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