Seasonal changes in the distribution of gonadal lipids and spermatogenetic tissue in the male phase of Monopterus albus (Pisces: Teleostei)

The gonad of Monopterus albus undergoes cyclical changes after the reversal of sex from female to male. The seasonally variable events include a prenuptial accumulation of cholesterol-positive lipid droplets in the cytoplasm of the interstitial cells when spermatogenetic activity is resumed in late February and early March. The development of the interstitial Leydig cells reaches a maximum in May just before spawning. There occurs a sudden depletion of the interstitial lipids during the breeding season in June at a time when the male animals exhibit active nuptial behaviour. After spermiation, the old interstitial cells degenerate, and during the succeeding phase of gonadal inactivity, become replaced by a new generation from connective tissue cells in the interstitium of the gonadal lamellae which gradually accumulate lipoidal material.
The lobular cycle comprises a postnuptial accumulation of amorphous intralobular lipids which become completely cleared in February when active spermatogenesis is restored. Spermatogenesis resumes shortly after spawning, but only advances as far as primary spermatocytes during the postnuptial period of inactivity.
The authors conclude that, as far as the seasonal variations in gonadal lipid distribution is concerned, the cycles in the gonad of the hermaphroditic teleost, M. albus , conform to the same pattern as those of the gonochoristic seasonal breeders studied.     

Paracloacal glands of Alligator mississippiensis: A histological and histochemical study

The histology of the paracloacal 'musk' glands of adult American alligators ( Alligator mississippiensis ) is described. The gland is a single secretory sac with a single duct and a central lumen partially occluded by a central, cylindrical conglomerate of cells and secretion product. The capsule of the gland consists of an outer layer of smooth muscle and an inner layer of connective tissue containing collagen and elastin fibres. Septa carrying blood vessels radiate from the connective tissue layer of the capsule to the border of the central conglomerate. Parenchymal cells containing lipid droplets enlarge from the periphery to the centre of the gland. Secretions formed by degeneration of cells in the central cylinder are concentrated near the secretory duct. Histochemical tests indicate lipids but not mucopolysaccharides in the glandular exudate.     

In vivo differentiation of brown adipocytes in adult mice: an electron microscopic study

The differentiation of brown adipocyte precursor cells was studied in interscapular brown adipose tissue of adult mice by electron microscopy. Different stages of cell differentiation were characterized in situ. Previous autoradiographic studies suggested that interstitial cells represent the precursor cells of fully differentiated brown adipocytes. The present observations provide morphological evidence for a progressive differentiation of interstitial stem cells into mature brown adipocytes. Four typical stages of development were identified: (1) interstitial cells, (2) protoadipocytes, (3) preadipocytes, and (4) mature brown adipocytes. Interstitial stem cells were small spindle shaped cells, situated between brown adipocytes and characterized by a high nuclear-cytoplasmic ratio, the scarcity of organelles, and the absence of lipid inclusions. Protoadipocytes resembled interstitial cells except that they contained a few tiny lipid droplets in their cytoplasm. Preadipocytes had a larger cytoplasm enclosing many mitochondria and lipid droplets; the smooth endoplasmic reticulum was well developed surrounding the lipid droplets, and was closely associated with the mitochondria. Preadipocytes had the typical structure of growing cells, developing long cytoplasmic processes between and around blood capillaries. Mature brown adipocytes represented the final stage of differentiation. Almost all their cellular volume was occupied by lipid droplets and numerous mitochondria with very dense cristae. Brown adipocytes were also characterized by a tight association with blood capillaries, as expected from metabolically active cells requiring oxygen and substrates. These observations provide direct ultrastructural evidence for a progressive differentiation of interstitial cells into brown adipocytes with a continuum of intermediate cellular types.     

