Localization of enkephalin‐like immunoreactive amacrine cells in the larval tiger salamander retina: A light and electron microscopic study

Immunohistochemistry was utilized to examine the light and electron microscopic localization of enkephalin‐like (enk) immunoreactive amacrine cells in the larval tiger salamander retina. The vast majority of enk‐immunoreactive cells were typical amacrine cells whose round or oval cell bodies (14–16 μm) were situated in the innermost cell row of the inner nuclear layer. A relatively small number of enk‐stained oval cell bodies (14–22 μm) were located in the ganglion cell layer and were designated as those of displaced amacrine cells. Enkephalin immunostaining was observed in the inner plexiform layer as a fine plexus in sublamina 1 and as a dense network of fibers in sublamina 5. In both the center and periphery of the retina the density of typical enk‐amacrine cells was determined to be 250 ± 16.36 cells per mm 2 surface area of the retina. At the ultrastructural level typical enk‐stained amacrine cells possessed a round, indented nuclear membrane. Enk‐immunoreactive processes sometimes contained dense‐core vesicles (60–115 nm) in addition to a rather homogeneous population of small, round, agranular synaptic vesicles (25–35 nm). In sublamina 1 the processes of enk‐amacrine cells were presynaptic to amacrine and bipolar cells. They also contacted processes devoid of synaptic vesicles which possibly arise from ganglion cells. As the postsynaptic element in sublamina 1, they received synaptic input from amacrine cells. In sublamina 5 the processes of enk‐amacrine cells were presynaptic to amacrine cells, bipolar cells, and the somas of cells situated in the ganglion cell layer. They also formed synaptic contacts onto processes devoid of synaptic vesicles, which may originate from ganglion cells. As the postsynaptic member in sublamina 5, the processes of enk‐amacrine cells received synapses from amacrine cells and bipolar cells.