Ischemia-induced modifications in hippocampal CA1 stratum radiatum excitatory synapses

Distinct mechanisms drive sequential internalization and degradation of GABAARs during global ischemia and reperfusion injury

Synaptic inhibition is critical for controlling neuronal excitability and function. During global cerebral ischemia (GCI), inhibitory synapses are rapidly eliminated, causing hyper-excitability which contributes to cell-death and the pathophysiology of disease. Sequential disassembly of inhibitory synapses begins within minutes of ischemia onset: GABAARs are rapidly trafficked away from the synapse, the gephyrin scaffold is removed, followed by loss of the presynaptic terminal. GABAARs are endocytosed during GCI, but how this process accompanies synapse disassembly remains unclear. Here, we define the precise trafficking itinerary of GABAARs during the initial stages of GCI, placing them in the context of rapid synapse elimination. Ischemia-induced GABAAR internalization quickly follows their initial dispersal from the synapse, and is controlled by PP1α signaling. During reperfusion injury, GABAARs are then trafficked to lysosomes for degradation, leading to permanent removal of synaptic GABAARs and contributing to the profound reduction in synaptic inhibition observed hours following ischemia onset.

Resveratrol Preconditioning Protects Against Ischemia-Induced Synaptic Dysfunction and Cofilin Hyperactivation in the Mouse Hippocampal Slice

Perturbations in synaptic function are major determinants of several neurological diseases and have been associated with cognitive impairments after cerebral ischemia (CI). Although the mechanisms underlying CI-induced synaptic dysfunction have not been well defined, evidence suggests that early hyperactivation of the actin-binding protein, cofilin, plays a role. Given that synaptic impairments manifest shortly after CI, prophylactic strategies may offer a better approach to prevent/mitigate synaptic damage following an ischemic event. Our laboratory has previously demonstrated that resveratrol preconditioning (RPC) promotes cerebral ischemic tolerance, with many groups highlighting beneficial effects of resveratrol treatment on synaptic and cognitive function in other neurological conditions. Herein, we hypothesized that RPC would mitigate hippocampal synaptic dysfunction and pathological cofilin hyperactivation in an ex vivo model of ischemia. Various electrophysiological parameters and synaptic-related protein expression changes were measured under normal and ischemic conditions utilizing acute hippocampal slices derived from adult male mice treated with resveratrol (10 mg/kg) or vehicle 48 h prior. Remarkably, RPC significantly increased the latency to anoxic depolarization, decreased cytosolic calcium accumulation, prevented aberrant increases in synaptic transmission, and rescued deficits in long-term potentiation following ischemia. Additionally, RPC upregulated the expression of the activity-regulated cytoskeleton associated protein, Arc, which was partially required for RPC-mediated attenuation of cofilin hyperactivation. Taken together, these findings support a role for RPC in mitigating CI-induced excitotoxicity, synaptic dysfunction, and pathological over-activation of cofilin. Our study provides further insight into mechanisms underlying RPC-mediated neuroprotection against CI and implicates RPC as a promising strategy to preserve synaptic function after ischemia.

An Electrophysiological and Proteomic Analysis of the Effects of the Superoxide Dismutase Mimetic, MnTMPyP, on Synaptic Signalling Post-Ischemia in Isolated Rat Hippocampal Slices

Metabolic stress and the increased production of reactive oxygen species (ROS) are two main contributors to neuronal damage and synaptic plasticity in acute ischemic stroke. The superoxide scavenger MnTMPyP has been previously reported to have a neuroprotective effect in organotypic hippocampal slices and to modulate synaptic transmission after in vitro hypoxia and oxygen-glucose deprivation (OGD). However, the mechanisms involved in the effect of this scavenger remain elusive. In this study, two concentrations of MnTMPyP were evaluated on synaptic transmission during ischemia and post-ischemic synaptic potentiation. The complex molecular changes supporting cellular adaptation to metabolic stress, and how these are modulated by MnTMPyP, were also investigated. Electrophysiological data showed that MnTMPyP causes a decrease in baseline synaptic transmission and impairment of synaptic potentiation. Proteomic analysis performed on MnTMPyP and hypoxia-treated tissue indicated an impairment in vesicular trafficking mechanisms, including reduced expression of Hsp90 and actin signalling. Alterations of vesicular trafficking may lead to reduced probability of neurotransmitter release and AMPA receptor activity, resulting in the observed modulatory effect of MnTMPyP. In OGD, protein enrichment analysis highlighted impairments in cell proliferation and differentiation, such as TGFβ1 and CDKN1B signalling, in addition to downregulation of mitochondrial dysfunction and an increased expression of CAMKII. Taken together, our results may indicate modulation of neuronal sensitivity to the ischemic insult, and a complex role for MnTMPyP in synaptic transmission and plasticity, potentially providing molecular insights into the mechanisms mediating the effects of MnTMPyP during ischemia.

Novel mechanism of hypoxic neuronal injury mediated by non-excitatory amino acids and astroglial swelling

In ischemic stroke and post-traumatic brain injury (TBI), blood-brain barrier disruption leads to leaking plasma amino acids (AA) into cerebral parenchyma. Bleeding in hemorrhagic stroke and TBI also release plasma AA. Although excitotoxic AA were extensively studied, little is known about non-excitatory AA during hypoxic injury. Hypoxia-induced synaptic depression in hippocampal slices becomes irreversible with non-excitatory AA, alongside their intracellular accumulation and increased tissue electrical resistance. Four non-excitatory AA (l-alanine, glycine, l-glutamine, l-serine: AGQS) at plasmatic concentrations were applied to slices from mice expressing EGFP in pyramidal neurons or astrocytes during normoxia or hypoxia. Two-photon imaging, light transmittance (LT) changes, and electrophysiological field recordings followed by electron microscopy in hippocampal CA1 st. radiatum were used to monitor synaptic function concurrently with cellular swelling and injury. During normoxia, AGQS-induced increase in LT was due to astroglial but not neuronal swelling. LT raise during hypoxia and AGQS manifested astroglial and neuronal swelling accompanied by a permanent loss of synaptic transmission and irreversible dendritic beading, signifying acute damage. Neuronal injury was not triggered by spreading depolarization which did not occur in our experiments. Hypoxia without AGQS did not cause cell swelling, leaving dendrites intact. Inhibition of NMDA receptors prevented neuronal damage and irreversible loss of synaptic function. Deleterious effects of AGQS during hypoxia were prevented by alanine-serine-cysteine transporters (ASCT2) and volume-regulated anion channels (VRAC) blockers. Our findings suggest that astroglial swelling induced by accumulation of non-excitatory AA and release of excitotoxins through antiporters and VRAC may exacerbate the hypoxia-induced neuronal injury.

