Lowenstein P R, Pereyra E N, González Solveyra C, Cardinali D P
Eur J Pharmacol. 1984 Feb 17;98(2):261-4. doi: 10.1016/0014-2999(84)90598-3.
Rats exposed to 14 light: 10 h dark photoperiods were given naloxone hydrochloride (10 mg/kg) s.c. 2 h before and 5 h after the lights were turned off. A smaller nocturnal pineal melatonin peak, as well as a slower decrease from peak values were observed in naloxone-treated rats. Naloxone (up to 10(-4) M) did not affect either in vitro rat pineal melatonin content or 3H-labeled transmitter release in glands previously incubated with [3H]norepinephrine. Hence a central, rather than a peripheral opioid synapse appears to be involved in naloxone effect on nocturnal melatonin increase.
