Circadian Locomotor Rhythms in Mice with Targeted Disruption of the Gene for the Carbon Monoxide Synthesizing Enzyme,Heme Oxygenase-2

Carbon monoxide (CO), generated in neurons by the enzyme heme oxygenase-2 (HO2), is postulated to be a gaseous signaling molecule in the mammalian brain. Because of the recent evidence suggesting an important role of another endogenously produced gas, nitric oxide (NO), in entrainment of circadian rhythms in mammals, we hypothesized that CO may also be involved in regulating these rhythms. Consistent with this idea, others have found a circadian rhythm of heme turnover and CO synthesis can be induced by bright light. Furthermore, HO2 is co-localized with guanylyl cyclase, the putative target of CO, throughout the brain, with high amounts of staining in the suprachiasmatic nucleus (SCN) of the hypothalamus. The goal of the present study was to evaluate the role of CO in photic entrainment in wild-type and HO2 deficient mice. HO2–/– mice did not display any abnormalities in circadian rhythmicity. Entrainment to a light–dark cycle, the ability to phase delay locomotor activity after a four hour phase shift in photoperiod, and the period of the free running rhythm (t) were similar between HO2–/– and wild-type mice. Taken together, these data suggest that CO does not play a major role in regulating circadian activity rhythms in mice.     

Circadian Rhythms of Locomotor Activity in the Nile Tilapia Oreochromis niloticus

Behavioral rhythms of the Nile tilapia were investigated to better characterize its circadian system. To do so, the locomotor activity patterns of both male and female tilapia reared under a 12:12 h light-dark (LD) cycle were studied, as well as in males the existence of endogenous rhythmicity under free-running conditions (DD and 45 min LD pulses). When exposed to an LD cycle, the daily pattern of activity differed between individuals: some fish were diurnal, some nocturnal, and a few displayed an arrhythmic pattern. This variability would be typical of the plastic circadian system of fish. Moreover, reproductive events clearly affected the behavioral rhythms of female tilapia, a mouth-brooder teleost species. Under DD, 50% (6 of 12) of male fish showed circadian rhythms with an average period (τ) of 24.1±0.2 h, whereas under the 45 min LD pulses, 58% (7 of 12) of the fish exhibited free-running activity rhythms with an average τ of 23.9±0.5 h. However, interestingly in this case, activity was always confined to the dark phase. Furthermore, when the LD cycle was reversed, a third of the fish showed gradual resynchronization to the new phase, taking 7–10 days to be completely re-entrained. Taken together, these results suggest the existence of an endogenous circadian oscillator that controls the expression of locomotor activity rhythms in the Nile tilapia, although its anatomical localization remains unknown.     

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.     

Stocking Density Affects Circadian Rhythms of Locomotor Activity in African Catfish,Clarias gariepinus

The effect of stocking density on the locomotor activity of African catfish C. gariepinus under different light regimes was investigated. C. gariepinus were stocked under different densities (1, 5, or 10 fish/tank), and their locomotor activity recorded under light-dark (LD), constant light (LL), constant darkness (DD), and LD-reversed (DL) regimens. Under the LD cycle, catfish showed a crepuscular activity pattern, irrespective of stocking density, with most of the daily activity concentrated around the light-onset and light-offset times. When fish were subjected to DD, all 4 tanks with medium (5 fish) and high (10 fish) stocking densities showed circadian rhythmicity, with an average period (τ) of 23.3?±?0.5 and 24.6?±?0.5?h, respectively. In contrast, only 2 low (1 fish) density tanks showed free-running rhythms. Under LL, activity levels decreased significantly in comparison with levels observed under LD and DD. Moreover, fish of 1, 2, and 3 out of the 4 tanks with low, medium, and high densities, respectively, showed free-running rhythms under these conditions. When the photocycle was reversed (DL), fish of 3, 2, and 4 out of the 4 tanks with low, medium, and high stocking densities, respectively, showed gradual resynchronization to the new phase, and transient cycles of activity were observed. These results suggest that stocking density of fish affected the display of circadian rhythmicity and the intensity of activity levels. Thus, fish kept in higher densities showed more robust rhythmicity and higher levels of daily activity, indicating that social interactions may have an influence on behavioral patterns in the African catfish. (Author correspondence: lmvera@um.es)     

Rhythms of Enzyme Activity Associated with Circadian Conidiation in Neurospora crassa

