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Spermatozoa are produced in seminiferous tubules of the testis, then they mature and are stored in the epididymis. However, they must travel through two structures, the rete testis (discussed in a previous article) and efferent ductules, in order to reach the epididymis. The efferent ductules ( ductuli efferentes ) are a series of parallel thin, delicate tubules that connect the rete testis to a single tube, the epididymis. They are unique because they are the only part of the male reproductive system that is lined by an epithelium having both absorptive cells and cells with motile cilia. The efferent ducts are often referred to as “conduits” because sperm travel so rapidly through these tubules into the epididymis. However, work in the efferent duct epithelium has revealed its intricate kidney-like physiological function of fluid reabsorption that provides an essential role in sperm transport, concentration and maturation and thus male fertility.

Interactions between cells are crucial for the normal physiology of any organ or tissue. In this article, the best known physical and structural cellular interactions present in the testis is discussed, focusing particularly in the junctions/interactions among the cells present in the seminiferous epithelium (i.e., Sertoli and germ cells) and the cells located in the interstitial/intertubular compartment such as Leydig cells and macrophage. As it can be noticed, these interactions provide the production of hormones and the adequate progression of spermatogenesis.

Endocrine regulation of rete testis and the efferent ductules involves a complex interaction of multiple steroid hormone receptors and their ligands, with what is now called an androgen/estrogen balance. Estrogen receptor-α shows constitutive expression and is unaltered by most experimental treatments, including DES. However, DES causes the loss of androgen receptor in the efferent duct epithelium. Pathological changes in this region often appear to be linked to either excessive fluid reabsorption or the opposite, an inhibition of reabsorption. With both deviations, there will be luminal dilation in the proximal region near the rete testis, and if the lesion is found closer to the testis there will be a greater involvement of rete testis and seminiferous tubules. Pathological changes have been associated with several diseases in man and typically involve the development of large cysts, as can be found in proximal tubule diseases of the kidney.

Seminiferous tubules of testis open into a continuous chamber of flattened and irregular-shaped anastomosing channels called the rete testis. Positioned at one pole of the testis (hilus), the rete is adjacent to the connective tissue capsule covering of the testis, known as the tunica albuginea. The hilus is also the location where blood vessels penetrate the capsule. The rete testis serves as a conduit and point of exit for newly released spermatozoa and seminiferous fluids derived from testicular seminiferous tubules. Emerging from the rete are many efferent ductules serving to transport sperm and fluids into the epididymis, the highly convoluted, tubular organ resting on the back of the testis and functioning in the storage and maturation of sperm. In rodents, the rete testis is situated primarily next to the tunica albuginea, while in man and large mammals it extends approximately 1/3–1/2 into the testis proper. The squamous to short cuboidal epithelium is highly active in endocytosis, where several proteins derived from the lumen of seminiferous tubules are taken up and degraded by lysosomes. Some of these proteins are secretory products of Sertoli cells that may interact with sperm as they are formed in the testis, but which are of limited functional importance as they head to the epididymis. The rete appears to be a clearing station for some proteins derived from the testis. Thus while a seemingly passive passageway, the rete has important roles in fine-tuning the lumen for sperm as they enter the efferent ducts. It may also serve in obstructions of the efferent ducts to expand and prevent disruption of the blood–testis barrier. Of clinical significance, the rete testis has over the past decade been used as an appropriate site to inject stem cells into the lumen of seminiferous tubules to restore a deficient or reduced spermatogenesis.

In this article, we cover the main aspects related to testis structure and function, particularly those related to germ cells and support cells present in the seminiferous epithelium and cytoarchitecture of steroidogenic Leydig cells located in the intertubular compartment. A brief description of spermatogenesis, from undifferentiated spermatogonia to sperm formation, as well the organization of germ cells in stages of the seminiferous epithelial cycle and its duration, is also presented. Finally, we describe the key functions accomplished by Sertoli and Leydig cells and the most important parameters related to the magnitude of sperm production in different mammalian species.

