The nerve supply of the mammary gland

Proper development and functioning of the mammary gland depends not only on hormones, but also on the nervous system. The aim of this paper was to summarize the existing knowledge on the innervation of the mammary gland in various mammalian species, including domestic animals. In general, the pattern of innervation of this gland is similar in all studied species, i.e. large farm animals, rodents, dogs and beavers, as well as humans. Using the pan-neuronal marker of neural structures PGP-9.5, it was found that the mammary gland is well supplied with nerve fibres. Very rich innervation was discovered in the nipple, and less numerous nerve endings were found in the parenchyma. Nerve fibres supply the skin, especially the nipple, and many nerve terminals are associated with blood vessels and smooth muscles throughout the organ. Immunohistochemical investigations have made it possible to distinguish two major subpopulations of nerve fibres supplying the mammary gland. One of them consists of putative sensory fibres expressing CGRP, SP, GAL and/or PACAP, and the other is presumably composed of adrenergic axons containing TH, DBH, SOM and/or VIP. Studies on the sources of innervation of the mammary gland have confirmed assumptions about the nature of the nerve fibres and have revealed that they derive from the spinal ganglia (DRG) and sympathetic trunk ganglia (SChG). In the rat, mammary gland-projecting (MGP) neurons were also found in the nodose ganglion. So far, the rat and the pig have been tested most comprehensively for the sources of the mammary gland innervation. The MGP sensory neurons were observed ipsilaterally in several consecutive DRG, suggesting that the same neurons supply several successive glands. In the case of the SChG, it was found that MGP neurons are located, among others, in the L1-L4 ganglia, which constitute a specific „mammary gland nerve centre”. Previous studies on the sources of nerve supply to female reproductive organs have revealed that the SChG L1-L4 ganglia also contain nerve cells that project to the ovary, fallopian tube and uterus. Some clinical implications of the mammary gland innervation are also discussed.

The Stage-Specific Plasticity of Descending Modulatory Controls in a Rodent Model of Cancer-Induced Bone Pain

Pain resulting from metastatic bone disease is a major unmet clinical need. Studying spinal processing in rodent models of cancer pain is desirable since the percept of pain is influenced in part by modulation at the level of the transmission system in the dorsal horn of the spinal cord. Here, a rodent model of cancer-induced bone pain (CIBP) was generated following syngeneic rat mammary gland adenocarcinoma cell injection in the tibia of male Sprague Dawley rats. Disease progression was classified as “early” or “late” stage according to bone destruction. Even though wakeful CIBP rats showed progressive mechanical hypersensitivity, subsequent in vivo electrophysiological measurement of mechanically evoked deep dorsal horn spinal neuronal responses revealed no change. Rather, a dynamic reorganization of spinal neuronal modulation by descending controls was observed, and this was maladaptive only in the early stage of CIBP. Interestingly, this latter observation corresponded with the degree of damage to the primary afferents innervating the cancerous tissue. Plasticity in the modulation of spinal neuronal activity by descending control pathways reveals a novel opportunity for targeting CIBP in a stage-specific manner. Finally, the data herein have translational potential since the descending control pathways measured are present also in humans.

A Method to Pre-Screen Rat Mammary Gland Whole Tissue Mounts followed by RNAscope in situ hybridization

Background: RNA in situ hybridization is an extremely useful gene expression analysis technique that preserves the spatiotemporal nature of tissue and allows for evaluation of specific cell populations and morphologies. This technique is especially useful in evaluating expression changes in disease progression models. Tissue processing procedures used to identify pathological disease morphologies in situ could compromise RNA integrity and the reproducibility and quantitative accuracy of RNA in situ hybridization assays. Methods: A combinatorial approach to pre-screen rat mammary gland tissue whole mounts for hyperplastic and malignant lesions that were not visually discernible without staining was used. This pre-screening process was followed by an RNA in situ hybridization analysis method known as RNAscope. Results: We show that there are no differences in the quantitative nature of RNAscope assays between tissue that was immediately formalin-fixed and paraffin embedded (FFPE), which is recommended by the manufacturer, and tissue that was whole mounted and pre-screened for lesions of interest prior to RNAscope. Conclusions: Preserving the integrity of RNA and quantitative nature of the RNAscope assay is important, as it allows unpalpable lesions to be directly identified, bypassing a need for labor-intensive serial sectioning of FFPE tissues to find lesions. This method is applicable to any epithelial-based disease progression model using whole-tissue mounts.

Chronic Exposure to Altered Gravity During the Pregnancy-to-Lactation Transition Affects Abundance of Cytoskeletal Proteins in the Rat Mammary Gland

The mammogenic, lactogenic, and lactopoetic effects of prolactin (PRL) in the mammary gland are mediated through a specific cytokine receptor, the PRL-receptor (PRLR). PRLR is anchored to the cytoskeleton and its activation, and subsequent signal transduction, is dependent on an integral/intact cytoskeletal organization. Previous studies revealed a down-regulation of PRLR and reduced metabolic output in the mammary gland of rats exposed to hypergravity (HG). Therefore, the objective of this study was to use quantitative immunohistochemistry to determine the effects of HG exposure during pregnancy on the pre- and postpartum abundance of the cytoskeletal proteins in the rat mammary gland. Pregnant rats were exposed to either 2xg [HG] or 1xg [Stationary control (SC)] from days 11 to 20 of gestation (G20) through postpartum days 1 (P1) and 3 (P3). Spectral characterization and quantitation of each antigen (actin, tubulin, cytokeratin, and vimentin) per lobule (n=3–7 lobules/micrograph; 4 micrographs/slide) was computed using the CRi Nuance multispectral system. At G20 and P3, increased (p<0.001) amounts of actin, tubulin, cytokeratin, and vimentin were detected in HG rats. Tubulin, cytokeratin, and vimentin were overexpressed (p<0.01) in HG group compared to SC at P1. These results suggest that atypical composition of cytoskeletal proteins contribute to the aberrant lactogenic signal transduction and associated reduced postpartum mammary metabolic output in rats exposed to altered inertial environment.