The role of the hypothalamic paraventricular nuclei for the regulation of pineal melatonin synthesis: new aspects derived from the vasopressin-deficient Brattleboro rat.

There is evidence for an involvement of the hypothalamic paraventricular nuclei (PVN) in the regulation of pineal melatonin synthesis in rats. Since electrical stimulation of the PVN or the systemic administration of arginine-vasopressin (AVP) result in a depression of the nocturnal melatonin surge, this neuropeptide appears to be pivotal for the transduction of PVN-efferent, pinealopetal signals. We therefore used an AVP-deficient animal model, the Brattleboro rat, to further investigate the mechanisms responsible for pineal regulation. Anesthetized adult male animals received 2 min of bilateral electrical stimulation of the PVN either during the day or at night. Thirty min later, pineal glands were removed and pineal N-acetyltransferase (NAT) activities and melatonin contents were determined. Stimulation resulted neither during the day nor at night in any significant alterations of pineal NAT activity or melatonin content when compared to control or sham-stimulated animals. These data further support the proposed modulatory role of AVP for the regulation of melatonin synthesis in the Epiphysis cerebri of genetically intact rats.