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.     

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.     

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 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.     

Locomotor activity rhythms in cave fishes from Chapada Diamantina, northeastern Brazil (Teleostei: Siluriformes)

Previous studies on the locomotor activity of troglobitic (exclusively subterranean) species have shown that circadian rhythmicity may be reduced in populations evolving in the absence of zeitgebers such as daily cycles of light and temperature; therefore, circadian activity rhythms, although not infradian nor ultradian rhythms, seem to have been selected by external, ecological factors. We studied the locomotor activity of a highly specialized Heptapteridae catfish (undescribed genus and species) from Chapada Diamantina, NE Brazil, compared to another specialized Brazilian troglobitic heptapterid, Taunayia sp. Locomotor activity was continuously measured in the laboratory with an infra-red photocell system. Seven specimens of the new genus were tested, each one during 14 consecutive days according to the following schedule: three days in DD → seven days in LD (12:12 h) → four days in DD. Data were submitted both to fast Fourier transform periodogram followed by Siegel's test of significance and Lombs - Scargle periodogram techniques in order to identify spectral composition of the time series. In general, results were similar to those obtained for Taunayia sp.: (a) for most specimens, absence of significant circadian components in locomotor activity under DD; (b) for all specimens, significant circadian components under LD, with higher levels of activity during the dark phase, as expected for species belonging to nocturnal epigean taxa; (c) for most specimens, no residual oscillations recorded when free-running conditions were reinstalled. Circadian locomotor activity detected under LD may thus be interpreted as a direct, masking effect of the LD cycle. This suggests a pattern for highly specialized troglobitic species, isolated for a long time in the subterranean habitat, with a progressive reduction of circadian time-keeping mechanisms. Our studies also demonstrate the potential of subterranean organisms for investigation of the origin, evolution, functioning and genetics of circadian rhthmicity.     

Endogenous rhythms of locomotion in the American horseshoe crab, Limulus polyphemus

American horseshoe crabs (Limulus polyphemus) exhibit clear circadian rhythms of visual sensitivity in the laboratory and in the field they exhibit seasonal patterns of mating behavior that are closely associated with the tides. Recent reports suggest that Limulus locomotor activity may be controlled by endogenous circadian and/or circatidal clocks and that light:dark (LD) cycles may affect the rhythmic output of both of these clocks. In this study, we examined locomotor behavior in the laboratory to determine the extent of this endogenous activity and to examine the influence of LD cycles on these rhythms. Thirty-three L. polyphemus were captured during the breeding season and their activity was monitored with activity boxes and “running wheels” in seawater kept at constant temperature and salinity. Activity patterns were analyzed using visual inspection of actograms and Chi-square and Lomb-Scargle periodograms. Overall, 36% of the animals was significantly more active during L, while only 12% was more active during D (52% showed no preference). Circatidal rhythms were observed in LD in 67% of the horseshoe crabs. Surprisingly, LD cycles appeared to synchronize these rhythms at times. In DD, the majority of animals tested (63%) exhibited circatidal rhythms that persisted for at least seven days. Overall, the results demonstrate that an endogenously controlled tidal rhythm of locomotion operates during, and significantly after, the breeding season in this species. In addition, the present results are consistent with the presence of circalunidian oscillators controlling these rhythms.     

Locomotor Activity Rhythms in Cave Catfishes, Genus Taunayia, from Eastern Brazil (Teleostei: Siluriformes: Heptapterinae)

We studied the locomotor rhythmicity in heptapterine catfishes, genus Taunayia, under free-running conditions (DD) and LD cycles (12:12). Taunayia sp., anophthalmic and depigmented undescribed species from a cave in northeastern Brazil, is the fourth Brazilian troglobitic catfish studied with focus on circadian rhythms. Weak free-running rhythmicity, with absence of significant circadian components, was observed for this species when compared to the epigean, eyed relatives. On the other hand, the studied troglobitic catfishes in general presented significant circadian rhythms under LD cycles, with activity peaks in the night phase probably corresponding to nocturnal activity pattern inherited from their epigean ancestors. However, no residual oscillations were observed after transition from LD to DD. This indicates masking of activity by light-dark cycles. Regression of circadian rhythmicity in the stable, permanently dark subterranean habitat was also observed for other cave fishes. Such regression corroborates the notion that circadian rhythmicity is mainly selected in the epigean environment by ecological factors, namely daily cycles of light and/or temperature.     

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.     

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.     

Presence of circadian rhythms in the locomotor activity of a cave-dwelling millipede Glyphiulus cavernicolus sulu (Cambalidae, Spirostreptida)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757-765, 2000)     

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.     

Internal Desynchronisation in Blow Fly (Calliphora vicina) Locomotor Activity Rhythms: Evidence for a Complex Circadian Pacemaker

The majority of blow flies (Calliphora vicina) display circadian locomotor activity rhythms that free-run with an unchanging period (τ) in darkness (DD), or entrain to a light-dark cycle (LD 1:23). However, a minority produce more complex patterns (spontaneous changes in τ, arrhythmicity, or 'split' rhythms) in DD, or undergo rhythm dissociation ('internal desynchronisation') when the light pulses of LD 1:23 initially illuminate the subjective night. These patterns are interpreted as evidence for a complex, multioscillatory and multicellular, structure of the insects' circadian system, and this complexity is discussed in terms of the neuronal architecture of the fly's brain.     

