Abstracts

Rationale: Seizure disorders are not uncommon, and according to the 2012 report of the Institute of Medicine (US) Committee on the Public Health Dimensions of the Epilepsies, epilepsy is among the 4^th most common of chronic neurological conditions. The excitatory tone of the brain mediated by glutamatergic transmission is well characterized, but very little is known about the role that purinergic (i.e. ATP-mediated) signaling plays, especially in abnormal, excessive, synchronous brain activity. Pannexin1 (Panx1), an ATP releasing channel, has previously been implicated in worsening seizure outcomes in a rodent model [Santiago et al., 2011 PLOS One 6(9):e25178], but the impact of these channels on the electrical activity is poorly characterized. Methods: Using both EEG recordings and hippocampal slice preparations from 2-3 weeks old wild-type (WT) and Panx1 KO, we evaluated the impact of these channels on ictal and interictal activity. Continuous EEG recordings were performed by implanting bilateral screw electrodes in the forebrain of 2 weeks old WT and Panx1-KO mice, before and 40 min after i.p. injection of KA (3.6 mg/kg). Hippocampal slices prepared from 3-weeks old WT and Panx1-KO were subjected to 1-hour of  zero-Mg²⁺ aCSF (artificial cerebrospinal fluid) and extracellular electrodes placed on CA1 and CA3 areas of the hippocampus. Statistical analyses were performed by comparing total duration of ictal and interictal activity, and significance considered p < 0.05. Results: EEG recordings indicated that WT displayed continuous ictal activity while only brief repetitive bursts of ictal activity were recorded in Panx1 KO mice. The total time spent in ictal activity was much reduced in the Panx1 KO compared to WT (P=0.002). In hippocampal slices subjected to the zero-Mg²⁺ model, we found a significant decrease in ictal (> 1 Hz) activity in the Panx1 KO compared to WT (p = 0.004); no statistical difference was observed in terms of interictal (= 1 Hz) activity between WT and Panx1 KO. Conclusions: These results showing that Panx1 channels contribute to sustain ictal activity are consistent with our previous findings showing that mice lacking Panx1 have improved seizure outcome. Further study is underway to evaluate the mechanism by which Panx1 affects ictal activity. Funding: NINDS-NIH: RO1-NS092726