The effect of NGF, BDNF and bFGF on expression of galanin in cultured rat dorsal root ganglia

Peripheral nerve injury causes a marked change in expression of the neuropeptide galanin in dorsal root ganglion (DRG) neurons. We have used DRG cell cultures to study whether growth factors, especially nerve growth factor (NGF), play a role in this regulation. Adult rat DRG cultures seem to represent a suitable model for this study, since the neurons are axotomized during culture preparation and are known to survive independently of added neurotrophic factors. The effect of NGF, brain derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF) was studied on the expression of galanin and galanin message-associated peptide (GMAP)-like immunoreactivities using immunohistochemistry, as well as of prepro-galanin (ppGAL) mRNA levels using radioactive and non-radioactive in situ hybridization. The results show that 100, but not 20 or 50 ng/ml NGF, as well as 10 ng/ml BDNF cause a 40% decrease in the number of GMAP expressing neurons in 72 h cell cultures. A 50% decrease was observed after treatment with 10 ng/ml bFGF. The high dose needed and the modest effect suggest that NGF is not a major factor involved in galanin regulation, whereas BDNF and bFGF may have a role. Moreover, the strong upregulation of galanin/GMAP and ppGAL mRNA levels in the untreated cultures indicates that DRG neurons in vitro have a phenotype similar to DRG neurons after axotomy, i.e. a phenotype distinctly different from normal DRG neurons.