Designer Receptors Exclusively Activated by Designer Drugs Approach to Treatment of Sleep-disordered Breathing.

Rationale: Obstructive sleep apnea is recurrent upper airway obstruction caused by a loss of upper airway muscle tone during sleep. The main goal of our study was to determine if designer receptors exclusively activated by designer drugs (DREADD) could be used to activate the genioglossus muscle as a potential novel treatment strategy for sleep apnea. We have previously shown that the prototypical DREADD ligand clozapine-N-oxide increased pharyngeal diameter in mice expressing DREADD in the hypoglossal nucleus. However, the need for direct brainstem viral injections and clozapine-N-oxide toxicity diminished translational potential of this approach, and breathing during sleep was not examined.Objectives: Here, we took advantage of our model of sleep-disordered breathing in diet-induced obese mice, retrograde properties of the adeno-associated virus serotype 9 (AAV9) viral vector, and the novel DREADD ligand J60.Methods: We administered AAV9-hSyn-hM3(Gq)-mCherry or control AAV9 into the genioglossus muscle of diet-induced obese mice and examined the effect of J60 on genioglossus activity, pharyngeal patency, and breathing during sleep.Measurements and Main Results: Compared with control, J60 increased genioglossus tonic activity by greater than sixfold and tongue uptake of 2-deoxy-2-[18F]fluoro-d-glucose by 1.5-fold. J60 increased pharyngeal patency and relieved upper airway obstruction during non-REM sleep.Conclusions: We conclude that following intralingual administration of AAV9-DREADD, J60 can activate the genioglossus muscle and improve pharyngeal patency and breathing during sleep.

Loss of Brain-Derived Neurotrophic Factor Mediates Inhibition of Hippocampal Long-Term Potentiation by High-Intensity Sound.

Exposure to noise produces cognitive and emotional disorders, and recent studies have shown that auditory stimulation or deprivation affects hippocampal function. Previously, we showed that exposure to high-intensity sound (110 dB, 1 min) strongly inhibits Schaffer-CA1 long-term potentiation (LTP). Here we investigated possible mechanisms involved in this effect. We found that exposure to 110 dB sound activates c-fos expression in hippocampal CA1 and CA3 neurons. Although sound stimulation did not affect glutamatergic or GABAergic neurotransmission in CA1, it did depress the level of brain-derived neurotrophic factor (BDNF), which is involved in promoting hippocampal synaptic plasticity. Moreover, perfusion of slices with BDNF rescued LTP in animals exposed to sound stimulation, whereas BDNF did not affect LTP in sham-stimulated rats. Furthermore, LM22A4, a TrkB receptor agonist, also rescued LTP from sound-stimulated animals. Our results indicate that depression of hippocampal BDNF mediates the inhibition of LTP produced by high-intensity sound stimulation.

Inhaled molecular hydrogen attenuates intense acute exercise-induced hippocampal inflammation in sedentary rats.

Physical exercise-induced inflammation may be beneficial when exercise is regular but it may be harmful when exercise is intense and performed by unaccustomed individuals/rats. Molecular hydrogen (H2) has recently emerged as a powerful anti-inflammatory, antioxidant and anti-apoptotic molecule in a number of pathological conditions, but little is known about its putative role under physiological conditions such as physical exercise. Therefore, we tested the hypothesis that H2 decreases intense acute exercise-induced inflammation in the hippocampus, since it is a brain region particularly susceptible to inflammation. Moreover, we also assessed hippocampus oxidative status. Rats ran on a sealed treadmill inhaling either the H2 (2% H2, 21% O2, balanced with N2) or the control gas (0% H2, 21% O2, balanced with N2) and hippocampal samples were collected immediately or 3 h after exercise. We measured hippocampal levels of cytokines [tumor necrosis factor-α (TNF-α), interleukin (IL)-1ß, IL-6 and IL-10] and oxidative markers [superoxide dismutase (SOD), thiobarbituric acid reactive species (TBARS) and nitrite/nitrate (NOx)]. Exercise increased TNF-α, IL-6 and IL-10 immediately after the session, whereas no change in IL-1ß levels was observed. Conversely, exercise did not cause any change in SOD activity, TBARS and NOx levels. H2 inhibited the exercise-induced surges in TNF-α and IL-6, and potentiated the IL-10 surge, immediately after the exercise. Moreover, no change in IL1-ß levels of rats inhaling H2 was observed. Regarding the oxidative stress markers, H2 failed to cause any change in SOD activity, TBARS and NOx levels. No significant change was observed in any of the assessed parameters 3 h after the exercise bout. These data are consistent with the notion that H2 acts as a powerful anti-inflammatory agent not only down-modulating pro-inflammatory cytokines (TNF-α and IL-6) but also upregulating an anti-inflammatory cytokine (IL-10) production without affecting the local oxidative stress status. These data indicate that H2 effectively decreases exercise-induced inflammation in the hippocampus, despite the fact that this region is particularly prone to inflammatory insults.

Firing properties of ventral medullary respiratory neurons in sino-aortic denervated rats.

NEW FINDINGS: What is the central question of this study? After sino-aortic denervation (SAD), rats present normal levels of mean arterial pressure (MAP), high MAP variability and changes in breathing. However, mechanisms involved in SAD-induced respiratory changes and their impact on the modulation of sympathetic activity remain unclear. Herein, we characterized the firing frequency of medullary respiratory neurons after SAD. What is the main finding and its importance? Sino-aortic denervation-induced prolonged inspiration was associated with a reduced interburst frequency of pre-inspiratory/inspiratory neurons and an increased long-term variability of late inspiratory neurons, but no changes were observed in the ramp-inspiratory and post-inspiratory neurons. This imbalance in the respiratory network might contribute to the modulation of sympathetic activity after SAD. ABSTRACT: In previous studies, we documented that after sino-aortic denervation (SAD) in rats there are significant changes in the breathing pattern, but no significant changes in sympathetic activity and mean arterial pressure compared with sham-operated rats. However, the neural mechanisms involved in the respiratory changes after SAD and the extent to which they might contribute to the observed normal sympathetic activity and mean arterial pressure remain unclear. Here, we hypothesized that after SAD, rats present with changes in the firing frequency of the ventral medullary inspiratory and post-inspiratory neurons. To test this hypothesis, male Wistar rats underwent SAD or sham surgery and 3 days later were surgically prepared for an in situ experiment. The duration of inspiration significantly increased in SAD rats. During inspiration, the total firing frequency of ramp-inspiratory, pre-inspiratory/inspiratory and late-inspiratory neurons was not different between groups. During post-inspiration, the total firing frequency of post-inspiratory neurons was also not different between groups. Furthermore, the data demonstrate a reduced interburst frequency of pre-inspiratory/inspiratory neurons and an increased long-term variability of late-inspiratory neurons in SAD compared with sham-operated rats. These findings indicate that the SAD-induced prolongation of inspiration was not accompanied by alterations in the total firing frequency of the ventral medullary respiratory neurons, but it was associated with changes in the long-term variability of late-inspiratory neurons. We suggest that the timing imbalance in the respiratory network in SAD rats might contribute to the modulation of presympathetic neurons after removal of baroreceptor afferents.

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

NEW FINDINGS: 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. ABSTRACT: Chronic intermittent hypoxia (CIH) and one-kidney, one-clip (1K, 1C) experimental models lead to sympathetic overactivity and hypertension. We hypothesized that previous exposure to CIH potentiates the development of 1K, 1C renal hypertension. Male rats were divided into the following four groups: Control-1K, 1C, maintained under normoxia followed by 1K, 1C surgery (n = 19); Control-Sham, maintained under normoxia, followed by sham surgery (n = 19); CIH-1K, 1C, exposed to CIH (10 days) and 1K, 1C surgery (n = 19); and CIH-Sham, exposed to CIH and sham surgery (n = 18). Animals were catheterized 8 days after 1K, 1C or Sham surgeries and cardiovascular and respiratory parameters recorded on the following day. Baseline mean arterial pressure was higher in Control-1K, 1C than in Control-Sham rats (P < 0.05) and was higher in CIH-1K, 1C than in CIH-Sham rats (P < 0.05). However, the increase in mean arterial pressure in CIH-1K, 1C animals was significantly blunted in comparison to Con-1K, 1C rats (P < 0.05), indicating that previous exposure to CIH attenuates the development of renal hypertension. Systemic administration of hexamethonium, a ganglionic blocker, promoted a larger hypotensive response in Con-1K, 1C compared with CIH-1K, 1C rats (P < 0.05), suggesting that sympathetic activity was attenuated in rats previously exposed to the CIH protocol. In addition, removal of the carotid bodies before 1K, 1C renal hypertension eliminated the protective effect of CIH preconditioning on the development of the 1K, 1C hypertension. We conclude that previous exposure to CIH attenuates the development of renal hypertension via a carotid body-dependent mechanism.

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

PURPOSE OF REVIEW: Surgical 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 FINDINGS: Recent studies show that baroreceptor afferent stimulation or removal (SAD) results in changes in the respiratory pattern. Changes in the neural respiratory network and in the respiratory pattern must be considered among mechanisms involved in the modulation of the MAP after SAD.

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

NEW FINDINGS: 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. Sino-aortic denervated (SAD) rats exhibit a mean arterial pressure (MAP) similar to that of control rats. Given that respiration modulates MAP, we hypothesized that conscious SAD rats show respiratory changes associated with the normal MAP. In this study, we evaluated the cardiovascular and respiratory activities and arterial blood gases in control and SAD rats. Male juvenile Wistar rats (postnatal day 19-21) were submitted to SAD, sham surgery or selective removal of the carotid bodies (CBX), and the three groups were evaluated 10 days after the surgery (SAD, n = 21; Sham, n = 18; and CBX, n = 13). The MAP in Sham, SAD and CBX groups was similar (P > 0.05), but the variability of MAP was significantly higher in SAD than in Sham and CBX rats (P < 0.0001). The duration of expiration and inspiration increased in SAD rats compared with Sham and CBX rats, which resulted in a reduced respiratory frequency and minute ventilation (P < 0.05). The arterial partial pressure of O2 and the haemoglobin saturation were reduced in SAD and CBX compared with Sham rats, whereas the arterial partial pressure of CO2 was increased in SAD compared with Sham rats. The short- and long-term respiratory variability were significantly higher in SAD than in Sham and CBX rats (P < 0.05). In addition, the reductions in MAP during deep breaths were greater in SAD than in Sham and CBX rats (P < 0.0001). The data show that SAD rats exhibit respiratory changes, which may be one of the compensatory mechanisms associated with the maintenance of normal levels of MAP in the absence of arterial baroreceptors.