The effect of modelling of hypogravity on postsynaptic acetylcholine receptors and activity of acetylcholinesterase in neuromuscular synapses of fast and slow muscles of rat.

Rats were subjected to antiorthostatic hindlimb unloading for 35 days. Using immunofluorescent techniques, we found increased intensity of fluorescence and decreased area of staining of acetylcholine receptors and the increased intensity and area of staining of acetylcholinesterase in neuromuscular synapses of 'fast' and 'slow' muscles. Changes in the ratio of the number of acetylcholine receptors on the postsynaptic membrane and acetylcholinesterase and the alterations in their spatial location relative to each other in neuromuscular synapses of 'fast' and 'slow' muscles were also observed. These modifications are in accordance with the electrophysiological data on the decreased amplitudes of miniature end plate currents in both muscles. They were accompanied by a decrease in the volume of muscle fibers. Antiorthostatic unloading, a model of hypogravity, resulted in increased functional activity of acetylcholinesterase associated with decreased area of the postsynaptic membrane occupied by acetylcholine receptors, which led to a decrease in the amplitude of postsynaptic excitatory potentials and thus, to the decreased reliability threshold of excitation transmission from a nerve to a muscle. [ABSTRACT FROM AUTHOR]