Muscarinic acetylcholine receptors (mAChRs) are a subfamily of G protein-coupled receptors that regulate numerous fundamental functions of the central and peripheral nervous systems. There are 5 subtypes¹ :
 

Muscarinic receptors are distributed throughout many areas of the body and are responsible for various activities based on location and receptor subtype, including^2-4:
 

• Neuronal activation and signaling
• Behavior, learning and memory
• Cardiac function
• Smooth muscle function
• Function of glands involved in saliva and insulin production

The activation of muscarinic receptors results in either an increase or decrease in signaling within the cell depending on the receptor subtype³:
 

M₁ and M₄ receptors are present in the central nervous system (CNS) and are localized in brain regions responsible for a variety of functions, including behavior and cognition.^3,5

Certain behavioral and cognitive symptoms of neuropsychiatric diseases may be caused by impairments of brain circuits that impact and can be modulated by M₁ and M₄ receptor activity and/or expression as well as acetylcholine, the neurotransmitter and molecule that binds to mAChRs. 
 

• Acetylcholine is released in the brain and binds to the M₁ and M₄ receptors to help regulate neurological function. 
• M₁ and M₄ receptors are located in areas of the brain thought to be associated with behavioral and cognitive symptoms. 
• Abnormal activity of M₁ and M₄ receptors in these areas of the brain may exacerbate those symptoms.⁶