Food Intake and Circadian Rhythms of Activity of Red-Winged Blackbirds (Agelaius phoeniceus). A Time-Course Study on the Effects of Alpha-Chloralose and Secobarbital

Anesthetic drugs like alpha-chloralose and secobarbital are used to capture wild birds. The doses are usually chosen on the basis of low mortality rates and high capture success. However, little information is available on the time necessary for the birds to fully recover from the drugs' effects after they have regained consciousness. In this work, we used circadian rhythms of activities to study the long-term effects of a mixture of alpha-chloralose and secobarbital on adult male Red-winged Blackbirds. The birds were housed individually in sound-proof boxes for 30 days, during which they received alpha-chloralose and secobarbital mixed with corn, either on day 3 or on day 15. On the day of treatment, the birds experienced a significant decrease in activity level, including feeding activities, which lasted more than 22 days for the birds treated on day 3, compared to about 8 days for the birds treated on day 15. Moreover, typical circadian distribution of activity was lost and many birds became aperiodic. Two weeks were needed for the birds treated on day 3 to recover normal rhythms, compared to less than 9 days for those treated on day 15. These results indicate that circadian parameters can be used to detect after-effects of intoxication long after the birds have regained consciousness.     

Ultradian Rhythm of Activity in Japanese Quail Groups under Semi-Natural Conditions during Ontogeny: Functional Aspects and Relation to Circadian Rhythm

The function of ultradian rhythms is not yet clearly elucidated. In particular, short-term rhythms are expressed during early ontogeny, especially in broods of precocial birds. We investigated the relationship between the clarity of the ultradian rhythm of the activity/rest cycle of a group of young Japanese quail (Coturnix japonica) and the level of social synchronisation and spatial cohesion between the birds within that group. The subjects were descended from two lines selected for either very pronounced rhythmic or arrhythmic circadian activity. We found a positive relationship between the clarity of the ultradian rhythm of the activity/rest cycle when birds were young and the clarity of the circadian rhythm of feeding activity when birds were older, but still immature. The temporal organisation of the behaviour of the chicks from these two lines was observed in outdoor aviaries, when they were 4, 8, 12 and 15 days old. The mean ultradian period expressed by groups of 12 chicks was variable, with a minimum of 6 minutes. The ultradian period lengthened regularly as chicks grew older, and reached approximately 40 min on day 15. The clarity of the ultradian rhythmicity of group activity was linked to the level of inter-individual social synchronisation and of spatial cohesion; the more pronounced the ultradian rhythms of a group, the greater the temporal and spatial cohesion of the chicks within the group. Moreover, these characteristics varied with the age of the chicks. Finally, chicks in the less rhythmic groups weighed less. These results stress the adaptive value of this temporal organisation strategy under natural conditions.     

Ultradian Rhythm of Activity in Japanese Quail Groups under Semi-Natural Conditions during Ontogeny: Functional Aspects and Relation to Circadian Rhythm

The function of ultradian rhythms is not yet clearly elucidated. In particular, short-term rhythms are expressed during early ontogeny, especially in broods of precocial birds. We investigated the relationship between the clarity of the ultradian rhythm of the activity/rest cycle of a group of young Japanese quail (Coturnix japonica) and the level of social synchronisation and spatial cohesion between the birds within that group. The subjects were descended from two lines selected for either very pronounced rhythmic or arrhythmic circadian activity. We found a positive relationship between the clarity of the ultradian rhythm of the activity/rest cycle when birds were young and the clarity of the circadian rhythm of feeding activity when birds were older, but still immature. The temporal organisation of the behaviour of the chicks from these two lines was observed in outdoor aviaries, when they were 4, 8, 12 and 15 days old. The mean ultradian period expressed by groups of 12 chicks was variable, with a minimum of 6 minutes. The ultradian period lengthened regularly as chicks grew older, and reached approximately 40 min on day 15. The clarity of the ultradian rhythmicity of group activity was linked to the level of inter-individual social synchronisation and of spatial cohesion; the more pronounced the ultradian rhythms of a group, the greater the temporal and spatial cohesion of the chicks within the group. Moreover, these characteristics varied with the age of the chicks. Finally, chicks in the less rhythmic groups weighed less. These results stress the adaptive value of this temporal organisation strategy under natural conditions.     

