bluuebunny/crossref_metadata_2025_split huggingface dataset:
Serotonergic modulation of the responses to excitatory amino acids of rat dorsal horn neurons in vitro: implications for somatosensory transmission
Authors: Lopez‐Garcia  
Published: March 2003

AbstractSerotonin (5‐HT) is one of the major transmitters involved in supraspinal control of somatic sensation and nociception. The aim of the present study was to investigate if the 5‐HT‐induced modulation of sensory transmission in the dorsal horn could be due to regulation of neuronal responses to excitatory amino acids. Experiments were performed in an in vitro preparation of the young rat spinal cord. Responses to dorsal root stimulation (DR‐EPSP) and to droplet application of N‐methyl‐d‐aspartic acid (NMDA) and α‐amino‐2,3‐dihydro‐5‐methyl‐3‐oxo‐4‐isoxazolepropanoic acid (AMPA) were obtained by means of intracellular recordings of dorsal horn neurons. Bath applications of 5‐HT (50 μm) generally caused reductions in amplitude and integrated area of DR‐EPSPs and of responses to NMDA but the responses to AMPA were unaltered. A linear correlation was found between the effects of 5‐HT on the DR‐EPSP and on the NMDA response measured as percentage change in amplitude (r2 = 0.45;P≤ 0.01) and integrated area (r2 = 0.77;P≤ 0.001). The NMDA receptor antagonist d‐AP5 (50 μm) completely abolished NMDA responses and caused a depression of the DR‐EPSP similar to that of 5‐HT. The 5‐HT1 receptor agonist 5‐carboxamidotryptamine (5‐CT; 1 μm) mimicked the depressant effects of 5‐HT but had a stronger depressant action on the DR‐EPSP than 5‐HT. The depression of NMDA responses induced by 5‐HT and 5‐CT was tetrodotoxin (1 μm) resistant. It is concluded that 5‐HT‐induced depression of NMDA responses explains partially the depressant action of 5‐HT on dorsal horn synaptic transmission activating a postsynaptic site sensitive to 5‐CT. The possible activation of coadjuvant mechanisms is discussed.
Hyperpolarizing after‐potentials regulate generation of long‐duration plateau depolarizations in rat paraventricular nucleus neurons
Authors: Bains Jaideep S. , Ferguson Alastair V. 
Published: March 2003

AbstractActivation of N‐methyl‐d‐aspartate (NMDA) receptors in a population of neurons of the paraventricular nucleus (PVN) results in long‐duration plateau depolarizations during which the membrane rapidly depolarizes, reaching a stable plateau near −20 mV. These responses were observed in 29% of the Type II PVN neurons tested with 1 μm NMDA agonist (n = 84). The stable plateau phase is characterized by an increase in ionic conductance, from 1.19 ± 0.11 nS to 5.24 ± 2.17 nS (n = 5). Bath application of tetrodotoxin (n = 4) or alternatively inclusion of QX‐314 in the pipette solution (n = 3) prevented the generation of these events. The remaining cells tested (n = 56) also depolarized in response to NMDA agonist, but long duration plateau depolarizations were not observed.Previous evidence from hypothalamic cultures has demonstrated synaptically driven plateau potentials following the blockade of repolarizing conductances. Pharmacological blockade of the post‐spike hyperpolarizing afterpotential with 4‐aminopyridine (200 μm), in cells that did not generate plateaux, resulted in the observance of long duration plateau depolarizations in response to a subsequent application of NMDA agonist (n = 4). Our results demonstrate that this 4‐aminopyridine‐sensitive ionic conductance plays a critical role in determining whether a cell will depolarize for a prolonged duration in response to NMDA receptor activation. As a prolonged depolarization of the postsynaptic membrane and accompanying membrane permeability changes are essential for neurotoxicity, these findings provide evidence for a potential protective mechanism that depends solely on the ability of the cell, through its ionic conductances, to control imposed changes in membrane potential.
A phenytoin‐sensitive cationic current participates in generating the afterdepolarization and burst afterdischarge in rat neocortical pyramidal cells
Authors: Kang Youngnam , Okada Takashi , Ohmori Harunori 
Published: March 2003

