Learned association between drugs of abuse and context is essential for the formation of drug conditioned place preference (CPP), which is believed to engage many brain regions including hippocampus and nucleus accumbens (NAc). The underlying mechanisms are not fully understood. Here, we examined whether glucocorticoid receptors (GRs) of hippocampus and NAc influenced the formation of morphine CPP in Sprague Dawley rats. We found that systemic or intrahippocampal infused DMSO vehicle (DMSO 20% in saline) 30 min before daily morphine (10 mg/kg, s.c.) conditioning did not affect the formation of morphine CPP. In contrast, systemic administration (5 mg/kg, s.c.) or intrahippocampal infusion (0, 0.1, 1.0, 10, 20 microg per side) of the GR antagonist RU38486 blocked or impaired the formation of CPP in a dose-dependent manner, respectively. Furthermore, intra-NAc infused RU38486 (10 microg per side) but not DMSO vehicle also prevented the formation of CPP. These results demonstrate that both the GRs of hippocampus and NAc are necessary for the formation of morphine CPP, suggesting a neural network function of the GRs in forming the opiate-associated memory.
2006 Wiley-Liss, Inc.