Opioid peptides have been detected in the auditory and vestibular efferent neurons where they colocalize with the major neurotransmitter, acetylcholine. We investigated the function of opioids to modulate neurotransmission mediated by hair cell's α9/α10-containing nicotinic acetylcholine receptors (α9/α10nAChRs). The endogenous opioid peptides, endomorphin-1 (mu agonist) and dynorphin B (kappa agonist), but not a delta agonist [D-Pen2,D-Pen-5]enkephalin, inhibited the acetylcholine-evoked currents in frog saccular hair cells and rat inner hair cells. This inhibition was noncompetitive, voltage-independent, and was accompanied by an acceleration of the rate of current decay. Selective mu- and kappa-opioid receptor antagonists did not block the inhibition, although partial reduction by naloxone was observed. All opioid antagonists tested also reduced the acetylcholine response. Endomorphin-1 and dynorphin B inhibited the acetylcholine-evoked currents in α9/α10-expressing Xenopus oocytes. Because oocytes lack opioid receptors, it provides strong evidence for the direct interaction of opioid peptides with α9/α10nAChR. Conclusion: α9/α10nAChR is a target for modulation by endomorphin-1 and dynorphin B, efferent cotransmitters in the inner ear.
ASJC Scopus subject areas
- Molecular Biology
- Cellular and Molecular Neuroscience
- Cell Biology