The mycelial growth front of the band strain of Neurospora grown on a solid surface exhibits a circadian rhythm of conidiation. Enzyme assays on extracts from that mycelium have shown that the activities of 6 of 13 enzymes (nicotinamide adenine dinucleotide nucleosidase, isocitrate lyase, citrate synthase, glyceraldehydephosphate dehydrogenase, phosphogluconate dehydrogenase, and glucose-6-phosphate dehydrogenase) and soluble-protein content oscillate with the visible morphological change. The rhythmic enzymes associated with the Krebs and glyoxylate cycles are more active during conidiogenesis, whereas the activities of the rhythmic enzymes of glycolysis and the hexose monophosphate shunt are reduced during that phase. The absence of enzyme oscillations in wild-type and fluffy strains which do not form conidia under the conditions employed suggests that the enzyme fluctuations are associated with conidiogenesis itself. Oscillations of enzyme activity as a function of time are restricted to the growth front. A permanent record of rhythmicity associated with conidial and nonconidial regions does, however, exist in the mycelial mat behind the growth front. The activities of three enzymes (nicotinamide adenine dinucleotide nucleosidase, glucose-6-phosphate dehydrogenase, and phosphogluconate dehydrogenase) are not directly influenced by CO(2) concentration, but are correlated with the prescence or absence of conidiation which is controlled by CO(2) concentration. In contrast, citrate synthase and malate dehydrogenase activities are correlated with changes in CO(2) concentration.     

用siRNA沉默人血红素加氧酶-1基因降低胆红素水平

拟通过RNA干扰技术特异下调人血红素加氧酶-1(human heme oxygenase-1,hHO-1)基因的表达,减少hHO-1的产量从而降低胆红素的产生,探讨在胆红素产生前就阻断其产生,为临床早期防治新生儿高胆红素血症及胆红素中毒性脑病探索一种新的有效手段。针对hHO-1基因设计并化学合成三对小分子干扰RNA(small interfering RNA,siRNA)。采用脂质体转染法将siRNA转染入人肝脏细胞株HL-7702;荧光显微镜检测siRNA转染细胞的效率;转染siRNA1~2天后经RT-PCR和Western印迹方法检测hHO-1表达水平和蛋白质量;并采用HO-1诱导剂血红素诱导或hHO-1表达质粒转染细胞以上调hHO-1表达,检测siRNA干扰后hHO-1产量和酶活性。结果显示:设计的三对siRNA能不同程度的特异下调hHO-1表达,筛选获得抑制效果最佳的siRNA-3。siRNA-3抑制hHO-1呈现浓度与时间依赖性。与非特异对照siRNA及未处理组比较,血红素诱导和hHO-1表达质粒转染均能上调HL-7702细胞内hHO-1表达,提高hHO-1产量,但转染siRNA-3后hHO-1表达明显抑制,同时hHO-1活性随着基因表达下调而下降。实验表明设计合成的siRNA-3抑制效果明显。siRNA-3通过降解hHO-1,减少hHO-1产量,降低酶活性,最终减少胆红素产生,从而使RNA干扰技术成为降低新生儿高胆红素血症和胆红素中毒性脑病发生的一种候选方法。     

Circadian Rhythms in Toxic Effects of the Serotonin Antagonist Ondansetron in Mice

The aim of the study was to learn whether the lethal and the motor incoordination (ataxia) side effect of ondansetron (Zophren®) administration is dosing‐time dependent. Ondansetron is a serotonin 5‐HT₃ receptor antagonist used primarily to control nausea and vomiting arising from cytotoxic chemo‐ and radiotherapy. A total of 210 male Swiss mice 10 to 12 weeks of age were synchronized for 3 weeks by 12h light (rest span)/12h dark (activity span). Different doses of ondansetron were injected intraperitoneally (i.p.) at fixed times during the day to determine both the sublethal (TD₅₀) and lethal (LD₅₀) doses, which were, respectively, 3.7 ± 0.6 mg/kg and 4.6 ± 0.5 mg/kg. In the chronotoxicologic study a single dose of ondansetron (3.5 mg/kg, i.p.) was administered to different and comparable groups of animals at four different circadian stages [1, 7, 13, and 19h after light onset (HALO)]. The lethal toxicity was statistically significantly dosing time‐dependent (χ² = 21.51, p < 0.0001). Drug dosing at 1 HALO resulted in 100% survival rate whereas drug dosing at 19 HALO was only one‐half that (52%). Similarly, lowest and highest ataxia occurred when ondansetron was injected at 1 and 19 HALO, respectively (χ² = 22.24, p < 0.0001). Effects on rectal temperature were also dosing‐time related (Cosinor analysis, p < 0.0001). The characteristics of the waveform describing the temporal patterns differed between the studied variables, e.g., lethal toxicity and survival rate showing two peaks and rectal temperature showing one peak in the 24h time series waveform pattern. Cosinor analysis also revealed a statistically significant ultradian (τ ≡ 8h) rhythmic component in the considered variables. Differences in curve patterns in toxicity elicited by ondansetron on a per end point basis are hypothesized to represent the phase relations between the identified 24h and 8h periodicities.     

