library_construction_protocol: Medial hypothalamic tissue was collected from frozen heads via a double-punch technique (two 1 mm diameter overlapping circular punches in a figure-8 configuration) during 100 μm coronal cryostat sectioning (Leica CM3050 S). Punching began when the third ventricle became visible (~5,000 μm caudal to the beak). Tissue was collected in cryotubes on dry ice and stored at −80°C. Samples were pooled by sex and condition (n=4 heat call pools, n=4 control pools; 5 punches per pool; 2 pools per sex × condition combination). Nuclei were isolated by lysis for 5 minutes in 500 μL chilled 0.1x lysis buffer (10 mM Tris-HCl, 10 mM NaCl, 3 mM MgCl2, 0.01% Tween-20, 0.01% Igepal CA-630, 0.001% Digitonin, 1% BSA, 1 mM DTT, 40 U/μL RNase inhibitor) with 15 homogenization strokes. Lysate was washed with 500 μL wash buffer (10 mM Tris-HCl, 10 mM NaCl, 3 mM MgCl2, 1% BSA, 0.1% Tween-20, 1 mM DTT, 40 U/μL RNase inhibitor) and filtered sequentially through Flowmi 70 μm (330 μL per pass), Flowmi 40 μm, and pluriStrainer Mini 20 μm cell strainers, with centrifugation at 500 rcf, 4°C, 5 min between steps. Final nuclei were resuspended in chilled 1% BSA in 1x PBS (target: 3,200–8,000 nuclei/μL) and quantified on a Countess II FL Cell Counter with DAPI fluorescence quality assessment. Nuclei were processed using the 10x Genomics Chromium Next GEM Single Cell Multiome ATAC + Gene Expression Reagent Kit (v1, CG000338, Rev G). Nuclei were transposed with ATAC Buffer B and ATAC Enzyme B at 37°C for 60 minutes. Simultaneous barcoding of transposed ATAC fragments and mRNA-derived cDNA was performed on the Chromium iX instrument using Chromium Next GEM Chip J to generate GEMs. Purified nucleic acids were obtained using Dynabeads MyOne SILANE and SPRIselect beads. Purified material underwent pre-amplification PCR before splitting for ATAC and GEX library construction. ATAC libraries were generated by sample index PCR with SI-PCR Primer B and Amp Mix (14–16 cycles) and double-sided SPRIselect size selection. GEX libraries were generated by cDNA PCR (12 cycles), fragmentation, end repair, A-tailing, adaptor ligation, indexing PCR (14–16 cycles), and double-sided SPRIselect size selection. Fragment QC used Agilent TapeStation High Sensitivity D5000 (ATAC) and D1000 (GEX) kits; concentration QC used Qubit 1X dsDNA HS kit. Libraries were pooled and sequenced on the Illumina NovaSeq X+.