In preclinical models, indwelling intravenous catheters and vascular access ports are often essential components of biomedical research aimed at modeling human disease. For instance, animal models of drug self-administration are used for many reasons, including to assess abuse liability, to study physiologic and neurologic consequences of drug exposure, and to examine the efficacy of behavioral and/or pharmacological interventions. The most frequent route of drug self-administration in preclinical animal models is the intravenous route via indwelling intravenous catheters. The present study examined 23 years of drug self-administration studies in Old World macaques used in drug self-administration studies at Wake Forest University School of Medicine. The medical records for individually or pair-housed adult rhesus monkeys (n = 10 females and 172 males) and socially housed cynomolgus monkeys (n = 64 females and 92 males), all implanted with indwelling intravenous catheters and associated vascular access ports, were examined. The most frequent vein catheterized was the femoral vein, followed by the internal and external jugular vein; the least frequent was the brachial vein. The infection rates over 23 years and >500 catheters in cynomolgus and rhesus monkeys were 13.7% and 10.3%, respectively. The average catheter remained patent and implanted in the vein for 22.5 months in cynomolgus monkeys and 15.5 months in rhesus monkeys. These findings highlight significant strengths in using Old World macaques, both rhesus and cynomolgus, in long-term, longitudinal studies involving indwelling intravenous catheters.

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.

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.

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.

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.

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.

Hemangiosarcoma is a malignant neoplasm of vascular endothelial cell origin that is rare in nonhuman primates (NHPs) and humans. This report describes the clinical, gross, and histopathologic findings of metastatic hemangiosarcoma in a rhesus macaque. A 4.8-year-old female Indian-origin rhesus macaque presented to the Tulane National Biomedical Research Center clinic with right hindlimb lameness and poor body condition. On physical examination, there was significant muscle atrophy of the right leg and pelvis. Radiographs revealed severe bone degeneration and lysis of the right tibia with pulmonary nodules. On necropsy, the right tibia was markedly thickened at least two times the normal size. Multifocal, 1- to 7-mm-diameter dark red nodules were present in the periosteum, compact cortical bone, and medullary cavity. Multifocal dark red nodules measuring 1-10 mm were present in the liver and lung. Histologically, the nodules were composed of neoplastic endothelial cells forming irregular vascular clefts and anastomosing vascular channels. Neoplastic cells often wrapped collagenous stroma. Neoplastic cells stained positive with CD31, as well as with von Willebrand factor immunohistochemical stains. Hemangiosarcoma in NHPs is exceptionally rare. To our knowledge, this represents the first case of metastatic hemangiosarcoma originating in bone in an NHP.

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).

Diabetes is a global health concern, with increasing prevalence attributed to factors such as obesity and sedentary lifestyles. Nonhuman primates (NHPs), particularly rhesus macaques (Macaca mulatta), serve as valuable models for studying type 2 diabetes mellitus due to their physiologic similarities to humans. However, there are currently no established normal ranges for glycated hemoglobin (A1C) in this species. This study aimed to determine normal A1C values in healthy, nonobese adult rhesus macaques to establish a reference for future diabetes research. A total of 210 Indian origin rhesus macaques (128 males, 82 females) 5-10 years of age were sampled. A1C was measured using the A1CNow+ kit, and blood glucose levels were assessed via a point-of-care glucometer and clinical laboratory analysis. Statistical analyses were performed using R, including a Shapiro-Wilks test for normality, regression analyses, and correlation coefficients. The mean A1C value was 5.92% (range, 4.4%-9.9%), with males exhibiting a mean of 6.07% and females 5.69%. No significant correlations were found between A1C and blood glucose levels, weight, body condition score, or age. However, males had significantly higher A1C levels than females (P = 0.004). Excluding outliers revealed a significant interaction between sex and weight (P = 0.03). The established mean A1C value for healthy adult rhesus macaques is higher than previously reported values for NHPs and human standards. This study provides a critical reference for A1C levels in rhesus macaques, facilitating future diabetes research and improving understanding of type 2 diabetes mellitus in both humans and NHPs.

