Population pharmacokinetics of daptomycin in critically ill patients receiving extracorporeal membrane oxygenation.

BACKGROUND: Daptomycin is widely used in critically ill patients for Gram-positive bacterial infections. Extracorporeal membrane oxygenation (ECMO) is increasingly used in this population and can potentially alter the pharmacokinetic (PK) behaviour of antibiotics. However, the effect of ECMO has not been evaluated in daptomycin. Our study aims to explore the effect of ECMO on daptomycin in critically ill patients through population pharmacokinetic (PopPK) analysis and to determine optimal dosage regimens based on both efficacy and safety considerations. METHODS: A prospective, open-label PK study was carried out in critically ill patients with or without ECMO. The total concentration of daptomycin was determined by UPLC-MS/MS. NONMEM was used for PopPK analysis and Monte Carlo simulations. RESULTS: Two hundred and ninety-three plasma samples were collected from 36 critically ill patients, 24 of whom received ECMO support. A two-compartment model with first-order elimination can best describe the PK of daptomycin. Creatinine clearance (CLCR) significantly affects the clearance of daptomycin while ECMO has no significant effect on the PK parameters. Monte Carlo simulations showed that, when the MICs for bacteria are  ≥1 mg/L, the currently recommended dosage regimen is insufficient for critically ill patients with CLCR > 30 mL/min. Our simulations suggest 10 mg/kg for patients with CLCR between 30 and 90 mL/min, and 12 mg/kg for patients with CLCR higher than 90 mL/min. CONCLUSIONS: This is the first PopPK model of daptomycin in ECMO patients. Optimal dosage regimens considering efficacy, safety, and pathogens were provided for critical patients based on pharmacokinetic-pharmacodynamic analysis.

Glia-derived adenosine in the ventral hippocampus drives pain-related anxiodepression in a mouse model resembling trigeminal neuralgia.

Glial activation and dysregulation of adenosine triphosphate (ATP)/adenosine are involved in the neuropathology of several neuropsychiatric illnesses. The ventral hippocampus (vHPC) has attracted considerable attention in relation to its role in emotional regulation. However, it is not yet clear how vHPC glia and their derived adenosine regulate the anxiodepressive-like consequences of chronic pain. Here, we report that chronic cheek pain elevates vHPC extracellular ATP/adenosine in a mouse model resembling trigeminal neuralgia (rTN), which mediates pain-related anxiodepression, through a mechanism that involves synergistic effects of astrocytes and microglia. We found that rTN resulted in robust activation of astrocytes and microglia in the CA1 area of the vHPC (vCA1). Genetic or pharmacological inhibition of astrocytes and connexin 43, a hemichannel mainly distributed in astrocytes, completely attenuated rTN-induced extracellular ATP/adenosine elevation and anxiodepressive-like behaviors. Moreover, inhibiting microglia and CD39, an enzyme primarily expressed in microglia that degrades ATP into adenosine, significantly suppressed the increase in extracellular adenosine and anxiodepressive-like behaviors. Blockade of the adenosine A2A receptor (A2AR) alleviated rTN-induced anxiodepressive-like behaviors. Furthermore, interleukin (IL)-17A, a pro-inflammatory cytokine probably released by activated microglia, markedly increased intracellular calcium in vCA1 astrocytes and triggered ATP/adenosine release. The astrocytic metabolic inhibitor fluorocitrate and the CD39 inhibitor ARL 67156, attenuated IL-17A-induced increases in extracellular ATP and adenosine, respectively. In addition, astrocytes, microglia, CD39, and A2AR inhibitors all reversed rTN-induced hyperexcitability of pyramidal neurons in the vCA1. Taken together, these findings suggest that activation of astrocytes and microglia in the vCA1 increases extracellular adenosine, which leads to pain-related anxiodepression via A2AR activation. Approaches targeting astrocytes, microglia, and adenosine signaling may serve as novel therapies for pain-related anxiety and depression.

Toward Antifragility: Social Defeat Stress Enhances Learning and Memory in Young Mice Via Hippocampal Synaptosome Associated Protein 25.

