Post-ictal generalized EEG suppression and seizure-induced mortality are reduced by enhancing dorsal raphe serotonergic neurotransmission

Abstract

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy. A proposed risk marker for SUDEP is the duration of post-ictal generalized EEG suppression (PGES). The mechanisms underlying PGES are unknown. Serotonin (5-HT) has been implicated in SUDEP pathophysiology. Seizures suppress activity of 5-HT neurons in the dorsal raphe nucleus (DRN). We hypothesized that suppression of DRN 5-HT neuron activity contributes to PGES and increasing 5-HT neurotransmission or stimulating the DRN before a seizure would decrease PGES duration. Adult C57BL/6 and Pet1-Cre mice received EEG/EMG electrodes, a bipolar stimulating/recording electrode in the right basolateral amygdala, and either a microdialysis guide cannula or an injection of adeno-associated virus (AAV) allowing expression of channelrhodopsin2 plus an optic fiber into the DRN. Systemic application of the selective 5-HT reuptake inhibitor citalopram (20 mg/kg) decreased PGES duration from seizures induced during wake (n = 23) and NREM sleep (n = 13) whereas fluoxetine (20 mg/kg) pretreatment decreased PGES duration following seizures induced from wake (n = 11), but not NREM sleep (n = 9). Focal chemical (n = 6) or optogenetic (n = 8) stimulation of the DRN reduced PGES duration following kindled seizures and reduced morality following maximal electroshock seizures (n = 6) induced during wake. During PGES, animals exhibited immobility and suppression of EEG activity that was reduced by citalopram pretreatment. These results indicate that 5-HT and the DRN may regulate PGES and seizure-induced mortality. Highlights- PGES consistently follows seizures induced by amygdala stimulation in amygdala-kindled mice. - Seizure-induced dysregulation of 5-HT neurotransmission from the dorsal raphe nucleus may contribute to PGES. - Systemic administration of 5-HT enhancing drugs and stimulation of the DRN reduces PGES duration. - PGES is associated with post-ictal immobility in kindled mice that can be reduced by pretreatment with citalopram. - Recovery of EEG frequencies to baseline occurs in a stepwise manner with the lowest frequencies recovering first.