Melatonin does not link the eyes to the rest of the circadian system in quail: a neural pathway is involved

Blinding by enucleation has a dramatic effect on the circadian activity rhythm of Japanese quail. The activity patterns of enucleated birds held under 24-hr light-dark cycles are disrupted, although entrainment can persist in many birds. In constant darkness (DD), blinded birds are rendered arrhythmic. These results demonstrate that the eyes are a major component of the circadian system, and that insofar as enucleation produces arrhythmicity in DD, the eyes' role is not merely a photosensory one. The eyes of quail can synthesize and secrete the hormone melatonin, which has been implicated as a blood-borne messenger relaying timing information between elements of the circadian system in some avian species. However, the way in which the eyes communicate with the rest of the circadian system in quail appears to be neural, since (1) optic nerve section produces the same effects as blinding by enucleation on the circadian activity rhythm, and (2) eyes subjected to optic nerve section retain their ability to synthesize and secrete melatonin.     

Period and phase control in a multioscillatory circadian system (Iguana iguana)

The circadian system of the lizard Iguana iguana is composed of several independent pacemakers that work in concert: the pineal gland, retinae of the lateral eyes, and a fourth oscillator presumed to be located in the hypothalamus. These pacemakers govern the circadian expression of multiple behaviors and physiological processes, including rhythms in locomotor activity, endogenous body temperature, electroretinogram, and melatonin synthesis. The numerous, easily measurable rhythmic outputs make the iguana an ideal organism for examining the contributions of individual oscillators and their interactions in governing the expression of overt circadian rhythms. The authors have examined the effects of pinealectomy and enucleation on the endogenous body temperature rhythm (BTR) and locomotor activity rhythm (LAR) of juvenile iguanas at constant temperature both in LD cycles and in constant darkness (DD). They measured the periods (tau) of the circadian rhythms of LAR and BTR, the phase relationships between them in DD (psiAT), and the phase relationship between each rhythm and the light cycle (psiRL). Pinealectomy lengthened tau of locomotor activity in all animals tested and abolished the BTR in two-thirds of the animals. In those animals in which the BTR did persist following pinealectomy, tau lengthened to the same extent as that of locomotor activity. Pinealectomy also delayed the onset of activity with respect to its normal phase relationship with body temperature in DD. Enucleation alone had no significant effect on tau of LAR or BTR; however, after enucleation, BTR became 180 degrees out of phase from LAR in DD. After both pinealectomy and enucleation, 4 of 16 animals became arrhythmic in both activity and body temperature. Their data suggest that rhythmicity, period, and phase of overt circadian behaviors are regulated through the combined output of multiple endogenous circadian oscillators.     

Circadian ovulatory rhythms in Japanese quail: role of ocular and extraocular pacemakers

Previous studies have shown that the circadian system of Japanese quail is composed of multiple photic inputs and multiple oscillators. Among these are extraretinal photoreceptors that mediate both circadian and photoperiodic responses and circadian pacemakers in the eyes that, via neural and hormonal outputs, help to maintain rhythmicity of central circadian clocks (presumably located in the suprachiasmatic area of the hypothalamus). Furthermore, a component of the central circadian system is influenced by reproductive hormones. Under certain conditions, the circadian system of female quail can be induced to split into two circadian components: one driven by ocular pacemakers and one driven by feedback from reproductive hormones. Importantly, ovulation is either inhibited or permitted as these two oscillators (or sets of oscillators) constantly change internal phase relationships with each other, suggesting an "internal coincidence" mechanism in the control of ovulation. The oviposition patterns of quail in light-dark (LD) cycles also support an internal coincidence mechanism. The authors tested the hypothesis that the ocular pacemakers are an important component of an internal coincidence mechanism controlling ovulation by examinig the effects of blinding by complete eye removal (EX), and the effects of eye-patching, on the body temperature and oviposition patterns of quail exposed to 24-h LD cycles. They also examined the effects of EX on quail exposed to continuous light (LL) and to continuous darkness (DD). Neither EX nor eye-patching affected the oviposition patterns of birds in LD. Furthermore, robust body temperature and oviposition rhythms continued in EX birds in LL, but body temperature became arrhythmic in DD with the cessation of ovulation. The results do not show a role for ocular pacemakers in the control of ovulation, but they do support the hypotheses that (1) entrainment of the central oscillators by extraretinally perceived light is sufficient to preserve a normal ovulatory pattern in LD in the absence of the ocular pacemakers, and (2) in LL, feedback of reproductive hormones onto the central oscillators is sufficient to organize the circadian system even in the absence of the ocular pacemakers. Whether or not the ocular pacemakers are normally involved in the control of ovulation is still an open question.     

