Postnatal development of cholinergic neurotransmitter enzymes in the mouse cerebellum. Biochemical, light microscopic and electron microscopic cytochemical investigations

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Abstract
The activity and distribution of the cholinergic neurotransmitter enzymes acetylcholinesterase (AChE) and choline acetyltransferase (ChAc) in the developing cerebellum of the mouse were investigated using biochemical assays and light microscopic histochemistry for AChE and ChAc, and electron microscopic histochemistry for AChE. Postnatal alterations in the levels of AChE and ChAc in the cerebellum of the mouse are characterized by a divergent pattern. During the first two postnatal weeks, AChE activity increases progressively, whereas ChAc activity remains low. Beyond day 14, when AChE activity is steady or gradually decreasing, ChAc increases sharply to reach a peak on day 32. Histochemically, AChE activity is associated with the glomeruli and the Golgi cells of the internal granular layer, the medullary layer, and the deep cerebellar nuclei. Purkinje cells exhibit transient staining between days 2 and 9. At the ultrastructural level, AChE staining is first demonstrated on day 6 within the Golgi cell soma, on day 9 at the mossy fiber–granule cell synapse, and on day 11 at the Golgi terminal–granule cell synapse. The staining intensity of these structures reaches that of the adult on day 19. The histochemical reaction for ChAc is localized to moderate number of presumed Bergmann glial cells, a few large cells of the deep cerebellar nuclei, small numbers of Golgi cells, and all immature Purkinje cells. The molecular layer, glomeruli, and the medullary layer fail to demonstrate ChAc activity. This distribution of ChAc sharply contrasts with the localization established by other methods previously and is interpreted in the light of the drawbacks of the histochemical procedure. The biochemical fluctuations in AChE activity, correlated with the histochemical and cytochemical data, suggest that the postnatal increases in the enzyme are related to the ingrowth of the mossy fibers and to the maturation of the AChE-positive Golgi cells. Histochemical evidence for the correlation between the ontogenetic increases in cerebellar ChAc activity and progressive mossy fiber innervation must await the application of the immunohistochemical method to the developing cerebellum.