bluuebunny/crossref_metadata_2025 huggingface dataset:
Androgen treatment of neonatal rats decreases susceptibility of cerebellar granule neurons to oxidative stress in vitro
Authors: Ahlbom E. , Grandison L. , Bonfoco E. , Zhivotovsky B. , Ceccatelli S.
Published: March 2003

Oxidative stress has been implicated in various neurodegenerative diseases. There is substantial evidence indicating that gonadal hormones can affect neuronal cell survival via both a genomic as well as a non‐genomic mode of action. In the present study, the potential protective activity of testosterone on neuronal cells was investigated by using an in vitro/ex vivo model. Cerebellar granule cells (CGC) were prepared from 7‐day‐old rats which had been treated with a single dose of oil or testosterone propionate on postnatal day 3. After 7 days in culture, cells were exposed to oxidative challenges, including hydrogen peroxide and the nitric oxide donor S‐nitrosocysteine (SNOC), which can induce CGC death via apoptosis. Colchicine, which causes apoptosis via a different mechanism, was also used. The cells were monitored for apoptotic morphology by propidium iodide and TUNEL staining. Additionally, the presence of chromatin fragmentation was determined. CGC obtained from testosterone‐treated rats were found to be more resistant to hydrogen peroxide and nitric oxide toxicity, as shown by a 75 and 45% decrease in apoptotic cells, respectively. In contrast, the susceptibility to colchicine was not modified. As CGC from testosterone‐treated pups were selectively protected from oxidative stress, different components of the antioxidant defence systems were analysed. A twofold increase in the activity of catalase and superoxide dismutase was found in the CGC prepared from testosterone‐treated rats. These results suggest that in vivo treatment with androgens render CGC less vulnerable to oxidative stress‐induced apoptosis by potentiating antioxidant defences.
Categorization of complex visual images by rhesus monkeys. Part 1: behavioural study
Authors: Vogels Rufin
Published: March 2003

In order to study how visual categories are coded by the activities of single neurons, it is necessary to first demonstrate that the animal subjects can categorize the visual stimuli employed in the single‐unit recordings. Thus, rhesus monkeys were trained in a visual categorization task designed to minimize rote learning of individual exemplars and to allow testing of transfer from old to novel exemplars of the category. The stimuli were presented during controlled fixation. The monkeys learned to distinguish complex colour images of trees from other objects and generalized from old to novel exemplars. An extensive series of tests with probe stimuli showed that simple form, colour and texture features had insufficient stimulus control to account for the categorization performance. Scrambling the images impaired categorization performance, suggesting that the configuration of stimulus components controlled the categorization. The animals also learned a fish/non‐fish categorization, but more slowly than a tree/non‐tree categorization. These results indicate that rhesus monkeys can learn to categorize socially neutral, complex, natural visual images and suggest that this categorization is based on a combination of low‐level features.
Categorization of complex visual images by rhesus monkeys. Part 2: single‐cell study
Authors: Vogels Rufin
Published: March 2003

In order to investigate the neural coding of ordinate‐level visual categories, single‐cell recordings were made in the anterior temporal cortex of two rhesus monkeys performing a categorization of colour images of trees versus images of other objects. Neurons showed a high average degree of selectivity for these complex colour images. Although most neurons responded to trees and non‐trees, about a quarter responded in a category‐specific manner, e.g. to trees but not non‐trees, and about one‐tenth responded almost exclusively to exemplars of the trained category. The responses of these neurons were largely invariant for stimulus transformations, e.g. changes in position or size, and decreased with the degree of image scrambling, mimicking the behavioural results. However, the responses of single neurons were insufficiently stimulus invariant to accommodate the entire range of variability present in the features of exemplars within the same category. This strong within‐category selectivity challenges the idea that a prototype is represented at the single neuron level, but suggests that ordinate‐level categorization is based on a population of neurons, each selective for a limited set of exemplars.
Effects of excitotoxic lesions of the rat prefrontal cortex on CREB regulation and presynaptic markers of dopamine and amino acid function in the nucleus accumbens
Authors: Dalley J. W. , Thomas K. L. , Howes S. R. , Tsai T. H. , Aparicio‐Legarza M. I. , Reynolds G. P. , Everitt B. J. , Robbins T. W.
Published: March 2003

The present study investigated the effects of excitotoxic lesions of the prefrontal cortex (PFC) on dopamine (DA) and excitatory amino acid (EAA) function in the nucleus accumbens core using in vivo microdialysis in freely moving rats. As a postsynaptic marker of neuronal function, the nuclear levels of the transcriptional factor CREB and its active phosphorylated form, CREB‐P, were measured in the ventral tegmental area (VTA), and in the core and shell subregions of the nucleus accumbens of sham and lesioned animals. PFC‐lesioned animals exhibited a greater locomotor response to novelty and amphetamine administration (125–500 μg/kg i.v.). No change was observed in extracellular levels of glutamate or saturable d‐aspartate binding (a marker for the high‐affinity EAA transporter) in the nucleus accumbens of PFC‐lesioned animals. Extracellular levels of DA were comparable in sham and lesioned animals under tonic conditions, however, following amphetamine administration, DA efflux was significantly attenuated in lesioned animals. No correlation was observed between microdialysate levels of amino acids and the attenuated dopaminergic response to amphetamine in lesioned animals. Further, no effect of the lesion was found on nuclear CREB protein in saline‐ and amphetamine‐treated rats. The density of CREB‐P immunoreactive nuclei, while remaining unchanged in the VTA, increased in the nucleus accumbens shell following amphetamine treatment in lesioned animals. The results show that an important modulatory role of the PFC on the behavioural response to novelty and amphetamine is associated with the level of immediate‐early gene regulation rather than levels of extracellular DA and amino acids in the ventral striatum.
Clusters of GABAA receptors on cultured hippocampal cells correlate only partially with functional synapses
Authors: Kannenberg Kai , Sieghart Werner , Reuter Harald
Published: March 2003

