Objective: Concentrations of quinolinic acid, an N-methyl-D-aspartate agonist, are often elevated for long periods of time in the cerebrospinal fluid (CSF) and brain tissue of patients with AIDS dementia complex (ADC). This study was designed to test the hypothesis that chronic exposure of human neurons to quinolinic acid levels equivalent to those in the CSF of ADC patients is neurotoxic.
Design and methods: Human fetal brain 14-16 weeks post-menses was cultured in medium with no detectable levels of quinolinic acid. After 4 weeks, 350 or 1200 nmol/l quinolinic acid was added to the feeding medium for a further 5 weeks. Neurotoxicity was evaluated using immunohistochemistry, transmission and scanning electron microscopy, and image analysis.
Results: A total of 1200 nmol/l quinolinic acid caused altered cell associations, a decrease in cell density and decreased microtubule-associated protein (MAP)-2 immunoreactivity compared with cultures exposed to 350 nmol/l quinolinic acid or controls. Image analysis of neurons in randomly selected fields revealed significantly swollen cells (P < 0.0001) compared with those treated with 350 nmol/l quinolinic acid or controls. Dendritic varicosities and discontinuous microtubular arrays were present in neurons exposed to both quinolinic acid concentrations, but not in control cultures.
Conclusions: This study is the first to assess quinolinic acid levels in the experimental medium, and demonstrates that chronic exposure of human neurons to concentrations of quinolinic acid equivalent to those in the CSF of patients with ADC leads to alterations in dendritic ultrastructure and MAP-2 immunoreactivity, which is consistent with ADC pathology.