bluuebunny/crossref_metadata_2025 huggingface dataset:
Glutamate‐enriched Inputs from the Mesopontine Tegmentum to the Entopeduncular Nucleus in the Rat
Authors: Clarke N. P. , Bolam J. P. , Bevan M. D.
Published: April 2006

In order to clarify the origin and to examine the synaptology of the projection from the mesopontine tegmentum to the entopeduncular nucleus, rats received discrete deposits of anterograde tracers in different regions of the mesopontine tegmentum. Anterogradely labelled fibres in the entopeduncular nucleus were analysed at the light and electron microscopic levels. To determine the neurochemistry of the projection, the distributions of GABA and glutamate immunoreactivity in anterogradely labelled boutons in the entopeduncular nucleus were studied by postembedding immunocytochemistry. The morphological characteristics of anterogradely labelled structures were compared to those of choline acetyltransferase‐immunopositive structures. The anterograde tracing demonstrated that the projection to the entopeduncular nucleus arises from the area defined by the cholinergic neurons of the pedunculopontine region and from the more medial and largely non‐cholinergic, midbrain extrapyramidal area. The anterogradely labelled terminals formed asymmetrical synaptic contacts with dendritic shafts, cell bodies and more rarely spines in the entopeduncular nucleus, and they were significantly enriched in glutamate immunoreactivity compared to identified GABAergic terminals in the same region. The morphology, trajectory and synaptology of the anterogradely labelled fibres showed similarities to those of choline acetyltransferase‐immunopositive fibres and terminals, providing indirect evidence in support of previous suggestions that at least part of the projection is cholinergic. The structures postsynaptic to the anterogradely labelled boutons also received input from other classes of terminals that had the morphological and neurochemical characteristics of boutons derived from the neostriatum, globus pallidus and subthalamic nucleus. These findings imply that the mesopontine tegmentum sends a projection to the entopeduncular nucleus that is heterogeneous with respect to its origin and also possibly its neurochemistry. The synaptology of the projection underlies one route through which the mesopontine tegmentum can exert effects on movement by modulating the direct and indirect pathways of information flow through the basal ganglia.
The Glutamatergic Innervation of Oxytocin‐ and Vasopressin‐secreting Neurons in the Rat Supraoptic Nucleus and its Contribution to Lactation‐induced Synaptic Plasticity
Authors: Majdoubi M. El , Poulain D. A. , Theodosis D. T.
Published: April 2006

The present ultrastructural study analysed the distribution of glutamatergic synapses on oxytocin‐ and vasopressin‐secreting neurons in the rat supraoptic nucleus (SON) after post‐embedding immunogold labelling for glutamate and GABA, oxytocin or vasopressin. About 20% of SON axo—somatic synapses were enriched in glutamate immunoreactivity, visible over synaptic‐like vesicles, mitochondria and synaptic densities. Double labelling for glutamate and GABA showed that putative glutamatergic terminals were distinct from GABAergic terminals. In ultrathin sections stained for glutamate and either oxytocin or vasopressin, the proportion of glutamatergic synapses was similar on oxytocinergic and vasopressinergic somata in virgin rats under basal conditions of peptide release as well as in lactating rats, in which oxytocin secretion is enhanced. Cross‐sectional soma areas were significantly increased in lactating rats: oxytocinergic profiles were, on average, ˜40% larger than in virgin rats. However, the incidence of axo—somatic glutamatergic synapses (assessed as mean number of synapses per 100 μm of plasmalemma or proportion of somatic surface apposed to synaptic active zones) did not diminish, indicating that there was a compensatory increase of synapses during lactation. Also, we found an increase in the number of glutamatergic terminals making synaptic contact simultaneously onto two or more oxytocinergic elements in the same plane of section. Our observations therefore indicate that SON oxytocinergic and vasopressinergic neurons are innervated to a similar extent by a relatively large proportion of glutamatergic synapses. They reveal, moreover, that glutamatergic afferents participate in the lactation‐induced synaptic plasticity of the oxytocinergic system.
Regional Variation in Expression of Calbindin and Inositol 1,4,5‐trisphosphate Receptor Type 1 mRNAs in the Cerebellum of the Staggerer Mutant Mouse
Authors: Nakagawa Shin , Watanabe Masahiko , Inoue Yoshiro
Published: April 2006

The Purkinje cells in the staggerer mutant mouse have various cellular abnormalities, including reduced cell number, ectopia, smaller size and absence of dendritic spines. It is also known that some of these abnormalities exhibit regional variations in the cerebellum. In this paper we have investigated expression in the staggerer Purkinje cells of the calbindin and inositol 1,4,5‐trisphosphate receptor type 1 mRNAs by in situ hybridization. Although the transcription levels of both mRNAs were significantly reduced compared with the wild‐type cells, the reduction among the Purkinje cell populations was not even, varying greatly from region to region. Purkinje cells with different transcription levels were distributed in discrete regions and arranged alternately in the mediolateral direction. Moreover, the cell bodies with higher transcription levels were larger in size and aligned in a monolayer between the granular and molecular layers, whereas those with lower levels were smaller in size, fewer in number and dispersed throughout the granular layer. These findings suggest that there is a distinct mediolateral heterogeneity in the staggerer cerebellum with respect to transcription levels of these Purkinje cell‐specific molecules, which might correlate with some cytological phenotypes.
Subthalamic Nucleus Lesion in Rats Prevents Dopaminergic Nigral Neuron Degeneration After Striatal 6‐OHDA Injection: Behavioural and Immunohistochemical Studies
Authors: Piallat Brigitte , Benazzouz Abdelhamid , Benabid Alim Louis
Published: April 2006