We describe a method to label γ‐aminobutyric acid (GABA)A receptors on the surface of living hippocampal neurons in primary culture, and we compare the distribution of receptors with that of active synapses. To visualize GABAA receptors, the affinity‐purified antibody β3(1–13), recognizing the extracellular N‐termini of the GABAA receptor β2‐ and β3‐subunits, was used in combination with fluorescent secondary antibodies. The β2‐ and β3‐subunits belong to the predominant GABAA receptor subunits in the hippocampus. As expected for aggregates of GABAA receptors in the somato‐dendritic plasma membrane, a patchy staining pattern similar to that seen by labelling neurons after fixation was obtained. An antiserum recognizing an intracellular epitope of GABAA receptor β3‐subunits did not label the receptors in living neurons. Whole‐cell recordings of GABA‐evoked Cl – currents were not affected after decorating GABAA receptors with antibody β3(1–13). Combining the staining of GABAA receptors with the labelling of active presynaptic terminals with the fluorescent dyes FM1‐43 or FM4‐64, consistently resulted in the detection of GABAA receptor clusters that were not located at active synapses. These amounted to ≈ 50% of all labelled GABAA receptor clusters. GABAA receptor clusters that were not associated with active presynaptic terminals partially colocalized with the synaptic vesicle marker protein sv2, while another fraction had no presynaptic counterpart at all. These findings suggest the presence of presynaptically silent GABAergic synapses in cultured hippocampal neurons. They also indicate that for the maintenance of GABAA receptor aggregates, the release of GABA from an opposing active terminal is not essential.
Contribution of endogenously formed arachidonic acid in the presynaptic facilitatory effects of NMDA and carbachol on dopamine release in the mouse striatum
Authors: L'hirondel M. , Chéramy A. , Artaud F. , Godeheu G. , Glowinski J.
Published: March 2003

Arachidonic acid stimulated the release of [3H]‐dopamine from striatal microdiscs in a concentration‐dependent and partially calcium‐dependent manner. Inhibitors of cytosolic and membrane‐bound phospholipase A2 were used to determine whether endogenously formed arachidonic acid also contributes to the release of [3H]‐DA (previously taken up in tissues or endogenously synthesized from [3H]‐tyrosine) evoked by N‐methyl‐d‐aspartate (NMDA) and carbachol alone or in combination. In the presence of magnesium, carbachol was found to remove the magnesium block of NMDA receptors and to facilitate the NMDA‐evoked release of [3H]‐DA from striatal microdiscs and synaptosomes. In addition, in the absence of magnesium, synergistic responses were induced by both agonists on microdiscs but not on synaptosomes. Responses induced by NMDA, carbachol or both agonists on microdiscs were reduced by phospholipase A2 inhibitors, the most striking effects being observed with mepacrine. Mepacrine was also shown to reduce the oxotremorine, but neither the nicotine‐ nor the potassium‐evoked release of [3H]‐DA. Tetrodotoxin decreased the release of [3H]‐DA evoked by the co‐application of NMDA and carbachol on microdiscs, but mepacrine still decreased this tetrodotoxin‐resistant response. Similarly, mepacrine still decreased the release of [3H]‐DA evoked by NMDA and carbachol on synaptosomes. Altogether, these results indicate that arachidonic acid which is formed in striatal neurons, and to a lesser extent in DA fibres, under stimulation of NMDA and muscarinic receptors, partially contributes to the presynaptic facilitation of DA release evoked by NMDA and carbachol.
Auditory activation of cortical visual areas in cats after early visual deprivation
Authors: Yaka Rami , Yinon Uri , Wollberg Zvi
Published: March 2003

Auditory activation of the primary visual cortex (area 17) and two extrastriate visual cortical areas – the anterolateral lateral suprasylvian area (ALLS) and anteromedial lateral suprasylvian area (AMLS), was investigated in visually impaired cats. Impairment was accomplished shortly after birth by bilateral eyelid suturing (binocularly deprived cats, BD) or bilateral enucleation (binocularly enucleated cats, BE). In BE cats, the optic nerve and chiasm were entirely degenerated. No cortical atrophy or cytoarchitectural malformation was noticed in either BD or BE cats. In both normal and impaired cats we found auditory‐responsive cells in the ALLS and AMLS, areas that are considered strictly visual. The most remarkable finding was an increase in the relative number of these auditory cells in the BD and BE cats, which was more prominent in the latter. Some auditory‐responsive cells were also found in area 17 of BE cats. On the basis of formal calculation, it is tempting to suggest that the increase in relative number of auditory cells in these areas reflects the transformation of all the visual cells in the ALLS of BD and BE cats into auditory cells. In BE cats, all bimodal cells and an appreciable percentage of non‐responsive cells also had transformed to auditory cells. In the AMLS of BD cats, it is primarily the bimodal cells that become auditory cells, whereas in BE cats all the visual and bimodal cells as well as non‐responsive cells undergo this transformation. This assumption, however, is one possible interpretation of our results but not the only one. Other modes of neuronal plasticity that might yield similar results in the visually deprived cats can not be ruled out.
Glucocorticoid receptor activation in the rat nucleus of the solitary tract facilitates memory consolidation: involvement of the basolateral amygdala
Authors: Roozendaal Benno , Williams Cedric L. , McGaugh James L.
Published: March 2003

