Buprenorphine via drinking water and combined oral-injection protocols for pain relief in mice

A buprenorphine depot formulation provides effective sustained post-surgical analgesia for 72 h in mouse femoral fracture models

Adequate pain management is essential for ethical and scientific reasons in animal experiments and should completely cover the period of expected pain without the need for frequent re-application. However, current depot formulations of Buprenorphine are only available in the USA and have limited duration of action. Recently, a new microparticulate Buprenorphine formulation (BUP-Depot) for sustained release has been developed as a potential future alternative to standard formulations available in Europe. Pharmacokinetics indicate a possible effectiveness for about 72 h. Here, we investigated whether the administration of the BUP-Depot ensures continuous and sufficient analgesia in two mouse fracture models (femoral osteotomy) and could, therefore, serve as a potent alternative to the application of Tramadol via the drinking water. Both protocols were examined for analgesic effectiveness, side effects on experimental readout, and effects on fracture healing outcomes in male and female C57BL/6N mice. The BUP-Depot provided effective analgesia for 72 h, comparable to the effectiveness of Tramadol in the drinking water. Fracture healing outcome was not different between analgesic regimes. The availability of a Buprenorphine depot formulation for rodents in Europe would be a beneficial addition for extended pain relief in mice, thereby increasing animal welfare.

Use of a Low-calorie Flavored Gel to Facilitate Oral Self-administration of Analgesics in Mice

The goals of this study were to determine whether mice would adapt to a low-calorie flavored water gel as their sole source of hydration and whether the addition of acetaminophen, tramadol, meloxicam, or buprenorphine to the gel would affect their intake. Water and gel intakes were measured during a 4-phase study, each of which lasted 1 wk: phase 1, standard water bottle only; phase 2, standard water bottle and a separate tube containing water gel; phase 3, water gel only; and phase 4, water gel containing an analgesic drug. Water consumption, corrected for body mass, was not different between male and female mice when water was available (phases 1 and 2). However, the total consumption of water and water gel was higher for females than males during phase 2, and female mice consumed more gel than males during phase 3. When male and female data were combined, total corrected water intake was not different among the first 3 phases of the study. Gel intake did not change significantly after the addition of acetaminophen, meloxicam, buprenorphine or tramadol as compared with untreated water gel. These data suggest that drugs presented in the low-calorie flavored water gel may be a viable alternative to injection or gavage for the administration of analgesic drugs.

Grimace scale, burrowing, and nest building for the assessment of post-surgical pain in mice and rats-A systematic review

Several studies suggested an informative value of behavioral and grimace scale parameters for the detection of pain. However, the robustness and reliability of the parameters as well as the current extent of implementation are still largely unknown. In this study, we aimed to systematically analyze the current evidence-base of grimace scale, burrowing, and nest building for the assessment of post-surgical pain in mice and rats. The following platforms were searched for relevant articles: PubMed, Embase via Ovid, and Web of Science. Only full peer-reviewed studies that describe the grimace scale, burrowing, and/or nest building as pain parameters in the post-surgical phase in mice and/or rats were included. Information about the study design, animal characteristics, intervention characteristics, and outcome measures was extracted from identified publications. In total, 74 papers were included in this review. The majority of studies have been conducted in young adult C57BL/6J mice and Sprague Dawley and Wistar rats. While there is an apparent lack of information about young animals, some studies that analyzed the grimace scale in aged rats were identified. The majority of studies focused on laparotomy-associated pain. Only limited information is available about other types of surgical interventions. While an impact of surgery and an influence of analgesia were rather consistently reported in studies focusing on grimace scales, the number of studies that assessed respective effects was rather low for nest building and burrowing. Moreover, controversial findings were evident for the impact of analgesics on post-surgical nest building activity. Regarding analgesia, a monotherapeutic approach was identified in the vast majority of studies with non-steroidal anti-inflammatory (NSAID) drugs and opioids being most commonly used. In conclusion, most evidence exists for grimace scales, which were more frequently used to assess post-surgical pain in rodents than the other behavioral parameters. However, our findings also point to relevant knowledge gaps concerning the post-surgical application in different strains, age levels, and following different surgical procedures. Future efforts are also necessary to directly compare the sensitivity and robustness of different readout parameters applied for the assessment of nest building and burrowing activities.