The Jamaican fruit bat (Artibeus jamaicensis; JFB) is a natural host and current experimental model for many viruses, including Middle East respiratory syndrome virus, dengue virus, Zika virus, rabies virus, influenza virus, tacaribe virus, and most recently SARS-CoV-2, due to their unique immune systems, which allow the harboring and transmission of disease without developing significant clinical disease themselves. In these studies, disease impact can be measured using changes in serum biochemical and protein electrophoretic blood values. However, no currently established reference intervals for JFB exist. In this study, we aimed to define these baseline parameters from our closed bat colony and determine sex differences, if any. We hypothesized that many chemistry values would be similar to other species of frugivorous bats with elevated creatine kinase and glucose due to hand capture and that sex differences would be minimal. One hundred thirty-four adult bats (62 males and 72 females) were randomly selected from an apparently healthy captive population of JFB for isoflurane euthanasia and blood collection by cardiocentesis. Serum samples were routinely processed using commercially available methods. Reference intervals for the total population and both sexes were established using the Reference Value Advisor 2.1 macro for Excel and the nonparametric method in accordance with current guidelines. When compared against reference values for other frugivorous bat species, JFB most notably had increased ALT, AST, GGT, and potassium values. Higher phosphorus and ALP levels may be attributed to sampling of juveniles, while elevated creatine kinase and glucose are secondary to capture. Males had considerably higher cholesterol, while females had higher glucose and γ-globulin. This information on serum biochemical values adds to our knowledge of the normal physiologic parameters of this species and will serve as a useful guide for future studies performed on Jamaican fruit bats.

This study aimed to establish a comprehensive and accurate numerical chest X-ray radiograph (CXR) scoring system in cynomolgus macaques by using image intensity values from healthy, tuberculosis (TB)-free animals as references. The CXRs were obtained in both dorsoventral and lateral postures from 90 macaques and viewed by the RadiAnt DICOM Viewer software version 2023.1. The mean and maximum intensity values were analyzed and showed significant differences between sex (male and female) and age class (juvenile and subadult/adult), varying based on body sizes. The cutoff values were, therefore, set separately and were tested for accuracy in detecting TB status in 18 naturally Mycobacterium tuberculosis-infected macaques, which were assessed for active tuberculosis infection (ATBI) using Xpert MTB/RIF Ultra at least once during a 12-month follow-up. Only the cutoff values of maximum lateral image intensity (MLIs) correctly identified TB infection in 100% of cases. Thus, the MLIs were selected to follow up on the development of TB lesions in those 18 Mycobacterium tuberculosis-infected macaques. The lateral digital radiograph was divided further into 9 areas, and the MLIs can predict the progression of TB lesions, which were most likely located in the dorsal part of the cranial lung lobe between thoracic vertebrae 1 (T1) to T4. Finally, the CXR results of another group of 8 Mycobacterium tuberculosis-exposed macaques, whose TB status was either uninfected, latent, or ATBI, were compared between a blind test by an expert radiologist and our established CXR scoring system. The blind test results showed 62.5% (5/8) agreement with our scoring system. This suggests that the CXR-MLI scoring system can be used as a supplementary tool for TB diagnosis in cynomolgus macaques.

Total intravenous anesthesia (TIVA) is an alternative to inhalant anesthesia when inhalant anesthesia is unavailable or contraindicated. This study investigated the anesthetic efficacy of tiletamine-zolazepam (TZ) through continuous rate infusion in sheep undergoing a 120-minute noninvasive imaging procedure. We hypothesized that the TZ continuous rate infusion would provide effective general anesthesia for imaging. Six male Dorset sheep were sedated with 4-6 mg/kg TZ intramuscularly, intubated, and maintained on 5-15 mg/kg/h TZ intravenous continuous rate infusion. Measured anesthetic parameters included heart rate, oxygen saturation (%SpO2), end-tidal carbon dioxide (ETCO2), body temperature, and direct arterial blood pressure (systolic, diastolic, and mean); blood gas analysis was performed during anesthesia. Time to extubation and standing (recovery) were measured. Other clinical observations (thrashing, activity, vocalization, and general appearance) were also assessed throughout recovery. Heart rate, %SpO2, ETCO2, body temperature, and direct arterial blood pressure were stable throughout imaging anesthesia. Time to extubation and standing (recovery) were 25 ± 6.5 and 34 ± 8.0 minutes, respectively. No abnormal clinical observations were noted. These data suggest that TZ TIVA provides effective general anesthesia for up to 120 minutes of noninvasive imaging.

