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

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.link_to_subscribed_fulltex

Postnatal development of canal-related brainstem neurons responsive to three-dimensional rotations in rats

Conference Theme: Improving the Health of an Aging Populatio

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

Session: 392. Vestibular System: Neurophysiology of VOR and Spatial Orientation PosterTo 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

Developmental responsiveness of vestibular-related brainstem neurons to horizontal rotational and translational motions

To investigate the distribution of functionally activated vestibular-related brainstem neurons during postnatal development, combined immuno-/hybridization histochemistry for c-fos expression was performed in Sprague-Dawley rats (P1–21; adult). Conscious animals were subjected to rotational or translational stimulus which activates hair cells on the horizontal semicircular canals or utricle, respectively. Neuronal activation within brainstem nuclei was defined by the expression of c-fos . Labyrinthectomized controls and normal stationary controls showed only a few sporadically scattered Fos-expressing neurons. During postnatal development, Fos-labeled vestibular nuclear (VN) neurons activated by cycles of constant angular acceleration and deceleration were observed by P4 while those by sinusoidal translational movement were not identifiable until P7. In both stimulation paradigms, an age-dependent increase in Fos-labeled neurons was observed in the VN and prepositus hypoglossal nucleus (PrH), the latter being a downstream area related to vestibulo-oculomotor function. In P7–9 rats, Fos-labeled neurons activated by canal or utricle input were evenly distributed throughout the rostro-caudal length of the VN complex (except the dorsal part of lateral VN) as well as groups x and y. At this age, PrH neurons were only activated with rotational stimulus and those activated with translational stimulus were not found until P11. In P21 and adult rats, the overlapping distribution of canal- and utricle-related Fos-labeled neurons was limited to the middle part of medial VN and caudal part of spinal VN. The rostral part of spinal VN was found to be constituted with neurons activated by translational motion. In the medial VN and PrH, a vast majority of the neurons was activated by rotational stimulus and only a small proportion was by translational stimulus. Taken together, we have demonstrated that canal- and otolith-related brainstem neurons that encode horizontal rotational and translational movements are histologically segregated and exhibit different developmental time frame. Acknowledgement: Supported by HKRGC.link_to_subscribed_fulltex

Maturation of canal-related brainstem neurons in the detection of horizontal angular acceleration in rats

We examined the functional maturation of canal-related brainstem neurons in Sprague-Dawley rats at postnatal day (P) 1 to adult. Conscious animals were subjected to cycles of angular acceleration and deceleration so as to selectively activate hair cells of the horizontal semicircular canals. Brainstem neurons were monitored for c-fos expression by immune-hybridization histochemistry as an indicator of neuronal activation. Fos-immunoreactive canalrelated neurons were identifiable from P4 onwards in the vestibular nucleus and downstream vestibular relay stations, propositus hypoglossal nucleus, and inferior olive. In the vestibular nucleus and prepositus hypoglossal nucleus, the number of canal-related neurons increased progressively with age, reaching the adult level by P21. Those in the inferior olive increased in number from P4to P14 but decreased significantly afterwards until adulthood. The topography was not clear in the vestibular nucleus and pre-positus hypoglossal nucleus. Canal-related neurons in P4 -7 rats were spread throughout the rostrocaudal length of each subnucleus but clusters of canal-related neurons tended to form within specific subnuclei by P21. These were concentrated in the caudal halves of medial and spinal vestibular nuclei and the rostral parts of superior vestibular nucleus and prepositus hypoglossal nucleus. In the inferior olive, the topography was evident early in the course of development. Canal-related neurons were exclusively located in four subnuclei: dorsal medial cell column, dorsal cap, subnucleus A, and subnucleus C, but not in other subnuclei. Taken together, our data revealed the developmental profile of neuronal subpopulations within the horizontal canal system, thus providing an internal neural representation for postnatal coding of horizontal head rotations in spatial perception. © 2009 Wiley-Liss, Inc.link_to_subscribed_fulltex