AbstractWe report here on the ionic mechanisms underlying the depolarizing afterpotential (DAP) in neocortical pyramidal cells, with special interest in those underlying the burst afterdischarge. Injections of short depolarizing current pulses under whole‐cell current clamp with a CsCl‐based internal medium generated, in most pyramidal cells, a single action potential with a plateau phase (plateau‐AP), followed by a slowly decaying DAP both in the absence and presence of TTX. Under voltage‐clamp, the same cells displayed a slow tail current (tail‐I) at the offset of depolarization. When intracellular free Ca2+ was chelated with 10 mm BAPTA or when extracellular Ca2+ was replaced with equimolar Ba2+, neither the slow DAP nor the slow tail‐I was observed. Extracellular application of Co2+ or Cd2+ reduced Ca2+ currents and the slow tail‐I. Cation substitution experiments revealed that the channel generating the slow tail‐I was permeable to K+ and Cs+ more than to Na+ (PK≈PCs > PNa > PNMDG≈PTEA). The cationic slow tail‐I was not reduced by applying antagonists of the metabotropic glutamate receptor (MCPG, 1 mm) and the muscarinic receptor (atropine, 1–10 μm). Thus, the slow DAP was produced by activation of the cationic channel whose gating is solely dependent on [Ca2+]i. An increase in [K+]o from 3 to 6 or 9 mm enhanced the slow DAP, and resulted in a generation of burst afterdischarges. An anticonvulsant, phenytoin (PT; 1–10 μm) suppressed the slow DAP while enhancing the plateau‐AP in the presence of TTX, most likely by blocking the cationic channel.
Presynaptic and postsynaptic localization of GABAB receptors in neurons of the rat retina
Authors: Koulen Peter , Malitschek Barbara , Kuhn Rainer , Bettler Bernhard , Wässle Heinz , Brandstätter Johann Helmut 
Published: March 2003

AbstractThe recently cloned GABAB receptors were localized in rat retina using specific antisera. Immunolabelling was detected in the inner and outer plexiform layers (IPL, OPL), and in a number of cells in the inner nuclear layer and the ganglion cell layer. Double‐labelling experiments for GABA (γ‐aminobutyric acid) and GABAB receptors, respectively, demonstrated a co‐localization in horizontal cells and amacrine cells. Electron microscopy showed that GABAB receptors of the OPL were localized presynaptically in horizontal cell processes invaginating into photoreceptor terminals. In the IPL, GABAB receptors were present presynaptically in amacrine cells, as well as postsynaptically in amacrine and ganglion cells. The postnatal development of GABAB receptors was also studied, and immunoreactivity was observed well before morphological and synaptic differentiation of retinal neurons. The present results suggest a presynaptic (autoreceptor) as well as postsynaptic role for GABAB receptors. In addition, the extrasynaptic localization of GABAB receptors could indicate a paracrine function of GABA in the retina.
NT‐4/5 and LIF, but not NT‐3 and BDNF, promote NPY mRNA expression in cortical neurons in the absence of spontaneous bioelectrical activity
Authors: Wirth Marcus J. , Obst Kirstin , Wahle Petra 
Published: March 2003

AbstractEpigenetic factors are known to influence the differentiation of neocortical neurons. The present study analyses the role of spontaneous bioelectrical activity (SBA) and neurotrophic factors on the expression of neuropeptide Y (NPY) in rat visual cortical neurons using organotypic monocultures prepared from newborn animals and in situ hybridization to detect the NPY messenger ribonucleic acid (mRNA).Spontaneously active cortex cultures display NPY mRNA expression in about 7% of all cortical neurons from 10 days in vitro (DIV) on. Blocking the SBA by chronic application of 10 mm Mg2+ for 3–30 DIV reduces the percentage of NPY neurons to about 2%. Allowing an initial phase of SBA (1–20 DIV) followed by an SBA blockade (for 21–50 DIV) results in 2% labelled neurons, indicating a dramatic reduction of NPY mRNA expression in the absence of SBA. Surprisingly, the reverse experiment (a period of SBA blockade for 1–20 DIV followed by a period of SBA recovery for 21–40 DIV) does not cause an upregulation of NPY mRNA expression. However, allowing cultures to differentiate as spontaneously active cultures, then applying a transient period of SBA blockade which is followed by a second period of SBA, does rescue the NPY mRNA expression in 7% of the cortical neurons. We conclude that SBA is a main trigger for NPY mRNA expression and it is particularly important during an early postnatal period of differentiation.We then analysed whether neurotrophic factors known to modulate cortical neuropeptide expression are able to do so in the absence of SBA. Supplementing chronically blocked cultures with the neurotrophins, brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT‐3), neurotrophin‐4/5 (NT‐4/5) and the cytokine, leukaemia inhibitory factor (LIF), reveals that BDNF and NT‐3 are unable to increase the percentage of NPY neurons. In contrast, LIF and NT‐4/5 increase the percentage of NPY neurons to 4 and 6–7%, respectively. Moreover, neurons treated with NT‐4/5 display a very high level of NPY mRNA expression in somata and in the dendritic trees. The data suggest a complex interplay and a hierarchy of epigenetic factors in regulating the neurochemical architecture of the developing neocortex.
Region‐specific expression of thyrotrophin‐releasing hormone‐degrading ectoenzyme in the rat central nervous system and pituitary gland
Authors: Heuer Heike , Ehrchen Jan , Bauer Karl , Schäfer Martin K. H. 
Published: March 2003

