bluuebunny/crossref_metadata_2025 huggingface dataset:
Cholera Toxin β Subunit Induces the Differentiation of Human Medulloblastoma Cell Line DEV in a Neuronal Pathway
Authors: Dufay Natalie , Belin Marie‐Françoise , Confavreux Christian , Touraine‐Moulin Françoise , Derrington Edmund A.
Published: April 2006

Medulloblastomas are primitive neuroectodermal tumours that are thought to arise from multipotent precursor cells in the cerebellum. Medulloblastoma cells may be undifferentiated or exibit glial, neuronal or ependymal characteristics, suggesting that they may conserve their ability to differentiate in appropriate circumstances. Medulloblastoma cell lines may thus provide models to study the commitment and differentiation of multipotent CNS progenitor cells. A human medulloblastoma cell line, DEV, has previously been shown to differentiate in an astrocytic pathway after infection by the retrovirus HTLV‐1. In this study immunofluorescence flow cytometry shows that cholera toxin β subunit (CTβ), which binds to the ganglioside GM1, induces a twofold increase in the number of DEV cells differentiating towards a neuronal pathway, as shown by the increased proportion and labelling intensity of cells stained by an anti‐neurofilament antibody. Immunocytochemistry shows that after 3 days in culture with CTβ, DEV cells develop processes which stain positive for neurofilaments and MAP‐1. This suggests that CTβ induces DEV cells to express a more neuronal phenotype.
The Contribution of GABA‐mediated Inhibition to Response Properties of Neurons in the Nucleus of the Optic Tract in the Rat
Authors: Schmidt Matthias , Lewald Jörg , van der Togt Chris , Hoffmann Klaus‐Peter
Published: April 2006

The contribution of GABA‐mediated inhibition to the generation of directional selectivity of neurons in the nucleus of the optic tract (NOT) and the dorsal terminal nucleus of the accessory optic system (DTN) was examined in anaesthetized rats by iontophoretic application of the GABAA receptor antagonist bicuculline methiodide. Spontaneous and visually evoked NOT‐DTN cell activities were always increased by bicuculline application. The directional selectivity of NOT‐DTN cells to slowly moving whole‐field stimuli, expressed as the direction index, was reduced for most neurons. However, the difference between firing rates during stimulus movements in the preferred and in the non‐preferred direction did not change systematically. On average, this difference was not significantly affected in the majority of the neurons, although bicuculline more strongly increased the activity during movement in the preferred or non‐preferred direction in some of the neurons. These results indicate that directionally selective neurons in the rat NOT‐DTN receive GABAergic inhibition which is most likely tonic and independent of the stimulus direction.
Involvement of AMPA Receptors in Trigeminal Post‐synaptic Potentials Recorded in Rat Abducens Motoneurons In Vivo
Authors: Ouardouz Mohamed , Durand Jacques
Published: April 2006

The pharmacology of trigeminal excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of the vibrissal pad was investigated in vivo in rat abducens motoneurons using intracellular recordings combined with microionophoretic applications of excitatory amino acid agonists [α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA), NMDA, kainate] and a selective non‐NMDA receptor antagonist (GYKI‐52466). Intravenous applications of GYKI‐52466 were also performed during synaptic and amino acid excitations. GYKI‐52466, applied intravenously or microionophoretically, reversibly antagonized AMPA‐induced depolarizations and trigeminal EPSPs in rat abducens motoneurons without affecting NMDA and kainate responses. The inhibition of AMPA‐induced depolarizations was similar following i.v. and ionophoretic applications of GYKI‐52466. Intravenous applications of GYKI‐52466 (0.3–4 mg/kg) reversibly and dose‐dependently reduced trigeminal EPSPs, which could be totally suppressed at the highest doses of GYKI‐52466 (2–4 mg/kg). The antagonist effect, which developed very quickly, could last several minutes and recovered gradually. The effect of GYKI‐52466 on the EPSPs and AMPA responses were compared in the same motoneurons. The partial inhibition of trigeminal EPSPs during microionophoretic applications of GYKI‐52466 was probably due to the distribution of the synapses in the dendritic arborization of abducens motoneurons. Our results show that AMPA receptors are involved in the generation of trigeminal EPSPs in rat abducens motoneurons in vivo.
Cultured Neurons from Mouse Brain Reproduce the Muscarinic Receptor Profile of Their Tissue of Origin
Authors: André C. , Santos G. Dos , Koulakoff A.
Published: April 2006

These studies investigate the regional variations in the muscarinic acetylcholine receptor (mAChR) profiles in neuron populations of the CNS using primary neuron cultures derived from three areas of the mouse brain–the cerebral hemispheres, the mesencephalon and the medulla‐pons–that have distinct mAChR systems. We first assessed the extent to which neurons reproduced their in vivo properties in culture by monitoring the binding capacity, the pharmacological profiles and the levels of mAChR transcripts in neuron cultures and their tissues of origin. We showed that the primary neuron cultures accumulated mAChRs with initial rates similar to those in vivo, had pharmacological profiles very close to those of their area of origin, and accumulated m1, m2, m3, m4 and m5 receptor transcripts according to patterns resembling those in the tissues. We conclude that most of the characteristics of the mAChRs in a given area are proper to the neuron population of that area, that the pattern is established early in ontogenesis, and that it is reproduced in vitro. We also show that the stimulation of phosphoinositide turnover is mediated by mAChRs with distinct pharmacological profiles in neuron cultures from the three brain areas.
Ultrastructural Evidence for Synaptic Interactions between Thalamocortical Axons and Subplate Neurons
Authors: Herrmann Kathrin , Antonini Antonella , Shatz Carla J.
Published: April 2006

