Figure 4.

Across species, mammals, birds, and fish have similar responses to stress induced changes in TRP-KYN metabolism. Stress responses include increased GC and catecholamine signaling, which elevate TRP metabolism through the KYN pathway, as indicated by the levels of downstream metabolites. While it is generally accepted that this occurs through hepatic TDO induction in mammals, the molecular mechanism is not yet clear in other vertebrate species. Figure created on biorender.com.