Revolutionary science: an improved running wheel for hamsters

Evaluation of small mammal pet supplies offered in German retail under animal welfare aspects

German retailers offer a large variety of accessories for pets. However, not all products are suitable for pet husbandry. Several articles can negatively influence the wellbeing of pets or cause injuries, but empirical studies that evaluate accessories for small pets under animal welfare aspects are rare. In the present study, we assessed articles manufactured or sold in Germany in the product categories pet cages, hay racks, running wheels, exercise balls, harnesses and leashes, tube systems, and hamster bedding. To do so, we searched 28 German websites, visited 50 pet shops and 13 home improvement and garden centers on site and afterwards examined the animal welfare compliance of the products according to various evaluation criteria. Most of the examined products were rated not suitable for pet husbandry and were animal-welfare-adverse. This result applies to 86.1% (n = 87) of the 101 assessed running wheel models, 82.7% (n = 172) of the 208 assessed pet cage models and 55.6% (n = 40) of the 72 assessed hay rack models. The articles in the product categories exercise balls, harnesses and leashes, tube systems, and hamster bedding were also found unsuitable due to animal welfare concerns. Furthermore, we found clear shortcomings regarding article declarations. In some cases, relevant product information (e.g., dimensions) were missing, or the presented information was too general (e.g., rodent cage). Improperly declared pet accessories make it difficult for pet owners to decide whether a product is suitable or unsuitable for the species they keep. A declaration duty for manufacturers of pet products could ensure that German retailers only offer properly declared pet accessories and facilitate the decision for pet owners to purchase products appropriate for the pets they keep. Furthermore, a voluntary product certification for manufacturers would allow retailers to check the animal welfare compliance of articles before including them in their assortment. If a product is unsuitable for pet husbandry because it does not meet the set requirements, it must be considered animal-welfare-adverse and removed from the assortment. As done for the Austrian “animal welfare label,” an independent, qualified third party could do the certification.

Voluntary exercise stabilizes photic entrainment of djungarian hamsters (Phodopus sungorus) with a delayed activity onset

The Djungarian hamsters of our breeding colony show unstable daily activity patterns when kept under standard laboratory conditions. Moreover, part of them develops a delayed activity onset (DAO) or an arrhythmic phenotype. In former studies, we have shown that the system of photic entrainment works at its limits. If the period length (tau) increases, which is the case in DAO hamsters, the light-induced phase advances are too small to compensate the daily delay of the activity rhythm caused by tau being longer than 24 h. Accordingly, under natural conditions, there must be further (environmental) factors to enable a stable entrainment. One of these may be the higher level of motor activity. Animals must cover long distances to search for food, sexual partners and others. In the laboratory, hamsters are kept singly in small cages. This does restrict animals' options for motor activity. Also, there is less need for moving around as the hamsters are fed ad libitum. In the present study, a series of experiments was performed to investigate the putative effect of the activity level. To begin with, wild type (WT) and DAO animals were given access to running wheels. 50% of DAO hamsters developed a WT activity pattern. As the main reason for the DAO phenomenon is their long tau together with a too weak photic phase response, the effect of wheel running on these parameters was investigated in further experiments. With higher activity level, tau decreased in WT hamsters but increased in DAO animals even though the increase for the activity onset was only close to significance. Moreover, the photic phase responses were weaker though significant only for the activity offset of DAO hamsters. Based on the assumptions that running wheel activity will affect the phase response and/or the free running period, the results of the present paper do not provide an explanation for why part of DAO hamsters developed a WT phenotype when they had access to running wheels. Obviously, mechanisms downstream from the suprachiasmatic nuclei must be taken into account when investigating the stabilizing, improving circadian entrainment effect of motor activity.

