Which receptor is listed among opioid receptor types alongside mu, delta, and kappa?

Which receptor is listed among opioid receptor types alongside mu, delta, and kappa?

• A. Mu
• B. GABA
• C. Nociceptin
• D. NMDA

Answer: (C)

Opioid receptor types commonly recognized are mu, delta, and kappa, and a related receptor that completes the family is the nociceptin receptor. Also called ORL-1 or NOPr, it responds to the endogenous ligand nociceptin/orphanin FQ and belongs to the same GPCR family as the classic opioid receptors, signaling through Gi/o to modulate pain pathways. The other options don’t fit because GABA and NMDA receptors are from different neurotransmitter systems (GABAergic and glutamatergic, respectively), and mu is one of the opioid receptors itself—nociceptin receptor is the fourth member frequently listed alongside mu, delta, and kappa.

Opioid receptor types commonly recognized are mu, delta, and kappa, and a related receptor that completes the family is the nociceptin receptor. Also called ORL-1 or NOPr, it responds to the endogenous ligand nociceptin/orphanin FQ and belongs to the same GPCR family as the classic opioid receptors, signaling through Gi/o to modulate pain pathways. The other options don’t fit because GABA and NMDA receptors are from different neurotransmitter systems (GABAergic and glutamatergic, respectively), and mu is one of the opioid receptors itself—nociceptin receptor is the fourth member frequently listed alongside mu, delta, and kappa.