OPIOID BLOCKADE ATTENUATES ACQUISITION AND EXPRESSION OF COCAINE-INDUCED PLACE PREFERENCE CONDITIONING IN RATS

Endogenous opioid systems have been implicated in experimental cocaine addiction. One aspect of this involvement may be the modulation of th e motivational properties of cocaine by endogenous opioids. The presen t study assessed the effect of opioid blockade with naloxone (NLX) on cocaine's motivational properties using the conditioned place preferen ce procedure. Treatment with doses of NLX that did not induce place av ersion (0.01-1.0 mg/kg(-1), SC), dose-dependently attenuated place pre ference induced by cocaine (10 or 20 mg/kg(-1) IP). This effect of NLX was present when administered during acquisition of cocaine-induced p lace preference and when administered before expression of cocaine's m otivational effects. These data support the notion that the (condition ed) motivational properties of cocaine are modulated through activatio n of opioid systems by endogenous opioid peptides. Furthermore, it is suggested that an interaction between endogenous opioid systems and do paminergic systems in the brain might be of importance in the motivati onal facilitation of experimental cocaine addiction.