Daily Rhythms Of Locomotor Activity Research Articles

Daily rhythms of locomotor activity and transcript levels of non-visual opsins in the brain of the blind Mexican cavefish (Astyanax mexicanus)

Most organisms possess endogenous circadian clocks that synchronise their physiology and behaviour with environmental cycles, with the light-dark (LD) cycle being the most potent synchronising signal. Consequently, it can be hypothesised that animals that have evolved in the dark, as in caves or deep sea, may no longer possess a functional light-entrained biological clock. In this research, the blind cavefish Astyanax mexicanus was selected as a model organism to investigate the potential effects of daily light conditions on the circadian timekeeping mechanisms. First, we focused on describing behavioural photic entrainment and the presence of a circadian endogenous rhythmicity by recording locomotor activity rhythms under different lighting regimes: LD 12:12, after a 6-h shift of LD, constant darkness (DD), and constant dim light (LLdim). Secondly, we aimed at characterising the mechanisms of photodetection by analysing the daily rhythms of expression of selected non-visual extraocular opsins (exo-rhod, opn3, rgra, rgrb, tmt1a and tmt1b) in the brain of this blind species using real-time quantitative PCR. Our results revealed that blind Mexican cavefish activity rhythms were entrained to the LD cycle, with a diurnal activity pattern that persisted in a circadian fashion under constant lighting conditions. Additionally, statistically significant daily variations and/or rhythms were observed in three out of the six non-visual opsin genes analysed (opn3, rgra and tmt1b), all of them displaying nocturnal acrophases. These findings suggest that daily rhythms in extraretinal non-visual opsins may be transducing daily photic cycles and contributing to the entrainment of locomotor activity and other light-synchronised rhythms in blind cavefish species.

Rhythmicity of locomotor behavior and body temperature in Felis catus maintained under controlled microclimate conditions

Rhythmicity of locomotor behavior and body temperature in Felis catus maintained under controlled microclimate conditions

Shedding light on the circadian clock of the threespine stickleback.

ABSTRACTThe circadian clock is an internal timekeeping system shared by most organisms, and knowledge about its functional importance and evolution in natural environments is still needed. Here, we investigated the circadian clock of wild-caught threespine sticklebacks (Gasterosteus aculeatus) at the behavioural and molecular levels. Although their behaviour, ecology and evolution are well studied, information on their circadian rhythms are scarce. We quantified the daily locomotor activity rhythm under a light:dark cycle (LD) and under constant darkness (DD). Under LD, all fish exhibited significant daily rhythmicity, while under DD, only 18% of individuals remained rhythmic. This interindividual variation suggests that the circadian clock controls activity only in certain individuals. Moreover, under LD, some fish were almost exclusively nocturnal, while others were active around the clock. Furthermore, the most nocturnal fish were also the least active. These results suggest that light masks activity (i.e. suppresses activity without entraining the internal clock) more strongly in some individuals than others. Finally, we quantified the expression of five clock genes in the brain of sticklebacks under DD using qPCR. We did not detect circadian rhythmicity, which could indicate either that the clock molecular oscillator is highly light-dependent, or that there was an oscillation but that we were unable to detect it. Overall, our study suggests that a strong circadian control on behavioural rhythms may not necessarily be advantageous in a natural population of sticklebacks and that the daily phase of activity varies greatly between individuals because of a differential masking effect of light.

Melatonin Prevents Non-image-Forming Visual System Alterations Induced by Experimental Glaucoma in Rats.

Glaucoma is a blindness-causing disease that involves selective damage to retinal ganglion cells (RGCs) and their axons. A subset of RGCs expressing the photopigment melanopsin regulates non-image-forming visual system functions, such as pupillary light reflex and circadian rhythms. We analyzed the effect of melatonin on the non-image-forming visual system alterations induced by experimental glaucoma. For this purpose, male Wistar rats were weekly injected with vehicle or chondroitin sulfate into the eye anterior chamber. The non-image-forming visual system was analyzed in terms of (1) melanopsin-expressing RGC number, (2) anterograde transport from the retina to the olivary pretectal nucleus and the suprachiasmatic nuclei, (3) blue- and white light-induced pupillary light reflex, (4) light-induced c-Fos expression in the suprachiasmatic nuclei, (5) daily rhythm of locomotor activity, and (6) mitochondria in melanopsin-expressing RGC cells. Melatonin prevented the effect of experimental glaucoma on melanopsin-expressing RGC number, blue- and white light-induced pupil constriction, retina-olivary pretectal nucleus, and retina- suprachiasmatic nuclei communication, light-induced c-Fos expression in the suprachiasmatic nuclei, and alterations in the locomotor activity daily rhythm. In addition, melatonin prevented the effect of glaucoma on melanopsin-expressing RGC mitochondrial alterations. These results support that melatonin protected the non-image-forming visual system against glaucoma, probably through a mitochondrial protective mechanism.

