bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heterogeneity of Metabotropic Glutamate Receptors in the Striatum: Electrophysiological Evidence
Authors: Calabresi Paolo , Pisani Antonio , Mercuri Nicola B. , Bernardi Giorgio 
Published: April 2006

AbstractIn order to investigate the functional role of metabotropic glutamate receptors (mGluRs) in the striatum we performed extracellular and intracellular recordings from a corticostriatal brain slice preparation. The effects of l‐2‐amino‐3‐phosphopropionic acid (l‐AP3), an antagonist of mGluRs, were studied both on long‐term synaptic depression (LTD) and on presynaptic inhibition of excitatory postsynaptic potentials (EPSPs) induced by different agonists of mGluRs. l‐AP3 produced a dose‐dependent (3 – 30 μM) reduction of the LTD evoked in the striatum by the tetanic stimulation of the corticostriatal pathway. In contrast to this action, l‐AP3 (10 – 100 μM) did not significantly affect the presynaptic inhibitory effect of 1‐amino‐cyclopentyl‐trans‐dicarboxylic acid (t‐ACPD), an agonist of mGluRs, on corticostriatal transmission. Higher concentrations of l‐AP3 (0.3 – 1 mM) reduced by themselves the EPSP amplitude. The inhibitory effect of t‐ACPD on the cortically evoked EPSPs was mimicked either by the active stereoisomer 1S,3R‐ACPD or by amino‐4‐phosphonobutyric acid (l‐AP4), a glutamate autoreceptor agonist. In some neurons, these inhibitory actions were coupled with membrane depolarizations. The depression of synaptic transmission caused by t‐ACPD, 1S,3R‐ACPD and l‐AP4 was not altered following the induction of LTD. Chronic lithium treatment of the animals (60–120 mg/kg i.p. for 10 days) blocked striatal LTD but not presynaptic inhibition mediated by mGluR agonists. The present findings show that the mechanisms underlying LTD and the presynaptic inhibition induced by different agonists of mGluRs exhibit functional and pharmacological differences. These data suggest heterogeneity of mGluRs in the striatum.
Synaptic Excitation Triggers Oscillations During NMDA Receptor Activation in Rat Abducens Motoneurons
Authors: Durand Jacques 
Published: April 2006

AbstractRat abducens motoneurons were intracellularly recorded in vivo during synaptic excitation and extracellular microionophoretic application of N‐methyl‐d‐aspartate (NMDA). Trigeminal excitatory post‐synaptic potentials (EPSPs) evoked in abducens motoneurons were studied during intracellular current injection. They were not sensitive to hyperpolarization or depolarization of the membrane potential in the range of –75 mV to –55 mV using current pulse intensities between –3 nA and + 1 nA. Microionophoretic applications of aminophosphonovalerate (APV), MK801 and i.v. injections of MK801 (1 – 3 mg/kg) or ketamine (10 mg/kg) did not modify trigeminal EPSPs, suggesting that NMDA receptors are not involved in this synaptic transmission. However, microionophoretic applications of NMDA on abducens motoneurons enhanced trigeminal EPSPs and gave rise to regenerative oscillations. The co‐activation of NMDA receptors and trigeminal synapses induced these oscillations. The trigeminal EPSP may delay and reset the oscillations depending on where it was evoked in the oscillatory cycle. Depolarizing current pulses intracellularly applied to abducens motoneurons could trigger a post‐hyperpolarization followed by rebound depolarization during NMDA application, confirming the activation of active membrane properties. However, depolarizing current pulses could not trigger oscillations similar to those entrained by the EPSPs. The importance of the location of trigeminal synapses in relation to those of NMDA receptors in the dendritic arborization of abducens motoneurons is discussed. Our results show that the same sensory stimulus may have different post‐synaptic effects on abducens motoneurons during the co‐activation of NMDA receptors. A complete modification of the motor output during NMDA receptor activation strongly supports an active role of abducens motoneurons provided that NMDA receptors are physiologically activated during motor pattern generation.
Monocularly Induced 2‐Deoxyglucose Patterns in the Visual Cortex and Lateral Geniculate Nucleus of the Cat: I. Anaesthetized and Paralysed Animals
Authors: Löwel Siegrid , Singer Wolf 
Published: April 2006