The Guide for the Care and Use of Laboratory Animals specifies that sipper tubes require weekly sanitization, although reduced frequency for sterile, disposable caging components may be justified with performance-based assessments; therefore, extending bottle duration beyond 1 week, and replacing instead at a lower volume limit, may be acceptable if it does not compromise mouse health or water quality. Weekly bottle change for sterile, disposable bottles results in excessive waste of both water and plastic-bottles are typically more than half full at 7 days. A volume-based replacement schedule is a visual alternative to weekly changes for systems using sterile, disposable bottles, reducing the number of bottles processed and facilitating operations by allowing spot changes without the need to date or track bottles. Furthermore, the gravity-drip design of Innovive's Aquavive bottle minimizes contamination, suggesting that water quality and cleanliness may be maintained for longer durations. To assess the impact of a volume-based replacement schedule on mouse health and water quality, C57BL/6NCrl mice at varying housing densities were monitored for changes in animal weight and mean water consumption. At bottle replacement, packed cell volume was collected from individual mice as a marker of hydration status, and water quality was assessed by visual inspection, culture for Escherichia coli and coliform bacteria, and total microbial count. Baseline measurements were collected over 7 days, followed by a volume-based replacement period, where bottles remained on the cage until they reached 100 mL (13-47 days). No significant differences were observed in animal body weight, body condition, water consumption, or packed cell volume, regardless of cage density or the amount of time the bottle was deployed. Microbial analysis showed no bacterial growth in any bottle, and visual inspection showed no turbidity or cloudiness. Based on this information, our institution allowed prefilled disposable, acidified water bottles to be maintained well beyond 7 days, using a volume-based replacement at 100 mL.

Laboratory rats (Rattus norvegicus) are common animal models used in biomedical, psychological, and toxicological research. Their long-established research use has driven the progressive refinement of experimental techniques so that associated pain/distress may be ameliorated. One of these refinements is the use of opioids to provide analgesia. Buprenorphine, a partial mu-opioid agonist with high affinity for mu receptors, is commonly used for rodents, as the longer duration of action compared with morphine reduces the need for direct handling during administration of supplemental doses. While conventional buprenorphine (CB) requires dosing two to four times per day to provide sufficient pain control in many mammalian species, a novel, highly concentrated formulation of buprenorphine (HCB; Simbadol) is the first FDA-approved, veterinary-specific opioid labeled for every 24-hour dosing in cats (Felis catus). We hypothesized that, at the labeled feline dose of 0.24 mg/kg SC, HCB would achieve buprenorphine serum concentrations ≥1 ng/mL in older adult female Sprague-Dawley rats for at least 12 to 24 hours. Mean peak serum concentrations of 13.79 ± 6.76 ng/mL occurred 0.5 hour after administration. Twelve hours postadministration, the mean serum concentration was 2.12 ± 0.59 ng/mL with all treated rats maintaining individual serum concentrations well above 1 ng/mL. Twenty-four hours postadministration, the mean serum concentration was 1.02 ± 0.33 ng/mL with 4 of 6 rats maintaining individual serum concentrations of greater than or equal to 0.99 ng/mL. With the exception of a minor, focal injection site reaction in one animal, none of the other known side effects of opioid administration in rats were observed. These results support that administration of HCB at 0.24 mg/kg SC to older adult female SD rats produces serum buprenorphine concentrations consistent with analgesia for at least 12 hours and for up to 24 hours in some rats.

Buprenorphine is an opioid used for pain management in veterinary medicine but which requires frequent dosing to maintain therapeutic levels. Sustained-release buprenorphine (BSR) formulations can overcome this limitation, but genera- or species-specific studies that determine the time profiles of buprenorphine after dosing are sparse for NHPs. The objective of this study was to determine the plasma buprenorphine concentrations for 72 hours after a single subcutaneous administration of 0.2 mg/kg BSR or Ethiqa XR (EXR), an FDA-indexed, extended-release buprenorphine formulation, in owl monkeys. Blood samples were taken before and at 1, 4, 8, 24, 48, and 72 hours after administering either formulation to determine plasma buprenorphine concentrations. Clinical observations were also performed. A single 0.2 mg/kg dose of BSR and EXR raised plasma buprenorphine concentrations above the hypothesized therapeutic threshold for NHPs of 0.1 ng/mL within 1 hour of administration and maintained these levels for at least 72 hours. However, this dose did not sustain buprenorphine concentrations above the human efficacy threshold of 0.5 ng/mL for 72 hours. A subsequent study evaluated a single dose of 0.3 mg/kg EXR to determine whether this dose sustained plasma buprenorphine levels >0.5 ng/mL for 72 hours. Most owl monkeys reached this threshold and maintained plasma buprenorphine concentrations >0.5 ng/mL with this dose, albeit with increased side effects, including sedation and ptyalism. Injection site reactions were not observed in any animals during any study. In sum, this work indicates that a single subcutaneous dose of 0.2 mg/kg BSR or EXR can maintain buprenorphine above the hypothesized therapeutic threshold for NHPs of 0.1 ng/mL for 72 hours, but the EXR dose must be increased to reach the human efficacy threshold for 72 hours in owl monkeys.

