Electromagnetic fields influence NGF activity and levels following sciaticnerve transection

Pulsed electromagnetic fields (PEMF) have been shown to increase the rate o f nerve regeneration. Transient post-transection loss of target-derived ner ve growth factor (NGF) is one mechanism proposed to signal induction of ear ly nerve regenerative events. We tested the hypothesis that PEMF alter leve ls of NGF activity and protein in injured nerve and/or dorsal root ganglia (DRG) during the first stages of regeneration (6-72 hr), Rats with a transe ction injury to the midthigh portion of the sciatic nerve on one side were exposed to PEMF or sham control PEMF for 4 hr/day for different time period s, NGF-like activity was determined in DRG, in 5-mm nerve segments proximal and distal to the transection site and in a corresponding 5-mm segment of the contralateral nonoperated nerve. NGF-Iike activity of coded tissue samp les was measured in a blinded fashion using the chick DRG sensory neuron bi oassay, Overall, PEMF caused a significant decrease in NGF-like activity in nerve tissue (P < 0.02, repeated measures analysis of variance, ANOVA) wit h decreases evident in proximal, distal, and contralateral nonoperated nerv e. Unexpectedly, transection was also found to cause a significant (P = 0.0 01) 2-fold increase in DRG NGF-like activity between 6 and 24 hr postinjury in contralateral but not ipsilateral DRG, PEMF also reduced NGF-like activ ity in DRG, although this decrease did not reach statistical significance. Assessment of the same nerve and DRG samples using ELISA and NGF-specific a ntibodies confirmed an overall significant (P < 0.001) decrease in NGF leve ls in PEMF-treated nerve tissue, while no decrease was detected in DRG or i n nerve samples harvested from PEMF-treated uninjured rats. These findings demonstrate that PEMF can affect growth factor activity and levels, and rai se the possibility that FEME might promote nerve regeneration by amplifying the early postinjury decline in NGF activity. J. Neurosci. Res. 55:230-237 , 1999. Published 1999 Wiley-Liss, Inc.(dagger)