Several studies have shown that antagonists of N‐methyl‐D‐aspartate receptors provide protection of the dopaminergic nigrostriatal pathway in animal models of Parkinson's disease. Since the substantia nigra compacta receives a moderate glutamatergic innervation from the subthalamic nucleus, we tried to determine whether subthalamic nucleus lesion could prevent the toxicity of the selective dopaminergic neurotoxin 6‐hydroxydopamine (6‐OHDA). Experiments were carried out on four groups of rats. Group 1 (n= 10) received a unilateral injection of 6‐hydroxydopamine in the striatum and group 2 (n= 10) received kainic acid in the subthalamic nucleus. Group 3 (n= 10) received an injection of kainic acid in the subthalamic nucleus and 1 week later an injection of 6‐OHDA in the striatum. Group 4 (n= 5) received the same treatment but kainic acid was replaced by saline. Apomorphine induced an ipsilateral rotation in rats of groups 2 and 3 and a contralateral rotation in rats of groups 1 and 4. The number of tyrosine hydroxylase‐immunoreactive cells in the pars compacta of the substantia nigra was not significantly different between injected and non‐injected sides in rats of groups 2 and 3, but was significantly decreased on the side ipsilateral to 6‐OHDA striatal injection in rats of groups 1 and 4. These results show that subthalamic nucleus lesion provides neuroprotection of the dopaminergic nigrostriatal pathway against 6‐OHDA toxicity and opens a new way for slowing or stopping the progression of Parkinson's disease.
Target Selectivity and Neurochemical Characteristics of VIP‐immunoreactive Interneurons in the Rat Dentate Gyrus
Authors: Hájos Norbert , Acsády László , Freund Tamás F.
Published: April 2006

Vasoactive intestinal polypeptide (VIP) has been shown to be present in a morphologically heterogeneous subpopulation of interneurons in the dentate gyrus, but the relationship between their input and output characteristics and neurochemical features has not been established. Three types of VIP‐immunoreactive cells have been identified on the basis of these criteria: (i) cells forming a dense axonal plexus in the hilus have always coexisted with the calcium binding protein calretinin (CR), but never with the neuropeptide cholecystokinin (CCK). The postsynaptic targets of these VIP‐positive cells were neurons visualized by immunostaining for substance P receptor, which is known to label different hilar non‐principal cells. (ii) VIP‐immunoreactive basket cells, innervating predominantly the somata and proximal dendrites of granule cells, were found in the stratum moleculare and stratum granulosum. They contained CCK, but not CR. (iii) Cells projecting to the stratum moleculare were found to have dendrites and axons restricted to this layer. In 75% of these cells VIP coexisted with CR but not with CCK, and they established multiple contacts largely with non‐principal cells. GABA was shown to be present but the calcium‐binding proteins calbindin D28K and parvalbumin were absent in all three types of VIP‐containing interneuron. On the basis of these observations we conclude that three different types of VIP‐positive neuron are present in this area, and are likely to subserve different inhibitory functions: cells with a hilar projection as well as those projecting to the stratum moleculare may synchronize the activity of hilar and other interneurons, or disinhibit granule cells by specific interneuron‐to‐interneuron connections. In contrast, basket cells control the activity of granule cells directly, via perisomatic inhibition.
Autocrine—paracrine Regulation of Hippocampal Neuron Survival by IGF‐1 and the Neurotrophins BDNF, NT‐3 and NT‐4
Authors: Lindholm Dan , Carroll Patrick , Tzimagiorgis Georgios , Thoenen Hans
Published: April 2006

In contrast to sympathetic and sensory neurons in the peripheral nervous system, the neurotrophic requirements for neurons in the central nervous system (CNS) have not been clearly identified. The inactivation of specific neurotrophic factors and their receptors by gene targeting has shown that there are no major changes in neuron numbers in the CNS. This suggests an overlap between the action of different neurotrophic factors in the brain during development. Here we have studied the survival of hippocampal neurons prepared from embryonic rats, using different culture conditions. Whereas the hippocampal neurons survive well in culture when plated at high density, they die at lower cell densities in the absence of appropriate neurotrophic factors. Under the latter conditions, both insulin‐like growth factor‐1 (IGF‐1) and the neurotrophins—brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT‐3) and neurotrophin‐4 (NT‐4)—rescued a large proportion of cultured neurons. In addition, hippocampal neurons from BDNF knockout mice exhibited enhanced cell death compared with cells from wild‐type animals. BDNF and IGF‐1 both increased the survival of the hippocampal neurons lacking BDNF, showing complementary action for these factors in supporting survival. Blocking antibodies against NT‐3 and IGF‐1 decreased hippocampal neuron survival at low cell densities, showing autocrine or paracrine action of the factors. At higher cell densities, however, the antibodies had no effect, demonstrating that there is a sufficient amount of endogenous factors supporting survival under these conditions. The present results show that hippocampal neurons depend for survival on local neurotrophic factors such as IGF‐1, BDNF and NT‐3, which act in an autocrine/paracrine manner. The multifactorial support of hippocampal neurons ensures a maximal degree of neuron survival even in the absence of an individual factor.
Perisynaptic Location of Metabotropic Glutamate Receptors mGluR1 and mGluR5 on Dendrites and Dendritic Spines in the Rat Hippocampus
Authors: Luján Rafael , Nusser Zoltan , Roberts J. David B. , Shigemoto Ryuichi , Somogyi Peter
Published: April 2006

