Pinealectomy abolishes the circadian rhythm of migratory restlessness

Circadian gene variation in relation to breeding season and latitude in allochronic populations of two pelagic seabird species complexes

Annual cues in the environment result in physiological changes that allow organisms to time reproduction during periods of optimal resource availability. Understanding how circadian rhythm genes sense these environmental cues and stimulate the appropriate physiological changes in response is important for determining the adaptability of species, especially in the advent of changing climate. A first step involves characterizing the environmental correlates of natural variation in these genes. Band-rumped and Leach's storm-petrels (Hydrobates spp.) are pelagic seabirds that breed across a wide range of latitudes. Importantly, some populations have undergone allochronic divergence, in which sympatric populations use the same breeding sites at different times of year. We investigated the relationship between variation in key functional regions of four genes that play an integral role in the cellular clock mechanism-Clock, Bmal1, Cry2 and Per2-with both breeding season and absolute latitude in these two species complexes. We discovered that allele frequencies in two genes, Clock and Bmal1, differed between seasonal populations in one archipelago, and also correlated with absolute latitude of breeding colonies. These results indicate that variation in these circadian rhythm genes may be involved in allochronic speciation, as well as adaptation to photoperiod at breeding locations.

Genetic Control of Avian Migration: Insights from Studies in Latitudinal Passerine Migrants

Twice-a-year, large-scale movement of billions of birds across latitudinal gradients is one of the most fascinating behavioral phenomena seen among animals. These seasonal voyages in autumn southwards and in spring northwards occur within a discrete time window and, as part of an overall annual itinerary, involve close interaction of the endogenous rhythm at several levels with prevailing photoperiod and temperature. The overall success of seasonal migrations thus depends on their close coupling with the other annual sub-cycles, namely those of the breeding, post-breeding recovery, molt and non-migratory periods. There are striking alterations in the daily behavior and physiology with the onset and end of the migratory period, as shown by the phase inversions in behavioral (a diurnal passerine bird becomes nocturnal and flies at night) and neural activities. Interestingly, there are also differences in the behavior, physiology and regulatory strategies between autumn and spring (vernal) migrations. Concurrent molecular changes occur in regulatory (brain) and metabolic (liver, flight muscle) tissues, as shown in the expression of genes particularly associated with 24 h timekeeping, fat accumulation and the overall metabolism. Here, we present insights into the genetic basis of migratory behavior based on studies using both candidate and global gene expression approaches in passerine migrants, with special reference to Palearctic-Indian migratory blackheaded and redheaded buntings.

Control and adaptability of seasonal changes in behavior and physiology of latitudinal avian migrants: Insights from laboratory studies in Palearctic-Indian migratory buntings

Twice-a-year migrations, one in autumn and the other in spring, occur within a discrete time window with striking alterations in the behavior and physiology, as regulated by the interaction of endogenous rhythms with prevailing photoperiod. These seasonal voyages are not isolated events; rather, they are part of an overall annual itinerary and remain closely coupled to the other annual subcycles, called seasonal life history states (LHSs). The success of migration depends on appropriate timing of the initiation and termination of each LHS, for example, reproduction, molt, summer nonmigratory, preautumn migratory (fattening and weight gain), autumn migratory, winter nonmigratory (wnM), prevernal (spring) migratory (fattening and weight gain), and spring migratory LHSs. Migration-linked photoperiod-induced changes include the body fattening and weight gain, nocturnal Zugunruhe (migratory restlessness), elevated triglycerides and free fatty acids, triiodothyronine and corticosterone levels. Hypothalamic expression of the thyroid hormone-responsive dio2 and dio3, light-responsive per2, cry1, and adcyap1 and th (tyrosine hydroxylase, involved in dopamine biosynthesis) genes also show significant changes with transition from wnM to the vernal migratory LHS. Concurrent changes in the expression of genes associated with lipid metabolism and its transport also occur in the liver and flight muscles, respectively. Interestingly, there are clear differences in the behavioral and physiological phenotypes, and associated molecular changes, between the autumn and vernal migrations. In this review, we discuss seasonal changes in the behavior and physiology, and present molecular insights into the development of migratory phenotypes in latitudinal avian migrants, with special reference to Palearctic-Indian migratory buntings.

