Figure 2. In vitro expression of cyclic guanosine monophosphate (cGMP) in the photoreceptor layer of a normal or detached pig retina. Small pieces of retina were incubated with IBMX (a non-specific PDE inhibitor) and the particulate guanylyl cyclase (pGC) stimulator atrial natriuretic peptide (ANP). The expression of cGMP (cGMP: green color) in the retina was then analyzed by immunohistochemistry and nuclei were counterstained with Hoechst 33342 (red). Under these conditions no cGMP signal was visible in the photoreceptor layer of the healthy retina (Panel A). The detached retina on the other hand displayed strong cGMP expression in the photoreceptor layer (Panels B and C). Panel B is a double staining exposure for the nuclei and cGMP, showing the presence of cGMP in the nuclei of the cells (yellow) and in the cytoplasma (green). In Panel C we only show the green signal, showing strong cGMP immunoreactivity in the same piece of retina. Scale bar represents 25 μm.