The Pars Tuberalis: The Missing Link in the Photoperiodic Regulation of Prolactin Secretion?

Morgan, Hiram

doi:10.1046/j.1365-2826.2000.00459.x

Cited by 88 publications

(84 citation statements)

References 99 publications

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“…Subsequently, the PT has been adopted as a model system to investigate the molecular mechanisms involved in decoding melatonin signal duration and long-term timing (Morgan 2000, Hazlerigg et al 2001. This rests on the ability to readily manipulate PT cells in vitro using primary cell cultures from animals set up on specific photoperiods, and the ability to study the long-term PT-control of prolactin secretion in vivo using hypothalamo-pituitary disconnected (HPD) sheep where the complications of direct inputs from the hypothalamus are removed (see below).…”

Section: Decoding the Melatonin Signal In The Pt Calendar Cellmentioning

confidence: 99%

“…Comprehensive in vivo studies in HPD sheep provide further evidence that there is an interval timer and/or circannual rhythm generator within the PT (Lincoln & Clarke 1994, 1997, 2000. In the HPD animal, the pituitary gland is physically isolated from the hypothalamus by the surgical removal of the arcuate nucleus and destruction of the median eminence (Clarke et al 1983, Lincoln et al 2001.…”

Section: Interval Timer/circannual Rhythm Generator In the Pt Calendamentioning

confidence: 99%

See 1 more Smart Citation

Clock genes in calendar cells as the basis of annual timekeeping in mammals--a unifying hypothesis

Lincoln

Andersson²,

Loudon³

2003

Journal of Endocrinology

193

145

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Melatonin-based photoperiod time-measurement and circannual rhythm generation are long-term time-keeping systems used to regulate seasonal cycles in physiology and behaviour in a wide range of mammals including man. We summarise recent evidence that temporal, melatonincontrolled expression of clock genes in specific calendar cells may provide a molecular mechanism for long-term timing. The agranular secretory cells of the pars tuberalis (PT) of the pituitary gland provide a model cell-type because they express a high density of melatonin (mt1) receptors and are implicated in photoperiod/circannual regulation of prolactin secretion and the associated seasonal biological responses. Studies of seasonal breeding hamsters and sheep indicate that circadian clock gene expression in the PT is modulated by photoperiod via the melatonin signal. In the Syrian and Siberian hamster PT, the high amplitude Per1 rhythm associated with dawn is suppressed under short photoperiods, an effect that is mimicked by melatonin treatment. More extensive studies in sheep show that many clock genes (e.g. Bmal1, Clock, Per1, Per2, Cry1 and Cry2) are expressed in the PT, and their expression oscillates through the 24-h light/darkness cycle in a temporal sequence distinct from that in the hypothalamic suprachiasmatic nucleus (central circadian pacemaker). Activation of Per1 occurs in the early light phase (dawn), while activation of Cry1 occurs in the dark phase (dusk), thus photoperiod-induced changes in the relative phase of Per and Cry gene expression acting through PER/CRY protein/protein interaction provide a potential mechanism for decoding the melatonin signal and generating a long-term photoperiodic response. The current challenge is to identify other calendar cells in the central nervous system regulating long-term cycles in reproduction, body weight and other seasonal characteristics and to establish whether clock genes provide a conserved molecular mechanism for long-term timekeeping.

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Section: Decoding the Melatonin Signal In The Pt Calendar Cellmentioning

confidence: 99%

Section: Interval Timer/circannual Rhythm Generator In the Pt Calendamentioning

confidence: 99%

Clock genes in calendar cells as the basis of annual timekeeping in mammals--a unifying hypothesis

Lincoln

Andersson²,

Loudon³

2003

Journal of Endocrinology

193

145

View full text Add to dashboard Cite

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“…This phenomenon is especially evident in seasonally breeding species. In sheep, the short day photoperiod, elevates plasma melatonin concentration which in turn leads to the inhibition in the secretion of PRL (Misztal et al, 1997;Morgan, 2000;Molik et al, 2007;Gomez-Brunet et al, 2008;Morgan and Hazlerigg, 2008;. Numerous data indicated that prolonged treatment with melatonin (i.e.…”

Section: Factors Inhibiting Prolactin Secretionmentioning

confidence: 99%

“…This supports the view that the suppression of prolactin secretion followed by a partial recovery (partial refractoriness) is a normal response to a short-day melatonin signal and that this is due to the action of melatonin in the pituitary gland. Indeed, it has been shown that melatonin inhibits PRL, acting within the pars tuberalis (PT) of the pituitary gland and that a protein factor called tuberalin, which governs both the synthesis and release of prolactin, participates in this mechanism (Morgan, 2000). A long-duration melatonin signal from short days, or a continuous melatonin signal from a melatonin implant, may suppress prolactin secretion by inhibiting the release of tuberalin from the PT.…”

Section: Factors Inhibiting Prolactin Secretionmentioning

confidence: 99%

Prolactin and the physiological regulation of its secretion. A review

Ciechanowska¹,

Misztal²,

Przekop³

2013

J. Anim. Feed Sci.

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“…Binding sites and transcripts for MT1 receptors are detected in the pre-mammillary hypothalamus, the site of melatonin action to control reproduction in sheep [14], but whether MT1 mediates the effects of melatonin on reproductive activity has yet to be determined. In contrast, the MT1 receptor expressed in the pars tuberalis (PT) of the pituitary, has been shown to mediate the effect of melatonin on seasonal changes in prolactin secretion [15][16][17]. In addition, in the PT, the number of binding sites has been shown to be significantly higher in -/-ewes when compared to +/+ ewes [12] using the radioligand 2-[ 125 I]-iodomelatonin.…”

Section: Introductionmentioning

confidence: 99%

Relationship between MT1 melatonin receptor gene polymorphism and seasonal physiological responses in Île-de-France ewes

et al. 2005

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-The gene encoding the MT1 melatonin receptor in sheep has a restriction fragment length polymorphism (RFLP) site to the MnlI enzyme whose incidence is associated to the expression of seasonality in several breeds. The aim of this study was to examine the relationship between this genetic marker and the physiological effects of MT1 receptor gene polymorphism on several seasonal functions in Île-de-France ewes. The study was performed using 12 pairs of half-sib adult Île-deFrance ewes. Within each pair, ewes were selected on the basis of their genotype at the MnlI RFLP site: group +/+ and -/-(presence and absence of MnlI restriction site, respectively). No difference in the dates of the beginning, the end or the length of the breeding season was observed between groups during the two-year study. The seasonal changes in prolactin secretion were not different between groups. Similarly, wool growth rate and primary follicle activity, measured for one year, varied with the time of the year in the same way in the two groups. Our study therefore failed to show any relationship between MT1 polymorphism and reproductive seasonality in Île-de-France ewes. This suggests that the influence of this polymorphism on the regulation of seasonal function is dependent upon the breed and/or environmental conditions. The MT1 polymorphism can explain only a small part of the genetic variability of seasonal functions and the implication of other genes must be investigated.

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The Pars Tuberalis: The Missing Link in the Photoperiodic Regulation of Prolactin Secretion?

Cited by 88 publications

References 99 publications

Clock genes in calendar cells as the basis of annual timekeeping in mammals--a unifying hypothesis

Clock genes in calendar cells as the basis of annual timekeeping in mammals--a unifying hypothesis

Prolactin and the physiological regulation of its secretion. A review

Relationship between MT1 melatonin receptor gene polymorphism and seasonal physiological responses in Île-de-France ewes

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