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.

Avian photoreceptors and their role in the regulation of daily and seasonal physiology

Birds time their activities in synchronization with daily and seasonal periodicities in the environment, which is mainly provided by changes in day length (=photoperiod). Photoperiod appears to act at different levels than simply entraining the hypothalamic clock via eyes in birds. Photoreceptor cells that transmit light information to an avian brain are localized in three independent structures, the retina of eyes, pineal gland and hypothalamus, particularly in the paraventricular organ and lateral septal area. These hypothalamic photoreceptors are commonly referred to as encephalic or deep brain photoreceptors, DBPs. Eyes and pineal are known to contribute to the circadian regulation of behavior and physiology via rhythmic melatonin secretion in several birds. DBPs have been implicated in the regulation of seasonal physiology, particularly in photoperiod induced gonadal growth and development. Here, we briefly review limited evidence that is available on the roles of these photoreceptors in the regulation of circadian and seasonal physiology, with particular emphasis placed on the DBPs.

A simple, specific high-throughput enzyme-linked immunosorbent assay (ELISA) for quantitative determination of melatonin in cell culture medium

A simple, specific, high-throughput enzyme-linked immunosorbent assay (ELISA) for quantitative determination of melatonin was developed for directly measuring melatonin in cell culture medium with 10% FBS. This assay adopts a commercial monoclonal melatonin antibody and melatonin-HRP conjugate, so it can be applied in multiple labs rapidly with low cost compared with commercial RIA and ELISA kits. In addition, the procedure is much simpler with only four steps: 1) sample/conjugate incubation, 2) plate washing, 3) TMB color reaction and 4) reading of results. The standards of the assay cover a wide working range from 100 pg/mL to 10 ng/mL. The sensitivity was 68 pg/mL in cell culture medium with 10% FBS and 26 pg/mL in PBS with as little as 25 μL sample volume. The recovery of melatonin from cell culture medium was 101.0%. The principal cross-reacting compound was 5-methoxytryptophol (0.1%). The variation coefficients of the assay, within and between runs, ranged between 6.68% and 15.76% in cell culture medium. The mean linearity of a series diluted cell culture medium sample was 105% (CV=5%), ranging between 98% and 111%, y=5.5263x+0.0646, R(2)=0.99. The assay enables small research and teaching labs to reliably measure this important neurohormone.

Nocturnal melatonin levels decode daily light environment and reflect seasonal states in night-migratory blackheaded bunting (Emberiza melanocephala)

We proposed two perhaps overlapping hypotheses.

Avian circadian organization: a chorus of clocks

In birds, biological clock function pervades all aspects of biology, controlling daily changes in sleep: wake, visual function, song, migratory patterns and orientation, as well as seasonal patterns of reproduction, song and migration. The molecular bases for circadian clocks are highly conserved, and it is likely the avian molecular mechanisms are similar to those expressed in mammals, including humans. The central pacemakers in the avian pineal gland, retinae and SCN dynamically interact to maintain stable phase relationships and then influence downstream rhythms through entrainment of peripheral oscillators in the brain controlling behavior and peripheral tissues. Birds represent an excellent model for the role played by biological clocks in human neurobiology; unlike most rodent models, they are diurnal, they exhibit cognitively complex social interactions, and their circadian clocks are more sensitive to the hormone melatonin than are those of nocturnal rodents.

Contributions of endocrinology to the migration life history of birds

Migration is a key life cycle stage in nearly 2000 species of birds and is a greatly appreciated phenomenon in both cultural and academic arenas. Despite a long research tradition concerning many aspects of migration, investigations of hormonal contributions to migratory physiology and behavior are more limited and represent a comparatively young research field. We review advances in our understanding of the hormonal mechanisms of migration with particular emphasis on the sub-stages of the migration life history: development, departure, flight and arrival. These sub-stages vary widely in their behavioral, ecological and physiological contexts and, as such, should be given appropriate individual consideration.

