Project Summary/Abstract Accumulation of α-synuclein (α-syn) into Lewy Bodies and Lewy Neurites is a hallmark of the Lewy Body Dementias (LBD), Dementia with Lewy Bodies and Parkinson’s Disease-Dementia. Additionally, some brain regions in Alzheimer’s Disease have pathological α-syn. Therefore, α-syn is likely a major cause of cognitive decline across several dementias. One possible mechanism underlying the core cognitive impairments centered around impaired executive function in LBD may be loss or dysfunction of projection neurons from the basal forebrain that produce acetylcholine (ACh). Across LBD, there is profound loss of cholinergic cells of the basal forebrain, which project to the prelimbic medial prefrontal cortex (PL-mPFC), a known key brain nucleus for executive function. Basal forebrain ACh acts through nicotinic and muscarinic ACh receptors (mAChR) to modulate PL-mPFC glutamatergic projection neurons critical for normal executive function. Recent evidence has further refined the mechanisms by which ACh regulates the PL-mPFC, and has suggested a key role for the M1 mAChR in regulating executive function. Despite this critical neuromodulatory role of ACh and M1 in the PL-mPFC in executive function, there are few studies that examine this important relationship in the context of α-syn related dementias. This has led to our overall hypothesis that cognitive decline in the context of α-syn linked dementias results from disrupted ACh signaling in the mPFC. We have used the pre-formed fibril (PFF) model of α-synucleinopathies to show that inputs into the PL-mPFC show enhanced ACh dependent long term depression in PFF injected mice. Additionally, layer 5 pyramidal cells of the PL-mPFC show decreased excitability in PFF injected mice compared to controls that may be attributable to ACh dependent changes in intrinsic properties of these cells. This suggests that α-syn dysregulates multiples aspects of the PL-mPFC through alterations in ACh release or signaling. To rigorously test this, we will perform a series of electrophysiology and behavioral experiments to determine, define, and dissect how α-ayn dysregulates the PL-mPFC through loss of ACh signaling or release. In Aim 1, we will test the hypothesis that α-syn dysregulates PL-mPFC inputs through altering ACh signaling. In Aim 2, we will test the hypothesis that α-syn alters intrinsic properties and output of PL- mPFC projection neurons through loss of ACh signaling. In aim 3, we will test the hypothesis that boosting cholinergic signaling will rescue deficits in executive function. Completion of these aims will provide fundamental understanding of how α-syn dysregulates ACh signaling to impair executive function in LBD.