Firing properties of ventral medullary respiratory neurons in sino‐aortic denervated rats

New Findings

What is the central question of this study?

After sino‐aortic denervation (SAD) rats present normal levels of mean arterial pressure (MAP), high MAP variability and changes in breathing. However, mechanisms involved in SAD‐induced respiratory changes and their impact on the modulation of sympathetic activity remain unclear. Herein, we characterized the firing frequency of medullary respiratory neurons after SAD.

What is the main finding and its importance?

SAD‐induced prolonged inspiration was associated with a reduced interburst frequency of Pre‐I/I and an increased long‐term variability of Late‐I neurons, but no changes were observed in the Ramp‐I and Post‐I neurons. This imbalance in the respiratory network may contribute to the modulation of sympathetic activity after SAD.

Abstract

In previous studies we documented that after sino‐aortic denervation (SAD) in rats there are significant changes in the breathing pattern, but no significant changes in sympathetic activity and mean arterial pressure (MAP) compared with Sham‐operated rats. However, the neural mechanisms involved in the respiratory changes after SAD and the extent to which they may contribute to the observed normal sympathetic activity and MAP remain unclear. Here, we hypothesized that after SAD, rats present with changes in the firing frequency of the ventral medullary inspiratory and post‐inspiratory neurons. To test this hypothesis, male Wistar rats underwent SAD or Sham surgery and 3 days later were surgically prepared for an in situ preparation. The duration of inspiration significantly increased in SAD rats. During inspiration, the total firing frequency of Ramp‐I, Pre‐I / I, and Late‐I neurons was not different between groups. During post‐inspiration, the total firing frequency of Post‐I neurons was also not different between groups. Furthermore, the data demonstrate a reduced interburst frequency of Pre‐I/I and an increased long‐term variability of Late‐I neurons in SAD compared with Sham rats. These findings indicate that the SAD‐induced prolonged inspiration was not accompanied by alterations in the total firing frequency of the ventral medullary respiratory neurons, but it was associated with changes in the long‐term variability of Late‐I neurons. We suggest that the timing imbalance in the respiratory network in SAD rats may contribute to the modulation of presympathetic neurons after removal of baroreceptor afferents.

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