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.     

Pineal-dependent locomotor activity of lamprey,Lampetra japonica,measured in relation to LD cycle and circadian rhythmicity

Summary Locomotor activity of the river lamprey, Lampetra japonica, was investigated under a light-dark (LD 1212) cycle and under continuous dark conditions. Intact lampreys were entrained to the light:dark cycle. They were active mainly in the early half of the dark period and inactive in light period. The light:dark entrainment continued in 72.7% of lampreys after the removal of bilateral eyes, but additional pinealectomy made the entrainment disappear in all lampreys. When lampreys were pinealectomized with their eyes intact, light: dark entrainment was abolished in most cases. The results indicate that the pineal organ of the lamprey is a photoreceptive organ responsible for synchronizing locomotor activity to LD cycle. Under continuous dark conditions, the locomotor activity began to free-run with a period of 21.3 ± 0.9 h (mean ± SD, n = 53). This circadian rhythmicity was not affected by the removal of lateral eyes but was abolished by pinealectomy. The pineal organ appears to function as an oscillator, or as one of the oscillators, for the circadian locomotor rhythm of lampreys.Abbreviations DD continuous dark - LD light:dark     

Contribution of pineal and retinae to the circadian rhythms of circulating melatonin in pigeons

Summary Melatonin levels in the plasma of homing pigeons were measured by radioimmunoassay. In a 1212 LD cycle a robust daily rhythm of plasma melatonin was found in intact birds. This rhythm is significantly reduced in amplitude after pinealectomy, and disappears completely after the pinealectomized animals have been bilaterally enucleated. The results indicate that in the pigeon 70% of the nighttime peak of blood-borne melatonin comes from the pineal gland, while 17% comes from the retina. In addition, there is a relatively large amount (13%) of non-rhythmic melatonin of unidentified origin. The melatonin rhythm appears to be circadian in nature, since melatonin levels begin to fall before lights-on in LD, and rhythmicity persists in intact and pinealectomized birds for at least two cycles in DD. In conjunction with earlier studies, the present results are consistent with the hypothesis that melatonin serves as mediator of circadian information in the pigeon.     

Circadian nature of the photoperiodic clock in Japanese quail

Summary The photoperiodic clock in quail (Coturnix colurnix japonica) is based upon a rhythm of photoinducibility (Øi) but the extent to which this rhythm is circadian remains unclear. Two types of experiment investigated this situation. In the first, gonadectomized quail were adapted to live in periods of darkness by training them on a schedule containing one short day and 3 days of darkness (SD/DD/DD/DD). They were then exposed to a single pulse of 6 or 10 h of light at different times across 3 days of darkness. The photoperiodic response, measured by the increase in LH secretion, showed clear rhythmicity, demonstrating unequivocally the circadian nature of Øi. The second set of experiments employed Nanda-Hamner cycles and varied the length of the photoperiod from 6 to 11 h. Responsiveness in a 36 h or a 60 h cycle was highly dependent upon the length of the photoperiod, something not predicted from theory. For instance, LD 6:30 was not photoperiodically inductive but LD 10:26 was clearly inductive. Close analysis of patterns of LH secretion indicated an unexpected delay before induction occurred and then a rapid rise to a stable level of induction. When LH was measured in every pulse under LD 10:26 there was no evidence that LH levels alternately increased and decreased. This is not consistent with the simplest interpretation of Nanda-Hamner experiments where alternate pulses of light are thought to entrain the rhythm or induce a photoperiodic response by coinciding with Øi. It is concluded that the quail's photoinducible rhythm is indeed based on a circadian rhythm but one that is only weakly self-sustaining. Possibly as a consequence of this, the rhythm's behaviour under abnormal photoperiodic cycles may be rather different from that found in other species and from other circadian rhythms in quail.Abbreviations Øi photoinducible phase - LH luteinizing hormone     

The effects of pinealectomy and blinding on the circadian locomotor activity rhythm in the Japanese newt,Cynops pyrrhogaster

