Anxiety disorders represent serious social problems worldwide. Recent neuroimaging studies have found that elevated activity and altered connectivity of the insular cortex might account for the negative emotional states in highly anxious individuals. However, the exact synaptic mechanisms of specific insular subregions have yet to be studied in detail. To assess the electrophysiological properties of agranular insular cortex (AIC) neurons, basic synaptic transmission was recorded and different protocols were used to induce presynaptic and postsynaptic long-term potentiation in mice with anxiety-related behaviors. The presynaptic membrane expression of kainate receptors (KARs) and pharmacologic manipulations were quantified to examine the role of Glukl subtype in anxiety-like behaviors. Fear conditioning occludes electrically induced postsynaptic-LTP in the AIC. Quantal analysis of LTP expression in this region revealed a significant presynaptic component reflected by an increase in the probability of transmitter release. A form of presynaptic-LTP that requires KARs has been characterized. Interestingly, a simple emotional anxiety stimulus resulted in selective occlusion of presynaptic-LTP, but not of postsynaptic-LTP. Finally, injecting GIuK1-specific antagonists into the AIC reduced behavioral responses to fear or anxiety stimuli in the mouse. These findings suggest that activity-dependent synaptic plasticity takes place in the AIC due to exposure to fear or anxiety, and inhibiting the presynaptic KAR function may help to prevent or treat anxiety disorder. (C) 2017 Elsevier Ltd. All rights reserved.
To date, the neuroprotective effects of statins on intracerebral hemorrhage (ICH) are not well established. This study explored the effect and potential mechanism of simvastatin treatment on ICH. In the present study, the effects of simvastatin on hematoma absorption, neurological outcome, CD36 expression and microglia polarization were examined in rat model of ICH model. In the meantime, inhibitory effect of PPARy inhibitor GW9662 was investigated following ICH. Additionally, the effect of simvastatin on PPARy activation was also investigated in rat ICH model and primary microglia culture. Much more, the role of PPARy and CD36 in simvastatin-mediated erythrocyte phagocytosis was also detected by using in vivo or in vitro phagocytosis models, respectively. After ICH, simvastatin promoted hematoma absorption and improved neurological outcome after ICH while upregulating CD36 expression and facilitating M2 phenotype polarization in perihematomal microglia. In addition, simvastatin increased PPARy activation and reinforced microglia-induced erythrocyte phagocytosis in vivo and in vitro. All above effects of simvastatin were abolished by PPARy inhibitor GW9662. In conclusion, our data suggested that simvastatin could enhance hematoma clearance and attenuate neurological deficits possibly by activating PPARy. (C) 2017 Elsevier Ltd. All rights reserved.
Cyclin-dependent kinase 5 (Cdk5) acts as an essential modulator for neural development and neurological disorders. Here we show that Cdk5 plays a pivotal role in modulating GABAergic signaling and the maturation of visual system. In adult mouse primary visual cortex, Cdk5 formed complex with the GABA synthetic enzyme glutamate decarboxylase GAD67, but not with GAD65. In addition to enhancement in the surface level of NR2B-containing NMDA receptors, inhibition of Cdk5 reduced the protein levels of GADS and Otx2, while leaving intact the expression of vesicular GABA transporter and subunits of GABA(A) or AMPA receptors. Whole-cell patch-clamp recording in layer pyramidal neurons revealed a decrease in the frequency of miniature inhibitory postsynaptic current (mIPSC). Consequently, pharmacological inhibition and genetic knockdown of Cdk5 in adult mice led to a restoration of juvenile-like ocular dominance plasticity in vivo and long-term synaptic potential in layer induced by white matter stimulation in vitro. Interestingly, we did not observe an alteration of perineuronal nets of extracellular matrix, but a reinstatement of the capability to evoke long-term depression at inhibitory synapses (iLTD), which depended on presynaptic endocannabinoid receptors and was a sign of the rejuvenated GABAergic synapses. Enhancement of GABA signaling by diazepam impeded ocular dominance plasticity rescued by Cdk5 inhibition. These results thus suggest that a physiological role of Cdk5 in visual cortex is to consolidate and stabilize neural circuits through controlling GABAergic signaling. (C) 2017 Elsevier Ltd. All rights reserved.
