Nerve growth factor induces expression of immediate-early genes NGFI-A (Egr-1) and NGFI-B (nur 77) in adult rat dorsal root ganglion neurons.

We have used primary cultures of adult rat dorsal root ganglia (DRG), enriched in sensory neurons, to investigate the induction of immediate-early genes by NGF and a variety of other growth factors. Using the polymerase chain reaction we have quantitatively amplified specific mRNA transcripts induced by NGF, in the presence and absence of the protein synthesis inhibitor cycloheximide. NGFIA (Egr-1) and NGFIB (nur 77) mRNAs were elevated in level within 60 min of NGF treatment and independently of de novo protein synthesis. This was consistent with the behaviour of immediate-early genes. These kinetics were seen at a range of NGF concentrations. NGFIA and NGFIB mRNAs were also found to be induced in DRG cultures by a variety of other growth factors. Different patterns of induction of NGFIA and NGFIB mRNA observed in DRG cultures suggested that transcript-specific pathways of signal transduction were operating within neurons, dependent upon the particular growth factor stimulus. Comparison of data reported from growth factor treatment of other cell types with data from DRG cultures also revealed patterns of NGFIA and NGFIB mRNA induction specific to DRG neurons.