In the present study, the effects of intra-basolateral amygdala (BLA) injection of GABAA receptor agonist and antagonist on morphine induced conditioned place preference (CPP) in male Wistar rats have been investigated. Subcutaneous (s.c.) administration of different doses of morphine sulfate (1–9 mg/kg) produced a dose-dependent CPP. Using a 3-day schedule of conditioning, it was found that the GABAA receptor agonist, muscimol (0.125, 0.25 and 0.5 Ag/rat) or the GABAA receptor antagonist, bicuculline (0.125, 0.25 and 0.5 Ag/rat), did not produce a significant place preference or place aversion. Intra-BLA administration of muscimol (0.25 and 0.5 Ag/rat) decreased the acquisition of CPP induced by morphine (6 mg/kg). On the other hand, intra-BLA injection of bicuculline (0.25 and 0.5 Ag/rat) in combination with an ineffective dose of morphine (1 mg/kg) elicited a significant CPP. The response of different doses of muscimol was attenuated by bicuculline (0.125 and 0.25 Ag/rat). Furthermore, intra-BLA administration of bicuculline but not muscimol before testing significantly decreased the expression of morphine (6 mg/kg)-induced place preference. The administration of the higher doses of bicuculline (0.25 and 0.5 Ag/rat) during acquisition and the higher dose of muscimol (2 Ag/rat) on the test day decreased the locomotor activity of the animals on the testing phase. It can be concluded that GABAA receptors in the amygdala are involved in morphine reward.
