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.     

Effect of pinealectomy on free-running reproductive cycle of tropical spotted munia

Summary The breeding cycle of the tropical spotted munia (Lonchura punctulata) is regulated by the photoperiodic synchronization of an endogenous circannual rhythm. Since the pineal gland has been implicated in circadian periodicity, in an attempt to understand the functioning of the mechanism(s) involved in photoperiodic synchronization of the circannual clock in the spotted munia the effect of pinealectomy on the reproductive cycle was studied in birds maintained in normal entrained (natural day length, NDL) and free-running (constant light, LL) conditions.Results indicate that pinealectomy had no effect in LL but that the reproductive cycle was altered marginally (in the first cycle only), and the body weight cycle drastically, in NDL conditions. It seems that the marginal effects observed on the overt reproductive cycle in the entrained condition may not be through the circannual oscillator itself but may perhaps reflect interference with processes involved in photoperiodic synchronization of the circannual rhythm. Alternatively, these effects could also result from general metabolic disturbances caused in the body by the absence of the pineal gland.Abbreviations LL constant light - NDL natural day length     

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.     

Simultaneous Recording of Circadian Rhythms of Brain and Intraperitoneal Temperatures and Locomotor and Drinking Activities in the Rat

In order to investigate the circadian oscillatory system, the present study performed simultaneous and continuous recordings of brain and intraperitoneal temperatures, drinking and locomotion in rats under light-dark (LD) cycles and continuous dim illumination (dim LL) for a total period of 16 days. Compared to circadian amplitudes under LD, those under dim LL were significantly reduced by 34% for drinking and 50% for locomotion, but were not for brain and intraperitoneal temperatures. On the other hand, means of steady circadian periods during last 10 days under dim LL were all within a close range between 24.2 and 24.3 h in these rhythms. Besides the steady periods, one rat exhibited weak circadian period of 23.7 and 24.6 h, but these multiple frequencies were also equally observed in the four rhythms. The similarity in the periodicities suggests that these temperature and activity rhythms might be driven by a common oscillatory system. Therefore differential reductions in the amplitudes of drinking and loc omotor rhythms might be caused by a masking effect of dim LL on their rhythm output-pathways. Hence rats may temporally coordinate various physiological and behavioral functions by such clock system under time cue free environment.     

Simultaneous Recording of Circadian Rhythms of Brain and Intraperitoneal Temperatures and Locomotor and Drinking Activities in the Rat

In order to investigate the circadian oscillatory system, the present study performed simultaneous and continuous recordings of brain and intraperitoneal temperatures, drinking and locomotion in rats under light-dark (LD) cycles and continuous dim illumination (dim LL) for a total period of 16 days. Compared to circadian amplitudes under LD, those under dim LL were significantly reduced by 34% for drinking and 50% for locomotion, but were not for brain and intraperitoneal temperatures. On the other hand, means of steady circadian periods during last 10 days under dim LL were all within a close range between 24.2 and 24.3 h in these rhythms. Besides the steady periods, one rat exhibited weak circadian period of 23.7 and 24.6 h, but these multiple frequencies were also equally observed in the four rhythms. The similarity in the periodicities suggests that these temperature and activity rhythms might be driven by a common oscillatory system. Therefore differential reductions in the amplitudes of drinking and loc omotor rhythms might be caused by a masking effect of dim LL on their rhythm output-pathways. Hence rats may temporally coordinate various physiological and behavioral functions by such clock system under time cue free environment.     

Arrhythmic perch hopping and rhythmic feeding of starlings in constant light: Separate circadian oscillators?

Summary Perch hopping activity and food intake were recorded in starlings in different intensities of continuous illumination (LL), varying from 0.1 to 1000 lux. Circadian rhythmicity in perch hopping disappeared in 10 lux and all higher intensities. In contrast, freerunning circadian rhythms in feeding were always present. In low light intensities, the perch hopping rhythm usually phase leads feeding, increasingly so with shorter circadian period. Locomotor activity may reflect motivational states unrelated to feeding.     

A phase response curve for circannual rhythm in the varied carpet beetle <Emphasis Type="Italic">Anthrenus verbasci</Emphasis>

We know that entrainment, a stable phase relationship with an environmental cycle, must be established for a biological clock to function properly. Phase response curves (PRCs), which are plots of phase shifts that result as a function of the phase of a stimulus, have been created to examine the mode of entrainment. In circadian rhythms, single-light pulse PRCs have been obtained by giving a light pulse to various phases of a free-running rhythm under continuous darkness. This successfully explains the entrainment to light-dark cycles. Some organisms show circannual rhythms. In some of these, changes in photoperiod entrain the circannual rhythms. However, no single-pulse PRCs have been created. Here we show the PRC to a long-day pulse superimposed for 4 weeks over constant short days in the circannual pupation rhythm in the varied carpet beetle Anthrenus verbasci. Because the shape of that PRC closely resembles that of the Type 0 PRC with large phase shifts in circadian rhythms, we suggest that an oscillator having a common feature in the phase response with the circadian clock, produces a circannual rhythm.     

