Circadian organization of running-wheel activity, food intake and drinking of old male rats

Circadian rhythms of running-wheel activity, food intake and drinking were monitored in old male rats of Long-Evans strain over 22 months of age in both entrained (light:dark 12:12, LD) and free running condition (continuous illumination, LL) and were compared with those of young adult male rats of 3.5 to 6.5 months of age. Twenty-four hour distribution of running activity, feeding events and licking events of young rats as well as old rats showed bi- or tri-modal patterns during the 12 hr dark period of the LD schedule. In the light period, 2 out of 8 old rats, 6 out of 10 old rats and 1 out of 6 old rats had 1 or 2 medium or high peaks in running activity, feeding events and licking events, respectively, leading to equal distribution between the dark and light period. In the LD schedule, old rats showed a decrease in running-wheel activity, its patterns and power spectra, a decrease in feeding events and its power spectra in 6 rats which lost circadian rhythms and increase in feeding events and its power spectra in 4 rats which still showed circadian rhythms and increase in licking events. LL suppressed running-wheel activity, its patterns and power spectra, licking events and its power spectra and feeding events in young rats. However, LL could suppress only feeding events of 4 rats which still showed circadian rhythms and licking events and its spectral level in old rats. The possible causes of decreased response to LL in old rats and its implication are discussed.     

Environmental modification and agonistic behavior in NIH/S male mice: nesting material enhances fighting but shelters prevent it

Outbred NIH/S male mice were housed from weaning in groups of 4 without enrichment (control) or with nesting material (nest), nesting material and a box (nest-and-box), or nesting material and a tube (nest-and-tube) as environmental modification. The aim of the study was to investigate effects of widely recommended nesting material and additional shelters on male mice. The aggressiveness of the mice in their home cages clearly increased in the nest group, as assessed by the number of wounds. In the nest group, fighting was a stressful situation for the mice, leading to changes in weight gain and in the weights of the thymus, adrenals, spleen, and epididymal adipose tissue. Moreover, the agonistic behavior of these mice toward an intruder was increased both in individual tests (an intruder with the individual mouse) and group tests (an intruder with a group of mice). The provision of a box or tube as a shelter, in addition to nesting material, prevented intracage fighting and did not lead to alterations in the weight gain or organ weights of the mice. However, the agonistic behavior of mice with shelters was slightly increased in behavioral tests. Anxiety in the elevated plus-maze was not affected by any of the housing systems. In conclusion, the agonistic behavior of NIH/S mice, an aggressive strain, seemed to be easily enhanced by these environmental modifications. The suitability of any enrichment should be carefully evaluated, especially when highly aggressive mice are used.     

Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents

When rodents have free access to a running wheel in their home cage, voluntary use of this wheel will depend on the time of day^1-5. Nocturnal rodents, including rats, hamsters, and mice, are active during the night and relatively inactive during the day. Many other behavioral and physiological measures also exhibit daily rhythms, but in rodents, running-wheel activity serves as a particularly reliable and convenient measure of the output of the master circadian clock, the suprachiasmatic nucleus (SCN) of the hypothalamus. In general, through a process called entrainment, the daily pattern of running-wheel activity will naturally align with the environmental light-dark cycle (LD cycle; e.g. 12 hr-light:12 hr-dark). However circadian rhythms are endogenously generated patterns in behavior that exhibit a ~24 hr period, and persist in constant darkness. Thus, in the absence of an LD cycle, the recording and analysis of running-wheel activity can be used to determine the subjective time-of-day. Because these rhythms are directed by the circadian clock the subjective time-of-day is referred to as the circadian time (CT). In contrast, when an LD cycle is present, the time-of-day that is determined by the environmental LD cycle is called the zeitgeber time (ZT).Although circadian rhythms in running-wheel activity are typically linked to the SCN clock^6-8, circadian oscillators in many other regions of the brain and body^9-14 could also be involved in the regulation of daily activity rhythms. For instance, daily rhythms in food-anticipatory activity do not require the SCN^15,16 and instead, are correlated with changes in the activity of extra-SCN oscillators^17-20. Thus, running-wheel activity recordings can provide important behavioral information not only about the output of the master SCN clock, but also on the activity of extra-SCN oscillators. Below we describe the equipment and methods used to record, analyze and display circadian locomotor activity rhythms in laboratory rodents.     

Activity feedback to the mammalian circadian pacemaker: influence on observed measures of rhythm period length.