Hippocampal metabolic recovery as a manifestation of the protective effect of ischemic preconditioning in rats

The ever-present risk of brain ischemic events in humans and its full prevention make the detailed studies of an organism's response to ischemia at different levels essential to understanding the mechanism of the injury as well as protection. We used the four-vessel occlusion as an animal model of forebrain ischemia to investigate its impact on the metabolic alterations in both the hippocampus and the blood plasma to see changes on the systemic level. By inducing sublethal ischemic stimuli, we focused on the endogenous phenomena known as ischemic tolerance. NMR spectroscopy was used to analyze relative metabolite levels in tissue extracts from rats' hippocampus and blood plasma in three various ischemic/reperfusion times: 3 h, 24 h, and 72 h. Hippocampal tissues were characterized by postischemically decreased glutamate and GABA (4-aminobutyrate) tissue content balanced with increased glutamine level, with most pronounced changes at 3 h reperfusion time. Glutamate (as well as glutamine) levels recovered towards the control levels on the third day, as if the glutamate re-synthesis would be firstly preferred before GABA. These results are indicating the higher feasibility of re-establishing of glutamatergic transmission three days after an ischemic event, in contrast to GABA-ergic. Tissue levels of N-acetylaspartate (NAA), as well as choline, were decreased without the tendency to recover three days after the ischemic event. Metabolomic analysis of blood plasma revealed that ischemically preconditioned rats, contrary to the non-preconditioned animals, did not show hyperglycemic conditions. Ischemically induced semi-ketotic state, manifested in increased plasma ketone bodies 3-hydroxybutyrate and acetoacetate, seems to be programmed to support the brain tissue revitalization after the ischemic event. These and other metabolites changes found in blood plasma as well as in the hippocampus were observed to a lower extent or recovered faster in preconditioned animals. Some metabolomic changes in hippocampal tissue extract were so strong that even single metabolites were able to differentiate between ischemic, ischemically preconditioned, and control brain tissues.

Metabolic Changes Induced by Cerebral Ischemia, the Effect of Ischemic Preconditioning, and Hyperhomocysteinemia

¹H Nuclear Magnetic Resonance (NMR) metabolomics is one of the fundamental tools in the fast-developing metabolomics field. It identifies and quantifies the most abundant metabolites, alterations of which can describe energy metabolism, activated immune response, protein synthesis and catabolism, neurotransmission, and many other factors. This paper summarizes our results of the ¹H NMR metabolomics approach to characterize the distribution of relevant metabolites and their alterations induced by cerebral ischemic injury or its combination with hyperhomocysteinemia in the affected tissue and blood plasma in rodents. A decrease in the neurotransmitter pool in the brain tissue likely follows the disordered feasibility of post-ischemic neurotransmission. This decline is balanced by the increased tissue glutamine level with the detected impact on neuronal health. The ischemic injury was also manifested in the metabolomic alterations in blood plasma with the decreased levels of glycolytic intermediates, as well as a post-ischemically induced ketosis-like state with increased plasma ketone bodies. As the 3-hydroxybutyrate can act as a likely neuroprotectant, its post-ischemic increase can suggest its supporting role in balancing ischemic metabolic dysregulation. Furthermore, the ¹H NMR approach revealed post-ischemically increased 3-hydroxybutyrate in the remote organs, such as the liver and heart, as well as decreased myocardial glutamate. Ischemic preconditioning, as a proposed protective strategy, was manifested in a lower extent of metabolomic changes and/or their faster recovery in a longitudinal study. The paper also summarizes the pre- and post-ischemic metabolomic changes in the rat hyperhomocysteinemic models. Animals are challenged with hyperglycemia and ketosis-like state. A decrease in several amino acids in plasma follows the onset and progression of hippocampal neuropathology when combined with ischemic injury. The ¹H NMR metabolomics approach also offers a high potential for metabolites in discriminatory analysis in the search for potential biomarkers of ischemic injury. Based on our results and the literature data, this paper presents valuable findings applicable in clinical studies and suggests the precaution of a high protein diet, especially foods which are high in Met content and low in B vitamins, in the possible risk of human cerebrovascular neuropathology.

Different changes in pre- and postsynaptic components in the hippocampal CA1 subfield after transient global cerebral ischemia

To date, ischemia-induced damage to dendritic spines has attracted considerable attention, while the possible effects of ischemia on presynaptic components has received relatively less attention. To further examine ischemia-induced changes in pre- and postsynaptic specializations in the hippocampal CA1 subfield, we modeled global cerebral ischemia with two-stage 4-vessel-occlusion in rats, and found that three postsynaptic markers, microtubule-associated protein 2 (MAP2), postsynaptic density protein 95 (PSD95), and filamentous F-actin (F-actin), were all substantially decreased in the CA1 subfield after ischemia/reperfusion (I/R). Although no significant change was detected in synapsin I, a presynaptic marker, in the CA1 subfield at the protein level, confocal microscopy revealed that the number and size of synapsin I puncta were significantly changed in the CA1 stratum radiatum after I/R. The size of synapsin I puncta became slightly, but significantly reduced on Day 1.5 after I/R. From Days 2 to 7 after I/R, the number of synapsin I puncta became moderately decreased, while the size of synapsin I puncta was significantly increased. Interestingly, some enlarged puncta of synapsin I were observed in close proximity to the dendritic shafts of CA1 pyramidal cells. Due to the more substantial decrease in the number of F-actin puncta, the ratio of synapsin I/F-actin puncta was significantly increased after I/R. The decrease in synapsin I puncta size in the early stage of I/R may be the result of excessive neurotransmitter release due to I/R-induced hyperexcitability in CA3 pyramidal cells, while the increase in synapsin I puncta in the later stage of I/R may reflect a disability of synaptic vesicle release due to the loss of postsynaptic contacts.

Delta Opioid Receptor Activation with Delta Opioid Peptide [d-Ala2, d-Leu5] Enkephalin Contributes to Synaptic Improvement in Rat Hippocampus against Global Ischemia

Global cerebral ischemia induced by cardiac arrest usually leads to poor neurological outcomes. Numerous studies have focused on ways to prevent ischemic damage in the brain, however clinical therapies are still limited. Our previous studies revealed that delta opioid receptor (DOR) activation with [d-Ala2, d-Leu5] enkephalin (DADLE), a DOR agonist, not only significantly promotes neuronal survival on day 3, but also improves spatial memory deficits on days 5-9 after ischemia. However, the neurological mechanism underlying DADLE-induced cognitive recovery remains unclear. This study first examined the changes in neuronal survival in the CA1 region at the advanced time point (day 7) after ischemia/reperfusion (I/R) injury and found a significant amelioration of damaged CA1 neurons in the rats treated with DADLE (2.5 nmol) when administered at the onset of reperfusion. The structure and function of CA1 neurons on days 3 and 7 post-ischemia showed significant improvements in both the density of the injured dendritic spines and the basic transmission of the impaired CA3-CA1 synapses following DADLE treatment. The molecular changes involved in DADLE-mediated synaptic modulation on days 3 and 7 post-ischemia implied the time-related differential regulation of PKCα-MARCKS on the dendritic spine structure and of BDNF- ERK1/2-synapsin I on synaptic function, in response to ischemic/reperfusion injury as well as to DADLE treatment. Importantly, all the beneficial effects of DADLE on ischemia-induced cellular, synaptic, and molecular deficits were eliminated by the DOR inhibitor naltrindole (2.5 nmol). Taken together, this study suggested that DOR activation-induced protective signaling pathways of PKCα-MARCKS involved in the synaptic morphology and BDNF-ERK-synapsin I in synaptic transmission may be engaged in the cognitive recovery in rats suffering from advanced cerebral ischemia.

