Journal of pineal research
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Since melatonin (N-acetyl-5-methoxytryptamine) decreases locomotor activity and rearing and increases grooming behavior in a similar manner as somatostatin (SRIF), we examined if melatonin could induce these changes through somatostatinergic neurotransmission in the rat frontoparietal cortex. Male Wistar rats (200-250 g) received a single injection of melatonin (25 microg/kg per day) subcutaneously (s.c.) and were sacrificed 5 hr later. Melatonin treatment increased the number of 125I-Tyr11-SRIF receptors in frontoparietal cortical membranes without any changes in the dissociation constant (Kd). ⋯ Administration of the melatonin receptor antagonist luzindole (10 mg/kg, s.c.) 30 min before melatonin injection did not change the melatonin-induced effects on the SRIF receptor effector system. In conclusion, the present results show that acute melatonin administration increases the activity of the SRIF receptor effector system and decreases Gialpha2 levels in the rat frontoparietal cortex. In addition, the coupling of Gs to AC is disturbed by melatonin.