Sectioning Mammary Gland Whole Mounts for Lesion Identification.

Normal mammary gland development may be altered by exposure to environmental toxicants and pharmaceutical products, excessive exposure to hormones, and genetic alterations. Mammary gland whole mounts are an inexpensive method to capture the progression of morphological changes that may arise after exposure. However, in later life, when abnormalities are more prone to develop, sole reliance on this one method may not always provide enough information to make a proper diagnosis of the abnormality. Historically, in chemical test guideline studies, a single mammary gland is removed at necropsy and prepared as a hematoxylin and eosin (H&E)-stained section. The incorporation of contralateral mammary whole-mount collection and analysis decreases the likelihood of a false-negative assessment. Evaluation of the whole mount is limited by the presence of one or two entire mammary glands on a slide, and in some cases, the abnormalities observed in the whole mount are not uniformly represented in the H&E section.  The goal of this study was to develop a protocol for converting coverslipped mammary whole mounts to H&E-stained sections so that lesions that would otherwise have been missed or that are difficult to diagnose can be identified. Here, we detail a method to produce a high-quality, paraffin-embedded H&E section from a mammary gland that was initially prepared as a whole mount. In comparison to a tissue that was intentionally prepared for H&E sectioning, the whole mount requires additional preparation for tissue removal and processing. However, this method is considered inexpensive, as it requires common lab reagents and little additional time. As a result, this method can provide invaluable information on how chemical and environmental exposures alter normal mammary development, as well as display changes that occur because of genetic modifications.

Mammary Gland Evaluation in Juvenile Toxicity Studies: Temporal Developmental Patterns in the Male and Female Harlan Sprague-Dawley Rat.

There are currently no reports describing mammary gland development in the Harlan Sprague-Dawley (HSD) rat, the current strain of choice for National Toxicology Program (NTP) testing. Our goals were to empower the NTP, contract labs, and other researchers in understanding and interpreting chemical effects in this rat strain. To delineate similarities/differences between the female and male mammary gland, data were compiled starting on embryonic day 15.5 through postnatal day 70. Mammary gland whole mounts, histology sections, and immunohistochemically stained tissues for estrogen, progesterone, and androgen receptors were evaluated in both sexes; qualitative and quantitative differences are highlighted using a comprehensive visual timeline. Research on endocrine disrupting chemicals in animal models has highlighted chemically induced mammary gland anomalies that may potentially impact human health. In order to investigate these effects within the HSD strain, 2,3,7,8-tetrachlorodibenzo-p-dioxin, diethylstilbestrol, or vehicle control was gavage dosed on gestation day 15 and 18 to demonstrate delayed, accelerated, and control mammary gland growth in offspring, respectively. We provide illustrations of normal and chemically altered mammary gland development in HSD male and female rats to help inform researchers unfamiliar with the tissue and may facilitate enhanced evaluation of both male and female mammary glands in juvenile toxicity studies.

Preparation of High-quality Hematoxylin and Eosin-stained Sections from Rodent Mammary Gland Whole Mounts for Histopathologic Review.

Identifying environmental exposures that cause adverse mammary gland outcomes in rodents is a first step in disease prevention in humans and domestic pets. "Whole mounts" are an easy and inexpensive tissue preparation method that can elucidate typical or abnormal mammary gland morphology in rodent studies. Here, we propose procedures to facilitate the use of whole mounts for histological identification of grossly noted tissue alterations. We noted lesions in mammary whole mounts from 14-month-old CD-1 mice that were not found in the contralateral gland hematoxylin and eosin (H&E)-stained section. Whole mounts were removed from the slide and carefully processed to produce high-quality histological sections that mirrored the quality of the original H&E-stained section in order to properly diagnose the unidentified gross abnormalities. Incorporation of this method into testing protocols that focus on human relevant chemical and endocrine disruptors exposure will increase the chances of identifying lesions in the gland and reduce the risk of false negative findings. This method can be especially invaluable when lesions are not always palpable during the course of the study or visible at necropsy, or when a single cross section of the mammary gland is otherwise used for detecting lesions.