Activation and inhibition of the micturition reflex by penile afferents in the cat

Coordination of the urinary bladder and the external urethral sphincter is controlled by descending projections from the pons and is also subject to modulation by segmental afferents. We quantified the effects on the micturition reflex of sensory inputs from genital afferents traveling in the penile component of the somatic pudendal nerve by electrical stimulation of the dorsal nerve of the penis (DNP) in alpha-chloralose anesthetized male cats. Depending on the frequency of stimulation (range, 1-40 Hz), activation of penile afferents either inhibited contractions of the bladder and promoted urine storage or activated the bladder and produced micturition. Stimulation of the DNP at 5-10 Hz inhibited distension-evoked contractions and increased the maximum bladder capacity before incontinence. Conversely, stimulation at 33 and 40 Hz augmented distension-evoked contractions. When the bladder was filled above a threshold volume (70% of the volume necessary for distension-evoked contractions), stimulation at 20-40 Hz activated de novo the micturition reflex and elicited detrusor contractions that increased voiding efficiency compared with distension-evoked voiding. Electrical stimulation of the DNP with a cuff electrode or percutaneous wire electrode produced similar results. The ability to evoke detrusor contractions by activation of the DNP was preserved following acute spinal cord transection. These results demonstrate a clear role of genital afferents in modulating the micturition reflex and suggest the DNP as a potential target for functional restoration of bladder control using electrical stimulation.     

Gentle Mechanical Skin Stimulation Inhibits Micturition Contractions via the Spinal Opioidergic System and by Decreasing Both Ascending and Descending Transmissions of the Micturition Reflex in the Spinal Cord

Recently, we found that gentle mechanical skin stimulation inhibits the micturition reflex in anesthetized rats. However, the central mechanisms underlying this inhibition have not been determined. This study aimed to clarify the central neural mechanisms underlying this inhibitory effect. In urethane-anesthetized rats, cutaneous stimuli were applied for 1 min to the skin of the perineum using an elastic polymer roller with a smooth, soft surface. Inhibition of rhythmic micturition contractions by perineal stimulation was abolished by naloxone, an antagonist of opioidergic receptors, administered into the intrathecal space of the lumbosacral spinal cord at doses of 2–20 μg but was not affected by the same doses of naloxone administered into the subarachnoid space of the cisterna magna. Next, we examined whether perineal rolling stimulation inhibited the descending and ascending limbs of the micturition reflex. Perineal rolling stimulation inhibited bladder contractions induced by electrical stimulation of the pontine micturition center (PMC) or the descending tract of the micturition reflex pathway. It also inhibited the bladder distension-induced increase in the blood flow of the dorsal cord at L5–S1, reflecting the neural activity of this area, as well as pelvic afferent-evoked field potentials in the dorsal commissure at the lumbosacral level; these areas contain long ascending neurons to the PMC. Neuronal activities in this center were also inhibited by the rolling stimulation. These results suggest that the perineal rolling stimulation activates the spinal opioidergic system and inhibits both ascending and descending transmissions of the micturition reflex pathway in the spinal cord. These inhibitions would lead to the shutting down of positive feedback between the bladder and the PMC, resulting in inhibition of the micturition reflex. Based on the central neural mechanisms we show here, gentle perineal stimulation may be applicable to several different types of overactive bladder.     

Sprouting of substance P-expressing primary afferent central terminals and spinal micturition reflex NK1 receptor dependence after spinal cord injury

The primary afferent neurotransmitter triggering the spinal micturition reflex after complete spinal cord injury (SCI) in the rat is unknown. Substance P detected immunohistochemically in the sacral parasympathetic nucleus was significantly higher in 12 SCI rats than in 12 spinally intact rats (P = 0.008), suggesting substance P as a plausible candidate for the primary afferent neurotransmitter. The effects of the tachykinin NK1 receptor antagonist L-733060 on the spinal micturition reflex were then determined by performing conscious cystometry in an additional 14 intact rats and 14 SCI rats with L-733060 (0.1-100 microg) administered intrathecally at L6-S1. L-733060 was without effect in intact rats, but blocked the spinal micturition reflex in 10 of 14 SCI rats and increased the intermicturition interval in 2 of 4 others at doses ranging from 10 to 100 microg. Both phasic and nonphasic voiding contractions, differentiated according to the presence of phasic external urethral sphincter (EUS) activity, were present in most SCI rats. Both types of contractions were blocked by high doses of L-733060. Interestingly, there was a relative decline in phasic voiding contractions at high doses as well as a decline in contraction amplitude in nonphasic voiding contractions. In other respects, cystometric variables were largely unaffected in either spinally intact or SCI rats. L-733060 did not affect tonic EUS activity at any dose except when the spinal micturition reflex was blocked and tonic activity was consequently lost. These experiments show that tachykinin action at spinal NK1 receptors plays a major role in the spinal micturition reflex in SCI rats.     

