Effects of bilateral striatal 6-OHDA lesions on circadian rhythms in the rat: a radiotelemetric study

The present work aims to document, in a previously described animal model of Parkinson (double bilateral striatal injection of 6-OHDA), the possible modifications of circadian markers rhythms i.e. temperature (T), heart rate (H) and locomotor activity (A) registered continuously by telemetry, in order to evaluate a possible perturbation of the circadian rythmicity. H, T and A were measured by radiotelemetry after surgical implantation of the transmitters (Data Sciences). After a recovery period, the study was divided into a control period (C) for baseline measurements of T, H and A daily rhythms. Then, the stereotaxic 6-OHDA striatal lesion was done to a group of 4 rats while the control rats were injected into striata with saline; a second period of four registration weeks was observed [D 1-7 (W1), D 8-14 (W2), D 15-21 (W3), D 22-28 (W4)]. Finally, at the end of this period the seven rats were decapited in order to determine their striatal dopamine (DA) content. Our data document that the circadian rhythms of H, T and A were differently affected according to time. Thus, a temporary loss of circadian periodicity was observed particularly for heart rate. 6-OHDA-induced modifications of H, T and A circadian rhythm characteristics were also observed: a significant decrease of the mesor was observed for the three rhythms as well as a phase advance. Concerning the amplitude of these rhythms, only H was significantly decreased. These perturbations were observed during the four weeks following the intervention, never reaching the initial control levels. Such observed perturbations would supply a basis for the future study of the chronopharmacology of antiparkinsonian drugs.     

Effects of Three‐Hour Restricted Food Access during the Light Period on Circadian Rhythms of Temperature,Locomotor Activity,and Heart Rate in Rats

The effects of food on biological rhythms may influence the findings of chronopharmacological studies. The present study evaluated the influence of a restricted food access during the rest (light) span of nocturnally active Wistar rats on the 24 h time organization of biological functions in terms of the circadian rhythms of temperature (T), heart rate (HR), and locomotor activity (LA) in preparation for subsequent studies aimed at evaluating the influence of timed food access on the pharmacokinetics and pharmacodynamics of medications. Ten‐wk‐old male Wistar rats were housed under controlled 12:12 h light:dark (LD) environmental conditions. Food and water were available ad libitum, excepted during a 3 wk period of restriction. Radiotelemetry transmitters were implanted to record daily rhythms in T, HR, and LA. The study lasted 7 wk and began after a 21‐d recovery span following surgery. Control baseline data were collected during the first wk (W1). The second span of 3 wk duration (W2 to W4) consisted of the restricted feeding regimen (only 3 h access to food between 11:00 and 14:00 h daily) during the L (rest span) under 12:12 h LD conditions. The third period of 3 wk duration (W5 to W7) consisted of the recovery span with ad libitium normal feeding. Weight loss in the amount of 5% of baseline was observed during W1 with stabilization of body weight thereafter during the remaining 2 wk of food restriction. The 3 h restricted food access during the L rest span induced a partial loss of circadian rhythmicity and the emergence of 12 h rhythms in T, HR, and LA. Return to ad libitum feeding conditions restored circadian rhythmicity in the manner evidenced during the baseline control span. Moreover, the MESORS and amplitudes of the T, HR, and LA 24 h patterns were significantly attenuated during food restriction (p<0.001) and then returned to initial values during recovery. These changes may be interpreted as a masking effect, since T, HR, and LA are known to directly react to food intake. The consequences of such findings on the methods used to conduct chronokinetic studies, such as the fasting of animals the day before testing, are important since they may alter the temporal structure of the organism receiving the drug and thereby compromise findings.     

Effects of three-hour restricted food access during the light period on circadian rhythms of temperature, locomotor activity, and heart rate in rats

