Retrospective chart review of substance abuse in patients with psychiatric emergencies in an emerging urban county.

Objectives: Substance abuse is common in patients with psychiatric emergencies. To further understand the connection between substance abuse and psychiatric disorders, a retrospective chart review was done that included positive drug screens among patients with psychiatric emergencies and to determine whether there was an association between substances used and the psychiatric diagnosis. Methods: A retrospective chart review of patients seen in an emergency department with psychiatric emergencies was conducted. The review comprised 1000 charts with diagnoses of anxiety, depression, schizophrenia, attention-deficit/hyperactivity disorder (ADHD), bipolar disorder, alcohol abuse, or schizoaffective disorder. Data collected included patient demographics, tobacco abuse, chief complaint, arrival mode, voluntary versus involuntary status, suicide attempt on presentation, psychiatric diagnoses, urine drug screen, and ethanol results. Chi-square statistical analysis was conducted to examine the relationship between substances of abuse and psychiatric diagnoses. Results: Approximately 58% of patients with a history of psychiatric illness had a positive urine drug screen. Of 245 patients with schizoaffective disorder, 69 (28%) were positive for tetrahydrocannabinol (THC) and 48 (20%) were positive for cocaine. Of 225 patients with depression, 59 (29%) were positive for THC and 33 (15%) were positive for cocaine. Cannabis was the most commonly reported substance used among patients with depression, schizophrenia, anxiety, schizoaffective disorder, and bipolar disorder, and ethanol was most common in patients with ADHD. No significant correlations were found between psychiatric diagnosis and positive drug screens. A statistically significant secondary end point was found that White people using cannabinoids were more likely to attempt suicide than were African American people (P = 0.02). Conclusions: Positive drug screens were common among patients presenting to an ED with psychiatric emergencies. Cannabis was the most commonly reported substance used among patients independent of diagnosis. Ethanol was the most common in patients with ADHD. Urine drug screens are unlikely to provide insights into relationships between specific substance use and psychiatric emergencies.

Knowledge Retention From Emergency Medicine Simulation-Based Learning Curriculum for Pre-clinical Medical Students.

Introduction Traditional medical school curricula rely on textbook-based learning during the first two years, often limiting students' clinical exposure. Simulation-based learning (SBL) provides an opportunity for students to gain clinical exposure and competency with common procedures as well as to gain knowledge related to common clinical topics. Retention of factual knowledge is a current topic of discussion as medical learners often have difficulty with long-term retention. The aim of this study was to assess if students would learn, retain, and enjoy emergency medicine (EM)-focused SBL. Materials and methods We developed an EM-focused SBL curriculum consisting of four main educational events: suturing, medical stabilization, mass casualty triage, and point-of-care ultrasound (POCUS). Participants were first- and second-year healthcare students enrolled in a traditional, preclinical curriculum, who completed pre- and post-event quizzes consisting of multiple-choice questions on topics covered during the SBL scenario. We compared pre- and post-event quiz scores using a one-way paired t-test. Quizzes were readministered up to 100 days after each SBL event to test knowledge retention, and scores were compared across time by repeated-measures analysis of variance (RMANOVA). Results For suture (n=22), mass casualty (n=20), and ultrasound simulations (n=17), post-event mean quiz scores increased significantly in comparison to mean quiz scores from before the event (p≤0.05). Medical stabilization simulation post-event scores were increased but did not reach statistical significance. Data collected at 45, 74, and 94 days following the suture lab as well as 29 and 49 days after the medical evacuation event, and 20 days after the mass casualty event showed no statistical decrease in quiz means suggesting retention of knowledge among learners. Subjective assessments of participant satisfaction demonstrated an enjoyment of the events. Discussion EM-focused SBL events offered enjoyable learning opportunities for students to effectively obtain and possibly retain clinical knowledge. Conclusion SBL has the potential to improve student retention of clinical knowledge during the preclinical years and, therefore, should be further explored and implemented as a core pillar of medical education as opposed to its current state as a learning adjunct.

Comparing cost of F(.ab')2AV vs FabAV in the treatment of copperhead envenomation-One center's experience.

