INVOLVEMENT OF 5-HT1A RECEPTOR MECHANISMS IN THE INHIBITORY EFFECTS OF METHAMPHETAMINE ON PHOTIC RESPONSES IN THE RODENT SUPRACHIASMATIC NUCLEUS

We examined the role of serotonin IA (5-HT1A) receptors in the inhibit ory effects of methamphetamine (MA) on photic entrainment to the circa dian pacemaker in the suprachiasmatic nucleus (SCN) of rodents. MA inh ibited optic nerve stimulation-evoked field potential in the SCN, ligh t-induced Fos expression in the SCN and light-induced phase shift of h amster wheel-running rhythm. NAN-190, a 5-HT1A receptor antagonist, el iminated the inhibitory effects of MA. NAN-190 has also been reported to antagonize alpha 1 adrenergic receptors. However, prazosin, which s electively antagonizes alpha(1) adrenergic receptors, did not affect t he inhibitory action of RIA on light-induced Fos expression. In additi on, parachloroamphetamine, which is known to be a 5-HT releaser, dose- dependently inhibited light-induced phase shift of wheel-running rhyth m. These findings suggest that elevation of endogenous 5-HT levels by RIA inhibits the photic entraining responses of the circadian pacemake r in the SCN via 5-HT1A receptor stimulation of the 5-HT released by M A.