Morphological and functional changes in a new animal model of Ménière's disease.

The purpose of this study was to clarify the underlying mechanism of vertiginous attacks in Ménière's disease (MD) while obtaining insight into water homeostasis in the inner ear using a new animal model. We conducted both histopathological and functional assessment of the vestibular system in the guinea-pig. In the first experiment, all animals were maintained 1 or 4 weeks after electrocauterization of the endolymphatic sac of the left ear and were given either saline or desmopressin (vasopressin type 2 receptor agonist). The temporal bones from both ears were harvested and the extent of endolymphatic hydrops was quantitatively assessed. In the second experiment, either 1 or 4 weeks after surgery, animals were assessed for balance disorders and nystagmus after the administration of saline or desmopressin. In the first experiment, the proportion of endolymphatic space in the cochlea and the saccule was significantly greater in ears that survived for 4 weeks after surgery and were given desmopressin compared with other groups. In the second experiment, all animals that underwent surgery and were given desmopressin showed spontaneous nystagmus and balance disorder, whereas all animals that had surgery but without desmopressin administration were asymptomatic. Our animal model induced severe endolymphatic hydrops in the cochlea and the saccule, and showed episodes of balance disorder along with spontaneous nystagmus. These findings suggest that administration of desmopressin can exacerbate endolymphatic hydrops because of acute V2 (vasopressin type 2 receptor)-mediated effects, and, when combined with endolymphathic sac dysfunction, can cause temporary vestibular abnormalities that are similar to the vertiginous attacks in patients with MD.