Pineal and gonadal function in the rat following cervical sympathectomy.

Abstract

The activity of the melatonin-forming enzyme, hydroxyindole-O-methyltransferase (HIOMT), is high in the pineals of rats kept in constant darkness and low in the glands of animals kept in constant light. The sympathetic innervation of the pineal is necessary to maintain this response to light. Following removal of the superior cervical ganglion (ganglionectomy) or section of the preganglionic fibers to the ganglion (decentralization), the pineal HIOMT response to light is lost. In addition, HIOMT levels after decentralization are significantly less than after ganglionectomy and these, in turn, are significantly less than constant-light, control levels. The decreases in pineal HIOMT content produced by ganglionectomy and decentralization are evident within 1 week and become maximal by 2 to 3 weeks after operation. Thereafter, they remain stable for at least 120 days. These data indicate that an intact sympathetic innervation to the pineal is necessary, not only for an HIOMT response to light, but, also, to maintain normal enzyme activity in the gland. The observation of a substantial decrease in HIOMT activity in the squirrel monkey pineal following decentralization suggests that this may be a more general phenomenon in mammals. Despite the effect on pineal HIOMT, denervation of the pineal does not alter the normal estrous cycle of the female rat kept in diurnal light, nor does it affect the alterations in estrous activity produced by prolonged exposure to constant light or blinding. These findings are in accord with the view that light-mediated alterations in pineal function are not essential in the rat to either the maintenance of normal estrous cycles or to estrous responses to conditions of continuous illumination.