Comparison of the Tripartite Organization of Synaptic Terminals in Intraocular Septal Transplants and in the Septal Area
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Comparison of the Tripartite Organization of Synaptic Terminals in Intraocular Septal Transplants and in the Septal Area of the Brain Z. N. Zhuravleva
UDC 611.81+616.853
Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavlova, Vol. 70, No. 3, pp. 375–382, May–June, 2020. Original article submitted September 12, 2019. Revised version received December 7, 2019. Accepted December 16, 2019. The septal area of the brain is functionally connected to other limbic structures and is involved in cognitive processes. Intraocular neural transplants provide an experimental model for studying the endogenous morphofunctional properties of the septum. The aim of the present work was to compare the structure of synaptic contacts in septal intraocular neural transplants and in the septal area of the brain in situ. Neurons are regarded as thee-component complexes including not only pre- and postsynaptic components, but also the astrocyte processes encircling them. Ultrastructural studies showed that despite the absence of normal afferent and efferent connections in intraocular neural transplants, their synapses reproduced the tripartite organization. Morphometric analysis of their parameters showed a decrease in the statistical mean area and perimeter of the presynaptic compartment as compared with normal. At the same time, the extent of encirclement by perisynaptic astrocyte processes in transplants was, conversely, significantly greater than in the septum in situ. The mean extents of active zones in synaptic profiles in transplanted neurons was greater than that in controls. The morphometric data obtained here indicate coordinated regulation of the sizes of the three compartments of synapses depending on the functional state of the synaptic apparatus overall. Keywords: septum, intraocular neural transplants, tripartite synapses, perisynaptic astrocyte process, ultrastructure, morphometry.
Introduction. Neural transplantation into the brain and anterior chamber of the eye (ACE) was introduced by Vinogradova into the arsenal of tools for studying the activity of septal and hippocampal neurons. This experimental approach made it possible to discriminate the roles of external afferents and endogenous factors in forming defined patterns of electrical activity. Furthermore, the method provides for assessment of the morphofunctional plastic reorganization of these parts of the limbic system in conditions of anomalous afferentation or the complete absence of contact with the brain. Studies have shown that neurons developing in transplants adapt to the new conditions and reproduce the
specific morphological and physiological characteristics of the donor structure [Vinogradova, 1988; Zhuravleva et al., 1985; 1986]. The distribution of synaptic terminals across the surfaces of neuron dendrites and bodies is not essentially different from the normal and their structure corresponds to classic concepts [Zhuravleva et al., 1986]. However, the interactions of the synaptic terminals of transplanted neurons with glial cells rem
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