Selective vulnerability of hippocampal cornu ammonis 1 pyramidal cells to excitotoxic insult is associated with the expression of polyamine-sensitive N-methyl-D-asparate-type glutamate receptors

A Capsicum annuum L. seed extract exerts anti-neuroexcitotoxicity in HT22 hippocampal neurons

The hippocampal memory deficit stands out as a primary symptom in neurodegenerative diseases, including Alzheimer's disease. While numerous therapeutic candidates have been proposed, they primarily serve to delay disease progression. Given the irreversible brain atrophy or injury associated with these conditions, current research efforts are concentrated on preventive medicine strategies. Herein, we investigated whether the extracts of Capsicum annuum L. seeds (CSE) and Capsicum annuum L. pulp (CPE) have preventive properties against glutamate-induced neuroexcitotoxicity (one of the main causes of Alzheimer's disease) in HT22 hippocampal neuronal cells. Pretreatment with CSE demonstrated significant anti-neuroexcitotoxic activity, whereas CPE did not exhibit such effects. Specifically, CSE pretreatment dose-dependently inhibited the elevation of excitotoxic elements (intracellular calcium influx and reactive oxygen species; ROS) and apoptotic elements (p53 and cleaved caspase-3). In addition, the glutamate-induced alterations of neuronal activity indicators (brain-derived neurotrophic factor; BDNF and cAMP response element-binding protein phosphorylation; CREB) were significantly attenuated by CSE treatment. We also found that luteolin is the main bioactive compound corresponding to the anti-neuroexcitotoxic effects of CSE. Our results strongly suggest that Capsicum annuum L. seeds (but not its pulp) could be candidates for neuro-protective resources especially under conditions of neuroexcitotoxicity. Its underlying mechanisms may involve the amelioration of ROS-mediated cell death and BDNF-related neuronal inactivity and luteolin would be an active compound.

Selective vulnerability of hippocampal CA1 and CA3 pyramidal cells: What are possible pathomechanisms and should more attention be paid to the CA3 region in future studies?

Transient ischemia and reperfusion selectively damage neurons in brain, with hippocampal pyramidal cells being particularly vulnerable. Even within hippocampus, heterogeneous susceptibility is evident, with higher vulnerability of CA1 versus CA3 neurons described for several decades. Therefore, numerous studies have focused exclusively on CA1. Pediatric cardiac surgery is increasingly focusing on studies of hippocampal structures, and a negative impact of cardiopulmonary bypass on the hippocampus cannot be denied. Recent studies show a shift in selective vulnerability from neurons of CA1 to CA3. This review shows that cell damage is increased in CA3, sometimes stronger than in CA1, depending on several factors (method, species, age, observation period). Despite a highly variable pattern, several markers illustrate greater damage to CA3 neurons than previously assumed. Nevertheless, the underlying cellular mechanisms have not been fully deciphered to date. The complexity is reflected in possible pathomechanisms discussed here, with numerous factors (NMDA, kainate and AMPA receptors, intrinsic oxidative stress potential and various radicals, AKT isoforms, differences in vascular architecture, ratio of pro- and anti-apoptotic Bcl-2 factors, vulnerability of interneurons, mitochondrial dysregulation) contributing to either enhanced CA1 or CA3 vulnerability. Furthermore, differences in expressed genome, proteome, metabolome, and transcriptome in CA1 and CA3 appear to influence differential behavior after damaging stimuli, thus metabolomics-, transcriptomics-, and proteomics-based analyses represent a viable option to identify pathways of selective vulnerability in hippocampal neurons. These results emphasize that future studies should focus on the CA3 field in addition to CA1, especially with regard to improving therapeutic strategies after ischemic/hypoxic brain injury.

Hippocampus of the APPNL-G-F mouse model of Alzheimer's disease exhibits region-specific tissue softening concomitant with elevated astrogliosis