The effects of food on biological rhythms may influence the findings of chronopharmacological studies. The present study evaluated the influence of a restricted food access during the rest (light) span of nocturnally active Wistar rats on the 24 h time organization of biological functions in terms of the circadian rhythms of temperature (T), heart rate (HR), and locomotor activity (LA) in preparation for subsequent studies aimed at evaluating the influence of timed food access on the pharmacokinetics and pharmacodynamics of medications. Ten-wk-old male Wistar rats were housed under controlled 12:12 h light:dark (LD) environmental conditions. Food and water were available ad libitum, excepted during a 3 wk period of restriction. Radiotelemetry transmitters were implanted to record daily rhythms in T, HR, and LA. The study lasted 7 wk and began after a 21-d recovery span following surgery. Control baseline data were collected during the first wk (W1). The second span of 3 wk duration (W2 to W4) consisted of the restricted feeding regimen (only 3 h access to food between 11:00 and 14:00 h daily) during the L (rest span) under 12:12 h LD conditions. The third period of 3 wk duration (W5 to W7) consisted of the recovery span with ad libitium normal feeding. Weight loss in the amount of 5% of baseline was observed during W1 with stabilization of body weight thereafter during the remaining 2 wk of food restriction. The 3 h restricted food access during the L rest span induced a partial loss of circadian rhythmicity and the emergence of 12 h rhythms in T, HR, and LA. Return to ad libitum feeding conditions restored circadian rhythmicity in the manner evidenced during the baseline control span. Moreover, the MESORS and amplitudes of the T, HR, and LA 24 h patterns were significantly attenuated during food restriction (p < 0.001) and then returned to initial values during recovery. These changes may be interpreted as a masking effect, since T, HR, and LA are known to directly react to food intake. The consequences of such findings on the methods used to conduct chronokinetic studies, such as the fasting of animals the day before testing, are important since they may alter the temporal structure of the organism receiving the drug and thereby compromise findings.     

WINTERTIME LOSS OF ULTRADIAN AND CIRCADIAN RHYTHMS OF BODY TEMPERATURE IN THE SUBTERRANEAN EUTHERMIC MOLE VOLE,ELLOBIUS TALPINUS

Subterranean common mole voles, Ellobius talpinus, were implanted with long-term recording electronic thermometers to obtain hourly body temperature (T_b) data during either the wintertime or summertime. The two individuals tested during the summertime had significant circadian and ultradian rhythms in their T_b. Four of the five mole voles tested during the wintertime lacked rhythmicity in their T_b. The fifth individual lacked circadian rhythms but had ultradian rhythms in its T_b. A loss of circadian rhythms in T_b during deep torpor or hibernation has been reported for a few species of mammals. Inasmuch as the mole voles' wintertime T_b remained at euthermic levels, our results show that a loss of circadian body temperature rhythms in mole voles does not require the low T_b of deep torpor or hibernation. A tentative conclusion, based on these few animals, is that in common mole voles the T_b rhythms may disappear during the wintertime even though their T_b remains high. (Author correspondence: eug_nov@ngs.ru)     

CIRCADIAN STUDY OF DECOMPRESSION SICKNESS SYMPTOMS AND RESPONSE-ASSOCIATED VARIABLES IN RATS

In order to study circadian rhythms and decompression sickness (DCS), we determined: 1) the baseline circadian time structure in noncompressed rats of potential response variables to compression/decompression (C/D), and 2) whether rats subjected to C/D display a circadian time-dependent difference in inflammatory response intensity and biological tolerance. Subgroups of male rats, standardized to a 12?h light/12?h dark schedule, were evaluated every 4?h over 24?h after they were either compressed to 683?kPa (group E) or remained at sea level (group C). During 60?min recovery, evaluation included gross DCS symptoms and pulmonary edema in all E rats, and cell counts, nitric oxide, protein, thromboxane B_2, and leukotriene E₄ levels in survivors. Chi-square, ANOVA, and 24?h cosinor analyses were used to test for time-of-day effects. C/D exposures near the end of dark/activity or during light/resting were generally better tolerated, with lowest signs of DCS symptoms and lowest responses by most of the variables monitored. More deaths were observed in the first half of the dark/activity span. Of the 16 subsets of inflammatory-associated variables, overall increases were observed in 13 and decreases in 2. Significant or borderline significant circadian time effects were found in 14 variables in group C, 12 variables in group E, and 13 variables in response (E%C). Thus, nearly all baseline indices of DCS demonstrated circadian time-dependencies in the sea-level exposed control rats (group C), and nearly all were modified by the circadian time of C/D. Such time-of-day effects of DCS are potentially relevant to the operational concerns of occupations involving decompression exposures and the investigation of prevention and treatment intervention strategies of DCS. (Author correspondence: Bruce.D.Butler@uth.tmc.edu).     

