Main effects of current and pimozide on prepared and learned self-stimulation behaviors are on performance not reward

This work examined four independent variables which influence behavior of self-stimulating rats: site of electrode placement (cingulate cortex versus lateral hypothalamus), type of operant response (lever press versus nose poke), current intensity (50, 100, 150 microA) and pimozide dosage (0.125, 0.250, 0.500 mg/kg). The dependent measures were: total responding, alternation between two identical manipulanda and mean duration per response. Naive rats made more nose pokes than lever presses, suggesting nose pokes are more "prepared." The cingulate cortex was insensitive to current and pimozide manipulations in contrast with hypothalamic sensitivity, tentatively suggesting a cingulate role in release of prepared behaviors, hypothalamic in plasticity of learned ones. Lever pressing, more prevalent with lateral hypothalamic stimulation, was more affected by current and pimozide manipulations than nose poking. More prepared nose pokes might thus be less susceptible to brain stimulation reward manipulations. Intensifying current produced more but shorter responses, increasing pimozide dosage produced fewer and nonsignificantly longer ones, suggesting a primary effect on motor performance not reward. Decrements in performance over nondrug days were tentatively attributed to long-lasting effects of pimozide.