Differential regulation of adipokines may influence migratory behavior in the white-throated sparrow (Zonotrichia albicollis)

White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat stores to fuel migration. Adipose tissue produces hormones and signaling factors in a rhythmic fashion and may be controlled by a clock in adipose tissue or driven by a master clock in the brain. The master clock may convey photoperiodic information from the environment to adipose tissue to facilitate pre-migratory fattening, and adipose tissue may, in turn, release adipokines to indicate the extent of fat energy stores. Here, we present evidence that a change in signal from the adipokines adiponectin and visfatin may act to indicate body condition, thereby influencing an individual's decision to commence migratory flight, or to delay until adequate fat stores are acquired. We quantified plasma adiponectin and visfatin levels across the day in captive birds held under constant photoperiod. The circadian profiles of plasma adiponectin in non-migrating birds were approximately inverse the profiles from migrating birds. Adiponectin levels were positively correlated to body fat, and body fat was inversely related to the appearance of nocturnal migratory restlessness. Visfatin levels were constant across the day and did not correlate with fat deposits; however, a reduction in plasma visfatin concentration occurred during the migratory period. The data suggest that a significant change in the biological control of adipokine expression exists between the two migratory conditions and we propose a role for adiponectin, visfatin and adipose clocks in the regulation of migratory behaviors.

Circadian Regulation of Bird Song, Call, and Locomotor Behavior by Pineal Melatonin in the Zebra Finch

As both a photoreceptor and pacemaker in the avian circadian clock system, the pineal gland is crucial for maintaining and synchronizing overt circadian rhythms in processes such as locomotor activity and body temperature through its circadian secretion of the pineal hormone melatonin. In addition to receptor presence in circadian and visual system structures, high-affinity melatonin binding and receptor mRNA are present in the song control system of male oscine passeriform birds. The present study explores the role of pineal melatonin in circadian organization of singing and calling behavior in comparison to locomotor activity under different lighting conditions. Similar to locomotor activity, both singing and calling behavior were regulated on a circadian basis by the central clock system through pineal melatonin, since these behaviors free-ran with a circadian period and since pinealectomy abolished them in constant environmental conditions. Further, rhythmic melatonin administration restored their rhythmicity. However, the rates by which these behaviors became arrhythmic and the rates of their entrainment to rhythmic melatonin administration differed among locomotor activity, singing and calling under constant dim light and constant bright light. Overall, the study demonstrates a role for pineal melatonin in regulating circadian oscillations of avian vocalizations in addition to locomotor activity. It is suggested that these behaviors might be controlled by separable circadian clockworks and that pineal melatonin entrains them all through a circadian clock.

Functional similarity in relation to the external environment between circadian behavioral and melatonin rhythms in the subtropical Indian weaver bird

The present study investigated whether the circadian oscillators controlling rhythms in activity behavior and melatonin secretion shared similar functional relationship with the external environment. We simultaneously measured the effects of varying illuminations on rhythms of movement and melatonin levels in Indian weaver birds under synchronized (experiment 1) and freerunning (experiment 2) light conditions. In experiment 1, weaverbirds were exposed to 12h light: 12h darkness (12L:12D; L = 20 lx, D = 0.1 lx) for 2.5 weeks. Then, the illumination of the dark period was sequentially enhanced to 1-, 5-, 10-, 20- and 100 lx at the intervals of about 2 to 4 weeks. In experiment 2, weaver birds similarly exposed for 2.5 weeks to 12L:12D (L = 100 lx; D = 0.1 lx) were released in constant dim light (LL(dim), 0.1 lx) for 6 weeks. Thereafter, LL(dim) illumination was sequentially enhanced to 1-, 3- and 5 lx at the intervals of about 2 weeks. Whereas the activity of singly housed individuals was continuously recorded, the plasma melatonin levels were measured at two time of the day, once in each light condition. The circadian outputs in activity and melatonin were phase coupled with an inverse phase relationship: melatonin levels were low during the active phase (light period) and high during the inactive phase (dark period). This phase relationship continued in both the synchronized and freerunning states as long as circadian activity and melatonin oscillators subjectively interpreted synchronously the daily light environment, based on illumination intensity and/or photophase contrast, as the times of day and night. There were dissociations between the response of the activity rhythms and melatonin rhythms in light conditions when the contrast between day and night was much reduced (20:10 lx) or became equal. We suggest that circadian oscillators governing activity behavior and melatonin secretion in weaverbirds are phase coupled, but they seem to independently respond to environmental cues. This would probably explain the varying degree to which the involvement of pineal/melatonin in regulation of circadian behaviors has been found among different birds.

