Locomotor Activity Rhythms Research Articles

The Neuropeptide PDF Is Crucial for Delaying the Phase of Drosophila’s Evening Neurons Under Long Zeitgeber Periods

Circadian clocks schedule biological functions at a specific time of the day. Full comprehension of the clock function requires precise understanding of their entrainment to the environment. The phase of entrained clock is plastic, which depends on different factors such as the period of endogenous oscillator, the period of the zeitgeber cycle (T), and the proportion of light and darkness (day length). The circadian clock of fruit fly Drosophila melanogaster is able to entrain to a wide range of T-cycles and day lengths. Here, we investigated the importance of the neuropeptide Pigment-Dispersing Factor (PDF) for entrainment by systematically studying locomotor activity rhythms of Pdf 0 mutants and wild-type flies under different T-cycles (T22 to T32) and different day lengths (8, 12, and 16 hour [h]). Furthermore, we analysed PERIOD protein oscillations in selected groups of clock neurons in both genotypes under T24 and T32 at a day length of 16 h. As expected, we found that the phase of Drosophila’s evening activity and evening neurons advanced with increasing T in all the day lengths. This advance was much larger in Pdf 0 mutants (~7 h) than in wild-type flies causing (1) pronounced desynchrony between morning and evening neurons and (2) evening activity to move in the morning instead of the evening. Most interestingly, we found that the lights-off transition determines the phase of evening neurons in both genotypes and that PDF appears necessary to delay the evening neurons by ~3 h to their wild-type phase. Thus, in T32, PDF first delays the molecular cycling in the evening neurons, and then, as shown in previous studies, delays their neuronal firing rhythms to produce a total delay of ~7 h necessary for a wild-type evening activity phase. We conclude that PDF is crucial for appropriate phasing of Drosophila activity rhythm.

Chronobiotics KL001 and KS15 Extend Lifespan and Modify Circadian Rhythms of Drosophila melanogaster

Chronobiotics are a group of drugs, which are utilized to modify circadian rhythms targeting clock-associated molecular mechanisms. The circadian clock is known as a controller of numerous processes in connection with aging. Hypothesis: KL001 and KS15 targeting CRY, affect lifespan, locomotor activity and circadian rhythm of Drosophila melanogaster. We observed a slight (2%, p < 0.001) geroprotective effect on median lifespan (5 µM solution of KL001 in 0.1% DMSO) and a 14% increase in maximum lifespan in the same group. KS15 10 µM solution extended males’ median lifespan by 8% (p < 0.05). The statistically significant positive effects of KL001 and KS15 on lifespan were not observed in female flies. KL001 5 µM solution improved locomotor activity in young male imagoes (p < 0.05), elevated morning activity peak in aged imagoes and modified robustness of their circadian rhythms, leaving the period intact. KS15 10 µM solution decreased the locomotor activity in constant darkness and minimized the number of rhythmic flies. KL001 5 µM solution improved by 9% the mean starvation resistance in male flies (p < 0.01), while median resistance was elevated by 50% (p < 0.0001). This phenomenon may suggest the presence of the mechanism associated with improvement of fat body glucose depos’ utilization in starvation conditions which is activated by dCRY binding KL001.

Elimination of glutamatergic transmission from Hb9 interneurons does not impact treadmill locomotion

The spinal cord contains neural circuits that can produce the rhythm and pattern of locomotor activity. It has previously been postulated that a population of glutamatergic neurons, termed Hb9 interneurons, contributes to locomotor rhythmogenesis. These neurons were identified by their expression of the homeobox gene, Hb9, which is also expressed in motor neurons. We developed a mouse line in which Cre recombinase activity is inducible in neurons expressing Hb9. We then used this line to eliminate vesicular glutamate transporter 2 from Hb9 interneurons, and found that there were no deficits in treadmill locomotion. We conclude that glutamatergic neurotransmission by Hb9 interneurons is not required for locomotor behaviour. The role of these neurons in neural circuits remains elusive.

Ambient Temperature as a Strong Zeitgeber of Circadian Rhythms in Response to Temperature Sensitivity and Poor Heat Dissipation Abilities in Subterranean African Mole-Rats.

