Presynaptic cholinergic receptors at the neuromuscular junction

Presynaptic cholinergic receptors at the neuromuscular junction (NMJ) are critical regulatory proteins located on the motor nerve terminal that modulate the release of acetylcholine (ACh). These receptors consist of two main classes: nicotinic (nAChR) and muscarinic (mAChR) autoreceptors (StatPearls, 2023). The presynaptic nAChRs, specifically the alpha-3-beta-2 subtype, are responsible for a positive feedback mechanism that facilitates the mobilization of ACh vesicles from the reserve pool to the ready-releasable pool during high-frequency stimulation, ensuring sustained synaptic transmission (BJA, 2001). Presynaptic mAChRs, including M1 (facilitatory) and M2 (inhibitory) subtypes, provide further fine-tuning of neurotransmitter release (NCBI, 2015). These receptors are clinically significant as they are targeted by non-depolarizing neuromuscular blocking agents (NMBAs) like vecuronium and rocuronium; blockade of these presynaptic receptors prevents vesicle mobilization and results in the fade phenomenon observed during neuromuscular monitoring. Dysfunction of these regulatory pathways is implicated in neuromuscular disorders and is a primary concern in managing anesthesia-induced muscle relaxation and its reversal (PubMed, 2018).

Other names

Presynaptic nicotinic acetylcholine receptorsPresynaptic muscarinic acetylcholine receptorsNMJ autoreceptorsNeuronal-type nicotinic receptors at the NMJAlpha-3-beta-2 nicotinic receptorM1 muscarinic receptorM2 muscarinic receptor

Non-depolarizing neuromuscular blocking agents (NMBAs) act as competitive antagonists at presynaptic nicotinic receptors (primarily alpha-3-beta-2 subtypes), which inhibits the positive feedback loop responsible for mobilizing acetylcholine vesicles from the reserve pool to the ready-releasable pool during repetitive nerve stimulation (StatPearls, 2023; BJA, 2001). This leads to a progressive decrease in acetylcholine release, manifesting as fade in the train-of-four (TOF) response. Presynaptic muscarinic receptors (M1 and M2) also modulate release via G-protein coupled pathways that influence calcium channel activity and vesicle fusion (NCBI, 2015).