Thalamic axons are known to accumulate in the subplate for a protracted period prior to invading the cortical plate and contacting their ultimate targets, the neurons of layer 4. We have examined the synaptic contacts made by visual and somatosensory thalamic axons during the transition period in which axons begin to leave the subplate and invade the cortical plate in the ferret. We first determined when geniculocortical axons leave the subplate and begin to grow into layer 4 of the visual cortex by injecting 1,1′‐dioctadecyl‐3, 3, 3′, 3′‐tetramethyl indocarbocyanine (Dil) into the lateral geniculate nucleus (LGN). By birth most LGN axons are still confined to the subplate. Over the next 10 days LGN axons grow into layer 4, but many axons retain axonal branches within the subplate. To establish whether thalamic axons make synaptic contacts within the subplate, the anterograde tracer PHA‐L was injected into thalamic nuclei of neonatal ferrets between postnatal day 3 and 12 to label thalamic axons at the electron microscope level. The analysis of the PHA‐L injections confirmed the Dil data regarding the timing of ingrowth of thalamic axons into the cortical plate. At the electron microscope level, PHA‐L‐labelled axons were found to form synaptic contacts in the subplate. The thalamic axon terminals were presynaptic primarily to dendritic shafts and dendritic spines. Between postnatal days 12 and 20 labelled synapses were also observed within layer 4 of the cortex. The ultrastructural appearance of the synapses did not differ significantly in the subplate and cortical plate, with regard to type of postsynaptic profiles, length of postsynaptic density or presynaptic terminal size. These observations provide direct evidence that thalamocortical axons make synaptic contacts with subplate neurons, the only cell type within the subplate possessing mature dendrites and dendritic spines; they also suggest that functional interactions between thalamic axons and subplate neurons could play a role in the establishment of appropriate thalamocortical connections.
Fast Inhibition of Inwardly Rectifying K+ Channels by Multiple Neurotransmitter Receptors in Oligodendroglia
Authors: Karschin Andreas , Wischmeyer Erhard , Davidson Norman , Lester Henry A.
Published: April 2006

An essential function of myelinating oligodendroglia in the mammalian central nervous system is the regulation of extracellular potassium levels by means of a prominent inwardly rectifying K+ current. Cardiac and neuronal K+ inward rectifiers are either activated by hyperpolarizing voltages or controlled by neurotransmitters through the action of receptor‐activated G proteins. Neuromodulation of inward rectifiers has not previously been considered as a way to regulate oligodendrocyte function. Here we report the expression of serotonin, somatostatin and muscarinic acetylcholine G protein‐coupled receptors in rat brain oligodendrocytes. Activation of these receptors leads to pertussis toxin‐sensitive inhibition of inwardly rectifying K+ channels within <1 s. By contrast, in the heart and in neurons, similar pathways activate an inwardly rectifying conductance. Thus, transmitter‐mediated blockade of inward rectifiers appears to be an oligodendrocyte‐specific variation of a common motif for convergent signalling pathways. In vivo, expression of this mechanism, which may be dependent on neuron‐glia signalling, may have a regulatory role in K+ homeostasis during neuron activity in the central nervous system.
The L2/HNK‐1 Carbohydrate is Carried by the Myelin Associated Glycoprotein and Sulphated Glucuronyl Glycolipids in Muscle but not Cutaneous Nerves of Adult Mice
Authors: Löw Karin , Orberger Georg , Schmitz Brigitte , Martini Rudolf , Schachner Melitta
Published: April 2006

We have previously shown that myelinating Schwann cells associated with motor, but not sensory, axons in peripheral nerves of adult mice express the L2/HNK‐1 carbohydrate epitope. This carbohydrate structure carried by glycolipids and neural cell adhesion molecules has been suggested to specifically foster regrowth of motor as opposed to sensory axons after infliction of a lesion. To determine which molecular components may be the carriers of the L2 carbohydrate in motor axon‐associated myelinating Schwann cells, we have isolated the purely sensory, cutaneous branch and the mixed sensory and motor muscle branch of the femoral nerve of adult mice, isolated the myelin fraction thereof and analysed the molecules expressing the L2 carbohydrate by several immunochemical methods. L2 immunoreactivity in myelin of the muscle branch was four to five times higher than that of the cutaneous branch. The 110 kDa L2‐immunoreactive glycoprotein in myelin of the muscle branch, which is not L2‐immunoreactive in the cutaneous branch, was identified as the myelin‐associated glycoprotein by a combination of immunoprecipitation and Western blot analysis. Myelin extraction with organic solvents additionally revealed the two L2‐carrying glycolipids, which amounted to‐40 ng glycolipid/mg dry weight in myelin of the muscle branch, whereas no significant amounts of the L2 glycolipids were found in myelin of the cutaneous branch. These observations suggest an astonishing degree of differential regulation of carbohydrate‐synthesizing activities in myelinating Schwann cells.
Evidence For Two Neurochemical Divisions in the Human Nucleus Accumbens
Authors: Voorn Pieter , Brady Linda S. , Schotte Alain , Berendse Henk W. , Richfield Eric K.
Published: April 2006