Ovarian interstitial tissue of the wood mouse, Apodemus sylvaticus

The ovary of the wood mouse contains an unusually large amount of interstitial tissue which appears to develop from undifferentiated cells of the ovarian stroma and also by transformation of theca or granulosa cells of atretic follicles. The cells are characterized by the presence of smooth endoplasmic reticulum, rounded mitochondria with tubular cristae, and abundant, large (1.5 micron diameter) lipid droplets containing cholesterol and its esters. 3 beta-Hydroxysteroid dehydrogenase activity occurs in the interstitial cells. Their ultrastructural characteristics suggest that the cells are not very active, but their abundance and the considerable amount of steroid hormone precursor they contain may compensate for low secretory activity and they may be an important and (from a developmental viewpoint) early source of steroid hormone.     

Cytochemical observations concerning the formation,release, and transport of lipid secretory products in the interstitial (thecal) cells of the rabbit ovary

Summary The release of lipid droplets from the ovarian interstitial gland cells of thecal origin into the circulating blood has been studied by cytochemical methods. Estrous, preovulatory, and postovulatory ovaries of rabbits were used. Ovulation was induced by human chorionic gonadotropin (HCG) administration. The cytoplasm in the gland cells of estrous ovaries is filled with lipid droplets consisting of cholesterol or its esters, triglycerides, and some phospholipids. Mitochondria, Golgi zone, and diffuse lipoproteins are well differentiated. The lipid droplets decrease in interstitial gland cells of preovulatory ovaries stimulated with HCG. The release of lipid droplets by the formation of vacuoles is closely accompanied by a considerable loss of cytoplasm and its organelles; consequently the cells are reduced in size. Degenerating gland cells do not release their lipids because they are refractory to gonadotropic stimulation. The released secretory products are found in the form of discrete bodies between gland cells, in regions adjacent to blood vessels, and in the lumen of the latter. The mechanism by which the liberated lipids are transported into the circulation could not be determined. The depletion of lipid droplets is clearly related with the production of 20a-OH steroid (20a-hydroxy-pregn-4-en-3-one) and progesterone studied by other workers.The replenishment of cytoplasm and its organelles, and the formation and storage of secretory lipid granules have also been studied both in the preovulatory and postovulatory ovaries. The organelles could not be seen to be visibly related to lipid synthesis.     

Ultrastructure of rhesus monkey renomedullary interstitial cells.

The fine structure of rhesus monkey renomedullary interstitial cells was studied by electron microscopy. These stellate cells contained variable numbers of lipid droplets, moderate numbers of mitochondria, moderate amounts of rough endoplasmic reticulum, and prominent Golgi zones. In rare instances, apparent release of lipid droplets into the interstitium was observed. The most prominent feature of the interstitial cells was larger nuclear pseudoinclusions which were observed in a high proportion of the animals examined.     

Organization of interstitial tissue in the testis of the salamander Necturus maculosus (Caudata: Proteidae)

In Necturus maculosus the organization of the interstitial tissue varies according to the stage of spermatogenesis. Leydig cells at various stages of differentiation and myoid cells are always present in this tissue. The Leydig cells are undifferentiated at all phases of germ cell activity and only hypertrophy following spermiation and degeneration of Sertoli cells. These Leydig cells are structurally analogous to mammalian Leydig cells. They do not form part of the lamina propria of the seminiferous lobules and hence cannot be referred to as lobule-boundary cells previously described in the urodele testis (Lofts, '74). When the Leydig cells hypertrophy, numerous unmyelinated axons appear in the interstitial tissue. These axons, often devoid of Schwann-cell cytoplasm, occur in close proximity to Leydig cells. Because the levels of both Substance P and neurotensin increased in the testis of Necturus maculosus as Leydig cells differentiated, we concluded that these neural elements may regulate Leydig-cell function locally, through the release of neuropeptides.     

