Apoptosis in the preterm and near term ovine fetal brain and the effect of intermittent umbilical cord occlusion.

Programmed cell death or apoptosis plays a central role during the development of the brain, but can also be activated by hypoxic/ischemic insult. The purpose of the present study was to determine the regional distribution of apoptotic cells in the preterm and near term ovine fetal brain and thus in relation to the maturation of neurobehavioural activity, and the effect of intermittent umbilical cord occlusion (UCO), which might then contribute to adverse neurodevelopment. Fetal sheep (control and experimental groups at 0.75 and 0.90 of gestation) were studied over 4 days with UCOs performed in the experimental group animals by complete inflation of an occluder cuff for 90 s every 30 min for 3 to 5 h each day. Animals were then euthanized and the fetal brain perfusion-fixed and prepared for subsequent histology and apoptosis staining using the TUNEL assay method. The number of TUNEL positive cells for both the preterm and near term control group animals was low but with a significant regional hierarchy whereby values were higher in the cerebellar peduncle and cortex and lower in the cortical grey and white matter, hippocampus, and pons. While the apoptotic indices (expressed as TUNEL positive cells/1000 cells or high powered field) for most brain regions were not significantly changed between the preterm and near term control group animals, that for the hippocampus and pons were increased approximately 5- and 4-fold, respectively, (both P<0.05), in the near term animals. Intermittent UCO with severe but limited hypoxemia and no cumulative acidosis to ensure longer term survival, had no significant effect on apoptotic indices in the brains of either the preterm or near term animals, although hippocampal values for both occlusion groups were increased approximately 2-3-fold. Levels of apoptosis noted for the ovine fetal brain at 0.75 to 0.90 of gestation are thus low and likely approaching the basal levels of later life, but there are regional differences and changes over this period although little change in response to intermittent cord occlusion as studied, with implications for behavioural state activity and antenatal hypoxic insults in the brain's development.