Abstracts

Rationale: Cardio-respiratory and autonomic dysfunction is implicated in sudden death in epilepsy (SUDEP). Serotonin (5-HT) regulates breathing and arousal. Duration of postictal generalized EEG suppression (PGES) and degree of postictal oxygen desaturation may be biomarkers for SUDEP risk. Selective serotonin reuptake inhibitors decrease post-seizure oxygen desaturation and prevent SUDEP-like deaths in mice. Human cortical neurons are depolarized via 5-HT2A receptors and rats knocked-down for 5-HT2A are more susceptible to seizures. Mice lacking serotonergic neurons (Lmx1bf/f/p) have lower seizure threshold, breathing arrest, and SUDEP.  These are prevented by a 5-HT2A  agonist, while citalopram reduced mortality but not in Lmx1bf/f/p mice.We therefore studied 5-HT2A receptor protein levels in temporal lobe tissue from epilepsy patients with different PGES durations. Methods: We studied temporal lobe neocortical surgical specimens from 30 subjects with treatment-resistant epilepsy.  For each patient, epileptologists reviewed postictal EEG following focal seizures recorded during their videoEEG monitoring evaluation to identify the presence and duration of PGES for each recorded focal seizure.  For all seizures recorded, the patient’s PGES was categorized based on the seizure with the most prolonged PGES.  Among the 30 subjects, 4 had prolonged PGES (>= 50s), 7 had intermediate PGES (Frozen brain tissue samples were homogenized, protein concentration determined by spectrophotometer, denatured, loaded onto gel, run and transferred in an enhanced chemiluminescence nitrocellulose membrane, incubated with anti-5-HT2A antibody (1:5000, Santa Cruz, Dallas, TX) and horseradish-peroxidase anti-rabbit secondary antibody, and exposed to autoradiography film.  Relative Optical Densities of the receptor to GAPDH bands were estimated using Image Studio™ Lite software (LI-COR, Lincoln, RE).  Statistical analyses used SPSS software (v.24 for Mac). ANOVA with Tukey post hoc test was used to test between-group differences in 5-HT2A receptor protein, age, duration of epilepsy, and age at epilepsy onset. Chi-square test was used to test sex difference between groups.  Results: Groups did not differ for age, duration of epilepsy, age at epilepsy onset, and sex. Subjects at prolonged PGES had lower 5-HT2A receptor protein (1.04±.69) in temporal lobe compared with subjects with intermediate PGES (2.51±.83; p=.008) and subjects without PGES (1.98±.58; p=.020). Conclusions: Less 5-HT2A protein in temporal lobe cortical samples of subjects with prolonged PGES versus those with shorter or no PGES, supports animal studies suggesting lower 5-HT2A receptors levels increase SUDEP risk and lower seizure threshold (see Rationale). 5-HT2A receptor level may be a SUDEP biomarker in patients who undergo epilepsy surgery and possibly in nonsurgical patients using 5-HT2A receptor-selective positron emission tomography tracers (e.g., 11C-MDL100907).  Finally, selective 5-HT2A agonists deserve consideration as a method to reduce SUDEP risk. Funding: NIH NS090415