P3.15 Friday, Jan. 6 The role of the diaphragm and scalenus in the ventilation of striped and spotted dolphins (Stenella spp.) ROBERTSON, J.J.**; DEAROLF, J.L.; Hendrix College, Conway, AR firstname.lastname@example.org
The major ventilatory muscle in most mammalian ventilatory systems is the diaphragm, yet its role in dolphin ventilation seems to be diminished. Research on the diaphragm of the bottlenose dolphin has shown that it is composed of mainly slow-twitch muscle fibers. The low number of fast-twitch fibers suggests that there are other muscles involved in dolphin ventilation that possess the contractile speed needed to power their explosive exhalation and rapid inhalation. Previous studies have shown that muscles that work together to drive inspiration have similar fiber-type profiles and levels of oxidative and glycolytic enzymatic activities. Thus, this experiment used histochemical analyses to calculate the fiber-type profiles of the scalenus and diaphragm of striped and spotted dolphins to determine if these muscles work jointly or independently to drive ventilation. Tissue samples were cut and stained for their myosin ATPase activity to distinguish fiber-types. Digital images of the stained tissues were taken and printed in order to count and calculate the percentages of fast-twitch fibers in the scalenus and diaphragm from each specimen. The samples were also stained for their NADH-TR (tetrazolium reductase) activities, an indicator of oxidative activity. Scion Image was used to measure the NADH-TR staining density in slow- and fast-twitch fibers. These measurements were converted to Z-scores and used to calculate the percentages of slow- and fast-twitch fibers staining lightly or darkly for NADH-TR. If the striped and spotted dolphin scalenus and diaphragm muscles are found to have similar fiber-type profiles and percentages of fibers staining darkly for NADH-TR, than these results strongly support the idea that the diaphragm and scalenus muscles of these cetaceans work jointly to drive ventilation.