Els van Asselt

Afferent bladder nerve activity in the rat: a mechanism for starting and stopping voiding contractions

The objective of this work was to study the relation between afferent bladder nerve activity and bladder mechanics and the mechanisms that initiate and terminate bladder contractions. Bladder nerve activity, pressure and volume were recorded during the micturition cycle in the rat. The highest correlation was found between afferent nerve activity and stress (pressure×volume). Afferent nerve activity depended linearly on stress within 6%, and both slope and offset were independent of the bladder-filling rate. The levels of afferent bladder nerve activity at the onset and cessation of efferent firing to the bladder were highly reproducible with coefficients of variation of ≤17%. We propose a model in which afferent activity is proportional to bladder wall stress, and bladder contraction is initiated when afferent activity exceeds a threshold due to an increasing pressure and volume. The contraction continues until afferent activity drops below a threshold again as a result of a decreasing volume.

Neurophysiological modeling of voiding in rats: urethral nerve response to urethral pressure and flow

In male urethan-anesthetized rats, activity was measured in nerves that run over the proximal urethra. The urethral nerve response to stepwise urethral perfusion could be described by a four-parameter model (fit error <6%). At the onset of perfusion, the urethra was closed and the pressure increased with the infused volume. The nerve activity (NA) increased linearly with this inserted volume to a maximum (NAmax), which was proportional to the instantaneous pressure. The duration of this first episode (δ t) was inversely proportional to the perfusion rate. After infusion of a fixed volume, the urethra opened and the NA decreased with a time constant ϕ-1 (∼1.8 s) to an elevated level (NAlevel). NAlevel was linearly related to the steady-state pressure. Accordingly, sensors in the urethra are sensitive to pressure rather than to the perfusion rate. The parameters NAmax, NAlevel, and δ t showed very good reproducibility (SD ∼19% of mean). The measured activity was most likely afferent and conducted to the major pelvic ganglion.In male urethan-anesthetized rats, activity was measured in nerves that run over the proximal urethra. The urethral nerve response to stepwise urethral perfusion could be described by a four-parameter model (fit error < 6%). At the onset of perfusion, the urethra was closed and the pressure increased with the infused volume. The nerve activity (NA) increased linearly with this inserted volume to a maximum (NAmax), which was proportional to the instantaneous pressure. The duration of this first episode (delta t) was inversely proportional to the perfusion rate. After infusion of a fixed volume, the urethra opened and the NA decreased with a time constant phi -1 (approximately 1.8 s) to an elevated level (NAlevel). NAlevel was linearly related to the steady-state pressure. Accordingly, sensors in the urethra are sensitive to pressure rather than to the perfusion rate. The parameters NAmax, NAlevel, and delta t showed very good reproducibility (SD approximately 19% of mean). The measured activity was most likely afferent and conducted to the major pelvic ganglion.

Pudendal nerve stimulation induces urethral contraction and relaxation

In this study we measured urethral pressure changes in response to efferent pudendal nerve stimulation in rats. All other neural pathways to the urethra were transected, and the urethra was continuously perfused. We found fast twitch-like contractions, superimposed on a slow relaxation. The amplitude of the twitches was independent of the stimulation frequency below 26 Hz, whereas the relaxation depended highly on this frequency. The twitches were caused by striated urethral muscles, and the relaxation was caused by smooth muscles. Both were mediated by acetylcholine. We calculated the effective urethral relaxation as the absolute relaxation multiplied by the time fraction between the twitches. Maximum effective relaxation occurred at 8-10 Hz, exactly the frequency of spontaneous oscillations during bladder voiding in rats. Although the oscillatory sphincter contractions in rats during voiding may be needed in other mechanisms for efficient voiding, our data suggest that they may be a side effect of the actual purpose: urethral relaxation.

Frequency analysis of urinary bladder pre-voiding activity in normal and overactive rat detrusor

To test the hypothesis that voiding in anesthetized rats is preceded by recurrent changes in the pattern of bladder pressure. To explore the use of frequency analysis as an analytical tool for automatically detecting these changes and to provide quantitative data on bladder pre‐voiding activity.

Neurophysiological modeling of bladder afferent activity in the rat overactive bladder model.

The overactive bladder (OAB) is a syndrome-based urinary dysfunction characterized by “urgency, with or without urge incontinence, usually with frequency and nocturia”. Earlier we developed a mathematical model of bladder nerve activity during voiding in anesthetized rats and found that the nerve activity in the relaxation phase of voiding contractions was all afferent. In the present study, we applied this mathematical model to an acetic acid (AA) rat model of bladder overactivity to study the sensitivity of afferent fibers in intact nerves to bladder pressure and volume changes. The afferent activity in the filling phase and the slope, i.e., the sensitivity of the afferent fibers to pressure changes in the post-void relaxation phase, were found to be significantly higher in AA than in saline measurements, while the offset (nerve activity at pressure ~0) and maximum pressure were comparable. We have thus shown, for the first time, that the sensitivity of afferent fibers in the OAB can be studied without cutting nerves or preparation of single fibers. We conclude that bladder overactivity induced by AA in rats is neurogenic in origin and is caused by increased sensitivity of afferent sensors in the bladder wall.

