Exosomes, secreted microvesicles transporting microRNAs (miRNAs), mRNAs, and proteins through bodily fluids, facilitate intercellular communication and elicit immune responses. Exosomal contents vary depending on the source and the physiological conditions of cells and can provide insights into how cells and systems cope with physiological perturbations. Previous analysis of circulating miRNAs in patients with complex regional pain syndrome (CRPS), a debilitating chronic pain disorder, revealed a subset of miRNAs in whole blood that are altered in the disease. To determine functional consequences of alterations in exosomal biomolecules in inflammation and pain, we investigated exosome-mediated information transfer in vitro, in a rodent model of inflammatory pain and in exosomes from patients with CRPS. Mouse macrophage cells stimulated with lipopolysaccharides (LPS) secrete exosomes containing elevated levels of cytokines and miRNAs that mediate inflammation. Transcriptome sequencing of exosomal RNA revealed global alterations in both innate and adaptive immune pathways. Exosomes from LPS-stimulated cells were sufficient to cause NF-kappaB activation in naïve cells, indicating functionality in recipient cells. A single injection of exosomes attenuated thermal hyperalgesia in a mouse model of inflammatory pain, suggesting an immunoprotective role for macrophage-derived exosomes. We also show that circulating miRNAs altered in patients with complex regional pain syndrome are trafficked by exosomes. Macrophage-derived exosomes carry a protective signature that is altered when secreting cells are exposed to an inflammatory stimulus. With their systemic signaling capabilities, exosomes can induce pleiotropic effects potentially mediating the multifactorial pathology underlying chronic pain and should be explored for their therapeutic utility.

Menthol is one of the most commonly used chemicals in our daily life, not only because of its fresh flavor and cooling feeling but also because of its medical benefit. Previous studies have suggested that menthol produces analgesic action in acute and neuropathic pain through peripheral mechanisms. However, the central actions and mechanisms of menthol remain unclear. Here, we report that menthol has direct effects on the spinal cord. Menthol decreased both ipsilateral and contralateral pain hypersensitivity induced by complete Freund's adjuvant in a dose-dependent manner. Menthol also reduced both first and second phases of formalin-induced spontaneous nocifensive behavior. We then identified the potential central mechanisms underlying the analgesic effect of menthol. In cultured dorsal horn neurons, menthol induced inward and outward currents in a dose-dependent manner. The menthol-activated current was mediated by Cl Ϫ and blocked by bicuculline, suggesting that menthol activates ␥-aminobutyric acid type A receptors. In addition, menthol blocked voltage-gated sodium channels and voltage-gated calcium channels in a voltage-, state-, and usedependent manner. Furthermore, menthol reduced repetitive firing and action potential amplitude, decreased neuronal excitability, and blocked spontaneous synaptic transmission of cultured superficial dorsal horn neurons. Liquid chromatography/tandem mass spectrometry analysis of brain menthol levels indicated that menthol was rapidly concentrated in the brain when administered systemically. Our results indicate that menthol produces its central analgesic action on inflammatory pain probably via the blockage of voltage-gated Na ϩ and Ca 2ϩ channels. These data provide molecular and cellular mechanisms by which menthol decreases neuronal excitability, therefore contributing to menthol-induced central analgesia.

Pharmacological intervention targeting mGluRs has emerged as a potential treatment for schizophrenia, whereas the mechanisms involved remain elusive. We explored the antipsychotic effects of a mGluR2/3 agonist in the MK-801 model of schizophrenia in the rat prefrontal cortex. We found that the mGluR2/3 agonist LY379268 effectively recovered the disrupted expression of NMDA receptors induced by MK-801 administration. This effect was attributable to the direct regulatory action of LY379268 on NMDA receptors via activation of the Akt/GSK-3β signaling pathway. As occurs with the antipsychotic drug clozapine, acute treatment with LY379268 significantly increased the expression and phosphorylation of NMDA receptors, as well as Akt and GSK-3β. Physiologically, LY379268 significantly enhanced NMDA-induced current in prefrontal neurons and a GSK-3β inhibitor occluded this effect. In contrast to the widely proposed mechanism of modulating presynaptic glutamate release, our results strongly argue that mGluR2/3 agonists modulate the function of NMDA receptors through postsynaptic actions and reverse the MK-801-induced NMDA dysfunction via the Akt/GSK-3β pathway. This study provides novel evidence for postsynaptic mechanisms of mGluR2/3 in regulation of NMDA receptors and presents useful insights into the mechanistic actions of mGluR2/3 agonists as potential antipsychotic agents for treating schizophrenia.