Mammary Cells 'remember' Earlier Pregnancy (IMAGE) Cold Spring Harbor Laboratory Caption These images show the effect of pregnancy hormones after 6 and 12 days on breast tissue in mice that have never been pregnant (top row) and mice that have been pregnant once before (bottom row). The mammary gland in previously pregnant mice responds earlier and produces more branching ductal structures, used in lactation. New research shows breast tissue retains a cellular memory of prior pregnancy that makes response more rapid and vigorous in subsequent pregnancies. Credit Hannon lab, CSHL Usage Restrictions please give credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.