The effect of vasoactive intestinal polypeptide (VIP) on the canine gallbladder motility.

1. VIP at doses of 10(-9) to 10(-8) M was ineffective and at doses of 5 x 10(-8) to 10(-7) M exerted a slight inhibitory effect on the tone of the canine gallbladder muscle strip. However, VIP (0.1-1 micrograms/kg) injected intravenously (i.v.) in conscious dogs dose-dependently decreased the gallbladder pressure. 2. VIP did not influence significantly the acetylcholine (ACh)- or carbachol- induced contractions of canine gallbladder under in vitro or in vivo conditions, but it decreased the electrically-induced, atropine-sensitive contractions of gallbladder muscle strips. 3. VIP (5 x 10(-9) to 5 x 10(-8) M) did not influence significantly the dose-response curve for cholecystokinin octapeptide (CCK OP) of canine and guinea-pig gallbladder muscle strips. VIP injected i.v. (0.1-0.5 micrograms/kg) in conscious dogs greatly decreased the CCK OP-induced gallbladder pressure.     

Effect of the NK-1 receptor antagonist GR 82,334 on reflexly-induced bladder contractions.

The effect of intrathecal administration of the novel tachykinin NK-1 receptor antagonist GR 82,334 has been tested in three reflexes which excite urinary bladder motility. GR 82,334 at 1 but not at 0.1 nmol/rat blocked the chemonociceptive micturition reflex induced by the topical application of capsaicin (4 micrograms/50 microliters) onto the urinary bladder. At the same dose proven effective in the chemonociceptive reflex, GR 82,334 did not affect either micturition reflex induced by bladder filling or the urinary bladder contraction induced by perineal pinching. These results suggest that, in urethane-anesthetized rats, specific stimuli applied in the periphery activate NK-1 receptors at spinal cord level facilitating urinary bladder reflex contractions.     

Activation of the external urethral sphincter central pattern generator by a 5-HT(1A) receptor agonist in rats with chronic spinal cord injury

We recently demonstrated that treatment with the 5-HT(1A/7) receptor agonist [(R)-(+)-8-hydroxy-2-di-n-propylamino]tetralin (8-OH-DPAT) increases bladder capacity in chloralose-anesthetized female cats with chronic spinal cord injury. In the current study, we investigated the effects of 8-OH-DPAT on bladder capacity and external urethral sphincter (EUS) activity in urethane-anesthetized female rats (initial body mass 175-200 g) with chronic spinal cord injury (transsection at T10). Cystometric study took place 8-12 wk posttranssection. Intravesical pressure was monitored in urethane-anesthetized rats with a transvesical catheter, and EUS activity was assessed electromyographically. Spinal cord injury disrupts phasic activity of the EUS, resulting in decreased voiding efficiency and increased residual volume. 8-OH-DPAT induced a dose-dependent decrease in bladder capacity (the opposite of its effect in chronic spinal cord-injured cats) with an increase in micturition volume and decrease in residual volume resulting from improvement in voiding efficiency. The unexpected improvement in voiding efficiency can be explained by the 8-OH-DPAT-induced emergence of phasic EUS relaxation. Phasic EUS relaxation was also altered by 8-OH-DPAT in spinally intact rats, whereas the 5-HT(1A) receptor antagonist N-tert-butyl-3-[4-(2-methoxyphenyl)-piperazin-1-yl]-2-phenylpropanamide (WAY-100635), on its own, was without effect. It remains to be determined when phasic relaxation is restored after spinal cord injury, and indeed whether it is ever truly lost or is only temporarily separated from excitatory input.     