Although thought as a selective serotonin reuptake inhibitor (SSRI), the antidepressant mechanisms of paroxetine remain unknown. Previous studies have shown the role of the mammalian target of rapamycin (mTOR) signaling in depression. In this study, we investigated whether the antidepressant effects of paroxetine require mTOR signaling. We first examined whether chronic paroxetine administration restores the effects of CUMS and CSDS on the mTOR signaling cascade in the hippocampus and prefrontal cortex. Then, the pharmacologcial inhibitors of mTOR signaling (LY294002, U0126 and rapamycin) were used to assay if the paroxetine-induced reversing effects in the CUMS and CSDS models were prevented by mTOR system blockade. Furthermore, gene knockdown of mTOR by mTOR-shRNA was also used to test whether mTOR is necessary for the antidepressant effects of paroxetine. It was found that paroxetine treatment fully reversed the effects of CUMS and CSDS on the mTOR signaling in the hippocampus, but not the prefrontal cortex. Pharmacological inhibition of the mTOR signaling significantly blocked the antidepressant effects of paroxetine in the CUMS and CSDS models. Moreover, gene silencing of hippocampal mTOR by mTOR-shRNA also abolished the antidepressant effects of paroxetine. Taken together, hippocampal mTOR signaling is necessary for the antidepressant effects of paroxetine. (C) 2017 Elsevier Ltd. All rights reserved.
Serotonin 5-HT2A receptor is widely distributed in the central nervous system and plays an important role in sensorimotor function, emotion regulation, motivation, executive control, learning and memory. We investigated its role in rat maternal behavior, a naturalistic behavior encompassing many psychological functions that the 5-HT2A receptor is involved in. We first showed that activation of 5-HT2A receptor by TCB-2 (a highly selective 5-HT2A agonist, 1, 2.5 or 5.0 mg/kg) disrupted maternal behavior dose-dependently, and this effect was reduced by pretreatment with a 5-HT2A receptor antagonist MDL 100907, but exacerbated by pretreatment with a 5-HT2C receptor antagonist SB242084 and a 5-HT2C receptor agonist MK212, indicating that the maternal disruptive effect of 5-HT2A activation is receptor specific and can be modulated by 5-HT2C receptor bidirectionally. We then microinjected TCB-2 into two brain regions important for the normal expression of maternal behavior: the medial prefrontal cortex (mPFC) and the medial preoptic area (mPOA) and found that only acute intra-mPFC infusion of TCB-2 suppressed pup retrieval, whereas intra-mPOA had no effect. Finally, using c-Fos immunohisto-chemistry, we identified that the ventral bed nucleus of stria terminalis (vBNST), the central amygdala (CeA), and the dorsal raphe (DR) were additionally involved in the maternal-disruptive effect of TCB-2. These findings suggest that the 5-HT2A receptor in the mPFC and other maternally related regions is required for the normal expression of maternal behavior through its intrinsic action or interactions with other receptors (e.g. 5-HT2C). Functional disruption of this neuroreceptor system might contribute to postpartum mental disorders (e.g. depression and psychosis) that impair the quality of maternal care. (C) 2017 Elsevier Ltd. All rights reserved.
Impulsivity is an important personality trait associated with several clinical syndromes including drug abuse. While repeated drug exposure is known to increase certain behavioral responses, such as locomotion, to subsequent drug exposure, few studies have examined whether such sensitization develops for impulsive behavior. In the current study we tested the effects of methamphetamine acutely, during the course of, and upon discontinuation of chronic methamphetamine treatment on impulsive behavior in two models, the 5-choice serial reaction time task (5-CSRTT) and the delay-discounting task which measure impulsive action and impulsive choice, respectively. We also examined whether the trace amine-associated receptor 1 (TAAR1) agonist R05263397 attenuated methamphetamine-induced effects in parallel tests. Acute methamphetamine dose-dependently increased premature responses in the 5-CSRTT and shifted the delay function upward in delay discounting. Up to 40 days of methamphetamine treatment did not significantly alter the dose-effect curve of methamphetamine-induced premature responses, but produced a significant effect in the delay-discounting task. R05263397 attenuated acute methamphetamine-induced premature responses, but this effect became non-significant over the course of chronic treatment. R05263397 did not significantly alter the delay-discounting performance. Discontinuation of methamphetamine treatment increased premature responses, which was attenuated by R05263397, but did not significantly alter the delay discounting function. These results suggest that acute discontinuation from prolonged methamphetamine treatment increases impulsivity, which can be reduced by a TAAR1 agonist. (C) 2017 Elsevier Ltd. All rights reserved.
