Maternal high-fat diet changes breathing pattern and causes excessive sympathetic discharge in juvenile offspring rat.

Early life over-nutrition, as experienced in maternal obesity, is a risk factor for developing cardiorespiratory and metabolic diseases. Here we investigated the effects of high-fat diet (HFD) consumption on the breathing pattern and sympathetic discharge to blood vessels in juvenile offspring from dams fed with HFD (O-HFD). Adult female Holtzman rats were given a standard diet (SD) or HFD from 6 wk before gestation to weaning. At weaning (P21), the male offspring from SD dams (O-SD) and O-HFD received SD until the experimental day (P28-P45). Nerve recordings performed in decerebrated in situ preparations demonstrated that O-HFD animals presented abdominal expiratory hyperactivity under resting conditions and higher vasoconstrictor sympathetic activity levels. The latter was associated with blunted respiratory-related oscillations in sympathetic activity, especially in control animals. When exposed to elevated hypercapnia or hypoxia levels, the O-HFD animals mounted similar ventilatory and respiratory motor responses as the control animals. Hypercapnia and hypoxia exposure also increased sympathetic activity in both groups but did not reinstate the respiratory-sympathetic coupling in the O-HFD rats. In freely behaving conditions, O-HFD animals exhibited higher resting pulmonary ventilation and larger variability of arterial pressure levels than the O-SD animals due to augmented sympathetic modulation of blood vessel diameter. Maternal obesity modified the functioning of cardiorespiratory systems in offspring at a young age, inducing active expiration and sympathetic overactivity under resting conditions. These observations represent new evidence about pregnancy-related complications that lead to the development of respiratory distress and hypertension in children of obese mothers.NEW & NOTEWORTHY Maternal obesity is a risk factor for developing cardiorespiratory and metabolic diseases. This study highlights the changes on the breathing pattern and sympathetic discharge to blood vessels in juvenile offspring from dams fed with HFD. Maternal obesity modified the functioning of cardiorespiratory systems in offspring, inducing active expiration and sympathetic overactivity. These observations represent new evidence about pregnancy-related complications that lead to the development of respiratory distress and hypertension in children of obese mothers.

Sympathetic dysregulation induced by postnatal intermittent hypoxia.

STUDY OBJECTIVES: Exposure to postnatal chronic intermittent hypoxia (pCIH), as experienced in sleep-disordered breathing, is a risk factor for developing cardiorespiratory diseases in adulthood. pCIH causes respiratory instability and motor dysfunction that persist until adult life. In this study, we investigated the impact of pCIH on the sympathetic control of arterial pressure in rats. METHODS AND RESULTS: Neonate male Holtzman rats (P0-1) were exposed to pCIH (6% O2 for 30 seconds, every 10 minutes, 8 h/day) during their first 10-15 days of life, while control animals were maintained under normoxia. In early adult life (P25-40), freely behaving pCIH animals (n = 13) showed higher baseline arterial pressure levels linked to augmented sympathetic-mediated variability than control animals (n = 12, p < 0.05). Using decerebrated in situ preparations, we found that juvenile pCIH rats exhibited a twofold increase in thoracic sympathetic nerve activity (n = 14) and elevated firing frequency of ventromedullary presympathetic neurons (n = 7) compared to control rats (n = 6-7, p < 0.05). This pCIH-induced sympathetic dysregulation was associated with increased HIF-1α (hypoxia-inducible factor 1 alpha) mRNA expression in catecholaminergic presympathetic neurons (n = 5, p < 0.05). At older age (P90-99), pCIH rats displayed higher arterial pressure levels and larger depressor responses to ganglionic blockade (n = 6-8, p < 0.05), confirming the sympathetic overactivity state. CONCLUSIONS: pCIH facilitates the vasoconstrictor sympathetic drive by mechanisms associated with enhanced firing activity and HIF-1α expression in ventromedullary presympathetic neurons. This excessive sympathetic activity persists until adulthood resulting in high blood pressure levels and variability, which contribute to developing cardiovascular diseases.

Inhibitory control of active expiration by the Bötzinger complex in rats.