Menthol Inhibits Detrusor Contractility Independently of TRPM8 Activation

Agonists such as icilin and menthol can activate the cool temperature-sensitive ion channel TRPM8. However, biological responses to menthol may occur independently of TRPM8 activation. In the rodent urinary bladder, menthol facilitates the micturition reflex but inhibits muscarinic contractions of the detrusor smooth muscle. The site(s) of TRPM8 expression in the bladder are controversial. In this study we investigated the regulation of bladder contractility in vitro by menthol. Bladder strips from wild type and TRPM8 knockout male mice (25–30 g) were dissected free and mounted in organ baths. Isometric contractions to carbachol (1 nM–30 µM), CaCl₂ (1 µM to 100 mM) and electrical field stimulation (EFS; 8, 16, 32 Hz) were measured. Strips from both groups contracted similarly in response to both carbachol and EFS. Menthol (300 µM) or nifedipine (1 µM) inhibited carbachol and EFS-induced contractions in both wild type and TRPM8 knockout bladder strips. Incubation with the sodium channel blocker tetrodotoxin (1 µM), replacement of extracellular sodium with the impermeant cation N-Methyl-D-Glucamine, incubation with a cocktail of potassium channel inhibitors (100 nM charybdotoxin, 1 µM apamin, 10 µM glibenclamide and 1 µM tetraethylammonium) or removal of the urothelium did not affect the inhibitory actions of menthol. Contraction to CaCl₂ was markedly inhibited by either menthol or nifedipine. In cultured bladder smooth muscle cells, menthol or nifedipine abrogated the carbachol or KCl-induced increases in [Ca²⁺]_i. Intravesical administration of menthol increased voiding frequency while decreasing peak voiding pressure. We conclude that menthol inhibits muscarinic bladder contractions through blockade of L-type calcium channels, independently of TRPM8 activation.     

Micturition-suppressing region in the periaqueductal gray of the mesencephalon of the cat

The periaqueductal gray (PAG) of the mesencephalon has been implicated to be involved in the control of micturition. We investigated the micturition-suppressing region in the PAG of the cat. Decerebrated 27 adult cats were used. A microelectrode was inserted stereotaxically into the PAG, and a region was searched where electrical stimulation suppressed isovolumetric bladder contractions. Simultaneous stimulation of the pontine micturition center (PMC) and micturition-suppressing region in the PAG was performed before and after an injection of bicuculline (GABA(A) blocker) into the PMC. The micturition-suppressing region was found at the dorsolateral margin of the rostral PAG. Bladder contractions were not provoked by simultaneous stimulation of the PMC and micturition-suppressing region in the PAG. However, after bicuculline injection into the PMC, partial bladder contractions were provoked by simultaneous stimulation of the PMC and the micturition-suppressing region in the PAG. These results suggest that the dorsolateral margin of the rostral PAG includes the micturition-suppressing region that seems to have neural connections with the PMC. GABA is assumed to be one of the neurotransmitters that are involved in the PMC inhibition from the micturition-suppressing region in the PAG.     

Role of pudendal afferents in voiding efficiency in the rat

The reciprocal activities of the bladder and external urethral sphincter (EUS) are coordinated by descending projections from the pontine micturition center but are subjected to modulation by peripheral afferent inputs. Transection of the somatic pudendal nerve innervating the striated EUS decreases voiding efficiency and increases residual urine in the rat. The reduction in voiding efficiency was attributed to the lack of phasic bursting activity of the EUS following denervation. However, transection of the pudendal nerve also eliminates somatic sensory feedback that may play a role in voiding. We hypothesized that feedback from pudendal afferents is required for efficient voiding and that the loss of pudendal sensory activity contributes to the observed reduction in voiding efficiency following pudendal nerve transection. Quantitative cystometry in urethane anesthetized female rats following selective transection of pudendal nerve branches, following chemical modulation of urethral afferent activity, and following neuromuscular blockade revealed that pudendal nerve afferents contributed to efficient voiding. Sensory feedback augmented bladder contraction amplitude and duration, thereby increasing the driving force for urine expulsion. Second, sensory feedback was necessary to pattern appropriately the EUS activity into alternating bursts and quiescence during the bladder contraction. These findings demonstrate that the loss of pudendal sensory activity contributes to the reduction in voiding efficiency observed following pudendal nerve transection, and illustrate the importance of urethral sensory feedback in regulating bladder function.     

