Abstracts

Rationale: Scn1a mutations are associated with Dravet Syndrome and higher rates of sudden unexpected death in epilepsy (SUDEP). Scn1a encodes a sodium channel that is expressed throughout the brain, including the medulla. Data from our laboratory indicate that postictal sudden death in mice with an Scn1a mutation involves respiratory arrest. We hypothesized that if SCN1A is expressed in neurons involved in respiratory control, a mutant channel could affect respiratory rhythm generation in vitro and breathing and respiratory chemoreception in vivo.Methods: In vitro experiments: Rhythmogenic brainstem slices containing the preBotzinger complex were prepared from P1-P5 wildtype(WT) and Scn1aR1407X/+ littermate mice. Recordings were made from hypoglossal nerve rootlets of slices in a chamber superfused with aCSF. Data were collected and analyzed using custom-written Matlab software. In vivo experiments: Whole animal plethysmography was used to measure breathing and the hypercapnic ventilatory response (HCVR) to 7% CO2 in WT and Scn1aR1407X/+ mice. Recordings were performed in a plethysmograph chamber (Buxco) and data were collected and analyzed using custom-written Matlab software. Animals were exposed to 50% O2/balance N2 for at least 15 minutes to obtain baseline data. The gas was then switched to 50% O2/7% CO2/balance N2 for at least 7 minutes. Data were excluded from analysis if there were any behavioral artifacts, such as: chewing, grooming, sleep, or movement.Results: Hypoglossal nerve bursting frequency of slices from Scn1aR1407X/+ mice was 5.83 ± 2.47 bursts min-1 (n=5) and from WT mice was 8.19 ± 2.61 bursts min-1 (n=6), which was not statistically significant (p=0.42). The fictive ventilation (burst frequency x burst amplitude) was not statistically different in slices from Scn1aR1407X/+ mice (2.36 ± 0.32; n=5) compared to WT mice (1.37 ± 1.91; n=6; p=0.08). In plethysmography from adult animals, there was no difference in relative minute ventilation (VE; arbitrary units) in 0% CO2 between Scn1aR1407X/+ (1.55 ± 0.35; n=7) and WT mice (1.72 ± 0.21; n=5; p=0.57). However, the HCVR in response to 7% CO2 was decreased by 27% in Scn1aR1407X/+ (from 1.55 ± 0.35 to 4.87 ± 0.53; n=7) compared to WT mice (from 1.72 ± 0.21 to 4.14 ± 0.73; n=5; p<0.05).Conclusions: These preliminary data suggest that there are differences in respiratory chemoreception, but not baseline breathing, between Scn1aR1407X/+ and WT mice. During the neonatal period, there was no statistical difference in burst frequency or fictive ventilation in slices from transgenic compared to WT mice. Moreover, there was not a difference in breathing in 0% CO2 in adult Scn1aR1407X/+ and WT mice. We did observe a blunted response to 7% CO2 in Scn1aR1407X/+ adult mice, indicating a deficit in respiratory chemoreception. These data suggest that mutation of the Scn1a gene in mice leads to an abnormal HCVR. This may decrease the ability of Scn1aR1407X/+ mice to detect increasing blood pCO2 during postictal respiratory arrest. This work was supported by NIH grant U01NS090414.