Effects of muscimol, amphetamine, and DAMGO injected into the nucleus accumbens shell on food-reinforced lever pressing by undeprived rats

► Injections of muscimol into the AcbSh increase food-reinforced operant responding. ► Injections of DAMGO into the AcbSh increase food-reinforced operant responding. ► Intra-AcbSh amphetamine does not increase food-reinforced operant responding. ► AcbSh GABAA and μ-opioid receptors can mediate food-directed operant behavior.