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The Role of NMDA Receptor Activity in Retinal Ganglion Cell Dendrite Development

Scientific poster example

 

This abstract was presented today at the 2014 Association for Research in Vision and Opthalmology (ARVO) meetings in Orlando, Florida by Eerik M. Elias, Ping Wang and Ning Tian.

Full size poster available here.

Purpose: To elucidate mechanisms underlying the dendrite developmental plasticity of retinal ganglion cells, we examined the role of glutamate receptors on retinal ganglion cell dendrite elongation and filopodia elimination.

Methods: We used the JamB genetically labeled subtype of RGCs as our working model. JamB-CreER:YFP ganglion cell dendritic arbors were imaged in whole mount retina using confocal microscopy. Dendrite length, area, branching, and filopodia number were traced and measured using Neurolucida. Visual inputs were blocked by dark-rearing pups after P5. Glutamatergic activity was blocked using daily intraocular injections of AP5 and CNQX from P9 to P13 or genetic ablation of the NMDA receptor in these RGCs.

Results: To test the role of visual inputs on dendrite development, we dark-reared mice from P5 to P30 and found a modest effect on filopodia elimination in JamB RGCs. Anticipating that spontaneous glutamatergic activity in the retina may also contribute to RGC filopodia elimination, we blocked spontaneous glutamatergic activity by daily intraocular injections of AP5 and CNQX from P9 to P13. This led to an increase in filopodia density due to decreased dendrite length but no change in filopodia number. We confirmed this result by examining NMDAR knockout JamB cells (JamB-CreER:YFP:Grin1-/-). As expected, Grin1-/- JamB RGCs have decreased dendrite outgrowth like the pharmacologic blockade. However, filopodia elimination in these cells was significantly decreased as well, suggesting that NMDA and non-NMDA glutamate receptors might regulate the RGC dendritic development in a differential manner. This effect was dramatic at P13. To test if this effect persists into adulthood, we examined Grin1-/- JamB RGCs at P30 and found that they are indistinguishable from wild-type JamB RGCs, suggesting that a compensatory mechanism exists to drive dendrite elongation and filopodia elimination in the absence of the NMDA receptor.

Conclusions: Our study demonstrated that ganglion cell dendrite outgrowth and pruning of filopodia require glutamatergic activity and visual input that act via NMDA and possibly non-NMDA glutamate receptors.

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Interesting: Gene Regulator, Onecut1 Important To Retinal Development And Integrity

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This paper, Onecut1 Is Essential for Horizontal Cell Genesis and Retinal Integrity in the Journal of Neuroscience by authors Fuguo Wu, Renzhong Li, Yumiko Umino, Tadeusz J. Kaczynski, Darshan Sapkota, Shengguo Li, Mengqing Xiang, Steven J. Fliesler, David M. Sherry, Maureen Gannon, Eduardo Solessio, and Xiuqian Mu describes the gene regulator Onecut1 as being the key to healthy retinal development and good vision in adulthood.

Essentially, Onecut1 is critical for the formation of horizontal cells, but of fundamental importance to retinal degenerative research, this work implies that horizontal cells might be necessary for the survival of photoreceptor cells.  Of course we have known for some years that horizontal cells are some of the very first cells to respond to retinal degeneration by extensively remodeling, but this is an interesting result that suggests a direct dependence of photoreceptors on the horizontal cells themselves for survival.

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Metabolic Differentiation In The Embryonic Retina

Michalis Agathocleous, Nicola K. Love, Owen Randlett, Julia J. Harris, Jinyue Liu, Andrew J. Murray and William A. Harris have published a very interesting story on proliferating cells of the Xenopus laevis retina that documents aerobic glycolysis rather than oxidative phosphorylation.  Historically, this shift in metabolism was termed the Warburg effect where it was originally described in tumorigenesis.  Could it be that this shift in metabolism is more widely used than previously anticipated?  Certainly in the proliferating developing Xenopus laevis retina, it appears so, even in the presence of oxygen.  The only other instance of aerobic glycolosis I am aware of is in T-cells, but that too is associated with oncogenicity.

This really opens up possibilities for metabolic control of a variety of processes in not only development, but also pathology with respect to alternative methods for defining metabolic states and deriving energy.