BERNICK, EP; MOFFETT, SB; MOFFETT, DF; Washington State University; Washington State University; Washington State University: A Visceral Muscle Network in Larval Aedes aegypti
Intrinsic gut muscle plays a vital role in digestive processes, and is under control of both neurons and enteroendocrine secretions. The structure of this muscle is especially interesting in some insects, where it is arranged in a grid-like manner (as opposed to continuous layers). Visceral muscle associated with the larval stomach of the yellow fever mosquito Aedes aegypti was identified by O’Brien in 1966. This larval tissue, however, remains poorly characterized in this species. In these studies, stomachs from 4th instar A. aegypti larvae were examined using both transmission and scanning electron microscopy. Over most of the gut surface, individual circular muscle fibers intersect with longitudinal fibers at right angles. Bilaterally, some circular fibers bifurcate to interlock with adjacent fibers; this interlocking zone is associated with longitudinally-running serotonergic axons. While the spacing between the circular fibers of the anterior and posterior stomach is similar (21.9±1.3 and 25.2±0.7 μ respectively, means ± SEM), there is disparity in their diameter. Circular fibers had a diameter of 2.3±0.3 μ in the anterior stomach and 4.0±0.8 μ in the posterior (means ± SEM). In contrast, the distance between the posterior longitudinal fibers was 25.4±1.3 μ while that of the anterior stomach was 14.5±0.9 μ (means ± SEM). The diameter of posterior longitudinal fibers was 4.6±0.4 μ while that of the anterior fibers was 1.7±0.2 μ. Extensive innervation of the muscle is visible, particularly flanking the gastric caeca and in the posterior stomach. Parallel studies of contractile responses to serotonin and neuropeptides are underway in our laboratory. (Supported by NSF Grant #IBN-0091208).