Locomotor Rhythms in the Fiddler Crab, Uca subcylindrica

The locomotor activities of individual specimens of Uca subcylindrica (Stimpson) collected from semi-arid, supratidal habitats in south Texas and northeastern Mexico were studied in the laboratory using periodogram analysis. When crabs were placed under constant darkness (DD) or constant illumination (LL), free-running circadian rhythms were observed in the activity recordings. The locomotor activity of strongly rhythmic crabs in LL has an average period length of 24.4 h. Crabs held in DD express motor rhythms with periods of approximately 24.0 h. In LL the most common wave form for activity is unimodal, while under DD it is bimodal. Recordings under natural illumination (NL) revealed that both period length and the time of maximum activity (phasing) varied through the year. During winter months, the crabs are primarily diurnal with peaks in activity occurring between 0900 and 2100 h and possess a circadian rhythm with a 23.9 h period. During summer, crabs were nocturnal with maximal activity between 1300 and 0600 and a circadian period closer to 24.0 h. In these experiments, the rhythmic locomotor activities of U. subcylindrica are best described as “circadian”. This is unusual for a genus known for its expression of circatidal and circalunidian rhythms.     

Daily Increments of Light Hours Near Vernal Equinox Synchronize Circannual Testicular Cycle of Tropical Spotted Munia

In some long-lived organisms, particularly in tropical birds and migrants that spend part of the year close to the equator, endogenous circannual rhythms have been demonstrated in seasonal events like reproduction, molt, and migration. These, like the circadian rhythms, are expressed only in constant conditions of illumination with a periodicity deviating from 1 yr. If birds followed this periodicity, they would soon be out of phase with the annual calendar and perish and, therefore, they would need to be synchronized. However, almost nothing is known as to how synchronization is achieved in birds. Herein, with the help of a suitable model, viz., the tropical spotted munia and long-term experiments conducted in series over a 5-yr period, we provide direct evidence for the first time indicating that the segment of annual photocycle with maximal rate of increase prior to vernal equinox (approximately between mid-February and mid-March) synchronizes the circannual reproductive cycle with the monsoon period of ample food supply through a phase delay. Data also indicate, contrary to the prevalent view, that birds in the tropics can perceive minor changes in day-length, that birds respond to progressive changes in day-length as distinct from responding to fixed photoperiods of particular durations, and that birds can actually distinguish the quality of the environmental signal, viz., vernal equinox from early spring, or increasing days of spring from decreasing days of autumn. The underlying mechanisms, although yet to be identified, appear to involve a gonado-inhibitory rather than the conventional gonado-stimulatory response to increasing day-length. The photoperiodic responses of spotted munia are distinctly different from that of any “long-day” birds described thus far and do not conform to the prevalent “circadian coincidence” hypothesis of photoperiodism.     

Daily increments of light hours near vernal equinox synchronize circannual testicular cycle of tropical spotted munia

In some long-lived organisms, particularly in tropical birds and migrants that spend part of the year close to the equator, endogenous circannual rhythms have been demonstrated in seasonal events like reproduction, molt, and migration. These, like the circadian rhythms, are expressed only in constant conditions of illumination with a periodicity deviating from 1 yr. If birds followed this periodicity, they would soon be out of phase with the annual calendar and perish and, therefore, they would need to be synchronized. However, almost nothing is known as to how synchronization is achieved in birds. Herein, with the help of a suitable model, viz., the tropical spotted munia and long-term experiments conducted in series over a 5-yr period, we provide direct evidence for the first time indicating that the segment of annual photocycle with maximal rate of increase prior to vernal equinox (approximately between mid-February and mid-March) synchronizes the circannual reproductive cycle with the monsoon period of ample food supply through a phase delay. Data also indicate, contrary to the prevalent view, that birds in the tropics can perceive minor changes in day-length, that birds respond to progressive changes in day-length as distinct from responding to fixed photoperiods of particular durations, and that birds can actually distinguish the quality of the environmental signal, viz., vernal equinox from early spring, or increasing days of spring from decreasing days of autumn. The underlying mechanisms, although yet to be identified, appear to involve a gonado-inhibitory rather than the conventional gonado-stimulatory response to increasing day-length. The photoperiodic responses of spotted munia are distinctly different from that of any "long-day" birds described thus far and do not conform to the prevalent "circadian coincidence" hypothesis of photoperiodism.     

