Cyclic melatonin synchronises the circadian rhythm of feeding activity in Japanese quail, Coturnix c. japonica

WOS:000175378300004International audienceIn Japanese quail, we can observe the circadian rhythm of feeding activity in constant conditions, especially in birds from selected lines. In order to try to test the importance of melatonin as hormonal output for the circadian system, we gave a 24-h period cycle of exogenous melatonin to some of these birds when they were free running. We used castrated males firstly in order to cancel the known effect of steroids on circadian organisation. Secondly, as castrated birds generally expressed a very short periodicity, it allowed us to check induced synchronisation more easily. We maintained ten castrated males in constant dim light. We divided the experiment into five successive phases. The birds received a 24-h period cycle of melatonin (M phase) or of control solution with only the alcoholic solvent (C phase) as a drink. Before and after each one of these two phases, we gave water continually to drink (W1, W2 and W3 phases).Thus, the successive phases were W1–M–W2–C–W3. We measured intake of liquids and plasma melatonin concentrations to check melatonin ingestion. We automatically recorded individual feeding activity by infrared detectors, and analysed this by spectral analysis. At the beginning of the experiment, eight birds showed a rhythmic feeding activity, with a mean period of 22.9 ± 0.2 h, and the two others an arrhythmic circadian activity. During the 24-h period cycle of exogenous melatonin, for the rhythmic birds, the circadian period became approximately 24 h (23.9 ± 0.2 h), the inactive phase corresponding to the period of melatonin availability. During the W2 and C phases, the circadian period was similar to that expressed during the W1 phase. Moreover, when birds only drink water, we found a significant positive relationship between the clarity of the circadian rhythm and the ratio, between the melatonin level of the inactive phase and that of the active phase. These facts support the hypothesis of the role of this hormone in the regulation of the circadian system, at least for feeding activity, in quail.Chez la caille japonaise, le rôle de la mélatonine sur la rythmicité circadienne est encore controversé. Dans la présente étude, nous nous proposons de tester son importance sur le contrôle de l’organisation temporelle du comportement alimentaire en administrant de manière cyclique de la mélatonine exogène à des cailles en libre cours. Les oiseaux testés proviennent d’une lignée sélectionnée pour une rythmicité marquée. Comme les stéroïdes sexuels ont des effets connus sur l’organisation circadienne, l’expérience sera réalisée avec des mâles castrés. Ceux-ci, de plus, expriment une période en libre cours relativement courte, nous permettant de visualiser plus efficacement une possible synchronisation sur un rythme de 24 h. Pour cela, dix mâles castrés ont été maintenus en lumière tamisée constante. L’expérimentation est alors divisée en cinq phases successives. Les oiseaux ont reçu comme boisson une solution de mélatonine (phase M) ou une solution contrôle avec seulement le solvant (phase C), suivant une période de 24 h. Avant et après chacune de ces deux phases, les oiseaux disposaient d’eau en continu (respectivement phases W1, W2 et W3). La succession des phases est donc : W1–M–W2–C–W3. Pour vérifier l’ingestion de mélatonine, nous avons mesuré la consommation de boisson et la concentration de mélatonine plasmatique. L’activité alimentaire individuelle était enregistrée automatiquement à l’aide de détecteurs à infrarouge et analysée par analyse de spectre. Au début de l’expérience, huit cailles ont présenté une activité alimentaire rythmée, avec une période circadienne de 22,9 ± 0,2 h, les deux autres oiseaux étant arythmiques au niveau circadien. Au cours de la phase où la mélatonine était donnée toutes les 24 h, pour les oiseaux rythmés, la période circadienne s’est allongée jusqu’à 24 h (23,9 ± 0,2 h). La phase inactive des oiseaux correspondait à la période de disponibilité en mélatonine. Pendant les phases W2, C et W3, les périodes circadiennes n’étaient pas différentes de celle exprimée pendant la phase W1. De plus, lorsque les oiseaux sont abreuvés avec de l’eau, nous avons trouvé une relation positive significative entre la clarté du rythme circadien et le rapport entre les niveaux plasmatiques de mélatonine pendant la phase inactive et la phase active. Tous ces éléments semblent étayer l’hypothèse du rôle de cette hormone dans la régulation du rythme circadien d’activité alimentaire chez la caille

