Short-term effects of a disturbed light–dark cycle and environmental enrichment on aggression and stress-related parameters in male mice

In the laboratory setting, environmental factors have a major influence on the well-being of laboratory animals. The present study shows the importance of a semi-natural light–dark cycle. In this experiment one cohort of mice was kept with a continuous lighting for one week. After the first week the artificial light–dark cycle was 12:12 with lights on at 07:00 h. The second cohort of mice was kept with this 12:12 h light–dark cycle from the start. Half of each cohort received environmental enrichment. In order to analyse corticosterone levels, urine samples were collected. To measure agonistic behaviour, the behaviour of the mice was recorded on videotape immediately after cage cleaning. A significant difference in corticosterone levels between cohorts was found during disturbed lighting, but not after lighting conditions were reset to 12:12 h. In the first test week, mice subjected to disturbed lighting also showed a significantly shorter agonistic latency than control mice. This difference had disappeared when in the second test week all mice experienced 12:12 h lighting. No effects of enriched housing were found. This experiment has shown that disturbed lighting for socially-housed male mice caused physiological and behavioural changes indicative of stress, not only leading to much higher levels of corticosterone but also to shorter agonistic latency within the groups.

Effects of Enrichment and Litter Parity on Reproductive Performance and Behavior in BALB/c and 129/Sv Mice

We examined the effect of adding species-appropriate environmental enrichment items to breeding cages of BALB/cAnNCrl and 129S2/SvPasCrl mice. The 3 enrichment conditions were: 1) cotton nesting material; 2) nesting material plus a paper shelter and rolled paper bedding; and 3) an igloo dome with an exercise wheel in addition to the shelter-group enrichments. We measured litter size, litter survival to weaning age, average pup weight at 21 d, and the interlitter interval to evaluate reproductive performance. A random subset of the first- or second-litter offspring from each enrichment condition and strain was assessed in multiple behavioral tests. Enrichment significantly affected anxiety-like behavior and sociability, with the direction of change dependent on strain and sex. Litter parity had greater effects on some reproductive parameters than did the enrichment condition, and this effect was not solely due to a difference between the first compared with subsequent litters. The significant effects of litter parity on the number of pups born and weaned, female pup weight, and interlitter interval were dependent on the enrichment condition in BALB/c but not 129/Sv mice. Offspring from the first or second litter were included in a generational component to investigate whether enrichment effects on reproduction persist in adult offspring after transfer to a different facility for breeding. Natal cage enrichment had no effect on any reproductive parameter in the transferred mice. Overall, additional enrichment beyond nesting material had a beneficial effect on the interlitter interval in BALB/c mice and on the number of pups weaned in 129/Sv mice.

Generating Chimeric Mice by Using Embryos from Nonsuperovulated BALB/c Mice Compared with Superovulated BALB/c and Albino C57BL/6 Mice

The reliable generation of high-percentage chimeras from gene-targeted C57BL/6 embryonic stem cells has proven challenging, despite optimization of cell culture and microinjection techniques. To improve the efficiency of this procedure, we compared the generation of chimeras by using 3 different inbred, albino host, embryo-generating protocols: BALB/cAnNTac (BALB/c) donor mice superovulated at 4 wk of age, 12-wk-old BALB/c donor mice without superovulation, and C57BL/6NTac-Tyr(tm1Arte) (albino B6) mice superovulated at 4 wk of age. Key parameters measured included the average number of injectable embryos per donor, the percentage of live pups born from the total number of embryos transferred to recipients, and the number of chimeric pups with high embryonic-stem-cell contribution by coat color. Although albino B6 donors produced significantly more injectable embryos than did BALB/c donors, 12-wk-old BALB/c donor produced high-percentage (at least 70%) chimeras more than 2.5 times as often as did albino B6 mice and 20 times more efficiently than did 4-wk-old BALB/c donors. These findings clearly suggest that 12-wk-old BALB/c mice be used as blastocyst donors to reduce the number of mice used to generate each chimera, reduce the production of low-percentage chimeras, and maximize the generation of high-percentage chimeras from C57BL/6 embryonic stem cells.

Long-Term Provision of Environmental Resources Alters Behavior but not Physiology or Neuroanatomy of Male and Female BALB/c and C57BL/6 Mice

Few studies have evaluated the long-term effects of providing environmental resources to mice. This consideration is important given that mice are often maintained in vivaria for months. We evaluated the effects of providing simple cage resources (wood wool, cotton nesting material, a plastic tunnel, and oat cereal) compared with standard housing (solid-bottom cage with hardwood chips) to group-housed adult male and female C57BL/6 and BALB/c mice (n = 20/sex/strain/group) over 6 mo to determine whether these resources had a lasting effect on animal physiology, anatomy, and behavior. Body weights increased in all groups over time but were proportionately higher in male and female BALB/c mice housed in resource-supplemented environments. Throughout the study, adding environmental resources had no effect on hematology and lymphocyte subsets, fecal corticoid metabolite levels, response to LPS injection, or dendritic spine length or density. Strain- or sex×environmentspecific changes occurred in dark-light activity and thermal nociceptive responses. Dominant agonistic behaviors, abnormal conspecific sexual behaviors, and social nonagonistic behaviors demonstrated sex and strain×environment interactions such that fewer maladaptive social behaviors were noted in mice that were provided with environmental resources. This association was particularly evident in male mice of both strains in resource-supplemented environments. A small but significant increase in brain weight:body weight ratios occurred in mice in resource-supplemented environments. Under the conditions evaluated here, consistent use of simple environmental resources had a positive long-term effect on the behavioral wellbeing of male and female BALB/c and C57BL/6 mice yet minimally affected other aspects of murine physiology and neuroanatomy.

The BALB/c mouse: Effect of standard vivarium lighting on retinal pathology during aging

BALB/cJ mice housed under normal vivarium lighting conditions can exhibit profound retinal abnormalities, including retinal infoldings, autofluorescent inflammatory cells, and photoreceptor degeneration. To explore the sensitivity of the outer retina to cyclic lighting during aging, a cohort of BALB/cJ mice was evaluated with Scanning Laser Ophthalmoscopy (SLO), Spectral-Domain Optical Coherence Tomography (OCT) and conventional histopathology. Mice were bred and reared in a low-illuminance (extracage/intracage: 13 lx/1 lx) vivarium under cyclic light (14 h light: 10 h dark). Retinal imaging (around postnatal day 70) was performed to screen for any pre-existing abnormalities and to establish a baseline. Mice with normal retinas were separated into groups (A, B, C) and placed on bottom (Groups A & B) or top (Group C) of the cage racks where cage illumination was <10 & 150 lx respectively. Experimental groups B & C were imaged multiple times over a 17 month period. Mice from group A (controls) were imaged only once post-baseline at various times for comparison to groups B & C. Mice were assessed by histology at 8, 15, 20, 36, and 56 weeks and immunohistochemistry at 15 weeks post-baseline. SLO and OCT retinal images were measured and the resulting trends displayed as a function of age and light exposure. Retinal lesions (RL) and autofluorescent foci (AFF) were identified with histology as photoreceptor layer infoldings (IF) and localized microglia/macrophages (MM), respectively. Few RL and AFF were evident at baseline. Retinal infoldings were the earliest changes followed by subjacent punctate autofluorescent MM. The colocalization of IF and MM suggests a causal relationship. The incidence of these pathological features increased in all groups relative to baseline. OCT imaging revealed thinning of the outer nuclear layer (ONL) in all groups at 1 year relative to baseline. ONL thinning followed an exponential rate of change but the decay constant varied depending on intensity of illumination of the groups. Advanced age and top row illuminance conditions resulted in significant photoreceptor cell loss as judged by decreased thickness of the ONL. Photoreceptor loss was preceded by both retinal infoldings and the presence of autofluorescent inflammatory cells in the outer retina, suggesting that these changes are early indicators of light toxicity in the BALB/cJ mouse.

