Centrally acting adrenomedullin in the long-term potentiation of sympathetic vasoconstrictor activity induced by intermittent hypoxia in rats

Prenatal cannabinoid exposure affects central cardiorespiratory control in young male and female rats

Cannabis use among pregnant women is rising globally, mainly for recreational and medical reasons to relieve symptoms like nausea, vomiting, anxiety, and insomnia. This trend is reinforced by the misconception that its natural origin guarantees safety, along with government policies promoting legalization. However, exposure to cannabinoids in utero can impact normal offspring's neurodevelopment and induce malfunctioning of various physiological systems, including the cardiorespiratory function. The present study investigated whether prenatal cannabinoid exposure disrupts the generation and control of autonomic and respiratory activities in early adulthood. Using in situ preparations of juvenile male and female rats (27-28 days old) exposed to a synthetic cannabinoid (WIN 55,212-2; 0.5 mg/kg/day, n = 4-9) or vehicle (n = 3-10) during gestation, we analyzed the activity of nerves innervating respiratory muscles and blood vessels. We noticed that females receiving WIN prenatally exhibited a reduced excitatory drive (postinspiratory activity, post-I) to laryngeal muscles under resting conditions, suggesting impaired control of upper airway patency. Moreover, males and females exposed to WIN displayed reduced post-I and abdominal expiratory motor activities during stimulation of carotid body chemoreceptors (mimicking low-oxygen situations) or exposure to high carbon dioxide levels, indicating an inability to mount appropriate reflex respiratory motor responses during blood gas disturbances. In addition, WIN-treated males showed attenuated sympathoexcitatory responses to carotid body activation or hypercapnia, evidencing a limited capacity to promote sympathetic-mediated hemodynamic changes. Thus, manipulating the fetal endocannabinoid system impacts the development of networks controlling respiratory and autonomic functions, leading to negative, long-term consequences for ventilation and cardiovascular function.NEW & NOTEWORTHY Cannabis use among pregnant women is rising globally; however, the impact on offspring's homeostatic physiological systems is still uncertain. We found that prenatal cannabinoid exposure impairs respiratory motor control in early adulthood. We also identified that sympathetic control is limited in juvenile males exposed to cannabinoids prenatally. Cannabinoids during pregnancy disrupt offspring's central cardiorespiratory control, highlighting the need for caution regarding cannabis use during pregnancy and its postnatal implications.

Exogenous H2S targeting PI3K/AKT/mTOR pathway alleviates chronic intermittent hypoxia-induced myocardial damage through inhibiting oxidative stress and enhancing autophagy

AIMS

Hydrogen sulfide (H2S) is a novel gas signaling molecule that has been researched in several physiological and pathological conditions, indicating that strategies targeting H2S may provide clinical benefits in diseases such as chronic cardiomyopathy. Here, we reveal the effect of H2S on chronic intermittent hypoxia (CIH)-related myocardial damage and its mechanistic relevance to phosphoinositol-3 kinase (PI3K).

MATERIALS

Mice were subjected to a 4-week CIH process to induce myocardial damage, which was accompanied by daily administration of NaHS (a H2S donor) and LY294002 (an inhibitor of PI3K). Changes in heart function were evaluated via echocardiography. Histological examination was applied to assess heart tissue lesions. Myocardial apoptosis was detected by TUNEL staining and apoptosis-associated protein expression. Furthermore, the effects of NaHS on autophagy and the PI3K/AKT/mTOR pathway were investigated. Finally, the level of inflammation is also affected by related proteins.

KEY FINDINGS

The CIH group presented increased myocardial dysfunction and heart tissue lesions. Echocardiography and histological analysis revealed that, compared with control mice, CIH-treated mice presented significantly more severe left ventricular remodeling and decreased myocardial contractile function. In addition, the apoptosis index and oxidative markers were significantly elevated in the CIH group compared with those in the control group. The autophagy marker Beclin-1 was decreased, while p62 was elevated by CIH treatment. H2S supplementation with NaHS significantly improved cardiac function and alleviated fibrosis, oxidative stress, and apoptosis but upregulated autophagy in CIH mice, and these effects were also observed in animals that underwent only PI3K blockade. Furthermore, PI3K/AKT pathway-mediated inhibition of the mammalian target of rapamycin (mTOR) pathway, the Nrf2/HO-1 pathway and proinflammatory NF-κB activity were shown to play a role in the therapeutic effect of NaHS after CIH stimulation.

Adrenomedullin-mediated depressor response with visceral afferent-specific membrane depolarization in isolated nodose ganglion neurons from adult female rat

Adrenomedullin (ADM) is an endogenous and vasoactive neuropeptide that possesses potent central/peripheral regulations on blood pressure (BP) and sex-related vasodilation under physiological conditions. However, the role of ADM on baroreflex afferent function is largely unknown. Here, BP was monitored in adult female rats while ADM was microinjected into the nodose ganglion (NG); Fluorescent intensity against ADM was analyzed in the tissue level and membrane responses elicited by ADM were tested in identified NG neurons isolated from adult female rats with gap-free protocol under current-clamp mode with or without ADM antagonist. The results showed that BP was reduced by ADM (30-300 nM) concentration-dependently; myelinated (HCN1-positive) neurons showed significantly higher fluorescent intensity against ADM antibody vs. unmyelinated (HCN1-negative) neurons. Interestingly, patch-clamp data indicated that membrane potential was not changed in 50 % (6/12) of identified A-types, only 4/12 was hyperpolarized by 30 nM ADM, while 100 nM ADM induced brief hyperpolarization followed by depolarization in 2/12 of recordings; Robustly, ADM depolarized 100 % tested myelinated Ah-type neurons with dramatic and concentration-dependent repetitive discharges; While, a majority (8/9) of unmyelinated C-types were depolarized and few with repetitive dischargers. By application of ADM (22-52), the depolarization elicited by ADM 100 nM was partially or completely abolished in Ah-types or C-types, respectively. These datasets demonstrated for the first time that baroreflex afferents especially female-distributed subpopulation of Ah-types would be a key player in ADM-mediated depressor response unveiling the dominate role of peripheral ADM in neurocontrol of hypotension via baroreflex afferent function and gender-dependent vasodilation promoted by female sex steroid.

Postinspiratory and preBötzinger complexes contribute to respiratory-sympathetic coupling in mice before and after chronic intermittent hypoxia

The sympathetic nervous system modulates arterial blood pressure. Individuals with obstructive sleep apnea (OSA) experience numerous nightly hypoxic episodes and exhibit elevated sympathetic activity to the cardiovascular system leading to hypertension. This suggests that OSA disrupts normal respiratory-sympathetic coupling. This study investigates the role of the postinspiratory complex (PiCo) and preBötzinger complex (preBötC) in respiratory-sympathetic coupling under control conditions and following exposure to chronic intermittent hypoxia (CIH) for 21 days (5% O2-80 bouts/day). The surface of the ventral brainstem was exposed in urethane (1.5 g/kg) anesthetized, spontaneously breathing adult mice. Cholinergic (ChAT), glutamatergic (Vglut2), and neurons that co-express ChAT and Vglut2 at PiCo, as well as Dbx1 and Vglut2 neurons at preBötC, were optogenetically stimulated while recording activity from the diaphragm (DIA), vagus nerve (cVN), and cervical sympathetic nerve (cSN). Following CIH exposure, baseline cSN activity increased, breathing frequency increased, and expiratory time decreased. In control mice, stimulating PiCo specific cholinergic-glutamatergic neurons caused a sympathetic burst during all phases of the respiratory cycle, whereas optogenetic activation of cholinergic-glutamatergic PiCo neurons in CIH mice increased sympathetic activity only during postinspiration and late expiration. Stimulation of glutamatergic PiCo neurons increased cSN activity during the postinspiratory phase in control and CIH mice. Optogenetic stimulation of ChAT containing neurons in the PiCo area did not affect sympathetic activity under control or CIH conditions. Stimulating Dbx1 or Vglut2 neurons in preBötC evoked an inspiration and a concomitant cSN burst under control and CIH conditions. Taken together, these results suggest that PiCo and preBötC contribute to respiratory-sympathetic coupling, which is altered by CIH, and may contribute to the hypertension observed in patients with OSA.

The Cardiovascular and Metabolic Effects of Chronic Hypoxia in Animal Models: A Mini-Review

Animal models are useful to understand the myriad physiological effects of hypoxia. Such models attempt to recapitulate the hypoxemia of human disease in various ways. In this mini-review, we consider the various animal models which have been deployed to understand the effects of chronic hypoxia on pulmonary and systemic blood pressure, glucose and lipid metabolism, atherosclerosis, and stroke. Chronic sustained hypoxia (CSH)-a model of chronic lung or heart diseases in which hypoxemia may be longstanding and persistent, or of high altitude, in which effective atmospheric oxygen concentration is low-reliably induces pulmonary hypertension in rodents, and appears to have protective effects on glucose metabolism. Chronic intermittent hypoxia (CIH) has long been used as a model of obstructive sleep apnea (OSA), in which recurrent airway occlusion results in intermittent reductions in oxyhemoglobin saturations throughout the night. CIH was first shown to increase systemic blood pressure, but has also been associated with other maladaptive physiological changes, including glucose dysregulation, atherosclerosis, progression of nonalcoholic fatty liver disease, and endothelial dysfunction. However, models of CIH have generally been implemented so as to mimic severe human OSA, with comparatively less focus on milder hypoxic regimens. Here we discuss CSH and CIH conceptually, the effects of these stimuli, and limitations of the available data.

Advancing respiratory-cardiovascular physiology with the working heart-brainstem preparation over 25 years

Twenty‐five years ago, a new physiological preparation called the working heart–brainstem preparation (WHBP) was introduced with the claim it would provide a new platform allowing studies not possible before in cardiovascular, neuroendocrine, autonomic and respiratory research. Herein, we review some of the progress made with the WHBP, some advantages and disadvantages along with potential future applications, and provide photographs and technical drawings of all the customised equipment used for the preparation. Using mice or rats, the WHBP is an in situ experimental model that is perfused via an extracorporeal circuit benefitting from unprecedented surgical access, mechanical stability of the brain for whole cell recording and an uncompromised use of pharmacological agents akin to in vitro approaches. The preparation has revealed novel mechanistic insights into, for example, the generation of distinct respiratory rhythms, the neurogenesis of sympathetic activity, coupling between respiration and the heart and circulation, hypothalamic and spinal control mechanisms, and peripheral and central chemoreceptor mechanisms. Insights have been gleaned into diseases such as hypertension, heart failure and sleep apnoea. Findings from the in situ preparation have been ratified in conscious in vivo animals and when tested have translated to humans. We conclude by discussing potential future applications of the WHBP including two‐photon imaging of peripheral and central nervous systems and adoption of pharmacogenetic tools that will improve our understanding of physiological mechanisms and reveal novel mechanisms that may guide new treatment strategies for cardiorespiratory diseases.