Studies on the Vestibular Compensation after Contralateral Labyrinthectomy in Unilateral Labyrinthectomized Rats

Kim, Jin Yong; Kim, Joon Ki; Kim, Kwang Tae; Park, Sang Young; Chun, Kyung Doo; Lee, Moon Young; Park, Byung Rim

Abstract

BACKGROUND AND OBJECTIVES: Vestibular compensation is a process of behavioral recovery following unilateral labyrinthectomy (ULX). The neural plasticity in vestibular compensation was assessed by observing changes of behavioral response and c-Fos expression following contralateral labyrinthectomy (second labyrinthectomy) in ULX rats. MATERIAL AND METHODS: Contrala-teral labyrinthectomy was performed 2 weeks after ULX in Sprague-Dawley rats, each weighing 250-300 gm. Changes of spontaneous nystagmus, head tilt, and c-Fos expression in the medial vestibular nucleus (MVN) and nucleus prepositus hypoglossi (PrH) were measured. RESULT: In ULX, spontaneous nystagmus with the slow phase directed to the lesion side was 3.5+/-0.5 beats/sec and head tilt deviated to the lesion side was 71+/-16 degrees just after ULX. Spontaneous nystagmus disappeared within 72 hours, but head tilt was maintained at 28+/-8 degrees until 2 weeks after ULX. The number of c-Fos proteins 2 hours after ULX was 81+/-25 and 212+/-63 in MVN of the lesion side and the intact side, respectively. And PrH showed 136+/-37 in the lesion side and 94+/-19 in the intact side, which was opposite of MVN in spatial expression of c-Fos. In second labyrinthectomy, direction of spontaneous nystagmus and head tilt was opposite to the first ULX and their decrement was faster. c-Fos was expressed more in the MVN of the first labyrinthectomized side than in the second one and PrH showed the opposite pattern to MVN, which was opposite to the first ULX in spatial expression.
CONCLUSION
These results suggest that recovery of vestibuloocular reflex in vestibular compensation is accomplished by restoration of neuronal activity in the central nervous system including MVN and PrH.