bluuebunny/crossref_metadata_2025_split huggingface dataset:
Release and elimination of dopamine in vivo in mice lacking the dopamine transporter: functional consequences
Authors: Benoit‐Marand M. , Jaber M. , Gonon F. 
Published: March 2003

AbstractIn mice lacking the dopamine transporter (DAT), the amplitude of dopamine (DA) release and the kinetics of dopamine elimination were measured in vivo using carbon fibre electrodes combined with amperometry. DA release was evoked by electrical stimulation of the medial forebrain bundle. The amplitude of DA release per pulse was lower (7% in striatum and 21% in nucleus accumbens) than in wild‐type mice. Inhibition of monoamine oxidases (MAOs) by pargyline, but not of catechol‐O‐methyltransferase (COMT) by tolcapone, slowed down DA elimination in knockout mice. As DA half‐life was two orders of magnitude higher in these mice, the DA diffusion distance was 10‐times higher than in wild‐types (100 and 10 μm, respectively). In knockout mice, α‐methyl‐p‐tyrosine induced a much faster decline of DA release and haloperidol was less effective in potentiating DA release. Therefore, DA release was more dependent on DA synthesis than in normal animals but was less influenced by D2 autoregulation. Dopaminergic neurons exhibit two kinds of discharge activity, i.e. single spikes and bursts of 2–6 action potentials. In wild‐type mice, stimuli mimicking bursts evoked significant increases in extracellular DA over its basal level sustained by tonic activity. However, in mice lacking the DAT, low frequency firing resulted in consistently high extracellular DA levels that could not be distinguished from DA levels achieved by high frequency firing. Therefore, the burst firing activity cannot be specifically translated into phasic changes in extracellular DA. This deficit might contribute to the difficulties of these mice in spatial cognitive function.
Generation and propagation of 4‐AP‐induced epileptiform activity in neonatal intact limbic structures in vitro
Authors: Luhmann H. J. , Dzhala V. I. , Ben‐Ari Y. 
Published: March 2003

AbstractWe examined the generation, propagation and pharmacology of 4‐aminopyridine (4‐AP)‐induced epileptiform activity (EA) in the intact interconnected limbic structure of the newborn (P0–7) rat in vitro. Whole‐cell recordings of CA3 pyramidal cells and multisite field potential recordings in CA3, CA1, dentate gyrus, and lateral and medial entorhinal cortex revealed 4‐AP‐induced EA as early as P0–1. At this age, EA was initiated in the CA3 region and propagated to CA1, but not to the entorhinal cortex. Starting from P3–4, EA propagated from CA3 to the entorhinal cortex. Along the CA3 septo‐temporal axis, EA arose predominantly from the septal pole and spread towards the temporal site. Whereas the onset of 4‐AP‐induced EA decreased with age from 21.2 ± 1.6 min at P0–1 to 4.7 ± 0.63 min at P6–7, the seizure duration increased in the same age groups from 98 ± 14 s to 269.4 ± 85.9 s, respectively. The EA was blocked by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) but not by dl‐2‐amino‐5‐phosphonovaleric acid (APV), (+)‐MK‐801 hydrogen maleate (MK‐801) or (±)‐alpha‐methyl‐4‐carboxyphenylglycine (MCPG), suggesting that they were mediated by α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA)/kainate receptor activation. We conclude that: (i) the septal pole of the hippocampal CA3 region plays a central role in the generation of EA in the neonatal limbic system; and (ii) AMPA/kainate receptor‐mediated EA can be generated in CA3 already at birth. Therefore, the recurrent collateral synapses and circuits required for the generation of EA are developed earlier than previously suggested on the basis of studies on hippocampal slices.
Regulation of the biosynthesis and processing of chromogranins in organotypic slices: influence of depolarization, forskolin and differentiating factors
Authors: Bauer Richard , Hoflehner Johannes , Doblinger Alfred , Kapeller Ingeborg , Laslop Andrea 
Published: March 2003