Fine structure of the gular gland of the free-tailed bat Tadarida brasiliensis

The gular gland of the bat Tadarida brasiliensis is a specialized sebaceous gland located in the skin of the suprasternal region of adult males. It consists of an aggregation of simple branched tubulo-acinar gland units, the number of which varies seasonally. Each acinus is composed of densely packed sebaceous cells at various stages of differentiation. Acinar basal cells and cells of the epithelium of the ducts can differentiate into sebaceous cells. Two main changes appear in the cytoplasm concurrent with the sebaceous transformation: the differentiation of cytoplasmic organelles and the deposition of lipid material. The appearance of a different type of mitochondrion and the development of large numbers of ribosomes and polyribosomes can be recognized in the cytoplasm at an early stage of differentiation. Concomitant with the deposition of significant numbers of lipid droplets, the cells develop abundant agranular endoplasmic reticulum occurring mainly as scattered tubular cisternae. These at times form whorls surrounding lipid droplets. At later stages, the cisternae of the agranular endoplasmic reticulum often occur in crystalline arrays between secretory oil droplets. The roles of the different cytoplasmic organelles, especially in relation to the production of sebum, are discussed.     

Morphology of the Harderian gland of the Gecko, Tarentola mauritanica

The Harderian gland of the gecko, Tarentola mauritanica, was studied at the histological, histochemical, and ultrastructural levels. It is a nonlobate compound acinar gland surrounded by a thin capsule of connective tissue. Numerous connective tissue-type mast cells, ultrastructurally similar to those described in other higher vertebrates, were identified in the interstitial tissue between the acini. Pyramidal or columnar-shaped secretory glandular cells were observed in the acini. In the glandular cells, two types of structures could be distinguished on the basis of their high or low electron density. Lipid droplets were found in the cytoplasm of the Harderian gland of both sexes. Histochemical tests showed that the Harderian gland of the gecko is a seromucous gland. The secretion is essentially merocrine, although an apocrine type of secretion is sometimes observed.     

Hormonal control of leydig cell differentiation

Summary The fine structure of the testicular interstitial cells of the 9-day-old mouse submitted to stimulation with human chorionic gonadotropin (HCG) is reported. As was previously described (Baillie 1964) the interstitial tissue of the prepubertal mouse testis is characterized by the presence of well differentiated epithelioid cells at a quiescent stage. They are characterized by large cytoplasmic depots of lipid droplets and glycogen particles in contrast to poorly developed membranous organelles. These cells are highly sensitive to the action of gonadotropins. Five daily injections of HCG cause their differentiation into cells with active secretory characteristics. The gonadotropin induces a marked depletion of the lipid droplets and glycogen content of the cytoplasm, concurrent with an unusual development of the membranes of the agranular endoplasmic reticulum. Golgi complexes and rough reticulum are prominent. Several changes also appear in the nucleus, especially in the nucleolus.The correlation of the present electron microscopic study of the interstitial cells under HCG stimulation with previous biochemical and physiological findings tentatively suggests that the immature Leydig cells exhibit the basic organization necessary for biosynthesis of steroid hormones.     

Histological and histochemical observations on the testis of Gobius paganellus

Summary Histological and histochemical observations on the testis of Gobius paganellus during all seasons of the year are described. In the yearly reproductive cycle, spawning in the Gulf of Naples occured from June through August, testicular recovery and relative inactivity from September through December, and active spermatogenesis from January to May.Germ cells develop as clones from single primary spermatogonia, each clone in a follicle enveloped by cells which are interpreted as Sertoli cell homologues.Glandular tissue is present in large amounts both in the form of interstitial islets and as a large mass along the length of the mesorchium. Cholesterolpositive lipids and ⁵-3-hydroxysteroid dehydrogenase, presumptive evidence for steroid production, are present exclusively in this tissue.Lipids are present in the glandular cells in acidic and neutral forms. The acid fats are the more abundant, but neutral lipids increase in amount in the period April-June. There is, furthermore, a cyclic variation in lipid droplet size, small droplets being present in the spring (during active spermatogenesis) and fewer, larger droplets during the fall (post-spawning period). Phospholipids are lacking.Lactic dehydrogenase activity was weak in the relatively inactive postspawning period, but was much more intense during active spermatogenesis.The glandular tissue in the testis of Gobius is interpreted as homologous with the interstitial (Leydig) tissue found in the testes of higher vertebrates.This investigation was supported by research grant RG-6455 from the Division of General Medical Sciences, U.S. Public Health Service.Postdoctoral Fellow from the Division of General Medical Sciences, U.S. Public Health Service. Supported in part by U.S. Public Health Service Training Grant 5 Tl GM-136, Department of Biological Structure, University of Washington, School of Medicine, Seattle, Washington, U.S.A.     

