Involvement of medullary raphe on active expiration.

Abstract

IntroductionIn rodents, the parafacial respiratory group (pFRG), located in the ventral lateral medulla, has been described as a conditional expiratory oscillator that emerges mainly in conditions of metabolic challenges to increase ventilation. However the mechanisms required to stimulate pFRG and generate active expiration have not been fully elucidated. Because the raphe region has long been described to be involved in breathing activity, we decided to investigate whether there were projections from raphe to pFRG and to analyze the effect of raphe inhibition on the active expiration generated by hypercapnia.ObjectiveInvestigate the possible involvement of the medullary raphe in active expiration mediated by hypercapnia.MethodsMale Wistar rats weighing 250–350g (CEUA: 80/13) were used. For anatomical experiments, animals received retrograde tracer FluorGold (FG) injections in the pFRG (n=4). Seven to ten days after the injections, immuhistochemistry for tryptophan hydroxylase (TrOH) was performed. For physiological experiments, urethane‐anesthetized rats received bilateral injection of the GABA‐A agonist muscimol (60 pmol/60 nl) in the Raphe Magnus (RMg) or Obscurus (ROb) regions, the electromyography of diaphragm (DiaEMG) and abdominal (AbdEMG) muscles were recorded.ResultsThe anatomical experiments showed that there were projections from serotonergic and non‐serotonergic neurons of RMg and ROb to pFRG region. The injection of muscimol in RMg or ROb did not significantly alter the frequency and amplitude of DiaEMG and did not generate active expiration. In these animals, hypercapnia after raphe inhibition did not produce significant changes on DiaEMG amplitude and frequency. However, inhibition of RMg or ROb produced an increase in the AbdEMG amplitude during hypercapnia.ConclusionOur results demonstrated that RMg and ROb project directly to pFRG and may be involved in active expiration. We propose that RMg and ROb may be modulating the activity of pFRG during hypercapnia.Support or Funding InformationFinancial support: FAPESP, CNPq and CAPESThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.