AbstractThyrotrophin‐releasing hormone (TRH), a hypothalamic neuropeptide hormone and a putative neuromodulator/neurotransmitter in the central nervous system is inactivated by the TRH‐degrading ectoenzyme (TRH‐DE), a TRH‐specific metallopeptidase localized on the surface of neuronal brain cells in culture and on lactotrophic cells of the pituitary. After succeeding in cloning the cDNA of TRH‐DE we now report on the cellular distribution pattern of this enzyme in rat brain, spinal cord and pituitary gland using in situ hybridization histochemistry. In the pituitary, TRH‐DE mRNA was found both in the anterior and the neural lobe but not in the intermediate lobe. After treatment with triiodothyronine (T3) a dramatic increase in the mRNA levels of the TRH‐DE and a decrease in the intensity of the TRH receptor could be observed in the anterior lobe of the pituitary. In brain, TRH‐DE transcripts were predominantly found in neo‐ and allocortical regions with strongest signals in the olfactory bulb, the piriform cortex, the cerebral cortex, the granular layer of the cerebellar cortex and the pyramidal cells of the Ammon's horn. In the diencephalon, the highest TRH‐DE mRNA levels were observed in the medial habenulae followed by several hypothalamic subregions. In the mesencephalon and brainstem, moderate signals were present in the superior colliculi, substantia nigra, dorsal raphe and in the periolivar region. In the spinal cord, TRH‐DE mRNA positive neurons were present in all layers. The very distinct distribution of TRH‐DE in the brain and the hormonal regulation of the adenohypophyseal enzyme support the concept that this peptidase serves very specialized functions.
Expression of the mitotic motor protein CHO1/MKLP1 in postmitotic neurons
Authors: Ferhat Lotfi , Kuriyama Ryoko , Lyons Gary E. , Micales Bruce , Baas Peter W. 
Published: March 2003

AbstractThe kinesin‐related motor protein CHO1/MKLP1 was initially thought to be expressed only in mitotic cells, where it presumably transports oppositely oriented microtubules relative to one another in the spindle mid‐zone. We have recently shown that CHO1/MKLP1 is also expressed in cultured neuronal cells, where it is enriched in developing dendrites (Sharp et al. 1997a) J. Cell Biol., 138, 833–843]. The putative function of CHO1/MKLP1 in these postmitotic cells is to intercalate minus‐end‐distal microtubules among oppositely oriented microtubules within developing dendrites, thereby establishing their non‐uniform microtubule polarity pattern. Here we used in situ hybridization to determine whether CHO1/MKLP1 is expressed in a variety of rodent neurons both in vivo and in vitro. These analyses revealed that CHO1/MKLP1 is expressed within various neuronal populations of the brain including those in the cerebral cortex, hippocampus, olfactory bulb and cerebellum. The messenger ribonucleic acid (mRNA) levels are high within these neurons well after the completion of their terminal mitotic division and throughout the development of their dendrites. After this, the levels decrease and are relatively low within the adult brain. Parallel analyses on developing hippocampal neurons in culture indicate that the levels of expression increase dramatically just prior to dendritic development, and then decrease somewhat after the dendrites have differentiated. Dorsal root ganglion neurons, which generate axons but not dendrites, express significantly lower levels of mRNA for CHO1/MKLP1 than hippocampal or sympathetic neurons. These results are consistent with the proposed role of CHO1/MKLP1 in establishing the dendritic microtubule array.
UV‐sensitive input to horizontal cells in the turtle retina
Authors: Ammermüller J. , Itzhaki A. , Weiler R. , Perlman I. 
Published: March 2003