The definitive treatment of North American crotalid snakebites is antivenin. In 2000, an FabAV antivenom (CroFab®) was introduced and in 2022, F(ab')2AV (Anavip®) was approved for treatment of copperhead bites. Our center that sees primarily copperhead snake bites added the recently approved treatment as a second option for the 2022 snake bite season. This brief report we describe our initial experience with the two antivenins via retrospective chart review: the cost, charge, laboratory differences, response to therapy, complications and duration of hospitalization of admitted patients with copperhead envenomation. Using three independent reviewers in this IRB exempt report we found 31 patients with copperhead bites (7 exclusions) leaving 19 adults and 7 children for analysis. We found there was no difference in age, sex, presence of lab abnormalities, total vials administered, or length of stay. There was significant differences in hospital costs and charges to the patient. Future research should include multi-center experiences comparing the two antivenins.

Morphine Resistance in Spinal Cord Injury-Related Neuropathic Pain in Rats is Associated With Alterations in Dopamine and Dopamine-Related Metabolomics.

Opioids are not universally effective for treating neuropathic pain following spinal cord injury (SCI), a finding that we previously demonstrated in a rat model of SCI. The aim of this study was to determine analgesic response of morphine-responsive and nonresponsive SCI rats to adjunct treatment with dopamine modulators and to establish if the animal groups expressed distinct metabolomic profiles. Thermal thresholds were tested in female Long Evans rats (N = 45) prior to contusion SCI, after SCI and following injection of morphine, morphine combined with dopamine modulators, or dopamine modulators alone. Spinal cord and striatum samples were processed for metabolomics and targeted mass spectrometry. Morphine provided analgesia in 1 of 3 of SCI animals. All animals showed improved analgesia with morphine + pramipexole (D3 receptor agonist). Only morphine nonresponsive animals showed improved analgesia with the addition of SCH 39166 (D1 receptor antagonist). Metabolomic analysis identified 3 distinct clusters related to the tyrosine pathway that corresponded to uninjured, SCI morphine-responsive and SCI morphine-nonresponsive groups. Mass spectrometry showed matching differences in dopamine levels in striatum and spinal cord between these groups. The data suggest an overall benefit of the D3 receptor system in improving analgesia, and an association between morphine responsiveness and metabolomic changes in the tyrosine/dopamine pathways in striatum and spinal cord. PERSPECTIVE: Spinal cord injury (SCI) leads to opioid-resistant neuropathic pain that is associated with changes in dopamine metabolomics in the spinal cord and striatum of rats. We present evidence that adjuvant targeting of the dopamine system may be a novel pain treatment approach to overcome opioid desensitization and tolerance after SCI.

Neuroscience Near-Peer-Led Flipped Classroom Improves Student Confidence With Clinical Application of Content and Test-Taking Skills.

Introduction: The ability to apply knowledge gained in neuroscience coursework to a clinical scenario is found to be difficult by many medical students. Neuroscience is both important for future clinical practice and an area frequently tested on USMLE Step 1 examinations. Methods: Second-year medical students created a peer-led flipped classroom to help first-year students practice applying medical neuroscience course information to clinical situations and demonstrate how that information might be tested in board-style questions. The second-year students designed a series of board-style questions that included explanations for both the correct and incorrect answers. We divided the first-year students (n = 80) into small groups during the flipped classroom sessions, where they were led by second-year medical students in discussion about the questions and clinical situations. Results: Students reported agreement that the session addressed gaps in their knowledge and provided them with useful critical thinking skills for approaching board-style questions (83% and 81% agreed or strongly agreed, respectively). Discussion: The flipped classroom improved student confidence in both applying neuroscience concepts to clinical scenarios and to board-style vignette questions.

Dopamine D1 or D3 receptor modulators prevent morphine tolerance and reduce opioid withdrawal symptoms.

