[Ultrastructure of the neuromuscular junctions in the rat soleus muscle under varying gravity conditions]

Changes in the ultrastructure of neuromuscular junctions have been considered as an index to adaptation of Wistar rats (whose pre- and postnatal ontogenesis proceeded on a centrifuge under constant rotation until the age of two months) to the hypergravity conditions (2G) and, then, to earth gravity (1G): on the 2nd and 15th days after centrifuge stoppage. The dynamic of synaptic vesicles was shown: their number increased at 2G and gradually decreased at 1G. Local damage of muscle fibers, partial separation of the motor axonal terminal from intrafusal fiber, and membrane twisting were noted at the increased gravity-dependent static load (2G). Neuromuscular junctions with signs of remodeling occurred more frequently in the experimental rats than in the control ones. It was proposed that adaptation of rats to 1G gravity after a prolonged sojourn under the hypergravity conditions (2G) was not completed within the studied period.