The neurochemical anatomy of the human nucleus accumbens was studied by comparing the distributional patterns of [3H]DAMGE (μ opioid receptor), [3H]bremazocine (κ opioid receptor), [3H]SCH‐23390 (D1‐like dopamine receptor), [3H]7‐OH‐DPAT (D3 dopamine receptor) binding, preproenkephalin mRNA and acetylcholinesterase activity in sections of post mortem human striatum. Our results demonstrate the presence of at least two neurochemically distinct divisions within the human nucleus accumbens, which may be homologous to the 'shell’and‘core’divisions of the nucleus as found in the rat.
Ciliary Neurotrophic Factor Enhances the Survival of Purkinje Cells In Vitro
Authors: Lärkfors Lena , Lindsay Ronald M. , Alderson Ralph F.
Published: April 2006

We have examined the effects of ciliary neurotrophic factor (CNTF) on the development of rat Purkinje cells in vitro. Cerebellar cells, derived from embryonic day 16 rat fetuses, were found to respond rapidly to CNTF treatment by induction of c‐Fos protein, such that 40% of the cells were immunopositive after 60 min. Treatment with low doses of CNTF (10‐100 pg/ml) for 8 days resulted in an ∼ 1.6‐fold increase in the number of Purkinje cells, identified by immunohistochemical staining for calbindin. Immunohistochemical staining for other Purkinje cell markers‐cyclic‐GMP‐dependent protein kinase and the low‐affinity nerve growth factor receptor‐verified increased Purkinje cell survival following CNTF treatment. In addition, CNTF increased specific high‐affinity GABA uptake by 45%, and the number of GABAergic neurons by 70%. A maximal increase in the number of Purkinje cells and GABA‐uptake was only achieved if CNTF was added within 48 h of plating the cells, further suggesting that CNTF enhances Purkinje cell survival in vitro. These results taken together strongly support a direct effect of CNTF in promoting the survival of Purkinje cells and possibly other GABAergic cerebellar neurons.
Long‐term Depression in the Hippocampal CA1 Region is Associated with Equal Changes in AMPA and NMDA Receptor‐mediated Synaptic Potentials
Authors: Xiao M.‐Y. , Wigström H. , Gustafsson B.
Published: April 2006

In the CA1 hippocampal region low‐frequency (1‐2 Hz) afferent activation leads to a long‐term depression of excitatory synaptic potentials that is induced by calcium influx through postsynaptic N‐methyl‐d‐aspartate receptor channels. In the present experiments using 2‐ to 3‐week‐old rats, long‐term depressions of field excitatory postsynaptic potentials mediated by amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) and by N‐methyl‐d‐aspartate receptor channels were examined in parallel, using a perfusion solution containing low concentrations of an AMPA receptor antagonist and of magnesium (0.1 mM). These experiments revealed that long‐term depression was associated with equal relative changes in the two components of the field potential, compatible with a presynaptic location of the expression mechanism for the long‐term depression.
Effects of Monoamines on Transmission from Group II Muscle Afferents in Sacral Segments in the Cat
Authors: Jankowska E. , Läckberg Z. Szabo , Dyrehag L. E.
Published: April 2006

The effects of one 5‐HT1A serotonin agonist (8‐OH‐DPAT) and of two α2 noradrenaline agonists (tizanidine and B‐HT 933) were tested on the transmission between group II muscle afferents and spinal neurons in the sacral segments of the spinal cord in the cat. These agonists have previously been found to depress transmission from group II muscle afferents either in the dorsal horn or in the intermediate zone of midlumbar segments, and this study addressed the question of whether their actions in the sacral segments are similarly selective. The drugs were applied ionophoretically and their effects were tested on field potentials evoked from group II muscle afferents. As judged by changes in the amplitude of the early components of these field potentials, the transmission is effectively depressed by the serotonin agonist (to 56 ± 26% after 2 min of ionophoresis of 8‐OH‐DPAT) but not by the noradrenaline agonists (to 97 ± 12% after 6 min of ionophoresis of B‐HT 933 and to 95 ± 17% after 6 min of ionophoresis of tizanidine). These data suggest that transmission from group II muscle spindle afferents in the sacral segments is under control of serotonin releasing neurons, as in the dorsal horn of midlumbar segments, but leave open the question of the similarities or differences in the mechanisms (pre‐and/or postsynaptic) of this control.
Expression of NMDA and High‐affinity Kainate Receptor Subunit mRNAs in the Adult Rat Retina
Authors: Brandstätter J. H. , Hartveit E. , Sassoè‐Pognetto M. , Wässle H.
Published: April 2006

The expression patterns of nine genes encoding theN‐methyl‐d‐aspartate (NMDA) receptor subunits NR1 and NR2A, NR2B, NR2C and NR2D, and the high‐affinity kainate receptor subunits KA1, KA2, GluR6 and GluR7, were studied in the adult rat retina byin situhybridization. Hybridization with [35S]dATP‐labelled oligonucleotide probes revealed the expression of four of the NMDA receptor subunits (NR1, NR2A, NR2B and NR2C) and three of the high‐affinity kainate receptor subunits (KA2, GluR6 and GluR7) in the retina. The NMDA receptor subunit NR2D and the high‐affinity kainate receptor subunit KA1 could not be detected. In the ganglion cell layer, virtually every ganglion cell or displaced amacrine cell expressed the receptor subunits NR1, NR2A, NR2B, NR2C, KA2 and GluR7. The GluR6 subunit was expressed in a more restricted manner in the ganglion cell layer. In the inner nuclear layer, the receptor subunits NR1 and KA2 were homogeneously distributed, and therefore are most likely expressed by all cell types in this layer. The GluR6, NR2A, NR2B and NR2C subunits were expressed by subsets of amacrine cells. Labelling for NR2C was also found above the middle of the inner nuclear layer, corresponding to the location of bipolar cell somata. The GluR7 subunit was expressed by most amacrine and bipolar cells. These findings suggest that NMDA and high‐affinity kainate receptor subunits could be present at a majority of glutamatergic retinal synapses.
Rat Hippocampal Kindling Induces Changes in the Glutamate Receptor mRNA Expression Patterns in Dentate Granule Neurons
Authors: Kamphuis W. , de Rijk T. C. , Talamini L. M. , Lopes da Silva F. H.
Published: April 2006

