Effects of tiagabine, a gamma-aminobutyric acid re-uptake inhibitor, on normal rat bladder function

PURPOSE: Previous reports have demonstrated the inhibitory effect of exogenous gamma-aminobutyric acid (GABA) on micturition. In the current study we tested whether tiagabine (Sanofi Synthelab., Newcastle-upon Tyne, United Kingdom), a GABA re-uptake inhibitor increasing endogenous GABA concentrations, would affect micturition in awake rats or influence rat detrusor contraction in vitro. MATERIALS AND METHODS: Nonanesthetized female Sprague-Dawley rats underwent cystometric investigation in a metabolic cage. Micturition was stimulated by infusing saline intravesically. Micturition parameters were recorded and compared before and after drug administration. In vitro the effects of tiagabine on electrical and carbachol induced contractions in bladder strips were investigated. Furthermore, it was studied whether tiagabine interfered with electrically induced release of acetylcholine. RESULTS: Intravenous administration of 5 and 20 mg. kg.-1 tiagabine in 7 and 9 rats decreased micturition pressure a mean plus or minus standard error of mean of 21% +/- 11% and 42% +/- 9%, and decreased voided volume a mean of 31% +/- 9% and 33% +/- 9%, respectively. At 20 mg. kg.-1 tiagabine intravenously increased post-void residual volume a mean of 300% +/- 120% and decreased bladder capacity a mean of 14% +/- 3%. Tiagabine (100 microg.) intrathecally in 7 rats reduced micturition pressure a mean of 34% +/- 10% and increased bladder capacity a mean of 30% +/- 9% and post-void residual volume a mean of 250% +/- 75%. However, voided volume was not changed. In vitro studies demonstrated that tiagabine attenuated bladder contractions induced by electrical field stimulation to a mean of 69% +/- 6% of controls at 100 microM. but did not affect contractions induced by carbachol. Release studies revealed that tiagabine inhibited electrical induced acetylcholine release to a mean of 82% +/- 5% of controls at 100 microM. CONCLUSIONS: The current results show that tiagabine has an inhibitory action on rat micturition. The site of action may be central and peripheral.     

Effects of alpha 1-adrenergic receptor subtype selective antagonists on lower urinary tract function in rats with bladder outlet obstruction

PURPOSE: Antagonists of alpha 1-adrenergic receptors (alpha 1ARs) relieve obstructive and irritative symptoms in patients with bladder outlet obstruction. However, to our knowledge mechanisms underlying the relief of irritative symptoms remain unknown. Because bladder alpha 1dARs are up-regulated in some rats with bladder outlet obstruction, we investigated the effect of the alpha 1aAR antagonist 5-methyl urapidil (5MU) vs the alpha 1a/alpha 1dAR antagonist tamsulosin on urinary frequency in obstructed rats. MATERIALS AND METHODS: Baseline frequency was measured using a chronic micturition recording system and then obstruction (40 rats) or sham obstruction surgery (11 rats) was performed. After 6 weeks frequency was reassessed, followed by subcutaneous implantation of osmotic pumps to deliver 5MU, tamsulosin or vehicle for 1 week. Upon the completion of drug treatment urinary frequency was again measured and the pressor response to the alpha 1AR agonist phenylephrine was documented. RESULTS: Obstructed bladder mass was an average of 4.9 times greater than bladder mass in sham operated rats (p <0.001). Urinary frequency was elevated in obstructed rats with a bladder mass of greater than 500 mg vs all rats with a bladder mass of under 255 mg (p = 0.01). Of rats with a bladder mass of greater than 500 mg frequency was decreased in those treated with tamsulosin (p = 0.03) but not in those treated with 5MU. Tamsulosin and 5MU inhibited the pressor response to phenylephrine. CONCLUSIONS: Urinary frequency is increased in rats with a bladder mass of greater than 500 mg. The combined alpha 1a/alpha 1dAR antagonist tamsulosin decreases urinary frequency more than the alpha 1aAR selective antagonist 5MU. This finding supports the hypothesis that the alpha 1dAR is important for mediating irritative symptoms.     

