The GABAB receptor-positive modulator GS39783 and the GABAB receptor agonist baclofen attenuate the reward-facilitating effects of cocaine:: Intracranial self-stimulation studies in the rat

There is an increasing interest in the development of nondopaminergic pharmacotherapies for cocaine abuse. Emerging preclinical and clinical data with the metabotropic GABA(B) receptor agonist baclofen support a role for the modulation of GABA(B) receptors in the treatment of drug addiction. Nevertheless, the muscle relaxant, hypothermic, and sedative properties of baclofen somewhat limit its widespread potential therapeutic utility. Recently, positive modulators of the GABA(B) receptor such as GS39783 (N'-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine) have been identified. These positive modulators enhance the effects of GABA (gamma-aminobutyric acid) through actions at an allosteric site and are devoid of intrinsic agonistic efficacy. The aim of the present study was to assess the ability of the novel GABA(B)-positive modulator GS39873 or baclofen to modulate the behavioral effects of cocaine. Drugs of abuse such as cocaine lower brain reward thresholds obtained using intracranial self-stimulation (ICSS). We demonstrate here that GS39783 had no intrinsic effects on ICSS reward thresholds (10-100 mg/kg p.o,) in rats, whereas the full GABA(B) receptor agonist baclofen (2.5-5 mg/kg p.o,) dose dependently elevated thresholds. Moreover, both GS39783 and baclofen attenuated the threshold lowering effect of cocaine administration (10 mg/kg intraperitoneally) in a dose-related manner. These data strongly suggest that activation of GABA(B) receptors attenuates the rewarding effects of acute cocaine, Therefore, GABA(B)-positive modulation may represent a novel therapeutic strategy for the treatment of cocaine dependence and possibly other drugs of abuse without the side effects of full GABA(B) receptor agonists.