Delta-6 desaturase-null mice ((-/-)) are unable to synthesize highly unsaturated fatty acids (HUFAs): arachidonic acid (AA), docosahexaenoic acid (DHA), and n6-docosapentaenoic acid (DPAn6). The (-/-) males exhibit infertility and arrest of spermatogenesis at late spermiogenesis. To determine which HUFA is essential for spermiogenesis, a diet supplemented with either 0.2% (w/w) AA or DHA was fed to wild-type ((+/+)) and (-/-) males at weaning until 16 weeks of age (n = 3-5). A breeding success rate of DHA-supplemented (-/-) was comparable to (+/+). DHA-fed (-/-) showed normal sperm counts and spermiogenesis. Dietary AA was less effective in restoring fertility, sperm count, and spermiogenesis than DHA. Testis fatty acid analysis showed restored DHA in DHA-fed (-/-), but DPAn6 remained depleted. In AA-fed (-/-), AA was restored at the (+/+) level, and 22:4n6, an AA elongated product, accumulated in testis. Cholesta-3,5-diene was present in testis of (+/+) and DHA-fed (-/-), whereas it diminished in (-/-) and AA-fed (-/-), suggesting impaired sterol metabolism in these groups. Expression of spermiogenesis marker genes was largely normal in all groups. In conclusion, DHA was capable of restoring all observed impairment in male reproduction, whereas 22:4n6 formed from dietary AA may act as an inferior substitute for DHA.

Delta-6 desaturase (D6D) catalyzes the first step in the synthesis of highly unsaturated fatty acids (HUFA) such as arachidonic (AA), docosapentaenoic (DPAn-6), and docosahexaenoic (DHA) acids, as well as the last desaturation of DPAn-6 and DHA. We created D6D-null mice (−/−), which enabled us to study HUFA deficiency without depleting their precursors. In −/−, no in vivo AA synthesis was detected after administration of [U-13C]linoleic acid (LA), indicating absence of D6D isozyme. Unexpectedly, all of the −/− developed ulcerative dermatitis when fed a purified diet lacking D6D products but containing ample LA. The −/− also exhibited splenomegaly and ulceration in duodenum and ileocecal junction. Male −/− lacked normal spermatozoa with a severe impairment of spermiogenesis. Tissue HUFAs in −/− declined differentially: liver AA and DHA by 95%, and a smaller decrease in brain and testes. Dietary AA completely prevented dermatitis and intestinal ulcers in −/−. DPAn-6 was absent in −/− brain under AA supplementation, indicating absence of D6D isozyme for DPAn-6 synthesis from AA. This study demonstrated a distinct advantage of the D6D-null mice (−/−) to elucidate (1) AA function without complication of LA deprivation and (2) DHA function in the nervous system without AA depletion or DPAn-6 replacement seen in traditional models.—Stroud, C. K., T. Y. Nara, M. Roqueta-Rivera, E. C. Radlowski, P. Lawrence, Y. Zhang, B. H. Cho, M. Segre, R. A. Hess, J. T. Brenna, W. M. Haschek, and M. T. Nakamura. Disruption of FADS2 gene in mice impairs male reproduction and causes dermal and intestinal ulceration.

Sertoli cell morphology has been thoroughly reviewed in the past from basic light and electron microscopy viewpoints, all of which pointed out the uniqueness of this “mother cell” that sends its cytoplasmic arms as “branches of trees” to hold and nurture the development of germ cells. During the past decade, major advancements in Sertoli cell biology have been made using immunofluorescence and three-dimensional imaging made possible with laser-scanning confocal microscopy. Here, we review our current understanding of Sertoli cell morphology with a specific focus on the cytoskeleton. The relationship of the cytoskeleton to intercellular junctions, ectoplasmic specializations, tubulobulbar complexes, and vesicular transport systems is re-examined. Although newer techniques provide a wealth of data on the molecular components of the Sertoli cell, the results will require additional experimental approaches and careful interpretation to provide consistency in data among anatomy, molecular biology, and cell physiology.

This chapter discusses the structure of the Sertoli cell. The total number of Sertoli cells establishes the upper limit of sperm production by the testis, and spermatogenic efficiency is highly correlated with Sertoli cell support capacity, which is the best indication of Sertoli cell function. Sertoli cell individual volume shows high variation in mammals, varying from approximately 2000–3000 μm 3 to 6000–7000 μm 3 in mammals already investigated. However, it is generally recognized that species in which Sertoli cell volume is high are those with the lowest spermatogenic efficiency. The volume density of Sertoli cells in the seminiferous epithelium also changes considerably in mammals and the mean figures range from approximately 15% in mice and rabbit. One of the first features of the Sertoli cell is the unique appearance of the nucleus and its tripartite nucleolus. The Sertoli cell nucleus is large (250–850 μm 3 ) and can take on several different shapes depending on the stage of the seminiferous cycle and age of development. From birth to adulthood, the nucleus is often elongated, extending toward the lumen, but there are definite changes in appearance as the testis matures. The early support cells of the seminiferous tubule are often called pre-Sertoli cells because the nuclear appearance differs from the adult form, yet in some species the pre-Sertoli cells still have the typical nuclear features of irregular shape and a prominent nucleolus.

