Calcitonin gene-related peptide-immunoreactive nerves in the rat kidney

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.

Impact of anesthesia, sex, and circadian cycle on renal afferent nerve sensitivity

Elevated renal afferent nerve (ARNA) activity or dysfunctional reno-renal reflexes via altered ARNA sensitivity contribute to hypertension and chronic kidney disease. These nerves contain mechano- and chemosensitive fibers that respond to ischemia, changes in intrarenal pressures, and chemokines. Most studies have utilized various anesthetized preparations and exclusively male animals to characterize ARNA responses. Therefore, this study assessed the impact of anesthesia, sex, and circadian period on ARNA responses and sensitivity. Multifiber ARNA recordings were performed in male and female Sprague-Dawley rats (250-400 g) and compared across decerebrate versus Inactin, isoflurane, and urethane anesthesia groups. Intrarenal artery infusion of capsaicin (0.1-50.0 μM, 0.05 mL) produced concentration-dependent increases in ARNA; however, the ARNA sensitivity was significantly greater in decerebrate versus Inactin, isoflurane, and urethane groups. Increases in renal pelvic pressure (0-30 mmHg, 30 s) produced pressure-dependent increases in ARNA; however, ARNA sensitivity was again greater in decerebrate and Inactin groups versus isoflurane and urethane. Acute renal artery occlusion (30 s) increased ARNA, but responses did not differ across groups. Analysis of ARNA responses to increased pelvic pressure between male and female rats revealed significant sex differences only in isoflurane and urethane groups. ARNA responses to intrarenal capsaicin infusion were significantly blunted at nighttime versus daytime; however, ARNA responses to increased pelvic pressure or renal artery occlusion were not different between daytime and nighttime. These results demonstrate that ARNA sensitivity is greatest in decerebrate and Inactin-anesthetized groups but was not consistently influenced by sex.NEW & NOTEWORTHY We determined the impact of anesthesia, sex, and circadian cycle on renal afferent nerve (ARNA) sensitivity to chemical and mechanical stimuli. ARNA sensitivity to renal capsaicin infusion was greatest in decerebrate > Inactin > urethane or isoflurane groups. Elevated renal pelvic pressure significantly increased ARNA; decerebrate and Inactin groups exhibited the greatest ARNA sensitivity. Sex differences in renal afferent responses were not consistently observed. Circadian cycle altered chemosensory but not mechanosensory responses.

Cutaneous and renal vasodilatory response to local pressure application: A comparative study in mice

BACKGROUND AND AIM

We have reported a novel relationship involving mechanical stimulation and vasodilation in rodent and human skin, referred to as pressure-induced vasodilation (PIV). It is unknown whether this mechanism exists in kidney and reflects the microcirculation in deep organs. Therefore, we compared the skin and kidney PIV to determine whether their changes were similar.

METHODS

In anesthetized mice fed a normal salt-diet, laser Doppler flux (LDF) signals were measured when an increase in local pressure was applied to the surface of the head skin with the rate of 2.2Pa/s (1mmHg/min) and to the left kidney with a rate of 4.4Pa/s (2mmHg/min). The mechanism underlying renal PIV was also investigated. The skin and kidney PIV were also compared during salt load (4% NaCl diet).

RESULTS

The kidney had higher baseline LDF and vascular conductance compared to those of the skin. Pressure application increased the LDF in the kidney as well as in the skin with a comparable maximal magnitude (about 25% from baseline value), despite different kinetics of PIV evolution. As we previously reported in the skin, the kidney PIV response was mediated by the activation of transient receptor potential vanilloid type 1 channels, the release of calcitonin gene-related peptide, and the participation of prostaglandins and nitric oxide. In the absence of hypertension, high salt intake abolished the cutaneous PIV response and markedly impaired the renal one.

CONCLUSION

PIV response in the mouse kidney results from a neuro-vascular interaction. Despite some differences between the skin and the kidney PIV, the similarities in their response and signaling mechanisms suggest that the cutaneous microcirculation could reflect, in part, the microcirculation of the renal cortex.

