摘要:

AbstractExcitatory amino acid‐induced death of central neurons may be mediated by at least two receptor types, the so‐called NMDA (N‐methyl‐d‐aspartate) and AMPA (α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionate) receptors. We have studied the neurodegenerative mechanisms set in motion by AMPA receptor activation using incubated slices of 8‐day‐old rat cerebellum and hippocampus. In both preparations, AMPA induced a pattern of degeneration that differed markedly from the one previously shown to be elicited by NMDA. In cerebellar slices, AMPA induced the degeneration of most Purkinje cells together with a population of Golgi cells; in hippocampal slices the neurons were affected in the order CA3>CA1>dentate granule cells. Three mechanisms could be discerned: an acute one in which neurons (e.g. cerebellar Golgi cells) underwent a rapid degeneration; a delayed one in which the neurons (Purkinje cells and hippocampal neurons) appeared to be only mildly affected immediately after a 30 min exposure but then underwent a protracted degeneration during the postincubation period (1.5–3 h); and finally a slow toxicity, which took place during long (2 h) exposures to AMPA (3–30 μM). Although Purkinje cells were vulnerable in both cases, the efficacy of AMPA was higher for the delayed mechanism than for the slow one. The pathology displayed by the acutely destroyed Golgi neurons was a classical oedematous necrosis, whereas most neurons vulnerable to the delayed and slow mechanisms displayed a ‘dark cell degeneration’, whose cytological features bore a close resemblance to those of neurons irreversibly damaged by ischaemia, hypog

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01668.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe mechanisms underlying the neurodegenerative effects of the glutamate receptor agonist, AMPA (α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate), were studied using brain slice preparations of young rat (8–9 days old) cerebellum and hippocampus. Rapid AMPA toxicity (exerted on some cerebellar interneurons) was inhibited by including the appropriate receptor blocker, CNQX (6‐cyano‐7‐nitroquinoxaline‐2,3‐dione, 10 μM), in the exposing solution. The degeneration of other neurons, including Purkinje cells and hippocampal pyramidal neurons, persisted. It could, however, be largely prevented if CNQX was included for 1.5 h during the post‐incubation period, suggesting that an enduring ‘rebound’ AMPA receptor activation was responsible for this delayed type of degeneration, not the exposure itself. In cerebellar slices, independent evidence for the occurrence, postexposure, of persisting AMPA receptor stimulation was obtained electrophysiologically. Omission of Ca2+during the exposure period (and for 10 min beforehand) markedly reduced rapid AMPA toxicity but was ineffective in protecting most of the Purkinje cells. However, if the slices were previously starved of Ca2+for 1 h, then most of these neurons survived, even if the ion was reinstated during the recovery period. Slow AMPA toxicity, which takes place during long (2 h) exposures, could be inhibited either by CNQX or by omission of Ca2+(30 min preincubation). The results indicate that the rapid oedematous necrosis induced by AMPA, like that caused byN‐methyl‐d‐aspartate and kainate, is likely to involve excessive influx of Ca2+. In contrast, the induction of the delayed mechanism, as well as its ‘expression’ during the postincubation period, probably depends on

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01669.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractBy use of the indirect immunofluorescence (IF) technique, radioimmunoassay (RIA) andin situhybridization (ISH) histochemistry, the staining pattern, content and expression of calcitonin gene‐related peptide (CGRP) in lumbar motoneurons of normal rats and rats subjected to sciatic nerve transection (SNT), ventral root transection (VRT), low thoracic spinal cord transection (SCT) alone or in combination with a subsequent SNT, as well as rats subjected to chemical lesioning of 5‐hydroxytryptamine (5‐HT) neurons by 5,7‐dihydroxytryptamine (5,7‐DHT), were studied. We here confirm that a large number of the lumbar motoneurons normally contain CGRP‐like immunoreactivity (LI) and CGRP mRNA. SNT induced a transient increase in CGRP‐LI, with a peak at days 2–5 after lesion, and normalized levels again after ∼2–3 weeks. Comparable results were obtained with IF and RIA. This increase is probably a consequence of increased CGRP synthesis, since a parallel up‐regulation of CGRP mRNA levels was seen. A normalization of CGRP mRNA did not occur during the period studied, despite an apparent normalization of peptide levels after 2 weeks, and this may in turn be due to an increased turnover and/or release of CGRP. The up‐regulation of CGRP is probably caused by the axon injury itself, since a similar cellular reaction with respect to CGRP was observed in motoneurons subjected to VRT. However, SNT, which also lesions dorsal root afferents and causes a decline in CGRP‐LI in the dorsal horn, induced an increase in CGRP‐LI in motoneurons on the contralateral side also. Thus, it may be that severance of dorsal root afferents and/or changes in reflex activity may also influence the production of CGRP in motoneurons. SCT, which severs all descending synaptic input to the motor nucleus and causes a paralysis of muscles innervated by motoneurons below the lesion, resulted in a marked decline in both content of CGRP‐LI (IF and RIA) and expression of CGRP mRNA. However, treatment with 5,7‐DHT, which lesions 5‐HT neurons, including those giving rise to the bulbospinal serotoninergic pathway, did not cause any dramatic changes in motor behaviour but induced an increase in both motoneuron content of CGRP‐LI and expression of CGRP mRNA. In rats first subjected to SCT, which depresses CGRP, followed 2 weeks later by SNT, we found a marked increase in both content of CGRP‐LI (IF and RIA) and expression of mRNA coding for CGRP. In summary our results show that the cellular production of the CGRP peptide, normally expressed in motoneurons, is influenced in a complex way by motoneuron injury as well as changes in the afferent input. There also appear to be important differences in the expression of CGRP in small (gamma) and large (alpha) motoneurons as well as between motoneurons of different nuclei,