Suppression of detrusor-sphincter dysynergia by GABA-receptor activation in the lumbosacral spinal cord in spinal cord-injured rats

We investigated the effects of intrathecal application of GABAA- or GABAB-receptor agonists on detrusor-sphincter dyssynergia (DSD) in spinal cord transection (SCT) rats. Adult female Sprague-Dawley rats were used. At 4 wk after Th9-10 SCT, simultaneous recordings of intravesical pressure and urethral pressure were performed under an awake condition to examine the effect of intrathecal application of GABAA and GABAB agonists (muscimol and baclofen, respectively) or GABAA and GABAB antagonists (bicuculline and saclofen, respectively) at the level of L6-S1 spinal cord. In spinal-intact rats, the effects of bicuculline and saclofen on bladder and urethral activity were also examined. During urethral pressure measurements, DSD characterized by urethral pressure increases during isovolumetric bladder contractions were observed in 95% of SCT rats. However, after intrathecal application of muscimol or baclofen, urethral pressure showed urethral relaxation during isovolumetric bladder contractions. The effective dose to induce inhibition of urethral activity was lower compared with the dose that inhibited bladder contractions. The effect of muscimol and baclofen was antagonized by intrathecal bicuculline and saclofen, respectively. In spinal-intact rats, intrathecal application of bicuculline induced DSD-like changes. These results indicate that GABAA- and GABAB-receptor activation in the spinal cord exerts the inhibitory effects on DSD after SCT. Decreased activation of GABAA receptors due to hypofunction of GABAergic mechanisms in the spinal cord might be responsible, at least in part, for the development of DSD after SCT.     

Urinary bladder function in conscious rat pups: a developmental study

Cystometric studies of bladder function in anesthetized neonatal rats have suggested specific changes in urodynamic parameters that coincide with the development of a mature bladder-to-bladder micturition reflex. Here, we used a conscious cystometry model that avoids the potentially confounding effects of anesthesia to characterize voiding patterns and urodynamic parameters during early postnatal development in healthy rat pups. Cystometry was performed on postnatal day (P)0, 3, 7, 14, and 21 rats with continuous intravesical instillation of NaCl via a bladder catheter. Micturition cycles were analyzed with respect to voiding pattern, nonvoiding contractions, infused volume, and basal, filling, threshold, and micturition pressures. Reproducible micturition patterns were obtained from all age groups. The time from stimulation to contraction was significantly longer (P ≤ 0.001) in ≤1-wk-old rats (～10 s) than that in older rats (～3 s). An interrupted voiding pattern was observed in ≤10-day-old subgroups. Micturition pressure progressively increased with age (from 21.77 ± 1.92 cmH(2)O at P0 to 35.47 ± 1.28 cmH(2)O at P21, P ≤ 0.001), as did bladder capacity. Nonvoiding contractions were prominent in the P3 age group (amplitude: 4.6 ± 1.3 cmH(2)O, frequency: ～4.0 events/100 s). At P7, the pattern of spontaneous contractions became altered, acquiring a volume-related character that persisted in a less prominent manner through P21. Bladder compliance increased with age, i.e., maturation. In conclusion, conscious cystometry in rat pups resulted in reproducible micturition cycles that yielded consistent data. Our results revealed immature voiding and prolonged micturition contractions during the first 10 neonatal days and provide evidence for age-related changes in urodynamic parameters.     

Role for pituitary adenylate cyclase activating polypeptide in cystitis-induced plasticity of micturition reflexes

Pituitary adenylate cyclase activating polypeptide (PACAP) peptides are expressed and regulated in sensory afferents of the micturition pathway. Although these studies have implicated PACAP in bladder control, the physiological significance of these observations has not been firmly established. To clarify these issues, the roles of PACAP and PACAP signaling in micturition and cystitis were examined in receptor characterization and physiological assays. PACAP receptors were identified in various tissues of the micturition pathway, including bladder detrusor smooth muscle and urothelium. Bladder smooth muscle expressed heterogeneously PAC(1)null, PAC(1)HOP1, and VPAC(2) receptors; the urothelium was more restricted in expressing preferentially the PAC(1) receptor subtype only. Immunocytochemical studies for PAC(1) receptors were consistent with these tissue distributions. Furthermore, the addition of 50-100 nM PACAP27 or PACAP38 to isolated bladder strips elicited transient contractions and sustained increases in the amplitude of spontaneous phasic contractions. Treatment of the bladder strips with tetrodotoxin (1 muM) did not alter the spontaneous phasic contractions suggesting direct PACAP effects on bladder smooth muscle. PACAP also increased the amplitude of nerve-evoked contractions. By contrast, vasoactive intestinal polypeptide had no direct effects on bladder smooth muscle. In a rat cyclophosphamide (CYP)-induced cystitis paradigm, intrathecal or intravesical administration of PAC(1) receptor antagonist, PACAP6-38, reduced cystitis-induced bladder overactivity. In summary, these studies support roles for PACAP in micturition and suggest that inflammation-induced plasticity in PACAP expression in peripheral and central micturition pathways contribute to bladder dysfunction with cystitis.     

