USMLE

M1 (Muscarinic) Receptors

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General Pharm
  1. Gs / Gi Pathway
  2. Gq Signaling Pathway
  3. Alpha-1 (Adrenergic) Receptors
  4. Alpha-2 (Adrenergic) Receptors
  5. Beta-1 (Adrenergic) Receptors
  6. Beta-2 (Adrenergic) Receptors
  7. Beta-3 (Adrenergic) Receptors
  8. M1 (Muscarinic) Receptors
  9. M2 (Muscarinic) Receptors
  10. M3 (Muscarinic) Receptors
  11. D1 (Dopamine) Receptors
  12. D2 (Dopamine) Receptors
  13. H1 (Histamine) Receptors
  14. H2 (Histamine) Receptors
  15. V1 (Vasopressin) Receptors
  16. V2 (Vasopressin) Receptors

Summary

M1 receptors are muscarinic receptors that act on many tissues, but most importantly in the Central Nervous System or Brain. Of note is that M1 receptors act via a Gq-protein subunit, which induce a downstream cascade of second messengers. Clinically, M1 receptors are important in cognitive processing, memory, and nausea. As such, M1 receptor antagonists that block signalling are used to treat motion sickness, while cholinesterases which increase M1 signalling via acetylcholine are used to treat Alzheimer Dementia.


Key Points

  • M1 Muscarinic Receptors
    • GPCR that responds to acetylcholine
      • Activates a Gq subunit
  • Locations
    • CNS
    • Enteric nervous system
  • Actions
    • Cognition/Memory
      • Antimuscarinics (e.g. atropine, anticholinergics) may lead to confusion and delirium
      • Acetylcholine deficiency implicated in Alzheimer dementia, which is treated with Cholinesterase Inhibitors
    • Vestibular Sensation and Vomiting
    • Tremor
      • M1 antagonists (e.g. benztropine and trihexyphenidyl) used to prevent tremor in Parkinson disease
      • Thought to function via inhibition of motor centers/basal ganglia