AbstractMicrospectrophotometry, electroretinography and behavioural studies have indicated that ultraviolet (UV) light contributes to functional vision in various vertebrate species. Based on behavioural evidence, this was also suggested for turtle vision. In order to reveal the interactions underlying detection of UV light in the distal retina, we recorded intracellularly the photoresponses of cones and horizontal cells in retinas of
Pseudemys scripta elegans and Mauremys caspica and calculated the action spectra of these cells under different conditions of adaptation. In the dark‐adapted retina, all three types of horizontal cells; luminosity‐type, red/green chromaticity‐type and yellow/blue chromaticity‐type exhibited increased sensitivity in the UV region of the spectrum. However, chromatic adaptation indicated that only the yellow/blue chromaticity‐type horizontal cells received excitatory input from UV‐sensitive cones with peak sensitivity ≈ 360 nm. The enhanced UV sensitivity of luminosity‐type horizontal cells probably reflected the β‐band of the long‐wavelength sensitive visual pigment as indicated by the action spectra of dark‐adapted L‐cones. It is suggested that the enhanced UV sensitivity of red/green chromaticity‐type horizontal cells reflects the β‐band of the medium‐wavelength sensitive visual pigment. Transmission measurements of the optical media (cornea, lens and vitreous) indicated that UV vision can be functional under normal circumstances.
Characterization of a directional selective inhibitory input from the medial terminal nucleus to the pretectal nuclear complex in the rat
Authors: Schmidt Matthias , Van Der Togt Chris , Wahle Petra , Hoffmann Klaus‐Peter 
Published: March 2003

AbstractThe receptive field properties of neurons in the medial terminal nucleus of the accessory optic system (MTN) that project to the ipsilateral nucleus of the optic tract (NOT) and dorsal terminal nucleus (DTN), as identified by antidromic electrical activation, were analysed in the anaesthetized rat. The great majority (88%) of MTN neurons that were antidromically activated from NOT and DTN preferred downward directed movement of large visual stimuli while the remaining cells preferred upward directed stimulus movement. Distinct retrograde tracer injections into the NOT/DTN and the ipsilateral inferior olive (IO) revealed that no MTN neurons project to both targets. MTN neurons projecting to the ipsilateral NOT/DTN were predominantly found in the ventral part of the MTN, whereas those projecting to the IO were found in the dorsal part of the MTN. In situ hybridization for glutamic acid decarboxylase (GAD) mRNA was used as a marker for GABAergic neurons. Up to 98% of MTN neurons retrogradely labelled from the ipsilateral NOT/DTN also expressed GAD mRNA. Earlier studies have shown that MTN neurons that prefer upward directed stimulus movements are segregated from MTN neurons that prefer downward directed stimulus movements. It also has been demonstrated that directionally selective neurons in the NOT/DTN prefer horizontal stimulus movements and receive an inhibitory input from ipsilateral MTN. Our results indicate that this input is mediated by GABAergic cells in the ventral part of MTN, which to a large extent prefer downward directed stimulus movements, and that the great majority of MTN neurons that prefer upward directed stimulus movements project to other targets one of which possibly is the IO.
Comparison of the electrophysiology and morphology of layers III and II neurons of the rat medial entorhinal cortex in vitro
Authors: van der Linden Solange , da Silva Fernando H. Lopes 
Published: March 2003

AbstractThe basic membrane characteristics of neurons in layers II and III of the medial entorhinal cortex (MEA) were recorded using the intracellular current clamp technique in in vitro slices of the rat brain. Two types of cells were distinguished according to the presence of a time‐dependent inward rectification (SAG current) with hyperpolarizing current pulses. The cells in which this inward rectification was not observed (No‐SAG cells) had a larger input resistance, a more negative resting membrane potential and a more depolarized firing threshold. They more often displayed a strongly adapting firing pattern, and their action potentials had a slower decay rate and lacked a depolarizing afterpotential, compared with the SAG cells. SAG cells typically had a prominent rebound depolarization at the end of a hyperpolarizing current and membrane potential oscillations (7 Hz) upon subthreshold depolarizations. Cs+ blocked the time‐dependent inward rectification. The rebound depolarization persisted, even in the presence of tetrodotoxin. Biocytin labelling showed that layer III consisted mainly of pyramidal‐shaped cells. Most layer III cells were of the No‐SAG type. All cells in layer II, stellate and pyramidal cells, were classified as SAG cells. We conclude that the cells in MEA layers II and III display different electroresponsiveness, but that this appears to be more related to the layer where they are located than to a specific morphology. As layer III consisted mainly of cells of the No‐SAG type, we suggest that layer III cells are less excitable than the SAG type layer II cells.
Cloning of a new gap junction gene (Cx36) highly expressed in mammalian brain neurons
Authors: Condorelli Daniele Filippo , Parenti Rosalba , Spinella Francesca , Salinaro Angela Trovato , Belluardo Natale , Cardile Venera , Cicirata Federico 
Published: March 2003

