The characteristics of spontaneous and evoked action potentials recorded from the rabbit's uterine nerves

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Abstract
A method is described for recording in vivo the action potentials of afferent and efferent fibers in whole nerves supplying the rabbit''s uterus. Examination of these nerves under the light microscope and the electron microscope showed them to be composed almost entirely of non-myelinated fibers. Two types of spontaneous action potential were observed; one travelled at about 4 m/sec and probably came from the myelinated fibers, the other travelled at 0.4-1.4 m/sec and certainly came from non-myelinated fibers. The efferent fiber spikes were shown to be faster and higher than the spikes from uterine afferent fibers, but slower and smaller than spikes from broad ligament afferent fibers. Apart from differences in conduction velocity and height, all spikes were basically similar, lasting about 1.5 msec. The height was related to the square of the velocity. Some more complex spikes were also observed. The compound action potential evoked by stimulation of the uterine nerve has 3 peaks, conducted at 1.3, 0.8 and 0.6 m/sec, respectively, and thought to correspond to the fast afferent fibers, the efferent fibers and the slow afferent fibers, respectively. There were also some late peaks due to reflexion of the antidromic action potentials from the ganglion cells. Stimulation of the hypogastric nerve also evoked a compound action potential in the uterine nerves. Stimulation of the pelvic nerves had no effect. By means of ganglion blocking agents, the uterine ganglia were shown to lie in the pelvic plexus, peripheral to the hypogastric nerve, but central to the uterine nerves. It is argued that the spontaneous action potentials came from individual fibers rather than Remak bundles, and that the recording technique used detected the activity of all but the smallest fibers.

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