These experiments examined the involvement of glucocorticoid receptors (GRs or type II) located in the A2‐noradrenergic cell group of the rat nucleus of the solitary tract (NTS) in modulating memory storage. Bilateral intra‐NTS infusions (0.5 μL) of the specific GR agonist RU 28362 (11β, 17β‐dihydroxy‐6,21‐dimethyl‐17α‐pregna‐4,6‐trien‐20yn‐3‐one), in doses ranging from 0.01 to 10.0 ng, immediately after inhibitory avoidance training produced a dose‐dependent enhancement of 48 h retention performance. Infusions of 0.1 or 1.0 ng of the agonist enhanced retention, whereas lower or higher doses were ineffective. Post‐training infusions of the GR antagonist RU 38486 [17β‐hydroxy‐11β‐(4‐dimethylaminophenyl)‐17α‐(1‐propynyl)‐oestra‐4,9‐dien‐3‐one, 0.01–10.0 ng] into the NTS did not significantly affect retention performance, but shifted the dose–response effects of post‐training systemic injections of the synthetic glucocorticoid dexamethasone to the right. These results indicate that activation of GRs in the NTS can influence memory formation for inhibitory avoidance training, and suggest that the effects of circulating glucocorticoids on memory are mediated, in part, by an activation of GRs in the NTS. Additionally, pretraining infusions of the β1‐adrenergic antagonist atenolol (0.5 μg in 0.2 μL) into the basolateral nucleus of the amygdala (BLA), a brain structure which receives noradrenergic projections from the NTS and is implicated in memory storage modulation, blocked the memory‐enhancing effects of the GR agonist (1.0 ng) infused into the NTS. These findings provide evidence that memory storage is modulated by glucocorticoid binding to GRs in noradrenergic cell bodies in the NTS and suggest that these modulatory effects are conveyed by ascending projections to the BLA.
Platelet‐activating factor receptor is not required for long‐term potentiation in the hippocampal CA1 region
Authors: Kobayashi Katsunori , Ishii Satoshi , Kume Kazuhiko , Takahashi Tomoyuki , Shimizu Takao , Manabe Toshiya
Published: March 2003

From pharmacological studies, platelet‐activating factor (PAF) has been proposed as a retrograde messenger for long‐term potentiation (LTP) in the hippocampal CA1 region. We re‐examined a possible contribution of PAF to LTP with a more specific approach using mice deficient in the PAF receptor. The PAF receptor‐deficient mice exhibited normal LTP and showed no obvious abnormality in excitatory synaptic transmission. We also performed pharmacological experiments on the wild‐type mice. Two structurally different antagonists of PAF receptors had no effects on LTP. Furthermore, the application of PAF itself caused no detectable changes in excitatory synaptic transmission. Thus, we conclude that the PAF receptor is not required for LTP in the CA1 region.

Introduction
Excitatory amino acids and synaptic transmission in embryonic rat brainstem motoneurons in organotypic culture
Authors: Launey Thomas , Ivanov Anton , Kapus Gàbor , Ferrand Nadine , Tarnawa Istvan , Gueritaud Jean‐Patrick
Published: March 2003

We used brainstem motoneurons recorded in organotypic slice co‐cultures maintained for more than 18 days in vitro, together with multibarrel ionophoretic applications of glutamate receptor agonists and bath applications of specific blocking agents, to study the responses of rat brainstem motoneurons to glutamate receptor activation, and the contribution of these receptors to synaptic transmission. Differentiated brainstem motoneurons in vitro are depolarized by glutamate, N‐methyl‐d‐aspartate (NMDA) and dl‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐propionic acid (AMPA) iontophoresis, and express NMDA, AMPA and also specific kainate receptors, as evidenced by (+/–)2‐amino‐5‐phosphonovaleric acid (APV)‐ and (–)1‐(4‐aminophenyl)‐3‐methyl‐carbamoyl‐4‐methyl‐7,8‐methylenedioxy‐3,4‐dihydro‐5H‐2,3‐benzo‐diazepine [GYKI 53784 (LY303070)]‐resistant depolarizations. Electrical stimulations applied to the dorsal part of the explant trigger excitatory synaptic potentials with latencies distributed in three regularly spaced groups. Excitatory postsynaptic potentials (EPSPs) in the earliest group have a similar latency and time course and correspond to monosynaptic activation. EPSPs in later groups have more scattered latencies and time courses and correspond to polysynaptic activation. Monosynaptic EPSPs are insensitive to the specific NMDA blocker APV, and are completely and reversibly suppressed by the non‐competitive AMPA receptor antagonist GYKI 53784 (LY303070). Detailed analysis of the spontaneous excitatory synaptic activity shows that APV decreases the frequency of spontaneous EPSPs without modifying their shape or amplitude. We conclude that excitatory synapses on brainstem motoneurons in vitro are mainly activated through AMPA receptors (AMPA‐Rs). NMDA receptors (NMDA‐Rs) are present in the membrane, but are located either at extrasynaptic sites or silent synapses, and are not directly involved in synaptic transmission on motoneurons. On the contrary, NMDA receptors contribute to synaptic transmission within the premotor interneuronal network.
Unexpected localization of the Na+/Cl–‐dependent‐like orphan transporter, Rxt1, on synaptic vesicles in the rat central nervous system
Authors: Masson J. , Riad M. , Chaudhry F. , Darmon M. , Aïdouni Z. , Conrath M. , Giros B. , Hamon M. , Storm‐Mathisen J. , Descarries L. , Mestikawy S. El
Published: March 2003

