Background: In the inner ear, evidence has been gathered indicating that
melatonin plays important roles in inner ear physiology and pathophysiology. However, no attempt has been made previously to investigate the localization or expression of
melatonin and its receptors in the whole inner ear. Aims/objectives: To analyze the presence of
melatonin and its receptors in the normal mouse inner ear. Material and methods: C57BL6/J mice were used in this study. The localizations of
melatonin, MT1a and MT1b in the inner ear, i.e. cochlea, vestibular end organs, vestibular
ganglion and endolymphatic sac (ES), were studied by immunohistochemistry. Results: The organ of Corti, spiral ganglion, vestibular
ganglion, vestibular sensory cells, vestibular dark and transitional cells, and ES epithelial cells showed an immunofluorescence reaction to
melatonin, MT1a and MT1b. Conclusion and significance: The present findings show that
melatonin and its receptors (MT1a and MT1b) are present in the inner ear, thus supporting the hypothesis that
melatonin plays a physiological role in the inner ear.