Avian circannual clocks: adaptive significance and possible involvement of energy turnover in their proximate control

Endogenous circannual clocks are found in many long-lived organisms, but are best studied in mammal and bird species. Circannual clocks are synchronized with the environment by changes in photoperiod, light intensity and possibly temperature and seasonal rainfall patterns. Annual timing mechanisms are presumed to have important ultimate functions in seasonally regulating reproduction, moult, hibernation, migration, body weight and fat deposition/stores. Birds that live in habitats where environmental cues such as photoperiod are poor predictors of seasons (e.g. equatorial residents, migrants to equatorial/tropical latitudes) rely more on their endogenous clocks than birds living in environments that show a tight correlation between photoperiod and seasonal events. Such population-specific/interspecific variation in reliance on endogenous clocks may indicate that annual timing mechanisms are adaptive. However, despite the apparent adaptive importance of circannual clocks, (i) what specific adaptive value they have in the wild and (ii) how they function are still largely untested. Whereas circadian clocks are hypothesized to be generated by molecular feedback loops, it has been suggested that circannual clocks are either based upon (i) a de-multiplication ('counting') of circadian days, (ii) a sequence of interdependent physiological states, or (iii) one or more endogenous oscillators, similar to circadian rhythms. We tested the de-multiplication of days (i) versus endogenous regulation hypotheses (ii) and (iii) in captive male and female house sparrows (Passer domesticus). We assessed the period of reproductive (testicular and follicular) cycles in four groups of birds kept either under photoperiods of LD 12L:12D (period length: 24h), 13.5L:13.5D (27 h), 10.5L:10.5D (23 h) or 12D:8L:3D:1L (24-h skeleton photoperiod), respectively, for 15 months. Contrary to predictions from the de-multiplication hypothesis, individuals experiencing 27-h days did not differ (i.e. did not have longer) annual reproductive rhythms than individuals from the 21- or 24-h day groups. However, in line with predictions from endogenous regulation, birds in the skeleton group had significantly longer circannual period lengths than all other groups. Birds exposed to skeleton photoperiods experienced fewer light hours per year than all other groups (3285 versus 4380) and had a lower daily energy expenditure, as tested during one point of the annual cycle using respirometry. Although our results are tantalizing, they are still preliminary as birds were only studied over a period of 15 months. Nevertheless, the present data fail to support a 'counting of circadian days' and instead support hypotheses proposing whole-organism processes as the mechanistic basis for circannual rhythms. We propose a novel energy turnover hypothesis which predicts a dependence of the speed of the circannual clock on the overall energy expenditure of an organism.     

Pinealectomy and LL Abolished Circadian Perching Rhythms but Did Not Alter Circannual Reproductive or Fattening Rhythms in Finches

In the subtropical finch, spotted munia (Lonchura punctulata) circannual rhythms (of gonads, fattening, feeding) have been demonstrated in an information-free environment of continuous illumination (LL), rendering it an ideal model for research on the physiology of the circannual clock. In an attempt to understand the involvement, if any, of the circadian system in the genesis of circannual rhythms, we studied the effect of pinealectomy (LL 15 lux) and strong continuous illumination (LL 300 lux), both known to abolish circadian rhythms, on the circadian perch-hopping rhythm and on the circannual rhythm of reproduction and fattening in the same birds. While both pinealectomy and LL 300 lux treatments abolished the circadian rhythm of motor activity, they had no effect on the circannual rhythms of gonadal size and fattening. If the endogenous circadian rhythm in perch-hopping can be taken to reflect the circadian clock mechanism associated with gonadal functioning, present results suggest that circannual rhythm of reproduction in spotted munia is independent of circadian events.     