Sensory neurone-specific receptor-mediated regulation of micturition reflex in urethane-anaesthetized rats

What's known on the subject? and What does the study add? A novel family of G‐protein‐coupled receptors has been identified in rat dorsal root ganglia and named as sensory neuron‐specific receptors (SNSRs) and these receptors are expressed exclusively in a subset of small‐diameter primary afferent neurons involved in transmission of nociceptive information. However, it is not known whether SNSRs have a role in the control of the micturition reflex. This study demonstrated that in urethane‐anaesthetised rats activation of SNSRs can inhibit the micturition reflex via the pathways independent of capsaicin sensitive C‐fibres.

OBJECTIVE

• ? To investigate the effect of sensory neurone‐specific receptors (SNSRs) activation on the micturition reflex in rats.

MATERIALS AND METHODS

• ? Continuous cystometrograms (CMGs, 0.04 mL/min) were performed in female Sprague‐Dawley rats under urethane anaesthesia.
• ? After stable micturition cycles were established, a selective rat SNSR1 agonist, bovine adrenal medulla 8–22 (BAM8–22), was administered intravenously (i.v.) or intrathecally (i.t.) in normal rats or rats pretreated with capsaicin 4 days before the experiments.
• ? Micturition variables were recorded and compared before and after drug administration.

RESULTS

• ? Administration (i.v.) of BAM8–22 (3–100 µg/kg) significantly increased intercontraction intervals in a dose‐dependent fashion, but did not affect residual urine or baseline pressure at any doses tested.
• ? Administration (i.t.) of BAM8–22 (0.01–0.3 µg) also increased intercontraction intervals in a dose‐dependent fashion, but did not affect residual urine or baseline pressure at any doses tested.
• ? These inhibitory effects of i.v. (30 µg/kg) or i.t. (0.3 µg) administration of BAM8–22 still occurred after capsaicin pretreatment.

CONCLUSIONS

• ? These results indicate that in urethane‐anaesthetized rats activation of SNSRs can inhibit the micturition reflex via pathways independent of capsaicin‐sensitive C‐fibres.
• ? Thus SNSRs could be a potential target for the treatment of bladder dysfunction, e.g. overactive bladder.

     

Characterization of pressor and visceromotor reflex responses to bladder distention in rats: sources of variability and effect of analgesics

PURPOSE: We assessed the usefulness of cardiovascular and visceromotor responses to bladder distention as measures of acute visceral nociception in rats by determining the reliability of these responses. MATERIALS AND METHODS: Halothane anesthetized male and female Sprague-Dawley rats were acutely instrumented with tracheal, jugular venous, carotid arterial and bladder cannulas. Wires were inserted into the abdominal musculature to enable myoelectrical activity measurement. Anesthesia was decreased until flexion reflexes were present. Repeat phasic and graded bladder distention was administered, and arterial blood pressure and abdominal electromyography activity were continuously monitored. We determined the effects of gender, vaginal smear estrous cycle stage and drug treatment on the measured responses. RESULTS: Bladder distention produced reliable pressor and visceromotor (abdominal contractile) responses. There was great inter-animal variability in response vigor but good reproducibility was noted within individual animals. During slow bladder filling bladder contractions were not noted at this level of anesthesia. Sex differences included a more vigorous reflex response in females than in males, which was most vigorous in females in proestrus. Repeat bladder distention led to increasingly vigorous pressor responses and the improved reliability of visceromotor responses. Intravenous morphine and lidocaine dose dependently inhibited the reflex responses. CONCLUSIONS: Pressor and visceromotor responses to bladder distention in halothane anesthetized rats are reliable measures of acute bladder nociception that may prove useful for analgesic screening and in studies of hormonal effects on nociception.     