AbstractExtending previous investigations of the topographic relationship between ocular dominance and orientation columns in the cat visual cortex the two systems were visualized with transneuronally transported [3H]proline and with activity‐dependent uptake of [14C]2‐deoxyglucose, respectively. In addition, we used the 2‐deoxyglucose method for a functional assay of both columnar systems. To this end, cats were injected with [3H]proline in the right eye. Two weeks later, they were stimulated monocularly through this eye by presenting contours of only a single orientation in the left and contours of many different orientations in the right visual hemifield while 2‐deoxyglucose was injected. The patterns of increased 2‐deoxyglucose uptake and of terminal labelling were analysed in flat‐mount sections of the visual cortices and in frontal sections of the lateral geniculate nuclei. In the lateral geniculate nucleus, regions of increased 2‐deoxyglucose uptake are in register with the [3H]proline‐labelled laminae of the open eye. In the visual cortex, the hemispheres stimulated with many different orientations showed a rather homogeneous accumulation of 2‐deoxyglucose over the entire extent and throughout all layers of area 17. The hemispheres stimulated with a single orientation displayed columnar patterns of orientation domains essentially similar to those obtained with binocular presentation of a single orientation. In particular and despite monocular stimulation, regions of increased 2‐deoxyglucose uptake were neither in register with the [3H]proline‐labelled terminals of the stimulated eye in layer IV nor confined to columns of neural tissue above and below these terminals. The maximal horizontal offset between the termination sites of thalamic afferents and activated orientation columns was in the order of 400 μm. These findings suggest several conclusions. (i) In the cat visual cortex, binocular convergence seems to occur so early in cortical processing that monocular stimulation with many orientations leads to a rather homogeneous activation of cortical tissue. (ii) From the termination zones of geniculate afferents activity is apparently distributed already within layer IV to the respective orientation columns. (iii) This horizontal spread of activity could be assured by target cells with radially extending dendrites and/or tangentially oriented fibres.
Functional Organization of Auditory Cortex in the Mongolian Gerbil (Meriones unguiculatus) II. Tonotopic 2‐Deoxyglucose
Authors: Scheich Henning , Heil Peter , Langner Gerald 
Published: April 2006

AbstractThe tonotopic organization of the auditory cortex in the Mongolian gerbil was mapped with 2‐deoxyfluoro‐D‐glucose (2DG) using narrow‐band frequency‐modulated tones of different centre frequency (FM tones) and tones periodically alternating between two different frequencies (alternating tones) as stimuli. Continuous tone bursts of a constant frequency and repetition rate were used in initial experiments. Continuous tones produced 2DG patterns similar to those observed in animals that were not specifically stimulated. With tone bursts of constant frequency and repetition rate variable patterns were observed, some of which could be interpreted only in retrospect in the light of results obtained with FM tones and alternating tones. These stimuli, in contrast, produced differential metabolic responses which in conjunction with 2DG data from monaural animals and electrophysiological data made it possible to distinguish a primary auditory field AI with its dorsal region Aid, an anterior auditory field AAF, a ventral field V, a dorsoposterior field DP and a ventroposterior field VP, a dorsal field D, and in addition an anteroventral field AV. In the largest field (AI) and the smaller rostrally adjacent field AAF, frequency‐specific dorsoventral bands of labelling (isofrequency contours) were mapped quantitatively. Bands shifted as a function of frequency relative to each other and to an independent spatial reference line in the lateral hippocampus. Spatial analysis of the single bands obtained with FM tones, and of the double bands obtained with alternating tones in both fields, revealed roughly mirror‐imaged tonotopic maps of AI and AAF. In AI the progression from low to high frequencies was from caudal to rostral and in AAF the gradient was reversed, leading to a common high‐frequency border of the two fields. In AI, the spatial resolution for frequencies below 16 kHz was in similar intervals per octave and higher for frequencies below 1 kHz. AI showed a somewhat higher spatial resolution for frequencies (at least below 1 kHz) as well as longer isofrequency contours than AAF. The 2‐deoxyglucose patterns provided average tonotopic maps and topological data on various fields, as well as reliable landmarks in the gerbil's auditory cortex.
PDGF‐BB Exerts Trophic Activity on Cultured GABA Interneurons from the Newborn Rat Cerebellum
Authors: Smits A. , Ballagi A. E. , Funa K. 
Published: April 2006

