Cell populations in the pineal gland of the viscacha (Lagostomus maximus). Seasonal variations

Pineal samples of the viscacha, which were taken in winter and in summer, were analysed using both light and electron microscopy. The differences found between the two seasons were few in number but significant. The parenchyma showed two main cell populations. Type I cells occupied the largest volume of the pineal and showed the characteristics of typical pinealocytes. Many processes, some of which were filled with vesicles, could be seen in intimate contact with the neighbouring cells. The presence in the winter samples of "synaptic" ribbons and spherules, which were almost absent in the summer pineals, suggests a seasonal rhythm. These synaptic-like structures, as well as the abundant subsurface cisterns present in type I cells, appeared as basic differential features which allowed these cells to be distinguished from type II cells. These latter cells, which can be classified as interstitial cells, showed some other distinguishing features, such as irregular-shaped nuclei, abundant deposits of glycogen-like particles and structures of unknown function consisting of concentric cisterns surrounding a dense body. In the summer, interstitial cells displayed numerous large round bodies, which contributed to increase the cellular volume slightly. Regarding other constituents, like glial cell processes, vessels of non-fenestrated endothelium and sympathetic innervation, no qualitative differences were observed between the two seasons studied. We have presented here some morphological evidences of the circannual rhythm of the viscacha pineal, as well as ultrastructural criteria for distinguishing the main cell populations of this organ, which could be useful for studies carried out in other mammals.     

Lithium effect on testicular tissue and spermatozoa of viscacha (Lagostomus maximus maximus). A comparative study with rats.

We investigated the effect of lithium chloride administration (Sigma): 1 mmol/kg b.w. i.p./day for 35 days on the testes and sperm of viscacha (Lagostomus maximus maximus), a nocturnal rodent found only in the pampas of Argentina. The histological study showed that hypospermatogenesis and the sperm number per mL decreased markedly in comparison with the controls (treatment group: 315 x 10(6) +/- 77 x 10(6); control group: 693 x 10(6) +/- 39 x 10(6), Means +/- SEM, Student's t-test: p < 0.05). The sperm motility and viability were also affected. Under the same treatment, the testicular tissue and the sperm of rats were not damaged. Moreover, lithium induced these changes when the plasm levels were within the therapeutic range in humans. Our results provide evidence for the claim that viscacha testes and sperm react very sensitively to low doses of lithium, whereas these concentrations do not produce damage in rats.     

Seasonal variations in the testis and epididymis of vizcacha (Lagostomus maximus maximus).

Seasonal changes in reproductive activity in the adult male vizcacha (Lagostomus maximus maximus), a South American rodent, were investigated. Monthly, for 2 yr, the animals were killed and decapitated during the night near their burrows in the vicinity of San Luis, Argentina. The testes, epididymides, and pineal glands were removed and used for biochemical and structural studies. Significant changes associated with seasonal cycles were found. 1) In July-August (winter in South America), a short hibernal period of sexual quiescence, decline in testicular and epididymal weights, arrest of spermatogenesis, and decrease of serum testosterone were observed. The gonads regressed during this period, with regression most pronounced in August. 2) During September-November (spring), a recovery period--without arrest of spermatogenesis--was observed, with significant expression of gonadal activity during April-May (autumn). In this season, gonadal weight was increased and spermatogenesis was complete. These results indicate an increase in sexual activity as well as in the ability to secrete testosterone. A gradual reduction of testicular activity appeared in June-July (early winter). Conversely, in this period, the pineal hydroxyindole-O-methyl transferase activity decreased in contrast to the highest values observed in winter. Our findings indicate that the male adult vizcacha under natural conditions exhibits an annual reproductive cycle. A possible relationship between increased pineal activity and gonadal regression is also suggested.     

