The effect of local/topical analgesics on incisional pain in a pig model

Mechanical and thermal thresholds before and after application of a conditioning stimulus in healthy Göttingen Minipigs

Minipigs are widely used in biomedical research for translational studies. However, information about pain elicited by experimental procedures is lacking. Non-invasive methods as quantitative sensory testing and conditioned pain modulation are particularly attractive. Our overarching aim was to explore and refine these methods for assessing post-operative pain in minipigs after myocardial infarction. As first step, we aimed at defining mechanical and thermal thresholds in healthy adults Göttingen Minipigs, evaluating their reliability, and testing their modifications after the application of a conditioning stimulus. Thresholds were assessed at different body sites before and after a painful conditioning stimulus (CS) (cuffed tourniquet) and sham CS (uncuffed tourniquet) in eleven animals. Thresholds' reliability was assessed using interclass correlation coefficient (ICC). The effect of the CS was assessed calculating absolute change, percentage change of the thresholds and standard error of measurement. Baseline mechanical thresholds (Newton) were: left hindlimb 81 [73; 81]; left forearm 81 [72.1; 81]; right forearm 81 [76; 81]; left chest 80.5 [68; 81]; right chest 81 [76.5; 81]; left neck 81 [70.3; 81]; right neck 74.8 [62.3; 80.5]. Reliability of mechanical thresholds was good at right chest (ICC = 0.835) and moderate at left chest (ICC = 0.591), left hindlimb (ICC = 0.606) and left neck (ICC = 0.518). Thermal thresholds showed poor reliability in all the tested sites. A modulatory effect was present at right chest, but it was seen when both a painful CS and a sham CS was applied. Minipigs tendentially showed a pro-nociceptive profile (i.e. conditioning pain facilitation). The measured thresholds are a reference for future trials in this species. Mechanical thresholds showed to be more reliable and, therefore, more useful, than thermal ones. The pain facilitation might be explained by the phenomenon of stress induced hyperalgesia, but this finding needs to be further investigated with a stricter paradigm.

Pharmacokinetics of single dose levobupivacaine after peri-incisional subcutaneous infiltration in anaesthetized domestic pigs

Increasing use of pigs as models in translational research, and growing focus on animal welfare are leading to better use of effective analgesics and anaesthetics when painful procedures are performed. However, there is a gap in basic knowledge such as pharmacokinetics of different anaesthetics in these species. The main objective of our study was to determine the pharmacokinetics of levobupivacaine in domestic pigs. Twelve female grower pigs weighing 31.17 ± 4.6 kg were subjected to general anaesthesia and experimental surgery, at the end of which they received 1 mg/kg levobupivacaine via peri-incisional subcutaneous infiltration. Plasma samples were collected before administration of levobupivacaine and at 0.5, 1, 2, 4, 8, 12, 24 and 48 h thereafter. Concentrations of levobupivacaine were determined by liquid chromatography coupled with tandem mass spectrometry. Following single dose of levobupivacaine, all animals had measurable plasma concentrations 0.5 h after drug administration, with most peak concentrations observed at the 1-h time point. In all 12 animals, levobupivacaine was below the limit of quantification 48 h after drug administration. The mean maximum plasma concentration, area under the curve and half-life were determined to be 809.98 μg/l, 6552.46 μg/l h and 6.25 h, respectively. Plasma clearance, volume of distribution and weight-normalized volume of distribution were 4.41 l/h, 35.57 l and 1.23 l/kg, respectively. Peak plasma concentrations in our study were well below concentrations that were found to produce toxicity in pigs.

Extended Release of Bupivacaine from Temperature-Responsive PNDJ Hydrogels Improves Postoperative Weight-Bearing in Rabbits Following Knee Surgery

