Behaviour-based assessment of the duration of laparotomy-induced abdominal pain and the analgesic effects of carprofen and buprenorphine in rats

Review of Rat (Rattus norvegicus), Mouse (Mus musculus), Guinea pig (Cavia porcellus), and Rabbit (Oryctolagus cuniculus) Indicators for Welfare Assessment

The monitoring and assessment of animals is important for their health and welfare. The appropriate selection of multiple, validated, and feasible welfare assessment indicators is required to effectively identify compromises or improvements to animal welfare. Animal welfare indicators can be animal or resource based. Indicators can be collated to form assessment tools (e.g., grimace scales) or animal welfare assessment models (e.g., 5 Domains) and frameworks (e.g., 5 Freedoms). The literature contains a wide variety of indicators, with both types needed for effective animal welfare assessment; however, there is yet to be an ideal constellation of indicators for animal-based welfare assessment in small mammals such as guinea pigs (Cavia Porcellus), mice (Mus musculus), rabbits (Oryctolagus cuniculus), and rats (Rattus norvegicus). A systematic review of grey and peer-reviewed literature was performed to determine the types of animal-based welfare indicators available to identify and assess animal health and welfare in these small mammals maintained across a wide variety of conditions. The available indicators were categorised and scored against a selection of criteria, including potential ease of use and costs. This review and analysis aim to provide the basis for further research into animal welfare indicators for these species. Future applications of this work may include improvements to animal welfare assessments or schemes, guiding better management, and implementing future strategies to enable better animal welfare.

High-dose Meloxicam Provides Improved Analgesia in Female CD1 Mice: A Pharmacokinetic and Efficacy Study

Meloxicam is a nonsteroidal anti-inflammatory analgesic drug that is often used in mice. However, doses of 1 to 5 mg/kg given twice daily were recently reported to provide inadequate analgesia. Some studies suggest that doses of up to 20 mg/kg may be necessary for adequate pain management. We investigated the analgesia provided by a high-dose of meloxicam in female CD1 mice. Pharmacokinetic analyses demonstrated that a subcutaneous injection of 10 mg/kg or 20 mg/kg of meloxicam produced therapeutic plasma concentrations for at least 12 h. Ovariectomies via ventral laparotomy were performed to assess analgesic efficacy. Mice were treated immediately before surgery with a high-dose of 10 mg/kg, a low-dose of 2.5 mg/kg, or saline, followed by every 12 h for 36 h. At 3, 6, 12, 24, and 48 h after surgery, mice were assessed for pain based on the following behaviors: distance traveled, time mobile, grooming, rearing, hunched posture, orbital tightening, and von Frey. Initially, some mice received a 20-mg/kg loading dose followed by 10 mg/kg every 12 h. This regimen caused severe morbidity and mortality in 2 mice. Subsequently, this regimen was abandoned, and mice assigned to the high-dose group received 10 mg/kg every 12 h. Mice that received the 10-mg/kg dose after surgery showed less orbital tightening between 3 to 6 h and reduced frequency of hunched posture for 48 h compared with mice that received either the low-dose or saline. However, mice were significantly less mobile for 6 to 12 h after surgery regardless of treatment. These data indicate that a meloxicam dose of 10 mg/kg every 12 h provides better analgesia than a 2.5-mg/kg dose but does not completely alleviate pain.

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.

Assessment of the Safety and Efficacy of Pre-emptive Use of Extended-release Buprenorphine for Mouse Laparotomy

Buprenorphine is commonly used to control postoperative pain in rodents. Short-acting formulations of buprenorphine (bup-HCl) require frequent handling and restraint of animals for appropriate dosing, which can be stressful and confound research outcomes. Ethiqa XR (bup-ER) is an FDA-indexed extended-release buprenorphine formulation that is an alternative to bup-HCl in mice and rats. In the current study, we first evaluated the pharmacokinetics of bup-ER in male C57BL/6J mice by sampling blood at 10 time points, ranging from 30 min to 72 h after administration (n = 3 mice per time point). Average plasma concentrations fell below therapeutic levels at 48 h after administration. We also evaluated the safety of bup-ER when administered prior to surgery in combination with common anesthetics and the efficacy of bup-ER in mouse laparotomy. Anesthetic safety was studied by measuring respiratory rate, rectal temperature, and recovery time in groups of mice (n = 8) given bup-HCl, bup-ER, or saline in combination with isoflurane or ketamine-xylazine anesthesia. No differences were seen between analgesic treatment groups with either of the general anesthetics. To evaluate efficacy, mice (n = 10) were randomly allocated to receive either bup-ER (3.25 mg/kg) once presurgically, bup-HCl (0.1 mg/kg) presurgically and then every 8 h, or saline once before surgery. Mice underwent a sham laparotomy and were assessed for pain based on changes in weight, cageside ethogram, nesting consolidation test, rearing frequency, and nociception to von Frey testing at 6, 12, 24, 48, and 72 h after surgery. Cageside ethogram, rearing frequency, and von Frey testing showed significant differences between bup-ER-treated mice and saline controls in the early postoperative period. No significant effects between treatment groups were seen in daily weights or nesting consolidation scores. This study demonstrates that bup-ER can be safely administered before surgery and provides analgesia for up to 48 h after administration based on pharmacokinetic and behavioral data.

Validation of the rabbit pain behaviour scale (RPBS) to assess acute postoperative pain in rabbits (Oryctolagus cuniculus)

Considering the widespread use of rabbits in research that potentially causes pain and discomfort and the limited number of pain assessment validated tools in this species, we aimed to develop and validate a scale of acute postoperative pain in rabbits (RPBS). Footage of 58 rabbits from previous studies were used, recorded at 'baseline' (before orthopaedic and soft tissue surgeries), 'pain' (after surgery), 'analgesia' (after analgesic), and '24h post' (24 hours after surgery). The videos were randomised and assessed twice by four evaluators, within one-month interval between evaluations. After content validation, RBPS was further refined using the criteria from the validation. According to the principal component analysis, RPBS was considered unidimensional. The intra- and inter-observer reliability was excellent (ICC>0.80) for all evaluators. There was a high Spearman's correlation of the RPBS with unidimensional scales (>0.80) and a moderate correlation with the Rabbit Grimace Scale (0.68), confirming criterion validity. According to the mixed linear model, the scale was responsive, shown by the increase in pain scores after surgery. Construct validity was confirmed by known-group approach and internal relationships among items. Adequate item-total correlation (>0.3) was observed for all items, except for the attention to the affected area (0.04). The internal consistency was very good (Cronbach's α coefficient = 0.78; Mcdonald's ω coefficient = 0.83). The cut-off score for rescue analgesia was ≥3, with an area under the curve >0.95, demonstrating a high discriminatory capacity of the instrument. Scores 3 and 4 were within the uncertainty diagnostic zone. Specificity was 87% and sensitivity was 90%. It was concluded that the RPBS presented content, criterion, and construct validities, responsiveness, and reliability to assess acute pain in rabbits submitted to orthopaedic and soft tissue surgeries. The cut-off for rescue analgesia serves as a basis for the administration of analgesics to rabbits submitted to painful procedures.