Pathological Comparisons of the Hippocampal Changes in the Transient and Permanent Middle Cerebral Artery Occlusion Rat Models

Ischemic strokes are categorized by permanent or transient obstruction of blood flow, which impedes delivery of oxygen and essential nutrients to brain. In the last decade, the therapeutic window for tPA has increased from 3 to 5-6 h, and a new technique, involving the mechanical removal of the clot (endovascular thrombectomy) to allow reperfusion of the injured area, is being used more often. This last therapeutic approach can be done until 24 h after stroke onset. Due to this fact, more acute ischemic stroke patients are now being recanalized, and so tMCAO is probably the "best" model to address these patients that have a potential good outcome in terms of survival and functional recovery. However, permanent occlusion patients are also important, not only to increase survival rate but also to improve functional outcomes, although these are more difficult to achieve. So, both models are important, and which target different stroke patients in the clinical scenario. Hippocampus has a vital role in memory and cognition, is prone to ischemic induced neurodegeneration. This study was designed to delineate the molecular, pathological, and neurological changes in rat models of t-MCAO, permanent MCAO (pMCAO), and pMCAO with diabetic conditions in hippocampal tissue. Our results showed that these three models showed distinct discrepancies at numerous pathological process, including key signaling molecules involved in neuronal apoptosis, glutamate induced excitotoxicity, neuroinflammation, oxidative stress, and neurotrophic changes. Our result suggests that the two commonly used MCAO models exhibited tremendous differences in terms of neuronal cell loss, glutamate excitotoxic related signaling, synaptic transmission markers, neuron inflammatory and oxidative stress molecules. These differences may reflect the variations in different models, which may provide valuable information for mechanistic and therapeutic inconsistences as experienced in both preclinical models and clinical trials.

Proteomic Analysis of Rat Cerebral Cortex in the Subacute to Long-Term Phases of Focal Cerebral Ischemia-Reperfusion Injury

Stroke is a leading cause of mortality and disability, and ischemic stroke accounts for more than 80% of the disease occurrence. Timely reperfusion is essential in the treatment of ischemic stroke, but it is known to cause ischemia-reperfusion (I/R) injury and the relevant studies have mostly focused on the acute phase. Here we reported on a global proteomic analysis to investigate the development of cerebral I/R injury in the subacute and long-term phases. A rat model was used, with 2 h-middle cerebral artery occlusion (MCAO) followed with 1, 7, and 14 days of reperfusion. The proteins of cerebral cortex were analyzed by SDS-PAGE, whole-gel slicing, and quantitative LC-MS/MS. Totally 5621 proteins were identified, among which 568, 755, and 492 proteins were detected to have significant dys-regulation in the model groups with 1, 7, and 14 days of reperfusion, respectively, when compared with the corresponding sham groups (n = 4, fold change ≥1.5 or ≤0.67 and p ≤ 0.05). Bioinformatic analysis on the functions and reperfusion time-dependent dys-regulation profiles of the proteins exhibited changes of structures and biological processes in cytoskeleton, synaptic plasticity, energy metabolism, inflammation, and lysosome from subacute to long-term phases of cerebral I/R injury. Disruption of cytoskeleton and synaptic structures, impairment of energy metabolism processes, and acute inflammation responses were the most significant features in the subacute phase. With the elongation of reperfusion time to the long-term phase, a tendency of recovery was detected on cytoskeleton, while inflammation pathways different from the subacute phase were activated. Also, lysosomal structures and functions might be restored. This is the first work reporting the proteome changes that occurred at different time points from the subacute to long-term phases of cerebral I/R injury and we expect it would provide useful information to improve the understanding of the mechanisms involved in the development of cerebral I/R injury and suggest candidates for treatment.

The temporal and spatial changes of actin cytoskeleton in the hippocampal CA1 neurons following transient global ischemia

Transient global ischemia usually results in delayed neuronal death in selective brain regions, prior to which a rapid loss of dendritic spines has been widely reported in these regions. Dendritic spines are characterized by a highly branched meshwork of actin cytoskeleton (F-actin), which is extremely vulnerable to the ATP-depleted conditions such as hypoxia/ischemia. However, the ischemia-induced changes of F-actin are still not clarified in the vulnerable brain areas. This study was designed to examine the temporal and spatial alterations of F-actin in the CA1 subfield of rat hippocampus following reperfusion after global cerebral ischemia. Phalloidin staining and confocal microscopic examination showed that F-actin disappeared from the dentritic spines in the CA1 stratum radiatum, but aggregated into thread- or fiber-like structures on days 1.5-2 after ischemia. This was followed by a nearly complete loss of F-actin in the CA1 subfield on days 3-7 after ischemia. Colocalization analysis demonstrated that the F-actin threads or fibers were located mainly within the dentritic trunks. As revealed by Nissl and Fluoro-Jade B staining, the decrease of F-actin proceeded concurrently with the evolution of ischemic damage. Consistently, western blots detected a significant decrease of F-/G-actin ratio in the dissected CA1 subfield after ischemia. To our knowledge, this is the first report on the change of F-actin in the ischemic brain. Although the underlying mechanisms remain to be elucidated, our findings may provide an important structural clue for the neuronal dysfunction induced by ischemia.

Melatonin Protects MCAO-Induced Neuronal Loss via NR2A Mediated Prosurvival Pathways

Stroke is the significant cause of human mortality and sufferings depending upon race and demographic location. Melatonin is a potent antioxidant that exerts protective effects in differential experimental stroke models. Several mechanisms have been previously suggested for the neuroprotective effects of melatonin in ischemic brain injury. The aim of this study is to investigate whether melatonin treatment affects the glutamate N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor signaling in cerebral cortex and striatum 24 h after permanent middle cerebral artery occlusion (MCAO). Melatonin (5 mg/kg) attenuated ischemia-induced down regulation of NMDA receptor 2 (NR2a), postsynaptic density-95 (PSD95) and increases NR2a/PSD95 complex association, which further activates the pro-survival PI3K/Akt/GSK3β pathway with mitigated collapsin response mediator protein 2 (CRMP2) phosphorylation. Furthermore, melatonin increases the expression of γ-enolase, a neurotrophic factor in ischemic cortex and striatum, and preserve the expression of presynaptic (synaptophysin and SNAP25) and postsynaptic (p-GluR1845) protein. Our study demonstrated a novel neuroprotective mechanism for melatonin in ischemic brain injury which could be a promising neuroprotective agent for the treatment of ischemic stroke.

Knockdown of CLC-3 in the hippocampal CA1 impairs contextual fear memory

Previous studies support a critical role of hippocampus in contextual fear memory. Structural and functional alterations of hippocampus occur frequently in posttraumatic stress disorders (PTSD). Recent reports reveal that knockout of CLC-3, a member of the CLC family of anion channels and transporters, leads to neuronal degeneration and loss of hippocampus. However, the role of CLC-3 in contextual fear memory remains unknown. Using adenovirus and adeno-associated virus gene transfer to knockdown CLC-3 in hippocampal CA1, we investigate the role of CLC-3 in contextual fear memory. CLC-3 expression is increased in hippocampal CA1 after formation of long-term contextual fear memory. Knockdown of CLC-3 by adenovirus infusion in hippocampal CA1 significantly attenuates the contextual fear memory, reduces spine density, induces defects of excitatory synaptic ultrastructure showed by the decreased PSD length, PSD thickness and active zone length, and impairs L-LTP induction and maintenance. Knockdown of CLC-3 also induces the synaptic NMDAR subunit composition to an increased GluN2A/GluN2B ratio pattern and reduces the activity of CaMKII-α. Furthermore, selectively knockdown of CLC-3 in excitatory neurons by adeno-associated virus driven from CaMKII-α promoter is sufficient to impair long-term contextual fear memory. These findings highlight that CLC-3 in hippocampal CA1 is necessary for contextual fear memory.

