Changes in nitric oxide content following injury to the neonatal rat brain.

Nitric oxide is an important mediator of inflammation in the brain, but it still remains unresolved whether its action is protective or not. In particular, it seems crucial to compare the effects observed in the mature brain with the developing brain of newborn animals. The influence of NO on tissue depends significantly on its concentration. In the present study we tried to find how NO production changes after brain injury in neonatal rats. 6-day-old rats received mechanical injury to the left brain hemisphere and the tissue was collected at subsequent time points, either for EPR analysis or histochemical examination with NADPH-diaphorase staining. Our data revealed that NO concentration in the lesioned hemisphere increases slightly at 1 and 2 days after injury but also 8 days later. However, changes in the number of NADPH-diaphorase positive cells showed a different pattern from changes in NO level. These data suggest that NO concentration in the brain depends on its developmental stage.