Histochemical and biochemical studies of butyrylcholinesterase activity in adult and developing cerebellum. Effects of abnormal thyroid state and undernutrition.

The cellular and subcellular localization of BuchE activity (EC.3.1.1.8) was studied in the developing and adult rat cerebellum at light and electron microscope levels. In the adult cerebellum, BuchE activity was exclusively localized to glial cells, myelin and endothelial cells. In the immature cerebellum, BuchE activity was additionally found transiently localized to the neuroblasts of the external germinative layer and in Purkinje cells of the nodulus. In both the immature and the adult animals, the main part of the activity seemed to be membrane-bound. The developmental pattern of cerebellar BuchE activity was assayed in developing normal, hypothyroid, thyroxine-treated and undernourished rats. In normal newborn rats, the specific activity was higher than in adults and it showed one characteristic peak at 6 days (1.8 times the adult value reached at 30 days). At the age of 5 days, the ratio of BuchE-containing astrocytes (numbered in the ganglionic layer) to Purkinje cells was the same as the ratio of Bergmann astrocytes to Purkinje cells determined at 35 days in Nissl preparations; their nucleus size already represented 80% of the adult value and their processes were well developed. The three experimental conditions modified the timing of BuchE development. During the early post-natal period, it was accelerated in the thyroxine-treated and undernourished animals, while in the hypothyroid rats it was delayed. During the same period, the number of labelled astrocytes per Purkinje cell was modified only by hypothyroidism and undernourishment. On the basis of these histochemical and biochemical results, BuchE can be considered as a good marker for the study of Bergmann glia development in the early post-natal period.