Impact of neuroimmune activation induced by alcohol or drug abuse on adolescent brain development

Evidence obtained in recent decades has demonstrated that the brain still matures in adolescence. Changes in neural connectivity occur in different regions, including cortical and subcortical structures, which undergo modifications in white and gray matter densities. These alterations concomitantly occur in some neurotransmitter systems and hormone secretion, which markedly influence the refinement of certain brain areas and neural circuits. The immaturity of the adolescent brain makes it more vulnerable to the effects of alcohol and drug abuse, whose use can trigger long-term behavioral dysfunction. This article reviews the action of alcohol and drug abuse (cannabis, cocaine, opioids, amphetamines, anabolic androgenic steroids) in the adolescent brain, and their impact on both cognition and behavioral dysfunction, including predisposition to drug abuse in later life. It also discusses recent evidence that indicates the role of the neuroimmune system response and neuroinflammation as mechanisms that participate in many actions of ethanol and drug abuse in adolescence, including the neurotoxicity and alterations in neurocircuitry that contribute to the dysfunctional behaviors associated with addiction. The new data suggest the therapeutic potential of anti-inflammatory targets to prevent the long-term consequences of drug abuse in adolescence.

SPARC and GluA1-Containing AMPA Receptors Promote Neuronal Health Following CNS Injury

The proper formation and maintenance of functional synapses in the central nervous system (CNS) requires communication between neurons and astrocytes and the ability of astrocytes to release neuromodulatory molecules. Previously, we described a novel role for the astrocyte-secreted matricellular protein SPARC (Secreted Protein, Acidic and Rich in Cysteine) in regulating α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) and plasticity at developing synapses. SPARC is highly expressed by astrocytes and microglia during CNS development but its level is reduced in adulthood. Interestingly, SPARC has been shown to be upregulated in CNS injury and disease. However, the role of SPARC upregulation in these contexts is not fully understood. In this study, we investigated the effect of chronic SPARC administration on glutamate receptors on mature hippocampal neuron cultures and following CNS injury. We found that SPARC treatment increased the number of GluA1-containing AMPARs at synapses and enhanced synaptic function. Furthermore, we determined that the increase in synaptic strength induced by SPARC could be inhibited by Philanthotoxin-433, a blocker of homomeric GluA1-containing AMPARs. We then investigated the effect of SPARC treatment on neuronal health in an injury context where SPARC expression is upregulated. We found that SPARC levels are increased in astrocytes and microglia following middle cerebral artery occlusion (MCAO) in vivo and oxygen-glucose deprivation (OGD) in vitro. Remarkably, chronic pre-treatment with SPARC prevented OGD-induced loss of synaptic GluA1. Furthermore, SPARC treatment reduced neuronal death through Philanthotoxin-433 sensitive GluA1 receptors. Taken together, this study suggests a novel role for SPARC and GluA1 in promoting neuronal health and recovery following CNS damage.

Learning and memory disabilities in IUGR babies: Functional and molecular analysis in a rat model

INTRODUCTION

1Intrauterine growth restriction (IUGR) is the failure of the fetus to achieve its inherent growth potential, and it has frequently been associated with neurodevelopmental problems in childhood. Neurological disorders are mostly associated with IUGR babies with an abnormally high cephalization index (CI) and a brain sparing effect. However, a similar correlation has never been demonstrated in an animal model. The aim of this study was to determine the correlations between CI, functional deficits in learning and memory and alterations in synaptic proteins in a rat model of IUGR.

METHODS

2Utero-placental insufficiency was induced by meso-ovarian vessel cauterization (CMO) in pregnant rats at embryonic day 17 (E17). Learning performance in an aquatic learning test was evaluated 25 days after birth and during 10 days. Some synaptic proteins were analyzed (PSD95, Synaptophysin) by Western blot and immunohistochemistry.

RESULTS

3Placental insufficiency in CMO pups was associated with spatial memory deficits, which are correlated with a CI above the normal range. CMO pups presented altered levels of synaptic proteins PSD95 and synaptophysin in the hippocampus.

CONCLUSIONS

4The results of this study suggest that learning disabilities may be associated with altered development of excitatory neurotransmission and synaptic plasticity. Although interspecific differences in fetal response to placental insufficiency should be taken into account, the translation of these data to humans suggest that both IUGR babies and babies with a normal birth weight but with intrauterine Doppler alterations and abnormal CI should be closely followed to detect neurodevelopmental alterations during the postnatal period.

Changes in synaptic plasticity and expression of glutamate receptor subunits in the CA1 and CA3 areas of the hippocampus after transient global ischemia

Excess glutamate release from the presynaptic membrane has been thought to be the major cause of ischemic neuronal death. Although both CA1 and CA3 pyramidal neurons receive presynaptic glutamate input, transient cerebral ischemia induces CA1 neurons to die while CA3 neurons remain relatively intact. This suggests that changes in the properties of pyramidal cells may be the main cause related to ischemic neuronal death. Our previous studies have shown that the densities of dendritic spines and asymmetric synapses in the CA1 area are increased at 12h and 24h after ischemia. In the present study, we investigated changes in synaptic structures in the CA3 area and compared the expression of glutamate receptors in the CA1 and CA3 hippocampal regions of rats after ischemia. Our results demonstrated that the NR2B/NR2A ratio became larger after ischemia although the expression of both the NR2B subunit (activation of apoptotic pathway) and NR2A subunit (activation of survival pathway) decreased in the CA1 area from 6h to 48h after reperfusion. Furthermore, expression of the GluR2 subunit (calcium impermeable) of the AMPA receptor class significantly decreased while the GluR1 subunit (calcium permeable) remained unchanged at the same examined reperfusion times, which subsequently caused an increase in the GluR1/GluR2 ratio. Despite these notable differences in subunit expression, there were no obvious changes in the density of synapses or expression of NMDAR and AMPAR subunits in the CA3 area after ischemia. These results suggest that delayed CA1 neuronal death may be related to the dramatic fluctuation in the synaptic structure and relative upregulation of NR2B and GluR1 subunits induced by transient global ischemia.

Tongxinluo reduces brain edema and inhibits post-ischemic inflammation after middle cerebral artery occlusion in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Tongxinluo (TXL), a widely used traditional Chinese medicine, has been proved multiple therapeutic effects in cerebral ischemic infraction. The purpose of this study was to investigate the protective effects of TXL on the brain edema and post-ischemic inflammatory response.

MATERIALS AND METHODS

Middle cerebral artery occlusion in the rat was used as the ischemia model. Rats were treated with TXL. In the first stage, the best dosage was chosen based on functional assessment and infarct size. In the second stage, rats were randomly divided into 5 groups: sham control (sham), ischemia and reperfusion (IR) 24h, TXL24h, I/R72h, TXL72h. TXL(1.6g/kg/day) administration was pre-performed for 3 days in TXL groups, and was post-performed for 24h (TXL24h group) or 72h (TXL72h group). Brain edema was measured by water content, MRI and AQP4 expression. Iba1, HMGB1, TLR4, NF-κB expression were examined by immunofluorescence staining or Western blot. TNF-α was determined by enzyme-linked immunosorbent assay.

RESULTS

High dose (1.6g/kg/day) of TXL remarkably reduced neurological deficit scores and cerebral infarct area. Compared with those results of I/R24h group, pre-post treatment with TXL for 3 days decreased brain water content, down-regulated AQP4 expression, lowered relative signal intensity of T2WI, reduced lesion volume ratio, and inhibited the activation of microglia, HMGB1, TLR4, NF-κB and TNF-α.

CONCLUSIONS

These results indicated that the TXL pre-post treatment for 3 days could be an effective therapy for brain ischemia by inhibiting the development of brain edema and post-ischemic inflammation.

