A histological study of the Harderian gland of mongolian gerbils,Meriones meridianus

The histological structure of the gerbil Harderian gland was investigated by means of light and transmission electron microscopy. The single excretory duct of the gland is directly continuous with endpieces at the hilus and opens nasally and ventrally to the third eyelid. The excretory duct is accompanied by many acini of small serous glands around it. The gland is composed of tubuloalveoli (tubular alveoli) with wide lumina and is not divided into lobules. There is no branched duct system within the gland. The tubuloalveoli themselves convey the secretory materials to the hilus where the excretory duct begins. The alveolar epithelium is composed of only one type of glandular cell as well as myoepithelial cells. The glandular cells contain many clear secretory vacuoles containing lipids and well-developed tubular smooth endoplasmic reticulum. The secretory vacuoles are surrounded by a unit membrane and are secreted by exocytosis. The interstices of the gland contain two types of autonomic nerve varicosities and a number of melanocytes. The surface of the gland is covered with the endothelium of the orbital venous sinus.     

Embryonic and fetal hemopoiesis in the mongolian gerbil (Meriones unguiculatus)

A study of the development of hemopoiesis in the Mongolian gerbil (Meriones unguiculatus) was conducted in order to determine the temporal sequence, the organs involved and the cytology of blood cell formation in this species. Hemopoiesis in the intrauterine life of the gerbil can be divided into four phases based on the site of blood cell formation: (1) the vitelline phase, (2) the hepatic phase, including thymic histogenesis, (3) the splenic phase and (4) the medullary phase, with the development of secondary lymphoid tissues. At the onset of each of these phases a blast-like cell was identifiable in each hemopoietic organ which, because of its morphology and its presumed multipo-tentiality was classified as a “lymphoid cell.” In the yolk sac phase (gestational day 12) two generations of erythrocytes, a primitive and a definitive, are formed. The liver is by day 15 erythropoietic and megakaryopoietic, but later, a few gran-ulocytes are also found in its extravascular compartment. The thymus is exclusively lymphopoietic from the appearance of its earliest cells on day 15. Splenic hemopoiesis is initiated with the presence of lymphoid cells (day 20) followed later by the appearance of morphologically identifiable blood cell lines. Early normoblastic and granulocytic activity begins in the marrow cavities on day 23, though the marrow is not considered to be a source of circulating blood cells during fetal life. Lymph node histogenesis occurs during the last four days of gestation, first in the cervical region and then in other parts of the body. The finding of undifferentiated lymphoid cells in all organs at the initiation of hemopoiesis and in the peripheral blood throughout gestation is discussed in light of the migratory theory of hemopoiesis.     

Brood patch function for the ventral scent gland of the female mongolian gerbil,Meriones unguiculatus

Infants of gerbil mothers whose ventral scent gland had been excised were compared on a number of developmental indices with pups of mothers who had had an equivalent section of lateral skin removed. The removal of the mother's ventral scent gland retarded the offsprings' pattern of ultrasounding during the 1st 21 days of development. In addition, infants from such mothers showed a retarded righting reflex. Inhibitions in the developmental behavior of gerbil pups might have resulted from less effective heat transfer during mother-pup contact. Indeed, excision of the gland resulted in lower ventral temperatures. The duality of function of the gland as an odor source for communication and as a heat source for offspring development suggests integrated communicative and thermoregulatory processes.     

The harderian gland and thermoregulation in the gerbil (Meriones unguiculatus)

Seven experiments with Meriones unguiculatus assessed the thermoregulatory consequence of Harderian secretion and fur anointment with lipids by autogrooming. Harderianectomy reduced the animal's capability to withstand cold (3–5°C) and wetness. During a 9 to 15 min exposure to cold-wet stress glandless animals lost an average of 4.6°C core body temperature, compared to an average loss of 1.6°C among intact animals. A comparable loss in body temperature occurred in animals whose fur lipids were removed with shampooing. Shaved animals coated with petroleum jelly withstood the cold-wet stress with a lesser decrease in body temperature than animals without the exogenous coat of jelly. The in vitro insulating qualities of fur lipids were demonstrated by blocking a cold air stream with various layers of lipids. The degree of insulation was related to the thickness of the lipid layers. Fur lipids were extracted from Harderianectomized and shampooed animals. Relative to controls, both procedures resulted in approximately 40–50% loss of fur lipds. The loss seen in gerbils following Harderianectomy was not found in the rat, golden hamster or C57 and DBA strains of inbred mice. Thus, in the gerbil the behavioral spread of Harderian lipids during a thermoregulatory groom insulated the gerbil from cold and wetness. The use of insulating lipids may be related to the gerbil's ecology in the cold deserts of Mongolia and Northeast China.     