Contribution of K(+) channels to endothelium-derived hypolarization-induced renal vasodilation in rats in vivo and in vitro

We investigated the mechanisms behind the endothelial-derived hyperpolarization (EDH)-induced renal vasodilation in vivo and in vitro in rats. We assessed the role of Ca(2+)-activated K(+) channels and whether K(+) released from the endothelial cells activates inward rectifier K(+) (Kir) channels and/or the Na(+)/K(+)-ATPase. Also, involvement of renal myoendothelial gap junctions was evaluated in vitro. Isometric tension in rat renal interlobar arteries was measured using a wire myograph. Renal blood flow was measured in isoflurane anesthetized rats. The EDH response was defined as the ACh-induced vasodilation assessed after inhibition of nitric oxide synthase and cyclooxygenase using L-NAME and indomethacin, respectively. After inhibition of small conductance Ca(2+)-activated K(+) channels (SKCa) and intermediate conductance Ca(2+)-activated K(+) channels (IKCa) (by apamin and TRAM-34, respectively), the EDH response in vitro was strongly attenuated whereas the EDH response in vivo was not significantly reduced. Inhibition of Kir channels and Na(+)/K(+)-ATPases (by ouabain and Ba(2+), respectively) significantly attenuated renal vasorelaxation in vitro but did not affect the response in vivo. Inhibition of gap junctions in vitro using carbenoxolone or 18α-glycyrrhetinic acid significantly reduced the endothelial-derived hyperpolarization-induced vasorelaxation. We conclude that SKCa and IKCa channels are important for EDH-induced renal vasorelaxation in vitro. Activation of Kir channels and Na(+)/K(+)-ATPases plays a significant role in the renal vascular EDH response in vitro but not in vivo. The renal EDH response in vivo is complex and may consist of several overlapping mechanisms some of which remain obscure.

Renal sympathetic denervation in resistant hypertension

Resistant hypertension remains a major clinical problem despite the available multidrug therapy. Over the next decades, its incidence will likely increase given that it is strongly associated with older age and obesity. Resistant hypertension patients have an increased cardiovascular risk, thus effective antihypertensive treatment will provide substantial health benefits. The crosstalk between sympathetic nervous system and kidneys plays a crucial role in hypertension. It influences several pathophysiological mechanisms such as the central sympathetic tone, the sodium balance and the systemic neurohumoral activation. In fact, studies using several animal models demonstrated that the renal denervation prevented and attenuated hypertension in multiple species. Large reductions in blood pressure were also observed in malignant hypertension patients submitted to sympathectomy surgeries. However, these approaches had an unacceptably high rates of periprocedural complications and disabling adverse events. Recently, an innovative non-pharmacological therapy that modulates sympathetic activation has been successfully developed. Renal sympathetic percutaneous denervation is an endovascular procedure that uses radiofrequency energy to destroy the autonomic renal nerves running inside the adventitia of renal arteries. This method represents a promising new approach to the strategy of inhibiting the sympathetic nervous system. The aim of this review is to examine the background knowledge that resulted in the development of this hypertension treatment and to critically appraise the available clinical evidence.

Autonomic control of the urogenital tract

The urogenital tract houses many of the organs that play a major role in homeostasis, in particular those that control water and salt balance, and reproductive function. This review focuses on the anatomical and functional innervation of the kidneys, urinary ducts and bladders of the urinary system, and the gonads, gonadal ducts, and intromittent organs of the reproductive tract. The literature, especially in recent years, is overwhelmingly skewed toward the situation in mammals. Nevertheless, where specific neurochemical markers have been investigated, common patterns of innervation can be found in representatives from most vertebrate classes. Not surprisingly the vasculature, epithelia and smooth muscle of all urogenital organs receives adrenergic innervation. These nerves may contain non-adrenergic non-cholinergic (NANC) neurotransmitters such as ATP and NPY. Cholinergic nerves increase motility in most urogenital organs with the exception of the kidney. The major NANC nerves found to influence urogenital organs include those containing VIP/PACAP, galanin and neuronal nitric oxide synthase. These can be found associated with both smooth muscle and epithelia. The role these nerves play, and the circumstances where they are activated are for the most part unknown.

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.

Renal microvascular actions of calcitonin gene-related peptide

Calcitonin gene-related peptide (CGRP) is a potent vasodilator that is suggested to act via ATP-sensitive K channels (KATP). In the present study, we examined the actions of CGRP on pressure- and angiotensin II-induced vasoconstriction, using the in vitro perfused hydronephrotic rat kidney. Elevated pressure (from 80 to 180 mmHg) and 0.1 nM angiotensin II elicited similar decreases in afferent diameter in this model. CGRP inhibited myogenic reactivity in a concentration-dependent manner, completely preventing pressure-induced constriction at 10 nM (95 +/- 10% inhibition). These effects were partially attenuated by 10 microM glibenclamide (62 +/- 16% inhibition, P = 0.025), indicating both KATP-dependent and -independent actions of CGRP. In contrast, 10 nM CGRP inhibited angiotensin II-induced vasoconstriction by only 54 +/- 11%, and this action was not affected by glibenclamide (41 +/- 11%, P = 0.31). CGRP also inhibited the efferent arteriolar response to angiotensin II in the absence and presence of glibenclamide. Pinacidil (1.0 microM), a KATP opener also preferentially inhibited pressure- vs. angiotensin II-induced vasoconstriction (97 +/- 5 and 59 +/- 13% inhibition, respectively; P = 0.034). We conclude that the renal vasodilatory mechanisms of CGRP are pleiotropic and involve both KATP-dependent and -independent pathways. The effectiveness of CGRP in opposing renal vasoconstriction and the role of KATP in this action appear to depend on the nature the underlying vasoconstriction. We suggest that this phenomenon reflects an inhibition of KATP activation by angiotensin II.

Characterization of binding sites for amylin, calcitonin, and CGRP in primate kidney

Analysis of receptor distributions for 125I-labeled amylin, 125I-labeled calcitonin, and 125I-labeled calcitonin gene-related peptide (CGRP) in Macaca fascicularis kidney by in vitro autoradiography revealed distinct patterns of binding for each peptide. 125I-rat amylin bound primarily to the cortex, being associated with the distal tubule, including apparent binding to the juxtaglomerular apparatus. 125I-salmon calcitonin displayed high-density binding in the cortex with low-density binding to the medulla. Emulsion autoradiography indicated that binding was associated with both distal tubule and thick ascending limb of the loop of Henle. Intense binding was also found often over juxtaglomerular apparatus. 125I-rat CGRP-alpha exhibited low- to moderate-density binding to the inner medulla/papilla with high-density binding over small-, medium-, and large-caliber arteries. Weak binding to the glomerulus was also seen, but no binding was associated with cortical tubules. Competition binding studies, performed with each of the radioligands, revealed peptide specificity profiles for CGRP and calcitonin receptors that were similar to those described in rat. However, the monkey amylin receptors differed from those in rat, exhibiting relatively higher affinity for calcitonin peptides but reduced affinity for CGRP peptides. These studies suggest potential roles for amylin, calcitonin, and CGRP in primate renal function.

Neurokinin A in rat renal afferent neurons and in nerve fibres within smooth muscle and epithelium of rat and guinea-pig renal pelvis

Neurokinin A-like immunoreactivity of dorsal root ganglion neurons innervating the kidney were studied with retrograde tracing of FluoroGold dye applied to the cut renal nerves. The proportions and sizes of renal afferent neurons with neurokinin A-like immunoreactivity were quantified in T9-L2 dorsal root ganglia from five rats. Of 240 renal afferent neuronal somata examined, 26 +/- 3% (S.E.M.) showed neurokinin A-like immunoreactivity. Compared with the overall size distribution of renal afferent neurons, those staining for neurokinin A were mostly small-sized neurons with a few medium-sized neurons. All somata with neurokinin A-like immunoreactivity were neurofilament-poor as judged by labelling with an anti-neurofilament antibody, RT97, and it is therefore likely that they had unmyelinated fibres. To examine the sites to which the renal afferent fibres with neurokinin A might project, sections of rat and guinea-pig kidney and upper ureter were examined. Fibres with neurokinin A-like immunoreactivity were found beneath and within the transitional epithelium lining the inner surface of the pelvis, and within the smooth muscle layer beneath the transitional epithelium. Epithelial innervation was found only in regions with underlying smooth muscle and loose connective tissue, and not in sites where the epithelium was closely applied to the renal parenchyma. The network of fibres was most dense towards the pelvo-uretic junction. Fibres with neurokinin A-like immunoreactivity were not seen beneath or within the cuboidal/columnar epithelium covering the papilla within the renal pelvis. Furthermore, only very few fibres with neurokinin A were observed penetrating the transitional epithelium of the upper ureter in both rat and guinea-pig. The distribution of fibres labelled with antibodies to substance P and calcitonin gene-related peptide in the renal pelvis was similar to that for fibres with neurokinin A-like immuno-reactivity, although a few fibres penetrated further into the fornices than fibres with neurokinin-A-like immunoreactivity. Thus, many afferent fibres in the renal pelvis may contain neurokinin A as well as substance P and calcitonin gene-related peptide. These fibres may be the source of the neurokinin A, substance P and calcitonin gene-related peptide which can be released by topical capsaicin treatment. In addition they may be the mechano- and chemo-receptive fibres in the renal pelvis that are known to play important roles in renal haemodynamics. The intra-epithelial position of some of these fibres in the epithelial layer suggests a possible chemosensory or osmosensory role.

Age-related changes in calcitonin gene-related peptide and substance P in renal afferent nerve soma in the rat. Association with afferent renal nerve activity

Renal afferent neurons were retrogradely labeled with FluoroGold in Sprague-Dawley rats at 50, 60, 70, 80, 90, 110, 130 and 200 days of age. Recordings of afferent renal nerve activity (ARNA) and immunofluorescent assessment of calcitonin gene-related peptide (CGRP)-like immunoreactivity (LI) and substance P (SP)-LI in spinal ganglia T10-L1 were obtained in the same rats. The frequency of renal afferent neurons positive for CGRP-LI declined abruptly from 88% in animals younger than 100 days of age (342 of 388 total cells) to 63% in rats older than 100 days of age (223 of the 353 total cells). The intensity of CGRP-LI (scaled 1-3) in renal afferent CGRP-positive neurons also declined significantly from a mean of 2.23 +/- 0.04 before 100 days to 1.48 +/- 0.05 in older rats (P < 0.001 in each age group). SP-LI positive neurons declined from 44% to 28% (P < 0.001). These changes in neuropeptide immunofluorescence coincided with an altered pattern of ARNA in which the excitatory response to complete renal ischemia increased from 274 +/- 69% above background to 1167 +/- 124% after the age of 100 days. Previous studies have shown that this alteration in the ARNA response to renal ischemia is due to the appearance of activity from R1 chemoreceptor nerves in ARNA. These data demonstrated that this transition in the electrophysiologic characteristics of ARNA is accompanied by profound alterations in CGRP-LI and SP-LI levels in renal afferent nerve cell bodies.

Immunoreactivity for apolipoprotein A-IV in tanycytes and astrocytes of rat brain

Immunoperoxidase and immunofluorescence procedures were used to visualize polyclonal antiserum binding to apolipoprotein (apo) A-IV in rat brain. With both methods, tanycytes and astrocytes were labeled throughout both white and gray matter. Within the cells, the labeling was granular and it was confined to the perinuclear zone and proximal regions of the processes. The labeling was abolished by absorption of the primary antiserum with purified apo A-IV but not by absorption with apo E. These results suggest either that apo A-IV is synthesized by astrocytes, or that apolipoprotein that is synthesized in the small intestine or liver is selectively taken up and stored by the astrocytes.

Autoradiographic localization of NK1 and NK3 tachykinin receptors in rat kidney

The distribution of neurokinin receptors in rat kidney, renal artery, renal vein, and proximal ureter was evaluated by autoradiography after in vitro labeling of NK1 sites with [125I]Bolton-Hunter substance P (BHSP) or NK3 sites with [125I][MePhe7]neurokinin B ([MePhe7]NKB). Film autoradiography using [125I][MePhe7]NKB revealed specific binding sites associated with the renal vein and its large branches, the renal pelvis, the inner strip of outer renal medulla, and the proximal ureter. High-resolution autoradiograms demonstrated that these sites were localized to the smooth muscle layer in the veins, pelvis, and ureter. Neither the renal arterial system nor the renal cortex contained specific [125I][MePhe7]NKB binding sites although a high level of nonspecific binding was associated with the renal artery. Specific binding of [125I]BHSP was associated with the renal artery and renal pelvis but not the renal veins. Arterial NK1 receptors appeared to be localized to the adventitia. The results indicate that at least two types of tachykinin receptor are present in the rat kidney. The distinct localization observed for most of the NK1 and NK3 receptors suggests that they have different functions.

Immunocytochemical properties of rat renal afferent neurons in dorsal root ganglia: a quantitative study

Immunocytochemical properties of dorsal root ganglion neurons innervating the kidney were studied with retrograde tracing of Fluorogold or Fast Blue dyes applied to the cut renal nerves in the rat. The proportions and sizes of renal afferent neurons labelled with a variety of markers were quantified in T9-L1 dorsal root ganglia from five rats. Compared with the overall size distribution in these ganglia, renal afferent neurons were mainly small with a few medium-sized neurons. The majority (79%) of renal afferent dorsal root ganglion neuronal somata were unlabelled by an anti-neurofilament antibody, RT79, and classified as neurofilament-poor with probable C-fibres. These had an approximately normal distribution of cell sizes. Only 21% were RT79-positive and classified as neurofilament-rich with probable A-fibres, and even these were small to medium sized cells, consistent with them being mostly A delta-fibre neurons. Percentages of renal afferent neurons showing labelling were as follows: peripherin-like immunoreactivity: 69%; calcitonin-gene related peptide: 93%; substance P: 37%; the lectins soybean agglutinin: 57% and peanut agglutinin: 68%; Calbindin D28k-like immunoreactivity: 21% (only weak labelling); carbonic anhydrase like immunoreactivity: 0%. There were differences between probable C-fibre and probable A-fibre neurons, classified according to their labelling with RT97. The percentages of RT97-negative and RT97-positive neurons respectively labelled with the other markers were as follows: peripherin-like immunoreactivity: 82%, 25%; calcitonin gene-related peptide-like immunoreactivity: 99%, 79%; substance P-like immunoreactivity: 43%, 0%; soybean agglutinin: 69%, 24%; peanut agglutinin: 76%, 47%; calbindin-like immunoreactivity: 26%, 0%. Thus, the biggest differences between the probable A- and C-fibre renal afferent neurons were in their peripherin, substance P and calbindin contents. Thus, renal afferent neurons in the dorsal root ganglion are not homogeneous and it is suggested the differences may relate to the known different afferent receptor types within the kidney. It is suggested that the low proportion of neurons with substance P-like immunoreactivity in the renal afferent innervation compared to that of other viscera may relate to the role of the renal vasculature in urine formation.

Localization of immunoreactive neuropeptides in the kidney of the bullfrog, Rana catesbeiana, by immunofluorescence

Indirect double immunofluorescence labelling for demonstrating nine neuropeptides in the kidney of the bullfrog, Rana catesbeiana, revealed for the first time the occurrence, distribution, and coexistence of certain neuropeptides in the kidney of the submammalian vertebrates. Substance P, neuropeptide Y, and calcitonin gene-related peptide were localized in nerve fibers distributed along the afferent arterioles connected with the glomeruli, and along the capillary network between uriniferous tubules. Neuropeptide Y and calcitonin gene-related peptide immunoreactive fibers were more numerous than substance P immunoreactive fibers. In these two regions, about one half of the neuropeptide Y or calcitonin gene-related peptide fibers contained substance P. No immunoreactivity of vasoactive intestinal polypeptide, somatostatin, FMRFamide, or leucine- and methionine-enkephalins was detected in the bullfrog kidney.

