Locus Coeruleus activity correlates with transient elevations in breathing during opioid-induced respiratory depression

The ongoing opioid epidemic causes opioid-related overdose deaths, and a history of opioid use significantly raises the risk. The locus coeruleus (LC), a key source of noradrenergic tone, is the site for opioid neuromodulation and tolerance. However, the impact of a history of opioid use on LC activity and opioid-induced respiratory depression (OIRD) remains unclear.

Researchers used plethysmography and fiber photometry to examine how fentanyl affects LC activity and OIRD before and after five days of repeat opioid use (ROU). Fentanyl increased LC burst frequency, regardless of exposure history, and was linked to short-term increases in breathing. LC-coupled ventilation (LC-Ve) continued through ROU.

After ROU, the severity of OIRD varied among mice. Mice that developed an adaptive ventilatory response (AVR) experienced smaller OIRD, better ventilation outside LC bursts, and reduced LC-Ve activity. In contrast, mice with a non-adaptive response (NVR) showed no improvement in OIRD or ventilation outside LC bursts, leading to continued reliance on LC-Ve.

While LC-Ve reflexively counters OIRD in the short term, it may also cause oscillations that destabilize blood gas homeostasis, perpetuating pathophysiology with repeated use.

In conclusion, LC-coupled breathing seems to be a physiological marker of divergent respiratory responses following a history of fentanyl exposure.