A model of new-onset refractory status epilepticus (NORSE) using intrahippocampal kainic acid in adolescent mice

New-onset refractory status epilepticus (NORSE) is a devastating neurological condition characterized by the sudden onset of prolonged, drug-resistant seizures in previously healthy individuals. A clinically relevant animal model is essential to elucidate its pathophysiology, improve treatment, and reduce morbidity and mortality in NORSE. We developed an adolescent mouse model of NORSE by inducing prolonged convulsive status epilepticus in postnatal day 40 (P40) C57BL/6 J mice-corresponding to human adolescence-via unilateral intrahippocampal kainic acid (IHKA, 150 ng) injection. Progression of recurrent spontaneous electrographic seizures was monitored through depth electrodes on days 3, 5, 7, and 21 post-IHKA. Cellular and immune responses were examined using immunohistochemistry, Nissl staining, and flow cytometry. Behavioral outcomes were assessed using open-field and Y-maze tests. IHKA-injected mice developed spontaneous recurrent seizures by day 3 (18.7 ± 3.2 seizures/hour). Seizure frequency nearly doubled by day 7 (35.2 ± 4.1 seizures/hour) and continued through day 21 (39.7 ± 4.8 seizures/hour). Significant neuroinflammatory changes were observed, including > 9-fold microglia activation, two-fold astrocytosis, cell death in the CA3 subfields, and monocyte infiltration into the hilus. Flow cytometry revealed a two-fold increase in CD8⁺ cytotoxic T cells and γδ T cells in the hippocampus. Behaviorally, IHKA mice exhibited increased anxiety and cognitive deficits by day 21. This adolescent IHKA model recapitulates hallmark features of NORSE-acute repetitive convulsive seizures with rapid progression to subclinical status epilepticus, marked immune activation, hippocampal injury, and behavioral impairment. Our murine model of NORSE provides a valuable platform for investigating NORSE pathogenesis and evaluating novel therapeutic strategies.