Lifetime reproductive efficiency of BALB/c mouse pairs after an environmental modification at 3 mating ages

The aim of this study was to evaluate the effects of an environment change and the age at which mating pairs were formed on the lifetime reproductive performance of BALB/c mice. We assigned 60 monogamous pairs to a randomized design in a 2 × 3 factorial arrangement (with or without an environmental modification and with 3 mating ages: 28, 45, or 60 d). Autoclaved cardboard tubes (length, 10 cm; diameter, 4 cm) were used as the environmental modification. Data were collected from a total of 456 litters over a period of 10 mo. The mice tore the cardboard tube and used its parts both as shelters and as nesting material. The presence of a cardboard tube decreased the preweaning litter mortality rate in the first 6 reproductive cycles. Mating at 28 or 45 d of age also decreased the preweaning mortality rate in the first 6 reproductive cycles, compared with monogamous pairs formed at 60 d of age. Treatments did not affect age at first parturition, number of litters, time between litters, or litter size and weight at birth and weaning. In addition to contributing to animal wellbeing, providing a cardboard tube improved productivity by decreasing the preweaning mortality rate. BALB/c siblings should be paired for mating when no older than 28 d, to reduce preweaning mortality of the offspring.

Effects of vaginal septa on the reproductive performance of BALB/cByJNarl mice

From March through December 2010, the incidence of vaginal septa in our SPF breeding colony of BALB/cByJNarl mice was 14.2%. In general, septa obstructed half of the vaginal orifice. Here we sought to determine the effect of this defect by comparing the reproductive performance of affected (septate) mice with that of unaffected (nonseptate) mice. Our results showed that the rates of both copulatory plugs and pregnancy were significantly lower in septate mice than in nonseptate mice. Specifically, 23 of 45 bred septate female mice (51%) had vaginal plugs compared with 49 of 68 bred nonseptate females (72%). Only 12 septate female mice (27%) had successful pregnancies, compared with 37 nonseptate females (54%). Septate mice had a 1-logfold fewer intrauterine sperm after mating than did nonseptate mice. Three cases of dystocia were noted among septate mice whereas none occurred in nonseptate mice. Septate dams had a higher percentage of septate pups (15.5%) than did nonseptate dams (6.1%). Our findings indicate that vaginal septa affect the reproductive performance of laboratory mice and that such a defect should be considered as an exclusion criterion for the selection of future breeders in a mouse colony.

Assessment of routine procedure effect on breathing parameters in mice by using whole-body plethysmography

We used whole-body plethysmography to investigate the effect of restraint, ear marking, tail vein and retroorbital blood sampling, and tail clipping on respiration in Balb/c × TCR-HA +/- F1 hybrid mice (F1h). Baseline values of breathing parameters were determined. During the experiment, mice experienced a procedure and then plethysmographic recordings were obtained immediately and at 4, 24, and 48 h afterward. Baseline breathing parameters showed significant differences between sexes. Restraint affected minute volume differently than did handling in male mice and to a lesser extent in female mice. Ear marking significantly changed minute volume compared with handling but not restraint in male mice and in the opposite manner in female mice. Tail vein blood sampling changed minute volume in a significant manner compared with restraint but not compared with handling in both sexes. Retroorbital blood sampling significantly changed minute volume compared with values for both handling and restraint in male mice but only compared with handling in female mice. Tail clipping modified minute volume significantly compared with handling in male mice and compared with restraint in both sexes. Analysis of data showed that routine procedures affect minute volume in mice depending on invasiveness of maneuver and in a sex-biased manner for as long as 24 h after the procedure. Our experiment shows that procedures performed on laboratory mice can change respiratory parameters and can be investigated by plethysmography.

Environmental enrichment during rearing alters corticosterone levels, thymocyte numbers, and aggression in female BALB/c mice

The goal of environmental enrichment for laboratory animals is to improve welfare, but some enrichment practices may affect research in unintended ways or even be harmful to the animals themselves. We previously found that mice raised at a commercial vendor then given multiple enrichment devices upon arrival at our facilities experienced thymic atrophy and greater variation in measured parameters than did their unenriched counterparts, suggesting that enrichment conditions affected corticosteroid expression in mice. The current study verified and expanded these results, examining 120 female BALB/c mice raised with or without nesting material at a commercial vendor (n = 60 per group) and allocated (n = 20 per group) to receive no enrichment, nesting material, or 'superenrichment' on arrival at our facilities. Nesting material provided prior to weaning was associated with higher levels of urinary corticosteroid, whereas superenrichment and nesting material during the adult period both led to increased thymic atrophy. Paradoxically, mice that never received enrichment, despite having the lowest corticosterone levels and least thymic atrophy, had increased tail wounds resulting from aggressive interactions. Therefore, enrichment devices that are as seemingly innocuous as nesting material, even if only provided in the preweaning period, may lead to significant, lasting changes in behavioral, physical, or immunologic measures with the potential to alter research outcomes.

Postsurgical food and water consumption, fecal corticosterone metabolites, and behavior assessment as noninvasive measures of pain in vasectomized BALB/c mice

Recognition of pain and stress is a common challenge when working with laboratory mice. The aim of the current study was to identify noninvasive parameters to assess the severity and duration of possible pain and stress after vasectomy in BALB/c mice. Mice underwent isoflurane anesthesia with or without vasectomy. Body weight, food and water intake, and fecal corticosterone metabolites (FCM) were measured 3 d before and 3 d after the procedure. Behavior was recorded 1, 2, 4, and 8 h after the procedure. Food and water consumption and defecation were reduced postoperatively in the vasectomized group compared with mice given anesthesia only. FCM were elevated the first day after anesthesia in the control mice but not in the vasectomized group. Vasectomy resulted in behavioral changes that were not seen in the group that was anesthetized only. In conclusion, food and water consumption and pain-related behaviors, but not FCM, may be useful as noninvasive parameters to assess postoperative pain and stress in vasectomized mice.

Relations between open-field, elevated plus-maze, and emergence tests as displayed by C57/BL6J and BALB/c mice

The relations between open-field, elevated plus-maze, and emergence tests were examined in two strains of mice. In the open-field, C57BL/6J mice had more ambulatory movements and rears but not stereotyped movements relative to BALB/c. In addition, C57BL/6J mice entered more often than BALB/c into enclosed and open arms of the elevated plus-maze. When placed inside a large enclosure, C57BL/6J mice emerged more quickly than BALB/c from a small toy object. In the entire series of mice, ambulation and rears in the open-field were linearly correlated with open and enclosed arm visits in the elevated plus-maze. Ambulatory movements and rears were also correlated with emergence latencies. In contrast, stereotyped movements were correlated with emergence latencies, but not with any elevated plus-maze value. These results specify the extent and limits of association between the three tests.