We examined the effects of pinealectomy and blinding (bilateral ocular enucleation) on the circadian locomotor activity rhythm in the Japanese newt, Cynops pyrrhogaster. The pinealectomized newts were entrained to a light-dark cycle of 12 h light and 12 h darkness. After transfer to constant darkness they showed residual rhythmicity for at least several days which was gradually disrupted in prolonged constant darkness. Blinded newts were also entrained to a 12 h light/12 h dark cycle. In subsequent constant darkness they showed free-running rhythms of locomotor activity. However, the freerunning periods noticeably increased compared with those observed in the previous period of constant darkness before blinding. In blinded newts entrained to the light/dark cycle the activity rhythms were gradually disrupted after pinealectomy even in the presence of the light/dark cycle. These results suggest that both the pineal and the eyes are involved in the newt's circadian system, and also suggest that the pineal of the newt acts as an extraretinal photoreceptor which mediates the entrainment of the locomotor activity rhythm.Abbreviations circadian period - DD constant darkness - LD cycle, light-dark cycle - LD 12:12 light-dark cycle of 12 h light and 12 h darkness     

Pinealectomy affects the circannual testicular rhythm in european starlings (Sturnus vulgaris)

Summary Pinealectomized and sham-operated European starlings were maintained for 16 months under a constant 12-h photoperiod and constant temperature conditions. In all birds, testicular width was measured at about monthly intervals and the onset and end of molt was determined. Shortly after the beginning of the experiment, the sham-operated birds went through a cycle of testicular growth and regression which was followed by a complete molt; subsequently most individuals initiated a second testicular cycle. Most of the pinealectomized birds, in contrast, failed to go through a second testicular cycle. Moreover, during the first cycle their testes regressed earlier than in the sham-operated birds and the subsequent molt was relatively advanced. In these respects the pinealectomized birds behaved like intact starlings under a 13-h photoperiod. Since pinealectomy probably changes the phase-relationship between circadian rhythms and the entraining light-dark cycle it is proposed that pinealectomy in the present experiment might have altered the phase-relationship between a circadian rhythm of photosensitivity and the light-dark cycle in such a way that the birds interpreted the 12-h photoperiod as a 13-h photoperiod.This work was supported by the Deutsche Forschungsgemeinschaft SPP Mechanismen biologischer Uhren.     

The quail's eye: a biological clock

The site (intraocular vs. extraocular) of the biological clock driving a rhythm in melatonin content in the eyes of Japanese quail was investigated by alternately patching the left and right eyes of individual birds, otherwise held in constant light, for 12-hr periods. This patching protocol, therefore, exposed each eye to a light-dark cycle (LD 12:12) 180 degrees (12 hr) out of phase with the LD cycle experienced by the other eye. The optic nerves to both eyes were transected prior to initiating the patching protocol. The ocular melatonin rhythm (OMR) of the left eyes of quail could be entrained by this procedure 180 degrees out of phase with the rhythm expressed by the right eyes. Since optic nerve section would have deprived any putative extraocular clocks of photic entrainment information, the results show conclusively that the clock driving the OMR is located within the eye itself. In addition, the OMR of Japanese quail is remarkably unaffected by removing two potential neural inputs to the eye (sympathetic innervation from the superior cervical ganglia, and input from the isthmo-optic nucleus of the midbrain); this suggests that these inputs are not required to maintain the OMR. Finally, the clock driving the OMR of one eye does not appear to be coupled to the clock driving the OMR in the other eye, since permanently patching one eye abolished the ability of the patched eye to re-entrain to an 8-hr shift in the phase of an LD 12:12 cycle, whereas the exposed eye rapidly re-entrained to the phase-shifted cycle.     

