Age-dependent changes of the sympathetic innervation of the rat kidney

Intrarenal Renin–Angiotensin System Involvement in the Pathogenesis of Chronic Progressive Nephropathy—Bridging the Informational Gap Between Disciplines

Chronic progressive nephropathy (CPN) is the most commonly encountered spontaneous background finding in laboratory rodents. Various theories on its pathogenesis have been proposed, but there is a paucity of data regarding specific mechanisms or physiologic pathways involved in early CPN development. The current CPN mechanism of action for tumorigenesis is largely based on its associated increase in tubular cell proliferation without regard to preceding subcellular degenerative changes. Combing through the published literature from multiple biology disciplines provided insight into the preceding cellular events. Mechanistic pathways involved in the progressive age-related decline in rodent kidney function and several key inflexion points have been identified. These critical pathway factors were then connected using data from renal models from multiple rodent strains, other species, and mechanistic work in humans to form a cohesive picture of pathways and protein interactions. Abundant data linked similar renal pathologies to local events involving hypoxia (hypoxia-inducible factor 1α), altered intrarenal renin–angiotensin system (RAS), oxidative stress (nitric oxide), and pro-inflammatory pathways (transforming growth factor β), with positive feedback loops and downstream effectors amplifying the injury and promoting scarring. Intrarenal RAS alterations seem to be central to all these events and may be critical to CPN development and progression.

Dopamine D4 receptor expression in rat kidney: evidence for pre- and postjunctional localization

Dopamine D4 receptors mediate inhibition of vasopressin-dependent sodium reabsorption by dopamine in collecting tubules. At present, the distribution of D4 receptors in other renal districts remains an open issue. The renal distribution of D4 receptor was assessed in normally innervated and denervated male Sprague-Dawley rats by quantitative immunohistochemistry using an anti-dopamine D4 receptor rabbit polyclonal antibody. D4 receptor protein immunoreactivity was observed perivascularly in the adventitia and the adventitia-media border. The density of perivascular dopamine D4 receptor was higher in afferent and efferent arterioles than in other segments of the renal vascular tree. Renal denervation abolished perivascular dopamine D4 receptor protein immunoreactivity. In renal tubules, the epithelium of collecting tubules showed the highest dopamine D4 receptor protein immunoreactivity, followed by the epithelium of proximal and distal tubules. No dopamine D4 receptor protein immunoreactivity was observed in the epithelium of the loop of Henle. Denervation did not change dopamine D4 receptor protein immunoreactivity in renal tubules. These results indicate that rat kidney expresses dopamine D4 receptors located both prejunctionally and nonprejunctionally in collecting, proximal, and distal tubules. This suggests that the dopamine D4 receptor may be involved in the control of neurotransmitter release and in renal hemodynamic and tubule function.

Age-related sympathetic ganglionic neuropathology: human pathology and animal models

Systematic studies of the autonomic nervous system of human subjects and development of well-defined animal models have begun to substantially improve our understanding of the pathogenesis of autonomic dysfunction in aging and may eventually provide strategies for intervention. Neuropathological studies of the sympathetic ganglia of aged human subjects and rodent models have demonstrated that neuroaxonal dystrophy involving intraganglionic terminal axons and synapses is a robust, unequivocal and consistent neuropathological finding in the aged sympathetic nervous system of man and animals. Quantitative studies have demonstrated that markedly swollen argyrophilic dystrophic axon terminals develop in the prevertebral superior mesenteric (SMG) and coeliac, but to a much lesser degree in the superior cervical ganglia (SCG) as a function of age, sex (males more than females) and diabetes. Dystrophic axons were immunoreactive for neuropeptide Y, tyrosine hydroxylase, dopamine-beta-hydroxylase, trkA and p75NTR, an immunophenotype consistent with their origin from postganglionic sympathetic neurons, and contained large numbers of highly phosphorylated neurofilaments or tubulovesicular elements. The sympathetic ganglia of aged rodents also showed the hallmark changes of neuroaxonal dystrophy as a function of age and location (many more in the SMG than in the SCG). Plasticity-related synaptic remodeling could represent a highly vulnerable target of the aging process. The fidelity of animal models to the neuropathology of aged humans suggests that similar pathogenetic mechanisms may be involved in both and that therapeutic advances in animal studies may have human application.

The process of aging changes the interplay of the immune, endocrine and nervous systems

The immune, endocrine and nervous systems interact with each other by means of cytokines, hormones and neurotransmitters. Interaction is dependent on specific receptors and respective signaling pathways in target cells. During aging, changes occur on many levels of these global systems which depend on oxidative damage, non-enzymatic glycosylation, mitochondrial mutations, defects in cell cycle control, mitotic dysregulation, genome instability, telomere shortening and other chromosomal pathologies. An alteration of the numerical value of a parameter of one system can lead to changes of the numerical value of a variable of another system. In a non-linear dynamic process these changes can contribute to the aging phenotype. Although it is extremely difficult to dissect linear interrelations of three global systems during aging, this review attempts to identify some simple linear pathways. Furthermore, it is demonstrated that chronic inflammatory diseases may accelerate the aging process. This review also reveals that new statistical and computational methods are necessary to unravel the complexity of the aging process.

Pharmacological characterisation and autoradiographic localisation of a putative dopamine D3 receptor in the rat kidney

The pharmacological profile and the microanatomical localisation of a putative dopamine D3 receptor in the rat renal cortex were investigated using radioligand binding assay and light microscope autoradiography techniques. [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([3H]7-OH-DPAT) was used as a ligand. [3H]7-OH-DPAT was bound specifically to sections of renal cortex. The binding was time-, temperature- and concentration-dependent, of high affinity and guanine nucleotide-insensitive. The dissociation constant (Kd) value was 0.57 +/- 0.02 nM and the maximum density of binding sites (Bmax) was 62.4 +/- 3.5 fmol/mg tissue. The pharmacological profile of [3H]7-OH-DPAT binding to sections of rat renal cortex suggests the labelling of a dopamine D3 receptor. Light microscope autoradiography revealed the accumulation of the radioligand primarily within cortical tubules and to a lesser extent in the glomerular tuft. In glomeruli, binding sites were found mainly in mesangium and mesangial cells. The demonstration of a putative dopamine D3 receptor in slide-mounted sections of rat renal cortex suggests that appropriate radioligand binding assay techniques combined with autoradiography, may contribute to characterise peripheral dopamine receptor subtypes.

Role of norepinephrine in hepatic gluconeogenesis: evidence of aging and training effects

This study examined the relationship among the sympathetic neurotransmitter norepinephrine (NE), hepatic gluconeogenesis, and glyconeogenesis in 63 (30 trained and 33 untrained) young (7 mo), middle-aged (15 mo), and old (25 mo) male Fischer 344 rats. Animals were trained 1 h/day, 5 days/wk for 10 wk at treadmill speeds of 75% of age-specific maximal capacity. Liver sections, removed at rest, were sliced and incubated in [14C]lactic acid and 0, 0.5, 1.0, 3.0, or 6.0 ng/ml NE. The rate of [14C]lactate incorporation into glucose was significantly greater in young compared with old animals in both training groups and at all NE concentrations. All trained animals had greater rates of glucose production from lactate than their untrained counterparts at 0.5, 1.0, 3.0, and 6.0 ng/ml NE. At each NE concentration, the old rats showed the lowest rates of glycogen synthesis from lactate. The untrained rats in all age groups were the least responsive to increases in NE concentration. Total hepatic glycogen synthase activity exhibited age-related declines as the young and middle-aged had significantly greater total activity compared with the old animals: 620.4 +/- 27.5, 590.0 +/- 37.9, and 436.3 +/- 44.5 disintegrations/min, respectively. No differences with training were found in total activity. The percent of glycogen synthase in the active form was significantly greater in young compared with old in both the trained (48.6 +/- 2.0 vs. 40.0 +/- 1.3% active) and untrained animals (44.7 +/- 2.2 vs. 35.4 +/- 1.5% active).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

A microscopical assay using a densitometric application of image analysis to quantify neurotransmitter dynamics

We have attempted to demonstrate the technical requirements and performance of a microscopical assay using a densitometric application of image analysis to measure immunohistochemical stain intensity. Not surprisingly, the techniques required were more demanding than those used for the quantification of field and object parameters in the nervous system. The following areas of methodology have been shown to be important: (1) use of buffers free of metallic ions for tissue processing, (2) selection and titration of first and second layer antibodies, (3) reduction and control of fading of fluorescence, (4) selection of microscopical and imaging equipment to give accurate, sensitive and uniform representations of low-light biological images, and (5) use of appropriate image analysis algorithms in order to generate binary images that match the spatial and intensity distributions of immunostaining. Incorporation of these techniques into our assay system gave sensitive measurements of the time-scale of uptake of 5-hydroxy-tryptamine (5-HT) into sympathetic nerve terminals. The microscopical assay appears to have advantages over alternative approaches used for studies of neurotransmitter dynamics, particularly in small, heterogeneous tissue samples.