The Pars tuberalis of the Monkey <i>(Macaca fascicularis)</i> Hypophysis: Cell Types and Hormone Expression

Abstract

The pars tuberalis (Pt) of most mammalian species contains specific cells which are structurally and functionally different from the pars distalis (Pd) cells. Pt-specific cells possess melatonin receptors and reveal morphological changes dependent on the duration of the photoperiod. Furthermore, in hamsters the transmission of photoperiodic stimuli to the endocrine system is influenced by melatonin, an effect which is likely to be mediated by Pt-specific cells. In monkeys, however, only little is known about this cell type. Therefore, we studied the ultrastructural differentiation of Pt-specific cells and describe the expression of different hormones and their mRNA by immunohistochemistry and in situ hybridization. Apparently the Pt consists of (1) cells similar to gonadotropic cells of the Pd, (2) folliculostellate cells and (3) a cell population which is morphologically and functionally clearly distinct from all other cell types found in the Pd. Morphologically they resemble the Pt-specific cells found in other species. Regarding the expression of secretory products there is evidence that they transcribe and translate the β-TSH subunit. Although there is a strong signal for the mRNA of the common α-chain, protein staining is much weaker. POMC mRNA is expressed in the Pt while there is no evidence for PRL mRNA. The present results lead to the conclusion that the Pt of the monkey contains Pt-specific cells which express different hormonal subunits as was already shown for other species. In context with previous findings of melatonin receptors in the monkey Pt further investigations are necessary to establish the possible role of Pt-specific cells in the photoperiod-dependent generation of endocrine rhythms.

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

“…This is similar to descriptions in sheep and rat (Gross, 1984;Rudolff et al, 1993;Böckers et al, 1994;Wittkowski et al, 1999). On the other hand, in monkey (macaca fascicularis), the gonadotrope cells are distributed along all the PT (Bock et al, 2001). In viscacha, some ACTH cells were detected in the zona tuberalis but not in the PT itself.…”

“…In the rabbit, granule diameter is 90 -116 nm, with no presence of glycogen, which constitutes a specific characteristic of this rodent (Cameron and Foster, 1972). In the monkey (macaca fascicularis), the diameter is in the 100 -120 nm range (Bock et al, 2001). The results obtained in this study show that Fig.…”

“…The morphology of the PT has been studied in a number of species: rat (Oota and Kurosomi, 1966), rabbit (Cameron and Foster, 1972), amphibians (Doerr Schott, 1971;Dellman et al, 1974), chicken (Grignon and Guedenet, 1968;Dellman et al, 1974), monkey (macaca fascicularis) (Bock et al, 2001), and guinea pig (Kameda, 1990). While some morphological characteristics are shared between species, others show species-specific variations.…”

MT1 Melatonin Receptor mRNA Expressing Cells in the Pars Tuberalis of the European Hamster: Effect of Photoperiod

“…The α‐GSU is detected in many PT cells of the European hamster. The α‐GSU has already been detected either by immunocytochemistry or in situ hybridization in the PT of the rat (13, 26, 27), the Siberian hamster (25, 28, 29), the sheep (30, 31) and the monkey (32). As the α‐GSU is present in many cells that do not seem to express any known β subunit, it was proposed that the PT may produce a specific and still unknown glycoprotein hormone, which was named tuberalin (27).…”