Sympathetic and angiotensinergic activity in spontaneously hypertensive rats treated with 3-amino-1,2,4-triazole.

Previous studies from our laboratory have shown that the pressor response to intracerebroventricular (icv) administered ANG II in normotensive rats or spontaneously hypertensive rats (SHRs) is attenuated by increased central H2O2 concentration, produced either by direct H2O2 icv injection or by increased endogenous H2O2 centrally in response to local catalase inhibition with 3-amino-1,2,4-triazole (ATZ). In the present study, we evaluated the effects of ATZ administered peripherally on arterial pressure and sympathetic and angiotensinergic activity in SHRs. Male SHRs weighing 280-330 g were used. Mean arterial pressure (MAP) and heart rate (HR) were recorded in conscious freely moving SHRs. Acute intravenous injection of ATZ (300 mg/kg of body weight) did not modify MAP and HR during the next 4 h, however, the treatment with ATZ (300 mg/kg of body weight twice per day) for 3 days reduced MAP (144 ± 6, vs. saline, 183 ± 13 mmHg), without changing HR. Intravenous hexamethonium (ganglionic blocker) produced a smaller decrease in MAP 4 h after ATZ (-25 ± 3, vs saline -38 ± 4 mmHg). Losartan (angiotensinergic AT1 receptor blocker) produced a significant depressor response 4 h after ATZ (-22 ± 4, vs. saline: -2 ± 4 mmHg) and in 3-day ATZ treated SHRs (-25 ± 5, vs. saline: -9 ± 4 mmHg). The results suggest that the treatment with ATZ reduces sympathetic activity in SHRs and simultaneously increases angiotensinergic activity.

Chronic administration of catalase inhibitor attenuates hypertension in renovascular hypertensive rats.

AIMS: Reactive oxygen species like hydrogen peroxide (H2O2) are produced endogenously and may participate in intra- and extracellular signaling, including modulation of angiotensin II responses. In the present study, we investigated the effects of chronic subcutaneous (sc) administration of the catalase inhibitor 3-amino-1,2,4-triazole (ATZ) on arterial pressure, autonomic modulation of arterial pressure, hypothalamic expression of AT1 receptors and neuroinflammatory markers and fluid balance in 2-kidney, 1clip (2K1C) renovascular hypertensive rats. MATERIALS AND METHODS: Male Holtzman rats with a clip occluding partially the left renal artery and chronic sc injections of ATZ were used. KEY FINDINGS: Subcutaneous injections of ATZ (600 mg/kg of body weight/day) for 9 days in 2K1C rats reduced arterial pressure (137 ± 8, vs. saline: 182 ± 8 mmHg). ATZ also reduced the sympathetic modulation and enhanced the parasympathetic modulation of pulse interval, reducing the sympatho-vagal balance. Additionally, ATZ reduced mRNA expression for interleukins 6 and IL-1ß, tumor necrosis factor-α, AT1 receptor (0.77 ± 0.06, vs. saline: 1.47 ± 0.26 fold change), NOX 2 (0.85 ± 0.13, vs. saline: 1.75 ± 0.15 fold change) and the marker of microglial activation, CD 11 (0.47 ± 0.07, vs. saline, 1.34 ± 0.15 fold change) in the hypothalamus of 2K1C rats. Daily water and food intake and renal excretion were only slightly modified by ATZ. SIGNIFICANCE: The results suggest that the increase of endogenous H2O2 availability with chronic treatment with ATZ had an anti-hypertensive effect in 2K1C hypertensive rats. This effect depends on decreased activity of sympathetic pressor mechanisms and mRNA expression of AT1 receptors and neuroinflammatory markers possibly due to reduced angiotensin II action.

The carotid body: A novel key player in neuroimmune interactions.

