K1vii: Serotonin Receptors

Serotonin = monoamine neurotransmitter

Location of Serotonin:

  • CNS & Platelets = 10%
  • Enterochromaffin cells of GI = 90%

Serotonin Receptors:

  • All GPCR except 5HT3 (ligand gated)
  • Effects:
    • CNS
      • Sleep-wake cycle
      • Temperature regulation
      • Appetite
      • Mood
      • Impulsivity
      • Anxiety & Depression
      • Sexual behaviour
    • RESPIRATORY
      • Bronchial smooth muscle constriction
    • CVS
      • Vasoconstriction
      • + inotropy & chronotropy

Rec

5HT1

Mechanism

GPCR

Gi →↓AC →↓cAMP

SoA

CNS Endothelium

Effect

Inhibits endothelial NO release = cerebral VC

Drugs

Agonist

Sumatriptan

VC to ↓migraine

Rec

5HT2

Mechanism

GPCR

Gq →↑Phospholipase C →↑IP3 + DAG →↑Ca++

SoA

CNS

Pre-frontal

Parietal

Somatosensory

Choroid Plx

GI tract

Plats

Effect

Plat aggregation & VC

Drugs

Agonist

LSD

Antagonist

Risperidone

Rec

5HT3

Mechanism

Ligand gated Na and K channel

SoA

CNS

Area Postrema

NTS (vom centre)

GI Tract

Parasymp nerve terminals

Effect

Emesis

Drugs

Antagonist

Ondansetron

Rec

5HT4

Mechanism

GPCR

Gs →

↑AC →↑cAMP

SoA

CNS

GI

Myenteric Plx

Secretory cells

Effect

GI peristalsis & secretions

Drugs

Agonist

Tegaserod