The long-term treatment of chronic pain by opioids is limited by tolerance and risk of addiction/dependence. Previously, we have shown that combination treatment of morphine with a dopamine D1 or D3 receptor modulator restored morphine analgesia in morphine-resistant neuropathic pain and decreased morphine's reward potential in an acute setting. Here, we investigated whether such adjunct therapy with a dopamine D1 receptor preferring antagonist (SCH 39166) or a dopamine D3 receptor preferring agonist (pramipexole) could prevent morphine tolerance and reduce withdrawal symptoms. Initially, tolerance to the combination of morphine + pramipexole was assessed in mice. Mice receiving intraperitoneal injections of morphine showed reduced thermal thresholds on Day 7 whereas those receiving morphine + pramipexole maintained analgesia at Day 7. Next, tolerance and withdrawal to both combinations were tested over 14 days in rats. Rats were assigned one of four drug conditions, (1) saline, 2) morphine, 3) morphine + SCH 39166, 4) morphine + pramipexole), for chronic administration via osmotic pumps. Chronic administration of morphine over 14 days resulted in a significant reduction of morphine analgesia. However, analgesia was maintained when morphine was administered with either the dopamine D1 receptor preferring antagonist or the D3 receptor preferring agonist. Withdrawal symptoms peaked at 48 h and were decreased in rats receiving either combination compared to morphine alone. The data suggests that adjunct therapy with dopamine D1 or D3 receptor preferring modulators prevents morphine tolerance and reduces the duration of morphine withdrawal symptoms, and thus this combination has potential for long-term pain management therapy.

Dopamine D1 and D3 receptor modulators restore morphine analgesia and prevent opioid preference in a model of neuropathic pain.

A secondary consequence of spinal cord injury (SCI) is debilitating chronic neuropathic pain, which is commonly morphine resistant and inadequately managed by current treatment options. Consequently, new pain management therapies are desperately needed. We previously reported that dopamine D3 receptor (D3R) dysfunction was associated with opioid resistance and increases in D1 receptor (D1R) protein expression in the spinal cord. Here, we demonstrate that in a model of SCI neuropathic pain, adjuvant therapy with a D3R agonist (pramipexole) or D1R antagonist (SCH 39166) can restore the analgesic effects of morphine and reduce reward potential. Prior to surgery thermal and mechanical thresholds were tested in three groups of female rats (naïve, sham, SCI). After surgery, testing was repeated under the following drug conditions: 1) saline, 2) morphine, 3) pramipexole, 4) SCH 39166, 5) morphine + pramipexole, and 6) morphine + SCH 39166. Reward potential of morphine and both combinations was assessed using conditioned place preference. Following SCI, morphine + pramipexole and morphine + SCH 39166 significantly increased both thermal and mechanical thresholds. Morphine alone induced conditioned place preference, but when combined with either the D3R agonist or D1R antagonist preference was not induced. The data suggest that adjunct therapy with receptor-specific dopamine modulators can restore morphine analgesia and decrease reward potential and thus, represents a new target for pain management therapy after SCI.

Predicting opioid use disorder in patients with chronic pain who present to the emergency department.

BACKGROUND: Emergency department (ED) patients with chronic pain challenge providers to make quick and accurate assessments without an in-depth pain management consultation. Emergency physicians need reliable means to determine which patients may receive opioid therapy without exacerbating opioid use disorder (OUD). METHODS: Eighty-nine ED patients with a chief complaint of chronic pain were enrolled. Researchers administered questionnaires and reviewed medical and state prescription monitoring database information. Participants were classified as either OUD or non-OUD. Statistical analysis included a bivariate analysis comparing differences between groups and multivariate logistic regression evaluating ORs. RESULTS: The 45 participants categorised as OUD had a higher proportion of documented or reported psychiatric diagnoses (p=0.049), preference of opioid treatment (p=0.005), current oxycodone prescription (p=0.043), borrowed pain medicine (p=0.004) and non-authorised dose increase (p<0.001). The state prescription monitoring database revealed the OUD group to have an increased number of opioid prescriptions (p=0.005) and pills (p=0.010). Participants who borrowed pain medicine and engaged in non-authorised dose increase were 5.2 (p=0.025, 95% CI 1.24 to 21.9) and 6.1 times (p=0.001, 95% CI 1.55 to 24.1) more likely to have OUD, respectively. LIMITATIONS: Major limitations of our study include a small sample size, self-reported measures and convenience sample which may introduce selection bias. CONCLUSION: Patients with chronic pain with OUD have distinguishable characteristics. Emergency physicians should consider such evidence-based variables prior to opioid therapy to ameliorate the opioid crisis and limit implicit bias.