The expression level of the mRNAs encoding the Flip and Flop versions of the AMPA‐selective glutamate receptor subunits A, B, C and D was studied usingin situhybridization in the hippocampus of rats kindled by Schaffer collateral/commissural fibre stimulation. The expression levels of the Flip variant of GluR‐A, B and C mRNAs were bilaterally enhanced in the dentate granule neurons of fully kindled animals 24 h after the last seizure. These changes were already observed after the sixth kindling stimulation (preconvulsive‐stage), but not after a single afterdischarge. Four weeks after the last seizure, when the animals were still hypersensitive to kindling stimulations, only GluR‐A Flip expression was enhanced. These results suggest that kindling epileptogenesis is accompanied by an increased number and enhanced sensitivity of the expressed AMPA type glutamate receptors in the fascia dentata, leading to an enhanced excitatory synaptic transmission which may contribute to the process of kindling epileptogenesis.
Neurotrophic Factor Receptors and Their Signal Transduction Capabilities in Rat Astrocytes
Authors: Rudge John S. , Li Yanping , Pasnikowski Elizabeth M. , Mattsson Karen , Pan Li , Yancopoulos George D. , Wiegand Stanley J. , Lindsay Ronald M. , Ip Nancy Y.
Published: April 2006

Until recently, astrocytes were not considered as sites for neurotrophic factor action. We show here that, both in vivo and in vitro, astrocytes express receptors for two separate families of neurotrophic factors. In the intact adult rat CNS, astrocytes express the extracellular domain of the neurotrophin receptor TrkB and, in a more restricted population, the low‐affinity nerve growth factor receptor p75LNGFR. In the lesioned CNS, expression of the alpha component of the receptor for ciliary neurotrophic factor (CNTFRα) switches from a purely neuronal localization to cells in the glial scar at the edge of the wound. Using cultured hippocampal astrocytes as a model to address the functional status of these receptors, we have found only the truncated forms of TrkB and TrkC, which are incapable of signal transduction as measured by protein tyrosine phosphorylation or immediate early gene induction. In contrast, a fully functional CNTF receptor complex capable of signal transduction is present on cultured astrocytes. Thus, the neurotrophin receptors may act primarily to sequester or present the neurotrophins, whereas in the case of CNTF a functional response can be initiated within the astrocyte.
Modular Organization of Human Extrastriate Visual Cortex: Evidence from Cytochrome Oxidase Pattern in Normal and Macular Degeneration Cases
Authors: Clarke Stephanie
Published: April 2006

The human extrastriate occipital cortex contains several visual areas that are probably analogues of macaque areas V2, V3, VP, V4 and V5. Tracing of callosal connections has led to the anatomical identification of these areas and to the characterization of some of them by cyto‐ and myeloarchitecture (Clarke and Miklossy, 1990). The pattern of cytochrome oxidase activity in these visual areas is now described in a normal case and in a case of age‐related bilateral macular degeneration. In normal cortex, the laminar distribution of cytochrome oxidase activity was similar in V2, V3, VP, V4 and V5; a prominent dark band covered most of layers III and IV, and its upper and lower limits were gradual. In V2, V3, V4 and V5 but not VP, layer II tended to be darker than the infragranular layers. The overall intensity of the staining varied between areas: VP was very light, V2, V3 and V4 were darker, and V5 was very dark. A different, two‐band pattern of cytochrome oxidase activity was found in a restricted region of the posterosuperior precuneus. The bilateral age‐related macular degeneration had led to a great loss of ganglion cells in the central, but not in the peripheral retinae. The central representation in the lateral geniculate nuclei showed abnormally weak staining for cytochrome oxidase, particularly in the parvocellular layers. In the cortex, the contrast between lightly and darkly stained regions was greater than in the normal case. In particular, V5 was very heavily stained, and in V1 and V2 there were two different types of dark stripes that may represent compartments driven predominantly by the magnocellular system.
Antisera to Glutathione: Characterization and Immunocytochemical Application to the Rat Cerebellum
Authors: Hjelle Ole P. , Chaudhry Farrukh A. , Ottersen Ole P.
Published: April 2006

