Serotonin-induced plasma extravasation in the murine inner ear: possible mechanism of migraine-associated inner ear dysfunction.

Sensitivity to sound and vertigo are often components of migraine. Recent studies suggest that plasma extravasation from intradural blood vessels may contribute to migraine pain. This study documented plasma extravasation in the mouse inner ear after intravenous administration of serotonin (5-HT). Horseradish peroxidase (HRP) was injected intravenously to trace protein extravasation in mice, followed 15 min later by intravenous 5-HT or saline. Forty-five minutes later, mice were euthanized. HRP extravasation was visualized immunohistochemically and quantified densitometrically. Baseline and evoked extravasation in stria vascularis and tectorial membrane were indistinguishable from skin, dura mater and tympanic membrane. Brain parenchyma, Scarpa's ganglion, basal spiral ganglion and modiolus, and the central vestibular nerve segment showed no significant 5-HT-induced extravasation. In contrast, 5-HT produced extravasation in the apical spiral ganglion, modiolus, and intralabyrinthine superior and inferior vestibular nerve. Thus, inner ear plasma extravasation is a potential mechanism for migraine-associated vertigo and sound sensitivity.