Opioidergic contribution to conditioned place preference induced by corn oil in mice

We previously reported that voluntary intake of corn oil in the light bos s howed place preference in the conditioned place preference (CPP) test in mi ce. In the present study, we investigated the contribution of opioidergic s ystems to the corn oil-induced CPP in mice. Acquisition of the place prefer ence by corn oil intake was blocked by i.p. injections of an opioid mu anta gonist, naloxone (0.1 and 0.3 mg/kg), and delta antagonists, 7-benzylidenen altrexone (0.5 mg/kg) and naltriben (0.5 mg/kg) 15 min before conditioning. The opioid kappa agonist U-504988H (1 and 3 mg/kg i.p.) also blocked corn oil-induced CPP. Naloxone (1 mg/kg, i.p.) and naltriben (0.5 m/kg, i.p.) di d not affect corn oil intake in the home cage. However. 7-benzylidenenaltre xone (0.5 mg/kg, i.p.) and U-5o488H (1 mg/kg i.p.) decreased and increased the corn oil intake, respectively. These results suggested that the rewardi ng effects of corn oil in the CPP test are at least partially mediated via opioidergic systems through mu and delta receptors. Further, we showed that an opioid kappa agonist reduced the rewarding effects of corn oil in the C PP test in mice, although it increased corn oil intake. (C) 2001 Elsevier S cience B.V. All rights reserved.