Acid-sensing ion channels (ASICs) have long been considered as extracellular proton (H(+))-gated cation channels, and peripheral ASIC3 channels seem to be a natural sensor of acidic pain. Here, we report the identification of a nonproton sensor on ASIC3. We show first that 2-guanidine-4-methylquinazoline (GMQ) causes persistent ASIC3 channel activation at the normal pH. Using GMQ as a probe and combining mutagenesis and covalent modification analysis, we then uncovered a ligand sensor lined by residues around E423 and E79 of the extracellular "palm" domain of the ASIC3 channel that is crucial for activation by nonproton activators. Furthermore, we show that GMQ activates sensory neurons and causes pain-related behaviors in an ASIC3-dependent manner, indicating the functional significance of ASIC activation by nonproton ligands. Thus, natural ligands beyond protons may activate ASICs under physiological and pathological conditions through the nonproton ligand sensor, serving for channel activation independent of abrupt and marked acidosis.

Transgenic overexpression of NMDA NR2B receptors in forebrain regions increased behavioral responses to persistent inflammatory pain. However, it is not known whether inflammation leads to the upregulation of NR2B receptors in these regions. Here, we show that peripheral inflammation increased the expression of NMDA NR2B receptors and NR2B receptor-mediated synaptic currents in the anterior cingulate cortex (ACC). In freely moving mice, the increase in NR2B receptors after inflammation contributed to enhanced NMDA receptor-mediated responses in the ACC. Inhibition of NR2B receptors in the ACC selectively reduced behavioral sensitization related to inflammation. Our results demonstrate that the upregulation of NR2B receptors in the ACC contributes to behavioral sensitization caused by inflammation.

Reduction of glucose metabolism in brain is one of the main features of Alzheimer's disease. Thiamine (vitamin B1)-dependent processes are critical in glucose metabolism and have been found to be impaired in brains from patients with Alzheimer's disease. However, thiamine treatment exerts little beneficial effect in these patients. Here, we tested the effect of benfotiamine, a thiamine derivative with better bioavailability than thiamine, on cognitive impairment and pathology alterations in a mouse model of Alzheimer's disease, the amyloid precursor protein/presenilin-1 transgenic mouse. We show that after a chronic 8 week treatment, benfotiamine dose-dependently enhanced the spatial memory of amyloid precursor protein/presenilin-1 mice in the Morris water maze test. Furthermore, benfotiamine effectively reduced both amyloid plaque numbers and phosphorylated tau levels in cortical areas of the transgenic mice brains. Unexpectedly, these effects were not mimicked by another lipophilic thiamine derivative, fursultiamine, although both benfotiamine and fursultiamine were effective in increasing the levels of free thiamine in the brain. Most notably, benfotiamine, but not fursultiamine, significantly elevated the phosphorylation level of glycogen synthase kinase-3alpha and -3beta, and reduced their enzymatic activities in the amyloid precursor protein/presenilin-1 transgenic brain. Therefore, in the animal Alzheimer's disease model, benfotiamine appears to improve the cognitive function and reduce amyloid deposition via thiamine-independent mechanisms, which are likely to include the suppression of glycogen synthase kinase-3 activities. These results suggest that, unlike many other thiamine-related drugs, benfotiamine may be beneficial for clinical Alzheimer's disease treatment.

Central serotonin (5-HT) dysregulation contributes to the susceptibility for mental disorders, including depression, anxiety, and posttraumatic stress disorder, and learning and memory deficits. We report that the formation of hippocampus-dependent spatial memory is compromised, but the acquisition and retrieval of contextual fear memory are enhanced, in central 5-HT-deficient mice. Genetic deletion of serotonin in the brain was achieved by inactivating Lmx1b selectively in the raphe nuclei of the brainstem, resulting in a near-complete loss of 5-HT throughout the brain. These 5-HT-deficient mice exhibited no gross abnormality in brain structures and had normal locomotor activity. Spatial learning in the Morris water maze was unaffected, but the retrieval of spatial memory was impaired. In contrast, contextual fear learning and memory induced by foot-shock conditioning was markedly enhanced, but this enhancement could be prevented by intracerebroventricular administration of 5-HT. Foot shock impaired longterm potentiation and facilitated long-term depression in hippocampal slices in WT mice but had no effect in 5-HT-deficient mice. Furthermore, bath application of 5-HT in 5-HT-deficient mice restored foot shock-induced alterations of hippocampal synaptic plasticity. Thus, central 5-HT regulates hippocampus-dependent contextual fear memory, and 5-HT modulation of hippocampal synaptic plasticity may be the underlying mechanism. The enhanced fear memory in 5-HT-deficient mice supports the notion that 5-HT deficiency confers susceptibility to posttraumatic stress disorder in humans.hippocampus ͉ long-term depression ͉ long-term potentiation ͉ anxiety T he neurotransmitter serotonin (5-HT) exerts a wide spectrum of actions in the nervous system by modulating neural development, synaptic plasticity, pain sensation, rhythm, food intake, and a variety of behaviors (1-4). It has been proposed that perturbation of the 5-HT level in the brain contributes to depression and anxiety, and posttraumatic stress disorder (PTSD) (5-8), which are often accompanied by learning and memory deficits (9-11). The hippocampus is known to be critical for the formation of spatial and contextual fear memories (12-15), and the retrieval of hippocampus-dependent memories was found to be impaired in patients with depression and PTSD (16)(17)(18). Recent studies have also implicated the hippocampus as one of the primary sites for antidepressants (6,(19)(20)(21)(22)(23). Aversive stimuli such as foot shock that led to anxiety, depression, and fear memory in rodents also altered activity-dependent hippocampal synaptic plasticity (24)(25)(26)(27)(28)(29). Because the modulation of 5-HT activity altered hippocampal long-term potentiation (LTP) and long-term depression (LTD) (30-32), it is possible that perturbation of 5-HT level in the brain may affect hippocampusdependent learning and memory, and changes in hippocampal synaptic plasticity may also contribute to mental disorders, including anxiety and fear memory.Inhibitors of 5-HT biosynthesis that...

