Journal of the American Association for Laboratory Animal Science : JAALAS最新文献

Guinea pigs have been a standard model in cardiovascular pharmacology and physiology research, but the advent of transgenic models has largely replaced them with mouse and rat models. However, guinea pigs remain important models in cardiac electrophysiology, drug-induced arrhythmias, or atherosclerosis research, and they have recently gained importance for studying one specific research question, that is, transplantation of pluripotent stem cell derived cardiomyocytes to repair the cryo-injured heart. Their human-like cardiac electrophysiology, together with their small size that facilitates handling and housing, make guinea pigs a valuable experimental model for these studies. However, repeated open heart surgeries in guinea pigs are technically demanding and accompanied by high mortality. In this study, we retrospectively examined sequential protocol modifications and describe how protocol refinements led to improved survival rates. Cryo-injury was performed in female Dunkin-Hartley guinea pigs under general anesthesia with a liquid nitrogen-cooled probe via a lateral thoracotomy. Cells were transplanted during a second surgery 7 days later. We analyzed data from up to 558 animals to determine mortality rates and morphologic and functional parameters. Initial studies revealed a mortality rate of ∼50%. Sequential modifications led to a significant reduction, with the refined protocol achieving a perioperative mortality rate of ∼30%. The procedures were completed in <35 minutes, and survival rates for the observation period (up to 8 weeks) were 70%. Scar size was evaluated in 144 (4 weeks, n = 92; 8 weeks, n = 52) animals and showed a significant, but shallow correlation with echocardiographically determined heart function. Taken together, refined surgery protocols allow safe and reproducible cryo-injury with subsequent cell injections in guinea pigs with an improved mortality rate.

Fischer 344 rats are a well-characterized laboratory animal. Of note, their popularity as a research model declined due to the high incidence of spontaneous tumor development in the strain. Among these tumors, testicular interstitial cell tumors (ICTs) are frequently observed. We describe here three aged male Fischer 344 rats that were submitted for diagnostic pathology due to an increase in morbidity (increased respiratory effort, general malaise, and weight loss) in the research cohort. In all animals, there was bilateral enlargement of the testes. On the cut surface, multiple well-demarcated masses were compressing and replacing the original testicular tissue. Histologically, these masses were identified as ICTs. The tumors were composed of 3 distinct cell types that correlate with varying degrees of interstitial cell maturation. In one rat, intravascular pulmonary metastases were observed, which resembled the ICT cells morphologically. Malignant ICTs are an unusual finding despite the very high incidence of ICTs in Fischer 344 rats. Our assessment suggests that there are no morphologic criteria that reliably predict malignant and metastatic behavior of ICTs in F344 rats, highlighting the need for clinical monitoring of animals for which castration is chosen as a treatment.

Rabbits are widely used in biomedical research as models for atherosclerosis with disease induction achieved through a high-cholesterol diet, transgenic approaches, or spontaneous development with aging. At our institution, New Zealand White rabbits were induced to develop atherosclerosis via a high-cholesterol diet followed by arterial balloon injury. This model was established to support intravascular molecular imaging studies aimed at tracking atheromatous plaque progression in vivo. To accelerate plaque development, a subcutaneous osmotic pump delivering angiotensin II at 50 ng/kg/min was implanted. While this method enhanced disease progression, unexpected clinical complications were observed. In this retrospective case report, we reviewed clinical records from 54 rabbits over a 2-year period. Clinically, most study animals showed different levels of inappetence. Three presented respiratory symptoms including cyanosis, dyspnea, or tachypnea, while another 3 exhibited neurologic signs such as altered mentation and paralysis. Eight rabbits (14.8%) were euthanized due to severe clinical signs. Necropsy findings in the affected animals commonly revealed pleural and/or peritoneal effusion; one case included chyloabdomen, a condition not previously reported in rabbits. Of these, 7 had myocardial degeneration and fibrosis. These findings suggest that angiotensin II infusion in this rabbit model of atherosclerosis may induce myocardial fibrosis as a significant adverse effect. This report highlights potential complications associated with the model and provides guidance for clinical monitoring, diagnosis, and management in future studies.

