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Neural Engineering

Neural Engineering - Poster Session E

Poster Z13 - Mapping Retina-Brain Projections at the Level of Distinct Mouse Retinal Ganglion Cells

Saturday, October 26, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Retinal ganglion cells (RGCs) are essential to the visual system as they serve as the connection between cells in the retina and the brain. RGCs receive visual information which is directed to the brain for additional processing and is known to influence both physiological function and behavior. More than forty distinct RGC sub-types have been identified in the mouse retina that differ in morphology, function, and connection to the brain. Furthermore, at least fifty-nine distinct regions within the mouse brain are known to receive retinal input. While extensive work has been done to identify these brain areas, our current knowledge of the projection map of each RGC type in the brain is very limited. Therefore, deciphering which RGC sub-type projects to what brain area will allow us to better understand the visual neural system in terms of what and how information is transmitted and potentially support the design of new and innovative solutions for the restoration of sight. Hence, the objective of this study is to map retina-to-brain connectivity at the level of individual RGCs using an anterograde viral tracing approach.

Materials and

Methods:  Three adeno-associated viruses (AAVs) along with a diluted Cre-dependent FLP recombinase (FLPo), known as the Vector Assisted Spectral Tracing (VAST), are injected intravitreally in VGlut2-Cre transgenic mice to sparsely fluorescently label RGCs. One month post-injection, animals are sacrificed, and the sub-type of each labeled RGC is identified by recording the cell’s electrical properties. Following electrical recording, a multi-spectral confocal microscope is used to image the dendritic morphology and unique spectral signature of each labeled RGC in the retina. Brains are sectioned and imaged with the same multi-spectral microscope to identify RGC terminal arbors in five predetermined retinorecipient areas in the brain: superior colliculus (SC), ventral (vLG) and dorsal (dLG) lateral geniculate complex, suprachiasmatic nucleus (SCN), and olivary pretectal nucleus (OPN). Subsequently, the spectral signatures of each imaged terminal arbor in the brain are used to identify its RGC of origin.

Results, Conclusions, and Discussions: 

Results: Our data indicate that sparse and distinct spectral labeling can be obtained with a 1:450-1:500 dilution of the Cre-dependent FLPo activator. Stable expression of three different fluorescent proteins throughout the membrane of each labeled cell has been achieved, with varied ratios of the fluorophores cell-to-cell. Specifically, initial findings for one mouse demonstrated ~15 RGCs were labeled, and of those labeled cells, 6 RGCs were recorded and identified. Terminal arbors were identified in all predetermined retinorecipient brain areas: 13 in SC, 5 in vLG, 11 in dLG, 7 in OPN, and 1 in SCN. Current efforts are focused on further development of a robust spectral analysis to achieve retina-to-brain color matching.

Conclusions: Our preliminary results demonstrate that a stochastic multi-spectral labeling technique like VAST holds promise to measure, for the first time, the divergence patterns of individual RGCs to multiple brain targets and to reveal the full retina-to-brain projectome. Taken together, this study represents a first step to better understand the visual neural system and to support the development of treatments for sight restoration.

Acknowledgements (Optional):  MTV is supported by the NURTURE Post-doctoral Scholars Program at Northwestern University.