Primary Cultures Of Rat Hippocampal Neurons Research Articles

Chemokine CCL2 enhances NMDA receptor-mediated excitatory postsynaptic current in rat hippocampal slices-a potential mechanism for HIV-1-associated neuropathy?

Human immunodeficiency virus type 1 (HIV-1)-infected mononuclear phagocytes (brain macrophages and microglial cells) release proinflammatory cytokines and chemokines. Elevated levels of chemokine CC motif ligand 2 (CCL2, known previously as monocyte chemoattractant protein-1) have been detected in serum and cerebrospinal fluid (CSF) of HIV-1-infected individuals and the raised CCL2 in the CSF correlates with HIV-1-associated neurocognitive disorders. To understand how elevated CCL2 induces HIV-1-associated neuropathy, we studied effects of CCL2 on excitatory postsynaptic current (EPSCs) in the CA1 region of rat hippocampal brain slices using whole-cell patch recording techniques. The AMPA receptor (AMPAR)-mediated EPSC (EPSCAMPAR) and N-Methyl-D-aspartate (NMDA) receptor (NMDAR)-mediated EPSCs (EPSCNMDAR) were isolated pharmacologically. Bath application of CCL2 produced a significant enhancement of the amplitudes of EPSCs, EPSCAMPAR and EPSCNMDAR. Further studies revealed that CCL2 potentiated NMDAR subtype NR2A-mediated EPSC (EPSCNR2AR) and NR2B-mediated EPSC (EPSCNR2BR). To determine the site of action, we recorded spontaneous mini EPSCs (mEPSC) before and during bath application of CCL2. Our results showed that CCL2 decreased inter event interval (IEI) and increased the frequency of mEPSCs without change on the amplitude, suggesting a presynaptic site of CCL2 action. CCL2 was also found to injure primary rat hippocampal neuronal cultures and neuronal dendrites in the CA1 region of hippocampal slices. The CCL2-associated neuronal and dendritic injuries were blocked by a specific NMDAR antagonist or by a CCR2 receptor antagonist, indicating that CCL2-associated neural injury was mediated via NMDARs and/or CCR2 receptors. Taken together, these results suggest a potential role CCL2 may play in HIV-1-associated neuropathology.

TREK1 channel blockade induces an antidepressant-like response synergizing with 5-HT1A receptor signaling

Current antidepressants often remain the inadequate efficacy for many depressive patients, which warrant the necessary endeavor to develop the new molecules and targets for treating depression. Recently, the two-pore domain potassium channel TREK1 has been implicated in mood regulation and TREK-1 antagonists could be the promising antidepressant. This study has screened a TREK1 blocker (SID1900) with a satisfactory blood–brain barrier permeation and bioavailability. Electrophysiological research has shown that SID1900 and the previously reported TREK1 blocker (spadin) efficiently blocked TREK-1 current in HEK293 cells and specifically blocked two-pore domain potassium channels in primary-cultured rat hippocampal neurons. SID1900 and spadin induced a significant antidepressant-like response in the rat model of chronic unpredictable mild stress (CUMS). Both two TREK1 blockers substantially increased the firing rate of 5-HT-ergic neurons in the dorsal raphe nuclei (DRN) and PFC of CUMS rats. SID1900 and spadin significantly up-regulated the expression of PKA-pCREB-BDNF signaling in DRN, hippocampus and PFC of CUMS rats, which were enhanced and reversed by a 5-HTR1A agonist (8-OH-DPAT) and antagonist (WAY100635) respectively. The present findings suggested that TREK1 channel blockers posses the substantial antidepressant-like effect and have the potential synergistic effect with 5-HT1A receptor activation through the common CREB-BDNF signal transduction.

Sequential expression of cyclooxygenase-2, glutamate receptor-2, and platelet activating factor receptor in rat hippocampal neurons after fluid percussion injury.

