Molecular forms of acetylcholinesterase in subcortical areas of normal and Alzheimer disease brain.

We have previously reported that the 10s molecular form (G4) of acetylcholinesterase (AChE) is selectively lost from several cortical areas of Alzheimer's disease (AD) brain. In the current follow-up study, we microdissected several areas of nondemented and AD brain, including the hippocampus, amygdala, and cingulate gyrus. Tissue homogenates were separated on sucrose density gradients and the resulting fractions were analyzed for AChE activity in order to define the ratios of the predominant AChE molecular forms (G4/G1). Both the hippocampus and amygdala exhibited distinct patterns of alterations in the G4/G1 ratio which correlate with the known distribution of histopathological changes in AD brain. In order to further define the major pool of AChE that is depleted in AD, we separated fractionated tissue homogenates into salt-soluble and detergent-soluble fractions. The G4/G1 ratios were only altered in the detergent-soluble fractions, indicating that the loss of the G4 AChE molecular form involves a selective depletion of the membrane pool. Available evidence would suggest that this form is the AChE molecular form physiologically relevant at the cholinergic synapse.