Subclinical exposure to low-dose endotoxin impairs EEG maturation in preterm fetal sheep

Exposure to chorioamnionitis is strongly associated with neurodevelopmental disability after premature birth; however, it remains unclear whether subclinical infection affects functional EEG maturation. Chronically instrumented 103-104-day-old (0.7 gestational age: term 147 days) fetal sheep in utero were randomized to receive either gram-negative LPS by continuous low-dose infusion (100 ng iv over 24 h, followed by 250 ng/24 h for 4 days; n = 6) or the same volume of normal saline (n = 9). Arterial plasma cortisol, ACTH, and IL-6 were measured. The delta (0-3.9 Hz), theta (4-7.9 Hz), alpha (8-12.9 Hz), and beta (13-22 Hz) components of the EEG were determined by power spectral analysis. Brains were taken after 10 days for histopathology. There were no changes in blood gases, cardiovascular variables, or EEG power during LPS infusion, but a transient rise in plasma cortisol and IL-6 (P < 0.05). LPS infusion was associated with loss of the maturational increase to higher frequency activity, with reduced alpha and beta power, and greater delta power than saline controls from 6 to 10 days (P < 0.05). Histologically, LPS was associated with increased numbers of microglia and TNF-α-positive cells in the periventricular white matter and frontoparietal cortex, increased caspase-3-positive cells in white matter, but no loss of CNPase-positive oligodendrocytes, Nurr-1 subplate cells, or gyral complexity. These data suggest that low-dose endotoxin exposure can impair EEG maturation in preterm fetal sheep in association with neural inflammation but without hemodynamic disturbances or cortical injury.