Testicular regression occurs during the non-breeding season in many mammals. This affects spermatogenesis, resulting in decreased or arrested activity. Both lead to a decrease or cessation in sperm production. In recent years, the cellular mechanisms that lead to infertility in males in non-reproductive periods have been studied in very different species of mammals. At the start of the present century, the main mechanism involved was considered as an increase in the apoptotic activity of germ cells during the regression period. The loss of spermatogonia and spermatocytes causes not only a decrease in spermatogenesis, but an arrest of the seminiferous epithelium activity at the end of regression. Recently, in some mammal species, it was found that apoptosis is the usual mechanism involved in epithelium activity arrest, although it is firstly atrophied by massive desquamation of the germ cells that are released from their binding with the Sertoli cells, and which are shed into the lumen of the seminiferous tubule. In other species, it has been shown that not only germ cell apoptosis, but also Sertoli cell apoptosis, including decreased proliferative activity, spermatophagy or autophagy, are involved in testicular regression. Furthermore, the most recent studies indicate that there are multiple patterns of seminiferous epithelium regression in seasonally breeding animals, which may not only be used by different species, but also by the same ones to reproduce in the best conditions, ensuring their survival. In conclusion, at this time, it is not possible to consider the existence of a paradigmatic cellular mechanism in the involution of the seminiferous epithelium applicable to all male mammals with seasonal reproduction, rather the existence of several mechanisms which participate to a greater or lesser extent in each of the species that have been studied to date.

Pigs are usually bred through artificial insemination with liquid semen preserved at 15-20 °C. While this method of preservation brings many benefits, including a greater reproductive performance compared to frozen-thawed sperm, the period of storage is a limiting factor. As the mitochondrion regulates many facets of sperm physiology, modulating its activity could have an impact on their lifespan. Aligned with this hypothesis, the present study sought to investigate whether inhibition of voltage-dependent anion channels (VDACs), which reside in the outer mitochondrial membrane and regulate the flux of ions between mitochondria and the cytosol in somatic cells, influences the resilience of pig sperm to liquid preservation at 17 °C. For this purpose, semen samples (N = 7) were treated with two different concentrations of TRO19622 (5 μM and 50 μM), an inhibitor of VDACs, and stored at 17 °C for 10 days. At days 0, 4 and 10, sperm quality and functionality parameters were evaluated by flow cytometry and computer-assisted sperm analysis (CASA). The effects of inhibiting VDACs depended on the concentration of the inhibitor. On the one hand, the greatest concentration of TRO19622 (50 μM) led to a decrease in sperm motility, viability and mitochondrial membrane potential, which could be related to the observed intracellular Ca²⁺ increase. In contrast, total sperm motility was higher in samples treated with 5 μM TRO19622 than in the control, suggesting that when VDACs channels are inhibited by the lowest concentration of the blocking agent the resilience of pig sperm to liquid storage increases. In conclusion, the current research indicates that mitochondrial function, as regulated by ion channels in the outer mitochondrial membrane like VDACs, is related to the sperm resilience to liquid preservation and may influence cell lifespan.

The morphophysiology of intratesticular sperm pathways in mammals, including humans, is poorly understood. The seminiferous tubule is continuous with the straight tubule; however, its final portion—the terminal segment (TS)—has a different tissue composition. This paper reviews the most important histological results from mammal studies from the last decades of the 20th century, including the different nomenclatures given to the TS. The TS presents a loss of spermatogenesis and is lined mainly with modified Sertoli cells. There is no unanimity among authors when it comes to naming and defining TS. In the last ten years, studies on rats and mice have highlighted the importance of this testicular zone, proposing that there is a high proliferation of modified Sertoli cells with an undifferentiated cellular profile associated with stem spermatogonia. In hamsters, an immunohistochemical study showed the existence of heterogeneity between these cells, and the surrounding interstitium presents numerous Leydig cells that are ultrastructurally different from those of the rest of the testis rest. In conclusion, we have only just begun to understand the tissue biology of TS. Emerging research is very promising; it can potentially modify our current knowledge of testicular biology and be very useful in promoting the advancement of male fertility restoration therapies in andrology.

