Seasonal variations of gonadotropins in the pars distalis male Viscacha pituitary. Effect of chronic melatonin treatment

Abstract

The gonadotropes, LH and FSH cells, were immunohistochemically identified in the pituitary pars distalis of the adult male viscacha (Lagostomus maximus maximus) using specific antibodies against hLH‚ and hFSH‚ with the streptavidinbiotin- peroxidase complex. The distribution, size and percentage immunopositive area of these cells were analyzed by image analysis in viscachas captured during the annual reproductive cycle and after the chronic administration of melatonin. The LH‚ and FSHb cells showed seasonal changes in the distribution, size and percentage immunopositive area. The LHb cells were found widely distributed throughout the pars distalis during the reproductive period, and they were found in the ventro-medial region in the pars distalis during the gonadal regression and gonadal recovery periods. The LHb cells reached the largest size and immunopositive area during the reproductive period and the smallest size and immunopositive area during the gonadal regression period. The FSHb cells were found in the ventro-medial region during reproductive and gonadal regression periods. The FSHb cells were found widely distributed throughout the pars distalis during the gonadal recovery period when they showed the maximum percentage immunopositive area. A decrease in the size of LH‚ and FSHb cells was observed after the chronic administration of melatonin. Moreover, it produces a decrease in the immunopositive area occupied by the LH‚ cells but not in the immunopositive area occupied by the FSHb cells. Our results show great activity of LHb and FSHb cells in different moments of the annual reproductive cycle demonstrating that these cells are not secrete in parallel. Moreover, melatonin acts differentially on the activity of the gonadotrope cells

Pituitary Pars Intermedia of Male Viscacha<i> (Lagostomus maximus maximus)</i>: A Morphometric Study of Seasonal and Age-Related Changes in Immunohistochemistry

“…The analyzed morphometric parameters can be considered as a measure of the cellular activity [Takahashi, 1991;Torres et al, 1995;Filippa et al, 2005;Mohamed, 2006a, b, 2008].…”

“…The adult male viscacha in its natural habitat exhibits an annual reproductive cycle synchronized by the environmental photoperiod and modulated by the pineal gland and its main hormone, melatonin [Dominguez et al, 1987;Fuentes et al, 2003]. This cycle presents 3 well-defined periods: reproductive (summer, early autumn), gonadal regression (winter) and gonadal recovery (spring) [Fuentes et al, 1991[Fuentes et al, , 1993Muñoz et al, 2001;Aguilera Merlo et al, 2005;Filippa et al, 2005]. In winter, the pinealocites cellular activity and serum values of melatonin were maximal [Dominguez et al, 1987;Cernuda-Cernuda et al, 2003;Fuentes et al, 2003].…”

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

“…The distribution of the gonadotropes, LH and FSH is immunohistochemically in the pituitary pars distalis of the adult male viscacha (Lagostomus maximus maximus) using specific antibodies against LH and FSH‚ with the streptavidinbiotin-peroxidase complex [6]. The distribution, size and percentage immunopositive area of these cells were analyzed by image analysis in viscachas captured during the annual reproductive cycle.…”

Histological Changes in the Retina Provoked by Lithium Treatment in a Nocturnal Rodent <b><i>(Lagostomus maximus maximus)</i></b>

“…They are seasonal breeders and present a reproductive cycle synchronized by the environmental photoperiod through the pineal gland and its main hormone, melatonin. This cycle is characterized by a gonadal regression period during the short winter days in South America [Dominguez et al, 1987;Fuentes et al, 1991Fuentes et al, , 2003Muñoz et al, 2001;Aguilera Merlo et al, 2005;Filippa et al, 2005]. The viscacha has been described to have an avascular, rod-rich retina with a specialized region spanning most of the equator of the eye, suggesting that this equatorial region might be a highly sensitive light detector related to foraging behaviors during the crepuscular or nocturnal hours.…”