(2R,6R)-Hydroxynorketamine elicits rapid antidepressant effects by promoting astrocytic µ-δ opioid receptor heterodimerization

Ketamine produces rapid antidepressant effects but is constrained by psychotomimetic properties and abuse potential. The ketamine metabolite (2R,6R)-hydroxynorketamine (HNK) shows antidepressant-like efficacy without N-methyl-D-aspartate receptor (NMDAR) blockade, yet its upstream targets remain unclear. Here we show that HNK potentiates hippocampal excitatory transmission and reverses stress-induced behavioural deficits through opioid receptor signaling. Pharmacological and genetic analyses reveal a requirement for both µ- and δ-opioid receptors in astrocytes. Chronic stress reduces µ-δ receptor heterodimers in the hippocampus, and a single dose of HNK restores their abundance. PAINT-MINFLUX nanoscopy quantifies increased µ-δ heterodimerization, and molecular dynamics simulations indicate selective binding of HNK to the µ-receptor protomer via Asp147 and Tyr148. Mutating these residues abolishes HNK-driven heterodimer formation, downstream signaling and rapid antidepressant-like effects in vivo . Astrocytic µ-δ opioid receptor heterodimers thus represent a targetable mechanism for next-generation rapid-acting antidepressants.