Social adversity not only causes severe psychological diseases but also may improve people's ability to learn and grow. However, the beneficial effects of social adversity are often ignored. In this study, we investigated whether and how social adversity affects learning and memory in a mouse social defeat stress (SDS) model. A total of 652 mice were placed in experimental groups of six to 23 mice each. SDS enhanced spatial, novelty, and fear memory with increased synaptosome associated protein 25 (SNAP-25) level and dendritic spine density in hippocampal neurons among young but not middle-aged mice. Chemogenetic inhibition of hippocampal CaMK2A+ neurons blocked SDS-induced enhancement of learning or memory. Knockdown of SNAP-25 or blockade of N-methyl-D-aspartate (NMDA) receptor subunit GluN2B in the hippocampus prevented SDS-induced learning memory enhancement in an emotion-independent manner. These findings suggest that social adversity promotes learning and memory ability in youths and provide a neurobiological foundation for biopsychological antifragility.

The neuroprotective effects of GPR55 against hippocampal neuroinflammation and impaired adult neurogenesis in CSDS mice.

Depression is one of the most prevalent mental illnesses in the world today, and the onset of depression is usually accompanied by neuroinflammation and impaired adult neurogenesis. As a new potential member of the endocannabinoid (eCB) system, G protein coupled receptor 55 (GPR55) has been associated with mood regulation. However, the role of GPR55 in the pathophysiology of depression remains poorly understood. Thus, a 10-day chronic social defeat stress (CSDS) paradigm was utilized as an animal model of depression to explore the potential role of GPR55 in depression. After CSDS, the protein level of GPR55 decreased significantly, but the mRNA expression did not change significantly, highlighting that although the GPR55 protein was involved in the progression of the depression- and anxiety-like phenotypes, its mRNA was not. Additionally, depression- and anxiety-like behaviors were also accompanied by neuroinflammation and impaired adult neurogenesis in the hippocampus. Interestingly, O-1602, a GPR55 agonist, remarkably prevented the development of depression- and anxiety-like behaviors as well as hippocampal neuroinflammation and neurogenesis deficits induced by CSDS. However, after electroacupuncture (EA) alleviated depression- and anxiety-like behaviors induced by CSDS, treatment with a GPR55 antagonist (CID16020046) reversed this effect. Our research demonstrated that downregulation of GPR55 expression in the hippocampus might mediate CSDS-induced depression- and anxiety-like phenotypes, and activation and upregulation of GPR55, which might be correlated with its anti-inflammatory and subsequent neuroprotective effects, could be a potential treatment for depression.

Protein Kinase C Lambda Mediates Acid-Sensing Ion Channel 1a-Dependent Cortical Synaptic Plasticity and Pain Hypersensitivity.

Chronic pain is a serious debilitating disease for which effective treatment is still lacking. Acid-sensing ion channel 1a (ASIC1a) has been implicated in nociceptive processing at both peripheral and spinal neurons. However, whether ASIC1a also contributes to pain perception at the supraspinal level remains elusive. Here, we report that ASIC1a in ACC is required for thermal and mechanical hypersensitivity associated with chronic pain. ACC-specific genetic deletion or pharmacological blockade of ASIC1a reduced the probability of cortical LTP induction and attenuated inflammatory thermal hyperalgesia and mechanical allodynia in male mice. Using cell type-specific manipulations, we demonstrate that ASIC1a in excitatory neurons of ACC is a major player in cortical LTP and pain behavior. Mechanistically, we show that ASIC1a tuned pain-related cortical plasticity through protein kinase C λ-mediated increase of membrane trafficking of AMPAR subunit GluA1 in ACC. Importantly, postapplication of ASIC1a inhibitors in ACC reversed previously established nociceptive hypersensitivity in both chronic inflammatory pain and neuropathic pain models. These results suggest that ASIC1a critically contributes to a higher level of pain processing through synaptic potentiation in ACC, which may serve as a promising analgesic target for treatment of chronic pain.SIGNIFICANCE STATEMENT Chronic pain is a debilitating disease that still lacks effective therapy. Ion channels are good candidates for developing new analgesics. Here, we provide several lines of evidence to support an important role of cortically located ASIC1a channel in pain hypersensitivity through promoting long-term synaptic potentiation in the ACC. Our results indicate a promising translational potential of targeting ASIC1a to treat chronic pain.

Distinct Function of Estrogen Receptors in the Rodent Anterior Cingulate Cortex in Pain-related Aversion.