Development and hormonal control of territorial marking in the male mongolian gerbil (Meriones unguiculatus)

Male Mongolian gerbils were either castrated or sham operated at 30 days of age. Assessment of territorial marking was carried out every 6 days beginning at 52 days of age and extending to 100 days of age. After each marking test, 10 intact males received 640 μg testosterone propionate subcutaneously; 10 other intact animals and 10 castrates received oil injections. The ventral sebaceous scent gland, used by the gerbil to deposit sebum on objects during the marking response, was measured after each test. Behavioral marking and the scent gland were entirely absent in castrates. Relative to controls, marking in hormone-treated animals began earlier and reached higher frequencies. Gland development was also responsive to the hormone, but lagged behind marking activity.     

Prenatal size–age relationships and external morphology in the mongolian gerbil (Meriones unguiculatus)

Embryos from timed matings were studied at days 12–24 of gestation with respect to crown-rump length and external appearance. A linear increase in length was observed from the twelfth (2.5 mm) to the twenty-fourth (27.7 mm) day with the largest increases occurring between days 20 and 21 (3.8 mm) and days 22 and 23 (4.2 mm). The smallest daily increases were observed between days 15 and 16 (1.01 mm) and days 21 and 22 (1.03 mm), while the average daily increment for the remaining days was between 1.5 mm and 2.5 mm. Major changes in external appearance occurred on days 13, 14, 17 and 20 of gestation. Those features which could be observed externally were described for each of the days during the period studied. Late prenatal development in the gerbil resembles that of other myomorph rodents but proceeds at a slower rate than in other species such as the mouse or hamster. This slower rate of development may be of value when precise timing of drug administration and recovery of embryos is necessary.     

Immunohistochemical characterization of a sebaceous gland carcinoma in a gerbil (Meriones unguiculatus)

Sebaceous gland carcinoma is a common tumour in male gerbils but, to date, no information is available on its immunohistochemical properties. This report describes the histopathological and immunohistochemical features of such a tumour from a 4.5-year-old male gerbil. The tumour immunoreactivity profile was studied in respect of p53 protein, CEA, EMA, c-erbB-2, cytokeratin (CK) 14 and the CKs detected by AE1/AE3 antibodies (i.e. high molecular weight CKs 1, 2, 3, 4, 5, 6, 10, 14, 15 and 16, and low molecular weight CKs 7, 8 and 19). The differences observed in p53 and c-erbB-2 immunolabelling between carcinomatous and hyperplastic areas suggest that p53 mutations and amplification of c-erbB-2 may play a significant role in the oncogenesis of sebaceous gland carcinoma in the gerbil.     

Changes in the secretory acinar cells of the rat parotid gland during aging

The secretory acinar cells of parotid glands from rats of varying ages have been examined by electron microscopy to determine what age-related changes occur in these cells. The most prominent change noted in these cells is the progressive increase in the amount of lipofuscin granules with age. Lipofuscin granules are membrane-bound structures consisting of lipids, other subcomponents, and a matrix. In addition, these cells contain lipid droplets that are not associated with any other components and tend to accumulate at the base of the cells in older rats. Also, many acinar cells in the glands of old rats contain altered secretory granules which appear to be in the process of degeneration. The accumulation of lipid and degenerating secretory granules appears to be related to the reduced level of cellular secretory activity in the glands of older rats. It is possible that these two types of inclusions contribute to the formation of lipofuscin granules. Lipofuscin and degenerating secretory granules are associated with acid phosphatase, which is demonstrated cytochemically, indicating that these granules are lysosomal structures.     

A comparative study on the morphology and topography of the ciliary ganglion in midday gerbil (Meriones meridianus) and turtle (Agrionemys horsfieldii).

