Modulation of Nicotine-Associated Behaviour in Rats By µ-Opioid Signals from the Medial Prefrontal Cortex to the Nucleus Accumbens Shell.

Nicotine addiction is a concern worldwide. Most mechanistic investigations are on nicotine substance dependence properties based on its pharmacological effects. However, no effective therapeutic treatment has been established. Nicotine addiction is reinforced by environments or habits. We demonstrate the neurobiological basis of the behavioural aspect of nicotine addiction. We utilized the conditioned place preference to establish nicotine-associated behavioural preferences (NABP) in rats. Brain-wide neuroimaging analysis revealed that the medial prefrontal cortex (mPFC) was activated and contributed to NABP. Chemogenetic manipulation of µ-opioid receptor positive (MOR+) neurons in the mPFC or the excitatory outflow to the nucleus accumbens shell (NAcShell) modulated the NABP. Electrophysiological recording confirmed that the MOR+ neurons directly regulate the mPFC-NAcShell circuit via GABAA receptors. Thus, the MOR+ neurons in the mPFC modulate the formation of behavioural aspects of nicotine addiction via direct excitatory innervation to the NAcShell, which may provide new insight for the development of effective therapeutic strategies.

COX2 expression plays a role in spinal cord injury-induced neuropathic pain.

BACKGROUND CONTEXT: Elucidating the mechanism of neuropathic pain (NeP) is crucial as it can result in motor dysfunction and negatively impact quality of life in patients with spinal cord injury (SCI). Although it has been reported that cyclooxygenase 2 (COX2) is involved in NeP in rat models of peripheral nerve injury and that COX2 inhibitors can alleviate NeP, these mechanisms after SCI have not been fully investigated. PURPOSE: The purpose is to investigate whether the thoracic SCI affects the expression of mRNAs for COX1 and COX2 in the lumbar spinal cord, and the effect of COX2 inhibitor on its behavior. STUDY DESIGN: Male Sprague-Dawley (SD) rats underwent thoracic (T10) spinal cord contusion injury using an Infinite Horizon (IH) impactor device. SCI rats received COX2 inhibitors (50 µg/day) on days 5 and 6 after SCI. METHODS: Male SD rats underwent T10 laminectomy under mixed anesthesia, and IH impactors were applied to the same site to create a rat SCI model. Rats that underwent only laminectomy were designated as sham. Lumbar spinal cord at the L4-5 level was harvested at 3, 5, 7, 14, and 28 days after SCI, and COX2 and COX1 were quantified by reverse-transcription PCR (RT-PCR). COX2 expression, expression site, and expression time were determined by immunohistochemistry (IHC) and in situ hybridization histochemistry (ISHH) at the same time points. The expression site and time of COX2 expression were also examined at the same time point by ISHH. On 5th and 6th day after SCI, saline and COX2 inhibitor (50 µg/day) were administered into the subarachnoid space as a single dose, and the two groups were compared in terms of mechanical withdrawal latency using the dynamic plantar esthesiometer, which is an automated von Frey-type system. RESULTS: COX2 was significantly increased at 5 and 7 days after SCI, but no significant difference in COX1 was observed after SCI by RT-PCR. ISHH targeting COX2 showed clear expression of COX2 in spinal cord vascular endothelial cells at 5 and 7 days after SCI. COX2 expression was almost abolished at day 14 and 28. Behavioral experiments showed that pain was significantly improved from day 2 after COX2 inhibitor administration compared to the saline group, with improvement up to day 14 after SCI, but no significant difference was observed after day 21. CONCLUSIONS: The present findings suggest that thoracic SCI increased COX2 in vascular endothelial cells in the lumbar spinal cord and that the administration of COX2 inhibitor significantly alleviated mechanical hypersensitivity of the hind-paw following the thoracic SCI. Therefore, endothelial cell derived COX2 in the lumbar spinal cord may be involved in the induction of neuropathic pain in the SCI model rats. CLINICAL SIGNIFICANCE: The findings in the present study regarding the induction of endothelial COX2 and the effect of its inhibitor on the mechanical hypersensitivity suggest that endothelial cell-derived COX2 is one of the focuses for the treatment for neuropathic pain in the acute phase of SCI.

