Coordinated activity of a central pathway drives associative opioid analgesic tolerance

Opioid analgesic tolerance, a root cause of opioid overdose and misuse, can develop through an associative learning. Despite intensive research, the locus and central pathway subserving the associative opioid analgesic tolerance (AOAT) remains unclear. Using a combination of chemo/optogenetic manipulation with calcium imaging and slice physiology, here we identify neuronal ensembles in a hierarchically organized pathway essen-tial for AOAT. The association of morphine-induced analgesia with an environmental condition drives glutama-tergic signaling from ventral hippocampus (vHPC) to dorsomedial prefrontal cortex (dmPFC) cholecystokininergic (CCKergic) neurons. Excitation of CCKergic neurons, which project and release CCK to baso-lateral amygdala (BLA) glutamatergic neurons, relays AOAT signal through inhibition of BLA mu-opioid receptor function, thereby leading to further loss of morphine analgesic efficacy. This work provides evidence for a circuit across different brain regions distinct for opioid analgesic tolerance. The components of this pathway are po-tential targets to treat opioid overdose and abuse.

Automated summary

Using a combination of chemo/optogenetic manipulation with calcium imaging and slice physiology, this study identifies neuronal ensembles in a hierarchically organized pathway essential for associative opioid analgesic tolerance. The signaling from the ventral hippocampus to dorsomedial prefrontal cortex cholecystokininergic neurons, and subsequently to baso-lateral amygdala glutamatergic neurons, relays the tolerance signal and leads to the loss of morphine analgesic efficacy.