Methylene blue induces an analgesic effect by significantly decreasing neural firing rates and improves pain behaviors in rats.

Methylene blue (MB) is a blue cationic thiazine dye and currently used in different medical settings. Notably, there have been several attempts to introduce MB for attenuating pain in the last decade. Some clinical studies reported remarkable results, which, however, have been much debated. In addition, accumulating evidence have revealed that MB diminishes voltage-gated sodium channel currents. Accordingly, in the present study, we conducted in vivo experiments, including in vivo single nerve recording and behavioral test, to investigate whether MB dampens neural firing rates and ultimately contributes to pain relief. As a result, neural firing rates significantly decreased and finally converged to zero after MB administration. This event lasted longer than that of lidocaine and was dose-dependently modulated. Furthermore, there was a marked improvement in pain behaviors. The withdrawal threshold and latency of hind paws significantly rose post-MB administration. Therefore, these results demonstrate that MB lessens pain by significantly weakening neural excitability, which implies a strong possibility that this dye may be developed as a pain-relieving medication in the future. This is the first in vivo study to elucidate the effect of MB on nerves and pain relief.

Pain-Relieving Effect of 4.4 MHz of Pulsed Radiofrequency on Acute Knee Arthritis in Rats.

OBJECTIVE: Drug injections and surgery are popular treatments for knee joint osteoarthritis. However, these treatments are invasive, and new noninvasive treatments with similar or better efficacy are needed. Here, we evaluated the application of 4.4 MHz of pulsed radiofrequency (PRF) as a new treatment. METHODS: Acute arthritis was induced by injection of carrageenan into the intra-articular space of the knee in male rats. At 4.5 hours after arthritis induction, PRF with the treatment protocol of three seconds on and off was applied to the affected knee joint for 20 minutes. The changes in pain behavior were evaluated by comparing the peak weight load values of both hind paws at pretreatment and four, six, seven, eight, and 24 hours after treatment. And we also used Western blotting and immunohistochemistry to measure the inflammatory changes in the synovial membrane of the inflamed knee. RESULTS: We found that the 20-minute application of PRF with the treatment protocol significantly recovered the weight load reduction at six-, seven-, and eight-hour time points after carrageenan injection. COX-2 and IL-1ß levels were significantly reduced in the inflamed rats after PRF application at six and eight hours post-carrageenan injection. Immunohistochemistry showed that PRF significantly reduced inflammatory cell infiltration at six hours post-carrageenan injection. CONCLUSIONS: . Our results indicate that noninvasive PRF application inhibited pain-related behavior and decreased inflammatory cytokine expression in the inflamed knee joints of rats. Accordingly, PRF application can serve as a potential therapeutic treatment to relieve pain associated with peripheral joint/tissue damage or inflammation.

Apoptotic changes in a full-lengthened immobilization model of rat soleus muscle.

INTRODUCTION: Lengthened immobilization may prevent muscle shortening, and help maintain normal muscle length. However, its apoptotic effects remain unclear. We evaluated the effects of long-term immobilization on apoptotic proteins. METHODS: Rat soleus muscles were immobilized by casting in a neutral (NEUT) or lengthened (LENG) position for 21 days. We evaluated dynamic weight load and muscle atrophy following the 21-day period using hematoxylin and eosin staining. We measured Bax (pro-apoptotic Bcl-2 family member), MyoD (myogenic differentiation factor D), MYH (myosin heavy chain), and cleaved poly(ADP-ribose)polymerase levels and examined apoptotic nucleus expression. RESULTS: Decreased dynamic weight load and muscle atrophy changes were observed in LENG. Both NEUT and LENG showed significantly reduced levels of MYH. LENG showed a significant increase in Bax and MyoD expression as well as in the number of apoptotic nuclei. CONCLUSIONS: Long-term lengthened immobilization may increase apoptotic changes and decrease muscle formation proteins in muscle. Muscle Nerve 59:263-269, 2019.

The effects of Chamaecyparis obtusa essential oil on pain-related behavior and expression of pro-inflammatory cytokines in carrageenan-induced arthritis in rats.

Chamaecyparis obtusa essential oil (COE) has been widely used to treat allergic diseases and was suggested to exert anti-inflammatory, antioxidant, and antimicrobial effects. This study evaluated the effects of COE on pain-related behavior and pro-inflammatory cytokines in rats with carrageenan (CGN)-induced arthritis. Reduced dynamic weight load on inflamed joint in voluntarily walking rats was used as the behavior test for arthritic pain; 10% COE-treated group was significantly attenuated pain (6-8 h post-CGN injection) compared to VEH (mineral oil)-treated group. In addition, the protein levels of interleukin (IL)-1ß, tumor necrosis factor-α, IL-6 (6-8 h), and cyclooxygenase (COX)-2 (8 h) within the synovial membrane, as well as IL-1ß, COX-2 (6-8 h), and IL-6 (5-7 h) within the meniscus, of 10% COE-treated group were significantly reduced. The current results implicate that COE has anti-inflammatory and anti-nociceptive effects on arthritis in rats.

Functional dissection of parabrachial substrates in processing nociceptive information.

