Effects of buprenorphine on model development in an adjuvant-induced monoarthritis rat model

Complete Freund’s adjuvant (CFA)-induced arthritis in rats is a common animal model for studying chronic inflammatory pain. However, modelling of the disease is associated with unnecessary pain and impaired animal wellbeing, particularly in the immediate post-induction phase. Few attempts have been made to counteract these adverse effects with analgesics. The present study investigated the effect of buprenorphine on animal welfare, pain-related behaviour and model-specific parameters during the disease progression in a rat model of CFA-induced monoarthritis. The aim was to reduce or eliminate unnecessary pain in this model, in order to improve animal welfare and to avoid suffering, without compromising the quality of the model. Twenty-four male Sprague Dawley rats were injected with 20 μl of CFA into the left tibio-tarsal joint to induce monoarthritis. Rats were treated with either buprenorphine or carprofen for 15 days during the disease development, and were compared to a saline-treated CFA-injected group or a negative control group. Measurements of welfare, pain-related behaviour and clinical model-specific parameters were collected. The study was terminated after 3 weeks, ending with a histopathologic analysis. Regardless of treatment, CFA-injected rats displayed mechanical hyperalgesia and developed severe histopathological changes associated with arthritis. However, no severe effects on general welfare were found at any time. Buprenorphine treatment reduced facial pain expression scores, improved mobility, stance and lameness scores and it did not supress the CFA-induced ankle swelling, contrary to carprofen. Although buprenorphine failed to demonstrate a robust analgesic effect on the mechanical hyperalgesia in this study, it did not interfere with the development of the intended pathology

Choice of rat strain in pre-clinical pain-research – Does it make a difference for translation from animal model to human condition?

Abstract Aims Translating preclinical drug-efficacy of analgesics from animal models to humans has proven challenging with many failures. Reasons are likely multifaceted, but lack of sufficiently rigorous study design, and phenotypical relevant animal models may be part of the explanation. Chronic pain is often associated with substantial comorbid burden, consisting of changes in affective state and cognitive impairment amongst other behavioral disturbances. Accordingly, many preclinical pain research activities have started to include assessment of comorbidity as a possible experimental outcome measure, but surprisingly, little consideration has been paid to the influence of animal-related factors to pain models. To address this essential issue, we have embarked on several comparative experiments in different pain-models, comparing Sprague Dawley’s (SD) from two different vendors with different inbred rat strains (Lewis (LEW), Fisher (F344) and Wistar Kyoto (WKY)) selected based on reported stress, depression, inflammatory and pain phenotypes. Methods Male rats were characterized in acute (hot-plate), inflammatory (Complete Freund’s Adjuvant (CFA)) and neuropathic (Spared Nerve Injury (SNI)) pain models, with dose-response to morphine (0.3–6.0 mg/kg) in hot-plate, CFA-induced hyperalgesia, and a locomotor motility-assay (LMA). Results F344 and SD’s were sensitive to morphine in hotplate and CFA (Minimum Effective Dose (MED) = 3.0 mg/kg). WKY rats developed a less robust mechanical hypersensitivity after CFA injection, and were less sensitive to morphine in both pain-tests (MED = 6.0 mg/kg). LEW rats were completely insensitive to morphine in the hot plate, in contrast to reversal of CFA-induced hyperalgesia (MED = 3.0 mg/kg). Additionally, neuropathic sensitivity developed with a later onset and less robustly in this strain after SNI. All strains tested in LMA exhibited sedative effects at 3.0 mg/kg. Conclusions Sensory phenotyping in response to acute, inflammatory and neuropathic pain, and sensitivity to morphine in these strains indicates that different pathophysiological mechanisms are engaged after injury. This could have profound implications for translating preclinical drug discovery efforts into pain-patients. </jats:sec

The analgesic efficacy of morphine varies with rat strain and experimental pain model: implications for target validation efforts in pain drug discovery

