Brain muscarinic receptor subtypes are differently affected in Alzheimer's disease and Parkinson's disease.

The muscarinic receptor subtypes determined by displacing [3H]quinuclidinyl benzylate by carbachol showed distinct profiles in Alzheimer's disease (AD) and in Parkinson's disease (PD). A decrease in the M2-receptor count was seen in the hippocampus in AD as compared to controls, while PD patients had unaltered binding. By contrast, PD patients had increased M2-binding in the frontal and temporal cortex, whereas unchanged binding was seen in AD. In PD the total number of cortical muscarinic receptors was negatively associated with the activity of ChAT, but had a positive correlation with the degree of dementia of the patients.