Protein kinase C-mediated mu-opioid receptor phosphorylation and desensitization in rats, and its prevention during early diabetes

Translation of Experimental Findings from Animal to Human Biology: Identification of Neuronal Mineralocorticoid and Glucocorticoid Receptors in a Sectioned Main Nerve Trunk of the Leg

The activation of the mineralocorticoid (MR) and glucocorticoid (GR) receptors on peripheral sensory neurons seems to modify pain perception through both direct non-genomic and indirect genomic pathways. These distinct subpopulations of sensory neurons are not known for peripheral human nerves. Therefore, we examined MR and GR on subpopulations of sensory neurons in sectioned human and rat peripheral nerves. Real-time PCR (RT-PCR) and double immunofluorescence confocal analysis of MR and GR with the neuronal markers PGP9.5, neurofilament 200 (NF200), and the potential pain signaling molecules CGRP, Nav1.8, and TRPV1 were performed in human and rat nerve tissue. We evaluated mechanical hyperalgesia after intrathecal administration of GR and MR agonists. We isolated MR- and GR-specific mRNA from human peripheral nerves using RT-PCR. Our double immunofluorescence analysis showed that the majority of GR colocalized with NF200 positive, myelinated, mechanoreceptive A-fibers and, to a lesser extent, with peripheral peptidergic CGRP-immunoreactive sensory nerve fibers in humans and rats. However, the majority of MR colocalized with CGRP in rat as well as human nerve tissue. Importantly, there was an abundant colocalization of MR with the pain signaling molecules TRPV1, CGRP, and Nav1.8 in human as well as rat nerve tissue. The intrathecal application of the GR agonist reduced, and intrathecal administration of an MR agonist increased, mechanical hyperalgesia in rats. Altogether, these findings support a translational approach in mammals that aims to explain the modulation of sensory information through MR and GR activation. Our findings show a significant overlap between humans and rats in MR and GR expression in peripheral sensory neurons.

An Insight into Potential Pharmacotherapeutic Agents for Painful Diabetic Neuropathy

Diabetes is the 4th most common disease affecting the world's population. It is accompanied by many complications that deteriorate the quality of life. Painful diabetic neuropathy (PDN) is one of the debilitating consequences of diabetes that effects one-third of diabetic patients. Unfortunately, there is no internationally recommended drug that directly hinders the pathological mechanisms that result in painful diabetic neuropathy. Clinical studies have shown that anticonvulsant and antidepressant therapies have proven fruitful in management of pain associated with PDN. Currently, the FDA approved medications for painful diabetic neuropathies include duloxetine, pregabalin, tapentadol extended release, and capsaicin (for foot PDN only). The FDA has also approved the use of spinal cord stimulation system for the treatment of diabetic neuropathy pain. The drugs recommended by other regulatory bodies include gabapentin, amitriptyline, dextromethorphan, tramadol, venlafaxine, sodium valproate, and 5 % lidocaine patch. These drugs are only partially effective and have adverse effects associated with their use. Treating painful symptoms in diabetic patient can be frustrating not only for the patients but also for health care workers, so additional clinical trials for novel and conventional treatments are required to devise more effective treatment for PDN with minimal side effects. This review gives an insight on the pathways involved in the pathogenesis of PDN and the potential pharmacotherapeutic agents. This will be followed by an overview on the FDA-approved drugs for PDN and commercially available topical analgesic and their effects on painful diabetic neuropathies.

Synthesis of the Mechanisms of Opioid Tolerance: Do We Still Say NO?

The use of morphine as a first-line agent for moderate-to-severe pain is limited by the development of analgesic tolerance. Initially opioid receptor desensitization in response to repeated stimulation, thought to underpin the establishment of tolerance, was linked to a compensatory increase in adenylate cyclase responsiveness. The subsequent demonstration of cross-talk between N-methyl-D-aspartate (NMDA) glutamate receptors and opioid receptors led to the recognition of a role for nitric oxide (NO), wherein blockade of NO synthesis could prevent tolerance developing. Investigations of the link between NO levels and opioid receptor desensitization implicated a number of events including kinase recruitment and peroxynitrite-mediated protein regulation. Recent experimental advances and the identification of new cellular constituents have expanded the potential signaling candidates to include unexpected, intermediary compounds not previously linked to this process such as zinc, histidine triad nucleotide-binding protein 1 (HINT1), micro-ribonucleic acid (mi-RNA) and regulator of G protein signaling Z (RGSZ). A further complication is a lack of consistency in the protocols used to create tolerance, with some using acute methods measured in minutes to hours and others using days. There is also an emphasis on the cellular changes that are extant only after tolerance has been established. Although a review of the literature demonstrates a lack of spatio-temporal detail, there still appears to be a pivotal role for nitric oxide, as well as both intracellular and intercellular cross-talk. The use of more consistent approaches to verify these underlying mechanism(s) could provide an avenue for targeted drug development to rescue opioid efficacy.

High-throughput screening and validation of antibodies against synaptic proteins to explore opioid signaling dynamics

Antibodies represent powerful tools to examine signal transduction pathways. Here, we present a strategy integrating multiple state-of-the-art methods to produce, validate, and utilize antibodies. Focusing on understudied synaptic proteins, we generated 137 recombinant antibodies. We used yeast display antibody libraries from the B cells of immunized rabbits, followed by FACS sorting under stringent conditions to identify high affinity antibodies. The antibodies were validated by high-throughput functional screening, and genome editing. Next, we explored the temporal dynamics of signaling in single cells. A subset of antibodies targeting opioid receptors were used to examine the effect of treatment with opiates that have played central roles in the worsening of the 'opioid epidemic.' We show that morphine and fentanyl exhibit differential temporal dynamics of receptor phosphorylation. In summary, high-throughput approaches can lead to the identification of antibody-based tools required for an in-depth understanding of the temporal dynamics of opioid signaling.

Loss of POMC-mediated antinociception contributes to painful diabetic neuropathy

Painful neuropathy is a frequent complication in diabetes. Proopiomelanocortin (POMC) is an endogenous opioid precursor peptide, which plays a protective role against pain. Here, we report dysfunctional POMC-mediated antinociception in sensory neurons in diabetes. In streptozotocin-induced diabetic mice the Pomc promoter is repressed due to increased binding of NF-kB p50 subunit, leading to a loss in basal POMC level in peripheral nerves. Decreased POMC levels are also observed in peripheral nervous system tissue from diabetic patients. The antinociceptive pathway mediated by POMC is further impaired due to lysosomal degradation of μ-opioid receptor (MOR). Importantly, the neuropathic phenotype of the diabetic mice is rescued upon viral overexpression of POMC and MOR in the sensory ganglia. This study identifies an antinociceptive mechanism in the sensory ganglia that paves a way for a potential therapy for diabetic neuropathic pain.

Tranilast attenuates neuropathic pain during type-2 diabetes by inhibiting hypoxia-induced pro-inflammatory cytokines in Zucker diabetic fatty rat model

BACKGROUND

The modulatory effect of tranilast on neuropathic pain in type-2 diabetes (T2DM) remains unclear.

METHODS

We monitored interleukin (IL)-1β, nuclear factor-κB (NF-κB) and tumour necrosis factor-α (TNF-α) levels during the progression of T2DM induced neuropathic pain in rats, and assessed the impact of tranilast treatment of increasing concentrations (0, 200 and 400 mg/kg/day via oral gavage in 1% NaHCO₃ delivered as 100 mg/kg twice a day) on the levels of cytokine production, as well as on the thermal hyperalgesia and mechanical allodynia.

RESULTS

The rats developed hyperglycaemia accompanied with elevated levels of NF-κB, IL-1β and TNF-α in the rostral ventromedial medulla at the age of 16 weeks. Tranilast administration dose dependently alleviated thermal hyperalgesia as well as mechanical allodynia, which was associated with its ability in inhibiting hypoxia-induced levels of NF-κB, IL-1β and TNF-α.

CONCLUSION

Tranilast plays crucial roles in modulating T2DM-related neuropathic pain, likely through inhibiting hypoxia.

Antinociceptive effects of IL-6R vs. glucocorticoid receptors during rat hind paw inflammatory pain

BACKGROUND

The glucocorticoid receptor (GR) plays a role in inflammatory pain modulation. However, the specific role played by interleukin 6 receptor (IL-6R) in these processes remains elusive. The present study aimed to investigate the extent of inflammation induced by IL-6R and GR.

METHODS

Male Wistar rats were treated with Freund's complete adjuvant to induce right hind paw inflammation. The levels of IL-6Rα and GR were evaluated in the spinal cord and dorsal root ganglion using Western blot and immunofluorescence assays. Subsequently, we examined the nociceptive behavioral changes following the binding of IL-6R with a GR agonist and/or antagonist, as well as the concentration levels of IL-6 and soluble IL-6R (sIL-6R) in the serum and cerebrospinal fluid. Moreover, the spinal levels of IL-6, IL-6Rα, gp130, JAK2, pJAK2, STAT3, pSTAT3, c-fos, GFAP, and Iba-1 were assessed following anti-IL-6R antibody, sgp130, and dexamethasone intrathecal administration.