The role of evolving concepts and new technologies and approaches in advancing pain research, management, and education since the establishment of the International Association for the Study of Pain.

ABSTRACT: The decades since the inauguration of the International Association for the Study of Pain have witnessed major advances in scientific concepts (such as the biopsychosocial model and chronic primary pain as a disease in its own right) and in new technologies and approaches (from molecular biology to brain imaging) that have inspired innovations in pain research. These have guided progress in pain management and education about pain for healthcare professionals, the general public, and administrative agencies.

[Introduction: Toward a Better Understanding of Pain].

Pain is an important manifestation of many diseases and may occasionally occur independent of the disease. Although many clinicians encounter the clinical symptom of pain on a daily basis in routine practice, the pathophysiology of various chronic pain conditions remains unclear; therefore, a standardized therapeutic approach is unavailable, and optimal pain management is challenging. Accurate understanding of pain represents the primary measure in pain alleviation, and much knowledge has been accumulated through basic and clinical research over time. We will continue research to gain deeper insight into the mechanisms underlying pain and aim to achieve "relief from pain," which constitutes the roots of medical care.

Axonal membrane stretch suppresses neuronal excitability by activating mechanosensitive K2P channels at the node of Ranvier.

Saltatory conduction is the propagation of action potentials along myelinated nerves, which enables fast propagation through the node of Ranvier. Recently, we demonstrated that K2P channels, TWIK-related K+ channel-1 (TREK-1), and TWIK-related arachidonic acid-activated K + channel (TRAAK), are highly expressed in the mammalian node of Ranvier of sensory nerves and have an important role in action potential repolarization instead of voltage-gated K+ channels. TREK-1/TRAAK channels are activated by membrane depolarization as well as various stimuli, such as temperature, pH, arachidonic acid, and mechanical membrane stretch. Although membrane mechanical stretch has been suggested to modulate action potential conduction, how membrane stretching modulates intrinsic electrophysiological properties at the node of Ranvier remains unclear. In the present study, we examined the effects of membrane stretch on neuronal membranes at the node of Ranvier in rat sciatic nerves. The single-channel conductance was approximately 90 pS at 80 mV. Membrane stretch increased the single-channel event numbers and open probability in a pressure-dependent manner. Consistent with single-channel activity, intra-pipette positive pressure increased outward leak currents and decreased membrane excitability in a whole-cell configuration. Furthermore, blockage of TREK-1/TRAAK channels by Ba2+ reversed the changes in the intrinsic electrophysiological properties induced by intra-pipette pressure. These results indicate that the activation of mechanosensitive TREK-1/TRAAK channels may suppress neuronal excitability following axonal stretch. Our findings suggest that TREK-1/TRAAK channels may play an important role in the prevention of ectopic action potential discharge at the axon by intense mechanical nerve stretch under physiological conditions.

Analgesic effect of gastrin-releasing peptide in the dorsal horn.

Itch and pain are both unpleasant, but they are discrete sensations. Both of these sensations are transmitted by C-fibers and processed in laminae I-II of the dorsal horn. To examine whether pruriception modulates pain, we first confirmed the activation of cells in the itch-related circuits that were positive for gastrin-releasing peptide (GRP) and GRP receptor (GRPR) using a paw formalin injection model. This pain model with typical biphasic pain behavior increased c-Fos but did not affect the expressions of GRP and GRPR mRNAs in the dorsal horn. Using c-Fos expression as a marker for activated cells, we confirmed that formalin injection increased the number of cells double-labeled for c-Fos and GRP or GRPR in the dorsal horn. The emergence of these neurons indicates the activation of itch-related circuits by acute pain signals. The effect of an antagonist for a GRPR was examined in the paw formalin injection model. Intrathecal chronic antagonization of spinal GRPR enhanced the onset of phase II of paw formalin injection-induced pain behavior. Exogenous intrathecal GRP infusion to the paw-formalin injection model not only showed significant reduction of pain behavior but also increased c-Fos in the inhibitory neurons in the dorsal horn. The anti-nociceptive effect of spinal GRP infusion was observed in the peripheral inflammation model (complete Freund's adjuvant injection model). In this study we suggest that painful stimuli activated itch-related neuronal circuits and uncovered the spinal activation of the itch-induced analgesic effect on acute and established inflammatory pain.