Ultrastructural and biochemical seasonal changes in epididymal corpus and cauda of viscacha (Lagostomus maximus maximus)

The reproductive and adaptative behavior of wild rodents is synchronized primarily by the photoperiod. The viscacha, a South American rodent of nocturnal habits and seasonal reproduction is photoperiod‐dependent and its reproductive behavior is regulated by the retinohypothalamic‐pituitary pineal axis. Adult males exhibit an annual reproductive cycle with periods of maximum gonadal activity (summer‐early autumn) and gonadal regression (winter). The corpus and the cauda, the most sensitive segments of the epididymis to changes induced by the photoperiod, were analyzed using electron microscopy and enzymatic biochemistry. During gonadal regression, principal and clear cells showed signs of involution with respect to the activity period. These were characterized by more irregular nuclei, smaller cytoplasms, large vacuoles, altered mitochondria, and glycogen deposits. All cellular populations of the epididymal epithelium in regression presented abundant lysosome‐like dense bodies during the active period. In addition, we measured the activity of four acid glycosidases in the cauda epididymis along the reproductive cycle. N‐acetyl‐β‐D‐glucosaminidase (NAG), an enzyme that degrades endocytosed substances from the epididymal lumen, increased significantly during gonadal regression relative to the active period. These results demonstrate that the viscacha epididymis exhibits significant ultrastructural and biochemical changes during the reproductive cycle. We demonstrate that during regression, melatonin secretion in viscacha increases. This study shows that the epididymal epithelium is reduced. Thus, we postulate that the changes observed in the epididymis are modulated by pineal melatonin. Despite these changes, the epididymis might maintain a microenvironment suitable for the survival of stored spermatozoa. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Unusual cytoplasmic bodies in chromaffin cells of the adrenal medulla of the viscacha (Lagostomus maximus maximus)

Complex structures can be seen associated with large areas of endoplasmic reticulum of the chromaffin cells in the viscacha adrenal medulla. These structures are cylindrical in shape and are formed by chains of globular subunits. A central lumen is observed within which there are bodies resembling chromaffin granules. Parallel cisternae of the endoplasmic reticulum are arranged surrounding these bodies. The functional significance of these structures in unknown.     

Morphological characteristics of the uterus and uterine cervix of the plains viscacha (Lagostomus maximus)

The plains viscacha is a hystricognathi rodent with special reproductive characteristics. Despite poly-ovulation of 800 oocytes, it generates a high embryonic mortality since from 10 to 12 implantations only one or two offspring are born. The present work analyses the morphological, morphometrical, histochemical and lectinhistochemical characteristics of the uterus and uterine cervix of pregnant and non-pregnant viscacha. Anatomically, the uterus has two horns each one continued with a short cervix devoid of glands. The structure of the uterus is like that of other species; however, the proportion and size of its glands varies according to the physiological state. In viscacha, there is no uterine body and cervices cannot be differentiated externally. The formation of two sack bottoms is determined by the presence of a middle raphe in the cranial portion of the vagina. The so-described anatomy is different from that described in other hystricognathi such as guinea pig and coypu. The cervix presents two microscopically differentiable regions: the endocervix and the ectocervix lined by epithelia with different characteristics. The general characteristics of the uterus of L. maximus do not show specific differences with those of other mammals that might explain its peculiar gestation.     

The myoglobin of rodents:Lagostomus maximus (viscacha) andSpalax ehrenbergi (mole rat)

The primary sequences of the myoglobins of two rodents (the South American viscacha and the Mediterranean mole rat) have been determined. Both myoglobins exhibit one polymorphism. The two rodent sequences have been compared with each other and with other known myoglobins. The myoglobin of the viscacha is similar to those of the diving mammals and penguin in having a high arginine content. Among mammalian sequences, the arginines at positions 77 (in one of the viscacha myoglobins) and 79 have been found only in the myoglobin from viscacha. Mole rat myoglobin has a lysine at position 31, where arginine or serine is found in all other known vertebrate myoglobins.     

Some observations on the ultrastructure of the thyroid gland of the pregnant Plains viscacha (Lagostomus maximus)

The thyroids from pregnant viscacha were examined in the electron microscope. The complex changes occurring in pregnancy are discussed. Of particular interest was the presence of numerous phagolysosomes. It is suggested that consideration be given to the terminology in this field.     

Histological and histochemical study of the duodenum of the plains viscacha (Lagostomus maximus) at different stages of its ontogenetic development

The general objective of this study focused on the duodenal histological and histochemical analysis of fetuses and adults of plains viscacha (Lagostomus maximus) from the Buenos Aires province (Argentina). Histological techniques, histochemical procedures for localizing and characterizing glycoproteins (GPs) and lectin histochemical techniques for the identification of specific sugar residues were used. The duodenal structure of all age groups here considered was typical of mammals. We identified a proliferation phase and an epithelial morphogenesis in mid‐gestational fetuses, an intermediate period of cell differentiation in at‐term fetuses and a posterior stage of physiological maturation in adults. According to histochemistry, the diverse GPs elaborated and secreted into the duodenum show a high degree of histochemical complexity related to the multiple functions of mucus in the digestive tract. The GPs in the duodenum of L. maximus and their glycosylation patterns varied according to the animal's age and the developmental state of the organ.     

