In addition, there were higher levels of IFN-γ, TNF-α and indoleamine 2,3 dioxygenase 1(IDO1) in the hippocampus of the recipient mice, indicating that gut microbiota modulate inflammatory response in the hippocampus via disruption of the microbiota-gut–brain axis to exacerbate anxiety and depressive-like symptoms [211]. Here, IDO1 is linked to Anxiety.