Kynurenic acid, an active metabolite of tryptophan, is synthesized through a kynurenine intermediate by kynurenine aminotransferases (KATs). It acts as an antagonist of both NMDA and AMPA receptors, as well as α7 nicotinic acetylcholine receptors (nAChRs; EC50s = 235, 101, and 7 µM, respectively), and functions as an agonist for the aryl hydrocarbon receptor (AhR) and G protein-coupled receptor 35 (GPR35; EC50s = 1.4 and 39 µM, respectively). In a neonatal rat model of cerebral hypoxic-ischemia, induced by carotid artery ligation, administration of kynurenic acid at 300 mg/kg prevents weight loss in the lesioned hemisphere. Additionally, at concentrations of 1 and 5 mg/ml, it protects against neurodegeneration in the rhabdomere of the eye in an Htt93QtransgenicDrosophila model of Huntington's disease. Elevated levels of kynurenic acid in the cerebrospinal fluid have been observed in patients with schizophrenia.