Developmental profile of central otolith neurons in the detection of vertical linear acceleration

Abstract

To investigate the time course of maturation of central otolith neurons in coding vertical head movements, Fos-immunohistochemical experiments were performed in an age-graded series of Sprague Dawley rats (P4 - 84). All conscious animals were subjected to sinusoidal linear acceleration along the vertical plane, thereby activating the saccules in the inner ear. In control experiments, labyrinthectomized rats subjected to accelerations and normal rats that remained stationary showed only sporadically labeled neurons in the vestibular nucleus and the neighboring prepositus hypoglossal nucleus. Functionally activated Fos-immunolabeled neurons were first identified at P7 in spinal vestibular nucleus, medial vestibular nucleus, group x, and prepositus hypoglossal nucleus. However, it is of interest to note that in group y, a region that receives heavy afferent input from the saccule, Fos-labeled neurons were only found from P9 onwards. The number of functionally activated neurons in these otolith-related areas gradually increased with age and reached adult level at P28. Our findings therefore reveal the developmental profile of central otolith neurons in coding vertical head movements during the first postnatal month. Supported by HK RGC