Mateus R. Amorim

Cardiovascular and respiratory responses to chronic intermittent hypoxia in adult female rats

What is the central question of this study? Chronic intermittent hypoxia (CIH) induces hypertension in male rats. There is evidence that the development of high blood pressure in females is attenuated in other models of hypertension. Due to the lack of information about the cardiovascular effect of CIH in female rats, we set out to determine whether female rats develop hypertension after CIH. What is the main finding and its importance? Different from other experimental models of hypertension, adult female rats develop high blood pressure after CIH. These findings provide new perspectives for a better understanding of the neural mechanisms underlying the development of hypertension in females.

Inspiratory modulation of sympathetic activity is increased in female rats exposed to chronic intermittent hypoxia

What is the central question of the study? There are sex differences in the respiratory network and in the regulation of arterial blood pressure. Female rats develop hypertension after chronic intermittent hypoxia (CIH). In this context, we evaluated the respiratory‐related mechanism underlying the development of hypertension in CIH‐exposed female rats. What is the main finding and its importance? Female rats exposed to CIH develop changes in the respiratory pattern related to inspiration and sympathetic overactivity phase locked to the inspiratory phase of the respiratory cycle, which is different from CIH‐exposed male rats. These data suggest a specific respiratory mechanism for sympathetic overactivity in hypertensive CIH‐exposed female rats.

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.

Role of respiratory changes in the modulation of arterial pressure in rats submitted to sino‐aortic denervation

What is the central question of this study? The arterial baroreflex regulates arterial pressure within a narrow range of variation. After sino‐aortic denervation (SAD), rats show a large increase in arterial pressure variability, but mean arterial pressure levels remain similar to those of control rats. Considering that breathing influences the control of arterial pressure, the question is: to what extent does SAD cause changes in breathing? What is the main finding and its importance? Removal of arterial baroreceptors produced changes in breathing in rats, marked by a reduction in respiratory frequency, but not hypertension. These findings are indicative of a possible interaction of respiratory and autonomic neural mechanisms in the regulation of arterial pressure after SAD.

Previous exposure to chronic intermittent hypoxia blunts the development of one‐kidney, one‐clip hypertension in rats

What is the central question of this study? Chronic intermittent hypoxia (CIH) and one‐kidney, one‐clip experimental models lead to sympathetic overactivity and hypertension. The present study explored the impact of previous exposure to CIH on one‐kidney, one‐clip renal hypertension; we hypothesized that CIH potentiates its development. What is the main finding and its importance? The development of one‐kidney, one‐clip renal hypertension was attenuated by previous exposure to CIH, and this protective effect was eliminated by carotid body denervation. These findings indicate that inputs from peripheral chemoreceptors in CIH‐preconditioned rats play a role in preventing the increase in sympathetic activity and arterial pressure induced by one‐kidney, one‐clip renal hypertension.

Changes in the inspiratory pattern contribute to modulate the sympathetic activity in sino‐aortic denervated rats

What is the central question of this study? Sino‐aortic denervated (SAD) rats present normal levels of sympathetic activity and mean arterial pressure. However, neural mechanisms regulating the sympathetic activity in the absence of arterial baroreceptors remain unclear. Considering that respiration modulates the sympathetic activity, we hypothesize that changes in the respiratory network contribute to keep the sympathetic outflow in the normal range after removal of arterial baroreceptors. What is the main finding and its importance? Despite longer inspiration observed in SAD rats, the respiratory–sympathetic coupling is working within a normal range of variation. These findings suggest that in the absence of arterial baroreceptors the respiratory modulation of sympathetic activity is maintained within the normal range.

Purinergic signalling and TRPV1 receptors are associated with the carotid body plasticity induced by an apnoea‐like stimulus

Aerobic organisms rely on oxygen (O2 ) as the final acceptor of the electrons from oxidative metabolism which is essential to keep electron flow through the respiratory chain, adenosine triphosphate (ATP) synthesis, and therefore cell function. This article is protected by copyright. All rights reserved.

Possible Breathing Influences on the Control of Arterial Pressure After Sino-aortic Denervation in Rats

Purpose of ReviewSurgical removal of the baroreceptor afferents [sino-aortic denervation (SAD)] leads to a lack of inhibitory feedback to sympathetic outflow, which in turn is expected to result in a large increase in mean arterial pressure (MAP). However, few days after surgery, the sympathetic nerve activity (SNA) and MAP of SAD rats return to a range similar to that observed in control rats. In this review, we present experimental evidence suggesting that breathing contributes to control of SNA and MAP following SAD.The purpose of this review was to discuss studies exploring SNA and MAP regulation in SAD rats, highlighting the possible role of breathing in the neural mechanisms of this modulation of SNA.Recent FindingsRecent studies show that baroreceptor afferent stimulation or removal (SAD) results in changes in the respiratory pattern.SummaryChanges in the neural respiratory network and in the respiratory pattern must be considered among mechanisms involved in the modulation of the MAP after SAD.

Sex differences in the respiratory-sympathetic coupling in rats exposed to chronic intermittent hypoxia

Obstructive sleep apnea (OSA) is a complex disease in which humans face episodes of intermittent hypoxia and it affects men and women. Patients with OSA present hypertension and sympathetic overactivity among several other dysfunctions. Therefore, one important question remains: are the autonomic dysfunctions associated with OSA similar in male and female? This is an unresolved question since sex factors are overlooked in most clinical and experimental studies. Epidemiological data indicate that sex exerts an important influence in the prevalence of OSA and associated comorbidities, such as hypertension. Sex hormones, genetic and neural factors probably are the main players underlying sex differences in the pathophysiology of OSA but they are not yet fully understood. We are using chronic intermittent hypoxia (CIH) as an experimental model of intermittent hypoxia such as those observed in OSA patients to investigate the cardiovascular, sympathetic and respiratory responses in female rats. Our recent studies show that adult and juvenile female rats exposed to CIH develop hypertension similar to age-matched CIH-male rats. Although both males and females develop hypertension after CIH, the most remarkable finding was that CIH-female rats develop changes in the respiratory modulation of sympathetic activity different from those observed in CIH-male rats, characterizing sex differences in the respiratory-sympathetic coupling in response to CIH. Specifically, in CIH-female rats, sympathetic overactivity is linked to inspiration while in CIH-male rats it is linked to the late phase of expiration. In this review we discuss the pathophysiological consequences of CIH, focusing in adult and juvenile female rats and how changes in the respiratory-sympathetic coupling may play a key role in CIH-induced sympathetic overactivity and hypertension in both male and female rats.

Corrigendum: Pacemaking Property of RVLM Presympathetic Neurons.

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