Water deprivation-induced oral self-administration of cocaine in the Lewis rat: Evidence for locomotor effects but not reinforcement

Abstract

Oral cocaine self-administration was studied in water-deprived Lewis rats. Liquid was available to rats only during daily 90-min sessions, in chambers equipped with spouts that delivered precise volumes of liquid following completion of lever-press responses. Blocks of training and testing sessions were alternately carried out during which increasing cocaine concentrations were presented: 0.0, 0.0125, 0.025, 0.05, 0.1, 0.2, 0.282, and 0.4 mg/ml. Although high cocaine intakes (23.3–33.0 mg/kg) were obtained, neither avoidance nor preference for cocaine developed. Subsequently, fixed-ratio size was increased, and then distinctive stimulus lights were correlated with each liquid. One rat showed a preference for water following these changes, but two rats continued to show no preference. To determine if the amounts of cocaine self-administered had behavioral effects, locomotor activity tests were run immediately following self-administration sessions. Locomotor activity was substantially higher following cocaine self-administration than following water self-administration. These results demonstrate that the cocaine intakes reached under the present conditions did produce locomotor, but not reinforcing, effects.