Ultrastructural analysis of adult mouse neocortex comparing aldehyde perfusion with cryo fixation

Analysis of brain ultrastructure using electron microscopy typically relies on chemical fixation. However, this is known to cause significant tissue distortion including a reduction in the extracellular space. Cryo fixation is thought to give a truer representation of biological structures, and here we use rapid, high-pressure freezing on adult mouse neocortex to quantify the extent to which these two fixation methods differ in terms of their preservation of the different cellular compartments, and the arrangement of membranes at the synapse and around blood vessels. As well as preserving a physiological extracellular space, cryo fixation reveals larger numbers of docked synaptic vesicles, a smaller glial volume, and a less intimate glial coverage of synapses and blood vessels compared to chemical fixation. The ultrastructure of mouse neocortex therefore differs significantly comparing cryo and chemical fixation conditions.

Activation of NMDA receptors thickens the postsynaptic density via proteolysis

The postsynaptic density (PSD) is a protein complex that is critical for synaptic transmission. Ultrastructural changes in the PSD are therefore likely to modify synaptic functions. In this study, we investigated the ultrastructural changes in the PSD in the hippocampal CA1 stratum radiatum following neuronal excitation. Oxygen-glucose deprivation-induced PSD thickening in hippocampal slice cultures was blocked by the N-methyl-d-aspartate (NMDA) receptor antagonist MK801. To gain more insight into the mechanisms underlying NMDA receptor-mediated PSD thickening, we assessed the area, length, and thickness of the PSD after NMDA treatment. The PSDs thickened with just 2 min of NMDA receptor stimulation, and this treatment was considered sublethal. When N-acetyl-leucyl-leucyl-norleucinal, an inhibitor of calpain, cathepsins, and the proteasome, was applied, NMDA-induced PSD thickening was abolished. Furthermore, the calcium-induced calcium release inhibitor, ryanodine, reduced NMDA receptor-mediated PSD thickening. These results suggest that NMDA receptor activation induces PSD thickening by proteolysis through intracellular calcium increase, including that induced by calcium.

Hydrogen sulfide induces neuroprotection against experimental stroke in rats by down-regulation of AQP4 via activating PKC

Hydrogen sulfide (H2S) is now known as an important neuromodulator in the central nervous system. The aim of the current study was to investigate whether exogenous H2S gas can attenuate brain edema induced by experimental stroke and to clarify the potential mechanisms. Rats underwent 2-h middle cerebral artery occlusion (MCAO) and received 40 ppm or 80 ppm H2S inhalation for 3h at the beginning of reperfusion. The effects of H2S were investigated by evaluating neurological function, infarct size, brain edema volume, and aquaporin4 (AQP4) protein expression at 24h after reperfusion. Moreover, to explore the possible mechanisms for the neuroprotective effects of H2S, protein kinase C (PKC) activity was detected and a PKC inhibitor, Go6983, was used via intracerebral ventricular injection. Our results showed that 40 ppm or 80 ppm H2S inhalation significantly reduced neurological deficits, infarct size, and brain edema after MCAO. The expression of AQP4 in the peri-infarct area of brain was also inhibited after inhalation of H2S. PKC was activated by H2S treatment and the PKC inhibitor attenuated the neuroprotection of H2S with an increased AQP4 expression at the same time. In conclusion, H2S inhalation attenuates brain edema, reduces infarct volume, and improves neurologic function in a rat experimental stroke model. The therapeutic benefits of H2S inhalation are associated with down-regulation of AQP4 expression via activating PKC.

Early Exposure to General Anesthesia Disrupts Spatial Organization of Presynaptic Vesicles in Nerve Terminals of the Developing Rat Subiculum

Exposure to general anesthesia (GA) during critical stages of brain development induces widespread neuronal apoptosis and causes long-lasting behavioral deficits in numerous animal species. Although several studies have focused on the morphological fate of neurons dying acutely by GA-induced developmental neuroapoptosis, the effects of an early exposure to GA on the surviving synapses remain unclear. The aim of this study is to study whether exposure to GA disrupts the fine regulation of the dynamic spatial organization and trafficking of synaptic vesicles in presynaptic terminals. We exposed postnatal day 7 (PND7) rat pups to a clinically relevant anesthetic combination of midazolam, nitrous oxide, and isoflurane and performed a detailed ultrastructural analysis of the synaptic vesicle architecture at presynaptic terminals in the subiculum of rats at PND 12. In addition to a significant decrease in the density of presynaptic vesicles, we observed a reduction of docked vesicles, as well as a reduction of vesicles located within 100 nm from the active zone, in animals 5 days after an initial exposure to GA. We also found that the synaptic vesicles of animals exposed to GA are located more distally with respect to the plasma membrane than those of sham control animals and that the distance between presynaptic vesicles is increased in GA-exposed animals compared to sham controls. We report that exposure of immature rats to GA during critical stages of brain development causes significant disruption of the strategic topography of presynaptic vesicles within the nerve terminals of the subiculum.

TLR4 elimination prevents synaptic and myelin alterations and long-term cognitive dysfunctions in adolescent mice with intermittent ethanol treatment

The adolescent brain undergoes important dynamic and plastic cell changes, including overproduction of axons and synapses, followed by rapid pruning along with ongoing axon myelination. These developmental changes make the adolescent brain particularly vulnerable to neurotoxic and behavioral effects of alcohol. Although the mechanisms of these effects are largely unknown, we demonstrated that ethanol by activating innate immune receptors toll-like receptor 4 (TLR4), induces neuroinflammation and brain damage in adult mice. The present study aims to evaluate whether intermittent ethanol treatment in adolescence promotes TLR4-dependent pro-inflammatory processes, leading to myelin and synaptic dysfunctions, and long-term cognitive impairments. Using wild-type (WT) and TLR4-deficient (TLR4-KO) adolescent mice treated intermittently with ethanol (3.0g/kg) for 2weeks, we show that binge-like ethanol treatment activates TLR4 signaling pathways (MAPK, NFκB) leading to the up-regulation of cytokines and pro-inflammatory mediators (COX-2, iNOS, HMGB1), impairing synaptic and myelin protein levels and causing ultrastructural alterations. These changes were associated with long-lasting cognitive dysfunctions in young adult mice, as demonstrated with the object recognition, passive avoidance and olfactory behavior tests. Notably, elimination of TLR4 receptors prevented neuroinflammation along with synaptic and myelin derangements, as well as long-term cognitive alterations. These results support the role of the neuroimmune response and TLR4 signaling in the neurotoxic and behavioral effects of ethanol in adolescence.

Effects of hypoxic preconditioning on synaptic ultrastructure in mice

Hypoxic preconditioning (HPC) elicits resistance to more drastic subsequent insults, which potentially provide neuroprotective therapeutic strategy, but the underlying mechanisms remain to be fully elucidated. Here, we examined the effects of HPC on synaptic ultrastructure in olfactory bulb of mice. Mice underwent up to five cycles of repeated HPC treatments, and hypoxic tolerance was assessed with a standard gasp reflex assay. As expected, HPC induced an increase in tolerance time. To assess synaptic responses, Western blots were used to quantify protein levels of representative markers for glia, neuron, and synapse, and transmission electron microscopy was used to examine synaptic ultrastructure and mitochondrial density. HPC did not significantly alter the protein levels of astroglial marker (GFAP), neuron-specific markers (GAP43, Tuj-1, and OMP), synaptic number markers (synaptophysin and SNAP25) or the percentage of excitatory synapses versus inhibitory synapses. However, HPC significantly affected synaptic curvature and the percentage of synapses with presynaptic mitochondria, which showed concomitant change pattern. These findings demonstrate that HPC is associated with changes in synaptic ultrastructure.

