Antinociceptive Effects of Sustained-Release Buprenorphine in a Model of Incisional Pain in Rats (Rattus norvegicus)

Effective management of postoperative pain is an essential component of the care and welfare of laboratory animals. A sustained-release formulation of buprenorphine (Bup-SR) has recently been introduced to the veterinary market and has been reported to provide analgesia for as long as 72 h. Using evoked mechanical and thermal hypersensitivity tests, we here evaluated the antinociceptive effects of Bup-SR in a model of incisional pain in rats. Paw withdrawal responses were obtained before and 1 through 4 d after surgery. Rats are assigned to receive Bup-SR (0.3, 1.2, or 4.5 mg/kg SC once) or buprenorphine HCl (Bup HCl, 0.05 mg/kg SC twice daily for 3 d). Responses to mechanical and thermal stimuli in the 1.2 and 4.5 Bup-SR groups did not differ from those of rats in the Bup HCl group. Thermal latency on day 3 in rats that received 0.3 mg/kg Bup-SR was significantly different from baseline, indicating that this dose effectively decreased thermal hypersensitivity for at least 48 h. Marked sedation occurred in rats in the 4.5 Bup-SR group. Our findings indicate that Bup-SR at 0.3 or 1.2 mg/kg SC is effective in minimizing hypersensitivity with minimal sedation for at least 48 h (thermal hypersensitivity) and 72 h, respectively, in the incisional pain model in rats.Abbreviation: Bup HCl, buprenorphine HCl; Bup-SR, sustained-release buprenorphineEffective management of postoperative pain management is an essential component of animal welfare that is emphasized in the 8th edition of The Guide for the Care and Use of Laboratory Animals.¹⁷ Not only is controlling pain an ethical obligation, but uncontrolled pain can act as a stressor, leading to the deterioration of the animal and contamination of research results. Adequate treatment of postoperative pain is essential, because postoperative pain can alter cardiovascular function, prevent normal pulmonary function, and change hemodynamic values.²²Buprenorphine HCl (Bup HCl) is a standard of care for postoperative analgesia in rodents.⁹ It is an opioid with both partial μ receptor agonistic and κ and δ receptor antagonistic activities.^23,30 It has a high therapeutic index^7,33 and is used ubiquitously in the laboratory environment for pain management.^20,29 Bup HCl has been shown to have analgesic properties both in acute and chronic rodent pain models and even shows promising results in the reduction of neuropathic pain.⁴ Bup HCl is more effective in managing pain than are carprofen, ketoprofen, acetaminophen, tramadol, and tramadol–gabapentin.^25,26 Although Bup HCl provides effective analgesia, it also can have negative clinical side effects after administration, including decreased body weight gain,¹ pica,⁵ respiratory depression,¹⁰ and decreased water consumption.^16,18 When buprenorphine HCl is used acutely, it does not alter natural killer cell or macrophage activity^15,28Important limitations of Bup HCl include the duration of action and method of administration. Administration of Bup HCl at 0.05 mg/kg has proven to be the standard of care, but doses must be administered at least every 12 h.^9,26 Handling, restraint, and readministration of the drug increases stress to the animal.²⁷ Recently introduced to the veterinary field, a sustained-release formulation of buprenorphine (Bup-SR) may eliminate (or at least greatly reduce) redosing requirements. A previous study¹³ in rats found that buprenorphine-SR is adequate for providing analgesia at 1.2 mg/kg (calculated as 0.2 mg/kg every 12 h for 72 h) in a tibial defect model and is capable of attenuating thermal sensitivity of the hindpaw. In light of these results, the authors¹³ concluded that Bup-SR may be an effective alternative for treating postsurgical pain in this model. In addition, Bup-SR has been tested in noninjured mice by using the hot-plate assay, and findings show that Bup-SR is effective for at least 12 h in male BalbC/J and SWR/J mice.³The aim of the current study was to investigate the antinociceptive effects of Bup-SR in the plantar incisional pain model in rats.² This well-established model recapitulates postoperative pain due to injury or a minor procedure. Our group has extensive experience with this model, and we find that this model is reproducible, produces mechanical and thermal hypersensitivity, and leads to mild to moderate pain in rats. In previous studies using this model,²⁶ we found that rats showed signs of thermal hypersensitivity for as long as 4 d but that mechanical weight-bearing was decreased for only 1 d after surgery. We hypothesized that the antinociceptive effects of Bup-SR at all doses is comparable to those of twice-daily dosing of Bup HCl.     