Biological clocks and regulation of seasonal reproduction and migration in birds

Timekeeping is important at two levels: to time changes in physiology and behavior within each day and within each year. For the former, birds have a system of at least three independent circadian clocks present in the retina of the eyes, the pineal gland, and the hypothalamus. This differs from the situation in mammals in which the input, pacemaker, and output are localized in different structures. Each bird clock interacts with at least one other clock, and together, they appear to form a centralized clock system that keeps daily time. These clocks have a powerful endogenous component, and the daily light-dark cycle entrains them to 24 h. The timing and duration of life history stages that make up annual cycle of an individual must also be controlled by some form of timekeeping. However, evidence for the existence of an equivalent endogenous circannual clock is less clear. Environmental cues, particularly photoperiod, appear to have a more direct role than simply entraining the clock to calendar time. For example, the timing of migration is probably greatly influenced by photoperiod, but its manifestation each day, as Zugunruhe, appears to be under circadian control. Migration involves marked changes in physiology to cope with the energetic demands. There is still much that we do not know about how organisms' timekeeping systems respond to their natural environment, particularly how salient signals from the environment are perceived and then transduced into appropriately timed biological functions. However, given that changes in environmental input affects the clock, increasing human disturbance of the environment is likely to adversely affect these systems.

Circadian and Masking Control of Migratory Restlessness in Gambel's White-Crowned Sparrow (Zonotrichia leucophrys gambelii)

Avian migration is a seasonal activity that requires intricate timing on both an annual and daily basis. With increasing evidence for endogenous regulation of daily activities in migrant species, we tested whether a circadian oscillator may be involved with the expressions of daily locomotor activities and specific behaviors of the long-distance migrant, Gambel's white-crowned sparrow ( Zonotrichia leucophrys gambelii). Our previous studies have identified both daytime and nighttime behavioral patterns under a photoperiod of 18L:6D. In 2 separate trials, birds in the vernal migratory life-history stage were exposed to constant dim light, (DD)dim, and constant bright light, LL, while locomotor activity and behavioral observations were collected. Under (DD)dim, the daytime behaviors that included active and quiescent components observed under 18L:6D were lost as migratory restlessness, the intense nighttime activity, persisted nonstop for 36.4 h. Furthermore, the specific behaviors of migratory restlessness that are normally confined to the dark phase of 18L:6D, beak-up and beak-up flight, were expressed also during the subjective day of (DD)dim. Birds exposed to LL retained similar patterns of activity to the 18L:6D condition for 3 days, after which they became arrhythmic. Behavioral observations of intense locomotor activity observed during the subjective night of LL revealed no beak-up and beak-up flight. Thus, the complete expression of migratory restlessness that includes beak-up and beak-up flight may not be regulated by a circadian oscillator but instigated by very low light intensity. Locomotor activity and associated daytime behaviors appear to be influenced by a circadian oscillator, given their persistent patterns under LL. Therefore, we suggest that the separate components of migratory behavior are regulated differentially by a circadian oscillator and ambient lighting conditions.

A separate circadian oscillator controls nocturnal migratory restlessness in the songbird Sylvia borin

When confined to a cage, migratory songbirds exhibit nocturnal migratory restlessness (also called Zugunruhe) during the spring and autumn migratory periods, even though these birds are exclusively diurnal during the remainder of the year. Zugunruhe, which has been demonstrated to be under the direct control of a circannual timer, is characterized by a stereotypic "wing-whirring" behavior while the bird is perched. To elucidate the role played by the circadian system in the regulation of Zugunruhe, the authors studied the activity of garden warblers (Sylvia borin), long-distance nocturnal migrants, under skeleton photoperiods of different lengths and under constant dim light. In 11.5D:1L:10.5D:1L skeleton photoperiods, the authors found that Zugunruhe free-ran in a substantial proportion of birds, while their normal daily activities (e.g., feeding and preening) remained synchronized to 24 h. Some birds expressing Zugunruhe under constant dim light continued to show 2 distinct bouts of activity: one corresponding to daily activities, the other to wing-whirring. In some cases, these 2 bouts crossed while free-running with different periods. Birds expressing Zugunruhe also had significantly longer free-running periods than birds that did not. The study data suggest that the seasonal appearance of Zugunruhe is the result of the interactions of at least 2 circadian oscillators and that it is the phase relationship of these 2 oscillators that determines when nocturnal migratory restlessness is expressed. Furthermore, these data are consistent with the previously proposed internal coincidence hypothesis as a model for the ontogeny of circannual rhythms.

