Reported analgesic and anaesthetic administration to rodents undergoing experimental surgical procedures

In vitro ketamine CYP3A-mediated metabolism study using mammalian liver S9 fractions, cDNA expressed enzymes and liquid chromatography tandem mass spectrometry

Ketamine is widely used in medicine in combination with several benzodiazepines, including midazolam. The objectives of this study were to develop a novel HPLC-MS/selected reaction monitoring (SRM) method capable of quantifying ketamine and norketamine using an isotopic dilution strategy in biological matrices and study the formation of norketamine, the principal metabolite of ketamine with and without the presence of midazolam, a well-known CYP3A substrate. The chromatographic separation was achieved using a Thermo Betasil Phenyl 100 × 2 mm column combined with an isocratic mobile phase composed of acetonitrile, methanol, water and formic acid (60:20:20:0.4) at a flow rate of 300 μL/min. The mass spectrometer was operating in selected reaction monitoring mode and the analytical range was set at 0.05-50 μm. The precision (CV) and accuracy (NOM) observed were 3.9-7.8 and 95.9-111.1% respectively. The initial rate of formation of norketamine was determined using various ketamine concentrations and Km values of 18.4, 13.8 and 30.8 μm for rat, dog and human liver S9 fractions were observed, respectively. The metabolic stability of ketamine on liver S9 fractions was significantly higher in human (T1/2  = 159.4 min) compared with rat (T1/2  = 12.6 min) and dog (T1/2  = 7.3 min) liver S9 fractions. Moreover significantly lower IC50 and Ki values observed in human compared with rat and dog liver S9 fractions. Experiments with cDNA expressed CYP3A enzymes showed that the formation of norketamine is mediated by CYP3A but results suggest an important contribution from other isoenzymes, most likely CYP2C particularly in rat.

Comparing the effects of isoflurane and pentobarbital on the responses of cutaneous mechanoreceptive afferents

BACKGROUND

While pentobarbital has been used extensively in neurophysiological experiments investigating activity in peripheral nerves, it has fallen out of favor as an anesthetic because of safety concerns and is often replaced with isoflurane. However, the effects of isoflurane on the excitability of mechanoreceptive afferents have yet to be conclusively elucidated.

METHODS

To fill this gap, we collected extracellular single-unit recordings of cutaneous mechanoreceptive afferents from the sciatic nerve of 21 rats during vibratory stimulation of the hindpaw. We then compared the strength and temporal structure of the afferent response measured under pentobarbital and isoflurane anesthesia.

RESULTS

We found that the strength and temporal structure of afferent responses were statistically equivalent whether these were evoked under isoflurane or pentobarbital.

CONCLUSIONS

We conclude that, if these two anesthetics have any effect on the responses of mechanoreceptive afferents, their effects are indistinguishable.

Safety and efficacy of buprenorphine for analgesia in laboratory mice and rats

Buprenorphine is a long-acting opiate with a high therapeutic index. The authors review the pharmacology, toxicity, analgesic effects and delivery of buprenorphine for use in laboratory mice and rats. Buprenorphine-based analgesic therapy has a substantial record of safety, and there is growing evidence of its effectiveness for treating post-operative pain. Nonetheless, more research is needed to determine optimal delivery systems and analgesic regimens for pain therapy in laboratory animals.

Carprofen for perioperative analgesia causes early anastomotic leakage in the rat ileum

Background

There is increasing evidence that perioperative use of NSAIDs may compromise the integrity of intestinal anastomoses. This study aims to characterize the negative effects of carprofen on early anastomotic healing in the rat ileum.

Results

In 159 male Wistar rats an anastomosis was constructed in the ileum. In experiment 1 eighty-four rats were divided over control and experimental groups, which received daily buprenorphine or carprofen, respectively, as an analgesic and were killed on day 1, 2 or 3 after surgery. In experiment 2 three groups of 15 rats received carprofen either immediately after surgery or with a delay of 1 or 2 days. Animals were killed after 3 days of carprofen administration. In experiment 3 three groups of 10 rats received different doses (full, half or quarter) of carprofen from surgery.

In significant contrast to buprenorphine, which never did so, carprofen induced frequent signs of anastomotic leakage, which were already present at day 1. If first administration was delayed for 48 hours, the leakage rate was significantly reduced (from 80 to 20%; p = 0.0028). Throughout the study, the anastomotic bursting pressure was lowest in animals who displayed signs of anastomotic leakage. Loss of anastomotic integrity did not coincide with reduced levels of hydroxyproline or increased activity of matrix metalloproteinases.

