Neurite outgrowth from cerebral cortical neurons is promoted by medium conditioned over heart cells

Abstract

Seven day chick embryo cerebral cortical neurons cultured at low density (10,000 cells/16 mm well) in serum‐free, defined medium in polylysine‐coated wells fail to extend neurites and assume a flattened phase‐dark morphology. Addition of serumfree, defined medium conditioned over chick embryo heart cells promotes neurite outgrowth and rounding of the cell body (which becomes phase bright). A sensitive bioassay, based on counting the number of phase‐bright neurons with processes at least equal to one cell body diameter after 20 hours in culture, was used to titrate neurite‐promoting activity in heart conditioned medium. This activity is completely destroyed by exposure to trypsin. As little as 2 μg/ml total conditioned medium protein elicits a half‐maximal response in this bioassay.