Tooth pulp-evoked jaw-opening reflex in the cat: evidence for central facilitation induced by noxious discharge in the intradental nerve fibers.
The tooth pulp-evoked jaw-opening reflex was studied in the barbiturate-anesthetized cat. At liminal intensity of the stimulus, a stable short-latency response was obtained in the digastricus and in the tongue. At a higher stimulus intensity, there occasionally appeared to be a prolonged discharge of variable duration in the digastricus, and a second period of activity in the tongue after a silent period. The threshold intensity for these late discharges was supraliminal for the intradental A-fibers and subliminal for intradental C-fibers. Noxious conditioning stimulation of a tooth led to a temporary decrease of the threshold for the jaw-opening reflex elicited from a contralateral or adjacent tooth; only conditioning stimulation at an intensity producing a marked arousal reaction was effective in this respect. Infiltration of the tooth apex with epinephrine produced a local elevation of the threshold for the tooth pulp-evoked jaw-opening reflex. Distant noxious conditioning stimulation (tail pinch) did not influence the jaw-opening threshold. The results indicated that based on some central mechanisms, conditioning noxious stimulation of a tooth can produce a facilitation of the jaw-opening reflex.
D000818:Animals; D002415:Cats; D003213:Conditioning, Psychological / Q000502:physiology; D003782:Dental Pulp / Q000294:innervation* / Q000502:physiology; D005152:Facial Muscles / Q000294:innervation / Q000502:physiology; D007568:Jaw / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D012018:Reflex