In vitro ischemia triggers a transcriptional response to down-regulate synaptic proteins in hippocampal neurons

Transient global cerebral ischemia induces profound changes in the transcriptome of brain cells, which is partially associated with the induction or repression of genes that influence the ischemic response. However, the mechanisms responsible for the selective vulnerability of hippocampal neurons to global ischemia remain to be clarified. To identify molecular changes elicited by ischemic insults, we subjected hippocampal primary cultures to oxygen-glucose deprivation (OGD), an in vitro model for global ischemia that resulted in delayed neuronal death with an excitotoxic component. To investigate changes in the transcriptome of hippocampal neurons submitted to OGD, total RNA was extracted at early (7 h) and delayed (24 h) time points after OGD and used in a whole-genome RNA microarray. We observed that at 7 h after OGD there was a general repression of genes, whereas at 24 h there was a general induction of gene expression. Genes related with functions such as transcription and RNA biosynthesis were highly regulated at both periods of incubation after OGD, confirming that the response to ischemia is a dynamic and coordinated process. Our analysis showed that genes for synaptic proteins, such as those encoding for PICK1, GRIP1, TARPγ3, calsyntenin-2/3, SAPAP2 and SNAP-25, were down-regulated after OGD. Additionally, OGD decreased the mRNA and protein expression levels of the GluA1 AMPA receptor subunit as well as the GluN2A and GluN2B subunits of NMDA receptors, but increased the mRNA expression of the GluN3A subunit, thus altering the composition of ionotropic glutamate receptors in hippocampal neurons. Together, our results present the expression profile elicited by in vitro ischemia in hippocampal neurons, and indicate that OGD activates a transcriptional program leading to down-regulation in the expression of genes coding for synaptic proteins, suggesting that the synaptic proteome may change after ischemia.

Evidence of lasting dysregulation of neuroendocrine and HPA axis function following global cerebral ischemia in male rats and the effect of Antalarmin on plasma corticosterone level

Abnormal function of the neuroendocrine stress system has been implicated in the behavioral impairments observed following brain ischemia. The current study examined long-term changes in stress signal regulation 30days following global cerebral ischemia. Experiment 1 investigated changes in the expression of corticotropin releasing hormone (CRH) and its subtype 1 receptor (CRHR1), glucocorticoid receptors (GR) in the paraventricular nucleus of the hypothalamus (PVN), the central nucleus of the amygdala (CeA), and the CA1 subfield of the hippocampus. Tyrosine hydroxylase (TH) was determined at the locus coeruleus (LC). Experiment 2 investigated the role of central CRHR1 activation on corticosterone (CORT) secretion at multiple time intervals following global ischemia after exposure to an acute stressor. Findings from Experiment 1 demonstrated a persistent increase in GR, CRH and CRHR1 immunoreactivity (ir) at the PVN, reduced GR and CRHR1 expression in pyramidal CA1 neurons, and increased LC TH expression in ischemic rats displaying working memory errors in the radial arm Maze. Findings from Experiment 2 revealed increased CORT secretion up to 7 days, but no longer present 14 and 21 days post ischemia. However upon an acute restraint stress induced 27 days following reperfusion, ischemic rats had increased plasma CORT secretions compared to sham-operated animals, suggesting HPA axis hypersensitivity. Antalarmin (2 μg/2 μl) pretreatment significantly attenuated post ischemic elevation of basal and stress-induced CORT secretion. These findings support persistent neuroendocrine dysfunctions following brain ischemia likely to contribute to emotional and cognitive impairments observed in survivors of cardiac arrest and stroke.

Melatonin renders neuroprotection by protein kinase C mediated aquaporin-4 inhibition in animal model of focal cerebral ischemia

AIM

Aquaporin-4(AQP4) expression in the brain with relation to edema formation following focal cerebral ischemia was investigated. Studies have shown that brain edema is one of the significant factors in worsening stroke outcomes. While many mechanisms may aggravate brain injury, one such potential system may involve AQP4 up regulation in stroke patients that could result in increased edema formation. Post administration of melatonin following ischemic stroke reduces AQP4 mediated brain edema and confers neuroprotection.

MATERIALS AND METHODS

An in-silico approach was undertaken to confirm effective melatonin-AQP4 binding. Rats were treated with 5mg/kg, i.p. melatonin or placebo at 30 min prior, 60 min post and 120 min post 60 min of middle cerebral artery occlusion (MCAO) followed by 24h reperfusion. Rats were evaluated for battery of neurological and motor function tests just before sacrifice. Brains were harvested for infarct size estimation, water content measurement, biochemical analysis, apoptosis study and western blot experiments.

KEY FINDINGS

Melatonin at 60 min post ischemia rendered neuroprotection as evident by reduction in cerebral infarct volume, improvement in motor and neurological deficit and reduction in brain edema. Furthermore, ischemia induced surge in levels of nitrite and malondialdehyde (MDA) were also found to be significantly reduced in ischemic brain regions in treated animals. Melatonin potentiated intrinsic antioxidant status, inhibited acid mediated rise in intracellular calcium levels, decreased apoptotic cell death and also markedly inhibited protein kinase C (PKC) influenced AQP4 expression in the cerebral cortex and dorsal striatum.

SIGNIFICANCE

Melatonin confers neuroprotection by protein kinase C mediated AQP4 inhibition in ischemic stroke.

Acid-sensing ion channels activation and hypoxia upregulate Homer1a expression

BACKGROUND

Recent studies have indicated that dynamic alterations in the structure of postsynaptic density (PSD) are involved in the pathogenesis of many central nervous system disorders, including ischemic stroke. Homer is the newly identified scaffolding protein located at PSD and regulates synaptic function. Homer1a, an immediate early gene, has been shown to be induced by several stimulations, such as glutamate, brain-derived neurotrophic factor, and trauma. However, whether acidosis mediated by acid-sensing ion channels (ASICs) and hypoxia during cerebral ischemia can change Homer1a expression remains to be determined.

RESULTS

We investigated that acidosis and hypoxia selectively and rapidly upregulated Homer1a expression, but not Homer1b/c in cultured cortical neurons. We also found that Homer1a exhibited induction expression in brain cortex of the middle cerebral artery occlusion (MCAO) rats. Additionally, acid-evoked Homer1a mRNA induction depended on extracellular signal-regulated kinase1/2 (ERK1/2) and Akt activity, and ASIC1a-mediated calcium influx whereas hypoxia depended only on ERK1/2 activity. Also, we demonstrated that continuous acidosis and hypoxia resulted in pronounced cell injury and Homer1a knockdown with small interfering RNA aggravated this damage induced by 3 h acid and hypoxia incubation in neuro-2a cells.

CONCLUSION

Homer1a might act as an activity-dependent regulator responding to extracellular stimuli during cerebral ischemia.

Aquaporin-4 inhibition mediates piroxicam-induced neuroprotection against focal cerebral ischemia/reperfusion injury in rodents

BACKGROUND AND PURPOSE

Aquaporin-4(AQP4) is an abundant water channel protein in brain that regulates water transport to maintain homeostasis. Cerebral edema resulting from AQP4 over expression is considered to be one of the major determinants for progressive neuronal insult during cerebral ischemia. Although, both upregulation and downregulation of AQP4 expression is associated with brain pathology, over expression of AQP4 is one of the chief contributors of water imbalance in brain during ischemic pathology. We have found that Piroxicam binds to AQP4 with optimal binding energy value. Thus, we hypothesized that Piroxicam is neuroprotective in the rodent cerebral ischemic model by mitigating cerebral edema via AQP4 regulation.

