[Morphological characteristic of a motor unit afferent limb in hypokinesia]

Neuromuscular spindles (NMS) of soleus muscle and their vascular bed was studied in 250 mature male Wistar rats following long-term (30, 60, 120 and 240 days) hypokinesia. Material was studied using Kulchitsky, Mason and Ranson histological staining, electron microscopic and histochemical methods (demonstration of succinate dehydrogenase). It was found that initial changes involved the decrease of the lumen of precapillary arterioles (by 25.4%) and blood capillaries (by 29.1%). These changes closely correlated with the increase of the subcapsular space width (by 34.7%), the decrease of NMS capsule thickness (by 48.7%) and equatorial zone diameter (by 17.9%). Activity of succinate dehydrogenase in the intrafusal muscle fibers was also decreased. As a result of disintegration of the majority of gamma-axon terminals, NMS cross sectional area was decreases by 75.6%. Thus, during hypokinesia initial changes were detected in the sources of NMS blood supply, while their structural remodelling involved destructive alterations.