Injectable anesthetics are commonly used in murine experimental procedures. However, these agents may result in neurotoxicity, which should be considered in interpretation of experimental results. We evaluated acute effects of 2 different anesthetic combinations on juvenile mouse brain development using structural MRI to assess impact on the brain. We compared the use of ketamine-xylazine, a commonly used injectable anesthetic combination in mice, to alfaxalone-xylazine in the context of noninvasive procedures requiring immobilization (that is, not a surgical plane of anesthesia). In this longitudinal study, we used MRI to produce three-dimensional scans of mouse brains at 2 time points (postnatal days 14 and 23), analogous to early childhood to prepubescence in humans. At postnatal day 16, mice were either dosed with ketamine-xylazine, alfaxalone-xylazine, or left untreated. From the scans, we quantified whole brain and structure volumes across the brain, comparing growth between time points and modeling the effect of both anesthetics compared with controls. Anesthetic parameters were measured, and general health and welfare were monitored during and after each injectable anesthesia drug condition. Results indicate that systemic and brain toxicity were reduced in mice treated with alfaxalone-xylazine compared with ketamine-xylazine. In addition, both ketamine-xylazine and alfaxalone-xylazine reliably anesthetized all mice, although mice administered ketamine-xylazine showed increased weight loss compared with the alfaxalone-xylazine in the postanesthetic period. These findings highlight alfaxalone-xylazine as a convenient and possibly safer alternative anesthetic for mouse brain development studies when compared with ketamine-xylazine and as a viable option as an injectable anesthetic in juvenile mice.

Escherichia coli strains are the most common bacterial cause of canine neonatal mortality, with rectal and vaginal contaminants from the mother reportedly serving as an important source of infection. Between July and September 2013, a canine research facility at Michigan State University experienced a spike in neonatal mortality. Thirteen of 14 puppies from 2 litters died, with 10 being submitted for necropsy. Three puppies from one litter struggled since birth to suckle and died. Five puppies from an additional litter died after presenting due to failure to thrive, depression, and lethargy. All puppies exhibited microscopic lesions consistent with septicemia represented by interstitial necrotizing pneumonia, random hepatocellular necrosis, or intravascular bacteria. Bacterial cultures of the lung and liver yielded numerous β-hemolytic Streptococcus group G and numerous Escherichia coli, which tested positive by PCR for the cytotoxic necrotizing factor 1 (cnf1) gene. Vaginal and rectal culture swabs taken from adult breeding females between 2013 and 2020 revealed that many were asymptomatic carriers of cnf1+ E. coli. The institution of prophylactic antimicrobial treatment for pregnant females testing culture positive for cnf1+ E. coli before parturition may have prevented additional puppy losses; however, it may have also contributed to resistance observed in future samples. While increased attention to pregnant females testing positive for cnf1+ E. coli prevented subsequent neonatal mortality, the source of the pathogen was not identified. More in-depth sampling of the facility environment could identify a reservoir; however, endemic carriers cannot be ruled out. Screening protocols may be warranted in facilities experiencing persistent cnf1+ E. coli infections.

Group or pair housing of social animals in laboratory settings is beneficial to animal welfare. Social housing of male mice can be difficult due to possible aggressive behaviors, leading to injury and resulting in animals not being able to continue in the study. Techniques used to decrease male mouse aggression and territorial behaviors have been described in recent literature, including pairing mice before sexual maturity, moving used nesting material over during cage changes, removing high-value items that can encourage territorial behaviors, and using low-stress handling techniques. Using these suggested tactics, we conducted a 28-day study determining the social compatibility of male CD-1 mice in a standard toxicological study design. Forty-eight mice, aged 5 weeks old, were equally divided into single and pair housing and were administered theophylline daily. Animals were exposed to common toxicology study procedures known to cause additional stress including repeated blood collections, daily dosing, weekly clinical observations and body weights, and terminal urine collections. Behavioral assays, including nest scores and time-to-integrate-nest-material testing, were performed weekly, and pelt scores were collected postmortem. Fecal samples were collected intermittently for fecal corticosterone metabolite analyses. No mouse pairs required separation throughout the dosing phase of study, and no significant differences were observed that would affect toxicology studies. This suggests that by using techniques to decrease agonistic behaviors, male mice can be successfully socially housed on acute and subacute toxicology studies.

