Immunohistochemical analysis of the developing inner plexiform layer in postnatal rat retina

PURPOSE. TO investigate the development from early postnatal life to adulth ood of neural cell processes that establish the circuitry of the inner plex iform layer (IPL). Emphasis was focused on the ontogeny of subsets of cGMP- and protein kinase C (PKC)-immunoreactive amacrine and bipolar cells. METHODS. Paraformaldehyde-fixed postnatal and adult retinas were used for l ight microscopic analysis of immunohistochemical labeling of cryo-sections. Synthesis of cGMP in neural structures was achieved by means of an in vitr o stimulation with a well-established nitric oxide donor. RESULTS. In vitro stimulation of postnatal and mature retina with the nitri c oxide donor results in NO-activated cGMP synthesis in subsets of bipolar and amacrine cells. NO-activated cGMP immunoreactivity is expressed in spec ific cell populations during the first postnatal week. Other cell subsets, consisting of amacrine cells and rod bipolar cells: express PKC immunoreact ivity during postnatal development. An increasing number of rod bipolar cel ls start to exhibit cGMP labeling after eye opening, and a colocalization w ith PKC is established in adult retinas. Processes from these cell populati ons terminate in several sublaminas in the developing IPL, but cGMP- and PK C-labeled terminals appear to be confined to ON-lamina as the retina mature s. CONCLUSIONS. The development of cGMP- and PKC-labeled fibers within the IPL appears to be in concert with events of neural differentiation and synapto genesis. These results suggest that the nitric oxide/cGMP signaling pathway and PKC may participate in activity-dependent processes during development char establish the mature circuitry of synaptic contacts within the LPL. T he presence of cGMP in mature rod bipolar cells suggests a role in the sign al transduction of rod bipolar cell-AII amacrine cell pathway.