Effects of neonatal asphyxia on the serotonin neuron system in the developing brain studied by immunohistochemistry

The effects of neonatal asphyxia on the serotonin neuron system were examined using the immunoperoxidase method. Male mice, 2 days of age, were exposed to total asphyxia (100% CO2) for 30 min. Mice that spontaneously survived were perfused transcardially with a fixative at 15, 30 and 60 days of age. Quantitative immunohistochemical analysis at 60 days of age demonstrated a significant decrease in the numbers of serotonin-immunoreactive cell bodies in the nucleus raphe dorsalis, the nucleus raphe pontis, the subpyramidal region, the total raphe system and the whole brain, while no significant reduction in the number of serotonin-immunoreactive cell bodies was observed in the caudal raphe system. Presumably degenerative changes in serotonin-immunoreactive fibers were observed in various parts of the brain of mice subjected to total asphyxia at 15 days of age, and the numbers of degenerated fibers decreased in almost all parts of the brain, the exception being the caudal portion of the brainstem, at 30 and 60 days of age. These results suggested that neonatal asphyxia induced permanent changes in the serotonin neuron system, with regional differences.