Plains viscacha were established in the laboratory to Spanish by Llanos & Crespo (), and some details of reproduction were given. Llanos, A. and J. Crespo. Ecología de la vizcacha (Lagostomus maximus maximus Blainv.) en el nordeste de la provincia de Entre Ríos. Rev. Llanos, A. C. and J. A. Crespo. Ecología de la vizcacha (Lagostomus maximus maximus Blainv.) en el nordeste de la Provincia de Entre Ríos. Revista de.

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Abstract Prolactin PRL is essential for the maintenance of the corpora lutea and the production of progesterone P4 during gestation of mice and rats, which makes it a key factor for their successful reproduction.

Une forte selectivite s’exprime dans les habitats et au cours des saisons a faible diversite vegetale. In female viscacha, melanin granules within lysosome-like dense bodies were also observed.

This suggests that melanin is not a constant characteristic in the pineal gland of mammals. The Masson-Fontana silver method for melanin resulted positive and the pigments manifested a strong argentaffin reaction.

Animal Handling Twenty-five female vizcachas, L. Some authors have indicated the presence of a few retinal antigens in the pinealocytes [ 40 — 43 ]. Finally, the slides were dehydrated, cleared in xylene, and mounted using a synthetic mounting medium.

The Masson-Fontana silver and the Schmorl histochemical techniques for melanin pigments determination were also performed. This is the first attempt to relate PRL as well as its ovarian receptor to some key steroidogenic markers involved in the production of P4 during gestation of vizcachas. Density of vizcacheras in each habitat was estimated following the Eberhardt method for transects with undefined width. A possible explanation of this decrement would be that, during lactation, the constant demand exerted by the litter through the stimulus of suckling may cause the newly synthesized hormone to be immediately poured into the circulatory system, preventing its accumulation into the lactotrophs.

PRL immunodetection was evidenced in the cytoplasm of lactotropic cells localized in the pars distalis as previously described by Filippa and Mohamed [ 55 ]. Two microhabitats, plains and rocky elevations, were distinguished in the study area of each habitat, in order to verify vizcacha’s preference for plains.


Proportions of Poa and Panicum were significantly higher in diet than in availa- bility. This method allows to correct the proportional loss of visibility with the distance from the transect, using a correlation between distances and frequencies of vizcacheras observed.

Faecal samples composed by 10 fresh pellets were collected from 10 vizcacheras selected on each sampling area.

Vizioli for his support during the collection of the data, E. Histochemical and ultrastructural studies of the pineal gland of female viscacha Lagostomus maximus maximus were performed to analyze the presence of pigmented cells under natural conditions and to evaluate a probable relation between pigment content and glandular activity during pregnancy.

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Identification of melanin in the bovine pineal gland. The nonpregnant viscachas showed the lowest number of pigmented cells in all the groups studied Table 2.

Inserra1,2 S. In the pinealocytes, the melanosomes were often found within lysosome-like dense bodies Figure 6 b. The morphology of the mammal pineal gland presents great variability [ 193839 ].

Therefore, the Selective Quality Hypothesis may be applied to vizcachas expressed as: A 40x objective was used for the observations.

Although dificulties in burrow construction could justify that no vizcachera was located in rocky elevations, other factors may prevent vizcachas from using this micro- habitat, since elevations were not visited for feeding, even those which where adjacent to active vizcacheras.

PRLR immunoreactivity was weak at the beginning of pregnancy; it became markedly stronger at midgestation and decreased again near parturition time. To receive news and publication updates for International Journal of Endocrinology, enter your email address in the box below. Neuromelanin of the substantia nigra: We studied ovarian LHR expression as a key marker of luteinization Figure 1. Primer sequences are shown in Supplementary Table 2.

In contrast, the pigmented cells number varied significantly according to sex in viscacha. The corpus luteum CL is a transient endocrine gland that biosynthesizes steroids under the control of luteotropic factors. More studies about herbi- vores dietary overlap, and their capability of habitat modification are needed in Nor- thern Patagonia. The blood was collected by cardiac puncture for the evaluation of serum hormone concentration.


The scarse plant cover and the high phane- rophytes availability distinguished rocky elevations of Escoriales from the other microhabitats. Intra- and interassay coefficients of variation were 7.

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Les preferences ali- mentaires et les strategies antipredation expliqueraient pourquoi la viscache restreint son habi- tat aux plaines. The ultrastructural features of the pineal pigment granules were also analyzed. Acknowledgments The authors wish to thank Mrs.

A light and electron microscopic study of the pineal gland of the viscacha Lagostomus maximus maximus Journal of Pineal Research. Comparative ultrastructural studies of the pineal gland of rodents. International Journal of Endocrinology. A formaldehyde-glutaraldehyde fixative of high osmolality for use in electron microscopy.

The pineal gland and the retina are formed from the developing diencephalon. This rodent exhibits a nocturnal behaviour, lives in extensive burrows, and emerges at dawn and dusk to feed. We detected PRL immunoexpression in the pituitary gland pars distalis in all the experimental groups Figure 6.

Transects were traversed in the sampling areas to determine plant cover as an estimator of food availability by the point-quadrat method Daget and Poissonet The electron micrograph shows a large amount of premelanosomes arrow and melanosomes m within a pinealocyte p and a pigmented cell pg. Revista Argentina de Producci6n Animal, 6: Maximum P4 and LH blood levels were recorded at midpregnancy as well.

This classification was established according to previous reports in our laboratory [ 32 — 34 ]. Higher availability of the preferred grass Poa in Escoriales may also facilitate a higher selectivity within cha- maephytes, dominated by the avoided Hyalis.

The presence of pigment has been demonstrated in different nervous structures such as those of retina, substantia nigraand locus coeruleus.