Immunohistochemical localization of FSH cells in the pars distalis of the pituitary gland in five-month-old laying hens

The present study was performed to determine the structural differences and immunohistochemical distribution of follicle-stimulating hormone (FSH) producing cells in the pars distalis region of the pituitary glands of 5 month-old laying hens, using the labeled avidin-biotin method. Hens begin to lay eggs at approximately the age of 5 months. It was observed that gonadotrophic cells containing FSH were present in both the cephalic and caudal zones and were densely distributed throughout the pars distalis. They appeared to be arranged in either cords or follicles in which branching and anastomosing occurred as well as being found as separate cells. The strongest positive FSH immunoreactivity was observed in most of the cells located in the caudal and cephalic zones of the pars distalis in 5 month-old laying hens. Furthermore, the total numbers of FSH immunoreactive cells (in 1 mu m(2)) were similar in the cephalic and caudal zones.