Gene Regulation of Iron-Deficiency Responses Is Associated with Carbon Monoxide and Heme Oxydase 1 in Chlamydomonas reinhardtii

Carbon monoxide (CO) as an endogenous gaseous molecule regulates a variety of biological processes in animals. However, CO regulating nutrient stress responses in green alga is largely unknown. On the other hand, heme oxydase (HO1 as a rate-limiting enzyme of the first step for heme degration and to catalyze heme into biliverdin (BV), which is concomitant with releasing of CO and ferrous ions, probably participates in the process of CO-regulating response to nutrient stress in green alga. In this paper, we described an observation that CO could regulate iron-homeostasis in iron-starving Chlamydomonas reinhardtii. Exogenous CO at 8 µM was able to prevent the iron deficient-inducing chlorosis and improve chlorophyll accumulation. Expression pattern of FOX1, FTR1 and ferredoxin was up-regulated by CO exposure in iron-deficient mediam. treatment with external CO increasing iron accumulation in iron-deficient C. reinhardtii. Moreover, to get insights into the regulatory role of HO1, we constructed a transgenic alga overexpressing HO1 and HO1 knock-out mutants. The results show that there was no significant influence on chlorosis with HO1 overexpression of C. reinhardtii under iron-deficiency and the chlorophyll accumulation, and gene expression associated with iron deficiency of mutant were greatly improved. Otherwise, those results from HO1 knock-out mutants were opposite to HO1 overexpression mutants. Finally, CO exposure induced NO accumulation in cells. However, such an action could be blocked by NO scavenger cPTIO. These results indicate that CO/HO1 may play an important role in improving green algae adaptation to iron deficiency or cross-talking with NO under the iron deficiency.     

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.     

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

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

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

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

Circadian Rhythms in Locomotor Activity of the Hagfish, Eptatretus burgeri VI. The Effects of Cutting the Spinal Cord

The present study is designed to clarify the mechanism by which the circadian pacemaker controls the locomotor activity of the hagfish and also to estimate the role of brain and spinal cord in the swimming behavior of the animal. We examined the effect of cutting the spinal cord at the 6 different positions on the circadian rhythm and the locomotor behavior of the animal. The most frontal cut was located between the brain and spinal cord, and the other 5 cuts were given to every 1/6 the length of the spinal cord. The relation between the locomotor activity and the cut position of spinal cord was summarized as follows. (1) When the ratio of frontal part before the cut was 0/6-1/6, the animal locomoted under initiative of caudal part, in random direction at the bottom and showed neither nocturnal rhythm in LD nor circadian rhythm in DD. (2) When the ratio of the frontal part before the cut was 4/6-5/6, the animal swam up to the surface under initiative of frontal part, and showed both nocturnal rhythm in LD and circadian rhythm in DD. (3) When the frontal ratio of spinal cord was 2/6 or 3/6, the animal showed both kinds of swimming behavior of (1) and (2). These results suggest that the descending system from the brain enable the hagfish to swim up to the surface and to express the rhythmicity of locomotor activity under control of the circadian pacemaker when at least frontal 2/6 of the spinal cord is connected to the brain by neuronal networks not by humoral factors.     

