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  • 1
    Electronic Resource
    Electronic Resource
    Seasonal variations in pineal 5-methoxytryptophol (5-ML) concentrations and in the daily pattern of pineal 5-ML and melatonin in the desert rodent Jaculus orientalis: Effect of prolonged illumination during the night (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of pineal research 13 (1992), S. 0 
    Details
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Seasonal variations in daytime pineal 5-methoxytryptophol (5-ML) and in the daily pattern of both pineal 5-ML and melatonin concentrations were measured by radioimmunoassay in male and female jerboas, Jaculus orientalis. Pineal 5-ML content was found to be low in winter and spring and showed a short but marked increase in summer. A clear daily rhythm was present in pineal 5-ML in September, with high concentrations during daytime and low concentrations during nighttime. In May there was a considerable drop in the daytime values and a marked decrease in the amplitude of the rhythm, while in December the daily rhythm completely disappeared. On the contrary, a clear daily rhythm was observed for pineal melatonin in September, December, and May with high values during nighttime and low values during daytime; no differences in the amplitude of the rhythm could be observed. Illumination during early night prevented both the nocturnal decrease of 5-ML and the increase of melatonin in September; in May illumination had no clear effect on 5-ML, while it prevented the normal increase of melatonin. These results suggest a possible desynchronization between the regulation of 5-ML and melatonin synthesis and release, and stress the complexity of the mechanisms involved in the environmental synchronization of seasonal functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-079X.1992.tb00051.x
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  • 2
    Electronic Resource
    Electronic Resource
    The Photoperiodic Response in Syrian Hamster Depends upon a Melatonin-Driven Circadian Rhythm of Sensitivity to Melatonin (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neuroendocrinology 7 (1995), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The pineal gland, via the daily pattern of melatonin (MEL) secretion, is directly involved in the conduction of photoperiodic information. The duration of MEL secretion is proportional to the duration of the dark period and, whatever the photoperiod is, MEL synthesis occurs 3 or 4 h after the dark onset in Syrian hamsters. In order to determine the relative importance of the duration or the coincidence hypothesis, a daily infusion protocol was used in sexually active pinealectomized hamsters. Long duration of MEL infusion (10 h) completely inhibit testes whereas short duration infusion (5 h) had no effect. When the animals were infused twice within 2 h 30 min separated by 3 h, they presented a complete gonadal atrophy, similar to the one observed with the 10 h infusion. Measurement of plasma MEL during the infusion and seperation periods revealed that MEL reached physiological nighttime values during the infusion period and fell to daytime values 1 h after the end of an infusion period. Thus, the results could not be due to a time additive action of the two MEL pulses. An intermediate response was observed when the 2 signals were applied across the light/dark transition. Gonadal regression did not occur when the 2 periods of infusion were separated by 5 h 30 min. The efficiency of this type of infusion was not dependent on the ambiant photoperiod since similar results were obtained in long and short photoperiods. The infusion was also as effective during the day as well as during the night. These results suggest that there is a rhythm of sensitivity to MEL, based on the coincidence hypotheses, that are important for transmission of photoperiodic information. This rhythm of sensitivity to MEL seems to be entrained by MEL itself, since the efficiency of the two pulses of MEL is not dependent of time of application and/or of photoperiod.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.1995.tb00731.x
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  • 3
    Electronic Resource
    Electronic Resource
    MT1 Melatonin Receptor mRNA Expressing Cells in the Pars Tuberalis of the European Hamster: Effect of Photoperiod (2003)
    Oxford, UK : Blackwell Science, Ltd
