Calcitonin gene-related peptide (CGRP)-immunoreactive nerve plexuses in the renal pelvis and ureter of rats

Identifying peristaltic pacemaker cells in the upper urinary tract

Urine expulsion from the upper urinary tract is a necessary process that eliminates waste, promotes renal filtration and prevents nephron damage. To facilitate the movement of urine boluses throughout the upper urinary tract, smooth muscle cells that line the renal pelvis contract in a coordinated effort to form peristaltic waves. Resident pacemaker cells in the renal pelvis are critical to this process and spontaneously evoke transient depolarizations that initiate each peristaltic wave and establish rhythmic contractions. Renal pacemakers have been termed atypical smooth muscle cells due to their low expression of smooth muscle myosin and poor organization of myofilaments compared to typical (or contractile) smooth muscle cells that perform peristalsis. Recent findings discovered that pacemaker cells also express the tyrosine kinase receptor PDGFRα, enabling their identification and purification amongst other renal pelvis cell types. Improved identification methods have determined that the calcium-activated chloride channel, ANO1, is expressed by pacemaker cells and may contribute to spontaneous depolarization. A greater understanding of pacemaker and peristaltic mechanisms is warranted since aberrant contractile function may underlie diseases such as hydronephrosis, a deleterious condition that can cause significant and irreversible nephron injury.

Ureteral motility

The pyeloureteral function is to transport urine from the kidneys into the ureter toward the urinary bladder for storage until micturition. A set of mechanisms collaborates to achieve this purpose: the basic process regulating ureteral peristalsis is myogenic, initiated by active pacemaker cells located in the renal pelvis. Great emphasis has been given to hydrodynamic factors, such as urine flow rate in determining the size and pattern of urine boluses which, in turn, affect the mechanical aspects of peristaltic rhythm, rate, amplitude, and baseline pressure. Neurogenic contribution is thought to be limited to play a modulatory role in ureteral peristalsis. The myogenic theory of ureteral peristalsis can be traced back to Engelmann (1) who was able to localize the peristaltic pressure wave's origin in the renal pelvis and suggested that the ureteral contraction impulse passes from one ureteral cell to another, the whole ureter working as a functional syncitium. Recent studies of ureteral biomechanics, smooth muscle cell electrophysiology, membrane ionic currents, cytoskeletal components and pharmacophysiology much improved our understanding of the mechanism of how the urine bolus is propelled, how this process is disturbed in pathological states, and what could be done to improve it.

Demonstration of intrinsic innervation of the guinea pig upper urinary tract using whole-mount preparation

AIMS

The morphology and functional importance of the autonomic nervous system in the upper urinary tract is still not completely understood. Previous histological studies investigating the innervation of the urinary tract have mainly used conventional sections in which the three-dimensional structure of the intramural innervation is difficult to achieve. In contrast, the whole-mount preparation technique is a suitable method for visualizing the distribution of the mesh-like neuronal networks within the urinary tract.

METHODS

The distribution and regional variation of neurofilament (NF), tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), and substance P-immunoreactive (SP-IR) neurons, as well as acetylcholinesterase (AChE) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)-positive neurons were investigated using whole-mount preparations of the guinea pig upper urinary tract.

RESULTS

Two distinct nervous plexuses were detected within the muscle layers containing NF, TH, ChAT, and SP-IR nerves. AChE-positive nerves were seen in all layers. Only moderate NADPH-d-positive innervation was found. Renal pelvis, upper and lower part of the ureter showed an overall increased innervation compared to the middle portion of the ureter. Ganglia were found at the pelviureteric border displaying NF and TH immunoreactivity.

CONCLUSION

The whole-mount preparation technique provides an elegant method for assessing the three-dimensional architecture of ureteral innervation. The guinea pig upper urinary tract is richly supplied with adrenergic, cholinergic, nitrergic, and sensory nerves which suggest that the autonomous nervous system plays an important role in controlling ureteral motility and blood flow.

Nuclear localization of SP, CGRP, and NK1R in a subpopulation of dorsal root ganglia subpopulation cells in rats

Signals generated by renal pelvic afferent nerves in response to stimulation are transmitted from peripheral processes of dorsal root ganglia neurons to their central terminals in the dorsal horn of the spinal cord to cause the release of neuropeptides, including SP and CGRP. All of the cellular activities of SP are considered to be mediated through interaction with NK(1)R located on the cell surface. We have investigated the colocalization and subcellular distribution of NK(1)R, SP, and CGRP in different subpopulations of neurons that innervate renal tissue. Our findings therefore provide the first evidence for the presence of NK(1)R, SP, and CGRP in the nuclei of DGR neural cells. The physiological significance of this localization remains unknown. One possibility is that pelvic sensory neurons may regulate their responses to different stimuli by modulating the ratio of CGRP and SP release and/or nuclear NK(1)R expression.

Expression and localization of NK(1)R, substance P and CGRP are altered in dorsal root ganglia neurons of spontaneously hypertensive rats (SHR)

The kidneys play a pivotal role in the pathogenesis of essential hypertension because of a primary defect in renal hemodynamics and/or tubule hydro-saline handling that results in the retention of fluid and electrolytes. Previous studies have shown that increasing the renal pelvic pressure increased ipsilateral afferent renal nerve activity (ARNA), the ipsilateral renal pelvic release of substance P (SP) and the contralateral urinary sodium excretion in Wistar--Kyoto rats (WKy). However, spontaneously hypertensive rats (SHR) present an impaired renorenal reflex activity associated, partly, with a peripheral defect at the level of the sensory receptors in the renal pelvis. Furthermore, the renal pelvic administration of SP failed to increase ARNA in most of SHR at concentrations that produced marked increases in WKy. Since we have assessed the expression and localization of NK(1) receptor (NK(1)R), SP and calcitonin gene-related peptide (CGRP) in different dorsal root ganglia (DRG) cell subtypes and renal pelvis of 7- and 14-week-old SHR. The results of this study show increased SP and CGRP expression in the dorsal ganglia root cells of SHR compared to WKy rats. Additionally, there was a progressive, significant, age-dependent, decrease in NK(1)R expression on the membrane surface in SHR DRG cells and in the renal pelvis. In conclusion, the results of the present study suggest that the impaired activation of renal sensory neurons in SHR may be related to changes in the expression of neuropeptides and/or to a decreased presence of NK(1)R in DRG cells. Such abnormalities could contribute to the enhanced sodium retention and elevation of blood pressure seen in SHR.

Activation of renal pelvic chemoreceptors in rats: role of calcitonin gene-related peptide receptors

Substance P and calcitonin gene-related peptide (CGRP) increase afferent renal nerve activity (ARNA). A substance P receptor antagonist but not a CGRP receptor antagonist, h-CGRP (8-37), blocks the ARNA response to renal mechanoreceptor (MR) stimulation. We have examined whether calcitonin gene-related peptide activates renal pelvic sensory receptors and whether such activation contributes to renal chemoreceptor stimulation. The calcitonin gene-related peptide receptor antagonist, h-CGRP (8-37) [0.01-10 micromol L-1] dose-dependently decreased (29 +/- 4-86 +/- 13%, P < 0.01) the ipsilateral afferent renal nerve activity in response to the renal pelvic administration of calcitonin gene-related peptide (0.26 micromol L-1). Renal pelvic perfusion with 900 mM NaCl also increased ipsilateral ARNA (23 +/- 3% increase, P < 0.02) and contralateral urinary sodium excretion (13 +/- 4% increase, P < 0. 05). However, these responses to hypertonic NaCl were unaltered by h-CGRP (8-37). Renal pelvic perfusion with 1 or 10 microM h-CGRP (8-37) also failed to alter the ARNA responses to KCl (31.25, 62.5 and 125 mM). These results indicate that there are sensory receptors in the renal pelvic area that are responsive to calcitonin gene-related peptide. The activation of these receptors elicits a contralateral natriuretic response. In contrast, the activation of renal calcitonin gene-related peptide receptors does not contribute to renal chemoreceptor activation.

Immunohistochemical detection of neuronal plexuses and nerve cells within the upper urinary tract of pigs

OBJECTIVE

To investigate the distribution and topography of nervous structures within the renal pelvis and upper part of the ureter of pigs, and thus help to determine the origin, propagation and mechanisms of the modulation of pelvi-ureteric peristalsis.

MATERIALS AND METHODS

Whole-mount preparations of renal pelves from adult pigs were stained using a universal immunostaining method with streptavidin-alkaline phosphatase. Anti-neuron-specific enolase antibody and anti-neurofilament antibody were used as neuronal markers.

RESULTS

The patterns of neuronal structures differed between the renal calyces, renal pelvis and upper ureter. In the calyx, there was one single dense nerve plexus; this network contained relatively thin nerve fibres running both circularly and longitudinally. In the wall of the renal pelvis and upper ureter there were two neuronal plexuses, one submucosal and another within the muscular layer; these nerve fibres were mainly orientated longitudinally. Some single nerve cells were also found at the pelvicalyceal border.

CONCLUSIONS

These findings suggest a potent nervous system within the upper urinary tract of pigs that connects the renal calyces with the renal pelvis, pelvi-ureteric junction and ureter. The presence of these dense neuronal networks and nerve cells within the wall of the renal pelvis and ureter suggests that propagation, coordination and modulation of pelvi-ureteric peristalsis in pigs may arise through intrinsic nervous stimulation.

Localisation of VIP-and CGRP-like substances in the skin and sinus hair follicles of various mammalian species

Using an ultrastructural postembedding immunogold technique, we demonstrated vasoactive intestinal polypeptide (VIP)- and calcitonin gene-related peptide (CGRP)-like immunoreactivity in the Merkel cell dense-cored granules of skin and sinus hair follicles of adult cat and dog. The VIP-like substance was located in cat Merkel cells while both VIP- and CGRP-like substances were colocalised in dog Merkel cells. In cat Merkel cells, the magnitude of labelling of VIP was qualitatively higher than in dog Merkel cells. In the dog Merkel cell, CGRP appeared as the most abundant peptide. Dense-cored granules were labelled for these peptides. In addition, mast cells encountered in the dermal region of dog skin were also found to be immunolabelled by VIP antiserum. The immunoreaction was found to be confined to the secretory granules of the cells. Furthermore, all non-myelinated nerve plexuses encountered in the dermal region of the skin and the sinus hair follicles of the various mammalian species studied were immunolabelled by CGRP antiserum. The specific location was again restricted to the dense-cored granules present in these nerves. As VIP and CGRP have potent vasodilatory effects, our observations suggest that Merkel cells may play a separate or synergistic role in regulatory functions of the skin neuroendocrine cell, exerting their influence by paracrine, endocrine and neurocrine pathways, or a combination of these. Different methodologies of double labelling with different sizes of gold particles are also discussed.

Nitric oxide synthase-immunoreactive, adrenergic, cholinergic, and peptidergic nerves of the female rat urinary tract: a comparative study

The distribution and frequency of NO synthase (NOS)-immunoreactive (IR) nerves in relation to the general autonomic innervation, adrenergic, cholinergic and some peptidergic nerves, were investigated in the female rat urinary tract. NOS nerves were very frequent in the smooth musculature of the urethra together with cholinergic, adrenergic and neuropeptide Y (NPY)-IR nerves, whereas vasoactive intestinal peptide (VIP)-IR and calcitonin-gene-related peptide (CGRP)-IR nerves were much less abundant. NOS-IR, CGRP-IR and cholinergic nerves were also frequent in the longitudinal smooth musculature of the distal ureters and the ureteral orifices into the bladder, where no adrenergic, NPY-IR and VIP-IR nerves were found. In contrast, in the detrusor NOS-IR nerves were scarce. Bilateral pelvic ganglionectomy very pronouncedly decreased the number of any of the populations of nerves studied, whereas bilateral pelvic decentralization selectively reduced the number of CGRP-IR nerves in all structures and locations. Outflow obstruction very overtly reduced the number of NOS-IR nerves in parallel with the general autonomic innervation. Thus, in the rat female urinary tract, NOS-containing nerves particularly occur in regions with sphincteric functions such as urethra and ureteric orifices. In these regions NO may exert a transmitter role, both directly or by interaction with other transmitters/modulators.

Nitric oxide synthase in rat nasal mucosa; immunohistochemical and histochemical localization

The localization of nitric oxide synthase (NOS) and its cofactor, nicotinamide-adenine dinucleotide hydrogen phosphate (NADPH)-diaphorase, was examined in the nasal mucosa of the rat by immunohistochemical and histochemical methods. In addition to cryostat sections, whole mount preparations were used to examine the distribution of nerves. Both in the nasal mucosa and in associated ganglia, the distribution of NOS-immunoreactive nervous structures essentially corresponded to that of NADPH-diaphorase-positive ones. The NOS-immunopositive nerve fibers in the respiratory area of the nasal mucosa were distributed around blood vessels and in submucosal glands. Part of the respiratory area was supplied with intraepithelial arborizations of the immunopositive fibers. The epithelial cells in the respiratory area were NADPH-diaphorase positive but NOS immunoreactivity negative. In the olfactory area, the NADPH-diaphorase- and NOS-positive nerve fibers were restricted to blood vessels located deep in the submucosa. Throughout the nasal mucosa, arterial endothelium was NADPH-diaphorase positive but NOS immunoreactivity negative. Both NOS immunoreactivity and NADPH-diaphorase activity were found in major populations of neuronal somata in the sphenopalatine ganglion. The present study provides the direct evidence supporting the notion that nitric oxide is richly produced in autonomic nerves of the nasal mucosa derived from the sphenopalatine ganglion.

CGRP inhibition of electromechanical coupling in the guinea-pig isolated renal pelvis

We aimed at studying the mechanism(s) of the inhibitory effect exerted by calcitonin gene-related peptide (CGRP) on the spontaneous activity of the guinea-pig isolated renal pelvis. In organ bath experiments, CGRP (1-100 nM) produced a concentration-dependent (EC50 8 nM) partial inhibition (Emax about 35% inhibition of motility index) of spontaneous contractions. The potassium (K) channel opener, cromakalim (3-10 microM) promptly suppressed the spontaneous contractions in a glibenclamide-(10 microM) sensitive manner. Glibenclamide (10 microM) did not affect the inhibitory action of CGRP. The calcium (Ca) channel agonist, Bay K 8644 (1 microM), markedly enhanced the spontaneous activity of the renal pelvis and reduced the inhibitory effect of CGRP. The protein kinase A inhibitors Rp-cAMPS (300 microM), H8 (100 microM) and H89 (10 microM), and the blockers of intracellular Ca handling by sarcoplasmic reticulum, ryanodine (100 microM) and thapsigargin (1 microM) did not affect the response to CGRP. The response to CGRP was likewise unaffected by the nitric oxide synthase inhibitor, L-nitroarginine (30 microM) and by the protein kinase G inhibitor, KT5823 (3 microM). Furthermore, the inhibitory action of CGRP was not modified by lowering the extracellular concentration of K (from 5.9 to 1.2 mM) nor by increasing (from 2.5 to 3.75 mM) or decreasing (from 2.5 to 0.25 mM) the extracellular Ca concentration. Replacement of 80% glucose with 2-deoxyglucose (2-DOG) reduced the amplitude of spontaneous contractions, both in the absence and presence of 10 microM glibenclamide. In the presence of 2-DOG, the inhibitory action of CGRP was enhanced at a similar extent, either in the absence or presence of glibenclamide. In sucrose gap, the effect of CGRP (0.1 microM for 5 min) was separately analyzed in the proximal (close to the kidney) and distal (close to the ureter) regions of the renal pelvis. Both preparations discharged spontaneous (pacemaker) action potentials having different shape, duration and frequently. CGRP had no effect on pacemaker potentials in the proximal renal pelvis while producing about 30% reduction of the frequency of pacemaker potentials and motility index in the distal renal pelvis. Cromakalim (3 microM) abolished pacemaker potentials in both regions of the renal pelvis. In conjunction with the results of previous studies in the guinea-pig ureter, the present findings document the existence of remarkable regional differences in the effector mechanisms initiated by CGRP receptor occupancy in the guinea-pig pyeloureteral tract. CGRP appears to be inherently unable to activate glibenclamide-sensitive K channels in the guinea-pig renal pelvis, a mechanism which is central for its ability to suppress latent pacemakers in the ureter. Within the renal pelvis, the sensitivity to the inhibitory effect of CGRP appears in the more distal region, from which an 'ureter-like' action potential is recorded.

Propagation of impulses in the guinea-pig ureter and its blockade by calcitonin gene-related peptide (CGRP)

The guinea-pig ureter was placed in a three-compartment organ bath to enable the application of electrical stimuli or drugs to its renal end (R-site), the middle region (M-site) or the bladder end (B-site) while recording mechanical activity at the R- and B-sites. All experiments were performed in ureters pre-exposed to capsaicin (10 microM for 15 min) to prevent the release of sensory neuropeptides from afferent nerves. Electrical field stimulation (EFS, 5-25 ms pulse width, 20 V) produced a phasic contraction at the site of stimulation ('direct' response to EFS) which propagated to the other end of the ureter. Section of the ureter at the M-site abolished the propagated response to EFS; after section, EFS applied at the M-site induced a phasic contraction at both the R- and B-sites. Likewise, the application of KCl at the M-site produced phasic contractions at both the R- and B-sites. Tetrodotoxin (1 microM), nifedipine (1 microM) or Bay K 8644 (1 microM) applied at the M-site had no influence on the direct or propagated responses to EFS; nifedipine (10 microM) applied at the M-site abolished the propagated responses without affecting the direct responses to EFS. Bay K 8644 (1 microM) applied at the R-site produced a marked enhancement of the direct response (EFS applied at R-site) while having no effect on the amplitude of the propagated response to EFS.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcitonin gene-related peptide (CGRP) regulates excitability and refractory period of the guinea pig ureter

Previous studies have indicated that calcitonin gene-related peptide (CGRP), released from the peripheral endings of capsaicin-sensitive primary afferent neurons, may play a role as an inhibitory transmitter in the guinea pig ureter. The aim of this study was to compare the effect of capsaicin desensitization and administration of a CGRP receptor antagonist on the excitability and refractory period of the guinea pig ureter to electrical field stimulation. Electrical field stimulation using a long (5 msec.) pulse width produced phasic contractions of the ureter which were unaffected by tetrodotoxin, that is, were produced through direct excitation of ureteral smooth muscle. Human alpha CGRP (1 to 10 nM.) produced a concentration-dependent transient suppression of the evoked contractions, and its effect was prevented by the CGRP receptor antagonist human alpha CGRP(8-37) (1 microM.). In vitro capsaicin pretreatment (10 microM. for 15 minutes) to block neuropeptide release from peripheral endings of sensory nerves or administration of the CGRP receptor antagonist enhanced the responsiveness of the guinea pig ureter to electrical stimulation. In control ureters, the application of two trains of electrical stimuli failed to produce a second contraction at intertrain intervals greater than 20 seconds. The intertrain interval required to obtain a second contraction averaging 50% of the amplitude of the first response (ITI50) of control ureters was about 50 seconds. In vitro capsaicin pretreatment or administration of the CGRP receptor antagonist reduced the refractory period of the ureter to electrical field stimulation: ITI50 averaged 8.8 and 9.1 seconds after capsaicin or CGRP antagonist pretreatment, respectively. These findings demonstrate that capsaicin pretreatment or blockade of CGRP receptors produced qualitatively and quantitatively similar excitatory effects on ureteral excitability and refractory period and are in general agreement with the idea that CGRP is a primary inhibitory transmitter in guinea pig ureter. Inhibition of motility by CGRP could be important for setting the frequency of ureteral peristalsis and suppression of latent pacemakers to prevent the occurrence of antiperistaltic waves.

