Melatonin Nocturnal Surge Modulates Nicotinic Receptors and Nicotine-Induced [3H]Glutamate Release in Rat Cerebellum Slices

In mammals, the most important synchronizer for endogenous rhythms is the environmental light/dark cycle. In this report we have explored the ability of light/dark cycle and melatonin, the pineal hormone released during the night, to modulate cerebel-lar cholinergic input by interfering with the nicotinic acetylcho-line receptors ’ (nAChRs) availability. Through the analysis of the response to selective cholinergic agonists and antagonists, we observed that nAChRs containing the 7 gene product mediate the release of [3H]glutamate from rat cerebellum slices. The [3H]glutamate overflow induced by 7 nAChR activation was higher during the dark phase, although the number of -[125I]bungarotoxin binding sites, but not the [3H]nicotine binding sites (Bmax), was reduced. On the other hand, gluta-mate-evoked [3H]glutamate release was not modified by th