The compensation of spontaneous nystagmus and head deviation following chemical unilateral labyrinthectomy (UL) induced by arsanilate was delayed compared with surgical UL. Surgical UL produced two ...phases of significant asymmetry of cFos-like (cFL) protein expression between the bilateral medial vestibular nuclei, with more expression in the contralateral medial vestibular nuclei to the injured side than in the ipsilateral medial vestibular nuclei 2 h after UL; the pattern reversed after 6 h and expression disappeared after 72 h. Chemical UL produced three phases of asymmetric expression, with more cFL protein expression in the contralateral medial vestibular nuclei than in the ipsilateral medial vestibular nuclei 6 h after UL and a reversed pattern after 12 h. Asymmetric expression 72 h after UL followed increased expression in the contralateral medial vestibular nuclei. These results suggest that the course of vestibular compensation and the temporal expression of cFL protein in the medial vestibular nuclei following UL differed between surgical and chemical labyrinthectomy.
The expression and regional distribution of cFos protein, which is an oncogene product and metabolic marker of neural excitation, were investigated in the vestibular nuclear complex following acute ...hypotension in adult Sprague–Dawley rats. Intravenous administration of nitroprusside elicited a 10–50% reduction in mean blood pressure for 10 min. Unilateral or bilateral chemical labyrinthectomies were performed 14 days before the start of the experiment to eliminate afferent signals from the peripheral vestibular receptors in the inner ear. All of the animals were sacrificed and the tissues were fixed 2 h after the onset of acute hypotension using the cardiac perfusion method for c-Fos immunohistochemical staining. The cFos-like immunoreactive (cFLI) neurons were expressed selectively in the central area of the medial vestibular nucleus following a 10% reduction in blood pressure. Once the blood pressure had fallen by 30%, bilateral expression of cFLI neurons was observed in the superior, medial, and spinal vestibular nuclei, but not in the lateral vestibular nucleus, of control rats with intact labyrinths. The expression of cFLI neurons increased proportionately with reductions in blood pressure. In unilaterally labyrinthectomized rats, acute hypotension induced the expression of cFLI neurons in vestibular nuclei contra lateral to the injured labyrinth, but not in the ipsilateral vestibular nuclei. However, cFLI neurons were not expressed in bilateral vestibular nuclei following acute hypotension in bilateral labyrinthectomized rats. These results suggest that afferent signals from the peripheral vestibular receptors are essential for cFos protein expression in the vestibular nuclei following acute hypotension.
