Effects of repeated ritanserin on middle-aged poor sleepers

The present study was designed to investigate the effect of U-50, 488H, a highly selective kappa opioid agonist, on ipsilateral and contralateral circling behavior induced by methamphetamine and by apomorphine, respectively. U-50, 488H (3.2–10 mg/kg IP) by itself failed to induce either ipsilateral or contralateral circling in rats with unilateral nigral lesions produced by an injection of 6-hydroxydopamine. U-50, 488H produced a significant dosedependent inhibition of methamphetamine (1.0 mg/kg SC)elicited ipsilateral circling. However, it had no effect on contralateral circling induced by apomorphine (0.5 mg/kg SC). The present results indicate that U-50, 488H presynaptically inhibits the release of dopamine in the rat striatum.