Regional differences of microglial accumulation within 72 hours of hypoxia-ischemia and the effect of acetylcholine receptor agonist on brain damage and microglial activation in newborn rats

• Brain inflammation after hypoxia-ischemia in developping brain was evaluated.
• The earliest accumulation of microglia was noted on the hippocampus.
• Microglial accumulation of white matter and cortex became gradually strong.
• Acetylcholine receptor agonist reduced early inflammation and tissue damage on hippocampus.

ObjectiveWe examined regional specificity of microglial activation in the developing rat brain for 72 hours after hypoxia-ischemia (HI) and the effect of acetylcholine receptor (AChR) agonist on microglial activation.Study designSeven-day-old Wistar rats were divided into two groups: one receiving a single dose of AChR agonist just before hypoxia (carbachol; 0.1 mg/kg) to investigate the reducing effect on brain damage with decreasing activation of microglia and the other group receiving saline as a control. Rats were subjected to left carotid artery ligation followed by 8% hypoxia. Brains were analyzed immunohistochemically at 24, 48, and 72 hours after HI. TNFα production was measured at respective times after HI.ResultsActivation of microglia on the hippocampus of the control group was strong for the first 48 hours and then weakened. In contrast, activation of microglia on white matter and the cortex was weak at 24 hours and then became stronger. A single dose of carbachol significantly reduced brain damage with a marked reduction of microglial activation on the hippocampus, whereas it was less effective regarding microglial activation on white matter and the cortex. TNFα production was low in both groups.ConclusionRegional specificity was observed for both microglial activation and susceptibility to carbachol for the first 72 hours after HI. Our data suggested that timely intervention along with region-specific microglial activation, apart from TNFα production, may be critical for the prevention of further brain damage after HI in the newborn.