Fig. 7: Trhr⁺ interneurons amplify cool information transmission to Calcrl⁺ SPB neurons.

a Representative traces showing the EPSCs of Calcrl⁺ SPB neurons in response to 1 μm icilin in control and Trhr^Lbx1-Abl mice. b Concentration-response curves of Calcrl⁺ SPB neurons from control and Trhr^Lbx1-Abl mice, p < 0.0001. Data are presented as mean ± SEM. c Representative traces of icilin-evoked AP firing in control and Trhr^Lbx1-Abl mice. d Quantification of icilin-evoked neuronal responses in Calcrl⁺ SPB neurons: (top) proportion of responsive neurons, and (bottom) total spike count within a 10 s interval following icilin application. Control: n = 18; Trhr^Lbx1-Abl: n = 16 neurons from 7 mice in each group. For icilin-eAP neurons (top): within 0.1 μM, p = 0.0023; within 0.3 μM, p = 0.0022; within 1 μM, p = 0.0169; within 3 μM, p = 0.0381; within 5 μM, p = 0.0544; within 10 μM, ns. For spike count (bottom): within 0.1 μM, p > 0.9999, within 0.3 μM, p = 0.9766, within 1 μM, p < 0.0001, within 3 μM, p < 0.0001, within 5 μM, p < 0.0001, within 10 μM, p < 0.0001. ^*p < 0.05, ^**p < 0.01, ^****p < 0.0001, ns no significance. Two-sided Chi-square test (d, top), two-way ANOVA with Šídák’s multiple comparisons (b; d, bottom). Data are presented as mean ± SEM. e, f Heatmaps showing the activity of SPB neurons (in ΔF/F0) in response to 4 °C, 15 °C, 50 °C, and pinch stimuli in control (e) and Trhr^Lbx1-Abl (f) mice. Control: n = 44 neurons from 3 mice; Trhr^Lbx1-Abl: n = 62 neurons from 3 mice. g Quantification of SPB neuron response to various stimuli (4 °C, 15 °C, 50 °C, and pinch) in control and Trhr^Lbx1-Abl mice, categorized based on their response to a 15 °C stimulus. Neuron responses are classified as Cool-specific (responding to 15 °C only), Cool-polymodal (responding to 15 °C and additional stimuli), Cool-insensitive (responding only to other stimuli but not 15 °C), and No response. Control: n = 44 neurons from 3 mice; Trhr^Lbx1-Abl: n = 62 neurons from 3 mice, ^****p < 0.0001, Two-sided Chi-square = 25.5, df = 3. h A diagram illustrating the cool sensation circuit: Trhr⁺ interneurons in lamina I–II of the SC receive input from TRPM8⁺ sensory neurons and connect to Calcrl⁺ SPB neurons. Proper transmission of cool-related information to the brain depends on Trhr⁺ neuron function, with their ablation compromising signal relay. Created in BioRender. Lee (2025) https://BioRender.com/hwvgy30. Source data are provided as a Source data file.