Speed of movement initiation performance predicts differences in [3H]spiroperidol receptor binding in normal rats.

Speed of movement initiation is altered in normal aging and in neurological disorders such as Parkinson's disease. This study was undertaken to extend our previous results, which suggested a relationship between nigrostriatal dopamine function and an animal model of movement initiation speed (reactive capacity). Fisher 344 rats exhibiting exceptionally fast or slow reactive capacity but otherwise normal were examined for differences in the striatal binding of the dopaminergic ligand, [3H]spiroperidol. Rats with fast reactive capacity (Fast rats) exhibited significantly higher binding than did rats with slow reactive capacity (Slow rats). Also, Fast rats responded nearly maximally on the reactive capacity task regardless of the duration of time provided in which to respond, whereas Slow rats reacted more slowly when more response time was provided. The differences in [3H]spiroperidol binding and the differential influence of time provided to respond on the response latency of these two normal groups of rats was similar to that observed in old or model Parkinson's disease rats having nigrostriatal dopamine deficits. These results strengthen the relationship between an animal model of reactive capacity and nigrostriatal dopamine function.