Lipopolysaccharide differentially alters systemic and brain glucocorticoid levels in neonatal and adult mice.

Glucocorticoids (GCs) are secreted by the adrenal glands and increase in response to stressors (e.g., infection). The brain regulates local GC levels via GC synthesis, regeneration and/or metabolism. Little is known about local GC regulation within discrete brain regions at baseline or in response to stress. We treated male and female C57BL/6J mice at postnatal day 5 (PND5) or PND90 with lipopolysaccharide (LPS; 50 μg/kg bw i.p.) or vehicle and collected blood and brain after 4 h. We microdissected the prefrontal cortex, hippocampus, hypothalamus and amygdala. We measured seven steroids, including corticosterone, via liquid chromatography-tandem mass spectrometry and measured transcripts for key steroidogenic enzymes (Cyp11b1, Hsd11b1, Hsd11b2) via qPCR. At both ages, LPS increased GC levels in blood and all brain regions; however, the increases were much greater at PND90 than at PND5. Interestingly, PND5 corticosterone levels were lower in prefrontal cortex than in blood, but higher in amygdala than in blood. These changes in corticosterone levels align with local changes in steroidogenic enzyme expression, demonstrating robust regional heterogeneity and a possible mechanism for the region-specific effects of early-life stress. In contrast, PND90 corticosterone levels were lower in all brain regions than in blood and similar among regions, and steroidogenic enzyme mRNA levels were generally not affected by LPS. Together, these data indicate that local GC levels within discrete brain regions are more heterogeneous at baseline and in response to LPS at PND5 than at PND90, as a result of increased local GC production and metabolism in the neonatal brain.