Immunoperoxidase staining for COX-2 in the cremaster muscle microvasculature of C57BL, BERK, and BERK + γ mice. (A) Negative control. Arrowheads indicate blood vessels. (B) The same vessels in an adjacent section from control C57BL cremaster muscle show negative to weakly positive reaction (arrowheads). (C and D) Strongly positive reaction for COX-2 in vascular endothelium of blood vessels in BERK mice (arrowheads). (E) BERK + γ mice show negative or weakly positive reaction for COX-2 in vessel walls (arrowheads).