Morphological and physiological properties of enhanced green fluorescent protein (EGFP)‐expressing wide‐field amacrine cells in the ChAT‐EGFP mouse line

Abstract

Mammalian retinas comprise a variety of interneurons, among which amacrine cells represent the largest group, with more than 30 different cell types each exhibiting a rather distinctive morphology and carrying out a unique function in retinal processing. However, many amacrine types have not been studied systematically because, in particular, amacrine cells with large dendritic fields, i.e. wide-field amacrine cells, have a low abundance and are therefore difficult to target. Here, we used a transgenic mouse line expressing the coding sequence of enhanced green fluorescent protein under the promoter for choline acetyltransferase (ChAT-EGFP mouse) and characterized a single wide-field amacrine cell population monostratifying in layer 2/3 of the inner plexiform layer (WA-S2/3 cell). Somata of WA-S2/3 cells are located either in the inner nuclear layer or are displaced to the ganglion cell layer and exhibit a low cell density. Using immunohistochemistry, we show that WA-S2/3 cells are presumably GABAergic but may also release acetylcholine as their somata are weakly positive for ChAT. Two-photon-guided patch-clamp recordings from intact retinas revealed WA-S2/3 cells to be ON-OFF cells with a homogenous receptive field even larger than the dendritic field. The large spatial extent of the receptive field is most likely due to the extensive homologous and heterologous coupling among WA-S2/3 cells and to other amacrine cells, respectively, as indicated by tracer injections. In summary, we have characterized a novel type of GABAergic ON-OFF wide-field amacrine cell which is ideally suited to providing long-range inhibition to ganglion cells due to its strong coupling.

Ectopic transgene expression in the retina of four transgenic mouse lines

“…Therefore, there is a possibility that overexpression of tau-GFP may contribute to the retinal neurodegeneration observed. However, the failure of ChAT-Rosa mice to label cholinergic amacrine cells was similar to that observed in ChAT-GFP mice (Haverkamp et al 2009; Knop et al 2014). The ectopic expression of fluorescent proteins in cells driven by the ChAT promoter also occurs in the cortex (von Engelhardt et al 2007) and hippocampus (Yi et al 2015).…”

“…In contrast, immunostaining for 5-HT3AR was found in synaptic hot spots in sublamina 1 of the inner plexiform layer and was not related to type 5 bipolar cells. Despite these results, the authors concluded that these mouse lines are extremely useful for microelectrode targeting of well-defined retinal neuron types; they have investigated one such transgenic cell type in detail, identifying it as a wide-field ON–OFF gamma-aminobutyric acid (GABA)-containing cell type (Knop et al 2014). …”

All Spiking, Sustained ON Displaced Amacrine Cells Receive Gap-Junction Input from Melanopsin Ganglion Cells

“…In salamander, amacrine cells include wide- vs. narrow-field varieties, which generate transient and sustained light responses respectively [19]. By contrast, in mammalian retinas, both transient [20–23] and sustained responses [24] have been recorded from wide-field amacrine cells, and also from narrow-field ones [25]. Here, we detected spiking, sustained ON light responses in displaced rat amacrine cells with very diverse field sizes.…”

Connexin36 Expression in the Mammalian Retina: A Multiple-Species Comparison

“…In contrast to group 1 and 2 retinas, however, dendritic processes of the CaR expressing inner retinal neurons showed narrow stratification in strata 2, 3, and 4 of the IPL. It has been documented that in both the mouse and the rat starburst-a and starburst-b ACs and WA-2/3 ACs can be accounted for the three CaR positive bands in the IPL (Gábriel and Witkovsky, 1998; Knop et al, 2014). To summarize these above results we conclude, that close relative species displayed similar CaR labels, for example most rodent retinas formed group 3, all carnivore species were in group 1 and the human and squirrel monkey retinas were in group 2.…”