VPT 321: Veterinary Neuropharmacology (2+1)

MUSCARINIC RECEPTORS

• These receptors are named because of their activity related to muscarine, an alkaloid.
• These  are  G - protein receptors and binding of acetylcholine to muscarinic receptors can cause an inhibition of adenylcyclase, activation of phospholipase C leading to formation of DAG or IP₃ and /or changes in ion channel activity.
• These receptors are blocked by atropine an alkaloid obtained from Atropa belladona.
• They are located primarily on the autonomic effector cells in the heart, blood vessels, eye, smooth muscles and glands of gastrointestinal, respiratory and urinary tracts, sweat glands etc. and in the central nervous system.
• Subsidiary muscarinic receptors are also present in the autonomic ganglia where they appear to play a modulatory role by inducing a long lasting late EPSP.
• Muscarinic autoreceptors are present prejunctionally on the post ganglionic cholinergic nerve endings. Activation of these receptors inhibits further release of acetylcholine.
• There are five Muscarinic receptor subtypes M₁, M₂, M₃, M₄ and M₅.
• Of these receptors, M₁, M₂ and M₃ are important.