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Post-inspiratory activity: its role in respiratory sympathetic- coupling and cardiorespiratory coordination in health and disease

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posted on 2024-08-02, 06:49 authored by Rahat Ul Ain Summan Toor
The respiratory system works together with the cardiovascular system to perform the basic function of life, such as to provide tissues with oxygen and to remove CO2. This is achieved by the coordinated activity of respiratory and sympathetic neurons, each of which independently controls the essential functions of breathing and blood pressure (including its maintenance and the differentiated regulation of blood flow to different organs) respectively. This coordination results from the coupling between various types of respiratory neurons to the sympathetic neurons. Despite many years of research, there is no clear understanding of how respiratory neurons couple to the sympathetic neurons. The literature is particularly scarce with respect to the post-inspiratory neurons and their role in coupling sympathetic nerve activity (SNA) to the central respiratory drive, a mechanism which may also be involved in the development of amplified SNA and the development of hypertension. This topic is the focus of my thesis.

In Chapter 4 we first determined the dynamical changes in post-I activity to understand the quantitative contribution of post-I neurons to SNA in comparison to inspiratory neurons during hypercapnia and hypoxemia because both conditions are thought to increase the strength of coupling between respiratory and sympathetic neurons. Our results showed that the post-I activity was strongly correlated to SNA during hypoxemia, a condition which also facilitates the increase in respiratory-sympathetic coupling.

In Chapter 5 we next studied the role of post-I neurons in the intermediate reticular formation (IRt) in how they control respiratory-sympathetic coupling under baseline conditions and during hypoxemia. We found that the post-I neurons in IRt contribute to respiratory-sympathetic coupling only under baseline condition but are not important for the hypoxemia-induced increase in respiratory-sympathetic coupling instead their activity is critical for fictive swallow.

In Chapter 6 we studied the role of post-I neurons in the Kölliker-Fuse nucleus (KF) in respiratory-sympathetic coupling under baseline conditions and during hypoxemia in normotensive and hypertensive rats. We found that the post-I neurons in KF are critical for respiratory-sympathetic coupling under both baseline and hypoxemic conditions. The results suggest that KF is critical for normal and augmented respiratory-sympathetic coupling and that the input from KF may contribute to the hypertensive phenotype in the spontaneously hypertensive rat—a model of neurogenic hypertension.

Funding

Macquarie University Research Excellence Scholarship

Postgraduate Research Fund (PGRF)

Macquarie University research funds (Department of Biomedical Sciences)

History

Table of Contents

1 Introduction -- 2 Literature review -- 3 General methods -- 4 Post-inspiratory activity is closely related to sympathoexcitation during hypoxemia -- 5 Neurons in the intermediate reticular nucleus coordinate post-inspiratory activity, swallowing, and respiratory-sympathetic coupling in the rat -- 6 Kölliker-fuse nucleus controls respiratory-sympathetic coupling and contributes to high blood pressure in spontaneously hypertensive rat (SHR) -- 7 General discussion -- 8 Reference

Notes

ADDITIONAL SUPERVISOR 3: Cara M. Hildreth

Awarding Institution

Macquarie University

Degree Type

Thesis PhD

Degree

Doctor of Philosophy

Department, Centre or School

Department of Biomedical Sciences

Year of Award

2023

Principal Supervisor

Jacqueline K. Phillips

Additional Supervisor 1

Qi-Jian Sun

Additional Supervisor 2

Simon McMullan

Rights

Copyright: The Author Copyright disclaimer: https://www.mq.edu.au/copyright-disclaimer

Language

English

Extent

212 pages

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