Modulation of exteroceptive suppression periods in human jaw-closing muscles induced by summation of nociceptive and non-nociceptive inputs.
Convergence of various afferent inputs onto brain-stem neurons may play an important role in the regulation of trigeminal motor function. The present study examined the efficacy of nociceptive and non-nociceptive perioral stimulation for the modulation of the two exteroceptive suppression periods (ES1 and ES2) in human jaw-closing muscles. The inhibitory jaw-reflexes, ES1 (10-15 ms onset) and ES2 (40-50 ms onset), were recorded as the surface electromyogram of masseter and temporalis muscles in 14 healthy subjects. Non-painful electrical stimuli were applied to the right mental nerve while the subject was biting at 50% of the maximal voluntary force. Five conditions were compared: baseline, repetitive tactile stimulation (1 Hz) on the right cheek, topical application of capsaicin (5%) on the right cheek, repetitive tactile stimulation plus capsaicin, and postbaseline. The perceived intensity of the electrical stimuli was evaluated by the subjects on a 0-10 rating scale. Capsaicin alone failed to induce significant changes of ES1 and ES2; tactile stimulation alone induced a significant delay in the onset of ES2 (P < 0.001). During repetitive tactile stimulation plus capsaicin, the duration of ES1 and ES2 was shortened (ES1 and ES2: P < 0.001) and the degree of suppression was reduced (ES1: P < 0.05; ES2: P < 0.005). Perceived intensity of the electrical stimuli was unchanged during the different experimental conditions. The present results suggest that summation of simultaneous nociceptive and non-nociceptive inputs plays an important role in the modulation of the neural pathways involved in the short-latency ES1 and long-latency ES2.
Romaniello
A
A
Center for Sensory-Motor Interaction, Aalborg University, Denmark.
Svensson
P
P
Cruccu
G
G
Arendt-Nielsen
L
L
D000328:Adult; D002211:Capsaicin / Q000008:administration & dosage; D004576:Electromyography; D005157:Facial Pain / Q000139:chemically induced / Q000503:physiopathology; D005260:Female; D006801:Humans; D007568:Jaw / Q000294:innervation* / Q000502:physiology*; D008297:Male; D008406:Masseter Muscle / Q000294:innervation* / Q000502:physiology*; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology; D009413:Nerve Fibers, Myelinated / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology* / Q000648:ultrastructure; D009619:Nociceptors / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012018:Reflex / Q000502:physiology; D014110:Touch / Q000502:physiology
D002211:Capsaicin