[Repeated 100 Hz TENS for the treatment of chronic inflammatory pain in rats: optimal parameters and possible neuro-chemical mechanisms].

AIMS: To establish a reliable animal model of chronic arthritic inflammatory pain, to find the optimal parameters and appropriate intervals of repeated 100 Hz transcutaneous electrical nerve stimulation (TENS) for the treatment of the chronic arthritic pain, and to explore the possible central neurochemical mechanisms.

THE

RESULTS

(1) Injection of water-in-oil type complete Freund's adjuvant into the tibio-tarsal joint of the rat produced a reliable, reproducible monoarthritic model. (2) The interval between 2 sessions of stimulations and the intensity of stimulation were important factors determining the therapeutic effects of repeated 100 Hz TENS on both acute and stable period of monoarthritis. (a) For acute period of monoarthritis, the optimal frequency is twice a week, while in the stable period, once a week seems better. (b) The effects of TENS in three intensities: the weaker stimulation was found to produce better results. (3) In the period from 2 to 9 weeks, the levels of spinal release of SP-ir in the TENS group were lower than the control group. This may constitute one of the possible neuro-chemical mechanisms underlying the therapeutic effects of multiple TENS treatment. (4) In both acute and stable period of adjuvant-induced monoarthritis, intrathecal microinjection of Nor-BNI produced dose-dependent increase of arthritic flexion pain scores (i.e. hyperalgesia), suggesting that spinal dynorphin/kappa system plays a role in suppressing arthritic pain.