This chapter discusses the discovery of Sertoli cell by Enrico Sertoli, an Italian physiologist and histologist who was a native of Sondrio. Sertoli collected several pieces of human testes preserved in a sublimate solution (a precipitating solution formed by adding ammonia to mercuric chloride). Sertoli used an innovative model to investigate the semniferous epithelium, because in humans, unlike in mice and rats, the Sertoli cell occupies about 37% of the epithelium. In contrast, the Sertoli cell occupies about 15–20% in the rodent species. The human testis has a higher ratio of Sertoli to germ cells due to the reduced efficiency of spermatogenesis. Sertoli used several different types of preparations of testes, including microdissections of individual seminiferous tubules, thin sections of the testis after sublimate incubation, pieces of fresh tissue, and frayed sections of tubules. Sertoli cells originated from germ cells or that part of the Sertoli cell population gave rise to germ cells and formed other Sertoli cells in an amitotic process.

Evidence exists for adverse effects of endocrine disruptors on wildlife populations, but there is as yet only limited evidence that links environmental exposure to these substances and adverse effects on human health. It has been suggested that exposure to endocrine disrupting chemicals may be responsible for a possible decline in human sperm production and increases other male reproductive problems such as testicular cancer. This chapter reviews the historical development of work on endocrine disruption and provides a concise description of the state of present knowledge in regards to the ability of chemicals to disrupt a number of hormone systems. In addition, the potential for these compounds to affect animal and human health is discussed. The major potential targets for environmental endocrine disruption are the reproductive, neurological, thyroid, and immune systems. Other endocrine organs, such as stomach, pancreas, kidney, and adrenals, are also potential targets but less is known about their susceptibility. The classes of compound with endocrine-disrupting activity are as follows: estrogens, androgens and antiandrogens, progesterone, steroid receptors such as pregnane X receptors (PXR), polychlorinated biphenyl (PCB), and aryl hydrocarbon receptors.

Histopathological evaluation provides one of the most sensitive end points for detecting the effects of' toxicants on the testis, and is used routinely in the :lSSessment of male reproductive toxicity. However, ~routine" histological methods are often inadequate for maintaining the "scnsitivity~ of this type o f evaluation. Improper fixation and inappropriate combinations or fixative: and embedding media result in unacceptable histological st:clions ( I ). TIle !.liSlor[ions inducctl by inalh:qualc methods can make (he deteCTion of differences be· tween treated and control tissues nearly impossible al all but [he highC!St dosages of a toxicant; thus, the sensitivity of the technique can be IOSlo However, Simply embedding the fixed tissues in a plastic medium such as glycol methac ryl3te medium (G!\.lA), rather than paraffin, can in some cases correct the distortions entirely. Unfortunately, there o;isl large difterences among 13OOra10· ries in the appli cation of these techniques, and thus, wide differences may be found in the interpretations of testicular pathogene.'iis. In the assessment of dlcmical toxicity in thc lestis, the rat is the most common laooratory animal tested. However, the rat testis Is difficuh to preserve: for optimal his{QlogicaJ evaluatiun because it is a fragile: organ, containing large open lymphatic spates and lacking dense connective tissue within the interstitium. Thus, if the tunica albuginea of the testis is cut, seminife.rous tubule.'i protrude like strands of soft spaghetti, and fixation after having opened the 'eslis does link to preserve the normal relati.onship bcrween tubules and interstitium. Because of these tissue·specific proble ms, there has bee n a consistent effort to impro\·e the histolOgical methods used with the ral testis ( for detailed discus· sions of these various improvements, .set" Refs. 19 ). In this chapter protocols of the most common histological methods, as weI! as some new procedures for preservation of the rat testis, arc presented. The meth· ods arc separated , first, by type of fixative; second, by routc or fixafion ; and third, by c mocdding media. 11lt= procedures section is followed by diS