Pinealectomy and LL Abolished Circadian Perching Rhythms but Did Not Alter Circannual Reproductive or Fattening Rhythms in Finches

In the subtropical finch, spotted munia (Lonchura punctulata) circannual rhythms (of gonads, fattening, feeding) have been demonstrated in an information-free environment of continuous illumination (LL), rendering it an ideal model for research on the physiology of the circannual clock. In an attempt to understand the involvement, if any, of the circadian system in the genesis of circannual rhythms, we studied the effect of pinealectomy (LL 15 lux) and strong continuous illumination (LL 300 lux), both known to abolish circadian rhythms, on the circadian perch-hopping rhythm and on the circannual rhythm of reproduction and fattening in the same birds. While both pinealectomy and LL 300 lux treatments abolished the circadian rhythm of motor activity, they had no effect on the circannual rhythms of gonadal size and fattening. If the endogenous circadian rhythm in perch-hopping can be taken to reflect the circadian clock mechanism associated with gonadal functioning, present results suggest that circannual rhythm of reproduction in spotted munia is independent of circadian events.     

The pineal clock affects behavioral circadian rhythms but not photoperiodic induction in the Indian weaver bird (Ploceus philippinus)

We investigated whether pineal is part of the circadian clock system which regulates circadian rhythms of activity and photosensitivity in the Indian weaver bird (Ploceus philippinus). Two experiments were performed. The first experiment examined the induction of testicular growth, and androgen-dependent beak pigmentation and luteinizing hormone (LH)-specific plumage coloration in pinealectomised (pinx) and sham-operated (sham) birds exposed to short day (8 h light: 16 h darkness, 8L:16D) and long day (16L:8D) for 9 months in the late breeding and early regressive phase (October), or the late regressive and preparatory phase (January) of the annual testicular cycle. As expected, short days were non-stimulatory, and long days stimulated testicular growth, beak pigmentation and plumage coloration. There was no difference in the response between pinx and sham birds subjected to short or long days in October, but the response was enhanced in pinx birds that were subjected to long day in January. In the second experiment circadian behavioral rhythms were studied (activity pattern in singly housed birds) in weaver birds first exposed at two different phases of the annual testicular cycle to a stimulatory photoperiod (12L:12D in preparatory phase or 13L:11D in early breeding phase) and then released into dim continuous light (LL_dim). All birds showed synchronization to the light period before and after the pinealectomy; there was no difference in the response between pinx and sham birds. When released into LL_dim, sham birds exhibited circadian rhythmicity continuously, whereas pinx birds lost circadian rhythmicity after some cycles. Considered together, these results suggest that circadian clock residing within the pineal gland regulates the circadian rhythm in activity, but not the circadian rhythm involved in photoperiodic induction of the Indian weaver bird.     

Neonatal Exposure to Atypical Zeitgeber in the Wistar Rat. Effects on Development of Circadian Rhythms of Drinking and Motor Activities

The data described concern the maturation of circadian motor and drinking rhythms immediately after weaning. We ran two experiments in both of which mother rats and their litters were subjected to either an atypical Zeitgeber or to standard conditions from the birth of the young up to weaning on the 19th day. In the experimental groups, the light and the temperature cycles were permanently in phase opposition and were shifted by 12 hours every 3 days. In the control groups, the cycles were the same except that they were in phase and were never shifted. In the first experiment, after weaning the young were subjected to an LD cycle; in the second experiment to constant conditions. The results of both experiments showed that the circadian rhythms of drinking and locomotor activities appeared with a delay of ten days in the experimental rats. These rats kept an ultradian structure for a longer time. During the constant conditions, a lengthening (around 25 min.) of the free-running period was observed. In conclusion, atypical environmental cycles during early neonatal life affect the development of the circadian system.     

