ANTI-NGF TREATMENT BLOCKS THE UP-REGULATION OF NGF RECEPTOR MESSENGER-RNA EXPRESSION ASSOCIATED WITH COLLATERAL SPROUTING OF RAT DORSAL-ROOT GANGLION NEURONS

The collateral sprouting of intact cutaneous sensory neurons has been shown to be dependent upon the presence of nerve growth factor (NGF). We have examined NGF receptor (NGFR) mRNA expression in DRG neurons undergoing sprouting and in dorsal root ganglion (DRG) neurons whose sprouting had been-prevented through exposure to anti-NGF antiserum during the course of the experiment. The results indicate that the low affinity p75 NGFR mRNA is increased by 4 days post-operatively in DRGs from control serum-treated animals, and that this increase is most pronounced in smaller neurons. In contrast, the expression of p75 mRNA was maintained at control levels in DRGs from anti-NGF-treated animals. Results for trkA expression indicate an increase in expression at days 4-6 post-op in both groups of animals, with the anti-NGF treatment having a delayed influence on mRNA levels. Examination of GAP-43 mRNA levels revealed an increased expression in sprouting DRG neurons, whereas this increase was not observed in DRGs from anti-NGF treated animals. Taken together, these results provide further evidence of NGF's role in the collateral sprouting of nociceptive neurons.