Burrowing behaviour of rats: Strain differences and applicability as well-being parameter after intracranial surgery

In mice, burrowing is considered a species-typical parameter for assessing well-being, while this is less clear in rats. This exploratory study evaluated burrowing behaviour in three rat strains during training and in the direct postoperative phase after complex intracranial surgery in different neuroscience rat models established at Hannover Medical School or Aachen University Hospital. Male Crl:CD (SD; n = 18), BDIX/UlmHanZtm (BDIX; n = 8) and RjHan:WI (Wistar; n = 35) rats were individually trained to burrow gravel out of a tube on four consecutive days. Thereafter, BDIX rats were subjected to intracranial injection of BT4Ca cells and tumour resection (rat glioma model), SD rats to injection of 6-hydroxydopamine (6-OHDA) or vehicle (rat Parkinson's disease model) and Wistar rats to endovascular perforation or sham surgery (rat subarachnoid haemorrhage (SAH) model). Burrowing was retested on the day after surgery. During training, BDIX rats burrowed large amounts (mean of 2370 g on the fourth day), while SD and Wistar rats burrowed less gravel (means of 846 and 520 g, respectively). Burrowing increased significantly during training only in Wistar rats. Complex surgery, that is, tumour resection (BDIX), 6-OHDA injection (SD) and endovascular perforation or sham surgery for SAH (Wistar) significantly reduced burrowing and body weight, while simple stereotactic injection of tumour cells or vehicle did not affect burrowing. Despite the training, burrowing differed between the strains. In the direct postoperative phase, burrowing was reduced after complex surgery, indicating reduced well-being. Reduced burrowing was accompanied with postoperative weight loss, a validated and recognised quantitative measure for severity assessment.

Pharmacokinetics and Efficacy of a Long-lasting, Highly Concentrated Buprenorphine Solution in Rats

Buprenorphine (Bup) is an opioid analgesic that is commonly used in laboratory rodents to provide postoperative analgesia. However, dosing every 4 to 6 h is necessary to maintain an analgesic plasma concentration of the drug. A long lasting, highly concentrated veterinary formulation of Bup (LHC-Bup) has been used to provide prolonged analgesia in cats and nonhuman primates. In the current study, we evaluated the duration of efficacy of LHC-Bup to determine if this formulation would provide a similarly prolonged analgesia in rats. Drug concentrations were measured after subcutaneous injection of 0.5 mg/kg LHC-Bup in both male and female rats. Plasma levels were measured at 0.25, 0.5, 1, 2, 4, 8, 12, 24, 36, 48, and 72 h. Male and female rats had peak plasma levels of LHC-Bup at 90 ng/mL and 34 ng/mL, respectively, at 15 min after administration, with a steady decrease by 24 h to 0.7 ng/mL in males and 1.3 ng/mL in females. Mechanical pain tolerance was evaluated after LHC-Bup administration using a Randall-Selitto analgesiometer to assess paw withdrawal. Male rats had a significantly longer paw withdrawal time for up to 12 h after administration, and females had longer paw withdrawal times for up to 24 h. An experimental laparotomy model was then used to assess the clinical efficacy of LHC-Bup at 0.5 mg/kg. LHC-Bup treatment was associated with a greater total distance traveled, reduced time to retrieve a food treat, and reduced grooming from 3 to 12 h after surgery as compared with saline controls. Groups receiving LHC-Bup showed coprophagy whereas other rats did not. These results suggest that administering LHC-Bup at 0.5 mg/kg provides therapeutic plasma concentrations for 12 to 24 h after administration and analgesic efficacy for at least 12 h after dosing. As such, LHC-Bup is a suitable alternative to Bup-HCl.

Assessing the severity of laparotomy and partial hepatectomy in male rats-A multimodal approach

This study assessed the postoperative severity after three different visceral surgical interventions in rats by using objective parameters pertaining to various disciplines. The objective was to evaluate whether the degree of severity increases with the invasiveness of the intervention and whether this is in accordance with the EU Directive 2010/63. 136 adult male WistarHan rats were assigned to three groups: Sham-laparotomy (Sham) [7 days post-surgical survival time]; 50% partial hepatectomy (PH); 70% PH [PH groups with 1, 3, or 7 days post-surgical survival times]. Post-surgical severity assessment was performed via several multimodal assessment tools: I) model-specific score sheet focusing on body weight, general condition, spontaneous behavior, and the animals' willingness to move as well as on wound healing; II) Open Field tests evaluating the total distance and velocity an animal moved within 10 minutes and its rearing behavior during the test; III) telemetric data analyzing heart rate and blood pressure; and IV) analysis of blood (AST, ALT, and hemogram) and fecal samples (fecal corticosterone metabolites). Significant differences among the experimental groups and models were observed. We demonstrated that the Open Field test can detect significant changes in severity levels. Sham-laparotomy and removal of 50% of the liver mass were associated with comparable severity (mild-moderate); the severity parameters returned to baseline levels within seven days. Removal of 70% of the liver tissue seemed to be associated with a moderate severity grade and entailed a longer recovery period (>7 days) for complete regeneration. We recommend the use of Open Field tests as part of multimodal objective severity assessment.

A novel excisional wound pain model for evaluation of analgesics in rats

Background

Management of pain from open wounds is a growing unmet healthcare need. However, the models available to study pain from wounds or to develop analgesics for the patients suffering from them have primarily relied on incisional models. Here, we present the first characterized and validated model of open wound pain.

Methods

Unilateral full-skin excisional punch biopsy wounds on rat hind paws were evaluated for evoked pain using withdrawal responses to mechanical and thermal stimulation, and spontaneous pain was measured using hind paw weight distribution and guarding behavior. Evaluations were done before wounding (baseline) and 2-96 hours post-wounding. The model was validated by testing the effects of buprenorphine and carprofen.

Results

Pain responses to all tests increased within 2 hours post-wounding and were sustained for at least 4 days. Buprenorphine caused a reversal of all four pain responses at 1 and 4 hours post-treatment compared to 0.9% saline (P < 0.001). Carprofen decreased the pain response to thermal stimulation at 1 (P ≤ 0.049) and 4 hours (P < 0.011) post-treatment compared to 0.9% saline, but not to mechanical stimulation.

Conclusions

This is the first well-characterized and validated model of pain from open wounds and will allow study of the pathophysiology of pain in open wounds and the development of wound-specific analgesics.

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.