Lidocaine and bupivacaine as part of multimodal pain management in a C57BL/6J laparotomy mouse model

While the use of local anesthesia as part of multimodal pain management is common practice in human and veterinarian surgery, these drugs are not applied routinely in rodent surgery. Several recommendations on the use of local anesthesia exist, but systematic studies on their efficacy and side effects are lacking. In the present study, male and female C57BL/6J mice were subjected to a sham vasectomy or a sham embryo transfer, respectively. We tested whether a mixture of subcutaneously injected Lidocaine and Bupivacaine in combination with systemic Paracetamol applied via drinking water results in superior pain relief when compared to treatment with local anesthesia or Paracetamol alone. We applied a combination of methods to assess behavioral, emotional, and physiological changes indicative of pain. Voluntary Paracetamol intake via drinking water reached the target dosage of 200 mg/kg in most animals. Local anesthesia did not lead to obvious side effects such as irregular wound healing or systemic disorders. No relevant sex differences were detected in our study. Sevoflurane anesthesia and surgery affected physiological and behavioral measurements. Surprisingly, Paracetamol treatment alone significantly increased the Mouse Grimace Scale. Taken together, mice treated with a combination of local anesthesia and systemic analgesia did not show fewer signs of post-surgical pain or improved recovery compared to animals treated with either local anesthesia or Paracetamol.

Mouse Models of Kidney Fibrosis

Chronic kidney disease (CKD) affects over 10% of the worldwide population and kidney fibrosis is a main driver of CKD and considered a therapeutic target. The mechanisms leading to kidney fibrosis are highly complexed and can be best studied in rodent models. Here we describe the most commonly used kidney fibrosis models in mice, the unilateral ureteral obstruction (UUO) model and the ischemia reperfusion injury (IRI) model. Both models are easy to learn and can be applied in animals of different age, sex, and strain.

Design and in vivo evaluation of a microparticulate depot formulation of buprenorphine for veterinary use

Buprenorphine is a frequently used analgetic agent in veterinary medicine. A major drawback, however, is the short duration of action requiring several daily administrations. We therefore designed a poly-lactic-co-glycolic acid (PLGA) based microparticulate drug formulation for sustained parenteral drug release. Particles were designed to allow for a fast onset of action and a duration of the analgesic effect of at least two days in laboratory mice. Microparticles were produced using a solvent evaporation technique. Release rate was dependent on polymer type and particle size. Spherical particles used for subsequent animal studies had a mean size of 50 µm and contained 4.5% of buprenorphine. Drug release was characterized by an initial burst release of 30% followed by complete release over seven days. In vivo pharmacokinetic experiments in female C57BL/6 J mice confirmed prolonged exposure in plasma and brain tissue and correlated with the pharmacological effect in the hot plate assay or after minor abdominal surgery. No adverse side effects with respect to food and water intake, body weight, local tolerability, or nesting behavior were observed. Our formulation is an attractive alternative to established immediate release formulations. A use for prolonged pain management in laboratory animals is proposed.

The Application of Humane Endpoints and Humane Killing Methods in Animal Research Proposals: A Retrospective Review

Refinement refers to the use of methods that help to minimise animal suffering in the laboratory. Research in this area has increased significantly over the past two decades. However, the extent to which refinements are applied in practice is uncertain. To provide an indication of the implementation and awareness of refinements, we reviewed the experimental techniques for 684 surgical interventions described in 506 animal research applications sent to the German competent authorities for approval in 2010. In this paper, we describe and discuss the appropriateness of the proposed humane endpoints and killing methods. We found that, when the investigators included humane endpoints in their application, these were often lacking in detail and/or were to be implemented at a late stage of suffering. In addition, the choice of method to kill the animals could be improved in the majority of the applications. We provide recommendations for future improvements, based on the recent literature. To ensure scientific rigour, avoid needless animal suffering and enable an accurate harm–benefit analysis, animal researchers have to be knowledgeable about refinement methods and apply them effectively. To assess compliance and ensure that only those studies in which potential benefits outweigh the harms are carried out, reviews such as ours — as well as retrospective assessments of actual harms and benefits — should be conducted widely and regularly, and the findings should be published.

Analgesics in Small Mammals

Managing pain effectively in any species is challenging, but small mammals present particular problems. Methods of pain assessment are still under development in these species, so the efficacy of analgesic therapy cannot be evaluated fully. Methods of assessing abdominal pain are established; however, applying these can be challenging. Alternative methods, using assessment of facial expression, may be more applicable to a range of painful procedures and across species. Multimodal and preventive analgesic strategies are most likely to be effective. Although data on analgesic dose rates are limited, sufficient information is available to enable analgesia to be provided safely.

The IMPROVE Guidelines (Ischaemia Models: Procedural Refinements Of in Vivo Experiments)

Most in vivo models of ischaemic stroke target the middle cerebral artery and a spectrum of stroke severities, from mild to substantial, can be achieved. This review describes opportunities to improve the in vivo modelling of ischaemic stroke and animal welfare. It provides a number of recommendations to minimise the level of severity in the most common rodent models of middle cerebral artery occlusion, while sustaining or improving the scientific outcomes. The recommendations cover basic requirements pre-surgery, selecting the most appropriate anaesthetic and analgesic regimen, as well as intraoperative and post-operative care. The aim is to provide support for researchers and animal care staff to refine their procedures and practices, and implement small incremental changes to improve the welfare of the animals used and to answer the scientific question under investigation. All recommendations are recapitulated in a summary poster (see supplementary information).

Premedication with fentanyl-midazolam improves sevoflurane anesthesia for surgical intervention in laboratory mice

Balanced anesthesia allows for a reduced dosage of each component, while inducing general anesthesia of sufficient depth with potentially fewer side effects. Here, we compare two anesthetic protocols combining sevoflurane anesthesia with pre-medication (ketamine [K] or fentanyl-midazolam [FM]) to a sevoflurane monoanesthesia (S) concerning their ability to provide reliable anesthesia suitable for moderate surgery in laboratory mice. Twenty-one female C57BL/6J mice assigned randomly to one of three protocols underwent a 50-min anesthesia and a sham embryo transfer. Heart rate and core body temperature were continuously recorded by telemetry intra-operatively and for three days pre- and three days post-surgery. Intra-operative respiratory rate was determined by counting thorax movements. Body weight, food, and water intake were measured daily for three days pre- and three days post-surgery. The heart rate in the KS group remained at baseline level throughout the 50-min of anesthesia and surgery. FMS caused a lower heart rate and S alone caused a higher heart rate compared to baseline values. Intra-operative body temperature was at baseline levels in all groups. A decreased respiratory rate was observed in all groups compared to baseline values obtained from resting mice of the same strain, sex and age-distribution. Surgical stimuli induced no significant changes in heart rate and respiratory rate in the KS or FMS group but significant respiratory alteration in the S group compared to baseline values obtained 10 s before applying the stimulus. Post-operative heart rate was above baseline values in all groups; with a significant deviation in the S group. There were no changes in body weight, food, and water intake. In summary, FMS was superior to KS and S for moderate surgery in laboratory mice resulting in less inter-individual variability in response to painful stimuli. Fentanyl and midazolam reduced the depressant effect of sevoflurane on the respiratory rate and the negative post-anesthetic effects on the heart rate. Impact statement With approximately 65 million animals used per year mice are still the most prevalent laboratory mammal species worldwide. In course of biomedical research projects approximately 40% of mice will undergo one or more short or long-term anesthesia. Sufficient anesthetic depth, cardiovascular stability, adequate analgesia, and short recovery times are essential requirements of anesthetic protocols to meet animal welfare. Anesthesia in mice and rats are only to be performed by personnel with appropriate basic training and experience. However, more and more adapted and advanced anesthetic protocols, required to answer very specific scientific questions, often exceed the skills acquired through basic training and present a major challenge to researchers. It is therefore of great importance to further develop and evaluate safe and reliable anesthetic protocols as presented in this study to provide new perspectives on this challenging problem.

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.