Effective treatment of postoperative pain lasting for multiple days without opioids is an important clinical need. We previously reported analgesia lasting up to 96 h in a porcine soft tissue model of postoperative pain using SBG004, an extended-release formulation of bupivacaine based on the temperature-responsive polymer poly(N-isopropylacrylamide-co-dimethylbutyrolactone acrylamide-co-Jeffamine M-1000 acrylamide) [PNDJ]. Orthopaedic surgical sites such as the knee can involve complex sensory innervation which presents a distinct challenge to local anesthetic delivery. The purpose of this work was to evaluate the pharmacokinetics and efficacy of SBG004 in an orthopaedic surgical model in comparison to currently available local anesthetics. Pharmacokinetics following periarticular (PA) or intraarticular (IA) injection of SBG004 were compared against liposomal bupivacaine (Lip-Bupi) PA in New Zealand White rabbits (all doses 14.5 mg/kg). Analgesic efficacy of SBG004 (IA, PA, or IA + PA), three active comparators, and saline was evaluated following knee surgery in New Zealand White rabbits. Analgesia was assessed via weight-bearing on the operated limb during spontaneous large steps in video recordings. Systemic bupivacaine exposure lasted at least 7 days for SBG004 PA, 4 days for SBG004 IA, and 2 days for Lip-Bupi PA. In the analgesia study, weight-bearing in all active groups except SBG004 IA was more frequent versus saline through 8 h postoperatively (p < 0.05). Only SBG004 IA + PA resulted in a higher proportion of weight-bearing rabbits at 24 h versus saline (6/7 versus 2/10, p = 0.015). Analysis of pooled data from 24-72 h showed significantly greater frequency of weight-bearing in rabbits receiving SBG004 IA + PA (71%) versus saline (37%), ropivacaine cocktail (41%), and Lip-Bupi PA (36%). The results indicate that the release profile from SBG004 PA or IA coincides reasonably with the time course of postoperative pain, and SBG004 may produce longer duration of analgesia than local anesthetics currently used in knee surgery, including during the period of 24-72 h recognized as a target for extended-release local anesthetics.

Evaluation of Efficacy of 2 Extended-release Bupivacaine Products in a Porcine Model of Incisional Pain

Extended-release (ER) local anesthetics are often incorporated in multi-modal analgesia or as an alternative when the effect of systemic analgesics may confound research. In this study, we compared the analgesic efficacy of 2 ER bupivacaine anesthetics with different ER mechanisms, a slow-release bupivacaine-meloxicam polymer (BMP) and a sucrose acetate isobutyrate bupivacaine (SABER-B) system. We used a full-thickness unilateral skin incision porcine model to evaluate the efficacy of these 2 ER bupivacaine analgesics. Eighteen male swine were randomized into 3 groups: control (saline; n = 6), bupivacaine:meloxicam (10 mg/kg, 0.3 mg/kg; n = 6), and SABER-B (10 mg/kg; n = 6). After surgery, pigs were assessed for changes in body weight, salivary cortisol level, and response to von Frey testing at 1, 3, 6, 24, 48, 72, 96, 120, and 168 h. Body weight and salivary cortisol levels were not significantly different between groups. Based on the von Frey testing, the pigs that received analgesics showed a significantly higher withdrawal threshold of nociceptive stimulus than those that received saline at 1, 3, 6, and 24 h after the surgery. At 48 h after surgery, the SABER-B group had a significantly higher withdrawal threshold than the saline group. The withdrawal threshold was not significantly different from the baseline measurement on intact skin at 3 and 6 h after surgery in the BMP group or 1 and 3 h for the SABERB group. The analgesic effects of BMP were greatest at 3 and 6 h after surgery and that of SABER-B as 1 and 3 h SABER-B provided an earlier onset of analgesia and longer analgesia duration than did BMP. This study demonstrates that ER bupivacaine can provide pigs with 24 to 48 h of analgesia for incisional pain.

Nociceptive and Transcriptomic Responses in a Swine Diabetic Wound Model Treated With a Topical Angiotensin 1 Receptor Antagonist

BACKGROUND

Painful, treatment-resistant wounds are prevalent among diabetic patients and significantly affect health-related quality of life (HRQOL). Topical treatments may help alleviate pain without risk of dependence or side effects. However, there is a lack of topical wound compounds targeting pain-specific receptors. One possible target is proinflammatory angiotensin 1 receptor (AT1R), which is upregulated in diabetic skin and has been implicated in nociception.

OBJECTIVES

We investigated the effects of topical valsartan, an AT1R antagonist, on pain (nociceptive thresholds) and gene expression changes (transcriptomics) in a swine model of diabetic wounds.

METHODS

Eight wounds were surgically induced in diabetic, hyperglycemic Yucatan miniature swine ( n = 4). Topical AT1R antagonist was applied to wounds on one side and vehicle on the other side. Nocifensive testing was conducted at baseline and then weekly, beginning 7 days after wound induction. Mechanical and thermal stimuli were applied to the wound margins until a nocifensive reaction was elicited or a predetermined cutoff was reached. After 7 weeks of testing, tissue from the dorsal horn, dorsal root ganglion, and wounds were sequenced and analyzed with DESeq2. Unbiased pathway analyses using Metascape were conducted on differentially expressed genes.