Management of nonhuman primates (NHPs) in the laboratory setting is complex. Medical management often involves techniques aimed at minimizing the impact on the animals' welfare, while considering the species-specific characteristics, research aims, and clinical needs of the patient. The current practice, at our institution, for administration of enrofloxacin has been to employ intramuscular injection, which may require brief restraint that can result in increased stress for the animal when applied throughout the course of a therapeutic regimen. Alternatively, oral dosing of standard veterinary tablet formulations has resulted in inconsistent administration, requiring supplementation with an injectable product if the animal becomes unwilling to take the medication. This inconsistency led us to investigate alternative methods of administration. Basing our efforts on previous work performed in macaques, we aimed to determine the pharmacokinetic characteristics of the injectable formulation of enrofloxacin when administered orally to one species of primate, the olive baboon (Papio anubis). Our work demonstrated that injectable enrofloxacin administered orally at 10 mg/kg resulted in higher serum levels than the intramuscular administration group for both enrofloxacin and its active metabolite, ciprofloxacin. In addition, our results support oral administration of enrofloxacin injectable product at intervals of up to once every 24 to 48 h when given at a dose of 10 mg/kg.

Cryopreservation of pronuclear stage embryos from superovulated mice is beneficial to safeguard genetically modified (GM) mouse strains as well as the efficient production of novel GM mouse strains. C57BL/6J female mice were superovulated with either anti-inhibin serum (AIS) or equine chorionic gonadotropin (eCG), and the resulting oocytes were inseminated via in vitro fertilization (IVF) to produce pronuclear stage embryos. A subset of fresh embryos was cultured in vitro to assess their developmental potential to the blastocyst stage, and the remaining embryos derived from either AIS or eCG superovulation methods were cryopreserved via vitrification and subsequently assessed to determine both in vitro and in vivo developmental competence. The percentage of IVF-derived fresh embryos that developed to 2-cell (92.9 ± 4.1 compared with 92.4 ± 4.2) and the blastocyst stage (91.9 ± 3.84 compared with 91.8 ± 7.9) from eCG and AIS, respectively, was not different (P = 0.89). The percentage of the vitrified pronuclear embryos that were intact after warming for eCG (93.08 ± 5.96) and AIS (88.0 ± 6.63) mice was different (P = 0.039). However, the percentage of IVF-derived vitrified warmed zygotes that developed to 2-cell (82.23 ± 7.18 compared with 83.9 ± 7.22) and the blastocyst stage (71.35 ± 7.76 compared with 74.52 ± 5.57) from eCG and AIS, respectively, was not different. Vitrified pronuclear embryos produced after either AIS or eCG-administered mice were in vitro cultured to 2-cell and surgically transferred into CD-1 surrogate mothers to compare pregnancy rates and live birth rates. There were no differences in percent pregnancy rates between eCG (85.7) and AIS (85.7) superovulation methods. Similarly, there were no differences in the percentage of live offspring between eCG (27.6) and AIS (23.2) superovulation methods. This study suggests that eCG and AIS superovulation methods yield similar in vitro and in vivo embryonic development rates following vitrification, and thus, AIS may be preferred, especially for the strains with difficulty in obtaining large quantities of oocytes or embryos for the production of GM mice or genome banking.

Buprenorphine is a commonly used analgesic in laboratory rodents for procedures of moderate to severe pain. We evaluated the pharmacokinetic properties of an immediate-release formulation of buprenorphine (Bup-IR) and an extended-release formulation (Bup-ER) in both sexes of 4 different strains of mice (C57BL/6, CD-1, BALB/c, and CB17 SCID) commonly used for dermatology and oncology research at our institution. Skin at the injection site was evaluated for 7 days postinoculation and scored for reactions and then collected for histopathologic analyses. Body weights were evaluated at 1 and 4 days postinoculation. We hypothesized that the administration of Bup-ER would provide a longer duration of blood drug concentration (>1 ng/mL; minimum analgesia threshold) compared with single-dose Bup-IR. We analyzed the standard dose for Bup-IR (0.3 mg/kg) and for Bup-ER (1 mg/kg), along with saline vehicle with blood collected at 1, 4, 24, 48, 72, and 96 hours following administration of Bup-ER and 0.25, 0.5, 1, 2, 3, 6, 9, 12, and 24 hours following administration of Bup-IR using MS. Bup-ER and Bup-IR levels were consistent among sexes of a given strain but varied between strains. Skin reactions, body weight loss, and histopathologic changes were greater in the Bup-ER-treated mice with some sex and strain differences. Due to changes found on histopathology of the skin sections taken from the injection site for Bup-ER-inoculated mice, a separate study to determine cytokine release following Bup-ER injection was performed and revealed only minor changes in a few cytokines. In conclusion, Bup-ER provided longer duration analgesia (>1 ng/mL) compared with Bup-IR. Based on differences found in the strains of mice evaluated, we recommend performing pharmacokinetic analyses for a given strain to determine the best dosing frequency and dose of buprenorphine (IR or ER) for procedures that require analgesia.