Painful stimuli elicit first-line reflexive defensive reactions and, in many cases, also evoke second-line recuperative behaviors, the latter of which reflects the sensing of tissue damage and the alleviation of suffering. The lateral parabrachial nucleus (lPBN), composed of external- (elPBN), dorsal- (dlPBN), and central/superior-subnuclei (jointly referred to as slPBN), receives sensory inputs from spinal projection neurons and plays important roles in processing affective information from external threats and body integrity disruption. However, the organizational rules of lPBN neurons that provoke diverse behaviors in response to different painful stimuli from cutaneous and deep tissues remain unclear. In this study, we used region-specific neuronal depletion or silencing approaches combined with a battery of behavioral assays to show that slPBN neurons expressing substance P receptor ( NK1R) (lPBN NK1R) are crucial for driving pain-associated self-care behaviors evoked by sustained noxious thermal and mechanical stimuli applied to skin or bone/muscle, while elPBN neurons are dispensable for driving such reactions. Notably, lPBN NK1R neurons are specifically required for forming sustained somatic pain-induced negative teaching signals and aversive memory but are not necessary for fear-learning or escape behaviors elicited by external threats. Lastly, both lPBN NK1R and elPBN neurons contribute to chemical irritant-induced nocifensive reactions. Our results reveal the functional organization of parabrachial substrates that drive distinct behavioral outcomes in response to sustained pain versus external danger under physiological conditions.

Effects of Emergency Transfer Coordination Center on Length of Stay of Critically Ill Patients in the Emergency Department.

INTRODUCTION: Critically ill patients are frequently transferred from other hospitals to the emergency departments (ED) of tertiary hospitals. Due to the unforeseen transfer, the ED length of stay (LOS) of the patient is likely to be prolonged in addition to other potentially adverse effects. In this study we sought to confirm whether the establishment of an organized unit - the Emergency Transfer Coordination Center (ETCC) - to systematically coordinate emergency transfers would be effective in reducing the ED LOS of transferred, critically ill patients. METHODS: The present study is a retrospective observational study focusing on patients who were transferred from other hospitals and admitted to the intensive care unit (ICU) of the ED in a tertiary hospital located in northwestern Seoul, the capital city of South Korea, from January 2019 - December 2020. The exposure variable of the study was ETCC approval before transfer, and ED LOS was the primary outcome. We used propensity score matching for comparison between the group with ETCC approval and the control group. RESULTS: Included in the study were 1,097 patients admitted to the ICU after being transferred from other hospitals, of whom 306 (27.9%) were transferred with ETCC approval. The median ED LOS in the ETCC-approved group was significantly reduced to 277 minutes compared to 385 minutes in the group without ETCC approval. The ETCC had a greater effect on reducing evaluation time than boarding time, which was the same for populations with different clinical features. CONCLUSION: An ETCC can be effective in systematically reducing the ED LOS of critically ill patients who are transferred from other hospitals to tertiary hospitals that are experiencing severe crowding.

Activation of peripheral group III metabotropic glutamate receptors inhibits pain transmission by decreasing neuronal excitability in the CFA-inflamed knee joint.

Peripheral group III metabotropic glutamate receptors (mGluRs) function to modulate pain signaling in inflammatory states. Here, we established in vivo experimental settings, including dynamic weight bearing test and in vivo single nerve recording, to elucidate how the group III mGluRs contribute to inhibiting pain transmission at the peripheral sensory nerve terminal in inflammatory states (1 and 3 days) elicited by Complete Freund's Adjuvant (CFA). As a result, CFA-induced nociceptive behaviors were significantly alleviated after administration of 100 and 200 µM L-AP4 (l-2-amino-4-phosphonobutylate; group III mGluR agonist). In addition, neuronal discharges evoked by 6- and 26-g von Frey filaments at the nerve significantly decreased after administration of 200 µM L-AP4. However, this event was not observed in non-inflammatory state. These results suggest that the group III mGluRs negatively regulate nociceptive behavior and pain transmission by lessening neuronal firing rates at the peripheral nerve in inflammation.

The contribution of activated peripheral kappa opioid receptors (kORs) in the inflamed knee joint to anti-nociception.

The systemic administration of opioids can be used for their strong analgesic effect. However, extensive activation of opioid receptors (ORs) beyond the targeted tissue can cause dysphoria, pruritus, and constipation. Therefore, selective activation of peripheral ORs present in the afferent fibers of the targeted tissue can be considered a superior strategy in opioid analgesia to avoid potential adverse effects. The purpose of this study was to clarify the role of peripheral kappa opioid receptors (kORs) in arthritic pain for the possible use of peripheral ORs as a target in anti-nociceptive therapy. We administered U50488 or nor-BNI/DIPPA, a selective agonist or antagonist of kOR, respectively into arthritic rat knee joints induced using 1% carrageenan. After the injection of U50488 or U50488 with nor-BNI or DIPPA into the inflamed knee joint, we evaluated nociceptive behavior as indicated by reduced weight-bearing on the ipsilateral limbs of the rat and recorded the activity of mechanosensitive afferents (MSA). In the inflamed knee joint, the intra-articular application of 1µM, 10nM, or 0.1nM U50488 resulted in a significant reduction in nociceptive behavior. In addition, 1µM and 10nM U50488 decreased MSA activity. However, in a non-inflamed knee joint, 1µM U50488 had no effect on MSA activity. Additionally, intra-articular pretreatment with 20µM nor-BNI or 10µM DIPPA significantly blocked the inhibitory effects of 1µM U50488 on nociceptive behavior and MSA activity in the inflamed knee joint. These results implicate that peripheral kORs can contribute to anti-nociceptive processing in an inflamed knee joint.