Somatostatin-like immunoreactive material in associational ganglion cells of human retina.

The retinal ganglion cell is classically viewed as the output cell of the retina, sending a single axon via the optic nerve to synapse in visual relay nuclei of the brain. However, some ganglion cells, termed associational ganglion cells, have axons which do not leave the retina and presumably serve intraretinal communication. Using high-affinity and specific monoclonal antibodies to somatostatin-14 and the avidin-biotin-peroxidase immunohistochemical procedure, somatostatin-immunoreactive associational ganglion cells are specifically stained in human retinas obtained at necropsy. These cells are more numerous in the inferior than the superior retina; they have dendrites which ramify in the inner plexiform layer; and they have sparsely branching axons, many of which can be traced over 1 cm. These axons do not enter the optic nerve. They follow remarkably straight courses at the border of the inner plexiform layer and ganglion cell layer and thereby form a gridwork of fibers covering the entire retinal area. These observations verify the existence of associational ganglion cells in the human and establish somatostatin as a neurotransmitter or neuromodulator candidate for these neurons. The morphology of these cells suggests that they are involved in long-distance interactions within the retina.