Rodent analgesia

Treatment of Pain in Rats, Mice, and Prairie Dogs

Recent myomorph and scuiromorph rodent analgesia studies are reviewed and evaluated for potential clinical application. Differences between laboratory animal studies and clinical use in diseased animals are discussed. Analgesia classes reviewed include local anesthetics, nonsteroidal anti-inflammatories, acetaminophen, opioids, and adjuvants such as anticonvulsants. Routes of administration including sustained-release mechanisms are discussed, as are reversal agents. Drug interactions are reviewed in the context of beneficial multimodal analgesia as well as potential adverse effects. Dosage recommendations for clinical patients are explored.

Improvement of Pain Management by Nefopam in a Rat Adjuvant-Induced Arthritis Model

Introduction

The adjuvant-induced arthritis (AIA) model is widely used in research to investigate arthritis pathogenesis. Hind paw inflammation is the main outcome in this model with high loss of mobility function partly related to pain. However, analgesics such as non-steroidal anti-inflammatory drugs or opioid drugs interfere with the inflammation process related to arthritis, thus reducing their beneficial use in this model. Therefore, we investigated the effect of nefopam on arthritis development in order to improve pain management in the AIA model.

Methods

Female Lewis rats were randomly divided into two groups, and each group received an injection of Mycobacterium butyricum on defining day (D) 0. At D6, rats (n = 10) received nefopam (intraperitoneally or orally) or NaCl 0.9% IP or 1% sucrose in water (n = 5 for each). Rats were monitored with the arthritic index (AI) and ankle circumference. Pain was assessed by scoring based on behavioral indicators. Histology, RT-qPCR, and microcomputed tomography were performed.

Results

The clinical parameter AI and ankle circumference were not different in both groups at various time points. However, pain score was significantly lower in the nefopam group at the early stage of the disease. At a later stage of the disease, inflammation was mildly lower whereas bone erosion and bone loss parameters increased in the nefopam group.

Conclusion

Nefopam provided a slight reduction in the level of pain at the arthritis onset without reducing arthritis severity and bone loss in the rat AIA model. However, it should be administrated orally for a shorter period to avoid inflammation reduction in the long run.

Development of an improved anesthesia protocol to increase CF1 mice survival in a portal vein infection with Echinococcus granulosus sensu lato protoscoleces

In order to optimize the survival rate of animals, the purpose of this study was to evaluate an injectable anesthesia protocol for the development of a murine model of hepatic cystic echinococcosis in female CF-1 mice. Three protocols of injectable anesthesia were evaluated during the infection of mice with Echinococcus granulosus sensu lato protoscoleces via the portal vein. The use or not of pre-anesthesia [atropine (0.4 mg/kg) and tramadol (2 mg/kg)] and the incorporation or not of yohimbine (0.5 mg/kg) (a reverser of xylazine) in mice anesthetized with ketamine/xylazine 80/8 mg/kg were evaluated. Most mice treated only with ketamine/xylazine 80/8 mg/kg did not achieve a deep surgical anesthetic plane. All mice treated with pre-anesthetic drugs achieved a deep surgical anesthetic plane after the administration of the anesthetic cocktail. Pre-anesthetic drugs application significantly reduced time induction of animals compared with those that received only anesthetic cocktail. Recovery time was significantly faster in the group that received yohimbine. Mice underwent laparotomy that did not receive yohimbine after surgery had a survival rate of 67%, whereas in the group treated with yohimbine the survival was 100 %. We recommend the protocol that applied pre-anesthetic drugs + ketamine/xylazine 80/8 mg/kg + yohimbine, as safe and reliable for the portal vein infection of mice with protoscoleces of E. granulosus sensu lato.

Injection-site Reactions to Sustained-release Meloxicam in Sprague-Dawley Rats

An extended-release formulation of the NSAID meloxicam (MSR) is used to provide 72 h of continuous analgesia in many species, including rodents. Although standard formulations of meloxicam are frequently used in rats with no observable injection-site reactions, the potential adverse effects from MSR have not been characterized sufficiently nor has a prospective study of these effects been performed in rats. To address this deficiency, we evaluated injection-site reactions after a single subcutaneous administration of MSR (n = 16) or sterile saline (SC, n = 6) in the flank of age- and sex-matched Sprague-Dawley rats. Mass and erythema scores were measured daily for 2 wk, and injection sites were collected for histopathology after euthanasia. Rats were randomly selected for euthanasia at 7 d (n = 12) or 14 d (n = 10) after injection to capture the subacute and chronic phases of mass and erythematic lesion formation. No rats in the SC group developed lesions, whereas all 16 MSR-treated rats developed masses. The median time to first mass in the MSR treatment group was 3 d (95% CI, 2-3 d), and nearly 8 d for erythema (95% CI, 6.7-9.1 d). The trajectory of mass lesion severity showed rapid progression from score 1 at onset (day 2 or 3) to score 2 for almost all animals by day 5 or 6. Histopathology was characterized by localized inflammation with central necrosis and peripheral fibrosis, with some sections showing developing draining tracts. Given the high prevalence and severity of localized skin reactions, MSR analgesia should be considered carefully for Sprague-Dawley rats.

