Cellular basis for elevated prolactin secretion during incubation behavior in Bantam chickens: analysis by reverse hemolytic plaque assay.

Incubation behavior in birds is characterized by elevated serum prolactin (PRL) levels. The objective of this study was to determine the cellular basis for increased PRL secretion. Incubation behavior of Bantam hens was induced by allowing the hens to accumulate their eggs. In experiment 1, hens were allowed to accumulate their eggs in floor pens for 0, 2, 12, or 24 days (Day 0, Day 2, Day 12, and Day 24 hens, respectively). Anterior pituitaries were dissociated into individual cells with trypsin, and the resulting cells were then subjected to reverse hemolytic plaque assays for PRL. The percentage of PRL-secreting cells and serum PRL levels were higher in Day 24 hens than in the other groups (p < 0.05; n = 3 separate trials). In experiment 2, hens were allowed to accumulate their eggs for 2, 14, 18, or 24 days (Day 2, Day 14, Day 18, and Day 24 hens, respectively). The percentage of PRL-secreting cells and levels of serum PRL were greater in Day 18 and Day 24 hens than in Day 2 hens (p < 0.05; n = 4). Results from Day 14 hens were intermediate and different (p < 0.05) from those from both Day 2 and Day 18 groups. Data indicate that an increase in the proportion of PRL secretors occurred between 14 and 18 days after hens began to accumulate their eggs. The area of plaques formed by lactotrophs from Day 14 and Day 18 hens was also increased (p < 0.05). In experiment 3, hens were allowed to accumulate their eggs for 0 and 24 days (Day 0 and Day 24 hens, respectively). Their anterior pituitaries were dissected into cephalic, middle, and caudal regions, and the percentage of PRL cells were analyzed in each region separately. The percentage of PRL secretors was increased (p < 0.05) in Day 24 compared to Day 0 hens in both the cephalic and middle regions of the anterior pituitary but not in the caudal portion. We conclude that increased PRL secretion during incubation behavior involves the recruitment of additional pituitary cells into the PRL-secreting population and an increase in the capacity of these cells to secrete hormone (p < 0.05). Furthermore, this increase in PRL-secreting cells is localized to the cephalic and middle regions of the anterior pituitary.