The Effects of Estrogen on Dorsal Root Ganglion Neurons

EFFECTS OF ESTROGEN ON DORSAL ROOT GANGLION NEURONS Sheila A. Scoville Eastern Virginia Medical School and Old Dominion University, 1997 Director Francis J. Liuzzi, Ph. D. Skin sensation is mediated by dorsal root ganglion (DRG) neurons. Data indicates that skin sensitivity in female rats is estrogen-dependent. Some DRG neurons have estrogen receptors (ERs) which are regulated by estrogen. In these cells, nerve growth factor (NGF) and estrogen receptors colocalize. Regulation o f NGF receptors and neuronal sensitivity to NGF may allow estrogen to regulate NGF-dependent genes. The goals o f the present study were to determine which DRG neurons express the ER gene and to analyze the effects o f long-term estrogen administration on the interrelated expression of tyrosine kinase A (trkA), preprotachykinin (PPT), and 68kD neurofilament (NF) genes and to compare warm thermal withdrawal latencies in these animals. The hypothesis tested by the current study was that estrogen upregulates trkA and by doing so, increases the sensitivity o f NGF-receptive neurons to the growth factor. Three groups o f ovariectomized (OVX) Sprague-Dawley rats were used: OVX (no replacement), IX (taw dose) and 10X (high dose). The replacement groups received daily Premarin injections. Rats from each group were killed at 56 or 90 days and their lumbar DRGs harvested. ER mRNA localization was done by in situ hybridization. Results showed that ER mRNA was o f taw abundance, but was evident in smaller neurons. Quantification revealed that both trkA and PPT mRNA was downregulated in both estrogen Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. replacement groups at both time points when compared to the OVX group. TrkA mRNA was localized predominantly in small DRG neurons. PPT mRNA was restricted to small neurons. Estrogen treatment slowed warm thermal plantar withdrawal, but not significantly. Neurofilament mRNA levels were dramatically increased by 56 days of estrogen treatment in a dose-dependent manner in all size populations o f DRG neurons. Ninety days o f estrogen treatment had a similar effect. These data indicate that estrogen regulates DRG neuronal gene expression. An overlapping population of DRG neurons express the ER, trkA and PPT genes. Estrogen may regulate the trkA and PPT genes by altering NGF sensitivity. Since the ER gene does not appear to be expressed by all DRG neurons, the effect o f estrogen on neurofilament gene expression must involve alternative mechanisms. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. To my husband, Marty, my daughter, Brooke, and my mother for their love, support and understanding In memory of R. Bruce Masterton, 1931-1996. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS I would especially like to thank my advisor and mentor, Dr. Frank Liuzzi who helped me, encouraged me and suffered with me during every phase o f my Ph. D. degree. His high standards for excellence in science set the benchmark for my achievement. Special thanks go to Dr. David Scott who gave me continuous and unwaivering support in my efforts as both a student and a teacher. I am grateful to my other committee members, Dr. Charles Morgan and Dr. Keith Carson who helped me with many special requests. They gave generously o f their time and expertise as members o f both my Guidance and Dissertation Committees. I am especially appreciative for the invaluable help from Susan Button. The high quality in situ hybridizations in this study would not have been possible without her effort and expertise. I would also like to thank Dr. Paul Kolm for his help on statistical analysis, Dr. Pauline Newlon for making available the Plantar Test Apparatus, and Dr. Gerald Pepe for his expertise on matters o f endocrinology. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.