Conclusions

Carprofen interferes with wound healing in the rat ileum at a very early stage. Although the mechanisms responsible remain to be fully elucidated, one should be aware of the potential of NSAIDs to interfere with the early phase of wound repair.

Effects of endotoxemia on the pharmacodynamics and pharmacokinetics of ketamine and xylazine anesthesia in Sprague-Dawley rats

Purpose

To evaluate the effects of endotoxemia on the pharmacokinetics and pharmacodynamics of ketamine and xylazine anesthesia in Sprague-Dawley rats.

Methods

Sprague-Dawley rats received ketamine (80 mg/kg) and xylazine (5 mg/kg) intramuscularly following the intraperitoneal administration of different lipopolysaccharide concentrations (1, 10, and 100 µg/kg) to simulate different levels of endotoxemia. Results were compared to control animals receiving saline intraperitoneally. During anesthesia, a toe pinch was performed to evaluate anesthesia duration, and selected physiological parameters (heart and respiratory rates, oxygen saturation, and rectal temperature) were taken. Blood samples were also taken during anesthesia at selected time points for the analysis of plasmatic ketamine and xylazine concentrations by liquid chromatography-mass spectrometry. Blood samples were taken 1 week prior to and 24 hours following anesthesia for blood biochemistry.

Results

Anesthesia duration significantly increased for moderate (10 µg/kg) and high (100 µg/kg) lipopolysaccharide groups. Liver histopathology showed minor to moderate necrosis in all lipopolysaccharide groups in some animals. The most important physiological change that occurred was a decrease in oxygen saturation, and for blood biochemistry a decrease in serum albumin. Ketamine pharmacokinetics were not affected except for the moderate (10 µg/kg) lipopolysaccharide group where a decrease in the area under the plasma concentration-time curve from time zero to the last measurable concentration, a decrease in half-life, and an increase in the clearance were observed. For xylazine, the area under the plasma concentration-time curve increased and the clearance decreased in the moderate (10 µg/kg) and high (100 µg/kg) lipopolysaccharide groups.

Conclusion

During ketamine-xylazine anesthesia, endotoxemia may alter xylazine pharmacokinetics and selected biochemical and physiological parameters, suggesting that anesthetic drug dosages could be modified for a more rapid recovery.

The effects of anesthetic regimen in 90% hepatectomy in rats

PURPOSE: To evaluate the influence of the anesthetic regimen on anesthetic recovery, survival, and blood glucose levels following a 90% partial hepatectomy in rats. METHODS: Thirty adult male Wistar rats were divided into two groups according to their anesthetic regimens: intraperitoneal ketamine and xylazine or inhaled isoflurane. In order to prevent hypoglycemia, glucose was administered intraperitoneally and glucose (20%) was added to the drinking water. RESULTS: Anesthetic recovery time was longer in the ketamine and xylazine group. The survival rate after 72 hours was lower (log rank=0.0001) in the ketamine and xylazine group (0.0%) than in the isoflurane group (26.7%). The blood glucose after six hours was lower (p=0.017) in the ketamine and xylazine group (63±31.7 mg/dL) than in the isoflurane group (98±21.2 mg/dL). The prolonged anesthesia recovery time associated with ketamine and xylazine decreased the survival rate and blood glucose levels after 90% hepatectomy. CONCLUSION: Isoflurane anesthesia reduced the recovery time and incidence of hypoglycemia and increased the survival rate in the early hours, providing a therapeutic window that is suitable for experimental studies.

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.

Reduction of the sevoflurane minimum alveolar concentration induced by methadone, tramadol, butorphanol and morphine in rats

