Figure 3. Tacr1- and Gpr83-expressing SPB neurons exhibit different responses to cutaneous stimuli, which is explained by their distinct synaptic inputs from primary sensory neuron subtypes.

a, Schematic of whole-cell patch clamp recordings from Tacr1⁺ and Gpr83⁺ SPB neurons using an ex vivo skin-spinal cord preparation. b, c, Representative traces of action potential (AP) firing evoked by von Frey filament indentations (b) and saline application with different temperatures (c). Underbars, time when stimuli were applied to the skin. d, Summary radar plots. e-g, Quantifications of peak instantaneous firing rates following application of mechanical (e) and temperature (innocuous (f) and noxious (g)) stimuli. Mann-Whitney test (two-tailed) (comparison for individual stimuli); Two-way ANOVA (comparison for different groups of stimuli), F_{[1, 29]} = 9.77 (e), F_{[1, 57]} = 4.41 (f); n = 16, 15 neurons for Tacr1⁺, Gpr83⁺, respectively. h, Schematic of whole-cell patch clamp recordings from Tacr1⁺ and Gpr83⁺ SPB neurons using a spinal cord slice preparation. The genetic labeling strategies are described in the methods. i, Representative images of tdTomato-expressing Tacr1⁺ and Gpr83⁺ SPB neurons in acute spinal cord slices. n = 39, 35 neurons for Tacr1⁺, Gpr83⁺, respectively. j, l, n, Representative traces of light-activated currents (left) and AP firing (right) upon photostimulation of CGRP⁺ (j), Mrgprb4⁺ (l), and Ntrk2⁺ (n) primary afferent terminals. The light-activated EPSCs were abolished in the presence of tetrodotoxin (TTX) and reinstated in the presence of 4-aminopyridine (4-AP) in addition to TTX, indicating the monosynaptic nature of the synaptic connections. Turquoise bars, 0.1 ms (EPSCs) and 1 ms (APs) LED (473 nm) stimulations. k, m, o, Quantifications of peak current density. Mann-Whitney test (two-tailed); n = number of neurons. Error bars, s.e.m.