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01670.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractTo investigate the expression of nerve cell‐specific transgene products in neural transplants, we implanted into the hippocampus of immunosuppressed adult Sprague – Dawley rats cell suspensions obtained from the septal region of the fetal brain of mice that carry the human neurofilament‐light (hNF‐L) gene. In grafts examined between 3 weeks and 7 months after transplantation, axons and nerve cell somata immunoreacted to antibodies specific to the human NF‐L subunit. Thus, the hNF‐L protein appears to be a suitable marker of these grafted neurons. Transgenic mice bearing the hNF‐L gene may be a convenient source of donor tissue or be used as hosts for neural transplantation studies. Furthermore, the hNF‐L promoter/enhancer elements in this transgene may help direct neuronal expression of heterologous genes that could influence nerve cell responses in either the transplant

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01671.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractLevels and cellular distribution of FOS, the product ofc‐fos(onco)gene, were studied by immunohistochemistry during the development of mouse brain at rest and after the administration of convulsants. Basal FOS immunoreactivity became detectable only after postnatal day 20 (P20). Metrazol and kainate at the appropriate doses induced convulsions at all ages but, in both cases, FOS accumulated in limbic areas (particularly in the dentate gyrus) only after a certain age: P20 for kainate and P30 for Metrazol. Surprisingly, considering the different molecular targets of Metrazol and kainate, respectively, and the different type of convulsions elicited, the cell groups in the limbic areas in which FOS increased were the same in the two cases. These results suggest that both drugs produced FOS increase by finally activating the same circuit. During ontogeny, the ability to accumulate FOS, which appears after P20, could be the sign of the attained maturity of signal transduction mechanisms in the cells of the hippocampal formation; endogenous signals originating from the activity of the nervous system increase the basal FOS levels and exogenous signals (i.e. like those given, probably locally, by kainate) further increase these levels. Metrazol manifests its capability to induce FOS accumulation only at later ages. We suggest that this occurs because the Metrazol target is probably distant from the hippocampal region and thus the maturity of a nerve pathway(s) is also required forc‐fosinduct

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01672.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPostmitotic cerebellar granule cells, maintained for 5–6 days in Dulbecco's modified essential medium supplemented with 25 mM KCl, have been studied in whole‐cell recording conditions to characterize calcium currents. With 10 mM Ba2+as the divalent charge carrier, and using a pipette solution highly buffered for Ca2+(30 mM EGTA, 100 mM HEPES–Tris, pH 7.2), only a high‐threshold voltage‐activated barium current was recorded from a holding potential of – 90 mV. The addition of 1 mM ATP to the pipette medium allowed stable recording for an average duration of 10 min, compatible with pharmacological studies of the barium current. Ninety‐six per cent of the current was half‐inactivated at low negative holding potential (‐76 mV). A total block of current was obtained with 1 μM Cd2+. Sixty‐three per cent of the mean current was abolished by 3 μM ω‐conotoxin (ω‐CgTx;Ki= 10 nM for a 15 min application), but individual cells showed either full sensitivity to this toxin or incomplete sensitivity. Seventy‐eight per cent of the mean current was also abolished by 10 μM nicardipine but with a higherKi, of 0.5 μM. After exposure to ω‐CgTx, BAY K 8644 had no effect on the remaining current, though it was suppressed by nicardipine. No sensitivity to diltiazem, desmethoxyverapamil or flunarizine could be detected. Our major conclusion is that at least half of the channels have a mixed pharmacology, showing sensitivity to both ω

