Abstracts

Rationale: Kainate receptors (KARs) are differentially expressed in the brain during development and peak in the late embryonic/early postnatal period. KARs have diverse functions related to the regulation of network activity and growing evidence supports their role in the pathogenesis of epilepsy. However, the role of KARs activation following hypoxia in regulating synaptic transmission in the immature brain is not known.Methods: The effects of hypoxia on KAR-mediated excitatory and inhibitory synaptic transmission were studied using patch-clamp electrophysiology in an in vitro asphyxia model (oxygen glucose deprivation [OGD]); to study the effects of hypoxia and reoxygenation independently. Miniature excitatory post-synaptic currents (mEPSCs) and miniature inhibitory post-synaptic currents (mIPSCs) were measured in visually identified CA1 pyramidal neurons from acute hippocampal slices of P7-10 mice. KARs were pharmacologically isolated using: DL-AP5 to block N-methyl-D-aspartate (NMDA) receptors; GYKI53655 to specifically block α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) and UBP310 to block KARs. UBP310 has been shown to block GluK1 subunit-containing KARs; homomeric GluK3 KARs and heteromeric GluK2/5 KARs. Finally, the glutamate antagonist CNQX was used to block both AMPARs and KARs.Results: We have previously shown that OGD results in increased mEPSC frequency in CA1 pyramidal neurons from P7-10 mice during both OGD and reoxygenation. Here, we found that UPB310 prevented the increase in mEPSCs observed during reoxygenation but not that observed during OGD. In the presence of UBP310, mEPSC frequency increased from 0.36 ± 0.04 Hz (baseline) to 0.42 ± 0.06 Hz (OGD, p=0.0005 vs. baseline, ANOVA) and subsequently significantly decreased to 0.23 ± 0.02 Hz (reoxygenation; p=0.0005 vs. baseline, ANOVA [n=7, 4 animals]). Additionally, a decrease in mEPSC amplitude was noted during both OGD and reoxygenation from 7.73 ± 1.16 pA at baseline to 6.98 ± 1.03 pA (OGD) and 7.01 ± 1.06 pA (reoxygenation, p=0.005, ANOVA). We also found that exposure to OGD in the presence of GYKI53655 resulted in decreased mIPSC frequency during the reoxygenation phase in CA1 pyramidal neuron from P7-10 mice. mIPSC frequency increased from 0.362 ± 0.06 Hz at baseline to 0.476 ± 0.07 Hz at the end of OGD (p=0.0003 vs. baseline, ANOVA) , subsequently decreasing to 0.285 ± 0.06 Hz during reoxygenation (p=0.0003 vs. baseline, ANOVA). No changes in amplitude were noted. This decrease in mIPSC frequency was not observed in similar experiments performed in the presence of CNQX to block both AMPARs and KARs, demonstrating that the observed decrease in mIPSC frequency is likely KAR-mediated.Conclusions: Together, these results suggest that KAR activation during OGD leads to enhanced glutamatergic synaptic transmission while decreasing inhibitory synaptic transmission in neonatal mice. This may represent one of the mechanisms of increased excitability following a hypoxic insult in the neonatal brain. Funding source: 5K08NS063118-03