Maternal inflammation leads to increased tryptophan metabolites tissue concentration in the fetal brain. Inflammation was induced by poly(I:C) injection (2 mg/kg) at E12. Fetal brain tissue concentration of 5-HIAA, 5-HT, and KYN were measured by HPLC. A, B, Maternal inflammation induces a significant increase of 5-HT in the fetal forebrain (A), but not hindbrain (B) 24 h after injection. KYN concentration is significantly increased in the fetal hindbrain only. C, D, Forty-eight hours after maternal poly(I:C) injection, 5-HT and KYN are significantly increased in the fetal forebrain (C), but not hindbrain (D). Brain 5-HIAA concentration is not significantly altered at any time point in either region. E, Placental TRP concentration is transiently increased 24 h but not 48 h after maternal poly(I:C) exposure. F, Rate of placental 5-HTP synthesis in vitro is correlated linearly to increasing input concentrations of TRP in both saline (control)- and poly(I:C)-exposed dams. *p < 0.05, **p < 0.005, two-way ANOVA with Bonferroni correction. Error bars indicate SD. n = 3–5 placentas per dam.