Nocturnal and diurnal birds exhibit differences in retinal wiring, specifically with regard to "retinal pooling," or the number of photoreceptor cells providing information to a single ganglion cell in the retina. Diurnal birds have low retinal pooling, which acts to increase acuity, since each photoreceptor cell is responsible for a proportional angle of visual space. Nocturnal birds have high retinal pooling; if multiple photoreceptors provide information to a single ganglion cell, light sensitivity is increased. The optic nerve (CN II) is comprised of the ganglion cell axons delivering visual information to the brain. This study tests the hypothesis that nocturnal birds consistently exhibit a smaller optic nerve and chiasm than diurnal birds, based on area measurements. Whole bird heads are preserved in 4% paraformaldehyde, and the optic nerve and chiasm are dissected and mounted in modeling clay and photographed. Areas are measured from the photographs in SigmaScan. ANOVA and regression analysis of the comparative size of the optic nerve supports our hypothesis that nocturnal birds have consistently smaller optic nerve and optic chiasm areas.Grant Funding SourceAAA Student Travel Award
Optic nerve fibers are the axons of retinal ganglion cells, and as such they can provide information about the visual acuity and sensitivity capabilities of an animal. Currently, consistent optic nerve fiber counts are not available for most avians. Those that are available are dependent on method, with different methods yielding different counts. Here, optic nerve fibers are counted at light level for the Great Horned Owl. Juxtaposed sections of a single optic nerve are stained using three different techniques: Bielschowsky's silver impregnation, Bodian's protargol, and Luxol Fast Blue stain. The optic nerve is also observed using H&E to demonstrate details of microanatomy. We test two hypotheses: 1) different staining methods yield different myelinated optic nerve fiber counts due to variations in nerve fiber staining; and 2) hand counts and computer‐generated counts will vary depending on the stain. Counts are estimated for the nerve from 25 digital pictures taken at 1000X at regular intervals. Hand counts are performed multiple times by different observers and compared. Computer‐generated counts are performed in Image J. Research support comes from Midwestern University.Grant Funding SourceAAA Annual Meeting Student/Postdoctoral & Young Faculty Travel Award Student Award
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