Investigations of photoperiodically induced fattening in migratory blackheaded bunting (Emberiza melanocephala)(Ayes)

The body fattening and weight gain preceding vernal migration in birds is timed by a set of environmental factors of which daylength is predominant. However, the mechanism(s) by which these events is determined is poorly understood. Previous investigations on a photoperiodic migratory species, the blackheaded bunting ( Emberiza melanocephala ), indicate the involvement of a light-sensitive circadian rhythm during initiation of fat deposition and body weight gain. This communication presents data from another set of experiments aimed to characterize further the mechanism(s) of fat deposition in the same species.
Groups of photosensitive, unstimulated and stimulated birds were subjected to transfer and superimposition experiments for 30 days. While the former set included shifting of long-day (LD) birds to DD, SD (short days), DD/LD and SD/LD, in the latter a 90-minute bright light was superimposed at two different times of the day during the dim-green lighted phase 15L:9D of varying intensity. Birds were weighed at the beginning and at the end of experiments. Those in transfer cycles were also weighed at 10-day intervals. The results suggest that the premigratory body fattening and weight gain in blackheaded buntings is light dependent and timed by environmental daylength in accordance with the photosensitive endogenous circadian rhythm (ECR). They also show that the photoperiodic responses in birds in general are mediated by circadian rhythm(s).     

Effect of Light Intensity on Circadian Activity in Developing Japanese Quail

The effects of constant light on the expression of the circadian rhythm of feeding activity in Japanese quail, and in particular on the clarity of the rhythm were investigated. We used 46 4-week-old birds (35 females and 11 males) issued from two lines selected for a more (line R: 25 females and 10 males) or less (line A: 10 females and 1 male) clear circadian rhythm of feeding activity. The birds, were placed successively under three light schedules: constant darkness (DD), constant dim green light (LLdim) and constant bright light (LLbright). Schedules were changed every 2 weeks. Feeding activity was recorded continuously, analysed by autocorrelation and spectral analysis, and the ratio of the correlation coefficients and the area of the spectrum peak were used as indexes to quantify the clarity of the circadian rhythm. During the experiment, some birds showed gonadal development. Therefore, we analysed separately birds showing either a high or low degree of sexual development at the end of the experiment. In DD, 35 birds showed a circadian feeding rhythm with a mean period of 22.5 ± 0.1 h, whereas 11 birds showed an arrhythmic activity. In LLdim, 27 birds were rhythmic (22 birds R and 5 birds A), and in LLbright, only 3 birds showed a rhythmic circadian activity. For the R-line birds (for females and males), the rhythm clarity decreased in LLdim compared to DD, except for the not developed females. For the A-line birds (for females), the rhythm clarity of the immature birds increased in LLdim and that of the developed birds remained stable. In LLbright, circadian activity became arrhythmic. In LLdim, the active phases of 12 birds showed two main peaks, with mean periods of 22.7 h and 25.1 h, respectively. Therefore, constant light appeared to have an inhibitory effect on the expression of the circadian rhythm. We postulate that two hierarchically coupled oscillators could control circadian feeding activity, and arrhythmia in LLbright could be the results of internal desynchronization of the pacemakers.     

Effect of Light Intensity on Circadian Activity in Developing Japanese Quail

The effects of constant light on the expression of the circadian rhythm of feeding activity in Japanese quail, and in particular on the clarity of the rhythm were investigated. We used 46 4-week-old birds (35 females and 11 males) issued from two lines selected for a more (line R: 25 females and 10 males) or less (line A: 10 females and 1 male) clear circadian rhythm of feeding activity. The birds, were placed successively under three light schedules: constant darkness (DD), constant dim green light (LLdim) and constant bright light (LLbright). Schedules were changed every 2 weeks. Feeding activity was recorded continuously, analysed by autocorrelation and spectral analysis, and the ratio of the correlation coefficients and the area of the spectrum peak were used as indexes to quantify the clarity of the circadian rhythm. During the experiment, some birds showed gonadal development. Therefore, we analysed separately birds showing either a high or low degree of sexual development at the end of the experiment. In DD, 35 birds showed a circadian feeding rhythm with a mean period of 22.5 ± 0.1 h, whereas 11 birds showed an arrhythmic activity. In LLdim, 27 birds were rhythmic (22 birds R and 5 birds A), and in LLbright, only 3 birds showed a rhythmic circadian activity. For the R-line birds (for females and males), the rhythm clarity decreased in LLdim compared to DD, except for the not developed females. For the A-line birds (for females), the rhythm clarity of the immature birds increased in LLdim and that of the developed birds remained stable. In LLbright, circadian activity became arrhythmic. In LLdim, the active phases of 12 birds showed two main peaks, with mean periods of 22.7 h and 25.1 h, respectively. Therefore, constant light appeared to have an inhibitory effect on the expression of the circadian rhythm. We postulate that two hierarchically coupled oscillators could control circadian feeding activity, and arrhythmia in LLbright could be the results of internal desynchronization of the pacemakers.     

