Circadian Rhythms in Heart Rate,Motility, and Body Temperature of Wild‐type C57 and eNOS Knock‐out Mice Under Light‐dark,Free‐run,and After Time Zone Transition

The nitric oxide (NO) system is involved in the regulation of the cardiovascular system in controlling central and peripheral vascular tone and cardiac functions. It was the aim of this study to investigate in wild‐type C57BL/6 and endothelial nitric oxide synthase (eNOS) knock‐out mice (eNOS‐/‐) the contribution of NO on the circadian rhythms in heart rate (HR), motility (motor activity [MA]), and body temperature (BT) under various environmental conditions. Experiments were performed in 12∶12 h of a light:dark cycle (LD), under free‐run in total darkness (DD), and after a phase delay shift of the LD cycle by ?6 h (i.e., under simulation of a westward time zone transition). All parameters were monitored by radiotelemetry in freely moving mice. In LD, no significant differences in the rhythms of HR and MA were observed between the two strains of mice. BT, however, was significantly lower during the light phase in eNOS‐/‐ mice, resulting in a significantly greater amplitude. The period of the free‐running rhythm in DD was slightly shorter for all variables, though not significant. In general, rhythmicity was greater in eNOS‐/‐ than in C57 mice both in LD and DD. After a delay shift of the LD cycle, HR and BT were resynchronized to the new LD schedule within 5–6 days, and resynchronization of MA occurred within 2–3 days. The results in telemetrically instrumented mice show that complete knock‐out of the endothelial NO system—though expressed in the suprachiasmatic nuclei and in peripheral tissues—did not affect the circadian organization of heart rate and motility. The circadian regulation of the body temperature was slightly affected in eNOS‐/‐ mice.     

Endothelial nitric oxide is not involved in circadian rhythm generation of blood pressure: experiments in wild-type C57 and eNOS knock-out mice under light-dark and free-run conditions

Endothelial nitric oxide synthase knock out mice (eNOS-/-) are mildly hypertensive in comparison to wild-type (WT) mice. Hypertension in eNOS-/- mice is partly the result of an increase in peripheral resistance due to the absence of the vasodilatory action of NO. No data are available for these animals regarding the 24 h blood pressure profile under the 12:12 h light-dark cycle (LD) and constant dark (DD) conditions. Therefore, this study aimed to investigate by radiotelemetry the circadian rhythms in systolic blood pressure (SBP) and diastolic blood pressure (DBP) of six eNOS-/- mice and five wild-type mice under LD and DD. Data were collected beginning 3 wks after operation (implantation of sensor) for 2 wks under LD and for another 2 wks thereafter under DD. Our results show that eNOS-/- mice were hypertensive under all experimental conditions. SBP and DBP were significantly higher by about 15% in eNOS-/- mice. No differences were found in the pattern of the circadian rhythms, rhythmicity, or period lengths during LD or DD. The genetic deletion of eNOS seems to lead to higher SBP and DBP, but the circadian blood pressure pattern is still preserved with higher values during the night (active phase) and lower values during the daytime (rest phase). Thus, endothelial-derived NO plays an important role in the regulation of vascular tone and haemodynamics, but it is not important for the circadian organization of SBP and DBP.     

Endothelial Nitric Oxide Is Not Involved in Circadian Rhythm Generation of Blood Pressure: Experiments in Wild‐Type C57 and eNOS Knock‐Out Mice under Light‐Dark and Free‐Run Conditions