Excitatory effects of bombesin receptors in urinary tract of normal and diabetic rats in vivo

Aims

Bombesin receptors (BB receptors) and bombesin related peptides are expressed in the lower urinary tract of rodents. Here we investigated whether in vivo activation of BB receptors can contract the urinary bladder and facilitate micturition in sham rats and in a diabetic rat model of voiding dysfunction.

Material and methods

In vivo cystometry experiments were performed in adult female Sprague–Dawley rats under urethane anesthesia. Diabetes was induced by streptozotocin (STZ; 65 mg/kg, i.p.) injection. Experiments were performed 9 and 20 weeks post STZ-treatment. Drugs included neuromedin B (NMB; BB1 receptor preferring agonist), and gastrin-releasing peptide (GRP; BB2 receptor preferring agonist).

Key findings

NMB and GRP (0.01–100 μg/kg in sham rats; 0.1–300 μg/kg in STZ-treated rats, i.v.) increased micturition frequency, bladder contraction amplitude and area under the curve dose dependently in both sham and STZ-treated rats. In addition, NMB (3, 10 μg/kg i.v.) triggered voiding in > 80% of STZ-treated rats when the bladder was filled to a sub-threshold voiding volume. NMB and GRP increased mean arterial pressure and heart rate at the highest doses, 100 and 300 μg/kg.

Significance

Activation of bombesin receptors facilitated neurogenic bladder contractions in vivo. Single applications of agonists enhanced or triggered voiding in sham rats as well as in the STZ-treated rat model of diabetic voiding dysfunction. These results suggest that BB receptors may be targeted for drug development for conditions associated with poor detrusor contraction such as an underactive bladder condition.     

Spinal mechanism of micturition reflex inhibition by naftopidil in rats

Aim

We investigated the spinal mechanism through which naftopidil inhibits the micturition reflex by comparing the effects of noradrenaline and naftopidil in rats.

Methods

The following were investigated: the influence of oral naftopidil on plasma monoamine and amino acid levels, the distribution of oral 14C-naftopidil, the effects of intravenous (IV) or intrathecal (IT) injection of noradrenaline or naftopidil on isovolumetric bladder contractions, amino acid levels in the lumbosacral spinal cord after IT noradrenaline or naftopidil, and the effects of IT naftopidil and strychnine and/or bicuculline on isovolumetric bladder contractions.

Key findings

Oral naftopidil decreased the plasma adrenaline level, while it increased the serotonin and glycine levels. After oral administration, 14C-naftopidil was detected in the spinal cord and cerebrum, as well as in plasma and the prostate gland. When the bladder volume was below the threshold for isovolumetric reflex contractions, IV (0.1 mg) or IT (0.1 μg) noradrenaline evoked bladder contractions, but IV (1 mg) or IT (0.01–1 μg) naftopidil did not. When the bladder volume was above the threshold for isovolumetric reflex contractions, IV or IT noradrenaline transiently abolished bladder contractions. IT noradrenaline decreased the levels of glycine and gamma-aminobutyric acid (GABA) in the lumbosacral cord, while IT naftopidil increased the GABA level. IT strychnine and/or bicuculline blocked the inhibitory effect of IT naftopidil on bladder contractions.

Significance

Naftopidil inhibits the micturition reflex by blocking α1 receptors, as well as by the activation of serotonergic, glycinergic, and GABAergic neurons in the central nervous system.     

Inhibitory effects of beta-alanine on the vagal efferent and afferent excitatory responses of the stomach to stimulation of vagal trunk in cats.

