Column And Zi Fish Thyroid Structure And Function Of Neuroendocrine Regulation. Amphioxus Comparative Study

Histology, immunohistochemistry and electron microscope were used to study the structures and functions of the endostyle of amphioxus (Branch iostma belcheri) and the thyroid gland of grey mullet (Mugil cephalus). The results are shown as following:In amphioxus the endostyle forms a groove in the floor of the pharynx and is lined by six paired, longitudinal zones of epithelial cells. Thyrotropin (TSH) is localized within nerve cells and nerve fibre of the brain and epithelial cells of the Hatschek抯 pit, and thyroglobulin (TG) within zone3 and zone5 of the endostyle. With the development and maturating of gonad, each zone of the endostyle becomes wider gradually and immunopositive reactions of TSH and TG both strengthen gradually, too.The thyroid gland of grey mullet is dispersedly distributed in the region of anterior branchial arch. Its follicles are enclosed in connective tissue. With the development and maturating of gonad, the number of thyroid follicles and the height of follicle epithelial cells both increase. There are much more well-developed rough endoplasmic reticulum and mitochondrias in cuboidal and pillared follicular epithelial cells than in flat cells. The nucleus of the follicular cell shows an irregular outline and, sometimes, the nuclear membrane sinks downward dividing the nucleus into two or three segments. The follicular cell has five kinds of vesicles. They are transporting vesicle, secretory vesicle, colloid droplet, primary lysosome and second lysosome. Thyotrophs are localized in proximal pas distalis (PPD) of the pituitary gland. Immunoreactivity of TG is found within the thyroid29follicle lumina and cytoplasm of follicle epithelial cells.Parts of the endostyle are homologous to and possibly also a primitive antecedent of the vertebrate thyroid gland. Compared with the thyroid gland of grey mullet, the endostyle of amphioxus is primitive. It is an open groove and has lots of cillia adjacent to the pharynx lumen. The endostyle can trap food particles by cilliary motion and mucus secreted by endostyle epithelial cells. The thyroid gland of grey mullet is a specific secretory gland and composed of follicles, i.e. monolayer spheres of thyroid epithelial cells without cillium. During the evolution an alimentary (food-collecting) organ (the endostyle of Protochordata) developed gradually to a secretory gland (the thyroid gland of Vertebrate).