Fig. 3. The α-1 antagonist prazosin restores clonidine analgesia in α-2C knockout mice. Total pain scores in α-2C knockout mice after administration of vehicle (DMSO), sulprostone, prazosin 100 ng/kg intraperitoneally, sulprostone plus prazosin, and sulprostone following clonidine pretreatment, with or without prazosin. The effect of prazosin alone was not significantly different from vehicle. α-1 blockade by prazosin restored clonidine analgesia in α-2C knockout mice with sulprostone-induced allodynia. Clon = clonidine; DMSO = dimethyl sulfoxide; Pra = prazosin; Sulp = sulprostone. ** P < 0.01, *** P < 0.001 versus sulprostone, N = 6 mice per group.