RESULTS

There was no significant difference in mechanical tolerance threshold between AT1R antagonist-treated and vehicle-treated wounds ( p = .106). Thermal tolerance was significantly higher in AT1R antagonist-treated wounds compared to vehicle-treated ( p = .015). Analysis of differentially expressed genes revealed enriched pathways of interest: interleukin-18 signaling in dorsal horn laminae IV-V and sensory perception of mechanical stimulus in wound tissue.

DISCUSSION

In this study, wounds modeling diabetic ulcers were created in hyperglycemic swine and treated with a topical AT1R antagonist. AT1R-antagonist-treated wounds had a higher tolerance threshold than vehicle-treated wounds for thermal hyperalgesia, but not mechanical allodynia. Pathway analyses of differentially expressed genes revealed several pathways of interest for future pain research. Although further studies are needed to confirm the findings, this study can improve nursing care by providing information about a potential future treatment that may be used to decrease pain and improve HRQOL in patients with diabetic wounds.

On determining the mechanical nociceptive threshold in pigs: a reliability study

Background

A pressure algometer is a valuable tool for assessing the mechanical nociceptive threshold (MNT) in clinical pain studies. Recent research has turned to large animal models of pain because of the closer anatomy and physiology to humans. Although the reliability and usefulness of the MNT have been extensively validated in humans, similar data from large animals is still sparse.

Objective

Therefore, the aim of the current study was to evaluate the reliability (within- and between-session) of MNT in the forelimb of pigs using a pressure algometer.

Methods

Nine animals were used (23-40 kg), and MNTs were measured at both the right and left limbs at three different sessions, with three repetitions per session. The intraclass correlation coefficient (ICC) was used as a metric for relative reliability. The standard error of measurement (SEM) and coefficient of variation (CV) was used to assess absolute reliability. Systematic bias was also evaluated.

Results

The average ICC was found to be 0.71 and 0.45 for the between-session and within-session, respectively. CV ranged from 17.9% to 20.5%, with a grand average of 19.1%. The grand average SEM was 249.5 kPa (16.6%). No systematic differences were found for the MNT between sessions, which suggests that there was no habituation to the stimulus.

Conclusion

The reliability indices obtained in this study are comparable to results obtained in other species or anatomical regions and substantiate the use of the pressure algometer as a valuable tool to investigate the nociceptive system in pigs and translation to the human nociceptive withdrawal reflex.

Extended Release of Bupivacaine from Temperature-responsive Hydrogels Provides Multi-day Analgesia for Postoperative Pain

OBJECTIVE

A local anesthetic that provides analgesia lasting at least three days could significantly improve postoperative pain management. This study evaluated the analgesic efficacy and safety of an extended-release formulation of bupivacaine based on the injectable hydrogel carrier poly(N-isopropylacrylamide-co-dimethylbutyrolactone acrylamide-co-Jeffamine M-1000 acrylamide) (PNDJ).

METHODS

The efficacy of PNDJ containing 4% bupivacaine (SBG004) given by peri-incisional subcutaneous injection (SBG004 SC) or wound filling instillation (SBG004 WF) was evaluated compared to saline, liposomal bupivacaine, bupivacaine collagen sponge, bupivacaine-meloxicam polyorthoester, and bupivacaine HCl in a porcine skin and muscle incision model. Mechanical allodynia was assessed by withdrawal from application of von Frey filaments, and local tolerance was evaluated by histology. Bupivacaine pharmacokinetics for SBG004 SC were measured in rabbits (16.5 mg bupivacaine/kg).

RESULTS

Animals demonstrated less mechanical allodynia at incisions receiving SBG004 SC for up to 96 hours postoperatively. Incisions treated with SBG004 SC tolerated more force without a withdrawal indicative of pain compared to saline for 96 hours, and compared to SBG004 WF and all active controls at 24, 48, and 72 hours except bupivacaine-meloxicam polyorthoester at 72 hours. By 49 days, SBG004 was histologically absent and was replaced with granulation tissue infiltrated with immune cells in some areas. In rabbits, Cmax was 41.6 ± 9.7 ng/mL with t1/2 82.0 ± 35.8 hours (mean ± SD).