AbstractPlatelet‐derived growth factor (PDGF) is a well known mitogen for mesenchyme‐derived cells and glial cells. Its presence in neuronal cells of the central nervous system has only recently been described. We have shown earlier that neurons of newborn rat brains in culture express PDGF β‐receptors and that PDGF‐BB, a homodimer of PDGF B‐chain, increases survival and promotes neurite outgrowth of newborn cerebellar cells (Smits et al., Proc. Natl Acad. Sci. USA, 88, 8159 – 8163, 1991). In this study, the effects of PDGF on early postnatal rat cerebellar cells were further explored. By using chemically defined serum‐free medium, we have established primary cell cultures of rat cerebella (postnatal day 4 – 5) containing 70 – 80% neuronal cells. During the first 10 days in vitro, no difference in total cell number was found between PDGF‐BB‐treated and untreated cultures. After this time period, however, increased survival of the PDGF‐BB‐treated cells was found. Within the first 10 days in vitro, the addition of PDGF‐BB to the cultures resulted in a relative increase in survival of interneurons expressing glutamic acid decarboxylase (GAD), the GABA biosynthetic enzyme. Moreover, addition of PDGF‐BB in the untreated cell culture resulted in a rapid increase of GAD mRNA. These results show that PDGF‐BB acts as a trophic factor on GABAergic interneurons of the cerebellum by up‐regulating GAD synthesis and prolonging the survival of these cells. Furthermore, in situ hybridization revealed that there are scattered cells present in the early postnatal cerebellum that express PDGF β‐receptor mRNA. The localization of these cells in the molecular layer and in the proximity of the internal granular layer corresponds to that of GABAergic interneurons in the developing cerebellum.
The High Sensitivity to Rotenone of Striatal Dopamine Uptake Suggests the Existence of a Constitutive Metabolic Deficiency in Dopaminergic Neurons From the Substantia Nigra
Authors: Marey‐Semper Isabel , Gelman Michèle , Lévi‐Strauss Matthieu 
Published: April 2006

AbstractThe toxicity of the 1‐methyl‐4‐phenylpyridinium ion (MPP+), an inhibitor of complex I of the respiratory chain, on nigrostriatal dopaminergic neurons contrasts with its relative inefficiency towards other catecholaminergic cell populations in spite of their ability to accumulate this neurotoxin through their high‐affinity uptake system. A constitutive metabolic deficiency of the nigrostriatal dopaminergic neurons could account for their particular vulnerability to MPP+. In order to substantiate this hypothesis, we compared the inhibitory effects of rotenone, an inhibitor of mitochondrial oxidative phosphorylation, on the uptake of dopamine, serotonin, noradrenaline and GABA in mouse striatal synaptosomes, and of dopamine, serotonin and GABA in cultured mesencephalic neurons. In both preparations, the uptake of dopamine was much more affected than that of other neurotransmitters by rotenone. This result was confirmed using two other unrelated inhibitors of oxidative phosphorylation. Moreover, dopamine uptake in synaptosomes from the dorsolateral striatum was more sensitive to rotenone than uptake in synaptosomes from the nucleus accumbens. This indicates that intrinsic metabolic properties of the nigrostriatal dopaminergic neurons may explain the strong inhibition by rotenone of striatal dopamine uptake. Altogether, these results suggest that a constitutive metabolic deficiency could account, at least in part, for the selective vulnerability of the nigrostriatal dopaminergic pathway to the action of the neurotoxin MPP+.
Enhancement of AMPA‐mediated Synaptic Transmission by the Protein Phosphatase Inhibitor Calyculin A in Rat Hippocampal Slices
Authors: Figurov Alexander , Boddeke Hendrick , Muller Dominique 
Published: April 2006

AbstractUsing the phosphatase inhibitor calyculin A, we have examined the influence of phosphorylation on synaptic transmission and plasticity in rat CA1 hippocampal slices. Bath application of 0.5 – 1 μM of calyculin A resulted in an increase of 42.6 ±2.9% in synaptic responses. The effect produced by calyculin A was not accompanied by changes in fibre volley, was not associated with changes in paired‐pulse facilitation, and could be reproduced by intracellular injection of the compound, thereby indicating a postsynaptic action. Also, the synaptic enhancement produced by calyculin A was expressed only by potentials mediated by amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors, but not by the NMDA responses recorded in the presence of the AMPA receptor antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and low magnesium. The effect of calyculin A could be prevented by KN‐62, an inhibitor of calcium/calmodulin‐dependent protein kinase II. Long‐term potentiation could still be induced in the presence of calyculin A, but the effect of the compound was slightly reduced on potentiated compared with control pathways. These results indicate that calyculin A can selectively increase the efficacy of AMPA receptor‐mediated synaptic transmission at excitatory synapses.
Confocal Microscopy and Computer‐assisted Image Reconstruction of Astrocytes in the Mammalian Retina
Authors: Rungger‐Brändle Elisabeth , Messerli J. Marius , Niemeyer Günter , Eppenberger Hans M. 
Published: April 2006