Rabbits were immunized with reduced glutathione (γ‐glutamyl‐cysteinyl‐glycine) coupled to bovine serum albumin by glutaraldehyde or a mixture of glutaraldehyde and formaldehyde. The antisera that were formed were tested qualitatively, by screening them against more than 50 amino acids and peptide conjugates that had been immobilized on cellulose discs (spot test), and quantitatively, by immunogold analysis of test conjugates that had been embedded in an epoxy resin. It was shown that the antisera selectively recognized the reduced and oxidized forms of glutathione and that they did not exhibit any significant crossreactivity with glutamate, cysteine, glycine, γ‐glutamyl‐cysteine or cysteinyl‐glycine. Immunocytochemistry of Vibratome sections of rat cerebellum suggested that glutathione occurs in glial cells as well as in neurons. This was confirmed by electron microscopic, immunogold cytochemistry of tissue from rat cerebellum that had been freeze‐substituted and embedded in Lowicryl under low temperature. Gold particles were concentrated over Golgi epithelial cells and perivascular glial processes, but also occurred over several types of neuronal profile including Purkinje and granule cell bodies, and mossy fibre terminals. At the subcellular level, glutathione‐like immunoreactivity was found in the cytoplasmic matrix, mitochondria and nuclei. The immunolabelling intensity was strongly reduced in animals that had been pretreated with buthionine sulphoximine, which is known to depress the level of glutathione by inhibiting γ‐glutamyl‐cysteine synthetase. The availability of antisera to glutathione is likely to further our understanding of the physiological and pathophysiological roles of this tripeptide.
Selective Allocation of GABAA Receptors Containing the α1 Subunit to Neurochemically Distinct Subpopulations of Rat Hippocampal Interneurons
Authors: Gao B. , Fritschy J. M.
Published: April 2006

The identification of a large variety of GABAA receptor subunits by molecular cloning suggests the existence of multiple receptor subtypes differing in localization and functional properties. In the present study we analysed immunohistochemically the cellular distribution of GABAA receptors containing the α1 subunit in the rat hippocampus with a subunit‐specific antiserum. Prominent staining of numerous interneurons was evident in Ammon's horn and the dentate gyrus, which contrasted with moderate and diffuse immunoreactivity in the dendritic layers of pyramidal and granule cells. Double immunofluorescence staining with antibodies to GABA revealed that a subset of GABAergic neurons in the hippocampus were immunoreactive for the α1 subunit. To determine whether these cells represent distinct subpopulations of interneurons, we analysed the co‐localization of the GABAA receptor α1 subunit with selective markers of hippocampal interneurons (selected calcium‐binding proteins and neuropeptides). In both Ammon's horn and the dentate gyrus, all parvalbumin‐positive neurons and 50% of calretinin‐positive neurons were double‐labelled, whereas interneurons containing calbindin‐D28k were devoid of α1 subunit staining. Similarly, most neurons positive for neuropeptide Y and a subset of somatostatin‐positive cells were double‐labelled, in contrast to cholecystokinin‐ and vasoactive intestinal peptide‐containing cells, which lacked the α1 subunit staining. These results demonstrate cell‐specific expression of GABAA receptors containing the α1 subunit among subsets of hippocampal interneurons, pointing to a pronounced functional specialization of these cells. Furthermore, the prominent expression of GABAA receptors by interneurons suggests that disinhibition may be of major functional relevance in regulating the balance between excitation and inhibition in hippocampal circuits.
Inhibitory Effects of L‐Glutamate on Central Processes of Crustacean Leg Motoneurons
Authors: Pearlstein E. , Marchand A. R. , Clarac F.
Published: April 2006

In crustaceans, glutamatergic excitation at the neuromuscular synapse has been extensively studied. Fewer reports exist of the central and possibly inhibitory actions of glutamate on neurons. The present study analyses the response of intracellularly identified motoneurons, which innervate the proximal leg muscles, to local glutamate pressure applications in the neuropil, in an in vitro thoracic preparation of the crayfish Procambarus clarkii. L‐Glutamate application always inhibited motoneuron activity, with a decrease in input resistance. The resulting depolarization or hyperpolarization could usually be reversed within 10 mV of the resting potential. The response persisted in neurons pharmacologically isolated with Cd2+ or tetrodotoxin. The reversal potential of the response to glutamate was displaced in a low‐chloride solution. Similar responses were obtained with GABA. Application of GABA blocked the glutamate response in a competitive manner. Both responses were suppressed by β‐guanidino‐propionic acid, a competitive antagonist for GABA receptors. This indicates that glutamate activates a chloride‐GABA receptor‐channel. Micromolar concentrations of picrotoxin reduced both the L‐glutamate and the GABA inhibitory responses, thereby unmasking a smaller, picrotoxin‐resistant effect of glutamate (but not of GABA), which was excitatory and sensitive to 6,7‐dinitroquinoxaline‐2,3‐dione (DNQX). These results suggest dual and opposite roles for motoneuron glutamatergic connections–a peripheral (well known) net excitatory one and a central net inhibitory one. Direct inhibition of motoneurons by L‐glutamatergic neurons is to be expected.
Learning‐related Alterations in the Visual Responsiveness of Neurons in a Memory System of the Chick Brain
Authors: Brown M. W. , Horn G.
Published: April 2006

The intermediate and medial hyperstriatum ventrale (IMHV) of the chick brain is known to be essential for the learning process of imprinting. The activity of neurons was recorded from the left IMHV of 2‐day‐old unanaesthetized chicks while the chicks were free to move in a running wheel. The chicks were either raised in complete darkness or visually trained (imprinted) with a set duration of exposure to a visual image. The first group of these birds was trained by exposure for 100 min to a rotating red box and the second was trained by similar exposure to a rotating blue cylinder. A third group was left untrained. Training more than doubled the proportion of sites that responded to the stimulus used to train the bird, relative to the proportion of sites responsive to the other stimulus and to the proportion of sites responsive in the untrained birds; the learning‐related increase was selective and highly significant. Behavioural monitoring indicated that the enhanced responsiveness could not be explained by overt differences in the alertness, attentiveness or movements of the birds. No significant effect of training was found on the proportion of sites responsive to a rotating stuffed jungle fowl or to the sound of a maternal call. The response at certain sites selectively signalled the presence of the training stimulus, while at others the response showed generalization across stimulus shape or colour. There was a non‐specific effect of training upon the pattern of spontaneous discharges of the neurons: the numbers of spikes occurring in clusters (bursts) was significantly reduced in trained birds compared with the dark reared controls.
Naloxone Ameliorates the Learning Deficit Induced by Pentylenetetrazol Kindling in Rats
Authors: Becker Axel , Grecksch Gisela , Brosz Mathias
Published: April 2006