AbstractSlices from rat hippocampus in organotypic culture were used to study the biosynthesis regulation of chromogranins A and B and secretogranin II. Additionally, we investigated the proteolytic conversion of secretogranin II and the levels of prohormone convertases putatively involved. Forskolin treatment and depolarization with potassium plus BayK 8644 led to significant increases in secretogranin II mRNA in the principal cells of the hippocampus. Enhanced expression of secretogranin II was also reflected by a rise in peptide levels. Despite this induction of biosynthesis the extensive processing to secretoneurin normally observed in brain was maintained. Both forskolin and depolarization upregulated the prohormone convertase (PC)1, but not PC2, indicating that PC1 levels are critical for secretoneurin production under stimulating conditions. Results obtained for chromogranins A and B were less consistent. For chromogranin A mRNA, changes were restricted to granule cells; for chromogranin B, a response in granule cells was observed to depolarization but not to forskolin, and effects in pyramidal neurons were weak. Accordingly, we were unable to detect alterations in chromogranin A and B protein levels. Furthermore, we tested several neurotrophic growth factors and found that only basic fibroblast growth factor raised secretogranin II expression without affecting chromogranins A and B. The hippocampal slice preparation allowed well controlled treatment with identification of neuronal subpopulations and yielded data largely matching experiments in vivo and in cell culture. The pronounced regulation of secretogranin II and its effective processing underlines the importance of the resulting peptide secretoneurin as an active neuropeptide in the nervous system.
Basal forebrain nitric oxide synthase (NOS)‐containing neurons project to microvessels and NOS neurons in the rat neocortex: cellular basis for cortical blood flow regulation
Authors: Tong X. K. , Hamel E. 
Published: March 2003

AbstractStimulation of basal forebrain neurons results in local increases in cortical cerebral blood flow that are dependent upon cholinergic and nitrergic mechanisms. In the present study, we investigated the possibility that basal forebrain nitric oxide synthase (NOS)‐containing neurons project to microvessels and NOS interneurons in the rat cerebral cortex. We performed quisqualic (QUIS) acid lesions of the basal forebrain and evaluated their effects on cortical NOS immunostained nerve terminals, with emphasis on those associated with microvessels and NOS interneurons, both at the light and/or electron microscopic levels. The results show that basal forebrain NOS neurons provide about one third of the overall cortical NOS innervation. Further, the data indicate that basalocortical NOS fibres establish privileged associations with microvessels and NOS neurons, as respective denervations of 60 and 45% were observed following lesion. At the electron microscopic level, most perivascular NOS neuronal elements corresponded to nerve terminals and a majority (∼ 25%) of these were located in the immediate vicinity of the blood vessels, similar to the perivascular distribution reported previously for classic neurotransmitters/neuromediators. NOS terminals abutting on cortical NOS neurons were primarily nonjunctional. Altogether, these results raise the possibility that not only cholinergic but also nitrergic basal forebrain neurons are involved in the flow response observed following stimulation of the basal forebrain. Further, they suggest interactions between basalocortical and intracortical NOS neurons. We conclude that these interactions are involved in the spatial and temporal regulation of cortical perfusion following basal forebrain activation, and that they may become dysfunctional in pathologies such as Alzheimer's disease which affects both the basal forebrain and the cortical NOS neurons.
Rescue of γ2 subunit‐deficient mice by transgenic overexpression of the GABAA receptor γ2S or γ2L subunit isoforms
Authors: Baer Kristin , Essrich Christian , Balsiger Sylvia , Wick Marilee J. , Harris R. Adron , Fritschy Jean‐Marc , Lüscher Bernhard 
Published: March 2003

AbstractThe γ2 subunit is an important functional determinant of GABAA receptors and is essential for formation of high‐affinity benzodiazepine binding sites and for synaptic clustering of major GABAA receptor subtypes along with gephyrin. There are two splice variants of the γ2 subunit, γ2 short (γ2S) and γ2 long (γ2L), the latter carrying in the cytoplasmic domain an additional eight amino acids with a putative phosphorylation site. Here, we show that transgenic mice expressing either the γ2S or γ2L subunit on a γ2 subunit‐deficient background are phenotypically indistinguishable from wild‐type. They express nearly normal levels of γ2 subunit protein and [3H]flumazenil binding sites. Likewise, the distribution, number and size of GABAA receptor clusters colocalized with gephyrin are similar to wild‐type in both juvenile and adult mice. Our results indicate that the two γ2 subunit splice variants can substitute for each other and fulfil the basic functions of GABAA receptors, allowing in vivo studies that address isoform‐specific roles in phosphorylation‐dependent regulatory mechanisms.
Behavioural changes produced by transgenic overexpression of γ2L and γ2S subunits of the GABAA receptor
Authors: Wick Marilee J. , Radcliffe Richard A. , Bowers Barbara J. , Mascia Maria Paola , Lüscher Bernhard , Harris R. Adron , Wehner Jeanne M. 
Published: March 2003

