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.     

Ultradian and circadian compartmentalization of respiratory and metabolic exchanges in small laboratory vertebrates

Carbon dioxide emission (VCO2) taken as an index of respiratory and metabolic exchanges, was continuously recorded during 4-30 consecutive days in 100 quail, 87 chicks, 347 rats, 665 mice and 70 guinea-pigs which were under controlled environmental parameters. Harmonic analysis, fast Fourier transform, chi-square periodograms, peak and trough intervals were computed with VCO2 values obtained with CO2 concentrations sampled every 20 min on the CO2 recordings. In LD 12:12 alternation, circadian rhythms were observed in all quail, chicks, rats and mice, but only in 80% of the guinea-pigs. Ultradian VCO2 rhythms, with periods which show statistically significant interspecies differences, were assessed. For each of the 5 species these computed periods, which were the same in LL and DD, were: 1.17 h for quail and chickens, 1.25 h for rats, 1.50 h for mice and 1.0 h for guinea-pigs. In LD 12:12 these periods were different during L and D in quail, chicks, rats and mice, but not in guinea-pigs. The amplitudes of these ultradian variations were, according to the species, 10-20% of their mean VCO2 levels. These ultradian rhythms persist in the absence (or masking) of circadian rhythms, e.g. in LD 12:12 in 20% of guinea-pigs and in LL in 87% of Japanese quail and in 23% of Sprague-Dawley rats. Moreover, these ultradian rhythms persist during starvation, locomotor activity restraint and ageing. These ultradian VCO2 cycles which are related to rest-activity variations appear to be basic physiological rhythms with a genetic origin.     

Ultradian and circadian CO2 emission variations in nocturnal and diurnal animals exposed to a light stimulus

1. Carbon dioxide emission (VCO2) has been continuously recorded in three laboratory animal species (Sprague-Dawley rats, Japanese quail, Hartley guinea-pigs) which differ by their nocturnal and diurnal activities. A 100 lux stimulus has been delivered at various time intervals. 2. A regular alternation of 12, 3 or 1.5 hr light (L) and darkness (D) gives VCO2 circadian and ultradian rhythms of 24, 6 or 3 hr periods, respectively, in quail and rats. 3. Such circadian and ultradian LD rhythms are not induced in all guinea-pigs. 4. The amplitudes of the VCO2 responses are greatest at D----L when the animals have a maximum diurnal activity and at L----D when their maximum activity is nocturnal. 5. Interactions between circadian and ultradian rhythms are seen in all LD experiments, as well as in continuous light (LL) or continuous dark (DD). 6. No more well-marked or even inverted VCO2 responses to the light stimuli may occur after several days of exposure to these LD alternations.     

Changes in rhythmicities of ambulatory and drinking activities after hypophysectomy in rats.

Effects of hypophysectomy on circadian rhythms of ambulatory and drinking activities in adult male rats were automatically recorded and investigated with a Gundai-type ambulodrinkometer. The rats were maintained under LL conditions following an LD condition. When free-running rhythms had stabilized, the rats were hypophysectomized. The rhythmicities of both activities became indistinct over the 2-4 weeks following surgery, and then gradually recovered. At this time phase shifts (phase advance) were observed in the hypophysectomized rats, while these changes were not observed in sham-operated rats. All rats entrained to lighting when kept under LD conditions again. These results suggest that the pituitary does not play an essential role in maintaining circadian rhythms, but does function as an important subordinal oscillator.     

Effects of exogenous melatonin on sun-compass orientation of homing pigeons

Experiments were performed to test whether melatonin plays a role in sun-compass orientation of homing pigeons. Birds were kept for a period of time in dim continuous light (LL) or in artificial light-dark (LD) cycles and then released under the sun from unfamiliar sites. Control birds in dim LL were oriented homeward in all cases. Birds with melatonin implants in LD were capable of a correct use of the sun compass at release. Birds with melatonin implants in dim LL, on the contrary, performed very poorly in orientation. The present results demonstrate for the first time that melatonin is involved in the control of the circadian rhythms underlying sun-compass orientation in birds.     

