Inhibition of nitric oxide synthase induces ultrastructural changes in the neurohypophysis of dehydrated rats

Neuroglial relations in the rat neurohypophysis have been shown previously to change significantly after an acute dehydration stimulus. Here, we demonstrate a significant role for nitric oxide as a mediator of this response. Adult male rats were injected (i.p.) with 1.5 M NaCl or with 1.5 M NaCl and N-omega-nitro-L-arginine methyl ester (L-NAME) an inhibitor of nitric oxide synthase. Five hours after the dehydration stimulus, animals were perfusion fixed and the ultrastructure of their neurohypophyses examined. Neurohypophyses of animals injected with L-NAME and NaCl had significantly less contact between the basal lamina and the membrane of axon terminals than those of animals injected only with NaCl. There was also a significantly larger number of axonal profiles enclosed within neurohypophysial astrocytes in L-NAME and NaCl injected animals than in animals injected only with NaCl. (C) 1997 Elsevier Science Ireland Ltd.