Traumatic brain injury causes gene expression changes in different brain regions. Occurrence and development of traumatic brain injury are closely related, involving expression of three factors, namely cyclooxygenase-2, glutamate receptor-2, and platelet activating factor receptor. However, little is known about the correlation of these three factors and brain neuronal injury. In this study, primary cultured rat hippocampal neurons were subjected to fluid percussion injury according to Scott's method, with some modifications. RT-PCR and semi-quantitative immunocytochemical staining was used to measure the expression levels of cyclooxygenase-2, glutamate receptor-2, and platelet activating factor receptor. Our results found that cyclooxygenase-2 expression were firstly increased post-injury, and then decreased. Both mRNA and protein expression levels reached peaks at 8 and 12 hours post-injury, respectively. Similar sequential changes in glutamate receptor 2 were observed, with highest levels mRNA and protein expression at 8 and 12 hours post-injury respectively. On the contrary, the expressions of platelet activating factor receptor were firstly decreased post-injury, and then increased. Both mRNA and protein expression levels reached the lowest levels at 8 and 12 hours post-injury, respectively. Totally, our findings suggest that these three factors are involved in occurrence and development of hippocampal neuronal injury.

Neuroprotective Effects of Ginsenoside Rb1 on High Glucose-Induced Neurotoxicity in Primary Cultured Rat Hippocampal Neurons

Ginsenoside Rb1 is one of the main active principles in traditional herb ginseng and has been reported to have a wide variety of neuroprotective effects. Endoplasmic reticulum (ER) stress has been implicated in neurodegenerative diseases, so the present study aimed to observe the effects of ginsenoside Rb1 on ER stress signaling pathways in high glucose-treated hippocampal neurons. The results from MTT, TUNEL labeling and Annexin V-FITC/PI/Hoechst assays showed that incubating neurons with 50 mM high glucose for 72h decreased cell viability and increased the number of apoptotic cells whereas treating neurons with 1 μM Rb1 for 72h protected the neurons against high glucose-induced cell damage. Further molecular mechanism study demonstrated that Rb1 suppressed the activation of ER stress-associated proteins including protein kinase RNA (PKR)-like ER kinase (PERK) and C/EBP homology protein (CHOP) and downregulation of Bcl-2 induced by high glucose. Moreover, Rb1 inhibited both the elevation of intracellular reactive oxygen species (ROS) and the disruption of mitochondrial membrane potential induced by high glucose. In addition, the high glucose-induced cell apoptosis, activation of ER stress, ROS accumulation and mitochondrial dysfunction can also be attenuated by the inhibitor of ER stress 4-phenylbutyric acid (4-PBA) and anti-oxidant N-acetylcysteine(NAC). In conclusion, these results suggest that Rb1 may protect neurons against high glucose-induced cell injury through inhibiting CHOP signaling pathway as well as oxidative stress and mitochondrial dysfunction.

Abstract 401: Ouabain-Digoxin Antagonism in Rat Arteries and Neurons: Acute Effects on Myogenic Tone and Neuronal Ca 2 + Signaling

