Volume-evoked Micturition Reflex Research Articles

Volume-evoked micturition reflex is mediated by the ventrolateral periaqueductal gray in anesthetized rats.

The central pathway of the micturition reflex in the rat was investigated functionally by acute blockade of synaptic neurotransmission using microinjection of cobalt chloride into the periaqueductal gray or pontine tegmental region. In 27 urethan-anesthetized (1.2 g/kg ip) rats, the bladder pressure response to continuous infusion of the bladder with saline (0.1-0.25 ml/min) was assessed. Electromyographic activity of external urethral sphincter and arterial blood pressure were also monitored. Bladder contractions and external urethral sphincter activity were reversibly attenuated after unilateral or bilateral stereotaxic injections of 10 mM cobalt chloride into the caudal (bregma -7.80 to -8.80) ventrolateral periaqueductal gray as well as into Barrington's nucleus. Blood pressure was not affected by injection into either area. The results demonstrate that the caudal ventrolateral periaqueductal gray, in addition to Barrington's nucleus, is a critical part of the long-routed micturition reflex circuitry in the anesthetized rat.

The inhibitory effect of nociceptin on the micturition reflex in anaesthetized rats.

1. We have investigated the effect of nociceptin on the micturition reflex evoked by distension or topical application of capsaicin on the urinary bladder of urethane-anaesthetized rats. 2. Nociceptin produced a dose-dependent (3-100 nmol kg(-1) i.v.) transient suppression of the distension-evoked micturition reflex: its effect was not modified by guanethidine (68 micromol kg(-1) s.c.) nor by bilateral cervical vagotomy, alone or in combination, and by naloxone (1.2 micromol kg(-1) i.v.). 3. Nociceptin (100 nmol/kg i.v.) slightly (about 30%) inhibited the contractions of the rat bladder produced by pre- or postganglionic electrical stimulation of the pelvic nerve. 4. Nociceptin almost totally abolished the reflex component of the response to topical capsaicin (1 microg in 50 microl). 5. In the rat isolated bladder, submaximal contractions produced by electrical field stimulation were slightly reduced (25+/-4% inhibition) by 1 microM nociceptin. Nociceptin did not affect the contraction of the rat bladder induced by acetylcholine (10 microM) or ATP (1 mM). 6. These findings indicate that nociceptin exerts a naloxone-resistant suppression of the volume-evoked micturition reflex which involves inhibition of transmitter release from postganglionic bladder nerves. An inhibitory effect on bladder afferent nerves is also suggested.

The Effect of Alpha2 Agonists and Antagonists on the Lower Urinary Tract of the Rat

The pharmacologic potential of selective alpha2 adrenergic agents in modulating vesicourethral function was evaluated in urethane-anesthetized and conscious rats. The bladder was exposed through a midline incision and intubated via a cystostomy to measure pressure. The bladder was filled with saline at 0.05ml./min. In six animals intravenous dexmedetomidine 0.6μg./kg. followed by 2μg./kg. was given. In another six rats the infusion was made with atipamezole at the same concentration. The parameters obtained were pressure/volume during cystometry, detrusor voiding pressures, and evidence of urine leakage.Conscious rats were placed in a restrainer outfitted with a voided volume sensor and a data recorder. The animals were divided in three groups. In controls, group I (n = 8), the animals were injected with a subcutaneous (SC) load of 5ml. saline in which furosemide 10.0mg./kg. was added. In group II (n = 6), dexmedetomidine was added, in group III (n = 6), atipamezole was added. Parameters obtained were volume per micturition, latency, frequency of micturition, and patterns of micturition (such as dribbling), and total volume produced after a three hour recording. Values are expressed as mean ± standard deviation.The results show that in an anesthetized preparation, the alpha2 agonist dexmedetomidine produced inhibitory effects on the volume evoked micturition reflex (VEMR) at a dose level of 2.0μg./kg. There was a significant decrease in peak pressure from 26.4 ± 3.6 to 6.8 ± 2.1cm. H20 (p <0.01). Urine leakage was observed at the external meatus. Atipamezole, the alpha2 agonist, gradually increased bladder baseline pressure and inhibited VEMR. At a critical pressure there was continuous leakage from the external meatus. There was a significant elevation of baseline bladder pressure by atipamezole from 6.3 ± 1.7 to 29.8 ± 4.6cm. H20 (p <0.005).In conscious rats, the alpha2 agonist produced urinary dribbling at ≈20 minutes after SC injection, while the antagonists produced delayed dribbling 70 minutes after SC injection. Leakage occurred in 3 of 6 rats at a dose of 10μg./kg. of atipamezole and in 5 of 6 rats at a dose of 30μg./kg. The alpha2 agonist caused a diuretic effect and a dose-dependent increase in the frequency of voiding (p <0.05), while the antagonist decreased the frequency of voiding. Bladder capacity was decreased with the alpha2 agonist while the antagonist increased capacity.