Chlamydia muridarum has reemerged as a prevalent infectious agent in research mouse colonies. Despite its prevalence and ability to persistently colonize the murine gastrointestinal tract, few studies have evaluated the potential impact of C. muridarum on experimental models of gastrointestinal disease. Studies were conducted to evaluate the impact of C. muridarum on the Citrobacter rodentium, Trichuris muris, and Il10-/- mouse models of intestinal inflammation, as well as on tumorigenesis in the ApcMin/+ mouse following administration of dextran sodium sulfate (DSS). Naïve C57BL/6J (B6), B6.129P2-Il10tm1Cgn/J (Il10-/-), and C57BL/6J-ApcMin/J (ApcMin/+) mice were infected with C. muridarum by cohousing with chronic C. muridarum-shedding BALB/cJ mice for 2 weeks; controls were cohoused with C. muridarum-free mice. After cohousing, B6 mice (n = 8 C. muridarum infected and free) were infected with C. rodentium (109 CFU orally) or T. muris (200 ova orally). Il10-/- mice (n = 8/group with and without Helicobacter hepaticus [108 CFU/mouse] and with and without C. muridarum) and ApcMin/+ mice (n = 8/group) that received 2% DSS for 7 days in drinking water after cohousing. Mice were euthanized 14 days post-C. rodentium infection, 18 days post-T. muris infection, 60 days post-H. hepaticus infection, or control with Il10-/- mice, and 28 days post-DSS administration to ApcMin/+ mice. The severity of the cecal and colonic lesions was evaluated and graded using a tiered, semiquantitative scoring system. C. muridarum infection attenuated colitis associated with C. rodentium (P = 0.03), had no effect on T. muris-associated pathology (P = 0.22), worsened colitis in Il10-/- mice in the absence of H. hepaticus (P = 0.007), and reduced chemically induced colonic tumorigenesis in ApcMin/+ mice (P = 0.004). Thus, C. muridarum colonization differentially impacts several models of intestinal inflammation and tumorigenesis, and the presence of this bacterium in mouse colonies should be considered as a variable in these experimental readouts.

Infection with Corynebacterium bovis causes significant clinical disease in immunocompromised mice. The impact of antibiotics, administered prophylactically or symptomatically, on body weight, clinical condition, skin histopathology, and gut microbiota was assessed in NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice infected with C. bovis. Mice were untreated (n = 5) or received oral amoxicillin, sulfamethoxazole/trimethoprim (TMS), or azithromycin a day prior to C. bovis exposure (n = 5/antibiotic) or after clinical signs developed (n = 5/antibiotic). Body weights and clinical scores were ascertained weekly. Mice were euthanized 24 weeks after infection, or earlier if humane endpoints were reached. Skin biopsies and fecal samples were collected at necropsy for histopathology scoring and gut flora characterization. Mice treated with amoxicillin had significant improvement in their clinical signs for the duration of treatment; however, 2 mice treated prophylactically experienced severe weight loss that necessitated euthanasia. Amoxicillin-treated mice had aberrant gut microbiota, including Clostridioides difficile colonization. In contrast, mice treated with TMS had no difference in their clinical scores, and their skin pathology was more severe, compared with untreated mice. There was no difference between symptomatic and prophylactic treatment. Clinical disease in azithromycin-treated mice improved for ∼5 weeks, but ultimately clinical disease recrudesced despite continuing therapy. Mice treated prophylactically with azithromycin experienced severe weight loss that necessitated euthanasia. Changes in the intestinal flora were not appreciated in mice treated with TMS or azithromycin as compared with untreated controls. While clinical signs of C. bovis infection in NSG mice improved when treated with amoxicillin, marked changes in the intestinal flora of these animals require careful consideration of both animal health and experimental outcomes before its use. TMS and azithromycin did not ameliorate C. bovis-associated disease, and their use as therapeutics for C. bovis is not recommended. Untreated C. bovis infection was not life-limiting for up to 24 weeks in NSG mice.