ABSTRACT
BACKGROUND AND OBJECTIVES: Several lines of evidence suggest that recovery of symptoms following unilateral labyrinthectomy (ULX) is due to the restoration of neuronal activity in the ipsilateral vestibular nuclei, leading to the reestablishment of bilateral symmetry in the resting neuronal activity. Effects of dizocilpine maleate (MK801), a non-competitive NMDA receptor antagonist, on vestibular compensation following unilateral labyrinthectomy (ULX) were investigated in adult Sprague-Dawley rats. MAERIAL AND METHODS: Responses of spontaneous nystagmus and neuronal activity of the contralateral medial vestibular nuclei (MVN) to labyrinthectomy were recorded in course of time after intraperitoneal injection of MK801. RESULT: Spontaneous nystagmus decreased gradually with time, but recovery of the nystagmus was aggravated 2 to 4 hours after administration of MK801 (p<0.05). In the labyrinthine intact rats, MK801 treatment significantly increased resting activity of type I and II in MVN compared with non-treated rats, and the effect of MK801 on neuronal activity was more prominent in the type I neurons than in the type II neurons. After 6 hours of ULX, the activities of type I and II neurons were decreased compared with labyrinthine intact rats, and type II neurons showed higher activity than the type I neurons. MK801 treated ULX rats showed higher resting activity in the type I and II neurons than in the labyrinthine intact rats or ULX rats, but lower resting activity than the MK801 treated labyrinthine intact rats. In the neuronal activity induced by sinusoidal rotation, gain was the highest in the MK801 treated ULX rats among the 4 experimental groups, and sensitivity was decreased in the type I & II neurons by treatment of MK801. CONCLUSION: These results suggest that MK801 deteriorates asymmetry of the resting activity in the bilateral MVN by inhibition of cerebellar Purkinje system inhibiting the intact MVN, which results in decompensation of the vestibular function following ULX.