Endothelial nitric oxide synthase knock out mice (eNOS‐/‐) are mildly hypertensive in comparison to wild‐type (WT) mice. Hypertension in eNOS‐/‐ mice is partly the result of an increase in peripheral resistance due to the absence of the vasodilatory action of NO. No data are available for these animals regarding the 24 h blood pressure profile under the 12:12 h light‐dark cycle (LD) and constant dark (DD) conditions. Therefore, this study aimed to investigate by radiotelemetry the circadian rhythms in systolic blood pressure (SBP) and diastolic blood pressure (DBP) of six eNOS‐/‐ mice and five wild‐type mice under LD and DD. Data were collected beginning 3 wks after operation (implantation of sensor) for 2 wks under LD and for another 2 wks thereafter under DD. Our results show that eNOS‐/‐ mice were hypertensive under all experimental conditions. SBP and DBP were significantly higher by about 15% in eNOS‐/‐ mice. No differences were found in the pattern of the circadian rhythms, rhythmicity, or period lengths during LD or DD. The genetic deletion of eNOS seems to lead to higher SBP and DBP, but the circadian blood pressure pattern is still preserved with higher values during the night (active phase) and lower values during the daytime (rest phase). Thus, endothelial‐derived NO plays an important role in the regulation of vascular tone and haemodynamics, but it is not important for the circadian organization of SBP and DBP.     

Circadian organization in male mice lacking the gene for endothelial nitric oxide synthase (eNOS-/-)

Circadian (approximately 24 h) rhythms in physiology and behavior are generated by the bilateral suprachiasmatic nucleus (SCN) of the anterior hypothalamus. For these endogenous rhythms to be synchronized with the external environment, light information must be transmitted to pacemaker cells within the SCN. This transmission of light information is accomplished via a direct retino-hypothalamic tract (RHT). Nitric oxide (NO), an endogenous gas that functions as a neurotransmitter, has been implicated as a messenger necessary for photic entrainment. Three isoforms of the enzyme that form NO, NO synthase, have been identified (a) in neurons (nNOS), (b) in the endothelial lining of blood vessels (eNOS), and (c) as an inducible form in macrophages (iNOS). The present study was undertaken to determine the specific role of eNOS in circadian organization and photic entrainment. Wild-type (WT) and eNOS-/- mice were initially entrained to a 14:10 light:dark (LD) cycle. After 3 weeks, the LD cycle was phase advanced. After an additional 3 weeks, animals were held in constant darkness (DD). eNOS-/- animals did not exhibit a deficit in the ability to entrain to the LD cycle, phase-shift locomotor activity, or free-run in constant conditions. Animals held in DD were killed after light exposure during either the subjective day or the subjective night to assess c-fos induction in the SCN. Light exposure during the subjective night increased c-fos protein expression in the SCN of both WT and eNOS-/- mice relative to animals killed after light exposure during the subjective day. Taken together, these findings suggest that endothelial isoform of NOS may not be necessary for photic entrainment in mice.     

Effect of NO synthase inhibition on cardiovascular circadian rhythms in wild-type and eNOS-knock-out mice

Cardiovascular functions (blood pressure [BP], heart rate [HR]) were radiotelemetrically studied in endothelial nitric oxide synthase (NOS) knock-out mice (eNOS-/-) and their wild type C57BL/6 (WT) controls. Studies were performed with and without inhibition of the NOS with the non-specific inhibitor N(omega)-Nitro-L-Arginin-Methylester (L-NAME). Six eNOS-/-and five WT mice, kept under a light:dark schedule of 12:12 h (lights on 07:00 h), were treated with L-NAME in tap water containing different concentrations (94, 282, and 940 mg/kg) each for three days. Under control conditions, the eNOS-/-mice are mildly hypertensive in comparison to WT. L-NAME increased systolic [SBP] and diastolic [DBP] blood pressures in WT mice to the levels of eNOS-/-mice after two days of L-NAME application with no dose-dependency, whereas L-NAME had no effects on SBP and DBP in eNOS-/-mice. In neither mouse strain were the circadian rhythms in BP and HR affected by drug treatment. The similarity of the 24 h BP profiles in eNOS-/-and L-NAME-treated WT mice support the notion that only the enothelial NOS and not other NOS isoenzymes are of importance for hypertension in the knock-out mouse strain.     

