Tamoxifen temporarily retards ductal elongation during pubertal mammary gland development. (A) Bar graph depicting the quantification of mammary gland outgrowth, showing relative elongation of the inguinal mammary gland between P23 and P43 in mice treated with sunflower oil (n = 4), 1 mg/25 g of tamoxifen (n = 4), or 4 mg/25 g of tamoxifen (n = 4). The position of the most distal tip of the lymph node is set at zero. (*P < 0.05, **P < 0.01). (B) Whole-mount preparations of carmine alum-stained mammary epithelium, showing representative images of the inguinal glands quantified in panel (A). Arrows indicate the relative outgrowth of the epithelium. Scale bar = 500 μm. (C) Close-up of the glands depicted in (B), showing loss of terminal-end bud structures in mice treated with 4 mg/25 g tamoxifen. Scale bar = 20 μm. (D) Whole-mount carmine alum staining of thoracic glands. Scale bar = 500 μm. (E) Close-up of thoracic glands depicted in (D). Scale bar = 20 μm.