REGIONAL DISTRIBUTION OF CHOLECYSTOKININ BINDING-SITES IN MACAQUE BASAL GANGLIA DETERMINED BY INVITRO RECEPTOR AUTORADIOGRAPHY

Cholecystokinin binding sites were labeled with [3H]cholecystokinin-8, [125I]cholecystokinin-33, and [125I]cholecystokinin-8 in major structures of macaque basal ganglia by in vitro receptor autoradiography. Analysis of autoradiograms revealed areas of heavy cholecystokinin binding in the neostriatum and substantia nigra that were set off, often quite sharply, from the adjacent globus pallidus and subthalamic nucleus where labeling was, by contrast, very light. Heavy label characterized the ventromedial and posterior parts of the caudate nucleus and adjacent putamen, binding was of moderate intensity in central areas of these regions, while, the dorsolateral margin of the head of the caudate and precommissural putamen, the dorsolateral one-third of the body of the caudate, and all but the most medial and ventral portions of the posterior putamen lateral to the pallidum were sparsely labeled. The pattern of cholecystokinin binding within the neostriatum was mottled; patches of reduced label stood out from the background of more prominent binding. However, those patches were only imperfectly correlated with the striosomal organization of both the caudate nucleus and putamen as revealed by acetylcholinesterase staining. Cholecystokinin binding in the substantia nigra was also intricately patterned. Moderately dense, vertically orientated bands of label were found in the dorsal one-third to half of the pars reticulata, providing a marked contrast to the near background levels in the ventral pars reticulata and overlying pars compacta. The present study shows that heavy cholecystokinin binding is confined to particular areas within the primate basal ganglia; the pattern of label within the substantia nigra and neostriatum can be linked to intrinsic and afferent connections of these structures. The confinement of binding sites to the dorsal pars reticulata suggests an association with dendrites of pars compacta neurons which invade this region; this interpretation is consistent with recent evidence of depletion of nigral cholecystokinin binding sites in macaques following chemical lesion of dopaminergic cells of the par compacta. In the neostriatum the distribution of binding shows overlap with its topographically organized corticostriatal innervation; portions of heavily labeled striatum coincide with regions innervated by association cortex of the frontal and temporal lobes, whereas regions of diminished binding correspond to areas innervated mainly by sensory and motor cortex. These latter findings suggest that cholecystokinin may have a particularly strong influence on cognitive aspects of striatal function. © 1990.