muscarinic receptor

n. A part of cholinergic transmission which is activated through a metabotropic route, necessarily slower than transmission at a nicotinic-ionic receptor site. Muscarinic receptor action requires a multiple-stage metabolic alteration involving a G-protein coupling to a second messenger, which may then open or close ionic channels in the neural membrane, leading to synaptic transmission. In addition, stimulation of a muscarinic receptor site may alter protein production within the neuron. Although nicotinic receptors are also found in the brain, muscarinic receptors predominate in the brain and are also found in the heart. Atropine (similar to ophthalmological eye drops used to dilate the pupil) inhibits cholinergic muscarinic receptor sites. – VS