Is the role of melatonin in induction of ovulation in the light-induced constant estrous anovulatory state mediated through the brain serotonergic system ?

In animals in constant estrous-anovulatory (CEA) state, induced by conti- nuous exposure to light (LL), the midbrain content of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) decreased significantly, but no significant variations were detected in the basal hypothalamus. Late afternoon chronic melatonin treatment provoked resumption of ovulation and increased the midbrain 5-HT content. Similar results were evident after replacing LL-CEA rats in normal light-dark cycles. Melatonin appeared to mimic the effect of the daily darkness phase by eliciting ovulation ; this effect might be mediated via the midbrain serotonergic system.