This study aimed to estimate the reduction in the minimum alveolar concentration (MAC) of sevoflurane induced by low and high doses of methadone (5 and 10 mg/kg), tramadol (25 and 50 mg/kg), butorphanol (5 and 10 mg/kg) or morphine (5 and 10 mg/kg) in the rat. A control group received normal saline. Sixty-three adult male Sprague-Dawley rats were anaesthetized with sevoflurane ( n = 7 per group). Sevoflurane MAC was then determined before and after intraperitoneal administration of the opioids or saline. The duration of the sevoflurane MAC reduction and basic cardiovascular and respiratory measurements were also recorded. The baseline MAC was 2.5 (0.3) vol%. Methadone, tramadol and morphine reduced the sevoflurane MAC (low dose: 31 ± 10, 38 ± 15 and 30 ± 13% respectively; high dose: 100 ± 0, 83 ± 17 and 77 ± 25%, respectively) in a dose-dependent manner. The low and high doses of butorphanol reduced the sevoflurane MAC to a similar extent (33 ± 7 and 31 ± 4%, low and high doses, respectively). Two rats developed apnoea following administration of high-dose butorphanol and methadone. These anaesthetic-sparing effects are clinically relevant and may reduce the adverse effects associated with higher doses of inhalational anaesthetics.

Rodent stereotaxic surgery and animal welfare outcome improvements for behavioral neuroscience

Stereotaxic surgery for the implantation of cannulae into specific brain regions has for many decades been a very successful experimental technique to investigate the effects of locally manipulated neurotransmitter and signaling pathways in awake, behaving animals. Moreover, the stereotaxic implantation of electrodes for electrophysiological stimulation and recording studies has been instrumental to our current understanding of neuroplasticity and brain networks in behaving animals. Ever-increasing knowledge about optimizing surgical techniques in rodents(1-4), public awareness concerning animal welfare issues and stringent legislation (e.g., the 2010 European Union Directive on the use of laboratory animals(5)) prompted us to refine these surgical procedures, particularly with respect to implementing new procedures for oxygen supplementation and the continuous monitoring of blood oxygenation and heart rate levels during the surgery as well as introducing a standardized protocol for post-surgical care. Our observations indicate that these modifications resulted in an increased survival rate and an improvement in the general condition of the animals after surgery (e.g. less weight loss and a more active animal). This video presentation will show the general procedures involved in this type of stereotaxic surgery with special attention to our several modifications. We will illustrate these surgical procedures in rats, but it is also possible to perform this type of surgery in mice or other small laboratory animals by using special adaptors for the stereotaxic apparatus(6).

The opiate analgesic buprenorphine decreases proliferation of adult hippocampal neuroblasts and increases survival of their progeny

Although opiate drugs of abuse have been shown to decrease adult hippocampal neurogenesis, the impact of opiate analgesics has not been tested. North American regulatory boards governing the ethical treatment of experimental animals require the administration of analgesics, such as buprenorphine, following minor surgical interventions. Here, we show that two commonly used post-operative buprenorphine dosing regimes significantly inhibit the proliferation of doublecortin-positive neuroblasts but not other hippocampal stem and progenitor cell populations in adult mice. Buprenorphine, administered in schedules of three 0.05 mg/kg subcutaneous injections over a single day or seven 0.05 mg/kg injections over a 3-day period decreased the number of actively proliferating 5-iodo-2'-deoxyuridine-labeled doublecortin-positive cells for up to 6 days after opiate withdrawal. The minimal (three injection), but not standard (seven injection), analgesic paradigm also reduced basal indices of hippocampal progenitor cell apoptosis and enhanced survival of newly born cells for up to 28 days. Taken together, these data provide the first evidence that the routine administration of opiate analgesics has transient but long-lasting effects on neurogenesis and further emphasize that analgesic dosage and schedule should be reported and considered when interpreting the magnitude of neural stem and progenitor cell activation in response to in vivo intervention.

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.

Anesthetics and control of breathing

An important side effect of general anesthetics is respiratory depression. Anesthetics have multiple membrane targets of which ionotropic receptors such as gamma-aminobutyric acid-A (GABA(A)), glycine, N-methyl-D-aspartate and nicotinic acetylcholinergic (nACh) receptors are important members. GABA, glutamate and ACh are crucial neurotransmitters in the respiratory neuronal network, and the ability of anesthetics to modulate their release and interact with their receptors implies complex effects on respiration. Metabotropic receptors and intracellular proteins are other important targets for anesthetics suggesting complex effects on intracellular signaling pathways. Here we briefly overview the effects of general anesthetics on protein targets as far as these are relevant for respiratory control. Subsequently, we describe some methods with which the overall effect of anesthetics on the control of breathing can be measured, as well as some promising in vivo approaches to study their synaptic effects. Finally, we summarize the most important respiratory effects of volatile anesthetics in humans and animals and those of some intravenous anesthetics in animals.

