Dopamine D2 receptor blockade reduces response likelihood but does not affect latency to emit a learned sensory-motor response: implications for Parkinson's disease.

Parkinsonian behavioral deficits are reduced in the presence of strong eliciting stimuli and are most pronounced when the response requires internal generation. In the present study, rats' head entries into a food compartment were measured in the presence and absence of an eliciting stimulus. The D2 receptor blocker raclopride suppressed the emission of spontaneous head entries but did not slow head entries emitted in response to a food cue. Rats subjected to a pharmacological disruption in dopamine (DA) transmission show response impairments that are reduced, and in this case eliminated, in the presence of strong eliciting stimuli. The present results support the view that neuroleptic-induced reductions in DA transmission do not produce an absolute limit on the speed with which an individual response can be generated but that they reduce the likelihood of response generation in the absence of strong eliciting stimuli.