Abstracts

Rationale: M-type (KCNQ2/3) K+ channels play play dominant roles in regulation of the active and passive neuronal discharge properties, such as resting membrane potential, spike-frequency adaptation, bursting behavior, and hyper-excitatory states. However, their role in acquired epileptogenesis is not well understood. Previous studies by our group found that KCNQ2 and KCNQ3 mRNA was upregulated in the hippocampus in response to chemoconvuslant seizure activity. Using transgenic mice with a GFP reporter to detect expression of KCQN2 mRNA (GENSAT KCNQ2-EGFP/FW221Gsat/Mmucd, 015412-UCD), we are able to visualize seizure-dependent effects on KCNQ2 expression in the subregions of the hippocampus. We therefore investigated the neuron-specific expressional changes in KCNQ2 after a single seizure episode. Methods: KCNQ2-GFP reporter mice were administered either the muscarinic agonist pilocarpine (230 mg/kg) or the GABAA receptor antagonist pentylenetetrazol (60 mg/kg) to induce clonic seizures in adult, 2-month old mice. Alternatively, a subset of animals were given 280 mg/kg pilocarpine to induce status epilepticus (SE). Brains were removed either 48 hours or 7 days after seizure induction and fixed in 4% PFA for immunohistochemistry. Dorsal hippocampus sections were immunostained with anti-GFP and anti-MAP2 antibodies and secondary fluorescent labels. GFP/MAP2 fluorescence was quantified for dentate gyrus (DG), CA1, and CA3 pyramidal regions. Brain-slice electrophysiology recordings of M-current were taken from CA1 and DG neurons in comparison of naive and pilocarpine seizure animals. Results: Chemoconvulsant seizures induced increase of KCNQ2 mRNA in CA1 and CA3 subregions, at the 48 hr time point, but no significant increase was observed in the DG. CA1 and CA3 levels of KCNQ2 mRNA increased in response to both pilocarpine or pentylentetrazol, signifying that KCNQ2 upregulation occurs independent of the mechanism of convulsant activity. Total KCNQ2 protein levels were also increased in the whole hippocampus. In hippocampi examined 7 days after seizure, levels of KCNQ2 mRNA were reduced in all regions below that of control. In a subset of mice experiencing SE, there was a significant increase in KCNQ2-expressing DG granule cells, but excitoxicity induced widespread neuronal death in CA1 and CA3 pyramidal neurons. CA1 demonstrated increased M-current after seizure challenge, however there were no significant changes in M-current between control and seizure DG granule cells. Conclusions: We demonstrate that a single seizure in a naive animal promotes KCNQ2 upregulation in the hippocampus in a region-specific manner. KCNQ2  channel plasticity may serve as a compensatory mechanism after a hyperexcitable event, such as occurs in the initial seizure insult in acquired epilepsy. The upregulation we describe could be potentially leveraged in anticonvulsant enhancement of KCNQ2 channels as therapeutic target for preventing epileptogenic seizures. Funding: Supported by NIH training grant T32 HL007446 (CMC) and R01 NS094461 (MSS).