Reported analgesic administration to rabbits undergoing experimental surgical procedures

Background

It has become widely accepted that whenever animals are used in scientific procedures, the 3Rs principle of replacement, reduction and refinement described by William Russell and Rex Burch should be adhered to. Animals should be replaced with non-sentient alternatives if possible, the number of animals used should be reduced and experimental procedures should be refined to minimise pain, suffering and distress. Administration of analgesic agents to animals undergoing surgical procedures is a refinement used to alleviate pain. In this study, a structured literature review was carried out to examine current trends in analgesic administration to rabbits undergoing experimental surgical procedures.

Results

128 papers from 51 peer-reviewed journals were selected for inclusion in this review. Reporting administration of systemic analgesia to rabbits in peer-reviewed scientific papers increased significantly from 16% to 50% between 1995-1997 and 2005-2007 (P < 0.001). Papers that reported ethical approval were more likely than papers that did not specify approval to report systemic analgesic administration (P < 0.001). When systemic analgesics were administered, buprenorphine was the most frequently used agent and non-steroidal anti-inflammatory drugs were used less frequently than opioids in both time periods.

Conclusions

Although this review provides evidence that systemic analgesic administration to rabbits undergoing surgical procedures is increasing, rabbits do not always receive analgesia when they undergo experimental surgery. Other practices in rabbit perioperative care that could be improved, highlighted by this survey include: 1) changing the timing of analgesic administration by giving systemic analgesics pre- or perioperatively rather than only postoperatively, 2) using multimodal analgesia when pain is likely to be moderate to severe and 3) increasing the use of non-steroidal anti-inflammatory drugs and use of other techniques such as epidural analgesia particularly for orthopaedic procedures.

Impact of anesthesia, analgesia, and euthanasia technique on the inflammatory cytokine profile in a rodent model of severe burn injury

Anesthetics used in burn and trauma animal models may be influencing results by modulating inflammatory and acute-phase responses. Accordingly, we determined the effects of various anesthetics, analgesia, and euthanasia techniques in a rodent burn model. Isoflurane (ISO), ketamine-xylazine (KX), or pentobarbital (PEN) with or without buprenorphine were administered before scald-burn in 72 rats that were euthanized without anesthesia by decapitation after 24 h and compared with unburned shams. In a second experiment, 120 rats underwent the same scald-burn injury using KX, and 24 h later were euthanized under anesthesia or carbon dioxide (CO2). In addition, we compared euthanasia by exsanguination with that of decapitation. Serum cytokine levels were determined by an enzyme-linked immunosorbent assay. In the first experiment, ISO was associated with elevation of cytokine-induced neutrophil chemoattractant 2 (CINC-2) and monocyte chemotactic protein 1 (MCP-1), and KX and PEN was associated with elevation of CINC-1,CINC-2, IL-6, and MCP-1. Pentobarbital also decreased IL-1". IL-6 increased significantly when ISO or PEN were combined with buprenorphine. In the second experiment, euthanasia performed by exsanguination under ISO was associated with reduced levels of IL-1", CINC-1, CINC-2, and MCP-1, whereas KX reduced CINC-2 and increased IL-6 levels. Meanwhile, PEN reduced levels of IL-1" and MCP-1, and CO2 reduced CINC-2 and MCP-1. In addition,decapitation after KX, PEN, or CO2 decreased IL-1" and MCP-1, although we found no significant difference between ISO and controls. Euthanasia by exsanguination compared with decapitation using the same agent also led to modulation of several cytokines. Differential expression of inflammatory markers with the use of anesthetics and analgesics should be considered when designing animal studies and interpreting results because these seem to have a significant modulating impact. Our findings indicate that brief anesthesia with ISO immediately before euthanasia by decapitation exerted the least dampening effect on the cytokines measured. Conversely, KX with buprenorphine may offer a better balance during longer procedures to avoid significant modulation. Standardization across all experiments that are compared and awareness of these findings are essential for those investigating the pathophysiology of inflammation in animal models.

Reporting the Implementation of the Three Rs in European Primate and Mouse Research Papers: Are We Making Progress?

