Structural and chemical features of the invertebrate otoliths.

In the course of evolution of the invertebrate gravity receptor endogenous intracellular mode of the otoliths formation (Coelenterata, Ctenophora) is changed for endogenous extracellular mode (Mollusca, Arthropoda). The intracellular otolith is represented by cristalline concretions whereas extracellular one may consists of many separate crystallic otoconia or one large spherolith. As a rule in all cases qualitative mineral composition is similar.

Ultrastructural peculiarities of the chemical transmission of the nerve impulse in the gravity receptors of some invertebrates.

Electron microscopic and cytochemical studies of the synapses of the gravity receptors in Coelenterata, Ctenophora, Annelids and Molluscs has shown the mediators both of cholinergic and adrenergic systems. As a rule, the two mediatros were connected with different receptor systems (Ctenophora) or with the synaptic structures of various parts of the chain: receptor--neuron--effector (Medusa, Annelids). The synaptic transmission in the gravity receptor of studied molluscs classes is carried out by means of either cholinergic or adrenergic systems.

The structural and functional organization of the vestibular apparatus of rats exposed to weightlessness for 20 days on board the Sputnik "Kosmos-782".

This investigation of the vestibular apparatus of rats exposed for 20 days to weightlessness on board an earth satellite and to acceleration during take-off and landing has revealed a set of changes in the structural and functional organization, such as adjoinment of the otolith to the utricle receptor surface and peripheral localization of the nucleoli inside the receptor cells' nuclei. Destruction of some receptor cells, apparently due to increased swelling of the vestibular apparatus tissue and alteration of the shape and structure of the otoconia were observed. In the horizontal crista, detachment of the cupula took place.

The role of gravity in the phylogeny of structure and function in animal sensors of spatial orientation, and their predicted action in weightlessness.

The evolution of the structural, functional and cytochemical organization of the gravity receptor which determines a body position in the gravitational field of the earth by means of muscular regulation was traced both invertebrates and vertebrates, using electron microscopic and histochemical methods. In the course of evolution of vertebrates, the specialized gravity receptor-statocyst which, as a rule, consists of primary sensory cells and supplies otoliths, is formed. In vertebrates, there exists a vestibular apparatus made up of secondary sensory cells and also having otoliths.