DISSOCIATION OF THE CIRCADIAN SYSTEM OF OCTODON DEGUS BY T28 AND T21 LIGHT-DARK CYCLES

Octodon degus is a primarily diurnal rodent that presents great variation in its circadian chronotypes due to the interaction between two phase angles of entrainment, diurnal and nocturnal, and the graded masking effects of environmental light and temperature. The aim of this study was to test whether the circadian system of this diurnal rodent can be internally dissociated by imposing cycles shorter and longer than 24?h, and to determine the influence of degus chronotypes and wheel-running availability on such dissociation. To this end, wheel-running activity and body temperature rhythms were studied in degus subjected to symmetrical light-dark (LD) cycles of T28h and T21h. The results show that both T-cycles dissociate the degus circadian system in two different components: one light-dependent component (LDC) that is influenced by the presence of light, and a second non–light-dependent component (NLDC) that free-runs with a period different from the external lighting cycle. The LDC was more evident in the nocturnal than diurnal chronotype, and also when wheel running was available. Our results show that, in addition to rats and mice, degus must be added to the list of species that show an internal dissociation in their circadian rhythms when exposed to forced desynchronization protocols. The existence of a multioscillatory circadian system having two groups of oscillators with low coupling strength may explain the flexibility of degus chronotypes. (Author correspondence: angerol@um.es)     

The possible role of estrogen and selective estrogen receptor modulators in a rat model of Parkinson's disease

AimThe aim of the present study was to assess and compare the effect of 17β-estradiol and two different selective estrogen receptor modulators (SERMs), tamoxifen and raloxifene, as well as a selective estrogen receptor alpha agonist, propyl-pyrazole-triol (PPT) and a selective estrogen receptor beta agonist, diarylpropionitrile (DPN), on behavioral and biochemical alterations in 6-hydroxydopamine (6-OHDA)-induced nigral dopaminergic cell death in rats.Main methods80 female Wister rats were used. Animals were divided into eight equal groups: Group I; Sham operated, Group II; subjected to ovariectomy (OVX), Group III; OVX rats received striatal injection of 6-OHDA, Groups IV–VIII; OVX rats received striatal injection of 6-OHDA and were injected daily with 17β-estradiol, tamoxifen, raloxifene, PPT and DPN respectively for 5 days before 6-OHDA and continued for further 2 weeks.Key findingsResults showed that striatal injection of 6-OHDA produced significant behavioral alteration suggestive of PD, together with significant decrease in striatal dopamine, homovanillic acid (HVA) and 3,4-dihydroxyphenyl acetic acid (DOPAC) concentrations. 6-OHDA-induced nigral dopaminergic cell death was characterized by oxidative stress, evidenced by significant decrease in striatal glutathione peroxidase activity, as well as apoptosis, evidenced by significant increase in nigral caspase-3 activity. Treatment with 17β-estradiol, raloxifene, PPT, but neither tamoxifen nor DPN, resulted in significant amelioration of the behavioral and biochemical alterations induced by 6-OHDA.SignificanceThese findings suggest that estrogen and some SERMs having estrogenic agonist activity in the brain, like raloxifene, might exert beneficial effect in PD.     

Fibroblast Circadian Rhythms of PER2 Expression Depend on Membrane Potential and Intracellular Calcium

The suprachiasmatic nucleus (SCN) of the hypothalamus synchronizes circadian rhythms of cells and tissues throughout the body. In SCN neurons, rhythms of clock gene expression are suppressed by manipulations that hyperpolarize the plasma membrane or lower intracellular Ca²⁺. However, whether clocks in other cells also depend on membrane potential and calcium is unknown. In this study, the authors investigate the effects of membrane potential and intracellular calcium on circadian rhythms in mouse primary fibroblasts. Rhythms of clock gene expression were monitored using a PER2::LUC knockin reporter. Rhythms were lost or delayed at lower (hyperpolarizing) K⁺ concentrations. Bioluminescence imaging revealed that this loss of rhythmicity in cultures was due to loss of rhythmicity of single cells rather than loss of synchrony among cells. In lower Ca²⁺ concentrations, rhythms were advanced or had shorter periods. Buffering intracellular Ca²⁺ by the calcium chelator 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester (BAPTA-AM) or manipulation of inositol triphosphate (IP₃)-sensitive intracellular calcium stores by thapsigargin delayed rhythms. These results suggest that the circadian clock in fibroblasts, as in SCN neurons, is regulated by membrane potential and Ca²⁺. Changes in intracellular Ca²⁺ may mediate the effects of membrane potential observed in this study. (Author correspondence: welshdk@ucsd.edu)     

