bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Specification of Neuronal Fate: A Common Precursor for Neurotransmitter Subtypes in the Rat Cerebral Cortex In Vitro
Authors: Götz Magdalena , Williams Brenda P. , Bolz Jürgen , Price Jack 
Published: April 2006

AbstractNeurotransmitter choice is a crucial step in neural development. In the cerebral cortex, pyramidal neurons use the excitatory neurotransmitter glutamate, whereas non‐pyramidal cells use the inhibitory neurotransmitter GABA. We are interested in how these two neuronal types are generated. We labelled precursor cells from embryonic rat cerebral cortex with a retroviral vector in dissociated cell cultures, and examined the neurotransmitter phenotype of their progeny immunohistochemically after 2 weeksin vitro.We discovered, first, that precursor cells in culture generate glutamatergic and GABAergic neurons in proportions similar to thosein vivo.Second, we found that neuronal precursor cells gave rise to both GABAergic and glutamatergic neurons. These results suggest that neuronal precursor cells in the cerebral cortex have the potential to generate both neuronal subtypes. Moreover, these data are consistent with a stochastic model of neurotransmitter specification.
Developmental Regulation of Full‐length trkC in the Rat Sciatic Nerve
Authors: Offenhäuser N. , Böhm‐Matthaei R. , Tsoulfas P. , Parada L. , Meyer M. 
Published: April 2006

AbstractIn order to gain insight into potential roles of neurotrophins in Schwann cell biology, the expression of neurotrophin receptors of the frk gene family was investigated in rat sciatic nerve development. This analysis revealed differential regulation of truncated and full‐length receptors. TrkA was undetectable even when analysed with a sensitive reverse transcriptase‐polymerase chain reaction (RT‐PCR) method. TrkB was present at the mRNA as well as protein level only in its truncated form. Surprisingly, multiple isoforms of trkC, including full‐length forms, were detected in early postnatal nerve. Specific antibodies detected truncated and full‐length trkC proteins in Western blotting, and RT‐PCR revealed the presence of two full‐length isoforms, one of them containing the 14 amino acid kinase insert. In situ hybridisation localized the expression of trkC to a subpopulation of Schwann cells. TrkC receptors are expressed already in nerves from day‐16 embryos. In contrast to early postnatal stages, full‐length trkC receptors are no longer expressed in adult nerves, which, however, maintain expression of truncated trkC transcripts. The presence of trkC kinases in peripheral nerve suggests a role for neurotrophin‐3, the only known trkC ligand, in peripheral nerve development.
Complex Deficits on Reaction Time Performance following Bilateral Intrastriatal 6‐OHDA Infusion in the Rat
Authors: Amalric M. , Moukhles H. , Nieoullon A. , Daszuta A. 
Published: April 2006

AbstractThe present study examined the ability of rats subjected to bilateral 6‐hydroxydopamine lesions of the terminal area of the nigrostriatal dopamine system to perform a prelearned reaction time task. This lesion model, the induction of a partial dopamine denervation of the striatum (74% depletion of dopamine striatal tissue content) with a retrograde degeneration of dopamine cell bodies in the substantia nigra, sparing the mesolimbic dopaminergic pathway, closely approximates the neuronal degeneration observed in human idiopathic Parkinson's disease. Rats were trained previously to release a lever, within a reaction time limit, after the presentation of a visual cue through reinforcement with food pellets. The onset of the light stimulus varied randomly after an unpredictable delay period of 0.25–1.0 s. Rats with dopaminergic lesions showed moderate to extensive performance deficits which were not compensated for the five postoperative weeks. More than half of the lesioned animals (64%) showed severe deficits, characterized by a concomitant increase in the number of anticipated (premature release of the lever before the visual cue) and delayed responses (lever release after the reaction time limit) with shortened reaction times in some cases. A smaller proportion (36%) of lesioned animals exhibited mild impairment of performance with a large increase in delayed responses and lengthening of reaction times but with no change in the number of anticipated responses. Asymmetric lesions had no effect on the reaction time performance. Examination of tyrosine hydroxylase immunostaining revealed that in the most impaired animals dopamine depletion was extensive in the medial striatum, whereas it was restricted to the dorsolateral striatum in the least impaired animals. Results suggest that a decrease in dopamine function at striatal level severely disrupts performance of a conditioned reaction time task. A partial dopamine depletion in the dorsolateral striatum induces motor initiation deficits (i.e. increases delayed response only). Larger striatal dopamine depletion may produce both motor and cognitive deficits (decrease in attentional control over response output and/or disruption of stimulus‐response associations) that could be related to similar events in Parkinson's disease.
Topographic Distribution of Fixation‐related Units in the Dorsomedial Frontal Cortex of the Rhesus Monkey
Authors: Lee Kyoungmin , Tehovnik Edward J. 
Published: April 2006

