Quinolinic acid is an endogenous N-methyl-D-aspartate receptor agonist synthesized from L-tryptophan via the kynurenine pathway and thereby has the potential of mediating N-methyl-D-aspartate neuronal damage and dysfunction. Elevated cerebrospinal fluid levels of quinolinic acid are correlated with the severity of neuropsychological deficits in patients who have AIDS. It can act as an endogenous brain excitotoxin when released by activated macrophages. Quinolinic acid is being used as a research tool to examine the role of excitotoxicity in neuronal degeneration associated with a number of neurological diseases (Alzheimer's disease, Huntington's disease, Parkinson's disease) which involve selective neurotransmitter deficits.