Abstracts

Rationale: : Kcna1-null (Kcna1-/- ) mice are a model of temporal lobe epilepsy and sudden unexpected death in epilepsy (SUDEP). It has been suggested that increased parasympathetic activity or bronchoconstriction could contribute to SUDEP. Here, we determined the effect of the parasympathomimetic methacholine (MCh), a compound commonly used to determine airway hyperresponsiveness, on respiration of Kcna1-/- mice. We recently demonstrated the progressive nature of epilepsy and mortality in Kcna1-/- mice; therefore, we also determined whether respiratory abnormalities where evident as the mice approached near-SUDEP age. Methods: A Buxco Finepointe NAM was used to determine respiratory parameters in conscious mice by monitoring the phase delay between nasal and thoracic flows. Kcna1+/+, Kcna1+/- and Kcna1-/- littermates were assessed in three age bins postnatal day (P) 32-36, P40-46 and P48-56 when up to ~30%, ~55% and ~90%, respectively, of Kcna1-/- have succumbed to SUDEP. After baseline stabilization increasing doses of methylcholine (MCh) were nebulized and the aerosol delivered only to the isolated nasal chamber. Lung and brain tissue was isolated from the three genotypes and Kv1.1alpha gene and protein expression was evaluated by qPCR and Western blot techniques. Results: Age-specific differences were found in baseline respiratory rates, inspiratory time, tidal volume, minute ventilation and specific airway resistance of Kcna1-/- mice relative to Kcna1+/- and Kcna1+/+ mice. Additionally, Kcna1-/- mice responded distinctively to methylcholine-induced bronchoconstriction compared to Kcna1+/- and Kcna1+/+ mice. In Kcna1-/- mice at all ages MCh inhalation caused increased respiratory rates, tidal volume and minute ventilation and decreased inspiratory and expiratory times and specific airway resistance. Concomitant with these respiratory changes, Kcna1-/- mice experienced seizures. The threshold MCh concentration required to induce these respiratory changes and seizures decreased with age from 48 mg/ml to 12 mg/ml. The number and severity of seizures also increased with age. In contrast, Kcna1+/- and Kcna1+/+ mice experienced decreased respiratory rates, tidal volume and minute ventilation and increased inspiratory and expiratory times and specific airway resistance in response to MCh; and did not exhibit seizures. Kcna1+/- mice had ~34% and ~40% Kcna1 expression in brain and lung compared to Kcna1+/+ mice; however, expression of Kcna1 was minimal in lung tissue compared to brain in both genotypes. Conclusions: Respiratory responses of Kcna1-/- mice to MCh are consistent with hyperventilation and the resulting seizure provocation is not dissimilar to the clinical use of hyperventilation to induce seizures and the contraindication of using the MCh-challenge for people with epilepsy. Presently, the mechanism of these responses are unclear, but likely involve hyperexcitable Kcna1-/- phrenic nerves. Increased sensitivity and responses exhibited by Kcan1-\- mice may have relevance to SUDEP susceptibility. Funding: This work is supported by NIH R01 grants NS072179 and NS085389.