Widespread neurodegeneration, enlargement of cerebral ventricles, and atrophy of cortical and hippocampal brain structures are classic hallmarks of Alzheimer's disease (AD). Prominent macroscopic disturbances to the cytoarchitecture of the AD brain occur alongside changes in the mechanical properties of brain tissue, as reported in recent magnetic resonance elastography (MRE) measurements of human brain mechanics. Whilst MRE has many advantages, a significant shortcoming is its spatial resolution. Higher resolution "cellular scale" assessment of the mechanical alterations to brain regions involved in memory formation, such as the hippocampus, could provide fresh new insight into the etiology of AD. Characterization of brain tissue mechanics at the cellular length scale is the first stepping-stone to understanding how mechanosensitive neurons and glia are impacted by neurodegenerative disease-associated changes in their microenvironment. To provide insight into the microscale mechanics of aging brain tissue, we measured spatiotemporal changes in the mechanical properties of the hippocampus using high resolution atomic force microscopy (AFM) indentation tests on acute brain slices from young and aged wild-type mice and the APPNL-G-F mouse model. Several hippocampal regions in APPNL-G-F mice are significantly softer than age-matched wild-types, notably the dentate granule cell layer and the CA1 pyramidal cell layer. Interestingly, regional softening coincides with an increase in astrocyte reactivity, suggesting that amyloid pathology-mediated alterations to the mechanical properties of brain tissue may impact the function of mechanosensitive astrocytes. Our data also raise questions as to whether aberrant mechanotransduction signaling could impact the susceptibility of neurons to cellular stressors in their microenvironment.

Resident Astrocytes can Limit Injury to Developing Hippocampal Neurons upon THC Exposure

Cannabis legalization prompted the dilemma if plant-derived recreational drugs can have therapeutic potential and, consequently, how to address their regulation and safe distribution. In parallel, the steady worldwide decriminalization of cannabis and the enhanced content of its main psychoactive compound Δ⁹-tetrahydrocannabinol (THC), exposes populations to increasing amounts of cannabis and THC across all ages. While adverse effects of cannabis during critical stages of fetal neurodevelopment are investigated, these studies center on neurons alone. Thus, a gap of knowledge exists on how intercellular interactions between neighboring cell types, particularly astrocytes and neurons, could modify THC action. Here, we combine transcriptome analysis, transgenic models, high resolution microscopy and live cell imaging to demonstrate that hippocampal astrocytes accumulate in the strata radiatum and lacunosum moleculare of the CA1 subfield, containing particularly sensitive neurons to stressors, upon long term postnatal THC exposure in vivo. As this altered distribution is not dependent on cell proliferation, we propose that resident astrocytes accumulate in select areas to protect pyramidal neurons and their neurite extensions from pathological damage. Indeed, we could recapitulate the neuroprotective effect of astrocytes in vitro, as their physical presence significantly reduced the death of primary hippocampal neurons upon THC exposure (> 5 µM). Even so, astrocytes are also affected by a reduced metabolic readiness to stressors, as reflected by a downregulation of mitochondrial proteins. Thus, we find that astrocytes exert protective functions on local neurons during THC exposure, even though their mitochondrial electron transport chain is disrupted.

Anti-Gad 65 encephalitis with rapidly progressive temporal atrophy reveals the involvement of the temporal lobe in the neuroanatomical basis of palilalia

Palilalia is an acquired speech disorder characterized by the reiteration of words or sentences, historically divided in two main subtypes: "palilalie heterolalique" and "palilalie homolalique". In the former, the reiteration is characterized by rate increase and volume decrease, while in the latter these features remain unaltered. While the "heterolalique" subtype has been mainly observed in the context of basal ganglia diseases, the neuroanatomical basis of the "homolalique" subtype has never been completely clarified. Here we report the case of an 81 years-old woman who developed an extremely repetitive and perseverative language with "homolalique" subtype features and a rapidly progressive course with severe bitemporal atrophy, as a consequence of anti-glutamic acid decarboxylase 65 (GAD 65) antibodies encephalitis. To the best of our knowledge, this is the first report of palilalia in the context of anti-GAD 65 encephalitis. Through the support of voxel-based morphometry and hippocampal subfields analysis, this case study provides a fascinating way of understanding the networks responsible for palilalia, shedding some light on the critical role of temporal areas in the onset of this rare language disorder.

Diffusion tensor imaging of the hippocampus reflects the severity of hippocampal injury induced by global cerebral ischemia/reperfusion injury

At present, predicting the severity of brain injury caused by global cerebral ischemia/reperfusion injury (GCI/RI) is a clinical problem. After such an injury, clinical indicators that can directly reflect neurological dysfunction are lacking. The change in hippocampal microstructure is the key to memory formation and consolidation. Diffusion tensor imaging is a highly sensitive tool for visualizing injury to hippocampal microstructure. Although hippocampal microstructure, brain-derived neurotrophic factor (BDNF), and tropomyosin-related kinase B (TrkB) levels are closely related to nerve injury and the repair process after GCI/RI, whether these indicators can reflect the severity of such hippocampal injury remains unknown. To address this issue, we established rat models of GCI/RI using the four-vessel occlusion method. Diffusion tensor imaging parameters, BDNF, and TrkB levels were correlated with modified neurological severity scores. The results revealed that after GCI/RI, while neurological function was not related to BDNF and TrkB levels, it was related to hippocampal fractional anisotropy. These findings suggest that hippocampal fractional anisotropy can reflect the severity of hippocampal injury after global GCI/RI. The study was approved by the Institutional Animal Care and Use Committee of Capital Medical University, China (approval No. AEEI-2015-139) on November 9, 2015.

