Recording phrenic afferent activity in a rodent model

The phrenic nerve supplies the primary inspiratory muscle, the diaphragm, and is composed of both motor (efferent) and sensory (afferent) axons. Phrenic afferents carry sensory information from the diaphragm to the central nervous system and have been shown to impact breathing. However, to our knowledge, phrenic afferent activity has only been recorded in large animal species including cat and dog. Since the majority of studies investigating respiratory neural control are performed in rodents, we aimed to record phrenic afferent output in adult rats. These studies are a necessary first step in characterizing phrenic afferent activity in naïve rats to enable future investigations focused on determining if phrenic afferent output is altered following neurologic disease. We hypothesized that in naïve rats, phrenic afferent discharge would show phasic respiratory-related activity. To test this hypothesis, we cut the left phrenic nerve proximally and recorded phrenic afferent output and right diaphragm electromyography (EMG) activity to identify inspiration/expiration in anesthetized and spontaneously breathing adult Sprague-Dawley rats (n=7). Our data shows that phrenic afferent output has a phasic component during inspiration as identified by diaphragm EMG. Tonic discharge observed during expiration is variable across naïve rats with some animals showing sparse activity and others showing higher levels of discharge. In animals with sparse tonic activity, we could observe discharge time-locked with the electrocardiogram (EKG) signal observed on EMG. We hypothesize this corresponds to activity of pericardial afferents found in the phrenic nerve. We have also started collecting pilot data to examine if phrenic afferent output is altered 8 weeks after the well-established model of cervical spinal cord injury, the C2 hemisection. Our preliminary data suggests that phrenic afferent discharge continues to show phasic inspiratory activity 8 weeks after C2 hemisection. Ongoing analysis is focused on determining if there are changes in phrenic afferent activity during the inspiratory or expiratory phase. In conclusion, we report phrenic afferent discharge in adult spinal intact rats and following chronic neurologic disease. Since phrenic afferent activity alters respiratory output, we hypothesize that afferent output is an important variable to examine and consider when designing therapeutic modalities to improve breathing after injury. Craig H. Neilsen Inclusion 993667 (KAS), National Center for Advancing Translational Sciences, National Institutes of Health, through Grant Number 2TL1 TR001437 (TCH). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.