The morphology and topography of the ciliary ganglia in the midday gerbil and turtle were studied with use of histochemical and histological techniques. The ciliary ganglion of the midday gerbil consisted of two cell agglomerations: the main ganglion and the accessory ganglion. The main ganglion was situated in the orbit and usually closely attached to the nerve for the inferior oblique muscle. The short ciliary nerves arose from the superior end of the main ganglion and reached the orbit. The accessory ciliary ganglion was smaller than the main ganglion. Usually it was attached to short ciliary nerves. The ganglionic neurocytes, 25.97 microm in diameter, were distributed regularly over the entire surface of the main ganglion. They typically had a single clear nucleus. The ciliary ganglion in the turtle formed a characteristic triangular structure on the inferior branch of the oculomotor nerve. The histological examination showed a small number of nerve cells in comparison to the nerve fibres. The neurocytes were placed mainly in the nasal part of ganglion and they had an irregular arrangement. The average diameter of neurons was 23.55 microm. Significant differences in density of ganglionic components in both species were observed. In midday gerbil the cells were densely packed and took up about 80% of a cross-section, while, in the turtle, neurocytes were located mainly in the surface part of ganglion.     

The ultrastructure of papillary cystadenoma lymphomatosum of the parotid gland

Summary The ultrastructure of papillary cystadenoma lymphomatosum (PCL), Warthin's tumor, of the parotid salivary gland has been described. The oncocytic cells are filled with mitochondria. Two morphologic forms of mitochondria are seen. The cells of the striate ducts in the normal parotid, have specializations associated with fluid transport and are structurally most nearly akin to the oxyphils. The subcellular hyperplasia of mitochondria may be a manifestation of aberrant function.

---

Die Ultrastruktur des papillÄren Cystadenoma lymphomatosum der Parotisdrüse

Zusammenfassung Die onkocytÄren Zellen sind voll von Mitochondrien. Zwei Formen von Mitochondrien sind nachweisbar. Die Zellen der Streifenstücke (Speichelrohre) der normalen Parotis besitzen besondere Einrichtungen, die mit dem Flüssigkeitstransport in Zusammenhang gebracht werden, und sind gestaltlich am nÄchsten mit den oxyphilen Zellen verwandt. Die subcellulÄre Hyperplasie der Mitochondrien könnte Ausdruck einer abwegigen Funktion darstellen.

---

---

This work was supported by a grant from the John A. Hartford Foundation.     

Placental development in the mongolian gerbil (Meriones unguiculatus). II. From the establishment of the labyrinth to term

Placental development was studied in 24 gerbils from day 13 to term. Allantoic mesoderm contacts and vascularizes the chorionic-trager plate of germinal cytotrophoblast on day 13. Soon villous extensions penetrate the plate, carrying with them a covering of three layers of trophoblast derived from it. As the villi elongate, clumps of germinal cytotrophoblast are carried peripherally by them. Further development of each villus results in a cylindrical mesenchymal core with a central arteriole, and radially arranged branching lamellar extensions carrying capillaries derived from the villus arteriole. Germinal cytotrophblast clusters disappear near term, but some indication always remains of the trilaminar covering of the villus and its lamellae. A typical countercurrent blood flow pattern occurs. The trophospongium is derived from the ectoplacental cone and the mesometrial surface of the germinal cytotrophoblastic plate. Although a few clusters of small cells occur, it is essentially a giant cell trophospongium and never contains cells resembling the clear cells of the rat. Late in pregnancy it becomes much reduced in thickness. The unique subplacental gland begins to degenerate soon after placental establishment and is gone by the last half of pregnancy. The metrial gland begins development at midterm and becomes a solid mass of cells filling the perivascular space of the mesometrial triangle at term.     