‘Classic’ cardiotonic steroids (CTS, e.g., digoxin and ouabain) selectively inhibit Na + ,K + -ATPase (the Na + pump) and, via Na/Ca exchange, exert cardiotonic and vasotonic effects. CTS action is more complex than previously thought: Prolonged infusion of ouabain, but not digoxin, induces hypertension; in fact, digoxin antagonizes ouabain’s hypertensinogenic effect. We studied acute interactions between CTS in two indirect assays of Na + pump function: myogenic tone (MT) in isolated, pressurized rat mesenteric small arteries, and Ca 2+ signaling in primary cultured rat hippocampal neurons. The ‘classic’ CTS (0.3-10 nM) were ‘agonists’: they all increased MT 70 (MT at 70 mm Hg) and augmented 3-4 μM glutamate-evoked Ca 2+ (fura-2) signals. For example, 3-10 nM ouabain, digoxin and bufalin all increased myogenic constriction by 20-40% and neuronal Ca 2+ signals by 80-200%. We then tested one CTS in the presence of another. Most CTS were either ouabain-like (ouabagenin, dihydroouabain, strophanthidin) or digoxin-like CTS (digoxigenin, digitoxin, bufalin). Within each group, the CTS were synergistic, but ouabain-like and digoxin-like CTS antagonized one another in both assays. For example, 3 nM ouabain-evoked increases in MT 70 and neuronal Ca 2+ signals were both reversibly attenuated by 65-75% by adding 10 nM digoxin or 10 nM bufalin. Conversely, 3 nM digoxin- or bufalin-evoked increases in MT 70 and Ca 2+ signals were attenuated by 65-75% by 10 nM ouabain, but augmentation by bufalin was not antagonized by digoxin and vice-versa. Rostafuroxin (PST2238, 5 μM), a digoxigenin derivative that displaces 3 H-ouabain from Na + ,K + -ATPase, and attenuates some forms of hypertension, antagonized ouabain's, but not digoxin's, effects. CTS bind to the α (catalytic) subunit of Na + pump αβ protomers in a 1:1 ratio. Analysis of potential models suggests that, in vivo , Na + pumps function as tetraprotomers [(αβ) 4 ] in which the binding of a single CTS to one protomer blocks all pumping activity. The paradoxical ability of digoxin-like CTS to reactivate the ouabain-inhibited complex can be explained by de-oligomerization of the tetrameric state. The interactions between these common CTS may be of considerable therapeutic relevance.

Biochemical and morphological characterization of A2BP1 in neuronal tissue

A2BP1 is considered to regulate alternative splicing of important neuronal transcripts and has been implicated in a variety of neurological and developmental disorders. A2BP1 was found in neuronal cells and was analyzed biochemically and morphologically. In this study, we prepared a specific antibody against A2BP1, anti-A2BP1, and carried out protein expression and localization analyses of A2BP1 in rat and mouse tissues. By Western blotting, A2BP1 showed tissue-dependent expression profiles and was expressed in a developmental-stage-dependent manner in the brain. A2BP1 was detected at high levels in neocortex and cerebellum in the rat brain. Immunohistochemical analyses demonstrated that A2BP1 was highly expressed in differentiated neurons but not in mitotically active progenitor cells in the cerebral cortex during developmental stages. In cortical neurons, A2BP1 had accumulated mainly in the nucleus and diffusely distributed in the cell body and dendrites. In differentiated primary cultured rat hippocampal neurons, although A2BP1 was enriched in the nucleus and diffusely distributed in the cytoplasm, it was found in a punctate distribution adjacent to synapses. The results suggest that in neuronal tissues A2BP1 plays important roles, which are regulated in a spatiotemporal manner.

Anti-apoptotic and Neuroprotective Effects of Oxysophoridine on Cerebral Ischemia Both In Vivo and In Vitro

In this study, we investigated the neuroprotective effect of oxysophoridine on ischemia and ischemia-like insults. Protection by oxysophoridine was studied at the in vivo level using a model of middle cerebral artery occlusion in mice and at the in vitro level using primary rat hippocampal neuronal cultures exposed to oxygen-glucose deprivation, a model of ischemia-like injury. The behavioral test was performed by using the neurological scores. The infarction volume of brain was assessed in the brain slices stained with 2,3,5-triphenyl tetrazolium chloride. The neuron apoptosis was evaluated by Hoechst 33342 staining. The morphological change in the neurons was examined using a Transmission Electron Microscope (TEM or EM). To evaluate neuron apoptosis, caspase-3, -9, and - 8 activities were measured using assay kits with an ELISA reader. The Western blotting assay was used to evaluate the release of cytochrome c and expression of caspase-3, Bcl-2, and Bax proteins. The quantitative real-time PCR assay was used to evaluate the release of cytochrome c and the expression of caspase-3 mRNA. Oxysophoridine-treated groups (62.5, 125, 250 mg/kg) markedly reduced neurological deficit scores and infarct volumes. Treatment with oxysophoridine (5, 20, 80 µmol/L) significantly attenuated neuronal damage, with evidence of decreased cell apoptosis and decreased cell morphologic impairment. Furthermore, treatment with oxysophoridine could effectively downregulate the expression of cytochrome c and caspase-3 in both mRNA and protein levels, and Bax in the protein level, and induce an increase of Bcl-2 in the protein level. The caspase-3, -9, and -8 activities were also inhibited. These findings suggested that oxysophoridine may be a potential neuroprotective agent for cerebral ischemia injury.