BACKGROUND: Brain-derived estrogen is implicated in pain-related aversion; however, which estrogen receptors mediate this effect remains unclear. This study hypothesized that the different estrogen receptors in the rostral anterior cingulate cortex play distinct roles in pain-related aversion. METHODS: Formalin-induced conditioned place avoidance and place escape/avoidance paradigms were used to evaluate pain-related aversion in rodents. Immunohistochemistry and Western blotting were used to detect estrogen receptor expression. Patch-clamp recordings were used to examine N-methyl-D-aspartate-mediated excitatory postsynaptic currents in rostral anterior cingulate cortex slices. RESULTS: The administration of the estrogen receptor-ß antagonist 4-(2-phenyl-5,7-bis [trifluoromethyl] pyrazolo [1,5-a] pyrimidin-3-yl) phenol (PHTPP) or the G protein-coupled estrogen receptor-1 antagonist (3aS*,4R*,9bR*)-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-3H-cyclopenta [c] quinolone (G15) but not the estrogen receptor-α antagonist 1,3-bis (4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy) phenol]-1H-pyrazole dihydrochloride (MPP) into the rostral anterior cingulate cortex blocked pain-related aversion in rats (avoidance score, mean ± SD: 1,3-bis [4-hydroxyphenyl]-4-methyl-5-(4-[2-piperidinylethoxy] phenol)-1H-pyrazole dihydrochloride (MPP): 47.0 ± 18.9%, 4-(2-phenyl-5,7-bis [trifluoromethyl] pyrazolo [1,5-a] pyrimidin-3-yl) phenol (PHTPP): -7.4 ± 20.6%, and [3aS*,4R*,9bR*]-4-[6-bromo-1,3-benzodioxol-5-yl]-3a,4,5,9b-3H-cyclopenta [c] quinolone (G15): -4.6 ± 17.0% vs. vehicle: 46.5 ± 12.2%; n = 7 to 9; P < 0.0001). Consistently, estrogen receptor-ß knockdown but not estrogen receptor-α knockdown by short-hairpin RNA also inhibited pain-related aversion in mice (avoidance score, mean ± SD: estrogen receptor-α-short-hairpin RNA: 26.0 ± 7.1% and estrogen receptor-ß-short-hairpin RNA: 6.3 ± 13.4% vs. control short-hairpin RNA: 29.1 ± 9.1%; n = 7 to 10; P < 0.0001). Furthermore, the direct administration of the estrogen receptor-ß agonist 2,3-bis (4-hydroxyphenyl)-propionitrile (DPN) or the G protein-coupled estrogen receptor-1 agonist (±)-1-([3aR*,4S*,9bS*]-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta [c]quinolin-8-yl)-ethanone (G1) into the rostral anterior cingulate cortex resulted in conditioned place avoidance (avoidance score, mean ± SD: 2,3-bis (4-hydroxyphenyl)-propionitrile (DPN): 35.3 ± 9.5% and (±)-1-([3aR*,4S*,9bS*]-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta [c]quinolin-8-yl)-ethanone (G1): 43.5 ± 22.8% vs. vehicle: 0.3 ± 14.9%; n = 8; P < 0.0001) but did not affect mechanical or thermal sensitivity. The activation of the estrogen receptor-ß/protein kinase A or G protein-coupled estrogen receptor-1/protein kinase B pathway elicited the long-term potentiation of N-methyl-D-aspartate-mediated excitatory postsynaptic currents. CONCLUSIONS: These findings indicate that estrogen receptor-ß and G protein-coupled estrogen receptor-1 but not estrogen receptor-α in the rostral anterior cingulate cortex contribute to pain-related aversion by modulating N-methyl-D-aspartate receptor-mediated excitatory synaptic transmission.

Prefrontal AMPA receptors are involved in the effect of methylphenidate on response inhibition in rats.

Response inhibition is a critical executive control function in many species. Deficits in response inhibition have been observed in many disorders, eg, attention deficit/hyperactivity disorder (ADHD). The stop-signal task (SST) is a unique behavior task for evaluating response inhibition via measuring the covert latency of a stop process, and it is widely used in studies of humans, nonhuman primates and rodents. Methylphenidate (MPH; Ritalin®) is a psychostimulant that is widely used for the treatment of ADHD and that effectively improves response inhibition in individuals with ADHD and normal subjects. However, its mechanism of improving response inhibition remains unknown. In this study we adopted a rodent nose-poking version of the SST to examine response inhibition by estimating the stop signal reaction time (SSRT) in rats. Administration of MPH (1 mg/kg, sc) 25 min before the SST test exerted a baseline-dependent effect of MPH on response inhibition, ie, it shortened the SSRTs only in the rats with larger baseline SSRTs, thereby improving response inhibition in these rats. The effect of MPH on response inhibition remained 3 h after MPH administration. Co-administration of PP2 (1 mg/kg, sc), a Src-protein tyrosine kinase (Src-PTKs) inhibitor that inhibited the upregulation of glutamate receptor expression on the plasma membrane of the prefrontal cortex (PFC), abolished the MPH-caused improvement in response inhibition. Furthermore, intra-PFC infusion of a selective AMPAR antagonist.NASPM (0.3 mmol/L, per side) via stainless guide cannulas implanted earlier abolished the effect of MPH on SSRT. These results suggest that AMPA receptors in the PFC are involved in the effect of MPH on response inhibition in rats.

