Aging impairs recovery from stress-induced depression in male rats possibly by alteration of microRNA-101 expression and Rac1/RhoA pathway in the prefrontal cortex.

Along with altering brain responses to stress, aging may also impair recovery from depression symptoms. In the present study, we investigated depressive-like behaviors in young and aged rats and assayed the levels of microRNA-101 (miR-101), Rac1/RhoA, PSD-95, and GluR1 in the prefrontal cortex (PFC) after stress cessation and after a recovery period. Young (3 months old) and aged (22 months old) male Wistar rats were divided into six groups; Young control (YNG), young rats received chronic stress for four weeks (YNG + CS), young rats received chronic stress for four weeks followed by a 6-week recovery period (YNG + CS + REC), Aged control (AGED), aged rats received chronic stress for four weeks (AGED + CS), and aged rats received chronic stress for four weeks followed by a 6-week recovery period (AGED + CS + REC). Stress-induced depression, evaluated by the sucrose preference test (SPT) and forced swimming test (FST), was yet observed after the recovery period in aged but not in young rats, which were accompanied by unchanged levels of miR-101, Rac1/RhoA, GluR1, and PSD-95 in the PFC of aged rats. These data suggested that impaired synaptic plasticity of glutamatergic synapses via the miR-101/Rac1/RhoA pathway may contribute to the delayed behavioral recovery after stress exposure observed in aging animals.

Ketamine attenuates the PTSD-like effect via regulation of glutamatergic signaling in the nucleus accumbens of mice.

Post-traumatic stress disorder (PTSD) is a devastating mental illness with high morbidity and major social and economic burden. Currently, there is no promising therapy available for the treatment of PTSD. Some clinical studies showed that ketamine could effectively alleviate PTSD symptoms. However, it is still unclear which brain region ketamine targets and how it attenuates the PTSD-like effects. In this study, we examined the effect of ketamine on fear generalization (a core symptom of PTSD) by using a mice model of fear generalization induced by fear conditioning procedure. Before retrieval, ketamine was locally infused into the nucleus accumbens (a brain region closely associated with PTSD). Fear generalization mice were subjected to behavioral testing and biochemical assessments, following ketamine infusion. The results showed that the foot shock strength-dependently induced fear generalization in mice with increased c-fos activity, and a lower level of GluR1(S845), GluR1(S831) protein, and a higher level of P-GluN2B protein in the nucleus accumbens (NAc). Local infusion of ketamine into NAc decreased the fear generalization together with an increased level of GluR1(S845), GluR1(S831) protein, and decreased level of P-GluN2B protein. Altogether, these results conclude that ketamine might affect the glutamatergic signaling in the NAc to attenuate the fear generalization in mice.

Effects of perampanel on cognitive behavior and GluR1 expression in immature mice of temporal lobe epilepsy.

Temporal lobe epilepsy (TLE) has a low antiepileptic drug (AED) treatment response rate, and about 70% of patients eventually progress to refractory epilepsy. Perampanel (PER) is a noncompetitive α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor antagonist, which is used clinically for the treatment of partially refractory epilepsy, but its mechanism of action is not completely clear. In this study, kainic acid (KA) was successfully used to induce TLE in 3-week-old C57BL/6 immature mice, and the effects of PER on the cognitive behavior of the epileptic mice were characterized using the Morris water maze paradigm. To determine the mechanism underlying the therapeutic effects of PER, the morphological evolution of the hippocampus and the expression of AP-1 and GluR1 were systematically evaluated. Compared to control TLE mice, escape latency was reduced and the number of target platform crossings was increased in the Morris water maze by treatment with PER. The therapeutic effects of PER were mediated mainly via inhibition of the expression of AP-1 and GluR1, as the TLE mice showed significantly improved learning and memory and decreased seizure frequency after treatment with PER.

Fulminant anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor GluR1 antibodies encephalitis in a Chinese boy: a case report.

BACKGROUND: Anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis is a rare autoimmune synaptic encephalitis associated with autoantibodies that cause a selective decrease in surface expression and changes in receptor localization. Anti-AMPAR encephalitis is poorly recognized, especially in children, and its clinical phenotype is incompletely described. CASE PRESENTATION: We report a case of anti-AMPAR GluR1 antibody-mediated autoimmune encephalitis in a 12-year-old male. The patient manifested as a fulminant course, with ataxia, cerebellar degeneration at the onset, and rapidly evolved into hyperthermia, coma and rhabdomyolysis. Antibodies against AMPAR GluR1 receptors were detected in the cerebrospinal fluid by cell-based assay. Diffuse slow waves were found by electroencephalograph, and the left cerebellar vermis and hemisphere were affected on brain magnetic resonance imaging (MRI). The patient was treated with intravenous immunoglobulin (IVIG), methylprednisolone combined with plasma exchange. Symptoms were alleviated after immunotherapy and the patient sustained clinical improvement. This is the first time that acute rhabdomyolysis symptom has been identified in a pediatric patient with anti-AMPAR encephalitis. CONCLUSIONS: This case expands the clinical spectrum of anti-AMPAR encephalitis and highlights that despite poor clinical manifestation at the outset, recovery remains possible.

Meridianins Inhibit GSK3ß In Vivo and Improve Behavioral Alterations Induced by Chronic Stress.

Major depression disorder (MDD) is a severe mental alteration with a multifactorial origin, and chronic stress is one of the most relevant environmental risk factors associated with MDD. Although there exist some therapeutical options, 30% of patients are still resistant to any type of treatment. GSK3ß inhibitors are considered very promising therapeutic tools to counteract stress-related affectations. However, they are often associated with excessive off-target effects and undesired secondary alterations. Meridianins are alkaloids with an indole framework linked to an aminopyrimidine ring from Antarctic marine ascidians. Meridianins could overcome several of the aforementioned limitations since we previously demonstrated that they can inhibit GSK3ß activity without the associated neurotoxic or off-target effects in rodents. Here, we show that meridianins delivered into the lateral ventricle inhibited GSK3ß in several brain regions involved with stress-related symptoms. We also observed changes in major signaling pathways in the prefrontal cortex (Akt and PKA) and hippocampus (PKC and GluR1). Moreover, meridianins increased synaptic activity, specifically in the CA1 but not in the CA3 or other hippocampal subfields. Finally, we chronically treated the mice subjected to an unpredictable mild chronic stress (CUMS) paradigm with meridianins. Our results showed improvements produced by meridianins in behavioral alterations provoked by CUMS. In conclusion, meridianins could be of therapeutic interest to patients with stress-related disorders such as MDD.

Maternal separation increases cocaine intake through a mechanism involving plasticity in glutamate signalling.

Early-life stress (ELS) is associated with negative consequences, including maladaptive long-lasting brain effects. These alterations seem to increase the likelihood of developing substance use disorders. However, the molecular consequences of ELS are poorly understood. In the present study, we tested the impact of ELS induced by maternal separation with early weaning (MSEW) in CD1 male mice at different phases of cocaine self-administration (SA). We also investigated the subsequent alterations on GluR2, GluR1, cAMP response element-binding (CREB), and CREB-phosphorylation (pCREB) in ventral tegmental area (VTA) and nucleus accumbens (NAc) induced by both MSEW and cocaine SA. Our results show that MSEW animals expressed a higher cocaine intake, an increased vulnerability to the acquisition of cocaine SA, and incapacity to extinguish cocaine SA behaviour. MSEW mice showed decreased GluR2 and increased GluR1 and pCREB in NAc. Also, results displayed reduction of basal levels of GluR1 and CREB and an elevation of GluR1/GluR2 ratio in the VTA. Such results hint at an enhanced glutamatergic function in NAc and increased excitability of VTA DA neurons in maternally separated mice. Altogether, our results suggest that MSEW induces molecular alterations in the brain areas related to reward processing, increasing the vulnerability to depression and cocaine-seeking behaviour.

Brain Biomarkers in Children After Mild and Severe Traumatic Brain Injury.

Brain biomarkers (protein S100b and neuron-specific enolase (NSE)), antibodies (aAb) to the NR2 subunit of N-methyl-D-aspartate (NR2(NMDA)) and to the GluR1 subunit of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (GluR1(AMPA)) subtype of glutamate receptors (GluR), NR2 and AMPA peptides, nitrogen oxides (NOx; "nitrites and nitrates"), and 3-nitrotyrosine (NT) were measured in blood from 159 children after mild traumatic brain injury (mTBI), moderate traumatic brain injury (mdTBI), or severe traumatic brain injury (sTBI) within 1-2 days and at intervals during the first 15 days after brain trauma. S100b and NSE levels on the first day were not a strict criterion for injury outcomes. Children with mTBI had the most significant elevations in antibodies to NR2(NMDA) and AMPA peptides, a slight increase in NOx, and, in 25% of cases, appearance of NT in the blood right after TBI. The lowest level of antibodies to NR2(NMDA) GluR detected shortly after the initial TBI was found in children with sTBI, with a negative outcome. The opposite characters of antibodies to NR2(NMDA) on the first day in children with mild and moderate versus severe TBI may be associated with an important mechanism aimed at protecting neurons from Glu excitotoxicity. We hypothesized that a slight increase in NOx after the onset of TBI rapidly activates the innate immune system and contributes to an increase in antibodies to NR2(NMDA). An increase in the AMPA peptide level in mTBI may be early signs of diffuse axonal injury.

Interferon-γ Receptor 1 and GluR1 upregulated in motor neurons of symptomatic hSOD1G93A mice.

Motor neurons are markedly vulnerable to excitotoxicity mostly by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) stimulation and are principal targets in the neurodegenerative disease Amyotrophic Lateral Sclerosis. Interferon-gamma (IFN-γ), a pro-inflammatory cytokine, can independently cause neuronal dysfunction by triggering calcium influx through a calcium-permeable complex of IFN-γ receptor 1(IFNGR1) subunit and AMPAR subunit GluR1. This receptor complex is formed via a non-canonical neuron-specific IFN-γ pathway that involves Jak1/Stat1 and Protein Kinase A. In this study, we explore the expression of the pathway's participants for the first time in the hSOD1G93A Amyotrophic Lateral Sclerosis mouse model. Elevated IFNGR1 and GluR1 are detected in motor neurons of hSOD1G93A symptomatic mice ex vivo, unlike the downstream targets - Jak1, Stat1, and Protein Kinase A. We, also, determine effects of IFN-γ alone or in the presence of an excitotoxic agent, kainate, on motor neuron survival in vitro. IFN-γ induces neuronal damage, but does not influence kainate-mediated excitotoxicity. Increased IFNGR1 can most likely sensitize motor neurons to excitotoxic insults involving GluR1 and/or pathways mediated by IFN-γ, thus, serving as a potential direct link between neurodegeneration and inflammation in Amyotrophic Lateral Sclerosis.

The role of IRAS/Nischarin involved in the development of morphine tolerance and physical dependence.

Morphine is a potent opioid analgesic used to alleviate moderate or severe pain, but the development of drug tolerance and dependence limits its use in pain management. Our previous studies showed that the candidate protein for I1 imidazoline receptor, imidazoline receptor antisera-selected (IRAS)/Nischarin, interacts with µ opioid receptor (MOR) and modulates its trafficking. However, there is no report of the effect of IRAS on morphine tolerance and physical dependence. In the present study, we found that IRAS knockout (KO) mice showed exacerbated analgesic tolerance and physical dependence compared to wild-type (WT) mice by chronic morphine treatment. Chronic morphine treatment down-regulated the expression of MOR in spinal cord of IRAS KO mice, while had no significant effect on MOR expression in WT mice. We observed the compensatory increase of cAMP accumulation in spinal cord after morphine tolerance, and this change was more significant in KO mice than WT mice. Furthermore, KO mice showed more elevation in the phosphorylation of AMPA receptor GluR1-S845 than WT mice, while the total expression of GluR1 remained unchanged after morphine dependence. Altogether, these data suggest that IRAS may play an important role in the development of morphine tolerance and physical dependence in vivo through modulating MOR expression, as well as AMPA GluR1-S845 phosphorylation, which might be one of the mechanisms underlying the development of opiate addiction.

Yy1 regulates Senp1 contributing to AMPA receptor GluR1 expression following neuronal depolarization.

BACKGROUND: Neuronal activity-induced changes in gene expression patterns are important mediators of neuronal plasticity. Many neuronal genes can be activated or inactivated in response to neuronal depolarization. Mechanisms that activate gene transcription are well established, but activity-dependent mechanisms that silence transcription are less understood. It is also not clear what is the significance of inhibiting these genes during neuronal activity. METHODS: Quantitative Real Time-PCR, western blot and immunofluorescence staining were performed to examine the expression of Senp1 and GluR1 in mouse cortical neurons. The alterations of Yy1 phosphorylation upon neuronal depolarization and the interaction of Yy1 with Brd4 were studied by protein co-immunoprecipitation. The regulators of Yy1 phosphorylation were identified by phosphatase inhibitors. Chromatin immunoprecipitation, in vitro DNA binding assay, luciferase assay and gene knockdown experiments were used to validate the roles of Yy1 and its phosphorylation as well as Brd4 in regulating Senp1 expression. RESULTS: We report that neuronal depolarization deactivates the transcription of the SUMO protease Senp1, an important component regulating synaptic transmission, scaling, and plasticity, through Yy1. In un-stimulated neurons, Senp1 transcription is activated by a Yy1-Brd4 transcription factor protein complex assembled on the Senp1 promoter. Upon membrane depolarization, however, Yy1 is dephosphorylated and the Yy1-Brd4 complex is evicted from the Senp1 promoter, reducing Senp1 transcription levels. Both Yy1 and Senp1 promote the expression of AMPA receptor subunit GluR1, a pivotal component in learning and memory. CONCLUSIONS: These results reveal an axis of Yy1/Brd4-Senp1 which regulates the expression of GluR1 during neuronal depolarization. This implicates a regulation mechanism in silencing gene expression upon neuronal activity.

Desflurane impairs hippocampal learning on day 1 of exposure: a prospective laboratory study in rats.

BACKGROUND: Quick and complete recovery of cognitive function after general anesthesia is desirable, particularly for working-age patients. Desflurane is less likely to have long-term effects than older-generation inhalational anesthetics, however, its short-term effects have not been fully investigated. Our objective was to elucidate the short-term effects of desflurane exposure on learning and memory in young adult rats. METHODS: Seven-week old male Sprague-Dawley rats were exposed to air (control), or desflurane at 0.7 or 1.2 minimum alveolar concentration (MAC) for 2 h (day 0). The inhibitory avoidance (IA) test was performed on day 1 to delineate the effects on contextual learning. Separate groups of control and 1.2 MAC desflurane animals underwent the IA test on days 3 and 7 to examine the time-dependent changes. Because the IA test is known to be dependent on the long-term potentiation (LTP) of the hippocampus and the trafficking of the GluR1 subunit of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor into the synapses, the effects of 1.2 MAC desflurane on these phenomena were evaluated on day 1. RESULTS: Desflurane at 1.2 MAC, but not 0.7 MAC, significantly decreased the IA latencies on day 1 compared with the control (one-way ANOVA, F [2,48] = 5.974, P = 0.005, post hoc Tukey's, mean difference [95% confidence interval], control vs. 1.2 MAC, 168 [49.9 to 287], P = 0.004; control vs. 0.7 MAC, 67.5 [- 51.2 to 186], P = 0.362). The latencies were not affected on days 3 and 7 (day 3, control vs. desflurane, P = 0.861; day 7, control vs. desflurane, P > 0.999). Consistently, hippocampal LTP on day 1 was significantly suppressed in the desflurane group compared with the control group (P = 0.006). Moreover, immunoblotting analysis of synaptic GluR1 expression revealed that desflurane exposure significantly suppressed GluR1 delivery to the synapses after IA training. CONCLUSION: Exposure to a relatively high concentration of desflurane caused reversible learning and memory impairment in young adult rats associated with suppression of GluR1 delivery to the synapses in the hippocampus.

Effect of Interleukin-10 on Localization of AMPA Receptors in Synapses during Long-Term Posttetanic Potentiation in Cultured Hippocampal Slices.

The effect of the anti-inflammatory cytokine IL-10 on the ultrastructural distribution of AMPA receptor GluR1 subunit in CA1 field of cultured hippocampal slices was studied by using immunohistochemical technique. It was found that long-term posttetanic potentiation increased the content of GluR1 in the postsynaptic density of the axo-spinous synapse. Addition of IL-10 in concentrations of 1 and 10 ng/ml to the medium facilitated long-term posttetanic potentiation thereby changing the distribution of GluR1 in the spine: the number of receptors increased in the cytoplasm and decreased in the postsynaptic density. It is assumed that activation of neuronal IL-10 receptors affects the distribution of AMPA receptors in axo-spinous synapses of hippocampal field CA1 through interplay of intracellular signaling pathways, thereby participating in the mechanisms of synaptic plasticity under normal conditions.

Association of social defeat stress-induced anhedonia-like symptoms with mGluR1-dependent decrease in membrane-bound AMPA-GluR1 in the mouse ventral midbrain.

Anhedonia is a core symptom of social defeat stress (SDS)-induced depression associated with the reward system. We previously reported that decreased membrane-bound AMPA-GluR1 in the reward system is associated with lipopolysaccharide-induced anhedonia-like symptoms. Since group I metabotropic glutamate receptor (mGluR) activation reduces the surface density of GluR1, we examined whether group I mGluR-dependent decrease in membrane-bound GluR1 in the reward system is involved in SDS-induced anhedonia-like symptoms. Mice exposed to SDS for 4 consecutive days had markedly decreased membrane-bound GluR1 and GluR2 in the prefrontal cortex (PFC) and membrane-bound GluR1 in the ventral midbrain (VM) along with lower sucrose preference (SP). Intra-PFC injection of the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG; 100 µmol) demonstrated decrease in membrane-bound GluR1 and GluR2 in the PFC 2 and 24 h and membrane-bound GluR1 in the VM 24 h after injection. Moreover, intra-PFC injection of DHPG decreased SP only in the second 24-h (24-48 h) period. Conversely, intra-VM injection of DHPG decreased SP in both the first and second 24-h period and decreased membrane-bound GluR1 in the VM 2 and 24 h after injection. Pre-treatment with the mGluR1 antagonist JNJ16259685 (30 mg/kg, subcutaneous) prevented SDS-decreased SP and membrane-bound GluR1 in the VM. The mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP; 10 mg/kg, subcutaneous) prevented SDS-induced decrease in membrane-bound GluR1 and GluR2 in the PFC, whereas MPEP did not affect SDS-induced decrease in SP and membrane-bound GluR1 in the VM. These results suggest that mGluR1-mediated decrease in membrane-bound GluR1 in VM is involved in SDS-induced anhedonia-like symptoms.

Fbxo3-Dependent Fbxl2 Ubiquitination Mediates Neuropathic Allodynia through the TRAF2/TNIK/GluR1 Cascade.

