Transcutaneous electrical nerve stimulation(TENS), Interferential current therapy(ICT) and Laser are commonly used physical modalities for pain relief in the field of rehabilitation medicine. As many other physical modalities for pain relief, the therapeutic benefits have not been confirmed neurophysiologically by animal research, because of its difficulty of applying to animal. But fictive tail-flick test is an animal research model under anesthesia to evaluate pain, which is capable of applying a physical modalities to animal.
To evaluate the pain relieving effect of physical modalities, we measure the latencies of fictive tail-flick reflex in rat before, immediately after and 20 minutes after TENS, ICT and Laser application. And β-endorphin levels in cerebrospinal fluid of rat were measured quantitatively by radioimmunoassay after TENS, ICT and Laser.
The results obtained were as follows:
1) The latencies of both immediately after and 20 minutes after TENS were 49.25±8.29 msec and 48.80±7.32msec were significantly delayed comparing with that of before TENS(32.97±4.79msec). The latencies of both immediately after and 20 minutes after ICT were 43.75±14.48msec and 47.42±15.07msec were also significantly delayed comparing with that of before ICT (33.23±6.76msec). But no significant chages were observed after Laser application.
2) The β-endorphin levels in cerebrospinal fluid were elevated significantly in TENS(68.19±26.03pmol/l) and ICT group(67.77±20.15pmol/l) comparing with control group(52.27±13.22 pmol/l). But no significant changes were observed in Laser group(49.22±14.06pmol/l).
Above results indicates that pain relief by TENS and ICT was confirmed neurophysiologically, which lasted after completion of TENS and ICT, and central descending inhibition of pain by β-endorphin proved to be a mechanism of pain relief by TENS and ICT.
