摘要:

AbstractSynchronous firing of spatially separate neurons was studied with multi‐electrode recordings in area 17 of the visual cortex of strabismic cats which had developed behaviourally verified amblyopia of the deviated eye. Responses of neurons were evoked with moving light bars or gratings of different spatial frequency. Neurons driven by the normal eye displayed stronger synchronization of their responses than neurons dominated by the amblyopic eye. These interocular differences were highly significant and particularly pronounced for grating stimuli of high spatial frequency. No interocular differences were noted with respect to the amplitudes of responses to the light bars and gratings. These results suggest reduced synchronization of population responses as a neurophysiological correlate of strabismic amblyopia and underline the importance of correlated firing of spatially separate cortical neurons for normal processing of visual informatio

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00556.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe 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 GABAAreceptor 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 stimu

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00557.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe pharmacology of trigeminal excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of the vibrissal pad was investigatedin vivoin 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 trigemina

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00558.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractCultures of dissociated striatal neurons from fetal rats were prepared, and were grown in the presence of neurotrophin‐4/5 (NT‐4/5) as well as the other known neurotrophins, nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF) and neurotrophin‐3 (NT‐3). We found that acute administration of NT‐4/5 to 7‐day‐old cultures stimulates the hydrolysis of phosphatidylinositol, an event involved in neurotrophin signal transduction. Growth of striatal cultures in the presence of NT‐4/5 resulted in increased cell survival, as indicated by elevations in cell number, protein content, and a measure of mitochondrial enzyme activity (MTT assay). NT‐4/5 increased GABA uptake and staining intensity in these cultures, as indicated by GABA immunocytochemistry, indicating a trophic action on GABAergic neurons, the predominant neuron type in the striatum. To further identify responsive cell populations we analysed for calretinin, a calcium‐binding protein known to colocalize with GABA in a number of neuronal cells. In cultures prepared from rats of embryonic day 15, NT‐4/5 strongly increased the number of calretinin‐positive cells as well as calretinin levels, as determined by Western blot analysis. When the cultures were prepared from embryonic day 18 rats, NT‐4/5 very strongly increased the morphological differentiation of calretinin‐positive cells, whereas the increase in cell number was less prominent. All effects produced by NT‐4/5 were mimicked by BDNF with similar potency. NT‐3 was less effective than NT‐4/5 and BDNF, and its effects were limited to cultures prepared from embryonic day 15 rats, suggesting a role in the regulation of cell survival at early developmental stages. NGF did not affect any of the measured parameters. Our findings identify NT‐4/5 as potent neurotrophic factor for striatal neurons, able to promo

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00559.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractWe trained two rhesus monkeys in a task in which they had to judge whether or not two successively presented gratings differed in orientation. In a first experiment, we trained a monkey for only a restricted set of orientations and then recorded from the temporal cortical visual area (TE) while he made discriminations at trained and untrained orientations. Although this orientation‐selective practice induced a marked anisotropy in his behavioural performance, this was not matched by a similar anisotropy in single‐cell response properties. In a second experiment, we compared the response properties of TE cells in two monkeys before and after practice in the discrimination of small orientation differences. The training had no effect on either the responsiveness or the orientation tuning. We did, however, observe alterations in the pattern of response modulations induced by the behavioural context. However, these changes with practice, although present in both monkeys, were not consistent from animal to animal. The relevance of these findings for the functional significance of behavioural context dependencies of TE cells, as well as for the plasticity of TE responses, is discus

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00560.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThese 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 theirin vivoproperties 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 thosein 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 reproducedin 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