A morphological,morphometric and histochemical study of the oviduct in pregnant and non‐pregnant females of the plains viscacha (Lagostomus maximus)

The oviduct is a very thin organ with a very tortuous appearance. It is divided into three segments: the infundibulum, the ampulla and the isthmus. Particularly, the oviduct of the viscacha lacks the intramural portion described in other species. The mucosa shows longitudinal pleats. The free edge of the infundibulum ends as small fimbriae that are of variable length and do not completely cover the ovary. The proportion of ciliated and secretory epithelial cells varied both in relation to the segments of the oviduct analysed and to the physiological state (anoestrus, follicular phase, early pregnancy and late pregnancy). The glycocalix and the apical region of the superficial epithelial cells are PAS and alcian‐blue positive. The muscular layers vary in thickness in different regions. Some lectins such as UEA‐1 and DBA showed variations in the binding pattern during the different physiological stages analysed whereas RCA‐1and WGA had a very stable pattern.     

The colonic groove of the plains viscacha (Lagostomus maximus): Histochemical evidence of an abrupt change in the glycosylation pattern of goblet cells

The ascending colon of most rodent species shows a longitudinal colonic groove that works as a retrograde transport pathway for a mixture of bacteria and mucus toward the cecum. We describe the morphology and glycosylation pattern of the colonic groove of Lagostomus maximus to analyze the role of mucins in this anatomical feature. We also studied the distribution pattern of the interstitial cells of Cajal (ICC) to evaluate their regulatory influence on gut motility. The groove originated near the cecocolic junction and extended along the mesenteric side of the ascending colon, limited at both ends by nonpapillated ridges. These ridges divided the lumen of the ascending colon into two compartments: a narrow channel and a large channel, called the groove lumen and the main lumen, respectively. The histochemical analysis showed differences in the glycosylation pattern of the goblet cells inside and outside the groove. Unlike the mucosa lining the main lumen of the colon, the groove was rich in goblet cells that secrete sulfomucins. The PA/Bh/KOH/PAS technique evidenced an abrupt change in the histochemical profile of goblet cells, which presented a negative reaction in the groove and a strongly positive one in the rest of the colonic mucosa. The anti‐c‐kit immunohistochemical analysis showed different ICC subpopulations in the ascending colon of L. maximus . Of all types identified, the ICC‐SM were the only cells located solely within the colonic groove.     

Histology,histochemistry and morphometry of the ovary of the adult plains viscacha (Lagostomus maximus) in different reproductive stages

Lagostomus maximus is a South American Hystricognathi rodent whose reproductive behaviour shows characteristics unusual for mammals, such as polyovulation (200–800 oocytes) and a high rate of embryo mortality. Thirty‐six mature females captured in the province of Buenos Aires showed different physiological reproductive stages. Most of them presented a postpartum oestrus in August–September. This characteristic is different from that reported in other geographical areas. The stages considered were: anoestrus, follicular phase, early pregnancy and late pregnancy. The ovaries were light‐pink and smooth and presented a tortuous cord‐like aspect. Many primordial follicles were found in all the females studied. Follicles in different states of maturation and primary and accessory corpora lutea were observed in the cortex. These structures were smaller than those present in other related species. Follicles did not project into the surface of the organ. Calcified follicles of diverse size were found in all the ovaries. Atretic follicles were found in all the stages analysed. Interstitial tissue surrounding the follicles and the corpora lutea was also observed. The number and proportion of different cortical structures varied in the physiological stages analysed. The ovaries of the viscacha have differential characteristics in comparison to other Hystricognathi, some of them related to polyovulation.     

Cytology of the pituitary gland of the Plains viscacha (Lagostomus maximu)

The anatomy of the pituitary gland of the Plains viscacha ( Lagostomus maximus ) is described. The pituitary gland in various physiological states has been investigated in order to localise the secretory sites of the trophic hormones. The various cell types of the pituitary gland were distinguished on the basis of their morphological characteristics, tinctorial properties and differential solubilities of the protein hormones in trichloroacetic acid solutions. Two cell types were found in the pars tuberalis, three cell types in the pars intermedia and six chromophi1 cell types in the pars anterior. Their possible functions are discussed.     