Changes in phase-angle under light-dark cycles influenced by nonphotic stimulation

Most work looking at nonphotic effects on circadian rhythms is conducted when animals are held under freerunning conditions, usually constant darkness. However, for nonphotic effects to be functionally significant, they should be demonstrable under conditions in which most animals live, i.e., a 24-hr light-dark cycle (LD). Syrian hamsters held in LD 6:18 were administered nonphotic stimulation in the form of a 3-hr confinement to a novel wheel starting about 6 hr before the start of their normal nightly activity bout. This resulted in a 2.5-hr advance of their activity rhythm on the next day that gradually receded to about 1.5 hr over the next 10 days. When hamsters held in LD 6:18 were given five novel wheel confinements over 13 days their nightly activity onset advanced 3 hr and remained at that phase for at least 2 weeks. Home cage wheel deprivation experiments indicated that high levels of home cage activity are necessary to maintain the advanced phase. These results show that nonphotic stimulation can have large, long-lasting effects on daily rhythms in LD and suggest a possible mechanism whereby nocturnal rodents might achieve phase flexibility in response to seasonal changes.

Nocturnal Activity in a Diurnal Rodent (Arvicanthis Niloticus): The Importance of Masking

It is known that day-active Nile grass rats, Arvicanthis niloticus, increase the amount of activity in the night relative to that in the day when provided with running wheels. This was confirmed in the present study. Animals without a wheel displayed 69.0% of their general activity in the L phase of a 12:12 h light-dark cycle; animals provided with wheels had only 48.6% of their wheel revolutions in the light. The contribution of direct (masking) responses to light to the increased nocturnality of animals with wheels was examined in two experiments. In experiment 1, masking was tested by exposing the animals to repeated cycles of 30 min of entraining light and 30 min of a different, usually dimmer light, during the L phase of a 12:12 h light-dark cycle. For animals with wheels, there was more running during the 30-min pulses of dim light or darkness than during the 30-min periods of entraining light. In contrast, for animals without wheels, there was more general activity during the 30-min periods of entraining light than during the 30-min pulses of dim light or darkness. In experiment 2, the animals were first exposed to a 12:12 h light-dark cycle and then put on a 1:10:1:12 h LDLD skeleton photoperiod. Animals with wheels increased their running during the subjective day of the skeleton photoperiod compared to that in the actual day of the 12:12 h light-dark cycle. Animals without wheels showed similar levels of general activity during the subjective day of the skeleton photoperiod and the actual day of the 12:12 h cycle. These experiments demonstrate that when Nile rats have running wheels, their increased nocturnal activity is associated with an increased suppression of locomotion in direct response to light. It is possible that changes in masking responses to light may be an essential and integral component of switching between diurnal and nocturnal activity profiles.

Behavioral and electrophysiological correlates of sleep and sleep homeostasis

The definition of what sleep is depends on the method that is applied to record sleep. Behavioral and (electro)-physiological measures of sleep clearly overlap in mammals and birds , but it is often unclear how these two relate in other vertebrates and invertebrates. Homeostatic regulation of sleep, where the amount of sleep depends on the amount of previous waking, can be observed in physiology and behavior in all animals this was tested in. In mammals and birds, sleep is generally subdivided into two states, non-rapid eye movement (NREM) sleep and REM sleep. In mammals the combination of behavioral sleep and the changes in the slow-wave range of the NREM sleep electroencephalogram (EEG) can explain and predict the occurrence and depth of sleep in great detail. For REM sleep this is far less clear. Finally, the discovery that slow-waves in the NREM sleep EEG are influenced locally on the cortex depending on prior waking behavior is an interesting new development that asks for an adaptation of the concept of homeostatic regulation of sleep. Incorporating local sleep into models of sleep regulation is needed to obtain a comprehensive picture.

