Neurosteroid replacement approaches for improving outcomes after compromised pregnancies and preterm birth.

The levels of the key neurosteroid of pregnancy, allopregnanolone, are very high in the fetal and maternal brain compared to after birth. These levels are maintained by the placenta which forms a placental connection to fetal brain development. Maternal stresses depress placental synthesis resulting in a fall in allopregnanolone levels leading to deficits in myelination that continue into childhood. This contributes to an increased incidence of behavioural disorders. Supplementing neurosteroid action with allopregnanolone analogues or raising endogenous production with mitochondrial translocator protein (TSPO) ligands reverses these deficits. Preterm birth leads to an early dramatic loss of neurosteroid support for brain development leading to marked deficits in myelination and susceptibility to hypoxic-ischaemic injury. Postnatal treatment with the allopregnanolone analogue ganaxolone improves myelination and reduces hyperactive behaviour. TSPO ligands such as emapunil have been shown to improve oligodendrocyte maturation. These findings support the use of allopregnanolone supplementation approaches after pregnancy compromises to improve outcome.