Effect of melatonin supplementation on the sexual development in European quail (Coturnix coturnix)

WOS:000167686700014International audienceAt the end of their wintering phase, male European quails were exposed to a stimulation photoperiod of light/dark 12:12 h for 10 days to induce sexual development. A daily oral melatonin supplementation was then given to one group Of treated males (N=11) and the alcohol solvent was given to a control group of males (N= 10). These solutions were provided during the final 3 h of the photophase for 28 days, then during the final 4 h for 18 days. There were no significant differences between the two groups with respect to fat levels. However, 3 weeks after the beginning of melatonin supplementation, the sexual development of the treated birds slowed down. The importance of this decline varied to a greater or lesser degree between individual birds. When melatonin supplementation stopped, sexual development resumed. Activity recordings revealed a decrease in feeding activity when melatonin supplementation was provided. However, this response showed important interindividual variability. The birds that produced the most marked responses to melatonin during the first 3 weeks of supplementation were those that also showed the most obvious decline in sexual development. It seems that, in European quail, a wild migratory species that always shows a natural biological annual rhythm, a melatonin signal could play a role in regulating reproduction. (C) 2001 Elsevier Science B.V. All rights reserved

Tamoxifen Stimulates Melatonin Secretion After Exposure to a Mammary Carcinogen, the Dimethyl Benz(a)Anthracene, in Sprague Dawley Female Rat

International audienceA single intragastric administration of 7,12-dimethylbenz(a)anthracene (DMBA) has been shown to induce mammary tumors in young cycling female Sprague-Dawley rats. The appearance of the tumors is preceded, during the la-tency phase, by a series of neuroendocrine disturbances, including attenuation of the preovulatory Luteinizing Hormone surge and Gonadotropin-Releasing Hormone release and amplification of the preovulatory 17-Estradiol (E2) surge. Also, E2 treatment leads to a complete blunting of the Isoproterenol-induced stimulation of Melatonin secretion.In this study, we examined the hypothesis that Tamoxifen, an antagonist of E2, would stimulate the Isoproterenol-induced Mela-tonin (MT) secretion from the pineal gland, during the latency phase. Sprague-Dawley rats, 55-60 days of age, received, on the Estrous day of the Estrous cycle, a single dose of 15 mg DMBA delivered by intragastric intubation. In order to avoid possible interactions with endogenous steroids or mammary tumor-derived compounds, they were ovariectomized 5 days later and, one month later, sacrificed by decapitation at 10 a.m. Then, pineal glands were removed and placed in perifusion chambers containing Hanks 199 medium. The medium was satured with O 2 /CO 2 (95 %/5 %) and its pH was 7.4. Ten independent chambers were immersed in a water bath at 37°C. Each pineal gland received medium (flow rate : 0.16 ml/min) through a system of input lines. The fractions were collected every 10 min, and immediately frozen at –20°C until Melatonin RIA. Experiments were repeated to obtain up to five experimental points for each treatment. Tamoxifen (10-9 to 10-7 M) was applied during the entire perifusion period (7 hours). Isoproterenol (10-6 M) was applied for 20 min after 3 hours in perifusion. Melatonin concentrations and Areas Under the Curves were compared using two-factor ANOVA as well as parametric or nonparametric two-sample methods after testing sample normality. In vehicle treated rats, Tamoxifen treatment, at the concentration of 10-9 M, leads to a non significant amplification of the Isoproterenol-induced stimulation of Melatonin secretion. In DMBA-treated rats, Tamoxifen treatment leads,starting from 10-9 M to a dose-dependent increase (up to 400% increase) of the Isoproterenol-induced stimulation of Melatonin. The results suggest that in addition to the well documented beneficial effects of Tamoxifen at the mammary gland level, this E2 antagonist may also have, after DMBA treatment, an additional beneficial effect at the pineal gland level throughout the stimulation of Melatonin, which exerts an inhibitory action on the induction and on the growth of breast cancers

Environmental control and adrenergic regulation of pineal activity in the diurnal tropical rodent, Arvicanthis ansorgei.