Sports-Related Concussions in Children: Differences in Care and Expectations When Seen in an Emergency Department Versus a Sports Medicine Clinic.

OBJECTIVES: Patient and parent expectations can potentially influence management of care. We compared expectations in the diagnosis of concussion between patients who presented to a pediatric emergency department (ED) and those who presented to a sports medicine clinic, and if there was a difference in computed tomography (CT) scans performed. METHODS: Head-injured athletes aged 8 to 18 years presenting to a pediatric ED and a sports medicine clinic were enrolled. Both groups completed questionnaires on their understanding of concussion and expectations of care. Charts were then reviewed. RESULTS: Forty patients were enrolled in the study: 23 from a pediatric ED and 17 from a sports medicine clinic. Forty-one percent of athletes received a head CT in the pediatric ED versus 12% of those in the clinic population with no abnormal findings (P = 0.04). Forty-one percent of athletes and 48% of parents in the pediatric ED setting reported that a CT was "necessary" to diagnose concussion versus 18% in both groups from the clinic (P = 0.12, P = 0.07). Athletes presenting to the clinic were more likely to have been evaluated by an athletic trainer after the injury than those presenting to the pediatric ED (80% vs 23%, P = 0.004). CONCLUSIONS: Patients and parents who presented to a pediatric ED for sports-related head injury had a trend toward higher expectations of a CT scan being necessary to diagnose concussion and did have a higher rate of CT scans performed. Education of athletes and parents engaging in organized sports may be worthwhile to assist in setting expectations in diagnosis of concussion.

Morphine responsiveness to thermal pain stimuli is aging-associated and mediated by dopamine D1 and D3 receptor interactions.

Morphine actions involve the dopamine (DA) D1 and D3 receptor systems (D1R and D3R), and the responses to morphine change with age. We here explored in differently aged wild-type (WT) and D3R knockout mice (D3KO) the interactions of the D1R/D3R systems with morphine in vivo at three different times of the animals' lifespan (2months, 1year, and 2years). We found that: (1) thermal pain withdrawal reflexes follow an aging-associated phenotype, with relatively longer latencies at 2months and shorter latencies at 1year, (2) over the same age range, a dysfunction of the D3R subtype decreases reflex latencies more than aging alone, (3) morphine altered reflex responses in a dose-dependent manner in WT animals and changed at its higher dose the phenotype of the D3KO animals from a morphine-resistant state to a morphine-responsive state, (4) block of D1R function had an aging-dependent effect on thermal withdrawal latencies in control animals that, in old animals, was stronger than that of low-dose morphine. Lastly, (5) block of D1R function in young D3KO animals mimicked the behavioral phenotype observed in the aged WT. Our proof-of-concept data from the rodent animal model suggest that, with age, block of D1R function may be considered as an alternative to the use of morphine, to modulate the response to painful stimuli.

Artificial neural networks: Predicting head CT findings in elderly patients presenting with minor head injury after a fall.

OBJECTIVES: To construct an artificial neural network (ANN) model that can predict the presence of acute CT findings with both high sensitivity and high specificity when applied to the population of patients≥age 65years who have incurred minor head injury after a fall. METHODS: An ANN was created in the Python programming language using a population of 514 patients ≥ age 65 years presenting to the ED with minor head injury after a fall. The patient dataset was divided into three parts: 60% for "training", 20% for "cross validation", and 20% for "testing". Sensitivity, specificity, positive and negative predictive values, and accuracy were determined by comparing the model's predictions to the actual correct answers for each patient. RESULTS: On the "cross validation" data, the model attained a sensitivity ("recall") of 100.00%, specificity of 78.95%, PPV ("precision") of 78.95%, NPV of 100.00%, and accuracy of 88.24% in detecting the presence of positive head CTs. On the "test" data, the model attained a sensitivity of 97.78%, specificity of 89.47%, PPV of 88.00%, NPV of 98.08%, and accuracy of 93.14% in detecting the presence of positive head CTs. CONCLUSIONS: ANNs show great potential for predicting CT findings in the population of patients ≥ 65 years of age presenting with minor head injury after a fall. As a good first step, the ANN showed comparable sensitivity, predictive values, and accuracy, with a much higher specificity than the existing decision rules in clinical usage for predicting head CTs with acute intracranial findings.

