摘要:

AbstractThe goal of this study was to examine the role of horizontal connections in rabbit striate neurons. Anaesthetized rabbits were prepared in the usual fashion for single‐cell recordings in area 17 of the visual cortex. We compared responses evoked by moving and stationary stimuli prior to, during and after recovery from lateral microinjection of either lidocaine (n= 61), γ‐aminobutyric acid (GABA,n =18) or bicuculline (n= 8) 2 mm from the recording site. This procedure allows evaluation of the contribution of neighbouring neurons in visual responses. Results showed that striate neurons are dependent on the adjacent cells1excitability. Modification of responses to stationary targets suggests that lateral interactions play a role in the generation of discharges to fixed stimuli. Lateral inactivation preferentially influenced non‐directional over direction‐selective units. This influence usually resulted in the non‐directional neuron becoming directional by attenuation of the visually driven response in one direction. Simple and complex cells tended to be influenced differently by lateral inactivation. Simple cells became less responsive, whereas complex cells became more responsive. This dichotomy among cellular types suggests that simple cells receive mainly excitatory horizontal influences, while complex cells are contacted mostly by lateral inhibit

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00603.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractCorticosterone, secreted by the adrenal glands, binds to central mineralocorticoid receptors with high affinity and to glucocorticoid receptors with a tenfold lower affinity. In previous studies we have shown that the selective activation of either mineralocorticoid receptors or glucocorticoid receptors exerts distinctly different behavioural effects. In this study we examined in particular the mineralocorticoid receptor‐mediated effect of corticosterone on the control of the behavioural response of male Wistar rats to spatial novelty. This analysis was based on our observation that in adrenal‐intact rats the presence of an object in the centre of an open field alters the time spent and distance walked in the centre compared to the peripheral area, i.e. the pattern of reactive locomotor activity is changed. Using this paradigm we found that 1 day after removal of the adrenals the rats increased their behavioural reactivity towards the object. Treatment of adrenalectomized rats with a low dose of corticosterone (50μg/kg s.c.) 1 h prior to testing restored the behavioural reactivity to the level of sham‐operated, intact rats. Surprisingly, a high dose of corticosterone (1000μg/kg s.c.) also increased the rat's reactivity towards the object. The same high dose of corticosterone given to adrenal‐intact rats also increased behavioural reactivity. Pretreatment of these rats with an intracerebroventricular injection of the selective mineralocorticoid receptor antagonist RU28318 (100 ng/μl) prevented the corticosterone‐induced increase in behavioural reactivity, while the blockade of glucocorticoid receptors with the antagonist RU38486 (100 ng/μl) was not effective. Administration of the mineralocorticoid receptor antagonist without corticosterone to adrenal‐intact rats also increased behavioural reactivity, but this increase did not reach statistical significance. General locomotor activity was not affected by either treatment. In conclusion, we found a U‐shaped relationship between the pattern of behavioural reactivity in a novel environment and the circulating plasma corticosterone level. The response to spatial novelty appeared to be sensitive with respect to the activation and blockade of central, presumably hippocampal mineraloco

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00604.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractExcitatory amino acids exert a depolarizing action on central nervous system cells through an increase in cationic conductances. Non‐NMDA receptors have been considered to be selectively permeable to Na+and K+, while Ca2+influx has been thought to occur through the NMDA receptor subtype. Recently, however, the expression of cloned non‐NMDA receptor subunits has shown thatα‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors are permeable to Ca2+whenever the receptor lacks a particular subunit (edited GluR‐B). The behaviour of recombinant glutamate receptor channels predicts that Ca2+would only permeate through receptors that show strong inward rectification and vice versa, i.e. AMPA receptors with linear current‐voltage relationships would be impermeable to Ca2+. Using the whole‐cell configuration of the patch‐clamp technique, we have studied the Ca2+permeability and the rectifying properties of AMPA receptors, when activated by kainate, in hippocampal neurons kept in culture or acutely dissociated from differentiated hippocampus. Cells were classified according to whether they showed outward rectifying (type I), inward rectifying (type II) or almost linear (type III) current‐voltage relationships for kainate‐activated responses. AMPA receptors of type I cells (52.2%) were mostly Ca2+‐impermeable(PcaIPcs= 0.1) while type II cells (6.5%) expressed Ca2+‐permeable receptors(PcaIPcs=0.9).Type III cells (41.3%) showed responses with low but not negligible Ca2+permeability (PcaIPcs= 0.18). The degree of Ca2+permeability and inward rectification were well correlated in cultured cells, i.e. more inward rectification corresponded to higher Ca2+permeability. In acutely dissociated neurons, the restricted activation of the receptors located either in dendritic or somatic membranes revealed that inward rectifying (i.e. Ca2+‐permeable) AMPA receptors are preferentially located in the dendritic shaft (i.e. synaptic field). Our results indicate that oligomeric AMPA receptors of different subunit composition are coexpressed in dissimilar proportions in different cells, which would explain the incomplete inward rectification and graded Ca2+permeability. In addition, Ca2+‐permeable AMPA receptors may exhibit no

