The pars tuberalis of the monkey (Macaca fascicularis) hypophysis: Cell types and hormone expression

The pars tuberalis (Pt) of most mammalian species contains specific cells w hich are structurally and functionally different from the pars distalis (Pd ) cells. Pt-specific cells possess melatonin receptors and reveal morpholog ical 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 t ype. Therefore, we studied the ultrastructural differentiation of Pt-specif ic cells and describe the expression of different hormones and their mRNA b y immunohistochemistry and in situ hybridization. Apparently the Pt consist s of (1) cells similar to gonadotropic cells of the Pd, (2) folliculostella te cells and (3) a cell population which is morphologically and functionall y clearly distinct from all other cell types found in the Pd. Morphological ly they resemble the Pt-specific cells found in other species. Regarding th e expression of secretory products there is evidence that they transcribe a nd translate the beta -TSH subunit. Although there is a strong signal for t he mRNA of the common a-chain, protein staining is much weaker. POMC mRNA i s 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-specif ic 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 possib le role of Pt-specific cells in the photoperiod-dependent generation of end ocrine rhythms. Copyright (C) 2001 S.Karger AG, Basel.