Receptors for leptin in the otic labyrinth and the cochlear–vestibular nerve of guinea pig are modified in hormone-induced anorexia

Abstract

Metabolic syndromic inner ear pathology is a recognized condition in clinical practice but the possible causes remain controversial. We have previously reported that chronically-implanted estrogen implants in guinea pig results in hyperprolactinemia and hearing loss together with otic bone dysmorphology. The animals also present with anorexia. The hormone leptin has major roles in the regulation of satiety as well as bone metabolism and so we hypothesized that leptin might contribute to pathology of the otic labyrinth. We employed immunohistochemistry to investigate leptin receptor (ObR) expression. In control animals, ObR immunolabeling was not detected in the bone of the otic capsule but immunolabeling was observed in the cochlear–vestibular nerve. The labeling was associated with the astrocytic glial dome area, which marks the transition between central and peripheral parts of the nerve. In estrogen-treated animals, positive-ObR immunolabeling was observed in osteoblasts in new bone of the otic capsule and the ObR labeling was reduced in the cochlear–vestibular nerve compared to controls. The data provide evidence that leptin may target the labyrinth – affecting the bone and the nerve – and so could contribute to ongoing protection of the inner ear. Leptin disturbance might contribute to metabolic syndromes involving the audiovestibular system.