Interspecies comparison of daily total locomotor activity between maned wolves (Chrysocyon brachyurus) and domestic dogs (Canis familiaris) maintained in captivity

The aim of the study was to extend the knowledge about to the total locomotor activity behavior in maned wolves (Chrysocyon brachyurus) through the comparison with domestic dogs (Canis familiaris). Five maned wolves housed individually in 4 m2 dens with nest boxes and runs allowing them to move in outdoors area of 250 m2 with natural vegetation; and five Beagles dogs living individually in a 12 m2 box with an outside area of 50 m2 were subjected to natural light-dark (L/D) cycle (maned wolves: 15 L/9D; dogs 14 L/10D) and environmental conditions (maned wolves: 22-26°C, 64Rh%; dogs 17-23°C, 65Rh%). In each animal, the monitoring of locomotor activity was performed for 2 days by means of an activity data logger (Actiwatch Cambridge Neurotechnology, Cambridge, UK), applied on a neck collar. Data were analyzed by the single Cosinor method. At the obtained rhythmic parameters, two-way analysis of variance was applied to verify differences due to day of monitoring and species. Maned wolves showed a nocturnal daily rhythm of locomotor activity. Dogs showed a diurnal daily rhythm of locomotor activity. The diurnality index was 0.29 and 0.93, respectively, for maned wolves and dogs. The two studied species showed statistically difference in mesor and amplitude of rhythm, higher in maned wolves (mesor: 3256.64 ± 364.87 arbitrary unit; amplitude: 3726.32 ± 327.50 arbitrary unit) than dogs (mesor: 414.06 ± 9.68 arbitrary unit; amplitude: 502.35 ± 18.78 arbitrary unit).We can claim that maned wolves, housed in captivity are more active than dogs and showed an opposed daily rhythm of locomotor activity.

Circadian Rhythm Disorders and Risk of Subsequent Depression: A Systematic Review and Meta-Analysis of Longitudinal Studies

Background: Patients with depression often suffer from circadian rhythm disruptions, such as insomnia and a lower amplitude of daily rhythms of locomotor activity. However, whether circadian disorders precede depression and act as a predictor for subsequent depression have not been unanimously approved. In light of increasing evidence of an association between disrupted circadian rhythms and affective symptoms, a meta-analysis was conducted to examine the effect of circadian disruptions on incident depression. Methods: A systematic search was performed in PubMed, Embase, Web of Science, PsycINFO, PsycArticles, CINAHL database. The search results were restricted to be published in English up to April 10, 2020.Reference lists from included studies and relevant reviews were also screened. We included longitudinal cohort studies that examined the predictive role of all various types of circadian disruption in incident depression. Two reviewers independently extracted information on study design, participants’ characteristics and diagnostic criteria for circadian disruption and depression. Study quality was assessed using the Newcastle-Ottawa Scale. Random-effect models were applied to all meta-analyses given potential heterogeneity. For insomnia, subgroup analyses were performed based on subject’s characteristics, insomnia symptom domains and numbers and the investigated methods. Pool-effect estimates of relative risks to develop incident depression in groups with circadian disruption compared to groups without. This study is registered with PROSPERO, CRD42020179135. Findings: A total of 49 studies were eligible for this meta-analysis. Of 49 eligible studies, included types of circadian disruption were sleep disturbances (n = 45), chronotype (n = 2), cortisol awakening response (n = 1) and rest - activity rhythm (n = 1). Insomnia, hypersomnia, excessive daytime sleepiness (EDS), short sleep duration, obstructive sleep apnea (OSA), restless legs syndrome (RLS), an evening preference, heightened levels of cortisol in awakening response and low robustness of rest - activity rhythm all acted as significant predictors of occurrence of depression. Among insomnia subtypes, difficulty initiating sleep (DIS) and difficulty maintaining sleep (DMS) predicted future depression. Of note, persistent insomnia (OR: 5.02) contributed to more than two - fold risk of incident depression compared to insomnia (OR: 2.34). Moreover, insomnia symptom numbers were associated with incident depression in a gradient trend. Interpretation: Different types of circadian disorders act as risk factors of onset of depression, which clinicians should be informed of. Future research should be aimed to determine the casual relationship between other types of circadian disorders and onset of depression, and moreover to further elucidate the underlying mechanisms. Funding Statement: This work was supported in part by the National Natural Science Foundation of China (no. 81871071 and 81171251) and Beijing Municipal Natural Science Foundation (no. 7162101). Declaration of Interests: All of the authors declare no conflict of interest.