Cause and Possible Treatments of Foot Lesions in Captive Syrian Hamsters (Mesocricetus auratus)

Syrian hamsters (Mesocricetus auratus) run extensively in exercise wheels. This running may cause paw lesions. Three treatments of these wounds (topical application of vitamin E, wheel blocking, and a combination of both) were compared using both sexes. A pretreatment period with or without wheels lasted 15 days and the ensuing treatment period lasted 45 days. At the end of the pre-treatment period, none of the animals without wheels had paw wounds, whereas at least 75% of the females and 100% of the males with wheels did. Females had fewer and smaller wounds than males at this point. At the end of the treatment period, no effect of vitamin E could be discerned, but significant wound healing occurred after wheel blocking in both males and females. Wheel blocking is an easy way to prevent or treat paw wounds, but it presents problems in terms of animal welfare, as wheels are an important cage enrichment for hamsters.

Effects of bedding material and running wheel surface on paw wounds in male and female Syrian hamsters

The present study investigated the effects of bedding material (pine shavings versus beta chip) and running wheel surfaces (standard metal bars versus metal bars covered with a plastic mesh) on the occurrence of wounds on the paws of male and female Syrian (golden) hamsters, Mesocricetus auratus. Four groups of 10 males and 10 females were each assigned to one of the following treatments: pine/no mesh, pine/mesh, chips/no mesh and chips/mesh. Each hamster paw was observed at 1–3-day intervals for 60 days. A total of 1–3 wounds, separate in time, developed on the paws (mostly the hind ones) of almost all animals. Wounds appeared as small pinpricks, cuts or scabs, mostly on the palms. Females ran 15% less than males, yet their front paws were more commonly affected and their wounds tended to last longer. Hamsters with plastic mesh inside their wheels took longer to develop wounds but once they appeared, the wounds were larger and lasted longer. Hamsters on pine shavings developed fewer wounds and had more wound-free days. Hamsters kept running at high levels and many wounds did not heal during the study, suggesting a need for veterinary intervention.

A molecular explanation of interactions between photic and non-photic circadian clock-resetting stimuli

Non-photic clock-resetting events (arousal and locomotor activity) in the subjective day reduced expression of Period genes in the suprachiasmatic nucleus of hamsters. This decrease was attenuated by a 30-min light pulse occurring during the last 0.5 h of 3.5 h of confinement to a novel running wheel. This provides an example at the molecular level of an interaction between different modalities of synchronizing agents.

Behaviour of golden hamsters (Mesocricetus auratus) kept in four different cage sizes

Cages for laboratory and pet hamsters are usually small. Using video recordings, the behaviour of sixty female golden hamsters (Mesocricetus auratus), housed individually in four different cage sizes, was compared in order to draw conclusions about their welfare. The cage sizes were 1,800 cm2, 2,500 cm2, 5,000 cm2, and 10,000 cm2. Enrichment items and litter depth were standardised and all cages were equipped with a running-wheel (30 cm diameter). Stereotypic wire-gnawing, usage of the provided space, weight gain, and reactions to mild husbandry stressors were used as welfare indicators. Stereotypic wire-gnawing was observed in all cage sizes, but hamsters in small cages gnawed significantly longer and more frequently. There were no significant differences in running-wheel activity. In small cages hamsters made use of the roof of their wooden shelters as an additional platform more often than in big cages, which could suggest that they needed more space. Therefore, the welfare of pet golden hamsters in cages with a minimal ground floor area of 10,000 cm2 seemed to be enhanced compared with smaller cages.