PI3K mediated activation of GSK-3ß reduces at-level primary afferent growth responses associated with excitotoxic spinal cord injury dysesthesias.

BACKGROUND: Neuropathic pain and sensory abnormalities are a debilitating secondary consequence of spinal cord injury (SCI). Maladaptive structural plasticity is gaining recognition for its role in contributing to the development of post SCI pain syndromes. We previously demonstrated that excitotoxic induced SCI dysesthesias are associated with enhanced dorsal root ganglia (DRG) neuronal outgrowth. Although glycogen synthase kinase-3ß (GSK-3ß) is a known intracellular regulator neuronal growth, the potential contribution to primary afferent growth responses following SCI are undefined. We hypothesized that SCI triggers inhibition of GSK-3ß signaling resulting in enhanced DRG growth responses, and that PI3K mediated activation of GSK-3ß can prevent this growth and the development of at-level pain syndromes. RESULTS: Excitotoxic SCI using intraspinal quisqualic acid (QUIS) resulted in inhibition of GSK-3ß in the superficial spinal cord dorsal horn and adjacent DRG. Double immunofluorescent staining showed that GSK-3ß(P) was expressed in DRG neurons, especially small nociceptive, CGRP and IB4-positive neurons. Intrathecal administration of a potent PI3-kinase inhibitor (LY294002), a known GSK-3ß activator, significantly decreased GSK-3ß(P) expression levels in the dorsal horn. QUIS injection resulted in early (3 days) and sustained (14 days) DRG neurite outgrowth of small and subsequently large fibers that was reduced with short term (3 days) administration of LY294002. Furthermore, LY294002 treatment initiated on the date of injury, prevented the development of overgrooming, a spontaneous at-level pain related dysesthesia. CONCLUSIONS: QUIS induced SCI resulted in inhibition of GSK-3ß in primary afferents and enhanced at-level DRG intrinsic growth (neurite elongation and initiation). Early PI3K mediated activation of GSK-3ß attenuated QUIS-induced DRG neurite outgrowth and prevented the development of at-level dysesthesias.

Efficacy of Trypsin in Treating Coral Snake Envenomation in the Porcine Model.

Antivenom is the definitive treatment for venomous snakebites. Alternative treatments warrant investigation because antivenom is sometimes unavailable, expensive, and can have deleterious side effects. This study assesses the efficacy of trypsin to treat coral snake envenomation in an in vivo porcine model. A randomized, blinded study was conducted. Subjects were 13 pigs injected subcutaneously with 1 mL of eastern coral snake venom (10 mg/mL) in the right distal hind limb. After 1 min, subjects were randomized to have the envenomation site injected with either 1 mL of saline or 1 mL of trypsin (100 mg/mL) by a blinded investigator. Clinical endpoint was survival for 72 h or respiratory depression defined as respiratory rate <15 breaths per minute, falling pulse oximetry, or agonal respirations. Fisher's exact t test was used for between group comparisons. Average time to toxicity for the saline control was 263 min (191-305 min). The development of respiratory depression occurred more frequently in control pigs than treated pigs (p = 0.009). Four of the six pigs that received trypsin survived to the end of the 3-day study. No control pigs survived. Two of the trypsin treatment pigs died with times to toxicity of 718 and 971 min. Survival to 12 and 24 h was significantly greater in the trypsin treatment group (p = 0.002, p = 0.009, respectively). Local injection of trypsin, a proteolytic enzyme, at the site of envenomation decreased the toxicity of eastern coral snake venom and increased survival significantly. Further investigation is required before these results can be extended to human snakebites.