Optimizing rearing and welfare in Senegalese sole (Solea senegalesensis) broodstock: Effect of ambient light intensity and handling time on stress response

Broodstock rearing conditions and handling procedures should be optimized in aquaculture species in order to benefit fish welfare and guarantee optimal conditions for spawning. In teleosts, basal cortisol levels display daily rhythms, oscillating along the 24 h of the day. In this sense, handling fish at different moments of the day may lead to different stress responses. The present study aimed at investigating the optimal rearing conditions for Senegalese sole broodstock, considering ambient light intensity and handling time. The optimal light intensity (50, 100 or 200 lx) was investigated by measuring fish cortisol levels and monitoring locomotor activity rhythms under each intensity tested. Results showed a significant increase in cortisol levels of fish exposed to 200 lx, when compared to values obtained under 100 lx, accompanied by changes in locomotor activity rhythms in both tanks under study. These results suggested that 200 lx may be too high as light intensity for this species, whereas 100 lx seems to be more adequate. Also, daily rhythms of stress response were investigated in breeders from different origins (Wild and first generation, G1). Basal cortisol levels and cortisol stress response after an acute stressor (air exposure) were monitored at two distinct moments of the day (Mid-Light and Mid-Dark). Basal levels were higher during the day in the wild group, while G1 fish seemed to have lost the daily fluctuations in basal cortisol plasma levels, as well as their daily rhythms of locomotor activity. Both groups showed lower stress responses during night-time, an indication that this is an adequate period of the day to handle this species. Senegalese sole breeders born in captivity presented more pronounced stress responses when compared to wild fish, reflecting their different life history in terms of stress challenges.

Behavioral and physiological processes in horses and their linkage with peripheral clock gene expression: A preliminary study

Behavioral and physiological processes have an innate 24-h cycle driven by the circadian master clock, which uses clock genes to generate rhythmicity and distribute temporal signals. Elucidating the blood gene expression in relation to the better known circadian rhythms in horses may contribute to improve the knowledge on the peripheral circadian rhythm control in this species. To do that, seven clinically healthy Italian saddle female horses were housed in individual boxes under natural photoperiod and environmental conditions. In each horse, locomotor activity was recorded continuously; blood samples and rectal temperature were recorded every 4 hours over a 48-hour period. To investigate the peripheral clock in horses, quantitative real-time RT polymerase chain reaction assays were designed to detected clock gene levels (Per 1, Per 2, and Cry 1) from blood samples. Blood cortisol serum level was also measured. Our results showed a daily expression of Per 1, Per 2, and Cry 1 in peripheral blood, associated with the daily rhythm of locomotor activity, rectal temperature and cortisol. In particular, a similar acrophase was observed for locomotor activity and Per 1; and for rectal temperature and Per 2. Rectal temperature and Per 2 also showed the same percentage of robustness of rhythm. We suggest the existence of a linkage between the peripheral clock genes Per 1 and Per 2 with locomotor activity and rectal temperature, although more studies are necessary to establish the exact mechanism of the peripheral clock.

Hypothalamic leptin sensitivity and health benefits of time-restricted feeding are dependent on the time of day in male mice.