Renal sensory receptor activation by calcitonin gene-related peptide

In anesthetized rats we examined whether calcitonin gene-related peptide activated renal pelvic sensory receptors and, if so, whether activation of renal pelvic calcitonin gene-related peptide receptors contributes to the inhibitory renorenal reflex response to renal mechanoreceptor stimulation. Calcitonin gene-related peptide (0.0026, 0.026, 0.26, and 2.6 mumol/L) administered into the renal pelvis increased ipsilateral afferent renal nerve activity in a concentration-dependent fashion (32 +/- 14%, 69 +/- 19%, 93 +/- 26%, and 253 +/- 48% [all P < .01], respectively). The increases in ipsilateral afferent renal nerve activity elicited by calcitonin gene-related peptide were associated with increases in contralateral urinary sodium excretion. The calcitonin gene-related peptide receptor antagonist human CGRP (h-CGRP) (8-37) (0.01, 0.1, 1.0, and 10 mumol/L) decreased the ipsilateral afferent renal nerve activity response to renal pelvic administration of calcitonin gene-related peptide (0.26 mumol/L) in a concentration-dependent fashion (29 +/- 4%, 33 +/- 12%, 76 +/- 9% [P < .01], and 86 +/- 13% [P < .01], respectively). In the presence of renal pelvic perfusion with vehicle, an increase in ureteral pressure of 5, 10, and 20 mm Hg increased ipsilateral afferent renal nerve activity by 13 +/- 7%, 41 +/- 7% (P < .01), and 95 +/- 15% (P < .01) and contralateral urinary sodium excretion by 8 +/- 1%, 24 +/- 4%, and 42 +/- 7% (all P < .05). The ipsilateral afferent renal nerve activity and contralateral natriuretic responses to graded increases in ureteral pressure (5 to 20 mm Hg) were unaltered by renal pelvic perfusion with h-CGRP (8-37) at 1.0 and 10 mumol/L.(ABSTRACT TRUNCATED AT 250 WORDS)

A thiorphan-sensitive mechanism regulates the action of both exogenous and endogenous calcitonin gene-related peptide (CGRP) in the guinea-pig ureter

The aim of this study was to assess the existence of mechanisms regulating the intensity and duration of action of calcitonin gene-related peptide (CGRP), the main candidate inhibitory transmitter released from capsaicin-sensitive afferents in the guinea-pig ureter. In a first series of experiments, performed in capsaicin-pretreated ureters, exogenously administered human alpha CGRP (h alpha CGRP) produced inhibition of contractions of the guinea-pig isolated ureter evoked by direct electrical stimulation of smooth muscle. The intensity and duration of the inhibitory effect of h alpha CGRP were potentiated by the inhibitor of neutral endopeptidase, thiorphan, while captopril and bestatin were without effect. In a second series of experiments, background motility of the guinea-pig ureter was evoked by administration of endothelin-1 (ET-1): electrical stimulation of intramural nerves produced a transient suppression of the ET-1-evoked contractions, ascribable to release of endogenous CGRP. Thiorphan enhanced the inhibitory effect produced by endogenous CGRP, while bestatin and captopril were without effect. These findings demonstrate that a thiorphan-sensitive mechanism, presumably neutral endopeptidase, regulates the intensity and duration of the inhibitory activity of both exogenous and endogenous CGRP in the guinea-pig ureter. The existence of a mechanisms for inactivation of the released peptide is consistent with the proposed role of CGRP as inhibitory neurotransmitter in this preparation.

Immunohistochemical demonstration of nerves and nerve cells in human and porcine ureters

There are divergent opinions about the origin of ureteral motility. It is either a myogenic or a neutral phenomenon. Furthermore, the existence of nerve cells in the ureter is also a controversial question. In the present study we applied immunohistochemical methods to human and porcine ureters in an attempt to clarify the mattern. As neuronal markers we used anti-PGP 9.5 and anti-NSE, and as a glial marker anti-S-100. In the whole mount preparations of pig ureter we observed two neuronal plexuses on both sides of the tunica muscularis. The inner plexus consisted of both nerve bundles and nerve cells, whereas the outer one did not contain any nerve cells. In the human ureter we found a ganglion with nerve cells beneath the tunica muscularis and the tunica adventitia.