From the retina to the brain: retinal ganglion cell subtype specific visual circuits

Abstract

Purpose : In the mammalian retina there are ~20 different subtypes of retinal ganglion cells (RGCs) and these RGCs project to ~46 different regions within the brain. To better understand how each subtype of RGC contributes to visual processing we use subtype specific transneuronal tracers to reveal visual circuits.

Methods : Two DNA recombinase and trans-cellular labeling was used to illustrate the synaptic circuits mediated by a direction selective RGC (DSRGC) known as BD. CreER-BD mice were crossed with RCE:FRT mice which harbor the R26R CAG-boosted EGFP (RCE) reporter allele with a FRT-flanked STOP cassette upstream of the enhanced green fluorescent protein (EGFP) gene. Mice received an intravitreal injection of a Cre-dependent AAV2-EF1a-DIO mCherry-IRES-WGA-Flpo vector and a 4-hydroxy tamoxifen injection. This viral vector promotes the expression of a WGA(wheat germ agglutinin)-Flpo fusion protein within Cre containing BD DSRGCs. WGA-Flpo can activate EGFP expression in BD DSRGCs and can be transported transneuronally. Neurons receiving WGA-Flpo are able to express EGFP as well. RGC specific circuits in the brain are illustrated based on EGFP expression and the projection sites in the brain were identified using The Allen Mouse Brain Atlas.

Results : 1) EGFP is expressed by BD DSRGCs in the retina and antibody labeling confirmed that BD DSRGCs in the retina expressed both EGFP and mCherry. 2) WGA-Flpo protein can be transported into neurons in the brain transneuronally. 3) Expression of EGFP can be activated in neurons receiving WGA-Flpo. 4) Eight regions/nuclie in the middle brain including the lateral geniculate nucleus (LGN), superior colliculus, and hippocampus were found to have EGFP positive cells with more areas yet to be identified. 5) Three cortical areas including retrosplenial, entorhinal, and visual were found to have EGFP positive cells. 6) All EGFP positive cells in the brain also contained WGA.

Conclusions : We have developed a mouse model that can label an entire circuit of a single subtype of RGC. Our data demonstrated that a single subtype of RGCs could connect to a variety of cortical areas and BD DSRGCs may be involved in integrating visual perception and smell.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

A) Allen Brain Atlas of similar area to Fig 1.B
B) Large scan of single brain slice with area labels

 

Various close up images of EGFP positive brain areas. Figs 2 A, B and E have WGA labeling.