Acetylcholinesterase activity in senile plaques of aged macaques

A modified acetylcholinesterase (AChE)-histochemical technique, which demonstrates axonal morphology to a high degree, was used to examine the neocortices of aged monkeys. This approach disclosed slender linear axonal profiles in young animals. In older monkeys, there was a variety of abnormalities of AChE-containing fibers, including multifocal distensions of individual fibers and aggregations of neurite-sized, AChE-rich swellings. Combined with thioflavin-T staining to visualize amyloid, this histochemical technique showed that some of these AChE-containing fibers were present in proximity to deposits of amyloid. This association suggests that abnormal AChE-rich axons participate in the formation of some senile plaques in the neocortices of aged nonhuman primates. While it is probable that many of these AChE-rich fibers are axons of cholinergic neurons residing in the basal forebrain, it is also likely that some of these fibers are derived from noncholinergic neuronal populations known to synthesize AChE. Immunocytochemical strategies can be used to assess the involvement of other systems, including cholinergic, noradrenergic, dopaminergic, somatostatinergic, and serotonergic neurons in the formation of senile plaques in the brains of aged nonhuman primates.