The role of chondroitin sulfate proteoglycans (CSPGs) on excitotoxic cell death and long-term survival of neurons were investigated in primary cultured neurons of the rat cortex. Soluble CSPGs were prepared from 10-day-old and adult rat brains by the ion-exchange chromatography on DEAE-Sephacel. CSPGs were added to the culture medium on culture day 4, and glutamate neurotoxicity was examined on culture day 7 by both microscopic cell count and measurement of lactate dehydrogenase activity in culture media. The effect on long-term survival was evaluated by counting viable neurons until culture day 28. CSPGs and core proteins, but not glycosaminoglycan chains (GAGs), protected cultured neurons from excitotoxic cell death induced by 24 h exposure to 1 mM glutamate, but CSPGs did not promote the long-term survival of neurons. The neuroprotective effect of CSPGs and core proteins was dose-dependent with ED50 about 10 microM hexuronate and 2 micrograms/ml protein respectively. This effect was not considered to be due to adsorption of glutamate by CSPGs because [3H]glutamate was not adsorbed by CSPGs added to the culture medium. Based on these findings, we suggested that CSPGs may exert their neuroprotective action through molecular interactions with the binding sites on neuronal membrane, neurotrophic factors, or other extracellular matrix molecules and may be involved in the pathogenesis of neuronal cell death in acute pathological conditions and chronic degenerative diseases of the brain.