    Journal of neuroendocrinology 15 (2003), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Melatonin, secreted only during the night by the pineal gland, transduces the photoperiodic message to the organism. One important target for the hormone is the pars tuberalis (PT) of the adenohypophysis which displays a very high number of melatonin binding sites in mammals and is implicated in the seasonal regulation of prolactin secretion. To gain insight into the mechanism by which the melatonin signal is decoded in the PT, we studied the effect of photoperiod on the PT cells expressing the MT1 melatonin receptor in a highly photoperiodic species, the European hamster. Recently, we showed that, in the rat, the MT1 receptor mRNA is expressed in PT-specific cells characterized by their expression of β-thyroid stimulating hormone (β-TSH) along with the α-glycoprotein subunit (α-GSU). As the cellular composition of the PT shows variability among species, we first identified the cell type expressing the MT1 receptor in the European hamster by combining immunocytochemistry and nonradioactive in situ hybridization for the MT1 receptor mRNA. Our results show that, in the European hamster, as in the rat, the MT1 receptor is only expressed by the PT-specific-cells, β-TSH and α-GSU positive. In a second step, we analysed the effects of photoperiod on the MT1 mRNA, and on β-TSH and α-GSU both at the mRNA and protein levels. Our data show that, compared to long photoperiod, short photoperiod induces a dramatic decrease of MT1, β-TSH and α-GSU expression. Protein levels of β-TSH and α-GSU were also dramatically reduced in short photoperiod. Together, our data suggest that melatonin exerts its seasonal effects in the PT by signalling to PT specific-cells through the MT1 receptor subtype.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.2003.01060.x
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  • 4
    Electronic Resource
    Electronic Resource
    Syrian Hamster and Rat Display Developmental Differences in the Regulation of Pineal Arylalkylamine N-Acetyltransferase (2002)
    Oxford, UK : Blackwell Science, Ltd
    Journal of neuroendocrinology 14 (2002), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In the Syrian hamster, the role of noradrenaline in the regulation of melatonin synthesis is less clear than in the rat. During pineal ontogenesis in the rat, noradrenaline is the major transmitter involved in the onset of melatonin synthesis and melatonin rhythm. We analysed the involvement of noradrenaline in the ontogenesis of melatonin synthesis in the Syrian hamster and compared it with that of the rat. We followed the developmental profile of melatonin content in parallel with those of mRNA expression and activity of AA-NAT, the melatonin rhythm-generating enzyme. In addition, we tested the effect of noradrenergic drugs at early steps of pineal ontogenesis. In the Syrian hamster, the night-time Aa-nat mRNA, first detected 3 days after birth, increases progressively up to a maximum reached at 30 days of age and then decreases significantly towards adulthood. The daytime level of Aa-nat mRNA remains always low. A significant day/night rhythm appears 10 days after birth, is maximal (200-fold nocturnal increase) 30 days after birth and decreases slowly towards adulthood. Ontogenesis of the AA-NAT activity rhythm is similar, although with a much lower amplitude of day/night variations (four-fold). The developmental pattern of melatonin content is similar to that of AA-NAT and could be correlated with the appearance of sympathetic innervation in the pineal gland. However, neither α- nor β-adrenergic antagonists inhibit the night-time Aa-nat mRNA transcription in the 9-day-old Syrian hamster, in contrast to what is observed in the adult. For comparison, the β-adrenergic antagonist propranolol inhibits Aa-nat gene expression in 2-day-old rat. These results show that both species are different in the regulation of the appearance of melatonin synthesis and that Syrian hamster is peculiar from birth in term of noradrenaline involvement in the activation of melatonin synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.2002.00850.x