The developmental regulation of glutamate receptor-mediated calcium signaling in primary cultured rat hippocampal neurons

We have studied the developmental changes of glutamate-induced calcium (Ca²⁺) response in primary cultured hippocampal neurons at three different stages of cultures, 3, 7-8, and 14-16 days in vitro (DIV), using fura-2 single-cell digital micro-fluorimetry. We found that glutamate-induced Ca²⁺ signaling was altered during development, and that two different ionotropic glutamate receptors, α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPARs) and N-methyl-D-aspartate receptors (NMDARs), were differently involved in the modulation of calcium response at different stages of neuronal culture. In the stages of culture at 3 and 8 DIV, glutamate-induced Ca²⁺ influx was mostly because of AMPAR activation and subsequent opening of voltage-dependent calcium channels, as Ca²⁺ response can be largely reduced by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and by nifedipine. In the advanced culture (14-17 DIV), glutamate-induced Ca²⁺ response was less sensitive to 6-cyano-7-nitroquinoxaline-2,3-dione and nifedipine. Furthermore, AMPA-induced Ca²⁺ response increased in a time-dependent manner during the cultures of 3-8 DIV and then reduced in the advanced culture of 14-17 DIV. NMDA-induced Ca²⁺ influx increased in a time-dependent manner, with a marked increase in the advanced culture (14-17 DIV). These results suggest that glutamate-induced Ca²⁺ signaling switched from AMPA-voltage-dependent calcium channel to NMDA-calcium signaling during development.

Endolysosome involvement in HIV-1 transactivator protein-induced neuronal amyloid beta production

The increased life expectancy of people living with HIV-1/AIDS is accompanied by increased prevalence of HIV–1-associated neurocognitive disorder. As well, these individuals are increasingly experiencing Alzheimer's disease (AD)-like neurocognitive problems and neuropathological features such as increased deposition of amyloid beta (Aβ) protein. Findings that Aβ production occurs largely in endolysosomes, that HIV-1 transactivator protein (Tat) disrupts endolysosome function—an early pathological feature of AD—and that HIV-1 Tat can increase Aβ levels prompted us to test the hypothesis that endolysosome dysfunction is associated with HIV-1 Tat-induced increases in neuronal Aβ generation. Using primary cultured rat hippocampal neurons, we found that treatment with HIV-1 Tat caused such morphological changes as enlargement of endolysosomes identified with LysoTracker dye and such functional changes as elevated endolysosome pH measured ratiometrically with LysoSensor dye. The HIV-1 Tat-induced changes in endolysosome function preceded temporally HIV-1 Tat-induced increases in Aβ generation measured using enzyme-linked immunosorbent assay. In addition, we demonstrated that HIV-1 Tat increased endolysosome accumulation of Aβ precursor protein and Aβ identified using immunostaining with 4G8 antibodies. Furthermore, we demonstrated that treatment of neurons with HIV-1 Tat increased endolysosome accumulation of beta amyloid-converting enzyme, the rate-limiting enzymatic step for Aβ production, and enhanced beta amyloid-converting enzyme activity. Together, our findings suggest that HIV-1 Tat increases neuronal Aβ generation and thereby contributes to the development of AD-like pathology in HIV–1-infected individuals by disturbing endolysosome structure and function.

Isoflurane Increases Neuronal Cell Death Vulnerability by Downregulating miR-214

Since accumulating evidence suggests the application of anesthetics may increase the risk of Alzheimer’s disease (AD), we investigated the cytotoxicity of inhaled general anesthesia in neurons and its underlying mechanism. Using primary cultured rat hippocampal neurons as the study model, here we show that isoflurane increases vulnerability to intracellular or extracellular amyloid β with or without serum deprivation. This isoflurane-induced effect is mediated by the downregulation of miR-214 level that lead to an elevated expression of Bax, a prominent target for miR-214. We conclude that isoflurane increases cell death in the presence of amyloid β by increasing Bax level through downregulating miR-214. Our data provide a new insight for inhaled anesthetics toxicity and indicate a possible mechanistic link between anesthetic application and neurodegenration in AD.

Ginsenoside Rb1 increases synaptophysin and microtubule-associated protein 2 mRNA expression in primary cultures of rat hippocampal neurons

Ginsenoside Rb1 has been determined to exert diverse neuromodulatory effects including a stimulatory effect on synaptic formation. Synaptophysin and microtubule-associated protein 2 (MAP2) are synaptic proteins which play vital roles in neurotransmission regulation and synaptic structural stability. The present data revealed that ginsenoside Rb1 enhanced mRNA expression of synaptic markers, synaptophysin and MAP2, in primary cultured rat hippocampal neurons. Our results newly add synaptophysin and MAP2 to the list of genes of which mRNA expression is modulated by ginsenosides. Our finding contributes further understanding of medical usefulness of ginsenoside Rb1 targeting hippocampal network alteration which is commonly observed in aging and neurodegenerative disorders.

Neuroprotective Effects of AMP-Activated Protein Kinase on Scopolamine Induced Memory Impairment

AMP-activated protein kinase (AMPK), an important regulator of energy metabolism, is activated in response to cellular stress when intracellular levels of AMP increase. We investigated the neuroprotective effects of AMPK against scopolamine-induced memory impairment in vivo and glutamate-induced cytotoxicity in vitro. An adenovirus expressing AMPK wild type alpha subunit (WT) or a dominant negative form (DN) was injected into the hippocampus of rats using a stereotaxic apparatus. The AMPK WT-injected rats showed significant reversal of the scopolamine induced cognitive deficit as evaluated by escape latency in the Morris water maze. In addition, they showed enhanced acetylcholinesterase (AChE)-reactive neurons in the hippocampus, implying increased cholinergic activity in response to AMPK. We also studied the cellular mechanism by which AMPK protects against glutamate-induced cell death in primary cultured rat hippocampal neurons. We further demonstrated that AMPK WT-infected cells increased cell viability and reduced Annexin V positive hippocampal neurons. Western blot analysis indicated that AMPK WT-infected cells reduced the expression of Bax and had no effects on Bcl-2, which resulted in a decreased Bax/Bcl-2 ratio. These data suggest that AMPK is a useful cognitive impairment treatment target, and that its beneficial effects are mediated via the protective capacity of hippocampal neurons.

Gastrodin protect primary cultured rat hippocampal neurons against amyloid-beta peptide-induced neurotoxicity via ERK1/2-Nrf2 pathway

One hallmark of Alzheimer's disease (AD) is amyloid-beta (Aβ) deposition, which can initiate a cascade of oxidative events that may result in neuronal death. The present study aimed to investigate the protective effects of gastrodin, a phenolic compound which shows antioxidant activity, on Aβ(1-42)-induced neurotoxicity and the underlying mechanism for this neuroprotection. Results indicate that Aβ(1-42)-induced neuronal toxicity as measured by cell viability, which was correlated with decreased catalase (CAT) content and superoxide dismutase (SOD) activity. Pre-treatment of primary hippocampal neurons with gastrodin significantly attenuated Aβ(1-42)-induced neurotoxicity and changes in SOD and CAT, and upregulated gene expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and extracellular signal-regulated kinases 1 and 2 (ERK1/2) phosphorylation. Pharmacological blockade of ERK1/2 abrogation this action of gastrodin. The ERK1/2 pathway may be involved in the neuroprotective effect of gastrodin against Aβ(1-42)-induced oxidative in primary cultured rat hippocampal neurons. These findings suggest that gastrodin could be of importance for the treatment of AD and other oxidative stress-related diseases.