Neonatal Exposure to Atypical Zeitgeber in the Wistar Rat. Effects on Development of Circadian Rhythms of Drinking and Motor Activities

The data described concern the maturation of circadian motor and drinking rhythms immediately after weaning. We ran two experiments in both of which mother rats and their litters were subjected to either an atypical Zeitgeber or to standard conditions from the birth of the young up to weaning on the 19th day. In the experimental groups, the light and the temperature cycles were permanently in phase opposition and were shifted by 12 hours every 3 days. In the control groups, the cycles were the same except that they were in phase and were never shifted. In the first experiment, after weaning the young were subjected to an LD cycle; in the second experiment to constant conditions. The results of both experiments showed that the circadian rhythms of drinking and locomotor activities appeared with a delay of ten days in the experimental rats. These rats kept an ultradian structure for a longer time. During the constant conditions, a lengthening (around 25 min.) of the free-running period was observed. In conclusion, atypical environmental cycles during early neonatal life affect the development of the circadian system.     

Effects of Simulated Hypo‐ and Hyper‐Reproductive Conditions on the Characteristics of Circadian Rhythm in Hypothalamic Concentration of Serotonin and Dopamine and in Plasma Levels of Thyroxine,Triiodothyronine, and Testosterone in Japanese Quail,Coturnix coturnix japonica

In this study, hypo‐ and hyper‐reproductive conditions, as measured by concentrations of plasma testosterone in male Japanese quail held on long days LD 16:8, were experimentally simulated with injections of 5‐hydroxytryptophan (5‐HTP) and L‐dihydroxyphenylalanine, (L‐DOPA) with 8 h and 12 h phase angle differences between them in intact and melatonin‐treated birds. The effects of these treatments were assessed on the characteristics of the circadian rhythm in the hypothalamic concentration of serotonin (5‐HT), dopamine (DA), and plasma levels of thyroxine (T₄), triiodothyronine (T₃), and testosterone (T). These rhythms were also studied in sham‐operated (SO), pinealectomized (Px), vehicle‐ (Veh), and melatonin (Mel)‐treated birds. On the basis of the circadian mesors of the testosterone rhythms, three distinct categories could be identified: category A (i.e., normal breeding concentrations of plasma testosterone), which includes control, sham‐operated, and vehicle‐treated groups; category A⁺ (i.e., concentrations of plasma testosterone higher than that found in normal breeding quail), which includes 12 h, 12 h+vehicle‐treated, and Px quails; and category A^? (concentrations of plasma testosterone lower than that found in normal breeding quail), which includes 8 h, melatonin‐, and 12 h+melatonin‐treated groups. It is evident that in normal and hypergonadal conditions (i.e., birds belonging to categories A and A⁺) the circadian rhythm in hypothalamic serotonin maintained a positive phase angle of about 16 h. In contrast, birds of category A^? (i.e., in a hypogonadal condition) exhibited a negative phase angle of about 2 h. The present results clearly suggest that the internal phase relationship between the circadian rhythms in hypothalamic serotonin and dopamine might play a crucial role in strategizing and conferring a particular reproductive status to the birds. The role of circadian mechanisms involving circulating thyroid hormones in conferring reproductive status is completely ruled out, as no definite internal phase angle between these two hormonal rhythms was witnessed vis‐à‐vis different treatment groups. The testosterone peaks always occurred at the same time irrespective of breeding status of the bird, but with significant variation in its amplitude (high in hypergonadal and low in hypogonadal condition). It is suggested that administration of 5‐HTP and L‐DOPA at specific time interval and variation in pineal functions that modulate reproductive responses also alter the circadian pattern (acrophase and amplitude) of hypothalamic serotonin and dopamine, maintaining a specific phase relation between these cycles and breeding status. These findings strengthen our previous reports that a specific circadian phase relation of serotonergic and dopaminergic oscillations regulates reproduction. The present study strongly supports interdependence and specific relation of the two systems (gonadal activity and circadian pattern/phase relation of neural oscillation) in both natural and experimentally simulated conditions.     

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.     