Involvement of sex, strain and age factors in high fat diet-induced obesity in C57BL/6J and BALB/cA mice

Although a number of obesity animal models have been reported, each model possesses different characteristics of obesity, suggesting care should be taken in choosing an animal model suitable for the experimental purpose. In this report, we fed 4-(young) and 52-week-old (middle-aged) C57BL/6J (B6) and young BALB/cA (BALB/c) mice with a high fat diet (HFD) for 9 weeks, and investigated the clinical and histological characteristics of obesity. In BALB/c mice, males gained more body weight and body fat weight and had higher energy intake than females by HFD feeding. Comparing the effect of HFD feeding between the strains of mice, BALB/c male mice accumulated more hepatic lipid than B6 male mice. In addition, middle-aged B6 mice increased the ratio of fat to body weight and hepatic lipid accumulation more than young mice. In conclusion, the characteristics of obesity induced by HFD feeding were influenced by the sex, strain and age of mice. Sex steroid hormones, hepatic lipid metabolism and systemic metabolism might be involved in these factors. The basic data in this study will be useful for the development of animal models of high fat diet-induced obesity.

Early life stress alters adult serotonin 2C receptor pre-mRNA editing and expression of the alpha subunit of the heterotrimeric G-protein G q

Infant maternal separation, a paradigm of early life stress in rodents, elicits long-lasting changes in gene expression that persist into adulthood. In BALB/c mice, an inbred strain with spontaneously elevated anxiety and stress reactivity, infant maternal separation led to increased depression-like behavioral responses to adult stress and robustly increased editing of serotonin 2C receptor pre-mRNA. Chronic fluoxetine treatment of adult BALB/c mice exposed to early life stress affected neither their behavioral responses to stress nor their basal 5-HT2C pre-mRNA editing phenotype. However, when fluoxetine was administered during adolescence, depression-like behavioral responses to stress were significantly diminished in these mice, and their basal and stress-induced 5-HT2C pre-mRNA editing phenotypes were significantly lower. Moreover, when BALB/c mice exposed to early life stress were raised in an enriched postweaning environment, their depression-like behavioral responses to adult stress were also significantly diminished. However, their 5-HT2C pre-mRNA editing phenotype remained unaltered. Hence, the similar behavioral effects of enrichment and fluoxetine treatment during adolescence were not accompanied by similar changes in 5-HT2C pre-mRNA editing. Enriched and nonenriched BALB/c mice exposed to early life stress also exhibited significantly increased expression of mRNA and protein encoding the G alpha q subunit of G-protein that couples to 5-HT2A/2C receptors. In contrast, G alpha q expression levels were significantly lower in fluoxetine-treated mice. These findings suggest that compensatory changes in G alpha q expression occur in mice with persistently altered 5-HT2C pre-mRNA editing and provide an explanation for the dissociation between 5-HT2C receptor editing phenotypes and behavioral stress responses.

Balb/Cj Male Mice Do Not Feminize after Infection with Larval Taenia crassiceps

Balb/cJ mice fail to mount an immune response capable of clearing infection with larval Taenia crassiceps. Additionally, male Balb/cJ mice display a lag in larval growth of approximately 3 wk as compared to growth in female mice. It has been reported that male Balb/ cAnN mice generate a protective immune response early in infection, and become permissive to larval growth after they feminize (200-fold increase in serum estradiol and 90% decrease in serum testosterone). To determine if a different strain of Balb/c mice (Balb/cJ) also feminize, serum was collected from infected male mice for 16 wk and levels of 17-beta-estradiol and testosterone were measured via ELISA. In addition, the mounting responses of 12- and 16-wk infected male mice, as well as uninfected control mice, were determined after isolation with a female mouse. The results of these experiments show that male Balb/cJ mice do not feminize during infection with larval T. crassiceps. There was no significant change in serum levels of either 17-beta-estradiol or testosterone during the course of infection (> 16 wk). Moreover, there was no significant decrease in the number of times infected male mice mounted the female mouse as compared to uninfected controls. These results suggest that there may be variances between the substrains of Balb/c mice that lead to the phenotypic differences reported for male Balb/cJ and Balb/cAnN mice.

Morphological study of the transition of haematopoietic sites in the developing mouse during the peri-natal period

The transition of fetal haematopoietic sites in mice was examined histologically from 12.5-day embryos (E12.5) until 10 days of age (D10), and the expression of the adhesive molecules VCAM-1 and fibronectin was examined immunohistologically. Erythropoiesis occurred in the liver (E12.5-18.5), spleen (E18.5-D4) and bone marrow (D6-10), in that sequence. Even at D10, some erythropoiesis occurred in the liver, and more so in the spleen, although the active haematopoietic site was the bone marrow. Similarly, granulopoiesis of neutrophils occurred in the liver, spleen and bone marrow in turn. Granulopoiesis still occurred in the spleen at D10, but no neutrophils were found in the liver after D4. VCAM-1 appeared in the liver, spleen and bone marrow in parallel with active erythropoiesis and granulopoiesis. The co-expression of VCAM-1 and fibronectin was recognized in the endothelial cells of the sinus at the onset of haematopoiesis. This study showed that haematopoiesis in the liver, spleen and bone marrow overlapped peri-natally, although it shifted sequentially. VCAM-1 appears to be closely associated with erythropoiesis and granulopoiesis, and the co-expression of VCAM-1 and fibronectin plays a role in inducing haematopoietic stem cells to move to the tissues.

Early maternal investment in mice: no evidence for compatible-genes sexual selection despite hybrid vigor

Confronting a recently mated female with a strange male can induce a pregnancy block ('Bruce effect'). The physiology of this effect is well studied, but its functional significance is still not fully understood. The 'anticipated infanticide hypothesis' suggests that the pregnancy block serves to avoid the cost of embryogenesis and giving birth to offspring that are likely to be killed by a new territory holder. Some 'compatible-genes sexual selection hypotheses' suggest that the likelihood of a pregnancy block is also dependent on the female's perception of the stud's and the stimulus male's genetic quality. We used two inbred strains of mice (C57BL/6 and BALB/c) to test all possible combinations of female strain, stud strain, and stimulus strain under experimental conditions (N(total) = 241 mated females). As predicted from previous studies, we found increased rates of pregnancy blocks if stud and stimulus strains differed, and we found evidence for hybrid vigour in offspring of between-strain mating. Despite the observed heterosis, pregnancies of within-strain matings were not more likely to be blocked than pregnancies of between-strain matings. A power analysis revealed that if we missed an existing effect (type-II error), the effect must be very small. If a female gave birth, the number and weight of newborns were not significantly influenced by the stimulus males. In conclusion, we found no support for the 'compatible-genes sexual selection hypotheses'.

