Role for GABA agonists in the nucleus accumbens in regulating morphine self-administration

In the present study, functional roles of GABA receptors in the nucleus accumbens on morphine self-administration behavior were investigated. Male Sprague-Dawley rats were trained to press lever for morphine (0.1 mg/kg per infusion) during daily 1-h self-administration session. After establishing stable baseline responses, rats were given microinjections of the GABA_A receptor agonist muscimol (0, 250 and 500 ng/μl, bilateral) or the GABA_B receptor agonist baclofen (0, 100 and 250 ng/μl, bilateral) into the nucleus accumbens immediately before the morphine self-administration. Microinjection of muscimol (250 and 500 ng/μl) into the nucleus accumbens, but not baclofen, decreased morphine self-administration responses. These results suggest that activation of GABA_A receptors, but not GABA_B receptors, in the nucleus accumbens plays a critical role in modulating the reinforcing effects of morphine.