Examining the relationship between Locus coeruleus (LC) activity and breathing in response to chemical exposure

Abstract

Objective: The control of breathing must continuously adapt in response to homeostatic changes. This is particularly important in the context of chemical exposure to substances such as opioids and anesthetic gases known to suppress the drive for breathing. While these agents suppress breathing through different modalities, how they affect neuromodulatory networks capable of influencing breathing remains unknown. This ongoing study aims to understand how exposure to the ultrapotent synthetic opioid (UPSO), fentanyl, and the anesthetic gas, isoflurane, affect the relationship between LC activity and breathing. Hypothesis: We hypothesize that fentanyl and isoflurane have divergent effects on the relationship between LC activity and breathing. Methods: Measurements were made using unrestrained whole-body plethysmography and fiber photometry in NET-cre positive mice expressing GCaMP8s while breathing room air (FiO2=21%) before and following the administration of either fentanyl (0.7 mg/kg i.p.) or exposure to isoflurane (1.5% inhaled). Post-hoc analyses were conducted using MATLAB. Results: Our analyses showed that awake mice (N=8) exhibited two types of LC activity. Type 1 LC activity coincided with high frequency respiratory transients (HFRTs); whereas Type 2 activity did not appear to coincide with changes in breathing. Both fentanyl (N=5) and isoflurane (N=3) suppressed breathing with a greater degree occurring with the UPSO. Furthermore, the frequency of LC activity increased during opioid-induced respiratory depression (OIRD) where both types of LC activity were evident. Isoflurane anesthetized mice showed decreased Type 1 LC activity and a reduction in the duration of Type 2 activity while breathing either room air or hypoxia (FiO2=10%). Conclusion: While isoflurane suppressed Type 1 LC activity in room air and hypoxia, fentanyl which caused a larger suppression in breathing, preserved Type 1 LC activity. These differential effects suggest that the contribution of LC activity to breathing fundamentally changes when exposed to either anesthesia or fentanyl, which may be relevant to understanding the physiological consequences of exposure to either agent. This work was supported by NIH: R01HL163965, R01DA057767. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.