Objective: Traumatic hemorrhage (HEM) is often associated with pain. The use of ketamine (KET) has increased both on the battlefield and in civilian emergency care for analgesia and sedation. We have reported that an analgesic dose of KET does not impact cardiorespiratory responses or survival after HEM (JAP 130: 1583-1593, 2021). In this study, we measured the effects of a larger, sedative, dose of KET on cardiovascular responses and survival to moderate (37% blood volume) HEM combined with extremity trauma (ET), and whether midazolam (MDZ), a drug often given in combination with KET alters these responses. Hypothesis: We hypothesized that either KET (50 mg/kg) or KET+MDZ (5 mg/kg) would compromise cardiovascular responses to HEM and thereby decrease survival. Methods: Male rats were implanted with a telemetry transmitter to measure mean arterial pressure (MAP) and heart rate (HR); buprenorphine SR was used to relieve pain associated with surgical procedures. Following 2 weeks recovery, rats were anesthetized using isoflurane, and a carotid catheter was implanted. The next day, rats were briefly anesthetized using isoflurane to perform ET (fibular fracture + hindlimb soft tissue crush injury) and were allowed to recover 90 min before starting conscious HEM (time = 0-25 min). Rats received either 1) saline vehicle (VEH, n=8); 2) KET (n=8); or 3) KET followed by MDZ (KET+MDZ; n=9) during a 15 min infusion (t = 25-40 min). The study continued for 200 minutes (time = 40-240 min). Data are mean ± SD. Results: There were no differences between groups in MAP or HR at either baseline (t = 0 min) or at end of HEM (t = 25 min). However, during the 20 min after treatment (t = 40-60 min), MAP and HR were significantly lower (P≤0.05) in KET (46 ± 3 mmHg; 220 ± 11 bpm) and KET+MDZ (45 ± 10 mmHg; 212 ± 24 bpm) compared to VEH (68 ± 20 mmHg; 297 ± 37 bpm). During this time, only 3 of 8 rats in the KET group survived HEM, while all rats survived in VEH and KET+MDZ groups. At the end of the study (t = 240 min), survival rate was significantly lower (P=0.003) in KET (37.5%) compared to VEH (87.5%) or KET+MDZ (100%). Similarly, survival time was significantly lower (P=0.004) in KET (115 ± 103 min) compared to VEH (227 ± 37 min) or KET+MDZ (240 ± 0 min). Summary of Results: A sedative dose of KET decreased survival following HEM, but the same dose of KET followed by MDZ was protective. The MDZ effect was not due to improvements in cardiovascular responses to the HEM. Conclusion: Sedation with ketamine alone after trauma and moderate HEM decreased survival. Further studies of the effects of sedation with KET alone or KET+MDZ on respiration and metabolic responses to HEM may provide insight on the overall effect on survival. Congressionally Directed Medical Research Program (CDMRP). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Background Approximately 40% of Service Members deployed in support of Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF) and an astounding 80% of Veterans overall report experiencing pain. Currently, drugs that adequately treat pain may result in addiction and substance abuse or negative side effects such as nausea, vomiting, renal and cardiovascular issues, among other physiological and cognitive problems. Inadequate acute pain management can lead to the development of chronic pain. Combat and non-combat injuries, acute and chronic pain all have the potential to impact return-to-duty rates/decisions, thereby negatively affecting the Fighting Force. To develop more effective pain therapeutics, the molecular mechanisms contributing to the development of neuropathic pain are under intense investigation and further research is needed to fully understand neuropathic pain induction and maintenance. The overarching objective of this study is to identify microRNA (miRNA) changes in key brain regions during the onset and progression of neuropathic pain in a rodent model. Results Changes in miRNA expression were observed at day 15 post-SNL in the amygdala and thalamus. The majority of changes were observed in the left side of the brain, contralateral to the right-sided SNL injury. The DE miRNAs identified mainly in the amygdala and thalamus did not overlap between brain regions. The altered miRNAs regulate key signaling pathways and genes important in pain development. Discussion The majority of epigenetic studies investigating altered miRNA expression in the pain field have explored the peripheral nervous system. Very few studies have evaluated miRNA dynamics in the brain following neuropathic pain development. This study provides key insights into changes occurring in the brain following peripheral nerve injury. Our lab has previously identified circulating extracellular vesicle (EV) miRNAs that are altered in the blood post-SNL. There is some overlap between the blood and brain miRNAs that may serve as key biomarkers in prognosis and/or diagnosis of a peripheral nerve injury and the development of chronic pain.