Cross-species surveillance of Leptospira in domestic and peri-domestic animals in Mahalla City, Gharbeya Governorate, Egypt

A survey of 179 animals (black rats, dogs, sheep, buffaloes, cattle, donkeys, weasels, and cats) for Leptospira infection was conducted in Mahalla City (Lower Egypt). Blood, urine, and kidney were collected and tested by culture, microscopic agglutination test (MAT), and/or polymerase chain reaction (PCR). Among rats, 26% were positive by PCR, including 7% that were also positive by culture for L. interrogans serovars Grippotyphosa, Pyrogenes, and Icterohaemorrhagiae. L. borpetersenii serovar Polonica was isolated for the first time in Egypt in three rats. MAT titers ≥ 1:800 were observed in 11% of rats and 12% of dogs. L. interrogans serovar Grippotyphosa was detected in one cat. Sheep and donkeys were negative for leptospirosis by all methods. Buffaloes and cattle were seropositive in 20% and 44% of animals, respectively. Data indicate that several pathogenic serovars are circulating in the animals, which may pose exposure risks and account for high rates of acute febrile illness.     

Someone to talk to: the association of mentorship and cyberbullying with suicidality among US high school students

Objective

Suicide is the second-leading cause of death in youth. We tested whether having a mentoring relationship associated with lower risks for suicidality, particularly among youth at higher risk due to cyberbullying.

Methods

This study pooled the 2017 Youth Risk Behavior Survey (YRBS) data from five jurisdictions that asked students if there was at least one teacher or other adult in their school that they could talk with, if they have a problem (mentorship). Students self-reported cyberbullying exposure and suicidality in the past 12 months. Odds of suicidal ideation, planning, and attempts were estimated using multivariable weighted logistic regression in overall and sex-stratified stepwise models. Interactions between mentorship and cyberbullying were also tested.

Results

Of the 25,527 student respondents, 87% reported having a mentoring relationship. Mentoring relationships were associated with lower odds of suicidal ideation (aOR, 0.44; 95% CI 0.33–0.57), planning (aOR, 0.59; 95% CI 0.41–0.85), and suicide attempts (aOR, 0.42; 95% CI 0.31–0.56). Stratified analyses showed a significant interaction between cyberbullying and mentorship with suicidal attempts among males, and a near-significant association between cyberbullying and mentorship with suicidal thoughts among females. Compared to male students with no cyberbullying and no mentorship, odds of attempting suicide were lower for males with no cyberbullying and mentorship (aOR, 0.55, 95% CI 0.32–0.92), higher for males with cyberbullying and no mentorship (aOR, 7.78, 95% CI 3.47–17.47), but not significantly different for males with cyberbullying and mentoring relationships (aOR, 1.49, 95% CI 0.86–2.48). Similarly, compared with females with no cyberbullying and no mentorship, odds of having suicidal thoughts were lower for females with no cyberbullying and mentorship (aOR, 0.40, 95% CI 0.28–0.57), and higher for females with cyberbullying and no mentorship (aOR, 2.54, 95% CI 1.59–4.07).

Conclusion

School-based mentoring may mitigate risk of suicidality among adolescents and limit the toxic effects of cyberbullying.

     

Carbon dioxide and oxygen levels in disposable individually ventilated cages after removal from mechanical ventilation

Disposable individually ventilated cages have lids that restrict air exchange when the cage is not mechanically ventilated. This design feature may cause intracage CO2 to increase and O2 to decrease (hypercapnic and hypoxic conditions, respectively) when the electrical supply to the ventilated rack fails, the ventilated rack malfunctions, cages are docked in the rack incorrectly, or cages are removed from the ventilated rack for extended periods of time. We investigated how quickly hypercapnic and hypoxic conditions developed within disposable individually ventilated cages after removal from mechanical ventilation and compared the data with nondisposable static cages, disposable static cages, and unventilated nondisposable individually ventilated cages. When disposable individually ventilated cages with 5 adult mice per cage were removed from mechanical ventilation, CO2 concentrations increased from less than 1% at 0 h to approximately 5% at 3 h and O2 levels dropped from more than 20% at 0 h to 11.7% at 6 h. The breathing pattern of the mice showed a prominent abdominal component (hyperventilation). Changes were similar for 4 adult mice per cage, reaching at least 5% CO2 at 4 h and 13.0% O2 at 6 h. For 3 or 2 mice per cage, values were 4.6% CO2 and 14.7% O2 and 3.04% CO2 and 17.1% O2, respectively, at 6 h. These results document that within disposable individually ventilated cages, a hypercapnic and hypoxic microenvironment develops within hours in the absence of mechanical ventilation.     