Endogenous opioid peptides modulate and regulate processes of central excitability. Furthermore, opioids are thought to interfere with processes of learning and memory storage. In order to study the effects of endogenous opioids on both processes we injected in the course of development of pentylenetetrazol kindling the opiate receptor antagonist naloxone, and tested the animals afterwards in a shuttle‐box task. It was found that naloxone pretreatment had dissociative effects. There was no effect on seizure outcome, whereas the learning deficit was ameliorated in the kindled group. The data suggest that endogenous opioid peptides contribute to the learning deficit found in pentylenetetrazol‐kindled rats.
Homotypic and Heterotypic Coupling Mediated by Gap Junctions During Glial Cell Differentiation In Vitro
Authors: Venance L. , Cordier J. , Monge M. , Zalc B. , Glowinski J. , Giaume C.
Published: April 2006

Intercellular communication mediated by gap junctions was investigated during oligodendrocyte differentiation in primary and secondary cell cultures from newborn and adult rats. Two types of communication were considered: ionic coupling and dye‐coupling between similar oligodendrocytes selected at the same stage of differentiation (homotypic) and dye‐coupling between oligodendrocytes and astrocytes (heterotypic), Intercellular diffusion of fluorescent probes and double whole‐cell recordings were used to test the incidence of dye and ionic communication respectively. Progenitor cells, identified with A265 antibodies, were characterized by the absence of ionic and dye‐coupling, whereas oligodendrocytes, identified with galactosylceramide antibodies, exhibited both types of communication. This homotypic coupling was inhibited by various uncoupling agents, but unaffected by treatments which increased the intracellular concentration of CAMP. In cocultures of astrocytes and oligodendrocytes, Lucifer yellow and sulphorhodamine B were exchanged in both directions. This heterotypic dye‐coupling, which could be blocked by octanol, first appeared after 3 weeks in culture and increased to an incidence of 25% after 6 weeks, a developmental pattern comparable to homotypic dye‐coupling between oligodendrocytes. In contrast, during the same period, progenitors and microglia were never observed to be dye‐coupled with astrocytes.
Properties of the Hyperpolarization‐activated Cation Current lh in Rat Midbrain Dopaminergic Neurons
Authors: Mercuri N. B. , Bonci A. , Calabresi P. , Stefani A. , Bernardi G.
Published: April 2006

abstract

Intracellular electrophysiological recordings in current‐ and voltage‐clamp mode were obtained from dopaminergic neurons of the rat mesencephalon in an in vitro slice preparation. In current‐clamp mode, a time‐dependent anomalous rectification (TDR) of the membrane was observed in response to hyperpolarizing current pulses. In single‐electrode voltage‐clamp mode, a slowly developing inward current (lh) underlying the TDR was studied by hyperpolarizing voltage commands from a holding potential of ‐50 to ‐60 mV. lh started to be activated at ‐69 mV, was fully activated at ‐129 to ‐141 mV, with half‐maximal activation at ‐87 mV, and showed no inactivation with time. The time course of development of Ih followed a single exponential, and its time constant was voltage‐dependent. At ‐81 mV, lh activated with a time constant of 379 2 47.6 ms, whereas at ‐129 mV lh activated with a time constant of 65 ? 2.2 ms. Its estimated reversal potential was ‐35 ± 4 mV. Raising the extracellular concentration of K+ from 2.5 to 6.5 and to 12.5 mM increased the amplitude of lh while reducing the extracellular concentration of Na+ from 153.2 to 27.2 mM caused a reduction in amplitude of lh. Bath application of caesium (1–5 mM) reversibly reduced or blocked the TDR/lh. Perfusion of tetrodotoxin (0.5–1 μM), tetraethylammonium (10–20 mM) or barium (0.3–2 mM) did not significantly affect lh. lh was also present in cells impaled with CsCI‐filled electrodes. When lh was substantially reduced by extracellular caesium (1 mM) the firing rate of the dopaminergic cells, which consisted of a spontaneous pacemaker discharge of action potentials, was not clearly changed. In addition, the holding current in voltage‐clamp experiments at ‐50 to ‐60 mV was not affected by 1 mM caesium. We conclude that although the lh current is a typical feature of the dopaminergic neurons, it is neither a significant factor underlying the spontaneous pacemaker activity nor does it contribute substantially to the setting of the normal resting potential level of the membrane. On the other hand, since lh starts at voltages lower than or equal to ‐69 mV (below firing threshold), it may play a modulatory role in the cell's excitability by limiting the amplitude and duration of any prolonged hyperpolarizing events in the dopaminergic cells.
Shape and Spatial Distribution of Receptive Fields and Antagonistic Motion Surrounds in the Middle Temporal Area (V5) of the Macaque
Authors: Raiguel S. , Van Hulle M. M. , Xiao D.‐K. , Marcar V. L. , Orban G. A.
Published: April 2006

