MORPHOLOGICAL-CHANGES OF SOMATOSTATIN NEURONS IN THE SUPRACHIASMATIC NUCLEUS BY HYPOPHYSECTOMY OF THE RAT

After hypophysectomy, behavioral circadian rhythmicities in the rat be came indistinct and phase shift was observed. Therefore, it was though t that the suprachiasmatic neucleus (SCN), which is the circadian osci llator in mammals, was affected by hypophysectomy. We investigated the effects of hypophysectomy on SCN neurons using immunohistochemical st aining. Wistar-Imamichi strain male rats were hypophysectomized at 60 days old. Their brains were fixed by acrolein perfusion at 10, 30 and 60 days after the operation, and then vasopressin (AVP) -, vasoactive intestinal polypeptide (VIP) and somatostatin (SRIH) - neurons in the SCN were stained immunohistochemically. Ten days after the operation, SRIH-neurons were not found in the SCN. At 30 and 60 days after the op eration, a few SRIH-positive cell bodies were recognized. In contrast, AVP-and VIP-neurons did not change in morphology in comparison with n ormal rats. These results suggest that hypophysectomy produces an esse ntial change in SRIH neurons in the SCN, and that such change is respo nsible or the abnormal behavioral rhythms.