Cryostat sections from the fibromuscular stroma of the transition zone of the human prostate. Immunohistochemical distribution of cGKIα and cGKIβ in the smooth musculature of the fibromuscular stroma demonstrated by laser fluorescence microscopy. Double-labelled staining indicates the presence of immunofluorescence specific for smooth muscle α-actin (A, goat anti-mouse IgG, green-fluorescent, 20×) and cGKI (B, goat anti-rabbit IgG, red-fluorescent, 20×). (C–F) The colocalization of cGMP (C and E, goat anti-rabbit IgG, green fluorescent, 20× and 40×, respectively) and its effector proteins cGKIα (D, rabbit anti-goat IgG, red fluorescent, 20×) and cGKIβ (F, rabbit anti-goat IgG, red fluorescent, 40×). (G) Control staining, omitting the primary antibodies, did not reveal fluorescence signals in any of the histological components of the transition zone (nonvascular and vascular smooth muscle, collagen, glandular epithelium; 10×).