Individual Variation in Sleep-Wake Rhythms in Free-Living Birds

Ultradian rhythms, such as sleep-wake periodicities, during the night might represent basic rest-activity cycles of organisms that are fundamental to the temporal organization and synchronization of behavior throughout the day. However, in contrast to circadian rhythms, little is known about the underlying oscillators and molecular mechanisms of higher-frequency rhythms. A fundamental step for the understanding of the mechanisms of these latter periodicities is the analysis of variation in sleep-wake cycles in free-living animals, which can help in estimating the relative importance of genetic and environmental influence on the rhythmicity. We analyzed variation in the level of rhythmicity and period length (τ) of behaviorally defined sleep-wake cycles in a natural population of blue tits Cyanistes caeruleus. Our results indicate that the expression of periodicity in sleep-wake patterns, but not τ, has a strong individual-specific basis. The within-individual repeatability estimate of the expression of periodicity was .45 (95% confidence interval: .35–.55) when data from males and females were combined. In addition, periodicity was influenced by specific environmental factors, such as night temperature, seasonal date, and age of the individual. Most strikingly, low nighttime temperature negatively affected periodicity of sleep-wake patterns, potentially via a hypothermic response of the birds. Our results further suggest that τ is influenced by photoperiod. Blue tits showed longer sleep-wake rhythms when the nights were longer. These observations suggest a genetic basis for the incidence of rhythmic sleep-wake behavior in addition to environmental modifications of their specific expression. (Author correspondence: mueller@orn.mpg.de)     

Effect of subthalamic nucleus or entopeduncular nucleus lesion on levodopa-induced neurochemical changes within the basal ganglia and on levodopa-induced motor alterations in 6-hydroxydopamine-lesioned rats

Inactivation of the subthalamic nucleus (STN) or the internal segment of the pallidum (GPi)/entopeduncular nucleus (EP) by deep brain stimulation or lesioning alleviates clinical manifestations of Parkinson's disease (PD) as well as reducing the side-effects of levodopa treatment. However, the effects of STN or entopeduncular nucleus (EP) lesion on levodopa-related motor fluctuations and on neurochemical changes induced by levodopa remain largely unknown. The effects of such lesions on levodopa-induced motor alterations were studied in 6-hydroxydopamine (6-OHDA)-lesioned rats and were assessed neurochemically by analyzing the functional activity of the basal ganglia nuclei, using the expression levels of the mRNAs coding for glutamic acid decarboxylase and cytochrome oxidase as molecular markers of neuronal activity. At the striatal level, preproenkephalin (PPE) mRNA levels were analyzed. We found in 6-OHDA-lesioned rats that a unilateral STN or EP lesion ipsilateral to the 6-OHDA lesion had no effect on either the shortening in the duration of the levodopa-induced rotational response or the levodopa-induced biochemical changes in the basal ganglia nuclei. In contrast, overexpression of PPE mRNA due to levodopa treatment was reversed by the STN or EP lesion. Our study thus shows that lesion of the EP or STN may counteract some of the neurochemical changes induced by levodopa treatment within the striatum.     

Disrupted circadian rhythms of body temperature,heart rate and fasting blood glucose in prediabetes and type 2 diabetes mellitus

We report a progressive disruption of 24-h rhythms in fasting blood glucose (FBG), body temperature (BT) and heart rate (HR) associated with metabolic dysfunction and the development of prediabetes (PD) and type 2 diabetes mellitus (T2DM) in overweight middle-aged (40–69 years old) humans. Increasing BT and HR mean values and declining 24-h BT and HR amplitudes accompany adverse changes in metabolic state. Increased nocturnal BT and a phase delay of the 24-h BT rhythm, deviant 24-h HR profile and a phase advance of the 24-h HR and FBG rhythms are early signs of the PD metabolic state. In T2DM, the 24-h FBG rhythm is no longer detectable, and the 24-h amplitudes of BT and HR are greatly diminished. In addition, lepton and creatinine values were lowered in T2DM. Moreover, positive correlations between FBG and body mass index, BMI, and negative correlations between the 24-h amplitude of FBG and BMI indicate that overweight is an additional factor causing disruption of the circadian rhythms. Further studies on circadian disruption as a consequence of metabolic dysfunction are necessary. The quantitative analysis of changing circadian BT and HR rhythms may provide prognostic markers of T2DM and therapeutic targets for its prevention and correction.     

