Abstracts

Rationale: Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy. While the exact etiology of SUDEP is unclear, it is believed seizure-related respiratory failure is a major contributor. SUDEP cases often occur at night, possibly during sleep. Serotonin (5-HT) is implicated in SUDEP. 5-HT importantly modulates breathing, sleep-wake, and seizure threshold and severity. We hypothesized that enhancing 5-HT neurotransmission prior to a seizure would increase postictal breathing frequency (f_R), tidal volume (V_T), minute ventilation (V_E) and breathing regularity and decrease ictal and postictal apnea. Since sleep state is implicated SUDEP, seizures were induced during both wake and NREM sleep. 5-HT₂ receptors were targeted as these have been implicated in respiratory regulation and SUDEP.

Methods: 16 adult (8-12 wks) male and female C57BL/6J mice were instrumented for EEG/EMG recording and implanted with a bipolar stimulating/recording electrode into the basolateral amygdala [AP: -1.3 mm; ML: -2.8 mm; DV: -4.7 mm]. After recovery, afterdischarge threshold determination and kindling (80-380 mA; 1 s train of 1 msec biphasic square waves; 60 Hz; 2x/day until the animal had consistent generalized seizures), seizures were induced via amygdala stimulation during wake and NREM sleep following treatment with vehicle; 5-HT₂ agonists, TCB-2 (10 mg/kg) and MK-212 (10 mg/kg); and selective 5-HT reuptake inhibitors (SSRI) citalopram (20 mg/kg) and fluoxetine (10 mg/kg), alone, or 15 min after 5-HT₂ receptor antagonists ketanserin (3 mg/kg) or RS-102221 (10 mg/kg). All drugs were given intraperitoneally 30-60 min prior to seizure.

Results: Citalopram and the 5-HT_2C agonist MK-212 had sleep state-dependent effects on f_R, V_T, and V_E during different postictal timepoints. Citalopram and fluoxetine eliminated ictal and postictal apneas, regardless of sleep state. MK-212 increased ictal apneas compared to vehicle when seizures were induced during NREM. Citalopram decreased breathing variability immediately after seizures compared to vehicle, but only with those induced during wake. This effect persisted when 5-HT₂ receptor antagonists were administered prior to citalopram. MK-212 decreased variability compared to vehicle in the later postictal period, regardless of sleep state. The 5-HT_2A agonist, TCB-2, had negligible effects on postictal breathing compared to vehicle.

Conclusions: Our results indicate that increasing available 5-HT and activating 5-HT₂ receptors cause distinct, sleep state-dependent changes in postictal breathing following seizures induced via amygdala stimulation in amygdala kindled animals. This suggests that the efficacy of 5-HT-enhancing treatments on postictal breathing is dependent on sleep state during seizure onset and that multiple serotonergic mechanisms govern recovery of eupneic breathing in the postictal period.

Funding: Please list any funding that was received in support of this abstract.: AES and NIH/NINDS F31NS113479 to A.N.P. NIH/NINDS R01NS095842 to G.F.B.