Medullary raphe and active expiration during hypercapnia: role of serotonergic modulation

Abstract

In the nervous system, serotonin (5-HT) is involved in several functions, including circadian rhythms, diet, emotional state, control of sleep and respiratory control. Respiration is a rhythmic process initiated in the central nervous system (CNS). At rest, expiration is a passive process, however, mammals recruit expiratory muscles (such as abdominal) under conditions of increased respiratory drive, such as during hypercapnia. Studying active expiration is critical, as it is activated under conditions essential to generate forced expiration. It also may be involved in pathological conditions. Studies have suggested that the RTN/pFRG is the main generator site of this activity. There are few studies on motor control and respiratory-related activity of the abdominal muscles (expiration), and there is no description of any other brainstem regions that may modulate this activity. In particular, medullary raphe 5-HT neurons, which are involved in the central CO2/pH chemoreception, since hypercapnia is a condition in which active expiration is present. The medullary raphe 5-HT neurons are considered to be an important component of CO2/pH chemoreception and through excitatory projections to RTN may influence and modulate active expiration. This type of serotonergic modulation on active expiration during hypercapnia has never been demonstrated, particularly in non-anesthetized animals and during sleep and wakefulness. Different methodology will be used, such as: EEG, EMG and reverse microdialysis. (AU)