Renato Willian Martins Sá

The parasympathetic efferent innervation to the respiratory airways controls bronchoconstriction and mucus secretion. It is known that the parasympathetic respiratory motoneurones (PRMNs) projecting to the airways are located in the nucleus ambiguus (NA) and dorsal motor nucleus of the vagus (DMV). Although NA PRMNs are known to regulate bronchoconstriction in both physiological and pathological conditions, the electrophysiological properties of DMV PRMNs and their functional role in regulating the airways are not entirely clear. Retrograde labelling, neuronal and ventilatory recordings, optogenetics, chemogenetics, and histological and molecular analyses in vitro and in vivo preparations of rats were performed to evaluate the electrophysiological characteristics controlling the activity of DMV PRMNs and their role in airway mucus secretion. DMV PRMNs present K ⁺ ‐dominated leak currents, mediated by two‐pore domain TWIK‐2 channels, which regulate their resting membrane potential, firing frequency and excitation by acidosis. Acidosis also reduces synaptic inhibition to these motoneurones and activates astrocytes in the DMV. Furthermore, optogenetic activation of astrocytes induced action potentials in DMV PRMNs, mediated by glutamatergic NMDA receptor excitation. Finally, chemogenetic activation of DMV PRMNs evoked mucus secretion in respiratory airways and increases sighing, without affecting inflammatory cell infiltration, pulmonary ventilation, oxygen consumption or heart rate. Therefore, our data demonstrate that TWIK‐2 leak channels and astrocytes signalling regulate the activity of DMV PRMNs and their role in airway mucus secretion of rats. image Key points: Parasympathetic respiratory motoneurones (PRMNs) of the dorsal motor nucleus of the vagus (DMV) present K+‐dominated leak currents, mediated by TWIK‐2 channels, regulating their resting membrane potential, firing frequency and excitation by acidosis. Acidosis also reduces synaptic inhibition to DMV PRMNs and activates astrocytes in the DMV. Activation of DMV astrocytes induced action potentials in PRMNs, mediated by glutamatergic NMDA receptor excitation. Activation of DMV PRMNs evoked mucus secretion in respiratory airways and increased sighing, without affecting pulmonary ventilation, oxygen consumption or heart rate. TWIK‐2 leak channels and astrocytes signalling regulate the activity of DMV PRMNs and their role in airway mucus secretion of rats.

BACKGROUND: Hypertension is the single most important risk factor for cardiovascular diseases and remains poorly controlled. Currently, 40% of treated patients remain hypertensive. We propose that this is in part due to excessive sympathetic activity. We hypothesized that neuronal expiratory oscillations, in the medullary lateral parafacial (pFL) region, become activated in conditions of neurogenic hypertension and that silencing their activity would be antihypertensive. METHODS: pFL neurons were manipulated by viral transfection. Using optogenetic and pharmacogenetic modulation, pFL neurons were either excited or inhibited in rats while recording sympathetic neurons from the rostral ventrolateral medulla (RVLM) and pontine noradrenergic A5 region, sympathetic activity, respiratory motor outflows, and arterial pressure from normotensive and hypertensive rats in vitro, in situ, and in vivo. Rats were made neurogenically hypertensive using chronic intermittent hypoxia. RESULTS: Optogenetic activation of pFL neurons triggered active expiration and positively modulated sympathetic activity during expiration, causing blood pressure to rise. pFL neurons projected to the RVLM and A5 presympathetic neurons and excited them during expiration, but in hypertension, only the pFL-RVLM synaptic transmission was enhanced. Pharmacogenetic inhibition of pFL neurons eliminated the expiratory-related sympatho-excitation and normalized arterial pressure in hypertensive rats. CONCLUSIONS: The heightened sympathetic activity inducing hypertension triggered by chronic intermittent hypoxia is caused, in the most part, by the emergence of pFL expiratory oscillations driving RVLM and A5 sympathetic vasomotor neurons and active expiration simultaneously. We propose that suppressing pFL neurons would have therapeutic potential.

Evidence suggests that hypertension induced by high salt intake is correlated with an autonomic imbalance that favours sympathetic hyperactivity and an increase in vascular resistance, indicating a neurogenic component to this pathology. Although there are several animal models in which to study salt‐induced hypertension with prolonged exposure to a high‐sodium diet, here we sought to investigate whether the increase in arterial blood pressure of rats subjected to a short exposure to high salt, with 2% NaCl drinking solution instead of water, relies on changes in the circulating blood volume. Male Wistar rats were divided randomly into three groups: euhydrated (EU, n = 10), salt loaded (SL, n = 13) and water deprived (WD, n = 6). The SL rats exhibited a significant increase in mean arterial blood pressure, with a large low‐frequency component of systolic arterial blood pressure variability, when compared with the EU group. Circulating blood volume did not differ between SL and EU rats, but it was lower in WD rats. Compared with EU rats, the [Na⁺] in cerebrospinal fluid was higher in SL rats and similar in magnitude to the WD rats. Plasma [Na⁺] did not differ between SL and EU rats, but it was higher in WD rats. Collectively, our data suggest that the hypertension induced by a short exposure to high salt intake closely resembles a neurogenic mechanism, but not a blood volume‐dependent mechanism, with cumulative [Na⁺] in the cerebrospinal fluid that could be associated with changes in the neurochemistry of autonomic nuclei, which are highly susceptible to osmotic stress related to high salt consumption.

New Findings: What is the central question of this study? In this study, we sought to investigate whether cardiovascular responses to peripheral chemoreflex activation of rats recovered from protein restriction are related to activation of AT₁ receptors. What is the main finding and its importance? This study highlights the fact that angiotensinergic mechanisms activated by AT₁ receptors do not support increased responses to peripheral chemoreflex activation by KCN in rats recovered from protein restriction. Also, we found that protein restriction led to increased resting ventilation in adult rats, even after recovery. The effects of a low‐protein diet followed by recovery on cardiorespiratory responses to peripheral chemoreflex activation were tested before and after systemic angiotensin II type 1 (AT₁) receptor antagonism. Male Fischer rats were divided into control and recovered (R‐PR) groups after weaning. The R‐PR rats were fed a low‐protein (8%) diet for 35 days and recovered with a normal protein (20%) diet for 70 days. Control rats received a normal protein diet for 105 days (CG₁₀₅). After cannulation surgery, mean arterial pressure, heart rate, respiratory frequency, tidal volume and minute ventilation were acquired using a digital recording system in freely moving rats. The role of angintensin II was evaluated by systemic antagonism of AT₁ receptors with losartan (20 mg kg⁻¹ i.v.). The peripheral chemoreflex was elicited by increasing doses of KCN (20–160 μg kg min⁻¹, i.v.). At baseline, R‐PR rats presented increased heart rate and minute ventilation (372 ± 34 beats min⁻¹ and 1.274 ± 377 ml kg⁻¹ min⁻¹) compared with CG₁₀₅ animals (332 ± 22 beats min⁻¹ and 856 ± 112 ml kg⁻¹ min⁻¹). Mean arterial pressure was not different between the groups. Pressor and bradycardic responses evoked by KCN (60 μg kg⁻¹) were increased in R‐PR (+45 ± 13 mmHg and −77 ± 47 beats min⁻¹) compared with CG₁₀₅ rats (+25 ± 17 mmHg and −27 ± 28 beats min⁻¹), but no difference was found in the tachypnoeic response. These differences were preserved after losartan. The data suggest that angiotensin II acting on AT₁ receptors may not be associated with the increased heart rate, increased minute ventilation and acute cardiovascular responses to peripheral chemoreflex activation in rats that underwent postweaning protein restriction followed by recovery.