AbstractMost cells in the dorsomedial frontal cortex of the rhesus monkey had activity related to saccadic eye movement and for visual fixation. This activity changed depending upon the position of a fixation target, which suggested coding for the target location in spatial coordinates. Further analysis of such activity revealed a topographical distribution of neurons: neurons in the rostral part of the area were more active with eyes to the contralateral position, while those in the caudal part were more active with eyes to the ipsilateral position; also, cells in the medial part of the area had higher activity with a downward fixation position, whereas those in the lateral part had higher activity with an upward fixation position. This distribution of units was in agreement with the map of termination zones of saccadic eye movements evoked by electrical stimulation of the same area. These observations provide evidence for the hypothesis that the dorsomedial frontal cortex is organized in spatial coordinates and is involved in specifying the position of visual fixation.
D1 and D2 Receptor Gene Expression in the Rat Frontal Cortex: Cellular Localization in Different Classes of Efferent Neurons
Authors: Gaspar Patricia , Bloch Bertrand , Le Moine Catherine 
Published: April 2006

AbstractThe dopaminergic input to the frontal cortex has an important role in motor and cognitive functions. These effects are mediated by dopamine receptors both of type D1 and of type D2, although the neural circuits involved are not completely understood. We used in situ hybridization to determine the cellular localization of D1 and D2 receptor mRNAs in the rat frontal cortex. Retrograde tracing was used in the same animals to identify the main cortical efferent populations. Fluorogold was injected into the different cortical targets of the frontal cortex and sections were hybridized with D1 and D2 35S‐labelled cRNA probes. D1 and D2 mRNA‐containing neurons were present in all the cortical areas investigated, with greater expression in the medial prefrontal, insular and cingulate cortexes and lower expression in the motor and parietal cortexes. Neurons containing D1 mRNA were most abundant in layer Vlb; they were also present in layers Vla and V of all cortical layers and in layer II of the medial prefrontal, cingulate and insular areas. Double labelling with fluorogold demonstrated that D1 mRNA was present in corticocortical, corticothalamic and corticostriatal neurons. Neurons containing D2 mRNA were essentially restricted to layer V, but only in corticostriatal and corticocortical neurons. Neither D1 nor D2 mRNA was found in corticospinal or corticopontine neurons. The present results demonstrate that D1 and D2 receptor genes are expressed in efferent cortical populations, with higher expression for D1. In spite of an overlap in some cortical layers, the expression of D1 and D2 receptor genes is specific for different categories of pyramidal neurons.
Ontogeny of a Photic Response in the Suprachiasmatic Nucleus in the Siberian Hamster (Phodopus sungorus)
Authors: Duffield Giles E. , Dickerson John M. , Alexander Iona H. M. , Ebling Francis J. P. 
Published: April 2006

