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 glycogenlike 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 nonfenestrated 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

Forma e função dos músculos perineais da viscacha (Lagostomus maximus)

Entre as espécies de roedores já estudadas podemos destacar a grande variação na morfologia do aparelho reprodutor masculino. Assim, considerando a importância ecológica dos roedores, e a grande representatividade numérica quanto geográfica destes animais, bem como a escassez que aborda a anatomia reprodutiva, desenvolvemos este trabalho com um roedor histricomorfo da América do Sul, a viscacha. Este animal apresenta algumas características reprodutivas bem peculiares, desta forma descreveremos a anatomia macroscópica da musculatura perineal, e o papel dos músculos no comportamento copulatório desta espécie. A região perineal da viscacha é composta por cinco músculos, sendo que três músculos encontram-se dispostos no diafragama urogenital superficial, Musculus ischiocavernosus, M. bulbocavernosus e M. bulbospongiosus, e pelos músculos que se encontram no diafragma pélvico, M. levator ani e M. retractor penis. Sendo assim, destacamos que o estudo do assoalho pélvico em animais silvestres é de grande valia, uma vez que contribuem com o melhor entendimento dos mecanismos relacionados â ereção e ejaculação; ou seja colaboram com os estudos sobre a reprodução dos animais