Background & Aims
Drug discovery and development entails substantial time and resources to find an effective drug that will progress to clinical trials, where it still has a high likelihood of failure. To develop novel pain therapeutics that successfully perform in clinical trials requires a comprehensive preclinical testing strategy with a wide array of behavioral assays. Novel methods of preclinical pain testing have recently been developed and utilized which complement historically used reflexive methods. These tests measure the emotional and cognitive (affective) components of pain which are largely lacking in the reflexive tests. Reflexive tests are primarily processed at the level of the spinal cord and do not reflect the affective components of pain signaling which are directed by the brain. The aim of this study was to assess a battery of behavioral tests that measure spontaneous, affective, and reflexive pain components and impact of pain on mobility in the extremity trauma (ET) model.
Methods
We tested pain behaviors in the ET model, developed previously in our lab [1]. ET rats (n=36) received soft tissue injury (crushing of the right gastrocnemius and semimembranosus muscles for 30 sec with forceps) and fibula fracture while anesthetized. Sham rats (n=24) were anesthetized and received no trauma. After completion of ET or sham, rats were allowed to recover. Pain behaviors were tested 90 min, 1 day, 3 days and 6 days after ET. The behavioral testing that was performed included mechanical and thermal sensitivity (reflexive pain), weight bearing (spontaneous pain), the mechanical avoidance conflict system (MACS) (affective pain), and gait analysis (effect of pain on mobility).
Results
A two-way repeated measures ANOVA with a Tukey post-test was used to evaluate thermal and mechanical sensitivities. Significant thermal sensitivity was observed at 90 mins, 3- and 6-days post ET injury whereas significant mechanical sensitivity was observed on days 1, 3, and 6 post ET injury. Spontaneous pain was measured by weight bearing using a two-way repeated measures ANOVA with a Dunnett post-test. There was a significant development of spontaneous pain at 90 mins and day 1 post ET injury, compared to baseline levels. Additionally, at 90 mins post injury, the rat was less likely to cross the aversive probes and enter the preferred dark box during the MACS test, when compared to the sham control. GaitScan is currently being utilized to evaluate characteristic parameters related to the pathophysiological condition, including stance time (paw on the belt), the swing time (paw in the air), total stride time, stride length, foot contact area size, foot pressure, and others.
Conclusions
A novel approach of assessing spontaneous pain, affective and reflexive components of pain and impact of pain on mobility after ET provided a comprehensive characterization of pain behaviors in this battlefield relevant pre-clinical model. This is the necessary first step in preclinical testing of candidate analgesics. Future studies can test novel analgesics in this model using the same battery of tests. This testing mechanism allows for the ability to progress compounds that have the best chance for clinical success, while eliminating those compounds that would have a lower chance for success based on easily quantifiable data. Establishing standard operating procedures for generating a reliable and reproducible battlefield pain model for screening novel pain therapeutics will greatly enhance the military’s ability to effectively treat battlefield pain in future conflicts.
References
1.Xiang, L., et al., A novel rat model of extremity trauma for prehospital pain management research. J Trauma Acute Care Surg, 2018. 85(1S Suppl 2): p. S49-S56.
Presenting Author
Natasha M Sosanya
Poster Authors
Topics
- Models: Acute Pain