Neuronal in vitro activity is more sensitive to valproate than intracellular ATP: Considerations on conversion problems of IC50 in vitro data for animal replacement.

•Mouse embryonic primary cortex cells were cultured in glass cell chips.•Electric activity and cellular ATP were detected under the influence of valproate.•Hormetic increases and biphasic behavior were detected for both parameters.•These hinder a simple extraction of IC50 and Hillslope values.•Different ways of parameter-fitting are discussed.