Effects of central amygdala GABA-B on expression of morphine-induced sensitivity in female rats

Dependence on morphine and its complications are considered as a major health problem in the world; however, efforts to overcome this problem have failed due to the severity of drug dependence. Amygdala core nucleus (CeA) is one of the most important areas affecting the effects of morphine rewards. The GABAergic system in this nucleus; especially the GABAB receptors plays an important role in modulating the morphine's euphoric effects. In this study, the effects of intra-CeA injection of baclofen (GABAB receptor agonist) and CGP35348 (GABAB receptor antagonist) were studied on morphine sensitivity expression by conditioned place preference (CPP). Five days after surgery, different doses of morphine (0.5, 1, 2, 2.5, 5, 7.5 and 10 mg/kg) were administered subcutaneously (S.C) to determine the effective and ineffective dosages of morphine. Importantly, in order to induce sensitivity, the effective dose of morphine (7.5 mg/kg) was injected once daily for 3 days; followed by 5 days’ rest, and on the 9th day, the CPP was started with the ineffective dose of morphine (2.5 mg/kg). Doses of 1.5, 6 and 12 μg/rat of baclofen and CGP35348 were injected into the CeA, 10 minutes before the CPP test. Both agonist and antagonist significantly reduced the expression of morphine sensitivity in the female rats. GABA-B receptors within the CeA may interfere with the conditioned place preference expression of morphine sensitive female rats. It is possible that these receptors could be used as drug abuse goals.