Morphine and Midazolam Sedation Shifts GABA-GHB Balance in Young Rats With Delirium-Like Behavior

Introduction: Despite clinical necessity, sedation is a key risk factor for ICU delirium and related complications. Underlying mechanisms remain unclear, but an imbalance between excitatory and inhibitory brain activity may contribute. During critical illness, sedation and inflammation may alter 𝛾-aminobutyric acid (GABA) metabolism, shifting neural control from fast GABA-mediated inhibition to GABA’s slower-acting metabolite, 𝛾-hydroxybutyrate (GHB). This may be especially disruptive in early childhood, when GABA manipulation can impair brain maturation.


Methods: We hypothesized that morphine and midazolam, combined with inflammatory stress, would reduce GABA and increase GHB in young rats with delirium-like behavior. To model critical illness, 18-23-day-old rats (early childhood equivalent, n=8/sex/group) received E. coli lipopolysaccharide (LPS) on days 1, 3, and 5 to stimulate inflammation. On days 2-6, they were sedated twice daily with morphine+midazolam (SED). Study groups included saline (SAL), LPS, SED, and LPS/SED. Behavior was assessed with whisker stimulation, wet dog shakes, open field, and buried food tests. Animals with z-scores >2 per test and composite z-score sums >8 were considered "delirium-like". GABA and GHB were measured in brain homogenate on day 6 with liquid chromatography-tandem mass spectrometry.


Results: Composite delirium scores increased across treatment groups: LPS (8.8±0.8 [mean±SEM]), SED (11.7±1.0), LPS/SED (13.9±0.9) vs SAL (3.5±0.2; p< 0.0001). GABA was reduced by SED and LPS/SED (164.9±2.5 µg/g, 159.3±2.1) vs both SAL and LPS (224.1±1.1, 267.2±2.5; p< 0.03). SED nearly doubled GHB (0.87±0.02 µg/g vs SAL 0.46±0.04; p< 0.01), while LPS did not (0.58±0.05; p=0.36). Notably, LPS/SED reduced GHB (0.36±0.05; p< 0.01).


Conclusions: These findings suggest that a common sedation strategy shifts GABA metabolism and impairs inhibitory control needed for normal cognition and behavior. Inflammation alone had no effect on GABA and delirium scores were more mild. Unexpectedly, combined sedation and inflammation reduced both GABA and GHB, potentially disrupting fast and slow inhibition to produce the highest delirium scores. Similar behaviors may arise from distinct disruptions of a shared pathway, with implications for ICU delirium management, recovery, and developmental outcomes.