Exposure to constant light increases pineal weight and RNA content in the pineal of the vizcacha (Lagostomus maximus maximus)

The following parameters, RNA and protein content, gland weight and nuclear size were studied in pineal glands of adult male vizcachas, maintained in captivity under permanent light (Lot I) and darkness (Lot II). The same determinations were performed in pineals of vizcachas shot at night in their normal habitat (Lot III, Control lot). A significant rise of gland weight and RNA content was observed in Lot I (with respect to the Control lot), while nuclear size and protein content were unchanged. The only significative differences between Lots I and II were also found in the pineal weight and RNA content. These results indicate that exposure of vizcachas to permanent light for 10 days does not produce inhibition of the parameters under study as occurs in other species. Apparently, the light acts as a stressor in these nocturnal mammals.     

A combined light and scanning electron microscopy study

The uppermost Eocene Florissant Formation, Rocky Mountains, Colorado, has yielded numerous insect, vertebrate and plant fossils. Three previous comprehensive palynological studies investigated sections of lacustrine deposits of the Florissant Formation and documented the response of plant communities to volcanic eruptive phases but overall found little change in plant composition throughout the investigated sections. These studies reported up to 150 pollen and spore phenotypes. In the present paper, we used a taxonomic approach to the investigation of dispersed pollen and spores of the Florissant Formation. Sediment samples from the shale units containing macrofossils were investigated using light microscopy (LM) and scanning electron microscopy (SEM). The general picture of the palynoflora is in agreement with previous studies. However, the combined LM and SEM investigation provides important complementary information to previous LM studies. While a fairly large amount of previous pollen determinations could be confirmed, the purported taxonomic affinities of several pollen phenotypes need to be revised. For example, pollen referred to as Podocarpus or Podocarpidites sp. belongs to the Pinaceae Cathaya, Malus/Pyrus actually belongs to Dryadoideae, pollen of the form genus Boehlensipollis referred to as Proteaceae/Sapindaceae/Elaeagnaceae or Cardiospermum belongs to Sapindaceae but not to Cardiospermum, and pollen of Persicarioipollis sp. B with previously assumed affinities to Polygonaceae actually belongs to Thymelaeaceae. Pandaniidites and one type of Malvacipollis cannot be linked with Pandanaceae and Malvaceae. A few taxa are new records for Florissant (Ebenaceae: Diospyros; Mernispermaceae; Trochodendraceae: Tetracentron). In general, SEM investigations complement the LM palynological studies and improve the identification of dispersed pollen and spores and enable integration of data from dispersed fossil pollen into a wide range of comparative morphological, taxonomic, evolutionary, biogeographic and phylogenetic studies.     

Germ cell differentiation and proliferation in the developing testis of the South American plains viscacha, Lagostomus maximus (Mammalia, Rodentia)

Cell proliferation and cell death are essential processes in the physiology of the developing testis that strongly influence the normal adult spermatogenesis. We analysed in this study the morphometry, the expression of the proliferation cell nuclear antigen (PCNA), cell pluripotency marker OCT-4, germ cell marker VASA and apoptosis in the developing testes of Lagostomus maximus, a rodent in which female germ line develops through abolished apoptosis and unrestricted proliferation. Morphometry revealed an increment in the size of the seminiferous cords with increasing developmental age, arising from a significant increase of PCNA-positive germ cells and a stable proportion of PCNA-positive Sertoli cells. VASA showed a widespread cytoplasmic distribution in a great proportion of proliferating gonocytes that increased significantly at late development. In the somatic compartment, Leydig cells increased at mid-development, whereas peritubular cells showed a stable rate of proliferation. In contrast to other mammals, OCT-4 positive gonocytes increased throughout development reaching 90% of germ cells in late-developing testis, associated with a conspicuous increase in circulating FSH from mid- to late-gestation. TUNEL analysis was remarkable negative, and only a few positive cells were detected in the somatic compartment. These results show that the South American plains viscacha displays a distinctive pattern of testis development characterized by a sustained proliferation of germ cells throughout development, with no signs of apoptosis cell demise, in a peculiar endocrine in utero ambiance that seems to promote the increase of spermatogonial number as a primary direct effect of FSH.