Korean J Physiol Pharmacol.  1997 Jun;1(3):275-284.

Effect of electrical stimulation of the vestibular system on vestibuloocular reflex and c-Fos expression in the medial vestibular nuclei of unilateral labyrinthectomized rats

Affiliations
  • 1 Department of Physiol., Wonkwang University Sch. Med., Wonkwang University, Iksan 570-749 South Korea.

Abstract

Unilateral labyrinthectomy (ULX) causes autonomic symptoms, ocular and postural asymmetries, which disappear over time in the process of equilibrium recovery known as vestibular compensation. In the present study, in order to elucidate mechanisms responsible for the effects of electrical stimulation on vestibular compensation and investigate the relationship between vestibular compensation and c-Fos expression in the medial vestibular nuclei following ULX, we measured spontaneous nystagmus, eye movement induced by sinusoidal rotation and c-Fos expression up to 72 hs after ULX in Sprague-Dawley rats. Experimental animals were divided into two groups: ULX group with ULX only, and electrical stimulation (ES) group with electrical stimulation of -2 ~ -5 V, 1.0 ms, 100 Hz to the lesioned vestibular system for 4 hs/day. Spontaneous nystagmus following ULX disappeared by 72 hs in ULX group and 36 hs in ES group. In eye movement induced by sinusoidal rotation, normal pattern of eye movement by rotation toward the lesioned side was recovered 24 hs after ULX at rotation of 0.1 Hz and 6 hs after at 0.2 Hz, 0.5 Hz in ULX group. In ES group, the eye movement recovered after 12 hs at 0.1 Hz, 6 hs at 0.2 Hz, and 4 hs at 0.5 Hz. Directional preponderance which represents the symmetry of bilateral vestibular functions showed significantly early recovery in ES group compared with that of ULX group. Expression of c-Fos immunoreactive cells in the bilateral medial vestibular nuclei was severely asymmetrical till 36 hs in ULX group, and then it became a symmetry and disappeared after 72 hs. However, ES group showed the symmetry of c-Fos expression after 6 hs, which was significantly early recovery in ES group. All these findings suggest that electrical stimulation ameliorates recovery of ventibuloocular reflex following ULX by the restoration of the balance of the resting activity between bilateral medial vestibular nuclei. In addition, c-Fos expression in the medial vestibular nuclei could be used as a marker of vestibular compensation since c-Fos expression is closely related to the course of recovery following ULX.

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