Repeated seizures cause neuroinflammation in a time- and site-dependent manner in brainstem regions of cardiorespiratory control

Abstract

Uncontrollable epilepsy increases risk for post-ictal cardiorespiratory failure and Sudden Unexpected Death in Epilepsy (SUDEP). Neuroinflammation, a key factor in epilepsy, is thought to be mediated primarily by resident microglia, astrocytes and their signaling molecules. Recruitment and dysfunction of these cells affect neuronal function in epilepsy. Our data using a novel audiogenic seizure rat model (KO of Kir5.1 channel in Dahl SS rat background, SS kcnj16-/- rats) largely recapitulates human SUDEP - suppression of post-ictal breathing frequency and heart rate worsened by repeated seizures. Knowledge gaps exist in defining a functional role of seizure-induced neuroinflammation on epilepsy-related impairment in cardiorespiratory control or increased SUDEP risk. We tested the hypothesis that repeated seizures lead to neuroinflammation in key brainstem regions important in respiratory control. Male SS kcnj16-/- rats aged 8-16 wks (n=4/group) were exposed to either 0 (naïve), 1 day (d), 2d, 3d, 5d, or 10d of seizures; the brains were harvested and flash-frozen for collecting bilateral punch biopsies from the nucleus ambiguous/pre-Bötzinger complex (NA/preBötC), Bötzinger complex (BötC) and the Raphe Magnus (RMg) and subjected to a 27 chemokine/cytokine assay. We found increases (in fold-change) in 10 different cytokines, including IL-1α and IL-1β in the preBötC after 5d of seizures, and primarily decreases (e.g. IL-4) in the BötC and very few changes in cytokines in RMg at the same time point. Based on these data and single nuclear-RNA sequencing data in the RMg showing activation of IL-1 signaling in microglia after repeated seizures, we blocked IL-1 receptors with anakinra (IL-1 receptor antagonist; 2.5 mg/kg IP) to test a functional role of this pathway. Male SS kcnj16-/- rats (aged 8-16 wks; n=12-14/group) were treated with anakinra or vehicle daily for 3 days prior to and during the 10d seizure protocol. Breathing was measured via whole-body plethysmography for 20 min before, during and 20 min after daily audiogenic seizures. Anakinra treatment led to higher mortality ( p<0.01) and more severe seizure scores at 1d, 3d, and 10d ( p<0.05). Across the 10d, acutely following a seizure, there were no apparent effects across ventilatory parameters. Overall, blocking IL-1 signaling led to detrimental effects in mortality, seizure score, and no benefit on ventilatory parameters during 10d of seizures compared to controls. These data suggest that repeated seizures induce time- and site-dependent brainstem neuroinflammation, where the activation of IL-1 signaling in vital cardiorespiratory control regions appears beneficial. Supported by HL122358, HL160122 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.