Fig. 4.

TRPV1⁺ neurons are responsible for mediating behavioral responses to IQ. (A) Scratching behavioral responses to IQ in various mutant mice (n = 12 for PLCβ3^+/+ and PLCβ3^−/− mice, n = 11 for TRPV1^+/+ and TRPV1^−/− mice, and n = 4 for mast-cell–deficient mice and their control animals). (B) Capsaicin-treated mice exhibit a profound loss of heat pain sensitivity. Withdrawal latency to radiant heat was measured 1 d after i.t. injection of capsaicin or vehicle. (C) TRPV1 immunostaining in lumbar dorsal horn after behavioral experiments. Shown are 1-μm confocal optical sections of adult mouse DRG neurons. (Scale bar, 100 μm.) (D) Ablation of central terminals of TRPV1-expressing neurons led to profound loss of behavioral responses to IQ (**P < 0.01, Student's t test, unpaired). n = 10 for capsaicin-treated or vehicle-treated mice.