Changes in regional cytochrome oxidase activity in the fetal, newborn and adult ovine brainstem.

Metabolic activity of specific brain regions (e.g. brainstem respiratory centers) may increase during the physiologic adaptations at birth. Since regional activity of cytochrome oxidase is correlated with the level of oxidative metabolism, cytochrome oxidase histochemistry was used to investigate whether there are sustained changes in metabolic activity within specific nuclei of the ovine brainstem during the perinatal period and whether further changes occur in the adult. Histochemistry was performed on 10-microns-thick frozen sections of the perinatal (130 d fetus, 140 d fetus, 8 h newborn and 10 d newborn) and adult ovine brainstem (n = 3 at each age). Computer-assisted image analysis was performed on 20 brainstem regions. A general decreasing trend, interrupted by a tendency for a transient increase at 8 h after birth was observed in most regions analyzed. Statistically significant decreases (P < 0.05) in cytochrome oxidase levels between the perinatal age groups and the adult were found in 7 brainstem nuclei studied: ambiguus, cuneate, inferior olivary, reticularis lateralis, spinal trigeminal, parabrachial and superior olivary nuclei. Within the perinatal period, the nucleus gracilis was the only region to show statistically significant decreases in 140 d fetus and 8 h newborns in all nuclei analyzed, but this change was not statistically significant (P > 0.1). These results indicate that the dramatic changes in physiology and environment at birth do not result in a significant change in the metabolic capacity of brainstem nuclei in the immediate perinatal period. However, more gradual developmental changes are observed in specific brainstem nuclei suggesting a decrease in neuronal activity occurs in these areas during development in the sheep.