AbstractTransgenic mice overexpressing either the mouse γ2L or γ2S subunit of the GABAA receptor were generated in a C57BL/6 J × DBA/2 J mixed background and expanded into transgenic lines. Transgenic mice and littermate controls were analysed with respect to altered behaviour indicative of anxiety, motor activity and acute effects of benzodiazepines and alcohol, as well as with regard to altered responses to alcohol withdrawal and acute functional tolerance to alcohol. Biochemical tests assessed flunitrazepam‐ and ethanol‐enhanced 36Cl– flux stimulated by muscimol in cerebellar and cortical microsacs and [3H]‐flunitrazepam binding to cerebellar membranes. There were no significant differences in any of these measures between the transgenic and control mice, except in tests of acute functional tolerance to acute injection of ethanol. Compared to controls, mice carrying either the γ2L or γ2S transgene developed significantly less tolerance to the ataxic effects of ethanol. We conclude that acute functional tolerance to ethanol is very sensitive to the amount of GABAA receptor γ2 subunit available (regardless of whether it is γ2L or γ2S) but overexpression of neither subunit isoform alters other behavioural and biochemical phenotypes.
Afferent ingrowth and onset of activity in the rat trigeminal nucleus
Authors: Waite P. M. E. , Ho S. M. , Henderson T. A. 
Published: March 2003

AbstractA novel in vitro preparation, consisting of the rat brainstem with the trigeminal ganglion attached, has been used to study the anatomical and functional development of the trigeminal nucleus from embryonic day (E)13 to postnatal day (P)6. Neurobiotin injections into the trigeminal ganglion showed that primary afferents had reached the trigeminal tract by E13 and had grown simple, mainly unbranched, collaterals into all levels of the nucleus by E15. By E17, these collaterals were extensively branched, with occasional boutons present. Patches of intense neurobiotin‐labelled terminals, corresponding to whisker‐related patterns, were first seen at E20 and became clearer over the next few days. Terminal arbours at this stage were relatively localized and densely branched, with many boutons. Responses from the trigeminal nucleus were recorded with suction electrodes, following stimulation of the trigeminal ganglion. Recordings from the main sensory nucleus showed a postsynaptic response was first present at E15. At E16, bath application of AP5 and DNQX showed that the response contained both NMDA and AMPA components, with NMDA predominating (75%). The NMDA : AMPA ratio remained high until P1, then gradually declined to 50% by P6. The postsynaptic response was also reduced by bath application of bicuculline, indicating the presence of a GABAA‐mediated excitatory component. GABAergic excitation was present at all ages but was maximal from E20 to P1, the age at which whisker‐related patterns are developing. It is hypothesized that both GABAergic excitation and NMDA receptor activation play a role in the consolidation of trigeminal connections, and are thus important in the development of whisker‐related patterns.
Connexin43 phosphorylation state and intercellular communication in cultured astrocytes following hypoxia and protein phosphatase inhibition
Authors: Li W. E. I. , Nagy J. I. 
Published: March 2003

AbstractThe effects of hypoxia and phosphatase inhibitors on connexin43 (Cx43) phosphorylation state, gap junctional intercellular communication (GJIC) and immunolabelling with anti‐Cx43 antibodies were investigated in cultured astrocytes. Astrocytes contained predominantly phosphorylated forms of Cx43 and these underwent dephosphorylation 30 min after hypoxia. This was preceded by a 77% reduction in GJIC 15 min after hypoxia, indicating that reduced GJIC occurs prior to Cx43 dephosphorylation. Hypoxia caused a reduction in punctate immunostaining (epitope masking) at cell–cell contacts with one anti‐Cx43 antibody, and increased labelling with another antibody (13–8300) that detects only a dephosphorylated form of Cx43. Inhibition of protein phosphatase (PP)‐1 and PP‐2A with okadaic acid or calyculin A had little effect on hypoxia‐induced Cx43 dephosphorylation. Inhibition of PP‐2B (calcineurin) with cyclosporin A or FK506 reduced Cx43 dephosphorylation and junctional uncoupling seen after hypoxia. These results demonstrate that responses of astrocytic Cx43 to hypoxia in vitro are similar to those seen after ischaemia in vivo, and that inhibition of protein phosphatase protects astrocytes from hypoxia‐induced Cx43 dephosphorylation and junctional uncoupling. In addition, calcineurin may play a direct role in the regulation of astrocytic GJIC and Cx43 phosphorylation state.
A quantitative study of gamma‐band activity in human intracranial recordings triggered by visual stimuli
Authors: Lachaux Jean‐Philippe , Rodriguez Eugenio , Martinerie Jacques , Adam Claude , Hasboun Dominique , Varela Francisco J. 
Published: March 2003