The idea that the nervous system communicates with the immune system to regulate physiological and pathological processes is not new. However, there is still much to learn about how these interactions occur under different conditions. The carotid body (CB) is a sensory organ located in the neck, classically known as the primary sensor of the oxygen (O2) levels in the organism of mammals. When the partial pressure of O2 in the arterial blood falls, the CB alerts the brain which coordinates cardiorespiratory responses to ensure adequate O2 supply to all tissues and organs in the body. A growing body of evidence, however, has demonstrated that the CB is much more than an O2 sensor. Actually, the CB is a multimodal sensor with the extraordinary ability to detect a wide diversity of circulating molecules in the arterial blood, including inflammatory mediators. In this review, we introduce the literature supporting the role of the CB as a critical component of neuroimmune interactions. Based on ours and other studies, we propose a novel neuroimmune pathway in which the CB acts as a sensor of circulating inflammatory mediators and, in conditions of systemic inflammation, recruits a sympathetic-mediated counteracting mechanism that appears to be a protective response.

Anti-hypertensive effect of hydrogen peroxide acting centrally.

Intracerebroventricular (icv) injection of hydrogen peroxide (H2O2) or the increase of endogenous H2O2 centrally produced by catalase inhibition with 3-amino-1,2,4-triazole (ATZ) injected icv reduces the pressor responses to central angiotensin II (ANG II) in normotensive rats. In the present study, we investigated the changes in the arterial pressure and in the pressor responses to ANG II icv in spontaneously hypertensive rats (SHRs) and 2-kidney, 1-clip (2K1C) hypertensive rats treated with H2O2 injected icv or ATZ injected icv or intravenously (iv). Adult male SHRs or Holtzman rats (n = 5-10/group) with stainless steel cannulas implanted in the lateral ventricle were used. In freely moving rats, H2O2 (5 µmol/1 µl) or ATZ (5 nmol/1 µl) icv reduced the pressor responses to ANG II (50 ng/1 µl) icv in SHRs (11 ± 3 and 17 ± 4 mmHg, respectively, vs. 35 ± 6 mmHg) and 2K1C hypertensive rats (3 ± 1 and 16 ± 3 mmHg, respectively, vs. 26 ± 2 mmHg). ATZ (3.6 mmol/kg of body weight) iv alone or combined with H2O2 icv also reduced icv ANG II-induced pressor response in SHRs and 2K1C hypertensive rats. Baseline arterial pressure was also reduced (-10 to -15 mmHg) in 2K1C hypertensive rats treated with H2O2 icv and ATZ iv alone or combined and in SHRs treated with H2O2 icv alone or combined with ATZ iv. The results suggest that exogenous or endogenous H2O2 acting centrally produces anti-hypertensive effects impairing central pressor mechanisms activated by ANG II in SHRs or 2K1C hypertensive rats.

Renovascular hypertension elevates pulmonary ventilation in rats by carotid body-dependent mechanisms.

The two kidney-one clip (2K1C) renovascular hypertension depends on the renin-angiotensin system and sympathetic overactivity. The maintenance of 2K1C hypertension also depends on inputs from the carotid bodies (CB), which when activated stimulate the respiratory activity. In the present study, we investigated the importance of CB afferent activity for the ventilatory responses in 2K1C hypertensive rats and for phrenic and hypoglossal activities in in situ preparations of normotensive rats treated with angiotensin II. Silver clips were implanted around the left renal artery of male Holtzman rats (150 g) to induce renovascular hypertension. Six weeks after clipping, hypertensive 2K1C rats showed, in conscious state, elevated resting tidal volume and minute ventilation compared with the normotensive group. 2K1C rats also presented arterial alkalosis, urinary acidification, and amplified hypoxic ventilatory response. Carotid body removal (CBR), 2 wk before the experiments (4th week after clipping), significantly reduced arterial pressure and pulmonary ventilation in 2K1C rats but not in normotensive rats. Intra-arterial administration of angiotensin II in the in situ preparation of normotensive rats increased phrenic and hypoglossal activities, responses that were also reduced after CBR. Results show that renovascular hypertensive rats exhibit increased resting ventilation that depends on CB inputs. Similarly, angiotensin II increases phrenic and hypoglossal activities in in situ preparations of normotensive rats, responses that also depend on CB inputs. Results suggest that mechanisms that depend on CB inputs in renovascular hypertensive rats or during angiotensin II administration in normotensive animals increase respiratory drive.