AbstractThe connexins are the protein subunits of the gap junction intercellular channels. In the present study a new rat connexin was cloned by degenerate reverse transcription‐polymerase chain reaction and its gene isolated from a mouse genomic library. The nucleotide sequence encodes a protein of 321 amino acids (called Cx36) with highly significant homology to the members of the connexin family. In situ hybridization analysis of rat brain and retina showed the strongest expression in neurons of the inferior olive, the olfactory bulb, the CA3/CA4 hippocampal subfields and several brain‐stem nuclei. An intense expression was also found in the pineal gland and in the retinal ganglion cell and inner nuclear layers. Experiments with neurotoxins, locally injected in the hippocampus or specifically acting on inferior olivary neurons, confirmed the neuronal localization of Cx36. It is the first connexin to be expressed predominantly in mammalian neurons and its identification paves the way for a molecular approach in the study of the role played by gap junctions in the physiology and the pathology of the mammalian brain.
The NMDA receptor subunit NR2B of neonatal rat brain: complex formation and enrichment in axonal growth cones
Authors: Herkert Matthias , Röttger Sabine , Becker Cord‐Michael 
Published: March 2003

AbstractThe N‐methyl‐d‐aspartate (NMDA) subtype of ionotropic glutamate receptors comprises a family of highly homologous subunits which assemble into oligomeric protein complexes. Alterations in subunit composition are developmentally regulated, leading to functionally distinct receptor populations. Here, the contribution of the subunit NR2B to NMDA receptor complex formation was analysed in neonatal rat brain, employing polyclonal antibodies raised against NR2B‐specific synthetic peptides. By hydrodynamic size fractionation of the solubilized receptor protein and chemical cross‐linking, NR2B antigen was found to be associated with several protein species of up to 690 kDa molecular weight. These observations show NR2B to be part of a multimeric receptor complex. Fractionation of cortex homogenates from E18 rat embryos on sucrose density gradients revealed NR2B polypeptide to be highly enriched in axonal growth cones. A similar distribution was found by fluorescence microscopy of immature hippocampal neurons, showing a preferential accumulation of NR2B antigen in axonal growth cones and varicosities. In mature cells, NR2B antigen displayed a punctated distribution pattern with redistribution to somato‐dendritic spheres. The association of NR2B with axonal growth cones and processes of immature neurons suggests a role of NMDA receptors in the regulation of neurite outgrowth and migration.
Accumulation of acetylcholine receptors is a necessary condition for normal accumulation of acetylcholinesterase during in vitro neuromuscular synaptogenesis
Authors: De S. , Porte La , Chaubourt E. , Fabre F. , Poulas K. , Chapron J. , Eymard B. , Tzartos S. , Koenig J. 
Published: March 2003

AbstractTo study a step of the very complex processes of the formation of the neuromuscular junction (NMJ), we have analysed the clustering of acetylcholine receptors (AChR) and acetylcholinesterase (AChE) in myotubes cultured in various conditions. On the surface of rat myotubes cultured in the presence of spinal cord cells from embryonic rat, numerous AChE clusters appeared. Such clusters are always co‐localized with AChR clusters, but the reverse is not true: the number of AChR clusters largely exceeds that of AChE clusters. Very few AChE clusters formed when such co‐cultures were treated with monoclonal antibodies (mAbs) against the main immunogenic region (MIR) of the AChR, which provoke internalization and degradation of the AChRs of the muscular membrane. The total levels of AChE and proportions of molecular forms were unaffected. We also used non‐innervated myotubes in which addition of agrin, a protein normally synthesized by motoneurons, transported to nerve terminals and inserted into the synaptic basal lamina, induces the formation of small clusters of AChE. When added to rat myotubes devoid of membrane AChR, agrin‐induced AChE clusters did not form. Finally, we analysed the capacity of the variant of the C2 mouse muscle cell line deficient in AChR (1R‐) to form clusters of AChE in co‐cultures with spinal cord cells from rat: no formation of AChE clusters could be observed. In all these different systems of cultures, the conditions which prevented clustering of AChR (anti‐AChR antibodies, deficiency of the variant C2 cell line) also suppressed AChE clustering. We concluded that clustering of AChR is a prerequisite for clustering of AChE, so that NMJ formation implies the sequential accumulation of these two components.