[Molecular mechanisms of NMDA receptor-MAPK-CREB pathway underlying the involvement of the anterior cingulate cortex in pain-related aversion].

The pain experience includes a sensory-discriminative component and an emotional-affective component. The great progress in the genetic, molecular, cellular and systemic levels on the study of the sensory dimension of pain has been made. However, the study of the emotional components of pain is relatively backward. A line of clinic observations indicates that chronic pain and pain-related negative emotion affect the physical and mental health of patients. This review summarizes the main progress from our and other laboratories regarding the affective component of pain, elaborates the neuronal mechanisms of pain-related aversive emotion in the anterior cingulate cortex (ACC), especially the critical role of NMDA receptors and ERK-CREB pathway. A variety of regulatory molecules, such as synapse associated protein SIP30 and estrogen contribute to pain-related aversive emotion via facilitating presynaptic glutamate release and postsynaptic NMDA receptor-mediated synaptic transmission. The far-reaching effects of pain-related negative emotion on patients with chronic pain are emphasized.

Delayed activation of spinal microglia contributes to the maintenance of bone cancer pain in female Wistar rats via P2X7 receptor and IL-18.

Accumulating evidence suggests that activation of spinal microglia contributes to the development of inflammatory and neuropathic pain. However, the role of spinal microglia in the maintenance of chronic pain remains controversial. Bone cancer pain shares features of inflammatory and neuropathic pain, but the temporal activation of microglia and astrocytes in this model is not well defined. Here, we report an unconventional role of spinal microglia in the maintenance of advanced-phase bone cancer pain in a female rat model. Bone cancer elicited delayed and persistent microglial activation in the spinal dorsal horn on days 14 and 21, but not on day 7. In contrast, bone cancer induced rapid and persistent astrocytic activation on days 7-21. Spinal inhibition of microglia by minocycline at 14 d effectively reduced bone cancer-induced allodynia and hyperalgesia. However, pretreatment of minocycline in the first week did not affect the development of cancer pain. Bone cancer increased ATP levels in CSF, and upregulated P2X7 receptor, phosphorylated p38, and IL-18 in spinal microglia. Spinal inhibition of P2X7/p-38/IL-18 pathway reduced advanced-phase bone cancer pain and suppressed hyperactivity of spinal wide dynamic range (WDR) neurons. IL-18 induced allodynia and hyperalgesia after intrathecal injection, elicited mechanical hyperactivity of WDR neurons in vivo, and increased the frequency of mEPSCs in spinal lamina IIo nociceptive synapses in spinal cord slices. Together, our findings demonstrate a novel role of microglia in maintaining advanced phase cancer pain in females via producing the proinflammatory cytokine IL-18 to enhance synaptic transmission of spinal cord nociceptive neurons.

[Effect of P2X7 receptor knock-out on bone cancer pain in mice].

