Cholinergic innervation of the human urethra and urinary bladder: a histochemical study and review of methodology

Dog and human bladders have different neurogenic and nicotinic responses in inner versus outer detrusor muscle layers

The aim of this study was to investigate layer and species variations in detrusor muscle strip responses to myogenic, neurogenic, and nicotinic, and muscarinic receptor stimulations. Strips from bladders of 9 dogs and 6 human organ transplant donors were dissected from inner and outer longitudinal muscle layers, at least 1 cm above urethral orifices. Strips were mounted in muscle baths and maximal responses to neurogenic stimulation using electrical field stimulation (EFS) and myogenic stimulation using potassium chloride (KCl, 120 mM) determined. After washing and re-equilibration was completed, responses to nicotinic receptor agonist epibatidine (10 μM) were determined followed by responses to EFS and muscarinic receptor agonist bethanechol (30 μM) in continued presence of epibatidine. Thereafter, strips and full-thickness bladder sections from four additional dogs and three human donors were examined for axonal density and intramural ganglia. In dog bladders, contractions to KCl, epibatidine, and bethanechol were 1.5- to 2-fold higher in the inner longitudinal muscle layer, whereas contractions to EFS were 1.5-fold higher in the outer (both pre- and post-epibatidine). Human bladders showed 1.2-fold greater contractions to epibatidine in the inner layer and to EFS in the outer, yet no layer differences to KCl or bethanechol were noted. In both species, axonal density was 2- to 2.5-fold greater in the outer layer. Dogs had more intramural ganglia in the adventitia/serosa layer, compared with more internal layers and to humans. These findings indicate several layer-dependent differences in receptor expression or distribution, and neurogenic responses in dog and human detrusor muscles, and myogenic/muscarinic differences between dog versus humans.

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.

Quantitative immunohistochemical study of the innervation of the guinea-pig lower urinary tract

OBJECTIVE

To study the innervation of the different muscle systems of the guinea-pig lower urinary tract, using immunohistochemical and enzyme histochemical methods.

MATERIALS AND METHODS

Serial cryostat sections of both genders (four guinea-pigs each) were quantitatively analysed for cholinergic, adrenergic and peptidergic nerve fibre density using specific antibodies or enzyme histochemical labelling. Smooth muscle cell nuclei and varicosities or sectioned nerves were counted in detrusor, internal vesical sphincter (VS), ventral longitudinal musculature (VLM), and dorsal longitudinal musculature (DLM), and the ratios of nerves/nucleus (for detrusor, VLM and DLM) were evaluated statistically. The striated and the smooth external sphincter were examined qualitatively.

RESULTS

Detrusor, VS, VLM and DLM had significantly different innervation patterns. In detrusor muscle parasympathetic nerve fibres dominated, while the VS and the urethral muscles had a major sympathetic nerve supply. Neuropeptide Y-positive nerve fibres were abundant in all of the muscles.

CONCLUSIONS

Smooth muscles of the lower urinary tract of the guinea-pig are distinct muscular units with distinct innervation patterns. Although there are no corresponding studies in humans the general innervation seems to be equivalent in human and guinea-pig, qualifying the guinea-pig for comparative urological studies.

A double-label immunohistochemical study of intramural ganglia from the human male urinary bladder neck

Double-label immunocytochemistry was used to investigate the colocalisation of various neuropeptides and the enzymes nitric oxide synthase (NOS) and tyrosine hydroxylase (TH) in intramural ganglia of the human male urinary bladder neck and trigone. Postmortem specimens were obtained from 7 male infants and children ranging in age from 2 mo to 3 y who had died as a result of cot death or accidental trauma. On average 60% of the intramural neurons were non-TH-immunoreactive (-IR) (i.e. presumptive cholinergic) and 40% were TH- and D beta H-IR (i.e. noradrenergic). Within the non-TH-IR population, calcitonin gene-related peptide (CGRP) was found in 65% of cells, neuropeptide Y (NPY) in 90%, nitric oxide synthase (NOS) in 45%, somatostatin (SOM) in 90%, and vasoactive intestinal polypeptide (VIP) in 40%. The corresponding values for the TH-IR neurons were CGRP (54%), NPY (70%), NOS (58%), SOM (73%) and VIP (40%). All the observed bombesin (BOM)-immunoreactivity was colocalised with TH while 90% of VIP and almost all the CGRP was colocalised with NPY. Less than 5% of neurons were immunoreactive for substance P (SP) or met-enkephalin (m-ENK) and some of these also contained TH. Varicose nerve fibres were seen in close proximity to some of the intramural neurons, the majority of such varicosities showing immunoreactivity to CGRP, VIP or TH. Less common were pericellular varicosities immunoreactive to NPY, SOM or SP. These results demonstrate the neurochemical heterogeneity of intramural neurons in the human bladder neck and provide indirect evidence for the complexity of the peripheral innervation of the human urinary bladder.

Regional variations in the neural control of the female pig urethra

OBJECTIVE

To establish the regional variation, if any, in the distribution of sympathetic and parasympathetic nerves within the urethra of the female pig and to correlate this with regional variations in the response of the smooth muscle to sympathetic and parasympathetic nerve stimulation and the application of phenylephrine and carbachol.

MATERIALS AND METHODS

Female pig urethras were obtained from a local abattoir. Serial sections were cut from the proximal, middle and distal regions of the urethra and stained using tyrosine hydroxylase immunohistochemistry and acetylcholinesterase histochemistry for the demonstration of sympathetic and parasympathetic nerves, respectively. Strips of smooth muscle dissected from the same regions of the urethra were also mounted in organ baths to record isometric tension. Responses to nerve stimulation and alpha-adrenoceptor and muscarinic receptor activation were recorded.

RESULTS

Tyrosine hydroxylase- and acetylcholinesterase-positive staining was demonstrated throughout the urethra. However, the density of sympathetic innervation was greatest in those strips dissected from the distal urethra, whilst the parasympathetic innervation was uniform throughout the length. Strips of urethral smooth muscle mounted for tension recording generated spontaneous tone. Smooth muscle dissected from the proximal urethra developed the greatest tone, whilst strips from the distal urethra generated significantly less. Responses to nerve stimulation were complex; sympathetic nerve stimulation elicited frequency-dependent contraction in all strips, but the response was most pronounced in the distal strips where tone was low. Conversely, parasympathetic nerve stimulation elicited the greatest contractile response from the proximal urethral strips. In all strips, but in particular those dissected from the proximal urethra, the contractile responses were attenuated by the occurrence of a non-adrenergic, non-cholinergic (NANC), non-nitrergic relaxation as stimulation frequency was increased. Phenylephrine and carbachol also produced concentration-dependent contraction of all urethral strips. Like the nerve-mediated responses, contraction in response to phenylephrine was most pronounced in the distal urethral strips whilst the response to carbachol was most pronounced in the proximal urethral strips.

CONCLUSIONS

The results demonstrated a regional variation in the distribution of sympathetic nerves within the urethra of the female pig which would appear to be mirrored not only in the responsiveness of the tissue to sympathetic nerve stimulation but also in its response to alpha-adrenoceptor stimulation. In contrast, although no regional variation in the distribution of parasympathetic nerves could be demonstrated histologically, responses to nerve stimulation and the muscarinic agonist carbachol were most pronounced in the proximal urethral strips.

Transneuronal labeling of neurons in the adult rat brainstem and spinal cord after injection of pseudorabies virus into the urethra

Transneuronal tracing techniques were used to identify sites in the central nervous system involved in the neural control of urethral function. The distribution of virus-infected neurons was examined in the spinal cord and brainstem at various intervals (56-96 hours) following pseudorabies virus (PRV) injection into the urethra. In the lumbosacral (L6-S1) spinal cord at 56 hours, neurons containing PRV immunoreactivity (PRV-IR) were located in the region of the sacral parasympathetic nucleus (SPN), around the central canal, and in the dorsal commissure. Some animals also exhibited PRV-IR in cells in the L6 dorsolateral motor nucleus. At longer survival times (72-96 hours), PRV-IR cells were observed in the superficial and deeper laminae of the dorsal horn, and increased numbers of PRV-IR cells were consistently detected in the region of the SPN, around the central canal, and in the dorsal commissure. PRV-IR fiber-like staining also occurred along the lateral edge of the dorsal horn extending from Lissauer's tract to the region of the SPN. In rostral lumbar segments (L1-L2), PRV-IR cells were located in the region of the dorsal commissure and the intermediolateral cell nucleus (IML), around the central canal, and in the dorsal horn. After 72-84 hours, PRV-IR cells were also noted at more rostral levels of the neuraxis including the medulla, pons, midbrain, and diencephalon. At 72 hours, PRV-IR cells were consistently observed in Barrington's nucleus (pontine micturition center), nucleus raphe magnus (RMg), parapyramidal reticular formation, and the A5 and A7 regions. At 78-84 hours, additional regions exhibited PRV-IR cells, including the periaqueductal gray, locus coeruleus, the dorsal and ventral subcoeruleus alpha, and the red nucleus. A few cells were also located in the lateral hypothalamic area. This distribution of PRV-labeled cells in the spinal cord and brainstem is similar in many respects to the distribution of cells labeled in previous studies by PRV injection into the urinary bladder. This overlap of urethra and bladder neurons is consistent with the results of physiological experiments indicating a close coordination between the central nervous control of bladder and urethral activity.

Detrusor bladder neck dyssynergia revisited

To our knowledge, direct measurement of active closure of the bladder neck during bladder contraction resulting in bladder neck dyssynergia and outflow obstruction has not yet been demonstrated. A total of 34 spinal cord injury patients underwent urodynamic investigation with 2 micro-transducer catheters in the urethrovesical and anorectal regions, respectively. Proper localization of the transducers was done with an image intensifier. The respective role of the striated and smooth muscles on bladder neck activity was evaluated after pudendal nerve blocks and phentolamine injections. Of the patients 25 had active bladder neck dyssynergia with concomitant detrusor-sphincter dyssynergia. Pressures were higher in the bladder neck than in the bladder. Pudendal blocks abolished detrusor-sphincter but not bladder neck dyssynergia, which was decreased by additional phentolamine but only in patients in whom bladder neck dyssynergia was associated with autonomic hyperreflexia. Evidence is presented that active bladder neck dyssynergia may exist in patients with a neurogenic bladder and that it is seemingly dependent on alpha 1-postsynaptic and alpha 2-presynaptic adrenoreceptors.

Renal and bladder functions in patients after spinal cord injuries

Thirty-eight patients with spinal cord lesions, 22 recent and 16 sustained more than three years previously, were investigated with intravenous pyelography, chrome EDTA clearance, cystoscopy and urodynamic studies. Analyses of bladder biopsies for tissue concentrations of nor-adrenaline and occurrence of acetylcholinesterase staining of nerves were also performed. Despite high incidence of fairly mild infections and trabeculation of the bladder, renal function was normal in most patients. Apart from incontinence, stone formation and recurrent urinary tract infections were the most common complications. The concentrations of noradrenaline and the numbers of acetylcholinesterase-stained nerves in bladder tissue specimens did not differ from control findings. The organization of the nerve structures did not vary with time after the injury, suggesting unchanged adrenergic and cholinergic innervation.

Distribution and function of the adrenergic and cholinergic receptors in the fetal calf bladder during mid-gestational age

Previous studies on the developing fetal bovine bladder demonstrate that compliance is low during early stages of fetal development and increases with fetal age. In addition, the pharmacological response of isolated fetal bovine bladder smooth muscle strips to field stimulation and bethanechol increased in proportion with the gestational age. In the adult bladder (rabbit), the contractile response to autonomic receptor stimulation and the autonomic receptor density showed a parallel gradation in the the bladder between bladder dome and the urethra. The present studies were designed to determine the distribution of the cholinergic and adrenergic receptors in the urinary bladder of the fetal calf at mid-gestational age, and to correlate the receptor density with the magnitude of the response to receptor stimulation. Each bladder body was separated into upper, middle, and lower segments. For the functional studies, circular and longitudinal strips were cut from each bladder segment and stimulated with field stimulation (FS), bethanechol, methoxamine, isoproterenol, and KCl. Autonomic receptor assays were performed using 3H-QNB (muscarinic cholinergic), 3H-DHE (alpha adrenergic), and 3H-DHA (beta adrenergic) as ligands. In general, there were no significant differences in receptor density among the three bladder segments. However, the density of muscarinic receptors was significantly greater than the density of alpha- or beta-adrenergic receptors for all bladder segments. The receptor densities correlated very well with the functional response of isolated bladder strips to the specific autonomic agonists. The contractile response of isolated bladder strips to the specific autonomic agonists. The contractile responses of the strips to FS, bethanechol, and methoxamine were not significantly different among the three different bladder segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution and function of cholinergic receptors in the sheep detrusor muscle

The distribution of cholinergic nerve fibres, as well as the characterization of the muscarinic receptors responsible for the contraction, were determined in the detrusor smooth muscle of the sheep. The results obtained demonstrated a rich presence of acetylcholinesterase (AChE)-positive fibres distributed throughout the bladder body forming dense neuromuscular, subepithelial and perivascular plexuses. Furthermore, intramural ganglia containing AChE-positive cell bodies were identified. However, acetylcholine and carbachol induced a dose-dependent contraction of detrusor smooth muscle. The effect observed with carbachol was competitively antagonized by atropine (pA2: 8.94), pirenzepine (pA2: 7.38), AF-DX 116 (pA2: 7.35), 4-DAMP (pA2: 9.26) and hexahydroxiladifenidol (HHSiD) (pA2: 8.49). The pA2 value for pirenzepine is intermediate between M1- and M2-receptors which suggests that this antagonist does not act on M1- or M2-receptors, but that it does on M3-receptors. The pA2 value for AF-DX 116 is consistent with the presence of M2-receptors in this tissue. Moreover, the pA2 values obtained for both 4-DAMP and HHSiD are in agreement with the presence of M3-receptors, due to the lack of effect of pirenzepine on M1-muscarinic receptors. These results indicate the existence of a rich parasympathetic innervation in the sheep detrusor muscle and suggest that its contraction could be mediated by the stimulation of muscarinic receptors belonging to both M3- and M2-subtypes.

Patients with lower motor spinal cord lesion: a decrease of vasoactive intestinal polypeptide, calcitonin gene-related peptide and substance P, but not neuropeptide Y and somatostatin-immunoreactive nerves in the detrusor muscle of the bladder

Specimens of the detrusor muscle of the bladder from four patients with lower motor neurone lesion and three patients with carcinoma of the bladder used as "controls", were studied immunohistochemically for vasoactive intestinal polypeptide, neuropeptide Y, calcitonin-gene related peptide, substance P and somatostatin. The greatest density of nerves in the bladder from "control" patients contained neuropeptide Y, followed in a decreasing order by vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P and somatostatin. Neuropeptide Y- and vasoactive intestinal polypeptide-immunoreactive nerves were found throughout the smooth muscle and the base of the mucosa, while calcitonin gene-related peptide-, substance P- and somatostatin-immunoreactive nerves were found predominantly in nerve bundles with a few single fibres at the base of the mucosa. Vasoactive intestinal polypeptide-, neuropeptide Y- and calcitonin gene-related peptide-immunoreactive nerves were also located around blood vessels. In patients with lower motor neurone lesion, there was a decrease in the density of vasoactive intestinal polypeptide-, calcitonin gene-related peptide- and substance P-immunoreactive nerves, but there was little change in neuropeptide Y- or somatostatin-immunoreactive nerves. Urinary retention, bladder areflexia and deficient sensation may be directly linked to neuropeptide neuropathy in patients with lower motor neurone lesion.

Autonomic innervation of the equine urinary bladder

The distribution and density of intrinsic autonomic nerve fibers and cells were studied in the equine urinary bladder by means of the peroxidase-antiperoxidase immunohistochemical method to localize tyrosine-hydroxylase (TH), and by means of a histochemical technique to detect acetylcholinesterase (AChE) activity. The results suggest that the equine urinary bladder, like that of other mammalian species, possesses a rich autonomic innervation which includes catecholaminergic and acetylcholinesterase positive nerves. At least a part of these nerve fibers have an intrinsic origin from ganglion cell bodies within the bladder wall.

A histochemical and immunohistochemical study of the autonomic innervation of the lower urinary tract of the female pig. Is the pig a good model for the human bladder and urethra?

The detrusor muscle, bladder neck, proximal, middle and distal regions of the urethra of the female pig were studied by histochemical and immunohistochemical methods to localize catecholamine-containing, acetylcholinesterase-positive and peptide-containing nerves. The peptides examined included: vasoactive intestinal polypeptide, substance P, somatostatin, [Met]enkephalin, bombesin and gastrin. The greatest density of nerves was found in the smooth muscle of the distal urethra, followed by the bladder neck, middle urethra, and proximal urethra, with the least in the detrusor muscle. The greatest number of nerve fibres stained for acetylcholinesterase, followed by vasoactive intestinal polypeptide- and catecholamine-containing fibres. Substance P-immunoreactive nerve fibres were confined to the bladder neck and distal urethral regions. [Met]enkephalin-and gastrin-immunoreactive nerves were most dense in the distal urethra but absent in detrusor muscle, while somatostatin-immunoreactive nerve fibres were sparsely distributed throughout the lower urinary tract. No nerve fibres showing immunoreactivity to bombesin were found. Catecholamine-containing, acetylcholinesterase-positive, vasoactive intestinal polypeptide-, substance P-, [Met]enkephalin- and gastrin-immunoreactive nerves were also found on the adventitial-medial border of blood vessels in the pig urinary tract. In the intrinsic external urethral sphincter, located in the distal urethra, vasoactive intestinal polypeptide- and gastrin-immunoreactive nerve fibres were found bordering a small number of individual striated muscle fibres, while catecholamine-containing nerves were found predominantly in the connective tissue surrounding the striated muscle fibres. Dense populations of acetylcholinesterase-positive nerve fibres were found associated with the striated muscle fibres, with end plates on some of them. Intramural ganglia, composed of two to 30 neurones, were found in the bladder neck and middle and distal regions of the urethra. In the smooth muscle, and in the vicinity of the striated muscle regions of the intrinsic external urethral sphincter, there were small ganglia, containing two to three neurones, which were vasoactive intestinal polypeptide-, [Met]enkephalin- and somatostatin-immunoreactive. The results are compared to the autonomic innervation of the human bladder and urethra as previously described and it is concluded that the lower urinary tract of the pig is a good model for some features of the lower urinary tract of man, but a poor model for others.

Changes in cholinergic innervation and neuropharmacologic properties in idiopathic hypotonic urinary bladders

Tissue specimens from hypotonic and normotonic human urinary bladders were investigated histochemically, chemically and neuropharmacologically. In hypotonic bladders the density of acetylcholinesterase (AChE)-positive nerves was markedly reduced and the nerve AChE staining intensity was weak. The concentration of acetylcholine was significantly lower than in specimens from normotonic bladders. At field stimulation the contractions were weak. The observations indicated that sparse cholinergic innervation and reduced acetylcholine synthesis are important for the impaired contractility in idiopathic dystonic bladder.

Action of pirenzepine on the human urinary bladder in vitro

The novel compound pirenzepine was tested for its antimuscarinic effect on the human urinary bladder "in vitro." Its behavior towards the contractions induced by acetylcholine or bethanechol and towards electrically induced contractions was identical to that of atropine. However, its potency was 100 to 300 times lower than that of atropine. Results obtained with ganglion blocking agents, tetrodotoxin and cooled preparations of urinary bladder seem to indicate the virtually total absence of ganglionic cells. On the other hand they point out the fundamental role of post-synaptic muscarinic M2 receptors as the most important component of the cholinergic system in the bladder. Of course the existence of other transmitters released at the cholinergic nerve endings after electrical field stimulation cannot be excluded on the basis of our experiments.

Peptide-containing nerves in human urinary bladder

Nerves containing immunoreactive vasoactive intestinal polypeptide (VIP), substance P and two newly discovered peptides, neuropeptide tyrosine (NPY) and PHI (peptide having N-terminal histidine and C-terminal isoleucine), have been found in the human urinary bladder by immunocytochemistry and radioimmunoassay. Somatostatin immunoreactivity was detected by radioimmunoassay. The VIP-immunoreactive nerves were widely distributed in all regions, but were particularly dense beneath the epithelium and in the muscle layer. Scattered intramural ganglia were found to be reactive to VIP antiserum. Higher concentrations of extractable VIP were detected in the trigone than in the dome. VIP- and PHI-immunoreactive nerves were similarly distributed, the latter being less numerous. NPY-immunoreactive nerves were seen mainly in the muscle layer, particularly in the trigonal area. The distribution patterns of VIP- and NPY-immunoreactive nerves resembled those of the previously reported cholinergic and adrenergic nerves, respectively. Many blood vessels were found to be innervated by both types of immunoreactive nerves. Scattered substance P-immunoreactive fibers were occasionally seen, being present in the submucosa and around the detrusor muscles. The significance of these nerves remains to be elucidated.

A novel non-adrenergic, non-cholinergic nerve-mediated relaxation of the pig bladder neck: an examination of possible neurotransmitter candidates

Electrical field stimulation of the isolated pig bladder neck preparation initiated rapid non-adrenergic, non-cholinergic nerve-mediated relaxations. A wide range of substances were examined as possible candidates for the neurotransmitter involved. Of these, only 5-hydroxytryptamine, vasoactive intestinal polypeptide, adenosine and adenosine 5'-triphosphate produced relaxations. Noradrenaline, acetylcholine, substance P, bradykinin and angiotensin II caused contraction, while neurotensin, somatostatin, bombesin and gamma-amino butyric acid were without effect. The nerve response was not blocked by methysergide, ketanserin, chymotrypsin, apamin or 8-phenyltheophylline, although methysergide antagonised the responses to 5-hydroxytryptamine, chymotrypsin blocked the responses to VIP, and 8-phenyltheophylline antagonised the responses to adenosine and ATP.