Modulation of hypercapnic respiratory response by cholinergic transmission in the commissural nucleus of the solitary tract.

The nucleus of the solitary tract (NTS) is an important area of the brainstem that receives and integrates afferent cardiorespiratory sensorial information, including those from arterial chemoreceptors and baroreceptors. It was described that acetylcholine (ACh) in the commissural subnucleus of the NTS (cNTS) promotes an increase in the phrenic nerve activity (PNA) and antagonism of nicotinic receptors in the same region reduces the magnitude of tachypneic response to peripheral chemoreceptor stimulation, suggesting a functional role of cholinergic transmission within the cNTS in the chemosensory control of respiratory activity. In the present study, we investigated whether cholinergic receptor antagonism in the cNTS modifies the sympathetic and respiratory reflex responses to hypercapnia. Using an arterially perfused in situ preparation of juvenile male Holtzman rats, we found that the nicotinic antagonist (mecamylamine, 5 mM), but not the muscarinic antagonist (atropine, 5 mM), into the cNTS attenuated the hypercapnia-induced increase of hypoglossal activity. Furthermore, mecamylamine in the cNTS potentiated the generation of late-expiratory (late-E) activity in abdominal nerve induced by hypercapnia. None of the cholinergic antagonists microinjected in the cNTS changed either the sympathetic or the phrenic nerve responses to hypercapnia. Our data provide evidence for the role of cholinergic transmission in the cNTS, acting on nicotinic receptors, modulating the hypoglossal and abdominal responses to hypercapnia.

Catalase blockade reduces the pressor response to central cholinergic activation.

Intracerebroventricular (icv) injection of hydrogen peroxide (H2O2), a reactive oxygen species, or the blockade of catalase (enzyme that degrades H2O2 into H2O and O2) with icv injection of 3-amino-1,2,4-triazole (ATZ) reduces the pressor effects of angiotensin II also injected icv. In the present study, we investigated the effects of ATZ injected icv or intravenously (iv) on the pressor responses induced by icv injections of the cholinergic agonist carbachol, which similar to angiotensin II induces pressor responses that depend on sympathoexcitation and vasopressin release. In addition, the effects of H2O2 icv on the pressor responses to icv carbachol were also tested to compare with the effects of ATZ. Normotensive non-anesthetized male Holtzman rats (280-300 g, n = 8-9/group) with stainless steel cannulas implanted in the lateral ventricle were used. Previous injection of ATZ (5 nmol/1 µl) or H2O2 (5 µmol/1 µl) icv similarly reduced the pressor responses induced by carbachol (4 nmol/1 µl) injected icv (13 ± 4 and 12 ± 4 mmHg, respectively, vs. vehicle + carbachol: 30 ± 5 mmHg). ATZ (3.6 mmol/kg of body weight) injected iv also reduced icv carbachol-induced pressor responses (21 ± 2 mmHg). ATZ icv or iv and H2O2 icv injected alone produced no effect on baseline arterial pressure. The treatments also produced no significant change of heart rate. The results show that ATZ icv or iv reduced the pressor responses to icv carbachol, suggesting that endogenous H2O2 acting centrally inhibits the pressor mechanisms (sympathoactivation and/or vasopressin release) activated by central cholinergic stimulation.

Cardiovascular and hidroelectrolytic changes in rats fed with high-fat diet.

Obesity activates the renin-angiotensin and sympathetic systems facilitating hypertension and changes in the hydroelectrolytic balance. In the present study, in rats fed with high-fat diet (HFD), we investigated daily water intake and urinary excretion, prandial consumption of water and the changes in blood pressure and water intake to intracerebroventricular (icv) angiotensin II (ANG II). Male Holtzman rats (290-320 g) were fed with standard diet (SD, 11% calories from fat) or HFD (45% calories from fat) for 6 weeks. Part of the animals received a stainless steel cannula in the lateral ventricle (LV) at the 6th week after the beginning of the diets and the experiments were performed at the 7th week. The pressor effect, but not the dipsogenic response to acute icv injection of ANG II, was potentiated in the HFD rats. Daily water intake and urinary volume were reduced in rats fed with HFD with no significant changes in sodium excretion. Prandial water consumption was also reduced in rats ingesting HFD, an effect almost totally reverted blocking salivation with atropine. These results show a potentiation of the pressor response to icv ANG II in HFD-fed rats, without changing icv ANG II-induced water intake. In addition, prandial and daily water intake and urinary volume were reduced in HFD-fed rats, without changing sodium excretion. Salivation in rats ingesting HFD may play a role in the reduced prandial and daily water intake.

