Deveopmental responsiveness of vestibularrelated brainstem neurons to horizontal rotational and translational motions

Abstract

To investigate the distribution of functionally activated vestibularrelated brainstem neurons during postnatal development, ombined immuno-/hybridization histochemistry of 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 of 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. With rotational stimulation that comprised cycles of constant angular acceleration and deceleration, Fos-labeled neurons were observed by P4 in the vestibular nucleus and downstream relay stations of vestibular pathways, such as the prepositus hypoglossal nucleus and inferior olive (subnuclei DMCC, IOA, IOC, IOK). A later maturation time was evidenced for the utricular system. Fos-labeled neurons were only identifiable in the vestibular nucleus by P7; in the prepositus hypoglossal nucleus and inferior olive (subnuclei DMCC and IO ) by P11. Within the vestibular nucleus of P7–9 rats, neurons activated by canal or utricular inputs were intermingled throughout its rostro-caudal length. In P21 and adult rats, neurons activated by canal or utricular inputs were intermingled in localized regions of the medial and spinal vestibular nuclei. However, neurons in the rostral half of spinal vestibular nucleus were activated only by utricular inputs. Taken together, we have demonstrated that canal- and otolithrelated brainstem neurons that encode rotational and translational movements in the horizontal plane are histologically segregated and exhibit different developmental time frame. Acknowledgement Supported by HKRGC.