Recovery of neuromuscular junction morphology following 16 days of spaceflight.

It has previously been established that spaceflight elicits alterations in the morphology of the neuromuscular system that includes expansion of the neuromuscular junction (NMJ) and myofiber atrophy. The purpose of this study was to determine the capacity of the neuromuscular system to recover from spaceflight-induced modifications upon return to normal gravity. Soleus muscles were obtained from rats participating in the 16-day Neurolab space shuttle mission at 1 day and 14 days after returning to Earth: solei were also taken at the same time points from ground-based control rats. Cytofluorescent techniques, coupled with confocal microscopy, were used to assess NMJ morphology. Histochemistry, in conjunction with phase contrast microscopy, was employed to examine myofiber size and type. Results indicate that 1 day after landing both pre- and postsynaptic stained areas of the NMJ were significantly (P < or = 0.05) larger in the spaceflight group than in controls. Moreover, significant myofiber atrophy was demonstrated in animals subjected to 0 gravity. By 14 days following return to the Earth, however, NMJ stained areas and muscle fiber size were no longer different from control values at that same interval. These results suggest that the neuromuscular system possesses a robust capacity to recover from spaceflight-induced perturbations upon return to normal gravitational influences.