Mice deficient in indoleamine-2,3-dioxygenase are protected from intracerebroventricular lipopolysaccharide-induced anhedonia. (a) Both wild-type (WT) and indoleamine-2,3-dioxygenase (IDO1) knockout (KO) mice had similar decreases in body weight in response to intracerebroventricular (ICV) lipopolysaccharide (LPS, 10 ng). (b) IDO1 KO mice maintained sucrose preference following ICV LPS treatment, but (c) had similarly increased tail suspension test (TST) immobility as WT mice. Data are average ± standard error of the mean. **P <0.01. n = 6 to 12 mice per group.