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)     

Inhaled NO restores lung structure in eNOS-deficient mice recovering from neonatal hypoxia

We have previously shown that neonatal mice deficient in endothelial nitric oxide synthase (eNOS-/-) are more susceptible to hypoxic inhibition of alveolar and vascular growth. Although eNOS is downregulated, the role of nitric oxide (NO) during recovery after neonatal lung injury is poorly understood. We hypothesized that lung vascular and alveolar growth would remain impaired in eNOS-/- mice during recovery in room air and that NO therapy would augment compensatory lung growth in the eNOS-/- mice during recovery. Mice (1 day old) from heterozygous (eNOS+/-) parents were placed in hypobaric hypoxia (Fi(O2) = 0.16). After 10 days, pups were to recovered in room air (HR group) or inhaled NO (10 parts/million; HiNO group) until 3 wk of age, when lung tissue was collected. Morphometric analysis revealed that the eNOS-/- mice in the HR group had persistently abnormal lung structure compared with eNOS-sufficient (eNOS+/+) mice (increased mean linear intercept and reduced radial alveolar counts, nodal point density, and vessel density). Lung morphology of the eNOS+/- was not different from eNOS+/+. Inhaled NO after neonatal hypoxia stimulated compensatory lung growth in eNOS-/- mice that completely restored normal lung structure. eNOS+/- mice (HR group) had a 2.5-fold increase in lung vascular endothelial growth factor (VEGFR)-2 protein compared with eNOS+/+ (P < 0.05). eNOS-/- mice (HiNO group) had a 66% increase in lung VEGFR-2 protein compared with eNOS-/- (HR group; P < 0.01). We conclude that deficiency of eNOS leads to a persistent failure of lung growth during recovery from neonatal hypoxia and that, after hypoxia, inhaled NO stimulates alveolar and vascular growth in eNOS-/- mice.     

Pharmacological effects of vinorelbine on body temperature and locomotor activity circadian rhythms in mice

The effects of vinorelbine (VRL) on the circadian rhythms in body temperature and locomotor activity were investigated in unrestrained B6D2F₁ mice implanted with radio-telemetry transmitters. A single intravenous VRL dose (24 or 12 mg/kg) was given at 7 h after light onset (HALO), a time of high VRL toxicity, and resulted in transient suppression of temperature and activity circadian rhythms in mice kept in light-dark (LD) 12h:12h. Such suppression was dose-dependent. It occurred within 1-5 d after VRL dosing. Recovery of both rhythms was partially complete within 5 d following the high dose and within 2 or 3 d after the low dose and was not influenced by suppression of photoperiodic synchronization by housing in continuous darkness. Moreover, VRL induced a dose-dependent relative decrease in amplitude and phase shift of the temperature circadian rhythm. The mesor and amplitude of the activity rhythm were markedly reduced following the VRL administration. The relevance of VRL dosing time was studied in mice housed in LD 12h:12h. Vinorelbine was injected weekly (20 mg/kg/injection) for 3 wk at 6 or 18 HALO. Vinorelbine treatment ablated the rest-activity and temperature rhythms 3-6 d after each dose, with fewer alterations after VRL dosing at 18 HALO compared to 6 HALO, especially for the body temperature rhythm. There was at least partial recovery 1 wk after dosing, suggesting the weekly schedule of drug treatment is acceptable for therapeutic purposes. Our findings demonstrate that VRL can transiently, yet profoundly, alter circadian clock function. Vinorelbine-induced circadian dysfunction may contribute to the toxicokinetics of this and possibly other anticancer drugs.     