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00605.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe goal of this study was to clarify pharmacological properties of GABAAreceptors in cells of the mouse retinal ganglion cell layerin situ.Spontaneous synaptic currents and responses to exogenous GABA were recorded from individual neurons in retinal whole mounts (postnatal days 1–3) or retinal stripe preparations (postnatal days 4–6). Drugs were applied by a fast local superfusion system. Current responses were measured with the patch‐clamp technique in the whole‐cell configuration. All cells responded to exogenous GABA (average EC50and Hill coefficient: 16.7 μM and 0.95 respectively) and generated GABAergic synaptic currents in response to elevated KCI. GABA‐induced currents of retinal ganglion cells were blocked by bicuculline, picrotoxin and Zn2+, as well as strychnine, and increased by pentobarbital, clonazepam and 3α‐hydroxy‐5α‐pregnan‐20‐one. In some retinal ganglion cells GABA caused an increase in the frequency of spontaneous synaptic currents, which points to a partially depolarizing action of this traditionally inhibitory neurotransmitter in the neural retina. Our major observation is that acetylcholine and acetylcarnitine blocked or reduced GABAergic inhibitory postsynaptic currents and responses to exogenous GABA. This effect was seen in only a fraction of retinal ganglion cells and occurred in both the undesensitized and the desensitized state of the GABAAreceptor. The block was voltage‐independent and persisted during coapplication with the nicotinic and muscarinic acetylcholine receptor antagonists D‐tubocurarine and atropine. In contrast to GABA‐activated Cl−currents, glycine‐activated Ch currents remained unaffected by acetylcholine and acetylcarnitine. Acetylcarnitine had no effect on voltage‐activated Ca2+channel currents and glutamate‐activated currents. Similar results were obtained in a dissociated cell culture preparation from the neonatal rat superior colliculus. In these cells acetylcholine induced a rightward shift in the dose ‐ response curve for GABA. Taken together, these results indicate that acetylcholine and acetylcarnitine can act directly at the GABAAbinding site and thereby reduce the

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00606.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe 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 r

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00607.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractMolecules coded by the major histocompatibility complex (MHC) are present on cell surfaces in most tissues, with the cells of the central nervous system and skeletal muscle as prominent exceptions. We show here that when rat skeletal muscles are rendered inactive by nerve impulse block, expression of MHC class I molecules occurs on the muscle fibres. In addition, the number of cells expressing MHC class II molecules in the muscle interstitium is increased by a factor of three after 2 weeks of impulse blockade. Similar effects obtained by denervation can be counteracted by direct electrical stimulation, Interferon‐γ‐like immunoreactivity accumulates in inactive muscle fibres, and interferon‐γ or a related cytokine could be a link between inactivity and MHC up‐regulation. These findings suggest that nerve‐evoked muscle activity influences not only the phenotype of the muscle cells themselves, but also processes in the interstitium that may increase the immunoreactivity of inactive mu

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00608.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe 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 epilepto