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of Melatonin Binding Sites in the Pars Tuberalis of the European Hamster (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neuroendocrinology 4 (1992), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Melatonin binding sites in the pars tuberalis of the European hamster (Cricetus cricetus) have been characterized using the radioligand 2-[125I]iodomelatonin. Specific 2-[125I]iodomelatonin binding was assessed using radioreceptor studies of pars tuberalis membrane preparations. Saturation studies revealed a single, high affinity site (Kd 39.8 (± 7.6 SEM) pM and Bmax 4.1 (± 0.5 SEM) fmol/mg protein, n=4). Kinetic experiments showed the 2-[125I]iodomelatonin binding to be rapid, saturable and reversible. The Kd calculated from the dissociation and association rate constants was 19.4 pM. The order of potency of different indoles for inhibition of 2-[125I]iodomelatonin binding was 6-chloromelatonin 〉 melatonin 〉 6-hydroxymelatonin 〉 N-acetylserotonin 〉 5-methoxytryptophol 〉 serotonin 〉 5-methoxytryptamine. GTP caused a dose-dependent inhibition of the 2-[125I]iodomelatonin binding. A saturation study showed that GTP reduced the number of binding sites by a third without altering their affinity. These results imply the presence of a G-protein-coupled melatonin receptor in the pars tuberalis of sexually active European hamsters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.1992.tb00158.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of Constant Light, Pinealectomy and Guanosine Triphosphate Gamma-S on the Density of Melatonin Receptors in the Rat Suprachiasmatic Nucleus: A Possible Implication of Melatonin Action (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neuroendocrinology 4 (1992), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We report here the effects of pinealectomy and exposition to constant light on the density of melatonin receptors in the suprachiasmatic nuclei of the rat using quantitative autoradiography. The Bmaxvalues were significantly increased when the animals were maintained in constant light for 3 days (8.22 ± 0.95 fmol/mg protein versus 4.55±0.14 fmol/mg protein in control group, 12 h light/12 h dark cycle (12L/12D), n = 6). A similar increase was also observed in rats pinealectomized 3 days before sacrifice and then maintained either under 12L/12D (Bmax7.56±0.80 fmol/mg protein) or in constant light (Bmax7.85±1.02 fmol/mg protein), while Kdvalues failed to show any variations after constant light and/or pinealectomy.The effect of GTPγS on the density of rnelatonin binding sites was also investigated in control animals and after 3 days of constant light. In 12L/12D animals, the Bmax shifted from 5.94 ± 0.14 fmol/mg protein in the absence of GTPγS to 3.97±0.22 fmol/ mg protein in the presence of 50μiM GTPγS. In animals maintained for 3 days in constant light, a similar decrease in the Bmax value was observed (8.95 ± 0.25 fmol/mg protein in absence and 5.95 ± 0.22 fmol/mg protein in presence of 50 μ GTPγS). In both cases, Kd values were not affected by GTPγS.Pinealectomy and constant light exposition are known to induce a suppression of the nocturnal peak of plasma rnelatonin and to keep plasma rnelatonin concentrations at a very low level. These results could suggest a regulatory effect of rnelatonin on the density of its own receptors which are shown here to be also coupled with a G-protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.1992.tb00193.x
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  • 7
    Electronic Resource
    Electronic Resource
    Melatonin: From Seasonal to Circadian Signal (2003)
    Oxford, UK : Blackwell Science, Ltd
    Journal of neuroendocrinology 15 (2003), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In mammals, the role of melatonin in the control of seasonality is well documented, and the sites and mechanisms of action involved are beginning to be identified. The exact role of the hormone in the circadian timing system remains to be determined. However, exogenous melatonin has been shown to affect the circadian clock. Identification of the molecular and cellular mechanisms involved in this well characterized chronobiotic effect will allow clarification of the role of endogenous melatonin in circadian organization
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.2003.01017.x
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  • 8
    Electronic Resource
    Electronic Resource
    Brain and Pituitary Melatonin Receptors in Male Rat during Post-Natal and Pubertal Development and the Effect of Pinealectomy and Testosterone Manipulation (1996)
    Oxford : Blackwell Science Ltd.
