Effects of peripheral and central dopamine blockade on lateral hypothalamic self-stimulation: evidence for both reward and motor deficits.

The effects of dopamine receptor antagonists on lateral hypothalamic self-stimulation were analyzed using a reward summation function (RSF) technique. This paradigm relates running speed in a runway to the number of stimulation pulses received as a reward, and it is able to separately characterize changes in reward pulse effectiveness and motor performance. Pimozide, administered peripherally (0.125, 0.25, 0.5 mg/kg, IP), dose-dependently shifted the RSF toward higher values of number of pulses indicating reduced reward. Pimozide also reduced the asymptotic running speed of the RSF, indicating a deficit in motor performance. In a second experiment, alpha-flupenthixol infused directly into the nucleus accumbens (0.5 micrograms-0.5 micrograms, bilaterally) induced changes in the RSF similar to those obtained with peripheral neuroleptic treatment. These findings are discussed from the perspective that dopamine is involved both in the perception of reward value and in the performance of the response to obtain reward.