Striosomes control dopamine via dual pathways paralleling canonical basal ganglia circuits.

Balanced activity of canonical direct D1 and indirect D2 basal ganglia pathways is considered a core requirement for normal movement, and their imbalance is an etiologic factor in movement and neuropsychiatric disorders. We present evidence for a conceptually equivalent pair of direct D1 and indirect D2 pathways that arise from striatal projection neurons (SPNs) of the striosome compartment rather than from SPNs of the matrix, as do the canonical pathways. These striosomal D1 (S-D1) and D2 (S-D2) pathways target substantia nigra dopamine-containing neurons instead of basal ganglia motor output nuclei. They modulate movement with net effects opposite to those exerted by the canonical pathways: S-D1 is net inhibitory and S-D2 is net excitatory. The S-D1 and S-D2 circuits likely influence motivation for learning and action, complementing and reorienting canonical pathway modulation. A major conceptual reformulation of the classic direct-indirect pathway model of basal ganglia function is needed, as well as reconsideration of the effects of D2-targeting therapeutic drugs. • Direct S-D1 and indirect S-D2 striosomal pathways target SNpc dopamine cells • The S-D2 indirect pathway targets a distinct central zone of the GPe • Stimulation of S-D2 increases, of S-D1 decreases, striatal dopamine and movement • S-D1-S-D2 and canonical D1-D2 pathways have opposite effects on voluntary movement Lazaridis et al. delineate a previously unrecognized pair of striosomal direct D1 and indirect D2 circuits that target substantia nigra dopamine-containing neurons, controllers of mood, action, and reinforcement learning. These striosomal circuits have effects opposing those of the canonical D1-direct/D2-indirect pathways, likely modulating them. [ABSTRACT FROM AUTHOR]