Abstract
The suppression of the tail flick reflex by Aβ afferent nerve impulses was investigated in lightly anesthetized rats. Peripheral electrical stimulation (PES) of the hindlimb and the forelimb were applied with the stimulus intensity for eliciting an Aβ component only of the compound action potentials in the common peroneal nerve and the brachial plexus. When only the Aβ component of the compound action potentials was evoked by PES of the hindlimb in the common peroneal nerve, the EMG activity of the tail muscle was suppressed without change of the skin temperature at the beginning of the tail flick (threshold temperature) and the tail flick latency ; the suppressive effect was the same as that of the direct stimulation of Aβ fibers in the common peroneral nerve transected under the capitulum fibulae. The forelimb stimulation also produced the suppression of the EMG activity without change of the threshold temperature and the tail flick latency. For the effect of naloxone, the suppressive effect of the forelimb stimulation was antagonized by naloxone, while that of the hindlimb stimulation failed to be antagonized by naloxone. These results suggest that the existence of the mechanism which suppresses only the EMG activity and should be taken into consideration that the mechanisms of the suppressive effect vary with the difference of dermatomes which receive applications of PES.
