Short-term estrogen replacement increases beta-preprotachykinin mRNA levels in uninjured dorsal root ganglion neurons, but not in axotomized neurons

Dorsal root ganglion (DRG) neurons that mediate nociception express the hig h affinity NGF receptor (trkA) gene and the preprotachykinin (PPT) gene. NG F has been shown to regulate both of these DRG neuronal genes. Our laborato ry has shown that these genes are also regulated by estrogen. Longterm dail y estrogen replacement, in adult ovariectomized (OVX) rats, causes a coordi nate decline in trkA and beta -PPT mRNA levels in lumbar DRG neurons, while short-term estrogen replacement increases trkA mRNA levels in uninjured as well as in axotomized lumbar DRG neurons. The purpose of the current study was to test the hypothesis that short-term estrogen replacement increases DRG beta -PPT mRNA levels in lumbar DRG neurons of OVX rats and that the in crease is dependent on target-derived NGF. Sciatic nerve transection (SNT) was used to eliminate target-derived NGF in L4 and L5 DRGs in adult OVX rat s. Seven days later, one-half of the SNT and one-half of the animals that h ad received sham sciatic nerve transactions (SHAM) received two daily injec tions of estradiol benzoate (EB), The remaining rats received two daily inj ections of vehicle alone. Quantitative in situ hybridization analyses of se ctions from L4 and L5 DRGs showed that two daily injections of EB significa ntly increased beta -PPT mRNA levels in DRGs of SHAM animals, but had no ef fect on beta -PPT mRNA levels in DRGs from SNT animals. These data coupled with our earlier observations of the effect of short-term estrogen replacem ent on DRG trkA mRNA levels, indicate that the regulation of DRG beta -PPT mRNA levels by estrogen requires target-derived NGF. (C) 2001 Academic Pres s.