Journal of Neuroscience, Vol 12, 4489-4500, Copyright © 1992 by Society for Neuroscience
Fos-defined activity in rat brainstem following centripetal acceleration
GD Kaufman, JH Anderson and AJ Beitz
Department of Veterinary Biology, University of Minnesota, St. Paul 55108.
To identify rat brainstem nuclei involved in the initial, short-term
response to a change in gravito-inertial force, adult Long-Evans rats were
rotated in the horizontal plane for 90 min in complete darkness after they
were eccentrically positioned off the axis of rotation (off- axis) causing
a centripetal acceleration of 2 g. Neural activation was defined by the
brainstem distribution of the c-fos primary response gene protein, Fos,
using immunohistochemistry. The Fos labeling in off- axis animals was
compared with that of control animals who were rotated on the axis of
rotation (on-axis) with no centripetal acceleration, or who were restrained
but not rotated. In the off-axis animals there was a significant labeling
of neurons: in the inferior, medial, and y-group subnuclei of the
vestibular complex; in subnuclei of the inferior olive, especially the
dorsomedial cell column; in midbrain nuclei, including the interstitial
nucleus of Cajal, nucleus of Darkschewitsch, Edinger-Westphal nucleus, and
dorsolateral periaqueductal gray; in autonomic centers including the
solitary nucleus, area postrema, and locus coeruleus; and in reticular
nuclei including the lateral reticular nucleus and the lateral parabrachial
nucleus. Also, there was greater Fos expression in the dorsomedial cell
column, the principal inferior olive subnuclei, inferior vestibular
nucleus, the dorsolateral central gray, and the locus coeruleus in animals
who had their heads restrained compared to animals whose heads were not
restrained. As one control, the vestibular neuroepithelium was destroyed by
injecting sodium arsanilate into the middle ear, bilaterally. This resulted
in a complete lack of Fos labeling in the vestibular nuclei and the
inferior olive, and a significant reduction in labeling in other nuclei in
the off-axis condition, indicating that these nuclei have a significant
labyrinth-sensitive component to their Fos labeling. The data indicate that
several novel brainstem regions, including the dorsomedial cell column of
the inferior olive and the periaqueductal gray, as well as more traditional
brainstem nuclei including vestibular and oculomotor related nuclei,
respond to otolith activation during a sustained centripetal acceleration.