突触小泡膜表面突起与微管联系的超微结构研究

本研究用透射电镜技术观察了大脑皮质（视区）和海马（CA1区和CA3区）的神经终末内的突触小泡和微管间的联系。结果揭示：在适当的超薄切片样品上，常显示出突触小泡膜表面上有短的突起，说明突触小泡是借其膜表面的短突与其它小泡和微管进行联系的。除小泡外，在微管的表面也见一些短突并与小泡发生接触。本文首次报道了用透射电镜方法观察脑内小泡-微管借表面短突连接的联系，提示突触小泡膜表面和微管表面的短突在轴浆运输机制中负有重要的作用。     

Suppression of hippocampal synaptic plasticity during slow-wave sleep

The influence of behavioral state on the induction of long-term enhancement (LTE) of hippocampal synapses was studied in chronically prepared animals. Perforant path evoked field potentials and EEG were recorded from fascia dentata during slow-wave sleep (SWS) and waking. LTE was strongly suppressed during SWS, suggesting that hippocampal information storage may be inactivated at certain phases of the sleep cycle. Normal LTE was observed in the same animals while awake.     

Differential Distribution of Syntaxin Isoforms 1A and 1B in the Rat Central Nervous System

Syntaxin 1 binds to several proteins of the synaptic terminal and is a central component in the pathway of protein–protein interactions that underlies docking and fusion of synaptic vesicles. Molecular studies revealed the occurrence of two isoforms, syntaxin 1A and syntaxin 1B, which coexpress in neural tissues. However, they display differential expression patterns in endocrine cell types. We generated isoform-specific antibodies that were used in Western blotting and immunocytochemical studies. First, we confirmed the sole presence of syntaxin 1A in endocrine pituitary cells. Second, we found distinctive immunolabelling patterns of each isoform in the rat olfactory system, hippocampus, striatum, thalamus and spinal cord. In addition, the principal white matter commissures displayed distinct immunoreactivity for each isoform. This report shows, for the first time, major differences between the distributions of syntaxin 1A and syntaxin 1B isoforms in the rat central nervous system.     

Serum modulates cyclic AMP-dependent morphological changes in cultured neurohypophysial astrocytes

The effects of serum on the morphological plasticity exhibited by pituicytes in explant cultures of the neurohypophysis of adult rats have been examined. Cultured pituicytes are normally nonstellate, protoplasmic, amorphous cells (< 25% are stellate with a distinct cell body and phase bright processes). After incubation (90 min) of pituicyte cultures in a HEPES buffered salt solution (HBSS) supplemented with isoproterenol or forskolin, the fraction of stellate pituicytes significantly increased. The increase in the fraction of stellate cells induced by isoproterenol was not reversed by subsequent incubation in isoproterenol-free HBSS for 90 min. In contrast, after stellation was induced in cultures by exposure to forskolin (90 min), the fraction of stellate cells was significantly reduced if these cultures were incubated in forskolin-free, serum (0.5%) supplemented HBSS for the same duration. Serum also blocked the increase in the fraction of stellate pituicytes induced by forskolin. These experiments suggest that serum components may have a significant role in controlling the plasticity of neuroglial relations in the neurohypophysis priviously demonstrated in vivo.     

Sound-generating (sonic) motor system in a teleost fish (Porichthys notatus): sexual polymorphisms and general synaptology of sonic motor nucleus

The sonic motor nucleus of the plainfin midshipman, Porichthys notatus, is a midline nucleus located at the junction of the caudal medulla and rostral spinal cord. Its motoneurons innervate sonic "drumming" muscles that are attached to the lateral walls of the swimbladder. There are two classes of sexually mature males referred to as Type I and Type II. The Type I males are larger and generate sounds during the breeding season. The Type II males are smaller and, like adult females, have not yet been shown to generate sounds. This study examined possible sex differences in the size of sonic motoneurons, and the type and distribution of their afferent terminal boutons. The average soma diameter of motoneurons of Type I males is about 50% larger than that of Type II males and females. There is also a small but significant difference in soma diameter between Type II males and females; they are smaller in the former class. There were no sex differences in the presence or distribution of different classes of axosomatic and axodendritic terminal boutons, which included: (1) active zones with either clear, round, or pleomorphic vesicles, (2) active zones with both clear, round vesicles, and larger dense core vesicles, (3) "mixed synapses" with gap junctions and active zones usually associated with pleomorphic vesicles. The results are discussed within the context of sexual differentiation of vertebrate motor systems and the functional organization of the sonic motor system in fishes. Sex differences in soma diameter correlate with a number of sex differences in the gross and ultrastructural features that distinguish the sonic muscles of Type I males from those of Type II males and females, which are similar to each other. The absence of qualitative sex differences in synaptic morphology suggest that the central neuronal circuitry of the sonic motor system is similar among all three adult morphs.     