Emerging evidence has indicated that the pathogenesis of neuropathic pain is mediated by spinal neural plasticity in the dorsal horn, which provides insight for analgesic therapy. Here, we report that the abundance of tumor necrosis factor receptor-associated factor 2 and NcK-interacting kinase (TNIK), a kinase that is presumed to regulate neural plasticity, was specifically enhanced in ipsilateral dorsal horn neurons after spinal nerve ligation (SNL; left L5 and L6). Spinal TNIK-associated allodynia is mediated by downstream TNIK-GluR1 coupling and the subsequent phosphorylation-dependent trafficking of GluR1 toward the plasma membrane in dorsal horn neurons. Tumor necrosis factor receptor-associated factor 2 (TRAF2), which is regulated by spinal F-box protein 3 (Fbxo3)-dependent F-box and leucine-rich repeat protein 2 (Fbxl2) ubiquitination, contributes to SNL-induced allodynia by modifying TNIK/GluR1 phosphorylation-associated GluR1 trafficking. Although exhibiting no effect on Fbxo3/Fbxl2/TRAF2 signaling, focal knockdown of spinal TNIK expression prevented SNL-induced allodynia by attenuating TNIK/GluR1 phosphorylation-dependent subcellular GluR1 redistribution. In contrast, intrathecal administration of BC-1215 (N1,N2-Bis[[4-(2-pyridinyl)phenyl]methyl]-1,2-ethanediamine) (a novel Fbxo3 inhibitor) prevented SNL-induced Fbxl2 ubiquitination and subsequent TFAF2 de-ubiquitination to ameliorate behavioral allodynia via antagonizing TRAF2/TNIK/GluR1 signaling. By targeting spinal Fbxo3-dependent Fbxl2 ubiquitination and the subsequent TRAF2/TNIK/GluR1 cascade, spinal application of a TNF-α-neutralizing antibody ameliorated SNL-induced allodynia, and, conversely, intrathecal TNF-α injection into naive rats induced allodynia via a spinal Fbxo3/Fbxl2-dependent modification of the TRAF2/TNIK/GluR1 cascade. Together, our results suggest that spinal TNF-α contributes to the development of neuropathic pain by upregulating TRAF2/TNIK/GluR1 signaling via Fbxo3-dependent Fbxl2 ubiquitination and degradation. Thus, we propose a potential medical treatment strategy for neuropathic pain by targeting the F-box protein or TNIK. SIGNIFICANCE STATEMENT: TNF-α participates in neuropathic pain development by facilitating the spinal TRAF2-dependent TNIK-GluR1 association, which drives GluR1-containing AMPA receptor trafficking toward the plasma membrane. In addition, F-box protein 3 modifies this pathway by inhibiting F-box and leucine-rich repeat protein 2-mediated TRAF2 ubiquitination, suggesting that protein ubiquitination contributes crucially to the development of neuropathic pain. These results provide a novel therapeutic strategy for pain relief.

Downregulation of Cdh1 signalling in spinal dorsal horn contributes to the maintenance of mechanical allodynia after nerve injury in rats.

BACKGROUND: Anaphase-promoting complex/cyclosome (APC/C) and its co-activator Cdh1 are important ubiquitin-ligases in proliferating cells and terminally differentiated neurons. In recent years, APC/C-Cdh1 has been reported as an important complex contributing to synaptic development and transmission. Interestingly, cortical APC/C-Cdh1 is found to play a critical role in the maintenance of neuropathic pain, but it is not clear whether APC/C-Cdh1 in spinal dorsal cord is involved in molecular mechanisms of neuropathic pain conditions. RESULTS: Immunostaining showed that Cdh1 was mainly distributed in dorsal horn neurons of the spinal cord in rats. Its expression was downregulated in the ipsilateral dorsal horn at 14 days after spared nerve injury. Rescued expression of Cdh1 in spinal cord by intrathecal administration of recombinant lentivirus encoding Cdh1 (Lenti-Cdh1-GFP) significantly attenuated spared nerve injury-induced mechanical allodynia. Furthermore, rescued expression of spinal Cdh1 significantly reduced surface membrane expression of GluR1, but increased the expression of GluR1-related erythropoietin-producing human hepatocellular receptor A4 and its ligand EphrinA1 in dorsal horn of spared nerve injury-treated animals. CONCLUSIONS: This study indicates that a downregulation of Cdh1 expression in spinal dorsal horn is involved in molecular mechanisms underlying the maintenance of neuropathic pain. Upregulation of spinal Cdh1 may be a promising approach to treat neuropathic pain.

ERK-GluR1 phosphorylation in trigeminal spinal subnucleus caudalis neurons is involved in pain associated with dry tongue.