Rapid evaluation of the efficacy of pharmacologic agents and their analogs in enhancing bladder capacity and reducing the voiding frequency

We report here the results of a simplified screening method to rapidly compare the pharmacologie action of drugs relevant to the urinary tract. This method avoids the use of anesthesia and of external infusion into the bladder relying on the physiological stimulation of the volume-evoked micturition reflex (VEMR) by diuresis. Mature female rats weighing 240–310 g were placed in restrainer cages that afforded access to food and water but limited movement. Under the rear of the rat, a collecting funnel and weight measuring device was secured. For each VEMR, the weight of the volume voided was recorded on a polygraph which also provided a record of the time of voiding. To evaluate the relative pharmacologie efficacy of the drug under study, 1 mg kg furosemide along with the drug to be evaluated was diluted in 5 ml of saline and injected subcutaneously. Rats received approximately equimolar concentrations of thiphenamil and 15 other analogs, Ca 2+ channel blockers, and K + channel openers. The furosemide was given to obtain a controlled level of diuresis and avoid the effects of circadian variations in urine flow. Parameters considered were 1) mean volume voided per VEMR, 2) frequency, 3) output, and 4) latency. This model allows the rapid evaluation of drugs designed to increase bladder capacity and decrease the frequency of voiding, and it is particularly useful in evaluating the relative efficacy of drugs that are chemical analogs.

摘出ラットぼうこう筋および生体位ラットぼうこう内圧に及ぼすＴｉｒｏｐｒａｍｉｄｅ ｈｙｄｒｏｃｈｌｏｒｉｄｅの影響

The effects of tiropramide on the isolated detrusor and intravesical pressure of the bladder in situ in rats were compared with those of flavoxate, oxybutynin and terodiline. The IC50 values (x 10(-5) M) of tiropramide for carbachol (CCh)-, K+ (60 mM)-, Ba2+ (10 mM)-, and electrical stimulation-induced contractions were 3.6, 4.2, 5.8, and 2.9, respectively. The four antispasmodics used (2 and 4 mg/kg, i.v., each) abolished the rhythmic bladder contractions in situ in anesthesized rats. Of the four compounds, oxybutynin was most potent and no significant differences were observed between the inhibitory effects of tiropramide, flavoxate and terodiline. The administration of flavoxate (30 and 60 mg/kg) into the duodenum little influenced the rhythmic bladder contractions. Tiropramide, flavoxate, oxybutynin and terodiline (8 and 12 mg/kg, i.v., each) dose-dependently prolonged the time to the volume-evoked micturition reflex, and the activity of tiropramide was not statistically different from those of the other three antispasmodics. Under unilateral pelvic and bilateral hypogastric nerve transection, both of the contractions induced by electrical stimulation of the peripheral and central cut ends of the pelvic nerve were dose-dependently inhibited to the same extent by tiropramide and terodiline. These results suggest that the effects of tiropramide on the function of urinary bladder in rats may be mainly due to direct actions on the smooth muscle, and that tiropramide is more potent than flavoxate and less potent than oxybutynin and terodiline.

The role of spinal and brainstem adenosine receptors in the modulation of the volume-evoked micturition reflex in the unanesthetized rat

The pharmacology of the spinal, subraspinal and peripheral adenosine receptor subtypes (A 1, A 2) and their influence on the volume-evoked micturition reflex (VEMR) was studied in a chronic unanesthetised rat model by cystometrography after intrathecal (i.t.), intracerebroventriculair (i.c.v.) and intravenous (i.v.) injection. Intrathecally administered A 1 adenosine agonist:N 6-( l-2-phenylisopropyl)adenosine (R-PIA) and A 2 adenosine agonist: 5′-(N-ethylcar☐amido)adenosine (NECA) were equally active with 1.0 nmol reliably producing an increase in the volume necessary to induce the VEMR. At a higher dose (3 nmol), a long-lasting blockade of the VEMR was produced by both agonists. These effects were reversed following intraperitoneal injection of caffeine, and adenosine antagonist. This inhibition of the VEMR outlasted the spinal antinociceptive action which we have previously reported for these two agonists. Contrary to the spinal effect of these agonists, i.c.v. (0.3–3 nmol) and i.v. (100–1000 nmol) injections of R-PIA and NECA resulted in a significant decrease in the volume required to evoke the VEMR. We conclude that at the spinal level a xanthine-sensitive adenosine receptor(s) inhibits the VEMR. Based on several indirect lines of evidence, we speculate that these effects are not mediated by an action on primary afferent input or directly on preganglionic neurons, but on an excitatory interneuronal link.

Similarities and differences in the action of resiniferatoxin and capsaicin on central and peripheral endings of primary sensory neurons

We have compared the ability of capsaicin and resiniferatoxin, a natural diterpene present in the latex of plants of the Euphorbia family to excite and desensitize capsaicin-sensitive primary afferents in a variety of models. Both capsaicin and resiniferatoxin inhibited the twitch contractions of the rat isolated vas deferens and prevented, in a concentration-related manner, the effect of a subsequent challenge with 1 μM capsaicin (desensitization). Resiniferatoxin was 1000–10,000 times more potent than capsaicin in both cases. The time course of action of resiniferatoxin was much slower than that of capsaicin, suggesting a slower penetration rate in the tissue. The action of resiniferatoxin was blocked by Ruthenium Red, a proposed antagonist at the cation channel coupled to the capsaicin receptor. Both capsaicin and resiniferatoxin produced a contraction of the rat isolated urinary bladder. Resiniferatoxin was about as potent as capsaicin in this assay although it was 500–1000 times more potent than capsaicin in desensitizing the primary afferents to a subsequent challenge with capsaicin itself. Resiniferatoxin did not affect motility in the isolated vasa deferentia or urinary bladder from capsaicin-pretreated rats. After topical application onto the rat urinary bladder both resiniferatoxin (10 nM) and capsaicin (10μM) increased bladder capacity as assessed in a volume-evoked micturition reflex model in rats without affecting micturition contraction. Intrarterial injection of resiniferatoxin or capsaicin in the ear of anesthetized rabbits evoked a systemic depressor reflex due to activation of para vascular nociceptors, resiniferatoxin being about three times more potent than capsaicin. Superfusion of the ear with capsaicin prevented the excitatory action of resiniferatoxin. Resiniferatoxin produced the simultaneous release of substance P- and calcitonin gene-related peptide-like immunoreactivity from the superfused rat isolated bladder and spinal cord (dorsal half) as well as from the perfused rabbit ear. No release of either peptide-like immunoreactivity was evoked by resiniferatoxin from the urinary bladder or spinal cord of rats pretreated with capsaicin. These findings are consistent with the idea that resiniferatoxin is a potent capsaicin analog and suggest a common site of action for these two substances (cross-desensitization and blockade by Ruthenium Red). Furthermore, the present findings indicate that the penetration rate of resiniferatoxin in tissues is much slower than that of capsaicin. As a consequence, the estimate of the relative potency of these two agents in exciting primary afferents is strongly influenced in non-equilibrium experimental conditions.

Micturition in the unanesthetized rat: effects of intrathecal capsaicin, N-vanillylnonanamide, 6-hydroxydopamine and 5,6-dihydroxytryptamine

Unanesthetized rats chronically implanted with vesical and intrathecal catheters were injected intrathecally (i.t.) with either capsaicin (CAP), N-vanillylnonanamide (VN), 6-hydroxydopamine (6-OHDA), or 5,6-dihydroxytryptamine (5,6-DHT). The volume-evoked micturition reflex was assessed by cystometrography before, and 2 h, 1 day and 7 days after injection. In control and vehicle-injected rats, the infusion of saline into the bladder resulted in a periodic contraction of the bladder with synergic sphincter relaxation. One day after i.t. CAP and VN (70 μg each), 50% and 30% of the animals displayed a blockade of the micturition reflex, respectively. In these animals, the infusion of saline resulted in a gradual rise in bladder pressure up to a plateau (overflow pressure) equivalent to the predrug bladder opening pressure. When the plateau was reached, continuous dribbling of urine with no bladder contractions was observed. Most of the affected rats displayed some micturition responses by day 7. Following i.t. injection of 5,6-DHT (20 μg) or 6-OHDA (20 μg), the micturition reflex displayed small but significant increases in bladder volume with no changes in pressure profile. Small primary afferents, sensitive to the neurotoxic effects of CAP and VN appear to play a major tonic role in the regulation of the micturition reflex in unanesthetized rats. Serotonergic and adrenergic descending pathways might play a role in the maintenance of resting bladder tone.

