[Morphology of the rat's brain in and after a space flight: ultrastructure of the "blue spot"]

Electron microscopy was used to explore ultrastructure of the livor extracted from the brain of rats on day-13 aboard U.S. space shuttle Columbia (STS-58), and in 5-6 hrs. after landing following the 14-d mission. As compared with the ground controls, the rats flown in microgravity reduced the total number of axodendrite synapses (ADS) by 21% and functional ADS--by 39.7%. After touchdown the total ADS number remained lowered by 16.5%; however, the percentage of highly active ADS exceeded this parameter in the ground controls. Results of the analysis of the ADS number in conjunction with the ultrastructural changes in axonal terminals and dendrites suggest a sharp decrease of the afferent influx towards the livor neurons during microgravity, whereas modifications of the livor neuron ultrastructure point to a decline in their functional activity. These data serve as an experimental proof of the hypothesized development of the hyponoradrenergic syndrome by mammals in microgravity.