Intravesical oxybutynin: a local anesthetic effect on bladder C afferents

PURPOSE: Intravesical oxybutynin is used to control bladder overactivity in patients who are refractory to or cannot tolerate oxybutynin given orally. Although it is clinically effective, the mode of action of intravesical oxybutynin remains unclear. We tested the influence of intravesical oxybutynin on single fiber pelvic nerve afferents from the rat bladder. MATERIALS AND METHODS: A total of 15 single afferent bladder units were identified. Based on conduction velocity they were grouped as Adelta or C fibers. The effect of repeat bladder filling was studied on the mechanosensitive properties of these units. Oxybutynin was than instilled and left in the bladder for 15 minutes. Unitary afferent activity was again analyzed 15, 60 and 90 minutes after the drug was removed. RESULTS: Repeat bladder filling did not change nerve activity in Adelta or C fibers. At 15 minutes after oxybutynin was washed out of the bladder C fiber afferents responded significantly less to intravesical pressure and volume compared with control filling. At 60 minutes C fibers partly regained mechanosensivity. After 90 minutes sensitivity still increased without achieving the response level before oxybutynin. No significant changes were noted in Adelta fibers during repeat bladder filling or after oxybutynin instillation. CONCLUSIONS: In this study we showed that intravesical oxybutynin has a direct anesthetic effect within the bladder wall. It temporarily desensitizes C fiber afferents, which could explain its clinical benefits in decreasing symptoms of bladder overactivity. No measurable effect was found on Adelta fibers.     

Intravesical resiniferatoxin decreases spinal c-fos expression and increases bladder volume to reflex micturition in rats with chronic inflamed urinary bladders

OBJECTIVE: To evaluate the effect of intravesical resiniferatoxin on spinal c-fos expression and bladder volume at reflex micturition in rats with chronic urinary bladder inflammation. MATERIALS AND METHODS: Of three groups of female Wistar rats, group 1 received cyclophosphamide (75 mg/kg body weight) intraperitoneally every third day (cyclophosphamide is an antitumoral agent that induces bladder inflammation after urinary excretion of its metabolite, acrolein); group 2 comprised sham-inflamed rats that received saline instead of cyclophosphamide, and group 3 received cyclophosphamide, as group 1, every third day but plus 10 nmol/L resiniferatoxin intravesically, through a urethral catheter, at 7 days. At 8 days, under urethane anaesthesia, a needle was inserted in the bladder dome and saline infused at 6 mL/h for 2 h. Finally the animals were perfusion-fixed through the ascending aorta with 4% paraformaldehyde. Transverse sections cut from L6 spinal cord segments were immunoreacted for Fos protein and positive cells in the dorsal horn counted. In a further set of equal groups the bladders were prepared in the same way under urethane anaesthesia and after 30-min of stabilization, saline was infused at 6 mL/h and the volume evoking reflex micturition determined. RESULTS: The mean (SD) number of positive c-fos cells per spinal cord section was 85 (21), 42 (9) (P = 0.002) and 55 (10) in groups 1 to 3, respectively; the values for group 2 and 3 were similar (P = 0.22) and statistically less than that of group 1 (P = 0.02). Reflex micturition occurred at, respectively, 0.26 (0.09), 0.49 (0.18) and 0.52 (0.11) mL, being similar in group 2 and 3 (P = 0.74) but lower in group 1 (P = 0.003). CONCLUSION: Intravesical resiniferatoxin decreases c-fos expression and increases bladder capacity in chronically inflamed rat bladders. These findings suggest that desensitizing the vanilloid receptor type 1 by intravesical resiniferatoxin is relevant to the treatment of pain and voiding frequency in patients with chronic inflammatory bladder conditions.     

