Pimozide attenuates lever pressing for water reinforcement in rats

Rats were trained to lever-press for water on a schedule of continuous reinforcement, then tested every fourth session on five occasions either under conditions of non-reinforcement or following injections of the dopamine receptor blocker pimozide (0.5 or 1.0 mg/kg) or the injection vehicle. The low dose of pimozide did not significantly attenuate responding until the fifth session. The high dose attenuated responding on all occasions, with residual responding decreasing progressively across repeated drug sessions. Responding in the pimozide conditions was never less than that of the non-reinforced control group. Responding in each condition was strongest in the early minutes of a session. After five sessions, rats were switched from the pimozide condition to the non-reinforced condition (or vice-versa) for one additional test day. Decreased responding continued for rats transferred from non-reinforcement to pimozide though not for rats transferred from pimozide to non-reinforcement. These data suggest a role for brain dopamine in behavior; they reflect the same patterns as have been seen with food reinforcement and with several centrally-acting reinforcers.