Cancer pain is one of the most common symptoms in patients with late stage cancer. Lung, breast and prostate carcinoma are the most common causes of pain from osseous metastasis. P2X7 receptor (P2X7R) is one of the subtypes of ATP-gated purinergic ion channel family, predominately distributed in microglia in the spinal cord. Activation of P2X7Rs in the spinal dorsal horn has been associated with release of proinflammatory cytokines from glial cells, causing increased neuronal excitability and exaggerated nociception. Mounting evidence implies a critical role of P2X7R in inflammatory and neuropathic pain. However, whether P2X7R is involved in cancer pain remains controversial. Here we established a bone cancer pain model by injecting the Lewis lung carcinoma cells into the femur bone marrow cavity of C57BL/6J wild-type mice (C57 WT mice) and P2X7R knockout mice (P2rx7(-/-) mice) to explore the role of P2X7R in bone cancer pain. Following intrafemur carcinoma inoculation, robust mechanical allodynia and thermal hyperalgesia in C57 WT mice were developed on day 7 and 14, respectively, and persisted for at least 28 days in the ipsilateral hindpaw of the affected limb. CatWalk gait analysis showed significant decreases in the print area and stand phase, and a significant increase in swing phase in the ipsilateral hindpaw on day 21 and 28 after carcinoma cells inoculation. Histopathological sections (hematoxylin and eosin stain) showed that the bone marrow of the affected femur was largely replaced by invading tumor cells, and the femur displayed medullary bone loss and bone destruction on day 28 after inoculation. Unexpectedly, no significant changes in bone cancer-induced hypersensitivity of pain behaviors were found in P2rx7(-/-) mice, and the changes of pain-related values in CatWalk gait analysis even occurred earlier in P2rx7(-/-) mice, as compared with C57 WT mice. Together with our previous study in rats that blockade of P2X7R significantly alleviated bone cancer pain, it is implied that P2X7R may play different roles in bone cancer pain in different species (e.g. rat vs mouse). These results implicated a huge difference between the pathophysiology discovered in the experimental animal models and that of human disease.

SIP30 is required for neuropathic pain-evoked aversion in rats.

SIP30 (SNAP25 interacting protein of 30) is a SNAP25 interaction protein of 30 kDa that functions in neurotransmitter release. Using a chronic constriction injury (CCI) model of neuropathic pain, we profiled gene expression in the rat spinal cord and brain and identified sip30, which was upregulated after CCI. Here, we show that CCI induced a bilateral increase of SIP30 in the rostral anterior cingulate cortex (rACC), a key brain region that has been implicated in pain affect. We put rats in a chamber with one half painted white (light area) and the other half painted black (dark area), and measured neuropathic pain-evoked place escape/avoidance paradigm (PEAP) to quantify the level of negative emotion evoked by painful stimuli using a Von Frey hair. Inhibition of CCI-mediated induction of SIP30 by intra-rACC injection of shRNA targeting the rat sip30 gene reduced PEAP. Interestingly, knockdown of SIP30 did not affect CCI-induced evoked pain such as heat hyperalgesia and mechanical allodynia. Neither did it affect general learning and memory. CCI-induced upregulation of SIP30 was correlated with activation of ERK, PKA, and CREB in the rACC. Intra-rACC administration of PKA or ERK inhibitors suppressed CCI-induced SIP30 upregulation and blocked the induction of PEAP. Additionally, knockdown of SIP30 suppressed the frequency of mEPSCs and increased paired-pulse ratios in rACC slices and decreased extracellular glutamate concentrations. Together, our results highlight SIP30 as a target of PKA and ERK in the rACC to mediate neuropathic pain-evoked negative emotion via modulation of glutamate release and excitatory synaptic transmission.

[Activation of microglia and astrocytes in different spinal segments after peripheral nerve injury in mice].

Spinal microglia and astrocytes play an important role in mediating behavioral hypersensitive state following peripheral nerve injury. However, little is known about the expression patterns of activated microglia and astrocytes in the spinal dorsal horn. The aim of the present study was to investigate the spatial distribution of microglial and astrocytic activation in cervical, thoracic, lumbar and sacral segments of spinal dorsal horn following chronic constriction injury (CCI) of sciatic nerve. The hind paw withdrawal threshold (PWT) of wild type (WT), CX3CR1(YFP) and GFAP(YFP) transgenic mice to mechanical stimulation was determined by von Frey test. Immunofluorescence staining was used to examine the spatial distribution of microglial and astrocytic activation in the spinal dorsal horn. Following CCI, all the WT, CX3CR1(YFP) and GFAP(YFP) mice developed robust allodynia in the ipsilateral paw on day 3 after CCI, and the allodynia was observed to last for 14 days. In comparison with sham groups, the PWTs of CCI group animals were significantly decreased (P < 0.01, n = 6). On day 14 after CCI, CX3CR1(YFP)-GFP immunofluorescence intensity was significantly increased in the ipsilateral lumbar spinal dorsal horn of the CX3CR1(YFP) mice (P < 0.01, n = 6), but no detectable changes were observed in other spinal segments. Increased GFAP(YFP)-GFP immunofluorescence intensity was observed in the ipsilateral thoracic, lumbar and sacral spinal segments of the GFAP(YFP) mice on day 14 after CCI. Iba-1 and GFAP immunofluorescence staining in WT mice showed the same result of microglia and astrocyte activation on day 14 after CCI. CX3CR1(YFP)-GFP and GFAP(YFP)-GFP immunofluorescence signal was colocalized with microglial marker Iba-1 and astrocytic marker GFAP, respectively. Interestingly, on day 3 after CCI, Iba-1-immunoreactivity was significantly increased in the ipsilateral thoracic, lumbar and sacral spinal segments of WT mice, whereas the significant upregulation of GFAP-immunoreactivity restrictedly occurred in the ipsilateral lumbar spinal segment. These results suggest that microglial and astrocytic activation may be involved in the development and maintenance of secondary allodynia in mice with neuropathic pain.

