Subsynaptic units as a universal system-forming and regulating factor of brain synapses

Abstract

Dense projections and postsynaptic density --specialized structures of the synaptic cytoskeleton --are regarded as a single functional system of subsynaptic units. From this viewpoint, interneuronal relations in health and after brain ischemia are analyzed. It is shown that hyperplasia and recombination of the system of subsynaptic units are the major mechanisms responsible for reorganization of functionally mature interneuronal junctions in the mammalian and human brain. Key Words: synapse; synaptic cytoskeleton; dense projections; postsynaptic densityThe relationship between form and content and between quality and quantity at the level of intemeuronal relations are of particular importance, taking into account the role of synapses in neuronal plasticity and the molecular biochemistry, immunohistochemistry, and electron microscopy data [4,7,16,24,38,41,47,65]. Basic structural components and biochemical composition of virtually all brain synapses have been identified. They include: 1) pre-and postsynaptic membranes with receptors and ionic channels and pumps, 2) synaptic cleft substance providing adhesion, transport, and deactivation of neurotransmitters, 3) intrasynaptic structures: simple (synaptic vesicles) and more complex vesicular (various vacuoles, rimmed vesicles, and multivesicular complexes) and filamentous-granular-vesicular (dendritic spikes), and 4) specific structures of presynaptic (dense projections) and postsynaptic (postsynaptic density) cytoskeleton [3,14,47,63,82]. Although large body of evidence has been collected, the problem of integrating structure(s) of the synapse unsolved [6].The idea that paramembrane structures of the cytoskeleton is a single functional system of subsynaptic units (SSU) that integrates the activity of Department of Histology and Embryology, Medical Academy, Omsk the entire synapse was put forward in the 1970s [1,5]. The search for the system-forming factors and their structural equivalents at the level of interneuronal junctions and new electron microscopic data on the structure of paramembrane zones in syalapses [14,18,22,30,44,70] led to the need of interpreting the contribution of dense projections (DP) and postssamptic densities (PSD) to impulse transmission across synapses [1] in structural and functional terms. It was demonstrated that pre-and postsynaptic structures are structurally and functionally continuous and operate as a single complex [1,5]. Molecular mechanisms by which all synaptic structures are integrated in a system of discrete information transfer between neurons have been elucidated [3,24,27,34,47,63,71,77,82].New information regarding synaptic function and the need for morphological indicators of integrative-triggering activity of the brain motivated our interest into the idea of the SSU in the light of recent findings [7][8][9][10][11]13]. We have formulated a concept of the SSU [7,12] and applied it to the analysis of specific pathological and functional states of the brain [7][8][9][10]75]. According to this concept, a SSU that was created o...

Synaptic Soluble and Membrane-Bound Choline Acetyltransferase as a Marker of Cholinergic Function In Vitro and In Vivo

“…This phenomenon of the transformation of synapses was found in electron microscopic experiments during 90 minutes of severe hypoxia [144,145]. It was shown that the change of a morphological type occurs due to the changes in the area, density and configuration of the network elements of the presynapses and in their configuration [153]. Almost all of these parameters can affect the density of the presynapses.…”

“…Both the cholinergic projective systems and interneurons of the rat cortex and hippocampus are actively involved in learning and memory processes in the Morris water maze model [28]. The presynapses of cholinergic interneurons in the cat temporal associative cortical area do not participate in inherited abilities for the analysis of images [25] but all of other associative cortical areas (frontal and parietal) active participated in cognitive processes [153].…”

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