Amacrine cells in the tiger salamander retina: Morphology, physiology, and neurotransmitter identification

Abstract

Amacrine cells of the vertebrate retina comprise multiple neurochemical types. Yet details of their electrophysiological and morphology properties as they relate to neurotransmitter content are limited. This issue of relating light responsiveness, dendritic projection, and neurotransmitter content has been addressed in the retinal slice preparation of the tiger salamander. Amacrine cells were whole-cell clamped and stained with Lucifer yellow (LY), then processed to determine their immunoreactivity (IR) to GABA, glycine, dopamine or tyrosine hydroxylase (TOH), and glucagon antisera. Widefield, ON-OFF amacrine cells were glycine-IR. The processes of these cells extended laterally in the inner plexiform layer (IPL) from 250-600 microns. They were either multistratified in the IPL or monostratified near the IPL midline. Three multistratified ON-OFF narrowfield glycine-IR cells also were found. Four types of ON amacrine cells were found to be GABA-IR; all types had their processes concentrated in the proximal IPL (sublamina b). Type I cells were narrowfield (approximately 100 microns) with a compact projection. Type II cells were widefield (220-300 microns) with a sparse projection. Type III cells had an asymmetrical projection and varicose processes. Type IV cells were pyriform and monostratified in sublamina b. One narrowfield ON-OFF amacrine cell, with processes broadly distributed in the middle of the IPL, was GABA-IR. This cell appeared similar to an ON-OFF cell that was glycine-IR and may comprise a type in which GABA and glycine colocalize. Another class of amacrine cell, with processes forming a major plexus along the distal border of the IPL and a lesser plexus in the proximal IPL, produced slow responses at light ON and OFF; these cells were dopamine/TOH-IR. A narrowfield class of transient ON-OFF amacrine cell, with processes ramifying throughout both sublaminae a and b of the IPL, were glucagon-IR; these cells appeared to be dye-coupled at the soma. We have shown that, with respect to GABA, glycine, dopamine, and glucagon, salamander amacrine cells fall into rather discrete groups on the basis of ramification patterns in the IPL and responses to photic stimulation. The physiological, structural, and neurochemical diversity of amacrine cells is indicative of multiple and complex roles in retinal processing.

Spike-Dependent GABA Inputs to Bipolar Cell Axon Terminals Contribute to Lateral Inhibition of Retinal Ganglion Cells

“…The GABAergic amacrine cell population in salamander is morphologically diverse with the processes of different amacrine cells extending laterally over a narrow or wide region of the IPL (Yang et al 1991). Distinct amacrine cell subtypes may make connections with bipolar and ganglion cells in the salamander retina.…”

Morphological and Functional Organization of ON and OFF Pathways in the Adult Newt Retina

“…However, they differed in other urodele species, such as a tiger salamander, which showed diffusely ramified dendritic pattern in the full depth of the IPL (Yang and Yazulla, 1986;Gläsener, et al, 1988). Glucagon-ir amacrine cells obtained by combination of patch-clamp recording and dye-injection with immunohistochemistry exhibited ON-OFF responses in tiger salamander (Yang et al, 1991).…”

“…Amacrine cells differ from one another in light response characteristics, neurotransmitter contents, level of cell body, size of dendritic fields and level of dendritic stratification (Yang et al, 1991;Pang et al, 2002). Therefore, classification of amacrine cells is highly dependent on the parameters chosen.…”

“…The high density and homogeneous of labeling in the IPL precludes any hope of determining the ramification pattern of a single cell type. Yang et al, (1991) have addressed this issue in tiger salamander retina and analyzed the retinal slice preparation by GABA immunostaining of Lucifer-yellow filling cells after recording photocurrents with whole-cell voltageclamp techniques. They identified GABA-ir ON amacrine cells with processes ramifying in sublamina b, ON-OFF amacrine cells with processes ramifying in both sublaminae a and b, and further predicted the existence of GABA-ir OFF type amacrine cells ramifying in sublamina a from a result obtained in other study (Maguire et al, 1989).…”

Colocalization of GABA-immunoreactivity in neuropeptide- and monoamine-containing amacrine cells in the retina of Bufo marinus.

“…These results indicate that neuropeptide-and GABA-immunoreactivity are colocalized in amacrine cells of the anuran retina. We propose a possible co-transmission for two classical neurotransmitters (GABA and 5HT) in some of the 5HT-containing amacrine cells.Previous studies have indicated that the y-aminobutyric acid (GABA)-ergic amacrine cell population is morphologically (POURCHO and GOEBEL, 1983;YANG et al, 1991) and immunohistochemically (VERSAUX-BOTTERI et al …”