Peripheral TGF-ß1 signaling is a critical event in bone cancer-induced hyperalgesia in rodents.

Pain is the most common symptom of bone cancer. TGF-ß, a major bone-derived growth factor, is largely released by osteoclast bone resorption during the progression of bone cancer and contributes to proliferation, angiogenesis, immunosuppression, invasion, and metastasis. Here, we further show that TGF-ß1 is critical for bone cancer-induced pain sensitization. We found that, after the progression of bone cancer, TGF-ß1 was highly expressed in tumor-bearing bone, and the expression of its receptors, TGFßRI and TGFßRII, was significantly increased in the DRG in a rat model of bone cancer pain that is based on intratibia inoculation of Walker 256 mammary gland carcinoma cells. The blockade of TGF-ß receptors by the TGFßRI antagonist SD-208 robustly suppressed bone cancer-induced thermal hyperalgesia on post-tumor day 14 (PTD 14). Peripheral injection of TGF-ß1 directly induced thermal hyperalgesia in intact rats and wide-type mice, but not in Trpv1(-/-) mice. Whole-cell patch-clamp recordings from DRG neurons showed that transient receptor potential vanilloid (TRPV1) sensitivity was significantly enhanced on PTD 14. Extracellular application of TGF-ß1 significantly potentiated TRPV1 currents and increased [Ca(2+)]i in DRG neurons. Pharmacological studies revealed that the TGF-ß1 sensitization of TRPV1 and the induction of thermal hyperalgesia required the TGF-ßR-mediated Smad-independent PKCε and TGF-ß activating kinase 1-p38 pathways. These findings suggest that TGF-ß1 signaling contributes to bone cancer pain via the upregulation and sensitization of TRPV1 in primary sensory neurons and that therapeutic targeting of TGF-ß1 may ameliorate the bone cancer pain in advanced cancer.

Up-regulation of interleukin-23 induces persistent allodynia via CX3CL1 and interleukin-18 signaling in the rat spinal cord after tetanic sciatic stimulation.

Tetanic stimulation of the sciatic nerve (TSS) induces sciatic nerve injury and long-lasting pain hypersensitivity in rats, and spinal glial activation and proinflammatory cytokines releases are involved. In the present study, we showed that spinal interleukin (IL)-23 and its receptor, IL-23R, are crucial for the development of mechanical allodynia after TSS. In the spinal dorsal horn, both IL-23 and IL-23R are expressed in astrocytes, and this expression is substantially increased after TSS. Inhibition of IL-23 signaling attenuated TSS-induced allodynia and decreased the induction of glial fibrillary acidic protein (GFAP, an astrocytic marker). Conversely, intrathecally delivered IL-23 induced a persistent allodynia. Similar to IL-23 signaling, an increase in IL-18 and its receptor, IL-18R, as well as CX3CL1 and its receptor, CX3CR1, was simultaneously observed in the spinal dorsal horn after TSS. Interestingly, IL-18 and CX3CR1 were exclusively expressed in microglia, while IL-18R was mainly localized in astrocytes. In contrast, CX3CL1 was predominately expressed in neurons and secondarily in astrocytes. The functional inhibition of CX3CL1 and IL-18 signaling attenuated TSS-induced allodynia and suppressed IL-23 and IL-23R upregulation. Activation of CX3CR1 and IL-18R induced similar behavioral and biochemical changes to those observed after TSS. These results indicate that the interaction among CX3CL1, IL-18 and IL-23 signaling in the spinal cord plays a critical role in the development of allodynia. Thus, interrupting this chemokine-cytokine network might provide a novel therapeutic strategy for neuropathic pain.

