TASK1 and TASK3 in orexin neuron of lateral hypothalamus contribute to respiratory chemoreflex by projecting to nucleus tractus solitarius

TWIK-related acid-sensitive potassium channels TASK-1 and TASK-3 may participate in the process of the coexistence of asthma and OSA

OBJECTIVE

To investigate the role of TWIK-related acid-sensitive potassium channels TASK-1 and TASK-3 in the mechanism of asthma combined with obstructive sleep apnea (OSA) in mice.

METHOD

C57BL/6 mice were randomly divided into four groups: control group (NS-RA), asthma group (OVA-RA), OSA group (NS-IH), and asthma combined with OSA group (OVA-IH). After monitoring lung function in each group, the expression levels of TASK-1 and TASK-3 mRNA and protein in lung tissues were measured, and the correlation between the changes of both and lung function was analyzed.

RESULTS

A total of 64 male mice were studied. Penh, serum IgE concentrations, and the percentage of eosinophils in bronchoalveolar lavage fluid (BALF) were higher in OVA-RA and OVA-IH mice compared with NS-RA (P < 0.05),while the above indexes were slightly elevated in NS-IH mice compared with NS-RA (P > 0.05), where the Penh and the percentage of eosinophils in BALF was higher in OVA-IH mice than NS-IH (P < 0.05).Increased TASK-3 mRNA expression (P < 0.05) as well as TASK-1 and TASK-3 protein expression (P > 0.05) in lung tissues of OVA-RA and NS-IH mice compared with NS-RA, and TASK-3 mRNA expression was slightly more in the OVA-IH group compared with NS-RA (P > 0.05), but less compared with OVA-RA (P < 0.05) or NS-IH (P > 0.05), while TASK-1 and TASK-3 protein expression was increased in the OVA-IH group compared with the remaining three groups, and TASK-3 protein expression was associated with lung function impairment was positively correlated with the degree of lung function impairment (P < 0.05).

CONCLUSION

Task-1 and Task-3 may be involved in the pathogenesis of asthma with OSA by affecting lung function.

Estrogens, age, and, neonatal stress: panic disorders and novel views on the contribution of non-medullary structures to respiratory control and CO2 responses

CO₂ is a fundamental component of living matter. This chemical signal requires close monitoring to ensure proper match between metabolic production and elimination by lung ventilation. Besides ventilatory adjustments, CO₂ can also trigger innate behavioral and physiological responses associated with fear and escape but the changes in brain CO₂/pH required to induce ventilatory adjustments are generally lower than those evoking fear and escape. However, for patients suffering from panic disorder (PD), the thresholds for CO₂-evoked hyperventilation, fear and escape are reduced and the magnitude of those reactions are excessive. To explain these clinical observations, Klein proposed the false suffocation alarm hypothesis which states that many spontaneous panics occur when the brain's suffocation monitor erroneously signals a lack of useful air, thereby maladaptively triggering an evolved suffocation alarm system. After 30 years of basic and clinical research, it is now well established that anomalies in respiratory control (including the CO₂ sensing system) are key to PD. Here, we explore how a stress-related affective disorder such as PD can disrupt respiratory control. We discuss rodent models of PD as the concepts emerging from this research has influenced our comprehension of the CO₂ chemosensitivity network, especially structure that are not located in the medulla, and how factors such as stress and biological sex modulate its functionality. Thus, elucidating why hormonal fluctuations can lead to excessive responsiveness to CO₂ offers a unique opportunity to gain insights into the neuroendocrine mechanisms regulating this key aspect of respiratory control and the pathophysiology of respiratory manifestations of PD.

The integrated brain network that controls respiration

Respiration is a brain function on which our lives essentially depend. Control of respiration ensures that the frequency and depth of breathing adapt continuously to metabolic needs. In addition, the respiratory control network of the brain has to organize muscular synergies that integrate ventilation with posture and body movement. Finally, respiration is coupled to cardiovascular function and emotion. Here, we argue that the brain can handle this all by integrating a brainstem central pattern generator circuit in a larger network that also comprises the cerebellum. Although currently not generally recognized as a respiratory control center, the cerebellum is well known for its coordinating and modulating role in motor behavior, as well as for its role in the autonomic nervous system. In this review, we discuss the role of brain regions involved in the control of respiration, and their anatomical and functional interactions. We discuss how sensory feedback can result in adaptation of respiration, and how these mechanisms can be compromised by various neurological and psychological disorders. Finally, we demonstrate how the respiratory pattern generators are part of a larger and integrated network of respiratory brain regions.

CO2 exposure enhances Fos expression in hypothalamic neurons in rats during the light and dark phases of the diurnal cycle

Orexinergic (OX) neurons in the lateral hypothalamus (LH), perifornical area (PFA) and dorsomedial hypothalamus (DMH) play a role in the hypercapnic ventilatory response, presumably through direct inputs to central pattern generator sites and/or through interactions with other chemosensitive regions. OX neurons can produce and release orexins, excitatory neuropeptides involved in many functions, including physiological responses to changes in CO₂/pH. Thus, in the present study, we tested the hypothesis that different nuclei (LH, PFA and DMH) where the orexinergic neurons are located, show distinct activation by CO₂ during the light-dark cycle phases. For this purpose, we evaluated the Fos and OXA expression by immunohistochemistry to identify neurons that co-localize Fos + OXA in the LH, LPeF, MPeF and DMH in the light-inactive and dark-active phase in Wistar rats subjected to 3 h of normocapnia or hypercapnia (7% CO₂). Quantitative analyses of immunoreactive neurons show that hypercapnia caused an increase in the number of neurons expressing Fos in the LH, LPeF, MPeF and DMH in the light and dark phases. In addition, the number of Fos + OXA neurons increased in the LPeF and DMH independently of the phases of the diurnal cycle; whereas in the MPeF, this increase was observed exclusively in the light phase. Thus, we suggest that OX neurons are selectively activated by hypercapnia throughout the diurnal cycle, reinforcing the differential role of nuclei in the hypothalamus during central chemosensitivity.

