Morphological change of the cupula due to an ototoxic agent: A comparison with semicircular canal pathology

Abstract

In over half of the cupulae in the 7- and 14-day groups, cupula changes such as shrinkage were observed. In about 50% of the total cases, the degree of cupula and sensory cell change correlated in the two groups. In the 14-day group, these changes were more marked. However, there were cases in which the changes of the cupula and sensory cells did not correlate, indicating that the cupula alone can sustain changes without sensory cell damage.

Changes in the cupula after disruption of the membranous labyrinth

“…For example, 3 days after GM injection, three of seven SCs with grade I cupular change already showed severe damage to the sensory epithelia [6]. In this labyrinthine puncture model, the cupular change tended to appear earlier than the damage to the sensory epithelia.…”

“…This prompted our studies of the cupula morphology. In the most recent experiment, the cupula shrank from either the top part or the margin after GM injection into the perilymphatic space [6]. Cupula shrinkage left a space between the cupula margin and the ampullary wall, thus hypermobilizing the cupula.…”

“…Subsequently, Ringer solution was gently flushed into the ampulla to exert pressure on the cupula and detach it from the crista. The morphology of the detached cupula was evaluated in accordance with the grading system of GM intoxication [6]: grade I, normal or limited change such as indentation of the apex; grade II, <50% shrinkage; grade III, 51-80% shrinkage; and grade IV, >80% shrinkage or absence. The details of this preparation technique were reported previously [4,6].…”

“…We previously performed a series of experiments on the physical properties of the cupula [4,5], which confirmed all these requirements. Our most recent experiment demonstrated that the cupula undergoes significant change after gentamicin (GM) administration [6]. Change was also observed in the sensory epithelia, but the degrees of cupular and sensory epithelial damage showed no correlation.…”

Experimental study on the aetiology of benign paroxysmal positional vertigo due to canalolithiasis: comparison between normal and vestibular dysfunction models

“…3 The bullfrogs were kept alive for 7-14 days. Then, the same procedure as in experiment 1 was performed and the time required for otoconial dislodgement was measured.…”