NR2C2 and Priapism: TR4 Comparing histological sections of penis tissue from a TR4+/+ mouse (no priapism), a TR4-/- mouse without priapism, and a TR4-/- mouse with priapism (Figure 2D-L), we found more red blood cells within the corpus cavernosa (CC), and corpus spongiosum(CS) (H & I vs G) and dorsal vein (DV) (K & L vs J) in TR4-/- tissue than in TR4+/+ tissue.