Influence of temperature on urethra to bladder micturition reflex in the awake ewe

AIMS: The flow of fluid along the urethra is known to facilitate detrusor contraction during micturition. This reflex, previously described in awake ewes, helps to achieve complete bladder emptying. In anesthetized cats, another urethra to bladder reflex involving urethral cold receptors has been described. The aim of this study was to investigate whether the urethral reflex first described in awake ewes could also be temperature-dependent. METHODS: Experiments were performed on 10 healthy ewes. Urethral flows were performed by injecting 10 ml saline (ranging from 17 to 43 degrees C) at the level of the proximal urethra. Catheterization of the bladder was performed so that detrusor pressure was continually recorded during the experiments. RESULTS: Urethral flows using body temperature saline (37-39 degrees C) consistently evoked detrusor contraction. Urethral flows using saline at temperatures between 40 and 43 degrees C induced detrusor contractions that were not significantly different from those observed at 37-39 degrees C. Urethral flows using saline at temperatures below 37-39 degrees C (17-36 degrees C) resulted in a weaker or absent detrusor contraction. CONCLUSIONS: In ewes, we have shown that urethral to bladder micturition reflex involving mechanoreceptors is decreased at temperatures below the physiological range. It is suggested that transient receptor potential vanilloid cation channels (e.g., TRPV4 which is activated by sheer/stress flows at near-body temperature) could be involved in this urethra to bladder reflex. In humans, this reflex has hardly been described and is still a matter of debate. Our results reinforce that its full investigation may require systematic use of a range of saline flows at different temperatures.     

Role of supraspinal serotonin receptors for micturition in normal conscious rats

Serotonin (5-HT) receptors are widely distributed in the central nervous system, including several areas involved in the control of micturition reflex pathways. However, the roles of the different subtypes of 5-HT receptors are not well known. We studied in normal, conscious rats, the effects on the cystometrogram of intracerebroventricular (i.c.v.) administration of 5-HT, 8-hydroxy-2-(di-N-propylaminotetralin) (8-OH-DPAT; agonist at 5-HT(1A) receptors), alpha-methyl-5-hydroxytryptamine maleate (agonist at 5-HT(2) receptors), 2-methyl-5-hydroxytryptamine hydrochloride (agonist at 5-HT(3) receptors), and 1-(4-amino-5-chloro-2methoxyphenyl)-3-(1-n-butyl-4piperidinyl)-1-propanone hydrochloride (RS67506; agonist at 5-HT(4) receptors). Female Sprague-Dawley rats, weighing approximately 230 g, were used. A polyethylene catheter was inserted into the bladder through the dome for cystometric investigations. For administration of drugs, a catheter was implanted into the right cerebral ventricle. Three days after implantation of the bladder catheter, continuous cystometry was performed. Administration of 5-HT (6 nmol/kg i.c.v.), 8-OH-DPAT (6 nmol/kg), alpha-methyl-5-hydroxytryptamine maleate (6 nmol/kg), or RS67506 hydrochloride (6 nmol/kg) significantly (P < 0.05) increased micturition pressure and decreased bladder capacity and micturition volume. The effects increased in a dose-dependent manner (18, 60 nmol/kg). Intracerebroventricular administration of 2-methyl-5-hydroxytryptamine hydrochloride (60 nmol/kg) caused no change in the cystometric parameters. The results suggest that in normal conscious rats, at the supraspinal level, 5-HT (via 5-HT(1A), 5-HT(2), and 5-HT(4) receptors) can enhance the micturition reflex induced by bladder filling. Whether this means that 5-HT(1A), 5-HT(2), and 5-HT(4) receptors can be targets for drugs meant for treatment of bladder hyperactivity, should be explored.     

The role of endothelin-1 in ischemia-reperfusion induced acute inflammation of the bladder in rats