Importance of the commissural nucleus of the solitary tract in renovascular hypertension.

The rodent renovascular hypertension model has been used to investigate the mechanisms promoting hypertension. The importance of the carotid body for renovascular hypertension has been demonstrated. As the commissural NTS (cNTS) is the first synaptic site in the central nervous system that receives information from carotid body chemoreceptors, we evaluated the contribution of cNTS to renovascular hypertension in the present study. Normotensive male Holtzman rats were implanted with a silver clip around the left renal artery to induce two-kidney, one-clip (2K1C) hypertension. Six weeks later, isoguvacine (a GABAA agonist) or losartan (an AT1 antagonist) was injected into the cNTS, and the effects were compared with carotid body removal. Immunohistochemistry for Iba-1 and GFAP to label microglia and astrocytes, respectively, and RT-PCR for components of the renin-angiotensin system and cytokines in the NTS were also performed 6 weeks after renal surgery. The inhibition of cNTS with isoguvacine or the blockade of AT1 receptors with losartan in the cNTS decreased the blood pressure and heart rate of 2K1C rats even more than carotid body removal did. The mRNA expression of NOX2, TNF-α and IL-6, microglia, and astrocytes also increased in the cNTS of 2K1C rats compared to that of normotensive rats. These results indicate that tonically active neurons within the cNTS are essential for the maintenance of hypertension in 2K1C rats. In addition to signals from the carotid body, the present results suggest that angiotensin II directly activates the cNTS and may also induce microgliosis and astrogliosis within the NTS, which, in turn, cause oxidative stress and neuroinflammation.

Importance of AT1 and AT2 receptors in the nucleus of the solitary tract in cardiovascular responses induced by a high-fat diet.

A high-fat diet (HFD) induces an increase in arterial pressure and a decrease in baroreflex function, which may be associated with increased expression of angiotensin type 1 receptor (AT1R) and pro-inflammatory cytokine genes and reduced expression of the angiotensin type 2 receptor (AT2R) gene within the nucleus of the solitary tract (NTS), a key area of the brainstem involved in cardiovascular control. Thus, in the present study, we evaluated the changes in arterial pressure and gene expression of components of the renin-angiotensin system (RAS) and neuroinflammatory markers in the NTS of rats fed a HFD and treated with either an AT1R blocker or with virus-mediated AT2R overexpression in the NTS. Male Holtzman rats (300-320 g) were fed either a standard rat chow diet (SD) or HFD for 6 weeks before commencing the tests. AT1R blockade in the NTS of HFD-fed rats attenuated the increase in arterial pressure and the impairment of reflex bradycardia, whereas AT2R overexpression in the NTS only improved the baroreflex function. The HFD also increased the hypertensive and decreased the protective axis of the RAS and was associated with neuroinflammation within the NTS. The expression of angiotensin-converting enzyme and neuroinflammatory components, but not AT1R, in the NTS was reduced by AT2R overexpression in this site. Based on these data, AT1R and AT2R in the NTS are differentially involved in the cardiovascular changes induced by a HFD. Chronic inflammation and changes in the RAS in the NTS may also account for the cardiovascular responses observed in HFD-fed rats.

Central muscarinic and LPBN mechanisms on sodium intake.

