Opioid Receptor - Major Subtypes

Major Subtypes

There are four major subtypes of opioid receptors:

Receptor Subtypes Location Function
delta (δ)
DOP
OP1 (I)		 δ1, δ2
  • brain
    • pontine nuclei
    • amygdala
    • olfactory bulbs
    • deep cortex
  • peripheral sensory neurons
  • analgesia
  • antidepressant effects
  • physical dependence
kappa (κ)
KOP
OP2 (I)		 κ1, κ2, κ3
  • brain
    • hypothalamus
    • periaqueductal gray
    • claustrum
  • spinal cord
    • substantia gelatinosa
  • peripheral sensory neurons
  • analgesia
  • sedation
  • miosis
  • inhibition of ADH release
  • dysphoria
mu (μ)
MOP
OP3 (I)		 μ1, μ2, μ3
  • brain
    • cortex (laminae III and IV)
    • thalamus
    • striosomes
    • periaqueductal gray
    • rostral ventromedial medulla
  • spinal cord
    • substantia gelatinosa
  • peripheral sensory neurons
  • intestinal tract
 μ1:
  • analgesia
  • physical dependence

μ2:

  • respiratory depression
  • miosis
  • euphoria
  • reduced GI motility
  • physical dependence

μ3:

  • possible vasodilation
Nociceptin receptor
NOP
OP4		 ORL1
  • brain
    • cortex
    • amygdala
    • hippocampus
    • septal nuclei
    • habenula
    • hypothalamus
  • spinal cord
  • anxiety
  • depression
  • appetite
  • development of tolerance to μ agonists

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