AbstractThe ontogeny of photic responsiveness in the suprachiasmatic nucleus of the Siberian hamster (Phodopus sungorus) was studied using the enhanced expression of the immediate early gene c‐fos as a marker of neuronal activation. c‐fos expression was assessed by immunocytochemical localization of its protein product. Hamsters were kept on a 16 h light:8 h dark photocycle. The adult Siberian hamster showed a marked increase in the number of c‐fos‐immunoreactive (c‐fos‐ir) cells within the suprachiasmatic nuclei (SCN) in response to a 1 h light pulse delivered 1–3 h after lights off, in comparison to controls kept in the dark. This is consistent with previous studies in the Syrian hamster and rat. The development of the photic response was examined. The first study investigated the effects of a light pulse on c‐fos induction in pups at 5, 9, 12 and 24 postnatal days of age (PD). The suprachiasmatic region was identified by immunocytochemical localization of peptide‐histidine‐isoleucine in adjacent sections, a peptide expressed early in the development of the rodent SCN. The distribution of c‐fos‐ir cells was also compared with the location of retinal efferents, as determined by intraocular injection of the tract tracer cholera toxin B subunit 24 h previously. At PD 9, 12 and 24, significant increases in the number of c‐fos‐ir cells occurred in the light pulsed animals in comparison to age‐matched control animals which were moved within the non‐illuminated room to provide a ‘dark’ pulse. Induction of c‐fos mainly occurred in the ventrolateral region of the medial and caudal SCN, the region which receives the greatest density of retinal innervation. The second study focused on the earliest age at which light could induce c‐fos expression in the SCN by investigating the effects of light on c‐fos‐ir cells in pups at PD 2–4. Animals at PD 3 and 4 showed enhanced c‐fos expression in the ventrolateral region, whilst PD 2 animals showed no response. The number of c‐fos‐ir cells in the SCN region in light‐pulsed animals increased from PD 3 to adulthood. These results indicate that retinal input can activate cells in the SCN even before the eyelids open on PD 11, and the SCN can potentially be entrained by photic inputs as early as day 3 after birth.
Electrophysiology of the Neurons in the Area of the Enkephalinergic Magnocellular Dorsal Nucleus of the Guinea‐pig Hypothalamus, Studied by Intracellular and Whole‐cell Recordings
Authors: Niespodziany Isabelle , Poulain Pierre 
Published: April 2006

AbstractThe electrophysiological characteristics of 103 hypothalamic neurons in the area of the guinea‐pig enkephalinergic magnocellular dorsal nucleus were studied in a thick slice preparation with sharp microelectrodes (63 neurons) and patch pipettes for whole‐cell recordings (40 neurons). Of the sampled cells, 79.6% displayed tetrodotoxin‐resistant, calcium‐dependent slow‐depolarizing potentials when the membrane potential was hyperpolarized to ˜70 mV (type I neurons). Half of them showed robust slow depolarizing potentials, generating bursts of fast action potentials. In the remaining neurons, the slow‐depolarizing potentials did not cause burst‐firing action potentials but triggered single action potentials. The other class of neurons (20.4% of the sample: type II neurons) did not exhibit calcium‐dependent slow‐depolarizing potentials. Resting potential, input resistance and the membrane time constant did not distinguish among the two classes of neurons. Current‐voltage relationships were heterogeneous. A transient outward rectification was observed in the two classes. This was not totally blocked by 2 mM 4‐aminopyridine but was abolished when using perfusion with cobalt instead of calcium. Input resistance and the time constant were higher when measured in the whole‐cell mode but the other electrical parameters and the sampling of the recorded neurons were strikingly similar between the two methods of recording. Intracellular staining of 22 neurons retrogradely labelled from the lateral septum allowed confirmation of their location within the magnocellular dorsal nucleus. The study indicates that the electrical properties of these neurons did not differ from those of neurons found throughout the area explored. It also indicates the presence of distinct electrophysiological types of cells in the magnocellular dorsal nucleus, although the nucleus is composed of a single type of enkephalinergic neuron. It provides a basis for the study of the regulation of activity of the neurons at the origin of an enkephalinergic tractus which is involved in neuroendocrine, psychoneuroendocrine and immune processes.
Characterization of Nerve Growth Factor (NGF) Release from Hippocampal Neurons: Evidence for a Constitutive and an Unconventional Sodium‐dependent Regulated Pathway
Authors: Blöchl A. , Thoenen H. 
Published: April 2006