PURPOSE: Endothelin (ET)-1 is causatively involved in ischemia-reperfusion induced acute inflammatory reactions and microcirculatory disturbances in many organs. We investigated the role of endothelin-1 in the microcirculatory consequences of ischemia-reperfusion of the bladder using intravital fluorescence videomicroscopy. MATERIALS AND METHODS: Male Sprague-Dawley rats were used in the experiments. The animals were randomly assigned to a sham operated group or to 1 of 2 ischemia-reperfusion groups that underwent 60 minutes of ischemia followed by 30 minutes of bladder reperfusion. In 1 ischemia-reperfusion group the animals were pretreated with BQ 610, a specific ET-A receptor blocker. The bladder was placed on an especially designed stage for intravital fluorescence videomicroscopy measurements. Venular red blood cell velocity, functional capillary density, venular and arteriolar diameter, venular and arteriolar macromolecular leakage, and leukocyte-endothelial cell interactions in postcapillary venules were determined using a computer assisted analyzing system. RESULTS: Functional capillary density, red blood cell velocity, venular and arteriolar diameter were significantly decreased and macromolecular leakage was significantly enhanced after bladder ischemia-reperfusion. The number of rolling and adherent leukocytes was significantly increased in postcapillary venules. Pretreatment with BQ 610 was effective for attenuating the effects of ischemia-reperfusion induced inflammation but could not completely prevent microcirculatory failure. CONCLUSIONS: Ischemia-reperfusion induced cystitis leads to significant impairment of the microcirculation and ET-1 is suggested to have an important role in this process. Pretreatment with an ET-A receptor antagonist reduces ischemia-reperfusion related microvascular disturbances in the bladder.     

Rectal distention inhibits bladder activity via glycinergic and GABAergic mechanisms in rats

PURPOSE: We examined the influence of rectal distention on the spinobulbospinal micturition reflex and the mechanism underlying the inhibition of bladder contraction. MATERIALS AND METHODS: A total of 22 female Sprague-Dawley rats were used in this study. Using urethane anesthesia isovolumetric cystometry was performed before and after distention of the rectum by inflation of a rectal balloon (0 to 3 cm3), followed by the intrathecal injection of strychnine (a glycine receptor antagonist, 0.001 to 10 microg) and/or bicuculline (a gamma-aminobutyric acid(A) receptor antagonist, 0.001 to 1 microg) at the lumbosacral level of the spinal cord. RESULTS: Rectal distention (1.5 to 3.0 cm3) prolonged the interval, decreased the amplitude and shortened the duration of bladder contraction and finally almost abolished bladder activity. After intrathecal injection of strychnine or bicuculline in animals with inhibition of the bladder by rectal distention the interval and duration of bladder contraction returned to baseline but amplitude only recovered to 47% to 54% of the control level. However, simultaneous intrathecal injection of strychnine and bicuculline (0.001 microg each) restored amplitude to the control level. There were no differences between strychnine and bicuculline with respect to their effects on the interval, amplitude and duration of bladder contraction. CONCLUSIONS: An inhibitory rectovesical reflex exists in the lumbosacral cord of rats. The afferent limb of the spinobulbospinal micturition reflex pathway may be additionally and redundantly inhibited by glycinergic and GABAergic mechanisms, while the efferent limb of this pathway may be synergistically inhibited by these mechanisms.     

Effects of selective beta2 and beta3-adrenoceptor agonists on detrusor hyperreflexia in conscious cerebral infarcted rats

PURPOSE: We evaluated the effects of beta-adrenoceptor agonists on detrusor hyperreflexia in cerebral infarcted rats. MATERIALS AND METHODS: To produce cerebral infarction in Sprague-Dawley rats the left middle cerebral artery was occluded by introducing a monofilament nylon thread into the artery. In sham operated rats the same artery was exposed but not occluded. After these operations cystometric and cardiovascular experiments were performed with no anesthesia or restraint. RESULTS: After the operation bladder capacity was significantly decreased and voiding pressure was significantly increased in cerebral infarcted but not in sham operated animals. The difference in cerebral infarcted and sham operated rats was significant for each parameter (p <0.01). Post-void residual urine volume was not affected in either group. In the cerebral infarction group intravenous administration of CL316243 ([R,R]-5-2-[[2-(3-chlorophenyl-2-hydroxyethyl]-amino]propyl] -1,3-benzodioxole-2,2-dicarboxylate) (Kissei Central Laboratories, Hotaka, Japan) a selective beta3-adrenoceptor agonist, significantly increased bladder capacity at 10 and 100 microgram./kg. without affecting voiding pressure or post-void residual urine volume. Procaterol, a selective beta2-adrenoceptor agonist, significantly increased bladder capacity and post-void residual urine volume at 10 microgram/kg. intravenously without affecting voiding pressure. In separate experiments procaterol (1 to 100 microgram./kg. intravenously) decreased mean blood pressure and increased heart rate in a dose dependent manner. In contrast, the effects of CL316243 (0.1 to 100 microgram./kg. intravenously) on mean blood pressure and heart rate were minimal. CONCLUSIONS: These results indicate that in cerebral infarcted rats detrusor hyperreflexia can be suppressed by the selective beta3-adrenoceptor agonist CL316243 without increasing post-void residual volume and without significant cardiovascular side effects. If the current results hold true in humans, selective beta3-adrenoceptor agonists may prove useful for treating detrusor hyperreflexia associated with cerebral infarction.     