Ionotropic and metabotropic (mGluR1a) glutamate receptors were reported to be segregated from each other within the postsynaptic membrane at individual synapses. In order to establish whether this pattern of distribution applies to the hippocampal principal cells and to other postsynaptic metabotropic glutamate receptors, the mGluR1a/b/c and mGluR5 subtypes were localized by immunocytochemistry. Principal cells in all hippocampal fields were reactive for mGluR5, the strata oriens and radiatum of the CA1 area being most strongly immunolabelled. Labelling for mGluR1b/c was strongest on some pyramids in the CA3 area, weaker on granule cells and absent on CA1 pyramids. Subpopulations of non‐principal cells showed strong mGluR1 or mGluR5 immunoreactivity. Electron microscopic pre‐embedding immunoperoxidase and both pre‐ and postembedding immunogold methods consistently revealed the extrasynaptic location of both mGluRs in the somatic and dendritic membrane of pyramidal and granule cells. The density of immunolabelling was highest on dendritic spines. At synapses, immunoparticles for both mGluR1 and mGluR5 were found always outside the postsynaptic membrane specializations. Receptors were particularly concentrated in a perisynaptic annulus around type I synaptic junctions, including the invaginations at ‘perforated’synapses. Measurements of immunolabelling on dendritic spines showed decreasing levels of receptor as a function of distance from the edge of the synaptic specialization. We propose that glutamatergic synapses with an irregular edge develop in order to increase the circumference of synaptic junctions leading to an increase in the metabotropic to ionotropic glutamate receptor ratio at glutamate release sites. The perisynaptic position of postsynaptic metabotropic glutamate receptors appears to be a general feature of glutamatergic synaptic organization and may apply to other G‐protein‐coupled receptors.
Acidic Calponin Cloned from Neural Cells is Differentially Expressed During Rat Brain Development
Authors: Ferhat Lotfi , Charton Gérard , Represa Alfonso , Ben‐Ari Yezekiel , der Terrossian Elisabeth , Khrestchatisky Michel
Published: April 2006

Calponin is an actin‐, tropomyosin‐ and Ca2+ calmodulin‐binding protein that inhibits in vitro the actomyosin MgATPase. Basic and acidic variants of calponin have been described to date. Although the cerebral expression of calponin remained controversial for some time, transcripts encoding acidic calponin in the adult rat brain and calponin immunoreactivity in rat and pig brain and in cultured cerebellar cells have been reported. In the present work, we report the expression of acidic calponin mRNAs and the isolation of cDNAs encoding the full‐length acidic calponin in cultured neuronal and glial cells and in adult rat brain. Sequence analysis reveals that acidic calponin in the brain is identical to that previously described in rat aortic vascular smooth muscle. In situ hybridization shows that calponin is highly expressed during ontogenesis in granule cells of the dentate gyrus of the hippocampus, in all layers of the olfactory bulb and in cerebellar granule neurons of the external and internal layers. In the adult rat brain, calponin expression decreased in these fields, but increased in choroid plexus cells. Bergmann glial cells were also labelled by a calponin probe. The reverse transcription‐coupled polymerase chain reaction confirms that calponin mRNA levels are highest in the early stages of hippocampal development and that expression levels are low in adult hippocampi. The developmental expression pattern of brain acidic calponin suggests that calponin could be involved in contractile activity associated with neural cell proliferation or neuronal migration.
Non‐synaptic Release of ATP by Electrical Stimulation in Slices of Rat Hippocampus, Cerebellum and Habenula
Authors: Hamann Martine , Attwell David
Published: April 2006

ATP is thought to be a fast neurotransmitter in the medial habenula region of the brain, and may be coreleased with other transmitters, for example with glutamase in the hippocampus. We monitored ATP release in rat brain slices using the bioluminescent indicator system luciferin—luciferase. Electrical stimulation of the hippocampus, cerebellum or habenula led to ATP release, but this release was calcium‐independent and was not blocked by tetrodotoxin, or by other agents found to block ATP release from red blood cells. Although calcium‐dependent ATP release may occur in response to electrical stimulation, it appears to be overwhelmed by calcium‐independent release, which may result from electroporation of cells close to the stimulating electrode. Consistent with this, uptake into cells of the fluorescent dye Lucifer yellow was promoted by electrical stimulation. Our data undermine a previous suggestion, based on use of the luciferin‐luciferase technique, that ATP is synaptically released with glutamate in the hippocampus.
Activation of Multiple Metabotropic Glutamate Receptor Subtypes Prevents NMDA‐induced Excitotoxicity in Rat Hippocampal Slices
Authors: Pizzi Marina , Consolandi Ornella , Memo Maurizio , Spano PierFranco
Published: April 2006

