Comparison of Age-Related Decline and Behavioral Validity in C57BL/6 and CB6F1 Mice.

Variability in physical resilience to aging prompts a comprehensive examination of underlying mechanisms across organs and individuals. We conducted a detailed exploration of behavioral and physiological differences between C57BL/6 and CB6F1 mice across various age groups. In behavioral assays, B6 mice displayed superior performance in rotarod tasks but higher anxiety while CB6F1 mice exhibited a decline in short-term memory with age. Grip strength, long-term memory, and voluntary wheel running declined similarly with age in both strains. Examining physiological phenotypes, B6 mice exhibited lower body fat percentages across ages compared to CB6F1 mice, though cataract severity worsened with age in both strains. Analysis of cardiac functions revealed differences between strains, with worsening left ventricular hypertrophy and structural heart abnormalities with age in CB6F1 mice along with higher blood pressure than B6. Lesion scores showed an age-related increase in heart, kidney, and liver lesions in both strains, while lung lesions worsened with age only in CB6F1 mice. This study underscores the validity of behavioral assays and geropathology assessment in reflecting age-related decline and emphasizes the importance of considering strain specificity when using mouse models to study human aging.

The CB6F1 mouse is a model for studying cognition and brain morphometry with increasing age.

Cognitive impairment associated with memory loss and dysfunctional communication is a common condition in older people. Regions of the brain have been reported to decrease in size with increasing age, but the relationship with cognitive impairment is not well understood. Inbred and hybrid mouse strains can be useful models to investigate cognitive impairment and morphological changes at older ages. CB6F1 hybrid mice, a cross between C57BL/6 and Balb/c mice, were tested for learning and memory using a radial water tread maze. Old CB6F1 male mice (30 months of age) had severe cognitive impairment, while it was virtually absent in young (6 months old) male mice. In these same mice, there was a significant decrease in sagittal flat surface area of the hippocampus and pons in old versus young animals. The aging CB6F1 mouse would be a potential model to study the relationship between changes in brain morphometry and cognitive impairment and the identification of possible therapeutic targets.

Carcinogenicity Evaluation of Baclofen in TgrasH2 Mice.

Baclofen is a γ-aminobutyric acid-B receptor agonist used for control of spastic muscle activity and as a treatment for alcohol abuse. The review of the nonclinical database suggested a data gap for potential carcinogenicity following long-term use. Regulatory requirements for pharmaceutical safety testing of cancer-causing potential have historically included 2-year rodent studies in rats and mice. The availability of transgenic models with greater specificity and sensitivity to carcinogens provides safety testing alternatives that align with the 3Rs. The carcinogenicity of baclofen was evaluated in CB6F1-TgrasH2 transgenic mice following daily oral administration at 45, 90, and 180 mg/kg/d for 26 weeks, preceded by a 2-week drug-conditioning period. There were no treatment-related palpable masses or neoplastic findings, and survival rates were not affected by the baclofen treatment. In conclusion, baclofen was considered as noncarcinogenic in CB6F1-TgrasH2 mice, which is consistent with results previously obtained in a 2-year rat study.

A 28-day oral gavage toxicity study of 3-monochloropropane-1,2-diol (3-MCPD) in CB6F1-non-Tg rasH2 mice.

3-Monochloro-1,2-propanediol (3-MCPD) is a well-known contaminant of foods containing hydrolyzed vegetable protein. However, limited toxicity data are available for the risk assessment of 3-MCPD and its carcinogenic potential is controversial. To evaluate the potential toxicity and determine the dose levels for a 26-week carcinogenicity test using Tg rasH2 mice, 3-MCPD was administered once daily by oral gavage at doses of 0, 25, 50, and 100 mg/kg body weight (b.w.)/day for 28 days to male and female CB6F1-non-Tg rasH2 mice (N = 5 males and females per dose). The standard toxicological evaluations were conducted during the in-life and post-mortem phase. In the 100 mg/kg b.w./day group, 3 males and 1 female died during the study and showed clinical signs such as thin appearance and subdued behavior accompanied by significant decreases in mean b.w. Microscopy revealed tubular basophilia in the kidneys, exfoliated degenerative germ cells in the lumen of the seminiferous tubule of the testes, vacuolation in the brain, axonal degeneration of the sciatic nerve, and cardiomyopathy in the 100, ≥25, ≥50, 100, and 100 mg/kg b.w./day groups, respectively. In conclusion, 3-MCPD's target organs were the kidneys, testes, brain, sciatic nerve, and heart. The "no-observed-adverse-effect level" (NOAEL) of 3-MCPD was ≤25 and 25 mg/kg b.w./day in males and females, respectively.

Characterization of growth performance of F1 hybrid CB6 F1 C57-ras transgenic mouse model / 中国比较医学杂志

Objective To obtain the basic growth parameters of a self-established F1 hybrid CB6F1 C57-ras transgenic mouse model, and to provide basic information for commercialization of this mouse model. Methods F1 hybrid mice (CB6F1) were produced by crossing C57-ras heterozygous transgenic (c-Ha-ras+/-) male mice and wild-type BALB/cJ female mice.The average litter size, weaning rate, sex ratio, growth performance and C57-ras transgenic positive rate were recorded and analyzed.Results The average litter size was eight, weaning rate was 90%, and sex ratio was approximately in accordance with prediction.The average body weight of newborn mice was 1.73 ±0.05 g.The average body weight of 10-week old c-Ha-ras transgenic female and male mice in CB6F1 background was 24.38 ±1.74 g and 29.42 ±1.72g, respectively, which had a significant difference (P<0.01).The c-Ha-ras transgenic positive rate was 46.9%. which was in accordance with genetic rules.Conclusions The F1 hybrid mice (CB6F1) produced by crossing C57-ras heterozygous transgenic ( c-Ha-ras +/-) male mice and wild-type BALB/cJ female mice show normal growth performance and development characteristics, and it can be used for large-scale commercial supply.