CONCLUSIONS

Peri-incisional SBG004 SC provided extended release of bupivacaine sufficient to reduce sensation of incisional pain for 96 hours, in vivo bupivacaine delivery for at least 7 days, and a favorable local and systemic toxicity profile.

Intraoperative abobotulinumtoxinA alleviates pain after surgery and improves general wellness in a translational animal model

Pain after surgery remains a significant healthcare challenge. Here, abobotulinumtoxinA (aboBoNT-A, DYSPORT) was assessed in a post-surgical pain model in pigs. Full-skin-muscle incision and retraction surgery on the lower back was followed by intradermal injections of either aboBoNT-A (100, 200, or 400 U/pig), vehicle (saline), or wound infiltration of extended-release bupivacaine. We assessed mechanical sensitivity, distress behaviors, latency to approach the investigator, and wound inflammation/healing for 5-6 days post-surgery. We followed with immunohistochemical analyses of total and cleaved synaptosomal-associated protein 25 kD (SNAP25), glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor protein-1(Iba1), calcitonin gene-related peptide (CGRP) and substance P (SP) in the skin, dorsal root ganglia (DRG) and the spinal cord of 400 U aboBoNT-A- and saline-treated animals. At Day 1, partial reversal of mechanical allodynia in aboBoNT-A groups was followed by a full reversal from Day 3. Reduced distress and normalized approaching responses were observed with aboBoNT-A from 6 h post-surgery. Bupivacaine reversed mechanical allodynia for 24 h after surgery but did not affect distress or approaching responses. In aboBoNT-A-treated animals cleaved SNAP25 was absent in the skin and DRG, but present in the ipsilateral dorsal horn of the spinal cord. In aboBoNT-A- versus saline-treated animals there were significant reductions in GFAP and Iba1 in the spinal cord, but no changes in CGRP and SP. Analgesic efficacy of aboBoNT-A appears to be mediated by its activity on spinal neurons, microglia and astrocytes. Clinical investigation to support the use of aboBoNT-A as an analgesic drug for post-surgical pain, is warranted.

Wound Healing Efficacy of Rosuvastatin Transethosomal Gel, I Optimal Optimization, Histological and In Vivo Evaluation

This study aimed to make a formulation and statistical optimization of transethosomal formulations of rosuvastatin (ROS) to enhance its topical wound healing efficiency. Design-Expert^® software was used to employ I optimal design. The formulation variables in the study were surfactant concentration (%w/v), ethanol concentration (%w/v) and surfactant type (span 60 or tween 80), while the dependent responses were entrapment efficiency percent (EE%), vesicle size (VS) and zeta potential (ZP). The numerical optimization process employed by the design expert software resulted in an optimum formula composed of 0.819439 (%w/v) span 60, 40 (%w/v) ethanol and 100 mg lecithin with a desirability of 0.745. It showed a predicted EE% value of 66.5517 vs. 277.703 nm and a ZP of -33. When it was prepared and validated, it showed less than a 5% deviation from the predicted values. The optimum formula was subjected to further characterizations, such as DSC, XRD, TEM, in vitro release, the effect of aging and wound healing efficiency. The DSC thermogram made a confirmation of the compatibility of ROS with the ingredients used in the formulation. XRD showed the encapsulation of ROS in the transethosomal vesicles. The TEM image pointed out the spherical nature of the nanovesicles with the absence of aggregation. Additionally, the optimum formula revealed an enhancement of drug release in comparison with the drug suspension. It also showed good stability for one month. Furthermore, it revealed good wound healing efficiency when compared with the standard silver sulphadiazine (1% w/w) ointment or the drug-loaded gel, which could be related to the enhanced penetration of the nanosized vesicles of TESMs into the skin, which enhances the wound healing process. So, it could be regarded as a promising carrier of ROS for the treatment of chronic wounds.