Daily Increments of Light Hours Near Vernal Equinox Synchronize Circannual Testicular Cycle of Tropical Spotted Munia

In some long-lived organisms, particularly in tropical birds and migrants that spend part of the year close to the equator, endogenous circannual rhythms have been demonstrated in seasonal events like reproduction, molt, and migration. These, like the circadian rhythms, are expressed only in constant conditions of illumination with a periodicity deviating from 1 yr. If birds followed this periodicity, they would soon be out of phase with the annual calendar and perish and, therefore, they would need to be synchronized. However, almost nothing is known as to how synchronization is achieved in birds. Herein, with the help of a suitable model, viz., the tropical spotted munia and long-term experiments conducted in series over a 5-yr period, we provide direct evidence for the first time indicating that the segment of annual photocycle with maximal rate of increase prior to vernal equinox (approximately between mid-February and mid-March) synchronizes the circannual reproductive cycle with the monsoon period of ample food supply through a phase delay. Data also indicate, contrary to the prevalent view, that birds in the tropics can perceive minor changes in day-length, that birds respond to progressive changes in day-length as distinct from responding to fixed photoperiods of particular durations, and that birds can actually distinguish the quality of the environmental signal, viz., vernal equinox from early spring, or increasing days of spring from decreasing days of autumn. The underlying mechanisms, although yet to be identified, appear to involve a gonado-inhibitory rather than the conventional gonado-stimulatory response to increasing day-length. The photoperiodic responses of spotted munia are distinctly different from that of any “long-day” birds described thus far and do not conform to the prevalent “circadian coincidence” hypothesis of photoperiodism.     

Circadian Rhythms and time Measurement in Locomotor Activity of the Scorpion Leiurus Quinquestriatus (Buthidae)

The circadian rhythms of locomotor activity of the scorpion Leiurus quinqueslriatus were examined under different light-dark cycles and in free-running conditions. The circadian rhythm is bimodal in LD 12:12 with alternating cycles of temperature (35°-25°C) with high intensity (1300 lux) or in LD 12: 12 with constant temperature 35° C with 300 lux. In LD 12:12 (1300 lux), in long or in short light spans with constant temperature, the bimodal pattern is slightly changed with the appearance of a third minor peak of activity. In free-running conditions, the bimodal rhythm of locomotor activity persists in DD with T about 24 hr, but in LL the rhythm becomes unimodal with T about 24 hr. Cosinor and power spectrum analysis showed the presence of more than one periodic component. It seems that there is a correlation between the range of light regimens, temperature, light intensity and the coincidence of these components. These components are independently entrained by the environmental light cycle. The mechanism of entrainment of components is discussed.     

Locomotor Rhythms in the Fiddler Crab,Uca subcylindrica

The locomotor activities of individual specimens of Uca subcylindrica (Stimpson) collected from semi-arid, supratidal habitats in south Texas and northeastern Mexico were studied in the laboratory using periodogram analysis. When crabs were placed under constant darkness (DD) or constant illumination (LL), free-running circadian rhythms were observed in the activity recordings. The locomotor activity of strongly rhythmic crabs in LL has an average period length of 24.4 h. Crabs held in DD express motor rhythms with periods of approximately 24.0 h. In LL the most common wave form for activity is unimodal, while under DD it is bimodal. Recordings under natural illumination (NL) revealed that both period length and the time of maximum activity (phasing) varied through the year. During winter months, the crabs are primarily diurnal with peaks in activity occurring between 0900 and 2100 h and possess a circadian rhythm with a 23.9 h period. During summer, crabs were nocturnal with maximal activity between 1300 and 0600 and a circadian period closer to 24.0 h. In these experiments, the rhythmic locomotor activities of U. subcylindrica are best described as “circadian”. This is unusual for a genus known for its expression of circatidal and circalunidian rhythms.     

Different circadian pacemakers control feeding and locomotor activity rhythms in European starlings

Summary In higher organisms, many physiological and behavioral functions exhibit daily variations, generated by endogenous circadian oscillators. It is not yet clear whether all the various rhythms that occur within an individual depend on one and the same pacemaker or whether different pacemakers are involved. To examine this question, the feeding and perch-hopping rhythms were measured in European starlings (Sturnus vulgaris) under light-dark cycles and continuous dim light. In dim light, the internal phase relationship between the feeding and perch-hopping rhythms changed systematically as a function of the circadian period, and the two rhythms could even dissociate and show different circadian periods in individuals with extremely long or extremely short circadian periods. Moreover, in some birds kept on lowamplitude light-dark cycles, the rhythm of feeding was synchronized 180° out of phase with the rhythm of locomotor activity. These results strongly suggest that in the European starling the feeding and locomotor activity rhythms are controlled by separate circadian pacemakers.     

Evidence for an endogenous circannual component in the control of the annual gonadal cycle in spotted munia

Abstract

For the first time evidence has been provided for a circannual gonadal cycle in any avian species (male spotted munia Lonchura punctulata, Estrildidae) held on continuous light. A model has thus been rendered available in which the “entraining effects” of photoperiod could be clearly distinguished from its direct “driving effects”.     

Circadian Rhythms of Enzymes' Activity in Mice Tissues During Exposure to Continuous Illumination

Activity rhythms of enzymes were determined in various tissues of C57BL/6J male mice. The determinations were carried out on mice which were kept in 14 hr light: 10 hr dark regimen, and on day 2, day 5 and day 21 during exposure to continuous illumination. Locomotor activity rhythms were followed in light: dark and up to the seventh day in constant light. All the activities exhibited a significant circadian rhythm in the light: dark regimen. During the exposure to continuous illumination, the locomotor activity exhibit a free running circadian rhythm with a consistent 24 hr and 40 min, major period component. At the same time recording the rhythms of enzyme activity; enzymes exhibited various formats of response which differed from those of the locomotor activity. The results suggest that rhythms of enzyme activity, as well as the desynchronization of the rhythms, are not enzyme specific.     

Rhythms of reproduction,metabolism and coat growth in deer: a model for all non-domesticated seasonal ungulates?

Seasonally-breeding deer living in cool temperate environments exhibit pronounced seasonal rhythms of voluntary food intake, growth rate and fattening and the growth and development of the coat. All of these rhythms are considered to be entrained by photoperiod and melatonin, although so far this has only been demonstrated to be the case in one species, the red deer. This paper reviewed current data on seasonal rhythms in several species of deer. A comparison of two species with different breeding seasons, the red deer and the Pere David's deer, indicated that seasonal reproduction, appetite and coat growth rhythms are linked and may be controlled by a single circannual rhythm generator. All of these seasonal rhythms should be considered as adaptive for species living in cool temperate environments with marked fluctuations in food supply and climatic conditions.     

Circadian and Circannual Rhythms of Hormonal Variables in Elderly Men and Women

A group of fourteen men (73 ± 5 yr of age), and eighteen women (77 ± 7 yr of age) institutionalized at the Berceni Clinical Hospital, Bucharest, Romania, were studied over a 24-hr span once during each season (winter, spring, summer and fall). All subjects followed a diurnal activity pattern with rest at night and ate three meals per day with breakfast at about 0830, lunch at about 1300 and dinner at about 1830. The meals were similar, although not identical for all subjects during all seasons. On each day of sampling blood was collected at 4-hr intervals over a 24-hr span. Seventeen hormonal variables were determined by radioimmunoassay. Statistically significant circadian rhythms were detected and quantitated by population mean cosinor analysis in pooled data from all four seasons in both sexes for ACTH, aldosterone, Cortisol, C-peptide, dehydroepiandrosterone-sulfate (DHEA-S), immunoreactive insulin, prolactin, 17-OH progesterone, testosterone, total T₄ and TSH. In women, estradiol and progesterone also were determined and showed a circadian rhythm during all seasons. Total T, and FSH showed circadian rhythm detection by cosinor analysis in the men only; LH showed no consistent circadian rhythm as group phenomenon in men or women.

A circannual rhythm was detected using the circadian means of each subject at each season as input for the population mean cosinor in the women for ACTH, C-peptide, DHEA-S, FSH, LH, progesterone, 17-OH progesterone and TSH. In the men, a circannual rhythm was detected for ACTH, FSH, insulin, LH, testosterone and T₃. There were phase differences between men and women in ACTH, FSH and LH. In those functions in which both the circadian and circannual rhythms were statistically significant, a comparison of the amplitudes showed in the women a higher circannual rather than circadian amplitude for DHEA-S. In 17-OH progesterone, TSH and C-peptide, the circadian amplitude in women was larger. In men, the circannual amplitude of T₃ was larger than the circadian amplitude and in insulin the circadian amplitude was larger than the circannual amplitude. There was no statistically significant difference between the circadian and circannual amplitudes in the women in ACTH and progesterone and in the men in ACTH and testosterone.