Vestibular nucleus N-methyl-D-aspartate receptors contribute to spontaneous nystagmus generation following unilateral labyrinthectomy in Guinea pigs

We investigated the effects of a non-competitive N-methyl-D-aspartate (NMDA ) receptor/channel antagonist ((+)MK-801) or an L-type Ca2+ channel antagon ist (nifedipine), delivered into the ipsilateral vestibular nucleus complex (VNC) before a unilateral labyrinthectomy (UL), on spontaneous nystagmus ( SN) generation. Guinea pigs received either (+)MK-801 (5 or 12.5 mu g); the less active enantiomer, (-)MK-801 (5 or 12.5 mu g); nifedipine (5 or 10 mu g); or vehicle, via cannula in the ipsilateral VNC. (+)MK-801, but not nif edipine, significantly decreased mean SN frequencies at 6 h post-UL, compar ed to controls (P < 0.02) and reduced the rate of SN compensation (P < 0.05 ). These results suggest that the SN expression is partly induced by NMDA r eceptor activation in the ipsilateral VNC at the time of the UL. (C) 2000 E lsevier Science Ireland Ltd. All rights reserved.