A systematic review of porcine models in translational pain research

Translating basic pain research from rodents to humans has proven to be a challenging task. Efforts have been made to develop preclinical large animal models of pain, such as the pig. However, no consistent overview and comparison of pig models of pain are currently available. Therefore, in this review, our primary aim was to identify the available pig models in pain research and compare these models in terms of intensity and duration. First, we systematically searched Proquest, Scopus and Web of Science and compared the duration for which the pigs were significantly sensitized as well as the intensity of mechanical sensitization. We searched models within the specific field of pain and adjacent fields in which pain induction or assessment is relevant, such as pig production. Second, we compared assessment methodologies in surrogate pain models in humans and pigs to identify areas of overlap and possible improvement. Based on the literature search, 23 types of porcine pain models were identified; 13 of which could be compared quantitatively. The induced sensitization lasted from hours to months and intensities ranged from insignificant to the maximum attainable. We also found a near to complete overlap of assessment methodologies between human and pig models within the area of peripheral neurophysiology, which allows for direct comparison of results obtained in the two species. In spite of this overlap, further development of pain assessment methodologies is still needed. We suggest that central nervous system electrophysiology, such as electroencephalography, electrocorticography or intracortical recordings, may pave the way for future objective pain assessment.

A comprehensive tool box for large animal studies of intervertebral disc degeneration

Preclinical studies involving large animal models aim to recapitulate the clinical situation as much as possible and bridge the gap from benchtop to bedside. To date, studies investigating intervertebral disc (IVD) degeneration and regeneration in large animal models have utilized a wide spectrum of methodologies for outcome evaluation. This paper aims to consolidate available knowledge, expertise, and experience in large animal preclinical models of IVD degeneration to create a comprehensive tool box of anatomical and functional outcomes. Herein, we present a Large Animal IVD Scoring Algorithm based on three scales: macroscopic (gross morphology, imaging, and biomechanics), microscopic (histological, biochemical, and biomolecular analyses), and clinical (neurologic state, mobility, and pain). The proposed algorithm encompasses a stepwise evaluation on all three scales, including spinal pain assessment, and relevant structural and functional components of IVD health and disease. This comprehensive tool box was designed for four commonly used preclinical large animal models (dog, pig, goat, and sheep) in order to facilitate standardization and applicability. Furthermore, it is intended to facilitate comparison across studies while discerning relevant differences between species within the context of outcomes with the goal to enhance veterinary clinical relevance as well. Current major challenges in pre-clinical large animal models for IVD regeneration are highlighted and insights into future directions that may improve the understanding of the underlying pathologies are discussed. As such, the IVD research community can deepen its exploration of the molecular, cellular, structural, and biomechanical changes that occur with IVD degeneration and regeneration, paving the path for clinically relevant therapeutic strategies.

Neuropathic pain: Spotlighting anatomy, experimental models, mechanisms, and therapeutic aspects

The International Association for the Study of Pain defines neuropathic pain as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system". The associated changes can be observed in the peripheral as well as the central nervous system. The available literature discusses a wide variety of causes as predisposing for the development and amplification of neuropathic pain. Further, key interactions within sensory pathways have been discovered, but no common molecular mechanism leading to neuropathic pain has been identified until now. In the first part of this review, the pain mediating lateral spinothalamic tract is described. Different in vivo models are presented that allow studying trauma-, chemotherapy-, virus-, and diabetes-induced neuropathic pain in rodents. We furthermore discuss approaches to assess neuropathic pain in these models. Second, the current knowledge about cellular and molecular mechanisms suggested to underlie the development of neuropathic pain is presented and discussed. A summary of established therapies that are already applied in the clinic and novel, promising approaches closes the paper. In conclusion, the established animal models are able to emulate the diversity of neuropathic pain observed in the clinics. However, the assessment of neuropathic pain in the presented in vivo models should be improved. The determination of common molecular markers with suitable in vitro models would simplify the assessment of neuropathic pain in vivo. This would furthermore provide insights into common molecular mechanisms of the disease and establish a basis to search for satisfying therapeutic approaches.

Analgesia for Sheep in Commercial Production: Where to Next?

Simple Summary

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on industry to alleviate pain associated with husbandry practices, injury and illness. Although a number of analgesic solutions are now available for sheep, providing some amelioration of the acute pain responses, this review has highlighted a number of potential areas for further research.

