Studies On Morphology And Development Of Pituitary In The Southern Catfish, Silurus Meridionalis Chen

From October, 2001 to April, 2002, by means of anatomy, histology, histochemistry and transmission electron microscopy, the morphology, histological structure and ultrastructure of pituitary in different developmental stage and physiological status of southern catfish have been studied in detail. The results indicate that:There are two major portions of the pituitary, the adenohypophysis and neurohypophysis. The adenohypophysis is further divided into pre-adenohypophysis, Mesoadenohypophysis and Meta-adenohypophysis. The volume of Mesoadenohypophysis in the adenohypophysis increases with gonadal development and maturation. The neurohypophysis is enveloped by adenohypophysis. The type of pituitary in Silurus meridionalis belongs to dorsal-pelvic.The adenohypophysis is comprised of seven secreting cells, namely, corticotrophs, prolactin cell, gonadotrophs, growth hormone cell , thyrotrophs, melanophore stimulating hormone cell and big dunk cell. Corticotrophs secretes actively during reproductive season. The amount of secretion granules, mitochondria and endoplasmic reticulum change obviously. Gonadotrophs distribute in pre-adenohypophysis, Mesoadenohypophysis and Meta-adenohypophysis. Gonadotrophs secretes actively and the dunk appears in the edge of Gonadotrophs during reproductive season. The secretion granules are released and the dunks fuse and almost occupy all the place of Gonadotrophs after reproduction. Under electron microscopy, there are three types of secretion, that is, small granules, big granules and anomaly gobbet in Gonadotrophs. According to the secretion and the change of cell physiology, Gonadotrophs is divided into two types. In type one, the electron density of secretion granules is high, the amount of secretion granules decreases, mitochondria is abundant and endoplasmic reticulum expands during reproductive season; After reproduction, a great deal of the secretion is released, The volume of cell deceased and the shape of nuclelus changed or disappeared. In type two, the electron density of secretion granules was low, Golgi complex and endoplasmic reticulum flourishedduring reproductive season; after reproduction, a great deal of the secretion was released and the shape of nuclelus changed. They both related to reproduction. Growth hormone cell extended from pre-adenohypophysis to Mesoadenohypophysis. They are also divided into two types. In type one, mitochondria is abundant, the secretion granules fuses, then its shape changed, finally it was secreted during reproductive season; After reproduction, almost all secretion was released and en'doplasmic reticulum expanded. They are all relative to reproduction. The type two did not change during reproductive season. It relates to growth. In Meta-adenohypophysis, there is another type of cell: the big dunk cell.The pituitary of the southern catfish origins from the epithliu cells of the original cavum oris during embryo and from the cells which were separated from the infundibulum. The former composes the adenohypophysis and the latter forms the neurohypophysis. The epithelium cells of the original cavum oris located at the bottom of the diencphalon in just hatched juvenile and touched the infundibulum; by 36 hours after hatch, the epithelium cells zygosised with those cells which originated from the infundibulum and the primary pituitary gland was formed; by 48 hours the pituitary can be distinguished into two parts: adenohypophysis and neurohypophysis; by 62 hours the cells started to differentiate; by 4 days and 17 hours the adenohypophysis was divided into three portions and the relationships of the pituicytes and the ependyma cells from the third ventricle wall are obvious; by 6 days and 6 hours the growth hormone cells had differentiated; by 21 days the cells in pre-adenohypophysis started to differentiate; by 30 days the cells in Meta-adenohypophysis started to differentiate; by 36 days the basophils appeared in Mesoadenohypophysis; by 48 days the morphological endocrine cell types except for Gonadotrophs in adenohypophysis...