MELATONIN INHIBITS THE INCREASE OF CYCLIC-AMP IN RAT SUPRACHIASMATIC NEURONS INDUCED BY VASOACTIVE-INTESTINAL-PEPTIDE

The effects of melatonin on basal and vasoactive intestinal peptide (V IP)-induced cAMP concentration was studied in dispersed cells of the r at suprachiasmatic nuclei (SCN). Our data indicate, that VIP induces a rapid increase of cAMP concentration in the cells followed by a slow and prolonged increase in the medium. The VIP-induced increase was dos e-dependent in the range of 1-100 nM. Melatonin had no effect on basal cAMP but inhibited the cAMP increase induced by VIP in a dose-depende nt manner (EC50 = 0.21 nM). Our observations indicate that melatonin a cts through the inhibition of cAMP in the SCN cells similar as shown i n other tissues. (C) 1998 Published by Elsevier Science Ireland Ltd. A ll rights reserved.