Maturation of otolith‐related brainstem neurons in the detection of vertical linear acceleration in rats

Abstract

To investigate the critical maturation time of otolith-related neurons in processing vertical orientations, rats (postnatal day 4 to adults) were studied for functional activation of c-fos expression in brainstem neurons by immuno-/hybridization histochemistry. Conscious rats were subjected to sinusoidal linear acceleration along the vertical plane. Labyrinthectomized and/or stationary controls showed only sporadically scattered Fos-labeled neurons in the vestibular nuclei, confirming an otolithic origin of c-fos expression. Functionally activated Fos expression in neurons of the medial and spinal vestibular nuclei and group x were identifiable by P7 and those in group y by P9. A small number of Fos-labeled neurons characterized by small soma size were found in the ventral part of lateral vestibular nucleus by P9. Other vestibular-related areas such as prepostitus hypoglossal nucleus, gigantocellular reticular nucleus and locus coeruleus of normal experimental rats showed functionally activated c-fos expression at P7. Neurons in dorsal medial cell column and beta subnucleus of the inferior olive only showed functionally activated c-fos expression by the second postnatal week. These findings revealed a unique critical maturation time for each of the vestibular-related brainstem areas in the recognition of gravity-related vertical head orientations. By mapping the three-dimensional distribution of Fos-immunoreactive neurons, we found an even distribution of otolith-related neurons within the spinal vestibular nucleus in groups x and y but a clustered distribution in the middle-lateral-ventral part of the medial vestibular nucleus. Taken together, our findings reveal the developmental profile of neuronal subpopulations within the vertical otolith system, thereby providing an anatomical basis for postnatal coding of gravity-related vertical head movements.

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

“…The neuronal expression of c-fos allows us to map the distribution of the second-order and higherorder neurons within the central circuitry of the horizontal canal system. Input of canal origin leading to Fos expression within the vestibular nucleus, PrH and IO was confirmed by the basal level of Fos signal in labyrinthectomized rats with or without rotation and in normal stationary rats (Chen et al, 2003;Lai et al, 2004Lai et al, , 2006Lai et al, , 2008Tse et al, 2008).…”

“…The Perspex restrainer was reported in detail by previous studies of our laboratories (Lai et al, 2004(Lai et al, , 2006. In brief, the acrylic tube was fitted in the restrainer by laterally extending aluminum bars and a dorsal screw.…”

“…Average tissue background was set at the minimum on a gray scale of 255 shades. Threshold was then established at the gray level of 190 units (Kaufman et al, 1993;Moratalla et al, 1996;Janusonis and Fite, 2001;Lai et al, 2006;Tse et al, 2008). In each experimental and control animal, positive Fos labeling was confirmed when the darkly stained nuclei of Fos-ir neurons reached a gray level above the threshold.…”

“…In the adult vestibular system, this approach was used to reveal the distribution pattern of brainstem neurons that engaged in vestibular compensation following unilateral labyrinthecotmy (Kaufman et al, 1992a(Kaufman et al, , 1993Cirelli et al, 1996;Darlington et al, 1996;Gustave et al, 1999Gustave et al, , 2000 or brainstem neurons activated by natural otolithic stimulation (Lai et al, 2004(Lai et al, , 2006. A similar strategy was used to determine the critical maturation time of otolith-related neurons along the vestibulo-olivary pathway in recognition of gravity-related 3D head orientations (Lai et al, 2004(Lai et al, , 2006. Neurons in the vestibular nuclei responded to otolith inputs as early as P7, whereas those in the inferior olive responded by P11.…”

Coexpression of GABA_BR1 and GABA_BR2 Receptor Subunits in the Rat Vestibular Nucleus

“…The vestibular information integrated in different vestibular subnuclei [2,3] is then sent to other neural areas for motor function (e.g. extraocular or spinal projections) [4][5][6][7] and spatial recognition (e.g.…”