Estrogen in the anterior cingulate cortex contributes to pain-related aversion.

The rostral anterior cingulate cortex (rACC) is a key structure of pain affect. Whether and how estrogen in the rACC regulates pain-related negative emotion remains unclear. Behaviorally, using formalin-induced conditioned place aversion (F-CPA) in rats, which is believed to reflect the pain-related negative emotion, we found that estrogen receptor (ER) inhibitor ICI 182, 780 (ICI, 7α,17ß-[9-[(4,4,5,5,5-Pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol) or inhibitor of aromatase androstatrienedione into the rACC completely blocked F-CPA in either sex. An analogous effect was also observed in ovariectomy rats. Furthermore, exogenous estrogen in the absence of a formalin noxious stimulus was sufficient to elicit CPA (E-CPA) in both sexes by activating the membrane estrogen receptors (mERs) and N-methyl-D-aspartic acid (NMDA) receptors (NMDARs). Electrophysiologically, we demonstrated that estrogen acutely enhanced the glutamatergic excitatory postsynaptic currents (EPSCs) in rACC slices by increasing the ratio of NMDA-EPSCs to α-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl) propanoic acid -EPSCs and presynaptic glutamate release. Interestingly, a brief exposure to estrogen elicited a persistent enhancement of NMDA-EPSCs, and this NMDA-long-term potentiation required the activation of the mERs, protein kinase A and NMDAR subunit NR2B. Finally, estrogen induced rapid dendritic spine formation in cultured rACC neurons. These results suggest that estrogen in the rACC, as a neuromodulator, drives affective pain via facilitating NMDA receptor-mediated synaptic transmission.

Augmented microglial endoplasmic reticulum-mitochondria contacts mediate depression-like behavior in mice induced by chronic social defeat stress.

Extracellular ATP (eATP) signaling through the P2X7 receptor pathway is widely believed to trigger NLRP3 inflammasome assembly in microglia, potentially contributing to depression. However, the cellular stress responses of microglia to both eATP and stress itself remain largely unexplored. Mitochondria-associated membranes (MAMs) is a platform facilitating calcium transport between the endoplasmic reticulum (ER) and mitochondria, regulating ER stress responses and mitochondrial homeostasis. This study aims to investigate how MAMs influence microglial reaction and their involvement in the development of depression-like symptoms in response to chronic social defeat stress (CSDS). CSDS induced ER stress, MAMs' modifications, mitochondrial damage, and the formation of the IP3R3-GRP75-VDAC1 complex at the ER-mitochondria interface in hippocampal microglia, all concomitant with depression-like behaviors. Additionally, exposing microglia to eATP to mimic CSDS conditions resulted in analogous outcomes. Furthermore, knocking down GRP75 in BV2 cells impeded ER-mitochondria contact, calcium transfer, ER stress, mitochondrial damage, mitochondrial superoxide production, and NLRP3 inflammasome aggregation induced by eATP. In addition, reduced GRP75 expression in microglia of Cx3cr1CreER/+Hspa9f/+ mice lead to reduce depressive behaviors, decreased NLRP3 inflammasome aggregation, and fewer ER-mitochondria contacts in hippocampal microglia during CSDS. Here, we show the role of MAMs, particularly the formation of a tripartite complex involving IP3R3, GRP75, and VDAC1 within MAMs, in facilitating communication between the ER and mitochondria in microglia, thereby contributing to the development of depression-like phenotypes in male mice.

Corticotropin-releasing hormone neurons control trigeminal neuralgia-induced anxiodepression via a hippocampus-to-prefrontal circuit.

Anxiety and depression are frequently observed in patients suffering from trigeminal neuralgia (TN), but neural circuits and mechanisms underlying this association are poorly understood. Here, we identified a dedicated neural circuit from the ventral hippocampus (vHPC) to the medial prefrontal cortex (mPFC) that mediates TN-related anxiodepression. We found that TN caused an increase in excitatory synaptic transmission from vHPCCaMK2A neurons to mPFC inhibitory neurons marked by the expression of corticotropin-releasing hormone (CRH). Activation of CRH+ neurons subsequently led to feed-forward inhibition of layer V pyramidal neurons in the mPFC via activation of the CRH receptor 1 (CRHR1). Inhibition of the vHPCCaMK2A-mPFCCRH circuit ameliorated TN-induced anxiodepression, whereas activating this pathway sufficiently produced anxiodepressive-like behaviors. Thus, our studies identified a neural pathway driving pain-related anxiodepression and a molecular target for treating pain-related psychiatric disorders.