A novel mouse model for preeclampsia by transferring activated th1 cells into normal pregnant mice

Immunological imbalances have been hypothesized as a cause for the onset of preeclampsia, which is a very severe, pregnancy-related disease. We recently described a novel preeclampsia mouse model by adoptively transferring activated BALB/c Th1-like splenocytes into allogeneically pregnant BALB/c female mice during late gestation. This cell transfer provoked preeclampsia symptoms (increased blood pressure and glomerulonephritis accompanied by proteinuria). Interestingly, preeclampsia-like symptoms could not be detected in nonpregnant animals receiving activated Th1-like cells. Adoptive cell transfer further affected pregnancy outcome by increasing fetal rejection through an inflammatory profile of uterine immune cells. This chapter describes the methods employed to develop the model as well as additional experiments developed to analyze cellular and molecular mechanisms involved.

Maternal influences on adult stress and anxiety-like behavior in C57BL/6J and BALB/cJ mice: a cross-fostering study

The quality of maternal care during early life has a dramatic impact on later stress reactivity and anxiety. Two inbred mouse strains, C57BL/6J and BALB/cJ, differ in levels of maternal care, stress reactivity, and anxiety-like behavior in adulthood. However, the relative contribution of early environmental factors and genetic predisposition to differences in these strains is not known. Maternal care, plasma corticosterone levels, emotionality, and hippocampal and paraventricular nucleus (PVN) glucocorticoid receptor mRNA levels were measured in adult C57BL/6J and BALB/cJ mice. Litters were then cross-fostered and anxiety-like behavior and stress reactivity was assessed in adulthood. Significantly less maternal care and elevated stress-induced corticosterone and emotionality was observed in BALB/cJ compared to C57BL/6J mice. Yet, no strain differences were found in hippocampal or paraventricular nucleus glucocorticoid receptor mRNA levels. Cross-fostering did alter anxiety-like behavior and basal corticosterone levels, which suggests that while genetic differences account for some of the variations between these two strains early rearing conditions also contribute.

Effects of housing density and cage floor space on three strains of young adult inbred mice

Some recommendations in the Guide for the Care and Use of Laboratory Animals (the Guide) are based on best professional judgment. Our current efforts are directed toward replacement with data-driven standards. We demonstrated earlier that young adult C57BL/6J mice could be housed with half the floor space recommended in the Guide without discernable negative effects. This report extends that work by examining optimal housing densities for young adult male and female BALB/cJ, NOD/LtJ, and FVB/NJ mice. These 8-week studies were initiated with 3-week-old BALB/cJ and NOD/LtJ mice and 3- to 5-week-old FVB/NJ mice housed in three cage types. We adjusted the number of mice per cage to house them with the floor space recommended in the Guide (approximately 12 in2 [ca. 77 cm2] per mouse) down to 5.6 in2 [ca. 36 cm2] per mouse. Early-onset aggression occurred among FVB/NJ male mice housed at all densities in cages having 51.7 in2 (ca. 333 cm2) or 112.9 in2 (ca. 728 cm2) of space. FVB/NJ male mice housed in shoebox (67.6 in2 [ca. 436 cm2]) cages did not exhibit aggression until the fifth week. Urinary testosterone output was density-dependent only for BALB/cJ male mice in shoebox cages (output decreased with increasing density) and FVB/NJ male mice. We conclude that all but FVB/NJ male mice can be housed with half the floor space specified in the Guide. The aggression noted for male FVB/NJ mice may have been due to their age span, although this did not impact negatively on the female FVB/NJ mice.

Spectrographic analysis of the ultrasonic vocalisations of adult male and female BALB/c mice

In this study, a spectrographic analysis was designed to improve the description of the shape, the modulations, the rate, length and frequencies of BALB/c mouse calls in different behavioural situations. Male and female calls emitted during investigation of cages with clean bedding, soiled with male or female bedding, and during same-sex encounters, were recorded and described. BALB/c male mice uttered different types of vocalisations both when investigating counterpart odour cues and when interacting with same-sex counterparts. BALB/c female mice vocalised solely during same-sex counterpart encounters and it appeared that calls were uttered mainly by the resident females. Male and female mice present a complex array of calls, which seem to be linked to particular behavioural situations. Further studies using this technology may help to improve our understanding of the role of vocal communication in natural rodent populations.

Long-term effects of husbandry procedures on stress-related parameters in male mice of two strains

In socially unstable groups of male laboratory mice, individuals may experience a chronic stress situation. Previous experiments have shown that the transfer of specific olfactory cues during cage cleaning, and the provision of nesting material decrease aggression and stress in group-housed male mice. In this study, the combined effect of these husbandry procedures were tested for their long-term effect on stress in groups of moderately aggressive (BALB/c) and severely aggressive (CD-1) male mice. The physiological and behavioural stress-related parameters used were body weight, food and water intake, spleen and thymus weight, adrenal tyrosine hydroxylase activity, urine corticosterone levels and behaviour in a cage emergence test. Long-term provision of nesting material and its transfer during cage cleaning was found to influence several stress-related physiological parameters. Mice housed in cages enriched with nesting material had lower urine corticosterone levels and heavier thymuses, and they consumed less food and water than standard-housed mice. Furthermore, marked differences were found between strains. CD-1 mice were less anxious in the cage emergence test, weighed more, ate and drank more, and had heavier thymuses but lighter spleens and lower corticosterone levels than BALB/c mice. We conclude that the long-term provision of nesting material, including the transfer of nesting material during cage cleaning, reduces stress and thereby enhances the welfare of laboratory mice.

Preference for social contact versus environmental enrichment in male laboratory mice

Due to their aggressive nature, male mice are less frequently used than female mice in biomedical research. When aggressive males are being used, individual housing is common practice. The question arises whether this is an acceptable housing for a social species. The present study was designed to gain more insight into the nature of inter-male social contact and into the potential of a form of environmental enrichment (nesting material) to compensate for the lack of social contact. In a series of tests, we analysed whether male mice of different ages preferred to spend time (1) near a familiar cage mate versus an empty cage, or (2) near to a familiar cage mate versus direct contact with nesting material (tissues). Dwelling time in each of the test cages and sleeping sites was recorded, as was the behaviour of the test mice. Results indicated that when other conditions were similar, male mice preferred to sleep in close proximity to their familiar cage mate. Furthermore, the need to engage in active social behaviour increased with age. Tissues were used to a large extent for sleeping and sleep-related behaviour. It is concluded that single housing in order to avoid aggression between male mice is a solution with evident negative consequences for the animals. When individual housing is inevitable due to excessive aggressive behaviour, the presence of nesting material could partly compensate for the deprivation of social contact.

