Visualization of intrarenal catecholamine-containing elements: fluorescence histochemistry and electron microscopy

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.

Catecholamine-containing, dopamine-beta-hydroxylase-immunoreactive perivascular nerve specializations in the rat kidney

Fluorescence histochemical visualization of catecholamines and immunolabeling of dopamine beta hydroxylase (DBH) were employed to study noradrenergic nerve terminals and perivascular nerve specializations in the rat kidney. Plexuses of catecholamine-containing and dopamine-beta-hydroxylase-immunoreactive nerves innervate the intrarenal arterial tree and larger intrarenal veins. Some perivascular nerve bundles have specialized segments composed of clusters of axonal enlargements that are immunoreactive for DBH and fluoresce intensely in ultraviolet light after fixation in a solution of formaldehyde and glutaraldehyde or treatment with glyoxylic acid. No fluorescent neural structures were found in denervated rat kidney sections treated with glyoxylic acid. Many such structures are associated with arteriolar branches of interlobar, arcuate, and interlobular arteries and are composed, in part, of axonal enlargements that contain mitochondria, microtubules, and one or more clusters of synaptic vesicles. These perivascular nerve specializations may be sites of axoaxonal interactions between noradrenergic axons or between these axons and other types of autonomic or sensory axons. The synaptic vesicles evidently store large amounts of catecholamine, but there is no evidence whether it is released into the surrounding tissue. These structures may be involved in changes in intrarenal innervation patterns which may occur as the rat ages. Regardless of the autonomic or sensory nature of intrarenal neural structures, close association of most such structures with arterioles suggests some neurovascular interaction.

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

Cryostat- and vibratome-cut sections of rat kidneys were singly or doubly labeled to visualize immunoreactive tyrosine hydroxylase (THI), dopamine beta-hydroxylase (DBHI), vasoactive intestinal peptide (VIPI), and neuropeptide Y (NPYI). Rats were perfusion fixed with 2-4% paraformaldehyde with or without 0.15% picric acid and rinsed in buffer for 18-48 hr. Single antigens were labeled with horseradish peroxidase in vibratome sections, whereas cryostat sections were used to label one antigen with peroxidase and another with a fluorophore in the same tissue section. A dense plexus of DBHI noradrenergic nerves innervates the renal arterial tree, and such nerves innervate the interlobar veins and renal calyx as well. Immunoreactive NPY is colocalized in most of these nerves, but some intrarenal noradrenergic nerves do not contain NPY but do contain VIP immunoreactivity. The distribution of NPYI nerves resembles that of DBHI nerves, whereas most perivascular noradrenergic nerves immunoreactive for VIP innervate selected arcuate and interlobular arteries. A small population of nonadrenergic, VIPI nerves innervates the renal calyx.

Small fluorescent cells in the rat kidney contain 5-hydroxytryptamine not a catecholamine

The rat kidney contains and excretes more dopamine than can be attributed solely to its originating from intrarenal noradrenergic nerves and plasma-free dopamine. It has recently been suggested that the source of this excess dopamine may be a population of small cells that are present in the renal medulla, and which by fluorescence and electron microscopy appear to contain high concentrations of a monoamine. We have therefore further investigated these cells. After formaldehyde treatment the fluorescence of the cells was characteristic of indoleamines rather than of catecholamine-containing structures. They did not form a visible precipitate with chromium salts in the classic chromaffin reaction. DOPA decarboxylase-like immunoreactivity was present in the adrenal medulla but not in the intrarenal cells or in mesenteric mast cells. 5-hydroxytryptamine (5-HT)-like immunoreactivity was seen in the intrarenal cells and in mesenteric mast cells, but was not evident in adrenal medullary cells. These results indicate that the intrarenal cells are 5-HT-containing mast cells and do not contribute to renal dopamine production.

An ultrastructural study of intrarenal catecholamine-containing elements

Histochemical visualization of catecholamines and electron microscopy in the same tissue sample were used to localize and study catecholamine-containing nerve enlargements or swellings in male Wistar and Sprague-Dawley rat kidneys. These swellings lie in the perivascular nerve plexuses of arcuate and interlobular arteries near the points of origin of arterioles, and are composed of modified axons and associated Schwann cells. Transverse sections of the enlarged nerves reveal that individual axons are also enlarged, have processes or folds and make contact with one another. The axonal enlargements contain small mitochondria with a dense matrix and clusters of small vesicles, many of which are associated with an organelle composed of parallel cisternae of smooth membranes.

Differentiation of noradrenergic and dopaminergic nerves in the rat kidney: evidence against significant dopaminergic innervation

In the rat kidney catecholaminergic nerve elements were identified by fluorescence histochemistry in perivascular plexuses around corticula arteries and juxtaglomerular arterioles and in medullary vascular bundles. Fluorescence was abolished in all areas 24 h after treatment with 6-hydroxydopamine (6-OHDA; 150 mg/kg i.v.). Protection of noradrenergic endings from destruction by 6-OHDA was afforded by pretreatment with desipramine (DMI; 25 mg/kg i.p.) which restored fluorescence towards control levels. By semiquantitative analysis fluorescence was identical in juxtaglomerular regions but slightly reduced around larger vessels in (DMI + 6-OHDA)-treated rats when compared to controls. Changes in tissue noradrenaline content, but not dopamine content, paralleled the changes in nerve fluorescence. Noradrenaline content was 4.10 pmol/mg protein (s.e.m. = 0.22, n = 32) in controls and was reduced by 90% to 0.40 pmol/mg (s.e.m. = 0.05, n = 23) in 6-OHDA-treated and by 26% to 3.01 pmol/mg (s.e.m. = 0.21, n = 23) in (DMI + 6-OHDA)-treated rats. Kidney dopamine content was 0.38 pmol/mg protein (s.e.m. = 0.05, n = 32) in controls and was reduced by 55% to 0.18 pmol/mg (s.e.m. = 0.02, n = 17) in 6-OHDA-treated and by 53% to 0.17 pmol/mg (s.e.m. = 0.02, n = 23) in (DMI + 6-OHDA)-treated rats. The renin response to haemorrhage was examined in pentobarbitone sodium-anaesthetized rats as a test of functional integrity of renal nerves in the three groups. Progressive 1 ml haemorrhages (to total blood loss of 4 ml, 1.3% body weight) resulted in similar increases in plasma renin activity in controls and (DMI + 6-OHDA)-treated animals but the response was significantly attenuated in 6-OHDA-treated rats. Renal catecholaminergic nerves appear to be predominantly noradrenergic. It is doubtful if a significant intrarenal dopaminergic system exists in the rat.

Location of dopamine stores in rat kidney

In normotensive and genetically hypertensive Wistar rats, chronic renal denervation reduces renal cortical levels of noradrenaline and dopamine by more than 90%. Non-neural stores of renal dopamine are therefore small or absent.

Catecholamines in discrete kidney regions. Changes in salt-sensitive Dahl hypertensive rats

Steady state levels of catecholamines (dopamine, norepinephrine, and epinephrine) were measured by the use of radioenzymatic techniques in discrete areas of the kidney (outer and inner cortex, outer and inner medulla) dissected by a "punch" technique from frozen kidney sections of salt-sensitive (DS) and salt-resistant (DR) Dahl rats fed a low or high salt diet. All three catecholamines were present in all areas of the kidney examined. There were gradients of concentrations of each catecholamine in different kidney areas. Renal medullary areas contained proportionally more dopamine than cortical areas. The proportion of epinephrine with respect to the total catecholamine content was relatively high in the inner medulla. Genetic factors and the amount of dietary salt influenced the catecholamine content in specific kidney areas, and these changes were different according to the area considered. DS rats when fed a high salt diet presented increased systolic blood pressure but no increased levels of dopamine in the inner medulla nor of norepinephrine in the outer medulla and outer cortex. Results suggest that either the uptake, release, storage, synthesis, or catabolism of kidney catecholamines is altered in Dahl salt-sensitive (DS) hypertensive rats and suggest specific roles for each catecholamine in discrete areas of the kidney.