Carbon Monoxide-Induced Early Thrombolysis Contributes to Heme Oxygenase-1-Mediated Inhibition of Neointimal Growth after Vascular Injury in Hypercholesterolemic Mice

Arterial thrombosis is a critical event in the pathogenesis of lesion development. In this study, we evaluated the effect of heme oxygenase-1 (HO-1), a stress-inducible enzyme with vasoprotective functions, on arterial thrombosis following vascular mechanical injury. The carotid arteries of apoE-deficient mice were subjected to angioplasty with a modified beaded-needle. Arterial thrombosis occurred at 12 h after injury. Treatment of the injured vessels with an adenovirus bearing HO-1 gene (Adv-HO-1) (1× 10⁸ pfu), but not saline or empty adenovirus (Adv), immediately after angioplasty resulted in earlier thrombolysis and restoration of blood flow detected at 24 h. Immunohistochemistry revealed that the arterial plasminogen activator inhibitor-1 (PAI-1) expression was markedly reduced in Adv-HO-1-treated injured arteries as compared to control counterparts. The thrombolytic effect was also observed by exposing animals with existing arterial thrombosis to carbon monoxide (CO) (250 ppm, 2 h), a byproduct derived from heme degradation by HO-1. In parallel with less fibrin(ogen) deposition, the macrophage infiltration, monocyte chemoattractant protein-1 expression and neointimal formation assessed at 2 weeks after angioplasty were substantially reduced in injured arteries treated with Adv-HO-1. These results support a role of early thrombolysis induced by CO in HO-1-mediated protection against intimal hyperplasia after vascular injury.     

Circadian Period Modulation and Masking Effects Induced by Repetitive Light Pulses in Locomotor Rhythms of the Cricket, Gryllus bimaculatus

Effects of 15 min light pulses given at various intervals (every 1, 2, 4, 6, 8 and 12 hr) under constant darkness on the locomotor rhythm were investigated in the adult male cricket, Gryllus bimaculatus. A single pulse per 24 hr induced period modulation in a circadian phase dependent manner, yielding a period modulation curve (PMC): the 15 min light pulse lengthened the period in the early subjective night (CT11-16) and shortened it during the late subjective night to the early subjective day (CT20-5). Frequent light pulses modulated the freerunning period of the rhythm dependent on the interval of the pulses: when compared with the freerunning period in DD (23.74 +/- 0.03 hr) the period was significantly shorter in intervals of 2 and 4 hr, but lengthened when the interval was 1 and 12 hr. Frequent light pulses also resulted in entrainment of the rhythm to run with the period of 24 hr and the ratio of the entrained animals varied from 12% to 72% depending on the interval of the light pulses. The period modulation and the entrainment by the repetitive light pulses could be interpreted according to the PMC. In about 15% of animals, the light pulses induced a rhythm dissociation, suggesting that the bilaterally paired circadian pacemakers have their own sensitivity to the entraining photic information. The light pulse caused a masking effect, i.e., an intense burst of activity. The magnitude of the light induced responses was dependent on the circadian phase. The strongest masking effect was observed in the subjective night. The phase of the prominent period modulation and of the marked masking effects well coincides with the previously reported sensitive phase of the photoreceptive system.     

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.     

Circadian Clock Gene Per2 Is Not Necessary for the Photoperiodic Response in Mice

In mammals, light information received by the eyes is transmitted to the pineal gland via the circadian pacemaker, i.e., the suprachiasmatic nucleus (SCN). Melatonin secreted by the pineal gland at night decodes night length and regulates seasonal physiology and behavior. Melatonin regulates the expression of the β-subunit of thyroid-stimulating hormone (TSH; Tshb) in the pars tuberalis (PT) of the pituitary gland. Long day-induced PT TSH acts on ependymal cells in the mediobasal hypothalamus to induce the expression of type 2 deiodinase (Dio2) and reduce type 3 deiodinase (Dio3) that are thyroid hormone-activating and hormone-inactivating enzymes, respectively. The long day-activated thyroid hormone T₃ regulates seasonal gonadotropin-releasing hormone secretion. It is well established that the circadian clock is involved in the regulation of photoperiodism. However, the involvement of the circadian clock gene in photoperiodism regulation remains unclear. Although mice are generally considered non-seasonal animals, it was recently demonstrated that mice are a good model for the study of photoperiodism. In the present study, therefore, we examined the effect of changing day length in Per2 deletion mutant mice that show shorter wheel-running rhythms under constant darkness followed by arhythmicity. Although the amplitude of clock gene (Per1, Cry1) expression was greatly attenuated in the SCN, the expression profile of arylalkylamine N-acetyltransferase, a rate-limiting melatonin synthesis enzyme, was unaffected in the pineal gland, and robust photoperiodic responses of the Tshb, Dio2, and Dio3 genes were observed. These results suggested that the Per2 clock gene is not necessary for the photoperiodic response in mice.     

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.