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 un dergoing sprouting and in dorsal root ganglion (DRG) neurons whose spr outing had been-prevented through exposure to anti-NGF antiserum durin g the course of the experiment. The results indicate that the low affi nity p75 NGFR mRNA is increased by 4 days post-operatively in DRGs fro m control serum-treated animals, and that this increase is most pronou nced in smaller neurons. In contrast, the expression of p75 mRNA was m aintained at control levels in DRGs from anti-NGF-treated animals. Res ults for trkA expression indicate an increase in expression at days 4- 6 post-op in both groups of animals, with the anti-NGF treatment havin g a delayed influence on mRNA levels. Examination of GAP-43 mRNA level s revealed an increased expression in sprouting DRG neurons, whereas t his increase was not observed in DRGs from anti-NGF treated animals. T aken together, these results provide further evidence of NGF's role in the collateral sprouting of nociceptive neurons.