Young and middle-aged mouse breathing behavior during the light and dark cycles.

Candace N Receno,Lara R Deruisseau,Brianna E Eassa,Caitlin M Cunningham

doi:10.14814/phy2.14060

Abstract

Unrestrained barometric plethysmography is a common method used for characterizing breathing patterns in small animals. One source of variation between unrestrained barometric plethysmography studies is the segment of baseline. Baseline may be analyzed as a predetermined time‐point, or using tailored segments when each animal is visually calm. We compared a quiet, minimally active (no sniffing/grooming) breathing segment to a predetermined time‐point at 1 h for baseline measurements in young and middle‐aged mice during the dark and light cycles. Additionally, we evaluated the magnitude of change for gas challenges based on these two baseline segments. C57BL/6JEiJ x C3Sn.BliA‐Pde6b +/DnJ male mice underwent unrestrained barometric plethysmography with the following baselines used to determine breathing frequency, tidal volume (VT) and minute ventilation (VE): (1) 30‐sec of quiet breathing and (2) a 10‐min period from 50 to 60 min. Animals were also exposed to 10 min of hypoxic (10% O2, balanced N2), hypercapnic (5% CO 2, balanced air) and hypoxic hypercapnic (10% O2, 5% CO 2, balanced N2) gas. Both frequency and VE were higher during the predetermined 10‐min baseline versus the 30‐sec baseline, while VT was lower (P < 0.05). However, VE/VO 2 was similar between the baseline time segments (P > 0.05) in an analysis of one cohort. During baseline, dark cycle testing had increased VT values versus those in the light (P < 0.05). For gas challenges, both frequency and VE showed higher percent change from the 30‐sec baseline compared to the predetermined 10‐min baseline (P < 0.05), while VT showed a greater change from the 10‐min baseline (P < 0.05). Dark cycle hypoxic exposure resulted in larger percent change in breathing frequency versus the light cycle (P < 0.05). Overall, light and dark cycle pattern of breathing differences emerged along with differences between the 30‐sec behavior observational method versus a predetermined time segment for baseline.

Highlights

Barometric plethysmography is an established methodology used to quantify breathing patterns in mice (Lundblad et al 2002; Dauger et al 2003; Receno et al 2018a)
Unrestrained barometric plethysmography at baseline – 30 sec versus 10 min Baseline frequency was significantly higher during the 10min baseline compared to the 30-sec quiet baseline (P < 0.001; Fig. 2A and B) with no differences resulting from age (P = 0.734) or circadian cycle segment (P = 0.361)
For VE measures, there was a main effect for the baseline segment used, where the 10-min baseline showed higher VE compared to the 30-sec calm breathing segment (P < 0.001; Fig. 2E and F)

Summary

Introduction

Barometric plethysmography is an established methodology used to quantify breathing patterns in mice (Lundblad et al 2002; Dauger et al 2003; Receno et al 2018a). It is noninvasive, utilized on unrestrained mice, and may be repeated. Investigators often use barometric plethysmography to measure breathing patterns with air along with other gas mixes that challenge the respiratory system (Renolleau et al 2001; Malik et al 2005; Fechtner et al 2015; Receno et al 2018a).

Objectives

Methods

Results

Discussion

Conclusion