NG2 cells originate from various brain regions and migrate to their destinations during early development. These cells express voltage-gated Na+ channels but fail to produce typical action potentials. The physiological role of Na+ channels in these cells is unclear. We found that GABA induces membrane depolarization and Ca2+ elevation in NG2 cells, a process requiring activation of GABAA receptors, Na+ channels, and Na+/Ca2+ exchangers (NCXs), but not Ca2+ channels. We have identified a persistent Na+ current in these cells that may underlie the GABA-induced pathway of prolonged Na+ elevation, which in turn triggers Ca2+ influx via NCXs. This unique Ca2+ signaling pathway is further shown to be involved in the migration of NG2 cells. Thus, GABAergic signaling mediated by sequential activation of GABAA receptors, noninactivating Na+ channels, and NCXs may play an important role in the development and function of NG2 glial cells in the brain.

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It is well documented that N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors play a pivotal role in ischaemic brain injury. Recent studies have shown that kainate (KA) receptors are involved in neuronal cell death induced by seizure, which is mediated by the GluR6*PSD-95*MLK3 signalling module and subsequent c-Jun N-terminal kinase (JNK) activation. Here we investigate whether GluR6 mediated JNK activation is correlated with ischaemic brain injury. Our results show that cerebral ischaemia followed by reperfusion can enhance the assembly of the GluR6*PSD-95*MLK3 signalling module and JNK activation. As a result, activated JNK can not only phosphorylate the transcription factor c-Jun and up-regulate Fas L expression but can also phosphorylate 14-3-3 and promote Bax translocation to mitochondria, increase the release of cytochrome c and increase caspase-3 activation. These results indicate that GluR6 mediated JNK activation induced by ischaemia/reperfusion ultimately results in neuronal cell death via nuclear and non-nuclear pathways. Furthermore, the peptides we constructed, Tat-GluR6-9c, show a protective role against neuronal death induced by cerebral ischaemia/reperfusion through inhibiting the GluR6 mediated signal pathway. In summary, our results indicate that the KA receptor subunit GluR6 mediated JNK activation is involved in ischaemic brain injury and provides a new approach for stroke therapy.

BackgroundThere is current interest in understanding the molecular mechanisms of tumor-induced bone pain. Accumulated evidence shows that endogenous formaldehyde concentrations are elevated in the blood or urine of patients with breast, prostate or bladder cancer. These cancers are frequently associated with cancer pain especially after bone metastasis. It is well known that transient receptor potential vanilloid receptor 1 (TRPV1) participates in cancer pain. The present study aims to demonstrate that the tumor tissue-derived endogenous formaldehyde induces bone cancer pain via TRPV1 activation under tumor acidic environment.Methodology/Principal FindingsEndogenous formaldehyde concentration increased significantly in the cultured breast cancer cell lines in vitro, in the bone marrow of breast MRMT-1 bone cancer pain model in rats and in tissues from breast cancer and lung cancer patients in vivo. Low concentrations (1∼5 mM) of formaldehyde induced pain responses in rat via TRPV1 and this pain response could be significantly enhanced by pH 6.0 (mimicking the acidic tumor microenvironment). Formaldehyde at low concentrations (1 mM to 100 mM) induced a concentration-dependent increase of [Ca2+]i in the freshly isolated rat dorsal root ganglion neurons and TRPV1-transfected CHO cells. Furthermore, electrophysiological experiments showed that low concentration formaldehyde-elicited TRPV1 currents could be significantly potentiated by low pH (6.0). TRPV1 antagonists and formaldehyde scavengers attenuated bone cancer pain responses.Conclusions/SignificanceOur data suggest that cancer tissues directly secrete endogenous formaldehyde, and this formaldehyde at low concentration induces metastatic bone cancer pain through TRPV1 activation especially under tumor acidic environment.