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00561.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe two main cell populations in brain tissues are neurons and astrocytes. Cultures of both bear muscarinic acetylcholine receptors (mAChRs). Available data indicate that astrocyte mAChRs are heterogeneous, but the particular subtypes on these cells are not known, nor is there any information as to whether there is a regional variation in the mAChR profile of astrocytes. This paper describes the mAChR profiles of cultured astrocytes derived from the cerebral hemispheres, mesencephalon and medulla‐pons, and is a continuation of our study on cultures of neurons from these same tissues. Pharmacological studies showed that the astrocytes accumulated small amounts of mAChRs with distinct pharmacological profiles which, for a given area, differed from those of neurons in culture. Northern blot analyses showed transcripts for ml and m3 mAChRs only. Their concentrations differed from one cell population to another. Astrocyte cultures from the mesencephalon contained ml mRNA amounts close to those in the tissue. Thus, at least part of the mAChR profilein vitromight be a true reflection of the cell's propertiesin vivo.Functional studies showed that mAChRs mediate the stimulation of phosphoinositide turnover in all three astrocyte cultures, that the amplitude of this response varies greatly with the origin of the cell, and that two pharmacological subclasses, M1 and M1–2‐, are involved in these responses, but to different extents. Thus the CNS contains discrete astrocyte populations which in culture differ in their mAChR profiles at the molecular, the pharmacological and the functional l

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00562.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract(+)‐HA‐966 [R‐(+)‐3‐amino‐1‐hydroxypyrrolid‐2‐one], a functional antagonist at the glycine modulatory site on the W‐methyl‐D‐aspartate (NMDA) receptor/ion channel complex, was evaluated in amygdala‐kindled rats, a model of epilepsy recently shown to exhibit enhanced susceptibility to the adverse effects of competitive and non‐competitive NMDA receptor antagonists. Since (+)‐HA‐966 displays weak partial agonistic effects at the glycine site (−10% efficacy of glycine), D‐cycloserine, a glycine ligand with much higher intrinsic activity, was evaluated in kindled rats for comparison. Following drug administration, electrographic activity was recorded from the basolateral amygdala (i.e. the focal site) as well as the ipsilateral piriform cortex, ventral hippocampus and nucleus accumbens. In addition to the evaluation of original recordings, power spectrum analysis was used to delineate drug effects. (+)‐HA‐966 (20–40 mg/kg i.p.) induced marked alterations in electrographic recordings, including increases in amplitude and isolated spiking, i.e. signs of paroxysmal activity. The severity or duration of fully kindled seizures was not changed by (+)‐HA‐966, but the drug dramatically increased the duration of immobilization and limbic seizure activity following a kindled motor seizure. In contrast to (+)‐HA‐966, D‐cycloserine did not induce any electrographic changes, even when administered in much higher doses than (+)‐HA‐966. The changes in electrographic recordings seen after administration of (+)‐HA‐966 in kindled rats were almost absent in non‐kindled rats, indicating that kindling had increased the sensitivity to the paroxysmal effects of the glycine/NMDA receptor ligand. The data indicate that functional glycine/NMDA antagonists with low i

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00563.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractCombined with a partial cholinergic deficiency, serotonergic lesions induce severe spatial learning deficits. Serotonergic lesions, however, have additional effects, such as reduced body weight and disruption of thermoregulation, which may be the cause of the observed learning deficits. Restoration of the serotonergic innervation of the hippocampus by raphe grafts reduces these learning deficits. The effects of the grafts may result from a direct support of spatial learning but may also be an indirect result of preventing some of the other effects of serotonergic lesions. In the present study we used raphe grafts to examine the selectivity and specificity of the effects of serotonergic lesions in the rat, and used the behavioural effects as an indication of successful transplantation in order to examine the fine details of such grafts. Raphe grafts in the hippocampus did not prevent the effects of the lesions on body weight, thermoregulation and exploratory behaviour but did minimize the effects of the lesions on spatial learning. In contrast, raphe grafts in the hypothalamus reduced the effects of the lesions on thermoregulation but failed to support learning. The grafted fibres showed termination specificity with the interneurons, which is typical of the serotonergic innervation of the normal hippocampus. The results indicate that the serotonergic innervation of the hippocampus functions locally to support spatial learning. This role of serotonin is independent of its involvement in modulation of body weight, thermoregulation or exploratory behaviour. The results confirm that the modes of serotonergic action in the hippocampus include the selective innervation of specific interneuron subpopulations.

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00564.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThalamic 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 thalamoc

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00565.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY