Reduced sympathetic activity is associated with the development of pain and muscle atrophy in a female rat model of fibromyalgia

Fibromyalgia (FM) is characterized by chronic widespread musculoskeletal pain accompanied by fatigue and muscle atrophy. Although its etiology is not known, studies have shown that FM patients exhibit altered function of the sympathetic nervous system (SNS), which regulates nociception and muscle plasticity. Nevertheless, the precise SNS-mediated mechanisms governing hyperalgesia and skeletal muscle atrophy in FM remain unclear. Thus, we employed two distinct FM-like pain models, involving intramuscular injections of acidic saline (pH 4.0) or carrageenan in prepubertal female rats, and evaluated the catecholamine content, adrenergic signaling and overall muscle proteolysis. Subsequently, we assessed the contribution of the SNS to the development of hyperalgesia and muscle atrophy in acidic saline-injected rats treated with clenbuterol (a selective β2-adrenergic receptor agonist) and in animals maintained under baseline conditions and subjected to epinephrine depletion through adrenodemedullation (ADM). Seven days after inducing an FM-like model with acidic saline or carrageenan, we observed widespread mechanical hyperalgesia along with loss of strength and/or muscle mass. These changes were associated with reduced catecholamine content, suggesting a common underlying mechanism. Notably, treatment with a β2-agonist alleviated hyperalgesia and prevented muscle atrophy in acidic saline-induced FM-like pain, while epinephrine depletion induced mechanical hyperalgesia and increased muscle proteolysis in animals under baseline conditions. Together, the results suggest that reduced sympathetic activity is involved in the development of pain and muscle atrophy in the murine model of FM analyzed.

Adrenalectomy attenuates hyperalgesia but does not regulate muscle wasting in a female rat model of fibromyalgia

Although it is well established that fibromyalgia (FM) syndrome is characterized by chronic diffuse musculoskeletal hyperalgesia, very little is known about the effect of this pathology on muscle tissue plasticity. Therefore, the present study aimed to characterize the putative alterations in skeletal muscle mass in female rats subjected to a FM model by inducing chronic diffuse hyperalgesia (CDH) through double injections of acidic saline (pH 4.0) into the left gastrocnemius muscle at 5-day intervals. To determine protein turnover, the total proteolysis, proteolytic system activities and protein synthesis were evaluated in oxidative soleus muscles of pH 7.2 (control) and pH 4.0 groups at 7 days after CDH induction. All animals underwent behavioural analyses of mechanical hyperalgesia, strength and motor performance. Our results demonstrated that, in addition to hyperalgesia, rats injected with acidic saline exhibited skeletal muscle loss, as evidenced by a decrease in the soleus fibre cross-sectional area. This muscle loss was associated with increased proteasomal proteolysis and expression of the atrophy-related gene (muscle RING-finger protein-1), as well as reduced protein synthesis and decreased protein kinase B/S6 pathway activity. Although the plasma corticosterone concentration did not differ between the control and pH 4.0 groups, the removal of the adrenal glands attenuated hyperalgesia, but it did not prevent the increase in muscle protein loss in acidic saline-injected animals. The data suggests that the stress-related hypothalamic-pituitary-adrenal axis is involved in the development of hyperalgesia, but is not responsible for muscle atrophy observed in the FM model induced by intramuscular administration of acidic saline. Although the mechanisms involved in the attenuation of hyperalgesia in rats injected with acidic saline and subjected to adrenalectomy still need to be elucidated, the results found in this study suggest that glucocorticoids may not represent an effective therapeutic approach to alleviate FM symptoms.

Perinatal environmental enrichment changes anxiety-like behaviours in mice and produces similar intergenerational benefits in offspring

Environmental enrichment implemented in early life is able to induce long-term changes in gene expression, synaptic function and behavioural responses. In this study, we evaluated the adult behavioural effects of perinatal environment enrichment in male and female mice (PEE), as well as the males and females of PEE male offspring (OPEE). For this purpose, animals were submitted to the following battery of behavioural analyses: elevated plus maze, open field test, light-dark box and novelty suppression feeding test. The frontal cortex and ventral hippocampus of PEE mice were collected for the evaluation of the expression of gamma-aminobutyric acid (GABA)-related genes. The PEE animals showed an increase in exploratory activity, associated with a reduction in anxiety-like behaviours on the elevated plus maze; this effect was mainly observed in males. Additionally, the male OPEE showed a reduction in anxiety-like behaviours on the elevated plus maze, mainly observed in a reduction of risk assessment-related behaviours. The PEE male mice also showed reduced expression of Gabra3 in the ventral hippocampus when compared to the control group. These results demonstrate that perinatal environmental enrichment promotes a reduction in anxiety-like behaviour that can be transferred intergenerationally.

Fasting increases circulating angiotensin levels and brain Agtr1a expression in male rats

In addition to being recognised for involvement in cardiovascular control and hydromineral balance, the renin-angiotensin system (RAS) has also been associated with the neuroendocrine control of energy balance. One of the main brain sites for angiotensin II (ANG II)/type 1 receptor (AT1 R) signalling is the subfornical organ (SFO), a circumventricular organ related to the control of autonomic functions, motivated behaviours and energy metabolism. Thus, we hypothesised that circulating ANG II may act on the SFO AT1 R receptors to integrate metabolic and hydromineral balance. We evaluated whether food deprivation can modulate systemic RAS activity and Agrt1a brain expression, and if ANG II/AT1 R signalling influences the hypothalamic expression of mRNAs encoding neuropeptides and food and water ingestion in fed and fasted Wistar rats. We found a significant increase in both ANG I and ANG II plasma levels after 24 and 48 h of fasting. Expression of Agrt1a mRNA in the SFO and paraventricular nucleus (PVN) also increased after food deprivation for 48 h. Treatment of fasted rats with low doses of losartan in drinking water attenuated the decrease in glycemia and meal-associated water intake without changing the expression in PVN or arcuate nucleus of mRNAs encoding selected neuropeptides related to energy homeostasis control. These findings point to a possible role of peripheral ANG II/SFO-AT1 R signalling in the control of refeeding-induced thirst. On the other hand, intracerebroventricular losartan treatment decreased food and water intake over dark time in fed but not in fasted rats.

Spatial transcriptomics reveal basal sex differences in supraoptic nucleus gene expression of adult rats related to cell signaling and ribosomal pathways

BACKGROUND

The supraoptic nucleus (SON) of the hypothalamus contains magnocellular neurosecretory cells that secrete the hormones vasopressin and oxytocin. Sex differences in SON gene expression have been relatively unexplored. Our study used spatially resolved transcriptomics to visualize gene expression profiles in the SON of adult male (n = 4) and female (n = 4) Sprague-Dawley rats using Visium Spatial Gene Expression (10x Genomics).

METHODS

Briefly, 10-μm coronal sections (~ 4 × 4 mm) containing the SON were collected from each rat and processed using Visium slides and recommended protocols. Data were analyzed using 10x Genomics' Space Ranger and Loupe Browser applications and other bioinformatic tools. Two unique differential expression (DE) analysis methods, Loupe Browser and DESeq2, were used.

RESULTS

Loupe Browser DE analysis of the SON identified 116 significant differentially expressed genes (DEGs) common to both sexes (e.g., Avp and Oxt), 31 significant DEGs unique to the males, and 73 significant DEGs unique to the females. DESeq2 analysis revealed 183 significant DEGs between the two groups. Gene Ontology (GO) enrichment and pathway analyses using significant genes identified via Loupe Browser revealed GO terms and pathways related to (1) neurohypophyseal hormone activity, regulation of peptide hormone secretion, and regulation of ion transport for the significant genes common to both males and females, (2) Gi signaling/G-protein mediated events for the significant genes unique to males, and (3) potassium ion transport/voltage-gated potassium channels for the significant genes unique to females, as some examples. GO/pathway analyses using significant genes identified via DESeq2 comparing female vs. male groups revealed GO terms/pathways related to ribosomal structure/function. Ingenuity Pathway Analysis (IPA) identified additional sex differences in canonical pathways (e.g., 'Mitochondrial Dysfunction', 'Oxidative Phosphorylation') and upstream regulators (e.g., CSF3, NFKB complex, TNF, GRIN3A).

CONCLUSION

There was little overlap in the IPA results for the two different DE methods. These results suggest sex differences in SON gene expression that are associated with cell signaling and ribosomal pathways.

Ageing restructures the transcriptome of the hypothalamic supraoptic nucleus and alters the response to dehydration

Ageing is associated with altered neuroendocrine function. In the context of the hypothalamic supraoptic nucleus, which makes the antidiuretic hormone vasopressin, ageing alters acute responses to hyperosmotic cues, rendering the elderly more susceptible to dehydration. Chronically, vasopressin has been associated with numerous diseases of old age, including type 2 diabetes and metabolic syndrome. Bulk RNAseq transcriptome analysis has been used to catalogue the polyadenylated supraoptic nucleus transcriptomes of adult (3 months) and aged (18 months) rats in basal euhydrated and stimulated dehydrated conditions. Gene ontology and Weighted Correlation Network Analysis revealed that ageing is associated with alterations in the expression of extracellular matrix genes. Interestingly, whilst the transcriptomic response to dehydration is overall blunted in aged animals compared to adults, there is a specific enrichment of differentially expressed genes related to neurodegenerative processes in the aged cohort, suggesting that dehydration itself may provoke degenerative consequences in aged rats.

Arcuate AgRP, but not POMC neurons, modulate paraventricular CRF synthesis and release in response to fasting

BACKGROUND

The activation of the hypothalamic-pituitary-adrenal (HPA) axis is essential for metabolic adaptation in response to fasting. However, the neurocircuitry connecting changes in the peripheral energy stores to the activity of hypothalamic paraventricular corticotrophin-releasing factor (CRF^PVN) neurons, the master controller of the HPA axis activity, is not completely understood. Our main goal was to determine if hypothalamic arcuate nucleus (ARC) POMC and AgRP neurons can communicate fasting-induced changes in peripheral energy stores, associated to a fall in plasma leptin levels, to CRF^PVN neurons to modulate the HPA axis activity in mice.

RESULTS

We observed increased plasma corticosterone levels associate with increased CRF^PVN mRNA expression and increased CRF^PVN neuronal activity in 36 h fasted mice. These responses were associated with a fall in plasma leptin levels and changes in the mRNA expression of Agrp and Pomc in the ARC. Fasting-induced decrease in plasma leptin partially modulated these responses through a change in the activity of ARC neurons. The chemogenetic activation of POMC^ARC by DREADDs did not affect fasting-induced activation of the HPA axis. DREADDs inhibition of AgRP^ARC neurons reduced the content of CRF^PVN and increased its accumulation in the median eminence but had no effect on corticosterone secretion induced by fasting.

CONCLUSION

Our data indicate that AgRP^ARC neurons are part of the neurocircuitry involved in the coupling of PVN^CRF activity to changes in peripheral energy stores induced by prolonged fasting.

Osmoregulation and the Hypothalamic Supraoptic Nucleus: From Genes to Functions

Due to the relatively high permeability to water of the plasma membrane, water tends to equilibrate its chemical potential gradient between the intra and extracellular compartments. Because of this, changes in osmolality of the extracellular fluid are accompanied by changes in the cell volume. Therefore, osmoregulatory mechanisms have evolved to keep the tonicity of the extracellular compartment within strict limits. This review focuses on the following aspects of osmoregulation: 1) the general problems in adjusting the "milieu interieur" to challenges imposed by water imbalance, with emphasis on conceptual aspects of osmosis and cell volume regulation; 2) osmosensation and the hypothalamic supraoptic nucleus (SON), starting with analysis of the electrophysiological responses of the magnocellular neurosecretory cells (MNCs) involved in the osmoreception phenomenon; 3) transcriptomic plasticity of SON during sustained hyperosmolality, to pinpoint the genes coding membrane channels and transporters already shown to participate in the osmosensation and new candidates that may have their role further investigated in this process, with emphasis on those expressed in the MNCs, discussing the relationships of hydration state, gene expression, and MNCs electrical activity; and 4) somatodendritic release of neuropeptides in relation to osmoregulation. Finally, we expect that by stressing the relationship between gene expression and the electrical activity of MNCs, studies about the newly discovered plastic-regulated genes that code channels and transporters in the SON may emerge.

Osmoregulation of the transcriptome of the hypothalamic supraoptic nucleus: A resource for the community

The hypothalamic supraoptic nucleus (SON) is a core osmoregulatory control centre that deciphers information about the metabolic state of the organism and orchestrates appropriate homeostatic (endocrine) and allostatic (behavioural) responses. We have used RNA sequencing to describe the polyadenylated transcriptome of the SON of the male Wistar Han rat. These data have been mined to generate comprehensive catalogues of functional classes of genes (enzymes, transcription factors, endogenous peptides, G protein coupled receptors, transporters, catalytic receptors, channels and other pharmacological targets) expressed in this nucleus in the euhydrated state, and that together form the basal substrate for its physiological interactions. We have gone on to show that fluid deprivation for 3 days (dehydration) results in changes in the expression levels of 2247 RNA transcripts, which have similarly been functionally catalogued, and further mined to describe enriched gene categories and putative regulatory networks (Regulons) that may have physiological importance in SON function related plasticity. We hope that the revelation of these genes, pathways and networks, most of which have no characterised roles in the SON, will encourage the neuroendocrine community to pursue new investigations into the new 'known-unknowns' reported in the present study.

Brain osmo-sodium sensitive channels and the onset of sodium appetite

The aim of the present study was to determine whether the TRPV1 channel is involved in the onset of sodium appetite. For this purpose, we used TRPV1-knockout mice to investigate sodium depletion-induced drinking at different times (2/24 h) after furosemide administration combined with a low sodium diet (FURO-LSD). In sodium depleted wild type and TRPV1 KO (SD-WT/SD-TPRV1-KO) mice, we also evaluated the participation of other sodium sensors, such as TPRV4, Na_X and angiotensin AT1-receptors (by RT-PCR), as well as investigating the pattern of neural activation shown by Fos immunoreactivity, in different nuclei involved in hydromineral regulation. TPRV1 SD-KO mice revealed an increased sodium preference, ingesting a higher hypertonic cocktail in comparison with SD-WT mice. Our results also showed in SD-WT animals that SFO-Trpv4 expression increased 2 h after FURO-LSD, compared to other groups, thus supporting a role of SFO-Trpv4 channels during the hyponatremic state. However, the SD-TPRV1-KO animals did not show this early increase, and maybe as a consequence drank more hypertonic cocktail. Regarding the SFO-Na_X channel expression, in both genotypes our findings revealed a reduction 24 h after FURO-LSD. In addition, there was an increase in the OVLT-Na_X expression of SD-WT 24 h after FURO-LSD, suggesting the participation of OVLT-Na_X channels in the appearance of sodium appetite, possibly as an anticipatory response in order to limit sodium intake and to induce thirst. Our work demonstrates changes in the expression of different osmo‑sodium-sensitive channels at specific nuclei, related to the body sodium status in order to stimulate an adequate drinking.

Acute body sodium depletion induces skin sodium mobilization in female Wistar rats

NEW FINDINGS

What is the central question of this study? Can Na⁺ depletion mobilize Na⁺ from the skin reservoir in ovariectomized rats? Does oestrogen replacement change the amount and the dynamics of skin Na⁺ storage? Is the reduced salt appetite after Na⁺ depletion in ovariectomized rats with oestrogen replacement related to changes in the skin Na⁺ ? What is the main finding and its importance? This work demonstrated that acute body Na⁺ depletion induced by frusemide mobilized the osmotically inactive skin Na⁺ reservoir to become osmotically active. Oestrogen treatment decreased the induced Na⁺ intake in ovariectomized rats but did not modulate the inactive Na⁺ reservoir in control conditions or its mobilization induced by Na⁺ depletion.

ABSTRACT

Oestradiol, which is an important hormone for water and electrolyte balance, also has a role in the inhibition of induced Na⁺ appetite. Sodium can be stored in the skin in osmotically active or inactive forms, and this skin Na⁺ reservoir may be involved in the control of body Na⁺ levels during physiopathological challenges. In this study, we investigated whether the effect of sodium depletion by frusemide can mobilize Na⁺ from the skin reservoir and whether oestradiol replacement changes or mobilizes the Na⁺ reserves in the skin. Ovariectomized Wistar rats were treated with vehicle or oestradiol for 7 days to evaluate the effects of oestrogen on the hydroelectrolyte balance, intake responses and skin Na⁺ and water content in basal conditions. Furthermore, the effects of oestrogen were evaluated after 24 h frusemide-induced whole-body Na⁺ depletion. Oestradiol-replaced rats exhibited reduced water intake without any significant changes in salt intake, Na⁺ excretion or water and Na⁺ skin content in basal conditions. After sodium depletion, both vehicle- and oestradiol-treated rats exhibited an increase in the osmotically active skin Na⁺ , which was associated with a decrease of the inactive skin Na⁺ reservoir. Oestrogen decreased the hypertonic saline intake induced by Na⁺ depletion, but it was not associated with any significant changes in the skin Na⁺ reservoir. Thus, sodium depletion is able to change the inactive-active skin Na⁺ reservoir balance. However, the oestrogenic modulation of sodium appetite after Na⁺ depletion is probably not related to the action of this hormone in the skin Na⁺ reservoir balance.

Estradiol replacement therapy regulates innate immune response in ovariectomized arthritic mice

Neuroendocrine changes are essential factors contributing to the progression and development of rheumatoid arthritis. However, the role of estrogen in the innate immunity during arthritis development is still controversial. Here, we evaluated the effect of estrous cycle, ovariectomy, estradiol replacement therapy and treatment with estrogen receptor (ER)α and ERβ specific agonists on joint edema formation, neutrophil recruitment, and articular levels of cytokines/chemokines in murine zymosan-induced arthritis. Our results showed that articular inflammation of proestus/estrus was similar to metaestus/diestrus animals indicating that the inflammatory response in acute arthritis is not affected by the estrous cycle. However, ovariectomy increased joint swelling, neutrophil migration, and TNF-α level. Treatment for six consecutive days with estradiol cypionate re-established the acute inflammation in ovariectomized arthritic mice to responses similar to those in SHAM-proestrus/estrus or naive mice. Moreover, treatment with propylpyrazoletriol and diarylpropionitrile, two ERα and ERβ selective agonists, respectively, inhibited both edema and neutrophil recruitment. Finally, the non-genomic properties of estradiol were analyzed with an acute treatment with β-estradiol-water soluble, which reduced the edema only. In the present study, estradiol replacement therapy improves the innate immune responses in ovariectomized arthritic mice by activating nuclear estrogen receptors. These results suggest that estradiol can induce a protective anti-inflammatory effect in arthritis during ovaries failure, as observed in the menopause.

Oestradiol acts through its beta receptor to increase vasopressin neuronal activation and secretion induced by dehydration

Vasopressinergic neurones of the supraoptic (SON) and paraventricular (PVN) nuclei express oestrogen receptor (ER)β and receive afferent projections from osmosensitive neurones that express ERα. However, which subtype of these receptors mediates the effects of oestradiol on vasopressin (AVP) secretion induced by hydromineral challenge has not yet been demonstrated in vivo. Moreover, AVP secretion induced by hyperosmolality is known to involve activation of TRPV1 (transient receptor potential vanilloid, member 1) in magnocellular neurones, although whether oestradiol modulates expression of this receptor is unknown. Thus, the present study aimed to clarify the mechanisms involved in the modulation exerted by oestradiol on AVP secretion, specifically investigating the involvement of ERβ, ERα and TRPV1 receptors in response to water deprivation (WD). We observed that treatment with an ERβ agonist potentiated AVP secretion and vasopressinergic neuronal activation induced by WD. This increase in AVP secretion induced by WD was reversed by an ERβ antagonist. By contrast to ERβ, the ERα agonist did not alter plasma AVP concentrations or activation of AVP neurones in the SON and PVN. Additionally, Fos expression in the subfornical organ was not altered by the ERα agonist. TRPV1 mRNA expression was increased by WD in the SON, although this response was not altered by any treatment. The results of the present study suggest that ERβ mediates the effects of oestradiol on AVP secretion in response to WD, indicating that the effects of oestradiol occur directly in AVP neurones without affecting TRPV1.