Entrainment of circadian locomotor activity rhythm of the nocturnal field mouse Mus booduga using daily injections of melatonin

In this paper, we report the effects of daily injections of melatonin on the locomotor activity rhythm of the nocturnal field mouse Mus booduga. The locomotor activity rhythm of 45 animals was first monitored in constant darkness (DD) of the laboratory for about 15 days. The animals were then divided into three groups (experimental, vehicle-treated control, and the nontreated control groups) and subjected to three different treatments. The animals from the experimental group (n=19) were administered daily a single subcutaneous (s.c.) injection of melatonin (1 mg/kg) for about 45 days. The vehicle treated controls (n=13) were administered daily injections of 50% dimethyl sulfoxide (DMSO) for about 45 days, and the nontreated controls (n=13) were handled similar to the other two groups without being administered injections. Following the treatments, the animals were maintained in DD for about 20 days, after which the experiments were terminated. A significantly larger percentage of animals from the experimental group either entrained or showed phase control to daily treatments, compared to the animals from the two control groups. These results suggest that externally administered melatonin can influence the phase of the circadian locomotor activity rhythm of M. booduga. The fact that none of the nontreated controls showed any sign of phase control to daily handling, clearly demonstrates that the entrainment or phase control in the melatonin treated group of animals is caused by melatonin alone and not due to handling.

Hatching controlled by the circatidal clock, and the roleof the medulla terminalis in the optic peduncle of the eyestalk, in an estuarine crabSesarma haematocheir

Embryos attached to the female crab Sesarma haematocheir hatch synchronously within 1 h. Hatching is also synchronized near the time of the expected nocturnal high tide. These events are governed by a single circatidal clock (or pacemaker) in the female crab. The present study examined the role of the optic peduncle of the eyestalk on hatching and hatching synchrony. Surgery was performed either from the tip of the eyestalk [to remove the region of the optic peduncle from the compound eye—retina complex to the medulla interna (MI)] or from a small triangle `window' opened on the eyestalk exoskeleton [to create lesions on the medulla terminalis (MT) of the optic peduncle]. Neither hatching nor hatching synchrony was affected by removal of the region of the optic peduncle from the compound eye—retina complex to the MI: the circatidal rhythm also remained. Removal of the MI probably caused damage to the sinus gland and the bundle of axons running from the sinus gland to the X organ. Nevertheless, maintenance of highly synchronized hatching indicates that the X organ—sinus gland system is not related to hatching. Hatching and hatching synchrony were not affected by dorsal-half cuts of the MT: the timing of hatching was not affected either. By contrast,transverse and ventral-half cuts of the MT caused severe damage to most females; hatching of many females was suppressed, while hatching of some females was either periodic, at intervals of approximately 24 h, or arrhythmic for a few days. The bundle of neuronal axons is tangled in the MT, and the axons inducing hatching pass through the ventral half of the MT. Complete incision of these axon bundles may have suppressed hatching. Incomplete incision of the axon bundle or partial damage to the neurons may have caused periodic or arrhythmic patterns of hatching. There are two possible roles for MT in hatching. One possibility is that neurons in the MT only induce hatching under the control of the circatidal pacemaker located in a site somewhere other than the optic peduncle. Another possibility is that the circatidal pacemaker is actually present in the MT. The second possibility seems more plausible. Each embryo has a special 48-49.5 h developmental program for hatching. This program could be initiated by the circatidal pacemaker in the female, and hatching synchrony may also be enhanced by the same pacemaker.

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.

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.