Abstract

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on livestock production industries to alleviate pain associated with husbandry practices, injury and illness. Over the past 15–20 years, there has been considerable research effort to understand and develop mitigation strategies for painful husbandry procedures in sheep, leading to the successful launch of analgesic approaches specific to sheep in a number of countries. However, even with multi-modal approaches to analgesia, using both local anaesthetic and non-steroidal anti-inflammatory drugs (NSAID), pain is not obliterated, and the challenge of pain mitigation and phasing out of painful husbandry practices remains. It is timely to review and reflect on progress to date in order to strategically focus on the most important challenges, and the avenues which offer the greatest potential to be incorporated into industry practice in a process of continuous improvement. A structured, systematic literature search was carried out, incorporating peer-reviewed scientific literature in the period 2000–2019. An enormous volume of research is underway, testament to the fact that we have not solved the pain and analgesia challenge for any species, including our own. This review has highlighted a number of potential areas for further research.

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.

Optimal Methods of Documenting Analgesic Efficacy in Neonatal Piglets Undergoing Castration

Analgesic products for piglet castration are critically needed. This requires extensive animal experimentation such as to meet regulatory-required proof of efficacy. At present, there are no validated methods of assessing pain in neonatal piglets. This poses challenges for investigators to optimize trial design and to meet ethical obligations to minimize the number of animals needed. Pain in neonatal piglets may be subtle, transient, and/or variably expressed and, in the absence of validated methods, investigators must rely on using a range of biochemical, physiological and behavioural variables, many of which appear to have very low (or unknown) sensitivity or specificity for documenting pain, or pain-relieving effects. A previous systematic review of this subject was hampered by the high degree of variability in the literature base both in terms of methods used to assess pain and pain mitigation, as well as in outcomes reported. In this setting we provide a narrative review to assist in determining the optimal methods currently available to detect piglet pain during castration and methods to mitigate castration-induced pain. In overview, the optimal outcome variables identified are nociceptive motor and vocal response scores during castration and quantitative sensory-threshold response testing and pain-associated behaviour scores following castration.

Topical wound anaesthesia: efficacy to mitigate piglet castration pain

OBJECTIVE

There is a critical need for safe and effective analgesic treatments to address pain resulting from surgical husbandry procedures in livestock. Piglet castration results in acute pain and stress to the animal; however, it is performed globally on millions of piglets annually, often without any analgesia what-so-ever. Tri-Solfen® (Animal Ethics Pty Ltd, Yarra Glen, Victoria, Australia) is a combination local anaesthetic and antiseptic formulation which, applied topically to wounds, has proven effective, and is registered for use to alleviate pain associated with castration (and other wounds) in lambs and calves in Australia and New Zealand. It is also reported to be effective to reduce pain in piglets following castration.

DESIGN

This randomised, blinded, placebo-controlled study examined the safety and efficacy of the formulation, administered via an adapted wound instillation method, to control pain both during and following piglet castration.

METHOD

Piglets received Tri-Solfen or placebo, instilled to the wound immediately following skin incision. A 30 s wait period was then observed prior to completing castration. Pain mitigation was assessed by grading nociceptive resistance movements and piglet vocal response during castration, as well as by grading response to mechanical sensory stimulation of the wound (von Frey and needlestick) following castration.

RESULTS

There was a significant reduction in nociceptive motor and vocal response during castration and in response to mechanical sensory wound stimulation up to and including 2 h following castration. There were no adverse events.

CONCLUSION

Administered via this method, Tri-Solfen is effective to mitigate acute peri-operative castration pain in piglets.

Early Neonatal Pain-A Review of Clinical and Experimental Implications on Painful Conditions Later in Life

Modern health care has brought our society innumerable benefits but has also introduced the experience of pain very early in life. For example, it is now routine care for newborns to receive various injections or have blood drawn within 24 h of life. For infants who are sick or premature, the pain experiences inherent in the required medical care are frequent and often severe, with neonates requiring intensive care admission encountering approximately fourteen painful procedures daily in the hospital. Given that much of the world has seen a steady increase in preterm births for the last several decades, an ever-growing number of babies experience multiple painful events before even leaving the hospital. These noxious events occur during a critical period of neurodevelopment when the nervous system is very vulnerable due to immaturity and neuroplasticity. Here, we provide a narrative review of the literature pertaining to the idea that early life pain has significant long-term effects on neurosensory, cognition, behavior, pain processing, and health outcomes that persist into childhood and even adulthood. We refer to clinical and pre-clinical studies investigating how early life pain impacts acute pain later in life, focusing on animal model correlates that have been used to better understand this relationship. Current knowledge around the proposed underlying mechanisms responsible for the long-lasting consequences of neonatal pain, its neurobiological and behavioral effects, and its influence on later pain states are discussed. We conclude by highlighting that another important consequence of early life pain may be the impact it has on later chronic pain states-an area of research that has received little attention.

