1999 — 2010 |
Ramirez, Jan M. |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Hypoxic Effects On Mammalian Respiratory Neural Network
DESCRIPTION (Adapted from the applicant's abstract): Every year numerous victims suffer brain damage from hypoxic and anoxic insults. To understand the underlying cellular mechanisms this project examines the anoxic effects on the central respiratory network of mice. This network can be isolated in a brainstem slice preparation which generates spontaneously respiratory rhythmic activity. Slices obtained from mice older than one week respond to anoxia in a very similar way as the chemoafferent-denervated but otherwise intact respiratory system. Therefore this preparation will be employed as a model to study the anoxic response of the central respiratory network. The research plan bridges the network, cellular and molecular level using various electrophysiological and pharmacological techniques. Extra and intracellular recording techniques as well as mapping and lesion experiments are performed to identify and characterize different portions of the respiratory system: a network in the so called pre- Boetzinger complex (pBC) which is responsible for generating normal respiration and its anoxia-induced interaction with a neural network which may be responsible for gasping. A model is proposed how the interaction between these neuronal networks leads to the biphasic response to anoxia, which includes an initial augmentation, depression, apnea and then gasping. To understand the neural mechanisms underlying this biphasic response, whole cell, cell attached, outside-out and inside-out patch clamp recording techniques are used. The planned experiments aim at characterizing in great detail the direct anoxic effects on different calcium and potassium channel subtypes. However, this characterization will be supplemented with an analysis of how these direct cellular changes affect indirectly the activation of other cellular properties that are involved in the generation of the respiratory rhythm. Thus, it is only possible to understand the biphasic response in an integrated multi-level approach. A hypothetical model is proposed as to how a suppression of the N-type calcium channel leads indirectly to changes in synaptic transmission and the open probability of calcium-dependent potassium channels. In this model, these alterations result in a decreased activation of the Ih current which will alter the mechanisms of respiratory rhythm generation. To examine this hypothesis, the cascade of these cellular and network events will be analyzed. A better understanding of these neural mechanisms will provide an important foundation for a more rational treatment of various breathing disorders that result in a cessation of breathing such as sleep apnea, recurrent apnea of the newborn and sudden infant death syndrome.
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0.936 |
2003 — 2007 |
Ramirez, Jan M. |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Substance P in the Central Respiratory Neural Network
[unreadable] DESCRIPTION (provided by applicant): Hyperventilation, breath-holding, central apnea and respiratory dysrhythmia is typical for patients with Rett Syndrome. In these patients, substance P is deficient in brainstem areas that are associated with the central control of breathing. Therefore we hypothesize that the irregular breathing in RS is due to the brainstem deficiency in Substance P ("Substance P hypothesis"). We also hypothesize that an understanding of how substance P (SP) controls breathing will be essential for developing rational therapies for the breathing disorders in RS. The proposed grant application, aimed at investigating the role of substance P in regulating the central nervous control of breathing, will isolate a critical portion of the respiratory network (the "pre- Botzinger complex") in a transverse brainstem slice from mice. The proposed research addresses 3 fundamental questions: (1) What type of ion channel is modulated by SP? Specific aim 1 examines the hypothesis that SP modulates a low-threshold sodium current in respiratory neurons. The hypothesized ion channel causes a long lasting depolarization in inspiratory non-pacemaker and pacemaker neurons resulting in an excitatory response of the respiratory network. (2) How does SP alter membrane properties of respiratory pacemaker neurons? Specific aim 2 tests the hypothesis that the low-threshold sodium current interacts with the ion channels responsible for the generation of pacemaker activity. We specifically examine whether this sodium channel leads to the activation of a CAN current, which dramatically enhances bursting in cadmium-sensitive pacemaker neurons. This aim will lead to a better understanding of the mechanisms responsible for the SP modulation as well as the ionic mechanisms underlying burst generation in respiratory pacemaker neurons. (3) Are pacemaker neurons dependent on the endogenous activation by SP? Specific aim 3 tests the hypothesis that endogenously released SP is required to maintain regular respiratory activity by modulating pacemaker neurons. Decreased levels of SP will lead to weakening of pacemaker activity and thus to irregular breathing. The expected outcome of this research plan will provide important concepts relevant for RS as it will lead to a better understanding of why low levels of SP cause irregular respiratory activity. [unreadable] [unreadable]
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0.936 |
2019 — 2021 |
Ramirez, Jan M. |
P01Activity Code Description: For the support of a broadly based, multidisciplinary, often long-term research program which has a specific major objective or a basic theme. A program project generally involves the organized efforts of relatively large groups, members of which are conducting research projects designed to elucidate the various aspects or components of this objective. Each research project is usually under the leadership of an established investigator. The grant can provide support for certain basic resources used by these groups in the program, including clinical components, the sharing of which facilitates the total research effort. A program project is directed toward a range of problems having a central research focus, in contrast to the usually narrower thrust of the traditional research project. Each project supported through this mechanism should contribute or be directly related to the common theme of the total research effort. These scientifically meritorious projects should demonstrate an essential element of unity and interdependence, i.e., a system of research activities and projects directed toward a well-defined research program goal. |
Brainstem Neural Mechanisms Mediating Sympathetic Activation by Chronic Intermittent Hypoxia
Project Summary- Project 2 Sleep apnea (SA) is a major health burden and chronic intermittent hypoxia (CIH) is a hallmark manifestation of SA. The overall goal of Project 2 aims at determine how CIH acting on key central nervous system (CNS) structures mediate sympathetic activation through the carotid body (CB). SA patients and CIH exposed rodents exhibit pronounced sympathetic nerve activation during the post-inspiratory phase of the respiratory cycle. While the Paraventricular nucleus (PVN) receives sensory input from the CB and is a major regulator of sympathetic tone. We recently discovered a neural network that mediates post-inspiratory activity in the brainstem: the post-inspiratory complex (PiCo). We test the hypothesis that PiCo and PVN are the major CNS areas that are critical for mediating CB reflex-dependent sympathetic excitation by CIH. We test this possibility using a combination of physiological, electrophysiological, and optogenetic approaches on rats and mice exposed to CIH, as well as in a mouse of model of sleep apnea, and brainstem slices. AIM 1 determines whether CIH increases excitability in PiCo. AIM 2 determines whether CIH alters the excitability of rostroventrolateral medulla sympathetic pre-motoneurons via PiCo. Experiments in AIM 3 addresses the influence of CIH on the interaction between PVN and PiCo. AIM 4 determines the functional role of PiCo and PVN in mediating the increased sympathetic drive caused by CIH. AIM 5 examines the role of PiCo and PVN in mediating increased sympathetic drive and apneas in HO-2 null mice which exhibit spontaneous sleep apnea. Major conceptual and technical innovations of Project 2 include: a) identification for role of PiCo in mediating increased sympathetic nerve activity by CIH, b) the delineation of a complete neural circuit responsible for increased sympathetic nerve activity by CIH, c) use of the state-of-the-art optogenetic approaches to determine the involvement of different neuronal circuits, and d) examination of central pre-motor circuits controlling sympathetic tone in a novel mouse model that exhibits spontaneous apneas. Members of the investigative team have long-standing experience and expertise with the proposed approaches, were the first to identify PiCo, and have an excellent track record of working together for number years as evidenced by joint publications. Successful completion of Project 2 is anticipated to establish a framework of understanding the CNS circuits causing increased sympathetic nerve activation and may lead to novel effective therapies for mitigating CB reflex- dependent sympathetic activation.
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0.936 |