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

Abstract

In the present study, an unbiased conditioned place preference paradigm was used to study the effects of intra-ventral tegmental area injections of Gama-amino-butyric acid (GABA)-A and B (GABA A and GABA B) receptor agonists and antagonists on the expression of morphine-induced conditioned place preference (CPP) in rats. Subcutaneous (s.c.) injections of morphine sulfate (5 mg/kg) induced CPP. Intra-ventral tegmental area administration of the GABA A receptor agonist, muscimol (6 μg/rat) reduced the expression of morphine-induced CPP. Muscimol (25 μg/rat) increased the expression of CPP induced by morphine. A reduction of the expression of morphine-induced CPP was observed on intra-ventral tegmental area injection of GABA A receptor antagonist bicuculline (25 μg/rat). Bicuculline (10 μg/rat) increased the expression of CPP induced by morphine. Baclofen (12 μg/rat) increased where as (19 and 25 μg/rat) reduced the expression of morphine-induced CPP. Injection of CGP38345 (10, 19, 25 and 50 μg/rat) into the ventral tegmental area significantly reduced the expression of CPP induced by morphine. It is concluded that GABA A and GABA B receptor subtypes within the ventral tegmental area may have different effects on the expression of morphine-induced CPP.