Vasopressin deficiency provides evidence for separate circadian oscillators of activity and temperature

Vasopressin-containing Long-Evans and vasopressin-deficient Brattleboro rats were maintained in individual cages while telemetered activity (AC) and body temperature (BT) data were collected. Rats were initially exposed to a 12 h/12-h light/dark cycle (photic zeitgeber) and were allowed ad-libitum access to food and water. Daily feeding, care, and handling (nonphotic zeitgebers) occurred at the beginning of the second hour of the dark cycle. After a 14-day habituation period, rats were subjected to continuous light (LL) or dark (DD) and nonphotic cues were presented irregularly. During the habituation period, both strains exhibited clear 24-h circadian rhythms of AC and BT. In LL or DD, photic cues were removed and nonphotic cues were presented irregularly. There was a shift in the rhythm for Long-Evans animals to 26 h for both AC and BT in LL and 24.6 h in DD. Feeding, care, and handling were seen as minor artifact. In Brattleboro rats, although there were robust 26-h and 24.6-h circadian rhythms of AC in the LL and DD, respectively, BT data were inconsistent and showed sporadic fluctuations. In the BT rhythm of Brattleboro animals, strong peaks were associated with feeding, care, and handling times and trough periods were characterized by a dramatic drop in temperature. This experiment demonstrates that AC and BT are controlled by separate oscillators. In addition, the importance of vasopressinergic fibers in the control of circadian rhythms of BT is evidenced by the loss of circadian rhythms in animals lacking these functional fibers when exposed to free-running paradigms where there is no entrainment of photic or nonphotic oscillators.     

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.     

Circadian rhythms of locomotor activity and temperature selection in sleepy lizards, <Emphasis Type="Italic">Tiliqua rugosa</Emphasis>

This study examined whether the daily rhythms of locomotor activity and behavioural thermoregulation that have previously been observed in Australian sleepy lizards (Tiliqua rugosa) under field conditions are true circadian rhythms that persist in constant darkness (DD) and whether these rhythms show similar characteristics. Lizards held on laboratory thermal gradients in the Australian spring under the prevailing 12-hour light : dark (LD) cycle for 14 days displayed robust daily rhythms of behavioural thermoregulation and locomotor activity. In the 13-day period of DD that followed LD, most lizards exhibited free-running circadian rhythms of locomotor activity and behavioural thermoregulation. The predominant activity pattern displayed in LD was unimodal and this was retained in DD. While mean levels of skin temperature and locomotor activity were found to decrease from LD to DD, activity duration remained unchanged. The present results demonstrate for the first time that this species’ daily rhythm of locomotor activity is an endogenous circadian rhythm. Our results also demonstrate a close correlation between the circadian activity and thermoregulatory rhythms in this species indicating that the two rhythms are controlled by the same master oscillator(s). Future examination of seasonal aspects of these rhythms, may, however, cause this hypothesis to be modified.     

Circadian rhythms of heart rate in freely moving and restrained American lobsters, Homarus americanus

While circadian rhythms of locomotion have been reported in the American lobster, Homarus americanus, it is unclear whether heart rate is also modulated on a circadian basis. To address this issue, both heart rate and locomotor activity were continuously monitored in light-dark (LD) cycles and constant darkness (DD). Lobsters in running wheels exhibited significant nocturnal increases in locomotor activity and heart rates during LD, and these measures were significantly correlated. In DD, most lobsters exhibited persistent circadian rhythms of both locomotion and heart rate. When heart rate was monitored in restrained lobsters in LD and DD, most animals also demonstrated clear daily and circadian rhythms in heart rate. Overall, this is the first demonstration of circadian rhythms of heart rate in H. americanus, the expression of which does not appear to be dependent on the expression of locomotor activity.     

Chronic Administration of Imipramine and Lithium Changes the Phase-Angle Relationship Between the Activity and Core Body Temperature Circadian Rhythms in Rats

Evidence suggests that there is an association between the pathophysiology of depression and a disturbance of circadian rhythms. Accordingly, attention has focused on the possible effects of antidepressants on circadian rhythms. In the present study, we examined the effects of chronic administration of two clinically effective antidepressant agents, imipramine and lithium, on several circadian rhythms in the rat. Activity, core body temperature, and drinking rhythms were assessed in constant darkness (DD) and light-dark (LD) conditions. In DD, lithium significantly lengthened the circadian period of the activity, temperature, and drinking rhythms, while imipramine had no effect. In LD, both drugs significantly delayed the phase of the activity rhythm, but did not change that of the other two rhythms. As a result, the phase-angle differences between the activity and temperature rhythms significantly increased. Neither lithium nor imipramine produced any effect on the resynchronization of these rhythms after an 8-h delay in the LD cycle. These results indicate that although both drugs produced different effects on the circadian period of individual rhythms, both caused a relative phase advance of the temperature rhythm as compared to the activity rhythm, and this effect may be related to the similarity in their antidepressant effects. (Chronobiology International, 13(4), 251-259, 1996)     

