Cholinergic mechanisms in the rat detrusor muscle

Identification of the origin of adrenergic and cholinergic nerve fibers within the superior hypogastric plexus of the human fetus

Nerve fibers contributing to the superior hypogastric plexus (SHP) and the hypogastric nerves (HN) are currently considered to comprise an adrenergic part of the autonomic nervous system located between vertebrae (T1 and L2), with cholinergic aspects originating from the second to fourth sacral spinal segments (S2, S3 and S4). The aim of this study was to identify the origin and the nature of the nerve fibers within the SHP and the HN, especially the cholinergic fibers, using computer-assisted anatomic dissection (CAAD). Serial histological sections were performed at the level of the lumbar spine and pelvis in five human fetuses between 14 and 30 weeks of gestation. Sections were treated with histological staining [hematoxylin-eosin (HE) and Masson's trichrome (TriM)] and with immunohistochemical methods to detect nerve fibers (anti-S100), adrenergic fibers (anti-TH), cholinergic fibers (anti-VAChT) and nitrergic fibers (anti-nNOS). The sections were then digitalized using a high-resolution scanner and the 3D images were reconstructed using winsurf software. These experiments revealed the coexistence of adrenergic and cholinergic fibers within the SHP and the HNs. One-third of these cholinergic fibers were nitrergic fibers [anti-VACHT (+)/anti-NOS (+)] and potentially pro-erectile, while the others were non-nitrergic [anti-VACHT (+)/anti-NOS (-)]. We found these cholinergic fibers arose from the lumbar nerve roots. This study described the nature of the SHP nerve fibers which gives a better understanding of the urinary and sexual dysfunctions after surgical injuries.

Rat: overview and innervation

Despite the development of molecular and cellular methods for examining physiological processes, the use of the whole animal model remains essential to advance knowledge regarding the integration and coordination of events associated with urinary tract function. The rat offers an inexpensive and versatile species to investigate bladder and urethral responses to drugs or pathology. Models for many disorders have been developed in rodents including diabetes, multiple sclerosis, spinal cord injury, Parkinson's disease, bladder outlet obstruction, pain, and aging. This review examines methodologies to evaluate lower urinary tract function and manipulations used to create pathological models in rodents.

Atropine-resistant transmission in partially depolarized rat urinary bladder

1. Phasic contractile responses of the intact rat urinary bladder to the muscarinic agonists carbachol and pilocarpine became nearly blocked as the concentrations were progressively increased to 200-500 microM. In contrast, tonic contractile responses remained elevated throughout progressive increases in agonist concentration. 2. Nerve-induced phasic contractions to 1 Hz stimuli were potentiated throughout progressive increases in the concentration of muscarinic agonists. However, these responses were more atropine sensitive than untreated controls and responses to 1 Hz stimuli were nearly abolished. 3. After inhibition of cholinesterase, the action of cholinergic transmitter released during prolonged nerve stimulation may extend to the tonic contractile state of the bladder and potentiate responses to 1H stimuli. Nerve-induced responses were more atropine sensitive than untreated controls. 4. Bladder tone was increased and nerve-induced contractions to 1-Hz stimuli were also potentiated in an elevated K+ environment. However, atropine sensitivity of nerve-induced responses w s reduced. 5. Nerve-induced bladder contractions were linked to the tonic contractile state of the bladder muscle, controlled physiologically by muscarinic receptors. Since phasic contractile responses to muscarinic agonists were abolished at high concentrations by receptor desensitization, nerve-induced responses must be elicited under these conditions by a non-cholinergic transmitter.

A calcium blocking and anticholinergic agent (terodiline) in the treatment of detrusor hyperreflexia: a placebo-controlled, cross-over trial

In 25 neurological patients with detrusor hyperreflexia terodiline reduced the number of total micturitions during daytime. Bladder capacity was increased and amplitude of the bladder contractions was reduced. An increase in residual urine was also observed. Mild anticholinergic side-effects were measured on pupillary motility and on heart rate variation. It is concluded that terodiline is a useful alternative in treatment of patients with detrusor hyperreflexia.

Further studies on the mechanisms of the tachykinin-induced activation of micturition reflex in rats: evidence for the involvement of the capsaicin-sensitive bladder mechanoreceptors

The relative ability of substance P, neurokinin A, neurokinin B and kassinin to activate the micturition reflex was investigated in urethane-anaesthetized rats. When administered topically neurokinin A, neurokinin B and kassinin were 14, 36 and 280 times, respectively, more potent than substance P to activate micturition. On the other hand substance P, neurokinin A and kassinin were practically equipotent (and neurokinin B was about 3-4 times less potent than substance P) to stimulate the contraction of the rat isolated bladder and to potentiate the contractions induced by electrical field stimulation. This indicates that neither a direct action on muscle cells nor a potentiating effect on efferent neurotransmission can account for the rank order of potency of tachykinins for activation of the micturition reflex. The ability of topical tachykinins to activate the micturition reflex was largely impaired in 2 months old rats pretreated with capsaicin (50 mg/kg s.c.) on their second day of life, indicating that integrity of the capsaicin-sensitive bladder mechanoreceptors is essential for the production of this effect. These findings indicate that an NK-B receptor, possibly located on sensory nerves in the bladder wall, participates in the tachykinin-induced activation of reflex micturition.

Peripheral effects of neurokinins: functional evidence for the existence of multiple receptors

The ability of six neurokinins (substance P, neurokinin A, neurokinin B, physalaemin, eledoisin and kassinin) to induce hypotension, salivary secretion and to activate motility of the duodenum and of the urinary bladder was investigated in urethane-anaesthetized rats. A comparison of the relative potency of these substances in producing a given biological effect yielded results consistent with the hypothesis of the existence of three distinct types of receptor in rat peripheral tissues, namely SP-P, SP-K and SP-E according to the nomenclature proposed by Buck, Burcher, Shults, Lovenberg & O'Donohue (1984), or NK-P, NK-A and NK-B according to that of Regoli, D'Orleans-Juste, Drapeau, Dion & Escher (1985). An NK-P receptor is responsible for the production of the hypotensive effect and for the activation of salivary secretion. An 'NK-P like' receptor subtype may be involved in determining the direct contractile effects on muscle cells of neurokinins in the rat isolated urinary bladder and the 'phasic' contraction of the rat duodenum. An NK-A receptor mediates the 'tonic' contraction of the rat duodenum while an NK-B receptor mediates the activation of the micturition reflex. Evidence is presented that multiple neurokinin receptors are present in the same organ and participate with different modalities to the regulation of smooth muscle function.

Urinary bladder innervation in children

Muscle strips from the fundus, trigone, and distal ureter obtained from children at operation for vesicoureteric reflux were studied using histochemical and immunohistochemical methods, and electrical nerve stimulation in an organ bath. A rich supply of cholinergic nerves was found and the transmitter causing contraction of the detrusor muscle was regarded as being acetylcholine. The adrenergic innervation was very sparse except around the ureteric orifices. No contractile alpha-adrenoceptors could be detected but beta-receptor-mediated relaxation was found. The type was not beta 1 or beta 2, suggesting a third type of beta-receptor. Peptidergic nerves containing vasoactive intestinal peptide (VIP) were demonstrated in a few nerve terminals. No nerves containing enkephalin, somatostatin, or substance P were found. VIP affected the detrusor muscle, indicating a possible role as a modulator of transmitter action. Imipramine, used for enuresis, had no anticholinergic effect on the bladder in the doses used clinically. The anticholinergic and calcium antagonistic drug terodiline inhibited all muscle activity, making it suitable for treatment of diurnal enuresis.

Functional evidence for the existence of a capsaicin-sensitive innervation in the rat urinary bladder

Capsaicin (0.03-3 microM) induces contractions of the rat isolated bladder which are unaffected by either atropine (3 microM) or tetrodotoxin (0.5 microM). In the presence of capsaicin (0.1 microM) an enhancement of field stimulation-induced contractions was observed. Capsaicin-desensitization did not modify the height of these. The neurogenic nature of the capsaicin-induced contractions was proved by the observation that 'chronic' (48 h) denervation prevented, while 'acute' (2 h) denervation did not modify the effect of capsaicin. Denervated bladders maintained their responsiveness to acetylcholine but not to field stimulation. Isolated bladders from rat pups (1-2 days old) did not respond to capsaicin while strong contractile responses to acetylcholine or field stimulation were obtained in these preparations. In bladders from two week old animals, capsaicin produced similar contractions to those observed in preparations from adult animals. The bladders from rats receiving a high dose of capsaicin (50 mg kg-1 s.c.) at birth were heavier than those of their age-matched, vehicle-treated controls. Isolated bladders from 2 month old animals pretreated with capsaicin at birth were unresponsive to capsaicin while responsiveness to acetylcholine, substance P or field stimulation was unaffected compared with that of vehicle-treated controls. These experiments provide evidence that a capsaicin-sensitive innervation exists in the rat urinary bladder which undergoes a postnatal development at end organ level.

An atropine-like inhibitory effect of DMPP on rat isolated urinary bladder

DMPP inhibits the nerve-mediated contractions of the rat isolated bladder, its effect being greater in preparations from newborn (2 day old) than adult animals. This effect of DMPP was unaffected by hexamethonium. In preparations from adult animals the effect of DMPP increased with frequency of stimulation and was fully prevented by the presence of atropine. In bladders from newborn rats low concentrations of furthrethonium (FHR) (10 nM) activated a series of rhythmic contractions which were unaffected by tetrodotoxin and abolished by DMPP through an hexamethonium-insensitive action. On the other hand DMPP did not affect rhythmic contractions produced by a low concentration of eledoisin (60 nM). In bladders from adult rats FHR (10 microM) and KCI (30 mM) produced contractures of comparable magnitude. DMPP inhibited, in concentration-related manner the FHR-induced tonic contraction but had little effect on that produced by KCI. These findings indicate that in the rat bladder, DMPP antagonizes selectivity cholinergically-mediated contractions through a mechanism which is unaffected by hexamethonium or tetrodotoxin. An "atropine-like' activity of DMPP should be considered.

Non-cholinergic inotropic responses evoked by electric field stimulation in the isolated rat urinary bladder. Possible participation of substance P

The present study explores whether a peptide, such as substance P (SP), has some role subserving the atropine-resistant component of electrically-evoked contractions, in isolated rat urinary bladders. The electric field stimulation (EFS) employed herein, consisted in square wave pulses of 5 Hz, 50 ms duration and supramaximal voltage (40 V), applied for 10 sec, every 3 min and conducted to the tissue via a pair of platinum ring electrodes, surrounding the isolated preparations. In order to assess whether electric stimuli, induced urinary bladder inotropism through the activation of nerve structures, degeneration of intramural nerve elements was attempted by cooling the tissue (48 h at 4-5 degrees C). After such procedure, 80-90% inhibition of responses to EFS, was detected. Moreover, tetrodotoxin, at 10(-6) M, evoked similar effects than cooling. Atropine, at 10(-6) M, failed to produce a significant decrement of contractile responses, whereas at 10(-5) M, the electrically-induced inotropism declined around 40%, in comparison with controls. In another set of experiments, atropinized urinary bladders (atropine at 10(-5) M) were exposed to capsaicin (5 X 10(-6) M) and this coincided with decreased (-43%) responses to EFS. Next, SP, at 10(-9) M, was added to the medium containing capsaicin and complete restoration of full contractile responses to EFS, was observed. Inasmuch as it has been proposed that capsaicin releases SP from sensory nerve fibers and since our experiments show that SP restored the inotropism elicited by electric stimuli on capsaicin-exposed preparations, it is suggested that SP could be involved, at least in part, in the non-cholinergic, EFS-evoked, contractile responses of isolated rat urinary bladders.

Pharmacological evidence for the existence of two components in the twitch response to field stimulation of detrusor strips from the rat urinary bladder

Isolated strips from the anterior dome of the rat urinary bladder respond to single pulse field stimulation with a contraction. Two distinct components of this contraction ("early' and "late') could be observed, both of which were unaffected by hexamethonium (10 microM) and almost abolished by tetrodotoxin (1 microM) indicating their dependence on neurotransmitter release from postganglionic nerve endings. Atropine (3 microM) inhibited the "late' component (over 60%) to a significantly greater extent than the "early' component (less than 10%) Amplitude of the "early' component was usually greater than that of the "late' component. There was almost no difference between the "early' and "late' component in respect of their relationship to stimulus strength and pulse duration. Physostigmine (0.03 microM) enhanced both components of the nerve-mediated contraction, although enhancement of the "late' component was much greater than that of the "early' one. Tetraethylammonium (TEA, 0.5-5 mM) enhanced, in a concentration-related manner, both "early' and "late' components of the nerve-mediated contraction. Following exposure to physostigmine or TEA (5 mM) both "early' and "late' components of contraction were almost completely inhibited by tetrodotoxin. Atropine inhibition was more evident on the "late' as compared to "early' component of contraction. These findings demonstrate the presence, in the twitch response of rat isolated urinary bladder to field stimulation, of two nerve-mediated components which exhibit a different susceptibility to atropine and physostigmine.

