The neurons of the corpus striatum receive an excitatory input from the cerebral cortex and the thalamus. The major outputs project to the globus pallidus and the substantia nigra pars reticula (SNr), and use gamma-aminobutyric acid (GABA) as a transmitter. Major efferent pathways from the globus pallidus interna and the SNr project to the thalamus. Feedback to the striatum is through the dopaminergic striatonigral pathway originating in the substantia nigra pars compacta (SNc; Figure 1). These separate pathways utilize different neuropeptides and dopamine receptors. The direct pathway from the striatum to the globus pallidus interna (GPi) and SNr expresses substance P and dynorphin, and uses D1 dopamine.