The effects of beta-alanine on the electrically evoked vagal efferent (hexamethonium-sensitive initial excitatory response) and afferent (hexamethonium-resistant delayed excitatory response) responses of the cat stomach were studied. beta-alanine (30 to 300 micrograms/kg, i.v.) dose-dependently inhibited both the efferent and afferent response. The IC50 values of beta-alanine on the efferent and afferent response were 296 +/- 65 micrograms/kg and 128 +/- 35 microgram/kg, respectively. Maximal inhibitory effects of beta-alanine (300 micrograms/kg, i.v.) appeared about 1 hr after the injection. Glycine and taurine (100 to 10,000 micrograms/kg) did not affect these responses. Treatment with hexamethonium (10 mg/kg, i.v.) prevented the efferent response, but augmented the afferent response. The treatment with hexamethonium abolished the inhibitory effect of beta-alanine on the afferent response. Both picrotoxin (100 and 500 micrograms/kg, i.v.) and bicuculline (2000 micrograms/kg, i.v.) antagonized the inhibitory effects of beta-alanine on the vagal efferent and afferent responses of the stomach. The present experiments clearly demonstrated that beta-alanine inhibited both the vagal efferent and afferent excitatory responses of stomach to electrical stimulation of vagal trunk in cats.     

Spawning period and migration of three species of cyprinids in a stream with Mediterranean regimen (SW Spain)

These studies investigated the effects of somatostatin on gastric motility in the rainbow trout. Two experimental models were used, the isolated vascularly-perfused stomach and isolated strips of gastrointestinal smooth muscle. Both models demonstrated that somatostatin can inhibit gastrointestinal motility and may therefore modulate gastric emptying in fish.
In the vascularly-perfused stomach, somatostatin (10–1000 n m ) decreased maximum and baseline intragastric pressure by 10–20% in the presence of stimulatory doses of carbachol or 5-hydroxytryptamine. In addition, somatostatin (1 μ m ) inhibited by 50% the magnitude of spontaneous contractions generated by distension. Somatostatin had little effect on the pressure gradient or contractile frequency. These results suggest that somatostatin may negatively modulate gastric emptying in the rainbow trout.
In isolated gastric smooth muscle strips, somatostatin (100 pmol) inhibited tension stimulated by carbachol (circular orientation of muscle) or 5-hydroxytryptamine (longitudinal orientation). These results correlated with those observed in the vascularly perfused stomach preparation. Somatostatin also decreased tension stimulated by carbachol and 5-hydroxytryptamine in intestinal smooth muscle strips, suggesting that under some conditions somatostatin could increase gastric emptying rate by relaxing intestinal musculature.     

Effect of naftopidil,an alpha1D/A-adrenoceptor antagonist,on the urinary bladder in rats with spinal cord injury

AimsAlpha_1D-adrenoceptors (α_1D-ARs) located in the spinal cord are involved in the control of lower urinary tract function. In order to clarify the effect of α_1D-ARs on storage function in the spinal cord, we examined the effect of oral administration and intrathecal injection of the α_1D/A-AR antagonist, naftopidil, on bladder activity, as well as the effect of naftopidil on bladder wall histology, in female rats with spinal cord injury (SCI).Main methodsAdult female Sprague–Dawley rats with Th9–10 spinal cord transection were used. In SCI rats with or without 5 mg/day of naftopidil for 4 weeks, bladder activity was examined via continuous cystometry. In other SCI rats, bladder activity was examined before and after intrathecal injection of naftopidil. In addition, bladder wall histology was compared between SCI rats with or without oral administration of naftopidil for 4 weeks.Key findingsOral administration of naftopidil decreased the number of non-voiding contractions (NVCs). Intrathecal injection of naftopidil prolonged the interval between voiding contractions, decreased the maximum voiding contraction pressure and the number of NVCs, and increased bladder capacity without affecting the residual urine volume. Oral administration of naftopidil also decreased bladder wall fibrosis.SignificanceThe α_1D/A-AR antagonist naftopidil might act on the bladder and spinal cord to improve detrusor hyperreflexia in the storage state in SCI female rats. Naftopidil also suppressed bladder wall fibrosis, suggesting that it may be effective for the treatment of neurogenic lower urinary tract dysfunction after SCI.     

