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.

Effects of dexamethasone and acetylsalicylic acid on inflammation caused by Complete Freund's adjuvant in the naked mole rat (Heterocephalus glaber).

The naked mole rat (NMR) is a fossorial rodent that has been observed to have a unique nociceptive system in comparison to others. In this study, we explored on characterization of chronic inflammation in the NMR using Complete Freund's adjuvant (CFA) and investigated the effects of dexamethasone and acetylsalicylic acid on the resulting inflammation. The NMRs were injected with 0.1 ml of CFA subcutaneously in the right hind paw, and an equivalent volume of normal saline was injected to the control group. Swelling of the injected right hind limb was observed within 24 h of injection, which involved the tibiotarsal joint, palmar surface and the digits of the injected paw. Swelling persisted for 6 weeks of experimentation and peaked between day 14 and 21. The resulting inflammation affected the mobility, stance and joint rigidity of CFA treated NMRs in comparison to the control group. Treatment of the chronic phase of the inflammation from the 11th day with dexamethasone and acetylsalicylic acid showed no statistical significance in paw circumference compared to the control group, other than on a few, negligible occasions. The present data showed that CFA was able to induce chronic inflammation in the NMR, and the NMR could thus be established as a model for chronic inflammation. There is, however, need for more sensitive parameters to evaluate the effects of anti-inflammatory drugs.

The effects of clonidine and yohimbine in the tail flick and hot plate tests in the naked mole rat (Heterocephalus glaber).

OBJECTIVE: The naked mole rat (NMR) (Heterocephalus glaber) is increasingly considered an important biomedical research model for various conditions like hypoxic brain injury, cancer and nociception. This study was designed to investigate the effects of clonidine and yohimbine, an alpha-2 (α2) adrenoceptor agonist and antagonist respectively in the tail flick and hot plate tests. RESULTS: A significant difference in tail flick latency was noted between saline control and 30 µg/kg clonidine, which was reduced after administration of 30 µg/kg yohimbine. A significant difference in hot plate latency was also noted between saline control and 30 µg/kg clodinine during the periods 30, 45, 60, 75 and 90 min after administration, and between saline control and 10 µg/kg clonidine during 30 min after administration. The hot plate latency by 30 µg/kg clonidine was also reduced by 30 µg/kg yohimbine during 30 min after administration. Since the tail-flick and hot plate tests mediate the effects at spinal and supraspinal levels respectively, the present study indicates the presence and involvement of noradrenergic receptors in thermal antinociception at spinal and supraspinal levels of the NMR, similar to what has been found in other mammals.

Investigation of noradrenergic receptor system in anti-nociception using formalin test in the naked mole rat (Heterocephalus glaber).

The naked mole rat (NMR) is a rodent that has gained importance as a biomedical research model for various conditions like hypoxic brain injury, cancer and nociception. This study was designed to investigate possible involvement of the noadrenergic receptor system in antinoception in the NMR, using the alpha-2 adrenergic receptor specific ligands clonidine (agonist) and yohimbine (antagonist) in the formalin test. Formalin test followed 30 min after intraperitoneal administration of ligands or control. A total of 96 naked mole rats were used. A significant reduction in nociceptive behaviours was demonstrated after administration of clonidine in the doses 1,3,10 and 30 µg/kg (n = 8 per group). Doses of clonidine above 30 µg/kg caused loss of motor and proprietion skills exhibited by prostration and failure to turn over when placed on their backs. The antinociception by 3 µg/kg clonidine was reversed by administration of 30 µg/kg of yohimbine. The present study demonstrates that the noradrenergic receptor system is present and involved in formalin test-related antinociceptive mechanisms in the NMR, similar to other mammals. Given the increasing importance of the NMR as a model for pain and nociception, the species may prove useful as an animal model for noradrenergic mechanisms in pain modulation.

Modulation of formalin-induced pain-related behaviour by clonidine and yohimbine in the Speke's hinged tortoise (Kiniskys spekii).

The study was designed to investigate the involvement of noradrenergic and serotonergic receptor systems in the modulation of formalin-induced pain-related behaviour in the Speke's hinged tortoise. Intradermal injection of 100 µL of formalin at a dilution of 12.5% caused pain-related behaviour (hindlimb withdrawal) that lasted for a mean time of 19.28 min (monophasic response). Intrathecal administration of clonidine (α2 -adrenergic receptor agonist) and yohimbine (α2 -adrenergic receptor antagonist) at a dose of 40 µg/kg and 37.5 µg/kg or 50 µg/kg, respectively, caused a highly significant reduction in the duration of the formalin-induced pain-related behaviour. The effect of clonidine was reversed by intrathecal administration of yohimbine at a dose of 26.7 µg/kg. The effect of yohimbine at a dose of 50 µg/kg was reversed by intrathecal injection of 20 µg/kg of the serotonergic receptor antagonist methysergide maleate. When performing antagonistic reactions, the administration of the antagonist was followed immediately by that of the agonist. The study indicates that for experimental purposes, intrathecal route of drug administration through the atlanto-occipital joint is effective in tortoises. The data also suggest that testudines have noradrenergic and serotonergic systems that appear to play a role in the modulation of pain in this species.

Correlations between serum levels of beta amyloid, cerebrospinal levels of tau and phospho tau, and delayed response tasks in young and aged cynomolgus monkeys (Macaca fascicularis).