Entrainment to light of circadian activity rhythms in tench (Tinca tinca)

The present article analyzes locomotor activity rhythms in Tinca tinca. To that end, three different experiments were conducted on 24 animals (20 g body weight) kept in pairs in 60-liter aquaria fitted with infrared sensors connected to a computer to continuously record fish movements. The first experiment was designed to study the endogenous circadian clock under free-running conditions [ultradian 40:40 min LD pulses and constant dark (DD)] and after shifting the LD cycle. Our results demonstrate that tench has a strictly nocturnal activity pattern, an endogenous rhythm being evident in 45.8% of the fish analyzed. The second experiment was conducted to test the influence of different photoperiods (LD 6:18, 12:12, 18:6, and 22:2) on locomotor activity, the results showing that even under an extremely long photoperiod, tench activity is restricted to dark hours. The third experiment examined the effect of light intensity on locomotor activity rhythms. When fish were exposed to decreasing light intensities (from 300:0 lux to 30:0, 3:0, and 0.3:0 lux) while maintaining a constant photoperiod (LD 12:12), the highest percentage of locomotor activity was in all cases associated with the hours of complete darkness (0 lux). In short, our results clearly show that (a) tench is a species with a strictly nocturnal behavior, and (b) daily activity rhythms gradually entrain after shifting the LD cycle and persist under free-running conditions, pointing to their circadian nature. However, light strongly influences activity rhythms, since (c) the length of the active phase is directly controlled by the photophase, and (d) strictly nocturnal behavior persists even under very dim light conditions (0.3 lux). The above findings deepen our knowledge of tench behavior, which may help to optimize the aquacultural management of this species, for example, by adjusting feeding strategies to their nocturnal behavior.     

Circadian rhythm of motor activity of the Brazilian rock cavy (Kerodon rupestris) under artificial photoperiod

Kerodon rupestris, a Brazilian caviidae rodent, lives in dry stony places. In a first experiment, seven animals were kept in LD (250:0 lux and 400:0 lux) during 40 days in each condition. In the second, four animals were kept in LD (470 lux: red dim light) for 47 days, then in LL (470 lux) for 18 days and in DD (red dim light) for 23 days. Motor activity was continuously recorded by infrared sensors. Animals showed entrained rhythms to the LD cycle being light and dark active, with higher values in phase transitions. When the light intensity was increased, four animals increased and two reduced the activity. In LL, three animals expressed an endogenous tau of 24.4, 26.5 and 24.6 h and one was arrhythmic; in DD, two expressed tau of 23.6 and 23.7 h and one was arrhythmic. Results indicate that Kerodon rupestris circadian rhythm is affected by light intensity but it is not yet possible to determine its habit.     

Possible evidence for shift work schedules in the media workers of the ant species Camponotus compressus