Intrathecal Somatostatin in Rats

Effects of intrathecal (i.t.) somatostatin (SST) (10, 30, and 100 micrograms) on nociception, and autonomic and motor function were evaluated in rats with chronically implanted lumbar i.t. catheters. Doses of 10 and 30 micrograms SST i.t. had no effect on thermal cutaneous nociception, (hot plate and tail flick response). Thirty micrograms SST i.t. did not effect the visceral chemical evoked nociception (acetic acid writhing test) as compared to saline control groups. Rats treated with 100 micrograms SST i.t. invariably showed temporary or permanent hindlimb motor dysfunction, with flaccid paralysis in the most severe cases (motor function tests, electromyographic response). Blockade of the tail flick and foot pinch response was observed to a variable degree, and only in the presence of detectable motor impairment. Out of 40 animals injected with 100 micrograms SST i.t., 25% died within 10 min following injection. Effects of SST on the volume evoked micturition reflex were assessed in rats with chronically implanted bladder catheters. Three of the nine surviving animals receiving 30 micrograms SST i.t. and all animals receiving an additional dose of 60 micrograms SST i.t. showed a complete block of the micturition reflex and subsequent development of an overflow bladder. Histological examination of spinal cords revealed a mild inflammatory response in four out of five animals treated with 30 micrograms SST i.t. In spinal cords of animals, which had received 100 micrograms SST i.t. (n = 4), mild or severe nucleolysis of ventral and dorsal horns in the presence of inflammatory reaction was observed. Present experiments clearly demonstrate highly toxic effects of SST in rats with no margin of safety between antinociception and motor dysfunction.

Drug effects on urinary bladder tone during spinal morphine-induced inhibition of the micturition reflex in unanesthetized rats.

In an unanesthetized chronic rat model involving the placement of one catheter in the bladder for cystometrography and one catheter in the intrathecal (IT) space for drug injections, 10 micrograms morphine sulfate injected intrathecally (it) produced long-lasting inhibition of the volume-evoked micturition reflex. During inhibition of the micturition reflex, intravesical pressure rose with infusion until a continuous emission of urine (dribbling) was observed. Such a level of intravesical pressure (overflow pressure) was significantly greater than the premorphine bladder opening pressure (+56%). During dribbling, no periodic vesical contractions were observed, and the effects of a variety of agents on bladder tone were assessed. Significant (P less than 0.05) increases in vesical pressure over that produced by morphine were observed after intraperitoneal (ip) injection of carbachol (+86%), bethanechol (+55%), norepinephrine (+53%), methoxamine (+88%), and ST-91, an alpha 2-adrenergic agonist (+70%). The increased vesical pressure was not accompanied by an increase in the rate of urine expression. Intraperitoneal injection of serotonin produced no effects on intravesical pressure or urine expression. Significant decreases in the otherwise elevated intravesical pressure were observed after ip injection of isoproterenol (-30%) and phentolamine (-21%), with no change in the rate of urine expression. In contrast, ip injection of apomorphine (dopamine agonist) resulted in significant decreases in vesical pressure (-49%) and near maximal emptying of the bladder. Apomorphine produced no effects on it morphine-induced antinociception as assessed by the tail flick response. Regarding potential treatments of spinal morphine-induced urinary retention, the present study suggests that: 1) cholinomimetic and alpha-adrenergic agonist agents might be harmful; 2) beta-adrenergic agonist and alpha-adrenergic blocking agents might be useful; and 3) dopaminergic agonist agents might be the drugs of choice.

Micturition in rats: a chronic model for study of bladder function and effect of anesthetics.

The volume-evoked micturition reflex (VEMR) and the effects of anesthetics on the VEMR were studied in a chronic unanesthetized rat model. The bladder catheter was implanted chronically through a laparotomy and externalized percutaneously. An intrathecal (IT) catheter was implanted chronically in animals scheduled for an IT injection. By 2 days after implantation, infusion of saline (200 microliter/min) in the bladder reliably resulted in a low base-line pressure (BP) followed by a transient increase in bladder pressure, an opening of the sphincter (bladder opening pressure, BOP) corresponding to expression of urine (volume of urination, V), then a further rise in pressure (peak pressure, PP) and a subsequent return to base line. Seven days after implantation, values (means +/- SE) for BP, BOP, PP, and V were 10 +/- 0.3, 30 +/- 2, 67 +/- 6 cmH2O, and 1.0 +/- 0.1 ml, respectively. Residual volumes were reliably less than 2-4% of the expressed volume. The VEMR was reliably evoked up to 28 days after implantation. V values in unimplanted and implanted animals were not different. In implanted animals, VEMR parameters were not different during infusion or during spontaneous urination after oral fluid load. Administration of pentobarbital sodium (50 mg/kg ip), alpha-chloralose (130 mg/kg ip), ketamine (100 mg/kg im), halothane (in air 2%), and local anesthetics (2-chloroprocaine 3% or bupivacaine 0.75%, 10 microliter IT) produced a complete blockade of the VEMR and overflow incontinence at pressures significantly higher than BOP values. To compare overflow pressures and passive compliance of the bladder, unanesthetized animals were decapitated.(ABSTRACT TRUNCATED AT 250 WORDS)

NERVOUS CONTROL OF MICTURITION.

NERVOUS CONTROL OF MICTURITION.