[Changes in the ultrastructure of striated muscles and neuromuscular synapses of rats under the effects of a 13-day space flight].

The ultrastructure of myofibers and neuromuscular synapses (NMS) of soleus, gastrocnemius and diaphragmatic muscles of rats flown on Cosmos biosatellite for 13 days was examined two days after landing. The myofibers showed atrophic and dystrophic changes that were different in various muscles: they were advanced in m. soleus, moderate in m. gastrocnemius and weak in the diaphragm. The greatest changes of NMS were seen in m. soleus, where the surface area of synaptic contacts decreased due to partial or total destruction of presynaptic structures. In m. gastrocnemius, structural changes in the synaptic apparatus included terminal sprouting. In the diaphragm, plastic changes of NMS were detected. It is stressed that electron microscopic changes in m. soleus reflect pathological shifts related to hemodynamic disorders that develop after landing.