2.325 35 0.026

*p*<0.05,

*p*<0.05,

**Figure 4.** *Ifn-γ* gene transfer. Original data from Ref. [47]. (a) Schematic depiction of the pCpG-Muγ plasmid construct (InvivoGen, San Diego, CA). (b) Schematic depiction of the time schedule for animal experiments. (c) Increase of IDO1 activity in the frontal cortex of mice 28 days after *Ifn-γ* gene transfer [47]. βGlo MAR, β-globin matrix attachment region; mCMV enh, mouse cytomegalovirus enhancer; hEF1 prom, human elongation factor1 promoter; I140, synthetic 5′UTR containing an intron 140; MCS, multi cloning site; SV40 pAn, Simianvirus 40 polyadenylation; IFN-β S/MAR, interferon β gene scaffold/matrix attachment region; EM2K, CpG-free version of the bacterial EM7 promoter; Zeo, Zeocin; R6K ori, R6K origin.

In order to clarify whether the activation of IDO1 by IFN-γ-affected behaviors, three tests, open-field test (OFT), the Y-maze test, and forced swimming test (FST), were performed in mice. Mice were transfected with either a pCpG-mcs plasmid (control vector) that did not contain the *Ifn-γ* gene [IFN-γ-transfected (−) mice] or a pCpG-Muγ plasmid that long-lasting expressed *Ifn-γ* [IFN-γ transfected (+) mice]. No significant differences in locomotor activity of the OFT was observed between IFN-γ transfected (−) and (+) mice. Similarly, in the Y-maze test, no significant differences in the alternation behavior were detected between the two groups of mice. However, in the FST, immobility time was significantly longer in IFN-γtransfected (+) mice (**Figure 5a**). Our findings strongly suggest that IDO1 induction by IFN-γ is a critical factor in depression-like behaviors but not in short-term memory or locomotor activity in mice.