Bulbocavernosus reflex during the micturition cycle in normal male subjects

BACKGROUND: To investigate normal changes in the bulbocavernosus reflex (BCR) during the micturition cycle, we examined the change in BCR during the micturition cycle using an evoked potential reaction of the BCR (BCR-EP). METHODS: Fourteen normal subjects were examined in the study. The BCR-EP was recorded at empty bladder, filled bladder, during voiding and at empty bladder after voiding. To elicit the BCR-EP, the dorsal nerve of the penis was stimulated by two ring electrodes and an electromyogram of the external urethral sphincter was recorded. The maximum amplitude was measured to evaluate changes in the BCR. RESULTS: The amplitude of the BCR was increased by bladder filling and the ratio of the amplitude at filled bladder/amplitude at empty bladder was 1.32 +/- 0.39. The stable BCR-EP elicited by stimulation at empty bladder disappeared during voluntary voiding in 13 of 14 subjects. However, as stimulation was increased in seven subjects, the BCR-EP was again seen clearly. CONCLUSIONS: The BCR varies during the micturition cycle, although in normal subjects this variation occurs within a relatively narrow range. Changes in the BCR out of the normal range (e.g. large acceleration by bladder filling or insufficient inhibition during voiding) could suggest the existence of neurogenic disease.     

Cholinergic and purinergic contribution to the micturition reflex in conscious rats with long-term bladder outlet obstruction

The urethra of female Wistar rats was partially obstructed for 15 weeks. The effects of atropine (1 mg/kg i.v.), suramin (100 mg/kg i.v.), and a combination of atropine and suramin on the peak micturition pressure (MP) were compared during cystometry in conscious rats controls or subjected to outlet obstruction. On the isolated bladder dome, we studied the inhibitory effect of 1 micromol/L atropine, 1 mmol/L suramin, and the combination of the two drugs on contractions induced by electrical field stimulation (EFS). We studied also the contractile response to 80 mmol/L KCl and the concentration-response curves to noradrenaline, phenylephrine, and carbachol on the bladder dome and bladder neck and alpha, beta-methylene adenosine triphosphate on the bladder dome. In conscious rats, the MP, bladder capacity, and micturition volume were significantly higher in obstructed rats than in controls. Suramin induced the same inhibition in the two groups of animals (-30.7 +/- 13.3% in controls and -29.2 +/- 8.5% in obstructed rats). Atropine decreased the MP, but this effect was twofold greater in obstructed animals (-28.1 +/- 3.1% and -65.1 +/- 6.9% in control and obstructed animals, respectively). However, the combined effect of atropine and suramin was additive in controls but not in obstructed (-56.7 +/- 5.4% and -55.9 +/- 9.4%, respectively). Similar results were obtained in vitro using 1 micromol/L atropine and 1 mmol/L suramin. In the obstructed bladder dome and bladder neck, we found a great reduction in KCl- and carbachol-induced contractility but no difference in the response to EFS. Responses to noradrenaline and phenylephrine were moderately reduced in the bladder neck only, whereas responses to alpha, beta-methylene adenosine triphosphate in the bladder dome were not reduced except at the concentration of 300 micromol/L. We conclude that long-term obstruction in rats could induce cholinergic nerve fiber proliferation as suggested by the decrease in M(3) muscarinic receptor contractility (desensitization) and by a greater sensitivity of the MP to atropine.     

