LPS elicits a much larger and broader inflammatory response than Escherichia coli infection within the hippocampus of neonatal rats.

An immune challenge during the neonatal period can significantly affect the development of the nervous and immune systems, such that long-term abnormalities in immune function and behavior persist into adulthood. Given that immune activation and individual cytokines have been linked to the etiology of many developmental neuropsychiatric disorders, a complete characterization of the neonatal immune response within the brain is warranted. In this study, rats were treated peripherally on postnatal day (P) 4 with either a live Escherichia coli (E. coli) infection or lipopolysaccharide (LPS), two common models of neonatal immune activation. Inflammatory gene expression was measured within the hippocampus 2 and 24h later. We determined that E. coli and LPS produce very distinct inflammatory profiles within the brain. Infection with E. coli produced a robust, yet relatively IL-1 pathway focused activation of the neonatal immune system within the brain, while LPS produced a very broad and robust immune response within the brain. This analysis also identified common inflammatory genes up-regulated by both E. coli and LPS treatment.