Direct And Indirect Striatal Output Pathways

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The principal output stations of the BASAL GANGLIA are the SUBSTANTIA NIGRA pars reticulata and the internal segment of the GLOBUS PALLIDUS (known as the ENTOPEDUNCULAR NUCLEUS in the rat) both of which send inhibitory projection to the THALAMUS and BRAINSTEM (notably the PEDUNCULOPONTINE TEGMENTAL NUCLEUS). The output of the STRIATUM (the largest element of the basal ganglia) to these runs via indirect and direct pathways.

The indirect output pathway travels to the internal segment of the globus pallidus via a synaptic relay in the external segment of the globus pallidus (which in the rat is known just as the globus pallidus, the internal segment being the entopeduncular nucleus). The direct output travels, of course, directly from striatum to the internal segment of the globus pallidus. The innervation of the substantia nigra pars reticulata is similarly divided: a direct output arrives from the striatum and an indirect output arrives from the striatum via a relay in the external segment of the globus pallidus.

See also: corticostriatal loops

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