Food availability affects circadian clock-controlled activity and Zugunruhe in the night migratory male blackheaded bunting (Emberiza melanocephala)

This study investigated the functional linkage between food availability and activity behavior in the Palaearctic Indian night migratory blackheaded bunting (Emberiza melanocephala) subjected to artificial light-dark (LD) cycles. Two experiments were performed on photosensitive birds. In the first one, birds were exposed to short days (LD 10/14; Experiment 1A), long days (LD 13/11; Experiment 1B), or increasing daylengths (8 to 13?h light/d; Experiment 1C) and presented with food either for the whole or a restricted duration of the light period. In Experiments 1A and 1B, illumination of the light and dark periods or of the dark period, alone, was changed to assess the influence of the light environment on direct and circadian responses to food cycles. In the second experiment, birds were exposed to LD 12/12 or LD 8/16 with food availability overlapping with the light (light and food presence in phase) or dark period (light and food presence in antiphase). Also, birds were subjected to constant dim light (LL(dim)) to examine the phase of the activity rhythms under synchronizing influence of the food cycles. Similarly, the presentation of food ad libitum (free food; FF) during an experiment examined the effects of the food-restriction regimes on activity rhythms. A continuous measurement of the activity-rest pattern was done to examine both the circadian and direct effects of the food and LD cycles. Measurement of activity at night enabled assessment of the migratory phenotype, premigratory restlessness, or Zugunruhe. The results show that (i) light masked the food effects if they were present together; (ii) birds had a higher anticipatory activity and food intake during restricted feeding conditions; and (iii) food at night alone reduced both the duration and amount of Zugunruhe as compared to food during the day alone. This suggests that food affects both the daily activity and seasonal Zugunruhe, and food cycles act as a synchronizer of circadian rhythms in the absence of dominant natural environmental synchronizers, such as the light-dark cycle.     

Ultradian, circahoral and circadian structures in endothermic vertebrates and humans

1. For more than 30 years many studies have been carried out concerning rhythms with periods approaching 24 hr (circadian rhythms). 2. The latter have been demonstrated as resulting from environmental 24 hr synchronizers (zeitgebers), but they usually persist in the absence of a 24 hr synchronization, which proves their endogenous nature. 3. Biological rhythms with periods less than 20 hr (ultradian rhythms) and particularly those approaching 1 hr (circahoral rhythms) have been determined: for motility, rest-activity, sleep phases, endocrine secretions and other physiological functions. 4. These ultradian and circahoral rhythms have been found in rodents, birds, monkeys and humans. 5. Existing at all stages of ontogeny, they have been proved to be endogenous and species and strain specific. 6. As these ultradian rhythms can be influenced by environmental factors and sometimes by circadian rhythms they are not truly periodic, so therefore cannot be computed by the usual processes of mathematical time analysis.     

On Melatonin Suppression from Polychromatic and Narrowband Light

This study investigates the relative strengths of food and light zeitgebers in synchronization of circadian rhythms of Indian weaver birds and the role of the pineal gland in food-induced synchronization of the circadian activity rhythms. Two experiments were performed. In the first experiment, six birds were concurrently exposed for 10 days to PA 12/12 (12 h food present: 12 h food absent) and LD 12/12 (12 h light: 12 h dark). Then, the PA 12/12 cycle was reversed: food was present during the dark period of the LD 12/12 cycle. After 15 days, birds were released into constant dim light (LL_dim). During exposure to overlapping light and food availability periods, birds were active only during the daytime. When light and food availability periods were presented in antiphase, two of six birds became night active. However, with the removal of the light zeitgeber (i.e., under LL_dim), all birds were synchronized with reversed PA 12/12; hence, they were active during the subjective night (i.e., the period corresponding to darkness [ZT12-0] of the preceding LD 12/12). The second experiment examined whether the pineal contributed to the food-induced synchronization. After two weeks of concurrent PA 12/12 and LD 12/12 exposure, six birds were released into LL_dim for 2.5 weeks. Under LL_dim, five of six birds were synchronized to PA 12/12 with the circadian period (tau, τ)?=?24 h. The LD 12/12 was restored, and after seven days, birds were pinealectomized (pinx). After 2.5 weeks, pinx birds were again released into LL_dim for 2.5 weeks. Under LL_dim, pinx birds did not become arrhythmic; instead, they appeared synchronized to PA 12/12 with τ?=?24 h (n?=?4) or ～24 h (n?=?2). We conclude that both food and light act as zeitgebers, although light appears to be the relatively stronger cue when the two are present together, as in the natural environment. We also found that the pineal is not necessary for food-induced synchronization. The findings suggest that food cycles could act as the synchronizer of circadian rhythmicity in biological functions in individuals held in an aperiodic environment.     