Circadian Locomotor Activity Rhythms in the African Clawed Frog, Xenopus laevis: The Role of the Eye and the Hypothalamus

The effects of hypothalamic lesioning and removal of the eyes on locomotor activity rhythms of African clawed frog, Xenopus laevis were examined under light-dark cycles (LD12:12) and constant conditions. Frogs were kept individually and the activity rhythms at the bottom layer of water tank were recorded by means of the infrared photocells. Intact frogs displayed clear entrained nocturnal activity and expressed freerunning activity rhythms in constant darkness (DD), while some frogs did not freerun under co nstant dim light (dimLL) and constant light (LL). Freerunning periods in intact frogs were significantly shorter in dimLL than in DD. Although freerunning periods were shortened after blinding in same individuals, no significant changes in the freerunning periods were observed after blinding under dimLL and LL. When electrolytic lesions to the hypothalamus were performed, all frogs with more than 70% damage of the SCN abolished freerunning rhythms and in frogs with less than 70% damage, 57% of the animals became arrhythmic. In conclusion, (1) There is a circadian pacemaker somewhere outside the eyes, and it is probably situated in the hypothalamusincluding the SCN. (2) Both the eyes and the SCN are involved in the circadian system of the frogs.     

Circadian Locomotor Activity Rhythms in the African Clawed Frog,Xenopus laevis: The Role of the Eye and the Hypothalamus

The effects of hypothalamic lesioning and removal of the eyes on locomotor activity rhythms of African clawed frog, Xenopus laevis were examined under light-dark cycles (LD12:12) and constant conditions. Frogs were kept individually and the activity rhythms at the bottom layer of water tank were recorded by means of the infrared photocells. Intact frogs displayed clear entrained nocturnal activity and expressed freerunning activity rhythms in constant darkness (DD), while some frogs did not freerun under co nstant dim light (dimLL) and constant light (LL). Freerunning periods in intact frogs were significantly shorter in dimLL than in DD. Although freerunning periods were shortened after blinding in same individuals, no significant changes in the freerunning periods were observed after blinding under dimLL and LL. When electrolytic lesions to the hypothalamus were performed, all frogs with more than 70% damage of the SCN abolished freerunning rhythms and in frogs with less than 70% damage, 57% of the animals became arrhythmic. In conclusion, (1) There is a circadian pacemaker somewhere outside the eyes, and it is probably situated in the hypothalamusincluding the SCN. (2) Both the eyes and the SCN are involved in the circadian system of the frogs.     

Effects of constant darkness and constant light on circadian organization and reproductive responses in the ram

The relationship between circadian rhythms in the blood plasma concentrations of melatonin and rhythms in locomotor activity was studied in adult male sheep (Soay rams) exposed to 16-week periods of short days (8 hr of light and 16 hr of darkness; LD 8:16) or long days (LD 16:8) followed by 16-week periods of constant darkness (dim red light; DD) or constant light (LL). Under both LD 8:16 and LD 16:8, there was a clearly defined 24-hr rhythm in plasma concentrations of melatonin, with high levels throughout the dark phase. Periodogram analysis revealed a 24-hr rhythm in locomotor activity under LD 8:16 and LD 16:8. The main bouts of activity occurred during the light phase. A change from LD 8:16 to LD 16:8 resulted in a decrease in the duration of elevated melatonin secretion (melatonin peak) and an increase in the duration of activity corresponding to the changes in the ratio of light to darkness. In all rams, a significant circadian rhythm of activity persisted over the first 2 weeks following transfer from an entraining photoperiod to DD, with a mean period of 23.77 hr. However, the activity rhythms subsequently became disorganized, as did the 24-hr melatonin rhythms. The introduction of a 1-hr light pulse every 24 hr (LD 1:23) for 2 weeks after 8 weeks under DD reinduced a rhythm in both melatonin secretion and activity: the end of the 1-hr light period acted as the dusk signal, producing a normal temporal association of the two rhythms. Under LL, the 24-hr melatonin rhythms were disrupted, though several rams still showed periods of elevated melatonin secretion. Significant activity rhythms were either absent or a weak component occurred with a period of 24 hr. The introduction of a 1-hr dark period every 24 hr for 2 weeks after 8 weeks under LL (LD 23:1) failed to induce or entrain rhythms in either of the parameters. The occurrence of 24-hr activity rhythm in some rams under LL may indicate nonphotoperiodic entrainment signals in our experimental facility. Reproductive responses to the changes in photoperiod were also monitored. After pretreatment with LD 8:16, the rams were sexually active; exposure to LD 16:8, DD, or LL resulted in a decline in all measures of reproductive function. The decline was slower under DD than LD 16:8 or LL.(ABSTRACT TRUNCATED AT 400 WORDS)     