Numerous features of its primary structure demonstrate that the orphan transporter Rxt1 belongs to the Na+/Cl–‐dependent neurotransmitter plasma membrane transporter superfamily, which includes the dopamine, norepinephrine, serotonin and γ‐aminobutyric acid (GABA) transporters. Initial immunocytochemical investigations with affinity‐purified antibodies have established that Rxt1 is localized, almost exclusively, in axon terminals of glutamatergic neurons and subsets of GABAergic neurons in the CNS. Further studies were carried out to determine its subcellular distribution. In a first series of experiments, PC‐12 cells were transfected with plasmids encoding either the dopamine transporter or Rxt1. Immunofluorescence experiments showed that the dopamine transporter was expressed in these cells, and, as expected, addressed to their plasma membrane. Surprisingly, this was never the case with Rxt1, which was targeted to the same subcellular compartment as synaptophysin, a vesicular protein. In a second set of experiments, subcellular fractionation of rat striatum showed that Rxt1, but not the dopamine transporter, was relatively abundant in the purified synaptic vesicle fraction. Finally, electron microscopic immunocytochemistry with anti‐Rxt1 antibodies showed peroxidase as well as pre‐ and post‐embedding immunogold labelling confined to the intracellular compartment in various brain regions. Moreover, quantitative analysis of post‐embedding experiments demonstrated that the immunogold particles corresponding to Rxt1 immunoreactivity were mostly localized to small synaptic vesicles. These data indicate that, in contrast with the other members of the Na+/Cl–‐dependent neurotransmitter transporter superfamily, which are targeted to the plasma membrane, Rxt1 is distributed as a vesicular protein in the CNS.
Absence of the dopamine D2 receptor leads to a decreased expression of GDNF and NT‐4 mRNAs in restricted brain areas
Authors: Bozzi Yuri , Borrelli Emiliana
Published: March 2003

Neurotrophic factors (NTFs) control the metabolic and electrophysiological properties of dopaminergic neurons in the brain. At the level of the substantia nigra, NTFs have been proposed to control dopamine release by regulating the firing rate of dopaminergic cells. This function is normally controlled by presynaptic dopaminergic autoreceptors. Dopamine has also been proposed to regulate the expression of NTFs and their receptors in the nigrostriatal pathway. Thus, an interaction between the signalling cascades activated by NTFs and dopamine receptors might possibly influence the physiology of dopaminergic neurons. Among dopamine receptors, D2 receptors (D2R) are the most abundant on dopaminergic neurons, where they exert autoreceptor functions. To test for an interaction between the NTF and dopaminergic pathways we have analysed the expression of NTFs and their receptors in D2R‐deficient (D2R –/–) mice. Our study shows that the mRNA levels of brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 and their corresponding receptors are not modified in the dopaminergic system of D2R –/– adult mice compared with wild‐type littermates. However, a marked reduction of glial cell line‐derived neurotrophic factor (GDNF) and neurotrophin‐4 (NT‐4) mRNAs is observed in the striatum and parietal cortex of D2R –/– mice, respectively. These results implicate dopamine, acting through D2 receptors, in the local control of specific NTF expression. The down‐regulation of GDNF and NT‐4 expression might also contribute to the locomotor phenotype of D2R –/– mice.
Distribution of synaptic vesicle proteins in the mammalian retina identifies obligatory and facultative components of ribbon synapses
Authors: Von Kriegstein Katharina , Schmitz Frank , Link Egenhard , Südhof Thomas C.
Published: March 2003

The mammalian retina contains two synaptic layers. The outer plexiform layer (OPL) is primarily composed of ribbon synapses while the inner plexiform layer (IPL) comprises largely conventional synapses. In presynaptic terminals of ribbon synapses, electron‐dense projections called ribbons are present at the synaptic plasma membranes. Ribbons bind synaptic vesicles and guide them to the synaptic membrane for fusion. In this manner, ribbons are thought to accelerate the delivery of vesicles for continuous exocytosis. In recent years, a large number of synaptic proteins has been described but it is not known if these protein colocalize in the same types of synapses. In previous studies, several proteins essential for synaptic function were not detected in ribbon synapses, suggesting that the mechanism of synaptic vesicle exocytosis may be very different in ribbon and conventional synapses. Using confocal laser scanning microscopy, we have now systematically investigated the protein composition of ribbon synapses. Our results show that, of the 19 synaptic proteins investigated, all except synapsin and rabphilin are obligatorily present in ribbon synapses. For example, rab3 which was reported to be absent from ribbon synapses, was found in bovine, rat and mouse ribbon synapses using multiple independent antibodies. In addition, we found staining in these synapses for PSD‐95 and NMDA receptors, which suggested a similar design for the postsynaptic component in ribbon and conventional synapses. Our data show that ribbon synapses are more conventional in composition than reported, that most synaptic proteins are colocalized to the same type of synapse, and that synapsin and rabphilin are likely to be dispensible for basic synaptic functions.
The isolated mammalian brain: an in vivo preparation suitable for pathway tracing
Authors: Von Bohlen Oliver , Halbach Und
Published: March 2003