Carprofen Permeation Test through Porcine Ex Vivo Mucous Membranes and Ophthalmic Tissues for Tolerability Assessments: Validation and Histological Study

Carprofen (CP), a non-steroidal anti-inflammatory drug (NSAID), is profusely used in veterinary medicine for its analgesic and anti-inflammatory activity. Some undesirable effects are associated with its systemic administration. Alternative local routes are especially useful to facilitate its administration in animals. The main aim of this paper is to validate the suitability of ex vivo permeation experiments of CP with porcine mucous membranes (buccal, sublingual and vaginal) and ophthalmic tissues (cornea, sclera and conjunctiva) intended to be representative of naïve in vivo conditions. Chromatographic analysis of CP in membrane-permeated samples and drug-retained have been validated following standard bioanalytical guidelines. Then, recovery levels of drugs in tissue samples were assessed with aqueous phosphate buffered saline (PBS) buffer to preserve the histological integrity. Finally, as a proof of concept, a series of CP permeation tests in vertical Franz diffusion cells has been performed to evaluate permeation flux and permeability constants in all tissues, followed by a histological study for critical evaluation. Furthermore, synthetic tissue retention-like samples were prepared to verify the value of this experimental study. Results show linear relationships with good determination coefficient (R² > 0.998 and R² > 0.999) in the range of 0.78 to 6.25 mg/mL and 3.125 mg/mL to 100 mg/mL, respectively. Low limits of quantification around 0.40 µg/mL were allowed to follow permeation levels until a minimum of 0.40% of the locally-applied dose. This method showed a good accuracy and precision with values lower than 2%. After the recovery technique, reproducible values below 30% were achieved in all tissues, suggesting it is a non-damaging method with low efficiency that requires the use of further solvents to enhance the extraction percentages. After permeation and histology tests, no relevant peak interferences were detected, and no cell or tissue damage was found in any tissue. In conclusion, results demonstrate the suitability of this test to quantify the distribution of CP with good histological tolerability.

Ex Vivo Permeation of Carprofen Vehiculated by PLGA Nanoparticles through Porcine Mucous Membranes and Ophthalmic Tissues

(1) Background: Carprofen (CP), 2-(6-chlorocarbazole) propionic acid, is used as an anti-inflammatory, analgesic and anti-pyretic agent and it belongs to the family of non-steroidal anti-inflammatory drugs (NSAIDs). CP has some adverse reactions in systemic administration; for this reason, topical administration with CP nanoparticles (CP-NPs) can be an optimal alternative. The main objective of this work is the investigation of ex vivo permeation of CP through different types of porcine mucous membranes (buccal, sublingual and vaginal) and ophthalmic tissues (cornea, sclera and conjunctiva) to compare the influence of CP-NPs formulation over a CP solution (CP-Solution). (2) Methods: The ex vivo permeation profiles were evaluated using Franz diffusion cells. Furthermore, in vivo studies were performed to verify that the formulations did not affect the cell structure and to establish the amount retained (Qr) in the tissues. (3) Results: Permeation of CP-NPs is more effective in terms of drug retention in almost all tissues (with the exception of sclera and sublingual). In vivo studies show that neither of the two formulations affects tissue structure, so both formulations are safe. (4) Conclusions: It was concluded that CP-NPs may be a useful tool for the topical treatment of local inflammation in veterinary and human medicine.

A Review of Pain Assessment Methods in Laboratory Rodents

Ensuring that laboratory rodent pain is well managed underpins the ethical acceptability of working with these animals in research. Appropriate treatment of pain in laboratory rodents requires accurate assessments of the presence or absence of pain to the extent possible. This can be challenging some situations because laboratory rodents are prey species that may show subtle signs of pain. Although a number of standard algesiometry assays have been used to assess evoked pain responses in rodents for many decades, these methods likely represent an oversimplification of pain assessment and many require animal handling during testing, which can result in stress-induced analgesia. More recent pain assessment methods, such as the use of ethograms, facial grimace scoring, burrowing, and nest-building, focus on evaluating changes in spontaneous behaviors or activities of rodents in their home environments. Many of these assessment methods are time-consuming to conduct. While many of these newer tests show promise for providing a more accurate assessment of pain, most require more study to determine their reliability and sensitivity across a broad range of experimental conditions, as well as between species and strains of animals. Regular observation of laboratory rodents before and after painful procedures with consistent use of 2 or more assessment methods is likely to improve pain detection and lead to improved treatment and care-a primary goal for improving overall animal welfare.

Clinical Management of Pain in Rodents

The use of effective regimens for mitigating pain remain underutilized in research rodents despite the general acceptance of both the ethical imperative and regulatory requirements intended to maximize animal welfare. Factors contributing to this gap between the need for and the actual use of analgesia include lack of sufficient evidence-based data on effective regimens, under-dosing due to labor required to dose analgesics at appropriate intervals, concerns that the use of analgesics may impact study outcomes, and beliefs that rodents recover quickly from invasive procedures and as such do not need analgesics. Fundamentally, any discussion of clinical management of pain in rodents must recognize that nociceptive pathways and pain signaling mechanisms are highly conserved across mammalian species, and that central processing of pain is largely equivalent in rodents and other larger research species such as dogs, cats, or primates. Other obstacles to effective pain management in rodents have been the lack of objective, science-driven data on pain assessment, and the availability of appropriate pharmacological tools for pain mitigation. To address this deficit, we have reviewed and summarized the available publications on pain management in rats, mice and guinea pigs. Different drug classes and specific pharmacokinetic profiles, recommended dosages, and routes of administration are discussed, and updated recommendations are provided. Nonpharmacologic tools for increasing the comfort and wellbeing of research animals are also discussed. The potential adverse effects of analgesics are also reviewed. While gaps still exist in our understanding of clinical pain management in rodents, effective pharmacologic and nonpharmacologic strategies are available that can and should be used to provide analgesia while minimizing adverse effects. The key to effective clinical management of pain is thoughtful planning that incorporates study needs and veterinary guidance, knowledge of the pharmacokinetics and mechanisms of action of drugs being considered, careful attention to individual differences, and establishing an institutional culture that commits to pain management for all species as a central component of animal welfare.

Concentration-dependent Toxicity after Subcutaneous Administration of Meloxicam to C57BL/6N Mice (Mus musculus)

Studies using the Mouse Grimace Scale have shown that for many NSAID, including meloxicam, minimal doses of at least 20 mg/kg may be necessary to achieve adequate peri- and post-operative analgesia in mice. However, more data are needed to determine whether such NSAID doses exceed the threshold for gastrointestinal ulceration or induce other relevant pathology. We administered equal volumes of saline or injectable meloxicam (1 or 5 mg/mL) at a dose of 20 mg/kg SC to 20 young adult male and female C57BL/6N mice daily for 6 d and performed necropsies on all mice on the seventh day. Mice given 5 mg/mL meloxicam subcutaneously developed significantly more severe pathology at the injection site than saline controls. Pathology was characterized by full-thickness epidermal necrosis; cavitary lesions within subcutis, muscle, or fat; steatitis; and myositis. Mice that received 1 mg/mL meloxicam subcutaneously developed lesions that were qualitatively similar but far less severe than those after 5 mg/mL. However, no pathologic lesions typically associated with NSAID toxicity, such as gastric ulceration and liver and kidney lesions, were seen. These results demonstrate that although meloxicam injected subcutaneously causes concentration-dependent skin pathology at the injection site, a dose of 20 mg/kg can be safely administered subcutaneously at a concentration of 1 mg/mL for as long as 6 d.