Sexually dimorphic micturition in rats: relationship of perineal muscle activity to voiding pattern

In the present study we examined the possibility that striated muscle activity may underlie sexually dimorphic micturition in rats. Micturition dynamics, the gross anatomy of the external urethral sphincter, and the participation of the striated perineal muscles in micturition were compared in urethane-anesthetized adult male and female rats. Bladder contraction characteristics, particularly the magnitude of bladder high-frequency pressure waves during voiding, differed between sexes. Dissections indicated that the sphincter was more extensive and thicker in males than in females. Electromyography showed that in both sexes the sphincter discharged in bursts that correlated with the rising phase of high-frequency bladder pressure oscillations. Regional differences in discharge pattern were seen in the sphincters of males, with the proximal part of the sphincter showing components activated during bladder filling. Bulbospongiosus, ischiocavernosus, and cremaster muscles also were activated during bladder contraction in males. In both sexes transection of the motor branch of the lumbosacral plexus eliminated the bladder high-frequency oscillations and reduced voided volume. Neurectomy did not affect bladder pressure but reduced voiding efficiency by 45% in males. In females the bladder pressure was dramatically decreased, but voiding efficiency only decreased by 24%. Our findings suggest that, in rats, striated perineal muscles contribute to the sexually dimorphic micturition. Activity of the dimorphic perineal muscles may regulate genital and urinary urethra expulsive functions, helping to expel seminal plug and fluids through the long urethra in the male.     

Nociceptin and the micturition reflex

The i.v. administration of nociceptin (10-100 nmol/kg) inhibits the micturition reflex in a naloxone-resistant manner. The effects induced by i.v. nociceptin were not observed in capsaicin-pretreated animals indicating that i.v. nociceptin inhibits the micturition reflex by inhibiting afferent discharge from capsaicin-sensitive nerves. Supporting this interpretation, nociceptin also inhibited the reflex but not the local bladder contraction induced by topical capsaicin and protects this reflex (but not the local contraction) by desensitization. Intrathecal nociceptin (10 nmol/rat) produces urodynamic modifications similar to those induced by the i.v. administration. Intracerebroventricular (i.c.v.) administration of nociceptin (0.3-1 nmol/rat) also inhibited the micturition reflex in a naloxone-resistant manner suggesting a direct effect on supraspinal sites controlling the micturition. Beyond the inhibitory effects exerted by nociceptin on the micturition reflex, a peripheral excitatory effect mediated by capsaicin-sensitive fibers was also detected. The application of nociceptin (5-50 nmol/rat) onto the bladder serosa when the intravesical volume was subthreshold for the triggering of the micturition reflex, activated the reflex in a dose-dependent manner; the same treatment produced a biphasic effect on the ongoing reflex. In addition to the triggering of micturition reflex, topical nociceptin evokes a local tonic-type contraction that was abolished by the coadministration of tachykinin NK(1) and NK(2) receptor antagonists. Altogether these results indicate that ORL(1) receptors are present at several sites for the integration of the micturition reflex, and that their activation may produce both excitatory or inhibitory effects, depending on the route of administration and the experimental conditions.     

Temporal differences in bladder dysfunction caused by diabetes, diuresis, and treated diabetes in mice

Diabetic bladder dysfunction is a common complication of diabetes mellitus (DM) with poorly understood natural history. This study examined the temporal changes in bladder function 3, 9, 12, and 20 wk after induction of DM by streptozotocin (STZ) in male C57BL/6 mice compared with that in age-matched diabetic mice treated with insulin, 5% sucrose-induced diuretic mice, and sham-treated control mice. Conscious cystometrograms of mice were examined in addition to the measurements of micturition cycle. Diabetes resulted in decreased body weight. Bladder weight, urine output, bladder capacity, and compliance increased in the DM and diuretic groups. Peak voiding pressure (PVP) increased initially in both DM and diuretic mice. However, in DM mice, PVP dropped dramatically at and after 12 wk. Similar changes in the capacity, compliance, and emptying ability of the bladder were seen during the first 9 wk of the diabetes or diuresis, whereas significant decline in the emptying ability of the bladder was only seen in diabetes after 12 wk of disease in mice. Long-term insulin replacement effectively reversed most changes in bladder function. These results suggest that the transition from a compensated to a decompensated bladder dysfunction occurs 9-12 wk after induction of DM in mice by STZ.