KEY POINTS: Contraction of abdominal muscles at the end of expiration during metabolic challenges (such as hypercapnia and hypoxia) improves pulmonary ventilation. The emergence of this active expiratory pattern requires the recruitment of the expiratory oscillator located on the ventral surface of the medulla oblongata. Here we show that an inhibitory circuitry located in the Bötzinger complex is an important source of inhibitory drive to the expiratory oscillator. This circuitry, mediated by GABAergic and glycinergic synapses, provides expiratory inhibition that restrains the expiratory oscillator under resting condition and regulates the formation of abdominal expiratory activity during active expiration. By combining experimental and modelling approaches, we propose the organization and connections within the respiratory network that control the changes in the breathing pattern associated with elevated metabolic demand. ABSTRACT: The expiratory neurons of the Bötzinger complex (BötC) provide inhibitory inputs to the respiratory network, which, during eupnoea, are critically important for respiratory phase transition and duration control. Here, we investigated how the BötC neurons interact with the expiratory oscillator located in the parafacial respiratory group (pFRG) and control the abdominal activity during active expiration. Using the decerebrated, arterially perfused in situ preparations of juvenile rats, we recorded the activity of expiratory neurons and performed pharmacological manipulations of the BötC and pFRG during hypercapnia or after the exposure to short-term sustained hypoxia - conditions that generate active expiration. The experimental data were integrated in a mathematical model to gain new insights into the inhibitory connectome within the respiratory central pattern generator. Our results indicate that the BötC neurons may establish mutual connections with the pFRG, providing expiratory inhibition during the first stage of expiration and receiving excitatory inputs during late expiration. Moreover, we found that application of GABAergic and glycinergic antagonists in the BötC caused opposing effects on abdominal expiratory activity, suggesting complex inhibitory circuitry within the BötC. Using mathematical modelling, we propose that the BötC network organization and its interactions with the pFRG restrain abdominal activity under resting conditions and contribute to abdominal expiratory pattern formation during active expiration observed during hypercapnia or after the exposure to short-term sustained hypoxia.

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.

Postnatal intermittent hypoxia enhances phrenic and reduces vagal upper airway motor activities in rats by epigenetic mechanisms.

NEW FINDINGS: What is the central question of this study? What are the alterations in respiratory motor activity that may underlie ventilatory dysfunctions in juvenile and adult animals exposed to postnatal chronic intermittent hypoxia? What is the main finding and its importance? Postnatal chronic intermittent hypoxia modifies the motor activity to pumping and upper airway respiratory muscles in rats, mediated by epigenetic DNA hypermethylation, enhancing resting pulmonary ventilation and predisposing to collapse of the upper airways in juvenile and adult life. ABSTRACT: Periods of apnoea, commonly observed in prematures and newborns, are an important risk factor for the development of cardiorespiratory diseases in adulthood. In the present study, we evaluated changes in pulmonary ventilation and respiratory motor pattern in juvenile and adult rats exposed to postnatal chronic intermittent hypoxia (pCIH). Newborn male Holtzman rats (P1) were submitted to pCIH (6% O2 for 30 s, every 9 min, 8 h a day (09.30-17.30 h)) during their first 10 days of life, while control animals were maintained under normoxic conditions (20.8% O2 ). Thereafter, animals of both groups were maintained under normoxia until the experiments. Unanaesthetized juvenile pCIH rats (n = 27) exhibited elevated tidal volume and respiratory irregularities (P < 0.05) compared to control rats (n = 7). Decerebrate, arterially perfused in situ preparations of juvenile pCIH rats (n = 11) displayed augmented phrenic nerve (PN) burst amplitude and reduced central vagus nerve activity in comparison to controls (n = 10). At adulthood, pCIH rats (n = 5) showed enhanced tidal volume (P < 0.05) and increased respiratory variability compared to the control group (n = 5). The pCIH-induced changes in ventilation and respiratory motor outputs were prevented by treatment with the DNA methyltransferase inhibitor decitabine (1 mg kg-1 , i.p.) during the exposure to pCIH. Our data demonstrate that pCIH in rats impacts, in a persistent way, control of the respiratory pattern, increasing PN activity to the diaphragm and reducing the vagal-related activity to laryngeal muscles, which, respectively, may contribute to improve resting pulmonary ventilation and predispose to collapse of the upper airways during quiet breathing.

Corrigendum: Pacemaking Property of RVLM Presympathetic Neurons.

[This corrects the article on p. 424 in vol. 7, PMID: 27713705.].

Pacemaking Property of RVLM Presympathetic Neurons.

Despite several studies describing the electrophysiological properties of RVLM presympathetic neurons, there is no consensus in the literature about their pacemaking property, mainly due to different experimental approaches used for recordings of neuronal intrinsic properties. In this review we are presenting a historical retrospective about the pioneering studies and their controversies on the intrinsic electrophysiological property of auto-depolarization of these cells in conjunction with recent studies from our laboratory documenting that RVLM presympathetic neurons present pacemaking capacity. We also discuss whether increased sympathetic activity observed in animal models of neurogenic hypertension (CIH and SHR) are dependent on changes in the intrinsic electrophysiological properties of these cells or due to changes in modulatory inputs from neurons of the respiratory network. We also highlight the key role of INaP as the major current contributing to the pacemaking property of RVLM presympathetic neurons.

