Fig. 4: TLHON ON responses report fast heating or cooling.

a–d 2-photon guided patch clamp electrophysiology of TLHONs reveals robust ON responses to heating and cooling and some modulation by absolute temperature. a Recording schematic. b Representative whole-cell current clamp recording (top; arrowheads = ON responses) and corresponding thermal stimulus (bottom, red). c Average firing rate histograms of TLHONs in response to a battery of temperature stimuli. ON responses (arrowheads) are independent of absolute temperature. d Steady-state firing rate quantifications demonstrates modulation by absolute temperature (c and d: N = 10, 13, 13 cells, 10 animals, line and shading in (c) indicate mean ± SEM, gray circles connected by lines in (d) indicate recordings from the same cells; black circles indicate mean ± SD; * = p < 0.05, p = 9.81E−06 1-way ANOVA, n.s. = not significant). e TLHON ON responses peak in correspondence with the fastest rate of heating or cooling. TLHON filtered membrane potential responses (top traces), stimulus temperature (middle traces), and rate of thermal change (temporal derivative of temperature stimuli; bottom traces). Green boxes to the right are x-axis expansions of gray shaded regions as indicated. Boxplots show temporal locking between peak response and peak stimulus rate. Delay (shown as boxplots) is quantified as the difference between the timing of the peak membrane potential or the peak firing rate and the timing of the peak rate of thermal change (N = 11 cells/2 samples per cell/8 animals, trace line and shading indicate mean ± SEM; boxplots: black line = median, box = interquartile range, whiskers = range, dots = individual cells). f–k TPN-III ON responses track the rate of temperature change over a broad range, while TLHONs respond to fast thermal change with an apparent threshold of >~0.2 °C/sec. f Schematics of recordings. g,h Peak firing rates for TLHONs (g) and TPN-IIIs (h) plotted against the maximum rate of temperature change of the corresponding stimulus (r² from left to right (g) 0.05, 0.13; (h) 0.35, 0.25; shading: ± 95% CI; gray circles: mean firing rate from a single cell during a single stimulus sweep, see methods for details; N = 176 data points from 20 cells/12 animals for TLHONs and N = 115 data points from 16 cells/8 animals for TPN-III). i,j Sequential responses from (i) TLHONs or (j) TPN-IIIs challenged with slow followed by fast thermal change (8 cells/6 animals for each, 4 heating and 4 cooling stimuli, responses from the same cells are connected; firing rates are background-subtracted; *= different from zero p = 0.001, n.s.= not different from zero p = 0.873; 1 sample, 2-tailed t-test; boxplots: pink line = median, box = interquartile range, whiskers = range, dots = individual cells). k Representative TLHON membrane potential traces (top, black) and firing rate histograms (gray) in response to sub-threshold (empty arrowhead) and suprathreshold (filled arrowhead) stimuli. Source data are provided as a source data file.