Synchronization between biologic clocks and metabolism is crucial for most species. Here, we examined the ability of leptin, important in the control of energy metabolism, to induce leptin signaling at the molecular as well as the behavioral level throughout the 24-h day in mice fed either a control or a high-fat diet (HFD). Furthermore, we investigated the effects of time-restricted feeding (TRF; a limitation of HFD access to 6 h each day) on energy metabolism during different periods throughout the 24-h day. In control mice, molecular leptin sensitivity was highest at zeitgeber time (ZT)0 (lights on), declining during the light phase, and increasing during the dark phase. Surprisingly, leptin resistance in HFD-fed mice was only present from the middle of the dark to the middle of the light period. Specifically, when TRF occurred from ZT21 to ZT3 (when leptin resistance in HFD-fed mice was most profound), it resulted in a disruption of the daily rhythms of locomotor activity and energy expenditure and in increased plasma insulin levels compared with other TRF periods. These data provide evidence that leptin sensitivity is controlled by the circadian rhythm and that TRF periods may be most efficient when aligned with the leptin-sensitive period.-Boucsein, A., Rizwan, M. Z., Tups, A. Hypothalamic leptin sensitivity and health benefits of time-restricted feeding are dependent on the time of day in male mice.

Evaluation of the patterns of daily total locomotor activity in maned wolf (Chryosocyon brachyurus) maintained in captivity

ABSTRACT The aim of this study was to evaluate the daily total locomotor activity in captive Chrysocyon brachyurus. Three maned wolves were housed individually under natural light–dark cycle and environmental conditions. In each animal, locomotor activity was monitoored for 30 days by means of an activity data logger (Actiwatch Cambridge©Neurotechnology, Cambridge, UK), applied on a neck collar. Locomotor activity was evaluated by visual inspection of actograms. The average amount of activity during light and dark phases and Cosine 20 Peak were calculated using Actiwatc Activity Analysis 5.06. Subject A was more active during the light phase, and subjects B and C were more active during the dark phase. The single cosinor method applied on the amount of activity recorded every hour showed a daily rhythm of locomotor activity only in subject B (2 years old). Acrophase was observed between 03:20 and 07:30, and robustness had a value between 37.00% and 63.40%. Only one subject due to their early withdrawal from its natural habitat, developed a manifest anthropic dependence, with a marked adaptation to the habitat of captivity presenting an anthropophilic behavior. This study would help to define more appropriate management and conservation strategies for this emblematic mammal of South America.

Time-Lag in Feeding Schedule Acts as a Stressor That Alters Circadian Oscillators in Goldfish.

The circadian system controls temporal homeostasis in all vertebrates. The light-dark (LD) cycle is the most important zeitgeber (“time giver”) of circadian system, but feeding time also acts as a potent synchronizer in the functional organization of the teleost circadian system. In mammals is well known that food intake during the rest phase promotes circadian desynchrony which has been associated with metabolic diseases. However, the impact of a misalignment of LD and feeding cycles in the entrainment of fish circadian oscillators is largely unknown. The objective of this work was to investigate how a time-lag feeding alters temporal homeostasis and if this could be considered a stressor. To this aim, goldfish maintained under a 12 h light-12 h darkness were fed at mid-photophase (SF6) or mid-scotophase (SF18). Daily rhythms of locomotor activity, clock genes expression in hypothalamus, liver, and head kidney, and circulating cortisol were studied. Results showed that SF6 fish showed daily rhythms of bmal1a and clock1a in all studied tissues, being in antiphase with rhythms of per1 genes, as expected for proper functioning clocks. The 12 h shift in scheduled feeding induced a short phase advance (4–5-h) of the clock genes daily rhythms in the hypothalamus, while in the liver the shift for clock genes expression rhythms was the same that the feeding time shift (∼12 h). In head kidney, acrophases of per genes underwent a 12-h shift in SF18 animals, but only 6 h shift for clock1a. Plasma cortisol levels showed a significant daily rhythm in animals fed at SF6, but not in SF18 fish fed, which displayed higher cortisol values throughout the 24-h. Altogether, results indicate that hypothalamus, liver, and head kidney oscillate in phase in SF6 fish, but these clocks are desynchronized in SF18 fish, which could explain cortisol alterations. These data reinforce the hypothesis that the misalignment of external cues (daily photocycle and feeding time) alters fish temporal homeostasis and it might be considered a stressor for the animals.