Yokukansan Suppresses Gastric Hypersensitivity and Eosinophil-associated Microinflammation in Rats With Functional Dyspepsia.

Background/Aims: Herbal medicine is an important complementary therapy for functional dyspepsia (FD). However, its effect against gastric hypersensitivity in patients with FD has rarely been evaluated. Yokukansan (YKS), a traditional Japanese herbal medicine, is effective against neuropathic and inflammatory pain. This study aims to use a maternal separation (MS) stress-induced FD model to investigate the effects of YKS against gastric hypersensitivity, gastric motility, and duodenal micro-inflammation. Methods: The MS stress model was established by separating newborn Sprague-Dawley rats from their mothers for 2 hours a day from postnatal days 1 to 10. At the age of 7-8 weeks, the rats were treated with YKS at a dose of 5 mL/kg (1 g/kg) for 7 consecutive days. After YKS treatment, electromyographic activity in the acromiotrapezius muscle by gastric distention and the gastric-emptying rate were assessed. Immunohistochemical analysis of eosinophils in the duodenum and phosphorylated extracellular signal-regulated kinase (p-ERK) 1/2 in the spinal cord was performed. Results: YKS treatment suppressed MS stress-induced gastric hypersensitivity and decreased the elevated levels of p-ERK1/2 in the spinal cord. In the gastroduodenal tract, YKS inhibited eosinophil-associated micro-inflammation but did not improve gastric dysmotility. Conclusions: YKS treatment improved gastric hypersensitivity by alleviating eosinophil-associated micro-inflammation in the gastroduodenal tract. This treatment may be considered an effective therapeutic option for epigastric pain and micro-inflammation in patients with FD.

Reactive Oxygen Species Cause Exercise-Induced Angina in a Myocardial Ischaemia-Reperfusion Injury Model.

Percutaneous coronary intervention (PCI) effectively treats obstructive coronary artery syndrome. However, 30-40% patients continue to have angina after a successful PCI, thereby reducing patient satisfaction. The mechanisms underlying persistent angina after revascularisation therapy are still poorly understood; hence, the treatment or guideline for post-PCI angina remains unestablished. Thus, this study aimed to investigate the mechanisms underlying effort angina in animals following myocardial ischaemia-reperfusion (I/R) injury. Phosphorylated extracellular signal-regulated kinase (p-ERK), a marker for painful stimulation-induced neuronal activation, was used for the investigation. After a forced treadmill exercise (FTE), the number of p-ERK-expressing neurons increased in the superficial dorsal horn of the I/R model animals. Moreover, FTE evoked hydrogen peroxide (H2O2) production in the I/R-injured heart, inducing angina through TRPA1 activation on cardiac sensory fibres. Notably, the treatment of a TEMPOL, a reactive oxygen species scavenger, or TRPA1-/- mice successfully alleviated the FTE-induced p-ERK expression in the dorsal horn. The production of H2O2, a reactive oxygen species, through physical exercise contributes to angina development following I/R. Hence, our findings may be useful for understanding and treating angina following revascularisation therapy.

Acid increases PGE2 in the duodenal mucosa in rats.