Benefits of non-invasive methods compared to telemetry for distress analysis in a murine model of pancreatic cancer

Prospective severity assessment is legally required in many countries to ensure high-quality research along with high welfare standards for laboratory animals. Mice and rats, the most common laboratory species, are prey animals that usually suppress signs of pain and suffering. Therefore, highly sensitive readout parameters are necessary to adequately quantify distress. The present study compared the performance of different non-invasive methods in determining animal distress, such as measuring body weight, distress score, faecal corticosterone metabolites, burrowing, and nesting behaviour, with continuous monitoring of heart rate, body temperature and activity by telemetry. The distress caused by two surgical interventions was compared and the burden caused by tumour growth was described. Transmitter implantation caused higher distress than laparotomy plus carcinoma cell injection into the pancreas. Surprisingly, no significant increase in distress was observed during tumour growth. The receiver operating characteristic curve analysis revealed that some non-invasive distress-parameters, i.e., distress-score and burrowing activity, exhibited slightly better performance to quantify distress than the most suitable parameters measured by telemetry. Due to the high burden caused by the implantation of the telemetric device, the use of non-invasive methods to assess distress in laboratory animals after surgical interventions should be favoured in future studies.

Comparing the Rat Grimace Scale and a composite behaviour score in rats

There is a growing interest in the use of voluntarily displayed ongoing behaviours in laboratory animals to assess the pain experience. In rats, two behavioural pain scales, the Rat Grimace Scale (RGS, a facial expression scale) and a composite behaviour score (CBS, a behavioural ethogram reliant on postural changes), are both promising pain assessment methods. Both scales have been used to assess pain in a laparotomy model, however, they have never been compared directly and the knowledge of how different analgesics may affect these two scales is limited. This study aimed to provide a comparison to discriminate the temporal and analgesic response in a laparotomy model. Female Wistar (n = 26) and Sprague Dawley rats (n = 26) were block randomized to receive saline, meloxicam (2 mg/kg) or buprenorphine (0.05 mg/kg) 30 minutes before laparotomy. Rats were video-recorded before surgery (BL) and at 30, 150, 270, and 390 minutes post-operatively. Videos were assessed according to both scales by a trained, blinded observer. Both CBS and RGS scores increased significantly at all post surgical timepoints in the saline group. Both buprenorphine and meloxicam reduced CBS scores to baseline levels following laparotomy; however, RGS scores were only reduced following buprenorphine. RGS scores in the meloxicam group remained similar to scores of the saline group. These findings suggest that the CBS and RGS differ in their sensitivity to discriminating analgesic effects.

Evaluation of Analgesic Efficacy of Meloxicam and 2 Formulations of Buprenorphine after Laparotomy in Female Sprague-Dawley Rats

Managing postoperative pain in rodents is an important part of any animal care and use program, and identifying an optimal analgesic plan for a surgical procedure is critical to providing for animal welfare. Opioids and NSAID are commonly used in rodents, but few studies have evaluated their efficacy in surgical models. The current study aimed to evaluate the therapeutic efficacy of clinically relevant doses of buprenorphine (2 formulations) or meloxicam used in combination with ketamine and xylazine anesthesia in a Sprague-Dawley rat ovariohysterectomy surgical model. Rats received either subcutaneous saline once daily for 3 d, low-dose (0.05 mg/kg SC) or high-dose (0.1 mg/kg SC) buprenorphine twice daily for 3 d, a single injection of sustained-release buprenorphine (1.2 mg/kg SC), or low-dose (1 mg/kg SC) or high-dose (2 mg/kg SC) meloxicam once daily for 3 d. Clinical analgesic efficacy was assessed over 8 d according to cageside observation scoring, body weight, and behavioral testing. Ovariohysterectomy was associated with 2 d of postoperative pain, and all 3 buprenorphine dosing strategies and both doses of meloxicam demonstrated varying amounts of analgesia. Given the results of the current study, we recommend 0.05 mg/kg SC buprenorphine at least twice daily or a single dose of 1.2 mg/kg SC of sustained-release buprenorphine for rats undergoing midline laparotomy with ovariohysterectomy. Alternatively, meloxicam at 1 to 2 mg/kg SC once daily could be used for this indication.

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.

Recommendation for severity assessment following liver resection and liver transplantation in rats: Part I

Score sheets were first introduced 30 years ago to assess pain, distress and suffering in animals. To date, however, there is still no general agreement on their use in research practice, and only a few publications can be found on this topic. In the present work, we demonstrate the use of a special score sheet for severity assessment in the first three postoperative days in two showcased studies performed on Wistar and Lewis rats undergoing liver resection or orthotopic liver transplantation, respectively. Scoring of different criteria and the total score were evaluated within each intervention. Additionally, both procedures were compared regarding their degree of severity. Suitability of these score sheets was evaluated for assessing severity of the procedures and these showed a minor severity within each investigated study. A comparison of both studies showed slightly higher scores involving liver transplantation. In contradiction to the common classification of these procedures as a moderate severity grade the score sheets applied here indicates a minor severity grade within each investigated study. Also, limitations and possible improvements in the design of our score sheets for defined interventions are reconsidered.

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.

Efficacy of Intrathecal Morphine in a Model of Surgical Pain in Rats

Concerns over interactions between analgesics and experimental outcomes are a major reason for withholding opioids from rats undergoing surgical procedures. Only a fraction of morphine injected intravenously reaches receptors responsible for analgesia in the central nervous system. Intrathecal administration of morphine may represent a way to provide rats with analgesia while minimizing the amount of morphine injected. This study aimed to assess whether morphine injected intrathecally via direct lumbar puncture provides sufficient analgesia to rats exposed to acute surgical pain (caudal laparotomy).In an initial blinded, randomised study, pain-free rats received morphine subcutaneously (MSC, 3mg.kg-1, N = 6), intrathecally (MIT, 0.2mg.kg-1, N = 6); NaCl subcutaneously (NSC, N = 6) or intrathecally (NIT, N = 6). Previously validated pain behaviours, activity and Rat Grimace Scale (RGS) scores were recorded at baseline, 1, 2, 4 and 8h post-injection. Morphine-treated rats had similar behaviours to NaCl rats, but their RGS scores were significantly different over time and between treatments. In a second blinded study, rats (N = 28) were randomly allocated to one of the following four treatments (N = 7): MSC, 3mg.kg-1, surgery; MIT, 0.2mg.kg-1, surgery; NIT, surgery; NSC, sham surgery. Composite Pain Behaviours (CPB) and RGS were recorded as previously. CPB in MIT and MSC groups were not significantly different to NSC group. MSC and MIT rats displayed significantly lower RGS scores than NIT rats at 1 and 8h postoperatively. RGS scores for MIT and MSC rats were not significantly different at 1, 2, and 8h postoperatively. Intraclass correlation value amongst operators involved in RGS scoring (N = 9) was 0.913 for total RGS score. Intrathecal morphine was mostly indistinguishable from its subcutaneous counterpart, providing pain relief lasting up to 8 hours in a rat model of surgical pain. Further studies are warranted to clarify the relevance of the rat grimace scale for assessing pain in rats that have received opioid analgesics.

