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

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.