Mammals have evolved circadian rhythms in internal biological processes and behaviors, such as locomotor activity (LA), to synchronize to the environmental conditions they experience. Photic entrainment of LA has been well established; however, non-photic entrainment, such as ambient temperature (Ta), has received much less attention. To address this dearth of knowledge, we exposed two subterranean endothermic-homeothermic African mole-rat species, the solitary Cape mole-rat (Georychus capensis [GC]) and social Mahali mole-rat (Cryptomys hottentotus mahali [CHM]), to varying Ta cycles in the absence of light. We showed that the LA rhythms of these two species entrain to Ta cycles and that the majority of LA occurred during the coolest 12-h period. LA confined to the coolest Ta periods may be the direct consequence of the poor heat dissipation abilities of African mole-rats brought about by physiological and ecological constraints. Recently, it has been hypothesized that Ta is only a strong zeitgeber for circadian rhythms in species whose thermoregulatory abilities are sensitive to changes in Ta (i.e., heterotherms and ectotherms), which previously has excluded endothermic-homeothermic mammals. However, this study demonstrates that Ta is a strong zeitgeber or entrainer for circadian rhythms of LA in subterranean endothermic-homeothermic mammals as a consequence of their sensitivity to changes in Ta brought about by their poor heat dissipation abilities. This study reinforces the intimate link between circadian rhythms and thermoregulation and conclusively, for the first time, provides evidence that Ta is a strong zeitgeber for endothermic-homeothermic mammals.

Notes on feeding, locomotor activity rhythms and orientation in the pygmy mole cricket Afrotridactylus cf. usambaricus in Kenya (Orthoptera: Tridactyloidea)

Immature individuals of Afrotridactylus cf. usambaricus (SjĂśstedt, 1910) were recorded on a marine sandy beach probably feeding on bacteria, microalgae and mesopsammic organisms. The larvae of this pygmy mole cricket probably obtain these organisms by manipulating grains of sand with their buccal apparatus during the excavation of tunnels close to the surface of the sand. This occurs in daytime during the ebb tide while direct migration to the sea is in progress. Therefore, the migration occurs according to a diurnal-tidal rhythm having been detected only in correspondence with the low diurnal tides. This rhythmic activity remains in phase with the diurnal-tidal periodicity even far from the sea, in a confined environment. Individuals tested in a transparent Plexiglas bowl are able to assume and maintain the sea-land direction of the beach constant throughout the day in the absence of the landscape vision.

Locomotor activity rhythms of North Atlantic coastal talitroids

ABSTRACT Locomotor activity rhythms of one hyalid and six talitrids were deterermined extending published rhythms to species in three new ecotopes previously not examined in this way: eulittoral – the hyalid, Apohyale prevosti (H. Milne Edwards 1830) with a circatidal rhythm, supralittoral/palustral – the talitrid, ‘Orchestia’ grillus Bosc 1802 and supralittoral/xylophagous talitrid, Macarorchestia remyi (Schellenberg 1950), where activity was random in both. A xylophagous-acclimated population of Platorchestia platensis (Krøyer 1845) living in a secondary ecotope also exhibited random activity. Endogenous diel rhthyms with maximum activity during darkness were present in the supralittoral wrack generalists [P. platensis and Orchestia gammarellus (Pallas 1766)] and sand-burrowing specialists [Americorchestia longicornis (Say 1818) and A. megalophthalma (Spence Bate 1862)]. The tentative order for talitrids examined here and in the literature, from high to low, in their susceptibility to passive, natural dispersal in wrack/driftwood is therefore as follows: O. gammarellus + P. platensis > O. mediterranea Costa 1853 > marsh-hoppers > sand-hoppers > driftwood-hoppers.

Effect of periodic social interaction and odour presentation of same and opposite-sex conspecifics on free-running mice

ABSTRACT Social interaction, a non-photic cue, plays a role in the synchronization of circadian rhythm under constant environmental conditions. However, little is known about the effect of sex-specific interaction and sex-specific odor on the free-running circadian clock of mice. Hence, in the present study, we investigated the effect of social interaction and odor presentation of same and opposite-sex conspecifics on the free-running rhythm of mice. In this investigation, stranger and dummy mice (saturated with either male- or female-associated odor) were separately exposed to the same and opposite-sex conspecifics of male and female runners and receivers, respectively for 30 min at CT15 for 10–12 d. The results showed that the daily exposure of runners with same and opposite-sex strangers entrained the free-running locomotor activity rhythm in a gender-specific manner. However, daily exposure of same and opposite-sex conspecific odors masked the circadian rhythm of receiver animals by increasing the activity. Further, social interaction and odor presentation caused lengthened and shortened period length, respectively. These results suggest that periodic social interactions can produce entrainment and conspecific odor can produce only masking on free-running circadian locomotor activity rhythm in mice.