Exogenous melatonin reduces the resynchronization time after phase shifts of a nonphotic zeitgeber in the house sparrow (Passer domesticus)

Continuous melatonin administration via silastic implants accelerates the resynchronization of the circadian locomotor activity rhythm in house sparrows (Passer domesticus) after exposure to phase shifts of a weak light-dark cycle. Constant melatonin might induce this effect either by increasing the sensitivity of the visual system to a light zeitgeber or by reducing the degree of self-sustainment of the circadian pacemaker. To distinguish between these two possible mechanisms, two groups of house sparrows, one carrying melatonin implants and the other empty implants, were kept in constant dim light and subjected to advance and delay shifts of a 12-h feeding phase. The resynchronization times of their circadian feeding rhythm following the phase shifts were significantly shorter when the birds carried melatonin implants than when they carried empty implants. In a second experiment, melatonin-implanted and control birds were released into food ad libitum conditions 2 days after either a delay or an advance phase shift. The number of hours by which the activity rhythms had been shifted on the second day in food ad libitum conditions was assessed. Melatonin-implanted house sparrows had significantly larger phase shifts in their circadian feeding rhythm than control birds. This is in accordance with the first experiment since a larger phase shift at a given time reflects accelerated resynchronization. Additionally, the second experiment also excludes any possible masking effects of the nonphotic zeitgeber. In conclusion, constant melatonin accelerates resynchronization even after phase shifts of a nonphotic zeitgeber, indicating that constant high levels of melatonin can reduce the degree of self-sustainment of the circadian pacemaker independent of any effects on the photoreceptive system.

Synchronization of circadian rhythms of house sparrows by oral melatonin: effects of changing period

House sparrows (Passer domesticus) whose circadian rhythms of locomotor activity and feeding had been abolished by pinealectomy were held in constant dim light and periodically exposed to melatonin in the drinking water. By alternating 8 h of melatonin water with variable phases of tap water, rhythms with periods (T) ranging from 21 to 27 h were produced. When melatonin was administered in rhythms with periods of 23, 24, and 25 h, feeding and locomotion behavior of most birds were rhythmic and synchronized with the exogenous melatonin rhythm. The rest phase coincided approximately with the phase of melatonin availability. Under melatonin cycles < 23 h and > 25 h, fewer birds had synchronized rhythms. Nonsynchronized birds were either arrhythmic or they expressed free-running rhythms. Under melatonin rhythms with periods between 23 and 26 h, the phase-angle difference between defined phases of the behavioral rhythms and the melatonin rhythm became more positive with increasing T. These data are consistent with the hypothesis (a) that periodic exogenous melatonin can substitute, at least to a certain degree, for the endogenous plasma melatonin rhythm normally resulting from the periodic melatonin secretion by the pineal gland, and (b) that this melatonin rhythm acts on another oscillator, possibly the SCN, as part of the overall circadian pacemaking system.

Comparison of circadian oscillation of melatonin release in pineal cells of house sparrow, pigeon and Japanese quail, using cell perfusion systems

We compared the circadian oscillation of melatonin release from cultured pineal cells in Japanese quail, pigeon and house sparrow, to determine whether the pineal gland of these species retains the circadian oscillator function in vitro. After dissociated pineal cells have been cultured for 4 days under 12 h: 12 h light-dark (LD) cycle, they were perfused at a flow rate of 0.25 ml/h for 6-7 days under LD or constant darkness (DD). Melatonin release increased during the dark period and low during the light period in all pineal cell cultures. Under DD conditions, the circadian rhythm of melatonin release persisted for up to 3-4 cycles in pigeon and house sparrow pineal cells, but the amplitude of the rhythm decreased gradually. However, in Japanese quail pineal cell culture the circadian oscillation of melatonin release was weak or abolished under DD conditions. These results strengthen the argument that the avian pineal gland's role in circadian organization differs between species. The direct demonstration of species-specific differences in the mechanism of the circadian oscillation of melatonin release from pineal cells should provide a useful model for the analysis of the pineal's circadian system at the cellular level.

