To identify rat brainstem nuclei involved in the initial, shortterm 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.Received Mar. 2, 1992; revised June 5, 1992; accepted June 12, 1992. We thank Jaw-Hem Lee and Huna Nauven for their sutmortine work in our labs. This work is made possible by a griduate student researchepprogram fellowship and NIH Grants DC01086, NS19208, DC001 10, DE06682, and DA06687.Correspondence should be addressed to Alvin J. Normal coordination of body movement and posture depends upon an accurate spatial reference. The otolith organs of the vestibular labyrinth are sensitive to the direction and magnitude of the earth's gravity and could provide a reference for integrating vestibular, visual, and somatosensory information to help control movement. When a sustained change in the gravitoinertial force occurs (e.g., from a novel linear motion, in a microgravity environment, or as a result of inner ear...

The purpose of this study was to determine the effect of the carotid artery bifurcation on the delivery of oxygen to the artery wall by measuring the transarterial wall oxygen gradient. Transarterial wall oxygen gradient measurements were performed in dogs anesthetized with thiopental sodium and isoflurane by means of an oxygen microelectrode. Measurements were performed at six locations along the carotid bifurcation. Oxygen tensions at the carotid sinus were decreased in the inner 40% of the artery wall compared with control locations. Oxygen tensions at the flow divider were increased throughout the artery wall compared with control locations. These effects were noted without differences in blood pressure, arterial blood oxygen tension, or histological evidence of atherosclerotic lesion formation. These findings suggest that the delivery of oxygen to the artery wall is altered by the bifurcation of the carotid artery. Low arterial oxygen tensions at the carotid sinus support a role for artery wall hypoxia in the formation of atherosclerotic lesions.