In the mouse, activity is precisely timed by the circadian clock and is normally most intense in the early subjective night. Since vigorous activity (e.g., wheel running) is thought to induce phase shifts in rodents, the temporal placement of daily exercise/activity could be a determinant of observed circadian rhythm period. The relationship between spontaneous running-wheel activity and the circadian period of free-running rhythms was studied to assess this possibility. With ad libitum access to a running wheel, mice exhibited a free-running period (tau) of 23.43 +/- 0.08 hr (mean +/- SEM). When running wheels were locked, tau increased (23.88 +/- 0.04 hr, p less than 0.03), and restoration of ad libitum wheel running again produced a shorter period (tau = 23.56 +/- 0.06 hr, p less than 0.05). A survey of free-running activity patterns in a population of 100 mice revealed a significant correlation between the observed circadian period and the time of day in which spontaneous wheel running occurred (r = 0.7314, p less than 0.0001). Significantly shorter periods were observed when running was concentrated at the beginning of the subjective night (tau = 23.23 +/- 0.04), and longer periods were observed if mice ran late in the subjective night (tau = 23.89 +/- 0.04), F (1, 99) = 34.96, p less than 0.0001. It was previously believed that the period of the circadian clock was primarily responsive to externally imposed tonic or phasic events. Systematic influences of spontaneous exercise on tau demonstrate that physiological and/or behavioral determinants of circadian timekeeping exist as well.     

Plasticity of circadian behavior and the suprachiasmatic nucleus following exposure to non-24-hour light cycles

Period aftereffects are a form of behavioral plasticity in which the free-running period of circadian behavior undergoes experience-dependent changes. It is unclear whether this plasticity is age dependent and whether the changes in behavioral period relate to changes in the SCN or the retina, 2 known circadian pacemakers in mammals. To determine whether these changes vary with age, Per1-luc transgenic mice (in which the luciferase gene is driven by the Period1 promoter) of different ages were exposed to short (10 h light: 10 h dark, T20) or long (14 h light: 14 h dark, T28) light cycles (T cycles). Recordings of running-wheel activity in constant darkness (DD) revealed that the intrinsic periods of T20 mice were significantly shorter than of T28 mice at all ages. Aftereffects following the shorter light cycle were significantly smaller in mice older than 3 months, corresponding with a decreased ability to entrain to T20. Age did not diminish entrainment or aftereffects in the 28-h light schedule. The behavioral period of pups born in DD depended on the T cycle experienced in utero, showing maternal transference of aftereffects. Recordings of Per1-luc activity from the isolated SCN in vitro revealed that the SCN of young mice expressed aftereffects, but the periods of behavior and SCN were negatively correlated. Enucleation in DD had no effect on behavioral aftereffects, indicating the eyes are not required for aftereffects expression. These data show that circadian aftereffects are an age-dependent form of plasticity mediated by stable changes in the SCN and, importantly, extra-SCN tissues.     

Western diet affects the murine circadian system possibly through the gastrointestinal microbiota

Consumption of a high-fat diet characteristic of human Western diet has been shown to affect the circadian system of laboratory rodents. The present study confirms an effect of Western diet on the circadian system of mice, specifically a shortening of the free-running circadian period of running-wheel activity, in addition to increased weight gain. Decimation of the gut microbiota by broad spectrum antibiotic treatment reversed the effect of Western-diet feeding on the free-running period, which suggests that the effect of Western-diet feeding on the circadian system is mediated by the gastrointestinal microbiota. This finding is particularly relevant in view of recent studies describing a relationship between gut microbes, circadian clock function, and obesity.     

Behavioral responses to combinations of timed light, food availability, and ultradian rhythms in the common vole (Microtus arvalis)

Light is the main entraining signal of the central circadian clock, which drives circadian organization of activity. When food is made available during only certain parts of the day, it can entrain the clock in the liver without changing the phase of the central circadian clock. Although a hallmark of food entrainment is a behavioral anticipation of food availability, the extent of behavioral alterations in response to food availability has not been fully characterized. The authors have investigated interactions between light and temporal food availability in the timing of activity in the common vole. Temporally restricted food availability enhanced or attenuated re-entrainment to a phase advance in light entrainment when it was shifted together with the light or remained at the same time of day, respectively. When light-entrained behavior was challenged with temporal food availability cycles with a different period, two distinct activity components were observed. More so, the present data indicate that in the presence of cycles of different period length of food and light, an activity component emerged that appeared to be driven by a free-running (light-entrainable) clock. Because the authors have previously shown that in the common vole altering activity through running-wheel availability can alter the effectiveness of food availability to entrain the clock in the liver, the authors included running-wheel availability as a parameter that alters the circadian/ultradian balance in activity. In the current protocols, running-wheel availability enhanced the entraining potential of both light and food availability in a differential way. The data presented here show that in the vole activity is a complex of individually driven components and that this activity is, itself, an important modulator of the effectiveness of entraining signals such as light and food.     

A Nonlinear Interrelationship Between Period Length and the Amount of Activity - Age-Dependent changes

The circadian activity rhythm undergoes changes in the course of postnatal development. Experiments without external time cues were performed to characterize the endogenous component and to investigate any age-dependent changes. Female laboratory mice were used. At the beginning of the experiment they were 3 (juvenile), 23 (adult) or 72 (senile) weeks old. Animals were kept in climatic chambers (constant darkness, food and water ad libitum, temperature: 22±2°C, rel. humidity: 55±5%). Locomotor activity was recorded continuously using infrared detectors. The data were stored and analysed by means of the “Chronobiology Kit” (Stanford University). The mean period lengths were not statistically different between age groups. The stability of the spontaneous activity rhythms was highest in adult mice, however. The mean activity/day decreased from juvenile to senile mice. A nonlinear interrelationship between period length and amount of activity was obtained. At lower activity levels the period length became shorter with increasing activity; at higher levels it became longer again. The general shape of the curve was similar in all age groups. With respect to the nonlinear curve, one could not establish a general age dependency of period length. At similar ranges of activity the period length would be shortest in senile animals. Taking into account, however, the decline with age of the amount of activity the period of old mice could be shorter than, equal to or longer than that of adult mice. The results show that the endogenous component of the circadian activity rhythm, including feedback loops, matures and stabilizes from the juvenile to the adult. An expected loss of stability in senile mice was not demonstrated, probably due to a high variance of the animals' biological age. These age-dependent changes contribute to the changes of circadian activity rhythms obtained under entrained conditions.     

Spring Time and Fall Time Effects of 1,25-Dihydroxyvitamin D3, Cobalt (II) and (CoCl2(1,25(OH)2D3)4) Complex on Renal and Cerebral Enzymatic Markers in Rats

The circadian activity rhythm undergoes changes in the course of postnatal development. Experiments without external time cues were performed to characterize the endogenous component and to investigate any age-dependent changes. Female laboratory mice were used. At the beginning of the experiment they were 3 (juvenile), 23 (adult) or 72 (senile) weeks old. Animals were kept in climatic chambers (constant darkness, food and water ad libitum, temperature: 22±2°C, rel. humidity: 55±5%). Locomotor activity was recorded continuously using infrared detectors. The data were stored and analysed by means of the “Chronobiology Kit” (Stanford University). The mean period lengths were not statistically different between age groups. The stability of the spontaneous activity rhythms was highest in adult mice, however. The mean activity/day decreased from juvenile to senile mice. A nonlinear interrelationship between period length and amount of activity was obtained. At lower activity levels the period length became shorter with increasing activity; at higher levels it became longer again. The general shape of the curve was similar in all age groups. With respect to the nonlinear curve, one could not establish a general age dependency of period length. At similar ranges of activity the period length would be shortest in senile animals. Taking into account, however, the decline with age of the amount of activity the period of old mice could be shorter than, equal to or longer than that of adult mice. The results show that the endogenous component of the circadian activity rhythm, including feedback loops, matures and stabilizes from the juvenile to the adult. An expected loss of stability in senile mice was not demonstrated, probably due to a high variance of the animals’ biological age. These age-dependent changes contribute to the changes of circadian activity rhythms obtained under entrained conditions.     

The period length of fibroblast circadian gene expression varies widely among human individuals

Mammalian circadian behavior is governed by a central clock in the suprachiasmatic nucleus of the brain hypothalamus, and its intrinsic period length is believed to affect the phase of daily activities. Measurement of this period length, normally accomplished by prolonged subject observation, is difficult and costly in humans. Because a circadian clock similar to that of the suprachiasmatic nucleus is present in most cell types, we were able to engineer a lentiviral circadian reporter that permits characterization of circadian rhythms in single skin biopsies. Using it, we have determined the period lengths of 19 human individuals. The average value from all subjects, 24.5 h, closely matches average values for human circadian physiology obtained in studies in which circadian period was assessed in the absence of the confounding effects of light input and sleep–wake cycle feedback. Nevertheless, the distribution of period lengths measured from biopsies from different individuals was wider than those reported for circadian physiology. A similar trend was observed when comparing wheel-running behavior with fibroblast period length in mouse strains containing circadian gene disruptions. In mice, inter-individual differences in fibroblast period length correlated with the period of running-wheel activity; in humans, fibroblasts from different individuals showed widely variant circadian periods. Given its robustness, the presented procedure should permit quantitative trait mapping of human period length.     

Behavioral Responses to Combinations of Timed Light,Food Availability,and Ultradian Rhythms in the Common Vole (Microtus arvalis)

Light is the main entraining signal of the central circadian clock, which drives circadian organization of activity. When food is made available during only certain parts of the day, it can entrain the clock in the liver without changing the phase of the central circadian clock. Although a hallmark of food entrainment is a behavioral anticipation of food availability, the extent of behavioral alterations in response to food availability has not been fully characterized. The authors have investigated interactions between light and temporal food availability in the timing of activity in the common vole. Temporally restricted food availability enhanced or attenuated re-entrainment to a phase advance in light entrainment when it was shifted together with the light or remained at the same time of day, respectively. When light-entrained behavior was challenged with temporal food availability cycles with a different period, two distinct activity components were observed. More so, the present data indicate that in the presence of cycles of different period length of food and light, an activity component emerged that appeared to be driven by a free-running (light-entrainable) clock. Because the authors have previously shown that in the common vole altering activity through running-wheel availability can alter the effectiveness of food availability to entrain the clock in the liver, the authors included running-wheel availability as a parameter that alters the circadian/ultradian balance in activity. In the current protocols, running-wheel availability enhanced the entraining potential of both light and food availability in a differential way. The data presented here show that in the vole activity is a complex of individually driven components and that this activity is, itself, an important modulator of the effectiveness of entraining signals such as light and food. (Author correspondence: vanderveen@nd.edu)     

Circadian clock functioning is linked to acute stress reactivity in rats

At least two major physiological systems are involved in the adaptation of the organism to environmental challenges: the circadian system and the stress reaction. This study addressed the possibility that interindividual differences in stress sensitivity and in the functioning of the circadian system are related. At 2 months of age, corticosterone secretion in response to a 20-min restraint stress was assessed in 9 Sprague-Dawley rats for which running wheel activity was recorded as a rhythmic behavioral marker of the circadian clock. Two weeks later, the adaptive response of the circadian system to an abrupt shift in the light:dark (LD) cycle was assessed in those rats using a jet-lag paradigm. Finally, after resynchronization to the new LD cycle, rats were transferred to constant darkness to assess the free-running period of their circadian rhythm of running-wheel activity. Results indicate that stress-induced corticosterone secretion was (1) positively correlated with the number of days to resynchronize the circadian activity rhythm to the new LD cycle, and with the value of its free-running period, and (2) negatively correlated with the intensity of daily locomotor activity. Those data, emphasizing the interactions between the stress response of an organism and the functioning of its circadian system, could explain interindividual differences in humans' susceptibility to shift work or other circadian-related disorders.     

Absence of circadian and photoperiodic conservation of energy expenditure in three rodent species

According to a traditional homeostatic view, living beings spend metabolic energy at a constant rate, just like a light bulb spends electrical energy, so that energy expenditure can be expressed in units of watts. However, research conducted during the last half-century has evinced pronounced circadian variation in physiological processes, not only demonstrating circadian rhythmicity in energy expenditure but also raising the hypothesis that energy expenditure may be regulated on a daily (circadian) basis rather than on a constant-rate (homeostatic) basis. In the present study, the hypothesis of circadian (and photoperiodic) conservation of energy expenditure was tested in three rodent species: domestic mice, Nile grass rats, and Syrian hamsters. Two correlates of energy expenditure (running-wheel activity and food intake) and a classic index (oxygen consumption) were used. Changes in energy expenditure were studied in animals maintained under light-dark cycles (LDs) with periods shorter or longer than 24 h as well as in animals maintained under 24-h LDs with short and long photophases. In none of the conditions in any of the species was evidence found in support of the hypothesis of circadian (or photoperiodic) conservation of energy expenditure. Energy expenditure was generally conserved on a homeostatic basis.     

Circadian periods of sensitivity for ramelteon on the onset of running-wheel activity and the peak of suprachiasmatic nucleus neuronal firing rhythms in C3H/HeN mice

Ramelteon, an MT(1)/MT(2) melatonin receptor agonist, is used for the treatment of sleep-onset insomnia and circadian sleep disorders. Ramelteon phase shifts circadian rhythms in rodents and humans when given at the end of the subjective day; however, its efficacy at other circadian times is not known. Here, the authors determined in C3H/HeN mice the maximal circadian sensitivity for ramelteon in vivo on the onset of circadian running-wheel activity rhythms, and in vitro on the peak of circadian rhythm of neuronal firing in suprachiasmatic nucleus (SCN) brain slices. The phase response curve (PRC) for ramelteon (90?μg/mouse, subcutaneous [sc]) on circadian wheel-activity rhythms shows maximal sensitivity during the late mid to end of the subjective day, between CT8 and CT12 (phase advance), and late subjective night and early subjective day, between CT20 and CT2 (phase delay), using a 3-day-pulse treatment regimen in C3H/HeN mice. The PRC for ramelteon resembles that for melatonin in C3H/HeN mice, showing the same magnitude of maximal shifts at CT10 and CT2, except that the range of sensitivity for ramelteon (CT8-CT12) during the subjective day is broader. Furthermore, in SCN brain slices in vitro, ramelteon (10 pM) administered at CT10 phase advances (5.6?±?0.29?h, n?=?3) and at CT2 phase delays (-3.2?±?0.12?h, n?=?6) the peak of circadian rhythm of neuronal firing, with the shifts being significantly larger than those induced by melatonin (10 pM) at the same circadian times (CT10: 2.7?±?0.15?h, n?=?4, p?相似文献   

Lesions of the thalamic intergeniculate leaflet alter hamster circadian rhythms

We have investigated the effects of destruction of the geniculo-hypothalamic tract (GHT) on the circadian system of golden hamsters. In the first experiment, intact hamsters were housed in constant darkness, and phase shifts in running-wheel activity rhythms were assessed following 15-min light pulses administered at circadian time (CT) 12 (defined as the beginning of activity), CT 14, CT 18, and CT 20. Responses to light pulses at the same CTs were then reassessed after GHT lesions. Hamsters with complete lesions showed decreases in phase advances caused by light pulses at CT 18 and CT 20. Phase delays elicited by light at CT 12 and CT 14 were not altered. In a second study, intact and GHT-ablated hamsters housed in constant light received 6-hr dark pulses at various CTs. Hamsters with complete GHT ablation showed smaller advances than controls to dark pulses centered on CT 8-10. After 110 days in constant light, 7 of 10 intact hamsters showed splitting of their activity rhythms into two components, while only 1 of the 8 similarly treated ablated hamsters displayed dissociated activity components. Ablated hamsters had significantly shorter free-running periods during the first 35 days of exposure to constant light than did the intact hamsters. These results demonstrate that destruction of the GHT in the hamster alters phase shifting in response to periods of light or dark, and they indicate a role for the GHT in mediating several photic effects on the circadian system.     

Free Access to a Running-Wheel Advances the Phase of Behavioral and Physiological Circadian Rhythms and Peripheral Molecular Clocks in Mice

Behavioral and physiological circadian rhythms are controlled by endogenous oscillators in animals. Voluntary wheel-running in rodents is thought to be an appropriate model of aerobic exercise in humans. We evaluated the effects of chronic voluntary exercise on the circadian system by analyzing temporal profiles of feeding, core body temperature, plasma hormone concentrations and peripheral expression of clock and clock-controlled genes in mice housed under sedentary (SED) conditions or given free access to a running-wheel (RW) for four weeks. Voluntary wheel-running activity advanced the circadian phases of increases in body temperature, food intake and corticosterone secretion in the mice. The circadian expression of clock and clock-controlled genes was tissue- and gene-specifically affected in the RW mice. The temporal expression of E-box-dependent circadian clock genes such as Per1, Per2, Nr1d1 and Dbp were slightly, but significantly phase-advanced in the liver and white adipose tissue, but not in brown adipose tissue and skeletal muscle. Peak levels of Per1, Per2 and Nr1d1 expression were significantly increased in the skeletal muscle of RW mice. The circadian phase and levels of hepatic mRNA expression of the clock-controlled genes that are involved in cholesterol and fatty acid metabolism significantly differed between SED and RW mice. These findings indicated that endogenous clock-governed voluntary wheel-running activity provides feedback to the central circadian clock that systemically governs behavioral and physiological rhythms.     

Exercise distributed across day and night does not alter circadian period in humans

In rodents, increased activity due to running-wheel access is associated with a change in observed circadian period. In humans, exposure to exercise has failed to demonstrate similar effects on period. Methodological issues with prior studies such as light exposure during exercise, length of study, and method of measuring period confounded those evaluations of the effect of exercise on period in humans. In the present experiment, the authors examined the effect of exercise on period in 8 subjects using a 44-day within-subjects inpatient study. They used a 20-h forced desynchrony protocol, in which subjects were exposed to exercise across circadian phases under dim light conditions. Exercise consisted of three 45-min sessions per wake period on an ergometer. Target exercise intensity was ~65% of maximal heart rate. Intrinsic circadian period was measured using both core body temperature and hourly plasma melatonin samples. Consistent with previous reports, the authors find no effect of exercise on endogenous circadian period as measured by either core body temperature or melatonin. Exercise distributed across biological day and night does not appear to affect circadian period.     

Evaluation of social and physical enrichment in modulation of behavioural phenotype in C57BL/6J female mice

Housing conditions represent an important environmental variable playing a critical role in the assessment of mouse behaviour. In the present study the effects of isolation and nesting material on the behaviour of female C57BL/6J mice were evaluated. The mice were subjected to different rearing conditions from weaning (at the age of 3 weeks). The study groups were group- and single-housed mice, divided further into groups with or without nesting material (species-specific enrichment). After 8 weeks spent in respective conditions the behavioural testing began. Both factors (social conditions and nesting material) appeared to have a significant impact on the behavioural phenotype. However, it is important to stress that the interaction between the factors was virtually absent. We established that isolation increased locomotor activity and reduced anxiety-like behaviour in several tests of exploration. In contrast, absence of nesting material increased anxiety-like behaviour. Neither factor affected rota-rod performance, nociception and prepulse inhibition. Contextual fear memory was significantly reduced in single-housed mice, and interestingly, in mice with nesting material. Cued fear memory was reduced by single-housing, but not affected by enrichment. Mice from enriched cages displayed faster and better learning and spatial search strategy in the water maze. In contrast, isolation caused significant impairment in the water maze. In conclusion, both isolation and species-specific enrichment have profound effects on mouse behaviour and should be considered in design of the experiments and in assessment of animal welfare issues.     

Cage enrichment with paper tissue, but not plastic tunnels, increases variability in mouse model of asthma

Environmental enrichment, besides having a great impact on animal welfare, can also be a potential variable in experimental research. Thus, we investigated whether enrichment of cages with paper tissues or plastic tunnels affects scientific outcome in the well-described mouse model of allergic asthma. BALB/cJ mice were introduced to paper tissues as nesting material, transparent plastic tunnels serving as shelters or kept in non-enriched cages. Afterwards, mice were sensitized to chicken egg ovalbumin (OVA) precipitated in aluminium sulphate and then intranasally challenged with OVA to induce allergic lung inflammation. Mice housed in cages enriched with paper tissues, but not with plastic tunnels, had increased total cell number, eosinophil number and IL-13 concentration in bronchoalveolar lavage fluid in comparison with the non-enriched control group. These results indicate that the effect of environmental enrichment on mice asthma models depends on the type of enrichment used. Therefore, it is important to consider the potential effects of any environmental enrichment on animal welfare and more importantly, on research results in order to standardize and obtain more accurate data from rodent studies.     

Altered Circadian Period of Locomotor Activity in Carbonic Anhydrase II-Deficient Mice

This study finds lengthened circadian period in a congenic strain of mice homozygous for a null mutation in carbonic anhydrase isoenzyme-II gene on proximal Chromosome 3. Carbonic anhydrase II has the highest turnover rate of any constitutive enzyme. It catalyzes the reversible hydration of carbon dioxide to control intercellular acid/base balance. A strain of congenic mice has a carbonic anhydrase II null mutation within a DBA/2J inbred strain insert on a C57BL/6J inbred strain background. The locomotor activity levels and period of circadian rhythms were examined in the homozygous null mutants and their progenitors, mice heterozygous for the region around the carbonic anhydrase gene. The heterozygous mice siblings and the wild-type siblings served as the controls. During behavioral studies, male and female offspring and parents were housed singly in constant darkness. Locomotor activity was monitored using an infrared photobeam array. Mice homozygous for the carbonic anhydrase null mutation had a longer circadian period than either heterozygote or wild type littermates. Carbonic anhydrase null mutants also had low locomotor activity compared to either heterozygous or wild-type litter mates. This implies that either the physiological changes resulting from absence of carbonic anhydrase II isozyme or the presence of DBA/2J alleles around the carbonic anhydrase locus influence the circadian period and level of locomotor activity in laboratory mice.