Distribution and diversity of intrinsically photosensitive retinal ganglion cells in tree shrew.


Intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate the pupillary light reflex, circadian entrainment, and may contribute to luminance and color perception. The diversity of ipRGCs varies from rodents to primates, suggesting differences in their contributions to retinal output. To further understand the variability in their organization and diversity across species, we used immunohistochemical methods to examine ipRGCs in tree shrew (Tupaia belangeri). Tree shrews share membership in the same clade, or evolutionary branch, as rodents and primates. They are highly visual, diurnal animals with a cone-dominated retina and a geniculo-cortical organization resembling that of primates. We identified cells with morphological similarities to M1 and M2 cells described previously in rodents and primates. M1-like cells typically had somas in the ganglion cell layer, with 23% displaced to the inner nuclear layer (INL). However, unlike M1 cells, they had bistratified dendritic fields ramifying in S1 and S5 that collectively tiled space. M2-like cells had dendritic fields restricted to S5 that were smaller and more densely branching. A novel third type of melanopsin immunopositive cell was identified. These cells had somata exclusively in the INL and monostratified dendritic fields restricted to S1 that tiled space. Surprisingly, these cells immunolabeled for tyrosine hydroxylase, a key component in dopamine synthesis. These cells immunolabeled for an RGC marker, not amacrine cell markers, suggesting that they are dopaminergic ipRGCs. We found no evidence for M4 or M5 ipRGCs, described previously in rodents. These results identify some organizational features of the ipRGC system that are canonical versus species-specific.





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Publication Info

Johnson, Elizabeth N, Teleza Westbrook, Rod Shayesteh, Emily L Chen, Joseph W Schumacher, David Fitzpatrick and Greg D Field (2017). Distribution and diversity of intrinsically photosensitive retinal ganglion cells in tree shrew. The Journal of comparative neurology. 10.1002/cne.24377 Retrieved from https://hdl.handle.net/10161/16625.

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Elizabeth Johnson

Adjunct Assistant Professor in the Department of Neurobiology

My research focuses on the mechanisms underlying vision, with an emphasis on the signals mediating color perception. This research is focused especially on the links between color and form vision, how these signals are transformed from the retina to early visual cortex, and the representation and functional architecture of these chromatic signals.

I am also exploring how facial skin coloration in humans is modulated with hormone changes, and how these color vision cues are used behaviorally.

In addition, through a Bass Connections: Brain & Society team, I am part of a collaborative project exploring the intersection of visual art and visual neuroscience. For this project, we use eye tracking to explore how human observers look at artistic depictions of faces and face-like configurations to understand more about how global and local features contribute to how we see others, how these processes unfold over time and with experience, how they are impacted in autism spectrum disorder (ASD), and how this might inform clinical diagnosis and assessment of response to therapy and treatment. 


Greg D. Field

Adjunct Associate Professor of Neurobiology

My laboratory studies how the retina processes visual scenes and transmits this information to the brain.  We use multi-electrode arrays to record the activity of hundreds of retina neurons simultaneously in conjunction with transgenic mouse lines and chemogenetics to manipulate neural circuit function. We are interested in three major areas. First, we work to understand how neurons in the retina are functionally connected. Second we are studying how light-adaptation and circadian rhythms alter visual processing in the retina. Finally, we are working to understand the mechanisms of retinal degenerative conditions and we are investigating potential treatments in animal models.

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