Seasonality and Melatonin Receptors in the Pars tuberalis in Some Long Day Breeders

Neurosignals ◽  
1994 ◽  
Vol 3 (2) ◽  
pp. 63-70 ◽  
Author(s):  
Mireille Masson-Pévet ◽  
François Gauer
Keyword(s):  
Melatonin Receptors ◽  
Pars Tuberalis ◽  
Long Day

scholarly journals What is the role of melatonin within the anterior pituitary?

2001 ◽  
Vol 170 (3) ◽  
pp. 493-501 ◽  
Author(s):  
DG Hazlerigg
Keyword(s):  
Anterior Pituitary ◽  
Cellular Level ◽  
Prolactin Secretion ◽  
Receptor Expression ◽  
Melatonin Receptors ◽  
Seasonal Effects ◽  
Pars Tuberalis ◽  
Melatonin Receptor ◽  
Functional Studies

The pineal hormone, melatonin, is uniquely defined by its role as hormonal time, but the processes whereby cells extract temporal information from the melatonin signal are not understood. Melatonin receptors are expressed in the pars tuberalis (PT) and, during fetal and perinatal life, in the pars distalis (PD). Functional studies suggest that the PT mediates the seasonal effects of melatonin on prolactin secretion, whilst the PD may be involved in photoperiodic programming of the developing gonadotrophic axis. To understand these effects at the cellular level we need to know the phenotype of melatonin-responsive cells. This review summarises current understanding in this area, and highlights present shortcomings. A case is presented for exploring the hypothesis that there is a functional association between melatonin receptor expression and cell differentiation in the anterior pituitary.

Melatonin Receptors in the Lamb Pars tuberalis/Median Eminence throughout the Day

1993 ◽  
Vol 58 (3) ◽  
pp. 359-365 ◽  
Author(s):  
Vincent Piketty ◽  
Jean Pelletier
Keyword(s):  
Median Eminence ◽  
Melatonin Receptors ◽  
Pars Tuberalis

scholarly journals A Novel Interaction Between Inhibitory Melatonin Receptors and Protein Kinase C-Dependent Signal Transduction in Ovine Pars Tuberalis Cells*

Endocrinology ◽  
1998 ◽  
Vol 139 (4) ◽  
pp. 1723-1730 ◽  
Author(s):  
Alexander W. Ross ◽  
Catriona A. Webster ◽  
Michael Thompson ◽  
Perry Barrett ◽  
Peter J. Morgan
Keyword(s):  
Signal Transduction ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Melatonin Receptors ◽  
Pars Tuberalis ◽  
Kinase C ◽  
Dependent Signal

Characterization of melatonin receptors in the ram pars tuberalis: influence of light

1990 ◽  
Vol 123 (5) ◽  
pp. 557-562 ◽  
Author(s):  
Jean Pelletier ◽  
Bertrand Castro ◽  
Georges Roblot ◽  
Renée Wylde ◽  
Marie-Madeleine de Reviers
Keyword(s):  
Median Eminence ◽  
Binding Sites ◽  
Melatonin Receptors ◽  
Scatchard Analysis ◽  
Pars Tuberalis

Abstract. The present study was conducted to assess the binding of [125I]melatonin to frozen unfixed sections of pars tuberalis/median eminence tissue from Ile-de-France rams exposed or not exposed to light before slaughter. The specificity of [125I]melatonin binding to the pars tuberalis tissue was revealed by autoradiography and the magnitude of binding as related to the pars tuberalis area was determined after incubation and counting of pars tuberalis/median eminence sections. Subsequent studies with sections incubated with [125I]melatonin indicated that 1. the binding sites were saturable; 2. binding was stable for 24 h at 20°C, but unstable at 28 or 37°C; 3. melatonin and [12 7I]melatonin had a similar potency to compete with [125I]melatonin for binding sites, whereas other ligands such as serotonin or N-acetylserotonin were devoid of activity, and 4. by Scatchard analysis, the constant affinity Ka was found to be high in the 1010 l/mol range. Rams exposed to light throughout the night prior to slaughter presented a significant increase in the apparent number of [125I]melatonin binding sites in comparison to animals maintained under darkness (2.25±0.30 vs 1.01±0.17 fmol/mm2 pars tuberalis, p<0.01), whereas Ka values were similar in both groups. These results indicate the presence of true melatonin receptors in the pars tuberalis of the ram. Furthermore, they suggest that their apparent number is light-dependent.

