Department of Physiology, Neuroscience and Mental Health Institute (NMHI), Women and Children's Health Research Institute (WCHRI), Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
Present address: Neurosciences & Mental Health, Peter Gilgan Centre for Research and Learning (PGCRL), The Hospital for Sick Children, Toronto, Ontario, Canada.
J Physiol. 2018 Aug;596(15):3245-3269. doi: 10.1113/JP274727. Epub 2017 Jul 27.
The ventilatory response to reduced oxygen (hypoxia) is biphasic, comprising an initial increase in ventilation followed by a secondary depression. Our findings indicate that, during hypoxia, astrocytes in the pre-Bötzinger complex (preBötC), a critical site of inspiratory rhythm generation, release a gliotransmitter that acts via P2Y receptors to stimulate ventilation and reduce the secondary depression. In vitro analyses reveal that ATP excitation of the preBötC involves P2Y receptor-mediated release of Ca from intracellular stores. By identifying a role for gliotransmission and the sites, P2 receptor subtype, and signalling mechanisms via which ATP modulates breathing during hypoxia, these data advance our understanding of the mechanisms underlying the hypoxic ventilatory response and highlight the significance of purinergic signalling and gliotransmission in homeostatic control. Clinically, these findings are relevant to conditions in which hypoxia and respiratory depression are implicated, including apnoea of prematurity, sleep disordered breathing and congestive heart failure.
The hypoxic ventilatory response (HVR) is biphasic, consisting of a phase I increase in ventilation followed by a secondary depression (to a steady-state phase II) that can be life-threatening in premature infants who suffer from frequent apnoeas and respiratory depression. ATP released in the ventrolateral medulla oblongata during hypoxia attenuates the secondary depression. We explored a working hypothesis that vesicular release of ATP by astrocytes in the pre-Bötzinger Complex (preBötC) inspiratory rhythm-generating network acts via P2Y receptors to mediate this effect. Blockade of vesicular exocytosis in preBötC astrocytes bilaterally (using an adenoviral vector to specifically express tetanus toxin light chain in astrocytes) reduced the HVR in anaesthetized rats, indicating that exocytotic release of a gliotransmitter within the preBötC contributes to the hypoxia-induced increases in ventilation. Unilateral blockade of P2Y receptors in the preBötC via local antagonist injection enhanced the secondary respiratory depression, suggesting that a significant component of the phase II increase in ventilation is mediated by ATP acting at P2Y receptors. In vitro responses of the preBötC inspiratory network, preBötC inspiratory neurons and cultured preBötC glia to purinergic agents demonstrated that the P2Y receptor-mediated increase in fictive inspiratory frequency involves Ca recruitment from intracellular stores leading to increases in intracellular Ca ([Ca ] ) in inspiratory neurons and glia. These data suggest that ATP is released by preBötC astrocytes during hypoxia and acts via P2Y receptors on inspiratory neurons (and/or glia) to evoke Ca release from intracellular stores and an increase in ventilation that counteracts the hypoxic respiratory depression.
氧减（缺氧）引起的通气反应呈双相性，包括通气初始增加，随后出现继发性抑制。我们的研究结果表明，在缺氧期间，前脑桥呼吸节律生成部位（preBötC）的星形胶质细胞释放一种神经胶质递质，通过 P2Y 受体发挥作用，刺激通气并减少继发性抑制。体外分析表明，preBötC 中的 ATP 兴奋涉及 P2Y 受体介导的细胞内储存 Ca 的释放。通过确定神经胶质递质传递以及 P2 受体亚型和信号机制在缺氧期间调节呼吸的作用，这些数据增进了我们对缺氧性通气反应机制的理解，并强调了嘌呤能信号和神经胶质递质传递在体内平衡控制中的重要性。临床上，这些发现与缺氧和呼吸抑制有关的情况有关，包括早产儿呼吸暂停、睡眠呼吸障碍和充血性心力衰竭。
缺氧性通气反应（HVR）呈双相性，包括通气初始增加，随后出现继发性抑制（进入稳定的 II 期），这在经常发生呼吸暂停和呼吸抑制的早产儿中可能是致命的。在延髓腹外侧区缺氧时释放的 ATP 减弱了继发性抑制。我们探索了一个工作假说，即在吸气节律生成网络的前脑桥呼吸节律生成部位（preBötC）中星形胶质细胞通过 P2Y 受体释放囊泡 ATP，以此来介导这种作用。双侧 preBötC 星形胶质细胞的囊泡胞吐作用阻断（使用腺相关病毒载体特异性表达破伤风毒素轻链在星形胶质细胞）降低了麻醉大鼠的 HVR，表明 preBötC 内神经胶质递质的胞吐释放有助于缺氧诱导的通气增加。单侧 preBötC 中 P2Y 受体的局部拮抗剂注射增强了继发性呼吸抑制，表明 II 期通气增加的一个重要组成部分是由 ATP 通过 P2Y 受体介导的。体外 preBötC 吸气网络、preBötC 吸气神经元和培养的 preBötC 胶质细胞对嘌呤能药物的反应表明，P2Y 受体介导的虚拟吸气频率增加涉及细胞内储存的 Ca 募集，导致吸气神经元和胶质细胞内细胞内 Ca（[Ca]）增加。这些数据表明，在缺氧期间，preBötC 星形胶质细胞释放 ATP，并通过 P2Y 受体作用于吸气神经元（和/或胶质细胞），从细胞内储存中释放 Ca，增加通气，从而抵消缺氧性呼吸抑制。
