DEVELOPMENT AND ALTERED GRAVITY DEPENDENT CHANGES IN GLUCOSE-6-PHOSPHATE-DEHYDROGENASE ACTIVITY IN THE BRAIN OF THE CICHLID FISH OREOCHROMIS-MOSSAMBICUS

Glucose-6-phosphate dehydrogenase activity was studied in the brain of the cichlid fish Oreochromis mossambicus during early ontogenetic dev elopment. In general a slight but continuous decrease in enzyme activi ty was found (9.5 +/- 0.5 nmol substrate cleaved per mg protein and pe r min at developmental stage 13 {=1 day post hatch at 28 degrees C) to a value of 7.9 +/- 0.6 in adult brain). In order to investigate the p ossible influence of altered gravity during early ontogenetic brain de velopment, fish larvae were exposed to an increased acceleration of th ree times earth gravity (3 g) or to functional weightlessness in a fas t-rotating clinostat for 7 days. A significant increase of brain G6PDH activity of approx. 15% was found after exposure to hyper gravity, wh ereas a significant decrease of the enzyme activity, similar to 10%, w as detected following functional weightlessness in respect to the corr esponding Ig controls. Analyses concerning the regain of normal contro l enzyme activity of the larvae revealed dramatic fluctuations within the first 5 h after exposure to an increased acceleration of 3 g. Ther eafter, between day 1 and day 3 after exposure, brain glucose-6-phosph ate dehydrogenase decreased slowly. At day 3 after exposure no further differences of the hyper-g larvae compared to the controls were found . Only slight changes in total brain glucose-6-phosphate dehydrogenase activity occur during ontogenetic development of cichlid fish. This s uggests that a more or less constant enzyme activity is important duri ng brain development, but is reacting very sensitively to changes in t he environmental factor gravity.