Evaluation of Using Behavioural Changes to Assess Post-Operative Pain in the Guinea Pig (Cavia porcellus)

To manage pain effectively in people and animals, it is essential to recognise when pain is present and to assess its intensity. Currently there is very little information regarding the signs of post-surgical pain or its management in guinea pigs. Studies from other rodent species indicate that behaviour-based scoring systems can be used successfully to detect pain and evaluate analgesic efficacy. This preliminary study aimed to establish whether behaviour-based scoring systems could be developed to assess post-surgical pain in guinea pigs. This prospective, randomised, placebo-controlled study used 16 guinea pigs, and evaluated changes in behaviour following either anaesthesia alone or anaesthesia and orchiectomy. Behaviour was assessed using a combination of manual and automated scoring of remotely obtained video footage. A small number of behaviours were identified that appeared to have high specificity for pain caused by orchiectomy. However, the behaviours were displayed infrequently. The most common was a change in posture from standing to recumbency, sometimes with one hind leg extended either to the side or behind the body. A composite behaviour score incorporating these abnormal behaviours differentiated between the effects of surgery and anaesthesia alone (p<0.0001), and between animals that received analgesia post-operatively compared to an untreated group (p<0.0001). Although behavioural changes occurred in these guinea pigs after orchiectomy, the changes were relatively subtle and the individual specific pain-related behaviours occurred infrequently. However, it may prove possible to develop a behaviour-based scoring system for routine use in this species using a combination of pain-related behaviours.

Real-time application of the Rat Grimace Scale as a welfare refinement in laboratory rats

Rodent grimace scales have been recently validated for pain assessment, allowing evaluation of facial expressions associated with pain. The standard scoring method is retrospective, limiting its application beyond pain research. This study aimed to assess if real-time application of the Rat Grimace Scale (RGS) could reliably and accurately assess pain in rats when compared to the standard method. Thirty-two male and female Sprague-Dawley rats were block randomized into three treatment groups: buprenorphine (0.03 mg/kg, subcutaneously), multimodal analgesia (buprenorphine [0.03 mg/kg] and meloxicam [2 mg/kg], subcutaneously), or saline, followed by intra-plantar carrageenan. Real-time observations (interval and point) were compared to the standard RGS method using concurrent video-recordings. Real-time interval observations reflected the results from the standard RGS method by successfully discriminating between analgesia and saline treatments. Real-time point observations showed poor discrimination between treatments. Real-time observations showed minimal bias (<0.1) and acceptable limits of agreement. These results indicate that applying the RGS in real-time through an interval scoring method is feasible and effective, allowing refinement of laboratory rat welfare through rapid identification of pain and early intervention.

Meloxicam prevents COX-2-mediated post-surgical inflammation but not pain following laparotomy in mice

BACKGROUND

Inflammation is thought to be a major contributor to post-surgical pain, so non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used analgesics. However, compared to rats, considerably less is known as to how successfully these prevent pain in mice.

METHODS

A fluorescent COX-2 selective probe was used for the first time to evaluate the post-surgical anti-inflammatory effects of meloxicam, and automated behaviour analyses (HomeCageScan; HCS), the Mouse Grimace Scale (MGS) and body weight changes to assess its pain-preventative properties. Groups of 8-9 BALB/c mice were subcutaneously injected with saline (0.3 mL) or meloxicam at (1, 5 or 20 mg/kg) 1 h before a 1.5-cm midline laparotomy. The probe or a control dye (2 mg/kg) was injected intravenously 3 h later. Imaging was used to quantify inflammation at 7, 24 and 48 h following surgery. HCS data and MGS scores were respectively obtained from video recordings and photographs before surgery and 24 h later.

RESULTS

Post-surgical inflammation was dose dependently reduced by meloxicam; with 5 or 20 mg/kg being most effective compared to saline. However, all mice lost weight, MGS scores increased and behavioural activity was reduced by surgery for at least 24 h with no perceivable beneficial effect of meloxicam on any of these potentially pain-associated changes.

CONCLUSIONS

Although meloxicam prevented inflammation, even large doses did not prevent post-laparotomy pain possibly arising due to a range of factors, including, but not limited to inflammation. MGS scoring can be applied by very naïve assessors and so should be effective for cage-side use.

Effects of acute chemotherapy-induced mucositis on spontaneous behaviour and the grimace scale in laboratory rats

Intestinal mucositis is a frequent side-effect of chemotherapy treatment. Many oncological research programs aim to identify novel treatments for this distressing condition, and these programs frequently use rat models. Little is known about the presence and progression of pain in these models and how this can best be treated by analgesic therapy. We used a number of behaviour-based methods of pain assessment to determine which tools were best suited for pain identification. Baseline measures for behavioural assessment, rat grimace score and sociability were determined through analysis of continuously recorded video data and an applied social interaction test ( n = 16). Mucositis was then induced by intraperitoneal injection of 5-fluorouracil (150 mg/kg) and further behavioural analyses undertaken. An assessment of enrichment interaction was also made by determining the mass of a plastic chew toy gnawed both pre- and post-chemotherapy injection. Behavioural scoring was performed 1, 6, 12, 24 and 48 h after injection, with facial expression being scored at the 12, 24 and 48 h time-points. Sociability testing was performed once during the post-injection period. No significant differences were found in grimace scores between baseline and later daily measures. Behaviours similar to those previously reported post-laparotomy were observed. Writhing, twitching and back-arching behaviours were most evident in rats affected by mucositis and were increased in frequency (respective P values: 0.002, 0.004 and 0.008) 48 h after chemotherapy injection compared with baseline, implying that pain onset occurred around this time-point. Social investigatory behaviour was also increased ( P = 0.002) following disease onset. Each day, rats post-5FU injection gnawed a greater percentage of their nylabone enrichment by weight than the saline-injected control rats ( P = 0.046). These data suggest that, of the tools tested, behavioural assessment scoring may find greatest utility in rodent models of intestinal mucositis and should be investigated further.

The conditioned place preference test for assessing welfare consequences and potential refinements in a mouse bladder cancer model

Most pre-clinical analgesic efficacy assays still involve nociceptive testing in rodents. This is despite concerns as to the relevance of these tests for evaluating the pain-preventative properties of drugs. More appropriate methods would target pain rather than nociception, but these are currently not available, so it remains unknown whether animal pain equates to the negatively affective and subjective/emotional state it causes in humans. Mouse cancer models are common despite the likelihood of substantial pain. We used Conditioned Place Preference (CPP) testing, assessments of thermal hyperalgesia and behaviour to determine the likelihood that MBT-2 bladder cancer impacts negatively on mouse welfare, such as by causing pain. There was no CPP to saline, but morphine preference in tumour bearing mice exceeded that seen in tumour-free controls. This occurred up to 10 days before the study end-point alongside reduced body weight, development of hyperalgesia and behaviour changes. These effects indicated mice experienced a negative welfare state caused by malaise (if not pain) before euthanasia. Due to the complexity of the assessments needed to demonstrate this, it is unlikely that this approach could be used for routine welfare assessment on a study-by-study basis. However, our results show mice in sufficiently similar studies are likely to benefit from more intensive severity assessment and re-evaluation of end-points with a view to implementing appropriate refinements. In this particular case, a refinement would have been to have euthanased mice at least 7 days earlier or possibly by provision of end-stage pain relief. CPP testing was found to be a helpful method to investigate the responses of mice to analgesics, possibly on a subjective level. These findings and those of other recent studies show it could be a valuable method of screening candidate analgesics for efficacy against cancer pain and possibly other pain or disease models.