BACKGROUND: Dry mouth is known to cause severe pain in the intraoral structures, and many dry mouth patients have been suffering from intraoral pain. In development of an appropriate treatment, it is crucial to study the mechanisms underlying intraoral pain associated with dry mouth, yet the detailed mechanisms are not fully understood. To evaluate the mechanisms underlying pain related to dry mouth, the dry-tongue rat model was developed. Hence, the mechanical or heat nocifensive reflex, the phosphorylated extracellular signal-regulated kinase and phosphorylated GluR1-IR immunohistochemistries, and the single neuronal activity were examined in the trigeminal spinal subnucleus caudalis of dry-tongue rats. RESULTS: The head-withdrawal reflex threshold to mechanical, but not heat, stimulation of the tongue was significantly decreased on day 7 after tongue drying. The mechanical, but not heat, responses of trigeminal spinal subnucleus caudalis nociceptive neurons were significantly enhanced in dry-tongue rats compared to sham rats on day 7. The number of phosphorylated extracellular signal-regulated kinase-immunoreactive cells was also significantly increased in the trigeminal spinal subnucleus caudalis following noxious stimulation of the tongue in dry-tongue rats compared to sham rats on day 7. The decrement of the mechanical head-withdrawal reflex threshold (HWT) was reversed during intracisternal administration of the mitogen-activated protein kinase kinase 1 inhibitor, PD98059. The trigeminal spinal subnucleus caudalis neuronal activities and the number of phosphorylated extracellular signal-regulated kinase-immunoreactive cells following noxious mechanical stimulation of dried tongue were also significantly decreased following intracisternal administration of PD98059 compared to vehicle-administrated rats. Increased number of the phosphorylated GluR1-IR cells was observed in the trigeminal spinal subnucleus caudalis of dry-tongue rats, and the number of phosphorylated GluR1-IR cells was significantly reduced in PD98059-administrated rats compared to the vehicle-administrated tongue-dry rats. CONCLUSIONS: These findings suggest that the pERK-pGluR1 cascade is involved in central sensitization of trigeminal spinal subnucleus caudalis nociceptive neurons, thus resulting in tongue mechanical hyperalgesia associated with tongue drying.

Hippocampal GluA1 expression in Gria1-/- mice only partially restores spatial memory performance deficits.

Spatial working memory (SWM) is an essential cognitive function important for survival in a competitive environment. In rodents SWM requires an intact hippocampus and SWM expression is impaired in mice lacking the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluA1 (Gria1-/- mice). Here we used viral gene transfer to show that re-expression of GluA1 in the hippocampus can affect the behavioral performance of GluA1 deficient mice. We found that Gria1-/- mice with hippocampus-specific rescue of GluA1 expression (Gria1Hpc mice) are more anxious, less hyperactive and only partly impaired in SWM expression in the Y-maze spatial novelty preference paradigm compared to Gria1-/- mice. However, Gria1Hpc mice still express SWM performance deficits when tested in the rewarded alternation T-maze task. Thus, the restoration of hippocampal function affects several behaviors of GluA1 deficient mice - including SWM expression - in different tasks. The virus-mediated GluA1 expression in Gria1-/- mice is not sufficient for a comprehensive SWM restoration, suggesting that both hippocampal as well as extra-hippocampal GluA1-containing AMPA receptors contribute to SWM.

3'-Deoxyadenosine (Cordycepin) Produces a Rapid and Robust Antidepressant Effect via Enhancing Prefrontal AMPA Receptor Signaling Pathway.

BACKGROUND: The development of rapid and safe antidepressants for the treatment of major depression is in urgent demand. Converging evidence suggests that glutamatergic signaling seems to play important roles in the pathophysiology of depression. METHODS: We studied the antidepressant effects of 3(')-deoxyadenosine (3'-dA, Cordycepin) and the critical role of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor in male CD-1 mice via behavioral and biochemical experiments. After 3'-dA treatment, the phosphorylation and synaptic localization of the AMPA receptors GluR1 and GluR2 were determined in the prefrontal cortex (PFC) and hippocampus (HIP). The traditional antidepressant imipramine was applied as a positive control. RESULTS: We found that an injection of 3'-dA led to a rapid and robust antidepressant effect, which was significantly faster and stronger than imipramine, after 45min in tail suspension and forced swim tests. This antidepressant effect remained after 5 days of treatment with 3'-dA. Unlike the psycho-stimulants, 3'-dA did not show a hyperactive effect in the open field test. After 45min or 5 days of treatment, 3'-dA enhanced GluR1 S845 phosphorylation in both the PFC and HIP. In addition, after 45min of treatment, 3'-dA significantly up-regulated GluR1 S845 phosphorylation and GluR1, but not GluR2 levels, at the synapses in the PFC. After 5 days of treatment, 3'-dA significantly enhanced GluR1 S845 phosphorylation and GluR1, but not GluR2, at the synapses in the PFC and HIP. Moreover, the AMPA-specific antagonist GYKI 52466 was able to block the rapid antidepressant effects of 3'-dA. CONCLUSION: This study identified 3'-dA as a novel rapid antidepressant with clinical potential and multiple beneficial mechanisms, particularly in regulating the prefrontal AMPA receptor signaling pathway.

