Time course of vestibular function changes of experimental endolymphatic hydrops in guinea pigs.
OBJECTIVE
To investigate the relationship between endolymphatic hydrops and vestibular dysfunction.


METHODS
20 pigmented guinea pigs were used: 15 for a hydrops group and 5 for a sham group. Endolymphatic hydrops was produced by electrocauterization of the endolymphatic sac on the left ears. In the horizontal vestibuloocular reflex (HVOR) study, HVOR responses were recorded before and 1, 2, and 4 weeks after surgery in 9 animals of the hydrops group and 5 animals of the sham group. HVOR gain under sinusoidal rotation with a maximal head velocity of 45 degrees /s and frequencies of 0.05, 0.1, 0.2, 0.4 and 0.8 Hz was analyzed. In the nystagmus study, spontaneous nystagmus was recorded in all animals of the hydrops and the sham groups for 1 h in the dark and the maximum slow-phase velocity was measured before and 1, 2, 4 weeks after surgery. Morphological changes in the inner ear were measured light microscopically.


RESULTS
In the hydrops group, the HVOR gains at all stimulation frequencies seemed to decrease 1 week after surgery and recover 2 or 4 weeks after surgery; however, there were no statistical differences among HVOR gains in any periods after surgery. The incidence of spontaneous nystagmus gradually increased after surgery and the direction and onset showed large variation. The duration of nystagmus was approximately 10 min. The degree of endolymphatic hydrops showed large variation. In the sham group, HVOR gains at all stimulation frequencies showed no statistically different change in any period after surgery. In the sham group, no animal showed spontaneous nystagmus.


CONCLUSIONS
Experimentally induced endolymphatic hydrops seems to contribute to vestibular dysfunction to some extent. We speculated that when endolymphatic hydrops is progressing, vestibular dysfunction might occur.
Kakigi
Akinobu
A
Department of Otolaryngology, Faculty of Medicine, University of Tokyo, Bunkyo-ku, Tokyo, Japan. kakigi-tky@umin.ac.jp
Taguchi
Daizo
D
Takeda
Taizo
T
Takeda
Setsuko
S
Nakatani
Hiroaki
H
D000818:Animals; D004195:Disease Models, Animal; D004584:Electronystagmography; D018159:Endolymphatic Hydrops / Q000503:physiopathology* / Q000601:surgery; D006168:Guinea Pigs; D019416:Head Movements; D009760:Nystagmus, Physiologic / Q000502:physiology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D013997:Time Factors