The three-dimensional cytoarchitecture of the interstitial tissue in the rat kidney

Summary The cytoarchitecture of the interstitial tissue of the rat kidney was studied by combined scanning and transmission electron microscopy. The renal interstitium is composed of an elaborate network of stellate sustentacular cells. In the cortex, sustentacular cells radiate thin branching processes to form a fine reticulum, which supports intertubular spaces. In the medulla, these cells extend thick processes horizontally along the basal surfaces of the thin limbs or vasa recta, reinforcing their attenuate walls. The horizontal processes connect with each other at their terminals, compartmentalizing the interstitial space into thin layers. The medullary sustentacular cells contain abundant small lipid droplets. The network of sustentacular cells houses vasa recta, keeping them in parallel position to each other and to the tubules. The arterial vasa recta are accompanied by pericytes, which frequently contain lipid droplets larger in size than those in the sustentacular cells. Venous vasa recta extend numerous basal microvilli, which anchor the venous wall to adjacent tubules or vessels. Numerous free cells, round in shape, are found in the sustentacular cell network, especially in the cortex. They consist of macrophages and occasional lymphocytes. Some macrophages extend long pseudopodia, while others make intimate contact with lymphocytes, suggesting their high level of activity.     

Stellate cells storing retinol in the liver of adult lamprey,Lampetra japonica

Summary Distribution, localization and fine structure of the stellate cells in the liver of lamprey, Lampetra japonica, were studied during the spawning migration by use of Kupffer's gold-chloride method, fluorescence microscopy for vitamin A (retinol) and electron microscopy. The stellate cells in the lamprey liver differ in some of their properties from those in mammalian livers. Stellate cells which store abundant retinol in lipid droplets, occur not only in the hepatic parenchyma, but also in the dense perivascular and capsular connective tissue of the liver and in the interstitium of pancreatic tissue. In the hepatic parenchyma these cells are located perisinusoidally or along thick bundles of collagen fibrils. The stellate cells display a number of large retinol-containing lipid droplets, granular endoplasmic reticulum, tubular structures, dense bodies, Golgi complex, microtubules, and microfilaments. In the space of Disse, the stellate cells and extracellular fibrilar components such as collagen fibrils and microfibrils (11–12 nm in diameter) are intervened between the two layers of basal laminae. Differentiation and possible functions of the stellate cells in the lamprey liver are discussed.     

The organization of testicular interstitial tissue and changes in the fine structure of the Leydig cells of European moles (Talpa europaea) throughout the year

Seasonal changes of the testicular interstitial tissue were studied by electron microscopy. During the breeding season in spring, clusters of Leydig cells are surrounded by wide lymphatic sinusoids. In sexually quiescent moles, these sinusoids collapse, and the abundant Leydig cells become closely packed and occupy most of the testis. During sexual activity, the Leydig cells contain abundant smooth endoplasmic reticulum (SER), mitochondria with tubular cristae, and lipid droplets. Some areas of the cytoplasm are occupied exclusively by tubular SER, arranged in parallel. During regression the SER appears tortuous, and large lipid droplets are found in the cytoplasm, although these gradually become smaller. During the long period of sexual quiescence, the size and abundance of Leydig cells and the appearance of SER, lipid droplets and mitochondria were similar to those observed during sexual activity.     