P2X(7) receptor in the kidneys of diabetic rats submitted to aerobic training or to N-acetylcysteine supplementation [corrected]

Previous studies in our laboratory showed that N-acetylcysteine supplementation or aerobic training reduced oxidative stress and the progression of diabetic nephropathy in rats. The P2X₇ receptor is up-regulated in pathological conditions, such as diabetes mellitus. This up-regulation is related to oxidative stress and induces tissue apoptosis or necrosis. The aim of the present study is to assess the role of P2X₇ receptor in the kidneys of diabetic rats submitted to aerobic training or N-acetylcysteine supplementation. Diabetes was induced in male Wistar rats by streptozotocin (60 mg/kg, i.v.) and the training was done on a treadmill; N-acetylcysteine was given in the drinking water (600 mg/L). By confocal microscopy, as compared to control, the kidneys of diabetic rats showed increased P2×7 receptor expression and a higher activation in response to 2′(3′)-O-(4-benzoylbenzoyl) adenosine5'–triphosphate (specific agonist) and adenosine triphosphate (nonspecific agonist) (all p<0.05). All these alterations were reduced in diabetic rats treated with N-acetylcysteine, exercise or both. We also observed measured proteinuria and albuminuria (early marker of diabetic nephropathy) in DM groups. Lipoperoxidation was strongly correlated with P2X₇ receptor expression, which was also correlated to NO^•, thus associating this receptor to oxidative stress and kidney lesion. We suggest that P2X₇ receptor inhibition associated with the maintenance of redox homeostasis could be useful as coadjuvant treatment to delay the progression of diabetic nephropathy.

Psychometric assessment of the Rat Grimace Scale and development of an analgesic intervention score

Our limited ability to assess spontaneous pain in rodent models of painful human conditions may be associated with a translational failure of promising analgesic compounds in to clinical use. If measurement of spontaneous pain behaviours can be used to generate an analgesic intervention score their use could expand to guide the use of analgesics, as mandated by regulatory bodies and ethical and welfare obligations. One such measure of spontaneous pain, the Rat Grimace Scale (RGS), has recently been described and shown to exhibit reliability. However, reliability of measurement scores is context and content specific, and further testing required to assess translation to a heterogenous setting (different model, raters, environment). The objectives of this study were to perform reliability testing with the Rat Grimace Scale in a heterogenous setting and generate an analgesic intervention score for its use. In a randomised, blinded study, sixteen adult female rats received one of three analgesia treatments (0.05 mg/kg buprenorphine subcutaneously, 1 mg/kg meloxicam subcutaneously, 0.2 mg/kg oral buprenorphine in jelly) peri-operatively (telemetry unit implantation surgery). Rats were video-recorded (before, 1-6 and 12 hours post-operatively) and images collected for independent scoring by three blinded raters using the RGS, and five experts based on "pain/no pain" assessment. Scores were used to calculate inter- and intra-rater reliability with an intraclass correlation coefficient and generate an analgesic intervention score with receiver operating characteristic curve analysis. The RGS scores showed very good inter- and intra-rater reliability (0.85 [0.78-0.90 95% CI] and 0.83 [0.76-0.89], respectively). An analgesic intervention threshold of greater than 0.67 was determined. These data demonstrate that the RGS is a useful tool which can be successfully employed in a heterogenous setting, and has the potential to guide analgesic intervention.

Comparative effects of vasectomy surgery and buprenorphine treatment on faecal corticosterone concentrations and behaviour assessed by manual and automated analysis methods in C57 and C3H mice

Establishing effective cage-side pain assessment methods is essential if post-surgical pain is to be controlled effectively in laboratory animals. Changes to overall activity levels are the most common methods of assessment, but may not be the most appropriate for establishing the analgesic properties of drugs, especially in mice, due their high activity levels. Use of drugs that can affect activity (e.g. opioids) is also a problem. The relative merits of both manual and automated behaviour data collection methods was determined in two inbred mouse strains undergoing vasectomy following treatment with one of 2 buprenorphine dose rates. Body weights and the effects of surgery and buprenorphine on faecal corticosterone were also measured.

Surgery caused abnormal behaviour and reduced activity levels, but high dose buprenorphine caused such large-scale increases in activity in controls that we could not establish analgesic effects in surgery groups. Only pain-specific behaviour scoring using the manual approach was effective in showing 0.05 mg/kg buprenorphine alleviated post-vasectomy pain. The C57 mice also responded better to buprenorphine than C3H mice, indicating they were either less painful, or more responsive to its analgesic effects. C3H mice were more susceptible to the confounding effects of buprenorphine irrespective of whether data were collected manually or via the automated approach. Faecal corticosterone levels, although variable, were higher in untreated surgery mice than in control groups, also indicating the presence of pain or distress.

Pain-specific scoring was superior to activity monitoring for assessing the analgesic properties of buprenorphine in vasectomised mice. Buprenorphine (0.01 mg/kg), in these strains of male mice, for this procedure, provided inadequate analgesia and although 0.05 mg/kg was more effective, not completely so. The findings support the recommendation that analgesic dose rates should be adjusted in relation to the potential severity of the surgical procedure, the mouse strain, and the individual animals' response.

A comparison of abdominal and scrotal approach methods of vasectomy and the influence of analgesic treatment in laboratory mice

Vasectomized mice are needed in the production of genetically-modified animals. The BVAAWF/FRAME/RSPCA/UFAW Joint Working Group on Refinement recommended that vasectomy should be performed via an incision in the scrotal sac, rather than via laparotomy, arguing that the former could be less painful due to minimal tissue trauma. This study was undertaken to assess the validity of this recommendation. Mice underwent vasectomy via either abdominal or scrotal approach surgery. Mice were filmed for 15 min presurgery and at one, 24 and 48 h postsurgery. Data were obtained using automated behaviour recognition software (HomeCageScan). Meloxicam was administered either alone or combined with acetaminophen prior to surgery. A third group received only saline subcutaneously. Postsurgery behaviour changes were compared between groups at each time point. Exploratory behaviours such as rearing, walking and sniffing were most greatly reduced at one hour following surgery whereas the duration of grooming increased. By 48 h these changes had largely subsided. Results indicated mice undergoing scrotal approach surgery fared better at one hour postsurgery, but the magnitude of this was relatively insignificant compared with the overall effects of surgery. If the observed behaviour changes resulted from pain, results suggested there was no significant advantage of scrotal versus abdominal approach vasectomy. These and other recently obtained data on the effects of non-steroidal anti-inflammatory drugs (NSAIDs) in mice suggest considerably larger doses of these or more potent analgesics, more precise monitoring of surgical outcomes, or a combination of these factors are needed to determine the extent of pain experienced by mice undergoing vasectomy.