An in vitro preparation of complete brain is presented which allows successful tracing with fast axonal tracers for at least 2 days after in vitro preparation. A simple procedure is used, by which the isolated brain is submerged in oxygenated artificial cerebrospinal fluid, enabling maintenance of adequate integrity without perfusion the vascular system. The use of an isolated brain has many advantages: virtually all brain areas are easily accessible; tracer applications are possible without problems of animal survival; and the tracers are be translocated by blood circulation. The viability of this isolated brain preparation was validated by successful recording of extracellular field potentials 1 day later.
Visual experience alters the molecular profile of NMDA‐receptor‐mediated sensory transmission
Authors: Binns K. E. , Turner J. P. , Salt T. E.
Published: March 2003

N‐methyl‐d‐aspartate (NMDA) receptors (NMDArs) may facilitate experience‐dependent changes in the visual system. Early sensory experience has an influence over the production of the molecular components from which NMDArs are assembled, and thereby alters the properties of functional receptors. Using the antagonists d‐2‐amino‐5‐phosphonovalerate (AP5) and 3‐(2‐carboxypiperazin‐4‐yl)‐propyl‐1‐phosphonate (CPP), which have some selectivity for different variants of the NMDAr, we demonstrate that visual deprivation (by dark rearing) has functional consequences for NMDArs in the superior colliculus. An increase in the sensitivity of visual responses to AP5 in dark‐reared rats indicated that NMDArs were more important for visual transmission in these individuals. We also observed a relative change in the efficacy of the antagonists against the visual responses of normal versus dark‐reared rats. AP5 reduced the visual responses of both groups, but CPP was ineffective against visual responses after dark rearing. In the same neurons, CPP blocked NMDA induced activity indicating that molecular adaptations of NMDArs are specific to those synapses mediating visual activity.
Contralateral trigeminal nerve lesion reduces polyneuronal muscle innervation after facial nerve repair in rats
Authors: Angelov Doychin N. , Skouras Emmanouil , Guntinas‐Lichius Orlando , Streppel Michael , Popratiloff Anastas , Walther Michael , Klein Johannes , Stennert Eberhard , Neiss Wolfram F.
Published: March 2003

Functional recovery after facial nerve surgery is poor. Axotomized motoneurons (hyperexcitable upon intracellular current injections, but unable to discharge upon afferent stimulation) outgrow supernumerary branches which are misrouted towards improper muscles. We hypothesized that alterations in the trigeminal input to axotomized electrophysiologically silent facial motoneurons might improve specificity of reinnervation. To test this we compared, in the rat, behavioural, electrophysiological, and morphological parameters after transection and suture of the buccal facial nerve (buccal–buccal anastomosis, BBA) with those after BBA plus excision of the ipsi‐ or contralateral infraorbital nerve (ION). After BBA, the mystacial vibrissae dropped and remained motionless until 18–21 days post operation (days PO). After BBA plus ipsilateral ION excision, there was no recovery of vibrissae whisking at all. Following BBA plus contralateral ION excision, full restoration of whisking occurred at 7–10 days PO. Electromyography of whiskerpad muscles showed normal waveform and amplitude was also most rapidly restored after BBA plus contralateral ION excision. Neuron counts after retrograde tracing showed that the intact buccal nerve contained axons of the superior (91%) and inferior (9%) buccolabial nerves. After BBA, the superior nerve comprised 56%, the inferior 21%, and 23% of the motoneurons projected within both nerves. After BBA plus ipsilateral ION excision, misdirection worsened and values changed to 48, 39 and 13%, respectively. After BBA plus contralateral ION excision, portions improved to 69, 23 and 8%. We conclude that, by reducing the redundant axon branching, lesion of contralateral ION provides the best conditions for recovery of vibrissae rhythmical whisking after reconstructive surgery on the facial nerve.
Distribution of fibroblast growth factor‐5 in rat hypothalamus, and its possible role as a regulator of feeding behaviour
Authors: Li Ai‐Jun , Ozawa Kazuo , Tsuboyama Hiroyuki , Imamura Toru
Published: March 2003

We previously reported that a transcript of fibroblast growth factor‐5 (FGF‐5) was more abundant in the brain of postnatal and adult mice than in the embryonic brain. This suggested that FGF‐5 plays some role in the mature brain. Here, we have investigated the spatiotemporal expression and function of FGF‐5 in the adult rat hypothalamus with the emphasis on feeding behaviour. In situ hybridization experiments demonstrated that, in both adequately fed and fasted (20 h) rats, FGF‐5 transcripts were present within several nuclei in the hypothalamus (viz. the magnocellular part of the paraventricular nucleus, supraoptic nucleus, arcuate nucleus, median eminence, and ventromedial hypothalamic nucleus), but not in the lateral hypothalamic area. Quantitative detection of FGF‐5 mRNA in the hypothalamus (especially in the paraventricular nucleus) indicated that food deprivation (20 h) reduced the expression of this gene to almost one‐half of that seen in the control (fed) rats. The expression recovered to the control level after 1 h re‐feeding, and this recovery persisted for several hours. Furthermore, FGF‐5, when infused into the third ventricle, consistently reduced food intake, water intake and body weight gain, all in a dose‐dependent manner. These results suggest that FGF‐5 in the hypothalamus acts as a physiological regulator of feeding behaviour, and that its decreased expression during food deprivation may be important in stimulating appetite.
Effects of unilateral cochlear removal on dendrites in the gerbil medial superior olivary nucleus
Authors: Russell F. Anne , Moore David R.
Published: March 2003

