Self-stimulation response decrement patterns differentiate clonidine, baclofen and dopamine antagonists from drugs causing performance deficit.

Fouriezos and co-workers have reported that rats treated with the neuroleptics, pimozide or d-butaclamol, barpress at baseline rates at the start of an intracranial self-stimulation (ICSS) session, but cease responding within a few minutes. They suggested that this response decrement pattern (RDP) resembles natural extinction, indicating attenuation of reward by neuroleptic treatment. In the present experiments, the RDPs produced by several different drug classes were systematically compared. Two dopamine receptor antagonists, haloperidol and metoclopramide, produced an extinctionlike RDP. In contrast, the alpha-1 adrenoceptor blocker, prazosin, and the muscle relaxant, methocarbamol, caused uniformly low response rates that did not decrease further as the session progressed. Clonidine, an alpha-2 adrenoceptor agonist, and baclofen, a novel GABAB receptor agonist, were associated with RDPs that resembled those of the dopamine antagonists tested. Analysis of drug-induced RDPs is characterized as a valuable tool for exploring the nature of drug effects on ICSS responding.