Chronic Treatment with Naltrexone Prevents Memory Retention Deficits in Rats Poisoned with the Sarin Analog Diisopropylfluorophosphate (DFP) and Treated with Atropine and Pralidoxime.

Humans and rats poisoned with sarin develop chronic neurological disabilities that are not prevented with standardized antidotal therapy. We hypothesized that rats poisoned with the sarin analogue diisopropylfluorophosphate (DFP) and resuscitated with atropine and pralidoxime would have long-term memory deficits that were preventable with naltrexone treatment. Long Evans rats (250-275 g) were randomized to: DFP (N = 8): single subcutaneous (SC) injection of DFP (5 mg/kg). Treatment (N = 9): DFP (5 mg/kg) followed by chronic naltrexone (5 mg/kg/day × 12 weeks). Control (N = 12): single SC injection of isopropyl alcohol, (DFP vehicle) followed by chronic naltrexone (5 mg/kg/day). If toxicity developed after injection, antidotal therapy was initiated with atropine (2 mg/kg) and pralidoxime (25 mg/kg) and repeated as needed. After 12 weeks, rats underwent testing for place learning (acquisition) across 5 days of training using the Morris Water Maze. On day 6 a memory retention test was performed. Statistical analysis was performed using IBM SPSS Statistics. Rats receiving DFP rapidly developed toxicity requiring antidotal rescue. No differences in acquisition were seen between the DFP vs. DFP + naltrexone rats. During memory testing, DFP-poisoned rats spent significantly less time (29.4 ± 2.11 versus 38.5 ± 2.5 s, p < 0.05) and traveled less distance (267 ± 24.6 versus 370 ± 27.5 cm, p < 0.05) in the target quadrant compared to the treatment group. Treatment rats performed as well as control rats (p > 0.05) on the test for memory retention. Poisoning with DFP induced impaired memory retention. Deficits were not prevented by acute rescue with atropine and pralidoxime. Chronic naltrexone treatment led to preserved memory after DFP poisoning.

Estimation of laceration length by emergency department personnel.

INTRODUCTION: Documentation and billing for laceration repair involves a description of wound length. We designed this study to test the hypothesis that emergency department (ED) personnel can accurately estimate wound lengths without the aid of a measuring device. METHODS: This was a single-center prospective observational study performed in an academic ED. Seven wounds of varying lengths were simulated by creating lacerations on purchased pigs' ears and feet. We asked healthcare providers, defined as nurses and physicians working in the ED, to estimate the length of each wound by visual inspection. Length estimates were given in centimeters (cm) and inches. Estimated lengths were considered correct if the estimate was within 0.5 cm or 0.2 inches of the actual length. We calculated the differences between estimated and actual laceration lengths for each laceration and compared the accuracy of physicians to nurses using an unpaired t-test. RESULTS: Thirty-two physicians (nine faculty and 23 residents) and 16 nurses participated. All subjects tended to overestimate in cm and inches. Physicians were able to estimate laceration length within 0.5 cm 36% of the time and within 0.2 inches 29% of the time. Physicians were more accurate at estimating wound lengths than nurses in both cm and inches. Both physicians and nurses were more accurate at estimating shorter lengths (<5.0 cm) than longer (>5.0 cm). CONCLUSION: ED personnel are often unable to accurately estimate wound length in either cm or inches and tend to overestimate laceration lengths when based solely on visual inspection.

Long-term efficacy of pressure immobilization bandages in a porcine model of coral snake envenomation.

