Poster Presentation & Flash Talk 46th Annual Meeting of the Fetal and Neonatal Physiological Society 2019

Ganaxolone increases expression of neurosteroid-sensitive GABAA receptors in the preterm hippocampus (#147)

Julia C Shaw 1 2 , Hannah K Palliser 1 2 , Gabrielle K Crombie 1 2 , Ryan P Sixtus 3 4 , Clint Gray 3 4 , Rebecca M Dyson 3 4 , Mary J Berry 3 4 , Jonathan J Hirst 1 2
  1. Mothers and Babies Research Centre, Hunter Medical Research Institute, New Lambton Heights, NSW, Australia
  2. University of Newcastle, New Lambton Heights, NSW, Australia
  3. Department of Paediatrics and Child Health, University of Otago, Wellington, New Zealand
  4. Centre for Translational Physiology, University of Otago, Wellington, New Zealand

Introduction: Placental progesterone is the essential precursor for synthesis of the fetal neurosteroid allopregnanolone. Allopregnanolone has a major role in maintaining fetal behaviour and promoting myelination. Preterm birth results in a premature decline in allopregnanolone levels, and its inhibitory actions mediated through GABAA receptor stimulation.  We propose that reinstating GABAA receptor action in preterm neonates will prevent programmed deficits in inhibitory pathways.

Methods: Dunkin Hartley guinea pig neonates were delivered preterm at gestational age 62 (GA62), or spontaneously at term (GA69). Preterm neonates received either 45% β-cyclodextrin (vehicle), 0.5mg/kg/day (low-GNX), 1mg/kg/day (mid-GNX), or 2.5mg/kg/day ganaxolone (high-GNX) via subcutaneous injection. Preterm neonates were euthanised at term equivalence age, and for the term neonates this occurred within 24 hours of birth. Relative mRNA expression of neurosteroid-sensitive GABAA receptor subunits α2, α4, and α5 was measured in the hippocampus by qPCR. Mature myelin was quantified in the CA1 region of the hippocampus, overlying subcortical white matter, and cingulum by myelin basic protein (MBP) immunostaining.

Results: Relative mRNA expression of the α2 and α4 subunits in preterm females receiving ganaxolone was increased in a dose-dependent manner (p=0.006 and p=0.05 respectively), with the highest expression in those receiving the high-GNX dose. Similarly, the relative mRNA expression of the α2 subunit also increased in a dose-dependent manner for preterm males receiving ganaxolone (p=0.04). There were no significant differences identified for the α5 subunit. There were no differences in MBP immunostaining across the treatment groups at the age examined.

Conclusion: These findings indicate ganaxolone increases expression of neurosteroid-sensitive GABAA receptor subunits in the hippocampus. This suggests a role for these subunits in mediating tonic inhibition that may protect against excitatory damage. If persisting, the upregulation of GABAA receptor subunits α2 and α4 may reduce the risk of ongoing disorders related to inhibitory and excitatory imbalance.