Kynurenic acid is a neuroactive metabolite in the kynurenine pathway, known for its role as an antagonist of excitatory neurotransmitter receptors, including NMDA and AMPA receptors, and a modulator of the alpha-7 nicotinic acetylcholine receptor. It has been implicated in various neurological and psychiatric disorders, making it a target for therapeutic research in conditions like schizophrenia, depression, and neurodegenerative diseases.