Daily Rhythms of Melatonin Binding Sites in the Rat Pars tuberalis and Suprachiasmatic Nuclei; Evidence for a Regulation of Melatonin Receptors by Melatonin Itself

1993 ◽  
Vol 57 (1) ◽  
pp. 120-126 ◽  
Author(s):  
François Gauer ◽  
Mireille Masson-Pévet ◽  
Debra Jean Skene ◽  
Berthe Vivien-Roels ◽  
Paul Pévet
Keyword(s):  
Binding Sites ◽  
Melatonin Receptors ◽  
Pars Tuberalis ◽  
Suprachiasmatic Nuclei ◽  
Daily Rhythms

scholarly journals Melatonin Receptors on Ovine Pars Tuberalis: Characterization and Autoradiographicai Localization

1989 ◽  
Vol 1 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Peter J. Morgan ◽  
Lynda M. Williams ◽  
Gary Davidson ◽  
Wilfred Lawson ◽  
Edward Howell
Keyword(s):  
Melatonin Receptors ◽  
Pars Tuberalis

Effects of two melatonin analogues, S-20098 and S-20928, on melatonin receptors in the pars tuberalis of the rat

1998 ◽  
Vol 25 (3) ◽  
pp. 172-176 ◽  
Author(s):  
M. Masson-Pévet ◽  
J. Recio ◽  
H. Y. Guerrero ◽  
E. Mocaer ◽  
Ph. Delagrange ◽  
...  
Keyword(s):  
Melatonin Receptors ◽  
Pars Tuberalis ◽  
Melatonin Analogues

The pars tuberalis of the hypophysis: a modulator of the pars distalis?

1992 ◽  
Vol 126 (4) ◽  
pp. 285-290 ◽  
Author(s):  
Werner H Wittkowski ◽  
Andreas H Schulze-Bonhage ◽  
Tobias M Böckers
Keyword(s):  
Close Contact ◽  
Melatonin Receptors ◽  
Portal System ◽  
Secretory Cells ◽  
Specific Cell ◽  
Pars Tuberalis ◽  
Pars Distalis ◽  
Functional Connection ◽  
Morphological Alterations ◽  
Functional Changes

The pineal hormone melatonin is known to influence circadian systems. Melatonin is also ascribed to mediate photoperiodic effects on the regulation of the hypothalamo-hypophyseal-gonadal axis. Other endocrine actions, especially a thyrotropic influence, have been postulated. Site and mechanism of action of melatonin, however, are still matters of speculation. In search of a functional cascade of (i) photoperiodic stimuli, (ii) their hormonal messenger melatonin, and (iii) endocrine targets, the pars tuberalis has gained a key position. The recent discovery and characterization of melatonin receptors located in the pars tuberalis of several species support such a functional significance. Earlier results point to a functional connection of the pars tuberalis with the pineal gland: the pars tuberalis is known for a pattern of differentiation distinctly different from other parts of the adenohypophysis. It contains a specific cell population with a morphology typical of peptide secreting cells. Like the hypothalamic nerve endings of the median eminence, they are in close contact with the primary plexus of the portal system. In contrast to secretory cells of the pars distalis, the specific cells of the pars tuberalis do not respond with morphological alterations to functional changes of peripheral endocrine glands. Yet, photoperiodic stimuli obviously influence morphology and functional activity of the pars tuberalis-specific cells. Investigations during recent years have led to the tentative conclusion that the pars tuberalis represents the hypophysial "receptor"for melatonin as the chemical messenger of photoperiodic stimuli. Depending on melatonin secretion pattern and melatonin receptivity, the pars tuberalis seems to modulate at least gonadotropic and thyrotropic activity of the pars distalis via a peptide hormone distributed in the pars distalis by the portal plexus. Such an intrahypophysial regulatory concept may explain the widespread actions of melatonin on endocrine targets.

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