Figure 8.

Compounds that modulate PLC, the enzyme responsible for PIP₂ breakdown, affect capsaicin-induced flinching. A, ICR mice were pretreated with U73122 (10 or 30 mg/kg, i.p.), a PLC inhibitor, intraperitoneally 1 h before intraplantar injection of capsaicin (10 μg). U73122 produced a 29% (10 mg/kg) and 49% (30 mg/kg) blockade of total number of capsaicin-evoked flinches, when compared with vehicle pretreated mice (*p < 0.001, n = 10). B, m-3M3FBS (5 mg/kg, i.p.), a PLC activator, was given 30 min before intraperitoneal administration of SR141716A (SR, 0.3 mg/kg). SR141716A was given 15 min before capsaicin (Cap) injection. The total number of capsaicin-induced flinches in 5 min was significantly inhibited by pretreatment with SR141716A (*p < 0.05), yet restored by pretreatment with m-3M3FBS but not by vehicle (n = 10–14). m-3M3FBS alone did not enhance capsaicin-induced flinching and had no effect on vehicle (data not shown).