DEVELOPMENTAL REGULATION OF HYPERCAPNIC RESPONSES

描述(申请人提供)：早产儿呼吸暂停，这是不成熟的中枢调节呼吸控制机制的表现，在低出生体重儿中仍然是一个令人头疼的问题。因此，大量早产儿接受黄嘌呤治疗，尽管他们的确切作用机制尚不清楚。在这项提案的前一个资金周期中，我们已经证明了-氨基丁酸(GABA)-ERIC通路在抑制呼吸计时方面做出了巨大贡献，而呼吸计时是新生儿呼吸反射反应的特征。作为这项工作的自然继续，我们现在集中在GABA在调节腺苷对新生儿呼吸控制的影响中的作用。我们最新的初步数据在大鼠幼鼠身上提供了证据，证明腺苷A2A受体在脑干呼吸相关区域显著存在，并存在于含有GABA的神经元上。此外，给予A2A受体激动剂会引起吸气抑制，这种抑制在幼年动物中最严重，这种作用可被GABAA受体拮抗剂荷包牡丹碱阻断。因此，在这个建议中，我们试图检验这样的假设，即腺苷通过激活含有GABA的神经元上的A2A受体而引起吸气抑制，并且吸气相关神经元的抑制次要于GABA能影响的增加。在目标1中，我们假设这些腺苷A2A/GABA能相互作用在出生后早期最大。在目标2中，我们假设暴露于重复低氧和/或高二氧化碳通过增加GABA能神经元上A2A受体的表达和延髓节律产生部位(前Btzinger复合体)吸气相关神经元上GABA受体的表达来增加中枢介导的呼吸抑制。在这两个目标中，我们将在成熟的大鼠中使用我们拥有专长的神经解剖学和生理学研究。神经解剖学研究将利用免疫组织化学和分子技术，结合逆行示踪剂，确定呼吸相关GABA能神经元上A(2A)受体在消息和蛋白水平的存在，以及延髓节律发生部位(PBC)的GABA(A)受体的存在。生理学研究将使用整个动物和体外延髓切片来测量膈和舌下神经输出，除了单单位记录，以响应在目标部位应用腺苷受体激动剂和不使用GABA(A)受体阻断的情况。这些研究将为呼吸控制成熟过程中关键抑制性神经递质之间的相互作用、它们在新生儿呼吸暂停发病机制中的作用以及我们对常见药物策略如何调节这些现象的理解提供新的线索。

DESCRIPTION (provided by applicant): Apnea of prematurity, which is a manifestation of immature centrally mediated respiratory control mechanisms, remains a troublesome problem in low birth weight infants. As a consequence large numbers of preterm infants receive therapy with xanthines, although their precise mechanism of action is not clearly understood. In the prior funding cycle of this proposal, we have demonstrated that ?-aminobutyric acid (GABA)-ergic pathways contribute greatly to the inhibition of respiratory timing that characterizes respiratory reflex responses in the newborn. As a natural continuation of this work, we now focus on the role of GABA in mediating the effects of adenosine on neonatal respiratory control. Our most recent preliminary data provide evidence in rat pups that adenosine A2A receptors are prominent in respiratory related areas of the brainstem, and present on GABA containing neurons. Furthermore, administration of A2A receptor agonists induces inspiratory inhibition, which is greatest in the youngest animals, and this effect is blocked by the GABAA receptor antagonist bicuculline. In this proposal we therefore seek to test the hypothesis that adenosine elicits inspiratory inhibition via activation of A2A receptors on GABA containing neurons, and that inhibition of inspiratory related neurons is secondary to increased GABAergic influences. In Aim 1 we hypothesize that these adenosine A2A/GABAergic interactions are greatest in early postnatal life. In Aim 2 we hypothesize that exposure to repetitive hypoxia and/or hypercapnia increases centrally mediated respiratory inhibition by increasing A2A receptor expression on GABAergic neurons and GABAA receptor expression on inspiratory related neurons at the medullary rhythm-generating site (preBtzinger complex, pBc). In both aims we will use neuroanatomic and physiologic studies, with which we have expertise, in maturing rats. The neuroanatomic studies will employ immunohistochemical and molecular techniques combined with retrograde tracers to identify the presence of A(2A) receptor at message and protein levels on respiratory related GABAergic neurons, and GABA(A) receptors at the medullary rhythm generating site (pBc). The physiologic studies will employ whole animals and in vitro medullary slices to measure phrenic and hypoglossal neural output, in addition to single unit recording, in response to application of adenosine receptor agonists with and without GABA(A) receptor blockade at targeted sites. These studies should shed new light on interaction between key inhibitory neurotransmitters during maturation of respiratory control, their role in the pathogenesis of neonatal apnea and our understanding of how a common pharmacologic strategy modulates these phenomena.