Attention has recently been paid to the duodenum as the pathophysiologic center of functional dyspepsia. However, the precise mechanisms of symptom generation remain unknown. We here investigated the effect of acid on duodenal prostaglandin E2 and localization of prostaglandin E2 related receptors. Sprague-Dawley rats were used for this study. Hydrochloric acid was administered in the duodenum, then prostaglandin E2 levels in the duodenum were measured using the ELISA. The expression and localization of prostaglandin receptors (EP1-4) and the mRNAs of prostaglandin synthases were investigated using in situ hybridization histochemistry in duodenal tissue. After acid perfusion, prostaglandin E2 levels in the duodenum significantly increased. EP3 was expressed mainly at the myenteric plexus in the duodenal mucosa, and EP4 at both the epithelial surface and myenteric plexus. Contrary, EP2 was sparsely distributed in the villi and EP1 were not clearly seen on in situ hybridization histochemistry. Prostaglandin-synthetic enzymes were also distributed in the duodenal mucosa. The prostaglandin E2 levels in the duodenum increased after acidification. Prostaglandin E2 receptors and prostaglandin E2-producing enzymes were both observed in rat duodenum. These observations suggest that duodenal prostaglandin E2 possibly play a role in the symptom generation of functional dyspepsia.

Atractylodin Produces Antinociceptive Effect through a Long-Lasting TRPA1 Channel Activation.

Atractylodin (ATR) is a bioactive component found in dried rhizomes of Atractylodes lancea (AL) De Candolle. Although AL has accumulated empirical evidence for the treatment of pain, the molecular mechanism underlying the anti-pain effect of ATR remains unclear. In this study, we found that ATR increases transient receptor potential ankyrin-1 (TRPA1) single-channel activity in hTRPA1 expressing HEK293 cells. A bath application of ATR produced a long-lasting calcium response, and the response was completely diminished in the dorsal root ganglion neurons of TRPA1 knockout mice. Intraplantar injection of ATR evoked moderate and prolonged nociceptive behavior compared to the injection of allyl isothiocyanate (AITC). Systemic application of ATR inhibited AITC-induced nociceptive responses in a dose-dependent manner. Co-application of ATR and QX-314 increased the noxious heat threshold compared with AITC in vivo. Collectively, we concluded that ATR is a unique agonist of TRPA1 channels, which produces long-lasting channel activation. Our results indicated ATR-mediated anti-nociceptive effect through the desensitization of TRPA1-expressing nociceptors.

Aberrant Axo-Axonic Synaptic Reorganization in the Phosphorylated L1-CAM/Calcium Channel Subunit α2δ-1-Containing Central Terminals of Injured c-Fibers in the Spinal Cord of a Neuropathic Pain Model.

In the dorsal horn of the spinal cord, peripheral nerve injury induces structural and neurochemical alterations through which aberrant synaptic signals contribute to the formation of neuropathic pain. However, the role of injured primary afferent terminals in such plastic changes remain unclear. In this study, we investigated the effect of nerve injury on the morphology of cell adhesion molecule L1-CAM [total L1-CAM (tL1-CAM)]-positive primary afferent terminals and on the synaptic contact pattern in the dorsal horn. In the confocal images, the tL1-CAM-positive terminals showed morphologic changes leading to the formation of hypertrophic varicosities in the c-fiber terminal. These hypertrophic varicosities in the dorsal horn were co-labeled with phosphorylated (Ser1181) L1-CAM (pL1-CAM) and shown to store neurotransmitter peptides, but not when co-labeled with the presynaptic marker, synaptophysin. Quantitative analyses based on 3D-reconstructed confocal images revealed that peripheral nerve injury reduced dendritic synaptic contacts but promoted aberrant axo-axonic contacts on the tL1-CAM-positive hypertrophic varicosities. These tL1-CAM-positive varicosities co-expressed the injury-induced α2δ-1 subunit of the calcium channel in the dorsal horn. Administration of the anti-allodynic drug, pregabalin, inhibited accumulation of α2δ-1 and pL1-CAM associated with a reduction in hypertrophic changes of tL1-CAM-positive varicosities, and normalized injury-induced alterations in synaptic contacts in the dorsal horn. Our findings highlight the formation of aberrant spinal circuits that mediate the convergence of local neuronal signals onto injured c-fibers, suggesting that these hypertrophic varicosities may be important contributors to the pathologic mechanisms underlying neuropathic pain.

