Larval Tiger Salamander Retina Research Articles

Synaptic connections between neurons in living slices of the larval tiger salamander retina

Synaptic connections between retinal cells were studied by recording simultaneously from pre- and postsynaptic cells in the retinal slice preparation. The time course and waveform of the pre- and postsynaptic light responses were monitored, and the postsynaptic voltage responses to presynaptic current injection were measured. Results obtained provide direct evidence showing that the rod-HBC and rod-HC synapses are sign-preserving, and the rod-DBC. HC-HBC and amacrine-DBC synapses are sign-inverting. Moreover, the synaptic delays between rods and bipolar cells are shorter than that between rods and horizontal cells. The methodology of making retinal slices and the subsequent recording and stimulation procedures are described. The advantages of the retinal slice preparation and its potential in retinal research are discussed.

Interactions between enkephalin and γ-aminobutyric acid in the larval tiger salamander retina

Both double-label and intracellular electrophysiological recording techniques were utilized to investigate the interactions between enkephalin and γ-aminobutyric acid in the larval tiger salamander retina.Double-label studies revealed that the vast majority ( 96%) 96%) of enkephalin-immunostained amacrine cells also exhibit high affinity uptake of [ 3H]γ-aminobutyric acid. Electrophysiological evidence demonstrated that morphine and γ-aminobutyric acid exert opposite effects on a population of On-Off ganglion cells. γ-Aminobutyric acid decreased the activity of these cells, while enkephalin increased their activity. These findings support the idea that opiate-mediated pathways inhibit GABAergic pathways in the vertebrate retina.

The light microscopic localization of substance P- and somatostatin-like immunoreactive cells in the larval tiger salamander retina

Light microscopic immunocytochemistry was utilized to localize the populations of substance P (SP)- and somatostatin (SOM)-like immunoreactive cells in the larval tiger salamander retina. Of 104 SP-immunostained cells observed, 82% were Type 1 amacrine cells. Another 8% of the SP-cells were classified as Type 2 amacrine cells, while 10% of the SP-cells had their cell bodies located in the ganglion cell layer and were designated as displaced amacrine cells. Each type of SP-like immunoreactive cell was observed in the central and peripheral retina. SP-immunopositive processes were observed in the inner plexiform layer as a sparse plexus in sublamina 1 and as a denser network of fibers in sublamina 5. Seventy-eight percent of the 110 somatostatin-immunopositive cells observed were designated as Type 1 amacrine cells. Another 12% of SOM-cells were classified as displaced amacrine cells, while only two SOM-immunopositive Type 2 amacrine cells were observed. Nine percent of the SOM-cells were designated as interplexiform cells, based on their giving rise to processes distributing in the outer plexiform layer as well as processes ramifying in the inner plexiform layer. Each type of SOM-immunoreactive cell was observed in the central and peripheral retina, with the exception of the Type 2 amacrine cells, whose somas were only found in the central retina. Lastly, SOM-immunopositive processes in the inner plexiform layer appeared as a fine plexus in sublamina 1 and as a somewhat denser network of fibers in sublamina 5.

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 microns) were situated in the innermost cell row of the inner nuclear layer. A relatively small number of enk-stained oval cell bodies (14-22 microns) 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 mm2 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of cholinesterase activity in the outer plexiform layer of the larval tiger salamander retina

Acetylcholinesterase activity, which may be indicative of cholinergic synapses, has been ultrastructurally localized in the outer plexiform layer of the larval tiger salamander retina using the cholinesterase staining method of Karnovsky and Roots. In the presence of the butyrylcholinesterase inhibitor, ethopropazine, precipitate is localized to discrete ‘stain laminae’ about 300 nm in their largest dimension and bounded by a 10 nm wide electron-lucent gap. Stain laminae are predominantly found adjacent to horizontal cell axon terminals which were identified by serial section analysis. Stain precipitate has not been found associated with horizontal cell dendrites and in only one case was a lamina found adjacent to a bipolar cell dendrite. Intracellular deposits of cholinesterase stain precipitate were also observed. In some cases, stain is found adjacent to synaptic ribbons in photoreceptor terminals. Likely artifacts appear to have been ruled out by control experiments in which retinas either were not treated with cholinesterase stain or were treated in the presence of the specific acetylcholinesterase inhibitor, BW284C51. Thus, the stain laminae probably result from specific, highly localized areas of acetylcholinesterase activity. The implications of the present study on current theories of cholinergic function in the vertebrate retina are discussed.