Alzheimer's disease (AD) is a progressively neurodegenerative disease with typical hallmarks of amyloid beta (A beta) plaque accumulation, neurofibrillary tangle (NFT) formation and neuronal death extension. Aggressive A beta accumulation promotes senile plaque formation and perturbs endoplasmic reticulum (ER) function to trigger the unfolded protein response (UPR) leading to neuronal apoptosis. The stress dependent activation of protein kinase RNA-like endoplasmic reticulum kinase (PERK) increases the phosphorylation of eukaryotic translation initiation factor-2 alpha (eIF2 alpha) to promote the preferential synthesis of beta-site APP cleavage enzyme 1 (BACE1) and A beta generation in turn. Additionally, dysfunction in autophagy has been reported to contribute to several neurodegenerative diseases including AD, and impairment in autophagy-mediated pathway may constitutively stimulate the generation of A beta in AD. Here we discovered that protopanaxadiol derivative 1-(3,4-dimethoxyphenethyl)-3-(3-dehydroxyl-20(s)-protopanaxadiol-3 beta-yl)-urea (DDPU) effectively improved the activity of daily living (ADL) and cognitive deficits in APP/PS1 transgenic mice. The crosstalk between A beta and ER stress has been intensively investigated by using DDPU as a probe. DDPU reduced A beta production mainly by inhibiting the PERK/eIF2 alpha signaling-mediated BACE1 translation and stimulated A beta clearance by promoting autophagy as a PI3K inhibitor through PI3K/AKT/mTOR signaling pathway, while exhibited neuroprotective effect involving attenuation of ER stress. DDPU might be the first reported ginsenoside derivative with dual effects on both autophagy promotion and ER stress amelioration. Our results have highlighted the potential of DDPU in the treatment of AD. (C) 2017 Elsevier Ltd. All rights reserved.
Alzheimer's disease (AD) is the most common cause of dementia. In addition to cognitive impairments, deficits in non-cognitive behaviors are also common neurological sequelae in AD. Here, we show that complex behavioral deficits in 7-month-old APPswe/PSEN1dE9 (APP/PSI) mice include impairments in object recognition, deficient social interaction, increased depression and buried marbles. Citalopram, one of the selective serotonin reuptake inhibitors (SSRIs), ameliorated the amyloid deposition in AD patients and transgenic animal models. After treatment for 4 weeks, citalopram rescued the deficits in short-term memory, sociability and depression in these mice. Further immunohistochemical analysis showed chronic citalopram treatment significantly attenuated beta-amyloid deposition and microglial activation in the brains of APP/PS1 mice as demonstrated previously. Parvalbumin (PV) interneurons, which are the primary cellular subtype of GABAergic neurons and considered indispensable for short-term memory and social interaction, also contributed to the progress of depression. Additionally, we found the citalopram could significantly increase the PV-positive neurons in the cortex of APP/PS1 mice without alteration in the hippocampus, which might contribute to the improvement of behavioral performance. Our findings suggest that citalopram might be a potential candidate for the early treatment of AD. (C) 2017 Elsevier Ltd. All rights reserved.
The inflammatory response of glial cells contributes to neuronal damage or repair after brain ischemia/reperfusion insult. We previously demonstrated a protective role of TP53-induced glycolysis and apoptosis regulator (TIGAR) in ischemic neuronal injury through increasing the flow of pentose phosphate pathway (PPP). The present study investigated the possible role of TIGAR in ischemia/reperfusion-induced inflammatory response of astrocytes. Male ICR mice were subjected to middle cerebral artery occlusion for 2 h followed by 24 h reperfusion and cultured primary astrocytes were subjected to oxygen glucose deprivation for 9 h followed by 24 h reoxygenation (OGD/R). Adenoviral vectors were used to alter the levels of TIGAR protein in brain and in culture primary astrocytes. We showed that during the OGD/R insult the protein levels of TIGAR were rapidly increased in astrocytes. Overexpression of TIGAR mediated increased the viability, levels of NADPH and rGSH, and reduced intracellular reactive oxygen species (ROS) in cultured primary astrocytes. Overexpression of TIGAR not only significantly reduced infarct volume after stroke insult but also markedly reduced long-term mortality and improved recovery of neurological functions. Overexpression of TIGAR tempered OGD/R- or ischemia/reperfusion-induced the upregulation of inducible nitric oxide synthase (iNOS), cyclooxygenases COX2 and the release of pro-inflammatory cytokines interleukin 1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha), while TIGAR knockdown produced opposite effects on these parameters. Moreover, Overexpression of TIGAR suppressed OGD/R-induced degradation of I kappa B alpha and NF-kappa B nuclear translocation in cultured primary astrocytes. The present study elucidates a novel mechanism by which TIGAR protects neurons against ischemia/reperfusion injury. (C) 2018 Elsevier Ltd. All rights reserved.