For most neurons, dendrites serve as the major pathway for incoming activity from other neurons. It might therefore be expected that dendrites are particularly sensitive to variations in the level of afferent input they receive. In the auditory brainstem, this expectation has been confirmed in neurons of the medial superior olivary nucleus (MSO). The MSO is uniquely suited to studies of afferent influences on dendrites, as lateral and medial dendrites of MSO neurons receive inputs almost exclusively from the ipsilateral and contralateral ears, respectively. Thus, the effects of unilateral afferent manipulations may be compared between defined dendrites on the same neurons. We have used unilateral deafening (by surgical destruction of the cochlea) in immature [postnatal day 18 (P18)] and adult gerbils to study the late maturation and effect of peripheral deafferentation on the dendrites of MSO neurons. In semi‐thin, frontal sections from unoperated animals, we found a change between P18 and adulthood from a lateral to a medial bias in the symmetry of MSO dendrites. Cochlear removal in adulthood led to a reduction in the density of dendritic profiles on the side of the ablation in both MSOs. Cochlear removal at P18 led to a rapid (< 3 days) and sustained dendritic atrophy that was most marked in the caudal part of the nucleus. Electron microscope (EM) measurements in the sagittal plane on MSO dendrite profiles of animals unilaterally deafened at P18 showed a reduction in the number, but not in the area, of profiles on the side of the deafened ear. These results demonstrate a developmental change in the symmetry of MSO medial and lateral dendrites, and a rapid and long‐lasting reduction in the number of distal dendrites produced by unilateral deafening either in infancy or adulthood.
Ca2+ activation of hSlo K+ channel is suppressed by N‐terminal GFP tag
Authors: Meyer Elisabeth , Fromherz Peter
Published: March 2003

The human slow poke (hSlo) K+ channel was tagged with GFP (green fluorescent protein) at the N‐terminus of its α‐subunit. The fusion protein was expressed transiently in HEK293 cells; it formed functional voltage‐gated channels as shown by whole cell patch‐clamp measurements. However, the tag lowered the voltage dependence of gating and it suppressed the typical left‐shift of gating by intracellular binding of Ca2+. The location of the GFP‐tagged N‐terminus was confirmed to be on the extracellular side by application of a monoclonal antibody to nonpermeabilized cells. Structural interpretations of the effects are discussed.
Reduced function of l‐AP4‐sensitive metabotropic glutamate receptors in human epileptic sclerotic hippocampus
Authors: Dietrich D. , Kral T. , Clusmann H. , Friedl M. , Schramm J.
Published: March 2003

Human temporal lobe epilepsy is characterized by strong synaptic reorganization that leads to abnormal recurrent excitatory synaptic connections among hippocampal neurons. In addition, electrophysiological studies show that synaptic activity of the main afferent input to the hippocampus, the perforant path, is prolonged and amplified by changes in postsynaptic glutamate receptors. The current view is that these morphological and physiological abnormalities contribute significantly to the hyperexcitability seen in the hippocampus of temporal lobe epilepsy. Recently, it was found that presynaptic inhibitory metabotropic glutamate receptors are an important negative feedback mechanism that controls synaptic release of glutamate in the hippocampus. In this study, we assessed the functionality of this feedback system by investigating the metabotropic glutamate receptor mediated depression of excitatory synaptic transmission in surgically removed hippocampi from patients with marked synaptic reorganization (Ammon's horn sclerosis group) and from patients without detectable reorganization (lesion group). We report here that this control of synaptic transmission is lost in hippocampi from the Ammon's horn sclerosis group whereas this control is preserved in hippocampi from the lesion group. The data presented here suggest that the loss of feedback inhibition mediated by metabotropic glutamate receptors could be a further, previously not recognized, mechanism in the pathophysiology of temporal lobe epilepsy.
Mobilization of intracellular calcium stores participates in the rise of [Ca2+]i and the toxic actions of the HIV coat protein GP120
Authors: Medina Igor , Ghose Sraboni , Ben‐Ari Yehezkel
Published: March 2003

The HIV envelope glycoprotein, GP120, increases intracellular Ca2+ concentration and induces degeneration of human and animal neurons in culture. Using patch‐clamp recordings and Ca2+ imaging techniques, we have now examined the contribution of intracellular stores of calcium in the effects of GP120. We report that in rat hippocampal neuronal cultures, GP120 induces a dramatic and persistent increase in [Ca2+]i which is prevented by drugs that either deplete (caffeine, carbachol, thapsigargin) or block (dantrolene) Ca2+ release from intracellular stores. In contrast, N‐methyl‐d‐aspartate (NMDA) receptors or voltage‐dependent calcium channels do not participate in these effects, as: (i) the increase in [Ca2+]i was not affected by NMDA receptor antagonists or calcium channel blockers; and (ii) and GP120 did not generate any current in whole‐cell recording. Dantrolene, a ryanodine stores inhibitor, also prevented neuronal death induced by GP120. Our results show that the GP120‐induced rise in [Ca2+]i originates from intracellular calcium stores, and suggest that intracellular stores of calcium may play a determinant role in the pathological actions of GP120.
Expression of TrkB and TrkC but not BDNF mRNA in neurochemically identified interneurons in rat visual cortex in vivo and in organotypic cultures
Authors: Gorba Thorsten , Wahle Petra
Published: March 2003

