Alpha2-adrenoceptor antagonists have been reported to stimulate colonic motor activity, but the effect on colonic motor dysfunction is unclear. We have investigated the effect of alpha 2-adrenoceptor antagonists on wrap-restraint stress-stimulated and normal colonic propulsion in rats. Colonic propulsion was evaluated by the transit of a charcoal marker along the colon. Faecal pellets output was also measured. A 30-min exposure to wrap-restraint stress starting 120 min after infusion of the charcoal marker significantly stimulated colonic transit with a concomitant increase in faecal pellets. Yohimbine and idazoxan, alpha 2-adrenoceptor antagonists, clonidine, an alpha 2-adrenoceptor agonist, and atropine suppressed wrap-restraint stress-stimulated colonic transit and faecal excretion in a dose-dependent manner. Ondansetron and YM060, 5-hydroxytryptamine3 (5-HT3) receptor antagonists, potently inhibited wrap-restraint stress-stimulated colonic transit, but only weakly inhibited faecal excretion. Neither alpha 2-adrenoceptor antagonists nor atropine had any significant effect on normal colonic transit, whereas clonidine and the 5-HT3 receptor antagonists inhibited it. alpha 2-Adrenoceptor antagonists as well as clonidine, atropine and 5-HT3 receptor antagonists inhibit the stress-induced colonic motor dysfunction in rats.
Motor unit action potentials (MUAPs) propagate bidirectionally from the myoneural junction along the muscle fibre. The propagation of excitation within single motor units can be detected during sustained isometric contraction using a surface electrode array. Electromyographic (EMG) signals from an adjacent pair of contacts along the muscle fibres show a very similar wave form with a time shift. In the present study, EMG signals of the masseter and the temporal muscles were obtained from two male adults during clenching in the intercuspal position using the multichannel surface electrode with 17 x 11 contacts. The two-dimensional location of the myoneural junction for each column from the source of the propagation was estimated. Each of the myoneural junctions was located in the lower portion of the masseter muscle and in the upper portion of the temporal muscle. However, the junction was distributed within 10 mm along the muscle fibres at different contraction levels in each muscle. This noninvasive technique of multiple surface electrodes enabled us to add to knowledge of the anatomical structure of the masticatory muscles examined.
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