ABOLITION OF CYSTITIS-INDUCED BLADDER INSTABILITY BY LOCAL SPINAL CORD COOLING

Anatomical tracer injections into the lower urinary tract may compromise cystometry and external urethral sphincter electromyography in female rats

Physiological and anatomical investigations are commonly combined in experimental models. When studying the lower urinary tract (LUT), it is often of interest to perform both urodynamic studies and retrogradely labeled neurons innervating the peripheral target organs. However, it is not known whether the use of anatomical tracers for the labeling of, e.g. spinal cord neurons may interfere with the interpretation of the physiological studies on micturition reflexes. We performed cystometry and external urethral sphincter (EUS) electromyography (EMG) under urethane anesthesia in adult female rats at 5-7 days after injection of a 5% fluorogold (FG) solution or vehicle into the major pelvic ganglia (MPG) or the EUS. FG and vehicle injections into the MPG and EUS resulted in decreased voiding efficiency. MPG injections increased the duration of both bladder contractions and the inter-contractile intervals. EUS injections decreased EUS EMG bursting activity during voiding as well as increased both the duration of bladder contractions and the maximum intravesical pressure. In addition, the bladder weight and size were increased after either MPG or EUS injections in both the FG and vehicle groups. We conclude that the injection of anatomical tracers into the MPG and EUS may compromise the interpretation of subsequent urodynamic studies and suggest investigators to consider experimental designs, which allow for physiological assessments to precede the administration of anatomical tracers into the LUT.

Differential effects of urethane and isoflurane on external urethral sphincter electromyography and cystometry in rats

Urethane is a common and often preferred anesthetic agent for urodynamic recordings in rats, but its use is often restricted to terminal procedures because of a prolonged duration of action and potentially toxic effects. When urodynamic recordings are part of survival procedures in rodent experimental models, inhalation anesthetics, such as isoflurane, are frequently used and generally well tolerated. In this study, we compared the effects of urethane and isoflurane on lower urinary tract function. For this purpose, adult female rats were anesthetized by subcutaneous administration of urethane (n=6) or by inhalation of isoflurane (n=5). Micturition reflexes were assessed by concurrent cystometrogram and external urethral sphincter (EUS) electromyography (EMG) recordings to determine bladder contractile properties, EUS activation patterns, and the coordination between bladder contractions and EUS activation. Compared with urethane, isoflurane reduced frequency of bursts, firing frequency, and amplitude of EUS EMG activity during voiding as well as the EUS EMG amplitude during the bladder filling phase. Isoflurane also prolonged the bladder intercontractile intervals. Other several key functional aspects of the bladder contractile properties as well as the coordination between bladder contractions were not different between the two experimental groups. We conclude that micturition reflexes were differentially affected by isoflurane and urethane. Specifically, isoflurane exhibited a significant suppression of the EUS EMG activity and prolonged the bladder intercontractile intervals compared with urethane. We suggest that these anesthetic properties be taken into consideration during the experimental design and interpretation of urodynamic recordings in rodent models.

Re-established micturition reflexes show differential activation patterns after lumbosacral ventral root avulsion injury and repair in rats

Previous studies have demonstrated that an acute implantation of lesioned lumbosacral ventral roots into the rat conus medullaris (CM) results in functional reinnervation of the lower urinary tract (LUT). Although the root implantation procedure results in a return of reflexive micturition, voiding efficiency (VE) remains incompletely recovered. Here, we performed a detailed urodynamic analysis of cystometry and external urethral sphincter (EUS) electromyography (EMG) recordings to determine underlying mechanisms for the incompletely recovered VE. For this purpose, adult female rats were studied at 12 weeks after a bilateral L5-S2 ventral root avulsion injury followed by an acute surgical implantation of the avulsed L6 and S1 ventral roots into the CM (n=6). Age-matched sham-operated rats (n=6) were included for control purposes. Compared to sham-operated controls, rats of the implanted series showed 1) reflex bladder contractions with a significantly shortened urine expulsion phase, 2) markedly decreased phasic EUS EMG activity during micturition, and 3) a pronounced bladder-sphincter dys-coordination, as demonstrated by a significantly delayed onset of the switch from low-amplitude tonic EUS EMG activity to either phasic EUS EMG activity or a large-amplitude tonic EUS EMG activity during the urine expulsion phase. Our findings provide a mechanistic explanation for the incomplete recovery of the VE following implantation of avulsed ventral roots into the spinal cord. Our future studies will aim to increase successful axonal regeneration in attempts to augment the recovery of the LUT after cauda equina injury and repair.

