Kainic acid lesions of the nucleus accumbens selectively attenuate morphine self-administration

The influence of kainic acid lesions of intrinsic and efferent neurons of the central medial nucleus accumbens on responding simultaneously maintained by food, water and morphine self-administration was assessed. Rats were trained on a multioperant baseline to respond on three different levers that resulted in either a food pellet, the presentation of a water dipper or an infusion of morphine. While responding on the morphine lever was related to dose (0.83-13.2 mg/infusion), increasing concentrations of the drug had little or no effect on responding maintained by food and water before the lesion. Bilateral infusions of the neurotoxin into the nucleus accumbens decreased morphine self-administration but did not appreciably alter food or water intake. Food extinction probes before the lesion produced significant increases in drug intake and decreases in responding on the water lever, but the neurotoxin lesion attenuated the food extinction induced decrease in water intake. These data suggested that kainic acid lesions of the nucleus accumbens decrease the reinforcing efficacy of morphine but do not alter the reinforcing properties of food and water. The neuronal systems potentially involved in mediating the reinforcing effects of environmental events are discussed.