Three-dimensional graphic reconstruction of the insect exoskeleton through confocal imaging of endogenous fluorescence.

The exoskeleton of the cockroach leg was imaged via confocal microscopy to generate digital graphic reconstructions of its three-dimensional structure. The cuticle is autofluorescent and can be visualized without staining, but is maximally imaged in aldehyde-fixed preparations viewed under krypton-argon laser illumination (yellow green (568 nm) excitation, commonly used in confocal microscopes). Images of the entire trochanteral segment of the leg were constructed as montages from optical sections taken as overlapping series that were coincident in the z-axis. Reconstructions of the exoskeleton from these images showed that strain sensing mechanoreceptors are located in association with buttresses and thickenings that form a consistent internal architecture in both juvenile and adult animals. Accuracy of reconstructions was gauged by embedding specimens in Spurr's resin and histologically sectioning them perpendicular to the optical plane of section (z-axis). Comparison of plastic sections with two-dimensional images generated by "resectioning" the software model showed that reconstructed exoskeleton had a high level of accuracy. Imaging of older and larger animals was limited by the sclerotization and increased thickness of the cuticle. Surface extraction algorithms were used to generate vector graphic files in CAD format for export to software used in engineering and design. Among other potential uses, these models have been studied by Finite Element Analysis to examine the distribution of mechanical strains in the exoskeleton that occur during posture and locomotion. The advantages and limitations of the techniques are discussed. These methods may be used in studying the exoskeleton and the anatomy of cuticular mechanoreceptors of other arthropods to similar advantage. Copyright 2000 Wiley-Liss, Inc.