Threshold for efferent bladder nerve firing in the rat

In this study, the mechanism involved in the initiation of voiding was investigated. Bladder pressure and bladder and urethral nerve activity were recorded in the anesthetized rat. Bladder nerve activity was resolved into afferent and efferent activity by means of a theoretical model. The beginning of an active bladder contraction was defined as the onset of bladder efferent firing at a certain time (t0). From t0 onward, bladder efferent activity increased linearly during deltat seconds (rise time) to a maximum. The pressure at t0 was 1.0 +/- 0.4 kPa, the afferent nerve activity at t0 was 2.0 +/- 0.6 microV (53 +/- 15% of maximum total nerve activity), and deltat was 11 +/- 13 s. Between contractions the afferent activity at t0 was never exceeded. Urethral afferent nerve activity started at bladder pressures of 2.1 +/- 1.1 kPa. Therefore, we concluded that urethral afferent nerve activity does not play a role in the initiation of bladder contractions; voiding contractions presumably are initiated by bladder afferent nerve activity exceeding a certain threshold.In this study, the mechanism involved in the initiation of voiding was investigated. Bladder pressure and bladder and urethral nerve activity were recorded in the anesthetized rat. Bladder nerve activity was resolved into afferent and efferent activity by means of a theoretical model. The beginning of an active bladder contraction was defined as the onset of bladder efferent firing at a certain time ( t 0). From t 0 onward, bladder efferent activity increased linearly during δ t seconds (rise time) to a maximum. The pressure at t 0 was 1.0 ± 0.4 kPa, the afferent nerve activity at t 0 was 2.0 ± 0.6 μV (53 ± 15% of maximum total nerve activity), and δ t was 11 ± 13 s. Between contractions the afferent activity at t 0 was never exceeded. Urethral afferent nerve activity started at bladder pressures of 2.1 ± 1.1 kPa. Therefore, we concluded that urethral afferent nerve activity does not play a role in the initiation of bladder contractions; voiding contractions presumably are initiated by bladder afferent nerve activity exceeding a certain threshold.

Urethane anesthesia in acute lower urinary tract studies in the male rat

Urethane is a widely used anesthetic in animal lower urinary tract research. Our objective was to investigate the quality of anesthesia and the correlation between bladder (voiding) contractions, micturition pressure, bladder capacity and urethane dosage and body weight. Urethane was given subcutaneously and/or intraperitoneally (1.0–1.2 g/kg). The bladder was filled with saline and the bladder pressure was recorded continuously. Animals in which the subcutaneous/intraperitoneal ratio was higher needed less urethane. Heavier animals needed less extra urethane. In animals, in which no bladder contractions could be evoked, the total amount of urethane given was similar to that in those that did show contractions. In the animals that did void, the bladder never emptied completely and residual volumes remained. There was no relationship between animal weight or total amount of urethane and mean capacity. Anesthesia lasted up till 14 h, during which bladder (voiding) contractions could be recorded. Considering all results, we conclude that urethane is a well suited anesthetic for acute lower urinary tract physiological research in the intact rat.

Effect of tibial nerve stimulation on bladder afferent nerve activity in a rat detrusor overactivity model.

To study the post‐stimulation effect of tibial nerve stimulation on rat bladder afferent activity, and urodynamic parameters in normal and acetic acid‐induced detrusor overactivity conditions.

Longitudinal leak point pressure measurements in rats using a modified port à cath system

Stress urinary incontinence, defined as involuntary loss of urine secondary to an increase in abdominal pressure, represents one of the most significant urological problems. Several animal models to simulate stress urinary incontinence have been presented, including methods to quantify leak point pressure. We have modified an existing leak point pressure procedure to longitudinally quantify stress urinary incontinence in rats by introducing the port à cath system. Reproducible leak point pressure measurements were carried out over a period of more than 40 days at different bladder volumes. Leak point pressure neither showed a significant relationship with the number of times anesthesia was applied nor a significant change over time. The port à cath system provided a reliable, sensitive device for longitudinal urinary bladder pressure measurements in animals with an implanted bladder catheter. This set-up therefore enables the evaluation of bladder pressure in different models for stress urinary incontinence, such as vaginal distention or pudendal transection over long periods of time within the same animal.Stress urinary incontinence, defined as involuntary loss of urine secondary to an increase in abdominal pressure, represents one of the most significant urological problems. Several animal models to simulate stress urinary incontinence have been presented, including methods to quantify leak point pressure. We have modified an existing leak point pressure procedure to longitudinally quantify stress urinary incontinence in rats by introducing the port à cath system. Reproducible leak point pressure measurements were carried out over a period of more than 40 days at different bladder volumes. Leak point pressure neither showed a significant relationship with the number of times anesthesia was applied nor a significant change over time. The port à cath system provided a reliable, sensitive device for longitudinal urinary bladder pressure measurements in animals with an implanted bladder catheter. This set‐up therefore enables the evaluation of bladder pressure in different models for stress urinary incontinence, such as vaginal distention or pudendal transection over long periods of time within the same animal.

The frequency spectrum of bladder non-voiding activity as a trigger-event for conditional stimulation: Closed-loop inhibition of bladder contractions in rats

To test the hypothesis that the frequency of bladder non‐voiding contractions (NVCs) can be used as a trigger event for closed‐loop conditional inhibition of detrusor contractions via tibial nerve (TN) or dorsal penile nerve (DPN) stimulation.