beta-Amyloid neurotoxicity in human cortical culture is not mediated by excitotoxins

beta-Amyloid is a metabolic product of the amyloid precursor protein, which accumulates abnormally in senile plaques in the brains of patients with Alzheimer's disease. The neurotoxicity of beta-amyloid has been observed in cell culture and in vivo, but the mechanism of this effect is unclear. In this report, we describe the direct neurotoxicity of beta-amyloid in high-density primary cultures of human fetal cortex. In 36-day-old cortical cultures, beta-amyloid neurotoxicity was not inhibited by the broad-spectrum excitatory amino acid receptor antagonist kynurenate or the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid under conditions that inhibited glutamate and NMDA neurotoxicity. In 8-day-old cortical cultures, neurons were resistant to glutamate and NMDA toxicity but were still susceptible to beta-amyloid neurotoxicity, which was unaffected by excitatory amino acid receptor antagonists. Treatment with beta-amyloid caused chronic neurodegenerative changes, including neuronal clumping and dystrophic neurites, whereas glutamate treatment caused rapid neuronal swelling and neurite fragmentation. These results suggest that beta-amyloid is directly neurotoxic to primary human cortical neurons by a mechanism that does not involve excitatory amino acid receptors.