Muscarinic M1 Receptor Coupling to G-protein is Intact in Parkinson’s Disease Dementia

BACKGROUND Postsynaptic cholinergic deficits, including reduced cortical muscarinic M1 receptor coupling to G-proteins, are neurochemical findings postulated to underlie the limited efficacy of presynaptically-targeted cholinergic replacement therapies in Alzheimer's disease (AD). While the loss of M1-G-protein coupling has been associated with β-amyloid (Aβ) burden in AD, the status of M1 coupling to G-proteins in Parkinson's disease-related or mixed dementias is unclear. OBJECTIVE To test the hypothesis that M1 receptor uncoupling is correlated with Aβ burden, we aimed to study muscarinic M1 neurochemical parameters in neurodegenerative dementias characterized by low and high Aβ loads. METHODS M1 receptors, M1 coupling to G-proteins as well as Aβ were measured in postmortem frontal cortex of a cohort of longitudinally assessed patients with Parkinson's Disease Dementia (PDD, low Aβ load) and AD with significant subcortical cerebrovascular disease (AD + CVD, high Aβ load). RESULTS We found unchanged levels of M1 receptors in both dementia groups, while M1 coupling was reduced only in AD + CVD (p