Autophagy facilitates secretion and protects against degeneration of the Harderian gland

The epithelial derived Harderian gland consists of 2 types of secretory cells. The more numerous type A cells are responsible for the secretion of lipid droplets, while type B cells produce dark granules of multilamellar bodies. The process of autophagy is constitutively active in the Harderian gland, as confirmed by our analysis of LC3 processing in GFP-LC3 transgenic mice. This process is compromised by epithelial deletion of Atg7. Morphologically, the Atg7 mutant glands are hypotrophic and degenerated, with highly vacuolated cells and pyknotic nuclei. The mutant glands accumulate lipid droplets coated with PLIN2 (perilipin 2) and contain deposits of cholesterol, ubiquitinated proteins, SQSTM1/p62 (sequestosome 1) positive aggregates and other metabolic products such as porphyrin. Immunofluorescence stainings show that distinct cells strongly aggregate both proteins and lipids. Electron microscopy of the Harderian glands reveals that its organized structure is compromised, and the presence of large intracellular lipid droplets and heterologous aggregates. We attribute the occurrence of large vacuoles to a malfunction in the formation of multilamellar bodies found in the less abundant type B Harderian gland cells. This defect causes the formation of large tertiary lysosomes of heterologous content and is accompanied by the generation of tight lamellar stacks of endoplasmic reticulum in a pseudo-crystalline form. To test the hypothesis that lipid and protein accumulation is the cause for the degeneration in autophagy-deficient Harderian glands, epithelial cells were treated with a combination of the proteasome inhibitor and free fatty acids, to induce aggregation of misfolded proteins and lipid accumulation, respectively. The results show that lipid accumulation indeed enhanced the toxicity of misfolded proteins and that this was even more pronounced in autophagy-deficient cells. Thus, we conclude autophagy controls protein and lipid catabolism and anabolism to facilitate bulk production of secretory vesicles of the Harderian gland.     

Autophagy facilitates secretion and protects against degeneration of the Harderian gland

The epithelial derived Harderian gland consists of 2 types of secretory cells. The more numerous type A cells are responsible for the secretion of lipid droplets, while type B cells produce dark granules of multilamellar bodies. The process of autophagy is constitutively active in the Harderian gland, as confirmed by our analysis of LC3 processing in GFP-LC3 transgenic mice. This process is compromised by epithelial deletion of Atg7. Morphologically, the Atg7 mutant glands are hypotrophic and degenerated, with highly vacuolated cells and pyknotic nuclei. The mutant glands accumulate lipid droplets coated with PLIN2 (perilipin 2) and contain deposits of cholesterol, ubiquitinated proteins, SQSTM1/p62 (sequestosome 1) positive aggregates and other metabolic products such as porphyrin. Immunofluorescence stainings show that distinct cells strongly aggregate both proteins and lipids. Electron microscopy of the Harderian glands reveals that its organized structure is compromised, and the presence of large intracellular lipid droplets and heterologous aggregates. We attribute the occurrence of large vacuoles to a malfunction in the formation of multilamellar bodies found in the less abundant type B Harderian gland cells. This defect causes the formation of large tertiary lysosomes of heterologous content and is accompanied by the generation of tight lamellar stacks of endoplasmic reticulum in a pseudo-crystalline form. To test the hypothesis that lipid and protein accumulation is the cause for the degeneration in autophagy-deficient Harderian glands, epithelial cells were treated with a combination of the proteasome inhibitor and free fatty acids, to induce aggregation of misfolded proteins and lipid accumulation, respectively. The results show that lipid accumulation indeed enhanced the toxicity of misfolded proteins and that this was even more pronounced in autophagy-deficient cells. Thus, we conclude autophagy controls protein and lipid catabolism and anabolism to facilitate bulk production of secretory vesicles of the Harderian gland.     

The effect of sex hormones on lipid content and mast cell number in the harderian gland of the female toad, Bufo viridis

The Harderian gland of the toad Bufo viridis is a dimorphic gland owing to the presence of lipid droplets in the female glandular cells present only during summer months. Ovariectomy causes the disappearence of sudanophilia and estrogen-treatment completely prevents this change, while testosterone-injection has little effect. Estradiol-treatment also provokes a proliferation of the interstitial connective tissue concomitantly with the mast cell number increase. Our results suggest that estradiol acts, stimulating both mast cell and connective tissue proliferation, and plays a role in determining the expression of the female type of the toad Harderian gland.     

