Morphological changes in white matter astrocytes in response to hypoxia/ischemia in the neonatal pig

Abstract

White matter damage is a significant problem in the human pre-term baby. Damage to white matter is usually associated with injury or insults to babies born prematurely, typically before 32 weeks' gestation, however there is increasing evidence of both grey and white matter damage occurring after 32 weeks' gestation. Astrocytes play a vital role in white matter, regulating molecules such as glutamate in the extracellular space and preventing excitotoxic damage to neighbouring oligodendrocytes and axons. We have previously described dramatic changes in grey matter astrocytes in response to a hypoxic/ischemic (H/I) insult around the time of birth. In this study, we have used GFAP immunohistochemistry and Golgi–Kopsch staining to examine the morphology of white matter astrocytes in control neonatal pig brains, and in the brains of animals exposed to the same (perinatal) H/I insult. We demonstrate that the areal percentage of the section occupied by GFAP-immunoreactive processes and cell bodies is significantly decreased (by 46%, P < 0.0001) in subcortical white matter from H/I brains. This loss of GFAP was accompanied by alterations in astrocyte morphology and an overall decrease in the size (field of section occupied by an individual astrocyte) of white matter astrocytes from 649 μm 2 to 426 μm 2, as revealed by Golgi–Kopsch staining and image analysis. These data suggest that astrocytes may contribute to the pathology of white matter damage following an H/I insult around the time of birth, and suggest that astrocytes may offer a novel target for therapies to improve outcomes after H/I.