MicroRNA Regulation of the Synaptic Plasticity-Related Gene Arc

Expression of activity-regulated cytoskeleton associated protein (Arc) is crucial for diverse types of experience-dependent synaptic plasticity and long-term memory in mammals. However, the mechanisms governing Arc-specific translation are little understood. Here, we asked whether Arc translation is regulated by microRNAs. Bioinformatic analysis predicted numerous candidate miRNA binding sites within the Arc 3′-untranslated region (UTR). Transfection of the corresponding microRNAs in human embryonic kidney cells inhibited expression of an Arc 3′UTR luciferase reporter from between 10 to 70% across 16 microRNAs tested. Point mutation and deletion of the microRNA-binding seed-region for miR-34a, miR-326, and miR-19a partially or fully rescued reporter expression. In addition, expression of specific microRNA pairs synergistically modulated Arc reporter expression. In primary rat hippocampal neuronal cultures, ectopic expression of miR-34a, miR-193a, or miR-326, downregulated endogenous Arc protein expression in response to BDNF treatment. Conversely, treatment of neurons with cell-penetrating, peptide nucleic acid (PNA) inhibitors of miR-326 enhanced Arc mRNA expression. BDNF dramatically upregulated neuronal expression of Arc mRNA and miR-132, a known BDNF-induced miRNA, without affecting expression of Arc-targeting miRNAs. Developmentally, miR-132 was upregulated at day 10 in vitro whereas Arc-targeting miRNAs were downregulated. In the adult brain, LTP induction in the dentate gyrus triggered massive upregulation of Arc and upregulation of miR-132 without affecting levels of mature Arc-targeting miRNAs. Turning to examine miRNA localization, qPCR analysis of dentate gyrus synaptoneurosome and total lysates fractions demonstrated synaptic enrichment relative to small nucleolar RNA. In conclusion, we find that Arc is regulated by multiple miRNAs and modulated by specific miRNA pairs in vitro. Furthermore, we show that, in contrast to miR-132, steady state levels of Arc-targeting miRNAs do not change in response to activity-dependent expression of Arc in hippocampal neurons in vitro or during LTP in vivo.

Biochemical and morphological characterization of MAGI‐1 in neuronal tissue

The membrane-associated guanylate kinase with inverted organization (MAGI) proteins consist of three members, MAGI-1, MAGI-2 (also known as S-SCAM), and MAGI-3. Although MAGI-2 has been analyzed and shown to interact with a variety of postsynaptic proteins, functional analyses and characterization of MAGI-1 in neuronal tissues have been rare. In this study, we prepared a specific antibody against MAGI-1, anti-MAGI-1, and carried out biochemical and morphological analyses of MAGI-1 in rat neuronal tissues. By Western blotting, a high level of MAGI-1 was detected in nervous tissues, especially in olfactory bulb. Biochemical fractionation clarified that MAGI-1 was relatively enriched in the synaptosomal vesicle and synaptic plasma membrane fractions, whereas MAGI-2 and MAGI-3 appeared to be in the synaptic plasma membrane and postsynaptic density fractions. Immunofluorescent analyses revealed diffuse distribution of MAGI-1 in the cell body and processes of primary cultured rat hippocampal neurons, whereas MAGI-2 and MAGI-3 were likely to be enriched at synapses. Immunohistochemical analyses demonstrated that MAGI-1 was expressed in Purkinje cells, in hypocampal neurons in CA1 region, in the glomerulus region of olfactory bulb, and at the dorsal root entry zone in embryonic rat spinal cord. These results suggest neuronal roles of MAGI-1 different from those of MAGI-2/3.

