A quick-frozen, freeze-fracture and deep-etched study of the cuticle of adult forms of Strongyloides venezuelensis (Nematoda).

Abstract

The cuticle of adult forms of Strongyloides venezuelensis was studied by routine transmission electron microscopy, conventional freeze-fracture and also using quick-freeze and deep-etch techniques. In routine thin sections the cuticle of S. venezuelensis comprises 7 layers: epicuticle, outer cortical, inner cortical, external medial, internal medial, fibrous and basal. Observation of replicas of specimens fractured across the thickness of the body wall, revealed at the epicuticle an ordered array of particles accompanying the cuticular annulations. At the level of the cortical and medial layers we observed few scattered particles embedded in an amorphous matrix without a particular arrangement. The fibrous layer was represented by several parallel lines of ordered particles of similar size. In tangentially fractured specimens, the epicuticle cleaves readily exposing 2 faces, one exhibiting intramembranous particles without any particular arrangement, immersed in a smooth matrix (P face), and the other showing depressions and very few particles (E face). In replicas of fractures submitted to etching, we observed at the level of the cortical, medial fibrous and basal layers an interconnecting fibrous and globous structure which was organized in a different direction at the fibrous layer. The association of freeze-fracture to deep-etch technique revealed the internal structural organization of the cuticle layers showing details that were not seen before using conventional freeze-fracture technique.