Meeting Abstract
P3.149 Thursday, Jan. 6 Denervation and testosterone changes muscle fiber types in the Zebra Finch syrinx. ALLRED, L.M.*; CHRISTENSEN, L.A.; MEYERS, R.A.; GOLLER, F.; Weber State University, Ogden, UT; Weber State University, Ogden, UT; Weber State University, Ogden, UT; University of Utah, Salt Lake City rmeyers@weber.edu
Male and female Zebra Finches show sexual dimorphism in singing behavior, where males sing and females do not. Paralleling this behavior is dimorphism in muscle fiber composition and cross sectional area of the syrinx, a complex vocal organ in birds. Using histochemistry and immunohistochemistry, our lab previously discovered that the syrinx is composed of fast and superfast muscle fibers. Male Zebra Finches show a higher percentage of superfast fibers than females (85% vs. 24%, respectively). We investigated the effects of denervation and testosterone on the morphology of the syrinx. Denervation experiments were performed on both sexes, each resulting in a change in fiber type composition. The tracheosyringeal nerve to the syrinx was cut unilaterally between 4 and 40 days prior to syrinx removal. By day 9 post-denervation, males showed the greatest decrease in superfast fiber percentages (85% to 64%). By day 40 the original fiber type percentages returned. Denervated female syringes possess a population of slow fibers. This implies that denervation causes the expression of slower myosin and a change from superfast to fast muscle fibers in males and from fast to slow fibers in females. Testosterone supplementation was performed on females and administered for three weeks prior to the removal of the syrinx. Testosterone-treated syringes became masculinized, with an increase in superfast fiber percentages from 24% to 74% along with an increase in cross sectional area and fiber diameters. Although female syringes resembled those of males, they were still incapable of producing song. Further study will include an increase in sample size, diversity of species, and change in location of the nerve excision. Supported by NIH grant # DC004390 and WSU.
