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L.D. Loopuijt, J. Kremers; Axon Thickness of Parvalbumin-containing Ganglion Cells of the Mouse . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5170.
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Purpose: to characterize parvalbumin-positive retinal ganglion cells in the mouse by means of their relative axon thickness. Methods: Two adult C57BL/6 mice were killed, eyes and optic nerves were removed and incubated in vitro in oxygenated AMES medium. Crystals of dextran coupled tetramethylrhodamine and biotin (DRB) were placed on the distal stump of the optic nerve and the dye was allowed to be transported retrogradely. After fixation of the tissue, whole retinae and transverse sections of the optic nerve were additionally immunostained for parvalbumin, using Extravidin-FITC as a label. Of two other mice, eyes and optic nerves were only immunocytochemically stained for parvalbumin. The whole mount preparations of the retina and the sections of the optic nerve were viewed at using a fluorescence microscope. Finally, diameters of DRB- and parvalbumin-labeled axons in optic nerve preparations were determined. Results: In animals, of which the retinae and optic nerves were labeled with both DRB and parvalbumin, part of the population of cell bodies, that were filled with DRB also showed parvalbumin immunoreactivity. In optic nerve sections, a restricted amount of axons were parvalbumin-positive, being localized at the periphery as viewed at in cross-section; in the center of the optic nerve, no parvalbumin-positive axons were observed. Comparison of the axon diameter of the total population in the optic nerve, as visualized by retrograde transport of DRB, with parvalbumin-positive axon profiles showed that parvalbumin-positive axon diameters exceeded the axon diameters of the total population by 24.4% (mouse 1; DRB profiles N=143; parvalbumin profiles N=119) and 12.9% (mouse 2; DRB profiles N=483; parvalbumin profiles N=533). Conclusions: Mouse ganglion cells with a parvalbumin-positive axon possess significantly thicker axons than ganglion cells, of which the axons do not contain parvalbumin. Possibly parvalbumin-containing ganglion cells belong to a group of cells that show fast propagation of action potentials.
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