The Time-Course of Changes in the State of Brain Monoaminergic Systems of Mice Under the Acute Hypoxia with Hypercapnia

Abstract—

The changes of monoaminergic systems under acute hypoxia with hypercapnia have been studied in male albino mice kept for a long time under the conditions of social isolation. Concentrations of noradrenaline, dopamine, serotonin, and their metabolites (dihydroxyphenylacetic, homovanillic and 5-hydroxyindoleacetic acids) have been measured using the HPLC method in cerebral cortex, hippocampus, and striatum of the right and left sides of the brain. In mice kept under the conditions of social isolation, which were not subjected to hypoxia with hypercapnia, higher levels of dopamine and serotonin in the left cortex were found. There was no asymmetry in monoamines and their metabolites in other studied brain structures. Ten min after the onset of exposure, acute hypoxia with hypercapnia resulted in a right-sided increase in the noradrenaline level and a decrease in the dopamine level in the striatum and serotonin levels in the hippocampus. In the cerebral cortex, 10 min after the beginning of the hypoxic treatment, there was a left-sided decrease in the dopamine content, while the initial asymmetry, found in the cortex of intact animals, disappeared. In mice kept under social isolation and died of hypoxia with hypercapnia, almost all parameters returned to the control level. The only exception was the ratio in the level of the serotonin metabolite (5-hydroxyindoleacetic acid) to the serotonin level: in the right cortex this parameter became lower than that of the control animals. It is suggested that in albino mice the brain monoaminergic systems are relatively resistant to the negative consequences of hypoxia and hypercapnia, and the changes in their parameters are obviously associated with the reflex brain response to changes in the gas composition of the respiratory air.