Paradoxical Kinesia in Parkinsonism Is Not Caused by Dopamine Release

Abstract
• Rats become akinetic after large dopamine-depleting brain lesions, yet they show an activation-induced restoration of motor function. In this study, rats were given intraventricular injections of the neurotoxin 6-hydroxydopamine to permanently reduce the dopamine content of the corpus striatum by 98%. Although the rats were akinetic in their home cages, they swam effectively when placed in deep water and escaped from a shallow floating ice bath. These behaviors were not abolished by pretreating the animals with the dopamine antagonists haloperidol and SCH-23390. In contrast, haloperidol completely blocked the brain-damaged animals' behavioral responses to amphetamine. These results suggest that the paradoxical kinesia of dopamine-depleted rats is not a consequence of dopamine release from residual dopaminergic fibers.