Development and altered gravity dependent changes in glucose-6-phosphate dehydrogenase activity in the brain of the...

Glucose-6-phosphate dehydrogenase activity was studied in the brain of the cichlid fish Oreochromis mossambicus during early ontogenetic development. In general a slight but continuous decrease in enzyme activity was found (9.5 +/- 0.5 nmol substrate cleaved per mg protein and per 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 possible influence of altered gravity during early ontogenetic brain development, fish larvae were exposed to an increased acceleration of three times earth gravity (3 g) or to functional weightlessness in a fast-rotating clinostat for 7 days. A significant increase of brain G6PDH activity of approx. 15% was found after exposure to hyper gravity, whereas a significant decrease of the enzyme activity, approximately 10%, was detected following functional weightlessness in respect to the corresponding 1 g controls. Analyses concerning the regain of normal control enzyme activity of the larvae revealed dramatic fluctuations within the first 5 h after exposure to an increased acceleration of 3 g. Thereafter, between day 1 and day 3 after exposure, brain glucose-6-phosphate 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 suggests that a more or less constant enzyme activity is important during brain development, but is reacting very sensitively to changes in the environmental factor gravity.