Testicular Responses to Melatonin are Altered by Lesions of the Suprachiasmatic Nuclei in Golden Hamsters

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Abstract
Destruction of the suprachiasmatic nuclei (SCN) prevented testicular regression in hamsters injected once daily with melatonin (25 .mu.g/injection) for 7 wk. Hamsters with SCN lesions, unlike controls with sham lesions, experienced complete gonadal collapse when melatonin was injected 3 times daily. The pattern of responsiveness to 1 or 3 daily injections was similar in pinealectomized hamsters, those with SCN lesions and those with combined destruction of the SCN and the pineal. Destruction of the SCN appears equivalent in this context to the removal of the pineal or to interference with its sympathetic innervation. The SCN are not essential target tissues for the regressive effects of melatonin on the hamster reproductive system, nor does their role in photoperiodism appear to be mediated by control of prolactin secretion. The altered pattern of responsiveness to melatonin after SCN damage is consistent with previous data suggesting that these nuclei participate in regulation of pineal metabolism and secretion. Alternatives to this hypothesis are discussed.