Marker rhythms of circadian system function: a study of patients with metastatic colorectal cancer and good performance status

Cancer patients may exhibit normal or altered circadian rhythms in tumor and healthy tissues. Four rhythms known to reflect circadian clock function were studied in 18 patients with metastatic colorectal cancer and good performance status. Rest-activity was monitored by wrist actigraphy for 72 h before treatment, and its circadian rhythm was estimated by an autocorrelation coefficient at 24h and a dichotomy index that compared the activity level when in and out of bed. Blood samples (9-11 time points, 3-6 h apart) were drawn on day 1 and day 4 of the first course of chronochemotherapy (5-fluorouracil: 800 mg/m2/day; folinic acid: 300 mg/m2/day; oxaliplatin: 25 mg/m2/day). Group 24h rhythms were validated statistically for plasma concentrations of melatonin, 6-alpha-sulfatoxymelatonin, and cortisol and for lymphocyte counts. Significant individual 24h rhythms were displayed in melatonin by 15 patients, cortisol by seven patients, lymphocytes by five patients, and prominent circadian rhythms in activity were displayed by 10 patients; only one patient exhibited significant rhythms in all the variables. The results suggest the rhythms of melatonin, cortisol, lymphocytes, and rest/activity reflect different components of the circadian system, which may be altered differently during cancer processes. Such 24h rhythm alterations appeared to be independent of conventional clinical factors.     

Circadian rhythms of finches under steadily changing light intensity: Are self-sustaining circadian rhythms self-excitatory?

Summary Finches (Chloris chloris, Fringilla montifringilla) showed clear freerunning circadian rhythms when exposed to constant dim light. Increasing the light intensity by doubling it each day made them become arrhythmic at a certain threshold intensity of illumination, showing continuous locomotor activity. When the light intensity was decreased steadily at the reversed rate, the finches became rhythmic again. 7 out of 8 finches had a clear start in their rhythms, from one day to the next, at light intensities about 4 times higher than the point where they had become arrhythmic. The last finch started its freerunning circadian rhythm gradually, a few days after the light intensity had reached a constant dim illumination (0.2 lux).The results of all birds are taken as proof of the self-excitatory capacity of the circadian system. This means, it characterizes the dynamics of the system that the clock mechanism is continuously in operation, and not only after a passive reaction to external stimuli exceeds any threshold. Simultaneously, the results of all but one bird allow the evaluation of the contribution of proportional and differential effects of light in the control of circadian rhythmicity. A relative change in light intensity by 100% in the course of one day is nearly equivalent to a change of 100% in the absolute intensity of illumination.     

Marker rhythms of circadian system function: a study of patients with metastatic colorectal cancer and good performance status

Cancer patients may exhibit normal or altered circadian rhythms in tumor and healthy tissues. Four rhythms known to reflect circadian clock function were studied in 18 patients with metastatic colorectal cancer and good performance status. Rest–activity was monitored by wrist actigraphy for 72 h before treatment, and its circadian rhythm was estimated by an autocorrelation coefficient at 24h and a dichotomy index that compared the activity level when in and out of bed. Blood samples (9–11 time points, 3–6 h apart) were drawn on day 1 and day 4 of the first course of chronochemotherapy (5-fluorouracil: 800 mg/m²/day; folinic acid: 300 mg/m²/day; oxaliplatin: 25 mg/m²/day). Group 24h rhythms were validated statistically for plasma concentrations of melatonin, 6-α-sulfatoxymelatonin, and cortisol and for lymphocyte counts. Significant individual 24h rhythms were displayed in melatonin by 15 patients, cortisol by seven patients, lymphocytes by five patients, and prominent circadian rhythms in activity were displayed by 10 patients; only one patient exhibited significant rhythms in all the variables. The results suggest the rhythms of melatonin, cortisol, lymphocytes, and rest/activity reflect different components of the circadian system, which may be altered differently during cancer processes. Such 24h rhythm alterations appeared to be independent of conventional clinical factors.     

