Abstract
The aim of this study was to determine the role of the endogenous dynorphin/kappa opioid receptor (DYN/KOP) system in ethanol-induced state-dependent conditioned place preference (CPP). To this end, mice lacking the pro-DYN gene and their wild-type littermates/controls were tested for baseline place preference on day 1, received 15-min morning and afternoon conditionings with saline or ethanol (2g/kg) each day for three consecutive days and were then tested for CPP under a drug-free state on day 5 and following a saline or ethanol (1 or 2g/kg) challenge on day 8. Given that compensatory developmental changes may occur in knockout mice, the effect of nor-binaltorphimine (nor-BNI), a KOP antagonist, on state-dependent CPP induced by ethanol was also studied in wild-type mice. On day 1, mice were tested for baseline place preference and, 4h later, treated with saline or nor-BNI (10mg/kg). On days 2-4, mice received 15-min morning and afternoon conditionings and were tested for CPP under a drug-free state on day 5 and following an ethanol (1g/kg) challenge on day 8. A comparable CPP was observed in mice lacking the pro-DYN gene and their wild-type littermates/controls as well as in wild-type mice treated with nor-BNI and their saline-treated controls. However, these mice compared to their respective controls exhibited a greater CPP response following an ethanol (1g/kg) challenge, suggesting that the endogenous DYN/KOP system may negatively regulate ethanol-induced state-dependent CPP.