TOPOGRAPHIC DISTRIBUTION OF THE AXONAL ENDINGS FROM THE SENSORIMOTOR AND ASSOCIATIVE STRIATUM IN THE MACAQUE PALLIDUM AND SUBSTANTIA-NIGRA

The striatopallidonigral connection was studied by injecting anterogra de tracers into either the associative or the sensorimotor striatum in ten macaques. The results were analyzed using a precise cartographic method. Injections into various parts of the associative striatum (cau date nucleus and ventromedial putamen) produced a labeling of axons in the dorsomedial and ventral pallidal regions. These associative regio ns occupied two-thirds of the lateral pallidum and one-third of the me dial pallidum. Bands of labeled axons from the sensorimotor striatum ( dorsolateral putamen) were found in the remaining, central part of the two pallidal nuclei. In the substantia nigra, the rostral associative striatum projected medially to the pars reticulata, while the caudal parts projected laterally. The whole pars reticulata and lateralis thu s appeared to receive associative striatal inputs. The sensorimotor st riatal territory projected to the central part of the pars reticulata/ lateralis. It was concluded that the two functional territories remain separate in the two pallidal nuclei but overlap in the middle third o f the substantia nigra. However, due to their great size, the pallidal neurons located at the border of the two territories may receive stri atal inputs from both the associative and the sensorimotor components in the same way that nigral neurons do.