CONTRASTING ACTIONS OF ACUTE OR CHRONIC PAROXETINE AND FLUVOXAMINE ONMORPHINE WITHDRAWAL-INDUCED PLACE CONDITIONING

The acute and chronic effects of paroxetine and fluvoxamine on naloxon e withdrawal-induced place aversion in morphine dependent rats were in vestigated. Acutely administered fluvoxamine (25 mg/kg s.c. given 30 m in prior to naloxone withdrawal pairing) and chronic daily paroxetine (10 mg/kg s.c.) coadministration with a morphine induction protocol, b oth attenuated morphine withdrawal place aversion. Conversely, acutely administered paroxetine (up to 25 mg/kg s.c.) or chronic daily fluvox amine (10 mg/kg s.c.) coadministration with morphine did not modify su bsequent withdrawal place aversion. Previous radioligand binding studi es indicate that fluvoxamine has opioid-displacing properties. It is s uggested therefore that acute fluvoxamine may have decreased withdrawa l aversion, probably through serotonin and also, in part, via an opioi d-like mechanism whereas chronic paroxetine decreased withdrawal avers ion by a serotonergic mechanism, but it is not clear whether opioid sy stems play any role in the action of paroxetine.