19: Sedation and Inflammation Alter Glutamate and Nmda Receptors in Young Rats With Delirium Behaviors

Introduction: Sedation and inflammation are known precipitants of ICU delirium, yet the underlying mechanisms remain unclear. Both interfere with excitatory glutamate signaling, which can trigger delirium. This is especially concerning in children, as glutamate regulates synapse formation and plasticity. In animal models, sedation increases synaptic density in young subjects but not adults. Excess drug-induced synapses may be poorly integrated and, along with glutamate dysregulation, could contribute to both delirium and post-discharge sequelae. Methods: We hypothesized that morphine and midazolam combined with inflammation would increase glutamate and N-methyl-D-aspartate receptors (NMDARs) in young rats with delirium behaviors. Early childhood-equivalent rats (18-23 days old, n=8/sex/group) received E. coli lipopolysaccharide (LPS) on days 1, 3, and 5 to induce inflammation. They received twice daily morphine+midazolam (SED) on days 2-6. Groups included: saline (SAL), LPS, SED, and LPS/SED. Behavior was evaluated with whisker stimulation, wet dog shakes, open field, and buried food tests. Rats with z-scores >2 per test and z-score sums >8 were defined as “delirium-like”. Glutamate and NMDAR subunit proteins (GluN1 and GluN2B) were assessed in brain tissue on day 6 with liquid-chromatography-tandem mass spectrometry and western blot. Results: Delirium scores increased across LPS, SED, and LPS/SED vs SAL (8.8±0.8, 11.7±1.0, 13.9±0.9 vs 3.5±0.2; p< 0.01). SED increased glutamate vs SAL and LPS (407.5±27.8 µg/g vs 322.1±9.3, 314.0±10.0; p< 0.01), while LPS/SED had a milder effect (358.8±9.9, p=0.07). GluN1 expression was 73% higher after LPS (p < 0.05), 53% higher after SED (p=0.05), and 76% higher after LPS/SED (p < 0.01). GluN2B was 58% higher after SED (p < 0.01), 93% higher after LPS/SED (p < 0.01), and LPS had no effect. Conclusions: Sedation increased glutamate and both NMDAR subunits while inflammation primarily increased GluN1, suggesting that complementary processes merged to produce more severe delirium in LPS/SED rats. Given its role in synaptic plasticity, GluN2B upregulation may mediate the increased synaptic density observed in pediatric sedation models. Excitotoxicity and abnormal connectivity may underlie not just acute delirium, but long-term functional deficits in critically ill children.