Kappa opioid receptor stimulation decreases amphetamine-induced behavior and neuropeptide mRNA expression in the striatum

The purpose of this study was to investigate the role that kappa opioid rec eptor stimulation has upon stimulant-induced behavior and neuropeptide gene expression in the striatum. Acute administration of amphetamine (2.5 mg/kg i.p.) caused an increase in behavioral activity and preprodynorphin. subst ance P, and preproenkephalin mRNA expression. When amphetamine-treated rats were pretreated with U69593, a kappa agonist (0.16 or 0.32 mg/kg s.c.), th ere was a significant decrease in behavioral activity. Quantitative in situ hybridization histochemistry revealed that 0.32 mg/kg U69593 significantly decreased amphetamine-induced mRNA expression of all three neuropeptides; however, only the induction of preproenkephalin mRNA was decreased by 0.16 mg/kg. These data suggest that stimulation of kappa receptors decreases acu te amphetamine-induced behavior and mRNA expression of neuropeptides in the rat striatum. (C) 2001 Elsevier Science B.V. All rights reserved.