Efeitos do treinamento físico sobre a pressão arterial, frequência cardíaca e morfologia de ratos hipertensos / Effects of physical training by blood pressure, heart rate and cardiac morphology in hypertensive rats

O objetivo desse estudo foi verificar o efeito da natação sobre as alterações morfológicas cardíacas e hemodinâmicas de ratos com hipertensão induzida por L-NAME. Quarenta ratos Wistar foram divididos nos grupos: controle sedentário (CS), controle treinado (CT), sedentário com L-NAME (LS) e treinado com L-NAME (LT). Os animais treinados realizaram natação por até 60 min durante quatro semanas. Os animais dos grupos L-NAME receberam 20 mg.kg-1 também durante quatro semanas. O grupo LS apresentou maiores valores de PAM (136,6±5,1 mmHg) comparado ao CS (107,1±1,8 mmHg). O grupo LT apresentou reduções na PAM comparado ao LS (121,2±1,4 e 136,6±5,1 mmHg, respectivamente). Por outro lado, os LT ainda permaneceram hipertensos comparados ao CT (121,0±1,4 e 107,1±1,8 mmHg, respectivamente). Em relação à FC, houve bradicardia de repouso para os animais treinados. Os grupos CS e CT não apresentaram alterações no peso relativo e absoluto do coração. Houve aumento do peso absoluto do coração para o grupo LS comparado ao CS e também se observou aumento para o peso relativo e absoluto do coração para o grupo LT comparado ao CT. A análise histológica demonstrou que o treinamento físico pode reduzir a quantidade de lesões provocadas pela administração crônica de LNAME. Conclui-se que a natação foi eficiente em reduzir a PAM de animais hipertensos, mas não reduziu em animais normotensos. Adicionalmente, o treinamento físico não promoveu hipertrofia cardíaca, mas a administração de L-NAME aumentou o peso absoluto e relativo do coração em animais sedentários e treinados...

The objective of this study was to investigate the effect of swimming on the cardiac morphological and hemodynamic changes in rats with hypertension induced by L-NAME.. Forty Wistar rats were divided into four groups: sedentary control (SC), trained control (TC), sedentary with L-NAME (LS) and trained with LNAME(LT). The animals in the training groups performed swimming lasting up to 60 min for four weeks. Animals in the L-NAME groups received 20 mg.kg-1 during four weeks. The results showed that animals in the LS group had higher mean arterial pressure (136.6±5.1 mmHg) compared to CS (107.1±1.8 mmHg).The LT group showed significant reductions in mean arterial pressure compared to LS (121.2±1.4 and 136.6±5.1 mmHg, respectively). On the other hand, the LT group animals still remained hypertensive compared to CT group (121.0±1.4 and 107.1±1.8 mmHg respectively). In relation to HR, was observed resting bradycardia for the trained animals. The groups CS and CT showed no changes in relative and absolute weight of the heart. An increase in the absolute weight of the heart to the LS group compared to the CS and also observed an increase in the relative and absolute weight for the LT group compared toCT. Histologic analysis showed that exercise training can reduce the amount of damage caused by chronicadministration of L-NAME. In conclusion, we observed that mild exercise was effective in reducing meanarterial pressure in hypertensive rats. Additionally, exercise training did not induced cardiac hypertrophy,but the L-NAME increase the absolute and relative weight of the heart in sedentary and trained rats...

Direct renin inhibitor therapy and swimming training: hemodynamic and cardiac effects in hypertensive and normotensive rats.

PURPOSE: This study aimed to analyze the hemodynamic and cardiac effects of direct renin inhibitor (DRI) treatment and swimming training in hypertensive rats. METHODS: Seventy-seven rats were divide into eight groups: sedentary normotensive (SN), trained normotensive (TN), sedentary normotensive treated with DRI (SN_DRI), trained normotensive treated with DRI (TN_DRI), sedentary hypertensive (SH), trained hypertensive (TH), sedentary hypertensive treated with DRI (SH_DRI), trained hypertensive treated with DRI (TH_DRI). Swimming training occurred for up to 60 min, five times a week for four weeks. The hypertensive animals were treated with 20 mg c kg(-1) c day(-1) L-NAME for four weeks. Groups treated with DRI received 10 mg c kg(-1) c day(-1) of aliskiren for four weeks. After the treatment period, all the animals underwent femoral artery catheterization surgery for direct measurement of cardiovascular variables. RESULTS: The SH group presented hypertension (136.4 ± 5.0 mmHg) compared to the SN (107.1 ± 1.7 mmHg). The TH group showed lower mean arterial pressure (MAP) than the SH (121.1 ± 1.3 mmHg), but the treatment with DRI did not attenuate hypertension (128.2 ± 4.9 mmHg). The analysis of collagen areas demonstrated that treatment with DRI may attenuate cardiac remodeling in situations of hypertension, in the condition of treatment alone or combined with physical training. CONCLUSION: Both interventions in combination may be more effective at reducing cardiovascular risk in hypertensive subjects.

Treatment with nebivolol combined with physical training promotes improvements in the cardiovascular responses of hypertensive rats.

The aim of this study was to determine whether exercise training combined with beta-blocker treatment promotes additional cardiovascular benefits compared with either intervention on its own. For this we used 76 Wistar rats distributed among different groups: normotensive sedentary (NS), normotensive trained (NT), normotensive sedentary treated with beta-blocker (NS_BB), normotensive trained treated with beta-blocker (NT_BB), hypertensive sedentary (HS), hypertensive trained (HT), hypertensive sedentary treated with a beta-blocker (HS_BB), and hypertensive trained rats treated with beta-blocker (HT_BB). Exercise training consisted of 4 weeks of swimming for 60 min a day, 5 days a week. Hypertension was induced with l-NAME (4 weeks), whereas the control rats received saline, and both the control and test rats received nebivolol. The animals underwent surgery to directly record their blood pressure. The HS group showed higher mean arterial pressure (MAP) (P = 0.000), systolic arterial pressure (P = 0.000), and diastolic arterial pressure (P = 0.000) compared with NS. MAP was higher in the HS compared with the HT (P = 0.002), HS_BB (P = 0.018), and HT_BB (P = 0.015) groups. Hearts from the HS group had a higher percentage of collagen compared with the NS and HS_BB groups. The HT_BB and HT groups only had a higher percentage of cardiac collagen by comparison with the HS_BB group. The HT_BB group showed higher levels of macrophages and neutrophils by comparison with the HT and HS_BB groups. Thus, treatment with a beta-blocker combined with physical training was associated with increased cardiovascular benefits over either intervention alone.

Renal sympathetic nerve activity is increased in monosodium glutamate induced hyperadipose rats.

The literature suggests that both obesity and hypertension are associated with increased sympathetic nerve activity. In the present study we evaluated the renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) in hyperadipose rats induced by neonatal administration of monosodium glutamate (MSG). Neonatal Wistar male rats were injected with MSG (4 mg/g body weight ID) or equimolar saline (control) for 5 days. At 90th day, all rats were anesthetized (urethane 1.4 g/kg) and prepared for MAP, HR and renal sympathetic nerve activity recordings. The anesthetized MSG rats presented baseline hypertension and increased baseline RSNA compared with control. Our results suggest the involvement of the renal sympathetic nervous system in the physiopathology of the MSG obesity.

Altered baroreflex and autonomic modulation in monosodium glutamate-induced hyperadipose rats.

We aimed to examine the cardiovascular function by tonic and baroreflex alterations in obese rats induced by monosodium glutamate (MSG). Neonatal male Wistar rats were injected with MSG (4 mg/g body weight) or equimolar saline (control, C). At 90 days, all rats were anesthetized for catheterization of the femoral artery for mean arterial pressure (MAP) and heart rate (HR) recordings in the conscious state. After baseline, we performed IV treatment with hexamethonium (25 mg/kg), or atropine (1 mg/kg) or propranolol (3 mg/kg). We also performed the spectral analysis of heart rate variability (HRV) and baroreflex sensitivity. Baseline comparison showed that obese rats are hypertensive compared with control (C=110±2 mmHg; MSG=: 123±3 mmHg, P<0.05). After ganglionic blockade with hexamethonium the differences in MAP between control and obese rats disappeared. Beta adrenergic blockade with propranolol induced a greater decrease in heart rate compared with control. The analysis of HRV showed that obese rats have increased modulation by both components of the autonomic nervous system compared with control rats. The baroreflex gain showed increased sensitivity for the parasympathetic component in the obese rats (C=-2.41±0.25; MSG=-3.34±0.23 bpm/mmHg) compared with control. Our data suggest that both components of autonomic cardiac tonus and the parasympathetic component of the baroreflex sensitivity are increased in the MSG obese rat. It is possible that the parasympathetic alterations observed in these MSG obese rats may have originated from central areas of cardiovascular control.