In testicular pathology, the accumulation of extracellular matrix and thickening of the peritubular lamina propria are associated with altered spermatogenesis. This study evaluated the immunoexpression of certain proteins in Sertoli and myoid cells of cryptorchid boar seminiferous tubule sections to determine the role of these cells in peritubular lamina propria thickening. Sections of normal seminiferous tubules and those with varying degrees of atrophy (I–III) were studied using histochemical and immunohistochemical techniques. A semiquantitative analysis of histochemical staining or immunostaining intensity in these sections was performed. Gradual thickening of the peritubular lamina propria was observed between stage II and III sections. HSP47 was present in myoid and Sertoli cells in normal sections and was significantly increased in stage II and III sections. The increase in stage II was dependent on Sertoli cells, while in stage III, it depended on myoid cells. The vimentin increases in stage I sections were due to Sertoli cells and later to myoid cells in stages II and III. α-actin and collagen IV immunoreactivity were observed from the early stage of atrophy, with a significant increase in stage III. In conclusion, in porcine spontaneous cryptorchidism, the seminiferous tubule exhibits gradual fibrotic alterations in the peritubular lamina propria, initially related to changes in the Sertoli cell phenotype and later, in the final stages, to myoid cells. Collagen I deposition appears to be caused by myoid cells, initiating the sclerosis of the seminiferous tubules.

Background: The oxytocin receptor (OR) is a G‐protein‐coupled receptor recently identified in human spermatozoa, whose origin and role in sperm physiology remain unknown. Objectives: In this study, using the pig as a model, we examine the presence of the OR in ejaculated spermatozoa through immunofluorescence and immunoblotting, and investigate the receptor's origin in the male gamete via immunohistochemistry in testicular and epididymal tissues. Additionally, we assess the involvement of the OR in in vitro capacitation and the acrosome reaction by utilizing physiological concentrations of agonists (oxytocin and carbetocin) and an antagonist (L‐371,257). Results: The results indicate that, in addition to the expected presence in ejaculated spermatozoa, the OR is expressed during spermatogenesis. Besides, this receptor is found in Leydig and Sertoli cells, as well as in the principal, basal, and apical cells of the epididymis. Furthermore, our data suggest that, during epididymal maturation, the OR could be incorporated in spermatozoa via extracellular vesicles within the apical blebs. The OR is involved in sperm capacitation, as the combination of the antagonist (L‐371,257) and the agonist (carbetocin) increases intracellular calcium levels and membrane lipid disorders, which are known as capacitation markers. Conclusions: The presence of the OR in mammalian spermatozoa could originate from both spermatogenesis and epididymal maturation. Moreover, in the male gamete, this receptor regulates sperm capacitation by interacting with its ligand in the female reproductive tract.

The follicular fluid (FF) is a complex and dynamic biological medium that surrounds the oocytes during their development and growth. This fluid provides the necessary nutrients to both the oocyte and the surrounding cells, enabling the proper maturation of the oocyte. Additionally, the FF is involved in key sperm function processes, such as capacitation, which occurs when sperm reach the oviduct and are exposed to this fluid. Nevertheless, how this happens in donkeys has not been investigated. For this reason, the present study aimed to evaluate the influence of the FF on sperm capacitation in the donkey. Preovulatory FF was obtained from five different Catalan jennies (two follicles per animal), and nine ejaculates from fertile Catalan donkeys were collected. Sperm were resuspended in four different treatments: non-capacitating medium (TBM), non-capacitating medium supplemented with 20 % FF (TBM+FF), capacitating medium (TCM), and capacitating medium supplemented with 20 % FF (TCM+FF). Samples were incubated at 38 °C for 120 min, and at 60 min, progesterone was added to induce the acrosome reaction. After 0, 60, 70, and 120 min of incubation, sperm motility, membrane lipid disorder, acrosome integrity, mitochondrial membrane potential (MMP), and intracellular concentrations of calcium, reactive oxygen species (ROS) and superoxides were evaluated. These results suggest that the preovulatory FF promotes sperm capacitation in donkeys, as it increases intracellular calcium, membrane lipid disorder, and acrosome exocytosis, while maintaining sperm motility and reducing ROS concentration. Although the results are not entirely conclusive and further tests are needed, this study supports that the FF modulates sperm capacitation and alleviates the oxidative stress associated with this process.