SLC6A15, a novel stress vulnerability candidate, modulates anxiety and depressive-like behavior: involvement of the glutamatergic system.

Major depression is a multifactorial disease, involving both environmental and genetic risk factors. Recently, SLC6A15 - a neutral amino acid transporter mainly expressed in neurons - was proposed as a new candidate gene for major depression and stress vulnerability. Risk allele carriers for a single nucleotide polymorphism (SNP) in a SLC6A15 regulatory region display altered hippocampal volume, glutamate levels, and hypothalamus-pituitary-adrenal axis activity, all markers associated with major depression. Despite this genetic link between SLC6A15 and depression, its functional role with regard to the development and maintenance of depressive disorder is still unclear. The aim of the current study was therefore to characterize the role of mouse slc6a15 in modulating brain function and behavior, especially in relation to stress as a key risk factor for the development of mood disorders. We investigated the effects of slc6a15 manipulation using two mouse models, a conventional slc6a15 knock-out mouse line (SLC-KO) and a virus-mediated hippocampal slc6a15 overexpression (SLC-OE) model. Mice were tested under basal conditions and following chronic social stress. We found that SLC-KO animals displayed a similar behavioral profile to wild-type littermates (SLC-WT) under basal conditions. Interestingly, following chronic social stress SLC-KO animals showed lower levels of anxiety- and depressive-like behavior compared to stressed WT littermates. In support of these findings, SLC-OE animals displayed increased anxiety-like behavior already under basal condition. We also provide evidence that GluR1 expression in the dentate gyrus, but not GluR2 or NR1, are regulated by slc6a15 expression, and may contribute to the difference in stress responsiveness observed between SLC-KO and SLC-WT animals. Taken together, our data demonstrate that slc6a15 plays a role in modulating emotional behavior, possibly mediated by its impact on glutamatergic neurotransmission.

Glutamate transporter type 3 regulates mouse hippocampal GluR1 trafficking.

BACKGROUND: Rapid trafficking of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) to the plasma membrane is considered a fundamental biological process for learning and memory. GluR1 is an AMPAR subunit. We have shown that mice with knockout of excitatory amino acid transporter type 3 (EAAT3), a neuronal glutamate transporter, have impaired learning and memory. The mechanisms for this impairment are not known and may be via regulation of AMPAR trafficking. METHODS: Freshly prepared 300µm coronal hippocampal slices from wild-type or EAAT3 knockout mice were incubated with or without 25mM tetraethylammonium for 10min. The trafficking of GluR1, an AMPAR subunit, to the plasma membrane and its phosphorylation were measured. RESULTS: Tetraethylammonium increased the trafficking of GluR1 and EAAT3 to the plasma membrane in the wild-type mouse hippocampal slices but did not cause GluR1 trafficking in the EAAT3 knockout mice. Tetraethylammonium also increased the phosphorylation of GluR1 at S845, a protein kinase A (PKA) site, in the wild-type mice but not in the EAAT3 knockout mice. The PKA antagonist KT5720 attenuated tetraethylammonium-induced GluR1 phosphorylation and trafficking in the wild-type mice. The PKA agonist 6-BNz-cAMP caused GluR1 trafficking to the plasma membrane in the EAAT3 knockout mice. In addition, EAAT3 was co-immunoprecipitated with PKA. CONCLUSIONS: These results suggest that EAAT3 is upstream of PKA in a pathway to regulate GluR1 trafficking. GENERAL SIGNIFICANCE: Our results provide initial evidence for the involvement of EAAT3 in the biochemical cascade of learning and memory.