Photic and non-photic effects on the daily activity pattern of Mongolian gerbils

The paper analyses the daily activity pattern of Mongolian gerbils with and without access to a running wheel. To evaluate the synchronizing and the masking effects of light, experiments were performed under different photoperiods (L:D=14:10 h and 10:14 h), and light and dark pulses were applied at different phases of the day-night cycle. In order to get a more direct estimate of the central pacemaker of the circadian system, the body temperature rhythm was investigated via implanted transmitters. Without access to a running wheel, the daily activity pattern was bimodal. One peak occurred in the first half of the light time, the other one around the light-dark transition. Also, the gerbils were more active during the light phase as compared to the dark phase. After unlocking the running wheel, the gerbils were active mainly during the dark time. The activity peak in the first half of the light phase remained, the second one shifted by a phase delay into the dark time. These results were found under both LD-regimens. Light during the night nearly completely suppressed running wheel activity, switching off the light during the day time induced wheel running. Whereas wheel running was clearly affected by light and dark pulses, the general activity was not. The body temperature rhythm also shows two peaks, with the second one being bigger and coinciding with the endogenous component of the circadian body temperature rhythm. It was found around light-off. After unlocking the running wheel, the maximum of the body temperature rhythm shifted to the night. This was not primarily a consequence of the changed activity pattern as shown by means of purification analysis. Removing the direct effects of motor activity led to a body temperature curve that could be described by a cosine function, and the delay shift was found also for the purified data, a better estimate of the endogenous circadian component. The wheel-associated increase in nocturnality is not only due to masking effects of wheel-running activity on the body temperature and activity rhythms. It also involves clock-related processes. Changes in the phase preference may serve as an adaptation mechanism to the changes in the animal's natural environment.

Circadian entrainment and phase resetting differ markedly under dimly illuminated versus completely dark nights

An endogenous circadian pacemaker uses photic input to synchronize mammalian physiological and behavioral rhythms to the 24 h day. Sunlight during dusk and dawn is thought to entrain the pacemaker of nocturnal rodents, whereas moonlight and starlight are presumed to exert little influence. We show that, to the contrary, dim illumination (<0.005 lux), similar in intensity to starlight and dim moonlight, markedly alters entrainment of hamster activity rhythms. Under 24 h light:dark:light:dark cycles (LDLD), for example, activity rhythms can disassociate, or split, into two distinct components, and the incidence of split entrainment is increased when daily scotophases are dimly lit rather than completely dark. The three present studies examine whether dim illumination promotes LDLD-induced splitting (1) by increasing nonphotic feedback during novelty-induced activity bouts, (2) by potentiating nonphotic and/or photic resetting, or (3) by influencing phase jumping responses under skeleton photoperiods simulating increases in day length. Experiment 1 illustrates that dim-exposed animals display split rhythms, while animals without dim light do not, despite equivalent activity levels. In Experiments 2 and 3, dim illumination potentiated both nonphotic and photic resetting, and the specific nature of these interactions suggests mechanisms through which dim illumination may alter entrainment under LDLD. Dim light likely promotes LDLD-induced splitting by facilitating both nonphotic resetting and bright light-induced phase jumping in animals entrained to short nights. The actions of dim illumination may be distinct from canonical responses to bright light, and potentially influence the interactions between oscillators comprising the circadian pacemaker.

Behavioral arousal blocks light-induced phase advances in locomotor rhythmicity but not light-induced Per1 and Fos expression in the hamster suprachiasmatic nucleus

Both photic and nonphotic stimuli entrain circadian rhythms. Although the adaptive significance of nonphotic clock resetting is unknown, one possibility is that nonphotic cues modulate circadian responses to light. Results of studies on the interaction between photic and nonphotic stimuli support this idea. During the day, light blocks the effects of nonphotic stimuli on the phase of locomotor rhythms and on expression of clock genes in suprachiasmatic nucleus (SCN) neurons. At night, novelty-induced activity prior to and during exposure to light attenuates the phase-shifting response to that light, but the effects of this manipulation on clock gene expression are unknown. The present experiments explore the interaction between behavioral state and response to light at the molecular level. We show that confining hamsters to novel wheels immediately after a light pulse during the late subjective night attenuates light-induced phase advances of wheel-running rhythms and the transient effects on circadian period. In contrast to the striking effect of novelty-induced activity on behavioral responses to light, Fos protein and Per1 mRNA were robustly expressed in the SCN of all light-pulsed animals, regardless of behavioral treatment. Our results are inconsistent with the idea that light and nonphotic stimuli block each other's effects on phase shifts by inducing or attenuating transcription of Per1. Photic regulation of clock genes and spontaneous rhythmic expression of clock genes are probably mediated by different mechanisms.

