Colloid in the pituitary pars distalis of viscacha (Lagostomus maximus maximus): Ultrastructure and occurrence in relation to season, sex, and growth

Abstract

Randomly distributed extracellular colloidal accumulations were observed in the pars distalis of viscacha (Lagostomus maximus maximus). They were preferentially located in the peripheral zone of the gland and showed variability in shape and size. Two different types of colloidal accumulations were found by electron microscopy: 1) those surrounded by nongranulated follicular cells that correspond to characteristic follicles, and 2) those surrounded by granulated cells. In the follicles lined by nongranulated follicular cells, long, prominent microvilli and cytoplasmic processes protruded into the lumen. The frequency of these accumulations varies during the year in adult male animals, showing an increase in number during summer and a decrease during winter. The lowest value was registered in August (winter). The mean follicular diameter did not vary seasonally. The number of colloidal accumulations did not vary seasonally in adult female viscachas, but a significant difference in the mean follicular diameter between pregnant and non-pregnant females was observed. Pituitaries of immature animals contain fewer colloidal accumulations than those of adults. In fetuses, these accumulations were absent. The administration of melatonin provoked a decrease in the number of these structures. The numeric changes of the colloidal accumulations observed in this study are associated with: 1) the seasonal reproductive activity in adult males, and 2) the reproductive condition, body weight and sexual maturity in males and females. The fact that melatonin administration decreases the population of colloidal accumulations in males suggests participation of the pineal gland in these changes.

Ultrastructural and immunocytochemical studies of the viscacha (Lagostomus maximus maximus) pituitary pars tuberalis

“…It is important to note that the follicles observed in the PT have characteristics similar to those described in the PD and PI of the same rodent in previous studies, in which we demonstrated the presence of glycoproteins (Scardapane et al, 1983) and the dependence of the number of follicles on the functional state of the gland (Mohamed et al, 2000). Kameda (1990) described the presence of follicles in the guinea pig PT and their modifications with age, suggesting a physiological role for these structures.…”

“…In our laboratory, studies have been conducted to determine the structural and ultrastructural characteristics of hypophyseal PD and pars intermedia (PI) (Scardapane et al, 1983;Mohamed et al, 1995). These two hypophyseal regions are characterized by the presence of follicular structures with colloidal material in the lumen and extracellular accumulation of colloid, which probably stores hormonal products (Mohamed et al, 2000). The viscacha has a seasonal reproductive cycle (Fuentes et al, 1991), with important participation of the pineal gland (Dominguez et al, 1987;Cernuda-Cernuda et al, 2003).…”

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.…”

Immunocytochemical and Ultra Structural Identification of Different Cell Types of the Anterior Pituitary Cells of Egyptian Herbivorous Adult Female Non Pregnant Rabbit Oryctolagus cunniculus

“…There are randomly distributed extracellular colloidal accumulation were observed in the pars distalis of Viscacha (Lagostomus maximus maximus) located in the peripheral zone of the gland and showed variability in shape and size [10]. In vespertilionid bat, Scotophilus heathi the electron microscopic studies revealed six distinct cells…”