Structural and experimental investigations of the functional anatomy and the turgor of the notochord in the larval tail of anuran tadpoles.

The premetamorphotic morphology and metamorphotic degeneration of the tail notochord of anuran tadpoles has been investigated. For this purpose the functional anatomy and origin of the notochord turgor was analysed in 10 species macroscopically and using light, transmission and scanning electron microscopic techniques. The notochord consists of the fibrous notochord sheath, which surrounds the notochord cells. Within the sheath these cells form a net-like unit. The inner cells are derived from the marginal notochord cells (chordoblasts). They are protected from mechanical overload by intracellular filaments and desmosomes. Due to their vacuoles, which are filled with a hyaline liquid, they have a constant volume but are deformable. Dissolved substances may pass from the vascularized fin to the notochord cells. The transport from marginal to inner cells occurs via cytopempsis and micropinocytosis. The morphological correlation of this process consists of multiple membrane invaginations and intracellular vesicles. Within the notochord cells a high turgor pressure has been observed. During metamorphosis the membrane vesiculation persists and the notochord cells degenerate. Due to the loss of turgor pressure the tight consistency of the notochord is lost. The collagen filaments and the elastic membrane of the notochord sheath dissolve. Notochord cells with their filaments, high turgor pressure and their central vacuole can function as a combined mechanical and physiological system, which is adaptable to the needs of pressure, compression, tensile and bending forces.

Structural analysis of physiological degeneration and lysis in the larval tail of anuran tadpoles during metamorphosis compared with human histopathology, especially myopathology.

The metamorphotic degeneration of the larval tail of anuran tadpoles was investigated for tissue-typical aspects and for correspondences or similarities with histopathological findings in human diseases. For this purpose, in ten species the premetamorphotic morphology and metamorphotic degeneration of cells and tissues in the larval tail was examined light- and electron-microscopically. Metamorphotic degeneration and lysis occurs in a tissue-specific manner. Thereby, filaments in notochord- and epidermis-cells as well as in the cross-striated musculature can aggregate to a variety of different "compact bodies". These bodies decompose or are taken up by phagocytizing cells. Collagen fibrils and filaments are completely dissolved. Lysed larval tail tissues are resorbed. During evolution, tissue typical degeneration patterns have developed in anuran tadpoles and, despite systematic differences, these are also recognizable in histopathological findings of human diseases, notably myopathies. Structure analyses of tissue degradation in metamorphosing anuran tadpoles may well be applicable as suitable experimental models for investigating the causes and courses of human diseases.