Low but not moderate amounts of caffeine increase co-consumption of ethanol in C57BL/6J mice

The increasingly popular combination of "energy drinks" containing high amounts of caffeine and alcohol has been shown to induce a stimulated, rather than sedated, state which may result in increased binge drinking and increased risk for alcohol-attributable accidents. We sought to examine consumption patterns of and withdrawal from alcohol and caffeine using a voluntary co-consumption animal model. Male and female adult C57BL/6J mice were given access to increasing doses of caffeine (0.01-0.05%) and/or alcohol (3-20%) in a two-bottle choice, intermittent access voluntary paradigm with fluid consumption recorded daily. Anxiety-like behavior during withdrawal was assessed via elevated plus maze or open field test in experiment 2. Increasing both alcohol and caffeine simultaneously in Experiment 1 resulted in no significant changes in co-consumption compared to mice given access to only alcohol or caffeine. Experiment 2 held caffeine concentration steady while slowly increasing alcohol content and resulted in mice consuming more alcohol when it was consumed in tandem with low dose caffeine. Both male and female mice consumed more caffeine when it was paired with alcohol; however, no significant differences were observed during withdrawal behavior. These results suggest that caffeine may dose-dependently positively influence alcohol consumption in mice and echo clinical literature suggesting that caffeine and alcohol together may result in a heightened state of stimulation and lead to further binge drinking. The intermittent access paradigm affords increased translational validity regarding investigations of alcohol and caffeine co-consumption and may be useful in identifying the neurobiological mechanisms concerning co-consumption of such substances.

Decoding signaling pathways involved in prolactin-induced neuroprotection: A review

It has been well recognized that prolactin (PRL), a pleiotropic hormone, has many functions in the brain, such as maternal behavior, neurogenesis, and neuronal plasticity, among others. Recently, it has been reported to have a significant role in neuroprotection against excitotoxicity. Glutamate excitotoxicity is a common alteration in many neurological and neurodegenerative diseases, leading to neuronal death. In this sense, several efforts have been made to decrease the progression of these pathologies. Despite various reports of PRL's neuroprotective effect against excitotoxicity, the signaling pathways that underlie this mechanism remain unclear. This review aims to describe the most recent and relevant studies on the molecular signaling pathways, particularly, PI3K/AKT, NF-κB, and JAK2/STAT5, which are currently under investigation and might be implicated in the molecular mechanisms that explain the PRL effects against excitotoxicity and neuroprotection. Remarkable neuroprotective effects of PRL might be useful in the treatment of some neurological diseases.

Conventional cardiovascular risk factors in Transient Global Amnesia: Systematic review and proposition of a novel hypothesis

Transient Global Amnesia (TGA) is an enigmatic amnestic syndrome. We conducted a systematic review to investigate the relationship between the conventional cardiovascular risk factors and TGA. MEDLINE, CENTRAL, EMBASE and PsycINFO were comprehensively searched and 23 controlled observational studies were retrieved. The prevalence of hypertension, diabetes mellitus, dyslipidemia and smoking was lower among patients with TGA compared to Transient Ischemic Attack. Regarding the comparison of TGA with healthy individuals, there was strong evidence suggesting a protective effect of diabetes mellitus on TGA and weaker evidence for a protective effect of smoking. Hypertension was associated with TGA only in more severe stages, while dyslipidemia was not related. In view of these findings, a novel pathophysiological hypothesis is proposed, in which the functional interactions of Angiotensin-II type-1 and N-methyl-D-aspartate receptors are of pivotal importance. The whole body of clinical evidence (nature of precipitating events, associations with migraine, gender-based association patterns) was integrated.