Protective effects of Lycium barbarum polysaccharide on neonatal rat primary cultured hippocampal neurons injured by oxygen-glucose deprivation and reperfusion

This study investigated the protective effects of Lycium barbarum polysaccharide (LBP) on alleviating injury from oxygen-glucose deprivation/reperfusion (OGD/RP) in primary cultured rat hippocampal neurons. Cultured hippocampal neurons were exposed to oxygen-glucose deprivation (OGD) for 2 h followed by a 24 h re-oxygenation. The MTT assay and the lactate dehydrogenase (LDH) release were used to determine the neuron viability. Superoxide dismutase (SOD), Glutathione peroxidase (GSH-PX), malondialdehyde (MDA) were determined by spectrophotometry using commercial kits. Mitochondrial membrane potential (MMP) and the intracellular free calcium concentration ([Ca(2+)](i)) in hippocampal neurons were measured using the confocal laser scanning microscope (CLSM). Treatment with LBP (10-40 mg/l) significantly attenuated neuronal damage and inhibited LDH release in a dose-dependent manner. Furthermore, LBP enhanced activities of SOD and GSH-PX but it decreased their MDA content, inhibited [Ca(2+)](i) elevation and decrease of MMP in ischemia-reperfusion treated hippocampal neurons. These findings suggested that LBP may be a potential neuroprotective agent for cerebral ischemia-reperfusion injury.

Role of Endolysosomes in HIV-1 Tat-Induced Neurotoxicity

Combined anti-retroviral therapeutic drugs effectively increase the lifespan of HIV-1-infected individuals who then have a higher prevalence of HAND (HIV-1 associated neurocognitive disorder). Soluble factors including HIV-1 proteins released from HIV-1-infected cells have been implicated in the pathogenesis of HAND, and particular attention has been paid to the HIV-1 Tat (transactivator of transcription) protein because of its ability to directly excite neurons and cause neuronal cell death. Since HIV-1 Tat enters cells by receptor-mediated endocytosis and since endolysosomes play an important role in neuronal cell life and death, we tested here the hypothesis that HIV-1 Tat neurotoxicity is associated with changes in the endolysosome structure and function and also autophagy. Following the treatment of primary cultured rat hippocampal neurons with HIV-1 Tat or as controls mutant-Tat or PBS, neuronal viability was determined using a triple staining method. Preceding observations of HIV-1 Tat-induced neuronal cell death, we observed statistically significant changes in the structure and membrane integrity of endolysosomes, endolysosome pH and autophagy. As early as 24 h after HIV-1 Tat was applied to neurons, HIV-1 Tat accumulated in endolysosomes, endolysosome morphology was affected and their size increased, endolysosome membrane integrity was disrupted, endolysosome pH increased, specific activities of endolysosome enzymes decreased and autophagy was inhibited, as indicated by the significant changes in three markers for autophagy. In contrast, statistically significant levels of HIV-1 Tat-induced neuronal cell death were observed only after 48 h of HIV-1 Tat treatment. Our findings suggest that endolysosomes are involved in HIV-1 Tat-induced neurotoxicity and may represent a target for therapeutic intervention against HAND.

Possible involvement of mitochondrial uncoupling protein-2 in cytotoxicity mediated by acquired N-methyl-d-aspartate receptor channels