GABA inhibits excitatory neurotransmission in rat pelvic ganglia

Intravenous GABA inhibited, in a bicuculline-sensitive manner, contractions of the urinary bladder induced by preganglionic nerve stimulation in urethane anaesthetized rats, while it had no significant effect on contractions produced by postganglionic nerve stimulation. In addition, intravenous GABA strongly inhibited DMPP-induced bladder contractions; this effect was also prevented by bicuculline. These experiments suggest that GABA inhibits excitatory neurotransmission in rat pelvic ganglia through a mechanism involving, at least in part, the activation of postsynaptic GABA A receptors.

Age-related changes in sensitivity of rat urinary bladder to autonomic agents

Experiments were done to determine if age-related changes occur in autonomic regulation of rat urinary bladder. The maximum contractile responses to acetylcholine were 63% and 15% greater in isolated bladders from 29-month and 17-month animals, respectively, as compared to 7-month animals. The amounts of [3H]quinuclidinyl benzilate bound to membrane preparations were 46% and 7% greater. In contrast, no age-related changes were observed in phenylephrine-induced contraction or in isoproterenol-induced relaxation of bladder. Thus, the urinary bladder of aged rats appears to develop increased sensitivity to cholinergic stimuli because of an increase in the number of muscarinic cholinergic receptors.

The effects of topical capsaicin on rat urinary bladder motility in vivo

The effects of topical capsaicin on urinary bladder motility were investigated following saline-induced distension of the bladder wall in urethane-anaesthetized rats and compared to the effects of topical substance P and acetylcholine. Capsaicin and substance P produced similar excitatory effects in both quiescent and rhythmically contracting bladders, i.e., a TTX resistant tonic contraction followed by a series of rhythmic, TTX sensitive, phasic contractions. Acetylcholine, in doses equieffective in producing TTX resistant contractions was less effective than capsaicin or substance P in triggering neurogenic rhythmic contractions of bladder muscle. Atropine pretreatment prevented the neurogenic component of the excitatory effect of both capsaicin and substance P. Repeated applications of capsaicin but not of substance P led to desensitization. Bladders of animals pretreated (4 days before) with a large dose of s.c. capsaicin developed insensitivity to topical capsaicin and a larger volume of saline was required to trigger neurogenic rhythmic contractions of the detrusor muscle. These results suggest that capsaicin acts by interfering with the mechanism(s) regulating the threshold for the micturition reflex to occur.

Effects of rociverine on the human ureter: in vivo and in vitro experimental study

An in vitro and in vivo study was conducted to verify the effects of rociverine--a new spasmolytic agent--on peristalsis in the human ureter. In vitro (human ureter strips), rociverine exerted a spasmolytic activity both on the baseline motility and on the spasm induced by direct contractants (eledoisin, KCl) or by histamine. It may therefore be concluded that rociverine is a predominantly myotropic spasmolytic. In the in vivo study, conducted in patients with cutaneous ureterostomy, the drug showed a marked inhibitory effect on the amplitude and frequency of the ureteral rhythmic spikes, without affecting the baseline tone.

GABAB receptor mediated inhibition of field stimulation induced contractions of detrusor muscle strips from newborn rats

