Localization of melatonin binding sites in the pars tuberalis of the mink at three times during the seasonal testicular cycle

Boissin-Agasse, Line; Barberis, Claude; Audigier, Sylvie; Roch, G; Boissin, J.

doi:10.1016/0304-3940(92)90737-r

Cited by 19 publications

(10 citation statements)

References 28 publications

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“…Among these the pars tuberalis (PT) of the anterior pituitary is noteworthy for containing the highest concentration of I-MEL-binding sites in all mammals studied to date. Moreover, in photoperiodic mustelids, no sites of I-MEL binding have been observed in areas other than the anterior pituitary (Weaver & Reppert 1990, Boissin-Agasse et al 1992, Bonnefond et al 1993, R Helliwell & PJ Morgan, unpublished observations), suggesting that the effects of melatonin are mediated exclusively through anterior pituitary sites in these species. Recent experiments in the ram and the ewe have attempted to determine which hypothalamic areas are responsible for mediating seasonal reproductive responses to melatonin by microimplantation (Lincoln & Maeda 1992, Malpaux et al 1993).…”

mentioning

confidence: 89%

The recovery of ovine pars tuberalis cells from melatonin-induced sensitization is a slow, protein synthesis-dependent phenomenon

Hazlerigg

Hastings²,

Morgan³

1994

Journal of Endocrinology

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The pars tuberalis (PT) of the anterior pituitary is characterized by the presence of a high concentration of melatonin receptors, and acute exposure of cells from this tissue to melatonin inhibits the accumulation of cyclic AMP (cAMP) stimulated by forskolin. Conversely, exposure of ovine PT (oPT) cells to melatonin for periods of up to 16 h causes a progressive increase in subsequent basal and forskolin-stimulated production of cAMP. These observations are consistent with the possibility that the PT is involved in the mediation of melatonin-dependent phenomena in mammals. If the chronic effects of exposure to melatonin are indeed functionally significant, then one would anticipate that those responses of oPT cells known to be dependent upon levels of cAMP would also show an enhanced response to stimulation following prolonged exposure to the hormone. In the present study, the activation of cAMP-dependent protein kinase and the synthesis of secretory protein by oPT cells were found to be sensitized by prolonged exposure to physiological concentrations of melatonin. In the case of the synthesis of secretory protein this effect of melatonin was confined to those proteins whose synthesis has been shown to be sensitive to melatonin in acute experiments. These observations support the hypothesis that melatonin-induced sensitization modulates the putative biosynthetic and secretory function of the PT. The present study also examined the mechanism of sensitization of oPT cells by melatonin. The development of sensitization was not affected by simultaneous exposure of oPT cells to forskolin (1 microM) during pretreatment with melatonin. This observation suggests that melatonin-induced sensitization occurs independently of the established acute effects of the hormone on cAMP levels in oPT cells. Since no effects of melatonin upon any other signalling cascade have been observed in these cells, the most plausible explanation for this finding is that sensitization is a direct consequence of prolonged activation of melatonin receptors. Such a mechanism might be linked to the partial down-regulation of melatonin receptors known to occur in oPT cells in response to prolonged exposure to the hormone. In order to test this hypothesis further, the process of recovery from the sensitizing effects of melatonin was examined. The recovery of oPT cells from the sensitizing effects of exposure to melatonin (100 pM, 16 h) took place gradually and, even after an interval of 16 h, cells that had previously been exposed to melatonin for 16 h remained sensitized to approximately 20% of the extent seen immediately following pretreatment with melatonin for 16 h.(ABSTRACT TRUNCATED AT 400 WORDS)

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mentioning

confidence: 89%

The recovery of ovine pars tuberalis cells from melatonin-induced sensitization is a slow, protein synthesis-dependent phenomenon

Hazlerigg

Hastings²,

Morgan³

1994

Journal of Endocrinology

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“…Since these initial stud ies, melatonin receptors have been demon strated in the PT of all mammalian species studied so far by autoradiography: rat [6][7][8]. Syrian hamster [7,9,10], Siberian hamster [7,11], European hamster [6], ferret [12], rabbit [13], sheep [14][15][16][17][18][19], goat [20], western spotted skunk [21], white-footed mouse [22], ground squirrel [23], mink [24,25], vervet monkey [26], baboon [26], rhesus monkey [27], hedge hog [28], Norwegian brown rat [29], guinea pig [29], dormouse, garden dormouse and jer boa [Masson-Pevet, unpubl. data].…”

Section: Introductionmentioning

confidence: 99%

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

Masson‐Pévet

Guilhot²

1994

Neurosignals

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The density of high-affinity melatonin receptors in the pars tuberalis of different long day breeders exhibits a seasonal variation, with high values in spring-summer and low values in autumn-winter. In all the studies, this decrease in receptor density was always associated with both a short photoperiod and sexual inactivity. Moreover, during the hibernation period, the reduction in receptor number was more marked in hypothermic than in normothermic animals. These seasonal changes in melatonin receptors were restricted to the pars tuberalis, which suggests that this structure represents an important target site for mediation of the photoperiodic effect of melatonin on seasonal functions. The mechanism of melatonin action at this level is discussed.

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“…I-MEL binding sites are lacking in the central nervous system of the adult mink (Boissin-Agasse et al 1992;Bonnefond et al 1993), as in that of other adult mustelids (Duncan and Mead 1992;Weaver and Reppert 1990). In the present study, film autoradiograms revealed specific I-MEL binding in discrete brain areas of near-term fetus and newborn mink: the olfactory epithelium, the cortex, the thalamus.…”

Section: Discussionmentioning

confidence: 97%

Ontogenesis of the retinohypothalamic tract, vasoactive intestinal polypeptide- and peptide histidine isoleucine-containing neurons and melatonin binding in the hypothalamus of the mink

Peytevin

Masson‐Pévet²,

Martinet

1997

Cell and Tissue Research

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The development of the retinohypothalamic tract (RHT) labeled with cholera toxin and of the vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine (PHI) systems was studied in the hypothalamus of neonatal mink by using immunohistochemistry. Retinal fibers were observed in the suprachiasmatic nucleus (SCN) from birth and were adult-like by day 14. VIP and PHI immunoreactivity was also present from birth. Melatonin binding was studied by autoradiography using [125I]melatonin as a ligand. A specific binding was detected in near-term fetal and neonate brains in the olfactory epithelium, various thalamic nuclei, the pineal gland, and the pars tuberalis of the pituitary gland, but never in the SCN. These results are discussed in the context of the potential role of daylight cycles and/or melatonin in entraining circadian rhythms in neonate mink.

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Localization of melatonin binding sites in the pars tuberalis of the mink at three times during the seasonal testicular cycle

Cited by 19 publications

References 28 publications

The recovery of ovine pars tuberalis cells from melatonin-induced sensitization is a slow, protein synthesis-dependent phenomenon

The recovery of ovine pars tuberalis cells from melatonin-induced sensitization is a slow, protein synthesis-dependent phenomenon

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

Ontogenesis of the retinohypothalamic tract, vasoactive intestinal polypeptide- and peptide histidine isoleucine-containing neurons and melatonin binding in the hypothalamus of the mink

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