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S. Chung, J. Korenbrot; Anatomical Characterization Of Developing Dendritic Trees In Ganglion Cells Of The Zebrafish Retina And The Effects Of Retinal Activity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2787.
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The dendritic tree of retinal ganglion cells changes in structure as embryological development proceeds. In the retina of fish, changes in RGC structure are associated with specific changes in the electrical properties of the neurons with respect to the ion channels expressed by the cells and the channel’s biophysical properties. The RGC electrical excitability and some features of their response to light also change in parallel with the structural maturation. To investigate whether these changes are causally related, we have studied the embryological development of RGC structure in zebrafish both under normal conditions and in the presence of specific inhibitors of retinal synaptic activity.
Individual RGC in the retina were labeled by injecting one cell fertilized eggs with a cDNA vector designed to express EGFP fluorescent protein under the control of the Brn3 promoter. Fluorescent images of individual RGC were captured in living, intact embryos between the ages of 2 and 6 days post fertilization (pfd). Images were acquired with a confocal fluorescence microscope.
Results and Conclusions: :
Under the Brn3 promoter, EGFP expression was observed in a variable and small number of RGC, on the order of tens, in the developing zebrafish retina. This is advantageous in our studies since only few cells were labeled and each could be identified and repeatedly observed as development proceeded. Label was detectable after 2 pfd and begins to fade away after 6 pfd. We limited our structural analysis to well resolved cells located along the dorso–ventral equator and within about 15 cell bodies of the optic nerve. RGC were identified not only by their location in the appropriate retinal layer, but also by following their labeled axon and confirming it joined the optic nerve. The RGC dendritic tree can be coarsely identified to exist in three distinct structural stages of development: bulge, transition and mature when classified according to 1) their branching 2) their extension into the IPL and, most especially, 3) their stratification within the IPL. Bulge cells have extremely short (no more than twice the body lengths) and sparse dendritic trees that extend only partially across the IPL thickness. Transition cells have long dendritic trees. The dendrites are elaborately branched and they extend across the full width of the IPL but are not stratified within the IPL. In mature cells, the dendritic trees do not reach across the full width of the IPL, rather, they terminates in well defined IPL sublaminae within which dendrites extend along a narrow streak.
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