BACKGROUND: Translating efficacy of analgesic drugs from animal models to humans remains challenging. Reasons are multifaceted, but lack of sufficiently rigorous preclinical study design criteria and phenotypically relevant models may be partly responsible. To begin to address this fundamental issue, we assessed the analgesic efficacy of morphine in three inbred rat strains (selected based on stress reactivity and affective/pain phenotypes), and outbred Sprague Dawley (SD) rats supplied from two vendors. METHODS: Sensitivity to morphine (0.3-6.0 mg/kg, s.c.) was evaluated in the hot plate test of acute thermal nociception, the Complete Freund's Adjuvant (CFA) model of inflammatory-induced mechanical hyperalgesia, and in a locomotor motility assay in male rats from the following strains; Lewis (LEW), Fischer (F344), Wistar Kyoto (WKY), and SD's from Envigo and Charles River. RESULTS: F344 and SD rats were similarly sensitive to morphine in hot plate and CFA-induced inflammatory hyperalgesia (Minimum Effective Dose (MED) = 3.0 mg/kg). WKY rats developed a less robust mechanical hypersensitivity after CFA injection, and were less sensitive to morphine in both pain tests (MED = 6.0 mg/kg). LEW rats were completely insensitive to morphine in the hot plate test, in contrast to the reversal of CFA-induced hyperalgesia (MED = 3.0 mg/kg). All strains exhibited a dose-dependent reduction in locomotor activity at 3.0-6.0 mg/kg. CONCLUSION: Sensory phenotyping in response to acute thermal and inflammatory-induced pain, and sensitivity to morphine in various inbred and outbred rat strains indicates that different pathophysiological mechanisms are engaged after injury. This could have profound implications for translating preclinical drug discovery efforts into pain patients. SIGNIFICANCE: The choice of rat strain used in preclinical pain research can profoundly affect the outcome of experiments in relation to (a) nociceptive threshold responses, and (b) efficacy to analgesic treatment, in assays of acute and tonic inflammatory nociceptive pain

Effects of buprenorphine on acute pain and inflammation in the adjuvant-induced monoarthritis rat model

Background and aim: Animal modelling of arthritis is often associated with pain and suffering. Severity may be reduced with the use of analgesia which is, however, often withheld due to concerns of introducing a confounding variable. It is therefore important to design and validate pain relief protocols that reduce pain without compromising the scientific objectives. The present study evaluated the effect of buprenorphine analgesia in the immediate post-induction period of an adjuvant-induced monoarthritic rat model. The aim of this study was to extend previous work on refinement of the model by alleviating unnecessary pain. Methods: Male and female Sprague Dawley rats were injected with 20 μl of complete Freund's adjuvant (CFA) into the left ankle. Rats were treated with buprenorphine, either injected subcutaneously or ingested voluntarily, and were compared to rats given subcutaneous injections with vehicle (saline or pure nut paste) or carprofen the first three days post CFA-injection. Measurements of welfare, clinical model-specific parameters and pain-related behaviour were assessed. Results: Buprenorphine, administered either subcutaneously (0.10 or 0.15 mg/kg, twice daily) or by voluntary ingestion in nut paste (1.0 or 3.0 mg/kg, twice daily), improved mobility, stance, rearing and lameness scores significantly 7 h post CFA-injection. Mechanical hyperalgesia peaked at 7 h and was significantly lower in buprenorphine-treated animals, compared to vehicle-treated animals. Joint circumference was highest 24–72 h after CFA injection. Animals treated with buprenorphine did not decrease in joint circumference, opposite carprofen treated animals. Conclusion: Buprenorphine, administered either subcutaneously or by voluntary ingestion, provides adequate analgesia for both sexes within the first 24 h post CFA-injection. Buprenorphine treatment improved clinical scores and appeared not to suppress the inflammatory response. The present study supports previous findings that voluntarily ingested buprenorphine is an effective alternative to repeated injections

Is there a reasonable excuse for not providing post-operative analgesia when using animal models of peripheral neuropathic pain for research purposes?

