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

Abstract

SUMMARY1. A method is described for recording in vivo the action potentials of afferent and efferent fibres in whole nerves supplying the rabbit's uterus.2. Examination of these nerves under the light microscope and the electron microscope showed them to be composed almost entirely of nonmyelinated fibres.3. Two types of spontaneous action potential were observed; one travelled at about 4 m/sec and probably came from the myelinated fibres, the other travelled at 0-4-1-4 m/sec and certainly came from nonmyelinated fibres.4. The efferent fibre spikes were shown to be faster and higher than the spikes from uterine afferent fibres, but slower and smaller than spikes from broad ligament afferent fibres.5. 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.6. The compound action potential evoked by stimulation of the uterine nerve had three peaks, conducted at 1-3, 0-8 and 0-6 m/sec, respectively, and thought to correspond to the fast afferent fibres, the efferent fibres and the slow afferent fibres, respectively. There were also some late peaks due to refiexion of the antidromic action potentials from the ganglion cells.7. Stimulation of the hypogastric nerve also evoked a compound action potential in the uterine nerves. Stimulation of the pelvic nerves had no effect.8. 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.9. It is argued that the spontaneous action potentials came from individual fibres rather than Remak bundles, and that the recording technique used detected the activity of all but the smallest fibres.

THE INNERVATION OF THE RATCERVIX AND ITS PHARMACOLOGY In vitro AND In vivo

“…Nakanishi & Wood (1971) by atropine. Also, electrical stimulation of the pre-ganglionic sacral parasympathetic nerves in the rabbit in vivo only occasionally produced cervical or uterine horn contractions (Schofield, 1952) and did not induce action potentials in uterine nerves (Bower, 1966). Therefore, to date, there has been little evidence for a cholinergic motor uterine innervation.…”

The activity of post‐ganglionic sympathetic nerves to the uterus of the rabbit

“…The action potentials of the afferent and efferent fibres in the uterine nerves were described in a previous paper, and the uterine ganglia were shown to lie in the pelvic plexus (Bower, 1966). In this paper the discharges in the post-ganglionic efferent fibres and ways in which they can be modified are described.…”

“…The activity in the post-ganglionic nerves supplying the uterus was recorded by the technique described previously (Bower, 1966), which was shown to detect the activity of all groups of fibres in the uterine nerves. For comparison records have also been obtained from fine nerves supplying the rabbit's ileum and rectum.…”

“…When either the preganglionic or the postganglionic uterine nerves were stimulated by a single shock, the compound action potentials recorded from the post-ganglionic nerve (Bower, 1966) were followed by a long after-discharge. Figure 4A shows an example of an after-discharge which followed stimulation of the preganglionic fibres in the hypogastric nerve by a single shock.…”

“…When the compound action potential was monitored, together with the after-discharge during stimulation of the post-ganglionic nerve, the threshold and maximum stimuli for the after-discharge were the same as those for the second wave of the compound action potential; that is, for the efferent fibres (Bower, 1966). An increase in the stimulus strength to excite the third wave (the slow afferent fibres) did not cause any increase in the after-discharge.…”