Opioid Receptors
Opioid receptors are currently classified into three groups, κ, δ and μ receptors. Subtypes within each group have been suggested including μ1, μ2, δ1, δ2, κ1, κ2, and κ3. An opioid-like receptor with a high degree of homology to μ, δ and κ-opioid receptors has been cloned and termed the orphan opioid receptor (NOP, ORL1). This receptor has a distinct pharmacological profile from the classical opioid receptors and an endogenous ligand, nociceptin (orphanin FQ) has been identified.
Opioid Receptor Data
| Receptor Subtype | μ (MOP, OP3) | δ (DOP, OP1) | κ (KOP, OP2) | NOP (ORL1, OP4) |
|---|---|---|---|---|
| G protein | Gi/o | Gi/o | Gi/o | Gi/o |
| Transduction Mechanism | Activation of inwardly rectifying K+ channels, inhibition of Ca2+ channels, inhibition of adenylyl cyclase | |||
| Localization in CNS | Anterior cingulate cortex, neocortex, amygdala, hippocampus, ventral dentate gyrus, presubiculum, nucleus accumbens, caudate putamen, thalamus, habenula, interpeduncular nucleus, pars compacta of the substantia nigra, superior and inferior colliculi, raphe nuclei | Medial habenula, hypothalamus, pons, medulla, dorsal root ganglion, caudate putamen, medial habenula, tegmentum, trigeminal nucleus | Claustrum, endopiriform nucleus, caudate putamen, nucleus accumbens, midline nuclear group of the thalamus, superficial grey layer of the superior colliculus, central grey, caudate putamen, nucleus accumbens, amygdala, thalamus, interpeduncular nuclei | Cortex, olfactory bulb, suprachiasmatic nucleus, amygdala, nucleus accumbens, thalamic nuclei, hypothalamus, hippocampus, septum, superior colliculus |
| Likely Physiological Roles | Respiration, cardiovascular functions, feeding, learning and memory, intestinal transit, locomotor activity, thermoregulation, hormone secretion, immune functions | Analgesia, motor integration, gastrointestinal motility, olfaction, respiration, cognitive function, mood driven behavior | Regulation of nociception, diuresis, feeding, neuroendocrine secretions | Motor and balance control, reinforcement and reward, nociception, the stress response, sexual behavior, aggression, autonomic control of physiological processes |
| Key Selective Agonists | Endomorphin-1 (1055) Endomorphin-2 (1056) DAMGO (1171) | SNC 80 (0764) SB 205607 (0921) DPDPE (1431) | (±)-U-50488 (0495) BRL 52537 (0699) Dynorphin A (3195) | Nociceptin (0910) MCOPPB (3763) SCH 221510 (3240) |
| Key Selective Antagonists | β-Funaltrexamine (0926) CTOP (1578) Cyprodime (2601) | Naltrindole (0740) Naltriben (0892) BNTX maleate (0899) | nor-Binaltorphimine (0347) DIPPA (0794) GNTI (1282) | UFP-101 (1552) (±)-J 113397 (2598) JTC 801 (2481) |
References
Dhawan et al (1996) International union of pharmacology. XII. Classification of Opioid Receptors. Pharmacol Rev. 48 567.
Cox et al (2009) Opioid receptors, introductory chapter. Last modified on 13/10/2009. Accessed on 27/02/2013. IUPHAR database (IUPHAR-DB).