Meloxicam is a nonsteroidal anti-inflammatory drug (NSAID) frequently administered every 24 hours to control mild to moderate pain in rodents. Extended-release meloxicam offers a refinement of less frequent dosing and an extended therapeutic window compared with the standard daily-dosed meloxicam formulation. The aim of this study was to compare the analgesic efficacy of 2 different extended-release meloxicam formulations to a standard meloxicam formulation in a rat incisional pain model. Adult Long-Evans rats (n = 33) were randomly assigned into one of 4 treatment groups (n = 8-9 per group): (1) saline (0.9% NaCl, 5 mL/kg, SC, once); (2) meloxicam (Melox; 2 mg/kg, SC, every 24 hours); (3) meloxicam extended-release polymer (Melox-ER; 4 mg/kg, SC, once); or (4) meloxicam extended-release suspension (Melox-XR; 4 mg/kg, SC, once). Under isoflurane anesthesia, a 1-cm longitudinal skin incision was made on the plantar hind paw 5 minutes after drug administration. Mechanical and thermal hypersensitivity assessments were performed one day before surgery (-24 hour), 4 hours after surgery (4 hour), and 3 consecutive days following surgery (24, 48, and 72 hours). Mechanical (4-48 hours) and thermal (4-72 hours) hypersensitivity were observed in the saline group. Melox-ER did not attenuate mechanical or thermal hypersensitivity at any time point. Melox and Melox-XR attenuated mechanical hypersensitivity at the 48-hour time point. No abnormal clinical signs were noted, but injection site reactions were noted in the Melox, Melox-ER, and Melox-XR groups. Further research is needed to evaluate rat meloxicam analgesic dosages for incisional pain.

Warmed inspired air circuits have proved to be effective in semiclosed heating modalities in veterinary species such as dogs, cats, and nonhuman primates, and thus, there is a gap in species requiring a nonrebreathing circuit. This study evaluated the efficacy of using warmed inspired air in addition to conductive mattress warming in the prevention of hypothermia in anesthetized rabbits (Oryctolagus cuniculus). Rabbits were divided into 2 groups: conductive warming only (control) or conductive warming and warmed inspired air. Our results showed that the addition of a warmed air anesthesia circuit had a significant positive effect on perianesthetic body temperature, maintaining a higher rectal temperature starting 10 minutes after induction and a higher final rectal temperature after a 45-minute anesthetic procedure. At 20 minutes after induction, the body temperature of the warmed air group was not significantly different from baseline compared with a significant drop from baseline in the control group. Infrared pinnal temperatures did not show a pairwise significance in the effect of heating modality and time; however, a clinically significant difference of 2-3 °F between groups was seen. There were no statistically significant differences between groups for time to full recovery and time to extubation. For procedures using rabbits, the addition of warmed inspired air should be considered a significant refinement that promotes normothermia during anesthesia based on consistent and improved overall body temperatures.

Simian T cell leukemia virus (STLV) is associated with lymphoma in many captive and wild Old World nonhuman primate (NHP) species and is readily transmitted by bodily fluids. The disease is best characterized in baboons with a predisposition for aged female animals. Asymptomatic infections are common; however, clinical signs may include generalized lymphadenopathy, lethargy, and anorexia. Herein, we report a case of disseminated lymphoma in a middle-aged female STLV-positive olive baboon (Papio anubis) that presented with generalized lymphadenopathy and a rapid onset of decreased visual acuity culminating in full vision loss. Postmortem examination revealed a metastatic focus of lymphoma compressing the occipital cortex and is the presumed mechanism of vision loss. To our knowledge, this is the first report of a neurologic complication associated with an STLV infection in a NHP species.

Intracardiac injection is a commonly used method to establish experimental metastases in mice, particularly in models of breast and prostate cancer. This technique enables rapid dissemination of tumor cells to the skeleton and brain but carries significant animal welfare concerns due to high rates of morbidity, including paralysis, weight loss, and multiorgan failure. This narrative review evaluates the welfare implications of the intracardiac model, synthesizing data from preclinical studies. Alternative techniques, such as intratibial, caudal artery, intracarotid, and intracranial injection, are compared in terms of procedural refinement, disease localization, survival time, and humane endpoints. These methods offer improvements in reproducibility and welfare while maintaining relevance to metastasis research. We discuss how these refinements can reduce animal burden and improve model selection in line with the 3Rs (Replacement, Reduction, and Refinement).