Immunocytochemical co-localization of substance P and calcitonin gene-related peptide in afferent renal nerve soma of the rat

Substance P, calcitonin gene-related peptide and somatostatin immunoreactivities have been demonstrated in putative afferent renal nerve fibers in the rat. Utilizing retrograde-tracing and immunohistochemistry, we labeled afferent renal nerve soma throughout dorsal root ganglia T9 to L1. Most (85%) of afferent renal nerve perikarya were immunoreactive for calcitonin gene-related peptide, 21% had substance P immunoreactivity and none had somatostatin immunoreactivity. All renal afferents immunoreactive for substance P also contained calcitonin gene-related peptide. These results provide evidence that calcitonin gene-related peptide and substance P are present and co-localized in afferent renal nerves, and therefore, mediate transmission of afferent renal input to the spinal cord in the rat.

Transitory noradrenergic and peptidergic nerves in the cat kidney

Indirect immunohistochemical methods were used to visualize nerves immunoreactive for tyrosine hydroxylase (TH), dopamine beta hydroxylase (DBH), neuropeptide Y, (NPY) and calcitonin gene-related peptide (CGRP) in sections of the kidneys of cats of different ages. Nerve terminals immunoreactive for TH, DBH and NPY innervated interlobar veins and the renal arterial tree including medullary vascular bundles of cats of each age studied. Most nerve terminals immunoreactive for CGRP innervated interlobar arteries. In kidneys of cats 2 to 10 weeks old, TH- and DBH-immunoreactive axons formed elaborate plexuses that were distributed throughout much of the outer two thirds of the inner medulla. Inner medullary NPY-immunoreactive nerve terminals formed sparse plexuses by comparison, thus suggesting a large population of TH-immunoreactive nerve terminals not immunoreactive for NPY. Plexuses immunoreactive for CGRP also innervated the inner medullae of young cats. Some inner medullary axons appeared degenerate in 8 and 10 week old cats, and no inner medullary nerve terminal plexuses were visualized in 12 week old or adult cats. Cell death or paring of axons resulting from mechanisms intrinsic to the neuronal population or from a change in trophic factors secreted or expressed by cells in the medulla may effect the loss of inner medullary nerve terminals in the kidneys of young cats.

The rat renal nerves during development

The prenatal and postnatal development of the innervation of the rat kidney has been investigated using immunocytochemical methods. The efferent innervation was studied using dopamine-beta-hydroxylase and neuropeptide Y antibodies. Calcitonin gene related peptide and substance P antibodies were used to investigate the afferent innervation. Kidneys from embryos of 14 to 20 days, from newborn rats, and from animals of 4, 10, 12, 21, 38, 60, and 90 days of age were studied. Slices of whole kidneys were analyzed, and frozen sections were used to investigate the location of the nerves in more detail. Both afferent and efferent nerves are observed inside the kidney by embryonic day 16. At birth, the afferent nerves are found (1) forming a rich plexus in the renal pelvis; (2) associated with the renal vasculature as far as the interlobular arteries (cortical radial arteries) and (3) in the corticomedullary connective tissue. The efferent innervation appears, at birth, to extend to the interlobular arteries and to the afferent arterioles of the perihilar juxtamedullary nephrons. The efferent innervation increases rapidly during the following days, and by postnatal day 21 a distribution of the innervation similar to that of the adult is observed. While the afferent innervation reaches the major target regions of the kidney by birth, the efferent does most of its expansion into the kidney postnatally. Afferent and efferent fibers are found, extrarenally and intrarenally, in the same nerve bundles. This proximity between afferent and efferent fibers may represent anatomical bases for their interaction in the adult as well as during development.