Locomotor activity rhythm in catfish Heteropneustes fossilis as a function of shoal size under different light regimens

ABSTRACT The information on the circadian characteristics of catfish in shoals is scanty. We examined the circadian locomotor activity rhythm of catfish Heteropneustes fossilis either singly housed (SS1) or in shoals of four (SS4) and six (SS6) under different light regimens. We carried out the study sequentially under LD1 (12:12), constant darkness (DD), LD2, continuous light (LL), LD3, and DL (12:12). Each condition was for at least 10–12 consecutive days. We analyzed the time-series data by employing Cosinor rhythmometry to detect circadian rhythm characteristics in locomotor activity at a fixed time window with a τ = 24 h. Results indicated that singly housed or shoals exhibited statistically significant (p < .001) circadian rhythm in locomotor activity under LD conditions with a higher activity level during the dark phase. Further, we observed free-running rhythms in locomotor activity under DD and LL, irrespective of the shoal sizes. In phase inverse DL, both singly housed and shoals demonstrated higher activity in the dark phase. The two-way ANOVA results revealed a significant effect of the factor ‘light regimen’ on amplitude and acrophase; the factor ‘shoal size’ produced a statistically significant impact on the mesor only. Both shoals showed significantly higher mesor than singly housed fish. The circadian amplitude declined under constant conditions of DD and LL. The locomotor activity rhythm exhibited a free-running pattern with a τFR greater than 24 h under both DD and LL conditions. We conclude that light is a more prominent factor for the entrainment of circadian activity in catfish H. fossilis. However, the extent of social aggregation (shoal size) has little or no effects on the characteristics of circadian locomotor activity rhythm in H. fossilis.

Chronic lead exposure alters photic entrainment of locomotor activity rhythm and neuronal photoactivation in the suprachiasmatic nucleus of the adult rat

Chronic lead (Pb) exposure affects the circadian physiological processes regulated by suprachiasmatic nucleus (SCN), which is synchronized (entrainment) by light. Disorders in the entrainment capacity of an organism alter its performance to interact with the environment, thus affecting its health status. The objectives of the present study were to evaluate whether chronic early Pb exposure affects the entrainment of the circadian rhythm of locomotor activity by light and to explore the possible mechanisms involved. Adult male Wistar rats, control and chronically exposed to Pb (320 ppm) in drinking water from gestation to adult age, were used. Assessment of the metal level showed a significant increase of Pb in the blood, hypothalamus and prefrontal cortex of the experimental rats. Continuous registrations of locomotor activity (12 h:12 h light-dark cycle) depicted that Pb induces important delay of this activity when the light was turned off. The Pb exposed animals entrained faster with a photoperiod delay of 6 h, (lights on at 13:00 h), and maintained the significant delay in the onset of activity at lights out. In continuous darkness, the animals were exposed to a light pulse at circadian time 23. This resulted in a significant decrease of photo-stimulated neurons (immunoreactivity to c-Fos) in the SCN of the metal-exposed animals. These results show that chronic early Pb exposure alters the photic entrainment of the rhythm of locomotor activity, which is evidenced by a significant decrease in both the number of photo-stimulated neurons and neuronal population (Nissl stain) of the SCN.

Locomotor activity rhythms in laboratory‐reared adults of the mangrove cricket, Apteronemobius asahinai

AbstractAdults of the mangrove cricket, Apteronemobius asahinai, collected in the field continuously show a circatidal rhythm in their locomotor activity. However, it remained unclear whether adult crickets reared from eggs in the laboratory, without cyclic tidal influence, show the circatidal rhythm. We show that under constant red dim light, slightly less than half of crickets showed a circatidal rhythm continuously for more than 10 days. On the other hands, Some others showed a unimodal daily rhythm either before or after the tenth day in the activity recording. Thus, some environmental factors other than the laboratory conditions should be required in order for all crickets to express a clear circatidal rhythm. Even under constant light, unimodal daily rhythm appeared. The unimodal daily rhythm was entrained to light–dark cycles in some crickets, but not in the others. Therefore, we cannot conclude whether the unimodal daily rhythm is a circadian rhythm or a rhythm derived from a circatidal rhythm with its period doubled.