The spatial organization of receptive fields in the middle temporal (MT) area of anaesthetized and paralysed macaque monkeys was studied. In all, 288 neurons were successfully recorded. The size and shape of the receptive field (RF) was mapped with small patches of translating random dots and the resulting data were fitted with a generalized Gaussian. Results show that the RF area increases with eccentricity, and is larger in lamina 5 than in other layers. Most of these RFs are elongated, and the axis of elongation tends to be orthogonal to the preferred direction of motion. The direction selectivity is maintained in all positions in the RF, but layer 5 cells are less direction‐selective than cells in other layers. In a second series of experiments, radial dimensions of the classical RF and the antagonistic surround were estimated from area summation tests. These data were fitted with the difference of the integrals of two Gaussians. Surrounds were weakest in layer 4 and strongest in layer 2. Optimal stimulus diameters, also estimated from the area summation curve, were larger in the infragranular layers than in the other layers. The maximum sensitivity of the surround was clearly displaced from the classical RF (CRF) centre, indicating that the surround is not concentric with the CRF. This radial offset and the extent of the surround were largest in layers 2 and 5 and smallest in 3a. The extent of the surround half‐height equalled, on average, 3–4 times that of the CRF. These results suggest that antagonistic surrounds are constructed in MT, probably through horizontal connections, and that a strong vertical organization exists in area MT, as has been shown for V1.
Native Nicotinic Acetylcholine Receptors in Human Imr32 Neuroblastoma Cells: Functional, Immunological and Pharmacological Properties
Authors: Gotti C. , Briscini L. , Verderio C. , Oortgiesen M. , Balestra B. , Clementi F.
Published: April 2006

IMR32 cells express two classes of surface nicotinic receptors: those labelled with high affinity by [125I]neuronal toxin, and those labelled by [125Iα‐bungarotoxin. Whole‐cell patch‐clamp recordings indicate that both classes of receptor are able to elicit inward currents that are totally blocked by d‐tubocurarine but only partially blocked by α‐bungarotoxin. In IMR32 cells, nicotine induces an increase in the intracellular level of free Ca2+. This increase, which is also completely blocked by d‐tubocurarine and only partially blocked by α‐bungarotoxin and Cd2+, is due to extracellular calcium influx through both the nicotinic receptors and the voltage‐activated Ca2+ channels. By using subunit‐specific polyclonal antibodies, we have demonstrated that the α‐bungarotoxin receptors contain the α7 subunit, but none of the other subunits whose transcripts are present in IMR32 cells. The pharmacological profile of these human α7‐containing α‐bungarotoxin receptors is similar to that observed in the native chick α7 receptor, but there are also some species‐specific differences.
The Double‐ticker: An Improved Fast Drug‐application System Reveals Desensitization of the Glutamate Channel from a Closed State
Authors: Tour O. , Parnas H. , Parnas I.
Published: April 2006

The present study describes a modification of the fast drug‐application technique (ticker) which combines two fast‐application systems, ‘the double‐ticker’. With the double‐ticker, drugs can be applied to excised patches from either one of the tickers permitting switching among three different solutions in the sub‐millisecond range. We made use of this advantageous feature of the double‐ticker to study two aspects of the glutamate receptor channel in crayfish muscle. The first concerns revealing the number of glutamate binding sites from measurements of a dose‐response relation (2–3 sites). The other relates to the state from which the receptor undergoes desensitization. For the quisqualate‐sensitive glutamate receptor desensitization occurs from a closed state. This is in addition to desensitization from an open state.
Epidermal Growth Factor Prevents Oxygen‐triggered Apoptosis and Induces Sustained Signalling in Cultured Rat Cerebral Cortical Neurons
Authors: Yamada Masashi , Enokido Yasushi , Ikeuchi Toshihiko , Hatanaka Hiroshi
Published: April 2006

Epidermal growth factor (EGF), a conventional mitogenic factor, acts as a neurotrophic factor on several types of neurons in the central nervous system. We found that EGF prevented the death of rat cerebral cortical neurons cultured in a 50% oxygen atmosphere. This high‐oxygen‐triggered cell death showed features of apoptotic cell death, which was blocked by inhibitors of RNA or protein synthesis. EGF prevented the oxygen‐induced death of the cultured cortical neurons in a dose‐dependent manner. Basic fibroblast growth factor (bFGF) also prevented this cell death, although there was no apparent additive effect of EGF and bFGF. Among the cultured cortical neurons, we observed neurons possessing the EGF receptor and cells expressing c‐Fos protein in response to EGF. The cortical neurons were cultured in the presence of cytosine arabinoside, and the number of glial fibrillary acidic protein‐positive astroglial cells was >0.5% of that of the corresponding microtubule‐associated protein 2‐positive neurons. Therefore, the effect of EGF on the cultured cortical neurons is thought to be due to a direct action. We also examined EGF‐induced signalling in the cultured cortical neurons. We found that EGF induced the sustained tyrosine phosphorylation of the EGF receptor and sustained the activation of mitogen‐activated protein kinase in the cultured cortical neurons. We suggest that EGF may exert the survival effect through the prolonged activation of the EGF signalling.
Dopamine‐Glutamate‐GABA Interactions and Ageing: Studies in the Striatum of the Conscious Rat
Authors: Porras Alberto , Mora Francisco
Published: April 2006

