Microcirculatory Dysfunction in the Brain Precedes Changes in Evoked Potentials in Endotoxin-Induced Sepsis Syndrome in Rats

Abstract

Background: During sepsis progression microcirculatory dysfunction precedes macrocirculatory failure, partly explaining the occurrence of early organ dysfunction. The matter concerning microcirculatory dysfunction in the brain under septic conditions is less clear. We investigated the integrity of the activation flow coupling during sepsis progression in a rat model of septic shock. Methods: Chloralose-anesthetized rats (n = 30) were subjected to electric forepaw stimulation. Over the somatosensory cortex electrical activity and hemodynamic responses were recorded with surface electrodes and laser Doppler. After baseline recordings, vehicle, 1 or 5 mg/kg lipopolysaccharide (LPS) from Escherichia coli was given intravenously, and activation flow coupling, blood pressure and blood gases were investigated at regular time points up to 270 min. In the end lactate, glucose, neuron-specific enolase (NSE) and S-100B protein levels were measured. Results: Besides stable data from the control group, all LPS-treated rats developed signs of septic shock, which were more pronounced in the 5 mg/kg LPS group. Cerebral hyperemia occurred and was similar between the sepsis groups despite lower blood pressure levels in the 5 mg/kg LPS group. While the activation flow coupling remained intact in the 1 mg/kg LPS group, an uncoupling occurred in the 5 mg/kg group. First, the evoked flow velocity responses dropped 60 min after sepsis induction before the somatosensory amplitudes also decreased 120 min later. From similar NSE levels we suggest a functional rather than structural deficit explaining the difference in evoked potentials. Conclusions: For the first time we demonstrate microcirculatory dysfunction in the activation flow coupling of the brain. Inappropriate blood supply of neurons might explain the disturbance of neuronal function.