Somatostatin immunocytochemistry in the rabbit retina

In previous work, radioimmunoassay was used to document the presence of somatostatin-like immunoreactive material in the rabbit retina. The present study was undertaken to determine the cellular localization of that material by light microscopic immunocytochemistry. Rabbit retinas were fixed by immersion in paraformaldehyde-lysine-periodate and reacted, either as whole retinas or as 50 microns Vibratome cross-sections, with an antiserum directed against somatostatin-14. Consistent staining of neuronal perikarya was seen only in the retinas of rabbits that had been pretreated with intravitreal injections of colchicine. Specifically stained cell bodies are present in the ganglion cell layer; the cells give rise to fibers in both the innermost and outermost sublaminas of the inner plexiform layer. In retinal whole mounts, the cells possess two or three primary dendrites with sparse branching. The dendritic fields are up to 1 mm in diameter, and adjacent dendritic fields overlap. Many cells have a thin varicose process arising from the soma or a proximal primary dendrite; these processes branch repeatedly within the retina and resemble intraretinal axons. The somatostatin-reactive cells may be associational ganglion cells or displaced amacrine cells; it is less likely that they are ganglion cells with axons projecting to the brain.