Index of mechanical efficiency in competitive and recreational long distance runners.

The purpose of this investigation was to compare external work and net energy expenditure during a bout of repetitive stretch-shortening cycles between competitive and recreational long-distance runners. Participants were divided into either competitive or recreational runners based on their maximal oxygen consumption and self-reported 1600 m times. The stretch-shortening cycle involved a repetitive hopping protocol on a force plate while measuring oxygen consumption and lactate accumulation for a total of 10 min. External work and net energy expenditure were calculated for 3 min after steady state was achieved and the ratio between these variables was utilised as an index of mechanical efficiency. Lower extremity stiffness was calculated during this interval as well. Net energy expenditure was significantly lower in competitive runners (152.6 ± 33.3 kJ) in comparison to recreational runners (200.6 ± 41.4 kJ) (P = 0.02) given similar amounts of external work performed in both groups (competitive runners = 65.6 ± 20.1 kJ, recreational runners = 68.8 ± 12.1 kJ) (P = 0.67). Index of mechanical efficiency was significantly different between competitive runners (43.2 ± 9.0%) and recreational runners (34.8 ± 5.3%) (P = 0.03). No significant differences were found in lower extremity stiffness (P = 0.64). Competitive distance runners can perform similar levels of external work with lower net energy expenditure and thus a higher index of mechanical efficiency during repetitive stretch-shortening cycles in comparison to recreational runners with similar values of lower extremity stiffness. This ability could possibly be due differences in muscle-tendon length changes, muscle pre-activation, cross-bridge potentiation and short-latency reflex responses as a result of training which should be considered for future investigation.

Mouse and rat anesthesia and analgesia.

Many animal models used in neuroscience research must be surgically created and/or anesthetized for imaging studies. The purpose of this unit is to review the advantages and disadvantages of various anesthetic and analgesic agents in rodents; to discuss state-of-the-art methods for monitoring anesthesia; and to provide tips for troubleshooting problems with anesthesia.

Effect of housing density on reproductive parameters and corticosterone levels in nursing mice.

The Guide for the Care and Use of Laboratory Animals (Guide) recommends minimum floor space per mouse based on weight, with no other factors considered. We conducted a randomized experiment to evaluate the effect of housing density on reproductive indices and corticosterone levels in lactating mice. Female mice matched for age, strain, and date-of-pregnancy were housed individually. At parturition the dams were randomly allocated to have litters culled or remain intact. The experimental group had litters culled to meet the Guide's space density requirement. Litters of the second group were maintained as the numbers born to each dam. Fecal corticosterone levels (first-generation mice only), growth, and weaning weights were measured for mice in all cages; in addition, the reproductive behavior of progeny generated under both housing conditions was assessed to determine whether a space x litter size interaction affected subsequent reproduction. The growth rates for pups from culled litters were significantly greater than those from intact litters. The first-generation pups showed no statistically significant differences in fecal corticosterone or reproductive parameters. The second-generation pups showed no statistically significant differences in growth rates. The results of the study suggest that a strict interpretation of space requirements as listed in Table 2.1 of the Guide is not warranted for lactating dams with litters.

Considerations for laboratory animal imaging center design and setup.

In vivo animal imaging is an outstanding noninvasive tool to study the pathophysiology of disease or response to therapy; additionally, serial imaging reduces the required number of experimental animals. Because of the tremendous capital investment, we recommend the imaging center be a shared resource to facilitate innovative and productive cross-disciplinary scientific collaborations. A shared center also enables a broader range of imaging, as equipment is often cost prohibitive for smaller facilities. A multitude of factors will determine the architectural design, facility efficiency, and functionality. Important considerations to determine during the planning stages include the types of animals to be imaged, types of imaging studies to be performed, types of imaging equipment and related services to be offered, and the location of the imaging center. Architects must work closely with manufacturers to accommodate equipment-related building specifications; facility planners and veterinarians can provide a practical logistical design that will ensure efficient functionality. Miscellaneous considerations include biosecurity levels, use of radioisotopes, and personnel safety in the imaging environment. The ideal imaging center will include space to house animals and perform necessary preimaging procedures, state-of-the-art in vivo imaging devices and the most up-to-date anesthesia, physiological support, and monitoring equipment. The center staff should include imaging specialists for technical development and data analysis. As it is difficult to provide a comprehensive manual for setting up an in vivo animal imaging center, we offer advice based on our experiences with the National Institutes of Health Mouse Imaging Facility. Because magnetic resonance imaging (MRI) is the most expensive imaging tool, requires specific building design considerations, and poses unique occupational health and safety risks, we focus on MRI as the foundation for an imaging facility design.

Gender influences infectivity in C57BL/6 mice exposed to mouse minute virus.

