Oral melatonin produces arrhythmia in sparrows

Natural melatonin fluctuation and its minimally invasive simulation in the zebra finch

Melatonin is a key hormone in the regulation of circadian rhythms of vertebrates, including songbirds. Understanding diurnal melatonin fluctuations and being able to reverse or simulate natural melatonin levels are critical to investigating the influence of melatonin on various behaviors such as singing in birds. Here we give a detailed overview of natural fluctuations in plasma melatonin concentration throughout the night in the zebra finch. As shown in previous studies, we confirm that “lights off” initiates melatonin production at night in a natural situation. Notably, we find that melatonin levels return to daytime levels as early as two hours prior to the end of the dark-phase in some individuals and 30 min before “lights on” in all animals, suggesting that the presence of light in the morning is not essential for cessation of melatonin production in zebra finches. Thus, the duration of melatonin production seems not to be specified by the length of night and might therefore be less likely to directly couple circadian and annual rhythms. Additionally, we show that natural melatonin levels can be successfully simulated through a combination of light-treatment (daytime levels during subjective night) and the application of melatonin containing skin-cream (nighttime levels during subjective day). Moreover, natural levels and their fluctuation in the transition from day to night can be imitated, enabling the decoupling of the effects of melatonin, for example on neuronal activity, from sleep and circadian rhythmicity. Taken together, our high-resolution profile of natural melatonin levels and manipulation techniques open up new possibilities to answer various melatonin related questions in songbirds.

Hypothalamic circadian organization in birds. II. Clock gene expression

While the site of the major circadian pacemaker in mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus, is very well characterized, little is known about hypothalamic circadian organization in birds. This paper reviews recent findings on clock gene expression in the hypothalamus of several bird species focusing on circadian pPer2 expression in the house sparrow. In contrast to mammals, rhythmic Per2 gene expression in the house sparrow hypothalamus is not restricted to a single cell group but occurs in two distinct hypothalamic nuclei, the SCN and the lateral hypothalamic nucleus (LHN). The complex temporal and spatial distribution of pPer2 expression suggests a longitudinal compartmentalization of the SCN with period gene expression being initiated in the most rostral portion before lights on. In the lateral hypothalamus, phasing of pPer2-rhythmicity appeared delayed. In pinealectomized house sparrows, the overall circadian pPer2 expression pattern is maintained indicating that rhythmic pPer2 transcription in the SCN and LHN of the house sparrow are not driven by the pineal gland. Rather, they reflect the activity of autonomous hypothalamic circadian oscillators. Certain changes in peak expression levels and the expression phase, however, suggest that the pineal melatonin rhythm affects both the phase and the amplitude of rhythmic hypothalamic pPer2 expression.

Circadian organization and the role of the pineal in birds

All organisms exhibit significant daily rhythms in a myriad of functions from molecular levels to the level of the whole organism. Significantly, most of these rhythms will persist under constant conditions, showing that they are driven by an internal circadian clock. In birds the circadian system is composed of several interacting sites, each of which may contain a circadian clock. These sites include the pineal organ, the suprachiasmatic nucleus (SCN) of the hypothalamus, and, in some species, the eyes. Light is the most powerful entraining stimulus for circadian rhythms and, in birds, light can affect the system via three different pathways: the eyes, the pineal, and extraretinal photoreceptors located in the deep brain. Circadian pacemakers in the pineal and in the eyes of some avian species communicate with the hypothalamic pacemakers via the rhythmic synthesis and release of the hormone melatonin. Often the hypothalamic pacemakers are unable to sustain persistent rhythmicity in constant conditions in the absence of periodic melatonin input from the pineal (or eyes). It has also been proposed that pineal pacemakers may be unable to sustain rhythmicity in constant conditions without periodic neural input from the SCN. Significant variation can occur among birds in the relative roles that the pineal, the SCN, and the eyes play within the circadian system; for example, in the house sparrow pacemakers in the pineal play the predominant role, in the pigeon circadian pacemakers in both the pineal and eyes play a significant role, and in Japanese quail ocular pacemakers play the predominant role.

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

At 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.

Circadian control of migratory restlessness and the effects of exogenous melatonin in the brambling, Fringilla montifringilla

Circadian pacemakers control both "daytime" activity and nocturnal restlessness of migratory birds, and the daily rhythm of melatonin release from the pineal has been suggested to be involved in the control of migratory activity. To study the phase relations between the two activity components during entrainment and when free running, locomotor activity of bramblings (Fringilla montifringilla) was recorded continuously under a 12:12 "cool light" to "warm light" cycle (CL:WL, ca. 5,000 K and ca. 2,500 K, respectively) or blue light to red light cycle (BL:RL. maxima at 440 and 650 nm, respectively) at different irradiance ratios. Migratory activity was expressed primarily during the WL or RL phase of the light cycles. Under free-running conditions, the circadian periods tau correlated with the phase relations between day and night (migratory) activity components during preceding entrainment. Bramblings with migratory activity had significantly longer tau at constant light intensity than the same individuals without migratory activity. Birds with migratory activity reentrained faster after a 6h phase shift of the CL:WL cycle than birds without migratory activity. When exogenous melatonin was given in the drinking water (200 microg/mL 1% ethanol or 0.86 mM) to bramblings exposed to 12:12 CL:WL cycles with constant irradiance, the amounts of activity, which were initially higher during the WL phase of the light cycle, were suppressed to similar low levels during both light phases. The systematic changes in the amounts of activity during melatonin treatment were not correlated with consistent changes in entrainment status. The data support the hypothesis that changes in the amplitude and level of the daily melatonin cycle are involved in regulating migratory restlessness, by either allowing or inhibiting nocturnal activity.

