Potassium-induced release of neuronotoxic activity by astrocytes.

Medium conditioned by newborn rat cerebral cortex microexplants contains neuronotoxic activity for cerebellar granule cells and hippocampal neurons. The neuronotoxic activity is associated with low-molecular weight molecule(s) (less than 1000 Da) and resists to heating and to freezing and thawing. Using nearly homogenous cultures of neurons or astrocytes, we show that the neuronotoxic activity is released by the latter cell type. This release is enhanced by increasing extracellular K+-concentration. Astrocytes also secrete neuronotrophic activity whose release is not affected by external K+. Neurons can be desensitized against the neuronotoxic activity.