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Abstract
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 microdialysis with electrochemical detection. Nociceptin administered
intracerebroventricularly (i.c.v.) at doses of 2, 5 and 10 nmol/rat changed neither
DA nor metabolites release in the shell of the nucleus accumbens or in the nucleus
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 administered 15 min before morphine
(5 or 10 mg/kg), it significantly reduced morphine-induced DA and metabolites release
in the shell of the nucleus accumbens, whereas only a slight, nonsignificant reduction
was observed in the nucleus caudate. Our data indicate that nociceptin may regulate
the stimulating action associated with morphine-induced DA release more in the nucleus
accumbens than in the nucleus caudate, and are consistent with recent observations
that nociceptin reversed ethanol- and morphine-induced conditioned place preference.
Therefore, the nociceptin-induced reduction of DA release stimulated by morphine in
the nucleus accumbens, and the results obtained 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.