The renal nerves in the newborn rat

Immunocytochemical methods were used to investigate the distribution of afferent [calcitonin gene-related peptide-(CGRP) immunoreactive and substance P-immunoreactive] nerves and efferent (neuropeptide Y-immunoreactive and dopamine beta-hydroxylase-immunoreactive) nerves in the kidneys of rats within the 1st day of life. The newborn rat kidney possesses an afferent and efferent innervation. Both afferent and efferent nerves reach the kidney in the same bundles. The afferent sensory fibers predominate overwhelmingly in the renal pelvis and ureter while the efferent fibers clearly predominate in the vasculature. The corticomedullary connective tissue contains both types of innervation with a more prominent afferent innervation (CGRP immunoreactive). Only afferent arterioles of perihilar nephrons were innervated by efferent sympathetic fibers. The distribution and extent of afferent and efferent innervation is consistent with the renal nerves playing a significant role in the transition from fetal to newborn life. The close proximity between afferent and efferent fibers suggests a possible interaction between the two systems.

Prenatal and postnatal development of the CGRP-immunoreactive innervation in the rat kidney

Calcitonin gene-related peptide (CGRP) immunoreactive afferent nerves were seen intrarenally by prenatal day 16. They grow rapidly and CGRP positive nerves are observed at birth associated with the arterial and venous vascular tree, forming a rich plexus in the pelvic region and in the connective tissue located near the corticomedullary region. The distribution and extent of CGRP immunoreactive nerves suggest that at birth the rat is able to provide information on the status of the kidney to be integrated in the mechanisms of body fluid homeostasis.

Simultaneous visualization of neuropeptide and acetylcholinesterase nerve subpopulations in the perivascular plexus

A simple method combining indirect immunofluorescence and histochemical techniques was developed in order to demonstrate the presence of both neuropeptide immunoreactivity and acetylcholinesterase activity in the same whole-mount preparation. It was found that the two methods can be combined without interfering with one another and may be viewed and photographed simultaneously. The guinea pig basilar artery was chosen as a model tissue. While vasoactive intestinal polypeptide immunoreactivity and acetylcholinesterase activity were found to occur in the same perivascular nerve fibres, tyrosine hydroxylase, neuropeptide tyrosine and calcitonin gene-related peptide immunoreactivity were present in distinct nerve subpopulations. It is possible using this double staining procedure, to analyse the interrelationship of putative cholinergic nerves with other components of the autonomic and sensory nervous system.

Sensory innervation of the rat kidney and ureter as revealed by the anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) from dorsal root ganglia

The sensory innervation of the rat kidney and ureter was investigated in wholemount preparations and sectioned materials by labeling the afferent nerve fibers with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) transported anterogradely from dorsal root ganglia. Labeled fibers were seen in large numbers in the ureter and in the lining of the renal pelvis, where they were located in the adventitia, smooth muscle, subepithelial connective tissue, and epithelium. Most of the fibers in the ureter and ureteropelvic junctional zone traveled parallel to the long axis of the organ. In contrast, fibers in the widest part of the funnel-shape renal pelvis were oriented predominantly in a circumferential fashion. Many of the pelvic afferents were extremely fine and appeared to terminate as free nerve endings. Modest networks of labeled axons were also observed around branches of the renal artery; the greatest innervation was supplied to the distal portions of the interlobar arteries and to the arcuate arteries. Only single axons were observed around the interlobular arteries, and very few fibers were seen around afferent arterioles or near glomeruli. In contrast to the arteries, branches of the renal vein were relatively sparsely innervated. Occasional labeled fibers entered the renal cortex and formed intimate associations with renal tubules; however, the vast majority of renal tubular elements were not contacted by labeled sensory fibers. Labeled fibers were never observed in the renal medulla or in the papilla. The present study represents the first time that the sensory innervation of the kidney and ureter has been investigated by using a highly specific anterograde nerve tracing technique. The pattern of innervation demonstrated here reveals an anatomical configuration of ureteral and renal pelvic sensory nerves consistent with a role in detection of ureteral and pelvic pressure and chemical changes and a renal vascular sensory innervation that may monitor changes in renal arterial and venous pressure and chemical content. Still other renal afferent nerve endings may signal renal pain.