Quantitative analysis of GAP-43 expression by neurons in microcultures using cell-ELISA

A cell-ELISA technique is described which allows the quantification of GAP-43 protein in a large number of microcultures of adult dorsal root ganglion neurons. GAP-43 is measured in the 1-10 ng range, corresponding to the amount of GAP-43 present in fewer than 500 DRG neurons. Specificity of the assay is confirmed using Western blotting and immunocytochemistry. The GAP-43 content of adult DRG microcultures rises during 2 weeks in culture, although the number of surviving neurons decreases. The GAP-43 content of cultured adult DRG neurons is not increased by chronic exposure to added nerve growth factor after 7 days in vitro. However, GAP-43 is increased in DRG taken from animals with prior peripheral nerve injury, and is decreased by chronic exposure to dibutyryl cyclic AMP after 7 days in vitro. The method affords the sensitivity and statistical power to document modest changes in GAP-43 protein abundance in complex cultures.