AbstractThis paper studies gamma‐band responses from two implanted epileptic patients during a simple visual discrimination task. Our main aim was to ascertain, in a reliable manner, whether evoked (stimulus‐locked) and induced (triggered by, but not locked to, stimuli) responses are present in intracranial recordings. For this purpose, we introduce new methods adapted to detect the presence of gamma responses at this level of recording, intermediary between EEG‐scalp and unicellular responses. The analysis relies on a trial‐by‐trial time–frequency analysis and on the use of surrogate data for statistical testing. We report that visual stimulation reliably elicits evoked and induced responses in human intracranial recordings. Induced intracranial gamma activity is significantly present in short oscillatory bursts (a few cycles) following visual stimulation. These responses are highly variable from trial to trial, beginning after 200 ms and lasting up to 500 ms. In contrast, intracranial‐evoked gamma responses concentrate around 100 ms latencies corresponding to evoked responses observed on the scalp. We discuss our results in relation to scalp gamma response in a similar protocol [Tallon‐Baudry et al. (1996) J. Neurosci., 16, 4240–4249] and draw some conclusions for bridging the gap between gamma oscillations observed on the scalp surface and their possible cortical sources.
β‐Amyloid neurotoxicity is mediated by a glutamate‐triggered excitotoxic cascade in rat nucleus basalis
Authors: Harkany T. , Ábrahám I. , Timmerman W. , Laskay G. , Tóth B. , Sasvári M. , Kónya C. , Sebens J. B. , Korf J. , Nyakas C. , Zarándi M. , Soós K. , Penke B. , Luiten P. G. M. 
Published: March 2003

AbstractWhereas a cardinal role for β‐amyloid protein (Aβ) has been postulated as a major trigger of neuronal injury in Alzheimer's disease, the pathogenic mechanism by which Aβ deranges nerve cells remains largely elusive. Here we report correlative in vitro and in vivo evidence that an excitotoxic cascade mediates Aβ neurotoxicity in the rat magnocellular nucleus basalis (MBN). In vitro application of Aβ to astrocytes elicits rapid depolarization of astroglial membranes with a concomitant inhibition of glutamate uptake. In vivo Aβ infusion by way of microdialysis in the MBN revealed peak extracellular concentrations of excitatory amino acid neurotransmitters within 20–30 min. Aβ‐triggered extracellular elevation of excitatory amino acids coincided with a significantly enhanced intracellular accumulation of Ca2+ in the Aβ injection area, as was demonstrated by 45Ca2+ autoradiography. In consequence of these acute processes delayed cell death in the MBN and persistent loss of cholinergic fibre projections to the neocortex appear as early as 3 days following the Aβ‐induced toxic insult. Such a sequence of Aβ toxicity was effectively antagonized by the N‐methyl‐d‐aspartate (NMDA) receptor ligand dizocilpine maleate (MK‐801). Moreover, Aβ toxicity in the MBN decreases with advancing age that may be associated with the age‐related loss of NMDA receptor expression in rats. In summary, the present results indicate that Aβ compromises neurons of the rat MBN via an excitotoxic pathway including astroglial depolarization, extracellular glutamate accumulation, NMDA receptor activation and an intracellular Ca2+ overload leading to cell death.
Spatio‐temporal distribution of cellular retinoid binding protein gene transcripts in the developing and the adult cochlea. Morphological and functional consequences in CRABP‐ and CRBPI‐null mutant mice
Authors: Romand R. , Sapin V. , Ghyselinck N. B. , Avan P. , Le Calvez S. , Dollé P. , Chambon P. , Mark M. 
Published: March 2003

AbstractThe expression patterns of the mouse cellular retinoid binding protein genes were investigated by in situ hybridization analysis in the inner ear from 10.5 days post coïtum (dpc) up to the adult stage. The cellular retinoic acid binding protein II (CRABPII) and cellular retinol binding protein I (CRBPI) were present in a widespread and abundant pattern in cochlear structures during embryogenesis. Expression of the cellular retinoic acid binding protein I (CRABPI) is restricted during development in Kölliker's organ whilst cellular retinol binding protein II (CRBPII) is only visible after birth with a ubiquitous distribution in most regions of the cochlea including nervous components. No CRABP or CRBP transcripts were observed in the auditory receptors. Morphological observations of CRBPI‐ and CRABPI/CRABPII‐null mutant fetus at 18.5 dpc do not show any structural modification at the level of the organ of Corti. Furthermore, electrophysiological tests performed by measuring distorsion‐product otoacoustic emissions and auditory brainstem evoked responses did not present significant alteration of the auditory function for the different types of mutants. The expression of retinoid binding proteins in cochlear structures during embryogenesis could suggest important roles for these proteins during ontogenesis and morphogenesis of the inner ear. Despite these observations, morphological and functional data from mutant mice did not present obvious modifications of the cochlear structures and auditory thresholds. It is therefore unlikely that CRABPs and CRBPI are directly involved in development of the cochlea and hair cell differentiation.
Basic properties of an inositol 1,4,5‐trisphosphate‐gated channel in carp olfactory cilia
Authors: Cadiou Hervé , Sienaert Ilse , Vanlingen Sara , Parys Jan B. , Molle Gérard , Duclohier Hervé 
Published: March 2003