Metabotropic glutamate receptors (mGluRs) belong to a relative large receptor family consisting of multiple members with important roles in a number of brain functions. We report here that activation of mGluRs prevents the neurotoxic effect induced by N‐methyl‐D‐aspartate (NMDA) in slices from the rat hippocampus. Neuroprotection was elicited when slices were simultaneously exposed to both the selective mGluR agonist (±)‐1‐aminocyclopentane‐trans‐1,3‐dicarboxylic acid (tACPD) and NMDA. Persisting stimulation of mGluRs after the toxic exposure did not improve the survival of pyramidal or granular cells. The neuroprotection elicited by tACPD was also evoked by its active isomer, (1 S,3R)‐ACPD, and was prevented by the selective mGluR antagonist (+)‐α‐methyl‐4‐carboxyphenyl‐glycine (500 μM), confirming that mGluR activation is involved in the mechanism of action of tACPD. The effect of 100 μM tACPD was reproduced by 100 μM quisqualate, an agonist for mGluR1 and mGluR5, and by 1 μM of (2S,1's,2's)‐2‐carboxycyclopropyl‐glycine, a preferential agonist of mGluR2 and mGluR3 subtypes. No neuroprotection was induced by L‐2‐amino‐4‐phospnonobutyrate, a selective agonist for mGluR4, mGluR6, mGluR7 and mGluR8, at 500 μM. Since the NMDA‐mediated cell death in hippocampal slices is considered relevant to ischaemia‐induced brain injury, these results indicate that mGluRs may be important safety devices used by neurons to decrease their sensitivity to excitotoxic stimuli and increase their chance of survival.
Thalamic and Basal Forebrain Afferents Modulate the Development of Parvalbumin and Calbindin D28k Immunoreactivity in the Barrel Cortex of the Rat
Authors: Alcántara Soledad , Soriano Eduardo , Ferrer Isidro
Published: April 2006

In the adult barrel cortex of the rat the calcium‐binding proteins calbindin D28k (CALB) and parvalbumin (PARV) are found in separate populations of GABAergic nonpyramidal neurons. In layers II to IV of the barrel cortex most PARV‐immunoreactive neurons are likely to derive from a subpopulation of CALB‐immunoreactive neurons whose CALB immunoreactivity ceases when they begin to express PARV between the second and third postnatal weeks. The aim of this study was to investigate the influence of subcortical afferents on the neurochemical differentiation of cortical PARV‐ and CALB‐immunoreactive nonpyramidal neurons during development of the barrel cortex. We produced unilateral excitotoxic lesions with a single injection of ibotenic acid (0.5 μ, 0.05 M) in different subcortical nuclei in 7‐to 8‐day‐old rats. Lesions involving the ventroposterior thalamic nuclei resulted in delayed development of PARV and CALB immunoreactivity in the barrel cortex. One week after ibotenic acid injections a transient decrease in the number of PARV‐immunoreactive neurons in layer IV was observed, together with increased numbers of CALB‐immunoreactive neurons in all cortical layers. The number of nonpyramidal neurons displaying coexistence of PARV and CALB in the lesioned hemisphere also increased compared with the numbers in the control hemisphere or control littermates. In contrast, lesions affecting the globus pallidus, zona incerta and reticular thalamic nucleus transiently increased the number of PARV‐immunoreactive neurons in layers II and III, but had no effect on the number of CALB‐positive cells. From 3 weeks onwards no differences were found between control and iesioned hemispheres after injections into either the ventroposterior thalamic nuclei or the magnocellular basal forebrain. These results suggest that CALB and PARV expression in nonpyramidal cortical neurons can be reversibly modulated in opposite directions by different cortical afferents during postnatal development.
Selective Immunolesioning of the Basal Forebrain Cholinergic System Disrupts Short‐term Memory in Rats
Authors: Leanza G. , Muir J. , Nilsson O. G. , Wiley R. G. , Dunnett S. B. , Björklund A.
Published: April 2006

Selective depletion of nerve growth factor receptor‐bearing neurons in the basal forebrain cholinergic nuclei by the immunotoxin 192 IgG‐saporin offers a new and highly useful tool for the study of the role of the forebrain cholinergic system in cognitive functions. In the present study, we have tested the effects of 192 IgG—saporin in an operant delayed matching‐to‐position task which has previously been used to discriminate between delay‐dependent learning impairments and delay‐independent disturbances of non‐mnemonic processes. Rats were first trained to criterion performance and then received intraventricular injections of 5 μg of 192 IgG—saporin 4 weeks prior to a second testing session. Rats with 192 IgG—saporin lesions displayed a significant delay‐dependent decline in performance compared to normal controls, indicating a deficit in short‐term memory. Administration of the muscarinic blocker scopolamine (0.5 mg/kg, i.p.) produced more pronounced impairment in the performance of the normal control rats across all delays, and induced further impairment also in animals with 192 IgG‐saporin lesions. These effects were not observed following control injections of methyl scopolamine, suggesting that the impairment induced by scopolamine was due to the blockade of central muscarinic receptors. No improvement in performance was observed in either group following systemic treatment with the muscarinic cholinergic agonist arecoline (1.0 mg/kg). Biochemical and morphological analyses confirmed the selective and severe (>90–95%) depletion of cholinergic neurons throughout the septal‐diagonal band area and the nucleus basalis region by the intraventricular 192 IgG—saporin treatment. Although the immunotoxin was observed to produce additional damage to the cerebellar Purkinje cells, no gross motor abnormalities were observed that could contribute to the effects on accuracy in the task used here. In conclusion, the results show that selective combined lesions of the basal forebrain cholinergic neurons in the septal—diagonal band area and nucleus basalis produce long‐lasting impairments in short‐term memory, thus providing further support for a role of this system in cognitive functions.
Brain‐derived Neurotrophic Factor Reverses Experience‐dependent Synaptic Modifications in Kitten Visual Cortex
Authors: Galuske Ralf A. W. , Kim Dae‐Shik , Castrén Eero , Thoenen Hans , Singer Wolf
Published: April 2006