Distribution of the vanilloid receptor (VR1) in the gastrointestinal tract

The gastrointestinal (GI) tract responds to a variety of stimuli through local and centrally mediated pathways. Changes in the intestinal microenvironment are sensed by vagal, spinal, and intrinsic primary afferent fibers. Sensory nerve endings located close to the lumen of the GI tract respond to pH, chemical composition of lumenal contents, or distortion of the mucosa. Afferents within the muscle layers are thought to be tension sensitive, whereas those located within the myenteric plexus are also thought to respond to changes in chemical composition and humoral substances. Subpopulations of these afferent fibers are activated by capsaicin. However, the exact location of these nerves is currently not known. The vanilloid receptor (VR1) is a nonselective cation channel that is activated by capsaicin, acid, and temperature. Antibodies to VR1 make it possible to determine the location of these afferents, their morphology, and their relationships with enteric nerves and other cell types in the GI tract. VR1-like immunoreactivity was observed on nerves within myenteric ganglia and interganglionic fiber tracts throughout the GI tract. VR1 nerves were also observed within the muscle layers and had an irregular profile, with varicose-like swellings along their lengths. Blood vessels within the GI wall had VR1-immunoreactive nerve fibers associated with them. VR1-like nerves and other immunopositive cells were also observed within the mucosa. In summary, VR1-like immunoreactivity was found in several locations within the GI tract and may provide sensory integration of chemical, physical, or inflammatory stimuli. VR1-like fibers appear to be predominantly spinal in origin, but a few vagal VR1-like fibers exist in the stomach.

Hereditary keratoconus-like keratopathy in Japanese wild mice mapped to mouse Chromosome 13

Human keratoconus is a common corneal disease with non-inflammatory corneal ectasia, and a subset of this disease is heritable. In an effort to establish animal models for this disease, we discovered Japanese keratoconus (JKC) mice among Mishima molosinus (MSM) mice, an inbred strain of Japanese wild mice (Mus musculus molossinus). Typical phenotypic corneas of JKC mice are, like human keratoconus, conical in shape, although the corneas were often associated with a red punctum at the tip. In contrast to human keratoconus, histological examination revealed the inflammatory changes such as infiltration of capillaries and hematocytes in JKC mouse corneas. Although JKC mouse corneal change is probably secondary to keratitis and is a mouse-specific keratopathy, its pathogenesis may be relevant to that of human keratoconus. Linkage analysis mapped the responsible gene at the markers D13Mit21, D13Mit252, D13Mit279, and D13Mit39, which are located between 21.9 and 34.0 cm of the mouse Chr 13. Candidate genes in this region include genes for cathepsins, interleukin, and chemotaxin. Further study of JKC mice may shed light on pathogenesis of human keratoconus.

Genetic diversity underlying capsaicin intake in the Mishima battery of mouse strains

Capsaicin is the active substance responsible for the pungent sensation produced by red pepper. In order to approach the underlying genetic mechanism for preference of red pepper, we conducted a 12-h, 1-bottle intake test of capsaicin solution using both male and female animals from the Mishima battery of mouse strains: 10 wild-derived inbred strains (PGN2, BFM/2, HMI, CAST/Ei, NJL, BLG2, CHD, SWN, KJR, MSM), 1 strain derived from the so-called fancy mouse (JF1), and 3 widely used laboratory strains (C57BL/6J, DBA/1J and BALB/cAnN). The concentration of capsaicin was increased from 0.5 to 15 microM successively. Gender differences were not observed in this test, but we found striking strain differences in capsaicin intake. Relative to baseline water intake, C57BL/6J and DBA/1J consumed 10%, whereas two wild strains, KJR and MSM, ingested approximately 60% of the 15-microM capsaicin solution. In a 2-bottle fluid preference test, both C57BL/6J and MSM strains reject capsaicin fluid even at the 0.5-microM concentration, which indicates that the receptors for capsaicin in these strains recognize capsaicin at a similar level. Thus, the strain differences at higher capsaicin concentrations in the 1-bottle test may reflect differences in central nervous system response to the capsaicin solution. The genetic difference in intake of capsaicin observed in these strains may provide a useful tool for identifying genes underlying response to red pepper in mice and other mammalian species.

Interstrain variation in murine aerobic capacity

PURPOSE

The contribution of genetic factors to aerobic capacity is unknown. The purpose of this study was to measure maximal aerobic performance among inbred strains of mice to provide basic heritability estimates.

METHODS

Eight female mice, 8 to 10 wk old, in 10 inbred strains (A/J, AKR/J, Balb/cJ, C(3)H/HeJ, C57Bl/6J, C57L/J, C(3)Heb/FeJ, CBA/J, DBA/2J, and SWR/J) were run on a treadmill until exhaustion. The protocol started at 22 m.min(-1) and increased in speed approximately 6 m.min(-1) every 4 min. After 4 min at 42.4 m.min(-1), the grade was increased 2% every 4 min thereafter until the mouse could not run off of the shock grid (150 V; 1.5 mA).

RESULTS

There were significant differences between inbred strains in maximal duration of exercise accomplished (P < 0.0001). The order of strain-specific exercise duration was Balb/cJ > SWR/J > CBA/J > C57L/J > C3H/HeJ > C3Heb/FeJ > C57Bl/6J > AKR/J > DBA/2J > A/J. Two measures of heritability in the broad sense, intraclass correlation (0.73), and the coefficient of genetic determination (0.58) were both significant.

CONCLUSION

These data indicate that there is a strong genetic contribution to aerobic capacity in mice.

Floor space needs for laboratory mice: BALB/cJ males or females in solid-bottom cages with bedding

Studies were initiated to determine the effects of restricted (32.2 cm2 per mouse), normal (96.8 cm2), or excess floor space (129.0 cm2) allowances by using a model of three mice per cage. BALB/cJ mice were bred on-site and weaned at 3 weeks of age into specially designed polycarbonate shoebox cages modified to each space allowance. Cages contained aspen shavings for bedding, and mice were fed and watered ad libitum. Body weight gains, feed and water use, and immunologic measures largely were not effected by floor space allowances. Female BALB/cJ mice were heavier and had increased lymphocyte blastogenesis to phytohemagglutinin (20 microg/mL) when given 32.2 cm2/mouse than when given 129 cm2/mouse. Female mice showed an increase in grooming and sitting behaviors when given 32.2 cm2/mouse, but male mice with restricted floor space spent more time lying down but showed no change in grooming or sitting behaviors compared to mice given more space. Among male mice, limited floor space did not significantly influence growth rates, but male mice given 32.2 cm2/mouse had less mortality than did mice given more space. We conclude that floor spaces as limited as 32.2 cm2/mouse did not cause behavior, health, immune or performance problems for BALB/cJ mice.

Vulnerability to noise-induced hearing loss in 'middle-aged' and young adult mice: a dose-response approach in CBA, C57BL, and BALB inbred strains

Vulnerability of the cochlea to noise-induced permanent threshold shifts (NIPTS) was examined in young adult (1-2 months) and 'middle-aged' (5-7 months) CBA/CaJ, C57BL/6J, and BALB/cJ inbred mice. For each age and strain, a dose-response paradigm was applied, whereby groups of up to 12 animals were exposed to intense broadband noise (110 dB SPL) for varying durations. Exposure durations reliably associated with <10% and >90% probability of a criterion amount of NIPTS (determined 2 weeks post-exposure) were identified, and the minimum NIPTS exposure and the slope of the dose-response relation were then derived by numerical modeling. For all three strains, young adult mice were more susceptible to NIPTS than older adults; That is, a shorter exposure was able to cause NIPTS in the younger mice. Strain comparisons revealed that C57 mice were more susceptible than CBAs in the older age group only. At both ages examined, however, BALB mice were most susceptible to NIPTS. When animals with a similar amount of NIPTS were compared, outer hair cell loss in the cochlear base was more widespread in the younger animals. BALB mice appear particularly susceptible to noise-induced outer hair cell loss throughout life. Our data suggest that the mechanism or site of noise injury differs between young adults and older adults, and may depend on genetic background. The finding that both BALB and C57 mice, which show pronounced age-related hearing loss, are also especially vulnerable to noise supports the notion that genes associated with age-related hearing loss often act by rendering the cochlea susceptible to insults.

