Different effects of tegmental GABAergic receptors on the expression of morphine-induced place preference in rat

In the present study, the effects of excitation and inhibition of GABAA and GABAB receptor subtypes on the expression of morphine-induced conditioned place preference (CPP) were investigated. For this purpose, male Wistar rats (250-300 g) were used in the experiments. Five days after surgical cannulation in the ventral tegmental area (VTA), different doses of morphine were injected into the animals and conditioned biased method was applied. The results showed that subcutaneous injections of morphine sulfate (1-10 mg/kg) induced CPP in a dose-dependent manner. Furthermore, administration of GABAA receptor agonist, muscimol (6 ng/rat) into ventral tegmental area reduced the morphine effects. The drug at doses of 12 and 25 ng/rat enhanced morphine-induced CPP. Reduction of morphine-induced CPP was observed following injection of GABAA receptor antagonist, bicuculline (6, 12 and 25 ng/rat) into VTA. Injection of baclofen as GABAB receptor agonist (6 ng/rat) into VTA caused an increase in CPP induced by morphine, whereas the drug at doses of 12 and 25 ng/rat reduced the morphine effects. Injection of CGP38345 (a GABAB receptor antagonist) into the VTA at doses of 6, 12 and 25 ng/rat significantly reduced the CPP induced by morphine. It could be concluded that excitation and inhibition of GABAA and GABAB receptor subtypes in the VTA may have different effects on morphine-induced CPP.