ABSTRACT
Relationships between recovery of vestibuloocular reflex and expression of c-fos immunoreactive cells in the medial vestibular nuclei following unilateral labyrinthectomy(ULX) were investigated in rats. Frequency of spontaneous nystagmus, velocity of eye movement induced by sinusoidal rotation of the whole body at frequencies of 0.1, 0.2, 0.5Hz, and the number of c-fos immunoreactive cells in the medial vestibular nuclei were measured for 72 hours after ULX. Frequency of spontaneous nystagmus was 3.9+/-0.5 beats/sec(M+/-SD) immediately after ULX and disappeared completely within 48 hours. On sinusoidal rotation, eye movement induced by rotation toward the lesioned side recovered normal pattern within 24 hours at 0.1Hz rotation, and 12 hours at 0.2, 0.5Hz. Directional preponderance which represents the symmetry of bilateral vestibular functions decreased to less than 20% at 72 hours, but did not recover normal limit. The number of c-fos immunoreactive cells in the bilateral medial vestibular nuclei was severe asymmetry till 24 hours of ULX. However, the symmetry was recovered after 48 hours. These results indicate that the recovery of vestibuloocular reflex correlates with the expression of c-Fos immunoreactive cells of the medial vestibular nuclei in the early stage of vestibular compensation following ULX. Therefore, the vestibular nuclei may play a key role in vestibular compensation.