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01673.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractTrans‐1‐amino‐cyclopentyl‐1,3‐dicarboxylic acid (trans‐ACPD), a specific agonist of the glutamate phosphoinositide‐coupled receptor (Qp receptor), increased the amplitude of the outward K+current recorded in the whole‐cell configuration of the patch‐clamp technique in mouse cultured cerebellar granule cells. This effect was abolished by buffering internal Ca2+with BAPTA [1,2‐bis(2‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetic acid]. Activation of a large‐conductance K+channel was observed when trans‐ACPD or quisqualic acid (QA), another Qp receptor agonist, was applied outside the cell‐attached patch pipettes. No activation was observed with alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA), a specific agonist of ionotropic non‐N‐methyl‐d‐aspartate (non‐NMDA) receptors. The effects of trans‐ACPD or QA were potentiated in the presence of external Ca2+. The channel was also directly activated by both micromolar concentrations of internal Ca2+and membrane depolarization. Its unitary conductance was 100–115 pS under asymmetrical K+and 195–235 pS under high symmetrical K+conditions. In the absence of agonist, the channel was blocked by 1 mM external tetraethylammonium. This is the first description of a large conductance Ca2+‐activated K+channel in cultured cerebellar granule cells. It possesses properties similar to those of the so‐called ‘big K+channel’ described in other preparations. Our cell‐attached experiments demonstrated an indirect coupling between Qp receptors and this channel. The most likely hypothesis is that the second messenger system inositol 1,4,5‐triphosphate (IP3)‐Ca2+was involved in the coupling process. This hypothesis was further strengthened by our whole‐cell experiments. On the basis of the voltage‐ and Ca2+‐sensitivities of the studied channel, we estimated an increase of 350 to 570 nM in internal Ca2+concentration when Qp receptors were stimulated by 100 μM trans‐ACPD. Under physiological conditions, stimulation of Qp receptors by the endogenous neurotransmitter should lead to similar K+channel activation and therefore would tend to reduce the effica

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01674.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractSaccades produced by electrical stimulation of the superior colliculus in primates are influenced primarily by the location of the stimulating electrode, with the suprathreshold intensity or frequency of the stimulating pulse train having little effect. Any given collicular site produces a characteristic movement of relatively fixed amplitude and velocity. In accordance with this finding, in models of the saccadic eye movement system the superior colliculus specifies the change of eye position: the velocity of movement components are determined by ‘pulse generators’ located between the superior colliculus and the oculomotor neurons. Previous findings in rodents, however, have suggested that eye and head movements induced by stimulation at some collicular sites may be critically dependent on stimulation parameters, implying that in these animals the superior colliculus has access to a non‐saccadic control system. To investigate this possibility, rats with electrodes implanted into the lateral intermediate layers were stimulated with pulse trains of varying frequency and duration, and the resultant head movements analysed from video tape. At seven of the nine sites studied, amplitude of the horizontal component of the head movement was linearly related to stimulating frequency for fixed‐duration trains, in some cases over a ten‐fold range. Subsequent variation of train duration showed that amplitude was affected not by frequency as such, but by the number of pulses in the train; frequency was related to the mean velocity of the movement. By appropriate setting of these parameters, independent control of head movement amplitude and velocity could be achieved. These results suggest that the rodent superior colliculus may be able to control head movement without recourse to a pulse generator, and thus influence the trajectory of the movement directly. If so, it may prove to be a useful preparation for testing theories of trajectory

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01675.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractWe tested the ability of a subject with cerebral achromatopsia to discriminate between colours and to detect chromatic borders. He was unable to identify colours or to arrange them in an orderly series or choose the odd colour out of an array or even to pick out a colour embedded in an array of greys. Nevertheless, he could select the odd colour when the colours were contiguous, even when they were isoluminant, and could discriminate an ordered from a disordered chromatic series as long as the colours in each row abutted one other. His verbal replies showed that he did so by detecting an edge between two stimuli that were, to him, perceptually identical. Introducing a narrow isoluminant grey stripe between adjacent colours abolished or greatly impaired this ability. As long as isoluminant colours were contiguous the patient could identify the orientation of the chromatic borders. Photopic spectral sensitivity showed evidence both for activity of three cone channels and for chromatic opponent processing, indicating that postreceptoral chromatic processing is occurring despite the absence of any conscious awareness of colour. The results indicate that both parvocellular colour opponent and magnocellular broad‐band channels are active and that the cortical brain damage has selectively disrupted the appreciation of colour but not the ability to detect even isoluminant chromatic borders, which would be invisible to a retinal achromat. The subject's performance on non‐colour tasks involving the discrimination of shape, texture, greyness and position was excellent. His disorder is therefore not like that of macaque monkeys in which cortical area V4 has been removed, and which are much more severely impaired at discriminating shape than col

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01676.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe patch clamp technique has been used to record single channel currents from the untreated surface of the intact frog optic nerve after the meninges and basal lamina have been mechanically removed. Cells filled via dialysis with Lucifer yellow (LY) from the patch pipette had a typical astrocyte morphology and were dye‐coupled to adjacent astrocytes. This is consistent with the electron‐microscopic observation that all the cells on the surface of this nerve are astrocytes. Two types of ion channels were studied in detached patches. One, identified as a K+channel, had a conductance of 88±4 (S.E.)n= 9 pS and an equilibrium potential of −59±8 mV in physiological K+solutions. The steady‐state open probability was not significantly altered by changing the membrane potential. A second channel had a large conductance of 300–1200 pS, a reversal potential of ∼ 0 mV in symmetrical and non‐symmetrical solutions, and was open only in the voltage range of ±20 mV. These are the characteristics of a large anionic channel described in other preparations including cul

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb01677.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY