Prolonged increase in micturition threshold volume by anogenital afferent stimulation in the rat

To investigate whether anogenital afferent stimulation induces a prolonged increase in the micturition threshold volume of anaesthetized rats.

Thirteen female rats, anaesthetized by alpha-chloralose and paralysed by pancuronium bromide were used for the experiments. The micturition threshold volume was determined by repeated cystometry. In two experiments, afferent activity was recorded from the exposed pudendal nerve; vaginal and anal afferents were stimulated electrically by ring electrodes. In one experiment, the dorsal clitoris nerves were exposed bilaterally and mounted for electrical stimulation. The afferents were stimulated continuously for 5 min at 10 Hz, using unipolar cathodic pulses of 0.5 ms duration with an amplitude of 10 mA (or 0.8 mA for the dorsal clitoral nerves).

Anogenital stimulation for 5 min induced a significant and prolonged increase in the micturition threshold volume (from a median value of 0.35 mL before to 0.45 mL after stimulation; P < 0.01). The increase in threshold volume was maintained for about 40 min after the end of stimulation. There was no obvious difference in effect between the stimulation sites nor with direct dorsal clitoral nerve stimulation. Neither the micturition threshold pressure nor the maximal contraction pressure were altered by stimulation. No tonic afferent after-discharge could be detected in the pudendal nerve recordings.

Artificial electrical stimulation of anogenital afferents induced a prolonged increase in the micturition threshold volume of anaesthetized rats. The change presumably involved the modulation of the synaptic transmission in the central micturition reflex pathway. It is proposed that the observed change represents the first step in the curative 're-education' process induced in patients with urge incontinence by electrical stimulation of anovaginal afferents.