Astrocytic μ-δ opioid receptor heterodimers mediate the antidepressant effects of ketamine’s metabolite

A deeper understanding of the targets and mechanisms of fast-acting antidepressants, exemplified by ketamine, remains indispensable for better therapeutic strategies and understanding depression. Beyond the canonical neuron-centric NMDAR inhibition hypothesis, brain opioid system and glia-mediated processes are increasingly implicated in ketamine’s antidepressant efficacy, yet their precise contributions remain poorly understood. Here, we demonstrate that one major metabolite of ketamine, (2R,6R)-hydroxynorketamine (HNK), selectively targets μ-δ opioid receptor heterodimers (μ-δ-ORs) on astrocytes. By promoting the formation and/or stabilization of μ-δ-ORs, HNK engages Gs-coupled signaling, elevates intracellular cAMP, phosphorylates CREB (p-CREB) levels and Ca²⁺ dynamics in astrocytes, and consequently restores key astrocytic proteins and functions in depression models. Disrupting μ-δ-OR assembly or Gs signaling abolishes HNK-mediated antidepressant responses both in vitro and in vivo. Collectively, astrocytic opioid receptor heterodimers are critical to antidepressant responses and HNK may serve as a prototype compound for targeting astrocyte dysfunction across a wide range of brain disorders.