Fig. 1: BDNF in the MPO is required for heat acclimation.

a Experimental procedure for HA. Mice were subjected to controlled conditions of 25 °C and 40% relative humidity (RH) in an incubator. The HA group underwent a 10-day training program consisting of daily 2-h sessions under conditions of 38 °C and 60% RH. b T_core changes in exposure to ambient temperature of 40 °C in the HTT from individual mice. The time taken for T_core to reach 41.5 °C was quantified on the right. c EPM under heat exposure (38 °C). The traveling speed, entries into open arm and time spent in open arm were quantified. d Expression of Bdnf mRNA in the MPO in response to a 2-h heat exposure (38 °C), determined by qPCR and RNAscope. The Bdnf mRNA expression of each neuron is quantified on the right. Scale bars, 400 μm (aside) and 100 μm (middle). e Basal firing rates at 36 °C, the thermosensitivity of MPO^BDNF neurons and the percentage of warm-sensitive neurons (WSNs) or cold-sensitive neurons (CSNs) within recorded BDNF⁺ neurons. f Protocol for HA training after blocking MPO^BDNF neurons with TeNT and the representative expression of AAV-DIO-TeNT-mCherry. AAV-DIO-TeNT was injected into the MPO of the BDNF-IRES-Cre mice (termed as MPO^BDNF-TeNT, TeNT group). Scale bar, 200 μm. g, h HTT (g) and EPM (h) after HA training in MPO^BDNF-TeNT mice. i Experimental design to test the effects of optogenetic activation (OA) of MPO^BDNF neurons. AAV-DIO-ChR2-GFP was injected into the MPO of the BDNF-IRES-Cre mice (termed as MPO^BDNF-ChR2, ChR2 group). j HTT of the MPO^BDNF-ChR2 mice after OA. k Axonal GFP expression of MPO^{BDNF-ChR2-GFP} neurons in the DMH and rRPa. Scale bars, 200 μm. l Protocol for HA training after blocking DMH/rRPa-projecting MPO^BDNF neurons and representative expression of AAV-fDIO-TeNT-mCherry. Retro-DIO-Flpo was injected into the DMH/rRPa and AAV-fDIO-TeNT-mCherry was injected into the MPO of the BDNF-IRES-Cre mice (MPO-DMH/rRPa TeNT group). Scale bars, 200 μm. m, n HTT (m) and EPM (n) after HA training in MPO-DMH/rRPa TeNT group. o Experimental design to knock down Bdnf in MPO by injecting Lenti-CMV-Bdnf-shRNA into C57 mice (termed as MPO^Bdnf-shRNA, shRNA group). p, q HTT (p) and EPM (q) after HA training in MPO^Bdnf-shRNA mice. r Experimental design to knock down TrkB in DMH neurons by injecting AAV-hSyn-Cre and AAV-DIO-TrkB-shRNA-GFP into C57 mice (termed as DMH^TrkB-shRNA, shRNA group). s, t HTT (s) and EPM (t) after HA training in DMH^TrkB-shRNA mice. u Experimental design to record postsynaptic currents in DMH neurons innervated by MPO^BDNF neurons using whole-cell patch configurations. v Representative traces and amplitudes of EPSCs recorded in DMH neurons following light stimulation (473 nm, 5 ms) of MPO^BDNF afferents. w Representative traces and amplitudes of EPSCs recorded in TrkB-knockdown DMH neurons after HA training in MPO^BDNF-ChR2 mice. x Summary of the role of BDNF in HA. All data are shown as mean ± SEM and analyzed by t-test. *P < 0.05, **P < 0.01, ***P < 0.001 vs corresponding control group; ns, not significant.