Modulation of the jaw-opening reflex by peripheral electrical stimulation

Modulation of the jaw-opening reflex (JOR) by peripheral electrical stimulation was studied in the rat. The JOR was evoked by electrical stimuli delivered to the tongue, infraorbital nerve, or tooth pulp chamber, and single-pulse conditioning stimuli were delivered to the forelimb, hind limb, or tail. Threshold current for eliciting the JOR was modulated in a biphasic manner with facilitation when the delay between conditioning and test stimuli was short (peaking at 10 to 15 ms) and inhibition at longer intervals (peaking at 40 to 60 ms). Modulation was similar for all peripheral conditioning sites and was not affected by Fentanyl, naloxone, or picrotoxin. Thus, the modulation of the JOR by single-pulse peripheral electrical stimulation is a widespread, nonsegmental phenomenon, and is probably not associated with the endogenous opiate system. Data collected during the course of this study call into question the usefulness of the JOR elicited by electrical stimulation in the rat incisor tooth pulp chamber as a pain model.