Nonphotic phase shifting in female Syrian hamsters: interactions with the estrous cycle

Nonphotic phase shifting of circadian rhythms was examined in female Syrian hamsters. Animals were stimulated at zeitgeber time 4.5 by either placing them in a novel running wheel or by transferring them to a clean home cage. Placement in a clean home cage was more effective than novel wheel treatment in stimulating large (> 1.5 h) phase shifts. Peak phase shifts (ca. 3.5 h) and the percentage of females showing large phase shifts were comparable to those found in male hamsters stimulated with novel wheels. The amount of activity induced by nonphotic stimulation and the amount of phase shifting varied slightly with respect to the 4-day estrous cycle. Animals tended to run less and shift less on the day of estrus. Nonphotic stimulation on proestrus often resulted in a 1-day delay of the estrous cycle reflected in animals' postovulatory vaginal discharge and the expression of sexual receptivity (lordosis). This delay of the estrous cycle was associated with large phase advances and high activity. These results extend the generality of nonphotic phase shifting to females for the first time and raise the possibility that resetting of circadian rhythms can induce changes in the estrous cycle.

Plasticity of hamster circadian entrainment patterns depends on light intensity

The multiple oscillatory basis of the mammalian circadian pacemaker is adduced by, among other phenomena, the occurrence of split locomotor activity rhythms in rodents after prolonged exposure to constant light. More recently, split rhythms entrained to a 24h light:dark:light:dark cycle have been documented following scheduled access of hamsters to a novel running wheel or by photoperiod manipulations alone. Because the incidence of constant light-induced splitting depends on light intensity, the role of this variable was assessed in this new splitting paradigm. Male Syrian hamsters, entrained to a 14h light:10h dark cycle, were transferred to individual running wheel cages 7h after light onset. Transfer coincided with the beginning of the scotophase of a new photocycle alternating between 5h of relative dark and 7h of light. For four weeks bright photophases (approximately 350 lux) were alternated with either dim (< 0.1 lux) or completely dark (0 lux) scotophases. An additional group received moderate intensity photophases (approximately 45 lux) paired with dim scotophase illumination. For an additional four weeks, all hamsters were exposed to the same bright:dim light:dark cycle. Dim light in the scotophase significantly increased the incidence of split activity rhythms relative to that observed with completely dark scotophases. Overall wheel-running rates and activity induced by a cage change were also increased in dim light-exposed animals. Group differences largely disappeared four weeks later when hamsters previously maintained in completely dark scotophases were exposed to dim scotophases. Photophase light intensity did not affect the overall incidence of splitting, but influenced the timing of activity in the afternoon scotophase. The effects of dim illumination may be mediated in part via enhanced locomotor responses to transfer to a new cage or by changes in coupling interactions between component oscillators.

Effect of cage enrichment on the daily use of running wheels by Syrian hamsters

Institutional animal care committees may one day require for the welfare of captive hamsters more floor space and the introduction of tunnels and toys. As hamsters are popular animal subjects in chronobiological research, and as clock phase is usually measured through running wheel activity, it is important to determine what effect cage enrichment might have on daily wheel use. Here the daily number of wheel revolutions, the daily duration of the running activity phase, the phase relationship between lights-off and onset of running activity, and the free-running period of circadian activity rhythms were measured in Syrian hamsters, Mesocricetus auratus, housed in single cages or in multiple cages linked by tunnels and supplied with commercial wooden toys. Free-running periodicity was not affected by cage enrichment. In multiple-cage systems, there were fewer daily revolutions, shorter wheel-running activity phases, and delayed running activity onsets. These effects, however, were small as compared to interindividual and week-to-week variation. They were statistically significant only under a light:dark cycle, not in constant darkness, and only when interindividual variation was eliminated through a paired design or when the number of cages was increased to five (the maximum tested). Daily wheel use is thus affected by cage enrichment, but only slightly.

