A septo-hypothalamic-medullary circuit directs stress-induced analgesia

Stress is a potent modulator of pain. Specifically, acute stress due to physical restraint induces stress-induced analgesia (SIA). However, where and how acute stress and pain pathways interface in the brain are poorly understood. Here, we describe how the dorsal lateral septum (dLS), a forebrain limbic nucleus, facilitates SIA through its downstream targets in the lateral hypothalamic area (LHA) of mice. Taking advantage of transsynaptic viral-genetic, optogenetic, and chemogenetic techniques, we show that the dLS→LHA circuitry is sufficient to drive analgesia and is required for SIA. Further, our results reveal that the dLS→LHA pathway is opioid-dependent and modulates pain through the pro-nociceptive neurons in the rostral ventromedial medulla (RVM). Remarkably, we found that the inhibitory dLS neurons are recruited specifically when the mice struggle to escape under restraint and, in turn, inhibit excitatory LHA neurons. As a result, the RVM neurons downstream of LHA are disengaged, thus suppressing nociception. Together, we delineate a poly-synaptic pathway that can transform escape behavior in mice under restraint to acute stress into analgesia. ### Competing Interest Statement The authors have declared no competing interest. Raw data will be made available upon request. * BSA : Bovine Serum Albumin CFA : Complete Freund’s adjuvant ChR2 : Channel rhodopsin 2 CNO : Clozapine N-Oxide DCM : Dichloromethane DCZ : Deschloroclozapine dLS : dorsal Lateral Septum DMSO : Dimetlysulfoxide DREADD : Designer Receptors Exclusively Activated by Designer Drugs DRN : Dorsal Raphe nucleus ELISA : Enzyme-linked immunosorbent assay GABA : Gamma-aminobutyric acid GAD67 : Glutamic acid decarboxylase GFP : Green Fluorescence protein GPU : Graphics Processing Unit Hipp : Hippocampus HRP : Horseradish peroxidase i.p. : Intraperitoneal ISH : In-situ hybridization LHA : Lateral Hypothalamic Area LHb : Lateral Habenula LPBN : Lateral parabrachial nucleus MP : Microparticle O.D. : Optical Density PAG : Periaqueductal gray PBS : Phosphate Buffered Saline PFA : Paraformaldehyde PLGA : Poly-DL-lactic-co-glycolic PV : Parvalbumin PVA : polyvinyl alcohol RS : Restraint Stress RVM : Rostral Ventromedial Medulla SIA : Stress Induced Analgesia SPF : Specific pathogen-free TetTox : Tetanus Toxin TMB : Tetramethylbenzidine VGat : Vesicular GABA Transporter Vglut2 : Vesicular glutamate transporter YFP : Yellow Fluorescence protein