Using a model of combat and operational stress reaction (COSR), our lab recently showed that exposure to an unpredictable combat stress (UPCS) procedure prior to a thermal injury increases pain sensitivity in male rats. Additionally, our lab has recently shown that circulating extracellular vesicle-microRNAs (EV-miRNAs), which normally function to suppress inflammation, were down-regulated in a male rat model of neuropathic pain. In this current study, male and female rats ex-posed to UPCS, followed by thermal injury, were evaluated for changes in circulating EV-miRNAs. Adult female and male Sprague Dawley rats were exposed to a UPCS procedure for either 2 or 4 weeks. Groups consisted of the following: nonstress (NS), stress (S), NS + thermal injury (TI), and S + TI. Mechanical sensitivity was measured, and plasma was collected at baseline, throughout the UPCS exposure, and post-thermal injury. EV-miRNA isolation was performed, followed by small RNA sequencing and subsequent data analysis. UPCS exposure alone resulted in mechanical allodynia in both male and female rats at specific time points. Thermal-injury induction occurring at peak UPCS resulted in increased mechanical allodynia in the injured hind paw compared to thermal injury alone. Differential expression of the EV-miRNAs was observed between the NS and S groups as well as between NS + TI and S + TI groups. Consistent differences in EV-miRNAs are detectable in both COSR as well as during the development of mechanical sensitivity and potentially serve as key regulators, biomarkers, and targets in the treatment of COSR and thermal-injury induced mechanical sensitivity. Perspective: This article presents the effects of unpredictable combat stress and thermal injury on EV-contained microRNAs in an animal model. These same mechanisms may exist in clinical patients and could be future prognostic and diagnostic biomarkers.(R) 2023 Published by Elsevier Inc. on behalf of United States Association for the Study of Pain, Inc All rights reserved.

Background: Multiple analgesics are used for acute pain relief following trauma in both the military and civilian settings. However, in addition to their ability to relieve pain, medical providers must also be concerned about secondary effects of the analgesics, especially effects on the cardiovascular and respiratory systems when the pain of trauma is associated with hemorrhage. Kalyra Pharmaceuticals has developed novel analogs of APAP to circumvent liver toxicity and improve analgesic efficacy. These analogs have the potential to replace opioids for severe pain while minimizing adverse effects. The objective of this study is to test a pain-reducing dose of D-112, an APAP analog, for its effects on survival to hemorrhage after extremity trauma (ET). We hypothesize that D-112 will not affect survival after either moderate or severe hemorrhage. Methods: Male Rats (~360 grams) were randomly assigned to receive either 0.9% saline (V) or 50 mg/kg D-112 (D) after either ~37% or ~50% of blood volume hemorrhage. All rats were surgically implanted with a carotid catheter under anesthesia. Carotid catheters were used for blood withdrawal and for injection of V or D. 24 hrs later, rats were briefly (~10 min) anesthetized again and ET consisting of soft tissue injury (crushing of the right gastrocnemius and semimembranosus muscles for 30 sec with forceps) and fibula fracture was performed. After completion of ET, rats were allowed to recover. 90 min after ET, rats underwent a conscious hemorrhage via the indwelling catheter. At the end of hemorrhage, rats received either V or D via the carotid catheter. Rats were observed for a maximum of 4 hrs after the start of the 25 min hemorrhage. Results: Survival after hemorrhage was recorded in the 4 groups: V-37% (n=13), D-37% (n=11), V-50% (n=10), D-50% (n=11). The survival proportions at 240 min were 92.3% for V-37%, 81.8% for D-37%, 60.0% for V-50%, and 18.1% for D-50%. While there was no significant difference in the survival curves of V-37% and D-37%, the survival curves of V-50% and D-50% were significantly different ( p = 0.036). Conclusions: The analgesic dose of D-112 tested decreased survival after ET and severe hemorrhage (~50% of blood volume), but not after ET and moderate hemorrhage (~37%). These results suggest that D-112 may not be an appropriate analgesic following traumatic hemorrhage. Applied Pain Research Program, US Army Clinical and Rehabilitative Medicine/Joint Program Committee 8, and US Army Combat Casualty Care Research Program, US Army Medical Research and Development Command. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.