Cochlear Functional Changes and CGRP Modulation in a Chronic Nitroglycerin Migraine-Like Rat Model

Auditory and vestibular symptoms in vestibular migraine, cochlear migraine, and Ménière's disease overlap, yet mechanisms linking migraine biology to inner ear dysfunction remain unclear. Calcitonin gene-related peptide (CGRP) is a key mediator of trigeminovascular activation and a major therapeutic target in migraine, but its contribution to cochlear dysfunction is not well defined. Using a repeated nitroglycerin (NTG) paradigm in male Wistar rats, we investigated whether a systemic migraine-like state affects cochlear function and whether these effects are dependent on CGRP. Rats received saline, NTG, or NTG followed by the CGRP receptor antagonist olcegepant (OLC). NTG increased plasma TNF-α and elevated trigeminal c-Fos; olcegepant partially normalized these markers, whereas behavioral changes in the open-field test were interpreted cautiously because baseline immobility differed across groups before treatment. NTG produced frequency-dependent changes in distortion-product otoacoustic emissions and auditory brain stem response thresholds. Electrocochleography showed limited changes, and scala media proportions did not differ significantly among groups, indicating no evidence of overt endolymphatic hydrops at the studied time point. Inner hair-cell synaptic markers showed no significant group differences for CtBP2, whereas GluR2 puncta differed between NTG and NTG + OLC (p = 0.012). Olcegepant attenuated NTG-associated cochlear functional changes and was associated with differences in postsynaptic GluR2 puncta, alongside region-specific changes in cochlear CGRP immunoreactivity. These findings support a mechanistic link between migraine-like trigeminovascular activation and early cochlear dysfunction and suggest that CGRP receptor blockade may benefit migraine patients with cochlear or vestibular symptoms. Future studies should assess females, estrous cycle tracking, hormones, and sex-specific auditory responses.