Evidence for loss of Purkinje cell dendrites during late development: a morphometric Golgi analysis in the mouse.

The late postnatal development of the Purkinje cell dendritic tree in mouse cerebellar vermis was investigated in Golgi preparations by morphometric techniques in order to determine at what age adult characteristics of the Purkinje cell are achieved in the rodent brain which grows continuously throughout adult life. B6D2F1 hybrid mice were sacrificed at 9, 15, 20, 35 and 250 days of age. "Hind-brain" weights (by direct weighing) and vermis volume (determined histometrically from Golgi sections), both increased rapidly from 9 to 20 days of age and continued to increase steadily with advancing age. The growth of Purkinje dendritic field areas, determined by planimetric measurements from Golgi sections paralleled the growth curves for vermis cross-sectional area, vermis volume and "hindbrain" weight. However, stereological determinations revealed an unexpected disparity between the growth of the Purkinje dendritic field areas and changes in the total length of dendrites of Purkinje cells. The total dendritic branch length per Purkinje cell increased sharply up to 20 days of age but thereafter declined with advancing age. Dendritic spine counts on Purkinje cells revealed no change in the number of dendritic spines per unit length of dendrites between 20 and 250 days of age, however, since the Purkinje cell total branch length declined-calculations suggest that the total number of spines per cell declined after 20 days of age. Thus, the size of the cerebellum and the Purkinje cell dendritic tree continued to enlarge during late postnatal development; however, the total dendritic surface area and the total number of dendritic spines on each Purkinje cell, after reaching a peak at 20 days of age, declined with advancing age. The data suggest that the late postnatal development of the Purkinje cell dendritic tree is characterized by resorption as well as dendritic growth. The functional significance of such developmental remodelling is unknown.