IMMUNOHISTOCHEMICAL STUDY OF POSTNATAL DEVELOPMENT OF PROLACTIN-PRODUCING CELLS IN C57BL MICE

Sexual dimorphic changes in postnatal development of prolactin (PRL)-producing cells in the anterior pituitary gland in C57BL mice were immunohistochemically investigated. When examined at birth, PRL cells were already present in both male and female mice. With advancement of age, PRL cells increased in number. The shape of PRL cells at birth was oval, but on day 7 irregular-shaped PRL cells appeared. The shape of immunoreactive secretory granules in PRL cells were spherical at birth and also at day 7. However, on day 14 polymorphic PRL granules began to appear in type III PRL cells in both male and female mice. The ratios among type I, II, and III PRL cells and also the total number of all types of PRL cells were not different between male and female mice until 4 weeks of age. Meanwhile, type II PRL cells were predominant in both sexes. From 5 weeks of age, type III PRL cells began to increase in number in female mice only, thus sexual dimorphism in PRL cell types became noticeable during pubertal changes. The present results suggest that postnatal morphological, particularly sexual dimorphic, changes observed in secretory granules as well as cell shapes of PRL cells are mainly due to the reflection of endocrine functions in pubertal female mice.