Tress Potentiation of Morphine-induced Dopamine Efflux N the Nucleus Accumbens Shell Is Dependent upon Tressor Uncontrollability and Is Mediated by the Orsal Raphe Nucleus

bstract—A single session of uncontrollable (inescapable ailshock, IS), but not controllable (escapable tailshock, ES), tress is known to selectively potentiate subsequent orphine-conditioned place preference in a dorsal raphe nuleus (DRN) serotonin (5-HT) dependent manner. Here, in ivo microdialysis is used to test the hypothesis that prior IS, ut not ES, will potentiate morphine-induced dopamine (DA) fflux in the nucleus accumbens (NAc) shell and that this ill occur by a pathway involving DRN 5-HT neurons. Male prague–Dawley rats were exposed to yoked IS, ES, or no tress. Twenty-four hours later, morphine (3 mg/kg s.c.) or aline was administered during microdialysis. As predicted, rior IS selectively potentiated morphine-induced DA, but not -HT, efflux in the NAc. This potentiation was due to morhine’s action in the DRN because it was blocked by intraRN microinjection of the opioid antagonist naltrexone 10 g). IS potentiation of morphine-induced DA efflux in the Ac was also dependent upon activation of 5-HT neurons in he DRN because it was blocked by intra-DRN microinjection f the 5-HT1A autoreceptor agonist 8-hydroxy-2-di-n-(proylamino)-tetralin (1 g). No effect of IS was found on morhine-induced 5-HT or DA efflux in the ventral tegmental area. hese results suggest a neural substrate for stress potentition of morphine reward involving 5-HT neurotransmission n the DRN. © 2004 IBRO. Published by Elsevier Ltd. All rights eserved.