The magnocellular and parvocellular divisions of the monkey subthalamic nucleus as revealed by cluster analysis of neuronal sizes

Abstract

Cluster analysis of neuronal somal sizes in the subthalamic nucleus of rhesus monkeys from newborn to adult age allows the segregation of two territories with predominance of small and large cells, respectively. The topographic distribution of the ‘parvocellular’ and ‘magnocellular’ segments is similar when samples are obtained from coronal, horizontal and sagittal series of sections. The parvocellular component occupies the rostral pole, the entire rostrocaudal extent of the medial tip and dorsomedial border, and probably also the caudal cap. The magnocellular segment is in the central core extending to the ventrolateral border except for the medial tip. These findings and their correlation with the results of other morphologic and physiologic studies allow the following conclusions. (1) The monkey subthalamic nucleus contains at least two differentially distributed cell subpopulations. (2) The magnocellular division is more related to the pallido-subthalamic-pallidal loop involving the lateral pallidal segment. (3) The parvocellular division appears strategically located to control the pallidal output to diencephalic and mesencephalic targets. (4) Cluster analysis can reveal the existence of more than one neuronal population in a particular brain structure where an overall unimodal distribution of cell sizes may suggest the presence of a single type.