摘要:

THE number of synapses in the adult, female hippo-campal CA1 region fluctuates naturally across the estrous cycle in an ovarian steroid-dependent manner. This phasic variation in synapse number occurs without identifiable degenerating synapses. Ultrastructural correlates of the dynamic aspect of this synapse loss and synapse formation thus remain undescribed. During early development, one hallmark of synaptogenesis is the presence of free postsynaptic densities (PSDs). Here we report that the incidence of free PSDs in CA1 fluctuates across the rat estrous cycle. The number of free PSDs is greatest on the afternoon of proestrus and is significantly decreased on the afternoon of estrus, 24 h later. We hypothesize that these free PSDs reflect synapse turnover in the adult CA1 region.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

ALG-2is a recently described pro-apoptosis gene that codes for a Ca2+-binding protein involved in T-cell receptor-, Fas- and glucocorticoid-induced cell death. We have usedin situhybridization histochemistry to examine the regional distribution of ALG-2 mRNA in the brain of 3- and 24-month old rats. There was widespread, predominantly neuronal distribution ofALG-2 mRNA throughout the brain. Areas expressing high levels included the granule and pyramidal cell layers of the hippocampus, choroid plexus, area postrema, and a number of hindbrain nuclei.ALG-2 mRNA levels in aged rats were not significantly different to young animals. The pattern of expression ofALG-2 mRNA in adult brain is similar to other apoptosis-related genes and suggests it may be involved in neuronal survival.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

MYELIN-ASSOCIATED glycoprotein (MAG) inhibits neurite outgrowth of postnatal spinal cord neurons, but its effect on embryonic neurons is unknown. The effect on neurite outgrowth of another myelin protein, myelinoligodendrocyte glycoprotein (MOG) is also unknown. We determined the effect of MAG and MOG on embryonic day 17 spinal cord neurons, which were cultured on MAG, MOG or control transfected CHO cells. Neurite outgrowth was examined and both total neurite length and longest neurite length were significantly enhanced by both MAG and MOG. These findings show that, in contrast to postnatal spinal cord neurons, MAG can enhance neurite outgrowth of embryonic spinal cord neurons. In addition, another myelin protein, MOG, can also modulate neurite outgrowth.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

VOLTAGE-GATED sodium channels (VGSCs) are concentrated in the postsynaptic membrane at the adult rat neuromuscular junction (NMJ). We have used immunolabelling to determine the pattern of initial VGSC accumulation during development. At birth, but not 3 days before, VGSC labelling is detectable at the NMJ and in the perijunctional (periJ) membrane but not elsewhere. A much higher density cluster of VGSCs forms at the NMJ itself 1–2 weeks later. If the nerve is cut 2 days after birth, VGSC labelling persists in the periJ region for at least 4 weeks but the clustering of VGSCs at the NMJ fails to develop. Thus an early, stable accumulation of VGSCs develops near the NMJ at least a week before high density postsynaptic VGSC clusters form.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

IRREVERSIBLE anoxic injury of axons in the rat optic nerve requires the presence of extracellular Ca2+. To test the hypothesis that Ca2+enters an intracellular compartment during anoxia we monitored [Ca2+]0in this CNS white matter tract using ion-sensitive microelectrodes. Periods of anoxia lasting 15 min resulted in a rapid, reversible increase in [Ca2+]0accompanied by transient loss of nerve conduction. This increase in [Ca2+]0was apparently the result of extracellular space shrinkage. Anoxic periods lasting 60 min resulted in an initial rise followed by a sustained fall in [Ca2+]0, indicative of net influx of Ca2+into an intracellular compartment. Following reoxygenation after 60 min of anoxia, [Ca2+]0slowly returned toward control levels but nerve conduction recovered incompletely, indicating irreversible loss of function. Removal of bath Ca2+lowered [Ca2+]0to about 100 μM, prevented the anoxia-induced fall in [Ca2+]0, and protected against irreversible loss of the compound action potential.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

IN order to substantiate event related paradigms in magnetic resonance functional neuroimaging, we assessed the temporal and spatial characteristics of oxygenation-sensitive MRI responses to 1 s periods of visual activation in repetitive protocols. A main finding is a reduction of the functional contrast between conditions (reversing checkerboard vs. darkness) for decreasing interstimulus intervals yielding 4.5% signal change for 89 s, 4% for 9 s, 3% for 6 s, and 1% for 3 s, respectively. Although rapid repetitions of identical stimuli preclude the development of the full positive and negative MRI signal deflections, pertinent responses leave the spatial pattern of activated brain regions unaffected and result in identical maps. These findings suggest the use of interstimulus intervals of the order of the response time from stimulus onset to maximum signal strength (5–6 s in the visual system). The resulting distinction in time will allow for separate mapping of stimulus-related responses with spatially overlapping cortical representations.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

IN view of the fact that the amygdala (AMG) and hypothalamic serotonin (5-HT) have an excitatory effect on the hypothalamo-pituitary-adrenal (HPA) axis, we have investigated the role of 5-HT in the AMG on this response. In intact freely moving rats, a mildly stressing short photic stimulation caused depletion of median eminence CRH-41, due to its release into the portal circulation and a rise in serum ACTH and corticosterone levels. This effect was significantly inhibited in rats in which 5-HT was depleted in the AMG following local 5,7-dihydroxytryptamine administration, which did not affect hypothalamic 5-HT content. Also, local pretreatment with ketanserin (a 5-HT2receptor antagonist) in the AMG had the same inhibitory effect on the HPA axis response. These results indicate that AMG 5-HT has an important role in the activation of the HPA axis following neural stimulation and that 5-HT2receptors are involved.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

THE effect of long-term adrenalectomy on NMDA receptors in the rat hippocampus was studied. Hippocampal sections of control and adrenalectomized rats were incubated with [3H]MK-801, a radiolabeled non-competitive inhibitor of the NMDA receptor. Analysis byin vitroautoradiography showed a significant decrease in [3H]MK-801 binding in the dentate gyrus, CA1 and CA4 areas, as well as the temporal cortex. Results of this study suggest that glucocorticoids are vital for the regulation of the NMDA receptors.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

THE amplitude of open-loop pointing movements to step displacements in target position is influenced by the amplitude of simultaneously produced saccadic eye movements. The time course over which this occurs was addressed in the present study. Analysis of the pointing kinematics showed that saccade amplitude had its effect only during the initial acceleration of the hand. Moreover, the magnitude of the initial acceleration was correlated with the difference in the onset times of the eye and hand movements: the closer in time the saccadic and pointing responses were initiated the larger the initial hand acceleration. Taken together, these results demonstrate that saccades influence the kinematics of simultaneously produced limb movements but only over a limited time frame.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

WE examined the effect of neonatal sensorineural hearing loss on synaptic density in the central nucleus of the inferior colliculus (ICC) of adult cats to evaluate the role of auditory experience in synaptogenesis. Three groups of animals were used: bilaterally deafened, uni-laterally deafened and normal hearing controls. Synaptic density in bilaterally deafened animals was significantly lower than in normal hearing animals. By contrast, there was no significant difference in synaptic density between normal hearing animals and unilaterally deaf animals. These results demonstrate, for the first time, that a sensorineural hearing loss during development can affect synaptogenesis in the auditory midbrain.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID