Functional bombesin receptors in urinary tract of rats and human but not of pigs and mice, an in vitro study

Psychological/mental stress-induced effects on urinary function: Possible brain molecules related to psychological/mental stress-induced effects on urinary function

Exposure to psychological/mental stress can affect urinary function, and lead to and exacerbate lower urinary tract dysfunctions. There is increasing evidence showing stress-induced changes not only at phenomenological levels in micturition, but also at multiple levels, lower urinary tract tissues, and peripheral and central nervous systems. The brain plays crucial roles in the regulation of the body's responses to stress; however, it is still unclear how the brain integrates stress-related information to induce changes at these multiple levels, thereby affecting urinary function and lower urinary tract dysfunctions. In this review, we introduce recent urological studies investigating the effects of stress exposure on urinary function and lower urinary tract dysfunctions, and our recent studies exploring "pro-micturition" and "anti-micturition" brain molecules related to stress responses. Based on evidence from these studies, we discuss the future directions of central neurourological research investigating how stress exposure-induced changes at peripheral and central levels affect urinary function and lower urinary tract dysfunctions. Brain molecules that we explored might be entry points into dissecting the stress-mediated process for modulating micturition.

[Central regulation mechanisms for stress-induced frequent urination]

Psychological stress can induce not only frequent urination but also exacerbation of bladder dysfunctions. However, the brain pathophysiological mechanisms underlying stress-induced effects on the micturition reflex are still unknown. Bombesin (BB)-related peptides and BB receptors in the brain have been reported to mediate and integrate stress responses. We have found that centrally administered BB induced frequent urination in rats through brain BB₁ and BB₂ receptors, serotoninergic nervous system/5-HT₇ receptors and corticotropin-releasing factor (CRF) type1 (CRF₁) receptors. Interestingly, the BB-induced frequent urination was independent of the BB-induced activation of the sympatho-adrenomedullary outflow, a representative response to stress. Because the outflow is well known to regulate micturition, the finding was very surprising. These findings indicate that brain BB₁, BB₂, 5-HT₇ and CRF₁ receptors could be new therapeutic targets for bladder dysfunction exacerbated by stress exposure.

Which molecular targets do we need to focus on to improve lower urinary tract dysfunction? ICI-RS 2017

AIMS

Update on some molecular targets for new drugs to improve lower urinary tract (LUT) dysfunction.

METHODS

Using PubMed, a search for literature on molecular targets in the LUT was performed to identify relevant clinical and animal studies. Keywords were entered as Medical Subject Headings (MeSH) or as text words. The Mesh terms were used in various combinations and usually included the terms lower urinary AND pharmacology. Other Mesh term included: bladder, urethra, CNS, physiology, afferent activity, ATP, prostanoids, cannabinoids, fibrosis. Search results were assessed for their overall relevance to this review.

RESULTS

In a normal bladder, ATP contributes little to detrusor contraction, but in a diseased bladder ATP may contribute to OAB. Selective decrease of ATP release via adenosine A1 receptor stimulation offers a potential treatment possibility. Candidates for relaxation of the smooth muscle of the urethra can be found among, for example, the receptor subtypes of PGE₂ , and PGD₂ . Drugs for relaxation of the striated sphincter can target the muscle directly or the spinal sphincter control. Fibrosis is a major problem in LUT dysfunction and agents with an inhibitory effect on the TGFβ pathway, for example relaxin and BMP7, may be promising avenues. Available drugs with a CNS site of action are often limited by low efficacy or adverse effects. Inhibitors of the glycine receptor Gly-T2 or antagonists of the adenosine A2 receptor may be new alternatives.

CONCLUSION

New molecular targets for drugs aiming at improvement of voiding function can be identified, but their translational impact remains to be established.

Urothelial bladder afferent neurons in the rat are anatomically and neurochemically distinct from non-urothelial afferents

There is mounting evidence underscoring a role for the urothelium in urinary bladder sensation. Previous functional studies have identified bladder primary afferents with mechanosensitive properties suggesting urothelial innervation and/or communication. The current study identifies a group of urothelium-innervating afferent neurons in rat, and characterizes and compares the properties of these and non-urothelial afferent neuron populations. Lumbosacral (LS) primary afferent neurons were retrogradely labeled using intraparenchymal (IPar) microinjection or intravesical (IVes) infusion of tracer into the bladder. Using these techniques, separate populations of neurons were differentiated by dorsal root ganglion (DRG) somata labeling and dye distribution within the bladder. IPar- and IVes-labeled neurons accounted for 85.0% and 14.4% of labeled L6-S1 neurons (P < .001), respectively, with only 0.6% of neurons labeled by both techniques. Following IVes labeling, dye was contained only within the periurothelial bladder region in contrast to non-urothelial distribution of dye after IPar labeling. Electrophysiological characterization by in situ patch-clamp recordings from whole-mount DRG preparations indicated no significant difference in passive or active membrane properties of IPar and IVes DRG neurons. However, calcium imaging of isolated neurons indicates that a greater proportion of IPar- than IVes-labeled neurons express functional TRPA1 (45.7% versus 25.6%, respectively; P < .05). This study demonstrates that two anatomically distinct groups of LS bladder afferents can be identified in rat. Further studies of urothelial afferents and the phenotypic differences between non-/urothelial afferents may have important implications for normal and pathophysiological bladder sensory processing.

Neuromedin B and Its Receptor: Gene Cloning, Tissue Distribution and Expression Levels of the Reproductive Axis in Pigs

Neuromedin B is one member of a family of bombesin-like peptides, which performs a variety of physiological functions via their receptor (NMBR) in most mammals. However, the genes encoding NMB and NMBR and their functions especially reproduction of the pigs are currently not fully understood. To research the physiological functions of NMB, we cloned and analyzed the NMB and NMBR genes, and systematically investigated the expression levels of NMB and NMBR mRNA using relative real-time PCR and the distribution of NMBR by immunohistochemistry (IHC). Experimental results show that the sequences of the amino acid and gene of NMB and NMBR were highly conservative and homology in many species, Significantly, the relative RT-PCR results revealed that NMB was mainly expressed in the central nervous system (CNS), whereas NMBR is highly expressed in peripheral tissues and organs, such as endocrine tissues, glands and reproductive organs. The IHC results show that NMBR positive cells were widely distributed in the body, such as respiratory and circulatory system, digestive system, urogenital system, in lymphatic organs and in the endocrine system. We also systematically investigated expression levels of NMB and NMBR in the reproductive axis using relative real-time PCR. In sow estrous cycle, the hypothalamic levels of both NMB and NMBR mRAN were similar, but the expression levels of the pituitary were negatively correlated. Expression levels in the ovarian system are lowest in metestrus phases and highest in proestrus and estrus phases. In boar post-natal development stages, the hypothalamic, pituitary and testicular levels of NMB and NMBR mRNAs showed developmental changes on postnatal day 30, 60, 90 and 120. Taken together, this study provided molecular and morphological data necessary for further research of physiological function of NMB/NMBR system in the pigs.

A Stress-Related Peptide Bombesin Centrally Induces Frequent Urination through Brain Bombesin Receptor Types 1 and 2 in the Rat

Stress exacerbates symptoms of bladder dysfunction including overactive bladder and bladder pain syndrome, but the underlying mechanisms are unknown. Bombesin-like peptides and bombesin receptor types 1 and 2 (BB1 and BB2, respectively) in the brain have been implicated in the mediation/integration of stress responses. In this study, we examined effects of centrally administered bombesin on micturition, focusing on their dependence on 1) the sympathoadrenomedullary system (a representative mechanism activated by stress exposure) and 2) brain BB receptors in urethane-anesthetized (1.0-1.2 g/kg, i.p.) male rats. Intracerebroventricularly administered bombesin significantly shortened intercontraction intervals (ICI) at both doses (0.1 and 1 nmol/animal) without affecting maximal voiding pressure. Bombesin at 1 nmol induced significant increments of plasma noradrenaline and adrenaline levels, which were both abolished by acute bilateral adrenalectomy. On the other hand, adrenalectomy showed no effects on the bombesin-induced shortening of ICI. Much lower doses of bombesin (0.01 and 0.03 nmol/animal, i.c.v.) dose-dependently shortened ICI. Pretreatment with either a BB1 receptor antagonist (BIM-23127; d-Nal-cyclo[Cys-Tyr-d-Trp-Orn-Val-Cys]-Nal-NH2; 3 nmol/animal, i.c.v.) or a BB2 receptor antagonist (BEA; H-d-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHEt; 3 nmol/animal, i.c.v.), respectively, suppressed the BB (0.03 nmol/animal, i.c.v.)-induced shortening of ICI, whereas each antagonist by itself (1 and 3 nmol/animal, i.c.v.) had no significant effects on ICI. Bombesin (0.03 nmol/animal, i.c.v.) significantly reduced voided volume per micturition and bladder capacity without affecting postvoid residual volume or voiding efficiency. These results suggest that brain bombesin and BB receptors are involved in facilitation of the rat micturition reflex to induce bladder overactivity, which is independent of the sympathoadrenomedullary outflow modulation.

Non-uniform changes in membrane receptors in the rat urinary bladder following outlet obstruction

The aim of the present study was to investigate the expression and distribution of membrane receptors after bladder outlet obstruction (BOO). Partial bladder outlet obstruction (BOO) was induced in female rats and bladders were harvested after either 10 days or 6 weeks of BOO. The expression of different receptors was surveyed by microarrays and corroborated by immunohistochemistry and western blotting. A microarray experiment identified 10 membrane receptors that were differentially expressed compared to sham-operated rats including both upregulated and downregulated receptors. Four of these were selected for functional experiments on the basis of magnitude of change and relevance to bladder physiology. At 6 weeks of BOO, maximal contraction was reduced for neuromedin B and vasopressin (AVP), consistent with reductions of receptor mRNA levels. Glycine receptor-induced contraction on the other hand was increased and receptor mRNA expression was accordingly upregulated. Maximal relaxation by the β3-adrenergic receptor agonist CL316243 was reduced as was the receptor mRNA level. Immunohistochemistry supported reduced expression of neuromedin B receptors, V1a receptors and β3-adrenergic receptors, but glycine receptor expression appeared unchanged. Western blotting confirmed repression of V1a receptors and induction of glycine receptors in BOO. mRNA for vasopressin was detectable in the bladder, suggesting local AVP production. We conclude that changes in receptor expression following bladder outlet obstruction are non-uniform. Some receptors are upregulated, conferring increased responsiveness to agonist, whereas others are downregulated, leading to decreased agonist-induced responses. This study might help to select pharmacological agents that are effective in modulating lower urinary tract symptoms in BOO.

Bladder smooth muscle strip contractility as a method to evaluate lower urinary tract pharmacology

We describe an in vitro method to measure bladder smooth muscle contractility, and its use for investigating physiological and pharmacological properties of the smooth muscle as well as changes induced by pathology. This method provides critical information for understanding bladder function while overcoming major methodological difficulties encountered in in vivo experiments, such as surgical and pharmacological manipulations that affect stability and survival of the preparations, the use of human tissue, and/or the use of expensive chemicals. It also provides a way to investigate the properties of each bladder component (i.e. smooth muscle, mucosa, nerves) in healthy and pathological conditions. The urinary bladder is removed from an anesthetized animal, placed in Krebs solution and cut into strips. Strips are placed into a chamber filled with warm Krebs solution. One end is attached to an isometric tension transducer to measure contraction force, the other end is attached to a fixed rod. Tissue is stimulated by directly adding compounds to the bath or by electric field stimulation electrodes that activate nerves, similar to triggering bladder contractions in vivo. We demonstrate the use of this method to evaluate spontaneous smooth muscle contractility during development and after an experimental spinal cord injury, the nature of neurotransmission (transmitters and receptors involved), factors involved in modulation of smooth muscle activity, the role of individual bladder components, and species and organ differences in response to pharmacological agents. Additionally, it could be used for investigating intracellular pathways involved in contraction and/or relaxation of the smooth muscle, drug structure-activity relationships and evaluation of transmitter release. The in vitro smooth muscle contractility method has been used extensively for over 50 years, and has provided data that significantly contributed to our understanding of bladder function as well as to pharmaceutical development of compounds currently used clinically for bladder management.