Developmental expression of c-fos in canal-related brainstem neurons of rats following horizontal angular acceleration

Abstract

To investigate the distribution of functionally activated canal-related brainstem neurons during postnatal development, conscious Sprague-Dawley rats (P1-adult) were subjected to constant horizontal angular acceleration for 60 min. This stimulation paradigm composed of alternate modes of angular acceleration (at 150o/s2) in the clockwise (8s) and counterclockwise direction (8s), activating all hair cells of the two horizontal canals. Neuronal activation within brainstem nuclei was defined by immuno-/hybridization histochemical expression of c-fos. Labyrinthectomized controls and normal stationary controls showed only sporadic c-fos-expressing neurons. In P1-4 rats, no Fos-labeled neurons were found in the vestibular nucleus. By P5, significant Fos labeling in the medial (MV), spinal (SpV), superior (SuV) vestibular nuclei, group x and group y was identifiable. From P5-14, Fos expression increased significantly, reaching adult level at P21. In P5 rats, Fos-labeled neurons were evenly distributed throughout the entire rostrocaudal length of the MV, SpV and SuV while in adult rats Fos-labeled neurons were clustered in the caudal end of MV and SpV as well as the rostral end of SuV. In each age group, no Fos-labeling was observed in the whole lateral vestibular nucleus. In other canal-related brainstem areas such as the prepositus hypoglossal nucleus and locus coerulus, there was also an age-dependent increase in the number of Fos-labeled neurons from P5 onwards. Our findings suggest that functional connectivity between canal afferents and central vestibular neurons is established during the first postnatal week.