Participation of retrotrapezoid nucleus in expiratory activity induced by hypercapnia

Abstract

The eupnoeic pattern of respiration consists of three phases: inspiration, post-inspiration (passive expiration, stage 1) and stage 2 of expiration. It is possible to create a functional map in the ventral surface of medulla with all the different classes of neurons involved in the respiratory control (Merrill, 1981). During breathing at rest, air is expired passively by recoil forces. Augmenting expiratory activity during the second phase of expiration (E2) is always present in the brainstem during eupnoea. An expressed phasic expiratory activity in this motor outflow is observed only during increased ventilatory demand such as during hipercapnia or hypoxia in the cat (Fregosi and Bartlett, 1988, Fregosi, 1994, Iizuka and Fregosi, 2007).The retrotrapezoid nucleus (RTN) is one of the region involved in the neural control of breathing. It is characterized by neurons involved in the control of inspiration (Dobbins e Feldman, 1994). However, because the origins and mechanisms of generation of this late expiratory activity remain poorly understood and several currently proposed concepts appear controversial, recently studies from literature have also tried to prove the involvement of RTN in the generation of expiratory activity (Janczewski e Feldman, 2006a, 2006b; Abdala e cols., 2009). In this way, the aim of this project is to investigate a real connection between RTN and the caudal ventral respiratory group neurons and if this connection is active during a hypercapnic condition, using electrophysiology approach. Male Wistar adults rats will be used (250-300g). The animals will be anesthetized with isoflurane and submitted to surgery procedures to blood pressure and electromiography of diaphragm (inspiratory activity) and abdominal (expiratory activity) recordings. It will be evaluated the changes in blood pressure and electromyography during hypercapnia after bilateral injection of saline or muscimol (GABA agonist) into the RTN. After the experiment, the animals will be sacrified and perfused and will have removed the brains for confirmation of injection site. (AU)