Abstracts

Rationale: Idiopathic generalized epilepsy has genetic causes in large percentage (2/3) of seizures patients (almost 3 million peoples in US). Meanwhile, epileptic activity onset mostly occurs during sleep-wake transition or quiet-wake period, suggesting that slow-wave oscillations during sleep-wake period may play important roles on seizure onset. Additionally, synaptic excitation and inhibition are proportionally balanced in cortical neurons. Thus we hypothesized that slow-wave oscillation (0.5 Hz) can amplify and exacerbate the imbalance between synaptic excitation and inhibition, which can cause seizure onset. Methods: Spontaneous(s) excitatory (EPSC) and inhibitory (IPSC) synaptic currents (using whole-cell voltage-clamp) were recorded in layer V pyramidal neurons of somatosensory cortex using ex vivo brain slice preparation from one idiopathic generalized epilepsy mouse model with GABAR Q390X mutation. sEPSCs were recorded at Cl- reversal potentials (-55.8mV, K-gluconate based intracellular solution), while sIPSC recorded at -60 mV (KCl/K-gluconate based solution) with AMPAR/KARs being blocked. The proportionality of sEPSC to sIPSC in neurons was examined in the same cells (sEPSC recorded at Cl- reversal potential, -51.2 mV; sIPSC recorded at cation reversal potential, -4.5 mV, Cs-based intracellular solution). Slow-wave oscillation (SWO, 10 min) in neurons (resting membrane potentials around -75 mV, current-clamp mode) was induced by injecting 0.5 Hz cosine oscillating/depolarizing currents with 4-5 spikes at the oscillation peaks. Results: In WT littermate mice, 0.5 Hz cosine SWO could potentiate both sEPSCs (from -19.16 ± 1.65 to -33.57 ± 3.45 pA, n=5, pair t-test p=0.006) and sIPSCs (from -22.74 ± 2.29 to -37.36 ± 3.46 pA, n=4; paired t-test p=0.01) and the synaptic current potentiation could maintain 20-30 min following SWO induction, suggesting that the dynamic balance between potentiated synaptic sEPSCs and sIPSCs in pyramidal neurons is maintained. However, in heterozygous Q390X mutant mice, SWO could potentiated only sEPSCs (from -18.44 ± 1.87 to -30.93 ± 4.67 pA, n=6, paired t-test p= 0.013, and not significant different from WT post-SWO sEPSCs, t-test p=0.672), not sIPSCs  (from -21.52 ± 1.41 to -20.42 ± 1.21 pA, n=5, paired t-test p=0.57, and significant different from WT post-SWO sIPSCs, t-test p= 0.001), suggesting that the dynamic balance between synaptic sEPSCs and sIPSCs in pyramidal neurons might be impaired in het mice. Moreover, both sEPSC and sIPSC frequency in WT and Het mice did not significantly change following SWO induction. Consistent with this, after SWO induction, the proportionality of sEPSC to sIPSC in pyramidal neurons from het mice was also increased compared with the proportionality in WT mice. Conclusions: Slow-wave oscillation during sleep and quiet-wake period could potentiate sEPSCs, not sIPSCs in layer V pyramidal neurons from heterozygous mice with Q390X mutation, generating the dynamic imbalance between sEPSCs and sIPSCs and exacerbating the imbalance between sEPSCs and sIPSCs in cortical neurons from heterozygous mice. This will likely initiate seizures in this idiopathic generalized seizures model during sleep-wake transition or quiet-wake period. Funding: NIH R21 NS096483-01A1