Locomotor activity and body temperature rhythms in the Mahali mole-rat (C. h. mahali): The effect of light and ambient temperature variations

African mole-rats (family: Bathyergidae) are strictly subterranean mammals that reside in extensive networks of underground tunnels. They are rarely, if ever, exposed to light and experience muted temperature ranges. Despite these constant conditions, the presence of a functional circadian clock capable of entraining to external light cues has been reported for a number of species. In this study, we examine a social mole-rat species, Cryptomys hottentotus mahali, to determine if it possesses a functional circadian clock that is capable of perceiving light and ambient temperature cycles, and can integrate these cues into circadian rhythms of locomotor activity and core body temperature. Eight male and eight female, non-reproductive individuals were subjected to six cycles of varying light and temperature regimes. The majority of the individuals displayed daily rhythms of locomotor activity and body temperature that are synchronised to the external light and temperature cycles. Furthermore, endogenous rhythms of both locomotor activity and core body temperature were displayed under constant conditions. Thus, we can conclude that C. h. mahali possesses a functional circadian clock that can integrate external light and temperature cues into circadian rhythms of locomotor activity and core-body temperature.

Interspecies comparison of daily total locomotor activity monitoring in different management conditions

Abstract The aim of this study was to compare total locomotor activity in 4 domestic species housed in different stable conditions under natural 12/12 light/dark photoperiod. The study subjects were 20 Italian saddle mares, 20 Comisana ewes, 20 Maltese goats, and 20 Holstein Friesian cattle. Two treatment groups were used, with 10 subjects for each species. The first group was housed in a 1-hectare paddock. The animals in the second group were housed in boxes. Horses were housed individually in 12-m 2 boxes. Sheep and goats were housed in 2 separated common stalls of 20 m 2 each. Cows were housed in a common stall of 150 m 2 . To record locomotor activity, an Actiwatch-Mini (Cambridge Neurotechnology Ltd., UK) was placed on each animal for 7 days. These actigraphy-based data loggers record a digitally integrated measure of motor activity. A trigonometric statistical model was used to describe the main rhythmic parameters: mesor, amplitude, acrophase, and robustness of rhythm. Analysis by the cosinor procedure indicated a daily rhythm of locomotor activity in each of the 4 species studied. A multivariate analysis of variance was applied to the circadian parameters (mesor, amplitude, acrophase, and robustness), which showed a significant effect of species and housing conditions on all rhythmic parameters. We can conclude that the influence of housing conditions on the characteristics of locomotor circadian rhythm should be taken into consideration to guarantee welfare in animal breeding.

Circadian Clock Protein Content and Daily Rhythm of Locomotor Activity Are Altered after Chronic Exposure to Lead in Rat.

Lead exposure has been reported to produce many clinical features, including parkinsonism. However, its consequences on the circadian rhythms are still unknown. Here we aimed to examine the circadian rhythms of locomotor activity following lead intoxication and investigate the mechanisms by which lead may induce alterations of circadian rhythms in rats. Male Wistar rats were injected with lead or sodium acetate (10 mg/kg/day, i.p.) during 4 weeks. Both groups were tested in the “open field” to quantify the exploratory activity and in the rotarod to evaluate motor coordination. Then, animals were submitted to continuous 24 h recordings of locomotor activity under 14/10 Light/dark (14/10 LD) cycle and in complete darkness (DD). At the end of experiments, the clock proteins BMAL1, PER1-2, and CRY1-2 were assayed in the suprachiasmatic nucleus (SCN) using immunohistochemistry. We showed that lead significantly reduced the number of crossing in the open field, impaired motor coordination and altered the daily locomotor activity rhythm. When the LD cycle was advanced by 6 h, both groups adjusted their daily locomotor activity to the new LD cycle with high onset variability in lead-intoxicated rats compared to controls. Lead also led to a decrease in the number of immunoreactive cells (ir-) of BMAL1, PER1, and PER2 without affecting the number of ir-CRY1 and ir-CRY2 cells in the SCN. Our data provide strong evidence that lead intoxication disturbs the rhythm of locomotor activity and alters clock proteins expression in the SCN. They contribute to the understanding of the mechanism by which lead induce circadian rhythms disturbances.