AbstractWe investigated the mechanism of neuronal nerve growth factor (NGF) release with regard to the potential function of NGF as a mediator of neuronal plasticity in the CNS. The analysis was performed in hippocampal slices and in primary cultures of hippocampal neurons, transiently transfected with an NGF cDNA construct to increase the level of NGF expression. In both systems there was activity‐dependent NGF release initiated by high potassium (KCl), veratridine, glutamate or carbachol. Replacement of 90% of sodium in the medium with N‐methyl‐glucamine strongly reduced this release. The KCl‐ and veratridine‐initiated NGF release was suppressed by tetrodotoxin; release by glutamate was less sensitive to tetrodotoxin but was sodium‐dependent. The glutamate effect could be inhibited by GYK152644, an antagonist of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid receptors, but not by MK‐801, an antagonist of NMDA receptors. The activity‐dependent release of NGF did not depend on extracellular Ca2+, but was sensitive to the intracellular Ca2+ chelator bis‐(o‐aminophenoxy)‐ethane‐N,N,N',N'‐tetraacetic acid tetra(acetoxymethyl)‐ester, and to depletion of intracellular calcium stores. Conversely, mobilization of Ca2+ from intracellular stores with caffeine and thapsigargin mimicked the effect of depolarization. Basal NGF release could be reduced by either temperature block (15°C) or tetrodotoxin to ˜50%. The combination of both treatments reduced NGF release to below the detection limit, suggesting that basal release has constitutive and regulated components, the latter presumably resulting from spontaneous activity of interconnected neurons.
Epileptiform Activity in the Guinea‐pig Neocortical Slice Spreads Preferentially along Supragranular Layers—Recordings with Voltage‐sensitive Dyes
Authors: Albowitz Birgit , Kuhnt Ulrich 
Published: April 2006

AbstractThe spread of epileptiform activity was monitored in guinea‐pig neocortical slices by the use of a voltage‐sensitive dye (RH795) and a fast optical recording technique. Epileptiform activity induced by bicuculline methiodide (10–20 μM) and single‐pulse stimulation spread from the stimulation site in layer I or in the white matter across most of the slice. Different lesions were made in the slice in order to specify the neuronal connections used for spread in the horizontal direction. In the slice, intracortical connections are necessary for the spread of epileptiform activity, as shown by vertical cuts through all cortical layers but sparing the white matter. Horizontal connections were interrupted by cuts parallel to the axis of pyramidal neurons through either supragranular or infragranular layers. Vertical connections were interrupted by cuts perpendicular to the axis of pyramidal neurons separating supragranular and infragranular layers. Spread of epileptiform activity in the horizontal direction was not hindered by horizontal cuts. Vertical cuts through infragranular layers also did not hinder the spread of epileptiform activity. In contrast, vertical cuts through supragranular layers either abolished completely (nine slices) or delayed significantly (ten slices) the spread of epileptiform activity. The mean delay at the supragranular lesion was 44 ms in layer III and 30 ms in layer V; at the infragranular lesion the mean delay was 2 ms in layer III and 6 ms in layer V. Also, with horizontal cuts, in three out of five slices the velocity of spread was significantly lower in infragranular as compared to supragranular layers. It is concluded that both supra‐ and infragranular layers if isolated possess the ability to initiate and propagate epileptiform activity independently. However, in the intact slice the influence of the supragranular networks on initiation and propagation of epileptiform activity appears to dominate.
Involvement of AMPA Receptors in Maintenance of Memory for a Passive Avoidance Task in Day‐old Domestic Chicks (Gallus domesticus)
Authors: Steele Robert J. , Stewart Michael G. 
Published: April 2006

AbstractDay‐old chicks (Gallus domesticus) were trained on a one‐trial passive avoidance task where the aversive stimulus was an unpleasant tasting substance, methyl anthranilate. Chicks were killed 6.5 h after training. The kinetic parameters of [3H] α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid ([3H]AMPA) binding were determined using quantitative receptor autoradiography and Scatchard analyses in 15 discrete forebrain regions of trained and control (water‐trained) chicks, revealing two components of binding in each. KD
values showed some regional variation, but were 22.2 ± 1.1 nmol l‐1 for the high‐affinity component and 685 ± 25 nmol l‐1 for the low‐affinity component of binding to whole forebrain sections from control chicks. Analyses also revealed that Hill coefficients were significantly less than 1 in all regions measured. A significant decrease in KD for the low‐affinity component occurred bilaterally in the intermediate andmedial hyperstriatum ventrale (IMHV; left, 34.8%; right, 33.3%), a region that has previously been shown to be implicated in the processes of memory formation, following passive avoidance training. A significant decrease in KD for the high‐affinity component occurred in the right palaeostriatum augmentatum (19.5%). Significant decreases in Bmax accompanied the KD alterations in both cases. Additionally, bilateral intracerebral injections (administered 4.5‐5.5 h after training) into the IMHV of 500 nmol l‐1 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), a selective antagonist of non‐NMDA glutamate receptors (particularly AMPA receptors), resulted in amnesia for one‐trial passive avoidance training in day‐old chicks tested 6.5 h after training. Unilateral injections administered 5.5 h after training had a significant but smaller effect. Injections administered before training or 5 min after training had no effect on learning or retention of memory for the task. These results show that the affinity of AMPA receptors increases at a time point after passive avoidance training at which their inhibition by CNQX blocks maintenance of long‐term memory for this task.
Subcellular Localization of the GABAA Receptor γ2 Subunit in the Rat Spinal Cord
Authors: Sur Cyrille , McKernan Ruth , Triller Antoine 
Published: April 2006