Thyroidectomy does not affect the daily or free-running rhythms of plasma melatonin in European starlings

Thyroidectomy results in the suppression of reproductive photoperiodic responses in starlings. Could this be a consequence of an effect on perception of daylength or on circadian pacemakers? Daily changes in plasma melatonin concentrations were monitored in intact and thyroidectomized starlings held in long days (LD 16:8) and short days (LD 8:16), and in intact and thyroidectomized starlings allowed to free-run in constant darkness from long days or short days. In long days and short days, melatonin was low during the light period and high during darkness. There was no difference between intact and thyroidectomized birds. In free-running birds, the melatonin profile of the preceding long day or short day was retained during the first day of constant darkness, with peak levels occurring at the same time they did during the light-dark cycles. Again there was no difference between intact and thyroidectomized birds. These data demonstrate that either the photoreceptive and circadian mechanisms driving melatonin secretion are independent of those concerned with reproductive photoperiodic responses, or that thyroidectomy affects reproduction "downstream" from the photoreceptive-circadian apparatus.

The effect of pinealectomy on circadian plasma melatonin levels in house sparrows and European starlings

We determined 24-hr plasma melatonin profiles in intact, sham-pinealectomized, and pinealectomized European starlings (Sturnus vulgaris) and house sparrows (Passer domesticus) in a light-dark (LD) cycle and in constant darkness (DD). In the intact and sham-pinealectomized birds of both species, a melatonin rhythm was found, with low levels during the day and high levels during the night. Pinealectomy abolished the nighttime peak of melatonin in both species; hence, levels were low at all times sampled. This uniform response of plasma melatonin to pinealectomy contrasts with the differential response of circadian activity rhythms to pinealectomy for these two species. In DD, locomotor activity in pinealectomized house sparrows is usually arrhythmic, whereas in starlings a rhythm usually persists. This suggests that in the latter species free-running circadian rhythms are not necessarily dependent on a rhythm in plasma melatonin. The same is true for the synchronized activity rhythm observed in pinealectomized birds of both species in LD, as well as for the damped rhythm that persists in pinealectomized house sparrows following an LD-to-DD transfer. The results are consistent with the hypothesis that the pineal and its periodic output of melatonin constitute only one component in a system of at least two coupled pacemakers. They also suggest that there are species differences in the relative role played by the pineal and other pacemakers in controlling circadian rhythms in behavior.

Dissociation of photoreceptor cells from the pineal organ of the lamprey, Lampetra japonica

Photoreceptor cells, nerve cells and supporting cells were dissociated from the pineal organ of the river lamprey, Lampetra japonica, by the use of 10 U/ml papain solution at 28 degrees C for 20 min, followed by repeated trituration. With the aid of Nomarski interference-contrast optics, photoreceptor cells, nerve cells and supporting cells were readily identified. Electron-microscopic examination revealed that isolated photoreceptor cells display an outer segment endowed with a few lamellar disks and connected to the inner segment (ellipsoid) via a connecting cilium. The structural features of the dissociated photoreceptor and supporting cells strongly resemble the morphology of the respective cellular elements in situ. We succeeded in culturing dissociated cells for time periods up to 48 h when the procedure described in detail was applied.

The timer

This article reviews the evidence that living systems at all levels, including cells, organs, organisms, groups, organizations, communities, societies, and supranational systems, have an information-processing system, the timer. The timer consists of one or more oscillators known as clocks or pacemakers, the phase of which can be reset. They measure duration or order in time or underlie rhythms of various sorts. The timer subsystem synchronizes internal processes of the system and coordinates the system with its environment. By 1965, 19 matter-energy and information processing subsystems were identified in living systems theory. Based on scientific evidence accumulated particularly in recent years, the timer is now recognized as an information processing subsystem, the 20th subsystem, which carries out an essential life process.

Differential effects of pinealectomy on circadian rhythms of feeding and perch hopping in the European starling

To study the effects of pinealectomy on the circadian rhythms of locomotor activity and feeding. European starlings (Sturnus vulgaris) were held in constant light (0.2 lux and 200 lux) and under constant temperature conditions. Locomotor activity was measured by means of perches with microswitches mounted underneath, and feeding with an infrared photocell system at the feeder. Pinealectomy consistently led to disturbances in perch-hopping rhythms and often to a complete loss of rhythmicity as revealed by periodogram analysis. In some birds, perch-hopping rhythms recovered following a period of initial arrhythmicity. When a perch-hopping rhythm was present, its period was usually shorter than it had been before pinealectomy. In contrast to its effects on perch hopping, pinealectomy had no effect on the persistence of feeding rhythmicity, although its period, like that of the hopping rhythm, decreased after this operation. These results support the hypothesis derived from previous studies that the circadian organization of feeding is different from that of perch hopping. Different circadian pacemakers may be involved, but other models may possibly explain the data just as well.