BACKGROUND: In an attempt to explore cynomolgus monkeys as an animal model for Alzheimer's disease, the present study focused on the Alzheimer's biomarkers beta amyloid 1-42 (Aß42 ) in serum, and total tau (t-tau) and phosphorylated tau (p-tau) levels in cerebrospinal fluid. METHODS: We measured biomarker levels in Young and Aged cynomolgus monkeys and correlated these with performance on three delayed response tasks. RESULTS: The Aß42 concentration of the Aged monkeys was significantly lower than in the Young subjects, while the t-tau and p-tau did not significantly differ between the groups. The Young subjects performed significantly better than the Aged individuals on the memory tests. Only Aß42 levels were significantly correlated with performance in the three delayed response tasks. CONCLUSIONS: Circulating Aß42 levels were lower in Aged monkeys and were correlated with inferior performance on delayed response tasks in Aged animals; therefore, both measures may be useful in establishing cynomolgus monkeys as models for studies of AD.

Effects of opioids in the formalin test in the Speke's hinged tortoise (Kinixy's spekii).

Little is known about analgesia in lower vertebrates such as the Speke's hinged tortoise (Kinixy's spekii), yet of late they are increasingly being adopted as pets. The effects of morphine (5, 7.5, 10 and 20 mg/kg), pethidine (10, 20, and 50 mg/kg) and naloxone (5 mg/kg) on nociception induced by the formalin test (12.5%, 100 microL) were studied in the Speke's hinged tortoise. Formalin induced a monophasic limb retraction behavioural response and its duration was recorded. The behaviour lasted for 16.4 +/- 0.8 min. Morphine (7.5, 10 and 20 mg/kg) and pethidine (20 and 50 mg/kg) induced significant decrease in the duration of limb retraction in the formalin test. The anti-nociceptive effects were naloxone (5 mg/kg) reversible. The data suggest that the formalin test is a good test for studying nociception and anti-nociception in tortoises and that the opioidergic system plays a role in the control of nociception in these animals.

Impact of surgical severity and analgesic treatment on plasma corticosterone in rats during surgery.

Tissue injury and anaesthesia during surgery induce a stress response associated with increased glucocorticoid secretion from the adrenal glands. This response alters the normal physiology and may cause postoperative morbidity, as well as affect the results during acute experiments. The aim of the present investigation was to study the effect of surgical severity and analgesic treatment on circulating corticosterone in male Sprague-Dawley rats. Male rats were treated with either lidocaine infiltrated during surgery, buprenorphine (0.05 or 0.1 mg/kg subcutaneously) or saline subcutaneously. Each treatment group was subjected to either arterial catheterisation or arterial catheterisation and laparotomy. A catheter was inserted in the common carotid artery and blood was collected during surgery and during anaesthesia 6 h after surgery. Lidocaine treatment reduced the corticosterone levels compared to saline treatment after catheterisation but not after laparotomy. Buprenorphine treatment reduced the corticosterone levels during the first hour after surgery after both catheterisation and laparotomy. The higher buprenorphine dose led to an earlier and more pronounced reduction, especially after laparotomy. In the present study, the corticosterone response during surgery in laboratory rats is correlated with the severity of the procedure, and buprenorphine reduces the surgical stress response more effectively than lidocaine treatment.

Reversal of ketamine/xylazine combination anesthesia by atipamezole in olive baboons (Papio anubis).

BACKGROUND: The potential of Atipamezole (ATI) to reverse Ketamine/Xylazine (KET/XYL) anesthesia in the Olive baboon (Papio anubis) was studied. METHODS: Anesthesia was induced with 10 mg/kg KET and 0.5 mg/kg XYL intramuscularly. Mean arousal time (MAT), heart rate (HR), systolic arterial blood pressure (SAP), rectal temperature, respiratory rate (RR), and hemoglobin oxygen saturation (SpO(2)) were monitored. Baboons were treated with: KET/XYL only, KET/XYL followed by 100 microg/kg ATI or by 200 microg/kg ATI administered 25 minutes after KET/XYL. RESULTS: Atipamezole rapidly reversed depressed HR and SAP (10 +/- 5.2 minutes), RR (5 +/- 2 minutes) and SpO(2) (3 +/- 6 minutes) and significantly decreased MAT (13 +/- 2.2 minutes) vs. KET/XYL alone (35 +/- 5 minutes). Emesis was absent and salivation was observed after administration of 200 microg/kg ATI only. CONCLUSIONS: Atipamezole at 100 microg/kg is sufficient for rapid and smooth reversal of KET/XYL anesthesia in the Olive baboon with minimal side effects.

Effect of subcutaneous injection and oral voluntary ingestion of buprenorphine on post-operative serum corticosterone levels in male rats.

BACKGROUND: Adequate peri-operative analgesia may reduce post-operative stress response and improve recovery in laboratory animals. We have established a method involving repeated automated blood sampling, allowing quantification of serum corticosterone levels in rats for stress assessment without stress-inducing handling or restraint. In the present study, the effects of the commonly used route of buprenorphine administration (0.05 mg/kg injected subcutaneously) were compared with oral administration (0.4 mg/kg mixed with Nutella and orally administered by voluntary ingestion) in male Sprague-Dawley rats. METHODS: A catheter was placed in the jugular vein and attached to an Accusampler for automated blood sampling. During 96 h after surgery, blood was collected at specified time points. Pre- and post-operative body weights and water consumption were registered. RESULTS: Buprenorphine significantly suppressed levels of circulating corticosterone after the oral but not after the subcutaneous treatment. Both buprenorphine treatments had a positive impact on maintenance of body weight and water consumption, compared to the control group that received no buprenorphine. CONCLUSION: The present investigation suggests that oral voluntary ingestion ad libitum is an efficacious, convenient and non-invasive way of administering peri-operative buprenorphine to rats, as judged by corticosteroid response and effects on body weight and water consumption.