Histology and ultrastructure of the pig parotid gland

Parotid glands of adult pigs were studied by light and electron microscopy. The parenchyma consists of acini, intercalated ducts, striated ducts, and excretory ducts. Acini had little affinity for periodic acid-Schiff and were alcian blue-negative at pH 2.6 or 0.5. These results indicate a paucity of neutral mucins and an absence of sialo- and sulfomucins. Histologically, acinar cells had vacuoles which corresponded ultrastructurally to large electron-lucent secretory granules. The latter contained electron-dense bodies and lipid droplets. Acinar cells differed histochemically and ultrastructurally from typical serous cells and were classified as special serous. Intercalated duct cells near acini contained electron-dense secretory granules and numerous microfilaments. Cells in distal segments lacked secretory granules. Striated ducts were lined by two types of columnar epithelial cells, light cells and dark cells. Light cells were characterized by numerous infoldings of the basal plasma membrane, mitochondria between the infoldings, and electron-lucent vesicles in the apical cytoplasm. The mitochondria contained tubular cristae. Dark cells were characterized by an abundance of microfilaments and numerous infranuclear processes which extended to the basement membrane. Excretory ducts, in addition to light and dark cells, also contained basal cells and goblet cells. Mitochondria in the light cells had flattened rather than tubular cristae. The pig parotid is a unique salivary gland and the most atypical mammalian parotid gland studied thus far. Mitochondria with tubular cristae and vacuolated special serous cells with lipid in the secretory granules are hallmarks of the pig parotid.     

Placental development in the mongolian gerbil (Meriones unguiculatus). I. Early development to the time of chorio-allantoic contact

Early gerbil development was studied from days 4 through 12 of gestation. Implantation occurs on day 8 in a shallow antimesometrial implantation crypt. The proamniotic cavity forms from an invagination of basal trophoblast and a folding together of the rim of the cup thus produced. The approximation of this rim gives rise to the ectoplacental cone. The further development and expansion of the ectoplacental cone is much like the rat. Amniogenesis is by folding into the proamniotic cavity. Between large glycogen-filled decidual cells occur many PAS-positive eosinophilic granular cells. A massive subplacental gland forms from proliferating uterine epithelium within the decidua basalis. Epithelial proliferation begins shortly after implantation, and soon short thick cellular processes extend from the antimesometrial side of the lumen whereas long branching cords penetrate the decidua basalis mesometrially. The function of this structure is unknown.     

Lamina formation in the Mongolian gerbil retina (Meriones unguiculatus)

Retinae of nocturnal rodents, such as mice and rats, are almost exclusively rod-dominated. The gerbil, in contrast, shows active periods during day and night and uses both rod- and cone-based vision. However, its retina has not been studied in detail, except for one developmental study analysing its prenatal period (Wikler et al. 1989). Here, the formation of the laminar structure of the gerbil retina was studied from birth until late adult stages. At birth, the retina consisted of a wide neuroblastic layer, with 30% of cells still dividing, a rate decreasing to nearly zero by P6. Shortly after birth, segregation of a ganglion cell layer began. All retinal layers reached their final size around P20, as determined from DAPI-stained cryosections. Müller glial cells developed their typical structure from P1 onwards, e.g. announcing an outer plexiform layer (OPL) at P5, as analysed by the Ret-G7 and glutamine synthetase antibodies. The analyses of the inner retina were performed by antibodies to calretinin (CR) and calbindin (CB). CR is expressed in ganglion cells followed by amacrine cells from P1 onwards; their processes formed four subbands in the inner plexiform layer (IPL) and appeared sequentially after P5 until P20. CB stained a subtype of horizontal cells with their processes into the OPL from P14 onwards. The rod-specific antibody rho4D2 announced photoreceptors at P4, showing signs of outer segments from P10 onwards. The study shows that the formation of all retinal layers in the gerbil occurs postnatally. This and the fact that the gerbil retina is not exclusively rod-dominated could render the gerbil a valuable model for in vitro studies of retinogenesis in rodents.     

The parathyroid glands of the Mongolian gerbil (Meriones unguiculatus).

The parathyroid glands of adult Mongolian gerbils were studied under an operation microscope, as well as with the aid of conventional light microscopy, and transmission and scanning electron microscopy. The mean serum level of calcium was 5.1 mEq/1 and that of phosphorus was 4.8 mg/100 ml. The animals possessed two small parathyroid glands, usually situated anteriorly and slightly laterally to the superior thyroid poles. The glands had a rich vascular supply and were composed of sheets of chief cells, which varied in electron density and content of organelles. No water-clear, oxyphil, or intraglandular fat cells were found. Some mitochondria exhibited electron lucent areas, and separation and bulbous projections of the membranes. The cell membranes were straight or tortuous and possessed microvilli, occasionally with central filamentous structures. The intercellular spaces were usually narrow. It is supposed that the variants of chief cells are interchangeable and that the differences in their morphological appearance are related to differences in functional state.