The effect of GABA on field stimulation (0.1 Hz) induced contractions have been examined on detrusor strips from adult and newborn rats. Field stimulation induced contractions were unaffected by hexamethonium (10(-5) M) but almost suppressed by tetrodotoxin (5 X 10(-7) M) in both age groups. Atropine (3 X 10(-6) M) produced a marked inhibition of twitches in detrusor strips from newborn rats but only a slight (10% or less) inhibition in strips from adult animals. Neither GABA (10(-4), homotaurine (10(-3) M) or (+/-)-baclofen (10(-4] affected twitches in detrusor strips from adults rats. On the other hand both GABA and (+/-)-baclofen inhibited, to about the same extent (55-60% inhibition) twitches in detrusor strips from newborn animals. Homotaurine had no significant effect. The effects of both GABA (10(-4) M) and (+/-)-baclofen (10(-4) M) on twitches in detrusor strips from newborn rats were reduced if the preparations were previously exposed to a low concentration of GABA (5 X 10(-6) M) thus indicating desensitization. The inhibitory effect of GABA on twitches in newborn rats were concentration dependent in the range of 10(-7) to 10(-4) M. The GABAA receptor antagonist picrotoxin (10(-4) M) had no effect on the GABA concentration response curve whereas the GABAB receptor antagonist, homotaurine, produced an antagonism of the competitive type. The calculated pA2 value for the GABA-homotaurine interaction was 4.4 +/- 0.07. Neither GABA (10(-4) M) nor (+/-)-baclofen (10(-4) M) produced any significant inhibition of acetylcholine (2 X 10(-7) M) induced contractions of detrusor of strips from newborn rats, while atropine (3 X 10(-6) M) completely suppressed them. These results indicate that GABA inhibits field stimulation induced contractions of detrusor strips from newborn rats by activating prejunctional receptors (presumably of the GABAB subtype) which inhibit the release of acetylcholine from the postganglionic nerve endings.

Reserpine-induced detrusor hyperreflexia: an in vivo model for studying smooth muscle relaxants at urinary bladder level

A new in vivo model for studying the effects of smooth muscle relaxant drugs at urinary bladder level has been developed. This involves the determination of a cystometrogram at a physiological filling rate in urethane anesthetized rats. The amount of infused saline required to elicit TTX-sensitive rhythmic contractions (micturition reflex) of urinary bladder was choosen as end point to evaluate the effect of test substances. Reserpine pretreatment significantly reduced the volume of saline required to elicit the micturition reflex. The effect of reserpine can be reproduced by intravenous prazosin, but not by propranolol or yohimbine, in control rats. Intravenous, but not topical, hexamethonium reversed the effects of reserpine pretreatment on the amount of infused saline required to elicit rhythmic contractions. The nature of rhythmic contractions produced by saline filling of the urinary bladder in these experimental conditions, as well as the potential mechanism(s) involved in the effects of reserpine, are discussed in view of the existing literature on the physiology and pharmacology of the micturition reflex. The effects of various drugs commonly used to produce a relaxation of bladder muscle suggest that this model might be useful for detecting substances of potential therapeutic usefulness in the treatment of bladder hypermotility disorders.

Atropine and micturition responses by rats with intact and partially innervated bladder

1 Micturition responses by a group of 17 rats wee recorded during a water diuresis. During a 2 h period, uniform volumes of urine were passes at regular intervals; the mean of the voiding responses by each animal was consistent from one water loading period to another. Residual urine volumes were physiologically insignificant. 2 Atropine treatment did not compromise seriously micturition by water-loaded rats. Treated animals micturated more frequently; the mean volume was 68% of control. The residual urine volume was equal to that of controls. 3 Several week after the surgical removal of half the motor innervation of the bladder, there was no significant effect on micturition. Mean voiding volumes were not different from those of controls; residual urine volumes were the same as before denervation. 4 After half the innervation of the bladder had been destroyed. The effect of atropine on micturition was enhanced. Volumes passes were 50% of control; large residual volumes remained when micturition was over. Only in this group could bladder distension be found. 5 It is concluded that functional responses of the rat urinary bladder are not only resistant to atropine but also to the sizeable reduction in the number of neuroeffector units in the bladder itself. The functional reserve of the rat bladder musculature is remarkably high when assessed by its ability to empty adequately.

The effect of troxypyrrolidinium, a choline uptake inhibitor, on the excitatory innervation of the rat urinary bladder

Troxypyrrolidinium, a choline uptake inhibitor, reduced but failed to abolish responses of the rat urinary bladder to electrical stimulation at 1-100 Hz although it reduced acetylcholine output during stimulation at 10 Hz to a level similar to that of spontaneous release. Inhibition of the response to stimulation was more complete at faster rates of stimulation and was partially reversed by choline. Troxypyrrolidinium produced a greater inhibition of the 'tonic' component of the response to electrical stimulation than of the 'phasic' component. Hemicholinium-3 or hyoscine produced a similar selective effect on the 'tonic' component. Hemicholinium-3 also reduced acetylcholine output during electrical stimulation to a similar extent as troxypyrrolidinium but hyoscine increased transmitter output. The results support the concept of a second transmitter in the excitatory innervation of the bladder.