Alternatively, the increased QUIN/KYN ratio in PTSD could also derive from a different distribution of KYN in body compartments, such as increased passage of this molecule through the BBB or its recruitment for binding to the aryl hydrocarbon receptor (Ahr) that promotes ROS modulation, all of which could potentially occur during the induction of cytokine release and inflammation present in these patients (142). Here, AHR is linked to post-traumatic stress disorder.