MEYERS, R.A.**; SCHMUTZ, D.; GOLLER, F.; Weber State University; Weber State University; University of Utah: Histochemical Analysis of Songbird Syringeal Muscles
Song production in birds results from the combined activity of respiratory and syringeal muscles, which regulate airflow and acoustical patterns. EMG studies of songbird syringeal muscles indicate that they contract faster than normal fast twitch fibers (up to 120 Hz) suggesting the presence of superfast myosin, which has been described in specialized muscles in the rabbit larynx and rattlesnake tailshaker complex. Histochemical analysis of 4 intrinsic syringeal muscles of European Starlings supports the presence of superfast fibers. Our results show two distinct muscle fiber populations based on size and type. A small fiber (mean diameter 11.9�3 �m) population makes up 38% of all intrinsic syringeal muscles and reacts like fast oxidative (Type lla) fibers with ATPase and antifast antibody reactions. A larger fiber (mean diameter 25.5�6 �m) population makes up 62% of the muscles and reacts negatively to both fast and slow antibodies. It has intermediate reactions in both acidic and alkaline ATPase and a low oxidative capacity. This unusual staining pattern is similar to that of superfast fibers seen in laryngeal muscles. Preliminary analysis suggests a higher percentage of superfast fibers in the tracheobronchial muscles than in the syringealis muscles. Furthermore, isolated fibers from Brown-headed Cowbird dorsal and ventral tracheobronchial muscles spanned 44 and 16 percent of total muscle lengths, respectively, whereas those of the dorsal and ventral syringealis muscles spanned 67 and 98 percent, respectively. These findings indicate that muscles more involved in the gating of airflow through the syrinx possess the highest percentage of superfast fibers and the shortest fibers relative to muscle length. These morphological differences between muscles are consistent with their respective roles in sound production. Supported by NIH grant # DC004390 and WSU.
