Identification of noradrenergic nerve terminals immunoreactive for neuropeptide Y and vasoactive intestinal peptide in the rat kidney

Function of Renal Nerves in Kidney Physiology and Pathophysiology

Renal sympathetic (efferent) nerves play an important role in the regulation of renal function, including glomerular filtration, sodium reabsorption, and renin release. The kidney is also innervated by sensory (afferent) nerves that relay information to the brain to modulate sympathetic outflow. Hypertension and other cardiometabolic diseases are linked to overactivity of renal sympathetic and sensory nerves, but our mechanistic understanding of these relationships is limited. Clinical trials of catheter-based renal nerve ablation to treat hypertension have yielded promising results. Therefore, a greater understanding of how renal nerves control the kidney under physiological and pathophysiological conditions is needed. In this review, we provide an overview of the current knowledge of the anatomy of efferent and afferent renal nerves and their functions in normal and pathophysiological conditions. We also suggest further avenues of research for development of novel therapies targeting the renal nerves.

Noradrenergic and Cholinergic Reinnervation of Islet Grafts in Diabetic Rats

Grafted islets become denervated due to the islet transplantation procedure. The aim of the present study was 1) to examine whether islet grafts in the liver, the spleen, and under the kidney capsule in rats become reinnervated following the transplantation and experimental procedures used in our laboratory, 2) whether there is any difference in reinnervation at these different sites, and 3) how these results relate to previous physiological experiments. Isogeneic isolated islets were transplanted into diabetic Albino Oxford rats, resulting in normoglycaemia. After at least 5 wk, graft-receiving organs were removed and several antibodies were employed to detect insulin, neuron-specific proteins, and cholinergic and noradrenergic nerve fibers. Islets in all three receiving organs contained viable insulin-positive B-cells. Neuron-specific enolase (NSE) as well as the growth-associated protein B-50 was observed at all sites. The cholinergic marker choline acetyltransferase (ChAT) was localized in islets grafts at all sites, but with the lowest density in the spleen. Staining for the noradrenergic markers tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH) was observed in islet grafts at all sites with the lowest density in grafts under the kidney capsule. All these neurochemical substances were most frequently observed in fibers associated with blood vessels, which may be the route along which nerves grow into the graft. It can be concluded that 1) islet grafts in the liver, in the spleen and under the kidney capsule become reinnervated; 2) the innervation pattern of the islet grafts differs only slightly from that in the control pancreatic islets; and 3) in combination with our previously physiological data, we can conclude that these nerve fibers are, at least partly, functionally active.

Angiotensinergic innervation of the kidney: present knowledge and its significance

Intrarenal neurotransmission implies the co-release of neuropeptides at the neuro-effector junction with direct influence on parameters of kidney function. The presence of an angiotensin (Ang) II-containing phenotype in catecholaminergic postganglionic and sensory fibers of the kidney, based on immunocytological investigations, has only recently been reported. These angiotensinergic fibers display a distinct morphology and intrarenal distribution, suggesting anatomical and functional subspecialization linked to neuronal Ang II-expression. This review discusses the present knowledge concerning these fibers, and their significance for renal physiology and the pathogenesis of hypertension in light of established mechanisms. The data suggest a new role of Ang II as a co-transmitter stimulating renal target cells or modulating nerve traffic from or to the kidney. Neuronal Ang II is likely to be an independent source of intrarenal Ang II. Further physiological experimentation will have to explore the role of the angiotensinergic renal innervation and integrate it into existing concepts.

Role of neuropeptide Y in the regulation of kidney function

The presence in the mammalian kidney of NPY and at least one of its receptor subtypes has been proven by several independent methodologies. Also, numerous studies using physiological and pharmacological approaches indicated that this peptide has the capacity to alter renal function. In particular, these studies suggest that NPY may exert renal vasoconstrictor and tubular actions that are species dependent, and may also influence renin secretion by the kidney. The question whether NPY plays an important role in the physiological regulation of renal hemodynamics and electrolyte excretion, remains largely unanswered at present. No major impairments in renal function have been reported in genetically models deficient in NPY or its Y1 receptor. Thus, additional studies are required to elucidate the role of NPY in the physiological and pathophysiological regulation of renal function.

Increased plasma levels of neuropeptide Y in hepatorenal syndrome

BACKGROUND/AIMS

To investigate the relationship between neuropeptide Y (NPY), a potent renal vasoconstrictor peptide released upon marked stimulations of sympathetic nervous system (SNS), and renal and circulatory function in cirrhosis.

METHODS

Plasma levels of NPY (radioimmunoassay) and norepinephrine and renal function parameters were determined in 17 healthy controls, nine patients with cirrhosis without ascites, and 37 patients with cirrhosis and ascites, of whom 12 had hepatorenal syndrome (HRS).

RESULTS

Patients with ascites showed circulating levels of NPY similar to those of patients without ascites and controls (73+/-4, +/-4 and 68+/-4 pmol/l, respectively; NS). However, patients with HRS had significantly increased levels of NPY with respect to the other groups (110+/-6 pmol/l; P<0.001). NPY levels correlated inversely with renal plasma flow and glomerular filtration rate and directly with norepinephrine. In patients with HRS (n=6) treatment with terlipressin and albumin was associated with a marked improvement in circulatory and renal function and marked suppression of NPY and norepinephrine levels.

CONCLUSIONS

Patients with HRS have increased levels of NPY which are related to circulatory dysfunction and SNS activation and may contribute to renal vasoconstriction.

Peptides and other neuronal markers in transplanted pancreatic islets

Functional alterations are developed in transplanted islets over time. Because islets in situ are densely innervated and isolation disconnects the endocrine organ from extrinsic nerves and from ganglia in the exocrine pancreas, it is important to examine the reinnervation of islet grafts. This review describes the patterns of appearances of intrinsic perikarya and reinnervating fibers demonstrating markers for parasympathetic, sympathetic or sensory nerve substances, most notably neuropeptides, in islet transplants. An altered innervation pattern, as compared to normal islets, develops. Presumably the expression of neuronal markers in the grafts is related to factors both in the islets and in the ectopic environment offered by the implantation organ.

Neuropeptide Y-enhanced diuresis and natriuresis in anaesthetized rats is independent of renal blood flow reduction

1. Neuropeptide Y (NPY) has been reported to enhance diuresis and natriuresis in anaesthetized rats although it is a potent renal vasoconstrictor in vitro in vivo in several species. Therefore, we have investigated anaesthetized rats to see whether reduction in renal blood flow (RBF) and enhancement of diuresis and natriuresis can occur concomitantly, and how diuresis and natriuresis might be enhanced despite reduced RBF. 2. Systemic or intrarenal NPY infusion (0.03-3 micrograms kg-1 min-1) had only a small effect on mean arterial pressure (maximal increase 15-20 mmHg) and heart rate (maximal decrease 30 beats min-1) but dose-dependently reduced RBF (maximal peak reduction 3 ml min-1) Endogenous creatinine clearance was not significantly altered. 3. In anaesthetized rats systemic infusion of 1 or 3 micrograms kg-1 min-1 NPY enhanced urine formation and sodium and calcium excretion by a maximum of 110, 110 and 45%, respectively, but did not alter potassium excretion. Enhancement of diuresis was also detectable in conscious rats. 4. The diuretic and natriuretic effects of systemically infused NPY were at least partly maintained in rats with decapsulated kidneys and in rats where NPY-induced increase of renal perfusion pressure was excluded mechanically by an adjustable clamp placed on the abdominal aorta. 5. Intrarenal infusion of 0.3 or 1 microgram kg-1 min-1 NPY reduced RBF to a greater extent than systemic infusion (maximal peak reduction 4 ml min-1) but caused a smaller enhancement or even a reduction of urine formation and sodium excretion. 6. We conclude that systemic infusion of NPY reduces RBF by a direct effect on the renal vasculature. Systemic NPY infusion enhances urine formation and sodium and calcium excretion. This occurs independently (at least in part) of pressure natriuresis by formation and/or release of an extrarenal factor which might act on distal tubules and/or collecting ducts.