Estrogen facilitates spinal cord synaptic transmission via membrane-bound estrogen receptors: implications for pain hypersensitivity.

Recent evidence suggests that estrogen is synthesized in the spinal dorsal horn and plays a role in nociceptive processes. However, the cellular and molecular mechanisms underlying these effects remain unclear. Using electrophysiological, biochemical, and morphological techniques, we here demonstrate that 17ß-estradiol (E2), a major form of estrogen, can directly modulate spinal cord synaptic transmission by 1) enhancing NMDA receptor-mediated synaptic transmission in dorsal horn neurons, 2) increasing glutamate release from primary afferent terminals, 3) increasing dendritic spine density in cultured spinal cord dorsal horn neurons, and 4) potentiating spinal cord long term potentiation (LTP) evoked by high frequency stimulation (HFS) of Lissauer's tract. Notably, E2-BSA, a ligand that acts only on membrane estrogen receptors, can mimic E2-induced facilitation of HFS-LTP, suggesting a nongenomic action of this neurosteroid. Consistently, cell surface biotinylation demonstrated that three types of ERs (ERα, ERß, and GPER1) are localized on the plasma membrane of dorsal horn neurons. Furthermore, the ERα and ERß antagonist ICI 182,780 completely abrogates the E2-induced facilitation of LTP. ERß (but not ERα) activation can recapitulate E2-induced persistent increases in synaptic transmission (NMDA-dependent) and dendritic spine density, indicating a critical role of ERß in spinal synaptic plasticity. E2 also increases the phosphorylation of ERK, PKA, and NR2B, and spinal HFS-LTP is prevented by blockade of PKA, ERK, or NR2B activation. Finally, HFS increases E2 release in spinal cord slices, which can be prevented by aromatase inhibitor androstatrienedione, suggesting activity-dependent local synthesis and release of endogenous E2.

[Involvement of peripheral NFκB in tetanic sciatic stimulation-induced neuropathic pain].

Tetanic stimulation of the sciatic nerve (TSS) induces long-term potentiation (LTP) of both C- and A-fiber-evoked field potentials in the spinal dorsal horn and long-lasting mechanical allodynia in rats. Though central mechanisms underlying those phenomena have been well studied, peripheral mechanisms still remain poorly known. Nuclear factor kappa B (NFκB) is an important transcription factor. In the spinal cord, NFκB plays a key role in regulating the expression of numerous pro-inflammation factors and contributes to glial activation in central nervous system, suggesting the involvement of spinal NFκB in central sensitization. To address whether NFκB in the dorsal root ganglion (DRG) participates in peripheral sensitization, we examined NFκB expression in the DRG and the effect of inhibiting NFκB activation on neuropathic pain using behavior test, Western blot analysis and immunohistochemical approaches. The results showed that TSS induced long-lasting mechanical allodynia in bilateral hind paws and increased phospho-NFκB expression in the bilateral DRG. The activated NFκB mainly expressed in nuclei not only of neurons, but also of Schwann cells and satellite glial cells. Moreover, NFκB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly alleviated TSS-induced allodynia. Our results suggest that peripheral NFκB may be involved in TSS-induced neuropathic pain, and provide new evidence for the peripheral mechanism of 'mirror pain'.

Neuroendocrine and neuroimmune mechanisms underlying comorbidity of pain and obesity.

Pain and obesity, as well as their associated impairments, are major health concerns. Understanding the relationship between the two is the focus of a growing body of research. However, early researches attribute increased mechanical stress from excessive weight as the main factor of obesity-related pain, which not only over-simplify the association, but also fail to explain some controversial outcomes arising from clinical investigations. This review focuses on neuroendocrine and neuroimmune modulators importantly involved in both pain and obesity, analyzing nociceptive and anti-nociceptive mechanisms based on neuroendocrine pathways including galanin, ghrelin, leptin and their interactions with other neuropeptides and hormone systems which have been reported to play roles in pain and obesity. Mechanisms of immune activities and metabolic alterations are also discussed, due to their intense interactions with neuroendocrine system and crucial roles in the development and maintenance of inflammatory and neuropathic pain. These findings have implications for health given rising rates of obesity and pain-related diagnoses, by providing novel weight-control and analgesic therapies targeted on specific pathways.