Ovoviviparity and the structure of the brood pouch in Melanoides tuberculata (Gastropoda: Prosobranchia: Thiaridae)

The freshwater gastropod Melanoides tuberculata broods its young in a pouch located in the anterodorsal region of the head-foot. The wall of the brood pouch is composed of smooth muscle surrounded by connective tissue. The lumen of the brood pouch is incompletely partitioned by trabeculae, formed by extensions or folds in the chamber wall that are composed of smooth muscle, connective tissue, nonciliated squamous epithelial cells, and some storage cells containing lipid and glycogen. The lumen of the chamber also contains a few cells with storage products. The general absence of secretory cells suggests that embryos derive little nutrition from the mother, and therefore embryonic development is probably ovoviviparous. Embryos in various stages of development were found within brood pouches, with later stage embryos varying in size. There was a negative relationship between embryo size and number of embryos in the brood pouch.     

Ultrastructure of the parathyroid gland of the japanese lizard in the spring and summer season

The ultrastructure of the parathyroid glands of adult Japanese lizards (Takydromus tachydromoides) in the spring and summer season was examined. The parenchyma of the gland consists of chief cells arranged in cords or solid masses. Many chief cells contain numerous free ribosomes and mitochondria, well-developed Golgi complexes, a few lysosome-like bodies, some multivesicular bodies and relatively numerous lipid droplets. The endoplasmic reticulum is mainly smooth-surfaced. Cisternae of the rough endoplasmic reticulum are distributed randomly in the cytoplasm. Small coated vesicles of 700-800 Å in diameter are found occasionally in the cytoplasm, especially in the Golgi region. The chief cells contain occasional secretory granules of 150-300 nm in diameter that are distributed randomly in the cytoplasm and lie close to the plasma membrane. Electron dense material similar to the contents of the secretory granules is observed in the enlarged intercellular space. These findings suggest that the secretory granules may be discharged into the intercellular space by an eruptocrine type of secretion. Coated vesicles (invaginations) connected to the plasma membrane and smooth vesicles arranged in a row near the plasma membrane are observed. It is suggested that such coated vesicles may take up extracellular proteins. The accumulation of microfilaments is sometimes recognized. Morphological evidence of synthetic and secretory activities in the chief cells suggests active parathyroid function in the Japanese lizard during the spring and summer season.     

The Harderian gland of the Cheesman's gerbil (Gerbillus cheesmani ) of the Kuwaiti desert

The Harderian gland is a large orbital structure. Several functions have been ascribed to the gland such as lubrication of the eye, a source of pheromones, thermoregulartory lipids and photoprotective secretions and a part of the retinal-pineal axis. In the present study, the Harderian gland of the Cheesman's gerbil, Gerbillus cheesmani, is described for the first time. The gland is located around the posterior portion of the eyeball. The gland is compound tubular, surrounded by a thin connective tissue capsule. Only one secretory epithelial cell type was recognized, characterized by the presence of lipid vacuoles and cytoplasmic slashes in high numbers; the former being more concentrated towards the apical part while the latter being more concentrated towards the central and basal parts. Some of the cytoplasmic slashes contained electron dense filamentous structures. Similar structures were observed in the lipid vacuoles. Thus, a functional relationship between the cytoplasmic slashes and the lipid vacuoles is suggested. A unique structure was observed, termed dome-like cells, located between the epithelial cells and the basement membrane. These cells were characterized by the extensive presence of pleomorphic mitochondria and compact lamellae of granular endoplasmic reticulum (GER) in the form of finger prints. The gland was found to be actively secreting porphyrins as well as lipids. Cellular debris was also seen in the tubular lumina. Myoepithelial cells with their spindle shape and elongated nuclei were evident between the basement membrane and the secretory epithelium. Sparse interstitial tissue was observed in-between the gland tubules of both male and female gerbils. Macrophages, dendritic melanocytes and lymphocytes are the most represented cellular components of the interstitium. Further studies are required to investigate the function of the dome-like cells as well as the role of lymphocytes in the rodents Harderian gland.