During a critical period of early postnatal development the functional architecture of the visual cortex is shaped by experience‐dependent circuit selection following a Hebbian mechanism. One consequence is that monocular deprivation (MD) leads to competitive repression of the input from the deprived eye. Recently it has been proposed that this process might involve activity‐dependent competition for neurotrophic substances because the synthesis of brain‐derived neurotrophic factor (BDNF) is regulated by visual input. Here we investigate the effects of intracortical infusion of BDNF and nerve growth factor (NGF) on MD effects in the visual cortex. Neuronal responses were monitored with optical and single‐unit recording techniques in the visual cortex of kittens that had been infused intracortically either with BDNF, NGF or cytochrome C while subjected to MD for 1 week during the peak of the critical period. NGF or cytochrome C had no effect on the consequences of MD. After BDNF treatment, by contrast, ocular dominance (OD) shifted towards the deprived eye in a zone extending 2.5–3.5 mm from the infusion cannula, and neurons lost their orientation selectivity. At intermediate distances both eyes activated the cortex equally well and responses were again tuned for orientation; at still larger distances OD was shifted towards the normal eye. Thus, BDNF antagonizes the functional effects of MD and at high concentrations causes paradoxical disconnection of non‐deprived afferents and a loss of orientation selectivity.
Pigmented Epithelium Sustains Cell Proliferation and Decreases Expression of Opsins and Acetylcholinesterase in Reaggregated Chicken Retinospheroids
Authors: Layer Paul G. , Rothermel Andrée , Hering Heike , Wolf Birgit , DeGrip Willem J. , Hicks David , Willbold Elmar
Published: April 2006

We investigated the effect of the retinal pigmented epithelium on cell proliferation and differentiation in rosetted retinospheroids, which are retina‐like spheres reaggregated in the complete absence of retinal pigmented epithelium from dissociated retinal cells of 6‐day‐old chick embryos in a rotation culture system. In spheroids raised in the absence of retinal pigmented epithelium (controls), acetylcholinesterase was expressed in cells of an inner nuclear‐like layer and their neuropil matrices. Moreover, the ratio between rods and cones was found to be approximately normal throughout the spheroid. When spheroids were cultured in the presence of retinal pigmented epithelium monolayers, cell proliferation in spheroids as determined by BrdU labelling was significantly increased and extended for 1 week, while acetylcholinesterase protein levels and specific activities in homogenates were decreased to ∼30%. At the same time, opsin immunoreactivity was completely suppressed within the spheroid and appeared slowly in cells around its periphery; i.e. the proportion of rhodopsin‐positive cells decreased from 14 to 3%. This study reveals that the retinal pigmented epithelium in vifro sustains cell proliferation but inhibits the differentiation of acetylcholinesterase‐positive cells and of photoreceptors.
The CCK‐B Agonist, BC264, Increases Dopamine in the Nucleus Accumbens and Facilitates Motivation and Attention After lntraperitoneal Injection in Rats
Authors: Ladurelle Nathalie , Keller Gérard , Blommaert Armand , Roques Bernard P. , Daugé Valérie
Published: April 2006

Although it is known that panic attacks are triggered by the cholecystokinin fragment CCK4, the specific involvement of peripheral or central cholecystokinin CCK receptors in various adaptive processes such as emotion, memory and anxiety has yet to be demonstrated. With this aim, we have investigated the biochemical and pharmacological effects resulting from the administration of BC264, a highly potent and selective CCK‐B agonist able to cross the blood‐brain barrier. Very low doses of BC264 (μg/kg i.p.), increased the exploration of animals submitted to an unknown territory but were devoid of anxiogenic properties in the elevated plus maze. BC264 increased locomotion and rearings of rats newly placed in an open field and improved their spontaneous alternation in a Y‐maze. The use of vagotomized animals showed that the increased alternation induced by BC264 did not require an intact vagus nerve, unlike the locomotor activation. These behavioural effects, prevented by the prior i.p. administration of the CCK‐B antagonist L‐365,260 but not by the CCK‐A antagonist L‐364,718, were shown to depend on dopaminergic systems, since they were blocked by D1 (SCH23390, 25 μg/kg i.p.) or D2 (sulpiride, 50 or 100 mg/kg i.p.) antagonists. In addition, bilateral perfusion in freely moving rats of BC264 at pharmacologically active doses, using a newly designed microdialysis system, was found to increase the extracellular levels of DA, DOPAC and HVA in the anterior part of the nucleus accumbens. These results show that activation of CCK‐B receptors by BC264 does not produce anxiogenic‐like effects but appears to improve motivation and attention, whereas other CCK‐B agonists such as BocCCK4 induce anxiogenic responses. Several explanations, including the existence of different sub‐sites of the CCK‐B receptor, could account for these differential effects.
Tetrahydrobiopterin as a Mediator of PC12 Cell Prolifeiation Induced by EGF and NGF
Authors: Anastasiadis Panagiotis Z. , Bezin Laurent , Imerman Bruce A. , Kuhn Donald M. , Louie Marisa C. , Levine Robert A.
Published: April 2006

Epidermal growth factor and nerve growth factor increased the proliferation of rat phaeochromocytoma PC12 cells through obligatory elevation of intracellular (6R)‐tetrahydrobiopterin (BH4). Epidermal growth factor and nerve growth factor increased intracellular BH4 by inducing GTP‐cyclohydrolase, the rate‐limiting enzyme in BH4 biosynthesis. Specific inhibitors of BH4 biosynthesis prevented growth factor‐induced increases in BH4 levels and proliferation. The induction of GTP cyclohydrolase, BH4 and cellular proliferation by nerve growth factor was mediated by CAMP. Elevation of BH4 biosynthesis occurred downstream from CAMP in the cascade used by nerve growth factor to increase proliferation. Thus, intracellular BH4 is an essential mediator of the proliferative effects of epidermal growth factor and nerve growth factor in PC12 cells.
Mouse Astrocytes Store and Deliver Brain‐derived Neurotrophic Factor Using the Non‐catalytic gp95trkB Receptor
Authors: Rubio Nazario
Published: April 2006