Increasing evidence has suggested that depression is a neuropsychiatric condition associated with neuroplasticity within specific brain regions. However, the mechanisms by which neuroplasticity exerts its effects in depression remain largely uncharacterized. In the present study we show that chronic stress effectively induces depression-like behaviors in rats, an effect which was associated with structural changes in dendritic spines and synapse abnormalities within neurons of the ventromedial prefrontal cortex (vmPFC). Moreover, unpredictable chronic mild stress (UCMS) exposure significantly increased the expression of miR-134 within the vmPFC, an effect which was paralleled with a decrease in the levels of expression and phosphorylation of the synapse-associated proteins, LIM-domain kinase 1 (Limk1) and cofilin. An intracerebral infusion of the adenovirus associated virus (AAV)-miR-134-sponge into the vmPFC of stressed rats, which blocks mir-134 function, significantly ameliorated neuronal structural abnormalities, biochemical changes and depression-like behaviors. Chronic administration of ginsenoside Rg1 (40 mg/kg, 5 weeks), a potential neuroprotective agent extracted from ginseng, significantly ameliorated the behavioral and biochemical changes induced by UCMS exposure. These results suggest that miR-134-mediated dysregulation of structural plasticity may be related to the display of depression like behaviors in stressed rats. The neuroprotective effects of ginsenoside Rg1, which produces an antidepressant like effect in this model of depression, appears to result from modulation of the miR-134 signaling pathway within the vmPFC. (C) 2018 Elsevier Ltd. All rights reserved.
Alzheimer's disease (AD) is a progressive neurodegenerative dysfunction characterized by memory impairment and brings a heavy burden to old people both in developing and developed countries. Amyloid hypothesis reveals that aggregation and deposition of amyloid plaques are the cause of AD neurodegeneration. SLOH, a carbazole-based fluorophore, is reported to inhibit amyloid beta (A beta) aggregation in vitro. In the current study, we intended to evaluate the protective effect of SLOH in a triple transgenic AD mouse model (3xTg-AD). 3xTg-AD (10-month-old) were treated with SLOH (0.5, 1 and 2 mg kg(-1)) for one month via intraperitoneal injection. After treatment, cognitive function was assessed by Morris Water Maze (MWM) and Y-maze tasks. In addition, biochemical estimations were used to examine the degree of A beta deposition, tau hyperphosphorylation and neuroinflammation in the brains of 3xTg-AD mice. An in vitro study was conducted on human neuroblastoma (SH-SY5Y) cells to determine the activity of SLOH on tau and GSK-3 beta using western blot and immunofluorescence staining. One month treatment with SLOH significantly ameliorated memory impairments in 3xTg-AD mice in MWM and Y-maze tests. Moreover, SLOH treatment mitigated the level of amyloid plaques, tau hyperphosphorylation and neuroinflammation in the mouse brain. SLOH also reduced tau hyperphosphorylation and down regulated GSK-3 beta activity in A beta induced neurotoxic SH-SY5Y cells. The promising results in mitigating amyloid plaques, tau hyperphosphorylation, neuroinflammation and ameliorating cognitive deficits following one-month treatment suggest that SLOH could be a potential multi-target molecule for the AD treatment. (C) 2018 Elsevier Ltd. All rights reserved.
Diabetic cognitive dysfunction has gained widespread attention for its deleterious impact on individuals with diabetes. However, few clinical interventions are available to prevent the disorder. The glucagon-like peptide-1 analog liraglutide exerts neuroprotective effects in several models of neurodegenerative diseases. We investigated the effect of liraglutide pretreatment on diabetes-induced cognitive decline and explored the underlying mechanisms in vivo and in vitro. Liraglutide pretreatment prevented diabetes-induced cognitive impairment as assessed by the Morris Water Maze test, and alleviated neuronal injuries and ultrastructural damage to synapses in the hippocampal CA1 region. Furthermore, liraglutide promoted autophagy as indicated by enhanced expression of the autophagy markers Microtubule-associated protein 1 light chain 3 (LC3)-II and Beclin 1, decreased expression of p62, and increased formation of autophagic vacuoles and LC3-II aggregates. In vitro, liraglutide treatment elevated phosphorylated (p)-AMP-activated protein kinase (AMPK) levels and reduced p-mammalian target of rapamycin (p-mTOR) expression. Additionally, the AMPK inhibitor Compound C exhibited an inhibitory effect on liraglutide-induced increased LC3-II expression and p62 degradation. Liraglutide exhibits neuroprotective effects against diabetes-induced hippocampal neuronal injuries and cognitive impairment by promoting autophagy via the AMPK/mTOR pathway. (C) 2018 Published by Elsevier Ltd.