Early Selective Vulnerability of the CA2 Hippocampal Subfield in Primary Age-Related Tauopathy

Primary age-related tauopathy (PART) is a neurodegenerative entity defined as Alzheimer-type neurofibrillary degeneration primarily affecting the medial temporal lobe with minimal to absent amyloid-β (Aβ) plaque deposition. The extent to which PART can be differentiated pathoanatomically from Alzheimer disease (AD) is unclear. Here, we examined the regional distribution of tau pathology in a large cohort of postmortem brains (n = 914). We found an early vulnerability of the CA2 subregion of the hippocampus to neurofibrillary degeneration in PART, and semiquantitative assessment of neurofibrillary degeneration in CA2 was significantly greater than in CA1 in PART. In contrast, subjects harboring intermediate-to-high AD neuropathologic change (ADNC) displayed relative sparing of CA2 until later stages of their disease course. In addition, the CA2/CA1 ratio of neurofibrillary degeneration in PART was significantly higher than in subjects with intermediate-to-high ADNC burden. Furthermore, the distribution of tau pathology in PART diverges from the Braak NFT staging system and Braak stage does not correlate with cognitive function in PART as it does in individuals with intermediate-to-high ADNC. These findings highlight the need for a better understanding of the contribution of PART to cognitive impairment and how neurofibrillary degeneration interacts with Aβ pathology in AD and PART.

Neurodegeneration, Myelin Loss and Glial Response in the Three-Vessel Global Ischemia Model in Rat

(1) Background: Although myelin disruption is an integral part of ischemic brain injury, it is rarely the subject of research, particularly in animal models. This study assessed for the first time, myelin and oligodendrocyte loss in a three-vessel model of global cerebral ischemia (GCI), which causes hippocampal damage. In addition, we investigated the relationships between demyelination and changes in microglia and astrocytes, as well as oligodendrogenesis in the hippocampus; (2) Methods: Adult male Wistar rats (n = 15) underwent complete interruption of cerebral blood flow for 7 min by ligation of the major arteries supplying the brain or sham-operation. At 10 and 30 days after the surgery, brain slices were stained for neurodegeneration with Fluoro-Jade C and immunohistochemically to assess myelin content (MBP+ percentage of total area), oligodendrocyte (CNP+ cells) and neuronal (NeuN+ cells) loss, neuroinflammation (Iba1+ cells), astrogliosis (GFAP+ cells) and oligodendrogenesis (NG2+ cells); (3) Results: 10 days after GCI significant myelin and oligodendrocyte loss was found only in the stratum oriens and stratum pyramidale. By the 30th day, demyelination in these hippocampal layers intensified and affected the substratum radiatum. In addition to myelin damage, activation and an increase in the number of microglia and astrocytes in the corresponding layers, a loss of the CA1 pyramidal neurons, and neurodegeneration in the neocortex and thalamus was observed. At a 10-day time point, we observed rod-shaped microglia in the substratum radiatum. Parallel with ongoing myelin loss on the 30th day after ischemia, we found significant oligodendrogenesis in demyelinated hippocampal layers; (4) Conclusions: Our study showed that GCI-simulating cardiac arrest in humans—causes not only the loss of pyramidal neurons in the CA1 field, but also the myelin loss of adjacent layers of the hippocampus.

Calpastatin Overexpression Protects against Excitotoxic Hippocampal Injury and Traumatic Spinal Cord Injury

Small molecule inhibitors of calcium-dependent proteases, calpains (CAPNs), protect against neurodegeneration induced by a variety of insults including excitotoxicity and spinal cord injury (SCI). Many of these compounds, however, also inhibit other proteases, which has made it difficult to evaluate the contribution of calpains to neurodegeneration. Calpastatin is a highly specific endogenous inhibitor of classical calpains, including CAPN1 and CAPN2. In the present study, we utilized transgenic mice that overexpress human calpastatin under the prion promoter (PrP-hCAST) to evaluate the hypothesis that calpastatin overexpression protects against excitotoxic hippocampal injury and contusive SCI. The PrP-hCAST organotypic hippocampal slice cultures showed reduced neuronal death and reduced calpain-dependent proteolysis (α-spectrin breakdown production, 145 kDa) at 24 h after N-methyl-D-aspartate (NMDA) injury compared with the wild-type (WT) cultures (n = 5, p < 0.05). The PrP-hCAST mice (n = 13) displayed a significant improvement in locomotor function at one and three weeks after contusive SCI compared with the WT controls (n = 9, p < 0.05). Histological assessment of lesion volume and tissue sparing, performed on the same animals used for behavioral analysis, revealed that calpastatin overexpression resulted in a 30% decrease in lesion volume (p < 0.05) and significant increases in tissue sparing, white matter sparing, and gray matter sparing at four weeks post-injury compared with WT animals. Calpastatin overexpression reduced α-spectrin breakdown by 51% at 24 h post-injury, compared with WT controls (p < 0.05, n = 3/group). These results provide support for the hypothesis that sustained calpain-dependent proteolysis contributes to pathological deficits after excitotoxic injury and traumatic SCI.