RESULTS

Right hind paw inflammation resulted in significant upregulation of IL-6Rα expression in spinal nociceptive neurons, astrocytes, and microglia cells, as well as increased of IL-6Rα and GR colocalization. Notably, anti-IL-6R or dexamethasone attenuated the nociceptive behavior in a dose-dependent manner. Isobologram analysis indicated the sub-additive effects with a concomitant decrease in the spinal levels of IL-6, pJAK2, pSTAT3, c-fos, GFAP, and Iba-1 and increase in the sIL-6R level.

CONCLUSION

The enhanced mechanical sensitivity accompanying the increase of IL-6Rα and GR was attenuated by anti-IL-6R and dexamethasone application, and the sub-additive effects were regulated by the decreased activation of neurons and glial cells and modulated by IL-6/JAK2/STAT3 signaling pathway, which might be attributed to IL-6 induced trans-signaling.

DAMGO-induced μ opioid receptor internalization and recycling restore morphine sensitivity in tolerant rat

This study investigated the effect of DAMGO-induced μ opioid receptor (MOR) internalization on morphine tolerance. Male Sprague-Dawley rats (200-250 g) aged 6-8 weeks were administered morphine via intrathecal (i.t.) injection (15 μg/10 μl twice daily for 6 days) to induce antinociceptive tolerance, which was evaluated using the tail-flick and paw-withdrawal tests. Response latency was calculated as the percentage of maximum possible effect (%MPE). A bolus of DAMGO was administered by i.t. injection on day 6, and the tail-flick and paw-withdrawal tests were carried out 24, 48, and 72 h later. Membrane and cytosolic MOR expression was assessed by western blotting. HEK293 cells were transfected with MOR-FLAG plasmid and after 6 days of morphine treatment (10 μM), the cells were treated with 1 μM DAMGO, and MOR localization was examined by immunofluorescence analysis 30 and 60 min later. Repeated morphine treatment induced tolerance after 5 days; however, i.t. DAMGO administration restored morphine sensitivity and enhanced acute morphine-induced antinociception after 24, 48, and 72 h. In HEK293 cells, DAMGO treatment stimulated MOR internalization after 30 min and MOR recycling to the membrane after 1 h. Membrane and cytoplasmic MOR expression in vivo was unchanged 24, 48, and 72 h after i.t. DAMGO injection. Morphine does not cause significant MOR internalization or downregulation, and can readily induce tolerance. DAMGO counters this effect by enhancing receptor endocytosis, thereby reversing morphine-induced antinociceptive tolerance and restoring its analgesic efficacy.

Neuronal aldosterone elicits a distinct genomic response in pain signaling molecules contributing to inflammatory pain

Background

Recently, mineralocorticoid receptors (MR) were identified in peripheral nociceptive neurons, and their acute antagonism was responsible for immediate and short-lasting (non-genomic) antinociceptive effects. The same neurons were shown to produce the endogenous ligand aldosterone by the enzyme aldosterone synthase.

Methods

Here, we investigate whether endogenous aldosterone contributes to inflammation-induced hyperalgesia via the distinct genomic regulation of specific pain signaling molecules in an animal model of Freund’s complete adjuvant (FCA)-induced hindpaw inflammation.

Results

Chronic intrathecal application of MR antagonist canrenoate-K (over 4 days) attenuated nociceptive behavior in rats with FCA hindpaw inflammation suggesting a tonic activation of neuronal MR by endogenous aldosterone. Consistently, double immunofluorescence confocal microscopy showed abundant co-localization of MR with several pain signaling molecules such as TRPV1, CGRP, Nav1.8, and trkA whose enhanced expression of mRNA and proteins during inflammation was downregulated following i.t. canrenoate-K. More importantly, inhibition of endogenous aldosterone production in peripheral sensory neurons by continuous intrathecal delivery of a specific aldosterone synthase inhibitor prevented the inflammation-induced enhanced transcriptional expression of TRPV1, CGRP, Nav1.8, and trkA and subsequently attenuated nociceptive behavior. Evidence for such a genomic effect of endogenous aldosterone was supported by the demonstration of an enhanced nuclear translocation of MR in peripheral sensory dorsal root ganglia (DRG) neurons.

Conclusion

Taken together, chronic inhibition of local production of aldosterone by its processing enzyme aldosterone synthase within peripheral sensory neurons may contribute to long-lasting downregulation of specific pain signaling molecules and may, thus, persistently reduce inflammation-induced hyperalgesia.

Post-translational Modifications of Opioid Receptors

Post-translational modifications (PTMs) are key events in signal transduction since they affect protein function by regulating their abundance and/or activity. PTMs involve the covalent attachment of functional groups to specific amino acids. Since they tend to be generally reversible, PTMs serve as regulators of signal transduction pathways. G-protein-coupled receptors (GPCRs) are major signaling proteins that undergo multiple types of PTMs. In this Review, we focus on the opioid receptors, members of GPCR family A, and highlight recent advances in the field that have underscored the importance of PTMs in the functional regulation of these receptors. Since opioid receptor activity plays a central role in the development of tolerance and addiction to morphine and other drugs of abuse, understanding the molecular mechanisms regulating receptor activity is of fundamental importance.

Aldosterone Synthase in Peripheral Sensory Neurons Contributes to Mechanical Hypersensitivity during Local Inflammation in Rats

Background

Recent emerging evidence suggests that extra-adrenal synthesis of aldosterone occurs (e.g., within the failing heart and in certain brain areas). In this study, the authors investigated evidence for a local endogenous aldosterone production through its key processing enzyme aldosterone synthase within peripheral nociceptive neurons.

Methods

In male Wistar rats (n = 5 to 8 per group) with Freund’s complete adjuvant hind paw inflammation, the authors examined aldosterone, aldosterone synthase, and mineralocorticoid receptor expression in peripheral sensory neurons using quantitative reverse transcriptase–polymerase chain reaction, Western blot, immunohistochemistry, and immunoprecipitation. Moreover, the authors explored the nociceptive behavioral changes after selective mineralocorticoid receptor antagonist, canrenoate-K, or specific aldosterone synthase inhibitor application.

Results

In rats with Freund’s complete adjuvant–induced hind paw inflammation subcutaneous and intrathecal application of mineralocorticoid receptor antagonist, canrenoate-K, rapidly and dose-dependently attenuated nociceptive behavior (94 and 48% reduction in mean paw pressure thresholds, respectively), suggesting a tonic activation of neuronal mineralocorticoid receptors by an endogenous ligand. Indeed, aldosterone immunoreactivity was abundant in peptidergic nociceptive neurons of dorsal root ganglia and colocalized predominantly with its processing enzyme aldosterone synthase and mineralocorticoid receptors. Moreover, aldosterone and its synthesizing enzyme were significantly upregulated in peripheral sensory neurons under inflammatory conditions. The membrane mineralocorticoid receptor consistently coimmunoprecipitated with endogenous aldosterone, confirming a functional link between mineralocorticoid receptors and its endogenous ligand. Importantly, inhibition of endogenous aldosterone production in peripheral sensory neurons by a specific aldosterone synthase inhibitor attenuated nociceptive behavior after hind paw inflammation (a 32% reduction in paw pressure thresholds; inflammation, 47 ± 2 [mean ± SD] vs. inflammation + aldosterone synthase inhibitor, 62 ± 2).

Conclusions

Local production of aldosterone by its processing enzyme aldosterone synthase within peripheral sensory neurons contributes to ongoing mechanical hypersensitivity during local inflammation via intrinsic activation of neuronal mineralocorticoid receptors.

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Pro- versus Antinociceptive Nongenomic Effects of Neuronal Mineralocorticoid versus Glucocorticoid Receptors during Rat Hind Paw Inflammation

Background

In naive rats, corticosteroids activate neuronal membrane–bound glucocorticoid and mineralocorticoid receptors in spinal cord and periphery to modulate nociceptive behavior by nongenomic mechanisms. Here we investigated inflammation-induced changes in neuronal versus glial glucocorticoid and mineralocorticoid receptors and their ligand-mediated nongenomic impact on mechanical nociception in rats.

Methods

In Wistar rats (n = 5 to 7/group) with Freund’s complete adjuvant hind paw inflammation, we examined glucocorticoid and mineralocorticoid receptor expression in spinal cord and peripheral sensory neurons versus glial using quantitative reverse transcription-polymerase chain reaction (qRT-PCR), Western blot, immunohistochemistry, and radioligand binding. Moreover, we explored the expression of mineralocorticoid receptors protecting enzyme 11-betahydroxysteroid dehydrogenase type 2 as well as the nociceptive behavioral changes after glucocorticoid and mineralocorticoid receptors agonist or antagonist application.