Whole body sodium depletion modifies AT1 mRNA expression and serotonin content in the dorsal raphe nucleus

Angiotensin II (Ang II) acts on Ang II type 1 (AT1) receptors located in the organum vasculosum and subfornical organ (SFO) of the lamina terminalis as a main facilitatory mechanism of sodium appetite. The brain serotonin (5-HT) system with soma located in the dorsal raphe nucleus (DRN) provides a main inhibitory mechanism. In the present study, we first investigated the existence of Ang II AT1 receptors in serotonergic DRN neurones. Then, we examined whether whole body sodium depletion affects the gene expression of the AT1a receptor subtype and the presumed functional significance of AT1 receptors. Using confocal microscopy, we found that tryptophan hydroxylase-2 and serotonin neurones express AT1 receptors in the DRN. Immunofluorescence quantification showed a significant reduction in 5-HT content but no change in AT1 receptor expression or AT1/5-HT colocalisation in the DRN after sodium depletion. Whole body sodium depletion also significantly increased Agtr1a mRNA expression in the SFO and DRN. Oral treatment with the AT1 receptor antagonist losartan reversed the changes in Agtr1a expression in the SFO but not the DRN. Losartan injection into either the DRN or the mesencephalic aqueduct had no influence on sodium depletion-induced 0.3 mol L^-1 NaCl intake. The results indicate the expression of Agtr1a mRNA in the DRN and SFO as a marker of sodium depletion. They also suggest that serotonergic DRN neurones are targets for Ang II. However, the function of their AT1 receptors remains elusive.

Alterations in hypothalamic synaptophysin and death markers may be associated with vasopressin impairment in sepsis survivor rats

The impairment in arginine vasopressin (AVP) secretion during sepsis is described in clinical and experimental studies and has been associated with oxidative stress, apoptosis, and diminished activation of hypothalamic neurons. Few studies have, however, assessed these abnormalities in sepsis survivors. Here we performed two sets of experiments on Wistar rats that had been subjected to sepsis by cecal ligation and puncture (CLP) or nonmanipulated (naive) as control. In the first set, tissues and blood were collected from survivor rats 10 days after CLP to quantify hypothalamic Bcl-2, cleaved caspase- 3 and synaptophysin content, and bacterial load. In the second set, survivor rats were submitted to an acute osmotic stimulus (hypertonic saline), and after 30 minutes the water intake and AVP secretion were analyzed. The sepsis-surviving rats did not show bacterial load in tissues, but their hypothalamic synaptophysin and Bcl-2 levels were decreased, and the cleaved caspase- 3 level was increased when compared with the control group. However, AVP secretion was significantly attenuated in the CLP survivor animals submitted to an acute osmotic stimulus. These results suggest that the persistent AVP impairment in sepsis survivor animals may be due to a hypothalamic dysfunction associated with a synaptic deficit and decreased anti-apoptotic protein expression. This article is protected by copyright. All rights reserved.

Central angiotensin-(1-7) increases osmotic thirst

NEW FINDINGS

What is the central question of this study? The central goal of this study was to understand the effects of central angiotensin-(1-7) on basal and osmotically stimulated water intake in rats. What is the main finding and its importance? This study demonstrated that central administration of angiotensin-(1-7) did not induce thirst in basal conditions but increased water intake after osmotic stimulation, such as water deprivation and salt loading. These results indicate a new function for this peptide, which, in turn, allows for future research on the mechanisms through which angiotensin-(1-7) influences osmotic thirst. Angiotensin-(1-7) [Ang-(1-7)] is generated by type 2 angiotensin-converting enzyme (ACE2) and binds to the MAS receptor. Although it is well known that Ang-(1-7) functionally antagonizes the effects of the classical renin-angiotensin system in several situations, the role of Ang-(1-7) in hydromineral homeostasis is not clear. The aim of this study was to assess the role of Ang-(1-7) on neuroendocrine responses to hyperosmolality in rats. Male Wistar rats were divided into the following three groups: control; 24 h of water deprivation (WD); and 24 h of salt loading (SL; 1.8% NaCl). Intracerebroventricular (i.c.v.) injections of Ang-(1-7) or vehicle were given to assess water intake and plasma concentration of vasopressin. Additionally, the brains from control and WD groups were collected to evaluate gene expression in the subfornical organ (SFO), paraventricular nucleus (PVN) and supraoptic nucleus (SON). It was found that i.c.v. Ang-(1-7) did not change water and salt intake in control rats; however, Ang-(1-7) increased water intake after WD and SL, with no change in salt intake. Plasma vasopressin was not changed by i.c.v. Ang-(1-7) in control or WD rats. Moreover, WD increased Mas gene expression in the SON and PVN, with no changes in Ace2 mRNA levels. In conclusion, Ang-(1-7) increases thirst after osmotic stimuli, indicating that a previous sensitization to its action is necessary. This finding is consistent with the increased Mas gene expression in the PVN and SON after water deprivation.

Sodium appetite elicited by low-sodium diet is dependent on p44/42 mitogen-activated protein kinase (extracellular signal-regulated kinase 1/2) activation in the brain

Sodium appetite is regulated by several signalling molecules, among which angiotensin II (Ang II) serves as a key driver of robust salt intake by binding to Ang II type 1 receptors (AT1R) in several regions in the brain. The activation of these receptors recruits the mitogen-activated protein kinase (MAPK) pathway, which has previously been linked to Ang II-induced increases in sodium appetite. Thus, we addressed the involvement of MAPK signalling in the induction of sodium appetite after 4 days of low-sodium diet consumption. An increase in extracellular signal-regulated kinase (ERK) phosphorylation in the laminae terminalis and mediobasal hypothalamus was observed after low-sodium diet consumption. This response was reduced by i.c.v. microinjection of an AT1R antagonist into the laminae terminalis but not the hypothalamus. This result indicates that low-sodium diet consumption activates the MAPK pathway via Ang II/AT1R signalling on the laminae terminalis. On the other hand, activation of the MAPK pathway in the mediobasal hypothalamus after low-sodium diet consumption appears to involve another extracellular mediator. We also evaluated whether a low-sodium diet could increase the sensitivity for Ang II in the brain and activate the MAPK pathway. However, i.c.v. injection of Ang II increased ERK phosphorylation on the laminae terminalis and mediobasal hypothalamus; this increase achieved a response magnitude similar to those observed in both the normal and low-sodium diet groups. These data indicate that low-sodium diet consumption for 4 days is insufficient to change the ERK phosphorylation response to Ang II in the brain. To investigate whether the MAPK pathway is involved in sodium appetite after low-sodium diet consumption, we performed i.c.v. microinjections of a MAPK pathway inhibitor (PD98059). PD98059 inhibited both saline and water intake after low-sodium diet consumption. Thus, the MAPK pathway is involved in promoting the sodium appetite after low-sodium diet consumption.

Reduced collagen accumulation and augmented MMP-2 activity in left ventricle of old rats submitted to high-intensity resistance training

Progressive fibrosis is a hallmark of the aging heart. Age-related fibrosis is modulated by endurance exercise training; however, little is known concerning the influence of resistance training (RT). Therefore we investigated the chronic effects of high-intensity RT on age-associated alterations of left ventricle (LV) structure, collagen content, matrix metalloproteinase-2 (MMP-2), and extracellular matrix-related gene expression, including transforming growth factor-β (TGF-β). Young adult (3 mo) and aged (21 mo) male Wistar rats were submitted to a RT protocol (ladder climbing with 65, 85, 95, and 100% load), three times a week for 12 wk. Forty-eight hours posttraining, arterial systolic and diastolic pressure, LV end-diastolic pressure (LVEDP) and dP/dt were recorded. LV morphology, collagen deposition, and gene expression of type I (COL-I) and type III (COL-III) collagen, MMP-2, tissue inhibitor of metalloproteinases-1 (TIMP-1), and TGF-β1 were analyzed by quantitative reverse transcriptase-PCR. MMP-2 content was assessed by zymography. Increased collagen deposition was observed in LV from aged rats. These parameters were modulated by RT and were associated with increased MMP-2 activity and decreased COL-I, TGF-β1, and TIMP-1 mRNA content. Despite the effect of RT on collagen accumulation, there was no improvement on LVEDP and maximal negative LV dP/dt of aged rats. Cardiomyocyte diameter was preserved in all experimental conditions. In conclusion, RT attenuated age-associated collagen accumulation, concomitant to the increase in MMP-2 activity and decreased expression of COL-I, TGF-β1, and TIMP-1 in LV, illustrating a cardioprotective effect of RT on ventricular structure and function.NEW & NOTEWORTHY We demonstrated the beneficial resistance-training effect against age-related left ventricle collagen accumulation in the left ventricle, which was associated with decreased type I collagen (COL-I), transforming growth factor-β1 (TGF-β1), and tissue inhibitor of metalloproteinases-1 (TIMP-1) gene expression and matrix metalloproteinase-2 (MMP-2) activity. Our findings suggest for the first time the potential effects of resistance training in modulating collagen accumulation and possibly fibrosis in the aging heart.

Oestradiol effects on neuroendocrine responses induced by water deprivation in rats

Water deprivation (WD) induces changes in plasma volume and osmolality, which in turn activate several responses, including thirst, the activation of the renin-angiotensin system (RAS) and vasopressin (AVP) and oxytocin (OT) secretion. These systems seem to be influenced by oestradiol, as evidenced by the expression of its receptor in brain areas that control fluid balance. Thus, we investigated the effects of oestradiol treatment on behavioural and neuroendocrine changes of ovariectomized rats in response to WD. We observed that in response to WD, oestradiol treatment attenuated water intake, plasma osmolality and haematocrit but did not change urinary volume or osmolality. Moreover, oestradiol potentiated WD-induced AVP secretion, but did not alter the plasma OT or angiotensin II (Ang II) concentrations. Immunohistochemical data showed that oestradiol potentiated vasopressinergic neuronal activation in the lateral magnocellular PVN (PaLM) and supraoptic (SON) nuclei but did not induce further changes in Fos expression in the median preoptic nucleus (MnPO) or subfornical organ (SFO) or in oxytocinergic neuronal activation in the SON and PVN of WD rats. Regarding mRNA expression, oestradiol increased OT mRNA expression in the SON and PVN under basal conditions and after WD, but did not induce additional changes in the mRNA expression for AVP in the SON or PVN. It also did not affect the mRNA expression of RAS components in the PVN. In conclusion, our results show that oestradiol acts mainly on the vasopressinergic system in response to WD, potentiating vasopressinergic neuronal activation and AVP secretion without altering AVP mRNA expression.

Estradiol and angiotensin II crosstalk in hydromineral balance: Role of the ERK1/2 and JNK signaling pathways

The angiotensin II (ANGII) receptor AT1 plays an important role in the control of hydromineral balance, mediating the dipsogenic and natriorexigenic effects and neuroendocrine responses of ANGII. While estradiol (E2) is known to modulate several actions of ANGII in the brain, the molecular and cellular mechanisms of the interaction between E2 and ANGII and its physiological role in the control of body fluids remain unclear. We investigated the influence of E2 (40 μg/kg) pretreatment and extracellular-signal-regulated kinase (ERK1/2) and c-Jun N-terminal kinase (JNK) cell signaling on the dipsogenic and natriorexigenic effects, as well as the neuroendocrine responses to angiotensinergic central stimulation in ovariectomized rats (OVX). We showed that the inhibitory effect of E2 on ANGII-induced water and sodium intake requires the ERK1/2 and JNK signaling pathways. On the other hand, E2 pretreatment prevents the ANGII-induced phosphorylation of ERK and JNK in the lamina terminalis. E2 therapy decreased oxytocin (OT) and vasopressin (AVP) secretion and decreased ERK1/2 phosphorylation in the supraoptic and paraventricular nuclei (SON and PVN, respectively). We found that the AVP secretion induced by ANGII required ERK1/2 signaling, but OT secretion did not involve ERK1/2 signaling. Taken together, these results demonstrate that E2 modulates ANGII-induced water and sodium intake and AVP secretion by affecting the ERK1/2 and JNK pathways in the lamina terminalis and ERK1/2 signaling in the hypothalamic nuclei (PVN and SON) in OVX rats.

In vitro differentiation between oxytocin- and vasopressin-secreting magnocellular neurons requires more than one experimental criterion

The phenotypic differentiation between oxytocin (OT)- and vasopressin (VP)-secreting magnocellular neurosecretory cells (MNCs) from the supraoptic nucleus is relevant to understanding how several physiological and pharmacological challenges affect their electrical activity. Although the firing patterns of OT and VP neurons, both in vivo and in vitro, may appear different from each other, much is assumed about their characteristics. These assumptions make it practically impossible to obtain a confident phenotypic differentiation based exclusively on the firing patterns. The presence of a sustained outward rectifying potassium current (SOR) and/or an inward rectifying hyperpolarization-activated current (IR), which are presumably present in OT neurons and absent in VP neurons, has been used to distinguish between the two types of MNCs in the past. In this study, we aimed to analyze the accuracy of the phenotypic discrimination of MNCs based on the presence of rectifying currents using comparisons with the molecular phenotype of the cells, as determined by single-cell RT-qPCR and immunohistochemistry. Our results demonstrated that the phenotypes classified according to the electrophysiological protocol in brain slices do not match their molecular counterparts because vasopressinergic and intermediate neurons also exhibit both outward and inward rectifying currents. In addition, we also show that MNCs can change the relative proportion of each cell phenotype when the system is challenged by chronic hypertonicity (70% water restriction for 7 days). We conclude that for in vitro preparations, the combination of mRNA detection and immunohistochemistry seems to be preferable when trying to characterize a single MNC phenotype.

Sexual dimorphism in autonomic changes and in the renin-angiotensin system in the hearts of mice subjected to thyroid hormone-induced cardiac hypertrophy

Based on the relevance of the renin-angiotensin system and the ongoing controversy regarding the role of the sympathetic nervous system in thyroid hormone-induced cardiac hypertrophy, the aim of the present study was to establish whether the putative difference in the degree of cardiac hypertrophy exhibited by males and females might be related to differences in the sympathetic-vagal balance and/or in the cardiac renin-angiotensin system in mice of different genders. Male and female mice (n = 117) were given 0.1 mg kg(-1) of triiodothyronine or normal saline each day for 10 days consecutively. At the end of that period, study of the heart rate variability, spectral analysis and histopathological examination were performed to assess the sympathetic-vagal balance and the diameter of cardiomyocytes. The cardiac levels of angiotensin I and II were also measured. Treatment with triiodothyronine induced a greater degree of cardiac hypertrophy in male (~73%) than in female mice (~42%). This difference was attributed to greater modulation of the sympathetic nervous system and higher levels of angiotensin I and II in male than in female mice. Our data indicate that thyroid hormone-induced cardiac hypertrophy was more intense in male mice due to the synergic effect of the sympathetic nervous system and the cardiac renin-angiotensin system.

Mapping and signaling of neural pathways involved in the regulation of hydromineral homeostasis

Several forebrain and brainstem neurochemical circuitries interact with peripheral neural and humoral signals to collaboratively maintain both the volume and osmolality of extracellular fluids. Although much progress has been made over the past decades in the understanding of complex mechanisms underlying neuroendocrine control of hydromineral homeostasis, several issues still remain to be clarified. The use of techniques such as molecular biology, neuronal tracing, electrophysiology, immunohistochemistry, and microinfusions has significantly improved our ability to identify neuronal phenotypes and their signals, including those related to neuron-glia interactions. Accordingly, neurons have been shown to produce and release a large number of chemical mediators (neurotransmitters, neurohormones and neuromodulators) into the interstitial space, which include not only classic neurotransmitters, such as acetylcholine, amines (noradrenaline, serotonin) and amino acids (glutamate, GABA), but also gaseous (nitric oxide, carbon monoxide and hydrogen sulfide) and lipid-derived (endocannabinoids) mediators. This efferent response, initiated within the neuronal environment, recruits several peripheral effectors, such as hormones (glucocorticoids, angiotensin II, estrogen), which in turn modulate central nervous system responsiveness to systemic challenges. Therefore, in this review, we shall evaluate in an integrated manner the physiological control of body fluid homeostasis from the molecular aspects to the systemic and integrated responses.

The role of angiotensin II on sodium appetite after a low-sodium diet

The present study aimed to investigate the role of angiotensin II (Ang II) on sodium appetite in rats subjected to a normal or a low-sodium diet (1% or > 0.1% NaCl) for 4 days. During sodium restriction, a reduction in water intake, urinary volume and sodium excretion was observed. After a low-sodium diet, we observed decreased plasma protein concentrations and haematocrit associated with a slight reduction in arterial pressure, without any significant changes in heart rate, natraemia, corticotrophin-releasing hormone mRNA expression in the paraventricular nucleus and corticosterone levels. After providing hypertonic saline, there was an increase in saline intake followed by a small increase in water intake, resulting in an enhanced saline intake ratio and the recovery of arterial pressure. Sodium deprivation increased plasma but not brain Ang I and II concentrations. A low-sodium diet increased kidney renin and liver angiotensinogen mRNA levels but not lung angiotensin-converting enzyme mRNA expression. Moreover, Ang II type 1a receptor mRNA expression was increased in the subfornical organ and the dorsal raphe nucleus and decreased in the medial preoptic nuclei, without changes in the paraventricular nucleus and the nucleus of solitary tract after a low-sodium diet. Blockade of AT(1) receptors or brain Ang II synthesis led to a reduction in sodium intake after a low-sodium diet. Intracerebroventricular injection of Ang II led to a similar increase in sodium and water intake in the control and low-sodium diet groups. In conclusion, the results of the present study suggest that Ang II is involved in the increased sodium appetite after a low-sodium diet.

Oestradiol potentiates hormone secretion and neuronal activation in response to hypertonic extracellular volume expansion in ovariectomised rats

Secretion of vasopressin (VP), oxytocin (OT) and atrial natriuretic peptide (ANP) is an essential mechanism for the maintenance of hydromineral homeostasis. Secretion of these hormones is modulated by several circulating factors, including oestradiol. However, it remains unclear how oestradiol exerts this modulation. In the present study we investigated the participation of oestradiol in the secretion of VP, OT and ANP and in activation of vasopressinergic and oxytocinergic neurones of the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus in response to extracellular volume expansion (EVE). For this purpose, ovariectomised (OVX) rats treated for 7 days with vehicle (corn oil, 0.1 ml/rat, OVX+O group) or oestradiol (oestradiol cypionate, 10 μg/kg, OVX+E group) were subjected to either isotonic (0.15 m NaCl, 2 ml/100 g b.w., i.v.) or hypertonic (0.30 m NaCl, 2 ml/100 g b.w., i.v.) EVE. Blood samples were collected for plasma VP, OT and ANP determination. Another group of rats was subjected to cerebral perfusion, and brain sections were processed for c-Fos-VP and c-Fos-OT double-labelling immunohistochemistry. In OVX+O rats, we observed that both isotonic and hypertonic EVE increased plasma OT and ANP concentrations, although no changes were observed in VP secretion. Oestradiol replacement did not alter hormonal secretion in response to isotonic EVE, but it increased VP secretion and potentiated plasma OT and ANP concentrations in response to hypertonic EVE. Immunohistochemical data showed that, in the OVX+O group, hypertonic EVE increased the number of c-Fos-OT and c-Fos-VP double-labelled neurones in the PVN and SON. Oestradiol replacement did not alter neuronal activation in response to isotonic EVE, but it potentiated vasopressinergic and oxytocinergic neuronal activation in the medial magnocellular PVN (PaMM) and SON. Taken together, these results suggest that oestradiol increases the responsiveness of vasopressinergic and oxytocinergic magnocellular neurones in the PVN and SON in response to osmotic stimulation.

Noradrenergic stimulation within midbrain raphe increases electrolyte excretion in rats

The present study was carried out to assess the influence of noradrenergic stimulation of the midbrain dorsal (DRN) and median raphe nuclei (MRN) on urinary volume and electrolyte excretion in hydrated rats. Wistar rats were implanted with a guide cannula into the MRN or DRN and then submitted to two intragastric administrations of water in order to attain an increased diuresis. The following treatments were performed. (1) Intra-DRN microinjections of saline (0.2 microl), alpha(1)-adrenergic agonist phenylephrine (PHE, 0.49 and 4.9 nmol in 0.2 microl), alpha(2)-adrenergic antagonist idazoxan (IDZ, 0.42 and 4.2 nmol in 0.2 microl) or the alpha(1)-adrenergic antagonist prazosin (PRZ, 0.24 and 2.4 nmol in 0.2 microl). (2) Intra-MRN microinjections of saline, IDZ (4.2 nmol in 0.2 microl), PHE (4.9 nmol in 0.2 microl) or PRZ (2.4 nmol in 0.2 microl). Urine samples were subsequently collected over 120 min at 20 min intervals for photometric measurement of sodium and potassium. Intra-DRN administration of PHE and IDZ significantly increased the urinary volume, natriuresis and kaliuresis. Intra-DRN microinjection of a higher dose of PRZ reduced the urinary volume and both sodium and potassium excretion. Intra-MRN microinjections of PHE, IDZ or PRZ did not induce any significant effect on urinary volume or electrolyte excretion. These data suggest that the increase of tonic excitatory noradrenergic input conveyed to DRN influences the hydroelectrolyte homeostasis, possibly through 5-HTergic circuitry.