A developmental atlas of rat mammary gland histology

The mammary gland is a dynamic tissue that undergoes epithelial expansion a nd invasion during puberty and cycles of branching and lobular morphogenesi s, secretory differentiation, and regression during pregnancy, lactation, a nd involution. The alteration in the mammary gland epithelium during its po stnatal differentiation is accompanied by changes in the multiple stromal c ell types present in this complex tissue. The postnatal plasticity of the e pithelium, endothelium, and stromal cells of the mammary gland may contribu te to its susceptibility to carcinogenesis. The purpose of this review is t o assist researchers in recognizing histological changes in the epithelium and stroma of the rat mammary gland throughout development.