Which receptor type mediates secretion of catecholamines in the peripheral nervous system?

• A. Muscarinic M1 receptors
• B. Peripheral neuronal nicotinic receptors
• C. Muscarinic M2 receptors
• D. Adrenergic receptors

Answer: (B)

Secretion of catecholamines in the peripheral nervous system is triggered by acetylcholine binding to nicotinic receptors on chromaffin cells of the adrenal medulla, which receive input from preganglionic sympathetic fibers. These neuronal-type nicotinic receptors (Nn) open ion channels that cause depolarization and calcium influx, leading to vesicle fusion and release of epinephrine and norepinephrine into the bloodstream. Muscarinic receptors (M1, M2) are different acetylcholine receptors that mediate various parasympathetic and CNS effects but do not drive adrenal catecholamine secretion. Adrenergic receptors respond to catecholamines, not to acetylcholine, so they don’t initiate the release process. Hence, the receptor mediating this secretion is the peripheral neuronal nicotinic receptor.