Nociceptin differentially affects morphine-induced dopamine release from the nucleus accumbens and nucleus caudate in rats

The effects induced by nociceptin on morphine-induced release of dopamine ( DA), 3,4-dihydroxyphenilacetic acid (DOPAC) and homovanillic acid (HVA) in the nucleus accumbens and nucleus caudate were studied in rats by microdial ysis with electrochemical detection. Nociceptin administered intracerebrove ntricularly (i.c.v.) at doses of 2, 5 and 10 nmol/rat changed neither DA no r metabolites release in the shell of the nucleus accumbens or in the nucle us caudate. Morphine administered intraperitoneally (i.p.) (2, 5, and 10 mg /kg) increased DA and metabolites release more in the shell of the nucleus accumbens than in the nucleus caudate. When nociceptin (5 or 10 nmol) was a dministered 15 min before morphine (5 or 10 mg/kg), it significantly reduce d morphine-induced DA and metabolites release in the shell of the nucleus a ccumbens, whereas only a slight, nonsignificant reduction was observed in t he nucleus caudate. Our data indicate that nociceptin may regulate the stim ulating action associated with morphine-induced DA release more in the nucl eus accumbens than in the nucleus caudate, and are consistent with recent o bservations that nociceptin reversed ethanol- and morphine-induced conditio ned place preference. Therefore, the nociceptin-induced reduction of DA rel ease stimulated by morphine in the nucleus accumbens, and the results obtai ned with nociceptin in the conditioned place preference procedure suggest a role for nociceptin in the modulation of the behavioral and neurochemical effects of abuse drugs. (C) 2000 Elsevier Science Inc. All rights reserved.