Endogenous ligands map to receptors as follows: Mu, Delta, and Kappa ligands.

Endogenous ligands map to receptors as follows: Mu, Delta, and Kappa ligands.

• A. Mu: Endorphins; Delta: Enkephalins; Kappa: Dynorphins
• B. Mu: Enkephalins; Delta: Dynorphins; Kappa: Endorphins
• C. Mu: Dynorphins; Delta: Endorphins; Kappa: Enkephalins
• D. Mu: Endorphins; Delta: Dynorphins; Kappa: Enkephalins

Answer: (A)

Mu receptors are primarily activated by endorphins, delta receptors by enkephalins, and kappa receptors by dynorphins. Endorphins, especially beta-endorphin, have the strongest affinity for mu receptors and drive analgesia and euphoria through this receptor. Enkephalins (met-enkephalin and leu-enkephalin) preferentially bind to delta receptors, contributing to analgesia and modulation of neurotransmitter release. Dynorphins are the preferred ligands for kappa receptors, involved in analgesia with distinct effects such as potential dysphoria. So the pairing of mu with endorphins, delta with enkephalins, and kappa with dynorphins aligns with established ligand-receptor affinities. Other options mix these peptides with different receptors, which does not fit the known selectivity patterns.

Mu receptors are primarily activated by endorphins, delta receptors by enkephalins, and kappa receptors by dynorphins. Endorphins, especially beta-endorphin, have the strongest affinity for mu receptors and drive analgesia and euphoria through this receptor. Enkephalins (met-enkephalin and leu-enkephalin) preferentially bind to delta receptors, contributing to analgesia and modulation of neurotransmitter release. Dynorphins are the preferred ligands for kappa receptors, involved in analgesia with distinct effects such as potential dysphoria.

So the pairing of mu with endorphins, delta with enkephalins, and kappa with dynorphins aligns with established ligand-receptor affinities. Other options mix these peptides with different receptors, which does not fit the known selectivity patterns.