A fictive tail flick reflex in the rat.

The discharges of motor axons participating in the tail flick reflex were recorded from nerve filaments innervating the medial longissimus muscles of anesthetized rats. The reflex discharges evoked by stimulation of the tail with either noxious radiant heat or pinch were recorded before and after paralysis of the animals. Nociceptive discharges recorded from motor axons in the paralyzed state showed a strong correlation with those observed in the absence of the paralytic agent. For this reason, the electrophysiological response triggered by noxious input was termed a 'fictive tail flick reflex'. To evaluate the potential applicability of this model in the analysis of pain blocking mechanisms, vaginal stimulation was found to produce a profound reduction to the nociceptive discharges of the fictive tail flick. By eliminating movement artifacts from the experimental paradigm, this model expands our ability to study a basic nociceptive response which was previously limited to behavioral observation.