Activity rhythms of wild and laboratory golden hamsters (Mesocricetus auratus) under entrained and free-running conditions

The golden hamster (Mesocricetus auratus) is one of the most frequently used laboratory animals, particularly in chronobiological studies. One reason is its very robust and predictable rhythms, although the question arises whether this is an inbreeding effect or rather is typical for the species. We compared the daily (circadian) activity rhythms of wild and laboratory golden hamsters. The laboratory hamsters were derived from our own outbred stock (Zoh:GOHA). The wild hamsters included animals captured in Syria and their descendants (F1). Experiments were performed under entrained (light: dark [LD] 14h:0h) and under free-running (constant darkness, DD) conditions. Locomotor activity was recorded using passive infrared detectors. Under entrained conditions, the animals had access to a running wheel for a certain time to induce additional activity. After 3 weeks in constant darkness, a light pulse (15 min, 100 lux) was applied at circadian time 14 (CT14). Both laboratory and wild hamsters showed well-pronounced and very similar activity rhythms. Under entrained conditions, all hamsters manifested about 80% of their total 24h activity during the dark portion of the LD cycle. The robustness of the daily rhythms was also similar. However, interindividual variability was higher in wild hamsters for both measures. All animals used the running wheels almost exclusively during the dark portion of the LD cycle, although the wild hamsters were three times more active. The period length, measured in constant darkness, was significantly shorter in wild (23.93h +/- 0.10h) than in laboratory hamsters (24.06 +/- 0.07h). The light-induced phase changes were not different (about 1.5h). In summary, these results indicate that the laboratory hamster is not much different from the wild type.

Exogenous corticosteroid and shifts of circadian rhythms in hamsters

We tested the hypothesis that glucocorticoid stimulation mediates the effect of exercise on circadian clock resetting in hamsters. We injected animals with 1 and 5 mg dexamethasone--a potent glucocorticoid agonist--at zeitgeber time (ZT) 4 and ZT6, circadian phases at which vigorous exercise induces maximal phase advances of about 3 h. Neither dose of dexamethasone induced phase shifts that were significantly larger than those induced by injections of saline vehicle at either of the phases tested. Some animals, however, showed quite large and consistent phase shifts to repeated injections whether with saline or dexamethasone, such that there was a statistically significant correlation between individuals' responses to the two treatments. The data indicate no role for increased glucocorticoid activity in mediating the effects of exercise on circadian phase shifting, but suggest a modest role for nonspecific stimulation, independent of exercise, in inducing phase shifts at ZT4-ZT6.

Rapid down-regulation of mammalian period genes during behavioral resetting of the circadian clock

The pervasive role of circadian clocks in regulating physiology and behavior is widely recognized. Their adaptive value is their ability to be entrained by environmental cues such that the internal circadian phase is a reliable predictor of solar time. In mammals, both light and nonphotic behavioral cues can entrain the principal oscillator of the hypothalamic suprachiasmatic nuclei (SCN). However, although light can advance or delay the clock during circadian night, behavioral events trigger phase advances during the subjective day, when the clock is insensitive to light. The recent identification of Period (Per) genes in mammals, homologues of dperiod, which encodes a core element of the circadian clockwork in Drosophila, now provides the opportunity to explain circadian timing and entrainment at a molecular level. In mice, expression of mPer1 and mPer2 in the SCN is rhythmic and acutely up-regulated by light. Moreover, the temporal relations between mRNA and protein cycles are consistent with a clock based on a transcriptional/translational feedback loop. Here we describe circadian oscillations of Per1 and Per2 in the SCN of the Syrian hamster, showing that PER1 protein and mRNA cycles again behave in a manner consistent with a negative-feedback oscillator. Furthermore, we demonstrate that nonphotic resetting has the opposite effect to light: acutely down-regulating these genes. Their sensitivity to nonphotic resetting cues supports their proposed role as core elements of the circadian oscillator. Moreover, this study provides an explanation at the molecular level for the contrasting but convergent effects of photic and nonphotic cues on the clock.