Circadian Control of Dendrite Morphology in the Visual System of Drosophila melanogaster

Background

In the first optic neuropil (lamina) of the fly''s visual system, monopolar cells L1 and L2 and glia show circadian rhythms in morphological plasticity. They change their size and shape during the day and night. The most pronounced changes have been detected in circadian size of the L2 axons. Looking for a functional significance of the circadian plasticity observed in axons, we examined the morphological plasticity of the L2 dendrites. They extend from axons and harbor postsynaptic sites of tetrad synaptic contacts from the photoreceptor terminals.

Methodology/Principal Findings

The plasticity of L2 dendrites was evaluated by measuring an outline of the L2 dendritic trees. These were from confocal images of cross sections of L2 cells labeled with GFP. They were in wild-type and clock mutant flies held under different light conditions and sacrified at different time points. We found that the L2 dendrites are longest at the beginning of the day in both males and females. This rhythm observed under a day/night regime (LD) was maintained in constant darkness (DD) but not in continuous light (LL). This rhythm was not present in the arrhythmic per⁰¹ mutant in LD or in DD. In the clock photoreceptor cry^b mutant the rhythm was maintained but its pattern was different than that observed in wild-type flies.

Conclusions/Significance

The results obtained showed that the L2 dendrites exhibit circadian structural plasticity. Their morphology is controlled by the per gene-dependent circadian clock. The L2 dendrites are longest at the beginning of the day when the daytime tetrad presynaptic sites are most numerous and L2 axons are swollen. The presence of the rhythm, but with a different pattern in cry^b mutants in LD and DD indicates a new role of cry in the visual system. The new role is in maintaining the circadian pattern of changes of the L2 dendrite length and shape.     

Optic lobe circadian pacemaker sends its information to the contralateral optic lobe in the cricket Gryllus bimaculatus

The bilaterally paired optic lobe pacemakers of the cricket Gryllus bimaculatus are mutually coupled. In the present study we recorded the neural activity conveyed from the brain toward the optic lobe with a suction electrode to examine the coupling signals. The results demonstrated that the brain efferents to the optic lobe encode the circadian information: Both in constant light (LL) and constant darkness (DD), the neural activity of brain efferents showed a clear circadian rhythm with a nocturnal peak. Since the rhythm survived the severance of the contralateral optic nerve but disappeared when the contralateral optic lobe was removed, it is apparent that the rhythm originates from the contralateral optic lobe. The amplitude of the rhythm was greater in LL than in DD, suggesting that light affects the amplitude of the rhythm. This was confirmed by the fact that the light-induced response was under circadian control, being greater during the subjective night. These data suggest that the bilaterally paired optic lobe pacemakers exchange circadian information as well as light information. The data are also consistent with the results of previous behavioral experiment.Abbreviations DD constant darkness - LD light dark cycle - LL constant light     

Seasonal variations in circadian rhythms of plasma melatonin in ruin lizards

We examined melatonin profiles of ruin lizards in different seasons (spring, summer, and autumn) under light:dark (LD) and concomitant responses when transferred to continuous darkness (DD) to determine the degree to which previously reported seasonally dependent effects of pinealectomy on locomotor behavior are related to melatonin secretion. The amplitude of the melatonin rhythm and the amount of melatonin produced over 24 h varied with season. In spring, the amount of melatonin produced was greatest and the amplitude 4- 5 times that found in summer or autumn. The degree of self-sustainment of the melatonin rhythm when transferred to DD also varied with season. In DD, melatonin levels remained high but did not exhibit circadian variation in spring. In summer, the melatonin profile persisted virtually unchanged in DD, showing the existence of a circadian rhythm. Finally, in the fall there was no circadian variation in DD and levels remained low. These responses correspond closely to previously reported effects of pinealectomy on locomotor behavior where there is little or no effect of pinealectomy in spring or fall but a profound alteration of locomotor behavior in summer. These results suggest that the seasonally dependent effects of pinealectomy on locomotor behavior in ruin lizards are related to a seasonally mediated change in the degree of self-sustainment of some component of the circadian pace-making system of which melatonin plays some role.     