METHODS

Rats were treated with Piroxicam OR placebo at 30 min prior, 2 h post and 4 h post 60 minutes of MCAO followed by 24 hour reperfusion. Rats were evaluated for neurological deficits and motor function just before sacrifice. Brains were harvested for infarct size estimation, water content measurement, biochemical analysis, RT-PCR and western blot experiments.

RESULTS

Piroxicam pretreatment thirty minutes prior to ischemia and four hour post reperfusion afforded neuroprotection as evident through significant reduction in cerebral infarct volume, improvement in motor behavior, neurological deficit and reduction in brain edema. Furthermore, ischemia induced surge in levels of nitrite and malondialdehyde were also found to be significantly reduced in ischemic brain regions in treated animals. This neuroprotection was found to be associated with inhibition of acid mediated rise in intracellular calcium levels and also downregulated AQP4 expression.

CONCLUSIONS

Findings of the present study provide significant evidence that Piroxicam acts as a potent AQP4 regulator and renders neuroprotection in focal cerebral ischemia. Piroxicam could be clinically exploited for the treatment of brain stroke along with other anti-stroke therapeutics in future.

NeuroProtective effects of adenosine receptor agonist coadministration with ascorbic acid on CA1 hippocampus in a mouse model of ischemia reperfusion injury

Ischemic brain injury is a leading cause of sever neurological and neurobehavioral deficits and death. The hippocampus plays vital roles in learning and memory processes and it is impaired by ischemic insults. Cerebral ischemia/reperfusion leads to Oxidative stress damage impairing the hippocampus. Here we tested whether ascorbic acid and adenosine receptor played a neuroprotective role in a mouse brain ischemia model induced by common carotid arteries occlusion. Adult male mice were randomly assigned into nine experimental groups. The animals were subjected to ischemia by the ligation of common carotid arteries for 15 min. Drugs were injected intrapritoneally once daily for 7 days. Behavioral tests performed at day 14 and then mice were killed at day 21 and their brains were fixed for microscopic studies and some samples were prepared for western blot analysis. Western blot analysis utilized to evaluate the expression of apoptosis-related proteinsin the hippocampus. Short-term memory was assessed by shuttle-box test. Our findings revealed that administration of vitamin C and N6-cyclopentyladenosine (CPA) significantly attenuated ischemia-induced brain injury. Vitamin C and CPA administration increased the expression of anti-apoptotic protein Bcl-2 and decreased the expression of pro-apoptotic protein Bax in the ischemic mice. Ischemia caused short-term memory loss that was improved by vitamin c and CPA treatment. Our results demonstrate that treatment with vitamin C and adenosine receptor agonist attenuated cerebral ischemia/reperfusion-induced brain injury as a potential neuroprotective agent.

Oxygen/Glucose Deprivation and Reperfusion Cause Modifications of Postsynaptic Morphology and Activity in the CA3 Area of Organotypic Hippocampal Slice Cultures

Brain ischemia leads to overstimulation of N-methyl-D-aspartate (NMDA) receptors, referred as excitotoxicity, which mediates neuronal cell death. However, less attention has been paid to changes in synaptic activity and morphology that could have an important impact on cell function and survival following ischemic insult. In this study, we investigated the effects of reperfusion after oxygen/glucose deprivation (OGD) not only upon neuronal cell death, but also on ultrastructural and biochemical characteristics of postsynaptic density (PSD) protein, in the stratum lucidum of the CA3 area in organotypic hippocampal slice cultures. After OGD/reperfusion, neurons were found to be damaged; the organelles such as mitochondria, endoplasmic reticulum, dendrites, and synaptic terminals were swollen; and the PSD became thicker and irregular. Ethanolic phosphotungstic acid staining showed that the density of PSD was significantly decreased, and the thickness and length of the PSD were significantly increased in the OGD/reperfusion group compared to the control. The levels of PSD proteins, including PSD-95, NMDA receptor 1, NMDA receptor 2B, and calcium/calmodulin-dependent protein kinase II, were significantly decreased following OGD/reperfusion. These results suggest that OGD/reperfusion induces significant modifications to PSDs in the CA3 area of organotypic hippocampal slice cultures, both morphologically and biochemically, and this may contribute to neuronal cell death and synaptic dysfunction after OGD/reperfusion.

Selective vulnerability of synaptic signaling and metabolism to nitrosative stress

SIGNIFICANCE

Nitric oxide (NO) plays diverse physiological roles in the central nervous system, where it modulates neuronal communication, regulates blood flow, and contributes to the innate immune responses. In a number of brain pathologies, the excessive production of NO also leads to the formation of reactive and toxic intermediates generically termed reactive nitrogen species (RNS). RNS cause irreversible or poorly reversible damage to brain cells.

RECENT ADVANCES

Recent work in the field focused on the ability of NO and RNS to yield protein modifications, including the S-nitrosation of cysteine residues, which, in many instances, impact cellular functions and viability.

CRITICAL ISSUES

The vast majority of neuropathological studies focus on the loss of cell viability, but nitrosative stress may also strongly impair the functions of neuronal processes: axonal projections and dendritic trees. The functional integrity of axons and dendrites critically depends on local metabolism and effective delivery of metabolic enzymes and organelles. Here, we summarize the existing literature describing the effects of nitrosative stress on the major pathways of energetic metabolism: glycolysis, tricarboxylic acid cycle, and mitochondrial respiration, with the emphasis on modifications of protein thiols.

FUTURE DIRECTIONS

We propose that axons and dendrites are highly vulnerable to nitrosative stress because of their low glycolytic capacity and high dependence on timely delivery of metabolic enzymes and organelles from the cell body. Thus, supplementation with the end products of glycolysis, pyruvate or lactate, may help preserve metabolism in distal neuronal processes and protect or restore synaptic function in the ailing brain.

Remodeling of synapses in the CA1 area of the hippocampus after transient global ischemia

Synapses are essential to neuronal functions. Synaptic changes occur under physiological and pathological conditions. Here we report the remodeling of synapses in the CA1 area of the hippocampus after transient global ischemia using electron microscopy. Much electron-dense material appeared in the cytoplasm of dendrites at 24h after ischemia. Many dark axons or terminals were found in the CA1 neuropil; some of which were phagocytized by dendrites. Interestingly autophagosomes appeared in many axons or dendrites at 48 h after ischemia. In addition, postsynaptic density (PSD) - like structures or synaptic - like structures were found inside spines and dendrites. Statistical analysis demonstrated that the thickness of PSDs in the CA1 neuropil increased from 12 to 48 h after ischemia. The frequency of autophagosomes appeared to escalate from 12 to 48 h after ischemia. The frequency of asymmetric synapses was significantly increased at 12h and 24h after ischemia in stratum oriens, proximal and distal stratum radiatum. Among asymmetric synapses, the number of perforated synapses consistently increased and reached a peak (approximately 10-fold increase) at 48 h after ischemia. On the other hand, the number of multiple synaptic boutons decreased after ischemia reaching a two to fourfold decrease at 48 h after ischemia. These results have shown that ischemia induces an increase of asymmetric synapses as well as synaptic autophagy, which may contribute to the neuronal death in the CA1 area after transient global ischemia.