Period and phase control in a multioscillatory circadian system (Iguana iguana)

The circadian system of the lizard Iguana iguana is composed of several independent pacemakers that work in concert: the pineal gland, retinae of the lateral eyes, and a fourth oscillator presumed to be located in the hypothalamus. These pacemakers govern the circadian expression of multiple behaviors and physiological processes, including rhythms in locomotor activity, endogenous body temperature, electroretinogram, and melatonin synthesis. The numerous, easily measurable rhythmic outputs make the iguana an ideal organism for examining the contributions of individual oscillators and their interactions in governing the expression of overt circadian rhythms. The authors have examined the effects of pinealectomy and enucleation on the endogenous body temperature rhythm (BTR) and locomotor activity rhythm (LAR) of juvenile iguanas at constant temperature both in LD cycles and in constant darkness (DD). They measured the periods (tau) of the circadian rhythms of LAR and BTR, the phase relationships between them in DD (psiAT), and the phase relationship between each rhythm and the light cycle (psiRL). Pinealectomy lengthened tau of locomotor activity in all animals tested and abolished the BTR in two-thirds of the animals. In those animals in which the BTR did persist following pinealectomy, tau lengthened to the same extent as that of locomotor activity. Pinealectomy also delayed the onset of activity with respect to its normal phase relationship with body temperature in DD. Enucleation alone had no significant effect on tau of LAR or BTR; however, after enucleation, BTR became 180 degrees out of phase from LAR in DD. After both pinealectomy and enucleation, 4 of 16 animals became arrhythmic in both activity and body temperature. Their data suggest that rhythmicity, period, and phase of overt circadian behaviors are regulated through the combined output of multiple endogenous circadian oscillators.     

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 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.     

Behavioral and molecular analyses suggest that circadian output is disrupted by disconnected mutants in D. melanogaster.

Mutations in the disconnected (disco) gene act to disrupt neural cell patterning in the Drosophila visual system. These mutations also affect adult locomotor activity rhythms, as disco flies are arrhythmic under conditions of constant darkness (DD). To determine the state of the circadian pacemaker in disco mutants, we constructed with pers double mutants (a short period allele of the period gene) and assayed their behavioral rhythms in light-dark cycles (LD), and their biochemical rhythms of period gene expression under both LD and DD conditions. The results demonstrate that disco flies are rhythmic, indicating that they have an active circadian pacemaker that can be entrained by light. They also suggest that disco mutants block or interfere with elements of the circadian system located between the central pacemaker and its outputs that mediate overt rhythms.     

Evidence of circadian rhythm of electric discharge in Eigenmannia virescens system

The gymnotid electric fish, Eigenmannia virescens, exhibits electric discharge rhythmicity both in alternate light-dark (LD; 12h light, 12h dark [LD 12:12]) and in constant dark (DD) conditions. It suggests that the electric discharge rhythm is under control of the circadian clock. The free-running periods (FRPs) of electric discharge rhythms at 21°C in DD are greater than, but close to, 24h. The maximum of the electric discharge in the Eigenmannia system peaks approximately at circadian time 6 (CT6) in the middle of the subjective day. The circadian oscillator in the system is temperature compensated. This original report reveals the relationship between electric discharge activity and the circadian pacemaker in Eigenmannia and provides an alternative system to investigate circadian rhythms in vertebrates. (Chronobiology International, 17(1), 43-48, 2000)     

Circadian locomotor rhythm masked by the female reproduction cycle in cockroaches

Blattella bisignata (Brunner) and B. germanica (L.) are oviparous cockroaches with cyclic reproductive behaviour, but in B. germanica only males show circadian rhythmicity of locomotion at 28°C and DD (constant darkness). In B. bisignata, males and virgin females cockroaches entrained by light–dark cycles show free‐running rhythmicity in DD, and most activities occur during the subjective night. Daily locomotor activities of virgin females show cyclic changes that coincided with ovarian development. Virgin females also exhibit calling behaviour during the subjective night, and this shows a free‐running rhythm. Male mate‐finding locomotion and female calling behaviour are under circadian control, so the timing for both behaviours is synchronized. However, most mated females do not show a locomotor free‐running rhythm under DD conditions. Our results indicate that only mated females could not express a circadian locomotor rhythm. Pregnancy reduces a female’s locomotory intensity and masks the expression of a circadian locomotor rhythm. We attribute the differences in circadian locomotory rhythms between these two species to their living environments and mate‐finding strategies.     

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)     

Circadian Locomotor Activity Under Artificial Light in the Freshwater Crab Pseudothelphusa americana

Long-term recordings of locomotor activity were obtained from intact freshwater crabs, Pseudothelphusa americana in constant darkness (DD), constant light (LL) and different light-dark (LD) protocols. Bimodal rhythms were typically observed in this crab when subjected to DD or LD, with bouts of activity anticipating lights-on and lights-off, respectively. Freerunning circadian rhythms were expressed in both DD and LL for longer than 30 days. In DD, we observed that some animals presented different period lengths for each activity component. During LL, activity was primarily unimodal, however spontaneous splitting of the rhythms were observed in some animals. When activity was recorded under artificial long days, the morning bouts maintained their phase relationship but the evening bouts changed their phase relationship with the Zeitgeber. Our results indicate that, bimodal locomotor activity rhythm in the crab Pseudothelphusa americana is variable among organisms. The characteristics of phase relationship with LD and responses to LL for morning and evening bouts, suggest that, locomotor activity could be driven by multiple oscillators, and that coupling between these oscillators may be regulated by light.