Behavioral, clinical, and physiologic analysis of mice used for ascites monoclonal antibody production

BACKGROUND AND PURPOSE

The effects of pristane inoculation, ascites accumulation, peritoneocentesis, and analgesics on the well-being of mice used in monoclonal antibody (MAb) production protocols were investigated.

METHODS

Four experiments, each containing 17 to 21, 6- to 8-week-old male Balb/c mice, were conducted. Each experiment involved a period in which baseline data were collected, followed by intraperitoneal injections of pristane or phosphate-buffered saline (PBS) inoculations into each mouse. One week later mice received intraperitoneal inoculations of either hybridoma cells or PBS. Parameters used to assess well-being throughout each of these periods included: wheel-running activity, food and water consumption, open-field box activity, clinical observation, and plasma corticosterone concentration.

RESULTS

Compared to controls, pristane inoculation had slight to no affect on mice. There was no evidence of distress in cell-inoculated mice prior to their gaining 25% of their baseline body weight. The number of times (up to three) that peritoneocentesis was performed did not have a significant impact on mice's well-being, but ascites yields were greater when multiple harvests were performed. Cell-inoculated mice that gained weight slowly or developed high-particulate ascites were at higher risk of being distressed.

CONCLUSION

Ascites yields can be maximized by performing multiple harvests; however, the well-being of mice used in such protocols should be closely monitored, as suggested here.

Effects of exposure to an augmented acoustic environment on auditory function in mice: roles of hearing loss and age during treatment

The effects of exposure to an augmented acoustic environment (AAE) on auditory function were evaluated in mouse strains that exhibit various degrees and time courses of progressive hearing loss (BXD-22, BXD-12, BXD-16, BXD-14, BALB/cJ), and in normal-hearing CBA/CaJ mice. Beginning at age 25 days, mice were exposed 12 h every night to a 70 dB SPL broadband noise AAE. The AAE was maintained for at least 30 days in each strain. Same-strain control mice were age-matched and maintained under normal vivarium acoustic conditions. The auditory brainstem response (ABR), acoustic startle response amplitude, and prepulse inhibition (PPI) were used to assess the auditory system. Exposure to the AAE resulted in improved auditory performance (better PPI, lower ABR thresholds) when hearing impairment was present, but not when hearing was normal. The ameliorative effects occurred irrespective of a mouse's age at the onset of hearing loss, as long as initiation of AAE treatment preceded the occurrence of severe hearing loss. If AAE treatment was delayed beyond such a point, loss of threshold sensitivity progressed as usual, although PPI could still benefit. Finally, AAE treatment can slow, but not prevent, the occurrence of severe genetically determined hearing loss.

[The determination of the parameters of anxiety in C57BL/6J, CBA/Lac and BALB/c mice under the influence of a serotonin C1A receptor agonist [correction of antagonist]

Three strains of inbred mice, C57BL/6J (C57), CBA/Lac (CBA), and BALB/c (BALB) were examined in the elevated plus-maze after the injection of an anxiotropic drug, a 5-HT1A agonist ipsapirone (3 mg/kg; i.p.; 30 min). Treatment with ipsapirone had different anxiogenic effects on the behavior of mice in accordance with their genotype. In C57 mice the drug produced a significant decrease in the percentage of the open-arm time and the number of open-arm entries as well as in the number of full entries (when an animal was between the half and the end of an open-arm) and in the number of head dippings. Besides; the number of C57 mice which performed full entries after the ipsapirone injection decreased. In CBA mice ipsapirone reduced the number of enclosed-arm entries, the number of the passages from one enclosed arm to another and the number of head dippings. Only the number of passages dropped in BALB mice after the drug injection. Probably, just these parameters reflect anxiety in mice of the genotypes under study. It was suggested that the sensitivity of 5-HT1A receptors in C57 mice is the highest.

Sodium intake and reproduction in BALB/C mice

The effect of sodium intake on the reproductive performance of BALB/C mice was assessed in four groups of 11 or 12 mice that received ad lib access to low or higher sodium food (LSF 4-5, HSF 120-143 mmol Na+/kg). The two groups that received HSF had (mean values) 100% matings, 83 and 91% litters, 5.9 pups/litter, pups weighing 2.05 and 2.22 g (3 days after birth) and 10.47 and 10.96 g at weaning (19 days). One of the HSF groups that also had 300 mM NaCl to drink did not show any benefit. Two groups received LSF, and one of them also received 30 mM NaCl. The group given LSF only had 83% matings, 20% litters, 1.5 pups/litter, and pups that were significantly smaller at birth and at weaning. However, the LSF group given 30 mM NaCl to drink performed almost as well as the two HSF groups. The results show that (a) the daily sodium requirement for optimal reproduction was > or = 400 (micromol/day, based on voluntary sodium intake late in gestation and lactation; (b) sodium deficiency was the cause of reproductive deficiency in mice on LSF; (c) severe sodium deficiency suppressed reproduction primarily at the gestation step; (d) this deficiency could be prevented by the voluntary sodium intake of mothers with access to salt solution; and (e) pups on the LSF showed an avid innate salt appetite when offered salt solution at 12 days of age.

[The effect of bromantane on the behavior of inbred mouse strains with different phenotypes of emotional stress reaction]

Per os administration of bromantan (2-[n-bromphenyl]-aminoadamantan) in doses of 40-50 mg/kg prevents the fixed posture reaction and reduces the level of defecation in Balb/c mice in the "open field" test and activates their behavior in the "elevated plus maze" test. It increases the motor activity of C57B1/c mice in both tests. It is concluded that an anxiolytic effect is present in the spectrum of pharmacological properties of bromantan.

Aspen wood-wool is preferred as a resting place, but does not affect intracage fighting of male BALB/c and C57BL/6J mice

Aspen wood-wool, provided as nesting material, was evaluated as a possible improvement of cage environment for 10-14-week-old inbred male mice maintained in groups of six (BALB/c n = 72 and C57BL/6J n = 36). The daily behaviour of mice was video recorded and their body weight, food consumption, weights of some organs and serum corticosterone concentrations were measured. Aggressive interactions between cage mates and against a strange intruder as well as the number of wounds on the back of the animals was monitored in order to evaluate the effect of nesting material on intermale aggression. Nesting material did not affect the daily active/passive behaviour patterns of mice, although animals clearly preferred it as a resting place. BALB/c mice given nesting material showed less weight gain and smaller brown adipose tissue weights than animals without nesting material. The other characteristics measured were not affected by the presence of nesting material in either strain. The presence of nesting material had no effect on fighting in cages. C57BL/6J mice were more aggressive than BALB/c mice according to the number of wounded animals in a cage. Wounded BALB/c mice had enlarged spleens and decreased epididymal adipose tissue weights. In conclusion, the nesting material used in this study did not adversely affect the animals. On the other hand, the material was clearly preferred to conventional bedding as a resting place. These findings suggest that nesting material may improve the cage environment of laboratory mice. Furthermore, there was an indication of strain differences in aggressive behaviour. It could be suggested that C57BL/6J mice are less tolerant towards intruders and housing six mice per cage is not suitable for this strain.

