Repeated seizures lead to neuroinflammation in a time- and site-dependent manner in brainstem regions of ventilatory control

Introduction: Patients with drug-resistant epilepsy are at increased risk of post-ictal cardiorespiratory failure and Sudden Unexpected Death in Epilepsy (SUDEP). A recognized factor in epilepsy is neuroinflammation mediated by resident microglia and astrocytes, which when activated can cause neurological dysfunction. Our novel rat model of audiogenic seizure due to Kir5.1 knockout (SSkcnj16-/- rats) recapitulates features of human SUDEP, including post-ictal breathing and heart rate suppression that worsens after repeated seizures. Here we tested the hypothesis that repeated seizures lead to neuroinflammation in key brainstem regions of ventilatory control.

Methods: Adult male SSkcnj16-/- rats (n = 4/group) were exposed to 0, 1, 2, 3, 5, or 10 seizures (1/day), brains collected and frozen and punch biopsies taken from the nucleus ambiguous/pre-Bötzinger complex (NA/preBötC), Bötzinger complex (BötC), and Raphe Magnus (RMg) for chemokines/cytokine array analyses. Separate male SSkcnj16-/- rats (n=12-14/group) were chronically treated with anakinra (IL-1R antagonist) or vehicle for 3 days before and up to 10 days of seizures (1/day) where breathing was measured for 20 min before, during and 20 min after seizures.

Results: We found that changes in cytokines occurred in a region-dependent manner and were greatest in the preBötC after 5 seizures whereas in other regions (BötC and RMg) cytokines decreased or were unchanged. Among the most significantly altered cytokines was IL-1α and IL-1ß, consistent previous RNA sequencing data showing IL-1 signaling activated in microglia after repeated seizures. Also, while Anakinra treatment prevented a progressive worsening of ventilatory suppression across the 10 days (p < 0.05) seizure-related mortality was greater than controls (p < 0.05).

Conclusion : Thus, repeated seizures induce brainstem neuroinflammation in a time- and region-dependent manner where chronically blocking IL1R signaling had both beneficial and detrimental effects. Consequently, further insights into time and site dependent IL1 signaling modulation post-seizure may provide novel therapeutic approaches for epilepsy patients.