Acetylcholine receptors (AChRs) mediate synaptic transmission at the neuromuscular junction. The channel-linked AChR that mediates rapid, excitatory actions of acetylcholine is called nicotinic AChR (nAChR) because it can be activated by nicotine. The non-channel linked AChR that medicates the slow actions of acetylcholine, which can be either inhibitory or excitatory, is called muscarinic AChR (mAChR) because it can be activated by muscarine. The mAChRs are present in neurons of the central and peripheral nervous systems, cardiac and smooth muscle and various exocrine glands. There are 5 subtypes (m1-m5) of the receptor that have a tissue specific pattern of expression. The m2 receptor is localized primarily in cardiac tissue and is also expressed at low levels in the hippocampus, cortex, striatum, thalamus, basal forebrain, brainstem, lung, vas deferens and uterus.
