SNr - Substantia Nigra, pars reticulata:

The SNr is now known to be histologically very similar to the Globus Pallidus, internal segment (GPi) and, like the GPi, is a major output nucleus of the basal ganglia (BG). And, also like GPi, it is made up almost exclusively of tonically active projecting GABAergic cells. As such, SNr provides tonic inhibition of thalamic relay cells (TRCs) which can be disinhibited by BG gating signals. SNr also projects to the superior colliculus (SC) where it also provides tonic inhibition.