Comparison of the effects of NMDA antagonists on medial vestibular nucleus neurons in brainstem slices from labyrinthine-intact and chronically labyrinthectomized guinea pigs.

The responses of ipsilateral medial vestibular nucleus (MVN) neurons in brainstem slices from guinea pigs compensated for a unilateral labyrinthectomy (UL), to the N-methyl-D-asparate (NMDA) receptor/channel antagonists CPP and MK801, were compared with those of MVN neurons in brainstem slices from labyrinthine-intact guinea pigs observed in a previous study. The average resting activity of ipsilateral MVN neurons from compensated animals was significantly higher than that for MVN neurons from labyrinthine-intact animals; however, there were no significant differences in the average magnitude of the decrease in firing rate from baseline in response to CPP or MK801 and the only significant difference in the number of responses was to MK801, where fewer ipsilateral MVN neurons from compensated animals responded with a decrease in firing rate. These results suggest that vestibular compensation is not associated with an up-regulation or increased affinity of NMDA receptors in the MVN ipsilateral to the UL.