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

Abstract

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 immuno-hybridization histochemistry as an indicator of neuronal activation. Fos-immunoreactive canal-related neurons were identifiable from P4 onwards in the vestibular nucleus and downstream vestibular relay stations, prepositus 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 P4 to P14 but decreased significantly afterwards until adulthood. The topography was not clear in the vestibular nucleus and prepositus 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.

Maturation of glutamatergic transmission in the vestibulo-olivary pathway impacts on the registration of head rotational signals in the brainstem of rats

“…The vestibular origin of Fos expression in these circuitries was confirmed using both labyrinthectomized rats with or without rotation and normal stationary rats (cf. Chen et al 2003;Lai et al 2008Lai et al , 2010Tse et al 2008). In normal experimental rats, Fos expression was only taken as an indicator of vestibular input when the average number of Fos-ir cells/section of each subnucleus was C4.…”

Maturation profile of inferior olivary neurons expressing ionotropic glutamate receptors in rats: role in coding linear accelerations

“…The tube was fitted with laterally extending aluminium bars and a dorsal screw that allowed the entire head immobilization device to be positioned within the restrainer (cf. Lai et al 1995, 2004, 2010). The trunk of each rat was also cushioned with foam padding to minimize movements during linear acceleration.…”

“…Threshold was then established at the gray level of 190 units (cf. Kaufman et al 1993; Janusonis and Fite 2001; Lai et al 2006, 2010; Moratalla et al 1996; Tse et al 2008). In each experimental and control animal, positive Fos labelling was confirmed when the darkly stained nuclei of Fos-ir neurons reached a gray level above the threshold.…”

“…All rats were subjected to sinusoidal linear acceleration on a moving table either along the horizontal plane or vertical plane. As described in previous studies, each conscious experimental rat was enclosed in a perspex restrainer with the head of the animal cushioned against a silicone head mask supported externally by an acrylic tube (Chen et al 2003; Lai et al 2004, 2010). The tube was fitted with laterally extending aluminium bars and a dorsal screw that allowed the entire head immobilization device to be positioned within the restrainer (cf.…”

Functional Development of the Vestibular System

“…Most of the convergence between canal and otoliths is reported in the LVN and DVN and to a lesser extent in the MVN (Uchino et al, 2005), while the SVN receives only sparse otolith inputs (ButtnerEnnever, 1999). Overall, there is little evidence for topographic segregation in the processing of canal and otolith inputs (Lai et al, 2010).…”