Voiding behavior in awake unrestrained untethered spontaneously hypertensive and Wistar control rats.

The spontaneously hypertensive rat (SHR), a genetic model of high blood pressure, has also been studied as a potential model of overactive bladder. In vivo studies have confirmed the presence of surrogate markers of overactive bladder, including detrusor overactivity, increased urinary frequency, decreased bladder capacity and voided volume (VV), and afferent hypersensitivity to bladder irritation. However, these observations were during awake cystometry using implanted bladder catheters tethered to an infusion pump and artificially filled. We conducted experiments in awake unrestrained untethered age-matched female SHRs and Wistar rats to quantify naïve consumption and voiding behavior and the effect of capsaicin desensitization on consumption and voiding behavior. Food and water consumption, body weight, voiding frequency, and VV were recorded. Rats were placed in metabolism cages for 24 h, up to twice a week, from 17 to 37 wk of age. Compared with Wistar rats, SHRs exhibited decrease in VV and did not exhibit diurnal variation in VV between light and dark periods, suggesting that SHRs may have bladder hypersensitivity. Furthermore, SHRs may also have smaller bladder capacities, as they consumed less water, voided less volume (regardless of light cycle), and had equal urinary frequencies compared with age-matched Wistar rats. We detected no change in SHR voiding behavior following capsaicin desensitization, which was in contrast to a prior awake in vivo cystometry study describing increased VV and micturition interval in SHRs and suggests that C-fiber activity may not contribute to bladder hypersensitivity in SHRs.NEW & NOTEWORTHY We characterized the long-term (20 wk) voiding, defecation, and consumption behavior of age-matched spontaneously hypertensive and Wistar rats without the influence of anesthesia or catheters. Spontaneously hypertensive rats exhibited bladder hypersensitiviy that persisted for the 20-wk duration and was unaffected by capsacin desensitization.

Timing of sacral neurostimulation is important for increasing bladder capacity in the anesthetized rat.

We assessed the effects of limited application of sacral neurostimulation (SNS) during bladder filling on bladder capacity using our previously published SNS model in rats. Female Sprague-Dawley rats (n = 24) were urethane anesthetized (1.2 g/kg sc) and implanted with jugular venous and transvesical bladder catheters. L6/S1 nerve trunks were isolated bilaterally, and two electrodes were placed on each exposed nerve. True bladder capacity (TBC) was determined using stable single-fill cystometrograms. In the first series of experiments, SNS was applied at the onset of bladder filling for 25%, 50%, 75%, and 100% of the previous control filling cycle duration (n = 10). In the second series of experiments, SNS was applied during the first, second, third, and fourth 25% and the first and second 50% of the control fill. In the first series, a significant increase in TBC was observed only when SNS was applied for 75% or 100% of the control fill duration (30% and 35%, respectively, P < 0.05). In the second series, significant increases in TBC only occurred during the fourth 25% period and second 50% period (32% and 43%, respectively, P < 0.001). Results from the second series also revealed an increase in subsequent single-fill bladder capacities (TBC) only when SNS was applied during the second 50% of the prior fill cycle. These data indicate that the application of SNS during the final 50% of the bladder fill cycle is necessary and sufficient for increasing bladder capacity.

The effects of bilateral bipolar sacral neurostimulation on urinary bladder activity during filling before and after irritation in a rat model.

AIMS: To design an optimal rat model for studying sacral neurostimulation (SNS), and examine the effect of SNS on myogenic non-voiding contractions (NVC) during filling before and after intraluminal irritation. METHODS: Bilateral paired bipolar SNS was performed in 10 female urethane anesthetized Sprague-Dawley rats at the L6-S1 trunks at 10 Hz, 0.1 msec pulse duration and 0.15-0.80 mA (below motor threshold). Transvesical cystometry was performed before and during SNS under conditions of control (saline, N = 10) and irritation [0.25% acetic acid (AA), N = 5]. RESULTS: Functional bladder capacity (FBC) and NVC count were significantly increased during SNS under both control and irritation conditions (P < 0.01 for all). In six instances (four in control, two in irritation), micturition reflexes were completely inhibited by SNS resulting in overflow incontinence. Filling compliance, NVC period and NVC maximum amplitude were not affected by SNS (P > 0.05 for all). Non-parametric two-way analysis of variance for repeated measures revealed increased FBC and NVC count during SNS under both control and irritation conditions (P = 0.004 for both, N = 5 rats). Linear regression analysis of NVC count versus FBC revealed a slope significantly different than zero, independent of control or irritation conditions (slope 33.10 ± 2.43, R(2) = 0.81, P < 0.001). CONCLUSIONS: This model achieved reliable, reversible and robust increases in bladder capacity up to overflow incontinence at stimulations below somatic motor threshold. SNS dramatically increased FBC and reversed AA-induced changes without affecting the character of normal NVC associated with bladder filling. Increased number of NVC is simply a consequence of increased fill time.

Characterizing the Bladder's Response to Onabotulinum Toxin Type A Using a Rat Model.

OBJECTIVES: The aim of this study was to characterize the response of the rat bladder neuromuscular system to intramural injection of onabotulinum toxin type A (BoNT/A) over 9 weeks using in vivo cystometry (CMG) and in vitro contractility (IVC). METHODS: Chronic bladder catheters were implanted in female Sprague-Dawley rats, and either (1) BoNT/A (10 units in 20 µL saline) or (2) saline (20 µL) was injected in 5 × 4 µL doses throughout the bladder wall. At 1, 3, 6, and 9 weeks after injection, conscious restrained CMG was performed. At each time point, 25% of each group (8 BoNT/A and 4 controls) was euthanized and bladders harvested for IVC. We measured IVC in response to electric field stimulation, carbachol, and potassium chloride. RESULTS: In total, 47 animals were included; 31 underwent BoNT/A injection, and 16 received sham (saline). Bladder capacities did not differ significantly between groups for each time point. One week after injection BoNT/A animals exhibited significantly longer bladder contraction durations and lower voiding efficiencies compared with controls. By 3 weeks these values returned to control levels. For BoNT/A animals, contractile response to carbachol stimulation was enhanced at 3 weeks. Otherwise, there were no differences in IVC responses. CONCLUSIONS: One week after BoNT/A injection, prolonged bladder contractions are noted in rats. This may reflect supraspinal compensation for denervation by increasing the duration of efferent drive during voiding. After 3 weeks postinjection, we observed no differences in either CMG or IVC responses suggesting either compensatory efferent sprouting, increased gap junction formation, or loss of BoNT/A effect.