Postoperative Analgesia Due to Sustained-Release Buprenorphine,Sustained-Release Meloxicam,and Carprofen Gel in a Model of Incisional Pain in Rats (Rattus norvegicus)

Postoperative analgesia in laboratory rats is complicated by the frequent handling associated with common analgesic dosing requirements. Here, we evaluated sustained-release buprenorphine (Bup-SR), sustained-release meloxicam (Melox-SR), and carprofen gel (CG) as refinements for postoperative analgesia. The aim of this study was to investigate whether postoperative administration of Bup-SR, Melox-SR, or CG effectively controls behavioral mechanical and thermal hypersensitivity in a rat model of incisional pain. Rats were randomly assigned to 1 of 5 treatment groups: saline, 1 mL/kg SC BID; buprenorphine HCl (Bup HCl), 0.05 mg/kg SC BID; Bup-SR, 1.2 mg/kg SC once; Melox-SR, 4 mg/kg SC once; and CG, 2 oz PO daily. Mechanical and thermal hypersensitivity were tested daily from day–1 through 4. Bup HCl and Bup-SR attenuated mechanical and thermal hypersensitivity on days 1 through 4. Melox-SR and CG attenuated mechanical hypersensitivity–but not thermal hypersensitivity–on days 1 through 4. Plasma concentrations, measured by using UPLC with mass spectrometry, were consistent between both buprenorphine formulations. Gross pathologic examination revealed no signs of toxicity in any group. These findings suggest that postoperative administration of Bup HCl and Bup-SR—but not Melox-SR or CG—effectively attenuates mechanical and thermal hypersensitivity in a rat model of incisional pain.Abbreviations: Bup HCl, buprenorphine HCl; Bup-SR, sustained-release buprenorphine; CG, carprofen gel; Melox-SR, sustained-release meloxicamPostoperative analgesia is a vital aspect of laboratory animal medicine. Investigators have a responsibility to follow an effective and safe pain management protocol for research animals that have undergone surgical procedures. Pain and distress are serious animal welfare concerns that directly affect animal physiology and can result in altered research data.^1,17,30 Continued refinement of pre-, intra-, and postoperative pain management in rodents is necessary to improve animal wellbeing, obtain high-quality research data, and ensure compliance with standards set forth by the Guide for the Care and Use of Laboratory Animals.²¹Many classes of analgesics are available to veterinary practitioners, but in the laboratory setting, the options tend to be simpler and typically involve 1 of 2 drug classes, opioids and NSAID. Buprenorphine HCl (Bup HCl), a partial μ-opioid receptor agonist, has long been the ‘gold standard’ for postoperative analgesia in laboratory animals due to the drug''s prolonged plasma half-life and effective analgesic properties.^15,28 Buprenorphine effectively controls mild to moderate postoperative pain in rodents for 6 to 12 h.¹⁶ Because many rodent surgical procedures might cause pain for at least 48 h, researchers must handle these animals at least twice daily during this time period to readminister buprenorphine. Repeated dosing requires frequent handling of surgically manipulated animals, resulting in handling-associated stress.¹ In addition, handling an animal frequently likely is disruptive to its cagemates and potentially to animals in the same room. Because of their analgesic and antiinflammatory properties, NSAID are often used either in conjunction with or as an alternative to opioids to control pain in laboratory animals.^11,33 Meloxicam and carprofen are 2 NSAID that preferentially inhibit cyclooxygenase 2 and thus prostaglandin synthesis.^10,11 Although generally considered safe, reported side effects of NSAID include gastrointestinal ulceration, altered platelet function, and renal dysfunction.¹¹Novel formulations of opioid and NSAID analgesics have recently been introduced to the veterinary market and include sustained-release injectables,^2,5,14,22 gel-based oral compounds,^6,19 and transdermal patches.^13,18,25,37 Our group previously demonstrated the effectiveness of sustained-release buprenorphine (Bup-SR) in controlling mild to moderate incisional pain in rats.⁷ Another study found that Bup-SR successfully controlled orthopedic surgical pain in rats.¹⁴ These alternative formulations show great potential in decreasing the stress associated with frequent handling and dosing requirements. Many of these products are still considered new in the veterinary market, and few evidence-based recommendations for their use in laboratory animal species are available. The main goal of the current study was to refine postoperative analgesia by using longer-lasting or gel-formulation products. To this end, we investigated whether Bup-SR, sustained-release meloxicam (Melox-SR), or carprofen gel (CG) provided postoperative analgesia in the rat plantar incisional model according to results of behavioral testing. We hypothesized that Bup-SR, Melox-SR, and CG would provide effective postoperative analgesia as evidenced by reduced pain responses in this model.