Circadian behavioral and melatonin rhythms in the European starling under light-dark cycles with steadily changing periods: evidence for close mutual coupling?

In European starlings exposed to constant conditions, circadian rhythms in locomotion and feeding can occasionally exhibit complete dissociation from each other. Whether such occasional dissociation between two behavioral rhythms reflects on the strength of the mutual coupling of their internal oscillators has not been investigated. To examine this, as well as to elucidate the role of melatonin in this system, we simultaneously measured the rhythms of locomotion, feeding and melatonin secretion in starlings exposed to light-dark (LD) cycles of low intensity with steadily changing periods (T). In birds initially entrained to T 24 LD cycles (12L:12D, 10:0.2 lx), beginning on day 15, T was either lengthened to 26.5 h (experiment 1) or shortened to T 21.5 h (experiment 2) by changing the daily dark period 4 min each day. After 18 and 19 cycles of T 26.5 and T 21.5, respectively, birds were released into constant dim light conditions (LL(dim); 0.2 lx) for about 2 weeks. Locomotor and feeding rhythms were continuously recorded. Plasma melatonin levels were measured at three times: in T 24, when T equaled 26 or 22 h and at the end of T 26.5 or T 21.5 exposure. The results show that, contrary to our expectations, the three rhythms were not dissociated. Rather they remained synchronized and changed their phase angle difference with the light zeitgeber concomitantly and at the same rate. The melatonin rhythm stayed in synchrony with the behavioral rhythms and as a consequence, peaked either during day or at night, depending on the phase relationship between the activity rhythm and the zeitgeber cycle.     

Malate Dehydrogenase Activity of Rat Testis: Circadian Rhythm and its Ontogeny

Malate dehydrogenase activity and soluble protein content in testes from rats exposed to a 14:00 h light:10:00 h dark photoperiod, have been determined every two or four hours over a 24 hour period in 5, 15, 25 and 120 day-old rats. By using the Cosinor method, the ontogeny of an unimodal rhythm was studied for MDH activity and soluble protein content in testis. In 5 and 15 day-old rats, the MDH acrophases were recorded around 19:00 h and 17:00 h, respectively. Rats aged 25 and 110 days showed the MDH acrophases during the dark period. An inversion of the MDH circadian rhythms was detected in 25 day-old compared to those of 5 and 15 day-old rats. An inversion of the protein circadian rhythm was also detected at 15 days compared to that at 5 days. These inversions persist in the adult rats. The amplitude of the MDH and protein rhythms reached the lowest value in adulthood. The mean daily value of testicular MDH increased between day 5 and 15, decreasing at day 35 and remaining unchanged until adulthood. The variation of malate dehydrogenase activity, soluble protein content levels, and the circadian rhythm parameters during the maturation process may be related to gonad development.     

Malate Dehydrogenase Activity of Rat Testis: Circadian Rhythm and its Ontogeny

Malate dehydrogenase activity and soluble protein content in testes from rats exposed to a 14:00 h light:10:00 h dark photoperiod, have been determined every two or four hours over a 24 hour period in 5, 15, 25 and 120 day-old rats. By using the Cosinor method, the ontogeny of an unimodal rhythm was studied for MDH activity and soluble protein content in testis. In 5 and 15 day-old rats, the MDH acrophases were recorded around 19:00 h and 17:00 h, respectively. Rats aged 25 and 110 days showed the MDH acrophases during the dark period. An inversion of the MDH circadian rhythms was detected in 25 day-old compared to those of 5 and 15 day-old rats. An inversion of the protein circadian rhythm was also detected at 15 days compared to that at 5 days. These inversions persist in the adult rats. The amplitude of the MDH and protein rhythms reached the lowest value in adulthood. The mean daily value of testicular MDH increased between day 5 and 15, decreasing at day 35 and remaining unchanged until adulthood. The variation of malate dehydrogenase activity, soluble protein content levels, and the circadian rhythm parameters during the maturation process may be related to gonad development.