Maternal dexamethasone and EEG hyperactivity in preterm fetal sheep.

Maternal treatment with synthetic corticosteroids such as dexamethasone (DEX)significantly reduces neonatal morbidity and mortality, but its effects on the fetal brain remain unclear. In this study we evaluated the effects of DEX on EEG activity in preterm fetal sheep. Ewes at 103 days gestation received two intramuscular injections of DEX (12 mg, n = 8) or saline vehicle (n = 7) 24 h apart. Fetal EEG activity was recorded from 6 h before until 120 h after the first injection (DEX-1). DEX-1 was associated with a marked transient rise in total EEG power, maximal at 12 h (P < 0.001), with a relative increase in delta and reduced theta, alpha and beta activity, resolving by 24 h. Continuous EEG records showed a shift to larger but less frequent transient waveforms (P < 0.001). Unexpectedly, evolving epileptiform activity, consistent with electrographic and clinical seizures, developed from 178 ± 44 min after DEX-1.Similar but smaller changes were seen after the second injection. Following the injections, total power returned to control values, but the proportion of alpha activity progressively increased vs. controls (P < 0.001), with reduced interburst interval duration and number (P < 0.001). No histological neural injury or microglial activation was seen. In summary, exposure to maternal dexamethasone was associated with dramatic, evolving low-frequency hyperactivity on fetal cortical EEG recordings, followed by sustained changes consistent with maturation of fetal sleep architecture. We postulate that these effects may contribute to improved neonatal outcomes.