The activity of the pituitary cells of the teleost Poecilia during the gestation cycle and the control of the gonadotropic cells

Abstract

The cytological changes occurring in the pituitary gland during the 24-day gestation cycle of Poecilia are described. Experimental treatments indicate that active gonadotropic cells have enlarged nuclei and nucleoli, increased vacuolation and PAS-positive granulation, and decreased amounts of aldehyde thionin staining granulation. The gonadotropic cells are active from days 1 to 4; decreased activity follows until days 10 and 11. There is then a slight increase in activity which is rapidly reversed to give inactive cells again by day 14 or 15. From day 16 to day 24, the end of the cycle, there is a gradual increase in activity. The neurosecretory fibres of the neurohypophysis that are close to the gonadotropic cells accumulate neurosecretion whenever the gonadotropic cells are inactive. On this basis, a model for the control of the gonadotropic cells is proposed. The cycle of thyrotropic cell activity parallels that previously described for the thyroid. The cells are active during the first 8 days and inactive from days 9 to 16. They are then variable but active until the end of the cycle. The somatotropic cells also show cyclical changes, but there is not sufficient evidence to interpret these changes. It is concluded that the changes seen in the pituitary reflect cycles of activity related to the maturation of ova and to the presence of a gestation cycle.