The mammalian visual cortex contains morphologically diverse populations of interneurons whose neurochemical properties are believed to be regulated by neurotrophic factors. This requires the expression of neurotrophin receptors. We have analysed whether brain‐derived neurotrophic factor (BDNF), its receptor trkB and the NT‐3 receptor trkC are expressed in interneurons of rat visual cortex in vivo, and in organotypic visual cortex cultures, paying particular attention to the subsets of neuropeptidergic neurons. In situ hybridization in combination with immunofluorescence for calcium‐binding proteins and neuropeptides revealed that BDNF is not expressed in interneurons in vivo or in vitro. For the neurotrophin receptors we found in vivo at postnatal day 70 (P70) that ≈ 80% of the parvalbumin‐immunoreactive (‐ir), but only 50% of the intensely calbindin‐ir, and only 20% of the calretinin‐ir neurons express trkB. Double labelling with neuropeptides revealed that ≈ 50% of the neuropeptide Y‐ir and ≈ 50% of the somatostatin‐ir neurons express trkB in a laminar‐specific way. Only 25% of the vasoactive intestinal polypeptide (VIP)‐ir neurons coexpress trkB. The coexpression of neuropeptide Y with trkB, but not with BDNF or trkC, was confirmed with a double in situ hybridization. In contrast, the percentages differed in the immature cortex; at P14 70% of the NPY‐ir neurons and 46% of the calretinin‐ir neurons revealed trkB expression, while the ratio for calbindin‐ir cells was fairly constant (59%). From the interneuron populations studied, only 12% of the parvalbumin‐ir neurons expressed trkC. A triple labelling revealed that some neurons coexpressed both trk mRNAs, while others had only trkC. The analysis of interneurons in organotypic cultures yielded very similar results. The results indicate that trkB ligands synthesized by pyramidal neurons influence neuropeptide or calcium‐binding protein expression in a paracrine or transsynaptic manner. However, in contrast to current belief, in the adult only about half of all interneurons appear responsive to trkB ligands. Although the proportion is higher in the immature cortex, not all of the interneurons appear neurotrophin‐receptive. With regard to the presence or absence of neurotrophin receptors, the molecular heterogeneity of GABAergic interneurons in the visual cortex is higher than currently assumed, and the responsiveness to neurotrophins changes with development in a cell type‐specific way.
Cleavage of the TrkA neurotrophin receptor by multiple metalloproteases generates signalling‐competent truncated forms
Authors: Díaz‐Rodríguez Elena , Cabrera Noemí , Esparís‐Ogando Azucena , Montero Juan Carlos , Pandiella Atanasio
Published: March 2003

The ectodomain of the neurotrophin receptor TrkA has been recovered as a soluble fragment from the culture media of cells by a process that involves endoproteolytic cleavage. This cleavage may be upregulated by several treatments, including NGF treatment or protein kinase C activation. In this report we have investigated the cellular site and proteolytic activities involved in TrkA cleavage, and the effects of ectodomain truncation on signalling. Cleavage occurs when the receptor is at, or near, the cell surface, and it can be prevented by agents that affect protein sorting. Cleavage generates several cell‐bound fragments, and their generation can be differentially blocked by inhibitors, documenting the involvement of multiple plasma membrane metalloendoproteases. The major cell‐bound receptor fragment (i) is tyrosine‐phosphorylated in vivo; (ii) does autophosphorylate in vitro; and (iii) is able to associate with intracellular signalling substrates. Artificial deletion of the TrkA ectodomain results in an active receptor that induced neurite outgrowth in pheochromocytoma cells. Cleavage by this natural cellular mechanism appears thus to serve not only as an outlet of receptor binding fragments, but also to generate signalling‐competent cell‐bound receptor fragments. In the nervous system this ligand‐independent receptor activation could play important roles in the development and survival of neurons.
Regional distribution of Y‐receptor subtype mRNAs in rat brain
Authors: Parker R. M. C. , Herzog H.
Published: March 2003

Molecular cloning techniques have recently led to the identification of a growing number of neuropeptide Y‐receptor subtypes, suggesting possible subtype‐specific involvement in different physiological processes. Here we report the first study which determines and compares the mRNA expression of all four cloned functional Y‐receptor subtypes (Y1, Y2, Y4 and Y5) in consecutive sections of the rat brain on a cellular level, using a uniform in situ hybridization technique. Our results demonstrate that Y‐receptor subtype mRNA expression is widely distributed throughout the rat brain. Interestingly, coexpression of all four Y‐receptors, at different levels, is particularly evident within the limbic system, including the hypothalamus, hippocampus, amygdala, piriform and cingulate cortices and tegmental areas, all of which are heavily involved in behaviour, emotion and homeostatic regulation. Particularly interesting is the demonstration that Y5‐receptor mRNA expression always coincides with the presence of Y1‐receptor mRNA (although not vice versa), possibly due to the overlapping organization and transcriptional control of their genes. However, it is also clear that several brain nuclei display preferential expression of one or a selective combination of Y‐receptor subtype mRNAs. Furthermore, it is evident that there is regionalization of expression within certain loci which express all four receptor subtype mRNAs, particularly within the paraventricular and arcuate hypothalamic nuclei. Our results suggest that some of neuropeptide Y's (NPY) effects may be mediated through one particular subtype, whereas other physiological processes might require the coordinated action of different subtypes within the same or discrete areas.
Biophysical properties of scorpion α‐toxin‐sensitive background sodium channel contributing to the pacemaker activity in insect neurosecretory cells (DUM neurons)
Authors: Lapied B. , Stankiewicz M. , Grolleau F. , Rochat H. , Zlotkin E. , Pelhate M.
Published: March 2003