Like nocturnal rodents, the diurnal tropical rodent Arvicanthis ansorgei shows a daily rhythm in pineal melatonin content. Seasonal and photoperiodic variations in the biosynthetic activity of the pineal gland: arylalkylamine-N-acetyltransferase (AA-NAT), hydroxyindole-O-methyltransferase (HIOMT) activities and melatonin content were measured in male and female A. ansorgei captured near Samaya, Mali, and kept either under artificial laboratory photoperiods [light-dark (LD) cycles: LD 14:10, LD 12:12 or LD 10:14 or caught in the field in Mali and killed at four different times of the year (January, April, June and November). Under artificial photoperiod, the duration of the nocturnal peak of AA-NAT activity and melatonin content increased with the duration of the dark period while the amplitude did not significantly change. In the field, annual variations in the amplitude of the nocturnal melatonin peak were observed with a maximum in April (highest temperature, low humidity and no grass availability, only seeds) and a minimum in November (high humidity, maximum green grass availability). The variations in the amplitude of the melatonin peak were not correlated with changes in AA-NAT HIOMT activities, suggesting that seasonal variations in the amplitude of the melatonin peak are not driven by these enzymes. Daytime injections of the beta-adrenergic agonist, isoproterenol, stimulated melatonin synthesis in January, April and June, but not in November. The annual differences in the amplitude of the melatonin peak as well as the seasonal differences in the response to an adrenergic stimulation suggest that environmental factors other than photoperiod, such as temperature, humidity and consequent food availability, could be important in the regulation of the annual variations in the pineal biosynthetic activity in this species

An (n-3) polyunsaturated fatty acid-deficient diet disturbs daily locomotor activity, melatonin rhythm, and striatal dopamine in Syrian hamsters

International audienceSeveral studies suggest that (n-3) PUFA may play a role in the regulation of cognitive functions, locomotor and exploratory activity, and affective disorders. Additionally, (n-3) PUFA affect pineal function, which is implicated in the sleep-wake rhythm. However, no studies to our knowledge have explored the role of PUFA on the circadian system. We investigated the effect of an (n-3) PUFA-deficient diet on locomotor and pineal melatonin rhythms in Syrian hamsters used as model species in circadian rhythm research. To assess the possible relationship between voluntary wheel running activity and dopaminergic neurotransmission, we also measured endogenous monoamine concentrations in the striatum. Two-month-old male hamsters, fed either an (n-3) PUFA-deficient or an (n-3) PUFA-adequate diet, were housed individually in cages equipped with run wheels. At 3 mo, cerebral structures were extracted for biochemical and cellular analysis. In (n-3) PUFA-deficient hamsters, the induced changes in the pineal PUFA membrane phospholipid composition were associated with a reduction in the nocturnal peak level of melatonin that was 52% lower than in control hamsters (P < 0.001). The (n-3) PUFA-deficient hamsters also had higher diurnal (P < 0.01) and nocturnal (P = 0.001) locomotor activity than the control hamsters, in parallel with activation of striatal dopaminergic function (P < 0.05). The (n-3) PUFA-deficient hamsters exhibited several symptoms: chronic locomotor hyperactivity, disturbance in melatonin rhythm, and striatal hyperdopaminergia. We suggest that an (n-3) PUFA-deficient diet lessens the melatonin rhythm, weakens endogenous functioning of the circadian clock, and plays a role in nocturnal sleep disturbances as described in attention deficit/hyperactivity disorder