A comparison between lick or lever-pressing contingent reward and the effects of neuroleptics thereon.

Rats implanted with an electrode in the lateral hypothalamus were trained to obtain brain-stimulation by either pressing a lever or by licking a steel drinking tube in subsequent 15-min sessions. Half of the rats began the sessions with lever-pressing, the other half began with licking. After stabilization of the response rates, rats were run in saline- or drug-sessions. During the drug sessions rats were treated with 4 doses of the following neuroleptics: haloperidol, pimozide, pipamperone, azaperone. These neuroleptics dose-relatedly inhibited licking for brain-stimulation but suppressed lever-pressing only at the highest dose tested. The lick response was thus inhibited at lower doses than lever-pressing. This differential sensitivity to neuroleptics appears not to be due to a difference in baseline response rates, schedule differences or to the motor activity involved in both responses, but rather to the different thresholds of reinforcement produced by licking and lever-pressing for brain-stimulation.