AbstractThe distribution of astrocytes in the vascularized retina of pigs, rats and cats was investigated by confocal microscopy and computer‐assisted image processing. In whole mounts, immunocytochemical identification was done by staining astrocytes for glial fibrillary acidic protein (GFAP), and blood vessels for α‐smooth muscle actin or collagen IV. Double‐staining was followed through consecutive optical sections and made it possible to precisely align the two markers in the inner retina. The resulting computer‐assisted image reconstructions revealed asymmetric ensheathment of blood vessels by GFAP‐positive fibres. The ultrastructural basis for this asymmetry, as studied by electron microscopy, was found to be different in pigs and cats. In the pig, astrocytes firmly ensheathed the vessel circumference, but glial filaments were much more abundant on the vitreal and lateral than on the scleral side. By contrast, in the cat astrocytes were generally confined to regions occupied by axonal bundles and constituted only part of the vascular glia limitans, else formed by Müller cells. Moreover, our observations unambiguously showed that individual astrocytes maintained simultaneous contact with axons and blood vessels and lined the vitreous body. The physical links provided by astrocytes suggest that they are able to function as central communicating elements between ganglion cells, the vasculature and the vitreous body.
Trophic Factors Produced by Retinal Cells Increase the Survival of Retinal Ganglion Cells In Vitro
Authors: de Araujo Elizabeth Giestal , Linden Rafael 
Published: April 2006

AbstractThe naturally occurring neuron death of normal development has been shown to depend on trophic factors produced and released by target cells. It has also been shown that the afferent supply and local interactions play a role in the control of this degenerative phenomenon. We studied the effect of trophic factors produced by intrinsic retinal cells on the survival of retinal ganglion cells in vitro. Retinae of newborn hooded rats were retrogradely labelled with horseradish peroxidase injected into the superior colliculus to permit the identification of retinal ganglion cells in culture. We tested the effect of conditioned media either from aggregates or from explants of retinal cells from neonatal rats on the survival of ganglion cells in vitro. Our results showed that both conditioned media increased the survival of these cells. The trophic activity was dose‐dependent, was maintained after dialysis against a 12 kDa membrane, was abolished by heating at 56°C for 30 min, and was not found in conditioned medium from cerebral cortical explants. Conditioned medium obtained without fetal calf serum presented the same trophic effect. These results suggest that the local control of developmental neuron death by intrinsic retinal cells may be mediated by neurotrophic factors.
Glutamate Receptors on type I Vestibular Hair Cells of Guinea‐pig
Authors: Devau Gina , Lehouelleur Jacques , Sans Alain 
Published: April 2006

AbstractAfferent nerve calyces which surround type I vestibular hair cells (VHCI) have recently been shown to contain synaptic‐like vesicles and to be immunoreactive to glutamate antibodies. In order to understand the physiological significance of these observations, the presence of glutamate receptors on type I vestibular sensory cells has been investigated. The effect of excitatory amino acids applied by iontophoresis was examined by spectrofluorimetry using fura‐2 sensitive dye. Glutamate application caused a rapid and transient increase in intracellular calcium concentration ([Ca2+]i), in a dose‐dependent manner. The ionotropic glutamate receptors agonists N‐methyl‐d‐aspartic acid (NMDA), α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA) and quisqualic acid (QA) induced an increase of [Ca2+]i. The NMDA receptor antagonist 2‐amino‐5‐phosphonovaleric acid and the AMPA receptor antagonist 6,7‐dinitro‐quinoxaline‐2,3‐dione partially blocked the glutamate response, by 39 ± 10 and 53 ± 11% respectively. Metabotropic receptors were also revealed by the specific agonist trans‐1‐amino‐cyclopentyl‐1,3‐dicarboxylate. The presence of different glutamate receptors on the VHCI membrane suggests two kinds of feedback, (i) At the base of the sensory cell, autoreceptors may locally control the synaptic transmission, (ii) At the apex, postsynaptic receptors may modulate sensory transduction from glutamate release at the upper part of the afferent nerve calyx. These feedbacks suggest presynaptic modulation of the vestibular hair cell response which could affect its sensitivity.
Elevated Seizure Threshold and Impaired Spatial Learning in Transgenic Mice with Putrescine Overproduction in the Brain
Authors: Halonen T. , Sivenius J. , Miettinen R. , Halmekytö M. , Kauppinen R. , Sinervirta R. , Alakuijala L. , Alhonen L. , MacDonald E. , Jänne J. , Riekkinen P. J. 
Published: April 2006