Standards for the use of animals in surgical research

Follow the ARRIVE guidelines

The effect of isoflurane anaesthesia and vasectomy on circulating corticosterone and ACTH in BALB/c mice

The use of blood corticosterone and faecal corticosterone metabolites as biomarkers of post-surgical stress and pain in laboratory animals has increased during the last decade. However, many aspects of their reliability in laboratory mice remain uninvestigated. This study investigated serum corticosterone and adrenocorticotropic hormone (ACTH) in mice subjected to isoflurane anaesthesia and vasectomy, and mice subjected to isoflurane anaesthesia without surgery. Serum levels of corticosterone and ACTH after pre-treatment with dexamethasone were analysed to provide further information about the stress hormone profiles. Vasectomy resulted in an increase in corticosterone for at least four hours after surgery with a peak 30min after the mice regained righting reflex. Mice subjected to isoflurane anaesthesia without surgery had the highest level of serum corticosterone 5min after regained righting reflex and the level returned to baseline levels four hours after the procedure. In vasectomised mice, treated with dexamethasone, high levels of corticosterone remained 30min after the procedure, whereas the anaesthetised mice, treated with dexamethasone, had significantly lower levels of corticosterone compared to anaesthetised mice not treated with dexamethasone. Thus, dexamethasone effectively inhibited the corticosterone response in the anaesthetised-only mice, but not in the mice subjected to surgery. In conclusion, both isoflurane anaesthesia and vasectomy during isoflurane anaesthesia resulted in an increase in serum glucocorticoids, but the negative feedback mechanism of newly operated mice, was altered. This may have consequences for the interpretation of glucocorticoids measurements as a biomarker of post-surgical stress in mice.

Optimizing the dosing interval of buprenorphine in a multimodal postoperative analgesic strategy in the rat: minimizing side-effects without affecting weight gain and food intake

Buprenorphine is commonly used as (part of) postoperative analgesic treatment with dosage dependent side-effects such as pica behaviour. No strict consensus exists about the optimal dosing interval of buprenorphine, as its duration of action has been described as being in the range of 6–12 h. In this study, dosing intervals of 8 h (thrice-a-day) and 12 h (twice-a-day) for buprenorphine in a multimodal analgesic strategy (concurrent administration of a non-steroidal anti-inflammatory drug) were compared on food intake, weight and side-effects (gnawing on plastic Petri dishes and growth rate, indicative of pica behaviour) in rats. The food intake and weight of both intervals were comparable, as the animals from the twice-a-day group did not lose more weight or consumed less food during the analgesic period. The rats from the thrice-a-day group suffered from more side-effects, as the growth rate was decreased and more plastic was gnawed on. It is recommended to carefully evaluate analgesic and side-effects when using buprenorphine. When side-effects are observed, the possibility of increasing the dosing interval of buprenorphine should be explored. In this study, increasing the dosing interval of buprenorphine in a multimodal analgesic regimen resulted in reduced unwanted side-effects, without increasing weight loss or decreasing food intake. Although this is suggestive of provision of comparable analgesia, future studies including more pain-related readout parameters to assess the effect of the dosing interval on analgesic efficacy are recommended.

Evaluation of EMLA cream for preventing pain during tattooing of rabbits: changes in physiological, behavioural and facial expression responses

BACKGROUND

Ear tattooing is a routine procedure performed on laboratory, commercial and companion rabbits for the purpose of identification. Although this procedure is potentially painful, it is usually performed without the provision of analgesia, so compromising animal welfare. Furthermore, current means to assess pain in rabbits are poor and more reliable methods are required. The objectives of this study were to assess the physiological and behavioural effects of ear tattooing on rabbits, evaluate the analgesic efficacy of topical local anaesthetic cream application prior to this procedure, and to develop a scale to assess pain in rabbits based on changes in facial expression.

METHODOLOGY/PRINCIPAL FINDINGS

In a crossover study, eight New Zealand White rabbits each underwent four different treatments of actual or sham ear tattooing, with and without prior application of a topical local anaesthetic (lidocaine/prilocaine). Changes in immediate behaviour, heart rate, arterial blood pressure, serum corticosterone concentrations, facial expression and home pen behaviours were assessed. Changes in facial expression were examined to develop the Rabbit Grimace Scale in order to assess acute pain. Tattooing without EMLA cream resulted in significantly greater struggling behaviour and vocalisation, greater facial expression scores of pain, higher peak heart rate, as well as higher systolic and mean arterial blood pressure compared to all other treatments. Physiological and behavioural changes following tattooing with EMLA cream were similar to those in animals receiving sham tattoos with or without EMLA cream. Behavioural changes 1 hour post-treatment were minimal with no pain behaviours identifiable in any group. Serum corticosterone responses did not differ between sham and tattoo treatments.

CONCLUSIONS

Ear tattooing causes transient and potentially severe pain in rabbits, which is almost completely prevented by prior application of local anaesthetic cream. The Rabbit Grimace Scale developed appears to be a reliable and accurate way to assess acute pain in rabbits.

High-frequency electroacupuncture versus carprofen in an incisional pain model in rats

The objective of the present study was to compare the effect of electroacupuncture (EA) and carprofen (CP) on postoperative incisional pain using the plantar incision (PI) model in rats. A 1-cm longitudinal incision was made through skin, fascia and muscles of a hind paw of male Wistar rats and the development of mechanical and thermal hypersensitivity was determined over 4 days using the von Frey and Hargreaves methods, respectively. Based on the experimental treatments received on the third postoperative day, the animals were divided into the following groups: PI+CP (CP, 2 mg/kg, po); PI+EAST36 (100-Hz EA applied bilaterally at the Zusanli point (ST36)); PI+EANP (EA applied to a non-acupoint region); PI+IMMO (immobilization only); PI (vehicle). In the von Frey test, the PI+EAST36 group had higher withdrawal force thresholds in response to mechanical stimuli than the PI, PI+IMMO and PI+EANP groups at several times studied. Furthermore, the PI+EAST36 group showed paw withdrawal thresholds in response to mechanical stimuli that were similar to those of the PI+CP group. In the Hargreaves test, all groups had latencies higher than those observed with PI. The PI+EAST36 group was similar to the PI+IMMO, PI+EANP and PI+CP groups. We conclude that 100-Hz EA at the ST36 point, but not at non-acupoints, can reduce mechanical nociception in the rat model of incisional pain, and its effectiveness is comparable to that of carprofen.

The assessment of post-vasectomy pain in mice using behaviour and the Mouse Grimace Scale

BACKGROUND

Current behaviour-based pain assessments for laboratory rodents have significant limitations. Assessment of facial expression changes, as a novel means of pain scoring, may overcome some of these limitations. The Mouse Grimace Scale appears to offer a means of assessing post-operative pain in mice that is as effective as manual behavioural-based scoring, without the limitations of such schemes. Effective assessment of post-operative pain is not only critical for animal welfare, but also the validity of science using animal models.