RHYTHMIC cFOS EXPRESSION IN THE VENTRAL SUBPARAVENTRICULAR ZONE INFLUENCES GENERAL ACTIVITY RHYTHMS IN THE NILE GRASS RAT,ARVICANTHIS NILOTICUS

Circadian rhythms in behavior and physiology are very different in diurnal and nocturnal rodents. A pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus is responsible for generating and maintaining circadian rhythms in mammals, and cellular and molecular rhythms within the SCN of diurnal and nocturnal rodents are very similar. The neural substrates determining whether an animal has a diurnal or nocturnal phase preference are thus likely to reside downstream of the SCN. The ventral subparaventricular zone (vSPVZ), a major target of the SCN that is important for the expression of circadian rhythmicity in nocturnal lab rats (Rattus norvegicus), exhibits different rhythms in cFos expression in diurnal Nile grass rats compared to lab rats. We examined the effects of chemotoxic lesions of the cFos-expressing cells of the vSPVZ on activity rhythms of grass rats to evaluate the hypothesis that these cells support diurnality in this species. Male grass rats housed in a 12:12 light:dark (LD) cycle were given bilateral injections of the neurotoxin n-methyl-D-L-aspartic acid (NMA) or vehicle aimed at the vSPVZ; cells in the SCN are resistant to NMA, which kills neurons in other brain regions, but leaves fibers of passage intact. vSPVZ-damaged grass rats exhibited highly unstable patterns of activity in constant darkness (DD) and in the LD cycle that followed. However, crepuscular bouts of activity could be seen in all animals with vSPVZ lesions. Damage to the vSPVZ reduced cFos expression in this area but not in the SCN. Using correlational analyses, we found that the number of cFos-ir cells in the vSPVZ was unrelated to several parameters of the activity rhythms during the initial post-surgical period, when animals were in LD. However, the number of cells expressing cFos in the vSPVZ was positively correlated with general activity during the subjective day relative to the subjective night when the animals were switched to DD, and this pattern persisted when a LD cycle was reinstated. Also, the number of cFos-ir cells in the vSPVZ was negatively correlated with the strength of rhythmicity in DD and the number of days required to re-entrain to a LD cycle following several weeks in DD. These data suggest that the vSPVZ emits signals important for the expression of stable diurnal activity patterns in grass rats, and that species differences in these signals may contribute to differences in behavioral and physiological rhythms of diurnal and nocturnal mammals. (Author correspondence: mschw009@umaryland.edu)     

Robustness of Circadian Timing Systems Evolves in the Fruit Fly Drosophila melanogaster as a Correlated Response to Selection for Adult Emergence in a Narrow Window of Time

Robustness is a fundamental property of biological timing systems that is likely to ensure their efficient functioning under a wide range of environmental conditions. Here we report the findings of our study aimed at examining robustness of circadian clocks in fruit fly Drosophila melanogaster populations selected to emerge as adults within a narrow window of time. Previously, we have reported that such flies display enhanced synchrony, accuracy, and precision in their adult emergence and activity/rest rhythms. Since it is expected that accurate and precise circadian clocks may confer enhanced stability in circadian time-keeping, we decided to examine robustness in circadian rhythms of flies from the selected populations by subjecting them to a variety of environmental conditions comprising of a range of photoperiods, light intensities, ambient temperatures, and constant darkness. The results revealed that adult emergence and activity/rest rhythms of flies from the selected stocks were more robust than controls, as they displayed enhanced stability under a wide variety of environmental conditions. These results suggest that selection for adult emergence within a narrow window of time results in the evolution of robustness in circadian timing systems of the fruit fly D. melanogaster. (Author correspondence: vsharma@jncasr.ac.in or vksharmas@gmail.com)     