Regulation of high-frequency rhythms of the behavioral activity by oligopeptides structurаlly related to oxytocin

The pharmacological regulation of high-frequency rhythms of the behavioral activity (with a period of up to 1/2 hour) is an actual direction of modern medical science. The aim of the study was to assess the influence of oligopeptides structurally related to oxytocin on the parameters of ultradian rhythms of locomotor activity (LA) in outbred ICR laboratory mice. LA was recorded automatically in a multichannel actometer (Ugo Basile, Italy) in the conditions of individual detection. Amplitude, acrophase, and mesor of biorhythms’ were determined by the Cosinor analysis. Oligopeptides structurally related to oxytocin fragments, as well as memantine under systemic (intraperitoneal) administration, had a pronounced influence on the ultradian LA biorhythms of mice. Memantine (10.0 mg/kg), Cyclo-(Leu-Gly) (0.025 mg/kg), Pro-Leu (0.5 mg/kg), and Leu-Gly (0.1 mg/kg) triggered the migration to the right of the acrophase of statistically significant 24-minute LA rhythms versus control. A further study of the peptidergic mechanisms of regulation of fluctuations in ultradian biorhythms can contribute to the development of the theoretical foundations of chronobiology, as well as to the search for the means correcting the desynchronoses.

Estrogen Receptor Alpha Is Required to Protect Daily Metabolic Rhythms From Disruption by High-Fat Feeding in Female Mice

The circadian system is a critical regulator of obesity in male mice, but its role in females is poorly understood. In our previous studies we found that estrogen regulates daily rhythms in female mice to confer resistance to diet-induced obesity, but the mechanism is unknown. Estrogen signals via the classical estrogen receptor alpha (ERα) to regulate metabolism and obesity. Therefore, in this study we tested the hypothesis that estrogen regulates daily metabolic rhythms in females via ERα. To do so, we studied daily rhythms in female global ERα knockout (ERα KO) with the circadian reporter, PERIOD2::LUCIFERASE, mice fed high-fat diet for 6 weeks. ERα KO female mice became obese and hyperglycemic when fed high-fat diet, while wild-type females were resistant to diet-induced obesity. Chronic high-fat diet feeding also reduced the amplitude of the daily rhythm of eating behavior in ERα KO, but not wild-type, female mice. In wild-type females, the amplitude of the locomotor activity rhythm increased during high-fat feeding. In contrast, high-fat feeding decreased the amplitude of the activity rhythm in ERα KO females. The temporal relationship between central and peripheral circadian tissue clocks was disrupted by high-fat feeding in ERα KO females since the phase of the liver PERIOD2::LUCIFERASE rhythm was advanced 4 hours by high-fat feeding in ERα KO mice compared to wild-type females. Taken together these results show that estrogen signals via ERα to protect daily metabolic rhythms from disruption by high-fat feeding in female mice.

Selective MT 2 Melatonin Receptor Antagonist Modulates Circadian Activity via Inhibition of the Endogenous Melatonin Signal in the East Bound Jet Lag Model

Activation of melatonin receptors facilitates re-entrainment of circadian activity rhythms following an advance of the dark onset. In an eastbound jet lag model, administration of exogenous melatonin, at the new dark onset, accelerates re-entrainment via activation of the MT1 receptor (Dubocovich et al., 2005). Conversely, melatonin proficient mice (C3H/HeN) with a targeted deletion of the MT2 receptor (MT2KO), but not the MT1 receptor (MT1KO), experience a deceleration in re-entrainment, probably due to impairment of the endogenous melatonin facilitated signaling mediated by activation of the MT2 receptor (Pfeffer et al., 2012). To further elucidate the functional modulatory role of melatonin receptors on the synchronization of the circadian clock, we assessed locomotor activity rhythms in C3H/HeN mice in response to pharmacological intervention to determine the ability of the MT2 selective antagonist, ATBT-23 (hMT1/hMT2 Ki=190), to decelerate re-entrainment by blocking the MT2 receptor, thus mimicking the MT2KO. Male C3H/HeN mice in a 12/12 L/D cycle were subjected to an eastbound jet lag paradigm in which Vehicle (30% ethanol/saline, s.c) or ATBT-23 (1 mg/kg in Vehicle, s.c) were administered on three consecutive days at the new dark onset following an abrupt 6-hour advance of the L/D cycle. The number of days to re-entrain and re-entrainment rates (hrs/day) were analyzed by two-way ANOVA (Tukey's post hoc test) and a mixed effect two-way repeated measure ANOVA (Sidak's post hoc test), respectively. WT (7.54±0.33 days, n=28) and MT1KO (7.36±0.54 days, n=14) mice treated with vehicle did not show a significant difference in the number of days necessary to attain re-entrainment. However, MT2KO (11.92±0.40 days, n=13) mice, treated with vehicle, took significantly longer to re-entrain when compared to WT and MT1KO mice (p<0.0001). This deceleration of re-entrainment in the MT2KO was reproduced by ATBT-23, which decelerated the rate of re-entrainment in both WT (p<0.0001, n=25) and MT1KO (p<0.01, n=12) males, increasing the number of days to re-entrain to 9.76±0.46 (p<0.01) and 10.00±0.63 (p<0.05) days, respectively. ATBT-23 (n=14) did not significantly affect the number of days to re-entrain in MT2KO mice, suggesting deceleration of re-entrainment is not mediated by the MT1 receptor. The present study suggests that ATBT-23 decelerates re-entrainment of circadian activity rhythms by blocking the potent acceleration of re-entrainment by endogenous melatonin via action on the MT2 receptor. Therefore, selective MT2 melatonin receptor antagonists can potentially be used to delay advanced circadian rhythms, as observed in depression and advance sleep phase disorders, when administered at proper circadian times.