Effect of Gosha-jinki-gan, a blended herbal medicine, on bladder activity in rats

PURPOSE: We investigated the effect of the blended herbal medicine Gosha-jinki-gan on bladder activity and the autonomic nervous system in rats. MATERIALS AND METHODS: A total of 42 female rats were divided into a control diet group of 21 and a Gosha-jinki-gan diet group of 21. Rats in the control diet group were fed a standard diet, while animals in the Gosha-jinki-gan were fed a special diet containing 1.08% Gosha-jinki-gan (TJ107, Tsumura Co., Tokyo, Japan). After 4 weeks 28 rats, including 14 in the control and 14 in the Gosha-jinki-gan group, underwent continuous cystometry with physiological saline or 0.1% acetic acid solution and bladder activity was recorded. The remaining 14 rats were anesthetized with halothane, and body weight, serum amino acid (glutamate and glycine) and plasma monoamine (noradrenaline, adrenaline, dopamine and serotonin) levels were measured. RESULTS: The amplitude of bladder contraction on continuous cystometry with physiological saline was lower in the Gosha-jinki-gan diet group than in the control diet group, and plasma dopamine and serotonin levels were also lower in the Gosha-jinki-gan group. When cystometry was done with 0.1% acetic acid, the interval between bladder contractions was shortened in the control and Gosha-jinki-gan groups. However, the interval and duration of bladder contractions were longer in the Gosha-jinki-gan than in the control group. CONCLUSIONS: These results suggest that Gosha-jinki-gan inhibits bladder activity by maintaining the balance of the sympathetic and parasympathetic nervous systems at a low level.     

Intrathecal glutamate promotes glycinergic neuronal activity and inhibits the micturition reflex in urethane-anesthetized rats

OBJECTIVES: In order to clarify the role of glutamate in the micturition reflex and in glutamatergic and glycinergic neuronal activity, we examined the effects of intrathecal (IT) injection of glutamate or MK-801 (an N-methyl-D-aspartate receptor antagonist) on bladder activity and on the glutamate and glycine levels in the lumbosacral cord of female rats with or without acute lower thoracic spinal cord injury (SCI). METHODS: Under urethane anesthesia, isovolumetric cystometry was performed in rats with or without SCI before and after IT injection of glutamate or MK-801 at the lumbosacral cord level. The glutamate and glycine levels of the whole lumbosacral cord were measured after IT injection of glutamate or MK-801 in both groups. RESULTS: In intact rats, IT glutamate (100 microg) prolonged the interval between bladder contractions and decreased the amplitude of contractions. IT MK-801 (3-100 microg) also prolonged the interval between bladder contractions and decreased the amplitude in intact rats. In SCI rats, cystometry demonstrated the disappearance of bladder contractions, and the glycine level in the lumbosacral cord was elevated. In intact rats, IT glutamate (0.3-100 microg) increased the glycine level in the lumbosacral cord. On the other hand, IT MK-801 (3-100 microg) decreased both glutamate and glycine levels in intact and SCI rats. CONCLUSIONS: These results suggest that glutamatergic neurons have stimulatory projections to both glutamatergic and glycinergic neurons in the lumbosacral cord, and that glutamatergic neurons inhibit the micturition reflex by stimulating glycinergic neurons.     

The vesicocavernosus reflex: Role in the act of micturition

The paper studies the action and clinical significance of a reflex termed vesicocavernosus in 24 healthy volunteers (mean age 44.6 years, 15 men and 9 women). A balloon-tipped catheter was introduced into the urinary bladder and inflated with air in increments of 50 ml up to 300 ml. The response of the two cavernosus muscles to rapid vesical inflation and deflation, as well as to interruption and termination of micturition, was displayed on an EMG apparatus. The muscles contracted upon rapid vesical inflation or deflation, and upon the interruption or termination of micturition. These results were reproducible. In the male, bulbocavernosus muscle contraction seems to compress and expel the urine into the bulbous urethra. Ischiocavernosus muscle contraction helps to elevate the penile shaft. The role of the cavernosus muscles at micturition in women is unknown. The vesicocavernosus reflex could be of diagnostic significance in neurologic conditions.     

