF) are synthesized by neurons in an activity‐dependent manner. Glutamate receptor activation increases whereas GABAergic stimulation decreases NGF and BDNF mRNA levels. Here we demonstrate that NGF and BDNF mRNA and NGF protein are up‐regulated in the rat hippocampus by the activation of muscarinic receptors. Conversely, NGF and BDNF enhance the release of acetylcholine (ACh) from rat hippocampal synaptosomes containing the nerve endings of the septal cholinergic neurons. NGF also rapidly increases the high‐affinity choline transport into synaptosomes. The reciprocal regulation of ACh, NGF and BDNF in the hippocampus suggests a novel molecular framework by which the neurotrophins might influence synaptic plasticity.
The NMDA Receptor Antagonist CPP Suppresses Long‐term Potentiation in the Rat Hippocampal — accumbens Pathway In Vivo
Authors: Feasey‐Truger K. J. , Ten Bruggencate G. 
Published: April 2006

AbstractExcitation of afferent fibres originating in the ventral subiculum of the hippocampus through stimulation of the fimbria elicits field potentials in the nucleus accumbens. When recorded in the dorsomedial aspect of the nucleus accumbens, the evoked field responses consisted of an early, negative‐going component (Nl) with a peak latency of 8–10 ms, followed by a second negative‐going peak (N2) with a latency of 22–24 ms. The N1 response reflects monosynaptic activation of nucleus accumbens neurons; the N2 component appears to be polysynaptic in origin. In control rats, high‐frequency stimulation of the fimbria (three trains at 250 Hz, 250 ms, delivered at 50 min intervals) resulted in a long‐lasting potentiation of both the N1 and N2 components. The magnitude of potentiation exhibited by the polysynaptic N2 response was typically greater than that of the monosynaptically evoked N1 response. Following delivery of the first train, the amplitude of the N1 and N2 components was increased by ‐20 and 50% respectively. Administration of the competitive N‐methyl‐d‐aspartate (NMDA) receptor antagonist 3‐[(±)‐2‐carboxypiperazin‐4‐yl]‐propyl‐1‐phosphonic acid (CPP, 10 mg/kg i.p.) had no significant effects on the evoked nucleus accumbens responses. High‐frequency stimulation failed to produce a significant increase in the amplitude of either the N1 or the N2 response when delivered 45–60 min after CPP administration. To test whether the suppressant effects of CPP were time‐dependent, two further high‐frequency trains were applied 90 and 180 min after administration of the drug. Significant increases in the amplitude of the N1 and N2 components were observed only after the third train, delivered 180 min after CPP injection. These results demonstrate that high‐frequency stimulation of hippocampal afferents to the nucleus accumbens induces LTP in both a monosynaptic and a polysynaptic pathway. In both cases, the induction of LTP is suppressed in a time‐dependent manner by the competitive NMDA receptor antagonist CPP. Thus, NMDA receptor activation appears to be prerequisite for the induction of LTP in the hippocampus ‐ accumbens pathway.
Immunohistochemical Characterization of the Shell and Core Territories of the Nucleus Accumbens in the Rat
Authors: Jongen‐Rêlo Ana L. , Voorn Pieter , Groenewegen Henk J. 
Published: April 2006

AbstractThe nucleus accumbens in the rat has been parcelled into shell and core subdivisions. Despite accumulating evidence for such a division of the nucleus accumbens, these territories have not been delineated throughout the rostrocaudal extent of the nucleus. In the present study, an attempt has been made to delineate the shell and core using the distribution of calcium‐binding protein immunoreactivity, substance P immunoreactivity and acetylcholinesterase activity in transverse and horizontal sections through the nucleus accumbens. It was found that the pattern of calcium‐binding protein immunoreactivity provides the most unequivocal criterion to divide the nucleus accumbens into a ventral and medial, peripheral shell displaying low to moderate immunostaining, and a more laterally and dorsally located, strongly stained inner core. In most parts of the nucleus, borders seen in the calcium‐binding protein immunoreactivity pattern can also be recognized in the distributions of substance P immunoreactivity and acetylcholinesterase activity. It is concluded that the shell occupies most of the rostral part of the nucleus accurnbens, whereas rostrally the core is represented only in the most lateral part. Differences in staining intensities for all three markers indicate that both the shell and core have a heterogeneous structure. Patterns of connectivity appear to support the division of the nucleus accumbens as indicated by calcium‐binding protein immunoreactivity in the present study.
The Entorhinal Cortex and a Delayed Non‐matching‐to‐place Task in Mice: Emphasis on Preoperative Training and Presentation Procedure
Authors: Cho Yoon H. , Jaffard Robert 
Published: April 2006

