What is the primary neurotransmitter released by parasympathetic postganglionic neurons?

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Primary Neurotransmitter Released by Parasympathetic Postganglionic Neurons

Acetylcholine is the primary neurotransmitter released by parasympathetic postganglionic neurons. 1

Neuroanatomical Evidence

  • Parasympathetic postganglionic neurons release acetylcholine at motor nerve endings, which is responsible for both resting and bronchoconstrictive airway responses 1
  • The parasympathetic nervous system works through cholinergic transmission, with acetylcholine being released from postganglionic nerve terminals to activate muscarinic receptors on target tissues 1
  • Parasympathetic postganglionic neurons located in ganglionated plexi release acetylcholine to provide diffuse control over various regions of the heart 1

Mechanism of Action

  • Acetylcholine released from parasympathetic postganglionic nerve endings binds to muscarinic receptors on target tissues, mediating the characteristic effects of parasympathetic stimulation 1
  • The release of acetylcholine from parasympathetic nerve terminals is subject to negative feedback control through presynaptic muscarinic receptors 2
  • Acetylcholine transmission across the neuromuscular junction can be blocked by botulinum toxin, which inhibits acetylcholine release from the presynaptic motor neuron terminal 1

Functional Significance

  • Parasympathetic activity through acetylcholine release is the dominant reversible component in patients with COPD and other respiratory conditions 1
  • Vagal-mediated tone through released acetylcholine at motor nerve endings controls airway smooth muscle function 1
  • Acetylcholine released from parasympathetic postganglionic neurons acts on the sinoatrial node of the heart to regulate heart rate, particularly during parasympathetic dominance such as fear-induced bradycardia 1

Pharmacological Evidence

  • Anticholinergic agents (muscarinic receptor antagonists) such as tiotropium block the effects of acetylcholine released from parasympathetic postganglionic neurons, providing bronchodilation in asthma and COPD patients 1
  • Acetylcholinesterase inhibitors like armin and neostigmine cause accumulation of acetylcholine in the myocardium by preventing its breakdown, leading to typical cholinergic effects that can be blocked by atropine 3
  • The characteristic flaccid paralysis in botulism results from blocking acetylcholine transmission across the neuromuscular junction by inhibition of acetylcholine release from the presynaptic motor neuron terminal 1

Clinical Relevance

  • Understanding acetylcholine as the primary neurotransmitter of parasympathetic postganglionic neurons is crucial for developing therapeutic strategies for conditions involving autonomic dysfunction 1
  • Muscarinic receptor antagonists like tiotropium provide significant improvement in lung function in asthma and COPD by blocking the effects of acetylcholine released from parasympathetic postganglionic neurons 1
  • Non-quantal release of acetylcholine from parasympathetic nerve terminals occurs even in the absence of vagal impulse activity, contributing to baseline parasympathetic tone 3

References

1
Guideline

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Dr.Oracle Medical Advisory Board & Editors, 2025

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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