Isolation of an insect circadian clock

Summary Under constant conditions the compound eyes of the ground beetleAnthia sexguttata exhibit sensitivity changes in a very clear circadian rhythm. Usually the rhythms in both eyes in constant darkness are mutually coupled. After transection of the optic tract between the lobula and the supraesophageal ganglion the circadian rhythms of the two eyes continue without interruption, but coupling between them is abolished. Even if the entire supraesophageal ganglion is removed, leaving the optic ganglia intact, the circadian rhythms in the eyes continue without interruption independently. But the rhythm is abolished if the region of the lobula is damaged.The experiments show thatAnthia has circadian pacemakers in the left and right optic ganglia in or close to the lobula. These pacemakers can function independently from the rest of the brain and control circadian rhythms of physiological events.Supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 45 Vergleichende Neurobiologie des Verhaltens E1     

Ocular clocks are tightly coupled and act as pacemakers in the circadian system of Japanese quail

Our previous studies showed that the eyes of Japanese quail contain a biological clock that drives a daily rhythm of melatonin synthesis. Furthermore, we hypothesized that these ocular clocks are pacemakers because eye removal abolishes freerunning rhythms in constant darkness (DD). If the eyes are indeed acting as pacemakers, we predicted that the two ocular pacemakers in an individual bird must remain in phase in DD and, furthermore, the two ocular pacemakers would rapidly regain coupling after being forced out of phase. These predictions were confirmed by demonstrating that 1) the ocular melatonin rhythms of the two eyes maintained phase for at least 57 days in DD and 2) after ocular pacemakers were forced out of phase by alternately patching the eyes in constant light, two components of body temperature were observed that fused into a consolidated rhythm after 5-6 days in DD, showing pacemaker recoupling. The ability to maintain phase in DD and rapidly recouple after out-of-phase entrainment demonstrates that the eyes are strongly coupled pacemakers that work in synchrony to drive circadian rhythmicity in Japanese quail.     

Circadian rhythms of oviposition and feeding activity in Japanese quail: effects of cyclic administration of melatonin

The aim of these experiments was to test the effect of a cyclic administration of melatonin, by mimicking the daily rhythm of hormone levels, on the circadian organization of two distinct functions in quail: oviposition and feeding activity. Laying and feeding rhythms under photoperiodic conditions and constant darkness (DD) were investigated. Under DD, where the two rhythms were free running, a daily rhythm of melatonin was administered. In LD 14h:10h, two different individual profiles of laying were established, with stable females laying at the same time each day and delayed females laying progressively later each day. For feeding activity, all birds were clearly synchronized to the photoperiodic cycle. In DD, the laying birds showed a free-running rhythm of oviposition with a period longer than 24 h for both profiles but the delayed profile females had a longer period than stable profile females. In comparison, the free-running period of feeding rhythm of the same birds was shorter than 24 h. A cyclic administration of melatonin had no effect on laying rhythm, which continued to free-run in DD, whereas feeding activity was synchronized as soon as the first cycle of melatonin was administered. From these results, it seems that two different circadian systems drive each of the two types of behavior separately. Melatonin could be the main synchronizer for the temporal control of feeding behavior, but it does not play a part in the control of oviposition in Japanese quail.     

Circadian Rhythms of Locomotor Activity in Lycosa tarentula (Araneae, Lycosidae) and the Pathways of Ocular Entrainment

Lycosa tarentula is a ground-living spider that inhabits a burrow where it awaits the appearance of prey or conspecifics. In this study, circadian rhythms of locomotor activity were examined as well as the ocular pathway of entrainment. Thirty-three adult virgin females were examined under constant darkness (DD); all of them exhibited robust circadian rhythms of locomotor activity with a period averaging 24.1h. Fourteen of these spiders were studied afterwards under an LD 12:12 cycle; they usually entrained to in the first or second day, even when the light intensity was as low as 1 lx. During the LD cycle, locomotor activity was generally restrained to the darkness phase, although several animals showed a small amount of diurnal activity. Ten males were also examined under LD; they were also nocturnal, but were much more active than the females. Seven females were examined under constant light (LL); under this they became arrhythmic. Except for the anterior median eyes (OMAs), all the eyes were capable of entraining the locomotor activity to an LD cycle. These results demonstrate that under laboratory conditions and low light intensities locomotor activity of Lycosa tarentula is circadian and in accordance with Aschoff's 'rule'. Only OMAs are unable to entrain the rhythm; the possible localization of circadian clock is therefore discussed.