AbstractThis study examined the effects of ibotenate lesions of the entorhinal cortex (EC) on performance of a spatial recognition memory task, the delayed non‐matching‐to‐place task (DNMTP), varying in level of difficulty according to the number of interpolated arm visits between sample‐place presentation and subsequent recognition in mice. Results of experiment 1, designed to test the rate of acquisition of the task, showed that experimental animals were impaired in the basic non‐matching task. However, with further training they were able to learn the task. Impairments were also observed when the amount of interpolating information inserted was gradually increased, and then all problem difficulties were pseudorandomly tested. There was no measurable recovery of function over time when the animals were retested on the task ∼1 month later. Experiment 2 showed that the animals that received extensive training on the task prior to lesions of the EC were only transiently impaired in the DNMTP task. These data suggest that the EC plays an important role in acquisition rather than retention of the spatial recognition memory task.
Corticosteroid Receptor Antagonists are Amnestic for Passive Avoidance Learning in Day‐old Chicks
Authors: Sandi Carmen , Rose Steven P. R. 
Published: April 2006

AbstractGlucocorticoids can modulate behavioural processes and neural plasticity. They are released during learning situations and can trigger neural actions through binding to brain receptors. We hypothesized that a glucocorticoid action could play a critical role in the mechanisms involved in long‐term memory formation. In order to test this hypothesis, chicks were trained on a passive avoidance learning task and given bilateral intracerebral injections of selective mineralocorticoid (RU‐28318) or glucocorticoid (RU‐38486) receptor antagonists. The results showed that both antagonists alter information processing when injected prior to the training session. Possible state‐dependent effects were discharged. Further experiments evaluating possible effects of the antagonists on concomitant aspects of the learning situation (such as novelty reaction and pecking pattern) indicated that, as opposed to the glucocorticoid receptor antagonist, the mineralocorticoid antagonist altered the birds' reactivity to non‐specific aspects of the training task. These results suggest that the two types of intracellular corticosteroid receptors could be mediating different aspects of the information processing and storage involved in avoidance learning. In addition, this study points out that passive avoidance learning in the chick could be a good model to investigate the biochemical mechanisms involved in corticosteroid actions on learning‐induced neural plasticity
Host Serotonin Axons Innervate Intrastriatal Ventral Mesencephalic Grafts After Implantation in Newborn Rats
Authors: Mounir Abderrahmane , Chkirate Mariem , Vallée Annie , Pierret Philippe , Geffard Michel , Doucet Guy 
Published: April 2006

AbstractThis study investigated the potential of immature and adult serotonin (5HT) neurons for axonal growth into intrastriatal grafts of ventral mesencephalic tissue. Implantation of dissociated fetal (embryonic days 14–15) ventral mesencephalic tissue was carried out in immature [postnatal days (P) 5–14] and adult rat neostriatum. The brains were processed 2–6 months later for dopamine and 5‐HT immunocytochemistry. A few grafts implanted into adult and P7 recipients contained small numbers of cotransplanted 5HT cell bodies. These also displayed a rich network of 5‐HT axons, even in adult rats prelesioned with 5,7‐dihydroxytryptamine, indicating the graft origin of these axons. All other grafts were totally devoid of 5‐HT cell bodies. After implantation in adults, such grafts contained rare 5‐HT axons. In contrast, in P5‐P7 recipients, they displayed many 5‐HT fibres, which were uniformly distributed. Such was no longer the case after implantation in P14 recipients, which showed minimal 5HT innervation, as in adult recipients. Processing of naïve rat brain at different ages for 5‐HT immunocytochemistry showed that 5‐HT axons were still clearly less numerous in the neostriatum at P21 than in adults, whereas in the substantia nigra the 5‐HT innervation developed more rapidly and was comparable, at P21, to that of adults. It was concluded that 5‐HT axons are able to grow into ventral mesencephalic grafts, but mainly at the fetal stage and with decreasing capacity after birth. Since 5‐HT axons are still normally growing in the developing striatum beyond P21, it appears that their inability to innervate mesencephalic grafts after P14 is not the result of a developmental decrease in growth capacity. Rather, the better temporal correlation with the maturation of the 5‐HT innervation in the substantia nigra suggests that this inability reflects an ontogenic change in the affinity of these axons for nigral tissue.