February 26, 2026Epilepsy Research0 citationsOpen Access

A Model of New-Onset Refractory Status Epilepticus (NORSE) Using Intrahippocampal Kainic Acid in Adolescent Mice

HSHaiYing Shen IBIrena Balzekas YJYoungjin Jung

Key Points

To create a reliable mouse model of new-onset refractory status epilepticus (NORSE) for studying its pathophysiology.
Developed a model using unilateral intrahippocampal kainic acid injection in C57BL/6 J mice
Monitored seizures through depth electrodes and evaluated cellular responses using various techniques
Assessed behavioral outcomes with open-field and Y-maze tests
Mice exhibited spontaneous seizures by day 3, with frequency increasing through day 21
Significant microglial activation (>9-fold) and astrocytosis were observed
Behavioral tests showed increased anxiety and cognitive deficits by day 21

Abstract

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. • First mouse NORSE model recapitulates subclinical seizures and cognitive impairment • Robust hippocampal immune infiltration and microglial activation in NORSE mice • NORSE model reveals neuroinflammation as key feature for therapeutic targeting • Preclinical platform ready for testing immunomodulatory NORSE therapies

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