Distribution of acetylcholinesterase in the granular layer of the cerebellum of the rhesus monkey (Macaca mulatta).

A nonuniform distribution of acetylcholinesterase (AChE) activity was identified in the granular layer of the cerebellum in rhesus monkeys. The distribution of darkly AChE-stained clumps in the granular layer was determined for each lobule of the vermis and the lateral cortex. The vermis contained a greater density of AChE reaction product than the lateral cortex. In the vermis, lobules IX and X had significantly the highest level of activity, followed by lobules VII and VIII, which were significantly higher than lobules II-VI. In the lateral cortex, the flocculus had the highest level of the AChE activity, followed by crus I and the dorsal paraflocculus, which had significantly higher levels than the remaining lobules. The high levels of AChE activity in the flocculonodular lobe and lobule IX may correspond to cholinergic mossy fiber transmission, but the high levels of AChE activity in other cerebellar regions probably involve noncholinergic functions. The significance of the nonuniform AChE distribution is not yet known, but may correspond to regional differences in neuronal or metabolic activity in the cerebellum that occur in conjunction with specific behaviors.