Two natural outbreaks of mouse minute virus (MMV) are described. Observations during management of the naturally infected colonies led to a study in which 4-wk-old C57BL/6NCr and C57BL/6Tac mice were inoculated oronasally with an immunosuppressive variant of MMV (MMVi), as were adult C57BL/6NCr lactating dams or their pups (age, 10 d). By day 28 postinoculation, 100% of the 4-wk-old male C57BL/6NCr and C57BL/6Tac mice, 56.2% of 4-wk-old C57BL/6NCr female and 62.5% of 4-wk-old C57BL/6Tac female mice, 100% of adult lactating C57BL/6NCr dams, and 100% of inoculated pups (10 d) had seroconverted. Serologically positive nursing dams did not infect their nursing pups. In contrast, when nursing pups were inoculated, 100% of their dams seroconverted by 28 d postinoculation. Only 1 of 4 facility sentinels (Tac:SW female mice) seroconverted to MMVi and none of the 4 research sentinels (Tac:SW female mice) seroconverted under a once-weekly bedding transfer program. Consequently, 4 new research Tac:SW sentinels of each gender (n = 8) were placed in known-positive cages at cage-change; 100% of the male mice but 0% of the females seroconverted by day 48. Study results suggest gender influences both infectivity and the ability to detect subclinical infections of MMVi. Other factors that may influence detection of MMV include mouse strain or stock, short shedding period, and prolonged time between cage changes. In light of the data from both the natural infections and the experimental cases, cessation of breeding likely will be beneficial when trying to eradicate this virus.

The role of the veterinary staff in mouse breeding colony management.

The rapid increase in the production and use of transgenic mice has been a boon for biomedical research and a challenge for the animal care and use programs responsible for providing housing and medical care to these animals. The authors suggest ways in which the veterinary staff can successfully organize and manage transgenic mouse breeding programs to reduce uncontrolled breeding and the problems associated with it.

Euthanasia of mouse fetuses and neonates.

We sought to determine whether any of the common methods of euthanasia for adult rodents would lead to an acceptable death for fetuses or neonates. We wanted to identify a method that was rapid, free of signs of pain or distress, reliable, and minimally distressful to the person performing the procedure and that minimized the amount of handling required to perform the procedure. We evaluated six methods of euthanasia, with and without anesthesia, in three age groups of mice: gravid mice (E14-20) and neonatal pups (P1-P7 and P8-P14). Euthanasia methods included: halothane inhalation, carbon dioxide inhalation, intraperitoneal sodium pentobarbital, intravenous potassium chloride, and cervical dislocation with and without anesthesia. Noninvasive echocardiography was used to assess heartbeat during euthanasia. With cardiac arrest as the definition of death, no method of euthanasia killed fetal mice. Halothane inhalation (5% by vaporizer) was not an acceptable method of euthanasia for mice of the age groups tested. Intraperitoneal administration of sodium pentobarbital for euthanasia required a higher dose than the previously established dose, and there is a risk of reduced efficacy in pregnant animals due to potential intrauterine injection. Carbon dioxide asphyxiation was the most efficient method of euthanasia for neonatal mouse pups P1-14. For pregnant adult mice, intravenous potassium chloride under anesthesia, carbon dioxide asphyxiation, and cervical dislocation alone or under anesthesia were excellent methods of euthanasia.

Inoculation of Staphylococcus xylosus in SJL/J mice to determine pathogenicity.

An experimental study was performed to investigate whether intradermal tail inoculations of Staphylococcus xylosus would result in pathologic lesions in the SJL/J strain of mice (Mus musculus). This organism historically has been classified as a nonpathogenic, commensal bacterium associated with skin and mucous membranes and rarely implicated in infections. In this study, SJL/J mice inoculated with S. xylosus developed cutaneous tail lesions post-inoculation, and the organism was recovered from those lesions. Inoculation was accomplished by surgically inserting silk suture impregnated with the concentrated suspension of bacteria. In addition, a superficial abrasion was created adjacent to the suture, and a bacterial suspension was applied. Approximately 80% of the mice in the inoculated groups developed dermatologic lesions, compared with 0% in the control group. Mice with lesions were treated with Sulfamethoxazole-Trimethoprim in the drinking water continuously for 28 days. For the mice assigned to the treatment group, this treatment resulted in resolution of the cutaneous tail lesions.

Urinary Bladder Catheterization of Female Mice and Rats.

Catheterization of the urinary bladder of rats and mice is necessary for a variety of clinical and experimental reasons. The anatomy of the female mouse and rat is unique in that the urinary orifice is external and just anterior to the vaginal opening. This characteristic makes the bladder of these species easier to catheterize than that of other species. Methods cited in the literature do not adequately describe techniques that facilitate ease of urinary bladder catheterization (1). We describe a simple technique for urinary catheterization in adult female mice and rats.

Spontaneous Rhabdomyosarcomas in (A/J x CBA/J)Fl Mice.

Spontaneous rhabdomyosarcoma is rare in laboratory rodents. Incidence was estimated as 2.4/100,000 in BALB/c mice; incidence of <0.5% for rodents is generally accepted. We describe spontaneous rhabdomyosarcoma in 2 aged, female ([A/J x CBA/ J]F1) mice. Part of a small breeding colony, these mice were experimentally naive; incidence was estimated as 12.5%. Tumors were located in the muscles of the thoracic wall and muscles of the dorsolumbar region. Cross-striations were detected, using phosphotung- stic acid hematoxylin stain; presence of cross-striations within the neoplasm are diagnostic for rhabdomyosarcoma.