Lateral habenula electrical stimulation with different intensities in combination with GABA(B) receptor antagonist reduces acquisition and expression phases of morphine-induced CPP

Abstract

The lateral habenula (LHb) plays a principal role in response to aversive stimuli and negative emotional states. In this study, we have evaluated the effects of unilateral electrical stimulation (e-stim) of the LHb on morphineconditioned place preference (CPP), before or after bilateral injections of Gamma-aminobutyric acid-B receptor (GABA(B)R) antagonist, phaclofen, in male rats. Morphine (5 mg/kg; s.c.) induced a significant CPP, using a 5day CPP paradigm. Intra-LHb microinjection of phaclofen or the LHb e-stim decreased only the acquisition of CPP. The 150 mu A stimulation plus phaclofen significantly suppressed the expression phase but induced aversion in the acquisition of CPP, and an e-stim of 25 mu A in combination with the antagonist, significantly prevented only the acquisition phase. The findings of this study confirm the possible role of GABA(B)Rs in the LHb on the acquisition and the expression of CPP. These results show that e-stim of LHb alone or plus phaclofen may change the GABA transmission, involving into CPP. Therefore, the GABAergic system, especially through GABA(B)Rs, may play a prominent role in the behavioral responses to morphine-induced CPP by LHb stimulation.