Nesting material and number of females per cage: effects on mouse productivity in BALB/c, C57BL/6J, DBA/2 and NIH/S mice

Two different materials-aspen wood-wool and paper towel-were compared as nesting material for three inbred mouse strains (BALB/c, C57BL/6J and DBA/2) housed in barrier conditions. In addition, the effect of varying the number of females per cage (one to three per cage) of these three strains and with NIH/S outbred mouse stock was studied. The number of litters, litter size and neonatal mortality were determined, as well as age, sex and weight of weanlings. The type of nesting material did not affect the characteristics monitored. In all strains, the number of weanlings per female was greatest in singly-housed females. In terms of the number of weanlings per cage, two females per cage gave the best result. In DBA/2 mice, neonatal mortality increased when several females were caged together.

Methods for exposure of laboratory animals to ultraviolet radiation

Two different sources of ultraviolet B (UVB) radiation, an electronically controlled UVB exposure unit, containing FS40 tubes, and a hand-held Kromayer lamp, were evaluated for actual irradiance in W/m2 and spectra (physical dosimetry and biological dosimetry (skin effects in rodents)). The technical studies of the FS40 sources demonstrated that the flux intensity of the lamps could be changed electronically, without affecting the spectrum. Thus it was possible to standardize UVB exposure electronically. The biologically effective doses of these sources were analysed in RIV-Tox Wistar rats and BALB/c mice. After low doses of UVB radiation, histopathological changes such as acanthosis, hyperkeratosis and dermal inflammation were observed in the skin without the presence of major side effects such as erythema and oedema. After higher doses of UVB radiation erythema and oedema were clearly visible. Quantitative studies showed that the minimal erythema dose, as a biological parameter, correlated well to the emission in J/m2. In addition, biological parameters such as acanthosis and inflammation in the skin correlated well to the actual exposure in J/m2 and were sensitive biomarkers for UVB-induced skin toxicity. Thus, in addition to minimal erythemal doses, acanthosis and inflammation may also be applied as biologically relevant doses for studies of the biological effects of UVB radiation.

Mouse urine collection using clear plastic wrap

Qualitative urinalysis using Multistix reagent strips for the detection of urinary pH, protein, glucose, bilirubin, blood, ketone, urobilinogen and creatinine can be carried out with a few drops of mouse urine. The use of metabolic cages is not practical for such qualitative studies particularly when several animals are involved. Here we describe two different methods for collecting pure mouse urine. The single animal method (SAM) involves allowing a single mouse to urinate on Glad cling wrap outside of the animal cage. The multiple animal method (MAM) involves partitioning seven mice into seven different make-shift compartments laid out on top of the cling wrap and allowing them to urinate. The voided urine, in each case, is then aspirated into micro-centrifuge tubes using a Pipetman. Without coercion pure urine was obtained as early as 12 s. Volumes in the range of 10-250 microl were obtained. Modifications of the SAM could prove useful for rat or mouse urine collection under conditions of microgravity.

Differences in delta opioid receptor antinociception, binding, and mRNA levels between BALB/c and CXBK mice

Mu and delta opioid receptors have been demonstrated to mediate supraspinal opioid antinociception. Whereas the recombinant inbred CXBK mouse is notably deficient in mu opioid receptor antinociception, binding density, and mRNA (MOR-1) levels, little is known about delta opioid receptor processes in this strain. The present study thus compared CXBK mice and their BALB/c strain progenitors with respect to delta opioid antinociception, whole-brain receptor binding levels, and mRNA (DOR-1) levels. Following intracerebroventricular injections of the selective delta1 and delta2 opioids DPDPE and [d-Ala2]deltorphin II, respectively, CXBK mice displayed relatively lower antinociception on the tail-flick test, resulting in significantly increased ED50 values for both agonists in this strain. Decreased whole-brain specific binding of [3H][d-Ala2]deltorphin II, but not [3H]DPDPE, was also observed in CXBK mice. Solution hybridization with a probe for the DOR-1 revealed increased transcript levels in the caudate-putamen, frontal cortex, and spinal cord of this strain. The present data demonstrate a deficiency in delta1 and delta2 opioid antinociception in CXBK mice concomitant with reductions in whole-brain delta2 receptor binding and regional increases in DOR-1. Whether these observations are causally related remains to be clarified.

Murine strain differences in airway inflammation caused by diesel exhaust particles

To elucidate whether immunoglobulin (Ig) E or IgG are involved in the murine asthma model, we compared the pathogenic features of mice that were high IgG responders (C3H/He) with mice that were high IgE responders (BALB/c) after intratracheal instillation of diesel exhaust particles (DEP) and ovalbumin sensitization. Both mouse strains received DEP intratracheally once a week for 5 weeks. After the second injection of DEP, ovalbumin and aluminium hydroxide were injected intraperitoneally. After the last DEP administration, the mice were challenged by exposure to an aerosol of ovalbumin. DEP caused increased IgG1 production and airway hyperresponsiveness after ovalbumin sensitization in C3H/He mice, although IgE production did not change in either strain. Furthermore, in C3H/He mice, the number of eosinophils and goblet cells in the bronchial epithelium, and the expression of interleukin-5 and interleukin-2 were increased by DEP and ovalbumin treatments. In contrast, the pathogenic changes in BALB/c mice were weak, even though the same protocol was used. In conclusion, murine strain differences in response to air pollutants and allergens seem to be related to antigen-specific immunoglobulin G1 production and cytokine expression in the lungs.

Light and electron microscopic examination of various doses of given vitamin A on the development of cornea in mice. Partly presented in ICEM 13-Paris

Vitamin A (0.2 micrograms, 0.6 micrograms, 1.2 micrograms) was administered orally to the mice on days 8-11 of gestation. Fetuses were removed on day 17 of gestation. No external malformation of the fetuses was seen on the stereomicroscope investigation. Corneal degeneration was seen on the light and electron microscopic examination. As a result it was accepted that vitamin A taken during the critical periods of gestation affected the development of cornea.

Temporal-regulation of serum lipids and stearoyl CoA desaturase and lipoprotein lipase mRNA in BALB/cHnn mice

Databases for genes expressed in humans or cell cultures are being developed as a part of the Human Genome Project. Because genomes respond to nutritional and other environmental variables, quantitative analyses of mRNA abundance under defined nutritional and physiological states are required to understand normal metabolism and to clarify differences between normal and disease phenotypes. Reported here are comparisons of food intake, growthp5erum lipids and expression of mRNA for hepatic stearoyl CoA desaturase (Scd1) and heart lipoprotein lipase (Lpl) in female BALB/cHnn mice following food deprivation and refeeding at the end of 2 wk of feeding semipurified diets with 3, 10 or 20% corn oils. Body weights and utilization of dietary energy were similar for mice fed all three diets. There were no differences in serum lipid concentrations associated with the level of dietary fat during subsequent food deprivation and refeeding, but significant differences in serum triglycerides and total serum cholesterol were observed between food-deprived and fed mice. Heart lipoprotein lipase and hepatic Scd1 mRNA expression levels were affected significantly by concentration of corn oil and by time after eating. These and other studies examining gene regulation by dietary variables and nutrient availability are discussed in relation to development of diet-regulated gene databases for laboratory animals fed semipurified diets.

