Independent respiratory and locomotor rhythms in running mice

Abstract

Examining whether and how the rhythms of limb and breathing movements interact is highly informative about the mechanistic origin of hyperpnoea to exercise. However, studies have failed to reveal regularities. In particular, whether breathing frequency is inherently proportional to limb velocity and/or imposed by a synchronization of breaths to strides is still unclear. Here, we examined the specifications of respiratory changes during running in mice, the premier model for investigating, in a standardized manner, complex integrative tasks including adaptive breathing. We show that respiratory rate increases during running to a fixed and stable value, irrespective of trotting velocities and of inclination. Yet, respiratory rate was further enhanced during gallop. We also demonstrate the absence of temporal coordination of breaths to strides at any speed, intensity or gait. Our work thus highlights a hardwired mechanism that sets respiratory frequency independently of limb movements but in relation with the engaged locomotor program.