Change in the distribution of gravity-related neurons in the vestibular circuitry after perinatal blockade of glutamate transmission in the vestibular nucleus of rats

Abstract

Head movement signals arising from the vestibular end organs are transmitted to the vestibular nuclei (VN) and are then relayed via the inferior olive (IO) and the thalamus to the cerebellum for motor coordination and cerebral cortex for spatial perception, respectively. To investigate the contribution of glutamate transmission in the VN to postnatal formation of gravity-related maps in the IO and thalamus, Elvax slices loaded with non-competitive NMDA receptor antagonist MK801 were implanted over the bilateral VN at postnatal day (P) 4 and 21. These operated Sprague–Dawley rats were allowed to recover until their adulthood. Immunohistochemical staining of Fos protein was then used to identify IO and thalamic neurons that were functionally activated by sinusoidal vertical linear acceleration. The consequential effects on the distribution of gravity-related neurons in the IO and thalamus of MK801-treated rats were compared with those in salinetreated rats. In saline-treated rats and in P21-MK801 rats, gravity-related Fos expressing neurons in the IO were found in the β subnucleus and dorsomedial cell column while those in the thalamus were in the midline nuclei (viz central medial, mediodorsal, paracentral, and rhomboid nuclei) and subthalamic nuclei (viz. subparafascicular and zona incerta). In P4-MK801-treated rats, however, our data showed both a significant decrease in Fos-expressing neurons as well as a derangement in the distribution of these neurons. This suggests that sensory deficiency in early postnatal period deters the establishment of internal spatial reference for vertical linear acceleration in the IO and thalamus of mature animals.