A study of the brain‐derived neurotrophic factor (BDNF)‐binding capacity of pure astrocytes demonstrated that these cells bind and endocytose [125l]BDNF rapidly using the gp95trkb truncated receptor. A linear Scatchard plot indicated the presence of only one type of receptor that bound the ligand, with a low Kd of 1.24 × 10−8 M. There were an average of 36 468 copies of this receptor on untreated astrocytes. Interestingly, the neurotrophin was not degraded intracellularly, as demonstrated by HPLC experiments. Furthermore, the stored molecule was released by a mechanism regulated by the extracellular BDNF concentration as a bioactive neurotrophic molecule that supports neuron survival, in a time‐ and temperature‐dependent manner. The data demonstrate that astrocytes exert an active role in the bioavailability of this neurotrophin, which is further enhanced in an inflammatory‐like situation induced experimentally in culture using interferon‐SgM.
Regional Distribution of the Anticonvulsant and Behavioural Effects of Bicuculline Injected into the Pontine Reticular Formation of Rats
Authors: Shehab Safa , Guadagno Joseph , Ferguson Karen , Redgrave Peter
Published: April 2006

Previous experimental work has established that activation of sites in the dorsal midbrain can suppress tonic hindlimb extension in the electroshock model of epilepsy. The most sensitive region for this effect is centred on the intercollicular area and is referred to as the dorsal midbrain anticonvulsant zone (DMAZ). Subsequent experiments have shown that the ipsilateral descending projection from this region to the ventrolateral pons is critically involved in mediating its tonic seizure‐suppressing properties. The purpose of the present investigation was to test whether direct anticonvulsant effects in the electroshock model could be obtained from selective manipulation of DMAZ target regions in the ventrolateral pons. Animals were prepared with chronically implanted guide cannulae through which microinjections could be made directly into the lateral pontine reticular formation. Animals received injections of saline or bicuculline (25–200 pmol) administered either bilaterally or unilaterally. The effects of these injections on the animals' behaviour were determined in an open arena, after which maximal electroshock (1s, 40 mA, 50 Hz AC) was administered via ear‐clip electrodes and the duration of tonic hindlimb extension was recorded. Bilateral injections of bicuculline (100 pmol) suppressed tonic seizures at a significantly higher proportion of sites centred on DMAZ target regions of the ventrolateral pons than surrounding areas. For injections centred on this region the suppressive effects of bicuculline were dose‐related in the range 25–100 pmol. Unilateral injections of bicuculline into the ventrolateral pons also effectively suppressed tonic seizures in the electroshock model. Within the ventral pons there was a significant association between the behavioural and anticonvulsant effects of bicuculline; injections suppressing tonic seizures were associated with the induction of fast continuous locomotor activity, These data confirm that the DMAZ recipient region of the ventrolateral pontine reticular formation is part of a circuit which can suppress the manifestation of tonic hindlimb extension in the electroshock model. Whether this property is related to the participation of this region in normal locomotion and posture remains to be determined.
Retinal Ganglion Cell Depletion Alters the Phenotypic Expression of GABA and GAD in the Rat Retina
Authors: Yamasaki Edna N. , da Costa Belmira L. S. Andrade , Barbosa Valéria D. , Hokoç Jan Nora
Published: April 2006

We have looked at the phenotypic expression of γ‐aminobutyric acid (GABA) and the two isoforms of its synthetic enzyme [glutamic acid decarboxylase (GAD)‐65 and ‐671 in adult rat retinas that had the superior colliculus, pretectum and optic tract lesioned unilaterally at birth. It has been shown previously that this type of manipulation induces retrograde degeneration of retinal ganglion cells presumably without affecting other intraretinal neurons. We present evidence that GABAergic amacrine cells are affected by such manipulation. The number of cells immunoreactive for GABA, GAD‐65 and GAD‐67 decreased in the inner nuclear layer. In the retinal ganglion cell layer, however, the number of GABA‐ and GAD‐65–labelled cells increased, while the number of GAD‐67–labelled cells did not change. Biochemical assay showed that overall GAD activity was not altered in retinas of lesioned animals. Our results support the notion that, while neonatal lesion reorganizes the expression of GABA and GAD in the retina, enzyme activity is maintained within normal levels.
Rolipram, a Selective Phosphodiesterase Type‐IV Inhibitor, Prevents Induction of Heat Shock Protein HSP‐70 and hsp‐70 mRNA in Rat Retrosplenial Cortex by the NMDA Receptor Antagonist DizociIpine
Authors: Hashimot Kenji , Tomitaka Shin‐ichiro , Bi Ying , Narita Natsuko , Minabe Yoshio , Lyo Masaomi
Published: April 2006