We have previously shown the possible involvement of mitochondrial membrane potential disruption in the mechanisms underlying the neurotoxicity seen after activation of N-methyl-d-aspartate (NMDA) receptors (NMDAR) in primary cultured rat hippocampal neurons. In this study, we attempted to demonstrate a pivotal role of mitochondrial uncoupling protein-2 (UCP2) as a determinant of the NMDA neurotoxicity by using acquired NMDAR channels artificially orchestrated in HEK293 cells. In cells with overexpression of UCP2, immunoreactive UCP2 was exclusively detected at intracellular locations stained with the mitochondrial marker MitoTracker. In cells with acquired NMDAR channels, exposure to either NMDA or the calcium ionophore A23187 similarly led to a significant increase in cytosolic Ca2+ levels determined by Fluo-3 imaging irrespective of the overexpression of UCP2. By contrast, NMDA, but not A23187, was significantly more effective in increasing mitochondrial Ca2+ levels determined by Rhod-2 fluorescence imaging in cells transfected with NMDAR subunit and UCP2 expression vectors than in those without UCP2 overexpression. Overexpression of UCP2 significantly increased the number of cells stained with propidium iodide in cultures with acquired NMDAR channels, but failed to significantly affect that in cells exposed to A23187. Immunocytochemical and immunoprecipitation analyses similarly revealed the possible interaction between GluN1 subunit and UCP2 in HEK293 cells with acquired NMDAR channels and UCP2 overexpression. These results suggest that UCP2 could play a role as a determinant of the neurotoxicity mediated by NMDAR through a mechanism related to the unidentified interaction with the essential GluN1 subunit toward modulation of mitochondrial Ca2+ levels in neurons.

A Neuroprotective Mechanism of YGY‐E in Cerebral Ischemic Injury in Rats

To investigate the anticerebral ischemic properties of YGY-E (apigenin-7-O-β-D-glucopyranosy l-4'-O-α-L-rhamnopy-ranosid, a flavonoid glycoside extracted from plant phoenix-tail fern), focusing on its effects on neuronal apoptosis. In vitro YGY-E treatment was examined in primary cultured rat hippocampal neurons subjected to hypoxia-reoxygenation (H-R) injury. In addition, in vivo effects of YGY-E on neuronal apoptosis were measured by Hoechst staining and in situ DNA end labeling (TUNEL). Finally, B cell lymphoma/lewkmia-2 (Bcl-2) level in ischemic rat brain tissue was evaluated with immunohistochemistry and western blot analyses. In vitro YGY-E (50-100 μg/mL) treatment increased the survival rate compared to that of the vehicle-treated group (P < 0.05 and P < 0.01, respectively). In in vivo experiments, YGY-E (2.5-10 mg/kg) decreased the percentage of apoptotic neurons (P < 0.01), increased Bcl-2 (P < 0.01) in ischemic rat brain tissue. These effects were dose dependent. Our findings indicate that YGY-E's neuroprotective effects may be because of its inhibition of neuronal apoptosis by increasing Bcl-2 expression.

Lycopene protects against trimethyltin-induced neurotoxicity in primary cultured rat hippocampal neurons by inhibiting the mitochondrial apoptotic pathway

Lycopene is a potent free radicals scavenger with demonstrated protective efficacy in several experimental models of oxidative damage. Trimethyltin (TMT) is an organotin compound with neurotoxic effects on the hippocampus and other limbic structures and is used to model neurodegenerative diseases targeting these brain areas. Oxidative stress is widely accepted as a central pathogenic mechanism of TMT-mediated neurotoxicity. The present study investigated whether the plant carotene lycopene protects against TMT-induced neurotoxicity in primary cultured rat hippocampal neurons. Lycopene pretreatment improved cell viability in TMT-treated hippocampal neurons and inhibited neuronal apoptosis. Microfluorometric imaging revealed that lycopene inhibited the accumulation of mitochondria-derived reactive oxygen species (ROS) during TMT exposure. Moreover, lycopene ameliorated TMT-induced activation of the mitochondrial permeability transition pore (mPTP) and the concomitant depolarization of the mitochondrial membrane potential (ΔΨm). Consequently, cytochrome c release from the mitochondria and ensuing caspase-3 activation were markedly reduced. These findings reveal that lycopene protects against TMT-induced neurotoxicity by inhibiting the mitochondrial apoptotic pathway. The anti-apoptotic effect of lycopene on hippocampal neurons highlights the therapeutic potential of plant-derived antioxidants against neurodegenerative diseases.