Mechanisms of acute and chronic pain after surgery: update from findings in experimental animal models

PURPOSE OF REVIEW

Management of postoperative pain is still a major issue and relevant mechanisms need to be investigated. In preclinical research, substantial progress has been made, for example, by establishing specific rodent models of postoperative pain. By reviewing most recent preclinical studies in animals related to postoperative, incisional pain, we outline the currently available surgical-related pain models, discuss assessment methods for pain-relevant behavior and their shortcomings to reflect the clinical situation, delineate some novel clinical-relevant mechanisms for postoperative pain, and point toward future needs.

RECENT FINDINGS

Since the development of the first rodent model of postoperative, incisional pain almost 20 years ago, numerous variations and some procedure-specific models have been emerged including some conceivably relevant for investigating prolonged, chronic pain after surgery. Many mechanisms have been investigated by using these models; most recent studies focussed on endogenous descending inhibition and opioid-induced hyperalgesia. However, surgical models beyond the classical incision model have so far been used only in exceptional cases, and clinical relevant behavioral pain assays are still rarely utilized.

SUMMARY

Pathophysiological mechanisms of pain after surgery are increasingly discovered, but utilization of pain behavior assays are only sparsely able to reflect clinical-relevant aspects of acute and chronic postoperative pain in patients.

Open field and a behavior score in PNT model for neuropathic pain in pigs

Background

Rodent models are frequently used in the research of pain and continue to provide valuable data on the mechanisms driving pain, although they are criticized due to limited translational ability to human conditions. Previously we have suggested pigs as a model for development of drugs for neuropathic pain. In this study, we investigate the spontaneous behavior of pigs following peripheral neuritis trauma (PNT)-induced neuropathic pain.

Methods

A computerized monitoring system was used to evaluate the changes in open field test in addition to applying a composite behavior scoring system. The data suggest that the PNT operation did not affect the animal’s ability to walk as the total distance walked by PNT animals was not significantly different from the total distance walked by sham-operated animals. However, PNT animals expressed a significant change in the pattern of walking. This effect was unrelated to the time that the animals spent in the open field. Following treatment with different drugs (morphine, buprenorphine, or gabapentin), the walking pattern of the animals in the open field changed in a drug-specific manner. In addition, the detailed behavior score revealed drug-specific changes following treatment.

Results

Pharmacokinetic analysis of the drug concentration in blood and cerebrospinal fluid correlated with the behavioral analysis.

Conclusion

The data of this study suggest that the open field test together with the detailed behavior score applied in this model are a powerful tool to assess the spontaneous behavior of pigs following PNT-induced neuropathic pain.

Local NGF and GDNF levels modulate morphology and function of porcine DRG neurites, In Vitro

Nerve terminals of primary sensory neurons are influenced by their environment through target derived trophic factors, like nerve growth factor (NGF) or glial cell line-derived neurotrophic factor (GDNF). In mice, subpopulations of DRG neurons express receptors either for NGF or GDNF and therefore differentially respond to these neurotrophic factors. We probed neurite endings from porcine DRG neurons cultured in either NGF or GDNF and examined their shape, elongation and stimulus-evoked CGRP release. A compartmentalized culture system was employed allowing spatial separation of outgrown neurites from their somata and use of different growth factors in the compartments. We show that neurites of GDNF cultured somata extend into lateral compartments without added growth factor, unlike neurites of NGF cultured ones. Neurites of NGF cultured somata extend not only into NGF- but also into GDNF-containing compartments. GDNF at the site of terminals of NGF responsive somata led to a strong neurite arborization and formation of large growth cones, compared to neurites in medium with NGF. Functionally, we could detect evoked CGRP release from as few as 7 outgrown neurites per compartment and calculated release per mm neurite length. CGRP release was detected both in neurites from NGF and GDNF cultured somata, suggesting that also the latter ones are peptidergic in pig. When neurites of NGF cultured somata were grown in GDNF, capsaicin evoked a lower CGRP release than high potassium, compared to those grown in NGF. Our experiments demonstrate that the compartmented culture chamber can be a suitable model to assess neurite properties from trophic factor specific primary sensory neurons. With this model, insights into mechanisms of gain or loss of function of specific nociceptive neurites may be achieved.