Prolonged enhancement of the micturition reflex in the cat by repetitive stimulation of bladder afferents

Abstract

1. Prolonged modulation of the parasympathetic micturition reflex was studied in cats anaesthetized by alpha-chloralose. Reflex discharges were recorded from a thin pelvic nerve filament to the bladder and evoked by stimulation of the remaining ipsilateral bladder pelvic nerves or urethral branches of the pudendal nerve. 2. Stimulation of bladder or urethral afferents at Adelta intensity evoked micturition reflexes with a latency of 90-120 ms. Such reflexes were much enhanced following repetitive conditioning stimulation of the same afferents at 20 Hz for 5 min. 3. The reflex enhancement lasted more than 1 h after the conditioning stimulation. The effect was not prevented by a preceding complete transection of the sympathetic supply to the bladder. A prolonged suppression of the reflex was obtained after conditioning stimulation of afferents in the dorsal clitoris nerves. 4. It is proposed that the prolonged modulations of the micturition reflex represent physiological adaptive processes, which preserve a flawless function of the bladder during life. The observations provide a theoretical explanation for the beneficial effect of electric nerve stimulation in patients with voiding disorders.

Figure 1. Schematic diagram of experimental arrangements

Reflex discharges were recorded in a transected thin bladder branch of the right pelvic nerve following electrical stimulation of Aδ afferents in the remaining ipsilateral pelvic nerve fibres to the bladder. In two animals, similar reflexes were evoked by stimulation of urethral branches of the pudendal nerve. Inhibitory effects were induced in three experiments by stimulation of the dorsal clitoris nerves. Two animals had their hypogastric nerves and sympathetic chains transected bilaterally. Further details are given in the text.

Figure 2. Effect of conditioning stimulation on the micturition reflex

A, upper trace shows a test response evoked by a train of three constant current stimuli (0.2 ms, 10 ms apart) applied to the ipsilateral bladder pelvic nerves. The stimulus repetition rate was 1 Hz and the intensity 30 μA, maximal for the Aδ reflex response. The middle trace is the same response full-wave rectified. The lower trace is an average of 20 consecutive rectified test reflex responses. B, similar responses as in A but evoked 20 min after a period of conditioning stimulation of the same bladder pelvic nerves. The conditioning consisted of 5 min of continuous repetitive stimulation at 20 Hz (single stimuli) at the same intensity as for the test response. The bladder was filled with 8 ml of saline. Time calibration in B refers to all traces.

Figure 3. Time course and selectivity of micturition reflex enhancement

Records in A show test reflexes evoked before (upper pair of traces) and 20 min after a period of conditioning stimulation of the bladder pelvic nerves (BPN) as in Fig. 2 (lower pair of traces). Each trace is the average of 32 consecutive test reflexes. The upper response in each pair was evoked by stimulation of bladder Aδ afferents (3 × 200 μA), the lower response by stimulation of urethral afferents (3 × 500 μA). The stimulation intensity was in both cases adjusted to give a maximal reflex discharge. The time calibration is for all records. B shows the time course of reflex enhancement after the same conditioning stimulation. The reflex size was determined from the area under the averaged response curve and normalized with respect to the mean prestimulus size. Reflexes evoked by bladder afferent stimulation are indicated by •, those from urethral afferents by ○. The bladder was empty and open throughout.

Figure 4. Depression of enhanced micturition reflex by stimulation of afferents in the dorsal clitoris nerve

The bladder Aδ reflex was enhanced by conditioning stimulation of the same bladder afferents (BPN, first column), as in Fig. 2 (same experiment). About 60 min later, a second period of conditioning stimulation of afferents in the dorsal clitoris nerve (DC, second bar; 10 Hz, 500 μA, 5 min) completely suppressed the reflex response. The reflex response was partially restored when the bladder, after about 20 min, was filled with an additional 10 ml of saline to the original 8 ml. A third period of conditioning stimulation of bladder afferents completely restored the reflex size to the same level as before the depression. •, normalized reflex response from averages of 20 individual reflexes.