Striatal and extrastriatal dopamine in the basal ganglia: An overview of its anatomical organization in normal and Parkinsonian brains

Degeneration of the nigrostriatal dopaminergic system is the characteristic neuropathological feature of Parkinson's disease and therapy is primarily based oil a dopamine replacement strategy. Dopamine has long been recognized to be a key neuromodulator of basal ganglia function, essential for normal motor activity, The recent years have witnessed significant advances ill Our knowledge of dopamine function in the basal ganglia. Although the striatum remains the main functional tar-et of dopamine. it is now appreciated that there is dopaminergic innervation of the pallidum, subthalamic nucleus. and substantia nigra. A new dopaminergic thalamic system has also been uncovered, setting the stage for a direct dopamine action on thalamocortical activity. The differential distribution of D1 and D2 receptors oil neurons in the direct and indirect striato-pallidal pathways has been re-emphasized, and cholinergic interneurons are recognized as all intermediary mediator of dopamine-mediated Communication between the two pathways. The importance and specificity of dopamine ill regulating morphological changes in striatal projection neurons provides further evidence for the complex and multifarious mechanisms through which dopamine mediates its functional effects in the basal ganglia. In this review. the role of basal ganglia dopamine and its functional relevance in normal and pathological conditions will be discussed. (c) 2008 Movement Disorder Society.