Is the avian circadian system a neuroendocrine loop?

Avian circadian organization is a result of a complex interaction of photoreceptive and oscillatory components. The known components include the pineal gland, the lateral eyes, the suprachiasmatic nuclei (SCN), and extraocular brain photoreceptors. The pathways by which these components integrate circadian rhythmicity suggest a neuroendocrine loop in which the SCN inhibits pineal and ocular oscillators during the course of subjective day via a multisynaptic neuronal pathway which includes the superior cervical ganglia (SCG). During the night, the pineal in turn inhibits SCN activity via its secretion of the hormone melatonin into the blood circulation. This neuroendocrine loop, it is proposed, synchronizes multiple oscillators within each component and maintains the stability and precision of the system.

Circadian organization in Japanese quail

Our recent studies have implicated both the eyes and pineal as major components of the circadian system of Japanese quail. We assessed the role of these organs by examining the effect of their removal on the circadian activity rhythm of quail exposed to either 24 hr light-dark (LD) cycles or to continuous darkness (DD). Removal of only the pineal had no effect on the activity rhythm of quail in either LD or DD. Blinding (by orbital enucleation) had a major effect under both LD and DD. One third of the blinded birds showed entrainment under LD although entrainment patterns were very variable, whereas two thirds of blinded birds were arrhythmic. All blinded plus pinealectomized birds were arrhythmic in LD as were all blinded and blinded plus pinealectomized birds in DD. Accordingly, effects of pinealectomy can be seen only when pinealectomy is combined with blinding. The fact that blinding disrupts circadian organization in both LD and DD indicates that the eyes must act as major components of the quail's circadian system. In view of the postulated role for melatonin, an indoleamine, in circadian systems, the eyes, pineal, and blood of quail were assayed for this compound. Robust daily rhythms in melatonin content were observed in all three tissues. The blood rhythm is due to secretion of melatonin into the vascular system by both the pineal and eyes. The ocular melatonin rhythm continued after sectioning of the optic nerve, was reentrainable to a shift in the phase of the LD cycle, and persisted for at least 2 days in DD. These data suggest that the eyes play a major role within the circadian system and support the hypothesis that circadian pacemakers may reside within the eyes of quail. The results are discussed in view of the findings of others in both quail and other avian species. A general model for circadian organization in birds is presented in which the eyes, the pineal, and the suprachiasmatic nuclei of the hypothalamus comprise major elements of a multioscillator circadian system.

Sympathetic regulation of chicken pineal rhythms

Adult hens were chronically cannulated and held in light-dark (LD) 12:12 h lighting regimes or in constant darknesS (DD). Periodic blood sampling for 5-9 days revealed circadian rhythms in plasma melatonin titres. Superior cervical ganglionectomy (SCG-X) performed 1 week after hatching had little or no effect on these rhythms in LD, but unlike normals. SCG-X birds did not sustain persistent rhythms in DD. In SCG-X birds, norepinephrine (NE) infusion for 12 h of each 24 h in DD significantly reduced plasma melatonin titres during the infusion and re-established a rhythm. After each experiment, hens were killed, their pineals were removed and assayed by HPLC-EC for NE, dopamine (DA), serotonin (5-HT) and 5-hydroxy-3-indole-acetic acid (5-HIAA). SCG-X resulted in a 90% depletion of pineal NE: DA content was reduced to undetectable levels. Pineal 5-HT and 5-HIAA were also reduced by SCG-X. The chicken pineal contains circadian oscillators which persist in vitro8.19.29. The results reported here suggest that noradrenergic fibres from the SCG regulate the pineal's inherent rhythmicity. NE normally released from sympathetic terminals during the bird's day may synchronize oscillators within the pineal by inhibiting melatonin synthesis.