[The participation of the right and left hemispheres in the realization of the maze habit in male mice of the BALB/c strain]

Motor, Searching and alimentary activity of male mice BALB/c as well as spatiomotor asymmetry was studied under conditions of training in symmetrical multi-alternative maze. In the period of realization of the stable optimal habit the right-side spatially motor asymmetry was observed in intact males. In animals with inactivated left or right hemisphere motor and alimentary activity was reduced and the structure of elaborated maze habit was broken. These changes were more expressed in mice with inactivated left hemisphere. Searching activity was augmented during cortical inactivation of the right hemisphere (this was associated with the right-side spatially motor asymmetry) and reduced during inactivation of the left hemisphere (associated with the left-side asymmetry). The left hemisphere was dominant in realization of all main components of elaborated maze habit (including the spatially motor asymmetry) in male mice BALB/c as in female ones.

Repeated measurement of respiratory function and bronchoconstriction in unanesthetized mice

A noninvasive forced oscillation technique was used to determine respiratory function in unanesthetized and spontaneously breathing mice. Pseudorandom noise pressure variations in a frequency range of 16-208 Hz were applied to the body surface, and the flow response was measured at the nose. From the pressure-flow relationship, respiratory transfer impedance was calculated. Study of intra-animal variability on a short- and a long-term basis revealed that the real part of respiratory transfer impedance was reproducible within 9%. The imaginary part appeared less reproducible (within 22%). Furthermore, bronchoconstrictive responses were investigated and analyzed by evaluation of respiratory resistance as measured at 16 Hz (Rrs16). During the first 15 min after ovalbumin challenge in ovalbumin-sensitized mice, Rrs16 was significantly increased [49 +/- 7% (SE)]. Inhalation of methacholine in untreated mice induced an increase in Rrs16 of 75 +/- 16% (SE). In saline-challenged animals, no significant changes were observed. This method enables evaluation of long-term respiratory function in mice and appeared to be a sensitive measure for bronchoconstriction.

Stress measurements in mice after transportation

Experiments were performed using physiological measures and behavioural parameters to find the acclimatization period in mice to common scientific procedures. Corticosterone levels were significantly elevated in mice killed immediately after being moved to an experimental room (P < 0.05) but levels returned to the normal in less than 1 day, despite mice being exposed to additional stressors such as novel environment, new cages, new bedding material, separation from their cage mates, regrouping, isolation in individually housed mice and a new handler. Behaviours such as rearing, climbing, grooming, feeding and sexual, changed significantly immediately after transportation of mice but most of these behaviours stabilized relatively quickly. In spite of the corticosterone levels, our behavioural observations suggest that even 4 days were not enough to allow the mice to acclimatize fully.

Experimental photoaging in C3H/HeN, C3H/HeJ, and Balb/c mice: comparison of changes in extracellular matrix components and mast cell numbers

Chronic exposure of human or murine skin to ultraviolet B (UVB) radiation alters dermal extracellular matrix composition and increases the number of mast cells and inflammatory cells. Experiments were designed to test the possible role of UVB-induced tumor necrosis factor-alpha in these photoaging changes based on reports that C3H/HeN, but not C3H/HeJ or Balb/c mice, produce excess TNF-alpha in response to UVB exposure. Pigmented C3H/HeN and C3H/HeJ strains were exposed to a total of 75 J/cm2 of UVB radiation, and unpigmented Balb/c mice were exposed to 19 J/cm2. The UVB-induced increases in collagen, glycosaminoglycans, and neutrophil number were similar or the same in all three strains. The elastin increase was greater in C3H/HeJ than in C3H/HeN mice. The most striking difference between the strains was a 7.7-fold UVB-induced increase in mast cells in C3H/HeN mice compared to no increase in irradiated C3H/HeJ mice and a 2.3-fold increase in Balb/c mice. These results suggest that excess TNF-alpha (or other mediator) produced in C3H/HeN skin (but not C3H/HeJ skin) in response to UVB exposure is involved in the mast cell increase and partial inhibition of elastin increase, but that neither these mediators nor mast cell products are important mediators for the chronic UVB-induced increases in neutrophils, glycosaminoglycans, and collagen. When a possible source of the excess TNF-alpha was investigated, it was found that isolated epidermal cells from all three strains produced increases in TNF-alpha in response to UVB radiation. These results, as well as the previous results showing differences between these strains in UVB-induced effects on cutaneous immune function, are consistent with a model in which UVB-induced mediators from the epidermis stimulate another cell type to produce excess TNF-alpha (and other mediators) in the C3H/HeN but not C3H/HeJ or Balb/c mice.

Variation among inbred and linecross mice in response to fescue toxicosis

Variation in response to fescue toxicosis was examined in inbred and linecross mice. In Exp. 1, exposure to a 50% endophyte-infected tall fescue diet (E+) reduced ADG of males from six inbred lines, but ADG of males from one line was modestly higher on E+. Lines differed (P < .01) for reproductive organ weight, but the diet x line interaction was not significant. In Exp. 2, an apparently susceptible (C57) and an apparently resistant line (FVB) were mated to produce inbred and linecross offspring. The reduction in weight gain caused by the E+ diet did not differ significantly among the genetic groups. In Exp. 3, C57 and C57 backcrosses had smaller reductions in ADG during E+ vs control feeding periods than FVB and FVB backcrosses (P < .10). In Exp. 4, the E+ diet reduced litter size of mates of C57 males by one pup, whereas litter size of mates of FVB males was four pups larger (interaction P = .07). Neither diet, line, nor their interaction affected male reproductive organ weights or tissue proportions in testis cross-sections. In Exp. 5, the E+ diet did not affect weight gain of C57 or FVB males, but effects of the E+ diet on litter size of mates were similar to those in Exp. 4. Percentage of abnormal sperm was increased in C57 males on the E+ diet but decreased in FVB males (Exp. 5). Differences among inbred lines in susceptibility to fescue toxicosis may depend on severity of the challenge and life cycle stage when the challenge is imposed.

[The role of the sex hormones in regulating the spermatogenesis process in different strains of mice irradiated at low doses of gamma quanta]

Intact BALB/c and CBA mice distinct in the total number of germ cells and testosterone level in blood plasma were exposed to doses of 0.1 and 0.25 Gy. Being tested 4-8 days after irradiation the BALB/c mice display compensatory-protective reaction which promote the maintenance of the germ cell number by active division of all spermatogonia types including the reserve ones. The CBA mice use the reserve later and only when the cells have reduced their proliferation activity or died. Testosterone plays a significant role in the process as the increase in its concentration stimulates proliferation activity and promotes mitosis block.