Kv4.3 Channel Dysfunction Contributes to Trigeminal Neuropathic Pain Manifested with Orofacial Cold Hypersensitivity in Rats.

Trigeminal neuropathic pain is the most debilitating pain disorder but current treatments including opiates are not effective. A common symptom of trigeminal neuropathic pain is cold allodynia/hyperalgesia or cold hypersensitivity in orofacial area, a region where exposure to cooling temperatures are inevitable in daily life. Mechanisms underlying trigeminal neuropathic pain manifested with cold hypersensitivity are not fully understood. In this study, we investigated trigeminal neuropathic pain in male rats following infraorbital nerve chronic constrictive injury (ION-CCI). Assessed by the orofacial operant behavioral test, ION-CCI animals displayed orofacial cold hypersensitivity. The cold hypersensitivity was associated with the hyperexcitability of small-sized trigeminal ganglion (TG) neurons that innervated orofacial regions. Furthermore, ION-CCI resulted in a reduction of A-type voltage-gated K+ currents (IA currents) in these TG neurons. We further showed that these small-sized TG neurons expressed Kv4.3 voltage-gated K+ channels, and Kv4.3 expression in these cells was significantly downregulated following ION-CCI. Pharmacological inhibition of Kv4.3 channels with phrixotoxin-2 inhibited IA-currents in these TG neurons and induced orofacial cold hypersensitivity. On the other hand, pharmacological potentiation of Kv4.3 channels amplified IA currents in these TG neurons and alleviated orofacial cold hypersensitivity in ION-CCI rats. Collectively, Kv4.3 downregulation in nociceptive trigeminal afferent fibers may contribute to peripheral cold hypersensitivity following trigeminal nerve injury, and Kv4.3 activators may be clinically useful to alleviate trigeminal neuropathic pain.SIGNIFICANCE STATEMENT Trigeminal neuropathic pain, the most debilitating pain disorder, is often triggered and exacerbated by cooling temperatures. Here, we created infraorbital nerve chronic constrictive injury (ION-CCI) in rats, an animal model of trigeminal neuropathic pain to show that dysfunction of Kv4.3 voltage-gated K+ channels in nociceptive-like trigeminal ganglion (TG) neurons underlies the trigeminal neuropathic pain manifested with cold hypersensitivity in orofacial regions. Furthermore, we demonstrate that pharmacological potentiation of Kv4.3 channels can alleviate orofacial cold hypersensitivity in ION-CCI rats. Our results may have clinical implications in trigeminal neuropathic pain in human patients, and Kv4.3 channels may be an effective therapeutic target for this devastating pain disorder.

Role of Rho-associated coiled-coil containing protein kinase in the spinal cord injury induced neuropathic pain.

