Structural and physiological change of the bullfrog semicircular canal due to gentamicin intoxication.

The effect of Gentamicin (GM) on the vestibular organ was studied using bullfrogs. The ototoxicity was compared among 3 different ways of administration, i.e., intraperitoneal (IP), intramuscular (IM) and intralabyrinthine (IL) injections. Morphological change of the posterior canal crista was observed by SEM. The posterior canal ampullary nerve action potentials (AP) were recorded, and were compared with SEM findings of the sensory epithelia. Morphological and physiological changes were severe in the order of IL greater than IM greater than IP. Morphological and physiological changes developed as the postinjection time elapsed. Morphological damage started at the narrow portion of the crista and developed towards the center and finally towards the periphery. Physiological change was already observed before the morphological damage. Physiological change tended to correlate with the morphological damage.