A standardised mini pig model for in vivo investigations of anticholinergic effects on bladder function and salivation

PURPOSE

The objective was to validate an in vivo model for evaluation of pharmacological effects on bladder function taking the most predominant anticholinergic side effect (hyposalivation) into account. Therefore, two anticholinergic properties (propiverine hydrochloride and tolterodine-L(+)-tartrate) were used to test the in vivo model. Sacral anterior root stimulation (SARS) was performed to induce reproducible and standardized bladder contractions. To evaluate hyposalivation standardised salivavary flow measurements by stimulating the lingual nerve was performed in addition to SARS.

MATERIALS AND METHODS

10 male mini pigs were anaesthetised. The carotid artery was cannulated for blood pressure measurement and the jugular vein for administration of propiverine 0.4 mg kg(-1) b.w. and tolterodine 0.06 mg kg(-1) b.w. For stimulation-induced salivary flow measurements both lingual nerves were exposed and a cuff electrode was placed around the nerves. The bladder was exposed and a cystostomy catheter was inserted to performed cystometrographic measurements during SARS.

RESULTS

In all experiments, for each animal reproducible intravesical pressure values (pves) and salivary flow rates were elicited during electrostimulation before administration of the drug. Bladder pressure: After administration of propiverine, neurostimulation-induced rise in pves had fallen by 60% from the initial value. After administration of tolterodine pves had fallen by about 50%. After additional administration of atropine pves decreased to about 15% of the initial value for both drugs. Salivation: After propiverine salivary flow had fallen by 61%. Inhibition of salivary flow under tolterodine was about 56%. Additional administration of atropine led in both drugs to a nearly complete blockade of salivation. Heart rate (HR) and blood pressure (BP): Directly following intravenous administration of both drugs, a short-term and reversible period of mild but significant fluctuations in HR was observed. There was also a slight but non-significant rise in blood pressure.

CONCLUSIONS

This model allows comparative investigations of various drugs with bladder inhibitory properties in terms of acute efficacy and side effects.

Control of the unstable urinary bladder by graded thermoelectric cooling of the spinal cord

OBJECTIVE

To evaluate local lumbosacral spinal-cord cooling (a novel technique for neuromodulating urinary bladder reflexes) for its feasibility in possible clinical use, by determining the efficacy and the optimum temperature for suppressing reflex urinary incontinence in two rat models of neurogenic urinary bladder instability.

MATERIALS AND METHODS

Overactivity of the detrusor muscle was induced by inflammation of the urinary bladder in a group of rats. A second group of rats was examined 6 weeks after complete midthoracic spinal cord transection, when all animals had developed neurogenic bladder hyper-reflexia. The intravesical pressure, urethral pressure and electromyographic (EMG) activity of the external urethral sphincter (EUS) were recorded simultaneously during repetitive local cooling and re-warming of the dorsal L6/S1 spinal cord segments, using a thermoelectric cooling device.

RESULTS

Spinal cord cooling at L6/S1 had no influence on the recorded values at >26 degrees C, but markedly suppressed detrusor contraction frequency at 21- 25 degrees C. Cooling to <20 degrees C completely and reversibly eliminated inflammation-induced bladder contractions in rats with an intact neural axis and significantly reduced the contraction amplitudes (mean reduction 61%) and duration of contractions in spinally transected rats. Cooling simultaneously increased tonic EUS EMG activity and urethral perfusion pressure in both experimental groups, indicating closure of the urethral outlet. Cooling of adjacent spinal cord segments had no influence on bladder and urethral functions.

CONCLUSION

Cooling the dorsal spinal cord at the origin of the parasympathetic innervation of the bladder can be used to reversibly suppress bladder instability with simultaneous closure of the urethral outlet. Therefore, local spinal cord cooling, e.g. as an implantable thermoelectric device, may offer a suitable method to treat detrusor overactivity and restore continence.