Morphological change of the cupula due to an ototoxic agent: a comparison with semicircular canal pathology.
CONCLUSIONS
The cupula shows various degrees of changes after gentamicin (GM) injection into the inner ear, with or without damage of the sensory cells. This cupula change may be a part of the etiology of peripheral vertigo, and is also potentially one of the mechanisms of reduced caloric response.


OBJECTIVE
To observe the morphological changes of the cupula after injecting GM in the frog inner ear and to compare the changes of the cupula with those of the ampullary sensory cells.


METHODS
We injected 300 microg (7.5 microl) of GM into the inner ear of 30 bullfrogs (Rana catesbeiana) using a microsyringe under ether anesthesia. The same amount of saline was injected into the other ear as control. The cupulae were observed at 3, 7, and 14 days after GM injection by stereoscopic microscope. The ampullae were fixed, and the sensory cells were assessed using a scanning electron microscope (SEM). The correlation between the changes in the cupula and sensory cells was evaluated using our own scale.


RESULTS
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.
Konomi
Ujimoto
U
Department of Otolaryngology, Tokyo Medical University School of Medicine, Tokyo, Japan. ujimotokn@hotmail.com
Suzuki
Mamoru
M
Otsuka
Koji
K
Shimizu
Akira
A
Inagaki
Taro
T
Hasegawa
Go
G
Shimizu
Shigetaka
S
Motohashi
Rei
R
D000818:Animals; D000900:Anti-Bacterial Agents / Q000633:toxicity*; D005839:Gentamicins / Q000633:toxicity*; D054777:Hair Cells, Ampulla / Q000187:drug effects / Q000473:pathology; D008855:Microscopy, Electron, Scanning; D011892:Rana catesbeiana; D012665:Semicircular Canals / Q000187:drug effects* / Q000473:pathology; D054776:Semicircular Ducts / Q000187:drug effects* / Q000473:pathology
D000900:Anti-Bacterial Agents; D005839:Gentamicins