BACKGROUND: Pressure immobilization bandages delay mortality for 8 hours after coral snake envenomation, but long-term efficacy has not been established. OBJECTIVE: The objective of this study is to determine the long-term efficacy of pressure immobilization bandages after coral snake envenomation in the absence of antivenom therapy. METHODS: A randomized, observational pilot study was conducted. Ten pigs (17.3-25.6 kg) were sedated, intubated for 5 hours, and injected subcutaneously with 10 mg of lyophilized Micrurus fulvius venom resuspended in water. Pigs were randomly assigned to a control group (no treatment) or a treatment group (compression bandage and splint) approximately 1 minute after envenomation. Bandage pressure was not controlled. Pigs were monitored daily for 21 days for signs of respiratory depression, decreased oxygen saturations, and paralysis. In case of respiratory depression, pigs were humanely euthanized and time to death recorded. Statistical analysis was performed with Fisher exact test, Mann-Whitney U test, and Kaplan-Meier survival curve as appropriate. RESULTS: Median survival time of control animals was 307 minutes compared with 1172 minutes in treated animals (P = .10). Sixty percent of pigs in the treatment group survived to 24 hours vs 0% of control pigs (P = .08). Two of the treatment pigs survived to the end point of 21 days but showed necrosis of the distal lower extremity. CONCLUSIONS: Long-term survival after coral snake envenomation is possible in the absence of antivenom with the use of pressure immobilization bandages. The applied pressure of the bandage is critical to allowing survival without necrosis. Future studies should be designed to accurately monitor the pressures applied.

Dopamine D3 receptor dysfunction prevents anti-nociceptive effects of morphine in the spinal cord.

Dopamine (DA) modulates spinal reflexes, including nociceptive reflexes, in part via the D3 receptor subtype. We have previously shown that mice lacking the functional D3 receptor (D3KO) exhibit decreased paw withdrawal latencies from painful thermal stimuli. Altering the DA system in the CNS, including D1 and D3 receptor systems, reduces the ability of opioids to provide analgesia. Here, we tested if the increased pain sensitivity in D3KO might result from a modified µ-opioid receptor (MOR) function at the spinal cord level. As D1 and D3 receptor subtypes have competing cellular effects and can form heterodimers, we tested if the changes in MOR function may be mediated in D3KO through the functionally intact D1 receptor system. We assessed thermal paw withdrawal latencies in D3KO and wild type (WT) mice before and after systemic treatment with morphine, determined MOR and phosphorylated MOR (p-MOR) protein expression levels in lumbar spinal cords, and tested the functional effects of DA and MOR receptor agonists in the isolated spinal cord. In vivo, a single morphine administration (2 mg/kg) increased withdrawal latencies in WT but not D3KO, and these differential effects were mimicked in vitro, where morphine modulated spinal reflex amplitudes (SRAs) in WT but not D3KO. Total MOR protein expression levels were similar between WT and D3KO, but the ratio of pMOR/total MOR was higher in D3KO. Blocking D3 receptors in the isolated WT cord precluded morphine's inhibitory effects observed under control conditions. Lastly, we observed an increase in D1 receptor protein expression in the lumbar spinal cord of D3KO. Our data suggest that the D3 receptor modulates the MOR system in the spinal cord, and that a dysfunction of the D3 receptor can induce a morphine-resistant state. We propose that the D3KO mouse may serve as a model to study the onset of morphine resistance at the spinal cord level, the primary processing site of the nociceptive pathway.

A randomized controlled trial of trypsin to treat brown recluse spider bites in Guinea pigs.

Brown recluse spider bites result in necrotic skin lesions for which there is no known antidote. Since venom toxins are proteins, a proteolytic enzyme like trypsin might be effective in reducing toxicity. The aim of this study was to conduct a randomized controlled trial of trypsin to treat brown recluse spider bites in guinea pigs. Subjects were 18 female guinea pigs. Anesthesia for injections was inhaled isoflurane. Analgesia was 0.05 mg/kg of buprenorphine twice a day as needed. Intervention was intradermal injection of 30 µg of brown recluse venom (Spider Pharm, Yarnell, AZ). Immediately after envenomation, subjects were randomized to two groups of nine: trypsin 10 µg in 1 mL normal saline and 1 mL of normal saline. The primary outcome was lesion area over a 10-day time period. Statistical analysis was performed with repeated measures ANOVA. Mean lesion area was smaller but not statistically different in the placebo group. Maximum lesion size occurred at day 4 in both groups, when lesion area was 76.1 ± 108.2 mm(2) in the placebo group and 149.7 ± 127.3 mm(2) in the treatment group. P value was 0.15 for placebo vs. treatment. This study did not establish a role for trypsin as a treatment for brown recluse spider bites in a guinea pig model.