The Cartesian clock metaphor for pineal gland operation pervades the origin of modern chronobiology

In theoretical descriptions formulated during the 1600s, R. Descartes attributed a clock-like role to the pineal gland. He established the belief that pineal function underlies the laws of the universe that determine the cyclic sleep-awake states in man. Recent reports about pineal circadian pacemakers now validate the brilliant accuracy of Cartesian thought, in relation to the relevant role of the pineal gland.

Melatonin supplementation does not prevent photostimulatory effects of night interruption lighting in Japanese quail

Male Japanese quail (Coturnix japonica) exposed to night interruption lighting were given melatonin either as single daily injections (10-100 mg/kg), or as continuous release implants. Birds were exposed to a base photoperiod of 8 hr of light, plus a 15 min night interruption pulse of light 14 hr after the beginning of the base photoperiod. Daily injections of melatonin were given 20 min prior to the night interruption pulse. Control birds either received no exogenous melatonin or received injections during the last 2 min of the night interruption pulse. Exogenous melatonin was able to induce sleep-like behavior at higher doses but did not prevent gonadal recrudescence as measured by the cloacal protrusion area. The role of melatonin in avian reproduction appears to be different from that in mammals. Perhaps melatonin's role in birds is to regulate circadian activities, not circannual ones such as the onset of reproduction.

Effects of exogenous melatonin on some endocrine, behavioural and metabolic parameters in Japanese quail Coturnix coturnix japonica

1. Melatonin administration in drinking water (5 micrograms/ml) to Japanese quail resulted in a 20-fold increase of plasma melatonin levels in comparison with the control, day time concentration (0.34 +/- 0.05 vs 6.88 +/- 1.10 nmol/l). 2. Plasma triiodothyronine levels increased (5.8 +/- 0.93 vs 7.97 +/- 0.64 nmol/l), corticosterone decreased (28.04 +/- 3.42 vs 15.96 +/- 2.56 nmol/l) and no significant changes were recorded in thyroxine concentration after the treatment. 3. A higher occurrence of sleeping and lower occurrence of pecking were found in melatonin treated quail. 4. Abdominal fat deposition as well as the content of total lipids in the breast muscle and triacylglycerols in plasma were decreased in treated birds indicating an inhibitory effect of melatonin on lipogenesis. 5. Melatonin increased RNA content in the breast muscle but did not affect plasma glucose concentration and body weight.

Effect of dose and time of melatonin injections on the diurnal rhythm of immunity in chicken

The effect of daily melatonin injections on the diurnal rhythm of immune parameters was examined in White Leghorn cockerels, kept from hatching in L:D 12:12 conditions. Subcutaneous injections of melatonin were made at the beginning of darkness or 4 h earlier for four weeks starting from one week of life. The melatonin dosage in one group was raised (10, 13, 16, and 20 ng per bird daily, respectively) during four consecutive weeks. The two other doses were 10 and 500 times higher and were increased every week as well. Control birds received equivalent injections of vehicle. Three-week-old chickens were immunized ip with sheep red blood cells and reimmunized one week later. Five-week-old birds were sacrificed during a 24 h period every 4 h. The existence of the diurnal rhythm was evaluated by cosinor analysis. The diurnal rhythm of total white blood cells and serum agglutinins was more dependent on the time of melatonin injections than on the hormone used. The effect of melatonin injections on the level of immune parameters examined was also dependent on the time of sample collection. Results obtained indicate the participation of pineal gland in the regulation of the diurnal rhythm of the examined indices of avian immune system function that exhibit diurnal changes in sensitivity to exogenous melatonin.

Circadian rhythm in pineal N-acetyltransferase activity: rapid phase reversal and response to shorter than 24-hour cycles (IV)

N-Acetyltransferase (NAT) is an enzyme whose rhythmic activity in the pineal gland and retina is responsible for circadian rhythms in melatonin. The NAT activity rhythm has circadian properties such as persistence in constant conditions and precise control by light and dark. Experiments are reported in which chicks (Gallus domesticus), raised for 3 weeks in 12 h of light alternating with 12 h of dark (LD12:12), were exposed to 1-3 days of light-dark treatments during which NAT activity was measured in their pineal glands. (a) In LD12:12, NAT activity rose from less than 4.5 nmol/pineal gland/h during the light-time to 25-50 nmol/pineal gland/h in the dark-time. Constant light (LL) attenuated the amplitude of the NAT activity rhythm to 26-45% of the NAT activity cycle in LD12:12 during the first 24 h. (b) The timing of the increase in NAT activity was reset by the first full LD12:12 cycle following a 12-h phase shift of the LD12:12 cycle (a procedure that reversed the times of light and dark by imposition of either 24 h of light or dark). This result satisfies one of the criteria for NAT to be considered part of a circadian driving oscillator. (c) In less than 24-h cycles [2 h of light in alternation with 2 h of dark (LD2:2), 4 h of light in alternation with 4 h of dark (LD4:4), and 6 h of light in alternation with 6 h of dark (LD6:6)], NAT activity rose in the dark during the chicks' previously scheduled dark-time but not the previously scheduled light-time of LD12:12. In a cycle where 8 h of light alternated with 8 h of dark (LD8:8), NAT activity rose in both 8-h dark periods, even though the second one fell in the light-time of the prior LD12:12 schedule.(ABSTRACT TRUNCATED AT 250 WORDS)