THERMOCYCLIC AND PHOTOCYCLIC ENTRAINMENT OF CIRCADIAN LOCOMOTOR ACTIVITY RHYTHMS IN SLEEPY LIZARDS,TILIQUA RUGOSA

Australian sleepy lizards (Tiliqua rugosa) exhibit marked locomotor activity rhythms in the field and laboratory. Light-dark (LD) and temperature cycles (TCs) are considered important for the entrainment of circadian locomotor activity rhythms and for mediating seasonal adjustments in aspects of these rhythms, such as phase, amplitude, and activity pattern. The relative importance of 24 h LD and TCs in entraining the circadian locomotor activity rhythm in T. rugosa was examined in three experiments. In the first experiment, lizards were held under LD 12:12 and subjected to either a TC of 33:15?°?C in phase with the LD cycle or a reversed TC positioned in antiphase to the LD cycle. Following LD 12:12, lizards were maintained under the same TCs but were subjected to DD. Activity was restricted to the thermophase in LD, irrespective of the lighting regime and during the period of DD that followed, suggesting entrainment by the TC. The amplitude of the TC was lowered by 8?°?C to reduce the intensity and possible masking effect of the TC zeitgeber in subsequent experiments. In the second experiment, lizards were held under LD 12.5:11.5 and subjected to one of three treatments: constant 30?°?C, normal TC (30:20?°?C) in phase with the LD cycle, or reversed TC. Following LD, all lizards were subjected to DD and constant 30?°?C. Post-entrainment free-run records revealed that LD cycles and TCs could both entrain the locomotor rhythms of T. rugosa. In LD, mean activity duration (α) of lizards in the normal TC group was considerably less than that in the constant 30?°?C group. Mean α also increased between LD and DD in lizards in the normal TC group. Although there was large variation in the phasing of the rhythm in relation to the LD cycle in reversed TC lizards, TCs presented in phase with the LD cycle most accurately synchronized the rhythm to the photocycle. In the third experiment, lizards were held in DD at constant 30?°?C before being subjected to a further period of DD and one of four treatments: normal TC (06:00 to 18:00 h thermophase), delayed TC (12:00 to 00:00 h thermophase), advanced TC (00:00 to 12:00 h thermophase), or control (no TC, constant 30?°?C). While control lizards continued to free-run in DD at constant temperature, the locomotor activity rhythms of lizards subjected to TCs rapidly entrained to TCs, whether or not the TC was phase advanced or delayed by 6 h. There was no difference in the phase relationships of lizard activity rhythms to the onset of the thermophase among the normal, delayed, and advanced TC groups, suggesting equally strong entrainment to the TC in each group. The results of this experiment excluded the possibility that masking effects were responsible for the locomotor activity responses of lizards to TCs. The three experiments demonstrated that TCs are important for entraining circadian locomotor activity rhythms of T. rugosa, even when photic cues are conflicting or absent, and that an interaction between LD cycles and TCs most accurately synchronizes this rhythm. (Author correspondence: david.j.ellis@adelaide.edu.au)     

Daily Changes in Ultraviolet Light Levels Can Synchronize the Circadian Clock of Bumblebees (Bombus terrestris)

Endogenous circadian clocks are synchronized to the 24-h day by external zeitgebers such as daily light and temperature cycles. Bumblebee foragers show diurnal rhythms under daily light:dark cycles and short-period free-running circadian rhythms in constant light conditions in the laboratory. In contrast, during the continuous light conditions of the arctic summer, they show robust 24-h rhythms in their foraging patterns, meaning that some external zeitgeber must entrain their circadian clocks in the presence of constant light. Although the sun stays above the horizon for weeks during the arctic summer, the light quality, especially in the ultraviolet (UV) range, exhibits pronounced daily changes. Since the photoreceptors and photopigments that synchronize the circadian system of bees are not known, we tested if the circadian clocks of bumblebees (Bombus terrestris) can be entrained by daily cycles in UV light levels. Bumblebee colonies were set up in the laboratory and exposed to 12?h:12?h UV?+?:UV? cycles in otherwise continuous lighting conditions by placing UV filters on their foraging arenas for 12?h each day. The activity patterns of individual bees were recorded using fully automatic radiofrequency identification (RFID). We found that colonies manipulated in such a way showed synchronized 24-h rhythms, whereas simultaneously tested control colonies with no variation in UV light levels showed free-running rhythms instead. The results of our study show that bumblebee circadian rhythms can indeed be synchronized by daily cycles in ambient light spectral composition. (Author correspondence: r.stanewsky@qmul.ac.uk)     

The daily pattern of heart rate, body temperature, and locomotor activity in guinea pigs.

We studied the characteristics of the rhythmicity of heart rate (HR), body temperature (BT), and locomotor activity (LA) in conscious and unrestrained guinea pigs using a telemetry system. HR and/or LA in some guinea pigs clearly showed circadian rhythms, but in others there were no significant daily patterns; BT did not show significant daily rhythms. These results suggest that guinea pigs might have different individual characteristics of rhythmicity, and we should, therefore, be careful when using guinea pigs in chrono-biomedical research. We believe that the results of this study may be useful for future biomedical studies using guinea pigs.