Immunocytochemical localization of GABAA receptors in goldfish and chicken retinas

A monoclonal antibody (mAb 62-3G1) to the GABAA receptor/benzodiazepine receptor/Cl- channel complex from bovine brain was used with light and electron microscopy in goldfish retina and light microscopy in chicken retina to localize GABAA receptor immunoreactivity (GABAr-IR). GABAr-IR was found in the outer plexiform layer (OPL) in both species, in three broad bands in the inner plexiform layer (IPL) of goldfish, and in seven major bands of the chicken IPL. A small percentage of amacrine cell bodies (composing at least three types) were stained in chicken. In goldfish OPL, GABAr-IR was localized intracellularly and along the plasma membrane of cone pedicles, whereas rod spherules were lightly stained, but always only intracellularly. In chicken, all three sublayers of the OPL were GABAr-IR. The presence of GABAr-IR on photoreceptor terminals is consistent with data indicating feedback from GABAergic horizontal cells to cones. In the goldfish IPL, GABAr-IR was localized to postsynaptic sites of amacrine cell synapses; intracellular staining of processes in the IPL also was observed in presumed "GABAergic" targets. A comparison of GABAr-IR with the distributions of 3H-muscimol uptake/binding, glutamate decarboxylase-IR, GABA-IR, and 3H-GABA uptake in the IPL showed either a reasonable correspondence or mismatch, depending on the marker, species, and lamina within the IPL. The distribution of GABAr-IR in the retina corresponded better with the 3H-muscimol than with 3H-benzodiazepine binding patterns yet overall was in excellent agreement with many other physiological and anatomical indicators of GABAergic function. We suggest that intracellular GABAr-IR represents the biosynthetic and/or degradative pathway of the receptor and we conclude that mAb 62-3G1 is a valid marker of GABAA receptors in these retinas and will serve as a useful probe with which to address the issue of mismatches between the localization of GABAA receptors and indicators of presynaptic GABAergic terminals.     

Polysialic acid, a unique glycan that is developmentally regulated by two polysialyltransferases, PST and STX, in the central nervous system: From biosynthesis to function

Polysialic acid is a developmentally regulated carbohydrate composed of a linear homopolymer of a-2,a-linked sialic acid residues. This unique glycan is mainly attached to the neural cell adhesion molecule (N-CAM) and implicated in many morphogenic events of the neural cells by modulating the adhesive property of N-CAM. Recently, the cDNA that encodes polysialyltransferase, which is responsible for the polysialylation of N-CAM, was successfully cloned from three mammalian species. This review focuses on the molecular cloning of human polysialyltransferase, designated PST. it then describes the number of enzymes actually required for the polysialylation of N-CAM using an in vitro polysialyltransferase assay. Comparisons between PST and another polysialyltransferase, sialyltransferase X (STX), are made and it Is demonstrated that both enzymes can independently form polysiatic acid In vitro , but that during neural development they coordinately but distinctly synthesize polysialic acid on N-CAM. The role of polysialic acid in the central nervous system is also discussed. Finally, evidence that the two polysialyltransferases, PST and STX, apparently have distinct roles in the development of neural cells is provided by using a neurite outgrowth assay.     

Transcranial magnetic stimulation: new insights into representational cortical plasticity

In the last decade, transcranial magnetic stimulation (TMS) has been used increasingly as a tool to explore the mechanisms and consequences of cortical plasticity in the intact human cortex. Because the spatial accuracy of the technique is limited, we refer to this as plasticity at a regional level. Currently, TMS is used to explore regional reorganization in three different ways. First, it can map changes in the pattern of connectivity within and between different cortical areas or their spinal projections. Important examples of this approach can be found in the work on motor cortex representations following a variety of interventions such as immobilization, skill acquisition, or stroke. Second, TMS can be used to investigate the behavioural relevance of these changes. By applying TMS in its "virtual lesion" mode, it is possible to interfere with cortical function and ask whether plastic reorganization within a distinct cortical area improves function. Third, TMS can be used to promote changes in cortical function. This is achieved by using repetitive TMS (rTMS) to induce short-term functional reorganization in the human cortex. The magnitude and the direction of rTMS-induced plasticity depend on extrinsic factors (i.e. the variables of stimulation such as intensity, frequency, and total number of stimuli) and intrinsic factors (i.e. the functional state of the cortex targeted by rTMS). Since conditioning effects of rTMS are not limited to the stimulated cortex but give rise to functional changes in interconnected cortical areas, rTMS is a suitable tool to investigate plasticity within a distributed functional network. Indeed, the lasting effects of rTMS offer new possibilities to study dynamic aspects of the pathophysiology of a variety of diseases and may have therapeutic potential in some neuropsychiatric disorders. Electronic Publication     

衰老时海马神经元树突的可塑性增生

用形态计量的方法对老年(30个月)和成年(17个月)大鼠脑(Golgi染色标本)的海马CA3区锥体细胞的树突分支进行分级计数和测量了终末支的长度。结果是CA3神经元基树突和顶树突共有9级分支,衰老时第4级和第9级分支有显著的增多(P<0.02,P<0.03)。基树突终末支的长度衰老时无明显改变,顶树突终末支长度较成年组增加(P<0.05)。提示衰老时海马神经元的树突仍具有一定的增生和分化能力。这可能是对神经元退变的一种代偿机制。     

Synaptic responses of neurons in the parietal associative cortex of the cat to stimulation of the red nucleus

Acute experiments on anesthetized and immobilized cats using intracellular recording were used to study the responses of neurons in the parietal associative cortex to stimulation of the red nucleus. Efferent neurons of the parietal cortex were identified by antidromal activation on stimulation of the intrinsic nuclei of the pons and motor cortex. Oligo- and polysynaptic EPSP in response to stimulation of the red nucleus were seen. The results are discussed in the light of the morphological organization of the rubrothalamic and cerebellothalamocortical tracts. Laboratory for Central Nervous System Physiology (Director V. V. Fanardzhyan), L. A. Orbel' Institute of Physiology, Armenian National Academy of Sciences, Erevan. Translated from Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 81, No. 12, pp. 64–69, December, 1995.