Abstracts

Rationale: Sudden unexpected death in epilepsy (SUDEP) is a major cause of mortality in people with drug-resistant epilepsy. We recently demonstrated that SUDEP in a mouse model of Dravet Syndrome (DS)is due to seizure-induced respiratory arrest. Our preliminary studies show that SUDEP in DS mice is greatly reduced with a ketogenic diet (KD), an effect that is independent of ketosis but is correlated with higher brain levels of serotonin (5-HT). Defects in the 5-HT system have been linked to both respiratory dysfunction and SUDEP. We hypothesize the rescue effect of the KD is not due to ketosis, but rather to a specific dietary component that alters 5-HT metabolism. Methods: To assess the effect of a KD on 5-HT metabolism in the mouse brain,C57BL/6J (WT) mouse littermates were placed either on a KD or a conventional diet for five days starting soon after weaning (P20). Brain levels of 5-HT, 5-hydroxyindole acetic acid (5-HIAA), L-tryptophan (Trp), dopamine (DA), homovanillic acid (HVA), 3,4-dihydroxyphenylacetic acid (DOPAC) and norepinephrine (NE) were measured from whole brain tissue using HPLC-ECD. Additionally, extracellular 5-HT and DA were measured in vivo using microdialysis in the amygdala, a region implicated in seizure propagation and postictal apnea, of WT mice before and after intragastric administration of decanoic acid (C10), a medium chain fatty acid found in KDs and known to be anticonvulsant, or vehicle. To measure the releasable pool of 5-HT and DA, 3,4-methylenedioxymethamphetamine (MDMA) was injected i.p. to cause heteroexchange release of 5-HT and DA and additional samples were collected. Results: Total brain 5-HT, 5-HIAA, Trp and NE were 1.3 to 1.5-fold higher in KD-fed mice compared to littermates fed a control diet (p < 0.05 with Mann-Whitney U-tests; n=8 per group). Preliminary data show that intragastric administration of C10 (n=3) or vehicle (n=2) had no effect on baseline extracellular 5-HT or DA levels over 3 hours. However, treatment with C10 led to a significant increase in MDMA-induced 5-HT release (2972% vs 522% of baseline), but not DA (318% vs 305%) from the amygdala compared to control diet. Conclusions: Our preliminary results indicate that a KD and C10 both alter 5-HT metabolism. We are currently examining the mechanisms of these effects. It has been suggested that MCFAs such as C10 displace Trp from its plasma protein-binding sites, which facilitates CNS entry of Trp and in turn increases 5-HT synthesis. 5-HT has been implicated in SUDEP due to its stimulatory effect on control of breathing and its anticonvulsant properties. We recently demonstrated that SUDEP in DS mice is due to seizure-induced respiratory arrest.C10, and possibly other constituents of KDs, may be protective in part by increasing brain 5-HT. Future experiments include testing effects of 5-HT depletion on in the efficacy of the KD in DS mice. Funding: NIH / NINDS U01 NS090414: SUDEP Research Alliance.