It is now more than 20 years since both Council of Europe Convention ETS123 and EU Directive 86/609?EEC were introduced, to promote the implementation of the Three Rs in animal experimentation and to provide guidance on animal housing and care. It might therefore be expected that reports of the implementation of the Three Rs in animal research papers would have increased during this period. In order to test this hypothesis, a literature survey of animal-based research was conducted. A randomly-selected sample from 16 high-profile medical journals, of original research papers arising from European institutions that featured experiments which involved either mice or primates, were identified for the years 1986 and 2006 (Total sample = 250 papers). Each paper was scored out of 10 for the incidence of reporting on the implementation of Three Rs-related factors corresponding to Replacement (justification of non-use of non-animal methods), Reduction (statistical analysis of the number of animals needed) and Refinement (housing aspects, i.e. increased cage size, social housing, enrichment of cage environment and food; and procedural aspects, i.e. the use of anaesthesia, analgesia, humane endpoints, and training for procedures with positive reinforcement). There was no significant increase in overall reporting score over time, for either mouse or primate research. By 2006, mouse research papers scored an average of 0 out of a possible 10, and primate research papers scored an average of 1.5. This review provides systematic evidence that animal research is still not properly reported, and supports the call within the scientific community for action to be taken by journals to update their policies.

An experimental protocol for maternal pulmonary exposure in developmental toxicology

To establish a protocol for studying effects of pulmonary exposure in developmental toxicity studies, the effects of intratracheal sham instillation under short-term isoflurane anaesthesia were evaluated with a protocol including multiple instillations during gestation. Twelve time-mated mice (C57BL/6BomTac) were anaesthetized with isoflurane and intratracheally instilled with saline containing 10% bronchoalveolar lavage (BAL) on gestation days 8, 11, 15 and 18. In addition, the early effects of the procedure were assessed in naive female mice. Control animals were not handled. Dams were followed until weaning, and the offspring were observed from birth to sexual maturation. The cell composition of BAL was examined in the females early after treatment (3 days) and in the dams at weaning (25 days). DNA damage in BAL and liver cells was determined by the comet assay. The procedure did not affect gestation or viability, growth and sexual maturation of the offspring. Lung markers of inflammation and DNA damage were comparable in control and treated dams. Livers of the anaesthetized and instilled females, dams and their offspring displayed no induction of DNA damage. Intratracheal instillation under isoflurane anaesthesia did not induce observable effects in pregnant mice or their offspring. We suggest that this procedure can be used as a means of exposure through the airways in studies of developmental toxicity.

Plasma concentrations of corticosterone and buprenorphine in rats subjected to jugular vein catheterization

The present study investigated the postoperative plasma concentrations of corticosterone and buprenorphine in male Wistar and Sprague-Dawley rats, treated with buprenorphine administered either through subcutaneous (SC) injection or through voluntary ingestion (VI). The animals were treated with buprenorphine for pre-emptive analgesia prior to surgical placement of a jugular catheter, followed by automated blood sampling during 96 h. Buprenorphine was administered on a regular basis throughout the experiment, and blood was collected on selected time points. Body weight was measured before and 96 h after surgery. It was found that the two rat stocks responded in a similar manner to both buprenorphine treatments, with the exception of body weight change in Wistar rats, in which body weight was reduced after SC treatment. The plasma concentration of corticosterone was significantly higher in the SC-treated animals than in the VI-treated animals during the first 18 h of the study, while plasma buprenorphine concentration was at least as high and more even over time after VI treatment. The present study shows that buprenorphine administration through VI is suitable for both Wistar and Sprague-Dawley rats, with lower stress response and higher plasma concentrations of buprenorphine than after the traditional SC route of administration.

A device for the simple and rapid transcervical transfer of mouse embryos eliminates the need for surgery and potential post-operative complications

We describe a novel device that can be used for the transcervical transfer of embryos into pseudopregnant female mice. This nonsurgical embryo transfer (NSET) device is as efficient as standard surgical embryo transfer in the production of transgenic mice, and can also be used for the transfer of embryonic stem cell-containing chimeric blastocysts and cryopreserved embryos. In addition to the elimination of surgery, recipient females do not have to be anesthetized. The NSET device eliminates a painful surgical procedure as well as potential complications associated with anesthesia/post-operative care, reduces the technical expertise and equipment needed for surgical transfer, and represents substantial cost savings and regulatory reduction. NSET technology provides an easy and rapid alternative to surgical embryo transfer. Address correspondence to Brett Spear, Room 210, Combs Building, University of Kentucky College of Medicine, 800 Rose Street, Lexington, KY, 40536-0298, USA. email: