The physiological and behavioral impact of sensory contact among unfamiliar adult mice in the laboratory

Housing mice in the laboratory in groups enables social interaction and is the way a laboratory should house mice. However, adult males show reciprocal aggression and are therefore frequently housed individually. Alternatively, a grid divider, which allows sensory contact by sight and smell but prevents fighting and injuries, can separate mice within 1 cage. This study examined the influence of this housing method on various physiological and behavioral parameters. Adult male mice housed for 10 days with sensory contact to an unfamiliar male displayed significant increases in heart rate (HR), body core temperature (BT), and motor activity (ACT). Furthermore, the mice suffered impaired nest-building behavior and significantly reduced body weight. Conversely, males housed in a similar manner with a female companion showed only a transient elevation of ACT, BT, and HR. Although no clear beneficial effect of housing males with sensory contact to females was evident, this study could not exclude it. On the other hand, housing of mature males in this way leads to sustained detrimental alterations of physiology and behavior, thus implying severe impairment of animal well-being.     

Effects of wire-bottom caging on heart rate, activity and body temperature in telemetry-implanted rats

Some experimental procedures are associated with placement of animals in wire-bottom cages. The goal of this study was to evaluate stress-related physiological parameters (heart rate [HR], body temperature [BT], locomotor activity [LA], body weight [BW] and food consumption) in rats under two housing conditions, namely in wire-bottom cages and in bedding-bottom cages. Telemetry devices were surgically implanted in male Sprague-Dawley rats. HR, BT and LA were recorded at 5 min intervals. Analysis under each housing condition was performed from 16:00 to 08:00 h of the following day (4 h light, 12 h dark). During almost all of the light phase, the HR of rats housed in wire-bottom cages remained high (371 ± 35 bpm; mean ± SD; n = 6) and was significantly different from that of rats housed in bedding-bottom cages (340 ± 29 bpm; n = 6; P < 0.001; Student's t-test). In general, BT was similar under the two housing conditions. However, when rats were in wire-bottom cages, BT tended to fluctuate more widely during the dark phase. LA decreased when animals were housed in wire-bottom cages, in particular during the dark phase. Moreover, there was a significant difference with respect to the gain in BW: BW of rats housed in bedding-bottom cages increased 12 ± 2 g, whereas that of rats in wire-bottom cages decreased by 2 ± 3 g (P < 0.001). Our results demonstrate that housing rats in wire-bottom cages overnight leads to immediate alterations of HR, BW and LA, which might be related to a stress response.     

Higher heart rate of laboratory mice housed individually vs in pairs

Many studies have shown that housing mice individually over a long period significantly alters their physiology, but in most cases measurement has required human interference and restraint for sampling. Using a radio-telemetry system with implantable transmitters, we recorded heart rate (HR), motor activity (ACT) and body temperature (BT) of freely moving male mice (NMRI) housed either individually or in pairs with an ovarectomized female. Data for each parameter were collected at 5 min intervals for two consecutive 24 h periods. Even after several weeks of habituation to the social conditions, HR was increased in mice housed individually compared with mice housed in pairs, although their measured ACT did not differ. Additionally, BT tended to be reduced in individually-housed mice. When the data were analysed according to different ACT levels, HR was increased in individually-housed mice during phases of low and high, but not intermediate, motor activity. Furthermore, individually-housed mice had more, but shorter, resting bouts, indicating disruption of the normal circadian sleep pattern. Enhanced HR in individually-housed mice does not necessarily indicate stress, but might be an important physiological indicator of discomfort. The fact that individual housing alters basic physiological parameters in laboratory mice highlights the need to control for housing-dependent variation, especially in experiments that are sensitive to changes in these parameters.     

Impact of 'living apart together' on postoperative recovery of mice compared with social and individual housing

Social housing is the optimal way of housing female laboratory mice. However, individual housing may be required in experimental designs, for example after surgery. We therefore investigated whether housing two female mice in a cage, separated by a grid partition ('living apart together', LAT), counters the adverse effects of individual housing on postoperative recovery. Ten individually housed (IND) mice, nine socially housed (SOC) mice and nine mice, housed LAT, were surgically implanted with a telemetry transmitter. From one week prior to surgery until three weeks thereafter, several physiological and behavioural parameters were measured in the mice subjected to surgery. The telemetry transmitter measured heart rate (HR), body temperature and activity continuously. Body weight, food and water intake were scored regularly, as were wound healing, ease of handling, nest building and behaviour. Results indicated that SOC mice appear to be less affected by abdominal surgery than IND mice, as indicated by HR and behaviour. LAT, however, did not appear to be beneficiary to the mice. Increased HR levels and differences in behaviour as compared with both SOC and IND animals indicate that LAT may even be the most stressful of the three housing conditions. We therefore conclude that mice benefit most from social housing after surgery. If, however, social housing is not possible, individual housing appears to be a better option than separating mice by a grid partition.     

Circadian rhythms in heart rate, motility, and body temperature of wild-type C57 and eNOS knock-out mice under light-dark, free-run, and after time zone transition

The nitric oxide (NO) system is involved in the regulation of the cardiovascular system in controlling central and peripheral vascular tone and cardiac functions. It was the aim of this study to investigate in wild-type C57BL/6 and endothelial nitric oxide synthase (eNOS) knock-out mice (eNOS-/-) the contribution of NO on the circadian rhythms in heart rate (HR), motility (motor activity [MA]), and body temperature (BT) under various environmental conditions. Experiments were performed in 12:12 h of a light:dark cycle (LD), under free-run in total darkness (DD), and after a phase delay shift of the LD cycle by -6 h (i.e., under simulation of a westward time zone transition). All parameters were monitored by radiotelemetry in freely moving mice. In LD, no significant differences in the rhythms of HR and MA were observed between the two strains of mice. BT, however, was significantly lower during the light phase in eNOS-/- mice, resulting in a significantly greater amplitude. The period of the free-running rhythm in DD was slightly shorter for all variables, though not significant. In general, rhythmicity was greater in eNOS-/- than in C57 mice both in LD and DD. After a delay shift of the LD cycle, HR and BT were resynchronized to the new LD schedule within 5-6 days, and resynchronization of MA occurred within 2-3 days. The results in telemetrically instrumented mice show that complete knock-out of the endothelial NO system—though expressed in the suprachiasmatic nuclei and in peripheral tissues—did not affect the circadian organization of heart rate and motility. The circadian regulation of the body temperature was slightly affected in eNOS-/- mice.     

Effect of restraint and injection methods on heart rate and body temperature in mice

Routine procedures in the laboratory, inducing acute stress, will have an impact on the animals and might thereby influence scientific results. In an attempt to gain more insight into quantifying this acute stress by means of the parameters heart rate (HR) and body temperature (BT), we subjected mice to different restraint and injection methods. We first compared the treatment response of HR and BT, measured by means of radiotelemetry, with the treatment response of plasma corticosterone (pCORT), a common and well-validated parameter for measuring acute stress responses. It was found that HR, and to a lesser extent also BT, parallels pCORT values after subjecting the animals to different methods of restraint. Secondly, the acute stress response caused by different injection methods was evaluated. Again, HR was found to be a more sensitive parameter than BT. We found that, in case of sham injections, the acute stress response after an intraperitoneal (i.p.) injection was more pronounced than after intramuscular (i.m.) or subcutaneous (s.c.) injections, but this difference was found to be inconsistent when saline was used as injection fluid. In a third experiment we investigated if the level of experience of the animal technician influenced the stress response after s.c. injections, but no differences were found. Overall, the results have indicated that HR might be considered as a useful parameter for measuring acute stress responses to routine procedures, but the value of BT seems to be of limited value in this respect.     

Circadian Rhythms in Heart Rate,Motility, and Body Temperature of Wild‐type C57 and eNOS Knock‐out Mice Under Light‐dark,Free‐run,and After Time Zone Transition

The nitric oxide (NO) system is involved in the regulation of the cardiovascular system in controlling central and peripheral vascular tone and cardiac functions. It was the aim of this study to investigate in wild‐type C57BL/6 and endothelial nitric oxide synthase (eNOS) knock‐out mice (eNOS‐/‐) the contribution of NO on the circadian rhythms in heart rate (HR), motility (motor activity [MA]), and body temperature (BT) under various environmental conditions. Experiments were performed in 12∶12 h of a light:dark cycle (LD), under free‐run in total darkness (DD), and after a phase delay shift of the LD cycle by ?6 h (i.e., under simulation of a westward time zone transition). All parameters were monitored by radiotelemetry in freely moving mice. In LD, no significant differences in the rhythms of HR and MA were observed between the two strains of mice. BT, however, was significantly lower during the light phase in eNOS‐/‐ mice, resulting in a significantly greater amplitude. The period of the free‐running rhythm in DD was slightly shorter for all variables, though not significant. In general, rhythmicity was greater in eNOS‐/‐ than in C57 mice both in LD and DD. After a delay shift of the LD cycle, HR and BT were resynchronized to the new LD schedule within 5–6 days, and resynchronization of MA occurred within 2–3 days. The results in telemetrically instrumented mice show that complete knock‐out of the endothelial NO system—though expressed in the suprachiasmatic nuclei and in peripheral tissues—did not affect the circadian organization of heart rate and motility. The circadian regulation of the body temperature was slightly affected in eNOS‐/‐ mice.     

Co-species housing in mice and rats: Effects on physiological and behavioral stress responsivity

Co-species housing of mice and rats is common practice at most breeding facilities and research laboratories, neglecting the possible effects on the animals. We investigated physiological as well as behavioral stress-reactivity in mice and rats which were either derived from a co-species or species-separated housing condition at the breeding facilities. The animals were kept under the housing condition they were used to or assigned to the opposite one. Co-species housing had a significant impact on acute stress reactivity in mice and rats but only if they were used to this housing condition throughout their lives. Moreover, the stress-effects appeared to be long lasting. Assigning animals, derived from a species-separated housing condition, to co-species housing led to chronic stress in mice and affected experimental behavior of rats.Our findings led to the conclusion that co-species housing in mice and rats should be avoided, supporting the recommendations by the U.S. National Institutes of Health (NIH) and the Dutch Ministry of Health, Welfare and Sport (VWS). In order to support the interpretation, facilitate the reproducibility and comparability and subsequently the generalizability of experimental results, breeding facilities should at least provide detailed information about their housing conditions.     

Characteristics of the thermoregulatory reactions of mice and rats to mediator-active substances

The effect of dopaminomimetics (apomorphine, piribedil, bromocriptine), cholinomimetics (oxotremorine, arecoline, pylocarpine), and neuroleptics (chlorpromazine, haloperidol, triperidol) on rectal temperature (Tr) and temperature of different parts of the skin has been investigated in albino mice and rats of either sex. In rats these drugs cause the decrease of Tr and significantly increase tail temperature (Tt), as well as the temperature of the fore- and hindpaws (Tfp and Thp correspondingly). In mice the drug-induced fall of Tr is more significant than in rats; however, only neuroleptics essentially increase Tfp and Thp, the increase in Tt being inconsistent and small. Cholinomimetics and usually dopaminomimetics decrease Tt. Cholinomimetics do not affect and dopaminomimetics cause only transient and small rise in Tfp and Thp. The data do not confirm the key role of enhanced heat dissipation through the skin as a mechanism of hypothermic effect of cholino- and dopaminomimetic drugs in mice under the room temperature. In contrast to mice, thermoregulatory skin reactions to drugs in rats are much more pronounced, and together with palmar and plantar surfaces of the paws the same role in thermoregulationss is played by the skin of the tail.     

Stressful animal housing conditions and their potential effect on sympathetic neurotransmission in mice

Although the sympathetic nervous system (SNS) plays a major role in mediating the peripheral stress response, due consideration is not usually given to the effects of prolonged stress on the SNS. The present study examined changes in neurotransmission in the SNS after exposure of mice (BALB/c) to stressful housing conditions. Focal extracellular recording of excitatory junction currents (EJCs) was used as a relative measure of neurotransmitter release from different regions of large surface areas of the mouse vas deferens. Mice were either group housed (control), isolation housed (social deprivation), group housed in a room containing rats (rat odor stress), or isolation housed in a room containing rats (concurrent stress). Social deprivation and concurrent stressors induced an increase of 30 and 335% in EJC amplitude, respectively. The success rate of recording EJCs from sets of varicosities in the concurrent stressor group was greater compared with all other groups. The present study has shown that some common animal housing conditions act as stressors and induce significant changes in sympathetic neurotransmission.     

Diurnal variation of heart rate, locomotor activity, and body temperature in interleukin-1 alpha/beta doubly deficient mice.

This study was investigated the roles of interleukin-1 (IL-1) on diurnal rhythms of heart rate (HR), locomotor activity (LA), and body temperature (BT). For this purpose, HR, LA, and BT were recorded from conscious and unrestrained IL-1 alpha/beta doubly deficient (KO) and normal C57BL/6J mice using a telemetry system. These parameters were continuously recorded from just after to 2 weeks after transmitter implantation, because we thought that the surgical stress-induced IL-1 might affect the biobehavioral activities of the animals. At 1 day after implantation, HR and LA in IL-1 alpha/beta KO mice were higher than those in C57BL/6J mice. While BT in IL-1 alpha/beta KO mice was lower than that in C57BL/6J mice. Moreover, diurnal rhythmicity in these parameters after implantation in IL-1 alpha/beta KO mice appeared earlier than in C57BL/6J mice. At 2 weeks after implantation, there were no significant differences in the light- and dark-phase values of each parameter between IL-1 alpha/beta KO and C57BL/6J mice, however, IL-1 alpha/beta KO mice showed clear ultradian rhythmicity. It is thought that a phenotypical difference in biobehavioral activities between IL-1 alpha/beta KO and C57BL/6J mice may reflect IL-1 induced febrile and behavioral responses. These results suggest that IL-1 may play important physiological and pathophysiological roles on biobehavioral activities.     

Vasopressin deficiency provides evidence for separate circadian oscillators of activity and temperature

Vasopressin-containing Long-Evans and vasopressin-deficient Brattleboro rats were maintained in individual cages while telemetered activity (AC) and body temperature (BT) data were collected. Rats were initially exposed to a 12 h/12-h light/dark cycle (photic zeitgeber) and were allowed ad-libitum access to food and water. Daily feeding, care, and handling (nonphotic zeitgebers) occurred at the beginning of the second hour of the dark cycle. After a 14-day habituation period, rats were subjected to continuous light (LL) or dark (DD) and nonphotic cues were presented irregularly. During the habituation period, both strains exhibited clear 24-h circadian rhythms of AC and BT. In LL or DD, photic cues were removed and nonphotic cues were presented irregularly. There was a shift in the rhythm for Long-Evans animals to 26 h for both AC and BT in LL and 24.6 h in DD. Feeding, care, and handling were seen as minor artifact. In Brattleboro rats, although there were robust 26-h and 24.6-h circadian rhythms of AC in the LL and DD, respectively, BT data were inconsistent and showed sporadic fluctuations. In the BT rhythm of Brattleboro animals, strong peaks were associated with feeding, care, and handling times and trough periods were characterized by a dramatic drop in temperature. This experiment demonstrates that AC and BT are controlled by separate oscillators. In addition, the importance of vasopressinergic fibers in the control of circadian rhythms of BT is evidenced by the loss of circadian rhythms in animals lacking these functional fibers when exposed to free-running paradigms where there is no entrainment of photic or nonphotic oscillators.     

Inapparent Streptococcus pneumoniae type 35 infections in commercial rats and mice

Streptococcus pneumoniae was isolated from specific-pathogen-free rodents in two rooms at a commercial breeding facility during vendor surveillance testing. In a survey of 274 animals from the two rooms over a period of 7 months, capsular serotype 35 S. pneumoniae was isolated from the upper respiratory tracts of 11% (9 of 82) of C57BL/6 mice in room A and 14% (10 of 72) of F344 rats in room B, but not from WKY rats, BALB/c mice or DBA/2 mice from room A. In both C57BL/6 mice and F344 rats, older rodents had higher colonization frequencies. Nasal lavage cultures gave the best results in identifying colonized rodents. No clinical illness or microscopic lesions were associated with pneumococcal colonization in rats or mice, and no other evidence of potential pathogen infection was found except for positive serologic tests for mouse rotavirus in mice. This is the first report of natural pneumococcal infection in mice, and the first report of type 35 S. pneumoniae infection in rodents. The findings support an earlier observation that pneumococcal infections in rat colonies tend to be monotypic and suggest that the same may be true in mice.     

Influence of environmental enrichment and handling on the acute stress response in individually housed mice

In this study we investigated the effect of environmental enrichment and handling on the acute physiological stress response caused by short periods of restraint in individually housed female mice. Heart rate (HR) and body temperature (BT) were measured by radiotelemetry and compared with plasma corticosterone (pCORT) levels. Also, postmortem thymus weight and tyrosine hydroxylase (TH) activity were assessed. The acute stress response was seen in both HR and BT. Enrichment and handling were found to increase rather than decrease this stress response, but pCORT values, measured 90 min after restraint, suggested a lower stress response in the enriched groups. No effect was found with thymus weight or TH as parameters.     

Comparative analysis and physiological impact of different tissue biopsy methodologies used for the genotyping of laboratory mice

Genotyping of genetically modified mice and control of authenticity of the genetic background of congenic or coisogenic strains by polymerase chain reaction (PCR) is a routine procedure that can be performed with different tissue biopsies causing variable grades of trauma. In this study, some invasive and non-invasive sampling methods were compared, with the main focus on the impact on animal physiology. We compared ear punch, tail biopsy, hair plugging, mouth and rectum swabs and the simple restraint of the animals, scoring for the impact on heart rate (HR), core body temperature (BT) and motor activity by telemetry, during biopsy and for the following 6 h. Furthermore, in order to correlate the physiological impact with the practicability and reliability of the genotyping results, we performed a PCR analysis of the biopsy samples obtained by using the same collection procedures analysed by telemetry. All sampling methods and restraint induced significant increase in HR and BT and a slight increase in motor activity for 1 h, independent of the invasiveness of the method used. Genotyping of all biopsies allowed the proper identification of transgenic animals, tail biopsies, ear punches and hair follicles giving clear signals, the last method being fast, but also susceptible to cross contaminations during sampling by large numbers of animals. Restraint and all biopsy methods provoked similar physiological changes, indicating that the handling of the animals is of major importance and that the sampling procedure does not strongly influence the physiological parameters.     

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.     

SHR Y chromosome enhances the nocturnal blood pressure in socially interacting rats

Our objective was to test the hypothesis that nocturnal mean arterial pressure (MAP), heart rate (HR), and activity would be increased in 1) colony over individually caged rats and 2) the spontaneously hypertensive rat (SHR) Y chromosome strain (SHR/y colony) compared with Wistar-Kyoto (WKY) rats. MAP, HR, and activity were monitored using radiotelemetry. The nocturnal MAP rise expressed as the percentage change in MAP from light to dark was increased (P < 0.05) in the SHR/y colony. The SHR Y chromosome increased MAP in both the colony and caged groups compared with WKY (P < 0.001). The SHR/y colony animals spent 23% of a 24-h period at a MAP >120 mmHg, whereas the WKY colony animals spent 2% of a 24-h period in this range. The MAP of the SHR/y colony on clonidine was reduced (P < 0.001) to WKY baseline values. Activity but not HR was increased (P < 0.01) in the WKY and SHR/y colonies compared with caged animals. In conclusion, colony housing and the SHR Y chromosome increased MAP compared with individually caged housing.     

Laboratory Rodent Welfare: Thinking Outside the Cage

This commentary presents the case against housing rats and mice in laboratory cages; the commentary bases its case on their sentience, natural history, and the varied detriments of laboratory conditions. The commentary gives 5 arguments to support this position: (a) rats and mice have a high degree of sentience and can suffer, (b) laboratory environments cause suffering, (c) rats and mice in the wild have discrete behavioral needs, (d) rats and mice bred for many generations in the laboratory retain these needs, and (e) these needs are not met in laboratory cages.     

The daily pattern of cardiovascular parameters in Kurosawa and Kusanagi-Hypercholesterolemic (KHC) rabbits.

We studied characteristics of the daily pattern of heart rate (HR), blood pressure (BP), body temperature (BT), and locomotor activity (LA) in conscious and unrestrained Kurosawa and Kusanagi-Hypercholesterolemic (KHC) rabbits and age-matched normal Japanese white (JW) rabbits, using a telemetry system. In all JW rabbits, nocturnal patterns were observed in HR, BT and LA. In the 5 months group of KHC rabbits, however, diurnal rhythm was observed in HR, and in the 10 months group of KHC rabbits, it was also shown in LA. The nocturnal pattern was observed only in BT in 10 months KHC rabbits. Mean blood pressure (MBP) in JW and KHC rabbits showed no clear daily pattern. The mean daily values of HR and BT were not altered between the 5 months and 10 months groups in KHC rabbits, although those in JW were lower in the 10 months group than in the 5 months group. Moreover, the daily values of HR and MBP in KHC rabbits tended to be higher than those in the age-matched JW rabbits. The pulse pressure in the 10 months group of KHC rabbits tended to be greater than the 5 months groups of KHC and JW rabbits. Furthermore, short-term variabilities in BP in the 5 months KHC rabbits were significantly lower than those in the other groups. From these results, it is suggested that the cardiovascular function, including the autonomic nervous function is altered with the development of atherosclerosis in KHC rabbits.     

NARCOBIT: a newly developed inhalational anesthesia system for mice.

NARCOBIT is the first anesthetic system for mice and rats to incorporate a ventilator. Therefore, it is expected to improve the reliability of mice and rat experiments by accurately controlling and maintaining the depth of anesthesia. In this study, we used NARCOBIT for inducing inhalational anesthesia in mice and evaluated the changes in their hemodynamic parameters. ICR mice were anesthetized with 5% isoflurane and room air, followed by endotracheal intubation. Subsequently, they were mechanically ventilated, and anesthesia was maintained by 2% isoflurane for a 60-min period (maintenance state) using NARCOBIT. In study 1, the heart rate (HR) and mean arterial blood pressure (MAP) were measured. The skin blood flow (SBF) from the hind legs was continuously measured during the maintenance state. Subsequently, the concentration-dependent effects of isoflurane on MAP were examined. In study 2, blood samples were obtained from the abdominal aorta for blood gas analysis. The HR and MAP decreased after anesthesia but were stable during the maintenance state. Decreased MAP and concentration-dependent effects of isoflurane were observed. The SBF increased slightly during the maintenance state but this increase was insignificant. The blood gas analysis showed neither hypoxia nor hypercapnia. Since the use of NARCOBIT enables the anesthetic concentration of isoflurane to be easily changed, a suitable anesthesia depth can be obtained for experimental purposes. Therefore, we conclude that NARCOBIT can be used for providing inhalational anesthesia to mice.