BACKGROUND CONTEXT: Spinal cord injury (SCI) can lead to increased phosphorylation of p38 in spinal cord microglia. This is one of the main causes for the development of persistent pain. Recently, we reported our study on the activation of p38 mitogen-activated protein kinases (MAPK) in spinal microglia, which has been considered the key molecule for the onset and maintenance of neuropathic pain after peripheral nerve injury, using a rat model. We also reported that the RhoA/Rho-associated coiled-coil containing protein kinase (ROCK) pathway mediates p38 activation in spinal microglia in peripheral nerve injury. But the precise mechanisms of neuropathic pain induced by SCI are still unclear. PURPOSE: This study aimed to examine the activation of microglia and the p38 MAPK expression in the lumbar spinal cord after thoracic SCI in rats, and the correlation to the therapeutic effect of ROCK inhibitor ripasudil in rats with SCI. STUDY DESIGN: Male Sprague-Dawley rats underwent thoracic (T10) spinal cord contusion injury using an Infinite Horizon impactor device. SCI rats received ROCK inhibitor ripasudil (24 nmol/day or 240 nmol/day) from just before SCI to 3 days after SCI. METHODS: The mechanical threshold in the rat's hind paws was measured over four weeks. Morphology of microglia and phosphorylation of p38 (p-p38) in the lumbar spinal cord and were analyzed using immunohistochemistry. RESULTS: The p-p38 positive cell and Iba1 (a maker of microglia) positive area were significantly increased at the lumbar spinal dorsal horn (L4-5) 3 days and 7 days after SCI compared with the sham-control (p<.05), whereas phosphorylated p38 was co-localized with microglia. Three days after SCI, the intensity of phosphorylated p38 and Iba1 immunoreactive cells in the dorsal horn was significantly lower in the ripasudil treated groups than in the saline group. However, administration of ROCK inhibitor did not affect the numbers of microglia. Moreover, the withdrawal threshold of the ripasudil-treated rats was significantly higher than that of the saline-injected rats on 14 days and 28 days after SCI. CONCLUSIONS: Our results suggest that activation of ROCK in spinal cord microglia is likely to have an important role in the activation of p38 MAPK, which has been considered as a key molecule that switches on neuropathic pain after SCI. Inhibition of ROCK signaling may offer a means in developing a novel neuropathic pain treatment after SCI. It may help patients with neuropathic pain after SCI. CLINICAL SIGNIFICANCE: The findings in the present study regarding intracellular mechanisms suggest that modulation of ROCK signaling may be a focus for novel treatment for neuropathic pain after SCI.

The ubiquitin E3 ligase Nedd4-2 relieves mechanical allodynia through the ubiquitination of TRPA1 channel in db/db mice.

Neural precursor cell-expressed developmentally downregulated protein 4-2 (Nedd4-2) is a member of the E3 ubiquitin ligase family that is highly expressed in sensory neurons and involved in pain modulation via downregulation of ion channels in excitable membranes. Ubiquitination involving Nedd4-2 is regulated by adenosine monophosphate-activated protein kinase (AMPK), which is impaired in the dorsal root ganglion (DRG) neurons of db/db mice. AMPK negatively regulates the expression of transient receptor potential ankyrin 1 (TRPA1), a recognised pain sensor expressed on the membrane of DRG neurons, consequently relieving mechanical allodynia in db/db mice. Herein, we studied the involvement of Nedd4-2 in painful diabetic neuropathy and observed that Nedd4-2 negatively regulated diabetic mechanical allodynia. Nedd4-2 was co-expressed with TRPA1 in mouse DRG neurons. Nedd4-2 was involved in TRPA1 ubiquitination, this ubiquitination, as well as Nedd4-2-TRPA1 interaction, was decreased in db/db mice. Moreover, Nedd4-2 levels were decreased in db/db mice, while an abnormal intracellular distribution was observed in short-term high glucose-cultured DRG neurons. AMPK activators not only restored Nedd4-2 distribution but also increased Nedd4-2 expression. These findings demonstrate that Nedd4-2 is a potent regulator of TRPA1 and that the abnormal expression of Nedd4-2 in DRG neurons contributes to diabetic neuropathic pain.

Localization of prostaglandin E2 synthases and E-prostanoid receptors in the spinal cord in a rat model of neuropathic pain.