Determination of hematological and visceral weight parameters of F1 carcinogenesis transgenic C57-ras model CB6F1 mice / 中国比较医学杂志

Objective To determine the normal range of hematological and visceral weight parameters of F 1 4-week and 8-week old, male and female transgenic CB6F1 mice.The influence of gender and week age on the biochemical parameters was assessed .Methods 4-week and 8-week old CB6F1 mice, half male and half female ( n=20 in each group) , were weighed alive , dissected to weigh the main viscera , and blood samples were collected to test the physiological and biochemical parameters .Results When 4-week old and 8-week old CB6F1 mice were compared , there were significant differences in 22 parameters (body weight, heart, liver, spleen, left ovary, left testis, right testis, WBC, RBC, HGB, HCT, MCV, MCH, PCT, MPV, PDW, LYM, TP, ALT, ALB, P and TG) (P<0.01 for all), and in 8 parameters (left kidney, right kidney, right adrenal, thymus, left ovary, RDW, MON%and BUN) (P<0.05 for all). When male and female 4-week CB6F1 mice were compared, there were significant differences in 14 parameters ( body weight, heart, liver, spleen, lung, left kidney, right kidney, MCHC, LYM, ALT, ALP, GLU, P and CHO) (P<0.01 for all), and in 6 parameters (right adrenal, WBC, PCT, MPV, TP and BUN) (P<0.05 for all).For male and female 8-week old CB6F1 mice, there were significant differences in 15 parameters (body weight, heart, liver, lung, left kidney, right kidney, MCV, PCT, LYM, LYM%, NEUT%, ALT, GLU, P and CHO) (P<0.01 for all), and in 5 parameters (WBC, RBC, MPV, NEUT and TP) (P<0.05 for all).Conclusions The normal range of hematological and visceral weight parameters of 4-week and 8-week old male and female CB6F1 mice are determined.Our study establishes normal detection indexes of CB6F1 mice and provides useful reference for its application .

Aging in the cerebellum and hippocampus and associated behaviors over the adult life span of CB6F1 mice.

In the present study we examined the effects of normal aging in the hippocampus and cerebellum, as well as behaviors associated with these substrates. A total of 67 CB6F1 hybrid mice were tested at one of five ages (4, 8, 12, 18 or 25 months) on the context pre-exposure facilitation effect (CPFE) modification of fear conditioning, rotorod, Barnes maze, acoustic startle, Morris water maze (MWM) and 500-ms trace eyeblink classical conditioning (EBCC). Behavioral tasks were chosen to increase the ability to detect age-related changes in learning, as trace EBCC is considered a more difficult paradigm (compared to delay EBCC) and the CPFE has been found to be more sensitive to hippocampus insults than standard contextual fear conditioning. To assess the effects of age on the brain, hippocampus volume was calculated and unbiased stereology was used to estimate the number of Purkinje neurons in the cerebellar cortex. A significant, age-related loss of Purkinje neurons was found-beginning at 12 months of age-and hippocampus volume remained stable over the adult life span. Age-related impairment was found, beginning at 12-18 months in the rotorod, and mice with fewer Purkinje neurons showed greater impairment in this task. CB6F1 mice retained auditory acuity across the life span and mice aged 25 months showed significant age-related impairment in the EBCC task; however, deficits were not associated with the loss of Purkinje neurons. Although the CPFE task is considered more sensitive to hippocampus insult, no age-related impairment was found. Spatial memory retention was impaired in the Barnes maze at 25 months, but no significant deficits were seen in the MWM. These results support the finding of differential aging in the hippocampus and cerebellum.

Profiling psychomotor and cognitive aging in four-way cross mice.

In part due to their genetic uniformity and stable characteristics, inbred rodents or their F1 progeny are frequently used to study brain aging. However, it is recognized that focus on a single genotype could lead to generalizations about brain aging that might not apply to the species as a whole, or to the human population. As a potential alternative to uniform genotypes, genetically heterogeneous (HET) mice, produced by a four-way cross, were tested in the current study to determine if they exhibit age-related declines in cognitive and psychomotor function similar to other rodent models of brain aging. Young (4 months) and older (23 months) CB6F1 × C3D2F1 mice were administered a variety of tests for cognitive, psychomotor, and sensory/reflexive capacities. Spontaneous locomotion, rearing, and ability to turn in an alley all decreased with age, as did behavioral measures sensitive to muscle strength, balance, and motor coordination. Although no effect of age was found for either startle response amplitude or reaction time to shock stimuli, the old mice reacted with less force to low intensity auditory stimuli. When tested on a spatial swim maze task, the old mice learned less efficiently, exhibited poorer retention after a 66-h delay, and demonstrated greater difficulty learning a new spatial location. In addition, the older mice were less able to learn the platform location when it was identified by a local visual cue. Because there was a significant correlation between spatial and cued discrimination performance in the old mice, it is possible that age-related spatial maze learning deficits could involve visual or motor impairments. Variation among individuals increased with age for most tests of psychomotor function, as well as for spatial swim performance, suggesting that four-way cross mice may be appropriate models of individualized brain aging. However, the analysis of spatial maze learning deficits in older CB6F1 × C3D2F1 mice may have limited applicability in the study of brain aging, because of a confounding with visually cued performance deficits.