Electromyographic Study on Reflex Activity in Abdominal Wall Muscles and Diaphragm Following Pelvic Afferent Excitation in Cats

The intra-abdominal pressure response following electrical stimulation of the central end of the pelvic nerve (pelvico-abdominal reflex) was studied by means of the electromyographic technique in anesthetized cats. The muscles of the abdominal wall and lower intercostal space, and the diaphragm were involved in the reflex activity. The response time distributed in the range of 60-120 msec. The muscle units which could be activated by a single shock to the pelvic nerve were small in number relative to those which could be activated by repetitive stimulation. The summating effect of the double shock stimulus was seen at the shock intervals of 2-30 msec with a maximum at 10-20 msec intervals. A single shock to the pelvic nerve produced a facilitatory state in the reflex arcs lasting approximately 0.5 sec. Repeated stimulation with low frequency pulses appeared to build up an excitatory state which initiated a recruitment of muscle activity and a long lasting after-discharge. Spontaneous firing of muscle activity was most sensitive to anesthesia. It was the first to be affected with a small dose of the drug while the reflex response to pelvic nerve stimulation still persisted. When the depth of anesthesia was increased to a certain extent, the train of reflex discharges was deprived of its delayed component with some prolongation of the response time. Among the group of muscles participating in the abdominal contraction, the abdominal wall muscles were more vulnerable component to anesthesia than the diaphragm.