Chronic Suppression of Bioelectric Activity and Cell Survival in Primary Cultures of Rat Cerebral Cortex: Biochemical Observations

Abstract

Chronic suppression of spontaneously occurring bioelectric activity (BEA) has been shown to increase neuronal cell death in tissue culture, but may also affect astrocytes. We investigated this process in primary cultures of rat cerebral cortex by measuring the levels of NSE (neuron-specific enolase) and GFAP (glial fibrillary acidic protein) in relation to general tissue markers, including measurements for cell death and proliferation. In electrically active (control) cultures, the content of DNA, protein, and NSE became maximal between 21 and 28 days in vitro (DIV) and thereafter decreased, whereas the content of GFAP rose continuously up to 43 DIV. Chronic suppression of BEA by tetrodotoxin (TTX; from 6 DIV) decreased the content of DNA, total protein, and especially NSE. The content of GFAP was decreased in all culture series investigated, but with great temporal variations among culture series. Chronic TTX treatment (started at 6 DIV) increased the efflux of lactate dehydrogenase, a marker for cell lysis, between 12 and 21 DIV, but this efflux was mainly derived from the supporting glial cells with which the cerebral cortex cultures were cocultured. Chronic, but not acute (7 h) TTX treatment decreased total [3H]thymidine incorporation into DNA from 14 DIV; this appeared to be due to a reduced number of astrocytes. Chronic suppression of BEA with xylocaine from 6 DIV had similar effects on DNA-, protein-, and NSE-content as TTX, but led to an increased content of GFAP at 21 DIV. Chronic suppression of synaptic transmission with 10 mM Mg2+ and 0.2 mM Ca2+, starting at 6 DIV, increased the content of DNA, protein, and GFAP at 21 DIV, but NSE was still decreased. We conclude that chronic suppression of BEA in cerebral cortex cultures enhances neuronal cell death, whereas astrocytes are differentially affected, depending on the suppressing agent. As astrocytes may have a modulating effect on neuronal survival, their involvement should be regarded when studying the effects of chronic suppression of BEA on neuronal development.