The Pituitary Intermediate Lobe of the Hydrated and Dehydrated Gerbil

Abstract

The pituitary intermediate lobe was studied by immunocytochemistry on semithin sections and by electron microscopy in gerbils (Gerbillus pyramidum) caught in summer and winter in the natural biotope or experimentally submitted to chronic hydration or dehydration. In the gerbil, the intermediate lobe was formed by a predominating population of tightly packed melanotrophic cells the immunocytochemical and morphological features of which were comparable to those described in other mammals. A few typical corticotrophic cells were scattered in the contact zone with the neural lobe. Folliculostellate cells labelled with antibodies against glial fibrillary acid protein and vimentin were interspersed between the glandular cells; they formed small follicles in the vicinity of which the apical cytoplasm contained conspicuous dense granules. Both glandular cell types were innervated by axons most probably colocalizing dopamine and γ-aminobutyric acid. In the pituitaries from the gerbils caught in winter, as from those having free access to hydrated food, the melanotrophic cells exhibited morphological characteristics of high functional activity. In the gerbils caught in summer or receiving exclusively dry food, the secretory activity of the cells was obviously depressed. The corticotrophic cells were unaffected. These observations raise the question of the role of the intermediate lobe in the adaptation to desert life.

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

“…Lincoln and Baker [1995] have reported a decrease in ␣ -MSH concentrations in Soay sheep during winter. Lebaili et al [1999] have described a marked hypersecretion of melanotrophs in hydrated gerbils. Corticotroph-like cells and folliculostellate cells (FSC) have also been observed in PI Lebaili et al, 1999;Takeuchi, 2001].…”

“…The pituitary FSC, also called follicular, stellate, agranulated or glial-like cells, have been reported in mammalian [Soji et al, 1994;Lebaili et al, 1999;Cardin et al, 2000;Inoue et al, 2002;Mabuchi et al, 2004;Marettová and Maretta, 2004;Shirasawa et al, 2004] and non-mammalian species [De Rijk et al, 1991;Chowdhury and Yoshimura, 2002]. At present, there is no agreement in the literature in relation to the exact function and embryological origin of these cells.…”

“…A subpopulation of these cells expressed the glial fibrillary acidic protein (GFAP) whose presence varied under numerous physiological conditions, probably indicating a regulatory function Sands and Chronwall, 1996]. In addition, some authors have reported that the FSC were immunostained with the anti-GFAP and anti-vimentin antisera in rats [Sands and Chronwall, 1996] and in gerbils [Lebaili et al, 1999]. Soji et al [1994] have shown an increase in the number of these cells in relation to age, suggesting that the expression of the S-100 protein indicates the cells` morphologic maturation stage in rats.…”

The Mammalian Pars Intermedia —Structure and Function—

“…Similarly, a well-developed pars intermedia is also found in other mammals adapted to arid environments. Lebaili et al (1999) reported that in hydrated Gerbils, marked hypersecretion by melanotrophic cells was morphologically evident. Nevertheless, Kobayashi suggested that excess drinking of supplemental NaCl at a concentration of up to 0.9% in a 5% glucose drinking solution, still evokes significant melanotrophic cell activity (unpublished data).…”

“…However, in many species including man, the pars intermedia has few blood vessels and there appears to be a paucity of blood vessels (Turner and Bagnara, 1976). The pars intermedia of laboratory animals such as the mouse and rat, and that of the small desert gerbil (Gerbillus pyramidum) also have few blood vessels (Lebaili et al, 1999). This sparse vascularity in the pars intermedia of the pituitary gland is unusual in the endocrine system.…”