AbstractThe fine subcellular organization of the GABAA receptor complex in the adult rat spinal ventral horn was analysed by immunocytochemistry using a specific polyclonal antiserum raised against the γ subunit. This subunit confers benzodiazepine sensitivity on the chloride channel of the GABAA receptor. With both fluorescent and peroxidase staining, the immunoreactivity was mainly observed in the grey matter and more specifically in the dorsal and ventral horns on medium and large neurons. A high number of immunostained somata were clustered in regions corresponding to motor nuclei. On the neuronal surface, labelling appeared as fluorescent dots over the more diffuse staining that was present on the soma and proximal part of dendrites. At the ultrastructural level, peroxidase end product was in most cases associated with the internal side of postsynaptic differentiations facing terminal boutons enriched with pleiomorphic small clear vesicles. The positively stained synapses were encountered on proximal dendrites of neurons and throughout the neuropil of the ventral horn (layers VII‐IX). An immunoreactivity on the postsynaptic membrane was occasionally found to decorate large pieces of membrane not directly apposed to presynaptic active zones. In addition, presynaptic labelling was observed at axoaxonic contacts and at extrasynaptic sites on membranes within boutons, sometimes themselves apposed to γ2 immunoreactivity. Finally, we also observed γ2 immunoreactivity at the cytosolic face of the plasma membrane of some glial elements. These results give morphological evidence for the involvement of GABAA receptors in both post‐ and presynaptic inhibition in the rat spinal ventral horn. The presence of γ2 subunit immunoreactivity at these different synaptic contacts suggests that the two types of inhibition can be modulated by benzodiazepine drugs. The findings also provide anatomical evidence for the possible regulation of GABA release through an autoreceptor, and for GABAergic communication between neuronal and glial components.
Regional Distribution and Developmental Variation of the Glycine Transporters GLYT1 and GLYT2 in the Rat CNS
Authors: Zafra Francisco , Gomeza Jesús , Olivares Luis , Aragón Carmen , Giménez Cecilio 
Published: April 2006

AbstractThe high‐affinity glycine transporter in neurons and glial cells is the primary means of inactivating synaptic glycine. Previous molecular cloning studies have indicated heterogeneity of glycine transporters in the CNS. Here the distribution of glycine transporter GLYT1 and GLYT2 transcripts and proteins in different regions and developmental stages of the rat brain were analysed by Northern, Western and in situ hybridization techniques. Sequence‐specific riboprobes and two specific antibodies raised against fusion proteins were used, containing either 76 or 193 amino acids of the C or N terminus of the GLTY1 and GLYT2 transporters respectively. High levels of GLYT1 transcripts were found in the spinal cord, brainstem and cerebellum, and moderate levels in forebrain regions such as the cortex or hippocampus. GLYT2 transcripts are restricted to the spinal cord, brainstem and cerebellum. The onset of both GLYT1 and GLYT2 expression in the brainstem occurred in late fetal life, and full expression of these proteins was observed before weaning. There was a stepwise increase in the levels of mRNA and protein for these two transporters, reaching a maximum by the second postnatal week, followed by a slight decrease until adult values were reached by the fourth postnatal week. These data reveal interesting parallelism between the distribution of different glycine transporters and glycine receptor subunits, and suggest discrete roles for distinct glycine transporters.