Tunnel use facilitates handling of ICR mice and decreases experimental variation.

We evaluated a handling method using tunnels to tame laboratory mice (ICR) in the context of animal welfare and ease of handling. During 1-week acclimation to handling and subsequent 1-week oral administration (once per day), voluntary interaction with the experimenter was much greater in mice handled by a tunnel compared to those picked up by the tail. According to a rating of the ease of handling laboratory mice, a tunnel facilitated mouse handling during acclimation to handling and oral gavage of saline compared to tail handling. In addition, mice handled by a tunnel showed less anxiety than mice handled by the tail in the open field test, but not in elevated plus maze. Calculation of experimental variation in behavioral tests, which were used to mimic pharmacological studies, suggested that mice handled by a tunnel exhibited the tendency of less variation compared to those picked up by the tail, in both groups that were intraperitoneally administered saline as placebo and diazepam as an active drug. Thus, tunnel use could be beneficial for improving animal welfare and facilitated handling of ICR mice in mouse studies.

Laboratory domestication changed the expression patterns of oxytocin and vasopressin in brains of rats and mice.

The process of domestication is recognized to exert significant effects on the social behaviors of various animal species, including defensive and cognitive behaviors that are closely linked to the expression of oxytocin (OT) and vasopressin (AVP) in selected areas of the brain. However, it is still unclear whether the behavioral changes observed under domestication have resulted in differences in the neurochemical systems that regulate them. In this study, we compared the differences in distribution patterns and regional quantities of OT and/or AVP staining in the forebrains of wild and laboratory strains of rats and mice. Our results indicated that, in the anterior hypothalamus (AH), laboratory strains showed significantly higher densities of OT-ir (immunoreactive) and AVP-ir cells than wild strains, while no significant difference in the densities of those cells in the lateral hypothalamus (LH) was detected between wild and laboratory strains. Laboratory strains showed higher densities of OT-ir and AVP-ir cells than wild strains in the medial preoptic area (MPOA), and differed in almost every MPOA subnucleus. Our results suggest that domestication significantly alters the expression of OT and AVP in related brain areas of laboratory rats and mice, an observation that could explain the identified changes in behavioral patterns.

Evaluation of rewarding effect of toluene by the conditioned place preference procedure in mice.

Toluene and many toluene-containing products are abused via inhalation. Previous investigations have used the place preference paradigm to evaluate the rewarding effects of commonly abused drugs such as morphine, cocaine, and amphetamine. A conditioning paradigm of toluene inhalation was developed in order to estimate the rewarding effect in mice. Conditioning sessions (five for toluene, five for air) were conducted twice daily for 5 days using a newly developed airtight inhalation shuttlebox (15x30x15 cm: wxlxh), which was divided into two compartments of equal size. One compartment was white with a textured floor, and the other was black with a smooth floor. All conditioning sessions were 20 min in duration, with a minimum of 7 h between sessions. Test sessions were carried out 1 day after the final training session with mice in a drug-free state. The time spent in each compartment during a 20-min session was measured using a digital video camera. Exposure to toluene vapors (700-3200 ppm) produced a significant conditioned place preference in mice. These results suggest that the conditioned place preference procedure using the newly developed airtight inhalation shuttlebox constitutes an important tool for studying the rewarding effect of abused solvents.

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.

Comparative analysis of the behavioral and biomolecular parameters of four mouse strains.

The use of mice as experimental models in pharmacological and biochemical research began over 100 years ago, during which time different mice strains with specific features were developed. Numerous studies demonstrate that the pharmacological efficacy of various compounds significantly varies among different animal strains, a factor which must be considered when analyzing experimental data. The Sabra strain, developed more than 35 years ago, is widely used for research in Israel but has an unclear origin and is not characterized as well as other strains. Comparative analyses of the molecular characteristics of Sabra and other strains should help to understand their characteristics and to enhance the validity of their experimental use. Thus, four mouse strains-outbred ICR and Sabra as well as inbred C57Bl/6J and Balb/c were compared. Animals' weight, blood corticosterone and hippocampal BDNF mRNA levels were measured, and animals' behavior was compared using the EPM, open field, FST, and hot plate tests. We found that although Sabra mice are bigger and heavier than other tested lines, this is not reflected in behavior or in biomolecular features, wherein Sabra mice lay within the diapason of other tested animals. Thus, behavioral tests of anxiety-like behavior and locomotor activity revealed that Sabra mice scored close to the mean of all tested lines. Analysis of blood corticosterone levels did not show significant differences among tested strains. We also found a correlation between general and locomotor activity of the tested strains and their hippocampal BDNF mRNA expression. In summary, we may conclude that Sabra mice have traits similar to the better known lines, and therefore they are good subjects for neuroscience research.

Environmental factors and age of puberty in female house mice.

Genetics, urinary chemosignals and related social influences, and ambient conditions affect reproduction in female mice. Five experiments tested the effects of environmental stressors on age at first vaginal estrus in female house mice. Environmental disruption in the form of changing the cage bedding and/or nesting material at various prescribed intervals resulted in different degrees of puberty delay relative to non-disrupted control mice. Disruption in the form of a male chasing the female for one to three 15-min intervals each day or the female being trapped and held in a live-trap for one to three 15-min intervals each day resulted in delays in puberty for treatments involving multiple daily disruptions. Food deprivation, but not water deprivation, influenced the onset of puberty. Variations in temperature and humidity resulted in differences in the age of puberty; low but not high temperatures and extremely low humidity levels delayed sexual maturation.