Effects of chlorpromazine on escape and avoidance responses: a closer look.

While a wealth of evidence has implicated the nigrostriatal dopamine system in the initiation of movement, most or all of these movements have been in a conditioned avoidance framework, and on the order of 3-14 seconds in latency. It is proposed here that an elucidation of dopaminergic involvement in movement initiation requires a behavioral paradigm wherein experimental animals must rapidly and voluntarily respond to a stimulus to move (i.e., in less than 300 msec, paralleling human reaction time). Such a paradigm was developed and implemented in a re-analysis of earlier reports of chlorpromazine (CPZ) effects on escape from an avoidance of electric shock. Catecholaminergic or dopaminergic receptor blocking by CPZ resulted in clear impairment of the ability to initiate rapid avoidance movements, but in contrast to earlier work, some impairment of escape responses was also seen. Results are seen as further support for dopaminergic involvement in the initiation of voluntary movement.