NOREPINEPHRINE CONTENT IN DISCRETE BRAIN-AREAS AND NEUROHYPOPHYSEAL VASOPRESSIN IN RATS AFTER A 9-D SPACEFLIGHT (SLS-1)

The norepinephrine (NE) content in discrete brain areas and the vasopr essin content in the neurohypophysial system were assessed in rats aft er a 9-d spaceflight and after a recovery period (9 d). The NE content in the locus coeruleus decreased significantly in spaceflight rats (2 .9 +/- 0.3 vs. 8.9 +/- 0.7 pmol . structure-1 for control rats, p < 0. 001), but showed no difference between control and flight animals afte r a 9-d recovery. These findings were probably due to an acute stress undergone during landing. The NE content was unchanged in the A2 and A 5 cell groups. In rats flown aboard SLS-1, the vasopressin content was increased in the posterior pituitary (1.47 +/- 0.1 vs. 0.86 +/- 0.1 m ug . structure-1 for control rats, p < 0.0 1), and was significantly d ecreased in the hypothalamus (8.95 +/- 2.0 vs. 17.6 +/- 2.2 ng . struc ture-1, for control rats, p < 0.05). We conclude that the NE depletion in the locus coeruleus and the alteration in vasopressin release were consistent with an acute stress, likely occurring during and/or after landing. These changes tend to mask the actual neuroendocrine modific ations caused by microgravity.