[Reaction of the neuronal population of rat's L5 spinal ganglia to primary and repeated modeling of microgravity effects].

Cytochrome oxidase activity as well as neurons' body and nuclei sizes were measured in the spinal L5 ganglia receiving the hindlimb afferent input during primary and repeated 14-d tail-suspension of rats. The measurements were performed using the quantitative cytochemical and morphometric techniques. The animals were suspended 30 days and returned to vivarium. Thirty day later, they were suspended again, together with a group of intact rats, this time for 14 days. Primary 14-day suspension reduced significantly the cytochrome oxidase activity in small, middle and large neurons (cross-section area of bodies less than 800, 800-2000 microm2 and more than 2000 microm2, respectively) and yielded a trend-like diminution of the nerve cells bodies and nuclei. The postponed repeated suspension, unlike the primary 14-d one, resulted in a substantial downsizing of bodies and nuclei of middle neurons suggesting a more dramatic hypofunction and a more dramatic decrease of afferent input. However, the cytochrome oxidase activity was not suppressed considerably in small and middle neurons which might be explained by initiation of the afferent input recovery.