Noradrenergic and cholinergic reinnervation of islet grafts in diabetic rats

Grafted islets become denervated due to the islet transplantation procedure. The aim of the present study was 1) to examine whether islet grafts in the liver, the spleen, and under the kidney capsule in rats become reinnervated following the transplantation and experimental procedures used in our laboratory, 2) whether there is any difference in reinnervation at these different sites, and 3) how these results relate to previous physiological experiments. Isogeneic isolated islets were transplanted into diabetic Albino Oxford rats, resulting in normoglycaemia. After at least 5 wk, graft-receiving organs were removed and several antibodies were employed to detect insulin, neuron-specific proteins, and cholinergic and noradrenergic nerve fibers. Islets in all three receiving organs contained viable insulin-positive B-cells. Neuron-specific enolase (NSE) as well as the growth-associated protein B-50 was observed at all sites. The cholinergic marker choline acetyltransferase (ChAT) was localized in islets grafts at all sites, but with the lowest density in the spleen. Staining for the noradrenergic markers tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) was observed in islet grafts at all sites with the lowest density in grafts under the kidney capsule. All these neurochemical substances were most frequently observed in fibers associated with blood vessels, which may be the route along which nerves grow into the graft. It can be concluded that 1) islet grafts in the liver, in the spleen and under the kidney capsule become reinnervated; 2) the innervation pattern of the islet grafts differs only slightly from that in the control pancreatic islets; and 3) in combination with our previously physiological data, we can conclude that these nerve fibers are, at least partly, functionally active.

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.

Reinnervation of isolated islets of Langerhans transplanted beneath the kidney capsule in the rat

Neural regulation of islets of Langerhans mediates responses to stress and food ingestion. Transplantation of isolated islets offers hope to patients with insulin dependent diabetes mellitus but denervation of isolated islets may affect the capacity for appropriate metabolic control. Previous examination of the endocrine response to stress in islet autografted dogs revealed differences consistent with loss of neural regulation. Therefore, in the present study, islets grafted in rats were examined for extent and nature of reinnervation. Islets isolated from syngeneic donors were grafted under the kidney capsule of Wistar-Furth rats (n = 7) after 3 wk of streptozotocin induced diabetes. After 4 mo, graft-bearing kidneys were recovered and processed for double immunofluorescence. Antibodies were directed against (a) neuron associated proteins: synapsin (SYN) and L1; (b) neurotransmitters; tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), and calcitonin gene-related peptide (CGRP); and (c) islet hormones: insulin and somatostatin. SYN and L1 immunoreactivities in nerve fibres suggested reinnervation of the grafted islets although fibres were not associated with structures within the transplanted islets as in intact islets. CGRP immunoreactivity was observed in fibres and in a subpopulation of cells within intact islets but only in cells of the grafted islets. VIP, TH, and NPY immunoreactivities were found in nerve fibres of intact islets but only VIP was observed in fibres of grafted islets suggesting an absence of sympathetic reinnervation. In conclusion, transplanted islets of Langerhans become reinnervated but with a distribution and complement of neurotransmitters distinct from intact islets.

Sympathetic and sensory innervation of the urinary tract in young adult and aged rats: a semi-quantitative histochemical and immunohistochemical study

The sympathetic innervation of the urinary tract of young adult (4 months) and aged (24+ months) rats has been examined by glyoxylic acid-induced fluorescence for the detection of noradrenaline and by immunofluorescence using antisera against tyrosine hydroxylase (TH) and neuropeptide Y (NPY). Immunostaining for calcitonin gene-related peptide (CGRP), known to be present in pelvic sensory nerves, was also performed. Semi-quantitative estimations of nerve densities were made of noradrenergic and peptidergic fibres innervating the smooth musculature of the ureter, bladder and urethra, and of the urinary tract vasculature. In the aged rats the overall patterns of innervation remained unchanged. However, with the exception of the vesical vasculature, the density of noradrenergic innervation decreased as did the intensity of histofluorescence. A similar pattern of results was observed by TH and NPY immunofluorescence. The results present evidence for a diminution in the sympathetic control of the urinary tract in aged rats. The pattern and density of CGRP-immunoreactive nerves was unchanged in the aged animals suggesting that pelvic visceral sensory innervation is more resistant to the effects of advancing age.

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.

Distributions of neuropeptide Y, vasoactive intestinal peptide and somatostatin in populations of postganglionic neurons innervating the rat kidney, spleen and intestine

Some peripheral peptidergic nerves selectively innervate different types of tissue in abdominal organs. Neuropeptide Y- and vasoactive intestinal peptide-immunoreactive nerve terminals have been identified in the kidney, spleen and intestine and these peptides may have important physiological actions. Somatostatin has been found in sympathetic ganglia, and nerve terminals containing this peptide have been identified in the intestine. We have used fluorescent retrograde tracers to identify renal, splenic and mesenteric postganglionic neurons in rat sympathetic ganglia and then used immunocytochemistry to determine the proportions of these three identified groups of neurons displaying immunoreactivity for neuropeptide Y, vasoactive intestinal peptide and somatostatin. Most renal, splenic and mesenteric neurons were immunoreactive for neuropeptide Y and less than 1% of cells innervating these organs were immunoreactive for vasoactive intestinal peptide. Somatostatin immunoreactivity was present only in a small percentage of mesenteric neurons and not in renal or splenic neurons. The present study demonstrates that (i) the rat kidney, spleen and intestine do not differ in the proportion of innervation by neuropeptide Y-immunoreactive neurons, (ii) the solar plexus, splanchnic ganglion and chain ganglia (T12 and T13) provide very little vasoactive intestinal peptide-immunoreactive inputs to these organs, and (iii) somatostatin-immunoreactive neurons innervate the intestine but not the kidney or spleen.

Acetylcholine and kinin augmentation of Cl- secretion stimulated by prostaglandin in a canine renal epithelial cell line

1. The actions of kinins and of acetylcholine upon transepithelial ion transport in a renal-derived cultured epithelium (Madin-Darby canine kidney cells, MDCK) have been investigated. 2. In voltage-clamped epithelial layers mounted in Ussing chambers and with prior stimulation of inward short-circuit current (SCC) by 5 or 10 microM-prostaglandin E1 (PGE1), both bradykinin (1 microM) and acetylcholine (0.1 mM) stimulate an additional, but transient, inward SCC. In the absence of PGE1 minimal effects of both bradykinin and acetylcholine upon SCC are observed. The SCC response to bradykinin and acetylcholine are attenuated with prior stimulation by 10 microM-adrenaline. 3. Measurements of bradykinin and acetylcholine-stimulated inward SCC with cation and anion replacement of the bathing media and the use of the Cl channel blocker 5-nitro-2(3-phenylpropylamino)-benzoic acid (NPPB) together with bumetanide to inhibit Na(+)-K(+)-Cl- 'co-transport', are consistent with the bradykinin- and acetylcholine-stimulated SCC being the result of basal to apical Cl- secretion. 4. Bradykinin (1 microM) is capable of stimulation of inward SCC from both epithelial surfaces, whilst acetylcholine is only effective from the basolateral surface. Kallidin (lys-bradykinin) was similar in effect to bradykinin from both epithelial surfaces whereas bradykinin (1-8) was ineffective, suggesting that B2 bradykinin receptors mediate the effect of bradykinin upon SCC. Dose-response relationships show that the response to kallidin and bradykinin was of higher sensitivity for additions to the apical cell aspects. 5. The data are discussed in relation to a model for epithelial Cl- secretion, and to the mechanism of natriuresis observed with kinins and acetylcholine in vivo.

Effects of neuropeptide-Y on renal function and its interaction with sympathetic stimulation in conscious dogs

1. The effects of neuropeptide-Y (NPY) on renal function were investigated in conscious foxhounds. 2. Dose-response curves (n = 7) were obtained for NPY by measuring renal blood flow (RBF), glomerular filtration rate (GFR), urine excretion (VU), sodium excretion (VNa), potassium excretion (VK) and plasma renin activity (PRA) at different infusion rates. All variables decreased with increasing infusion rates except for PRA, which surprisingly did not change during the different infusion rates. 3. The influence of the non-constrictor dose of NPY at control pressure, and after servo-controlling renal arterial pressure at 80 mmHg, was determined for these parameters (n = 6). 4. This was repeated during a reflex sympathetic activation via carotid sinus hypotension, in order to quantify a possible interaction between the sympathetic transmitter and co-transmitter (n = 6). 5. The subthreshold NPY dose raised plasma NPY-like immunoreactivity (NPY-LI IR) significantly (renal venous plasma: 54 +/- 13 vs. 405 +/- 117 pg ml-1; P less than 0.05) and enhanced the pressure-dependent (80 mmHg) antidiuresis (0.48 +/- 0.06 vs. 0.24 +/- 0.02 ml min-1; P less than 0.05), antinatriuresis (46 +/- 11 vs. 25 +/- 3 mumol min-1; P less than 0.05), antikaliuresis (19 +/- 4 vs. 9 +/- 0.7 mumol min-1; P less than 0.05) and pressure-dependent renin release (0.95 +/- 0.27 vs. 3.0 +/- 1.1 ng angiotensin I ml-1 h-1; P less than 0.05). These effects are consistent with a non-uniform vasoconstrictor action of NPY in the renal vascular bed (see accompanying papers). 6. The effects of NPY plus sympathetic activation were less than the sum of the two individual effects, which may rely on a presynaptic mechanism.

Differential effect of neuropeptide-Y on membrane potential of cells in renal arterioles of the hydronephrotic mouse

1. The effects of neuropeptide-Y (NPY) on the membrane potential of vascular smooth muscle cells were studied in renal arterioles of hydronephrotic mouse kidneys. 2. Kidney vessels are only weakly coupled with length constants of less than 10 microns and are most probably 'multiunit' vessels. 3. The vasoconstrictor peptide NPY reversibly depolarizes only smooth muscle cells in arterioles at distances greater than 200 microns from the glomerulus, whereas no changes of the membrane potential can be evoked close to the glomerulus (distance less than 50 microns). 4. The depolarizations, when present, are dose dependent. 5. Regardless of distance from the glomerulus cells respond uniformly to application of the vasoconstrictor angiotensin II.

Renal sodium excretion following systemic infusion of vasoactive intestinal peptide in the rat

1. The aim of this clearance study was to examine the renal effects of systemic infusion of vasoactive intestinal peptide (VIP) in the intact rat. 2. Mean arterial blood pressure (MAP), plasma electrolytes and haematocrit, glomerular filtration rate (GFR), and urinary sodium and potassium excretion were measured in a baseline period and following VIP infusion (0.1-1.2 nmol/h per 200 g), as well as during a time control study. 3. During infusion of low doses of VIP (0.1 and 0.4 nmol/h per 200 g), a small increase in fractional and absolute excretion of sodium occurred but this did not differ from that occurring in the time control group. In the high dose VIP group (1.2 nmol/h per 200 g), significant falls occurred in MAP and GFR, and absolute sodium excretion fell (though not significantly) from its baseline level. 4. These findings suggest that systemic VIP has no net natriuretic effect in the rat, but produces haemodynamic changes associated with reduced sodium excretion at high doses. This study does not exclude the possibility of direct effects on tubular sodium transport of VIP released from renal nerves.

