ACh-induced neurotransmission takes place when ACh binds with either of two cholinergic receptors: muscarinic or nicotinic. Decreased densities of nicotinic receptors and certain muscarinic receptor subtypes (M2) have been observed in the cortical areas of AD patients. When presynaptic nicotinic receptors are activated, several neurotransmitters are released, including ACh, dopamine and other monoamines. The release of these neurotransmitters is important to both memory and learning.