Magnesium sulphate reduces tertiary gliosis but does not improve EEG recovery or white or grey matter cell survival after asphyxia in preterm fetal sheep

Abstract: Maternal magnesium sulphate (MgSO₄) treatment is widely recommended before preterm birth for neuroprotection. However, this is controversial because there is limited evidence that MgSO₄ provides long-term neuroprotection. Preterm fetal sheep (104 days gestation; term is 147 days) were assigned randomly to receive sham occlusion with saline infusion (n = 6) or i.v. infusion with MgSO₄ (n = 7) or vehicle (saline, n = 6) from 24 h before hypoxia–ischaemia induced by umbilical cord occlusion until 24 h after occlusion. Sheep were killed after 21 days of recovery, for fetal brain histology. Functionally, MgSO₄ did not improve long-term EEG recovery. Histologically, in the premotor cortex and striatum, MgSO₄ infusion attenuated post-occlusion astrocytosis (GFAP⁺) and microgliosis but did not affect numbers of amoeboid microglia or improve neuronal survival. In the periventricular and intragyral white matter, MgSO₄ was associated with fewer total (Olig-2⁺) oligodendrocytes compared with vehicle + occlusion. Numbers of mature (CC1⁺) oligodendrocytes were reduced to a similar extent in both occlusion groups compared with sham occlusion. In contrast, MgSO₄ was associated with an intermediate improvement in myelin density in the intragyral and periventricular white matter tracts. In conclusion, a clinically comparable dose of MgSO₄ was associated with moderate improvements in white and grey matter gliosis and myelin density but did not improve EEG maturation or neuronal or oligodendrocyte survival. (Figure presented.). Key points: Magnesium sulphate is widely recommended before preterm birth for neuroprotection; however, there is limited evidence that magnesium sulphate provides long-term neuroprotection. In preterm fetal sheep exposed to hypoxia–ischaemia (HI), MgSO₄ was associated with attenuated astrocytosis and microgliosis in the premotor cortex and striatum but did not improve neuronal survival after recovery to term-equivalent age, 21 days after HI. Magnesium sulphate was associated with loss of total oligodendrocytes in the periventricular and intragyral white matter tracts, whereas mature, myelinating oligodendrocytes were reduced to a similar extent in both occlusion groups. In the same regions, MgSO₄ was associated with an intermediate improvement in myelin density. Functionally, MgSO₄ did not improve long-term recovery of EEG power, frequency or sleep stage cycling. A clinically comparable dose of MgSO₄ was associated with moderate improvements in white and grey matter gliosis and myelin density but did not improve EEG maturation or neuronal or oligodendrocyte survival.