Cultured astroglia release a neuronotoxic activity that is not related to the excitotoxins

Neuronal death after brain injury is thought to be in part the result of the activity of the excitotoxins, a family of excitatory amino acids which are released by neurones. We have also described an astroglial cell-derived neuronotoxic activity of low molecular weight whose release can be induced by depolarizing events such as an increase in extracellular potassium concentration. We study here the relationship between this astroglia-derived neuronotoxic activity present in astroglia-conditioned medium (ACM) and the excitotoxins. Using a colorimetric assay of neuronal survival, we show that the ACM neuronotoxic activity, is able to induce the death of all types of neurones tested, including those which are insensitive to excitotoxins. Furthermore, the ACM neuronotoxic activity does not require for its action the extracellular ionic composition which is needed for the activity of excitotoxins. Finally, the ACM neuronotoxic activity is not blocked by competitive or non-competitive antagonists of the various classes of excitotoxin receptors. Those data demonstrate that the astroglia-derived neuronotoxic activity is not related to the excitotoxins. Still, because astrocytes can also be depolarized by members of the excitotoxin family, the possibility exists that the release of astroglia-derived neuronotoxic activity would follow the rise in extracellular excitatory amino acid concentration during nervous system injury.