    Journal of neuroendocrinology 8 (1996), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Using quantitative autoradiography, melatonin receptors have been studied during post-natal and pubertal development of the rat in 2 brain and 2 pituitary structures. In the pars distalis of anterior pituitary, melatonin receptors decrease gradually in density after birth and disappear in 30 day-old animals. In contrast melatonin binding is only expressed in the paraventricular nuclei of the thalamus at the age of 21–23 days and is always present in adult animals. In the suprachiasmatic nuclei and in the pars tuberalis of the pituitary, melatonin receptor density decreases after birth, remains stable for approximately 1 month and increases again at puberty to reach the birth values in the adult. This increase was absent in pinealectomized and in castrated animals but present in castrated animals receiving testosterone suggesting that it depends upon circulating testosterone and melatonin levels. These results show that melatonin receptors are differentially regulated during post-natal development in each of the 4 structures studied, and that melatonin and testosterone are 2 factors which could be involved in the regulation of melatonin receptor density in the suprachiasmatic nuclei and pars tuberalis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.1996.tb00690.x
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  • 9
    Electronic Resource
    Electronic Resource
    Interindividual differences in the pattern of melatonin secretion of the Wistar rat (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of pineal research 27 (1999), S. 0 
    Details
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: In vivo trans-pineal microdialysis was performed in male Wistar rats maintained under a 12 hr light: 12 hr dark (LD 12: 12) cycle. Collected dialysates were assayed by radioimmunoassay for melatonin concentrations. A non-linear regression was fitted through the obtained datapoints to determine the time points at which a 50% increase (IT50) and decrease (DT50) of the nocturnal melatonin peak were reached. In a first experiment, the nocturnal melatonin profiles of four animals were determined throughout 5 consecutive days. In a second experiment, we analysed the melatonin profiles during the night in rats originating from three different breeding colonies (Dépré, Harlan, and Iffa-Crédo). A low intraindividual variability was found on the phase markers IT50 and DT50, as on peak duration of melatonin rhythms estimated over 5 subsequent days in the same animal. In contrast, animals showed a large interindividual variability in their profile phase markers and the values were dependent on the origin of the breeding colony. Each rat colony was characterized by early or late IT50 and DT50 as long or short peak length. It is concluded from experiment 1 that the melatonin rhythm is a very stable circadian marker. Nevertheless, great caution must be taken in the choice of animal groups while studying circadian rhythms due to the large interindividual variability observed in experiment 2. Therefore, as the technique allows the use of the animal as its own control, the present study demonstrated that the use of the microdialysis technique is of interest in studies on the circadian system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-079X.1999.tb00615.x
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  • 10
    Electronic Resource
    Electronic Resource
    Daily and light-at-night induced variations of circulating 5-methoxytryptophol (5-ML) in ewes with respectively high and low nocturnal melatonin secretion. (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of pineal research 27 (1999), S. 0 
    Details
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The aim of the present study was to determine whether the genetic differences previously reported in ewe plasma melatonin concentrations were correlated with differences in the synthesis and release of other 5-methoxyindoles. To determine if 5-methoxytryptophol (5-ML), which is known to be present in large amounts in the sheep pineal gland, is released, as is melatonin, into the general circulation, and if some temporal relationships between 5-ML and melatonin release could be observed, two groups of ewes were selected with respect to their endogenous melatonin secretion: in the first experiment, ten ewes from the low melatonin group (low group) and ten ewes from the high melatonin group (high group). 5-ML was measured every hour during a 24-hr period by radioimmunoassay. In all ewes, 5-ML was released during day-time, the rhythm of 5-ML concentrations being inversely related with the melatonin rhythm. Both day-time and night-time 5-ML concentrations were higher in the ewes from the high group than in the ewes from the low group (14.7 ± 1.0 pg/mL plasma versus 6.4 ± 0.3 pg/mL plasma during the day, 3.1 ± 0.2 pg/mL plasma versus 1.9 ± 0.2 pg/mL plasma during the night). The 5-ML/melatonin ratio appeared much higher during the day than during the night but was very similar in both groups (day-time: 1.03 in the high group versus 1.16 in the low group, night-time: 0.01 in both groups). In a second experiment, six low group and seven high group ewes were submitted to 1 hr of extra light at night. 5-ML increased and melatonin decreased during extra light. Our results clearly show for the first time a daily variation in circulating 5-ML. and that the strong genetic contribution in the variability in melatonin concentrations in sheep are clearly correlated with a similar variability in 5-ML concentrations. Whether 5-ML, like melatonin, plays a physiological role in the different adaptation processes to the environment remains to be determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-079X.1999.tb00620.x
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