Microbiota and cardiorespiratory control: Ventilatory responsiveness to chemostimulation in adult male rats following chronic antibiotic treatment
Authors: O'Connor Karen M. , Lucking Eric F. , Burns David P. , Golubeva Anna V. , Cryan John F. , O'Halloran Ken D. 
Published: November 2023

The gut microbiome is important for physiological homeostasis, including a vast array of brain functions. We previously demonstrated in rats that prenatal stress results in dysregulated breathing and altered ventilatory responsiveness, which persists into adulthood. These effects correlate with concomitant alterations in gut microbiota. We hypothesise that disruption of the microbiota‐brain axis will result in respiratory maladaptation. To test this hypothesis, chronic administration of antibiotics was used to assess the effects of microbiota depletion on respiratory homeostasis.Eight‐week old male Sprague Dawley rats (n=40) were studied. To deplete the microbiota, rats (n=20) were treated with an established antibiotic (ABX) cocktail for 4 weeks, prepared in autoclaved deionised water, changed every 2 days. Sham animals (n=20) received autoclaved deionised water. Half the animals in each group were studied after 4 weeks; following a washout period of 72 hours, the remaining animals in both groups received transplantation by oral gavage of pooled sham faeces and were transferred to sham bedding for a period of 4 weeks. Ventilation and metabolism during room air and in response to hypoxia (FiO2 = 0.10) and hypercapnic (FiCO2=0.05) gas challenges were assessed by whole‐body plethysmography. Under urethane anaesthesia (1.5g/kg i.p.), cardiorespiratory assessments were performed in response to hypercapnia (FiCO2=0.05 and FiCO2=0.10). Caecal faeces were collected to assess microbiota composition and diversity. Data are reported as mean±SD (sham vs ABX) and compared via unpaired Student's t‐test and 2‐way ANOVA with Bonferroni post hoc.Baseline ventilation (VE) was unaffected by ABX compared with sham under both sleeping (0.49±0.07 vs 0.50±0.06 ml/min/g; p=0.814) and anaesthetised conditions (0.36±0.05 vs 0.36±0.04 ml/min/g; p=0.846). Peak inspiratory flow (PIF) was unaffected by ABX (p=0.713). Resting metabolism (VCO2 production) was not different between the two groups (0.018±0.002 vs 0.016±0.003 ml/min/g; p=0.118). Ventilatory responsiveness to hypercapnia was blunted in sleeping ABX animals. Thus, VE/VCO2 was reduced in ABX animals compared with sham during 5% CO2 ‐‐challenge (96.4 ± 36.8 vs 49.3 ± 5.2; p<0.001). There was a significant reduction in PIF in ABX compared with sham (0.015±0.002 vs 0.011±0.002 ml/min/g; p=0.006). Metabolism during hypercapnia was not different between groups. Under anaesthesia, the ventilatory response to 5% and 10% CO2 challenges did not differ between ABX and sham (p=0.98, p=0.64 respectively). After recolonization, baseline ventilation and ventilation during hypercapnic exposure in sleeping animals were not different in sham and ABX animals.Our data reveals that ABX blunts ventilatory responsiveness to hypercapnic chemostimulation in sleeping rats, which could suggest aberrant plasticity in central networks key to the maintenance of respiratory homeostasis.Support or Funding InformationSupported by the Departments of Physiology, and Anatomy & Neuroscience, and the APC Microbiome Institute, University College Cork.