Quantification of Fos immunoreactivity in cortical cultures treated with growth factors

Among the effects mediated by growth factors in vivo are the switch to growth arrest and differentiation during normal development of the nervous system, survival during the period of naturally occurring cell death, and plasticity and repair of neurons in the adult brain. Much interest has focused on the signalling pathways utilised by growth factors with a large proportion of experiments carried out using the phaeochromocytoma cell line. Here we have quantified Fos immunoreactivity following stimulation of primary cultures of rat cortical neurons with a variety of growth factors including neurotrophins and cytokines. Expression of Fos has been quantified in these cultures using an ELISA technique, and immunocytochemistry followed by digital stereology. Treatment of cultures with brain derived neurotrophic factor (BDNF) or neurotrophin-4 (NT-4) causes a dose-dependent increase in Fos expression, while neurotrophin-3 (NT-3) causes an increase but at high concentrations only. A sub-population of cortical neurons within the cultures express Fos in response to fibroblast growth factor-1 or fibroblast growth factor-2 but no cells respond with Fos expression on treatment with insulin-like growth factor-1. We conclude that BDNF and NT-4 cause dose-dependent increases in the number of Fos immunoreactive cells.