Changes in the population of proliferating cells in chicken anterior pituitary during induced molting: an immunocytochemical analysis for proliferating cell nuclear antigen.

The goal of this study was to determine whether cell proliferation is increased in the anterior pituitary during an induced molting period in chickens. The anterior pituitaries were collected from: 1) laying hens before initiation of an induced molt (control hens), 2) molting hens 2 to 16 d after cessation of lay, and 3) second cycle laying hens 1 d after returning to lay. Pituitary cephalic and caudal lobes were processed for immunocytochemistry of proliferating cell nuclear antigen (PCNA), and positive cells were counted by an image analyzer using light microscopy. In cephalic and caudal lobes, a small number of positive cells were observed in controls and molting hens 2 d after cessation of lay. The frequency of PCNA-positive cells started to increase from 7 d after cessation of lay (3 d after refeeding), and a significantly higher frequency of positive cells was observed in both lobes of molting hens 13 d after cessation of lay when compared to control hens, molting hens 2 d after cessation of egg lay, and second cycle laying hens. The frequency of PCNA-positive cells in second cycle laying hens decreased to a similar level to that of control hens. These results suggest that anterior pituitary tissue may be remodeled partially by a proliferation of cells during induced molting in hens.