IDO2 and type 1 diabetes mellitus: In type 1 diabetes models, the downregulation of presynaptic 5‐HT1AR enhances spinal 5‐HT release, reduces quinolinic acid levels, inhibits tryptophan 2,3‐dioxygenase (Tdo), indoleamine 2,3‐dioxygenase (Ido) 1, and Ido2 expression, and improves neuronal degeneration and pain‐related behaviors [562].