Optogenetic Activation Of Prebotzinger 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. Neurons expressing tachykinin precursor 1 peptide (TAC1) located in the preBötzinger Complex (preBötC) also co-express neurokinin-1 receptors (NK1R) and MORs. NK1R neurons are preferentially inhibited by opioids and play an essential role in mediating opioid-induced respiratory depression. Objective Here, we tested the hypothesis that optogenetic activation of TAC1-expressing preBötC cells will prevent or reverse respiratory rate depression by opioids. Methods Using a Cre-loxP recombination approach, we injected, in TAC1 Cre recombinase mice the adeno-associated virus containing the gene cassette of the excitatory channelrhodopsin-2 ChETA flanked between loxP sites. After a four weeks period to allow ChETA expression in targeted cells, a 200 µm optical fiber was positioned above the preBötC for laser stimulation with blue light (wavelength: 480 nm). Respiratory rate was measured in anesthetized mice with electromyographic recordings of thediaphragm and genioglossus muscles activity. Once breathing was stable (>20 min), the clinically-relevant µ-opioid drug fentanyl (1mg/kg) was administered by intramuscular injection. About 5 minutes after fentanyl injection, targeted preBötC cells were stimulated using laser stimulations (frequency: 30Hz, duration of stimulation: 330ms). Results Data show that fentanyl depressed respiratory rate by about 40% in 5 minutes and stimulation of TAC1-expressing preBötC cells increased breathing rate back to baseline level when the laser was on; an effect that was reversible. Conclusion TAC1-expressing 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.