Urokinase receptor deficiency results in EGFR-mediated failure to transmit signals for cell survival and neurite formation in mouse neuroblastoma cells

Urokinase-type plasminogen activator uPA and its receptor (uPAR) are the central players in extracellular matrix proteolysis, which facilitates cancer invasion and metastasis. EGFR is one of the important components of uPAR interactome. uPAR/EGFR interaction controls signaling pathways that regulate cell survival, proliferation and migration. We have previously established that uPA binding to uPAR stimulates neurite elongation in neuroblastoma cells, while blocking uPA/uPAR interaction induces neurite branching and new neurite formation. Here we demonstrate that blocking the uPA binding to uPAR with anti-uPAR antibody decreases the level of pEGFR and its downstream pERK1/2, but does increase phosphorylation of Akt, p38 and c-Src Since long-term uPAR blocking results in a severe DNA damage, accompanied by PARP-1 proteolysis and Neuro2a cell death, we surmise that Akt, p38 and c-Src activation transmits a pro-apoptotic signal, rather than a survival. Serum deprivation resulting in enhanced neuritogenesis is accompanied by an upregulated uPAR mRNA expression, while EGFR mRNA remains unchanged. EGFR activation by EGF stimulates neurite growth only in uPAR-overexpressing cells but not in control or uPAR-deficient cells. In addition, AG1478-mediated inhibition of EGFR activity impedes neurite growth in control and uPAR-deficient cells, but not in uPAR-overexpressing cells. Altogether these data implicate uPAR as an important regulator of EGFR and ERK1/2 signaling, representing a novel mechanism which implicates urokinase system in neuroblastoma cell survival and differentiation.

Volumetry of Mesiotemporal Structures Reflects Serostatus in Patients with Limbic Encephalitis

BACKGROUND AND PURPOSE

Limbic encephalitis is an autoimmune disease. A variety of autoantibodies have been associated with different subtypes of limbic encephalitis, whereas its MR imaging signature is uniformly characterized by mesiotemporal abnormalities across subtypes. Here, we hypothesized that patients with limbic encephalitis would show subtype-specific mesiotemporal structural correlates, which could be classified by supervised machine learning on an individual level.

MATERIALS AND METHODS

T1WI MPRAGE scans from 46 patients with antibodies against glutamic acid decarboxylase and 34 patients with antibodies against the voltage-gated potassium channel complex (including 10 patients with leucine-rich glioma-inactivated 1 autoantibodies) and 48 healthy controls were retrospectively ascertained. Parcellation of the amygdala, hippocampus, and hippocampal subfields was performed using FreeSurfer. Volumes were extracted and compared between groups using unpaired, 2-tailed t tests. The volumes of hippocampal subfields were analyzed using a multivariate linear model and a binary decision tree classifier.

RESULTS

Temporomesial volume alterations were most pronounced in an early stage and in the affected hemispheric side of patients. Statistical analysis revealed antibody-specific hippocampal fingerprints with a higher volume of CA1 in patients with glutamic acid decarboxylase-associated limbic encephalitis (P = .02), compared with controls, whereas CA1 did not differ from that in controls in patients with voltage-gated potassium channel complex autoantibodies. The classifier could successfully distinguish between patients with autoantibodies against leucine-rich glioma-inactivated 1 and glutamic acid decarboxylase with a specificity of 87% and a sensitivity of 80%.

CONCLUSIONS

Our results suggest stage-, side- and antibody-specific structural correlates of limbic encephalitis; thus, they create a perspective toward an MR imaging-based diagnosis.

Chlorogenic acid ameliorates memory loss and hippocampal cell death after transient global ischemia