Social interaction masking contributes to changes in the activity of the suprachiasmatic nucleus and impacts on circadian rhythms

Light is the most powerful temporal cue that entrains physiology and behavior through modulation of the suprachiasmatic nucleus (SCN) of the hypothalamus. However, on a daily basis, individuals face a combination of light and several non-photic cues, such as social interaction. In order to investigate whether SCN activity and SCN-driven rhythms are altered by social interaction, adult male C57BLJ/6 mice were maintained in groups of 3–4 animals per cage or 1 animal per cage (socially isolated) under 12:12 h / light:dark (LD) cycles or constant darkness (DD). Analysis of the two anatomical subdivisions (ventral, v and dorsal, d) of the medial SCN revealed an effect of housing conditions on the d-SCN but not on the v-SCN on the number of c-Fos immunoreactive (ir) neurons. As such, 2 h after the light-phase onset d-SCN c-Fos-ir number was lower in single-housed mice under LD. Importantly, under DD there were no effect of housing conditions in the number of c-Fos-ir SCN neurons. Social isolation increased the amplitude and strength of SCN-driven rhythm of body temperature (Tc) entrained to LD and it advanced its onset, uncoupling with spontaneous locomotor activity (SLA) rhythm, without altering endogenous Tc and SLA rhythms expressed under DD. Associated with reduced Tc in the light phase, single-housed mice showed reduced body weight. However, these phenotypes were not accompanied by changes in the number of c-Fos-ir neurons in the preoptic area (POA), which are known to regulate energy metabolism and Tc. Altogether, these results imply that the social interaction masking effect on the d-SCN is added to that of light stimulus, in order to achieve full c-Fos expression in the SCN, which, in turn seems to be required to maintain daily-phase coherence between the photo-entrained rhythms of Tc and SLA. There might be an inter-relationship between masking (social interaction) and entrainment stimulus (light) that impacts the circadian parameters of the photo-entrained Tc rhythm. As such, in the absence of social interactions a more robust Tc rhythm is shown. This inter-relationship seems to occur in the dorsal subdivision of the SCN but not in the POA.

Locomotor activity rhythm of catfish Heteropneustes fossilis are prominently regulated by light-dark cues

It is interesting to explore, the circadian locomotor activity rhythm of dark adapted fishes. Therefore, it is aimed to investigate the circadian locomotor activity rhythm of catfish, Heteropneustes fossilis under different light regi-mens- light-dark condition LD 12:12, constant dark condition DD, constant light LL and dark-light condition DL 12:12 in both male and female. The study was conducted sequentially under LD 12: 12 (LON 0500 and LOFF 1700) and thereafter under the DD, LL and DL each for at least 10-12 consecutive days. The locomotor activity was monitored using Stanford Chronobiology Kit at a fixed period of 24 h. The three rhythm parameters obtained were Mesor (M, rhythm-adjusted 24-h average), amplitude (A) and acrophase (peak, Ø). All fish exhibited a statistically significant (p&lt;0.001) circadian rhythm in locomo-tor activity under all light regimens LD, DD, LL and DL. The circadian ampli-tude was significantly declined under constant DD and LL. A significant shift was displayed in the circadian acrophase in all fish under each photic re-gimes LD, DD, LL and DL. The effect of light condition on M, A and Ø was sig-nificant, while gender imposed no effect. Chi-square periodogram revealed τ &gt; 24 h in locomotor activity of most of the replicates under DD and LL. The respective study suggests that the endogenous circadian clocks in catfish H.fossilis are weakly expressed under constant conditions and requires light-dark LD or dark- light DL cues to generate/express the circadian rhythm in locomotor activity.