Circadian organization of running-wheel activity, food intake and drinking of old male rats

Circadian rhythms of running-wheel activity, food intake and drinking were monitored in old male rats of Long-Evans strain over 22 months of age in both entrained (light:dark 12:12, LD) and free running condition (continuous illumination, LL) and were compared with those of young adult male rats of 3.5 to 6.5 months of age. Twenty-four hour distribution of running activity, feeding events and licking events of young rats as well as old rats showed bi- or tri-modal patterns during the 12 hr dark period of the LD schedule. In the light period, 2 out of 8 old rats, 6 out of 10 old rats and 1 out of 6 old rats had 1 or 2 medium or high peaks in running activity, feeding events and licking events, respectively, leading to equal distribution between the dark and light period. In the LD schedule, old rats showed a decrease in running-wheel activity, its patterns and power spectra, a decrease in feeding events and its power spectra in 6 rats which lost circadian rhythms and increase in feeding events and its power spectra in 4 rats which still showed circadian rhythms and increase in licking events. LL suppressed running-wheel activity, its patterns and power spectra, licking events and its power spectra and feeding events in young rats. However, LL could suppress only feeding events of 4 rats which still showed circadian rhythms and licking events and its spectral level in old rats. The possible causes of decreased response to LL in old rats and its implication are discussed.     

Circadian rhythms of demand-feeding and locomotor activity in rainbow trout

Under free-running conditions, most rainbow trout displayed circadian feeding rhythms, although the expression of circadian rhythmicity depended on the experimental condition: 16·7% of fish under constant dim light (LL dim), 66·1% under a 45 :45 min light-dark cycle (LD pulses), and 83·8% under constant light (LL). Under LD pulses, the period length of the free-running rhythms for feeding was significantly shorter (21·9 ± 0·7 h, n =8) than under LL (26·2 ± 0·3 h, n =10). Period length for locomotor activity under LL was 25·8 ± 0·6 h ( n =4). Under LD conditions, the daily demand-feeding profile was always confined to the light phase and chiefly composed of two main episodes, directly after lights on (light elicited) and in anticipation to lights off (endogenous). Contrasting to feeding, the diel locomotor activity profile varied remarkably: a diurnal activity pattern at the bottom, while a clearly nocturnal pattern at the surface. These results contribute to a better understanding of feeding and locomotor rhythms of rainbow trout, providing evidence for the existence of a biological clock involved in their circadian control. This finding contrasts with the previously recorded lack of an endogenous oscillator in the pineal organ driving the rhythmic secretion of melatonin, which suggests different locations from the pineal for the circadian pacemakers in this species.     

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.     

GIGANTEA and SPINDLY genes linked to the clock pathway that controls circadian characteristics of transpiration in Arabidopsis

Several "clock" genes that regulate the circadian system in Arabidopsis thaliana have been identified. The GIGANTEA (GI) gene has been shown to participate in the circadian system that is linked to overt rhythms in gene expression, leaf movements, hypocotyl elongation, and photoperiodic control of flowering in Arabidopsis. During continuous light (LL), circadian expression patterns in gi-2 mutants show reduced amplitudes and altered period lengths when compared with controls. Rhythms in stomatal function, such as transpiration, have been shown to be endogenous and persist in constant lighting conditions. In order to test for a physiologic variable that might be affected by the circadian clock via the GI gene, we compared circadian characteristics of transpiration between three Arabidopsis mutants (gi-2, spy-4, spy-4/gi-2) and wild-type (WT) controls in synchronized (LD for 2.5d) and free-running (LL for 3d) conditions. Each genotype showed a significant circadian rhythm in LD at p < 0.001, with acrophases located near the middle of the daily 14h L-span, with average amplitudes for WT: 18.9%, gi-2: 16.1%, spy-4: 7.7%, and spy-4/gi-2: 5.3%. On the first day in LL, the circadian amplitude was dramatically reduced to 3.1% for gi-2 compared with WT (11.9%), while amplitudes for spy-4 (6.9%) and spy-4/gi-2 (5.7%) were not significantly changed from LD. The amplitude for gi-2 remained low during days 2 (4.2%) and 3 (2.1%) in LL, while it slowly dampened for the WT (8.6 and 6.6%). The amplitudes for spy-4 (6.6%) and spy-4/gi-2 (5.6%) on day 2 in LL were indistinguishable from the LD span, but finally dampened on day 3 in LL (1.9 and 2.3%, respectively). These data suggest that transpiration is a physiologic variable controlled by a circadian system that involves both the GI and SPY proteins.     

