Partial bladder outlet obstruction in the fetal rabbit

Antenatal biological models in the characterization and research of congenital lower urinary tract disorders

Congenital lower urinary tract disorders are a family of diseases affecting both urinary storage and voiding as well as upstream kidney function. Current treatments include surgical reconstruction but many children still fail to achieve urethral continence or progress to chronic kidney disease. New therapies can only be achieved through undertaking research studies to enhance our understanding of congenital lower urinary tract disorders. Animal models form a critical component of this research, a corner of the triangle composed of human in-vitro studies and clinical research. We describe the current animal models for two rare congenital bladder disorders, posterior urethral valves (PUV) and bladder exstrophy (BE). We highlight important areas for researchers to consider when deciding which animal model to use to address particular research questions and outline the strengths and weaknesses of current models available for PUV and BE. Finally, we present ideas for refining animal models for PUV and BE in the future to stimulate future researchers and help them formulate their thinking when working in this field.

An evaluation of laparoscopic tissue harvesting for human adult urological smooth muscle physiological experimentation

OBJECTIVE

To evaluate the properties of laparoscopically harvested bladder neck and ureteric smooth muscle, compared with tissue obtained at open surgery.

MATERIALS AND METHODS

Bladder neck was harvested from patients undergoing open (eight) or laparoscopic radical prostatectomy (11). Ureter was obtained from patients undergoing nephrectomy (laparoscopic or open) and cystectomy (open only); obtained openly from 16 and laparoscopically from seven. Muscle strips dissected from these samples were perfused in a Brading-Sibley organ bath, and stimulated using standard agonists (100 micromol/L carbachol for bladder neck, 100 mmol/L KCl-enriched Krebs' solution for ureteric muscle). Tensions produced were recorded using strain gauges and analysed using data-acquisition software. Results were compared by a two-tailed Fisher's exact test to determine significance.

RESULTS

Openly harvested bladder neck muscle strips from six patients showed a measurable response to the standard agonist. Laparoscopically harvested bladder neck strips from only two patients showed any measurable response. Openly harvested ureteric muscle strips from 12 patients responded to K-enriched solution, while one patient's laparoscopically harvested strips responded to stimulation. This difference was significant in both tissue groups separately (P < 0.025). Histological evaluation identified no specific differences between openly and laparoscopically harvested tissue.

CONCLUSION

The yield of smooth muscle available for research is significantly less when the resection is laparoscopic; this might be a result of diathermy damage at a subcellular level. With the increasing use of the laparoscopic approach in urological surgery, the effect on tissue availability for human smooth muscle physiological study is important to researchers in this field.

Uropathic observations in mice expressing a constitutively active point mutation in the 5-HT3A receptor subunit

Mutant mice with a hypersensitive serotonin (5-HT)3A receptor were generated through targeted exon replacement. A valine to serine mutation (V13'S) in the channel-lining M2 domain of the 5-HT3A receptor subunit rendered the 5-HT3 receptor 70-fold more sensitive to serotonin and produced constitutive activity when combined with the 5-HT3B subunit. Mice homozygous for the mutant allele (5-HT3Avs/vs) had decreased levels of 5-HT3A mRNA. Measurements on sympathetic ganglion cells in these mice showed that whole-cell serotonin responses were reduced, and that the remaining 5-HT3 receptors were hypersensitive. Male 5-HT3Avs/vs mice died at 2-3 months of age, and heterozygous (5-HT3Avs/+) males and homozygous mutant females died at 4-6 months of age from an obstructive uropathy. Both male and female 5-HT3A mutant mice had urinary bladder mucosal and smooth muscle hyperplasia and hypertrophy, whereas male mutant mice had additional prostatic smooth muscle and urethral hyperplasia. 5-HT3A mutant mice had marked voiding dysfunction characterized by a loss of micturition contractions with overflow incontinence. Detrusor strips from 5-HT3Avs/vs mice failed to contract to neurogenic stimulation, despite overall normal responses to a cholinergic agonist, suggestive of altered neuronal signaling in mutant mouse bladders. Consistent with this hypothesis, decreased nerve fiber immunoreactivity was observed in the urinary bladders of 5-HT3Avs/vs compared with 5-HT3A wild-type (5-HT3A+/+) mice. These data suggest that persistent activation of the hypersensitive and constitutively active 5-HT3A receptor in vivo may lead to excitotoxic neuronal cell death and functional changes in the urinary bladder, resulting in bladder hyperdistension, urinary retention, and overflow incontinence.

Distal urinary obstruction

Despite the sound experimental basis and initial promise of early animal models, the results of antenatal intervention have been disappointing, with high rates of misdiagnosis of urethral valves, complications from vesicoamniotic shunting, perinatal mortality, and long-term renal impairment and bladder dysfunction in survivors. The recent development of a cystoscopic approach might obviate some of these problems, but to date the procedure been limited by technical difficulty in negotiating the urethrovesical angle. Overcoming these difficulties through equipment modifications might allow definitive testing of whether or not alleviating distal urinary obstruction in utero is beneficial.