AChE in the cerebellum

Biochemical measurement of distinct levels of acetylcholine (McIntosh, 1941 Kasa et al., 1982) and its biosynthetic enzyme, choline acetyltransferase (ChAT) in cerebellar tissue (Kasa and Silver, 1969 Salvaterra and Foders, 1979 Hayashi, 1987 and others) indicated the presence of a cholinergic innervation in the cerebellum. ChAT activity varies among different lobules with the highest levels in the nodulus and ventral uvula. Following deafferentation of the cerebellar cortex, ChAT activity is considerably de- 

Early anatomical studies have employed acetylcholinesterase (AChE) histochemistry. However, AChE activity is disproportionally high in the cerebellum (reviewed in Silver, 1974), and its widespread distribution in non-cholinergic cells and fiber systems precludes its use as a marker for cholinergic neurons. 

The distribution of ChAT-positive mossy fibers roughly corresponds to that of unipolar brush cells (see Section 3.6.3.), which raises the question whether these mossy fibers innervate these cells. Electron microscopic analysis of ChAT-immunoreactivity in the nodulus showed that a minority (10-20%) of ChAT-immunoreactive mossy fiber terminals synapse on brush cell profiles, and that a minority (10-30%) of the mossy fiber terminals contact unipolar brush cells that are immunoreactive for ChAT (Jaarsma, 1995c). 

Barmack et al. (1992a) noted a dense population of small ChAT-positive mossy fiber-like terminals in the tip of lobules IXa,b of rat cerebellum that are significantly smaller than the other ChAT positive rosettes (Fig. 83). This type of labelling was not described by Ojima et al. (1989) but could be observed in their Fig. 4. The source and characteristics of this peculiar population of terminals is still unknown. 

Ojima et al. (1989) showed that all cerebellar nuclei in rat are innervated by ChAT-immunoreactive fibers. The density of these fibers varies between the different nuclei. Moderately dense innervation was found in most of the medial nucleus and in the magnocellular part of the lateral nucleus, whereas only a few ChAT-immunoreactive fibers invade the ventromedial parvicellular portion of the lateral nucleus and most of the interposed. Also in the cerebellar nuclei of man a moderate density of ChAT-positive fibers has been observed (DeLacalle et al., 1993). Both in rat and man these fibers did not form pericellular networks. DeLacalle et al. (1993) and Ikeda et al. (1991) also found 

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Fig. 121. Zonal distribution of AChE in the cerebellum of the cat. A. Whole mount preparation of the anterior lobe. B. Transverse section through the anterior lobe. HEM = hemisphere m = midline AChE-positive band L = parasagittal AChE-positive band arrows = lateral border of L. Marani (1986).

Zebrin I in rat cerebellum was compared to the distribution of AChE in the cerebellum of the rat (Boegman et al., 1988). These authors stressed the congruence of Zebrin-positive Purkinje cells with the accumulations of AChE in patches in the underlying granular layer. AChE in these patches is present in glomeruli, in certain Golgi cells and in other, unidentified components of the neuropil. 

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