Correlation of altered gravity and cytochrome oxidase activity in the developing fish brain.

The mitochondrial enzyme, cytochrome oxidase, was localized cytochemically in the nucleus magnocellularis, a primary relay nucleus of vestibular information within the area octavolateralis in the fish brain. Cichlid fish larvae were analyzed after long-term exposure (9 days) to altered gravity situations: increased acceleration in a centrifuge (3 g) and near weightlessness during space flight. Controls (1 g) were reared under identical conditions in the centrifuge but without rotation on earth or with an acceleration resulting in gravity of 1 g in space shuttle. Quantification of highly reactive mitochondria reveals a correlation of gravity and cytochrome oxidase activity: low enzyme activity in respect to 1 g controls under near weightlessness conditions and an increased activity after hyper-g exposure in a centrifuge. This gravity effect on the energy metabolism of vestibular nuclei of developing cichild fish seems to reflect adaptational processes in response to gravity stimulation.