Orexin facilitates the ventilatory and behavioral responses of rats to hypoxia

Orexin neurons are sensitive to CO2 and contribute to cardiorespiratory homeostasis as well as sensorimotor control. Whether orexin facilitates respiratory and behavioral responses to acute hypoxia is unclear. We hypothesized that orexin neurons are activated by acute hypoxia and that orexin facilitates the hypoxic ventilatory response (HVR), as well as the arterial blood pressure (ABP) and behavioral (movement) responses to acute hypoxia. We further hypothesized that orexin has greater effects in the active phase of the rat circadian cycle, when orexin neurons have high activity. Using whole body plethysmography with EEG, EMG, and the dual-orexin receptor (OxR) antagonist suvorexant (20 mg/kg ip), we determined the effect of OxR blockade on the respiratory, ABP, and behavioral responses of adult rats to acute, graded hypoxia ([Formula: see text]= 0.15, 0.13, 0.11, and 0.09) and hyperoxic hypercapnia ([Formula: see text]= 0.05; [Formula: see text]= 0.95). OxR blockade had no effect on eupnea. OxR blockade significantly reduced the HVR in both inactive and active phases, with a stronger effect in the active phase. OxR blockade reduced the behavioral response to acute hypoxia in the active phase. The central component of the ventilatory and the ABP responses to hypercapnia were reduced by OxR blockade solely in the inactive phase. In the inactive phase, hypoxia activated ∼10% of orexin neurons in the perifornical hypothalamus. These data suggest that orexin neurons participate in the peripheral chemoreflex to facilitate the ventilatory and behavioral responses to acute hypoxia in rats, particularly in the active phase. Orexin also facilitates central chemoreflex responses to CO2 in the inactive phase.

Neuroanatomical Basis for the Orexinergic Modulation of Anesthesia Arousal and Pain Control

Hypothalamic orexin (hypocretin) neurons play crucial roles in arousal control. Their involvement in anesthesia and analgesia remains to be better understood. In order to enhance our view on the neuroanatomy, we systematically mapped the projections of orexin neurons with confocal microscope and light sheet microscope. We specifically expressed optogenetic opsins tagged with fluorescence markers in orexin neurons through adeno-associated viral infection in the mouse brain. The imaging results revealed fine details and novel features of the orexin projections throughout the brain, particularly related to the nuclei regulating arousal and pain. We then optogenetically activated orexin neurons in the lateral hypothalamus to study the effects on anesthesia-related behaviors. cFos staining showed that optogenetic stimulation can activate orexin neurons in the ChR2-mCherry group, but not the control mCherry group (62.86 ± 3.923% vs. 7.9 ± 2.072%; P < 0.0001). In behavior assays, optogenetic stimulation in the ChR2-mCherry group consistently elicited robust arousal from light isoflurane anesthesia (9.429 ± 3.804 s vs. 238.2 ± 17.42 s; P < 0.0001), shortened the emergence time after deep isoflurane anesthesia (109.5 ± 13.59 s vs. 213.8 ± 21.77 s; P = 0.0023), and increased the paw withdrawal latency in a hotplate test (11.45 ± 1.185 s vs. 8.767 ± 0.7775; P = 0.0317). The structural details of orexin fibers established the neuroanatomic basis for studying the role of orexin in anesthesia and analgesia.

Sleep-disordered breathing in school-aged children with Prader-Willi Syndrome

STUDY OBJECTIVES

Studies of sleep-disordered breathing (SDB) in children with Prader-Willi syndrome (PWS) have focused on early childhood and growth hormone (GH)-naïve children, but little is known about older children, including those on long term GH therapy. This study aimed to describe the nature and prevalence of SDB in school-aged children with PWS in the growth hormone era.

METHODS

This retrospective single-center chart review included children aged 6-18 years with PWS who had overnight polysomnography not involving respiratory support over five years (2012-2017). The main outcome measures were the presence of obstructive sleep apnea, central sleep apnea or hypoventilation defined by an elevated PCO₂ as per standard pediatric criteria.

RESULTS

Seventeen children (8 male, median age 11.6y, range 6.6-16.1y) were included. Fifteen demonstrated SDB of different types: central sleep apnea (18%), obstructive sleep apnea (24%), both obstructive and central sleep apnea (29%), or hypoventilation without obstructive or central sleep apnea (18%). Twelve (71%) children had evidence of hypoventilation. Those with hypoventilation had a higher central apnea-hypopnea index (AHI) but no difference in the obstructive AHI, age, sex, growth parameters, or the presence of scoliosis or sleep-related symptoms compared to those without hypoventilation.

CONCLUSIONS

Sleep-related hypoventilation is common in school-aged children with PWS. The presence of central sleep apnea, including the quantification of central hypopneas, but not obstructive sleep apnea or clinical factors predicted the presence of hypoventilation. Long-term polysomnography surveillance in children with PWS should include identification of central hypopneas and measurement of continuous pCO₂.