AbstractWe have studied the role of putrescine by using transgenic mouse lines overexpressing the human ornithine decarboxylase gene in most of their tissues. The aberrant expression of the transgene is most strikingly manifested in the brain, leading to an increase of up to 20‐fold in putrescine content. We report that the transgenic mice with grossly elevated putrescine in all brain regions analysed (cortex, striatum, hippocampus and cerebellum) showed a significantly elevated seizure threshold to chemical and electrical stimuli, and impaired performance in spatial learning and memory tests. The view that putrescine may be primarily responsible for these changes was supported by the fact that the concentrations of the major neurotransmitter amino acids, glutamate and GABA in the brain, were not changed in the transgenic animals, and by the finding that a further increase in brain putrescine, achieved by inhibition of the catabolism of l‐ornithine, appeared to provide additional protection against electroshock‐induced seizures. These results suggest that the commonly observed increase in ornithine decarboxylase activity and the massive increase in brain putrescine in connection with neuron damage is a neuroprotective measure rather than a cause of the damage.
aFGF, bFGF and flg mRNAs Show Distinct Patterns of Induction in the Hippocampus Following Kainate‐induced Seizures
Authors: Bugra Kuyas , Pollard Hélène , Charton Gérard , Moreau Joëlle , Ben‐Ari Yezekiel , Khrestchatisky Michel 
Published: April 2006

AbstractWe report that kainic acid‐induced seizures lead to marked increases in mRNAs encoding basic and acidic fibroblast growth factors (bFGF and aFGF, respectively) and fig, one of their receptors, in the rat hippocampus. Anticonvulsant pretreatment inhibits the up‐regulation of these mRNAs. The observed increase in fig mRNA levels involves the pyramidal cells of all hippocampal subfields and the granular ceils of the dentate gyrus. The increased expression of aFGF and bFGF mRNAs is limited to neuron populations that are resistant to seizure‐induced injury, the granular cells of dentate gyrus and pyramidal cells of CA1 region, respectively. The results suggest that the increase in the FGFs and fig may play pivotal roles in neuron survival and in long‐term changes occurring in the hippocampus following seizure activity.
Early Postnatal Changes in the Somatodendritic Morphology of Ankle Flexor Motoneurons in the Rat
Authors: Dekkers Joanna , Becker David L. , Cook Jeremy E. , Navarrete Roberto 
Published: April 2006

AbstractThe development of locomotor function in the rat spans the first 3 postnatal weeks. We have studied morphological features of the soma and dendrites of motoneurons innervating the physiological flexor muscles of the ankle, tibialis anterior and extensor digitorum longus, by intracellular injection in vitro between the first and ninth postnatal days. We obtained serial optical sections of 96 adequately filled motoneurons in whole‐mounted hemisected spinal cords by confocal microscopy, projected them onto a single plane and analysed them morphometrically. On the day after birth, the somatodendritic surfaces of most such motoneurons were covered in growth‐associated spiny, thorny or hair‐like appendages. These had disappeared from the soma by the fourth postnatal day and from most proximal dendrites by day 7, but were still common distally on day 9. During this period there was little or no net growth of either the soma (which was still much smaller than in the adult) or the dendritic tree. A dorsal dendritic bias was present and ‘sprays’ of long, loosely bundled dorsal dendrites were often seen. The mean number of primary dendrites remained constant at about eight, and their combined diameter was already significantly correlated with mean soma diameter, as in the adult cat. Thus, the critical neonatal period during which these ankle flexor motoneurons are known to change their electrophysiological properties and to be particularly sensitive to interference with neuromuscular interaction is characterized by major changes in the neuronal surface, presumably linked to synaptogenesis.