Differentiation of Purkinje cells and their relationship to other components of developing cerebellar cortex in man

Abstract

The differentiation of Purkinje cells and their relationship to other components of the developing cerebellar cortex were analyzed by the Golgi impregnation method and by EM in human specimens of various pre- and postnatal ages. The 3 stages of Purkinje cell maturation previously recognized in other species were also evident in man; the 1st stage occupied primarly the 4th fetal month (12-16 wk); the 2nd stage lasted through the 5th, 6th and 7th fetal months (16-28 wk); the 3rd stage extended throughout the remaining period of intrauterine life, and the 1st postnatal year and continued at a slow rate thereafter. During the 1st stage, Purkinje cells were distributed in a layer, several rows deep. Their bipolar somas were relatively smooth and had only a few processes at the apical and basal cell poles. In the 3-mo. period of the 2nd stage, Purkinje cells became gradually organized into a single row. Their somas became invested with additional randomly oriented dendritic processes and numerous somatic spines (pseudopodia). The 1st morphologically well-defined synapses appeared on the Purkinje cell somatic spines and on their immature dendritic shafts at the beginning of the 2nd stage and become more prominent during the period from 18-24 wk. In the 3rd stage, the dendritic arbor becames flattened in the plane transverse to the folium and somatic spines disappeared. Spines appeared on the secondary and tertiary dendrites between the 24th and 28th fetal wk and continued to increase in number during the entire 3rd stage as new dendritic branches develop. Cellular maturation and synaptogenesis in the primate cerebellum may differ from these events in non-primate species, with respect to time of birth, in the relative duration of each phase and in the total time necessary for neuronal differentiation. The protracted time of differentiation and the slow growth of Purkinje cell dendrities in man may be due to the numerically complex relationships existing between granule and Purkinje cells. It is probably not simply a reflection of the larger size of human Purkinje cells and their dendrites.