Response Properties of Urethral Distension Evoked Unifiber Afferent Potentials in the Lower Urinary Tract

It is well known that afferent input from the urethra can modulate bladder function. Nevertheless, little is known about the functional properties of urethral afferents. In the current study we investigated the effect of urethral distension on single fiber afferent activities of the lower urinary tract in the female rat.

Female Sprague Dawley® rats were anesthetized. Single fiber afferent activities were recorded from the left L6 dorsal root and classified by conduction velocity. The response of pelvic and pudendal units on urethral distension (60 seconds) was measured. Two distension diameters were measured in the proximal and the distal urethra.

A total of 93 pelvic and 72 pudendal units were isolated in 15 rats. Of the units 20 (8 pelvic and 12 pudendal) were responsive to urethral distension. Three patterns of response could be distinguished, including a fast adapting and 2 groups of slow adapting afferents. The largest grade of distension resulted in the greatest response in both nerves. Five pelvic and 3 pudendal units responded exclusively to proximal distension, 2 pelvic and 5 pudendal units responded to distal distension, and 1 pelvic and 4 pudendal units responded to both types of distension. The responses were reproducible. No association was found between the type of nerve and the location of the response to distension.

This electrophysiological study demonstrates the presence of urethral distension evoked afferents in the pelvic and pudendal nerves, and describes their response to distension. Differences in sensory signaling in type and in location were demonstrated. The current technique can be used for further investigation of urethral afferents.