Ginsenoside Rb1 has been demonstrated to protect dopaminergic (DA) neurons from death in vitro. However, the neuroprotective effects and underlying mechanism of Rb1 in treating Parkinson's disease (PD) remain uncharacterized. In this study, we explored the effects of Rb1 on the movement disorder and the underlying mechanisms based on the glutamatergic transmission and excitotoxicity in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. Here, for the first time, we report that Rb1 treatment ameliorates motor deficits, prevents DA neuron death, and suppresses alpha-synuclein expression and astrogliosis in the MPTP mouse model of PD. Rb1 attenuates glutamate excitotoxicity by upregulating glutamate transporter expression and function, and modulating the nigrostriatal and cortico-nigral glutamatergic transmission pathways. Our results demonstrate that Rb1 increases glutamate transporter expression via nuclear translocation of nuclear factor-kappa B, regulates glutamate receptor expression and promotes synaptic protein expression. These results indicate that Rb1 suppresses glutamate excitotoxicity and modulates synaptic transmission to improve the impairments in motor functions of the MPTP model of PD, suggesting that Rb1 may serve as a potential therapeutic agent for PD. (C) 2017 The Authors. Published by Elsevier Ltd.
Emerging data have identified certain drugs such as scopolamine as rapidly acting antidepressants for major depressive disorder (MDD) that increase glutamate release and induce neurotrophic factors through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) activation in rodent models. However, little research has addressed the direct mechanisms of scopolamine on AMPAR activation or vesicular glutamate transporter 1 (VGLUT1)-mediated glutamate release in the prefrontal cortex (PFC) of mice. Herein, using a chronic unpredictable stress (CUS) paradigm, acute treatment with scopolamine rapidly reversed stress-induced depression-like behaviors in mice. Our results showed that CUS-induced depression-like behaviors, accompanied by a decrease in membrane AMPAR subunit 1 (GluA1), phosphorylated GluA1 Ser845 (pGluA1 Ser845), brain-derived neurotrophic factor (BDNF) and VGF (non-acronymic) and an increase in bicaudal C homolog 1 gene (BICC1) in the PFC of mice, and these biochemical and behavioral abnormalities were ameliorated by acute scopolamine treatments. However, pharmacological block of AMPAR by NBQX infusion into the PFC significantly abolished these effects of scopolamine. In addition, knock down of VGLUT1 by lentiviral-mediated RNA interference in the PFC of mice was sufficient to induce depression-like phenotype, to decrease extracellular glutamate accumulation and to cause similar molecular changes with CUS in mice. Remarkably, VGLUT1 knockdown alleviated the rapid antidepressant-like actions of scopolamine and the effects of scopolamine on membrane GluA1-mediated BDNF, VGF and BICC1 changes. Altogether, our findings suggest that VGLUT1-mediated glutamate release and membrane GluA1 activation may play a critical role in the rapid-acting antidepressant-like effects of scopolamine in mice. (C) 2017 Elsevier Ltd. All rights reserved.
Alterations of glycoprotein glycans contribute to a wide variety of diseases. Bisecting N-acetylglucosamine (GIcNAc) levels increased in the cerebrospinal fluid of most Alzheimer's disease (AD) patients, and the mRNA levels of N-acetylglucosaminyltransferase III (GnT-III), a glycosyltransferase responsible for synthesizing a bisecting GIcNAc residue, were found highly expressed in the brains of AD patients. In our previous studies, glucagon-like peptide-1 (GLP-1) and its mimetics showed neuroprotective effects. Here, we confirmed that four weeks' treatment of exendin-4 could rescue memory deficits and neuropathological changes in APP/PS1 mice. We further explored the underlying mechanism and especially the role of GnT-III in it. We demonstrated for the first time that the levels of GnT-III and bisecting GIcNAc were increased in APP/PS1 mice and A beta(25-35)-treated PC12 cells, and GLP-1 receptor agonists (GLP-1RA) could downregulate aberrant neuronal expression of GnT-III and bisecting GIcNAc. We also found that GLP-1RA recovered the phosphorylation levels of Akt (Ser473) and GSK-3 beta (Ser9) and the levels of beta-catenin in mice and cell models. Furthermore, the results indicated that inhibitor LY294002 attenuated these effects of GLP-IRA in PC12 cells, and beta-catenin siRNA abolished the effect of GLP-IRA on GnT-III. In summary, our results suggest that GnT-III plays an important role in AD and GLP-1RA could downregulate aberrant GnT-III expression through the Akt/GSK-3 beta/beta-catenin signaling pathway in neurons. (C) 2017 Elsevier Ltd. All rights reserved.