Locomotory and stridulatory circadian rhythms in the cricket, Teleogryllus commodus

Male crickets of the species Teleogryllus commodus express circadian rhythms in both their stridulatory and locomotory behaviours. Both forms of activity show the same free-running period (τ) in either DD (23·4 hr) or LL (25·1 hr). Although some overlap is seen between periods of locomotion and stridulation, the majority of each activity is found in different phases of the circadian cycle: locomotion occurs mainly in the subjective day and stridulation in the subjective night. Entraining LD cycles with photoperiods of 12 hr produce exogenous effects that can obscure endogenous components of the rhythms. Red light (λ>600 nm) causes the period to lengthen and RD cycles can entrain both rhythms. Single white light pulses of 2 or 6 hr did not produce significant phase shifts, but did cause τ to shorten when given in the subjective night. The significance of these observations is discussed. Given the results obtained to date, it is not likely that each rhythm is under the control of a separate circadian pacemaker.     

Circadian organization of a subarctic rodent, the northern red-backed vole (Clethrionomys rutilus)

Arctic and subarctic environments are exposed to extreme light: dark (LD) regimes, including periods of constant light (LL) and constant dark (DD) and large daily changes in day length, but very little is known about circadian rhythms of mammals at high latitudes. The authors investigated the circadian rhythms of a subarctic population of northern red-backed voles (Clethrionomys rutilus). Both wild-caught and third-generation laboratory-bred animals showed predominantly nocturnal patterns of wheel running when exposed to a 16:8 LD cycle. In LL and DD conditions, animals displayed large phenotypic variation in circadian rhythms. Compared to wheel-running rhythms under a 16:8 LD cycle, the robustness of circadian activity rhythms decreased among all animals tested in LL and DD (i.e., decreased chi-squared periodogram waveform amplitude). A large segment of the population became noncircadian (60% in DD, 72% in LL) within 8 weeks of exposure to constant lighting conditions, of which the majority became ultradian, with a few individuals becoming arrhythmic, indicating highly labile circadian organization. Wild-caught and laboratory-bred animals that remained circadian in wheel running displayed free-running periods between 23.3 and 24.8 h. A phase-response curve to light pulses in DD showed significant phase delays at circadian times 12 and 15, indicating the capacity to entrain to rapidly changing day lengths at high latitudes. Whether this phenotypic variation in circadian organization, with circadian, ultradian, and arrhythmic wheel-running activity patterns in constant lighting conditions, is a novel adaptation to life in the arctic remains to be elucidated.     

Effect of short light-dark cycles on young and adult TGR(mREN2)27 rats

Animals placed under short light-dark (LD) cycles show a dissociation of their circadian rhythms. However, this effect has only been studied in Wistar rats and with the motor activity (MA) rhythm. Thus, in the present experiment, we studied in TGR(mREN2)27 (TGR) rats, a strain of hypertensive rats, the effect of a short LD cycle on the circadian rhythms of MA, heart rate (HR), and blood pressure (BP). Our aim was [1] to investigate whether the exposure of TGR rats to a short LD cycle induced a dissociation of their circadian rhythms, [2] to study the effect of short LD cycles on the development of the circadian rhythms of TGR rats, and [3] to compare the effect of short LD cycles on young and adult TGR rats. One group of TGR rats was maintained under LD cycles of 22h periods (group G22). The progress in time of their rhythms was compared to that of TGR rats of the same age that had been kept under LD cycles of 24h periods (group G24). For the third point, the rhythms of a group of 5-week-old TGR rats kept under LD 22h cycles (young rats) were compared to those of a group of 11-week-old TGR rats (adult rats). Results showed that there is a dissociation of the circadian rhythms of all the variables monitored in TGR rats maintained under LD 22h cycles, independent of age. We have also found that group G22 showed a higher increase in BP with age and a higher mortality due to malignant hypertension compared to group G24. Finally, it seems that it is harder for young rats to entrain to short LD cycles than for adult rats, and young rats have a higher mortality due to malignant hypertension than adult rats. In conclusion, we demonstrated that short LD cycles produce a dissociation in the HR, BP, and MA circadian rhythms. The results of this experiment, compared to those previously obtained in Wistar rats, suggest that the light perception, the responses of the circadian system to light, or both are altered in the TGR rats. (Chronobiology International, 18(4), 641-656, 2001)     

Forced desynchronization of dual circadian oscillators within the rat suprachiasmatic nucleus

The circadian clock in the suprachiasmatic nucleus of the hypothalamus (SCN) contains multiple autonomous single-cell circadian oscillators and their basic intracellular oscillatory mechanism is beginning to be identified. Less well understood is how individual SCN cells create an integrated tissue pacemaker that produces a coherent read-out to the rest of the organism. Intercellular coupling mechanisms must coordinate individual cellular periods to generate the averaged, genotype-specific circadian period of whole animals. To noninvasively dissociate this circadian oscillatory network in vivo, we (T.C. and A.D.-N.) have developed an experimental paradigm that exposes animals to exotic light-dark (LD) cycles with periods close to the limits of circadian entrainment. If individual oscillators with different periods are loosely coupled within the network, perhaps some of them would be synchronized to the external cycle while others remain unentrained. In fact, rats exposed to an artificially short 22 hr LD cycle express two stable circadian motor activity rhythms with different period lengths in individual animals. Our analysis of SCN gene expression under such conditions suggests that these two motor activity rhythms reflect the separate activities of two oscillators in the anatomically defined ventrolateral and dorsomedial SCN subdivisions. Our "forced desychronization" protocol has allowed the first stable separation of these two regional oscillators in vivo, correlating their activities to distinct behavioral outputs, and providing a powerful approach for understanding SCN tissue organization and signaling mechanisms in behaving animals.     

Circadian variation of nitric oxide synthase activity in mouse tissue

Endogenous nitric oxide (NO) is an important mediator in the processes that control biological clocks and circadian rhythms. The present study was designed to elucidate if NO synthase (NOS) activity in the brain, kidney, testis, aorta, and lungs and plasma NO_x levels in mice are controlled by an endogenous circadian pacemaker. Male BALB/c mice were exposed to two different lighting regimens of either light-dark 14:10 (LD) or continuous lighting (LL). At nine different equidistant time points (commencing at 09:00h) blood samples and tissues were taken from mice. The plasma and tissue homogenates were used to measure the levels of NO₂+ NO₃^- (NO_x) and total protein. The NO_x concentrations were determined by a commercial nitric oxide synthase assay kit, and protein content was assessed in each homogenate tissue sample by the Lowry method. Nitric oxide synthase activity was calculated as pmol/mg protein/h. The resulting patterns were analyzed by the single cosinor method for pre-adjusted periods and by curve-fitting programs to elucidate compound rhythmicity. The NOS activity in kidneys of mice exposed to LD exhibited a circadian rhythm, but no rhythmicity was detected in mice exposed to LL. Aortic NOS activity displayed 24h rhythmicity only in LL. Brain, testis, and lung NOS activity and plasma NO_x levels displayed 24h rhythms both in LD and LL. Acrophase values of NOS activity in brain, kidney, testis, and lungs were at midnight corresponding to their behavioral activities. Compound rhythms were also detected in many of the examined patterns. The findings suggest that NOS activity in mouse brain, aorta, lung, and testis are regulated by an endogenous clock, while in kidney the rhythm in NOS activity is synchronized by the exogenous signals.     

Leptin-sensitive neurons in the arcuate nuclei contribute to endogenous feeding rhythms

Neural sites that interact with the suprachiasmatic nuclei (SCN) to generate rhythms of unrestricted feeding remain unknown. We used the targeted toxin, leptin conjugated to saporin (Lep-SAP), to examine the importance of leptin receptor-B (LepR-B)-expressing neurons in the arcuate nucleus (Arc) for generation of circadian feeding rhythms. Rats given Arc Lep-SAP injections were initially hyperphagic and rapidly became obese (the "dynamic phase" of weight gain). During this phase, Lep-SAP rats were arrhythmic under 12:12-h light-dark (LD) conditions, consuming 59% of their total daily intake during the daytime, compared with 36% in blank-SAP (B-SAP) controls. Lep-SAP rats were also arrhythmic in continuous dark (DD), while significant circadian feeding rhythms were detected in all B-SAP controls. Approximately 8 wk after injection, Lep-SAP rats remained obese but transitioned into a "static phase" of weight gain marked by attenuation of their hyperphagia and rate of weight gain. In this phase, Arc Lep-SAP rats exhibited circadian feeding rhythms under LD conditions, but were arrhythmic in continuous light (LL) and DD. Lep-SAP injections into the ventromedial hypothalamic nucleus did not cause hyperphagia, obesity, or arrhythmic feeding in either LD or DD. Electrolytic lesion of the SCN produced feeding arrhythmia in DD but not hyperphagia or obesity. Results suggest that both Arc Lep-SAP neurons and SCN are required for generation of feeding rhythms entrained to photic cues, while also revealing an essential role for the Arc in maintaining circadian rhythms of ad libitum feeding independent of light entrainment.     

Food-Entrained Feeding and Locomotor Circadian Rhythms in Rats Under Different Lighting Conditions

It has been suggested that two endogenous timekeeping systems, a light-entrainable pacemaker (LEP) and a food-entrainable pacemaker (FEP), control circadian rhythms. To understand the function and interaction between these two mechanisms better, we studied two behavioral circadian rhythmicities, feeding and locomotor activity, in rats exposed to two conflicting zeitgebers, food restriction and light-dark cycles. For this, the food approaches and wheel-running activity of rats kept under light-dark (LD) 12:12, constant darkness (DD), or constant light (LL) conditions and subjected to different scheduled feeding patterns were continuously recorded. To facilitate comparison of the results obtained under the different lighting conditions, the period of the feeding cycles was set in all three cases about Ih less than the light-entrained or free-running circadian rhythms. The results showed that, depending on the lighting conditions, some components of the feeding and wheel-running circadian rhythms could be entrained by food pulses, while others retained their free-running or light-entrained state. Under LD, food pulses had little influence on the light-entrained feeding and loco-motor rhythms. Under DD, relative coordination between free-running and food-associated rhythms may appear. In both cases, the feeding activity associated with the food pulses could be divided into a prominent phase-dependent peak of activity within the period of food availability and another afterward. Wheel-running activity mainly followed the food pulses. Under LL conditions, the food-entrained activity consisted mainly of feeding and wheel-running anticipatory activity. The results provide new evidence that lighting conditions influence the establishment and persistence of food-entrained circadian rhythms in rats. The existence of two coupled pacemakers, LEP and FEP, or a multioscillatory LEP may both explain our experimental results.     

Societal synchronization in groups of rats or quail submitted to various lighting regimens

Groups of rats or of quail that had been previously synchronized in a light (L = 100 lux) dark (D) phase opposition (PO = LD and DL) were placed together in a L12:D12 or D12:L12 alternation or in continuous light (LL) or continuous darkness (DD). Emission of carbon dioxide (VCO2) which was continuously recorded in groups of individuals placed in respiratory chambers under controlled environmental conditions allows an index of their overall respiratory and metabolic exchanges to be found. In PO animals placed in LD or DL, the VCO2 circadian light dark synchronization comes back less quickly in rats than in quail, and the VCO2 variations at the light dark transitions (L-D and D-L) remain unchanged in rats, but are modified in quail. When PO animals are placed for 18 days in LL or DD, respiratory circadian rhythms disappear except in the grouped rats where they reappear after 4-5 days in DD.