Sterility and Stability of Diluted Meloxicam in Compounded Multi-dose Vial after 365 Days

Meloxicam is a common analgesic for rodents. Because meloxicam is only formulated commercially for companion animals, it requires dilution to achieve doses appropriate for small, laboratory species. Compounded multidose vial (cMDV) are often created to dilute and store a diluted drug. However, chronic cMDV use runs the risk of contamination and becoming a potential source of nosocomial infection. In this study, we created 15 cMDV by diluting meloxicam with sterile water (dilution, 1:10). cMDV were punctured once daily for 30 d. To determine the sterility of the diluted meloxicam, we assessed 8 cMDV for bacterial growth on days 0, 10, 20, 30, and 365 and tested them for endotoxin on days 0, 30, and 365. In addition, the stability of the remaining 7 cMDV was assessed on days 0, 10, 20, 30, and 365, by using liquid chromatography-diode assays. No bacterial growth or endotoxin was detected at any time point, and the drug concentrations remained stable over 365 d. Given the results this study, we believe that cMDV of diluted meloxicam can remain sterile and stable for 365 d.

Exotic Mammal Orthopedics

Orthopedic disorders are a common clinical presentation for the exotic clinician. Before treating the fracture it is vital to stabilize the patient. Small exotic mammals are characterized by relatively thinner bones, adding to the difficulty the small size already represents. A combination of conservative and surgical treatment options are available. The principles of orthopedic surgery and ideas behind the treatment options remain the same as for small mammals, but not all techniques can be directly extrapolated. Historically, the tie-in fixator has been the preferred surgical choice whenever feasible, but further development in bone plates represents a promising advancement.

Voluntary intake of paracetamol-enriched drinking water and its influence on the success of embryo transfer in mice

Embryo transfer (ET) in mice is a key technique in biomedical research, and is carried out mostly via surgery by transferring founder embryos into pseudo-pregnant recipient females. To cover post-operative analgesic requirements in surrogate mothers, oral self-administration of painkillers has several advantages, but its effectiveness has also been criticized as voluntary ingestion of the drug can be uncertain. Additionally, concerns about potential negative side effects of analgesics on embryo viability and development have been raised. In this regard, we investigated the impact of orally administered analgesia by comparing the outcome of ET with and without paracetamol in the drinking water (3.5mg/ml) of surrogate mothers. Water intake increased significantly when paracetamol, as a sweet-tasting formulation (children's syrup), was added to the drinking water. Measurements of paracetamol concentrations in blood serum confirmed reasonable drug uptake. Success rate of ETs and the body weight of newborn offspring were not different whether paracetamol was administered for two days after surgery or not. In conclusion, paracetamol in drinking water was consumed voluntarily in substantial doses, without detectable side-effects, by freshly operated surrogate mothers, and can therefore be recommended as a feasible method for providing analgesic treatment for surgical ET in mice.

A murine model of lung ischemia and reperfusion injury: tricks of the trade

BACKGROUND

Pulmonary ischemia-reperfusion injury (IRI) causes postoperative morbidity in patients undergoing lung transplantation, isolated lung perfusion, and cardiopulmonary bypass and may lead to potentially lethal pathologies such as respiratory shock. In-depth study of this pathology requires a reliable animal model. Mice are a popular species to develop experimental models because of their logistic advantages and the availability of knock outs. However, their small size warrants microsurgical techniques and a skilled surgeon.

MATERIALS AND METHODS

We developed a murine model of pulmonary anoxic IRI through hilar clamping using adult female Swiss mice. After left thoracotomy, we expose the pulmonary hilum keeping the ribs and the muscles of back and forepaw intact. A microvascular clamp is placed over the entire hilum, occluding bronchus, pulmonary artery, and vein.

RESULTS

Our model proved to be simple, reliable, and reproducible, showing minimal preoperative and postoperative mortality. Histopathologic analysis indicated all characteristic features of pulmonary IRI, such as an early recruitment of lymphocytes followed by neutrophil influx.

CONCLUSIONS

This article presents a murine surgery model for pulmonary IRI based on a muscle-sparing thoracotomy. The minimal approach limits manipulation of lung tissue, minimizing mortality and non-IRI-induced injury.