AbstractIn addition to the activation of cAMP‐dependent pathways, odorant binding to its receptor can lead to inositol 1,4,5‐trisphosphate (InsP3) production that may induce the opening of plasma membrane channels. We therefore investigated the presence and nature of such channels in carp olfactory cilia. Functional analysis was performed by reconstitution of the olfactory cilia in planar lipid bilayers (tip‐dip method). In the presence of InsP3 (10 μm) and Ca2+ (100 nm), a current of 1.6 ± 0.1 pA (mean ± SEM, n = 4) was measured, using Ba2+ as charge carrier. The I/V curve displayed a slope conductance of 45 ± 5 pS and a reversal potential of −29 mV indicating a higher selectivity for divalent cations. This current was characterized by two mean open times (3.0 ± 0.4 ms and 42.0 ± 2.6 ms, n = 4) and was strongly inhibited by ruthenium red (30 μm) or heparin (10 μg/mL). Importantly, the channel activity was closely dependent on the Ca2+ concentration, with the highest open probability (Po) at 100 nm Ca2+ (Po = 0.50 ± 0.02, n = 4). Po is lower at both higher and lower Ca2+ concentrations. A structural identification of the channel was attempted by using a large panel of antibodies, raised against several InsP3 receptor (InsP3R)/Ca2+ release channel isoforms. The type 1 InsP3R was detected in carp cerebellum and whole brain, while a lower molecular mass InsP3R, which may correspond to type 2 or 3, was detected in heart, whole brain and the soma of the olfactory neurons. None of the antibodies, however, cross‐reacted with olfactory cilia. Taken together, these results indicate that in carp olfactory cilia an InsP3‐dependent channel is present, distinct from the classical InsP3Rs localized on intracellular membranes.
A high GluR1 : GluR2 expression ratio is correlated with expression of Ca2+‐binding proteins in rat forebrain neurons
Authors: Kondo Masahiro , Okabe Shigeo , Sumino Rhyuji , Okado Haruo 
Published: March 2003

Abstractα‐Amino‐3‐hydroxy‐5‐methyl‐4‐isoxazle propionic acid (AMPA) receptors are ubiquitously expressed; however, their subtypes and abundance vary from region to region. We classified the neurons in various forebrain regions (hippocampus, striatum, amygdala, piriform cortex and somatosensory cortex) into six types: [R1+/R2+], [R1–/R2+], [R1+/R2–], [R1–/R2–], [R1++/R2+] and [R1++/R2–], and analysed the expression of Ca2+‐binding proteins, such as parvalbumin and calbindin‐D28k, using a triple‐staining method. The neurons showing a high GluR1 : GluR2 expression ratio, [R1+/R2–], [R1++/R2+] and [R1++/R2–] neurons, comprised 13–30% of the total neuronal population. In addition, the expression of Ca2+‐binding proteins was mainly observed in these three types of neurons. The results suggest that Ca2+‐binding protein‐positive neurons express Ca2+‐permeable AMPA receptors, because the Ca2+‐permeability of AMPA receptors is enhanced by the relative scarcity of the GluR2 subunit. To directly test the possibility that Ca2+‐binding protein‐positive neurons express Ca2+‐permeable AMPA receptors, we performed Ca2+‐imaging experiments in cultured cortical neurons. Ca2+ influx through AMPA receptors was measured selectively by addition of AMPA together with cyclothiazide in the presence of blockers of other Ca2+ influx routes. More than half of the calbindin‐D28k‐positive neurons showed a large increase in the intracellular Ca2+ concentration ([Ca2+]i), whilst most of the calbindin‐D28k‐undetectable neurons exhibited only a slight rise in [Ca2+]i after AMPA addition. These results suggest that the expression of calbindin‐D28k is related to the expression of Ca2+‐permeable AMPA receptors.