Central cholinergic activation stimulates water intake, but also NaCl intake when the inhibitory mechanisms are blocked with injections of moxonidine (α2 adrenergic/imidazoline agonist) into the lateral parabrachial nucleus (LPBN). In the present study, we investigated the involvement of central M1 and M2 muscarinic receptors on NaCl intake induced by pilocarpine (non-selective muscarinic agonist) intraperitoneally combined with moxonidine into the LPBN or by muscimol (GABAA agonist) into the LPBN. Male Holtzman rats with stainless steel cannulas implanted bilaterally in the LPBN and in the lateral ventricle were used. Pirenzepine (M1 muscarinic antagonist, 1 nmol/1 µl) or methoctramine (M2 muscarinic antagonist, 50 nmol/1 µL) injected intracerebroventricularly (i.c.v.) reduced 0.3 M NaCl and water intake in rats treated with pilocarpine (0.1 mg/100 g of body weight) injected intraperitoneally combined with moxonidine (0.5 nmol/0.2 µL) into the LPBN. In rats treated with muscimol (0.5 nmol/0.2 µL) into the LPBN, methoctramine i.c.v. also reduced 0.3 M NaCl and water intake, however, pirenzepine produced no effect. The results suggest that M1 and M2 muscarinic receptors activate central pathways involved in the control of water and sodium intake that are under the influence of the LPBN inhibitory mechanisms.

The lateral parabrachial nucleus and central angiotensinergic mechanisms in the control of sodium intake induced by different stimuli.

Angiotensin II (ANG II) is a typical facilitatory stimulus for sodium appetite. Surprisingly, hyperosmolarity and central cholinergic stimulation, two classical antinatriorexigenic stimuli, also facilitate NaCl intake when they are combined with injections of the α2-adrenoceptor/imidazoline agonist moxonidine into the lateral parabrachial nucleus (LPBN). In the present study, we tested the relative importance of central angiotensinergic and cholinergic mechanisms for the control of water and NaCl intake by combining different dipsogenic or natriorexigenic stimuli with moxonidine injection into the LPBN. Adult male Holtzman rats (n=9-10/group) with stainless steel cannulas implanted in the lateral ventricle and LPBN were used. Bilateral injections of moxonidine (0.5 nmol) into the LPBN increased water and 0.3M NaCl intake in rats that received furosemide+captopril injected subcutaneously, ANG II (50ng) or carbachol (cholinergic agonist, 4 nmol) injected intracerebroventricularly (icv) or 2M NaCl infused intragastrically (2ml/rat). Losartan (AT1 antagonist, 100µg) or atropine (muscarinic antagonist, 20 nmol) injected icv abolished the effects on water and 0.3M NaCl of moxonidine combined to either 2M NaCl intragastrically or carbachol icv. However, atropine icv did not change 0.3M NaCl intake produced by direct central action of ANG II like that induced by ANG II icv or furosemide+captopril combined with moxonidine into the LPBN. The results suggest that different stimuli, including hyperosmolarity and central cholinergic stimulation, share central angiotensinergic activation as a common mechanism to facilitate sodium intake, particularly when they are combined with deactivation of the LPBN inhibitory mechanisms.

Lateral parabrachial nucleus and opioid mechanisms of the central nucleus of the amygdala in the control of sodium intake.

Facilitatory and inhibitory mechanisms in the central nucleus of the amygdala (CeA) and the lateral parabrachial nucleus (LPBN), respectively, are important for the control of sodium and water intake. Here we investigated the importance of the opioid mechanisms in the CeA for water and 0.3M NaCl intake in euhydrated or hyperosmotic rats treated with injections of muscimol (GABAA agonist) or moxonidine (α2 adrenergic/imidazoline agonist) into the LPBN, respectively. Male Holtzman rats (n=4-8/group) with stainless steel cannulas implanted bilaterally in the CeA and in the LPBN were used. The ingestion of 0.3M NaCl and water by euhydrated rats treated with muscimol (0.5nmol/0.2µl) into the LPBN (29.4±2.7 and 15.0±2.4ml/4h, respectively) was abolished by the previous injections of naloxone (opioid antagonist, 40µg/0.2µl) into the CeA (0.7±0.3 and 0.3±0.1ml/4h, respectively). The ingestion of 0.3M NaCl by rats treated with intragastric 2M NaCl (2ml/rat) combined with moxonidine (0.5nmol/0.2µl) into the LPBN (17.0±3.8ml/2h) was also strongly reduced by the previous injections of naloxone into the CeA (3.2±2.5ml/2h). Sucrose intake was not affected by naloxone injections into the CeA, which minimized the possibility of non-specific inhibition of ingestive behaviors with this treatment. The present results suggest that opioid mechanisms in the CeA are essential for hypertonic NaCl intake when the LPBN inhibitory mechanisms are deactivated or attenuated with injections of muscimol or moxonidine in this area.

Short-term cross-sensitizion of need-free sugar intake by combining sodium depletion and hypertonic NaCl intake.

History of sodium depletion cross-sensitizes the effects of drugs of abuse. The objective of the present study was to find out if history of sodium depletion also cross-sensitizes a natural reward such as sugar intake in the rat. Sodium depletion was induced by furosemide combined with removal of ambient sodium for 24 h; it was repeated seven days later. The depletion was immediately followed by 0.3 M NaCl intake in a sodium appetite test (active sodium repletion). Seven days after the last depletion, hydrated and fed (need-free) sucrose-naïve animals were offered 10% sucrose in a first 2-h sucrose test. The sucrose test was repeated once a day in a series of five consecutive days. History of sodium depletion enhanced sucrose intake in the first and second tests; it had no effect from the third to fifth sucrose test. The effect on the initial sucrose intake tests disappeared if the rats did not ingest 0.3 M NaCl in the sodium appetite test. Prior experience with sucrose intake in need-free conditions had no effect on sodium appetite. History of intracellular dehydration transiently influenced sucrose intake in the first sucrose test. We found no evidence for thirst sensitization. We conclude that history of dehydration, particularly that resulting from sodium depletion, combined to active sodium repletion, produced short-term cross-sensitization of sucrose intake in sucrose-naïve rats. The results suggest that the cross-sensitization of sucrose intake related with acquisition of sugar as a novel nutrient rather than production of lasting effects on sugar rewarding properties.

Overexpression of AT2R in the solitary-vagal complex improves baroreflex in the spontaneously hypertensive rat.

The aim of this study was to investigate the physiological effects of increased angiotensin II type 2 receptor (AT2R) expression in the solitary-vagal complex (nucleus of the solitary tract/dorsal motor nucleus of the vagus; NTS/DVM) on baroreflex function in non-anaesthetised normotensive (NT) and spontaneously hypertensive rats (SHR). Ten week old NT Holtzman and SHR were microinjected with either an adeno-associated virus expressing AT2R (AAV2-CBA-AT2R) or enhanced green fluorescent protein (control; AAV2-CBA-eGFP) into the NTS/DVM. Baroreflex and telemetry recordings were performed on four experimental groups: 1) NTeGFP, 2) NTAT2R, 3) SHReGFP and 4) SHRAT2R (n=4-7/group). Following in-vivo experimental procedures, brains were harvested for gene expression analysis. Impaired bradycardia in SHReGFP was restored in SHR rats overexpressing AT2R in the NTS/DMV. mRNA levels of angiotensin converting enzyme decreased and angiotensin converting enzyme 2 increased in the NTS/DMV of SHRAT2R compared to SHReGFP. Increased levels of pro-inflammatory cytokine mRNA levels in the SHReGFP group also decreased in the SHRAT2R group. AT2R overexpression did not elicit any significant change in mean arterial pressure (MAP) in all groups from baseline to 4weeks post viral transfection. Both SHReGFP and SHRAT2R showed a significant elevation in MAP compared to the NTeGFP and NTAT2R groups. Increased AT2R expression within the NTS/DMV of SHR was effective at improving baroreflex function but not MAP. We propose possible mediators involved in improving baroreflex are in the ANG II/ACE2 axis, suggesting a potential beneficial modulatory effect of AT2R overexpression in the NTS/DMV of neurogenic hypertensive rats.

Resistance training prevents the cardiovascular changes caused by high-fat diet.

AIMS: Aerobic exercise is indicated for prevention and treatment of obesity-induced cardiovascular disorders. Although the resistance training (RT) may also produce effects similar to aerobic exercise, this is not completely clear yet. In the present study, we tested if RT in moderate intensity might prevent alterations in blood pressure (BP), sympathetic modulation of systolic blood pressure (SBP), baroreflex function and the changes in renin-angiotensin system (RAS) and cytokines mRNA expression within the nucleus of the tract solitary (NTS) in rats fed with high-fat diet (HFD). MAIN METHODS: Male Holtzman rats (300-320 g) were divided into 4 groups: sedentary with standard chow diet (SED-SD); sedentary with high-fat diet (SED-HFD); RT with standard chow diet (RT-SD); and RT with high-fat diet (RT-HFD). The trained groups performed a total of 10 weeks of moderate intensity RT in a vertical ladder. In the first 3 weeks all experimental groups were fed with SD. In the next 7 weeks, the SED-HFD and RT-HFD groups were fed with HFD. KEY FINDINGS: In SED-HFD, BP and sympathetic modulation of SBP increased, whereas baroreflex bradycardic responses were attenuated. RT prevented the cardiovascular and inflammatory responses (increases in tumoral necrosis factor-α and interleukin-1ß) produced by HFD in SED rats. The anti-inflammatory interleukin-10, angiotensin type 2 receptor, Mas receptor and angiotensin converting enzyme 2 mRNA expressions in the NTS increased in the RT-HFD compared to SED-HFD. SIGNIFICANCE: The data demonstrated that moderate intensity RT prevented obesity-induced cardiovascular disorders simultaneously with reduced inflammatory responses and modifications of RAS in the NTS.

Hydrogen peroxide centrally attenuates hyperosmolarity-induced thirst and natriuresis.

Intragastric hypertonic NaCl that simulates the ingestion of osmotically active substances by food intake induces thirst, vasopressin and oxytocin release, diuresis and natriuresis. Reactive oxygen species (ROS) produced endogenously in central areas may act modulating autonomic and behavioral responses. In the present study, we investigated the effects of H2O2 injected centrally on water intake and renal responses induced by increasing plasma osmolality with intragastric (ig) administration of 2M NaCl (2 ml/rat). Male Holtzman rats (280-320 g) with stainless steel cannula implanted in the lateral ventricle (LV) were used. Injections of H2O2 (2.5 µmol/1 µl) into the LV reduced ig 2M NaCl-induced water intake (3.1 ± 0.7, vs. PBS: 8.6 ± 1.0 ml/60 min, p<0.05), natriuresis (769 ± 93, vs. PBS: 1158 ± 168 µEq/120 min, p<0.05) and diuresis (4.1 ± 0.5, vs. PBS: 5.0 ± 0.5 ml/120 min, p<0.05). Injections of H2O2 into the LV also decreased meal associated water intake (4.9 ± 1.5, vs. PBS: 11.0 ± 1.7 ml/120 min). However, H2O2 into the LV did not modify 2% sucrose intake (3.3 ± 1.5, vs. PBS: 5.4 ± 2.3 ml/120 min) or 24h food deprivation-induced food intake (8.2 ± 2.0, vs. PBS: 11.0 ± 1.6g/120 min), suggesting that this treatment does not produce nonspecific inhibition of ingestive behaviors. The data suggest an inhibitory role for H2O2 acting centrally on thirst and natriuresis induced by hyperosmolarity and on meal-associated thirst.

Participation of α2 -adrenoceptors in sodium appetite inhibition during sickness behaviour following administration of lipopolysaccharide.

Sickness behaviour, a syndrome characterized by a general reduction in animal activity, is part of the active-phase response to fight infection. Lipopolysaccharide (LPS), an effective endotoxin to model sickness behaviour, reduces thirst and sodium excretion, and increases neurohypophysial secretion. Here we review the effects of LPS on thirst and sodium appetite. Altered renal function and hydromineral fluid intake in response to LPS occur in the context of behavioural reorganization, which manifests itself as part of the syndrome. Recent data show that, in addition to its classical effect on thirst, non-septic doses of LPS injected intraperitoneally produce a preferential inhibition of intracellular thirst versus extracellular thirst. Moreover, LPS also reduced hypertonic NaCl intake in sodium-depleted rats that entered a sodium appetite test. Antagonism of α2 -adrenoceptors abolished the effect of LPS on sodium appetite. LPS and cytokine transduction potentially recruit brain noradrenaline and α2 -adrenoceptors to control sodium appetite and sickness behaviour.

Importance of the central nucleus of the amygdala on sodium intake caused by deactivation of lateral parabrachial nucleus.

The lateral parabrachial nucleus (LPBN) and the central nucleus of the amygdala (CeA) are important central areas for the control of sodium appetite. In the present study, we investigated the importance of the facilitatory mechanisms of the CeA on NaCl and water intake produced by the deactivation of LPBN inhibitory mechanisms. Male Holtzman rats (n=7-14) with stainless steel cannulas implanted bilaterally in the CeA and LPBN were used. Bilateral injections of moxonidine (α2-adrenoceptor/imidazoline agonist, 0.5 nmol/0.2 µl) into the LPBN increased furosemide+captopril-induced 0.3M NaCl (29.7 ± 7.2, vs. vehicle: 4.4 ± 1.6 ml/2h) and water intake (26.4 ± 6.7, vs. vehicle: 8.2 ± 1.6 ml/2h). The GABAA agonist muscimol (0.25 nmol/0.2 µl) injected bilaterally into the CeA abolished the effects of moxonidine into the LPBN on 0.3M NaCl (2.8 ± 1.6 ml/2h) and water intake (3.3 ± 2.3 ml/2h). Euhydrated rats treated with muscimol (0.5 nmol/0.2 µl) into the LPBN also ingested 0.3M NaCl (19.1 ± 6.4 ml/4h) and water (8.8 ± 3.2 ml/4h). Muscimol (0.5 nmol/0.2 µl) into the CeA also abolished 0.3M NaCl (0.1 ± 0.04 ml/4h) and water intake (0.1 ± 0.02 ml/4h) in euhydrated treated with muscimol into the LPBN. The present results show that neuronal deactivation of the CeA abolishes NaCl intake produced by the blockade of LPBN inhibitory mechanisms, suggesting an interaction between facilitatory mechanisms of the CeA and inhibitory mechanisms of the LPBN in the control of NaCl intake.

Sodium intake, brain c-Fos protein and gastric emptying in cell-dehydrated rats treated with methysergide into the lateral parabrachial nucleus.

Previous studies from our laboratory have shown that methysergide, a serotonergic antagonist, injected into the lateral parabrachial nucleus (LPBN) combined with a pre-load of 2 M NaCl, given by gavage, induces 0.3 M NaCl intake. The mechanisms involved in this paradoxical behavior are still unknown. In the present work, we investigated the effect of serotonergic blockade into the LPBN on hindbrain and hypothalamic activity, gastric emptying and arterial blood pressure in cell-dehydrated rats. Methysergide plus 2 M NaCl infused intragastrically or intravenously promoted 0.3 M NaCl intake in two-bottle tests. In cell-dehydrated rats with no access to fluids, methysergide compared to vehicle increased Fos immunoreactivity in the medial nucleus of the solitary tract, area postrema and non-oxytocinergic cells of the ventral portion of the hypothalamic paraventricular nucleus (PVN). There was no alteration in the number of neurons double-labeled for Fos-ir and oxytocin in the PVN and supraoptic nuclei. There was also no alteration in plasma oxytocin and vasopressin, or arterial pressure. In rats cell-dehydrated by i.v. 2 M NaCl, methysergide also did not change the amount of an intragastric load of 0.3 M NaCl retained in the stomach or intestine. The results suggest that methysergide injected into the LPBN of cell-dehydrated rat does not alter primary inhibitory signals that control sodium intake. The inhibitory signals blocked by methysergide in the LPBN possibly originated from activation of brain osmoreceptors, second order visceral/hormonal signals or a combination of both.