Changes in the Firing Frequency of Medullary Respiratory Neurons of Juvenile Female Rats Exposed to Chronic Intermittent Hypoxia

Abstract

Juvenile female rats exposed to chronic intermittent hypoxia (CIH) presented a significant reduction in the time of inspiration and increase in sympathetic activity during this phase of respiratory cycle, characterizing changes in the respiratory‐sympathetic coupling. There is evidence that the firing frequency of the pre‐sympathetic neurons is modulated by the respiratory neurons activity. In this context, we hypothesized that: in CIH‐female rats, the enhanced sympathetic activity during inspiration is due to the increased inspiratory neurons activity that modulates the pre‐sympathetic neurons firing frequency. We aimed to evaluate the respiratory neurons activity in the ventral surface of the medulla in juvenile female rats exposed to CIH. For this purpose, juvenile female rats (P20–21) were exposed to CIH (FiO2=6%) for 10 days and after this protocol we performed extracellular single unit recordings of medullary respiratory neurons using the working heart‐brainstem preparation (ventral approach). The respiratory neurons were identified and classified by their activity (firing frequency) in relation to the phrenic nerve activity. All experimental protocols were approved by the institutional ethical committee (#091/2013). Pre‐inspiratory/Inspiratory (Pre‐I/I) neurons of CIH‐female rats (n=12) presented a reduced firing frequency (39.3 ±5 vs 61.5 ±8 Hz, p=0.027) when compared to control (n=10). Ramp‐I, Post‐I and Aug‐E neurons presented no significant changes in their firing frequency in CIH‐female rats compared to control. We concluded that Pre‐I/I neurons presented a reduced firing frequency in CIH‐female rats, which may explain the reduced time of inspiration.Support or Funding InformationFAPESP, CAPES and CNPq.