Immediate post-injury HMGB1 neutralization prevents synaptic dysfunction in burn and hindlimb unloaded rats

Introduction – Severe burns are known to provoke neuroinflammation and contribute to cognitive deficits, but the mechanism of action remains poorly understood. We hypothesize that early release of extracellular high mobility group box 1 (HMGB1), a key driver for inflammation, triggers the burn−induced hyperinflammation and associated synaptic dysfunction. Unavoidable immobilization prolongs inflammation and worsens burn outcomes. We examined the therapeutic potential of an anti−HMGB1 neutralizing antibody in improving the neurological outcomes in burned and immobilized rats. Methods – Adult male rats received >30% total body surface area (TBSA) scald burns. After injury, animals received either no treatment, chicken anti−HMGB1, or isotype control IgY antibody (2 mg/kg, intraperitoneal or combined with subcutaneous Alzet pump delivery). Burn−injured, treated rats underwent 14 days of hindlimb unloading (HLU) in metabolic cages, followed by 7 days of mobile recovery. Burned rats without treatment were pair−fed and housed in standard cages without suspension, as were sham−burn controls. All animals were euthanized 21 days post−injury for sample collection. Hippocampal synaptic integrity was evaluated using field electrophysiological recordings at Schaffer collateral synapses. Results – Burn wound size was significantly increased in rats subjected to hindlimb unloading, accompanied by elevated IL−10 and IL−1β levels. These alterations were mitigated by anti−HMGB1 antibody treatment. Furthermore, anti−HMGB1 administration moderated the activated CD4⁺T cells and NK cells response. Electrophysiological analysis of hippocampal slices showed that burn−HLU rats treated with vehicle, exhibited pronounced postsynaptic hyperexcitability and left−shifted presynaptic excitability curves, consistent with synaptic dysfunction. These animals also demonstrated disrupted slope profiles and loss of basal-excitatory resolution, indicating heightened excitability and increased vulnerability to degeneration. Anti−HMGB1 antibody treatment restored normal potentiation patterns and preserved both pre− and postsynaptic function in burned rats with 14-days hindlimb unloading. Discussion – Prolonged immobilization provoked pre− and post-synaptic hyperexcitability at Schaffer collateral synapses and exacerbated burn−induced brain impairment in rats. Early reduction of systemic HMGB1 activity protected against inflammation, preserved the hippocampal synaptic plasticity, and restored long−term potentiation and hippocampal integrity following burn injury and hindlimb unloading in rats.