EFFECTS OF DEVELOPMENT AND ALTERED GRAVITY CONDITIONS ON CYTOCHROME-OXIDASE ACTIVITY IN A VESTIBULAR NUCLEUS OF THE LARVAL TELEOST BRAIN - A QUANTITATIVE ELECTRON-MICROSCOPIC STUDY

The mitochondrial enzyme, cytochrome oxidase, was localized cytochemic ally in the nucleus magnocellularis, a primary relay nucleus of vestib ular information within the area octavolateralis in the fish brain. La rvae of the cichlid fish Oreochromis mossambicus were analyzed at diff erent developmental stages (4, 10, and 35 days post-hatching) and afte r long-term exposure (8 days) to increased gravity (2-4 g). Quantifica tion of highly reactive, moderately reactive, and nonreactive mitochon dria reveals differences in the cytochrome oxidase activity of various cellular structures, for example, perikarya of neurons, presynaptic t erminals, and myelinated and nonmyelinated cell profiles. Cytochrome o xidase activity in the mitochondria of neuronal perikarya increases du ring development which parallels the differentiation of the area octav olateralis. This possibly reflects the increasing energy demand during maturation and innervation of the magnocellular nucleus. Hyper-g-expo sure of the larvae for 8 days (centrifuge) caused a further augmentati on of cytochrome oxidase activity in the perikarya within the nucleus magnocellularis. This may reflect an increased oxidative metabolism re sulting from the need for compensation of altered inputs from gravity- sensitive epithelia in the inner ear. Another possibility is that acce leration within a centrifuge causes physiological stress for the anima ls and, therefore, influences the cytochrome oxidase activity in neuro ns. (C) 1993 John Wiley & Sons, Inc.