Enhancement of central norepinephrinergic neurotransmission contributes to inhibition of seizure-induced respiratory arrest by targeting the beta-1 adrenergic receptor (β1-AR) locating in the cardiomyocytes in the DBA/1 mouse SUDEP model

Abstract

Sudden unexpected death of epilepsy (SUDEP) is the leading cause of of death in patients with epilepsy. Due to the complicated pathogenesis of SUDEP, however, the exact mechanism of SUDEP remains elusive. Currently, although it is recognized that the seizure-induced respiratory arrest (S-IRA) may be a main cause for SUDEP, other factors resulting in SUDEP can not be excluded e.g arrhythmias. Our previous findings indicated that the incidence of S-IRA and SUDEP evoked by acoustic stimulation or pentetrazol (PTZ) injection was significantly reduced by atomoxetine, a norepinephrine reuptake inhibitor (NRI), suggesting that noradrenergic neurotransmission modulates S-IRA and SUDEP. Given that norepinephrine acts on the target to modulate respiratory and circulation function by targeting adrenergic receptor and beta (a-AR and {beta}-AR) and the arrhythmias can be contributed to SUDEP. Meanwhile, to further test whether cardiac factors are implicated in S-IRA and SUDEP, we choose esmolol hydrochloride, a selective antagonist of {beta}1-AR to test it in our models. Our findings demonstrated that the lower incidence of S-IRA and SUDEP evoked by acoustic stimulation or PTZ injection in DBA/1 mice by administration with atomoxetine was significantly reversed by intraperitoneal (IP) of esmolol hydrochloride. Importantly, the data of electrocardiogram (ECG) showed that the cardiac arrhythmia including the ventricular tachycardia, ventricular premature beat and atrioventricular block can be evoked by acoustic stimulation or PTZ injection in our model. Administration of atomoxetine significantly reduced these arrhythmias and the incidence of S-IRA and SUDEP in our models. However, administration of esmolol hydrochloride with the dose without affecting ECG and mortality changing of DBA/1 significantly blocking the protective effects of atomoxetine on S-IRA and SUDEP in our models. Thus, the dysfunction of respiratory and circulation may be implicated in the pathogenesis of S-IRA and SUDEP. Enhancing the central norepinephrinergic neurotransmission in the brain contributes to inhibition of seizure-induced respiratory arrest by targeting {beta}1-AR locating in the cardiomyocytes. Furthermore, the suppression effects of S-IRA by atomoxetine was significantly reversed by the norepinephrine neuronal degradation in the LC in our models. Furthermore, PTZ-induced Tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of norepinephrine, activity but not TH content from the serum of left ventricle and the whole heart tissue was reduced following the S-IRA. Our findings will show a new light on decoding the pathogenesis of SUDEP concerning the pathway between the LC and heart.