Functional importance of cholinergic and purinergic neurotransmission for micturition contraction in the normal, unanaesthetized rat

ATP as a cotransmitter in sympathetic and parasympathetic nerves - another Burnstock legacy

Geoff Burnstock created an outstanding scientific legacy that includes identification of adenosine 5'-triphosphate (ATP) as an inhibitory neurotransmitter in the gut, the discovery and characterisation of a large family of purine and uridine nucleotide-sensitive ionotropic P2X and metabotropic P2Y receptors and the demonstration that ATP is as an excitatory cotransmitter in autonomic nerves. The evidence for cotransmission includes that: 1) ATP is costored with noradrenaline in synaptic vesicles in postganglionic sympathetic nerves innervating smooth muscle tissues, including the vas deferens and most arteries. 2) When coreleased with noradrenaline, ATP acts at postjunctional P2X1 receptors to elicit depolarisation, Ca²⁺ influx, Ca²⁺ sensitisation and contraction. 3) ATP is also coreleased with acetylcholine from postganglionic parasympathetic nerves innervating the urinary bladder, where it stimulates postjunctional P2X1 receptors, and a second, as yet unidentified site to evoke contraction of detrusor smooth muscle. In both systems membrane-bound ecto-enzymes and soluble nucleotidases released from postganglionic nerves dephosphorylate ATP and so terminate its neurotransmitter actions. Currently, the most promising potential area of therapeutic application relating to cotransmission is treatment of dysfunctional urinary bladder. This family of disorders is associated with the appearance of a purinergic component of neurogenic contractions. This component is an attractive target for drug development and targeting it may be a rewarding area of research.

Effect of pregnancy on the cholinergic responses of the bladder: role of acetylcholinesterase

OBJECTIVES

Pregnancy is associated with many functional changes of the urinary bladder. It was reported that most of healthy women complain from urinary symptoms during pregnancy. The parasympathetic system is mainly mediating bladder emptying. The aim of the study is to investigate the cholinergic effect and the role of acetylcholinesterase in the bladder during pregnancy.

METHODS

Sixteen rats were used in the present study as control group (non-pregnant) and pregnant group (18-20 days pregnant). Isolated urinary smooth muscle strips were suspended in organ baths filled with Krebs' solution for isometric tension recording.

RESULTS

Electric field stimulation (EFS), (0.1-40 Hz), of the control and pregnant bladder preparations produced frequency-dependent contractions. Atropine (1 µM) inhibited EFS-induced contractions in the two groups by 65% and 50% respectively indicating the response of cholinergic innervation. Neostigmine significantly enhanced EFS responses, confirming its selectivity for inhibiting acetylcholinesterase which is responsible for termination of acetylcholine. Concentration-response curves for acetylcholine were reduced in pregnant group than control. Concentration-response curves for ATP were increased in pregnant group than control. Neostigmine augmented concentration-response curves for acetylcholine in control and pregnant groups. The effect of neostigmine on acetylcholine contractile responses in pregnancy group was higher than in control.

CONCLUSIONS

Urinary bladder dysfunction during pregnancy might be due to augmentation of acetylcholinesterase effect. This will lead to the decrease in response to cholinergic stimuli. New pharmaceutical drugs specifically affecting the enzyme in the bladder can help in avoiding the unpleasant urinary symptoms during pregnancy.

BDNF overexpression in the bladder induces neuronal changes to mediate bladder overactivity

Elevated levels of brain-derived neurotrophic factor (BDNF) in urine of overactive bladder (OAB) patients support the association of BDNF with OAB symptoms, but the causality is not known. Here, we investigated the functionality of BDNF overexpression in rat bladder following bladder wall transfection of either BDNF or luciferase (luciferase) transgenes (10 µg). One week after transfection, BDNF overexpression in bladder tissue and elevation of urine BDNF levels were observed together with increased transcript of BDNF, its cognate receptors (TrkB and p75^NTR), and downstream PLCγ isoforms in bladder. BDNF overexpression can induce the bladder overactivity (BO) phenotype which is demonstrated by the increased voiding pressure and reduced intercontractile interval during transurethral open cystometry under urethane anesthesia. A role for BDNF-mediated enhancement of prejunctional cholinergic transmission in BO is supported by the significant increase in the atropine- and neostigmine-sensitive component of nerve-evoked contractions and upregulation of choline acetyltransferase, vesicular acetylcholine transporter, and transporter Oct2 and -α1 receptors. In addition, higher expression of transient receptor channels (TRPV1 and TRPA1) and pannexin-1 channels in conjunction with elevation of ATP and neurotrophins in bladder and also in L6/S1 dorsal root ganglia together support a role for sensitized afferent nerve terminals in BO. Overall, genomic changes in efferent and afferent neurons of bladder induced by the overexpression of BDNF per se establish a mechanistic link between elevated BDNF levels in urine and dysfunctional voiding observed in animal models and in OAB patients.

Purinergic signalling and development of the autonomic nervous system

Most early studies of the role of nucleotides in development have evidenced their crucial importance as carriers of energy in all organisms. However, an increasing number of studies are now available to suggest that purines and pyrimidines, acting as extracellular ligands specifically on receptors of the plasma membrane, may play a pivotal role throughout pre- and postnatal development in a wide variety of organisms including amphibians, birds, and mammals. Purinergic receptor expression and functions have been studied in the development of many organs, including the autonomic nervous system (ANS). Nucleotide receptors can induce a multiplicity of cellular signalling pathways via crosstalk with bioactive molecules acting on growth factors and neurotransmitter receptors which are fundamental for the development of a mature and functional ANS. Purines and pyrimidines may influence all the stages of neuronal development, including neural cell proliferation, migration, differentiation and phenotype determination of differentiated cells. Indeed, the normal development of the ANS is disturbed by dysfunction of purinergic signalling in animal models. To establish the primitive and fundamental nature of purinergic neurotransmission in the ontogeny of the ANS, in this review the roles of purines and pyrimidines as signalling molecules during embryological and postnatal development are considered.

ATP as a cotransmitter in the autonomic nervous system

The role of adenosine 5'-triphosphate (ATP) as a major intracellular energy source is well-established. In addition, ATP and related nucleotides have widespread extracellular actions via the ionotropic P2X (ligand-gated cation channels) and metabotropic P2Y (G protein-coupled) receptors. Numerous experimental techniques, including myography, electrophysiology and biochemical measurement of neurotransmitter release, have been used to show that ATP has several major roles as a neurotransmitter in peripheral nerves. When released from enteric nerves of the gastrointestinal tract it acts as an inhibitory neurotransmitter, mediating descending muscle relaxation during peristalsis. ATP is also an excitatory cotransmitter in autonomic nerves; 1) It is costored with noradrenaline in synaptic vesicles in postganglionic sympathetic nerves innervating smooth muscle preparations, such as the vas deferens and most arteries. When coreleased with noradrenaline, ATP acts at postjunctional P2X1 receptors to evoke depolarisation, Ca(2+) influx, Ca(2+) sensitisation and contraction. 2) ATP is also coreleased with acetylcholine from postganglionic parasympathetic nerves innervating the urinary bladder and again acts at postjunctional P2X1 receptors, and possibly also a P2X1+4 heteromer, to elicit smooth muscle contraction. In both cases the neurotransmitter actions of ATP are terminated by dephosphorylation by extracellular, membrane-bound enzymes and soluble nucleotidases released from postganglionic nerves. There are indications of an increased contribution of ATP to control of blood pressure in hypertension, but further research is needed to clarify this possibility. More promising is the upregulation of P2X receptors in dysfunctional bladder, including interstitial cystitis, idiopathic detrusor instability and overactive bladder syndrome. Consequently, these roles of ATP are of great therapeutic interest and are increasingly being targeted by pharmaceutical companies.

Purinergic signalling in the urinary tract in health and disease

Purinergic signalling is involved in a number of physiological and pathophysiological activities in the lower urinary tract. In the bladder of laboratory animals there is parasympathetic excitatory cotransmission with the purinergic and cholinergic components being approximately equal, acting via P2X1 and muscarinic receptors, respectively. Purinergic mechanosensory transduction occurs where ATP, released from urothelial cells during distension of bladder and ureter, acts on P2X3 and P2X2/3 receptors on suburothelial sensory nerves to initiate the voiding reflex, via low threshold fibres, and nociception, via high threshold fibres. In human bladder the purinergic component of parasympathetic cotransmission is less than 3 %, but in pathological conditions, such as interstitial cystitis, obstructed and neuropathic bladder, the purinergic component is increased to 40 %. Other pathological conditions of the bladder have been shown to involve purinoceptor-mediated activities, including multiple sclerosis, ischaemia, diabetes, cancer and bacterial infections. In the ureter, P2X7 receptors have been implicated in inflammation and fibrosis. Purinergic therapeutic strategies are being explored that hopefully will be developed and bring benefit and relief to many patients with urinary tract disorders.

Voltage-gated Na+ channel blockers reduce functional bladder capacity in the conscious spontaneously hypertensive rat

OBJECTIVE

To evaluate the consequence of pharmacologic inhibition of voltage-gated Na(+) channels (Nav) in the conscious rat, based on Nav having been implicated as modulators of rodent urodynamics using knockout as well as antisense oligodeoxynucleotide approaches.

METHODS

The urodynamic response to standard Nav blockers, lamotrigine, amitriptyline, mexiletine, and carbamazepine were evaluated using conscious, continuous-filling cystometry in spontaneously hypertensive rats (SHRs). As a selectivity evaluation, the activity of the Nav blockers at muscarinic receptors was assessed via effect on carbachol-evoked bladder contractions.

RESULTS

Lamotrigine, amitriptyline, mexiletine, and carbamazepine decreased peak micturition pressure, micturition interval, and void volume. These effects were markedly similar to observations with muscarinic antagonists. Therefore, we evaluated the selectivity of these agents against bladder muscarinic receptors. Lamotrigine, mexiletine, and carbamazepine had no effect on muscarinic bladder contractions, whereas amitriptyline displayed a robust antagonism of carbachol-induced contractility.

CONCLUSION

Three Nav blockers--lamotrigine, mexiletine, and carbamazepine--demonstrated a reduction in micturition pressure and functional bladder capacity, similar to previous observations with muscarinic antagonists. These 3 Nav blockers are free of muscarinic antagonism, consistent with their cystometric effects being mediated via their Nav blocking activities. The negative findings reported here with Nav blockers suggest that Nav channel blockade is unlikely to reflect an improved treatment strategy for bladder disorders over currently prescribed muscarinic antagonists.

Large conductance Ca2+ -activated K+ channel activation with NS1619 decreases myogenic and neurogenic contractions of rat detrusor smooth muscle

Large conductance voltage- and Ca(2+)-activated K(+) (BK) channels are important in regulating detrusor smooth muscle (DSM) function. Here, we examined systematically how the BK channel pharmacological activation modulates DSM contractility. NS1619, a potent BK channel activator, was utilized as a pharmacological tool to investigate the effect of BK channel activation on rat DSM contractility. Isometric tension recordings of DSM strips isolated from rat urinary bladder were performed systematically under various experimental conditions. NS1619 (30 μM) substantially diminished DSM spontaneous contraction amplitude, muscle force integral, frequency, duration and muscle tone. This effect was blocked by iberiotoxin, a BK channel selective inhibitor. NS1619 inhibited the phasic and tonic contractions in DSM strips pre-contracted with either the cholinergic agonist, carbachol (0.1 μM), or the depolarizing agent, KCl (20mM). In the presence of elevated KCl (60 mM KCl), the inhibitory effect of NS1619 was significantly reduced, indicating that BK channel activation is the underlying mechanism of NS1619 action. BK channel activation with NS1619 dramatically decreased the amplitude of electrical field stimulation (EFS)-induced contractions under a range of stimulation frequencies (0.5-50 Hz). In the presence of specific neurotransmitter inhibitors, BK channel activation with NS1619 significantly decreased both cholinergic and purinergic components of EFS-induced contractions. We conclude that BK channel activation with NS1619 significantly inhibited spontaneous, pharmacologically induced and nerve-evoked DSM contractions. Targeting the BK channel with selective openers may offer a unique opportunity to control DSM contractile activity, including pathophysiological conditions such as overactive bladder and detrusor overactivity, regardless of the underlying cause.

ATP and P2X purinoceptors in urinary tract disorders

The pharmacological concept of specifically targeting purinoceptors (receptors for ATP and related nucleotides) has emerged over the last two decades in the quest for novel, differentiated therapeutics. Investigations from many laboratories have established a prominent role for ATP in the functional regulation of most tissue and organ systems, including the urinary tract, under normal and pathophysiological conditions. In the particular case of the urinary tract, ATP signaling via P2X1 receptors participates in the efferent control of detrusor smooth muscle excitability, and this function may be heightened in disease and aging. Perhaps of greater interest, ATP also appears to be involved in bladder sensation, operating via activation of P2X3-containing receptors on sensory afferent neurones, both on peripheral terminals within the urinary tract tissues (e.g., ureters, bladder) and on central synapses in the dorsal horn of the spinal cord. Such findings are based on results from classical pharmacological and localization studies in nonhuman and human tissues, gene knockout mice, and studies using recently identified pharmacological antagonists - some of which have progressed as candidate drug molecules. Based on recent advances in this field, it is apparent that the development of selective antagonists for these receptors will occur that could lead to therapies offering better relief of storage, voiding, and sensory symptoms for patients, while minimizing the systemic side effects that curb the clinical effectiveness of current urologic medicines.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Purinoceptors as therapeutic targets for lower urinary tract dysfunction

Lower urinary tract symptoms (LUTS) are present in many common urological syndromes. However, their current suboptimal management by muscarinic and alpha(1)-adrenoceptor antagonists leaves a significant opportunity for the discovery and development of superior medicines. As potential targets for such therapeutics, purinoceptors have emerged over the last two decades from investigations that have established a prominent role for ATP in the regulation of urinary bladder function under normal and pathophysiological conditions. In particular, evidence suggests that ATP signaling via P2X(1) receptors participates in the efferent control of detrusor smooth muscle excitability, and that this function may be heightened in disease and aging. ATP also appears to be involved in bladder sensation, via activation of P2X(3) and P2X(2/3) receptors on sensory afferent neurons, both within the bladder itself and possibly at central synapses. Such findings are based on results from classical pharmacological and localization studies in non-human and human tissues, knockout mice, and studies using recently identified pharmacological antagonists--some of which possess attributes that offer the potential for optimization into candidate drug molecules. Based on recent advances in this field, it is clearly possible that the development of selective antagonists for these receptors will occur that could lead to therapies offering better relief of sensory and motor symptoms for patients, while minimizing the systemic side effects that limit current medicines.

Frequency encoding of cholinergic- and purinergic-mediated signaling to mouse urinary bladder smooth muscle: modulation by BK channels

In the urinary bladder, contractions of the detrusor muscle and urine voiding are induced by the neurotransmitters ACh and ATP, released from parasympathetic nerves. Activation of K(+) channels, in particular the large-conductance Ca(2+)-activated K(+) (BK) channels, opposes increases in excitability and contractility of urinary bladder smooth muscle (UBSM). We have shown that deleting the gene mSlo1 in mice (Slo(-/-)), encoding the BK channel, leads to enhanced nerve-mediated and neurotransmitter-dependent contractility of UBSM (38). Here, we examine the location of the BK channel in urinary bladder strips from mouse. Immunohistochemical analysis revealed that the channel is expressed in UBSM but not in nerves that innervate the smooth muscle. The relationship between electrical field stimulation and force generation of the cholinergic and purinergic pathways was examined by applying blockers of the respective receptors in UBSM strips from wild-type and from Slo(-/-) (knockout) mice. In wild-type strips, the stimulation frequency required to obtain a half-maximal force was significantly lower for the purinergic (7.2 +/- 0.3 Hz) than the cholinergic pathway (19.1 +/- 1.5 Hz), whereas the maximum force was similar. Blocking BK channels with iberiotoxin or ablation of the Slo gene increased cholinergic- and purinergic-mediated force at low frequencies, i.e., significantly decreased the frequency for a half-maximal force. Our results indicate that the BK channel has a very significant role in reducing both cholinergic- and purinergic-induced contractility and suggest that alterations in BK channel expression or function could contribute to pathologies such as overactive detrusor.

Urodynamic effects of oxybutynin and tolterodine in conscious and anesthetized rats under different cystometrographic conditions

Background

Antimuscarinic agents are the most popular treatment for overactive bladder and their efficacy in man is well documented, producing decreased urinary frequency and an increase in bladder capacity. During cystometry in rats, however, the main effect reported after acute treatment with antimuscarinics is a decrease in peak micturition pressure together with little or no effect on bladder capacity. In the present experiments we studied the effects, in rats, of the two most widely used antimuscarinic drugs, namely oxybutynin and tolterodine, utilising several different cystometrographic conditions. The aim was to determine the experimental conditions required to reproduce the clinical pharmacological effects of antimuscarinic agents, as seen in humans, in particular their ability to increase bladder capacity.

Results

Intravenous or oral administration of tolterodine or oxybutynin in conscious rats utilized 1 day after catheter implantation and with saline infusion at constant rate of 0.1 ml/min, gave a dose-dependent decrease of micturition pressure (MP) with no significant change in bladder volume capacity (BVC). When the saline infusion rate into the bladder was decreased to 0.025 ml/min, the effect of oral oxybutynin was similar to that obtained with the higher infusion rate. Also, experiments were performed in rats in which bladders were infused with suramin (3 and 10 μM) in order to block the non-adrenergic, non-cholinergic component of bladder contraction. Under these conditions, oral administration of oxybutynin significantly reduced MP (as observed previously), but again BVC was not significantly changed.

In conscious rats with bladders infused with diluted acetic acid, both tolterodine and oxybutynin administered at the same doses as in animals infused with saline, reduced MP, although the reduction appeared less marked, with no effect on BVC.

In conscious rats utilized 5 days after catheter implantation, a situation where inflammation due to surgery is reduced, the effect of tolterodine (i.v.) and oxybutynin (p.o.) on MP was smaller and similar, respectively, to that observed in rats utilized 1 day after catheter implantation, but the increase of BVC was not statistically significant.

In anesthetized rats, i.v. administration of oxybutynin again induced a significant decrease in MP, although it was of questionable relevance. Both BVC and threshold pressure were not significantly reduced. The number and amplitude of high frequency oscillations in MP were unmodified by treatment.

Finally, in conscious obstructed rats, intravenous oxybutynin did not modify frequency and amplitude of non-voiding contractions or bladder capacity and micturition volume.

Conclusion

Despite the different experimental conditions used, the only effect on cystometrographic parameters of oxybutynin and tolterodine in anesthetized and conscious rats was a decrease in MP, whereas BVC was hardly and non-significantly affected. Therefore, it is difficult to reproduce in rats the cystometrographic increase in BVC as observed in humans after chronic administration of antimuscarinic agents, whereas the acute effects seem more similar.

Urodynamic properties and neurotransmitter dependence of urinary bladder contractility in the BK channel deletion model of overactive bladder

Overactive bladder and incontinence are major medical issues, which lack effective therapy. Previously, we showed (Meredith AL, Thornloe KS, Werner ME, Nelson MT, and Aldrich RW. J Biol Chem 279: 36746-36752, 2004) that the gene mSlo1 encodes large-conductance Ca2+-activated K+ (BK) channels of urinary bladder smooth muscle (UBSM) and that ablation of mSlo1 leads to enhanced myogenic and nerve-mediated contractility and increased urination frequency. Here, we examine the in vivo urodynamic consequences and neurotransmitter dependence in the absence of the BK channel. The sensitivity of contractility to nerve stimulation was greatly enhanced in UBSM strips from Slo-/- mice. The stimulation frequency required to obtain a 50% maximal contraction was 8.3 +/- 0.9 and 19.1 +/- 1.8 Hz in Slo-/- and Slo+/+ mice, respectively. This enhancement is at least partially due to alterations in UBSM excitability, as muscarinic-induced Slo-/- contractility is elevated in the absence of neuronal activity. Muscarinic-induced Slo-/- contractility was mimicked by blocking BK channels with iberiotoxin (IBTX) in Slo+/+ strips, whereas IBTX had no effect on Slo-/- strips. IBTX also enhanced purinergic contractions of Slo+/+ UBSM but was without effect on purinergic contractions of Slo-/- strips. In vivo bladder pressure and urine output measurements (cystometry) were performed on conscious, freely moving mice. Slo-/- mice exhibited increased bladder pressures, pronounced pressure oscillations, and urine dripping. Our results indicate that the BK channel in UBSM has a very significant role in urinary function and dysfunction and as such likely represents an important therapeutic target.

CYSTOMETRIC FINDINGS IN MICE LACKING MUSCARINIC M 2 OR M 3 RECEPTORS

PURPOSE

The physiological importance of muscarinic M3 and M2 receptors for bladder function was investigated in vivo using mice lacking M3 or M2 receptors and littermate WT controls.

MATERIALS AND METHODS

Unanesthetized mice of each sex underwent continuous cystometry before and after administration of atropine (1 mg/kg).

RESULTS

Male M3 knockout (KO) mice had longer voiding intervals, and larger micturition volumes and bladder capacity than M2 KO or WT males. There was no significant difference in any cystometric parameters between male M2 KO and WT mice. In females M3 KO and M2 KO mice had longer voiding intervals and larger micturition volumes than WT animals. Atropine had marked inhibitory effects on voiding efficacy in WT and M2 KO mice but it had no effect on any cystometric parameters in M3 KO mice.

CONCLUSIONS

The current results confirm that M3 receptor is the principal muscarinic receptor subtype responsible for bladder contraction and the role of M2 receptors is of minor importance. Functional impairments found in M3 KO mice were milder than those elicited by acute blockade of muscarinic receptors by atropine in WT mice, suggesting that noncholinergic mechanisms can compensate for a chronic loss of M3 receptors.

Transmitters contributing to the voiding contraction in female rats

OBJECTIVES

To assess in detail the contribution of acetylcholine and ATP to the different phases of the voiding contraction, urine flow and rhabdosphincter electromyographic (RB-EMG) activity in rats, using alpha,beta-methylene-ATP (desensitizing purinoceptors) and atropine (blocking muscarinic receptors). These agents and possibly other transmitters contribute to bladder emptying in rats, but how they contribute to the different phases of the micturition cycle, including the intraluminal pressure high-frequency oscillations (IPHFOs) is unclear.

MATERIALS AND METHODS

Adult anaesthetized female Sprague-Dawley rats were used; intravesical pressure, RB-EMG and urine flow from the distal urethra were recorded. After baseline recordings, alpha,beta-methylene-ATP (0.5 mg/kg), atropine (1 mg/kg), or both, were injected intravenously.

RESULTS

Alpha,beta-Methylene-ATP significantly decreased the maximum bladder pressure during the first micturition phase, whereas atropine had little effect; the maximum bladder pressure during the second phase was also reduced. IPHFOs were apparent after both treatments. Atropine significantly reduced the maximum bladder pressure during the third phase. The maximum urinary flow rate was reduced by both alpha,beta-methylene-ATP and atropine; after exposure to both agents together, urinary flow was markedly reduced or stopped, and overflow incontinence developed.

CONCLUSIONS

ATP contributes mainly to the initial and acetylcholine to the later phases of the voiding cycle in the rat. Neither agent abolished the IPHFOs; even after blocking the receptors for one transmitter and in the presence of IPHFOs, the bladder can still empty. However, if both receptors are blocked, overflow incontinence develops, suggesting that even if further transmitters are taking part in the voiding contraction, their physiological significance is questionable.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Investigation of the effects of P2 purinoceptor ligands on the micturition reflex in female urethane-anaesthetized rats

1 The effects of purinoceptor ligands for P2X1 and/or P2X3 receptors (alpha,beta-meATP, IP(5)I, TNP-ATP, MRS 2179, PPADS, Phenol red and RO116-6446/008; i.v., n=4-5) and for P2Y1 receptors (PPADS, MRS 2179 and MRS 2269; i.v., n=3-5) were investigated on the distension-evoked 'micturition reflex' in the urethane-anaesthetized female rat. 2 Alpha,beta-meATP (180 nmol kg(-1) min(-1)), IP5I (10, 30 and 100 nmol kg(-1)), TNP-ATP (1 micromol kg(-1)), MRS 2179 (1 micromol kg(-1)) and PPADS (17 micromol kg(-1)) each caused maintained bladder contractions to occur during the infusion of saline into the bladder. PPADS (17 micromol kg(-1) min(-1)) had a similar effect when infused intravesicularly. Regular bladder contractions were not observed until the infusion of saline was halted. For IP5I, TNP-ATP, MRS 2179 and PPADS, the magnitude of postinfusion isovolumetric contractions was significantly reduced and, for IP5I, this action was also associated with a significant reduction in urethral relaxation. Additionally, TNP-ATP caused a significant increase in the pressure and volume thresholds required to initiate a reflex. 3 Phenol red (a P2X1/P2X3 antagonist; 0.1 and 1 micromol kg(-1)) caused a significant increase in the pressure and volume thresholds required to initiate a reflex and, at the higher dose, also caused a reduction in postinfusion isovolumetric contractions. 4 RO116-6446/008 (a P2X1-selective antagonist; 1 and 10 micromol kg(-1)) only caused a reduction in postinfusion isovolumetric contractions. 5 It is concluded that P2X1 and P2X3 receptors play a fundamental role in the micturition reflex in urethane-anesthetized female rats. P2X3 receptor blockade raised the pressure and volume thresholds for the reflex, whereas P2X1 receptor blockade diminished motor activity associated with voiding. P2Y1 receptors may be involved in inhibition of rat detrusor tone.

Effects of Tramadol on Rat Detrusor Overactivity Induced by Experimental Cerebral Infarction

OBJECTIVE

Cerebrovascular disease, such as stroke, frequently results in incontinence by reducing suprapontine micturition control. Intraluminal occlusion of the middle cerebral artery (MCA), which produces detrusor overactivity, has been introduced as a useful model of stroke-induced lower urinary tract dysfunction. Recently, the effective analgesic tramadol, was found to possess inhibitory actions on normal rat micturition. The current study aimed to examine the potential effect of tramadol on rat detrusor overactivity due to cerebral infarction.

METHODS

In female Sprague-Dawley rats, cerebral ischemia was induced by occlusion of the MCA and the urinary bladder was catheterised. Three days later, continuous cystometry was performed in awake animals and the effects of tramadol given intravenously were studied.

RESULTS

In cerebral infarcted rats, bladder capacity was lower (48+/-9%) and micturition pressure higher (76+/-21%) than in control rats. Tramadol 5 mg x kg(-1) given i.v., increased bladder capacity (59+/-29%) and threshold pressure (47+/-32%) to values similar to those in control rats. However, micturition pressure was not significantly altered. Tramadol induced diuresis in some, but not all, cerebral infarcted rats.

CONCLUSION

Tramadol normalised detrusor overactivity in MCA-occluded rats. The drug might have a treatment potential in patients with detrusor overactivity after stroke.

Effects of intravenous and infravesical administration of suramin, terazosin and BMY 7378 on bladder instability in conscious rats with bladder outlet obstruction

OBJECTIVE

To evaluate the effect of the nonselective purinergic antagonist suramin and the alpha1-adrenergic antagonists, terazosin and BMY 7378, given intravenously or infused directly into the bladder during cystometry in conscious rats with bladder outlet obstruction induced by urethral ligation.

MATERIALS AND METHODS

Cystometry was performed in conscious female rats recording bladder volume capacity (BVC), evaluated as the amount of saline infused between two voiding cycles, and micturition volume (MV). Changes in frequency and amplitude of spontaneous non-voiding bladder contractions (NVC) were also recorded. The effects of the intravenous administration of suramin (100 mg/kg), BMY 7378 (1 mg/kg), and terazosin (0.3 mg/kg) on NVC, BVC and MV were evaluated in obstructed rats with bladder infusion of saline. The effects of infravesical infusion of suramin (3-10 micromol/L), terazosin (1 micromol/L) and BMY 7378 (10 micromol/L) were also evaluated and compared with values observed in control rats during saline infusion into the bladder.

RESULTS

Intravenous injection with suramin had no effects on NVC, BVC and MV, but suramin infused into the bladder induced a consistent reduction in the amplitude of NVC (significantly different from matched control animals) with a tendency to reduce their frequency. BVC and MV were slightly but significantly decreased by infravesical infusion of suramin. In contrast, BMY 7378 and terazosin, given intravenously, were extremely potent at inhibiting the frequency and amplitude of the NVC, but were inactive on NVC when infused into bladder.

CONCLUSIONS

These findings confirm a role for alpha1-adrenergic receptors in bladder instability caused by bladder outlet obstruction. In addition, a purinergic neurotransmitter, presumably ATP, is shown to be involved.

Role of protein kinase C in central muscarinic inhibitory mechanisms regulating voiding in rats

To evaluate the role of protein kinase C in central muscarinic mechanisms regulating voiding, cystometry was performed in conscious rats. Oxotremorine methiodide, a muscarinic agonist was injected i.c.v. in a dose (0.1 microg/rat) shown previously to alter voiding function. Oxotremorine methiodide was also tested after i.c.v. injection of chelerythrine chloride (a protein kinase C inhibitor, 2 microg/rat) or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7, a protein kinase inhibitor, 5 nmol/rat). In untreated rats, oxotremorine methiodide elicited a bimodal response consisting of an initial increase in bladder capacity, maximal voiding pressure, pressure threshold and post voiding intravesical pressure, but reduced voiding efficiency and bladder compliance. The second response consisted of a decrease in bladder capacity and bladder compliance, increases in maximal voiding pressure and post voiding intravesical pressure, but no change in pressure threshold or voiding efficiency. However, approximately 20 min after pre-treatment with chelerythrine chloride or H-7 in doses that did not alter voiding function, oxotremorine methiodide decreased bladder capacity, increased maximal voiding pressure, but did not change pressure threshold or voiding efficiency. These results indicate that inhibitory and facilitatory muscarinic mechanisms in the brain that control voiding function involve different second messenger systems. Inhibitory mechanisms which are blocked by chelerythrine chloride or H-7 must involve protein kinase C and normally be inactive because the protein kinase inhibitors alone did not alter voiding. On the other hand, facilitatory muscarinic mechanisms which previous studies showed were tonically active are not mediated by chelerythrine chloride or H-7 sensitive signaling pathways.

Effects of beta(3)-adrenoceptor stimulation on prostaglandin E(2)-induced bladder hyperactivity and on the cardiovascular system in conscious rats

AIMS

To investigate the effects of selective beta(2)- and selective beta(3)-adrenoceptor (AR) agonists on prostaglandin (PG) E(2)-induced bladder hyperactivity in conscious free-moving rats.

METHODS

Female Sprague-Dawley rats were anesthetized for implantation of bladder, intravenous, and intra-arterial catheters. The effects of a beta(3)-AR agonist (CL316,243) on cystometric and cardiovascular parameters were assessed in conscious rats. Intravesical instillation of PGE(2) (20-60 microM, 6 mL/hr) in conscious rats produced a concentration-dependent increase in voiding frequency.

RESULTS

In this model i.v. CL316,243 (beta(3)-AR agonist) reduced basal bladder pressure, increased micturition volume, and prolonged micturition interval in a dose-dependent manner, without affecting threshold pressure or micturition pressure. On the other hand, i.v. procaterol (beta(2)-AR agonist) did not counteract the bladder hyperactivity. Atropine (muscarinic antagonist) reduced micturition pressure and micturition volume, and shortened micturition interval. CL316,243 slightly decreased mean blood pressure and increased heart rate only when given at high doses (10 and 100 microg/kg, i.v.). In contrast, procaterol caused a significant decrease in mean blood pressure and a significant increase in heart rate. Atropine significantly increased heart rate.

CONCLUSIONS

The present results clearly demonstrated that the beta(3)-AR agonist prolonged the micturition interval without producing significant cardiovascular side effects. The human detrusor, like the rat detrusor, relaxes on beta(3)-AR stimulation. Provided that these results are valid in humans, selective beta(3)-AR agonists might be clinically useful for controlling a certain type of bladder overactivity.

Effect of muscarinic antagonists on micturition pressure measured by cystometry in normal, conscious rats

OBJECTIVES

To establish an in vivo model to screen new muscarinic antagonists for the treatment of overactive urinary bladder and to calculate the respective ID(50) values.

METHODS

The conscious rat cystometry model was modified to determine a complete dose-response curve in each animal. Spontaneous micturition was induced by infusion of room-temperature saline into rat bladders at a constant rate of 12 mL/hr. Cumulative doses of muscarinic antagonists administered in the femoral vein caused dose-dependent inhibition of the urinary bladder contraction measured as the micturition pressure. In addition, the in vitro pK(B) values for atropine, PNU-200577 (DD01), tolterodine, oxybutynin, and terodiline were determined in carbachol-contracted rat bladder strips.

RESULTS

The rank order of the in vivo ID(50) values were atropine (14 +/- 4 nmol/kg), PNU-200577 (22 +/- 12 nmol/kg), tolterodine (94 +/- 20 nmol/kg), oxybutynin (175 +/- 89 nmol/kg), darifenacin (236 +/- 144 nmol/kg), desethyloxybutynin (313 +/- 209 nmol/kg), propiverine (4561 +/- 2079 nmol/kg), and terodiline (18,339 +/- 5348 nmol/kg). Tolterodine and PNU-200577 caused a parallel shift of the in vitro concentration-response curve to the right and did not alter the maximal contraction. The ID(50) values correlated significantly with the in vitro rat pK(B) and human bladder pA(2) values.

CONCLUSIONS

The present results suggest that the rat cystometry model can be used in in vivo screening for new muscarinic antagonists.

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.

Influence of pump compliance (peristaltic vs. infusion) on urodynamic measurement during cystometry in conscious rats

Cystometry, employing natural or pump-induced bladder filling, is the most widely used method for studying bladder reflexes and micturition in conscious rats. However, discrepancies in basal values of urodynamic parameters are often reported, especially for micturition pressure. The aim of this study was to establish whether the type of pump used (peristaltic or infusion) might yield different urodynamic parameters. Differences between natural filling (evaluated in water-loaded animals and considered "physiological micturition") and pump-evoked cystometrograms, as well as the compliance of these systems, and the effects of pharmacologically diverse drugs (prazosin, oxybutynin, and naproxen) acting on the bladder voiding were evaluated. Micturition pressure recorded from pump-evoked cystometrograms showed differences from natural micturition that were related to the total compliance of the system (pump + tube) and not only to the nature of the pump used. Drug-induced changes of micturition pressure during natural micturition resembled those recorded during bladder infusion with a peristaltic pump more than those with an infusion pump. Other basal values and drug-induced changes of bladder capacity were the same during natural and pump-evoked micturition. The present findings indicate that cystometrographic parameters obtained during pump-evoked micturition with a system at high compliance (peristaltic pump) are equivalent to those observed during physiological micturition.

Role of dopamine D1 and D2 receptors in the micturition reflex in conscious rats

To clarify the role of dopamine D1 and D2 receptors in the volume-induced micturition reflex, conscious, female rats were investigated cystometrically before and after intravenous administration of SKF 38393 (a selective D1 receptor agonist), SCH 23390 (a selective D1 receptor antagonist), quinpirole (a selective D2 receptor agonist), and remoxipride (a selective D2 receptor antagonist). The effect of quinpirole was also investigated in the presence of remoxipride. Intravenous administration of SKF 38393 (0.01-3.0 mg/kg) did not affect any cystometric parameters investigated. On the other hand, SCH 23390 (0.1-1.0 mg/kg i.v.) reduced bladder capacity and micturition volumes and increased the micturition pressure in a dose-dependent manner. Quinpirole (0.01-0.1 mg/kg) given intravenously, dose-dependently decreased bladder capacity and micturition volumes. Pre-treatment with remoxipride (1.0 mg/kg i.v.) significantly attenuated the effect of quinpirole (0.1 mg/kg i.v.). Remoxipride (0.1-1.0 mg i.v.) itself did not cause any significant changes in the cystometric parameters. These results suggest that in conscious rats, D1 receptors tonically inhibit the micturition reflex and that D2 receptors are involved in facilitation of the micturition reflex. It may be speculated that detrusor hyperreflexia associated with Parkinson's disease results from activation failure of D1 receptors and that administration of D2 receptor agonists might worsen the condition.

P2X receptor expression in mouse urinary bladder and the requirement of P2X(1) receptors for functional P2X receptor responses in the mouse urinary bladder smooth muscle

1. We have used subtype selective P2X receptor antibodies to determine the expression of P2X(1 - 7) receptor subunits in the mouse urinary bladder. In addition we have compared P2X receptor mediated responses in normal and P2X(1) receptor deficient mice to determine the contribution of the P2X(1) receptor to the mouse bladder smooth muscle P2X receptor phenotype. 2. P2X(1) receptor immunoreactivity was restricted to smooth muscle of the bladder and arteries and was predominantly associated with the extracellular membrane. Diffuse P2X(2) and P2X(4) receptor immunoreactivity not associated with the extracellular membrane was detected in the smooth muscle and epithelial layers. Immunoreactivity for the P2X(7) receptor was associated with the innermost epithelial layers and some diffuse staining was seen in the smooth muscle layer. P2X(3), P2X(5) and P2X(6) receptor immunoreactivity was not detected. 3. P2X receptor mediated inward currents and contractions were abolished in bladder smooth muscle from P2X(1) receptor deficient mice. In normal bladder nerve stimulation evoked contractions with P2X and muscarinic acetylcholine (mACh) receptor mediated components. In bladder from the P2X(1) receptor deficient mouse the contraction was mediated solely by mACh receptors. Contractions to carbachol were unaffected in P2X(1) receptor deficient mice demonstrating that there had been no compensatory effect on mACh receptors. 4. These results indicate that homomeric P2X(1) receptors underlie the bladder smooth muscle P2X receptor phenotype and suggest that mouse bladder from P2X(1) receptor deficient and normal animals may be models of human bladder function in normal and diseased states.

Multiple functional defects in peripheral autonomic organs in mice lacking muscarinic acetylcholine receptor gene for the M3 subtype

Muscarinic acetylcholine receptors consist of five distinct subtypes and have been important targets for drug development. In the periphery, muscarinic acetylcholine receptors mediate cholinergic signals to autonomic organs, but specific physiological functions of each subtype remain poorly elucidated. Here, we have constructed and analyzed mutant mice lacking the M(3) receptor and have demonstrated that this subtype plays key roles in salivary secretion, pupillary constriction, and bladder detrusor contractions. However, M(3)-mediated signals in digestive and reproductive organs are dispensable, likely because of redundant mechanisms through other muscarinic acetylcholine receptor subtypes or other mediators. In addition, we have found prominent urinary retention only in the male, which indicates a considerable sex difference in the micturition mechanism. Accordingly, this mutant mouse should provide a useful animal model for investigation of human diseases that are affected in the peripheral cholinergic functions.

Neural mechanisms of impaired micturition reflex in rats with acute partial bladder outlet obstruction

To determine the contribution of neural elements to micturition, we evaluated, in intact rats, the cystometrogram, pelvic afferent nervous activity, pelvic efferent nervous activity and external urethral sphincter-electromyogram activity in the normal and acute partial bladder outlet obstruction states. In the normal state, in response to saline filling, mechanoreceptor-dependent pelvic afferent nervous activity gradually activated and finally triggered a voiding reflex, including four phases of detrusor contractions. Phase 1 was characterized by an initial rising intravesical pressure, Phase 2 was characterized by a series of high-frequency oscillations in intravesical pressure, Phase 3 contraction was characterized by a rebound intravesical pressure and Phase 4 contraction was characterized by a rapid fall in intravesical pressure. In the acute partial bladder outlet obstruction state, Phase 1 contraction rose and high-frequency oscillations fell in Phase 2. This voiding dysfunction is ascribed to the bursting extraurethral sphincter activity being converted to tonic extraurethral sphincter activity. In summary, the suppressed high-frequency oscillations in Phase 2 of the detrusor muscle contraction could be detrimental to efficient voidings in the acute partial bladder outlet obstructed rat.

Synthesis and antimuscarinic activity of a series of 4-(1-Imidazolyl)-2,2-diphenylbutyramides: discovery of potent and subtype-selective antimuscarinic agents

In a study directed toward the development of new, selective agents with potential utility in the treatment of altered smooth muscle contractility and tone, for example, as seen in urinary incontinence associated with bladder muscle instability, a series of 4-(1-imidazolyl)-2,2-diphenylbutyramide derivatives was prepared. These compounds were examined for M1, M2, and M3 muscarinic receptor subtype selectivity in isolated tissue assays. The compounds that showed potency and/or selectivity in these tests were further evaluated for in vivo anticholinergic effects on various organs and tissues, including urinary bladder, salivary gland, and eye in rats. The structure activity relationships for the series of 4-(1-imidazolyl)-2,2-diphenylbutyramide derivatives are also discussed. This study led to the identification of 4-(2-methyl-1-imidazolyl)-2,2-diphenylbutyramide (KRP-197) as a candidate drug for the treatment of urinary bladder dysfunction.

Bladder afferent pathway and spinal cord injury: possible mechanisms inducing hyperreflexia of the urinary bladder

Lower urinary tract dysfunction is a common problem in patients with spinal cord injury (SCI). Since the coordination of the urinary bladder and urethra is controlled by the complex mechanisms in spinal and supraspinal neural pathways, SCI rostral to the lumbosacral level disrupts voluntary and supraspinal control of voiding and induces a considerable reorganization of the micturition reflex pathway. Following SCI, the urinary bladder is initially areflexic. but then becomes hyperreflexic because of the emergence of a spinal micturition reflex pathway. Recent electrophysiologic and histologic studies in rats have revealed that chronic SCI induces various phenotypic changes in bladder afferent neurons such as: (1) somal hypertrophy along with increased expression of neurofilament protein; and (2) increased excitability due to the plasticity of Na+ and K+ ion channels. These results have now provided detailed information to support the previous notion that capsaicin-sensitive, unmyelinated C-fiber afferents innervating the urinary bladder change their properties after SCI and are responsible for inducing bladder hyperreflexia in both humans and animals. It is also suggested that the changes in bladder reflex pathways following SCI are influenced by neural-target organ interactions probably mediated by neurotrophic signals originating in the hypertrophied bladder. Thus, increased knowledge of the plasticity in bladder afferent pathways may help to explain the pathogenesis of lower urinary tract dysfunctions after SCI and may provide valuable insights into new therapeutic strategies for urinary symptoms in spinal cord-injured patients.

Postnatal development of purinoceptors in rat visceral smooth muscle preparations

1. Adenosine and ATP have well-established functions as neuromodulator and neurotransmitter, respectively, in smooth muscle preparations, and purinergic control may be an early form of autonomic control in both evolution and ontogenesis. 2. This review describes the postnatal development of responses mediated by the various receptors for adenosine and for nucleotides in the rat duodenum, colon, urinary bladder and vas deferens and considers the implications that this development may have for the importance of purinergic control in neonates and adults.

Evidence for purinergic neurotransmission in the urinary bladder of pithed rats

The purpose of this study was to investigate the contribution of adenosine-5'-triphosphate (ATP) to segmental (L6-S2) spinal electrical stimulation evoked increases in intra-vesical pressure in pithed rats. Exogenous ATP and substance P produced dose-dependent increases in intra-vesical pressure (ED10 mmHg (dose required to elicit 10 mmHg increase in intra-vesical pressure)= 1.7 mg/kg and 1.1 microg/kg, i.v., respectively). Desensitisation (or antagonism) of P2x purinoceptors with alpha,beta-methylene ATP (alpha,beta-meATP; 30 microg/kg per min, i.v.) or pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; 10 mg/kg, i.v.) significantly (p < 0.05) antagonized the intra-vesical pressure responses to ATP (> 8 and 3.6-fold increase in ED10 mmHg, respectively) but had no significant effect on intra-vesical pressure responses to substance P. Spinal stimulation evoked frequency-dependent increases in intra-vesical pressure (EF20 mmHg (frequency required to produce 20 mmHg increase in intra-vesical pressure) = 3.4 Hz). Blockade of muscarinic cholinoceptors and adrenoceptors with atropine (3 mg/kg, i.v.), propranolol (3 mg/kg, i.v.) and phentolamine (10 mg/kg, i.v.) produced marginal attenuation of the intra-vesical pressure responses to spinal stimulation indicating a major non-adrenergic non-cholinergic (NANC) component in the overall response. The NANC responses were significantly (p < 0.05) antagonized by alpha,beta-meATP (30 microg/kg per min, i.v.) and PPADS (10 mg/kg, i.v.) (> 2.6-fold increase in EF20 mmHg), consistent with involvement of a purinergic neurotransmitter, presumably ATP. Comparative studies in young (4-6 months) and old (21-23 months) Fischer rats revealed no age-dependent changes in the relative contribution of the cholinergic and purinergic systems, with the latter being the dominant one. These findings suggest that purinergic neurotransmission, presumably mediated by ATP acting via P2x purinoceptors, represents a major component of excitatory innervation to the urinary bladder in pithed rats.

In vitro functional properties of the rat bladder regenerated by the bladder acellular matrix graft

PURPOSE

To assess the response of rat urinary bladder regenerated by the homologous bladder acellular matrix graft (BAMG) to in vitro electrical and pharmacologic stimuli.

MATERIALS AND METHODS

In Sprague-Dawley rats, partial cystectomy (>50%) was performed, followed by BAMG augmentation cystoplasty. After 4 months, organ bath studies of tissue strips in 10 were used to compare the contractility of the BAMG regenerates and the corresponding host detrusor smooth muscle.

RESULTS

The BAMG regenerates exhibited contractile activity to electrical field stimulation and a qualitatively identical pattern of response to muscarinic, purinergic, alpha- and beta-adrenergic drug administration and nitric oxide. At 4 months after surgery, the maximum forces of contraction of the BAMG regenerates to carbachol stimulation amounted to close to 80% of the host bladder response. With electrical field stimulation, they equaled 44% and 62% of the host bladder response after 2.5 and 4 months, respectively. Histological and immunohistochemical studies confirmed the presence of receptors for neurotransmitters that these functional in vitro studies implied.

CONCLUSIONS

The present study provides further evidence that augmentation cystoplasty with the BAMG leads to functional regeneration of the rat bladder detrusor smooth muscle.

Neurogenic and non-neurogenic responses in the urinary bladder of hibernating hamster

1. Purinergic and cholinergic components of parasympathetic neurotransmission and contractile responses to exogenous alpha,beta-methylene ATP, acetylcholine, substance K, substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide and capsaicin have been investigated in the urinary bladder of hibernating hamsters (4 weeks), cold exposed (4 weeks) and age-matched controls. 2. Electrical field stimulation (EFS) evoked increased frequency-dependent contractions in the detrusor strips from hibernating hamsters compared with those obtained from cold-exposed and age-matched animals. Tetrodotoxin (10(-6) M) completely blocked the frequency-dependent contractions in all groups. 3. The purinergic component of the parasympathetic neurotransmission was not affected in hibernating and cold-exposed animals while the cholinergic component was increased with respect to age-matched animals. The neurogenic response to EFS, still present after incubation with atropine (10(-6) M) and suramin (10(-4) M), was attenuated by indomethacin (10(-6) M) and blocked by tetrodotoxin (10(-6) M). 4. Exogenous administration of alpha,beta-methylene ATP elicited a significantly reduced contraction in strips from hibernating and cold-exposed hamsters relative to age-matched animals. The contractile response to exogenous acetylcholine was greater in the detrusors from hibernating hamsters than in cold-exposed and age-matched animals. Substance K elicited reduced contractions in preparations from hibernating animals compared with cold-exposed and control animals. Calcitonin gene-related peptide, vasoactive intestinal polypeptide, substance P and capsaicin did not elicit any relaxant or contractile response either at resting tone or in carbachol (5 x 10(-7) M)-precontracted tissues. 5. In summary, our findings indicate that 4 weeks of hibernation can significantly increase neurogenic responses in the hamster urinary bladder. This appears to be due to an increase in postjunctional responses to acetylcholine. In contrast, there was a decrease of the postjunctional responses to the parasympathetic cotransmitter ATP and also to the sensory-motor neurotransmitter substance K.

A pharmacological and histochemical study of hamster urethra and the role of urothelium

1. Electrical field stimulation (EFS) of circular strips of hamster proximal urethra caused frequency-dependent relaxations at raised tone. Phentolamine (10(-6) M), propranolol (10(-6) M) and atropine (10(-6) M) were present throughout the experiment. Neurogenic relaxation was attenuated by L-NG-nitroarginine methyl ester (L-NAME) (10(-4) M), was restored by L-arginine (3 x 10(-3) M) but not by D-arginine (3 x 10(-3) M) and completely blocked by tetrodotoxin (10(-6) M). Neurogenic relaxation was also reduced by suramin (10(-4) M) and totally blocked by suramin together with L-NAME. Strips of hamster urethra devoid of urothelium showed little, if any, relaxant response to EFS. 2. An immunohistochemical study showed nitric oxide synthase-immunoreactive nerves in the smooth muscle layers and in the lamina propria, just beneath the urothelium, but no nitric oxide synthase (NOS) staining in the urothelial layer. 3. Noradrenaline elicited a significantly greater contraction in strips without urothelium than in control strips. L-NAME (10(-4) M) did not affect noradrenaline-induced contraction in both control and urothelium-free strips. The contractile response to acetylcholine was not dependent on the presence or absence of urothelium. Nevertheless the response induced by exogenous acetylcholine (10(-3) M) was increased by L-NAME (10(-4) M), both in intact and in urothelium-free strips. 4. Prostaglandin E2 (10(-8)-5 x 10(-6) M) and 2-methyl-thio-ATP (10(-9)-10(-5) M) relaxed proximal urethra. Suramin (10(-4) M) significantly inhibited the relaxation induced by 2-methyl-thio-ATP. The amplitude of these responses was not significantly different between intact and urothelium-free strips and was not blocked by L-NAME (10(-4) M). 5. These results suggest that nitric oxide (NO) is the principal transmitter involved in the non-adrenergic, non-cholinergic (NANC) relaxation of hamster proximal urethra possibly together with another inhibitory transmitter released from nerves. NO can be released from nerves located in the circular smooth muscle layer and in the lamina propria rather than in the urothelium. The reduced neurogenic relaxation in urothelium-free preparations suggests that a NO-dependent inhibitory factor is released from the urothelium. In addition, ATP and prostaglandin E2 may be involved, together with NO, in the urethra during micturition.

Functional, biochemical and anatomical changes in the rat urinary bladder induced by perigangliar injection of colchicine

The aim of this study was to assess the effect of blocking the axonal transport of sensory neuropeptides, by local injection of colchicine at pelvic ganglia level, on the sensory and efferent functions mediated by capsaicin-sensitive primary afferent neurons innervating the rat urinary bladder. Bilateral injection of colchicine in the prostatic tissue underneath the pelvic ganglia of male rats induced a time-dependent reduction (maximal at 72 h, 100% reduction) of the in vitro contraction of the bladder strips induced by capsaicin (1 microM). The response to electrical field stimulation was also reduced, although to a lesser extent. The direct contractions induced by substance P (100 nM) or KCl (80 mM) were not affected by colchicine pretreatment. In vivo, perigangliar injection of colchicine (72 h before) greatly increased bladder capacity, and reduced the amplitude of micturition contractions and micturition frequency. Capsaicin-induced plasma protein extravasation was abolished in the urinary bladder and reduced in the distal, but not the proximal ureter of colchicine-treated rats. Topical application of capsaicin onto the urinary bladder or onto the stomach induced a cardiovascular pressor reflex in urethane-anaesthetized, spinalized rats. Colchicine pretreatment reduced (by about 50%) the pressor response elicited by chemonociceptive stimulation of the bladder but not that arising from the stomach. Colchicine pretreatment did not produce overt changes of nerve profiles immunoreactive for calcitonin gene-related peptide- or tachykinin-like material in the rat urinary bladder. A more intense staining of nerve fibres positive for calcitonin-gene related peptide-like immunoreactivity and tachykinin-like immunoreactivity was observed in pelvic ganglia of colchicine-pretreated rats. No changes were detected in the dorsal horns of spinal cord segments where pelvic bladder afferents project (L6-S1). Colchicine pretreatment reduced, but did not abolish, bladder levels of substance P-, neurokinin A-, calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity. However, vasoactive intestinal peptide-like immunoreactivity levels were not changed. The capsaicin-evoked (1 microM) release of calcitonin gene-related peptide was abolished in capsaicin as well as in colchicine-pretreated animals. The present findings demonstrate that local treatment of pelvic ganglia with colchicine totally eliminates the "efferent" functions of capsaicin-sensitive afferent nerves in the urinary bladder. Although reduced, tissue levels of sensory neuropeptides are not completely depleted, thus indicating the existence of a releasable versus non-releasable pool. The chemically induced blockade of axoplasmic transport also induces a limited impairment of the sensory function of capsaicin-sensitive afferents, and of the parasympathetic efferent system.

Prostaglandin E2-induced bladder hyperactivity in normal, conscious rats: involvement of tachykinins?

In normal conscious rats investigated by continuous cystometry, intravesically instilled prostaglandin (PG) E2 facilitated micturition and increased basal intravesical pressure. The effect was attenuated by both the NK1 receptor selective antagonist RP 67,580 and the NK2 receptor selective antagonist SR 48,968, given intra-arterially, suggesting that it was mediated by stimulation of both NK1 and NK2 receptors. Intra-arterially given PGE2 produced a distinct increase in bladder pressure before initiating a micturition reflex, indicating that the PG had a direct contractant effect on the detrusor smooth muscle. The effect of intra-arterial PGE2 could not be blocked by intra-arterial RP 67,580 or SR 48,968, which opens the possibility that the micturition reflex elicited by intra-arterial PGE2 was mediated by pathways other than the reflex initiated when the PG was given intravesically. The present results thus suggest that intra-arterial PGE2, given near the bladder, may initiate micturition in the normal rat chiefly by directly contracting the smooth muscle of the detrusor. However, when given intravesically, PGE2 may stimulate micturition by releasing tachykinins from nerves in and/or immediately below the urothelium. These tachykinins, in turn, initiate a micturition reflex by stimulating NK1 and NK2 receptors. Prostanoids may, via release of tachykinins, contribute to both urge and bladder hyperactivity seen in inflammatory conditions of the lower urinary tract.

Effects of purinoceptor agonists on smooth muscle from hypertrophied rat urinary bladder

Tension responses induced by the purinoceptor agonists ATP and the stable ATP analogue alpha, beta-methylene ATP were investigated in isolated muscle strips from normal and hypertrophic urinary bladders from the rat. Hypertrophy was induced by a partial ligation of the urethra giving an increase in mean bladder weight from 65 mg to 300 mg. Activation with ATP and alpha, beta-methylene ATP caused phasic, concentration-dependent, contractions. The sensitivity to ATP was about 100-fold lower than that for alpha, beta-methylene ATP. The force of the contractions induced by the purinoceptor agonists was significantly lower in the hypertrophied bladder compared to the controls. The kinetics of the ATP-induced responses was studied by photolytic release of ATP from caged-ATP in intact fibre bundles. The rate of contraction following photolytic release of ATP was slower, and the force amplitude lower, in the hypertrophic preparations compared to the controls. The results suggest changes in the purinoceptor function or in the responses of the contractile system to transient increases in intracellular Ca2+ in the hypertrophic bladder.

Purinergic and cholinergic components of bladder contractility and flow

The role of ATP as a neurotransmitter/neuromodulator in the urinary tract has been the subject of much study, particularly whether ATP has a functional role in producing urine flow. Recent studies suggested significant species variation, specifically a variation between cat and other species. This study was performed to determine the in vivo response of cat urinary bladder to pelvic nerve stimulation (PNS) and to the exogenous administration of cholinergic and purinergic agents. In anesthetized cats, bladder contractions and fluid expulsion was measured in response to PNS and to the exogenous administration of cholinergic and purinergic agents. Fluid was instilled into the bladder and any fluid expelled by bladder contractions induced by PNS or exogenous agents was collected in a beaker. The volume was measured in a graduated cylinder and recorded. PNS, carbachol and APPCP produced sustained contractions with significant expulsion of fluid. ATP, ACh and hypogastric nerve stimulation did not produce any significant expulsion of fluid. Atropine, a cholinergic antagonist, inhibited PNS contractions and fluid expulsion with no effect on purinergic actions. There was a significant relationship between the magnitude of the contraction, duration of the contractions and volume of fluid expelled. The data and information from other studies, strongly suggests a functional role for ATP as a cotransmitter in the lower urinary tract different from ACh's role. ATP stimulation of a specific purinergic receptor plays a role in initiation of bladder contractions and perhaps in the initiation of urine flow from the bladder. ACh's role is functionally different and appears to be more involved in maintenance of contractile activity and flow.

Micturition and premicturition contractions in unanesthetized rats with bladder outlet obstruction

The cholinergic and purinergic neurotransmission involved in micturition contraction and premicturition contractile activity (bladder hyperactivity) were investigated by continuous cystometry in unanesthetized rats with outlet obstruction. Adenosine triphosphate (ATP), administered intra-arterially close to the bladder, produced rapid, phasic dose-dependent increases in bladder pressure and micturition immediately after the injections. The percentage volume expelled was 74 +/- 9% after 5 mg/kg. Intra-arterial alpha,beta-methylene ATP also produced a rapid, phasic increase in bladder pressure and micturition immediately after the injection. The percentage volume expelled was 96 +/- 3% after 1 mg./kg; the residual volume of the following voidings increased, and the micturition pressure tended to decrease. However, dribbling incontinence was not produced. The amplitude of the premicturition contractions decreased significantly (p < 0.01) after the administration. Intra-arterial carbachol produced rapid, longlasting dose-dependent increases in bladder pressure and micturition. The percentage volume expelled was 88 +/- 4 after 5 micrograms./kg. Bladder capacity and micturition volume decreased significantly (p < 0.05) during the following spontaneous voidings. Intra-arterial atropine (1 mg./kg.) increased bladder capacity (p < 0.01) and residual volume (p < 0.01), and tended to decrease micturition pressure (by 25%) and micturition volume. However, micturition contractions still remained after the injection, even if they changed appearance, and were of shorter duration. Atropine had no effect on the premicturition contractions. In the presence of atropine, alpha,beta-methylene ATP initially produced a rapid, phasic increase in bladder pressure with micturition. Then, dribbling incontinence was observed in 1 of 5 animals. Hexamethonium, administered intra-arterially in doses producing urinary retention and dribbling incontinence (20 or 40 mg./kg.), increased the amplitude of the premicturition contractions, but decreased the frequency of the contractions. Intra-arterial tetrodotoxin (15 micrograms./kg.) inhibited micturition, and produced dribbling incontinence in all animals tested (n = 6). However, the amplitude of the premicturition contractions was not suppressed. Intra-arterial (+/-)-pinacidil (0.2 mg./kg.) significantly (p < 0.05) decreased both amplitude and frequency of these contractions. It is concluded that both cholinergic and purinergic transmission seem to be of importance for pressure generation and emptying of the bladder in rats with outlet obstruction. The present results also give further support for the view that the premicturition contractions seen in these animals are of myogenic origin.

Effects of omega-conotoxin on adrenergic, cholinergic and NANC neurotransmission in the rabbit urethra and detrusor

1. The effects of omega-conotoxin GVIA (an inhibitor of N-type voltage-operated calcium channels; VOCCs) were compared on adrenergic, cholinergic and non-adrenergic, non-cholinergic (NANC) responses induced by electrical field stimulation (EFS) in the rabbit urethra and detrusor. 2. EFS induced a relaxation in urethral smooth muscle and lamina propria precontracted by arginine vasopressin (AVP). The relaxation was abolished by tetrodotoxin (TTX) or the nitric oxide (NO) synthase inhibitor N omega-nitro-L-arginine. omega-Conotoxin inhibited the relaxation induced by EFS, but not that elicited by the NO donor 3-morpholino-sydnonimin. The inhibition, however, decreased with increasing frequencies of stimulation. Nimodipine, tetramethrin and nickel did not affect the omega-contoxin-resistant relaxation in lamina propria, suggesting that neuronal L or T VOCCs were not involved in the response. 3. EFS contracted urethral smooth muscle at resting tension. The contractions were virtually abolished by TTX or prazosin. omega-Conotoxin effectively inhibited the contractile responses to EFS, but not those to exogenous noradrenaline. An omega-conotoxin-resistant contraction was, however, observed at high frequencies of stimulation. 4. The detrusor responded with frequency-dependent contractions upon EFS. A TTX-resistant contraction less than 10% of controls remained at 30 Hz stimulation. At a stimulation frequency of 10 Hz, scopolamine reduced the EFS-induced contraction by 71%. omega-Conotoxin inhibited the responses in both the absence and presence of scopolamine. The inhibition decreased with increasing frequencies of stimulation (examined in the absence of scopolamine). omega-Conotoxin did not affect the contractile responses to carbachol or adenosine 5'-triphosphate. 5. The adrenergic contraction (25 Hz) and NANC relaxation (10 Hz) in the urethra, and cholinergic and NANC contractions (10 Hz) in the detrusor were inhibited concentration-dependently by omega-conotoxin.The adrenergic contraction in the urethra was 10 times and the cholinergic contraction in the detrusor was three times more sensitive to omega-conotoxin than the NANC responses.6. These results suggest that NANC neurotransmission is less inhibited by omega-conotoxin than transmission mediated by adrenergic and cholinergic nerves in the rabbit lower urinary tract. In the urethra a marked omega-conotoxin-resistant component of the NANC relaxation was observed which increased with increasing stimulation frequencies and was unaffected by inhibitors of L and T type VOCCs. This raises the question whether VOCCs of a type other than L, T, and N is involved in the mediation of this response.