PROJECTIONS OF GLOBUS PALLIDUS AND ADJACENT STRUCTURES - AUTORADIOGRAPHIC STUDY IN MONKEY

Because the globus pallidus gives rise to the principal efferent system of the corpus striatum and is traversed by several fibers systems, attempts were made to study the projections of its cells by autoradiographic techniques. Tritiated amino acids (L-leucine, L-proline and L-lysine) were injected into the medial pallidal segment (MPS), the MPS and the substantia innominata (SI), portions of the MPS and the lateral pallidal segment (LPS), and parts of the putamen. Cells labeled by injections of the MPS transported isotope to thalamic nuclei (ventral anterior, VApc, ventral lateral, VLo and VLm, and the centromedian, CM), the pedunculopontine nucleus (PPN) and the lateral habenular nucleus (Hbl). Labeled cells of the MPS and SI transported isotope to thalamic nuclei (VLo, VLm and CM), PPN, Hbl, lateral and posterior regions of the hypothalamus, and extensive dorsal regions of the substantia nigra (SN). Comparisons of label transported from uptake of isotope by cells of the MPS, and cells of both pallidal segments, suggested that the LPS projects fibers only to the subthalamic nucleus (STN). Not all regions of the STN appeared to receive fibers from the LPS. Selectively labeled neurons of the putamen transported isotope to broad regions of both pallidal segments and to the pars reticulata of the SN. Cells of the MPS apparently project profusely and topographically to the rostral ventral tier thalamic nuclei (VApc, VLo and VLm), lateral portions of CM, and the PPN. Fibers of the lenticular fasciculus appear to terminate preferentially in VLo. Cells in sublenticular portions of SI, and those extending into the medullary laminae of the pallidum, appear to project to HBl via the stria medullaris, the pars compacta of SN, lateral and posterior regions of the hypothalamus, and the so-called nucleus of the ansa lenticularis. Some fibers from cells of SI appear to join the dorsal stria terminalis, but none enter the inferior thalamic peduncle and none project to any part of the dorsomedial nucleus of the thalamus.