Ventral pallidostriatal pathway in the monkey: evidence for modulation of basal ganglia circuits

This study describes the organization of the ventral and dorsal pallidostriatal pathway in the monkey. Both retrograde and anterograde tracers were injected into various regions of the ventral and dorsal pallidum as well as into the striatum. The data indicate that the pallidostriatal pathway is an extensive pathway in the monkey. The projections are organized in a topographic manner preserving a general, but not strict medial-to-lateral and ventral-to-dorsal organization. The terminal arrangement of pallidostriatal fibers is widespread. Non-adjacent pallidal regions send fibers to the striatum which overlap considerably, suggesting convergence of terminals from different pallidal regions. The pallidostriatal pathway is found to have a reciprocal but also a large non-reciprocal component to the striatopallidal pathway. On the basis of these data it is concluded that segregation of different corticobasal ganglia-cortical pathways is maintained in the striatopallidal direction as described earlier (Haber et al. [1990] (J. Comp. Neurol. 293:282-298). However, the pallidostriatal projection to a large region of the striatum allows the modulation of several cortico-basal ganglia circuits.