The effects of apomorphine, a D1–D2 dopamine receptor agonist, on the extracellular concentrations of glutamate and GABA were investigated in the striatum of young, middle‐aged and aged rats. In vivo intracerebral perfusions were undertaken in the conscious rat using a concentric push‐pull cannula system. Amino acid concentrations in samples were determined by HPLC with fluorometric detection. Apomorphine produced a concentration‐related rise in striatal glutamate and GABA concentrations in young rats. Maximal increases were obtained at 20 μM apomorphine, and concentrations reached 184 and 191% of the basal value for glutamate and GABA respectively. Apomorphine failed to produce similar increases in glutamate concentration in middle‐aged and aged rats. Apomorphine, at 10 μM, also failed to produce an increase in GABA concentration in the aged rat. However, at 20 μM apomorphine produced increases in GABA concentration in middle‐aged and aged rats similar to those produced in young rats. These data are indicative of a change in threshold for GABA release induced by dopamine receptor stimulation in the aged rat. These results indicate that an interaction among dopamine, glutamate and GABA exists in the striatum of the rat, and that this type of interaction deteriorates with age.
Inertial, Substratal and Landmark Cue Control of Hippocampal CA1 Place Cell Activity
Authors: Wiener Sidney I. , Korshunov Victor A. , Garcia René , Berthoz Alain
Published: April 2006

Hippocampal ‘place cells’ discharge when a rat occupies a location that is fixed in relation to environmental landmarks. A principal goal of this study was to determine whether hippocampal place cell activity could be influenced by inertial cues. Water‐deprived rats were trained in a square‐walled open field in a dark room. The behavioural task required alternating visits to water reservoirs in the centre and in the four corners of the arena. The rat and arena were rotated in total darkness through ±90, 180 or 270°. The next water reward was then presented in the corner at the same position relative to the outside room as before the rotation. A cue card was later illuminated in this corner as a visual cue for the extra‐arena (room) reference frame. Fifteen out of 97 recorded hippocampal CA1 complex spike cells had spatially selective discharges in non‐central parts of the arena. After arena rotations, the firing fields of three units shifted between corners of the arena to maintain a fixed orientation relative to the room. This indicates that the hippocampus updated its representation of the position and heading direction of the rat using vestibular‐derived inputs concerning rotation angle. Other spatially selective discharges were guided to landmark cues (cue card or position of the reward: two units) or arena‐locked ‘substratal’ cues (eight units). In six cells, place cell activity suddenly ceased or appeared following rotations. These results provide evidence for contributions of inertial as well as substratal and landmark information to hippocampal spatial representations.
Targeted Delivery of Nerve Growth Factor via Fibronectin Conduits Assists Nerve Regeneration in Control and Diabetic Rats
Authors: Whitworth Ian H. , Terenghi Giorgio , Green Colin J. , Brown Robert A. , Stevens Elizabeth , Tomlinson David R.
Published: April 2006

This study examined the influence of fibronectin conduits joining two halves of a sectioned sciatic nerve, with and without preimpregnation with nerve growth factor, on regeneration in rats with streptozotocin‐induced diabetes mellitus. Regeneration, measured morphometrically in fibres containing immunoreactivity to calcitonin gene‐related peptide (CGRP) and GAP‐43, was significantly less (P < 0.0001 for all comparisons) in diabetic rats with fibronectin mat grafts without nerve growth factor compared to similarly treated controls. Regeneration distances in diabetic rats were reduced to 43% (CGRP‐reactive fibres) and 44% (GAP‐43‐reactive fibres) of controls, and the total amounts of immunoreactivities in the conduits were also reduced, though by lesser amounts (55 and 61% of controls respectively). Impregnation of the conduits with nerve growth factor before implantation increased the distance and amounts of regenerating immunoreactivity in both control and diabetic rats for both CGRP and GAP‐43, such that these regeneration parameters were similar in nerve growth factor‐treated diabetic rats to those in control rats implanted with untreated fibronectin mat conduits. These findings implicate impaired neurotrophic support in the defective regeneration characteristic of diabetic neuropathy.
The Nitric Oxide/cGMP System in the Antennal Lobe of Apis mellifera is Implicated in Integrative Processing of Chemosensory Stimuli
Authors: Müller Uli , Hildebrandt Herbert
Published: April 2006

The high concentration and the localization of nitric oxide synthase in the olfactory system of both vertebrates and invertebrates suggest that the diffusible messenger nitric oxide plays a central role in the processing of chemosensory information. This paper describes the nitric oxide releasing system in the antenna and the antennal lobes of Apis mellifera using the NADPH diaphorase technique, and analyses the contribution of the nitric oxide system in the neuronal processing of chemosensory signals using a behavioural assay in vivo. In the antenna the strongest NADPH diaphorase staining is found in non‐neuronal auxiliary and/or epithelial cells, while the sensory cells and the antennal nerve are stained at a low level. At the major site of chemosensory signal integration, the antennal lobes, the highest nitric oxide synthase activity is located in the glomeruli, which are ideally suited to act as diffusion compartments. We demonstrate that inhibition of nitric oxide synthase in the antennal lobes specifically interferes with neuronal processing of repetitive chemosensory stimuli but does not affect the response to single stimuli, and is independent of parameters such as satiation level, stimulus strength, interstimulus interval and duration of sensory stimuli. Since inhibition of the soluble guanylate cyclase, a major target of nitric oxide, also particularly affects the adaptive component, the physiological effects of nitric oxide appear to be mediated by the action of cGMP. These findings suggest that the nitric oxide/cGMP system in the antennal lobes is a component of the molecular machinery involved in adaptive and/or integrative mechanisms during chemosensory information processing in vivo.