Seasonal Variations in the Testis and Epididymis of Vizcacha (Lagostomus Maximus Maximus)1

Abstract

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.

Seasonal Changes in Morphology and Immunoreactivity of PDGF-A and its Receptor PDGFR-α in the Epididymis of Wild Ground Squirrels (<i>Citellus dauricus</i> Brandt)

“…This is an efficient strategy to ensure energy metabolism and successful breeding as an adaptation to the annually changing conditions in their habitat [27]. Meanwhile, these findings were also similar to the observations in roe deer [23], viscacha [25,28] and mountain cavy [24]. In roe deer, the epididymal duct with its surrounding tissue expanded as the breading season approached.…”

“…The enlargement of the caput was primarily caused by growth of the epithelial compartment, whereas in the cauda, it was predominantly attributed to dilatation of the lumen [23]. In viscacha, the corpus and cauda were the most sensitive segments to changes induced by the photoperiod, and spermatogenesis did not cease during the regression period [25,28]. In mountain cavy, a decrease in the weight of the testis and epididymis was found during the nonbreeding season, which was independent of the change in body weight [24].…”

Daily morphological variations in the viscacha (Lagostomus maximus maximus) retina. Probable local modulatory action of melatonin

“…Previous studies demonstrated that the pineal gland and its hormone, melatonin, are involved in its reproductive rhythmicity (Domínguez et al, 1987;Fuentes et al, 1991;Pelzer et al, 1999;Muñ oz et al, 1999Muñ oz et al, , 2001Mohamed et al, 2000). Lascano et al (1999) demonstrated an avascular, rod-rich retina, with a specialized region spanning through most of the equator of the eye of the viscacha, suggesting that this equatorial region could be a highly sensitive light detector related to foraging behaviors during crepuscular or nocturnal hours.…”

Expression of Androgen Receptor, Estrogen Receptors Alpha and Beta and Aromatase in the Fetal, Perinatal, Prepubertal and Adult Testes of the South American Plains Vizcacha, <i>Lagostomus maximus</i> (Mammalia, Rodentia)

“…Much attention has been paid to the female germ line, since this species displays a number of unique and exceptional reproductive characteristics including massive polyovulation, abolished apoptosis-dependent germ cell attrition and follicular atresia, ovulation at mid-gestation and natural embryo selection in early post-implantation development [17][18][19][20]. However, male reproductive physiology in L. maximus has been mainly investigated by focusing on adult testicular changes related to the photoperiod, and endocrine variation caused by light/dark cycle fluctuation, which induces changes in the morphology of Leydig and Sertoli cells and spermatogonia [21][22][23][24][25]. Recently, we reported that the fetal testis of the South American plains vizcacha displays a distinctive pattern of development characterized by a sustained proliferation of germ cells with little or no apoptosis.…”