METHODOLOGY/PRINCIPAL FINDINGS

This study compared changes in behaviour assessed using both an automated system ("HomeCageScan") and using manual analysis with changes in facial expressions assessed using the Mouse Grimace Scale (MGS). Mice (n = 6/group) were assessed before and after surgery (scrotal approach vasectomy) and either received saline, meloxicam or bupivacaine. Both the MGS and manual scoring of pain behaviours identified clear differences between the pre and post surgery periods and between those animals receiving analgesia (20 mg/kg meloxicam or 5 mg/kg bupivacaine) or saline post-operatively. Both of these assessments were highly correlated with those showing high MGS scores also exhibiting high frequencies of pain behaviours. Automated behavioural analysis in contrast was only able to detect differences between the pre and post surgery periods.

CONCLUSIONS

In conclusion, both the Mouse Grimace Scale and manual scoring of pain behaviours are assessing the presence of post-surgical pain, whereas automated behavioural analysis could be detecting surgical stress and/or post-surgical pain. This study suggests that the Mouse Grimace Scale could prove to be a quick and easy means of assessing post-surgical pain, and the efficacy of analgesic treatment in mice that overcomes some of the limitations of behaviour-based assessment schemes.

Predictive validity of behavioural animal models for chronic pain

Rodent models of chronic pain may elucidate pathophysiological mechanisms and identify potential drug targets, but whether they predict clinical efficacy of novel compounds is controversial. Several potential analgesics have failed in clinical trials, in spite of strong animal modelling support for efficacy, but there are also examples of successful modelling. Significant differences in how methods are implemented and results are reported means that a literature-based comparison between preclinical data and clinical trials will not reveal whether a particular model is generally predictive. Limited reports on negative outcomes prevents reliable estimate of specificity of any model. Animal models tend to be validated with standard analgesics and may be biased towards tractable pain mechanisms. But preclinical publications rarely contain drug exposure data, and drugs are usually given in high doses and as a single administration, which may lead to drug distribution and exposure deviating significantly from clinical conditions. The greatest challenge for predictive modelling is, however, the heterogeneity of the target patient populations, in terms of both symptoms and pharmacology, probably reflecting differences in pathophysiology. In well-controlled clinical trials, a majority of patients shows less than 50% reduction in pain. A model that responds well to current analgesics should therefore predict efficacy only in a subset of patients within a diagnostic group. It follows that successful translation requires several models for each indication, reflecting critical pathophysiological processes, combined with data linking exposure levels with effect on target.

Voluntary ingestion of buprenorphine in mice

Buprenorphine is a widely used analgesic for laboratory rodents. Administration of the drug in a desirable food item for voluntary ingestion is an attractive way to administer the drug non-invasively. However, it is vital that the animals ingest the buprenorphine-food-item mix as desired. The present study investigated how readily female and male mice (Mus musculus) of two different strains consumed buprenorphine mixed in a commercially available nut paste (Nutella®), and whether variation between genders and strains would affect the subsequent serum concentrations of buprenorphine. Buprenorphine at different concentrations mixed in Nutella® was given to male and female C57BL/6 and BALB/c mice in a complete cross-over study. Pure Nutella® or buprenorphine (1.0-3.0 mg kg−1 bodyweight [bw]) mixed in 10 g kg−1 bw Nutella® were given to the mice at 1500h. The mice were video recorded until the next morning, when blood was collected by submandibular venipuncture. The concentration of buprenorphine in the Nutella® mix did not affect the duration of ingestion in any of the groups. However, female mice consumed the Nutella® significantly faster than males. Repeated exposure significantly reduced the start time of voluntary ingestion, but not the duration of eating the mixture. These differences did not however affect the serum concentration of buprenorphine measured 17 h post administration.

Analgesic effects of tramadol, carprofen or multimodal analgesia in rats undergoing ventral laparotomy

In this study, the authors evaluated the analgesic efficacy of tramadol (an opioid-like analgesic), carprofen (a nonsteroidal anti-inflammatory drug) and a combination of both drugs (multimodal therapy) in a rat laparotomy model. The authors randomly assigned rats to undergo either surgery (abdominal laparotomy with visceral manipulation and anesthesia) or anesthesia only. Rats in each group were treated with tramadol (12.5 mg per kg body weight), carprofen (5 mg per kg body weight), a combination of tramadol and carprofen (12.5 mg per kg body weight and 5 mg per kg body weight, respectively) or saline (anesthesia control group only; 5 mg per kg body weight). The authors administered analgesia 10 min before anesthesia, 4 h after surgery or (for the rats that received anesthesia only) anesthesia and 24 h after surgery or anesthesia. They measured locomotor activity, running wheel activity, feed and water consumption, body weight and fecal corticosterone concentration of each animal before and after surgery. Clinical observations were made after surgery or anesthesia to evaluate signs of pain and distress. The authors found that carprofen, tramadol and a combination of carprofen and tramadol were all acceptable analgesia regimens for a rat laparotomy model.

Potential behavioural indicators of post-operative pain in male laboratory rabbits following abdominal surgery

This study aimed to identify behaviours that could be used to assess post-operative pain and analgesic efficacy in male rabbits. In consideration of the ‘Three Rs’, behavioural data were collected on seven male New Zealand White rabbits in an ethically approved experiment requiring abdominal implantation of a telemetric device for purposes other than behavioural assessment. Prior to surgery, rabbits were anaesthetised using an isoflurane/oxygen mix and given Carprofen (2 mg kg−1) as a peri-operative analgesic. Rabbits were housed individually in standard laboratory cages throughout. Data were collected at three time periods: 24-21 h prior to surgery (T1) and, post-surgery, 0-3 h (T2) and 3-6 h (T3). Behavioural changes were identified using Observer XT, significance of which was assessed using a Friedman's test for several related samples. The frequency or duration of numerous pre-operative behaviours was significantly reduced in T2 and T3, as compared to T1. Conversely, novel or rare behaviours had either first occurrence or significant increase in T2 into T3 as compared to T1, these include ‘full-body-flexing’, ‘tight-huddling’, ‘hind-leg-shuffling’. We conclude that reduced expression of common pre-operative behaviours and the appearance of certain novel post-operative behaviours may be indicative of pain in rabbits. Behaviours identified as increased in T2 as compared to T1 but not consistently elevated into T3 were considered separately due to the potentially confounding effect of anaesthesia recovery. These included lateral lying, ‘drawing-back’, ‘staggering’ and ‘closed eyes’. We postulate that for effective application of best-practice post-operative care, informed behavioural observation can provide routes by which carers may identify requirements for additional post-operative analgesia. Additionally, improvement of the peri-operative pain management regimen may be required to ameliorate the immediate effects of abdominal surgery. Comparisons with other studies into post-operative pain expression in rabbits suggest behavioural indicators of pain may differ, depending on housing and surgical procedure.

Rodent analgesia

Rodents of all species are frequently kept as companion animals, with increasing client expectations for the care of their animals. Fortunately, specialist veterinary interest and information is now available for treatment of rodents. In the field of rodent analgesia particularly, much can be learned from the methods developed for preventing and alleviating pain in animals undergoing research studies in laboratories throughout the world. This article reviews advances in pain detection techniques in rodents and makes recommendations on analgesic agents that are available for the alleviation of pain.