The locomotor activity rhythm of the media workers of the ant species Camponotus compressus was monitored under constant conditions of the laboratory to understand the role of circadian clocks in social organization. The locomotor activity rhythm of most ants entrained to a 24 h light/dark (12:12 h; LD) cycle and free-ran under constant darkness (DD) with circadian periodicities. Under entrained conditions about 75% of media workers displayed nocturnal activity patterns, and the rest showed diurnal activity patterns. In free-running conditions these ants displayed three types of activity patterns (turn-around). The free-running period (τ) of the locomotor activity rhythm of some ants (10 out of 21) showed period lengthening, and those of a few (6 out of 21) showed period shortening, whereas the locomotor activity rhythm of the rest of the ants (5 out of 21) underwent large phase shifts. Interestingly, the pre-turn-around τ of those ants that showed nocturnal activity patterns during earlier LD entrainment was shorter than 24 h, which became greater than 24 h after 6-9 days of free-run in DD. On the other hand, the pre-turn-around τ of those ants, which exhibited diurnal patterns during earlier LD entrainment, was greater than 24 h, which became shorter than 24 h after 6-9 days of free-run in DD. The patterns of activity under LD cycles and the turn-around of activity patterns in DD regime suggest that these ants are shift workers in their respective colonies, and they probably use their circadian clocks for this purpose. Circadian plasticity thus appears to be a general strategy of the media workers of the ant species C. compressus to cope with the challenges arising due to their roles in the colony constantly exposed to a fluctuating environment.     

Postnatal Constant Light Compensates Cryptochrome1 and 2 Double Deficiency for Disruption of Circadian Behavioral Rhythms in Mice under Constant Dark

Clock genes Cryptochrome (Cry1) and Cry2 are essential for expression of circadian rhythms in mice under constant darkness (DD). However, circadian rhythms in clock gene Per1 expression or clock protein PER2 are detected in the cultured suprachiasmatic nucleus (SCN) of neonatal Cry1 and Cry2 double deficient (Cry1 ^-/-/Cry2 ^-/-) mice. A lack of circadian rhythms in adult Cry1 ^-/-/Cry2 ^-/- mice is most likely due to developmentally disorganized cellular coupling of oscillating neurons in the SCN. On the other hand, neonatal rats exposed to constant light (LL) developed a tenable circadian system under prolonged LL which was known to fragment circadian behavioral rhythms. In the present study, Cry1 ^-/-/Cry2 ^-/- mice were raised under LL from postnatal day 1 for 7 weeks and subsequently exposed to DD for 3 weeks. Spontaneous movement was monitored continuously after weaning and PER2::LUC was measured in the cultured SCN obtained from mice under prolonged DD. Surprisingly, Chi square periodogram analysis revealed significant circadian rhythms of spontaneous movement in the LL-raised Cry1 ^-/-/Cry2 ^-/- mice, but failed to detect the rhythms in Cry1 ^-/-/Cry2 ^-/- mice raised under light-dark cycles (LD). By contrast, prolonged LL in adulthood did not rescue the circadian behavioral rhythms in the LD raised Cry1 ^-/-/Cry2 ^-/- mice. Visual inspection disclosed two distinct activity components with different periods in behavioral rhythms of the LL-raised Cry1^-/-/Cry2^-/- mice under DD: one was shorter and the other was longer than 24 hours. The two components repeatedly merged and separated. The patterns resembled the split behavioral rhythms of wild type mice under prolonged LL. In addition, circadian rhythms in PER2::LUC were detected in some of the LL-raised Cry1^-/-/Cry2^-/- mice under DD. These results indicate that neonatal exposure to LL compensates the CRY double deficiency for the disruption of circadian behavioral rhythms under DD in adulthood.     

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.     

The circadian system of Trypanosoma cruzi-infected mice

The effects of Chagas disease on the mammalian circadian system were studied in Trypanosoma cruzi-infected C57-Bl6J mice. Animals were inoculated with CAI or RA strains of T. cruzi or vehicle, parasitism confirmed by blood specimen visualization and locomotor activity rhythms analyzed by wheel-running recording. RA-strain infected mice exhibited significantly decreased amplitude of circadian rhythms, both under light-dark and constant dark conditions, probably due to motor deficiencies. CAI-treated animals showed normal locomotor activity rhythms. However, in these mice, reentrainment to a 6h phase shift of the LD cycle took significantly longer than controls, and application of 15min light pulses in DD produced smaller phase delays of the rhythms. All groups exhibited light-induced Fos expression in the suprachiasmatic nuclei. We conclude that the main effect of T. cruzi infection on the circadian system is an impairment of the motor output from the clock toward controlled rhythms, together with an effect on circadian visual sensitivity.