INHIBITION OF A SOMATIC NOCICEPTIVE REFLEX BY GASTRIC DISTENSION IN HUMANS

Background/Aims: The spinal nociceptive RIII reflex, an exteroceptive cutaneous-muscular flexion reflex, is powerfully and specifically inhi bited by painful heterotopic somatic stimuli. The aim of the present s tudy was to evaluate the effects of nonpainful and painful visceral st imuli on this reflex. Methods: In nine healthy volunteers, the effects of five levels of gastric distention were tested on the RIII reflex, recorded from the biceps femoris, and elicited by electrical stimulati on of the ipsilateral sural nerve. Distentions were performed by means of a balloon that was placed in the proximal part of the stomach and connected to an electronic barostat. The sensations evoked by gastric distention were scored using a graded (0-6) questionnaire. Results: Th e 200- and 400-mL distention levels elicited no significant modificati ons of the RIII reflex; the 600-, 800-, and 1000-mL levels inhibited t he RIII reflex by 25%, 35%, and 55%, respectively. The magnitude of th is inhibition correlated significantly (P < 0.0001) with both the leve l of distention and the intensity of visceral perception. Conclusions: Gastric distention produces volume-dependent inhibition of the somati c RIII reflex in humans. This model may provide an interesting tool fo r objective and quantitative evaluation of normal and disturbed viscer al sensations in humans.