A scorpion α‐toxin‐sensitive background sodium channel was characterized in short‐term cultured adult cockroach dorsal unpaired median (DUM) neurons using the cell‐attached patch‐clamp configuration. Under control conditions, spontaneous sodium currents were recorded at different steady‐state holding potentials, including the range of normal resting membrane potential. At −50 mV, the sodium current was observed as unclustered, single openings. For potentials more negative than −70 mV, investigated patches contained large unitary current steps appearing generally in bursts. These background channels were blocked by tetrodotoxin (TTX, 100 nm), and replacing sodium with TMA‐Cl led to a complete loss of channel activity. The current–voltage relationship has a slope conductance of 36 pS. At −50 mV, the mean open time constant was 0.22 ± 0.05 ms (n = 5). The curve of the open probability versus holding potentials was bell‐shaped, with its maximum (0.008 ± 0.004; n = 5) at –50 mV. LqhαIT (10–8m) altered the background channel activity in a time‐dependent manner. At −50 mV, the channel activity appeared in bursts. The linear current–voltage relationship of the LqhαIT‐modified sodium current determined for the first three well‐resolved open states gave three conductance levels: 34, 69 and 104 pS, and reversed at the same extrapolated reversal potential (+52 mV). LqhαIT increased the open probability but did not affect either the bell‐shaped voltage dependence or the open time constant. Mammal toxin AaHII induced very similar effects on background sodium channels but at a concentration 100 × higher than LqhαIT. At 10–7m, LqhαIT produced longer silence periods interrupted by bursts of increased channel activity. Whole‐cell experiments suggested that background sodium channels can provide the depolarizing drive for DUM neurons essential to maintain beating pacemaker activity, and revealed that 10–7 m LqhαIT transformed a beating pacemaker activity into a rhythmic bursting.
Modelling the mosaic organization of rod and cone photoreceptors with a minimal‐spacing rule
Authors: Galli‐Resta L. , Novelli E. , Kryger Z. , Jacobs G. H. , Reese B. E.
Published: March 2003

The mosaic of photoreceptors is regarded as a prime example of the precise control of cellular positioning in the vertebrate nervous system. This study was undertaken with the idea that understanding the intrinsic geometrical features of photoreceptor mosaics is a necessary step to unveil the biological mechanisms governing their formation. We show in the retina of the ground squirrel that the arrays of both the rods and S cones are non‐random, but that nothing more than a simple minimal‐spacing rule constraining receptor positioning is sufficient to account for the spatial organization of both mosaics. The size of this ‘exclusion zone’ is an intrinsic characteristic of each cell type, and it is simply the difference in the size of this domain that accounts for the regularity of the S cone array and the irregularity of the rod array at identical density. Consequently, regularity in receptor mosaics is produced by two independent biological events, one embodying the exclusion zone, and another specifying the local density of a given receptor type.
Relationships between trait and state anxiety and the central benzodiazepine receptor: a PET study
Authors: Abadie P. , Boulenger J. P. , Benali K. , Barré L. , Zarifian E. , Baron J. C.
Published: March 2003

The central benzodiazepine receptor (cBZr) has long been implicated in anxiety disorders on the basis of: (i) the well‐known anxiolytic and anxiogenic properties of cBZr agonists and inverse agonists, respectively; (ii) a possibly reduced sensitivity to benzodiazepines in anxious subjects; and (iii) a putative endogenous ligand. Thus, two main hypothesis have been advanced, namely changes in the concentration or properties of the latter, and changes in the GABAA complex conformation, which contains the cBZr. Neither postmortem studies nor appropriate animal models are available to investigate these ideas. We have used positron emission tomography (PET) to measure both the density and affinity of the cBZr in multiple brain regions in unmedicated patients and age‐ and sex‐matched healthy volunteers, and have looked for differences between groups as well as correlations between cBZr parameters and state and trait anxiety scores. We studied 10 unmedicated patients (sex ratio 1 : 1; mean age: 39 years), prospectively recruited using DSM III‐R criteria, and 10 age‐ and gender‐matched healthy unmedicated volunteers. Thanks to a PET procedure using two successive administrations of 11C‐flumazenil (at high and low specific radioactivity) and previously validated by us, we estimated the Bmax, Kd and bound : free (B/F) ratios in 11 neocortical areas and in the cerebellum. Before and after the PET session, anxiety scores from Spielberger's and Covi's scales were obtained. There was no statistically significant difference in Bmax, Kd or B/F‐values between the two groups for any region. Across the two groups, there were only a few marginally significant anxiety‐score–PET correlations, suggesting chance findings. This is the first fully quantitative study to report on the relationships between cBZr parameters and anxiety. Using two independent approaches (i.e. group comparison and across‐group correlations), we found no evidence for a link between anxiety trait or state and the cBZr in neocortex or cerebellum in this sample. These findings, if confirmed by studies on larger samples, have implications for the pharmacotherapy of anxiety disorders, and will need to be considered when designing new neurobiological models of anxiety.