Changes In The Autonomic And Respiratory Patterns Of Mice Submitted To Short-Term Sustained Hypoxia

NEW FINDINGS: -Mice submitted to SH present changes in the respiratory pattern with an increase in parasympathetic and a reduction in sympathetic activities. What is the central question of this study? -Do mice submitted to SH present autonomic and respiratory changes similarly to rats? What is the main finding and its importance? -Arterial pressure in the normal range, reduced baseline heart rate and tachypnea were observed in behaving SH mice. Recordings in the in situ preparation of SH mice show an increase in cervical vagus nerve activity and a simultaneous reduction in thoracic sympathetic nerve activity correlated with changes in the respiratory cycle. Therefore, mice are an important model for studies on the modulation of sympathetic activity to the cardiovascular system and the vagus innervation of the upper airways due to changes in the respiratory network induced by SH. ABSTRACT: Short-term sustained hypoxia (SH) in rats induces sympathetic overactivity and hypertension due to changes in sympathetic-respiratory coupling. However, there is no consistent data about the effect of SH on mice due to the different protocols of hypoxia and difficulties associated with the handling of these rodents under different experimental conditions. In situ recordings of autonomic and respiratory nerves in SH mice have not been performed yet. Herein, we evaluated the effects of SH (FiO2 = 0.1 for 24 h) on baseline mean arterial pressure (MAP), heart rate (HR), respiratory frequency (f ) and responses to chemoreflex activation in behaving SH mice. A characterization of changes in cervical vagus (cVN), thoracic sympathetic (tSN), phrenic (PN) and abdominal nerves (AbN) in SH mice using the in situ working heart-brainstem preparation was also performed. SH mice presented normal MAP, significant reduction in baseline HR, increase in baseline f , as well as increase in the magnitude of bradycardic response to chemoreflex activation. In in situ preparations, SH mice presented a reduction in PN discharge frequency, increases in the time of expiration and in the incidence of late-expiratory bursts in AbN activity. Nerves recordings also indicated a significant increase in cVN activity and a significant reduction in tSN activity during expiration in SH mice. These findings make SH mice an important experimental model for better understanding how changes in the respiratory network may impact on the modulation of vagal control to the upper airways, as well as in the sympathetic activity to the cardiovascular system. This article is protected by copyright. All rights reserved.