Developmental Expression of Fos Protein in Horizontal Canal-Related Vestibular Nuclear Neurons of Postnatal Rats following Angular Acceleration

Abstract

To investigate the postnatal distribution of horizontal canalrelated neurons within the vestibular nucleus, conscious young (1–21 days) and adult Sprague-Dawley rats were subjected to constant angular acceleration on the horizontal plane for 60 minutes. This stimulation paradigm, composed of alternate modes of angular acceleration (at 50–200º/s 2 ) in the clockwise (8s) and counterclockwise direction (8s), activates hair cells in both horizontal canals. Neuronal activation within brainstem nuclei was defined by the expression of Fos protein. Labyrinthectomized controls and normal stationary controls showed only a few sporadically scattered Fos-labeled eurons. In P1–4 rats, no Fos-labeled neurons were found in the vestibular nucleus and prepositus hypoglossal nucleus (PrH). In the vestibular nucleus, significant Fos labelling was identified in the medial (MV), spinal (SpV) nuclei and group ! subnucleus as early as P5. From P5 to P14, Fos expression in both the MV and SpV progressively increased, reaching an adult level at P21. In P5–7 rats, Fos-labeled neurons, though few in number, were evenly distributed throughout the entire rostrocaudal length of the MV and SpV. In P21 and adult rats, however, the number of Fos-labeled neurons tended to cluster in the caudal end of the MV and SpV. In the PrH, an area related to vestibulo-ocular functions, an age-dependent increase in the number of Fos-labeled neurons was observed from P7 onwards. These were mainly distributed in the rostral PrH. The present results provide evidence that functional connectivity between canal receptors and central vestibular neurons is established during the first postnatal week. Acknowledgement: Supported by HK RGC.