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00609.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractWe compared the effectiveness of Ca2+entering by Na+/Ca2+exchange with that of Ca2+entering by channels produced by membrane depolarization with K+in inducing catecholamine release from bovine adrenal chromaffin cells. The Ca2+influx through the Na+/Ca2+exchanger was promoted by reversing the normal inward gradient of Na+by preincubating the cells with ouabain to increase the intracellular Na+and then removing Na+from the external medium. In this way we were able to increase the cytosolic free Ca2+concentration ([Ca2+]c) by Na+/Ca2+exchange to 325 ± 14 nM, which was similar to the rise in [Ca2+]cobserved upon depolarization with 35 mM K+of cells not treated with ouabain. After incubating the cells with ouabain, K+depolarization raised the [Ca2+]cto 398 ± 31 nM, and the recovery of [Ca2+]cto resting levels was significantly slower. Reversal of the Na+gradient caused an −6‐fold increase in the release of noradrenaline or adrenaline, whereas K+depolarization induced a 12‐fold increase in noradrenaline release but only a 9‐fold increase in adrenaline release. The ratio of noradrenaline to adrenaline release was 1.24 ± 0.23 upon reversal of the Na+/Ca2+exchange, whereas it was 1.83 ± 0.19 for K+depolarization. Reversal of the Na+/Ca2+exchange appeared to be as efficient as membrane depolarization in inducing adrenaline release, in that the relation of [Ca2+]cto adrenaline release was the same in both cases. In contrast, we found that for the same average [Ca2+]c, the Ca2+influx through voltage‐gated channels was much more efficient than the Ca2+entering through the Na+/Ca2+exchanger in inducing noradrenaline release from chromaffin ceils. This greater effectiveness of membrane depolarization in stimulating noradrenaline release suggests that there is a pool of noradrenaline vesicles which is more accessible to Ca2+entering through voltage‐gated Ca2+channels than to Ca2+entering through the Na+/Ca2+exchanger, whereas the adrenaline vesicles do not distinguish between the

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00610.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIt has been shown previously that impulses in axons of the descending branches of myelinated afferents in rat dorsal columns may suffer a blockade of transmission along their course in the dorsal columns. This paper tests the effect of the mechanism of primary afferent depolarization on the orthodromic movement of impulses in descending dorsal column primary afferent axons originating in the L1 dorsal root. Orthodromic impulses were recorded in the L5 and 6 dorsal columns after stimulation of the L1 dorsal root. Twenty‐seven out of 82 axons (33%) suffered a temporary transmission block if primary afferent depolarization had been induced by L5 stimulation before the L1 stimulus. The tendency to block peaked at 10–15 ms and persisted for up to 30–40 ms. The number of single unit orthodromic impulses originating from the L1 root and recorded during a search of the dorsal columns 15 mm caudal to L1 increased by a factor of 3.1 after the systemic administration of bicuculline (1 mg/kg). The number of single unit orthodromic impulses originating from the L1 root and recorded in axons descending in the dorsal columns 20 mm caudal to the root increased by a factor of 8.7 after the systemic administration of picrotoxin (5 mg/kg). It is concluded that the transmission of impulses in the long range caudally running axons from dorsal roots to dorsal columns may be blocked during primary afferent depolarization and that conduction may be restored by the administration of GABA antago

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00611.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe avian archistriatum has been demonstrated to play a role in agonistic behaviours and avoidance learning. However, the extent of its role in learning is unknown. The involvement of the archistriatum in the learning process of filial imprinting was therefore investigated in day‐old chicks. Bilateral archistriatal lesions, lateral cerebral area lesions or sham archistriatal penetrations were made in dark‐reared, day‐old chicks, which were subsequently exposed to either a rotating red box or blue cylinder for 2 × 1 h training sessions. Three hours later, the approach of chicks to their training object and to the other, novel object was measured. Chicks with archistriatal lesions ran a similar distance towards each stimulus and therefore failed to display a preference for their training object. However, chicks with sham archistriatal penetrations or lateral cerebral area lesions exhibited a significant preference for the object they had been trained upon. These results demonstrate that the archistriatum is essential for the expression of an imprinted preference. All chicks approached their training object significantly more on their second compared to their first training exposure, suggesting that some aspects of imprinting behaviour remain intact in chicks with archistriatal lesions. Taken together with the results of previous work, the current data suggest that the archistriatum may be involved in retention of significant aspects of the imprinting experience, or in motivation to approach imprinting o

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00612.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY