A simple, low-cost implant for reliable diaphragm EMG recordings in awake, freely behaving rats

Abstract

Breathing is a complex neuromuscular process vital to sustain life. In pre-clinical animal models, the study of respiratory motor control is primarily accomplished through neurophysiologic recordings and functional measurements of respiratory output. Neurophysiologic recordings that target neural or muscular output via direct nerve recordings or respiratory muscle electromyography (EMG) are commonly collected during anesthetized conditions. While offering tight control of experimental preparations, the use of anesthesia results in respiratory depression, may impact cardiovascular control, eliminates the potential to record volitional non-ventilatory behaviors, and can limit translation. Since the diaphragm is a unique muscle which is rhythmically active and difficult to access, placing diaphragm EMGs to collect chronic recordings in awake animals is technically challenging. Here, we describe methods for fabricating and implanting indwelling diaphragm EMG electrodes to enable recordings from awake rodents for longitudinal studies. These electrodes are relatively easy and quick to produce (∼1 hour), are affordable, and provide high quality and reproducible diaphragm signals using a tethered system that allows animals to freely behave. This system is also designed to work in conjunction with whole body plethysmography to facilitate simultaneous recordings of diaphragm EMG and ventilation. We include detailed instructions and considerations for electrode fabrication and surgical implantation. We also provide a brief discussion on data acquisition, material considerations for implant fabrication, and the physiological implications of the diaphragm electromyography signal.

Significance Statement Investigations of respiratory neuromuscular output have frequently involved the diaphragm muscle, given its role as the main inspiratory muscle in mammals. While anesthetized preparations are fundamental to our understanding of respiratory neuromuscular control, using awake, freely behaving models enhances translatability, particularly when developing and evaluating therapeutic strategies in conditions that result in respiratory pathology and impaired breathing. Here, we describe an affordable and easy-to-produce electromyography implant that enables stable recordings of diaphragm output in awake, behaving rodents over long-term experimental protocols and offer a brief commentary on data acquisition and analysis of these signals.