Intensive longitudinal characterization of multidimensional biobehavioral dynamics in laboratory rats.

Rats have been used as animal models for human diseases for more than a century, yet a systematic understanding of basal biobehavioral phenotypes of laboratory rats is still missing. In this study, we utilize wireless tracking technology and videography, collect and analyze more than 130 billion data points to fill this gap, and characterize the evolution of behavior and physiology of group-housed male and female rats (n= 114) of the most commonly used strains (Lister Hooded, Long-Evans, Sprague-Dawley, and Wistar) throughout their development. The resulting intensive longitudinal data suggest the existence of strain and sex differences and bi-stable developmental states. Under standard laboratory 12-h light/12-h dark conditions, our study found the presence of multiple oscillations such as circatidal-like rhythms in locomotor activity. The overall findings further suggest that frequent movement along cage walls or thigmotaxic activity may be a physical feature of motion in constrained spaces, critically affecting the interpretation of basal behavior of rats in cages.

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.

Relationship between locomotor activity rhythm and corticosterone levels during HCC development, progression, and treatment in a mouse model.

Cancer-related fatigue (CRF) and stress are common symptoms in cancer patients and represent early side effects of cancer treatment which affect the life quality of the patients. CRF may partly depend on disruption of the circadian rhythm. Locomotor activity and corticosterone rhythms are two important circadian outputs which can be used to analyze possible effects on the circadian function during cancer development and treatment. The present study analyzes the relationship between locomotor activity rhythm, corticosterone levels, hepatocellular carcinoma (HCC) development, and radiotherapy treatment in a mouse model. HCC was induced in mice by single injection of diethylnitrosamine (DEN) and chronic treatment of phenobarbital in drinking water. Another group received chronic phenobarbital treatment only. Tumor bearing animals were divided randomly into four groups irradiated at four different Zeitgeber time points. Spontaneous locomotor activity was recorded continuously; serum corticosterone levels and p-ERK immunoreaction in the suprachiasmatic nucleus (SCN) were investigated. Phenobarbital treated mice showed damped corticosterone levels and a less stable 24hours activity rhythm as well as an increase in activity during the light phase, reminiscent of sleep disruption. The tumor mice showed an increase in corticosterone level during the inactive phase and decreased activity during the dark phase, reminiscent of CRF. After irradiation, corticosterone levels were further increased and locomotor activity rhythms were disrupted. Lowest corticosterone levels were observed after irradiation during the early light phase; thus, this time might be the best to apply radiotherapy in order to minimize side effects.

Repetitive optogenetic stimulation of glutamatergic neurons: An alternative to NMDA treatment for generating locomotor activity in spinalized zebrafish larvae.

N‐methyl‐d‐aspartate (NMDA) application has conventionally been used to activate spinal networks to induce locomotion in spinalized animals. We recently described an alternative approach in which application of continuous blue light activates channelrhodopsin‐2 in vesicular glutamate transporter 2a (vglut2a)‐expressing spinal neurons to produce organized, rhythmic locomotor activity in spinally‐transected larval zebrafish. This technique arguably enhances research validity, because endogenous glutamate is released into existing synapses instead of activating only a subset of glutamatergic (NMDA) receptors with an exogenous compound. Here, we explored the viability of this approach in the context of using it for longer‐term experiments. Fictive swimming was induced through repetitive application of 10‐s blue light stimuli to spinalized preparations for up to 60 min at intervals of 1, 3, or 15 min. Locomotor activity was maintained throughout the experimental timecourse, demonstrating the robustness of the system. Although locomotor bursts remained organized into episodes of activity, the number of bursts elicited during each successive stimulus decreased. This was in contrast to NMDA bath application, in which bursts became less episodically organized while the overall number of bursts remained unchanged. The efficacy of the repetitive optogenetic stimulation paradigm was demonstrated through application of exogenous dopamine, which reversibly decreased the number of bursts produced per stimulus compared with untreated preparations. Finally, increasing the stimulus interval to 15 min lessened, but did not eliminate locomotor fatigue from repetitive activation. Altogether, we established repetitive optogenetic stimulation of vglut2a‐expressing neurons as a viable alternative to NMDA application for activation of the zebrafish spinal locomotor network.