Results

Hind paw inflammation resulted in significant upregulation of glucocorticoid receptors in nociceptive neurons of spinal cord (60%) and dorsal root ganglia (15%) as well as mineralocorticoid receptors, while corticosteroid plasma concentrations remained unchanged. Mineralocorticoid (83 ± 16 fmol/mg) but not glucocorticoid (104 ± 20 fmol/mg) membrane binding sites increased twofold in dorsal root ganglia concomitant with upregulated 11-betahydroxysteroid dehydrogenase type 2 (43%). Glucocorticoid and mineralocorticoid receptor expression in spinal microglia and astrocytes was small. Importantly, glucocorticoid receptor agonist dexamethasone or mineralocorticoid receptor antagonist canrenoate-K rapidly and dose-dependently attenuated nociceptive behavior. Isobolographic analysis of the combination of both drugs showed subadditive but not synergistic or additive effects.

Conclusions

The enhanced mechanical sensitivity of inflamed hind paws accompanied with corticosteroid receptor upregulation in spinal and peripheral sensory neurons was attenuated immediately after glucocorticoid receptor agonist and mineralocorticoid receptor antagonist administration, suggesting acute nongenomic effects consistent with detected membrane-bound corticosteroid receptors.

Endogenous Opiates and Behavior: 2016

This paper is the thirty-ninth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2016 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

RAGE-dependent potentiation of TRPV1 currents in sensory neurons exposed to high glucose

Diabetes mellitus is associated with sensory abnormalities, including exacerbated responses to painful (hyperalgesia) or non-painful (allodynia) stimuli. These abnormalities are symptoms of diabetic peripheral neuropathy (DPN), which is the most common complication that affects approximately 50% of diabetic patients. Yet, the underlying mechanisms linking hyperglycemia and symptoms of DPN remain poorly understood. The transient receptor potential vanilloid 1 (TRPV1) channel plays a central role in such sensory abnormalities and shows elevated expression levels in animal models of diabetes. Here, we investigated the function of TRPV1 channels in sensory neurons cultured from the dorsal root ganglion (DRG) of neonatal mice, under control (5mM) and high glucose (25mM) conditions. After maintaining DRG neurons in high glucose for 1 week, we observed a significant increase in capsaicin (CAP)-evoked currents and CAP-evoked depolarizations, independent of TRPV1 channel expression. These functional changes were largely dependent on the expression of the receptor for Advanced Glycation End-products (RAGE), calcium influx, cytoplasmic ROS accumulation, PKC, and Src kinase activity. Like cultured neurons from neonates, mature neurons from adult mice also displayed a similar potentiation of CAP-evoked currents in the high glucose condition. Taken together, our data demonstrate that under the diabetic condition, DRG neurons are directly affected by elevated levels of glucose, independent of vascular or glial signals, and dependent on RAGE expression. These early cellular and molecular changes to sensory neurons in vitro are potential mechanisms that might contribute to sensory abnormalities that can occur in the very early stages of diabetes.

Accessibility of axonal G protein coupled mu-opioid receptors requires conceptual changes of axonal membrane targeting for pain modulation

The mechanisms of axonal trafficking and membrane targeting are well established for sodium channels, which are the principle targets for perineurally applied local anaesthetics. However, they have not been thoroughly investigated for G protein coupled receptors such as mu-opioid receptors (MOR). Focusing on these axonal mechanisms, we found that axonal MOR functionality is quite distinct in two different pain states, i.e. hindpaw inflammation and nerve injury. We observed axonal membrane MOR binding and functional G protein coupling exclusively at sites of CCI nerve injury. Moreover at these axonal membrane sites, MOR exhibited extensive co-localization with the membrane proteins SNAP and Na/K-ATPase as well as NGF-dependent enhanced lipid rafts and L1CAM anchoring proteins. Silencing endogenous L1CAM with intrathecal L1CAM specific siRNA, disrupting lipid rafts with the perineurial cholesterol-sequestering agent MβCD, as well as suppressing NGF receptor activation with the perineurial NGF receptor inhibitor K252a abrogated MOR axonal membrane integration, functional coupling, and agonist-elicited antinociception at sites of nerve injury. These findings suggest that local conceptual changes resulting from nerve injury are required for the establishment of functional axonal membrane MOR. Axonal integration and subsequent accessibility of functionally coupled MOR are of great relevance particularly for patients suffering from severe pain due to nerve injury or tumour infiltration.

Pathological alterations in liver injury following congestive heart failure induced by volume overload in rats

Heart failure has emerged as a disease with significant public health implications. Following progression of heart failure, heart and liver dysfunction are frequently combined in hospitalized patients leading to increased morbidity and mortality. Here, we investigated the underlying pathological alterations in liver injury following heart failure. Heart failure was induced using a modified infrarenal aortocaval fistula (ACF) in male Wistar rats. Sham operated and ACF rats were compared for their morphometric and hemodynamic data, for histopathological and ultrastructural changes in the liver as well as differences in the expression of apoptotic factors. ACF-induced heart failure is associated with light microscopic signs of apparent congestion of blood vessels, increased apoptosis and breakdown of hepatocytes and inflammatory cell inifltration were observed. The glycogen content depletion associated with the increased hepatic fibrosis, lipid globule formation was observed in ACF rats. Moreover, cytoplasmic organelles are no longer distinguishable in many ACF hepatocytes with degenerated fragmented rough endoplasmic reticulum, shrunken mitochondria and heavy cytoplasm vacuolization. ACF is associated with the upregulation of the hepatic TUNEL-positive cells and proapoptotic factor Bax protein concomitant with the mitochondrial leakage of cytochrome C into the cell cytoplasm and the transfer of activated caspase 3 from the cytoplasm into the nucleus indicating intrinsic apoptotic events. Taken together, the results demonstrate that ACF-induced congestive heart failure causes liver injury which results in hepatocellular apoptotic cell death mediated by the intrinsic pathway of mitochondrial cytochrome C leakage and subsequent transfer of activated caspase 3 into to the nucleus to initiate overt DNA fragmentation and cell death.

Histopathological Changes in the Kidney following Congestive Heart Failure by Volume Overload in Rats

BACKGROUND

This study investigated histopathological changes and apoptotic factors that may be involved in the renal damage caused by congestive heart failure in a rat model of infrarenal aortocaval fistula (ACF).

METHODS

Heart failure was induced using a modified approach of ACF in male Wistar rats. Sham-operated controls and ACF rats were characterized by their morphometric and hemodynamic parameters and investigated for their histopathological, ultrastructural, and apoptotic factor changes in the kidney.

RESULTS

ACF-induced heart failure is associated with histopathological signs of congestion and glomerular and tubular atrophy, as well as nuclear and cellular degeneration in the kidney. In parallel, overexpression of proapoptotic Bax protein, release of cytochrome C from the outer mitochondrial membrane into cell cytoplasm, and nuclear transfer of activated caspase 3 indicate apoptotic events. This was confirmed by electron microscopic findings of apoptotic signs in the kidney such as swollen mitochondria and degenerated nuclei in renal tubular cells.

CONCLUSIONS

This study provides morphological evidence of renal injury during heart failure which may be due to caspase-mediated apoptosis via overexpression of proapoptotic Bax protein, subsequent mitochondrial cytochrome C release, and final nuclear transfer of activated caspase 3, supporting the notion of a cardiorenal syndrome.

Acute mechanical sensitization of peripheral nociceptors by aldosterone through non-genomic activation of membrane bound mineralocorticoid receptors in naive rats

Recently, there is increasing interest in the role of peripheral mineralocorticoid receptors (MR) to modulate pain, but their localization in neurons and glia of the periphery and their distinct involvement in pain control remains elusive. In naive Wistar rats our double immunofluorescence confocal microscopy of the spinal cord, dorsal root ganglia, sciatic nerve and innervated skin revealed that MR predominantly colocalized with calcitonin-gene-related peptide (CGRP)- and trkA-immunoreactive (IR) nociceptive neurons and only marginally with myelinated trkB-IR mechanoreceptive and trkC-IR proprioreceptive neurons underscoring a pivotal role for MR in the modulation of pain. MR could not be detected in Schwann cells, satellite cells, and astrocytes and only scarcely in spinal microglia cells excluding a relevant functional role of glia-derived MR at least in naïve rats. Intrathecal (i.t.) and intraplantar (i.pl.) application of increasing doses of the MR selective agonist aldosterone acutely increased nociceptive behavior which was reversible by a MR selective antagonist and most likely due to non-genomic effects. This was further substantiated by the first identification of membrane bound MR specific binding sites in sensory neurons of dorsal root ganglia and spinal cord. Therefore, a crucial role of MR on nociceptive neurons but not on glia cells and their impact on nociceptive behavior most likely due to immediate non-genomic effects has to be considered under normal but more so under pathological conditions in future studies.