INTRODUCTION: The induction of neuropathic pain-like behaviors in rodents often requires surgical intervention. This engages acute nociceptive signaling events that contribute to pain and stress post-operatively that from a welfare perspective demands peri-operative analgesic treatment. However, a large number of researchers avoid providing such care based largely on anecdotal opinions that it might interfere with model pathophysiology in the longer term. // OBJECTIVES: To investigate effects of various peri-operative analgesic regimens encapsulating different mechanisms and duration of action, on the development of post-operative stress/welfare and pain-like behaviors in the Spared Nerve Injury (SNI)-model of neuropathic pain. // METHODS: Starting on the day of surgery, male Sprague-Dawley rats were administered either vehicle (s.c.), carprofen (5.0mg/kg, s.c.), buprenorphine (0.1mg/kg s.c. or 1.0mg/kg p.o. in Nutella®), lidocaine/bupivacaine mixture (local irrigation) or a combination of all analgesics, with coverage from a single administration, and up to 72 hours. Post-operative stress and recovery were assessed using welfare parameters, bodyweight, food-consumption, and fecal corticosterone, and hindpaw mechanical allodynia was tested for assessing development of neuropathic pain for 28 days. // RESULTS: None of the analgesic regimes compromised the development of mechanical allodynia. Unexpectedly, the combined treatment with 0.1mg/kg s.c. buprenorphine and carprofen for 72 hours and local irrigation with lidocaine/bupivacaine, caused severe adverse effects with peritonitis. This was not observed when the combination included a lower dose of buprenorphine (0.05mg/kg, s.c.), or when buprenorphine was administered alone (0.1mg/kg s.c. or 1.0mg/kg p.o.) for 72 hours. An elevated rate of wound dehiscence was observed especially in the combined treatment groups, underlining the need for balanced analgesia. Repeated buprenorphine injections had positive effects on body weight the first day after surgery, but depressive effects on food intake and body weight later during the first week. // CONCLUSION: Post-operative analgesia does not appear to affect established neuropathic hypersensitivity outcome in the SNI model

Applying refinement to the use of mice and rats in rheumatoid arthritis research

Rheumatoid arthritis (RA) is a painful, chronic disorder and there is currently an unmet need for effective therapies that will benefit a wide range of patients. The research and development process for therapies and treatments currently involves in vivo studies, which have the potential to cause discomfort, pain or distress. This Working Group report focuses on identifying causes of suffering within commonly used mouse and rat ‘models’ of RA, describing practical refinements to help reduce suffering and improve welfare without compromising the scientific objectives. The report also discusses other, relevant topics including identifying and minimising sources of variation within in vivo RA studies, the potential to provide pain relief including analgesia, welfare assessment, humane endpoints, reporting standards and the potential to replace animals in RA research

Voluntary ingestion of buprenorphine in mice

AbstractBuprenorphine 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.</jats:p

Drug distribution in spinal cord during administration with spinal loop dialysis probes in anaesthetized rats

The present investigation aimed to study two methodological concerns of an experimental model, where a spinal loop dialysis probe is used for administration of substances to the spinal cord and sampling of neurotransmitters by microdialysis from the same area of anaesthetized rats. [3H]Epibatidine in concentrations of 1, 10 and 100 nM was dissolved in Ringer's solution and administered through the dialysis membrane into the dorsal region of the cervical spinal cord. First, the outflow of [3H]epibatidine from the probe into the spinal cord was examined with respect to different concentrations and changes over time. Then, the distribution of the different [3H]epibatidine concentrations along the spinal cord was studied. It was found that the percentage of [3H]epibatidine entering the spinal cord did not differ between different administered concentrations after a stabilization period of 60 min. The administered [3H]epibatidine was found to be distributed to the area closest to the dialysis probe and not dispersed along the spinal cord, and the distribution was equal for all concentrations. The data presented in this investigation provide information, which is important for interpretation of data from intraspinal administration of substances through the spinal loop dialysis probe.</p