Prostaglandin E2 (PGE2) is a lipid mediator which plays a role in the generation of inflammatory and neuropathic pain. In the peripheral nervous system, PGE2 sensitizes nociceptive afferent neurons through E-prostanoid (EP) receptors. In the central nervous system, PGE2 modulates pain sensitivity and contributes to the development of neuropathic pain. However, the distribution of PGE2 and EP receptors in the spinal cord remains unclear. In the present study, we examined the expression of PGE2 synthases (microsomal PGE synthase [mPGES]-1, mPGES-2, and cytosolic PGE synthase [cPGES]) and EP receptors (EP1-4) in a rat model of neuropathic pain. We identified that mPGES-1 mRNA was upregulated in spinal endothelial cells after nerve injury and exhibited co-localization with cyclooxygenase-2 (COX-2). We detected that mPGES-2 mRNA and cPGES mRNA were expressed in spinal neurons and noted that their expression level was not affected by nerve injury. With respect to EP receptors, EP2 mRNA and EP4 mRNA were expressed in spinal neurons in the dorsal horn. EP3 mRNA was expressed in motor neurons, whereas EP1 mRNA was not detected in the spinal cord. Intrathecal injection of tumor necrosis factor alpha (TNFα) upregulated mPGES-1 mRNA in blood vessels in the spinal cord. Intrathecal injection of a TNFα-neutralizing antibody partially inhibited the upregulation of mPGES-1 mRNA after nerve injury. These results indicate that PGE2 is synthesized by COX-2/mPGES-1 in spinal endothelial cells after nerve injury. These results suggest that in neuropathic pain condition, endothelial cell-derived PGE2 may act on EP2 and EP4 receptors on spinal neurons and modulate pain sensitivity.

Eosinophil-associated microinflammation in the gastroduodenal tract contributes to gastric hypersensitivity in a rat model of early-life adversity.

Gastric hypersensitivity is a major pathophysiological feature of functional dyspepsia (FD). Recent clinical studies have shown that a large number of patients with FD present with gastroduodenal microinflammation, which may be involved in the pathophysiology of FD. However, no animal model reflecting this clinical characteristic has been established. The underlying mechanism between microinflammation and FD remains unknown. In this study, using a maternal separation (MS)-induced FD model, we aimed to reproduce the gastroduodenal microinflammation and reveal the interaction between gastroduodenal microinflammation and gastric hypersensitivity. The MS model was established by separating newborn Sprague-Dawley rats for 2 h a day from postnatal day 1 to day 10. At 7-8 wk of age, electromyography was used to determine the visceromotor response to gastric distention (GD) and immunohistochemistry was performed to detect distension-associated neuronal activation as well as immunohistological changes. Our results demonstrated that MS-induced FD rats underwent gastric hypersensitivity with GD at 60 and 80 mmHg, which are related to increased p-ERK1/2 expression in the dorsal horn of T9-T10 spinal cords. Eosinophils, but not mast cells, were significantly increased in the gastroduodenal tract, and the coexpression rate of CD11b and major basic protein significantly increased in MS rats. Treatment with dexamethasone reversed gastric hypersensitivity in MS-induced FD rats by inhibiting eosinophil infiltration. These findings indicated that neonatal MS stress induces eosinophil-associated gastroduodenal microinflammation and gastric hypersensitivity in adulthood in rats. Microinflammation contributes to gastric hypersensitivity; therefore, anti-inflammatory therapy may be effective in treating patients with FD with gastroduodenal microinflammation.NEW & NOTEWORTHY We showed for the first time that neonatal MS stress-induced FD rats undergo gastroduodenal eosinophil-associated microinflammation in adulthood. Suppression of microinflammation attenuated gastric hypersensitivity in MS rats. These findings established a functional link between microinflammation and gastric hypersensitivity, which may provide a potential clue for the clinical treatment of FD.

Daikenchuto attenuates visceral pain and suppresses eosinophil infiltration in inflammatory bowel disease in murine models.

