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It is well known that the hippocampal formation requires primary vestibular sensory information to generate spatial memory during self motion in human. The purpose of the present study was to evaluate the effect of unilateral deafferentation of vestibular sensory information on cFos and FosB proteins, a family of immediate early gene-related proteins known as metabolic marker for neural excitation in the hippocampal formation of rats. Adult Sprague-Dawley rats weighing 250 - 300 g were surgically ablated of the peripheral vestibular system in the inner ear and sacrific: d at 2, 6, 24, 48, 72 hours after surgical operation. Immunohistochemical staining and Western blot method were acapted to see change in expression of cFos and FosB proteins in the hippocampal formation. A significant charge of Fos B immunoreactivity was observed in granular cell layer of the dentate gyrus, CAI subfield of the hipocampus at 2 hours after unilateral labyrin thectomy. Thereafter, the number of FosB like imrnunoreactive neurons in these areas increased rapidly, peaked at 48 hours post operatively time. Western blot for FosB protein supported further time-dependent change of FosB revealed by immunohistochemical staining. In addition, granuL .r cell layer showed more significant expression of FosB LI neurons in the caudal dentate gyrus than the rostral one. In contrast, moderate number of cFos LI neurons was detected in polymorphic cell layer of the dentate gyms, pyramidal cell layer of CAI, and subiculum but not in granular cell layer of the dentate gyros at 2 hours afte labyrinthectomy. The number of cFos LI neurons in the hippocampal formation was rapidly decreased at 6 1 ours and then returned to basal value 24 hours after operation. These results suggest that unilateral ablation of the peripheral vestibular sensory information elicit spatio-temporal differences of cFos and FosB expressions in the hippocampal formation of rats.
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