The non‐competitive NMDA receptor antagonists, such as (+)‐MK‐801 (dizocilpine), cause the expression of heat shock protein HSP‐70 and pathomorphological damage in the retrosplenial cortex of the rat brain. However, the precise mechanism(s) underlying the neurotoxicity of NMDA receptor antagonists is unknown. The present study was undertaken to examine the role of phosphodiesterase type IV in the expression of heat shock genes induced by dizocilpine. Heat shock protein HSP‐70, which is known as a sensitive marker of neuron injury, was induced in the retrosplenial cortex of the rat brain 24 h after a single administration of dizocilpine (1 mg/kg). Pretreatment with the specific phosphodiesterase type IV inhibitor rolipram (2.5, 5 or 10 mg/kg, 15 rnin before dizocilpine) attenuated the expression of HSP‐70 and hsp‐70 mRNA induced by dizocilpine (1 mg/kg) in a dose‐dependent manner. Furthermore, another phosphodiesterase type IV inhibitor, Ro 20–1724 (5 or 10 mg/kg, 15 min before dizocilpine), and a non‐selective phosphodiesterase inhibitor, 3–isobutyl‐1–methylxanthine (IBMX) (5 or 10 mg/kg, 15 min before dizocilpine), significantly attenuated the expression of HSP‐70 protein and hsp‐70 mRNA induced in the retrosplenial cortex by dizocilpine. However, the induction of the immediate early gene c‐fos and microglial activation in the retrosplenial cortex after administration of dizocilpine was not attenuated by pretreatment with rolipram (5 or 10 mg/kg, 15 min before dizocilpine). Moreover, histopathological study indicated that pretreatment with rolipram (5 or 10 mg/kg, 15 min before dizocilpine) did not prevent the formation of vacuoles caused by treatment with dizocilpine. The present findings suggest that phosphodiesterase type IV may play a significant role in the expression of HSP‐70 protein and hsp‐70 mRNA in the rat retrosplenial cortex after administration of dizocilpine, and that phosphodiesterase type IV may not play a role in the neurotoxicity of NMDA receptor antagonists such as dizocilpine.
Critical Period‐dependent Reduction of the Permissiveness of Cat Visual Cortex Tissue for Neuronal Adhesion and Neurite Growth
Authors: Schoop Veronika M. , Gardziella Stefan , Müller Christian M.
Published: April 2006

During postnatal development, the visual cortex undergoes an experience‐dependent refinement of its circuitry. This process includes synapse formation, as well as synapse elimination. Both mechanisms appear to be restricted to a limited ‘critical period’ which lasts for ∼2 months in cats. We tested whether the termination of the critical period for cortical malleability is paralleled by changes in the growth permissiveness of the tissue. These changes may inhibit progressive reorganization of functional circuitries mediated by axon growth. Embryonic cortical neurons were cultured on unfixed cryostat sections of the visual cortex obtained from cats aged 2–50 weeks. After 2–3 days in vitro the distribution of viable cells and the percentage of neurite‐bearing cells were determined and analysed with respect to the developmental age and subdivisions of the underlying tissue substrate. It was shown that cell adhesion and neurite formation are correlated with the developmental age of the substrate tissue and the time period of myelination. While embryonic neurons adhered and survived on grey and white matter tissue from 2‐ and 4‐week‐old kittens, there was a significant reduction in cell adhesion on the myelinated white matter regions of the tissue sections of older animals. Quantitative analyses showed that neurite formation by cultured neurons also became successively impaired on grey and white matter areas of tissue substrates, corresponding to the time course of the critical period for cortical malleability. On grey matter tissue this effect was most pronounced between the second and sixth postnatal weeks. The effects were not antagonized by coating the substrate sections with the growth‐promoting molecule laminin. It is therefore proposed that neurite growth‐inhibiting factors, most probably associated with central nervous system myelin, are gradually expressed postnatally and may contribute to the termination of the critical period in the visual cortex of cats.
Effects of NMDA and AMPA Receptor Antagonists on Corticosterone Facilitation of Long‐term Memory in the Chick
Authors: Venero César , Sandi Carmen
Published: April 2006

Long‐term memory formation for a weak passive avoidance task in day‐old chicks is facilitated by corticosterone administration. Since (i) glutamatergic systems, through different receptor types, play a key role in learning and memory processes, and (ii) glucocorticoids increase glutamate concentrations in learning‐related regions of the mammalian brain, we reasoned that glutamatergic activation might be a mechanism by which corticosterone facilitates the formation of an enduring memory. To assess this hypothesis, long‐term retention was evaluated in chicks trained on a weak passive avoidance task and intracerebrally injected with NMDA and a‐amino‐3‐hydroxyd‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor antagonists (MK‐801 and 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione) with regard to training and corticosterone injection respectively. The results indicated that either of the antagonists prevented the facilitating effect of corticosterone when administered before the training trial, but failed to interfere with the steroid effect when injected before corticosterone administration in the post‐training period, suggesting that their early effectiveness was not related to corticosterone‐induced actions but to training‐triggered mechanisms. In addition, administration of the AMPA antagonist, 5.5 h after training, was also effective in impairing the long‐term memory‐potentiating effect of corticosterone. These results support the view that corticosterone facilitates the formation of an enduring memory in this learning model, through the modulation of late events during the consolidation period, including the activation of the AMPA receptor type.
Spatial Resolution and Contrast Sensitivity of Single Neurons in Area 19 of Split‐chiasm Cats: A Comparison With Primary Visual Cortex
Authors: Tardif Eric , Richer Louis , Bergeron André , Lepore Franco , Guillemot Jean‐Paul
Published: April 2006

Electrophysiological recordings were carried out in the callosal recipient zone of area 19 in normal and split‐chiasm cats and, for comparison purposes, at the border of areas 17 and 18 of split‐chiasm cats. The influences of retinothalamic and callosal inputs on a single cortical neurons were thereby evaluated. Extracellular recordings of single cells were made in anaesthetized and paralysed cats in the zone representing the central visual field. Receptive field properties were assessed using sine wave gratings drifting in optimal directions. Results showed that in area 19 and areas 17/18 one‐third of the cells were binocularly driven after section of the optic chiasm. In area 19, the spatial resolution and contrast sensitivity of cells driven via the dominant eye were similar in the normal and split‐chiasm groups. In areas 17/18 and area 19 of split‐chiasm cats, binocular cells showed significant interocular matching of their receptive field properties (spatial resolution and contrast threshold), although small differences were observed. These small interocular differences were related to the cell's Ocular dominance rather than to the signal transmission route (thalamic or callosal).
Immunocytochemical Localization of a High‐affinity Glutamate‐Aspartate Transporter, GLAST, in the Rat and Guinea‐pig Cochlea
Authors: Furness David N. , Lehre Knut P.
Published: April 2006

Glutamate transporters play an important role in the reuptake of glutamate after its release from glutamatergic synapses. Four such transporters have so far been cloned from the rat brain. One, the glutamate‐aspartate transporter GLAST, has been detected in the mammalian cochlea, in which the principal afferent synapse of the auditory nerve, between the inner hair cells and neurites of type I spiral ganglion neurons, has been suggested to be glutamatergic. The distribution of GLAST was therefore investigated to provide clues to the handling of glutamate in the cochlea. This was studied using light and electron microscopic immunocytochemistry in rats and guinea pigs with antibodies raised against synthetic peptides based on the sequence for GLAST. Significant immunoreactivity was found in the myelin sheath formed by satellite cells surrounding the type I spiral ganglion neurons, and along the plasma membranes of supporting cells around the inner hair cells; other cells in both locations were only weakly labelled, if at all. The absence of substantial numbers of synapses in the spiral ganglion suggests that GLAST is unlikely to be associated with the uptake of synaptic glutamate after release in this region. lmmunoreactivity associated with the inner hair cells is consistent with the utilization of glutamate at the afferent synapse.
Age‐dependent Variations in Potassium Sensitivity of A‐Currents in Rat Hippocampal Neurons
Authors: Klee Rolf , Eder Claudia , Ficker Eckhard , Heinemann Uwe
Published: April 2006

Hippocampal pyramidal neurons were either cultured from prenatal rats or acutely isolated from the brain of newborn and juvenile rats. The influence of lowering the concentration of the extracellular potassium concentration ([K+]0) on isolated fast transient outward K+ currents (IA) was studied in these neurons using the patch clamp technique in the whole cell configuration. With respect to the response of IA to lowering [K+]0, three types of cells were observed. The first subpopulation of neurons was characterized by a complete suppression of IA over the whole voltage range under potassium‐free solutions (type A neurons). A second proportion of cells showed an increase of IA at test pulses below ‐0 mV and a decrease of IA at voltages above ‐0 mV (type B neurons). In a third group of neurons, amplitudes of lA increased at all potentials tested during omission of potassium ions from the extracellular superfusate (type C neurons). Whereas type A and type B neurons were preferentially found in freshly plated cultures and newborn rats, the majority of type C cells was detected in long‐term cultures and in animals of older ages. Thus, hippocampal A‐currents lose their sensitivity to extracellular potassium ions during early ontogenesis.
Electrophysiological Evidence That Neurokinin A Acts Via NK‐1 Receptors in the Cat Dorsal Horn
Authors: Radhakrishnan V. , Henry J. L.
Published: April 2006

The aim of the present study was to investigate the effects of the non‐peptide NK‐2 receptor antagonist, SR 48968 on the responses of dorsal horn neurons to iontophoretic application of the endogenous NK‐2 receptor ligand, neurokinin A, and on synaptically elicited responses in chloralose‐anaesthetized cats. The effect of iontophoretic application of neurokinin A was tested on 51 dorsal horn neurons. Of these, 43 were wide dynamic range and the rest non‐nociceptive neurons. Neurokinin A induced a slow, prolonged excitation of 25 of the wide dynamic range neurons. All remaining neurons were unaffected. SR 48968 (50 pg to 1.0 mg/kg, i.v.) did not affect the on‐going basal activity (n= 8) or the slow excitation induced by neurokinin A in any of the nine wide dynamic range neurons tested. To eliminate the possibility that systemically administered SR 48968 may not be reaching central sites, SR 48968 was also applied iontophoretically (70–120 nA) to five neurons and tested against excitatory responses to iontophoretically applied neurokinin A. The on‐going activity of these cells were unaffected by SR 48968. The responses to neurokinin A were also unaffected suggesting that neurokinin A did not mediate its effects via NK‐2 receptors. SR 48968 also had no effect on the excitatory responses of seven neurons to iontophoretic application of the NK‐1 receptor agonist, substance P indicating that substance P actions are not mediated via NK‐2 receptors and that SR 48968 did not react with NK‐1 receptors. Responses of the neurons to non‐noxious (hair) stimulation (n = 10), noxious mechanical (n= 5) and noxious thermal (n= 8) stimulation of the receptive field were also unaffected by SR 48968, suggesting a lack of participation of NK‐2 receptors in these responses. However, responses of wide dynamic range neurons to neurokinin A were totally blocked by i.v. administration (0.5 mg/kg) of the NK‐1 receptor antagonists CP‐96,345 (n= 7) and CP‐99,994 (n= 5) but not by CP‐96,344 (n= 4), the inactive enantiomer of CP‐96,345. These data suggest that neurokinin A, like substance P may be acting via NK‐1, rather than NK‐2 receptors, to produce excitation of wide dynamic range neurons in the dorsal horn of the cat spinal cord.