BACKGROUND AND AIM: Daikenchuto (DKT), a traditional Japanese formula, comprises four herbal medicines and is used for abdominal pain. Inflammatory bowel disease (IBD) includes ulcerative colitis (UC) and Crohn's disease (CD) and is characterized by colonic inflammation and chronic abdominal pain. The present study aimed to investigate whether DKT suppresses colonic hypersensitivity and inflammation associated with IBD in animal models. METHODS: Sprague-Dawley rats were administered 4% sodium dextran sulfate (DSS) or trinitrobenzene sulfate (TNBS) in the colon to establish UC or CD models, respectively. DKT and 5-aminosalicylic acid (5-ASA) were administered orally once a day from Days 3 to 7 after induction of colitis. On Day 7, visceral pain and inflammation were evaluated by measuring the visceromotor response (VMR) to colorectal distention (CRD) and inflammatory indicators, including histological score, length of leukocyte infiltration, MPO activity, and eosinophil count. RESULTS: DSS and TNBS increased VMR to CRD and the inflammation indicators. DKT, but not 5-ASA, suppressed the VMR to CRD in DSS- and TNBS-treated rats. DKT and 5-ASA decreased the eosinophil count in both IBD models. In DSS-treated rats, 5-ASA, but not DKT, suppressed the MPO activity. In TNBS-treated rats, neither 5-ASA nor DKT suppressed MPO activity. CONCLUSION: These results suggest that DKT is beneficial for abdominal pain associated with IBD. The anti-inflammatory effect of DKT on IBD may involve inhibition of eosinophils. The mechanism of anti-inflammatory effect of DKT partially differs from that of 5-ASA. Coapplication of DKT and conventional medicine may produce a positive synergy effect for IBD treatment.

Association of higher arterial ketone body ratio (acetoacetate/ß-hydroxybutyrate) with relevant nutritional marker in hemodialysis patients.

BACKGROUND: An association of higher levels of ß-hydroxybutyrate (ß-HB) in serum with greater mortality in hemodialysis (HD) patients has been reported. This study examined the significance of arterial ketone body ratio (AcAc/ß-HB), a relevant marker of energy state, in HD patients. METHODS: The levels of arterial AcAc and ß-HB, and AcAc/ß-HB ratio were determined in 49 HD patients just before undergoing an HD session. Additionally, changes in those levels during the session were examined to investigate their associations with clinical nutritional markers. RESULTS: Arterial ß-HB, but not AcAc, was significantly higher at the baseline in 25 patients with type 2 diabetes mellitus (T2DM) as compared to 24 non-DM patients, with a significant reduction in arterial AcAc/ß-HB ratio seen in those with DM. Although the arterial AcAc/ß-HB ratio before the HD session was significantly higher in the non-DM group, it did not differ significantly after the session between the groups, indicating a faster rate of ß-HB disappearance from circulation in non-DM HD patients during the interdialytic period. Multiple regression analysis, which included age, gender, presence/absence of DM, log HD duration, log ß-HB, and log AcAc/ß-HB ratio as independent variables, revealed an independent and significant association of log AcAc/ ß-HB ratio, but not log ß-HB, with serum albumin and uric acid. CONCLUSION: We found that a decreased AcAc/ß-HB ratio resulting from increased ß-HB, but not increased ß-HB itself, was a significant factor independently associated with decreased levels of serum albumin and uric acid, known to be related to higher mortality in HD patients. Furthermore, it is possible that higher mortality in DM HD patients can be explained by reduced arterial AcAc/ß-HB ratio.

TREK-1 and TRAAK Are Principal K+ Channels at the Nodes of Ranvier for Rapid Action Potential Conduction on Mammalian Myelinated Afferent Nerves.

Rapid conduction of nerve impulses is critical in life and relies on action potential (AP) leaps through the nodes of Ranvier (NRs) along myelinated nerves. While NRs are the only sites where APs can be regenerated during nerve conduction on myelinated nerves, ion channel mechanisms underlying the regeneration and conduction of APs at mammalian NRs remain incompletely understood. Here, we show that TREK-1 and TRAAK, the thermosensitive and mechanosensitive two-pore-domain potassium (K2P) channels, are clustered at NRs of rat trigeminal Aß-afferent nerves with a density over 3,000-fold higher than that on their somas. These K2P channels, but not voltage-gated K+ channels as in other parts of nerves, are required for rapid AP repolarization at the NRs. Furthermore, these channels permit high-speed and high-frequency AP conduction along the myelinated afferent nerves, and loss of function of these channels at NRs retards nerve conduction and impairs sensory behavioral responses in animals.