Preliminary Results on the Daily and Seasonal Rhythms of Cuttlefish Sepia officinalis (Linnaeus, 1758) Locomotor Activity in Captivity

This research was aimed at characterizing the daily rhythms of locomotor activity of cuttlefish Sepia officinalis (Linnaeus, 1758), a promising aquaculture species, in a captive environment. Cuttlefish were distributed within two tanks equipped with infrared photocells, allowing the monitoring of locomotor activity continuously from August to February. Results showed a preference of cuttlefish for being active during the night in summer (24.2 ± 1.3 °C) and in autumn (18.4 ± 3.4 °C), with maximum activity peaks observed, respectively, at 01:09 h and 21:47 h, in close relation with sunset time. In winter (12.7 ± 1.4 °C), this preference changed, with higher levels of activity observed during the afternoon in December (15:20 h) and in January (18:13 h), thus suggesting this species as possessing a dualistic behaviour. Levels of activity progressively decreased during autumn and winter, likely related to low temperatures. The present study offers new insights on the behaviour of Sepia officinalis, presenting a variability of patterns across seasons, regulated by environmental synchronizers; photoperiod determining the activity periods, and temperature modulating the levels of activity. Such information may be a valuable tool for the improvement of cuttlefish culture protocols in aquaculture, and consequently its welfare.

Effects of bilateral anterior agranular insula lesions on food anticipatory activity in rats.

Food anticipatory activity (FAA) refers to a daily rhythm of locomotor activity that emerges under conditions of food restriction, whereby animals develop an intense, predictable period of activity in the few hours leading up to a predictable, daily delivery of food. The neural mechanisms by which FAA is regulated are not yet fully understood. Although a number of brain regions appear to be involved in regulating the development and expression of FAA, there is little evidence to date concerning the role of the anterior agranular insular cortex (AICa). The AICa plays a critical role in integrating the perception of visceral states with motivational behaviour such as feeding. We assessed the effect of bilateral electrolytic or ibotenic acid lesions of the AICa on FAA in male Wistar rats receiving food for varying lengths of time (2 h, 3 h, or 5 h) during the middle of the light phase (starting at either ZT4 or ZT6). Contrary to our initial expectations, we found that both electrolytic and ibotenic acid lesions significantly increased, rather than decreased, the amount of FAA expressed in lesioned rats. Despite increased FAA, lesioned rats did not eat significantly more during restricted feeding (RF) periods than control rats. Similar to controls, AlCa-lesioned rats showed negligible anticipatory activity to a restricted treat suggesting that the increased anticipatory activity in lesioned rats is associated with food restriction, rather than the appetitive value of the meal. Monitoring behaviour in an open field indicated that increased FAA in AlCa-lesioned rats was not explained by a general increase in locomotor activity. Together, these findings suggest that the AICa contributes to the network of brain regions involved in FAA.

Light and dark rations and the photic entrainment of circadian locomotor activity patterns in the South American Silver Catfish (Rhamdia quelen, Quoy & Gaimard, 1824)

The aim of this study was to evaluate the daily rhythm of locomotor activity in Rhamdia quelen (R. quelen). A total of 30 fish were enrolled in the study and were equally divided in 10 groups and maintained in 100 liters tanks. The locomotor activity was measured in fish maintained under the LD 12:12 photoperiod regime; thereafter, the LD cycle was reversed to DL in order to study the resynchronization and to explore the endogenous pacemaker. Subsequently, the fish were subjected to constant conditions of light to test whether or not locomotor rhythms are regulated by the endogenous circadian clock. The effect of increasing light length and intensity was studied on daily rhythm of locomotor activity of fish. Our results showed that the R. quelen is a strictly diurnal species, the rhythm of locomotory activity resynchronized quickly after inverting the LD cycle and persist under free course LL, suggesting a circadian origin. The light showed a significant masking effect often blocking the expression of the biological rhythm. The strictly diurnal behavior is controlled directly by the photoperiod and maintained even under very dim light (30 lux).

Influence of temperature on daily locomotor activity in the crab Uca pugilator.

