Nitric oxide induces morphological changes in cultured neurohypophysial astrocytes

Cultured pituicytes, derived from the neurohypophysis of adult rats, have previously been reported to change from a non-stellate form to a stellate form when incubated in medium containing a beta-adrenoreceptor agonist. This study was designed to determine whether the same morphological change could be induced by direct activation of adenylate cyclase or of soluble guanylate cyclase. The fraction of stellate cells was normally low (< 0.25) when the pituicytes were incubated (90 min) in a HEPES buffered salt solution (HBSS); most pituicytes had an amorphous protoplasmic appearance. The fraction of stellate cells was significantly increased when pituicytes were incubated in HBSS supplemented with isoproterenol (10 microM) or forskolin (5 microM) or with either of the nitric oxide donors nitroprusside (10-25 microM) and 3-morpholinosydnonimine (SIN-1; 10 microM). The effect of forskolin was mimicked by 8-bromo cyclic AMP, a membrane permeable analog of cyclic AMP, but not by the inactive forskolin analog 1, 9 dideoxyforskolin. The effect of nitroprusside was blocked by methylene blue, an inhibitor of soluble guanylate cyclase, and was mimicked by 8-bromo cyclic GMP, a membrane permeable analog of cyclic GMP. These results demonstrate that activation of adenylate cyclase and also of soluble guanylate cyclase can induce pituicytes to undergo morphological changes in vitro. The data suggest that the activity of both enzymes may be important in control of the plastic relationship that exists between neuronal and glial elements in the neurohypophysis in vivo.