Vasoactive intestinal polypeptide nerve fibers in human and monkey (Macaca fascicularis and Macaca mulatta) kidneys

Nerve fibers immunoreactive for vasoactive intestinal polypeptide (VIP) were demonstrated for the first time by the indirect immunofluorescence technique in human and monkey kidneys. VIP-immunoreactive nerve fibers showing varicosities were observed in the adventitia of arcuate arteries and their branches. The density of VIP-immunoreactive nerve fibers decreased from the juxtamedullary region to the cortex. Occasionally a VIP-immunoreactive varicose nerve fiber was observed near the vascular pole of a glomerulus, but no direct innervation of afferent or efferent arterioles in either monkey or human kidney was found. The distribution of VIP-immunoreactive nerve fibers in the monkey and human kidneys was similar to that reported in other species, with less density. The functional role of VIP in the innervation of the kidney is not known, but various suggestions have been made regarding the possible involvement of VIP on vasodilation of selective intrarenal blood vessels, renin secretion, and/or effects on tubules. While none of these questions were established at this time they would appear to be logical areas for further study.

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

Cryostat- and vibratome-cut rat kidney secretions were singly or doubly labeled to visualize immunoreactive calcitonin-gene-related peptide (CGRPI) and substance P (SPI). Rats were perfused with 2-4% paraformaldehyde + 0.15% picric acid then rinsed with buffer. Horseradish peroxidase (HRP) was used to visualize CGRP in vibratome sections, and combined HRP and fluorophore were used to visualize the two peptides simultaneously in cryostat sections. There is a complex, multilayered plexus of CGRP nerves on the renal pelvis and a less dense, single-layered plexus on the major branches of the renal artery and on interlobar arteries and veins. A few axons innervate finer branches of the arterial tree and other intrarenal structures. Results of double immunolabeling suggest that SPI axons comprise a subpopulation of the CGRP axon population in the rat kidney. There was no evidence for a separate population of SPI axons.

Co-localization of vasoactive intestinal polypeptide and neuropeptide Y immunoreactivities in the nerve fibers of the rat adrenal gland

The co-localization of Vasoactive Intestinal Polypeptide (VIP) with Neuropeptide Y (NPY) or its C-flanking peptide (C-PON) was investigated with immunocytochemistry methods in the adrenal gland of the rat. Most of the VIP immunoreactive (+) nerve fibers found in the capsule/glomerular zone also exhibited NPY or C-PON immunoreactivity (IR). We found that at least two populations of VIP varicose nerve fibers can be observed, the most prevalent exhibited both VIP/NPY or VIP/C-PON IR and the other which was rather scarce lacked NPY or C-PON IR. In the superficial cortex VIP/NPY or VIP/C-PON IR nerve fibers were often associated with capsular or subcapsular vascularization and extended into the zona glomerulosa. In the deeper layers of the adrenal cortex radial fibers were closely associated with the inner vascularization of the zona fasciculata and reticularis. In the adrenal medulla NPY or C-PON immunoreactivity was associated with ganglion neurons as well as chromaffin cells; these last cells were always VIP (-). VIP and NPY/C-PON IR could be co-localized in catecholaminergic nerve terminals of the adrenal cortex but not in the adrenal medulla.

Neuropeptide Y (NPY)-like immunoreactive nerve fibers in the human and monkey (Macaca fascicularis) kidney

Nerve fibers immunoreactive for neuropeptide Y (NPY) are demonstrated for the first time by the indirect immunofluorescence technique in the human and monkey kidney. NPY-like immunoactivity (NPY-LI) is shown in a bundle of nerve fibers in the surrounding connective tissue of arteries and to a lesser extent, veins, mainly at the juxtamedullary region. Varicose nerve terminals are shown associated with blood vessels and passing between tubules in the mid and lower cortex. NPY-LI nerve fibers are also seen surrounding afferent and occasionally efferent arterioles at the vascular pole of the glomeruli. The distribution of NPY-LI nerve fibers in the monkey and human kidneys is similar to that of other species, only the quantity of the nerve fibers varies.