Optogenetic activation of preBötzinger Complex cells alleviates respiratory depression by opioids

Rationale Opioids are extensively used for their analgesic properties but present a variety of unwanted side effects, including tolerance, dependence and respiratory depression. The analgesic effect of opioids is due to activation of μ‐opioid receptors (MOR) in the central nervous system and no treatments are currently available to prevent respiratory depression without reducing their analgesic properties. The neural circuits and mechanisms regulating respiratory depression, sedation, and analgesia by opioids often overlap, therefore making challenging the identification of the mechanisms regulating respiratory depression. We previously showed that neurons expressing neurokinin‐1 receptors located in the preBötzinger Complex (preBötC) also co‐express the peptide somatostatin (SST) and MORs. Neurokinin‐1 receptors are preferentially inhibited by opioids and play an essential role in mediating opioid‐induced respiratory depression. The role of SST preBötC cells in regulating respiratory depression by opioids is unknown. Objective Here, we tested the hypothesis that optical stimulation of SST‐expressing preBötC cells will prevent or reverse respiratory rate depression by opioids. Methods Using a Cre‐loxP recombination approach, we injected stereotaxically, in SST Cre recombinase mice the adeno‐associated virus containing the gene cassette of the excitatory channelrhodopsin‐2 ChETA flanked between loxP sites. A three week recovery period is usually enough to allow ChETA expression in SST cells. A 200 μm optical fiber was then positioned above the preBötC for laser stimulation with blue light (wavelength: 480 nm). Respiratory rate was measured in anesthetized mice with electromyographic recordings of the diaphragm and genioglossus muscles activity. Once breathing was stable (>30 min), the clinically‐relevant μ‐opioid drug fentanyl (1mg/kg) was administered by intramuscular injection. About 15 min after fentanyl injection, SST preBötC cells were stimulated using laser stimulations (frequency: 20Hz, duration of stimulation: 300ms). Results Our preliminary data showed that fentanyl depressed respiratory rate by about 40% in 15 min consistent with our previous studies using mice. Stimulation of SST‐expressing preBötC cells increased breathing rate back to baseline level when the laser was on. Once the laser stimulation was stopped, respiratory depression continued to progressively decrease. Conclusion SST preBötC may constitute cell targets to prevent respiratory rate depression by opioids. These results may help identify the cells mediating respiratory depression by opioids, an essential step toward the development of therapeutic targets to reduce the risk of opioids overdose and associated mortality. Support or Funding Information Supported by CIHR and FRQS