Animals living in the intertidal zone are exposed to prominent temperature changes. To cope with the energetic demands of environmental thermal challenges, ectotherms rely mainly on behavioral responses, which may change depending on the time of the day and seasonally. Here, we analyze how temperature shapes crabs’ behavior at 2 different times of the year and show that a transition from constant cold (13.5°C) to constant warm (17.5°C) water temperature leads to increased locomotor activity levels throughout the day in fiddler crabs (Uca pugilator) collected during the summer. In contrast, the same transition in environmental temperature leads to a decrease in the amplitude of the daily locomotor activity rhythm in crabs collected during the winter. In other words, colder temperatures during the cold season favor a more prominent diurnal behavior. We interpret this winter-summer difference in the response of daily locomotor activity to temperature changes within the framework of the circadian thermoenergetics hypothesis, which predicts that a less favorable energetic balance would promote a more diurnal activity pattern. During the winter, when the energetic balance is likely less favorable, crabs would save energy by being more active during the expected high-temperature phase of the day—light phase—and less during the expected low-temperature phase of the day—dark phase. Our results suggest that endogenous rhythms in intertidal ectotherms generate adaptive behavioral programs to cope with thermoregulatory demands of the intertidal habitat.

Synchronization to light and mealtime of daily rhythms of locomotor activity, plasma glucose and digestive enzymes in the Nile tilapia (Oreochromis niloticus)

The light–dark cycle and feeding can be the most important factors acting as synchronizers of biological rhythms. In this research we aimed to evaluate synchronization to feeding schedule of daily rhythms of locomotor activity and digestive enzymes of tilapia. For that purpose, 120 tilapias (65.0±0.6g) were distributed in 12 tanks (10 fish per tank) and divided into two groups. One group was fed once a day at 11:00h (zeitgeber time, ZT6) (ML group) and the other group was fed at 23:00h (ZT18) (MD group). The fish were anesthetized to collect samples of blood, stomach and midgut at 4-hour intervals over a period of 24h. Fish fed at ML showed a diurnal locomotor activity (74% of the total daily activity occurring during the light phase) and synchronization to the feeding schedule, as this group showed anticipation to the feeding time. Fish fed at MD showed a disruption in the pattern of locomotor activity and became less diurnal (59%). Alkaline protease activity in the midgut showed daily rhythm with the achrophase at the beginning of the dark phase in both ML and MD groups. Acid protease and amylase did not show significant daily rhythms. Plasma glucose showed a daily rhythm with the achrophase shifted by 12h in the ML and MD groups. These results revealed that the feeding time and light cycle synchronize differently the daily rhythms of behavior, digestive physiology and plasma metabolites in the Nile tilapia, which indicate the plasticity of the circadian system and its synchronizers.

Chronic Light Exposure in the Middle of the Night Disturbs the Circadian System and Emotional Regulation.

In mammals, the circadian system is composed of a principal circadian oscillator located in the suprachiasmatic nucleus (SCN) and a number of subordinate oscillators in extra-SCN brain regions and peripheral tissues/organs. However, how the time-keeping functions of this multiple oscillator circuit are affected by aberrant lighting environments remains largely unknown. In the present study, we investigated the effects of chronic light exposure in the middle of the night on the circadian system by comparing the mice housed in a 12:4:4:4-h L:DLD condition with the controls in 12:12-h L:D condition. Daily rhythms in locomotor activity were analyzed and the expression patterns of protein products of clock genes Period1 and Period2 (PER1 and PER2) were examined in the SCN and extra-SCN brain regions, including the dorsal striatum, hippocampus, paraventricular nucleus (PVN), and basolateral amygdala (BLA). Following 2 weeks of housing in the L:DLD condition, animals showed disturbed daily rhythms in locomotor activity and lacked daily rhythms of PER1 and PER2 in the SCN. In the extra-SCN brain regions, the PER1 and PER2 rhythms were affected in a region-specific pattern, such that they were relatively undisturbed in the striatum and hippocampus, phase-shifted in the BLA, and abolished in the PVN. In addition, mice in the L:DLD condition showed increased anxiety-like behaviors and reduced brain-derived neurotropic factor messenger RNA expression in the hippocampus, amygdala, and medial prefrontal cortex, which are brain regions that are involved in emotional regulation. These results indicate that nighttime light exposure leads to circadian disturbances not only by abolishing the circadian rhythms in the SCN but also by inducing misalignment among brain oscillators and negatively affects emotional processing. These observations serve to identify risks associated with decisions regarding lifestyle in our modern society.