Differential Expression of Serotonin, Tryptophan Hydroxylase and Monoamine Oxidase A in the Mammary Gland of the Myotis velifer Bat

Abstract

The mammary gland has long drawn the attention of the scientific community due to the limited knowledge of some fundamental aspects involved in the control of its function. Myotis velifer, a microchiropteran species, provides an interesting model to study some of the regulatory factors involved in the control of the mammary gland cycle. Having an asynchronous, monoestrous reproductive pattern, female M. velifer bats undergo drastic morphological changes of the breast during the reproductive cycle. Current research on non-chiropteran mammals indicates that serotonin (5-HT) plays a major role in the intraluminal volume homeostasis of the mammary gland during lactation; however, an analysis of both the expression and localization of the main components of the serotonergic system in the bat mammary gland is lacking. Thus, the objectives of the present study were: to describe the gross and histological anatomy of the mammary gland of M. velifer to establish the lactation period for this species; to analyze the distribution and expression of the main serotonergic components in the mammary tissues of these bats under the physiological conditions of lactation, involution and the resting phase; and to provide information on the involvement of 5-HT in the regulation of the physiological function of this organ. To assess the expression and localization of serotonergic components, multiple immunofluorescence, Western blot and HPLC methods were used. 5-HT and the enzyme that catalyzes its synthesis (TPH) were located in both myoepithelial and luminal epithelial cells, while the enzyme responsible for the catabolism of this neurohormone (MAO A) was found in luminal epithelial cells as well as in secreted products. We also found an increased expression of serotonergic components during lactation, indicating that elements of the serotonergic system may play an important role in lactation in this species of bat in a way similar to that of other mammal species.

Indolaminergic System in Adult Rat Testes: Evidence for a Local Serotonin System

“…In mammals, a few studies have reported the presence and distribution of 5-HT in reproductive organs from both male and female individuals, but its functional contributions remain obscure (Fujinoki, 2011;Jiménez-Trejo et al, 2012, 2013Vela-Hinojosa et al, 2013). In a first attempt to decipher its role, we have described the distribution of several elements of the serotoninergic system in the testes during spermatogenesis, the mating period, fertilization, and the sperm maturation processes occurring in the caput epididymis (Jiménez-Trejo et al, 2007, 2012, 2018.…”

Characterization of mammary-specific disruptions for Tph1 and Lrp5 during murine lactation

“…In an autocrine-paracrine fashion, serotonin is known to regulate tight junctions between mammary epithelial cells to control milk volume 9 and β-casein expression 10 , specifically through the serotonin receptor 7 11 in mouse and human epithelial cells. Serotonergic regulation appears to be conserved across species: the bovine mammary gland is known to express several serotonin receptor isoforms 12 and the Myotis velifer bat mammary gland shows differential expression of serotonin and Tph 13 . Serotonin has also been implicated in the regulation of a variety of broader physiological processes during lactation.…”

Serotonin Suppresses β-Casein Expression <i>via</i> Inhibition of the Signal Transducer and Activator of Transcription 5 (STAT5) Protein Phosphorylation in Human Mammary Epithelial Cells MCF-12A

“…19) Although we did not determine levels of the 5-HT7 receptor or occurrence of apoptosis in this study, the decrease in β-casein protein upon 5-HT treatment is likely induced via signaling through the 5-HT7 receptor, accompanied by apoptosis. Furthermore, a 5-HT transporter has been detected in human mammary epithelial cells, 20) and levels of tryptophan hydroxylase 1 (TPH1), a rate-limiting enzyme in 5-HT biosynthesis, are elevated during pregnancy and lactation in mouse and bat mammary epithelial cells. 14,21) Fluoxetine, an SSRI that perturbs serotonin balance by binding to the serotonin reuptake transporter within mammary glands, inhibits β-casein expression in primary bovine mammary epithelial cells.…”