Differential role of type I and type II vestibular hair cells in two anti-gravity reflexes in the rat
AbstractThe tail-lift reflex and the air-righting reflex in rats are anti-gravity reflexes that depend on vestibular function. We assessed reflex loss in relationship to the graded lesions caused in the vestibular sensory epithelia by varying doses of an ototoxic compound. Using high-speed video recording, we obtained nose-back of the neck-tail angles from the tail-lift reflex and time to right in the air-righting test. We then correlated these measures with type I (HCI), type II (HCII) and all hair cell (HC) counts in central and peripheral zones of the crista, utricle, and saccule. Correlations varied with the cell type, zone and end-organ considered, and those of tail-lift angles were strikingly greater with HCI counts that HCII counts. A similar HCI vs HCII difference was not recorded for air-righting times. We conclude that these two reflexes depend differently on HCI and HCII function and that the tail-lift angle measures HCI function.