Neuroprotective effect of phosphocreatine on focal cerebral ischemia-reperfusion injury

Phosphocreatine (PCr) is a natural compound, which can donate high-energy phosphate group to ADP to synthesize ATP, even in the absence of oxygen and glucose. At present, it is widely used in cardiac and renal ischemia-reperfusion (IR) disease. In this study, to examine the protective efficacy of PCr against cerebral IR, disodium creatine phosphate was injected intravenously into rats before focal cerebral IR. Intracranial pressure (ICP), neurological score, cerebral infarction volume, and apoptotic neurons were observed. Expression of caspase-3 and aquaporin-4 (AQP4) was analyzed. Compared with IR group, rats pretreated with PCr had better neurologic score, less infarction volume, fewer ultrastructural histopathologic changes, reduced apoptosis, and lower aquaporin-4 level. In conclusion, PCr is neuroprotective after transient focal cerebral IR injury. Such a protection might be associated with apoptosis regulating proteins.

Comparative ultrastructural analysis of mitochondria in the CA1 and CA3 hippocampal pyramidal cells following global ischemia in Mongolian gerbils

Post-ischemic injury of the hippocampus unrolls at different levels and has both functional and structural implications. The deficiency in neuron energy metabolism is an initiating factor. We performed transmission electron microscopic (TEM) comparative analysis of mitochondria in excitatory spine synapses in CA1 stratum radiatum and CA3 hippocampal areas after 5 min of global cerebral ischemia in Mongolian gerbils, 4 and 7 days after reperfusion. Electron microscopy and unbiased morphometric methods were used to evaluate synaptic plasticity, and the number and size of mitochondria in synaptic terminals. We compared the morphological organization of mitochondria in presynaptic terminals between CA1 and CA3 areas in control and post-ischemic condition according to the following morphometric parameters: mitochondrial volume fraction, mitochondrial frequency in CA1 and CA3 terminals, mean number of mitochondria per presynaptic terminal, frequency of damaged mitochondria in terminals, and density of presynaptic terminals. Our ultrastructural study revealed statistically significant differences in morphometric parameters between CA1 and CA3 areas in control conditions, as well as in post-ischemic conditions. Also, we found temporal differences in measured parameters obtained 4 and 7 days after reperfusion. This study showed significant morphological differences in the organization of mitochondria in excitatory spine synapses between CA1 and CA3 areas, which corresponded with already known differences in functionality and sensitivity to the ischemic insult. Our conclusion is that revealed post-ischemic changes in mitochondrial distribution in presynaptic CA1 and CA3 terminals could be an indicator of hippocampal metabolic dysfunction and synaptic plasticity.

Blockade of endogenous neuraminidase leads to an increase of neuronal excitability and activity-dependent synaptogenesis in the rat hippocampus

Polysialic acids are widely distributed in neuronal tissue. Due to their position on glycoproteins and gangliosides on the outer cell membranes and anionic nature, polysialic acids are involved in multiple cell signaling events. The level of sialylation of the cellular surface is regulated by endogenous neuraminidase (NEU), which catalyses the hydrolysis of terminal sialic acid residues. Using the specific blocker of endogenous NEU, N-acetyl-2,3-dehydro-2-deoxyneuraminic acid (NADNA), we show that downregulation of the endogenous NEU activity causes a significant increase in the level of hippocampal tissue sialylation. Acute application of NADNA increased the firing frequency and amplitude of spontaneous synchronous oscillations, and frequency of multiple unit activity in cultured hippocampal slices. The tonic phase of seizure-like activity in the low-magnesium model of ictogenesis was significantly increased in slices pretreated with NADNA. These data indicate that the degree of synchronization is influenced by the amount of active NEU in cultured hippocampal slices. Pretreatment with NADNA led to an increase of the density of simple and perforated synapses in the hippocampal CA1 stratum radiatum region. Co-incubation of slices with NADNA and high concentrations of calcium eliminated the effect of the NEU blocker on synaptic density, suggesting that synaptogenesis observed following downregulation of the endogenous NEU activity is an activity-dependent process.

αβγ-Synuclein triple knockout mice reveal age-dependent neuronal dysfunction

Synucleins are a vertebrate-specific family of abundant neuronal proteins. They comprise three closely related members, α-, β-, and γ-synuclein. α-Synuclein has been the focus of intense attention since mutations in it were identified as a cause for familial Parkinson's disease. Despite their disease relevance, the normal physiological function of synucleins has remained elusive. To address this, we generated and characterized αβγ-synuclein knockout mice, which lack all members of this protein family. Deletion of synucleins causes alterations in synaptic structure and transmission, age-dependent neuronal dysfunction, as well as diminished survival. Abrogation of synuclein expression decreased excitatory synapse size by ∼30% both in vivo and in vitro, revealing that synucleins are important determinants of presynaptic terminal size. Young synuclein null mice show improved basic transmission, whereas older mice show a pronounced decrement. The late onset phenotypes in synuclein null mice were not due to a loss of synapses or neurons but rather reflect specific changes in synaptic protein composition and axonal structure. Our results demonstrate that synucleins contribute importantly to the long-term operation of the nervous system and that alterations in their physiological function could contribute to the development of Parkinson's disease.

Long-lasting inhibition of presynaptic metabolism and neurotransmitter release by protein S-nitrosylation

Nitric oxide (NO) and related reactive nitrogen species (RNS) play a major role in the pathophysiology of stroke and other neurodegenerative diseases. One of the poorly understood consequences of stroke is a long-lasting inhibition of synaptic transmission. In this study, we tested the hypothesis that RNS can produce long-term inhibition of neurotransmitter release via S-nitrosylation of proteins in presynaptic nerve endings. We examined the effects of exogenous sources of RNS on the vesicular and nonvesicular L-[(3)H]glutamate release from rat brain synaptosomes. NO/RNS donors, such as spermine NONOate, MAHMA NONOate, S-nitroso-L-cysteine, and SIN-1, inhibited only the vesicular component of glutamate release with an order of potency that closely matched levels of protein S-nitrosylation. Inhibition of glutamate release persisted for >1h after RNS donor decomposition and washout and strongly correlated with decreases in the intrasynaptosomal ATP levels. Post-NO treatment of synaptosomes with thiol-reducing reagents decreased the total content of S-nitrosylated proteins but had little effect on glutamate release and ATP levels. In contrast, post-NO application of the end-product of glycolysis, pyruvate, partially rescued neurotransmitter release and ATP production. These data suggest that RNS suppress presynaptic metabolism and neurotransmitter release via poorly reversible modifications of glycolytic and mitochondrial enzymes, one of which was identified as glyceraldehyde-3-phosphate dehydrogenase. A similar mechanism may contribute to the long-term suppression of neuronal communication during nitrosative stress in vivo.

Brain plasticity after ischemic episode

Brain plasticity describes the potential of the organ for adaptive changes involved in various phenomena in health and disease. A substantial amount of experimental evidence, received in animal and cell models, shows that a cascade of plastic changes at the molecular, cellular, and tissue levels, is initiated in different regions of the postischemic brain. Underlying mechanisms include neurochemical alterations, functional changes in excitatory and inhibitory synapses, axonal and dendritic sprouting, and reorganization of sensory and motor central maps. Multiple lines of evidence indicate numerous points in which the process of postischemic recovery may be influenced with the aim to restore the full capacity of the brain tissue injured by an ischemic episode.