Effects of a selective metabotropic glutamate receptor agonist on the micturition reflex pathway in urethane-anesthetized rats

AIMS: To determine a possible role of metabotropic glutamate receptors in the spinobulbospinal micturition reflex pathway in the rat. MATERIALS AND METHODS: A selective metabotropic glutamate receptor agonist, trans-(+/-)-1-amino1,3-cyclopentanedicarboxylic acid (trans-ACPD) was administered to the lumbosacral spinal cord via an intrathecal catheter in urethane anesthetized rats. Amplitude of reflex bladder contractions evoked by bladder distension under isovolumetric condition as well as amplitude of bladder contractions elicited by electrical stimulation of the pontine micturition center (PMC) were examined before and after administration of trans-ACPD. The effect of trans-ACPD on the urethral activity during isovolumetric bladder contractions was also examined by monitoring urethral perfusion pressure and electromyography of the external urethral sphincter (EUS-EMG). RESULTS: Trans-ACPD (3-10 microg) completely inhibited reflex bladder contractions evoked by bladder distension and the duration of inhibition was dose dependent (3 microg: 11.4 +/- 2.8 min, 5 microg: 13.2 +/- 1.3 min, 10 microg: 36.2 +/- 2.4 min). The mean amplitude of bladder contractions evoked by electrical stimulation of the PMC was reduced to 12.6 +/- 2.3% of control by 10 microg of trans-ACPD. In addition, bursting activity of EUS-EMG and corresponding high frequency oscillations of urethral pressure during isovolumetric bladder contractions were completely abolished by 10 microg of trans-ACPD. CONCLUSIONS: These results indicate that intrathecal administration of a selective metabotropic glutamate receptor agonist to the lumbosacral spinal cord has an inhibitory effect on the spinobulbospinal micturition reflex pathway in urethane-anesthetized rats. This pharmacological action is attributed at least to the inhibitory effect on the descending pathway from the PMC to the lumbosacral spinal cord.     

Urethral dysfunction in diabetic rats

PURPOSE: We investigated the effects of diabetes mellitus (DM) on urethral relaxation mechanisms during reflex bladder contractions in rats. MATERIALS AND METHODS: Five weeks after streptozotocin injection (65 mg/kg intraperitoneally) the effects of DM on urethral relaxation mechanisms were evaluated by simultaneous recordings of intravesical pressure under isovolumetric conditions and urethral perfusion pressure (UPP) using urethane anesthesia. RESULTS: In diabetic rats the UPP nadir during urethral relaxation and intravesical pressure thresholds for inducing urethral relaxation were significantly higher (199% and 92%, respectively) than in normal rats, while baseline UPPs were not significantly different. The mean rate and amplitude of high frequency oscillations of urethral striated muscle in diabetic rats were also significantly lower (17% and 64%, respectively) compared with normal rats. Following alpha-bungarotoxin treatment to eliminate striated muscle sphincter contractions intravenous administration of L-arginine (200 mg/kg) [corrected] , the substrate of nitric oxide (NO) synthase, decreased the UPP nadir (36% and 22%, in diabetic and normal rats) as well as intravesical pressure thresholds (49% and 22%, respectively). The effect was greater (61% to 126%) in diabetic rats than in normal rats. In each group of rats the effect of L-arginine was inhibited by Nomega-nitro-L-arginine (100 mg/kg intravenously) [corrected], a NO synthase inhibitor. CONCLUSIONS: During reflex bladder contractions streptozotocin induced diabetic rats exhibited smooth and striated muscle dysfunctions of the urethral outlet. L-arginine therapy, which could augment urethral smooth muscle relaxation by increasing NO production, may be useful for partially restoring the urethral relaxation mechanism in DM.