Pallidal and cerebellar afferents to pre-supplementary motor area thalamocortical neurons in the owl monkey: A multiple labeling study

In the present study, we determined where thalamic neurons projecting to th e presupplementary motor area (pre-SMA) are located relative to pallidothal amic and cerebellothalamic inputs and nuclear boundaries. We employed a tri ple-labeling technique in the same owl monkey (Aotus trivirgatus). The cere bellothalamic projections were labeled with injections of wheat germ agglut inin conjugated to horseradish peroxidase, and the pallidothalamic projecti ons were labeled with biotinylated dextran amine. The pre-SMA was identifie d by location and movement patterns evoked by intracortical microstimulatio n and injected with the retrograde tracer cholera toxin subunit B. Brain se ctions were processed sequentially using different chromogens to visualize all three tracers in the same section. Alternate sections were processed fo r Nissl cytoarchitecture or acetylcholinesterase chemoarchitecture for nucl ear boundaries. The cerebellar nuclei primarily projected to posterior (VLp ), medial (VLx), and dorsal (VLd) divisions of the ventral lateral nucleus; the pallidum largely projected to the anterior division (VLa) of the ventr al lateral nucleus and the parvocellular part of the ventral anterior nucle us (VApc). However, we also found zones of overlapping projections, as well as interdigitating foci of pallidal and cerebellar label, particularly in border regions of the VLa and VApc. Thalamic neurons labeled by pre-SMA inj ections occupied a wide band and were especially concentrated in the VLx an d VApc, cerebellar and pallidal territories, respectively. Labeled thalamoc ortical neurons overlapped cerebellar inputs in the VLd and VApc and overla pped pallidal inputs in the VLa and the ventral medial nucleus. The results demonstrate that inputs from both the cerebellum and globus pallidus are r elayed to the pre-SMA. J. Comp. Neurol. 417:164-180, 2000. (C) 2000 Wiley-L iss, Inc.