Postnatal NMDA receptor blockade alters the characteristics of canal-related inferior olivary neurons

Abstract

Glutamate mediates excitatory neurotransmission from the vestibular afferents to target neurons in the vestibular nucleus (VN). Postnatal changes in the expression pattern of ionotropic glutamate receptor subunits were observed among canal-related VN neurons of Sprague-Dawley rats. With the use of c-fos expression as a marker for postsynaptic activation after sinusoidal rotations in the vertical or horizontal plane, we showed that neurons in the inferior olive (IO) subnuclei, a downstream relay of the vestibulo-olivary pathway, exhibited unique directional responsiveness. To investigate whether perinatal modification of glutamatergic transmission within VN can affect the recognition characteristics of canal-related neurons in the mature brain, NMDA receptors in VN were chronically blocked by implanting MK801-impregnated Elvax over the bilateral VN of neonatal rats. The rats were allowed to recover and the consequential effects on directional tuning features of IO neurons in MK801-treated rats were compared with those in control rats at different time points after implantation. As compared to the control rats, MK801-treated rats showed qualitative changes in the distribution pattern of Fos-labeled IO neurons that were responsive to rotational stimulations. Taken together, our results suggest that the postnatal establishment of glutamatergic transmission in the VN is crucial for functional networking of canal-related IO neurons in the mature animals.