Changes in expression of NGF and related factors in the dorsal root ganglion after median nerve transection

Autor: Ming-Chuan Chang, 張銘娟
Rok vydání: 2007
Druh dokumentu: 學位論文 ; thesis
Popis: 95
Nerve growth factor (NGF) is believed to play a critical role in altering the phenotypic and functional properties of dorsal root ganglion cells after peripheral nerve injury. It is well known that expression of NGF and pain-related neuropeptide in the primary afferent neurons change after peripheral nerve injury of lower limb, but remains uncertain following median nerve injury. In this study, immunocytochemical technique and western blot methods were used to investigate the expression and distribution of NGF, TrkA, p75, substance P and CGRP in the C6 dorsal root ganglion (DRG) at various time points following complete median nerve transection. Quantitative examination showed that the percentage of NGF immunoreactivity (NGF-IR) neurons in the C6 DRG increased at 1 day postoperation (PO) but decreased dramatically at 1 week (24.1%) PO compared with control (32.4%), and it recovered at 2 weeks (26.2%) PO. NGF western blot analysis and immunocytochemistry showed a similar expression pattern, except for the result at 2 weeks. The percentage of TrkA-IR neurons in the DRG increased at 1 week (36.7%) PO compared with control (31.3%) and significantly decreased at 2 weeks (20.2%), then it recovered at 4 weeks (22%). The percentage of p75-IR neurons had no manifest change between various time points, but we found that the p75-IR glia cell surrounding large-diameter neurons was significantly increased with post-injury times. Following p75 western blot analysis showed that the p75 protein level was increased at 1 week PO and peaked at 2 weeks PO. On the other hand, the cell size distribution of NGF-IR neuron was examined. It displayed that the proportions of medium-large neurons increase at 1 week (14.09%) compared with control (8.07%). In addition, we examined the percentage of substance P and CGRP immunoreactive DRG neurons after median nerve transection. The percentage of substance P-IR and CGRP-IR neurons dramatically decreased at 1 week PO and recovered at 2 weeks. These expression patterns are similar to that of NGF. With Fluorogold (FG) injection into the proximal end of transected median nerve, we examined the percentage of NGF-IR, TrkA-IR, substance P-IR and CGRP-IR neurons labeled with FG, respectively, was decreased at 4 weeks compared with that at 1 week. Taken together, the results in this study suggest that the above-mentioned four immunoreactive neurons derived from uninjured neuronal element increase as the extent of nerve injured course. Moreover, under electron microscopy examinations, we detected that several satellite cells surrounding the neurons were expressed NGF and TrkA, it maybe provided evidence to support such implication. Finally, we also examined the expression of NGF and TrkA in the DRG by pre-emptive lidocaine (local analgesic) and tetrodotoxin (TTX, electrical activity blocker) treatments on the median nerve prior to its transection. At 4 weeks PO, there was no significant difference in the expression of NGF and TrkA between pre-empitve and control groups. In the future, we will examine the effect of pre-emptive treatment the on the expression of NGF and TrkA in the DRG at 1 week PO.
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