Chlorogenic acid (CGA) is known to have antioxidant potentials, yet the effect of CGA on brain ischemia has not been sufficiently understood. Brain ischemia such as transient global ischemia disrupts many areas of the brain of rats, including the hippocampus. Male Wistar rats were randomly assigned into five groups, that is, sham-operated (SO), bilateral common carotid occlusion (BCCO), and BCCO+ 15, 30, and 60 mg/kg bw CGA groups (CGA15, CGA30, and CGA60, respectively). Brain ischemia was induced in Wistar rats with BCCO for 20 min followed by intraperitoneal injection of CGA. The rats were examined for the spatial memory in a Morris water maze test on the 3rd day and were euthanized on the 10th day after BCCO. The total number of pyramidal cells was estimated, and the mRNA expressions of Bcl2, Bax, caspase-3, SOD2, SOD1, GPx, ET-1, eNOS, CD31, and VEGF-A were measured. The BCCO group spent less time and distance in the target quadrant than any other group in the spatial memory retention test. The CA1 pyramidal cell numbers in the BCCO and CGA15 groups were lower than in the CGA30 and CGA60 groups. The mRNA expressions of Bcl2, SOD2, and CD31 in the BCCO group were lower than in the CGA15, CGA30, and CGA60 groups. The ET-1 expression was higher in the BCCO and CGA15 groups than in the SO, CGA30, and CGA60 groups. CGA improves the spatial memory and prevents the CA1 pyramidal cell death after BCCO by increasing Bcl2, SOD2, and CD31 expressions and decreasing ET-1 expression.

Hippocampal glutamate metabolites and glial activation in clinical high risk and first episode psychosis

Alterations in glutamate neurotransmission have been implicated in the pathophysiology of schizophrenia, as well as in symptom severity and cognitive deficits. The hippocampus, in particular, is a site of key functional and structural abnormalities in schizophrenia. Yet few studies have investigated hippocampal glutamate in antipsychotic-naïve first episode psychosis patients or in individuals at clinical high risk (CHR) of developing psychosis. Using proton magnetic resonance spectroscopy (1H-MRS), we investigated glutamate metabolite levels in the left hippocampus of 25 CHR (19 antipsychotic-naïve), 16 patients with first-episode psychosis (13 antipsychotic-naïve) and 31 healthy volunteers. We also explored associations between hippocampal glutamate metabolites and glial activation, as indexed by [18F]FEPPA positron emission tomography (PET); symptom severity; and cognitive function. Groups differed significantly in glutamate plus glutamine (Glx) levels (F(2, 69) = 6.39, p = 0.003). Post-hoc analysis revealed that CHR had significantly lower Glx levels than both healthy volunteers (p = 0.003) and first-episode psychosis patients (p = 0.050). No associations were found between glutamate metabolites and glial activation. Our findings suggest that glutamate metabolites are altered in CHR.

Hippocampal Subfields Volume Reduction in High Schoolers with Previous Verbal Abuse Experiences

Objective

Reduced hippocampal volume and alterations in white matter tracts have been frequently reported in adults having the history of emotional maltreatment. We investigated whether these structural change occur in adolescents with previous verbal abuse (VA) experiences.

Methods

Hippocampal subfield volume and white matter structural connectivity measures were assessed in 31 first year male high school students with various degrees of exposure to parental and peer VA.

Results

The high VA group showed significant volume reduction in the left cornu ammonis (CA) 1 and left subiculum compared to the low VA group (p＜0.05). Volumes of left hippocampal subfields CA1 and subiculum were negatively correlated with previous VA experiences (p＜0.05). Increased mean diffusivity (MD) of the splenium of the corpus callosum was related to high VA score across all subjects (p＜0.05). There was an inverse relationship between volume of the CA1 and subiculum and MD of the splenium (p＜0.05).

Conclusion

Exposure to parental and peer VA may affect development of the left hippocampal subfields and the splenium of corpus callosum. These structural alterations can be discernible during adolescence.

Broad-spectrum protein kinase inhibition by the staurosporine analog KT-5720 reverses ethanol withdrawal-associated loss of NeuN/Fox-3

Chronic, intermittent ethanol (CIE) exposure is known to produce neuroadaptive alterations in excitatory neurotransmission that contribute to the development of dependence. Although activation of protein kinases (e.g., cyclic AMP [cAMP]-dependent protein kinase) is implicated in the synaptic trafficking of these receptors following CIE exposure, the functional consequences of these effects are yet to be fully understood. The present study sought to delineate the influence of protein kinase in regulating cytotoxicity following CIE exposure, as well as to examine the relative roles of ethanol exposure and ethanol withdrawal (EWD) in promoting these effects. Rat hippocampal explants were exposed to a developmental model of CIE with or without co-application of broad-spectrum protein kinase inhibitor KT-5720 (1 μM) either during ethanol exposure or EWD. Hippocampal cytotoxicity was assessed via immunofluorescence (IF) of neuron-specific nuclear protein (NeuN) with thionine staining of Nissl bodies to confirm IF findings. Concomitant application of ethanol and KT-5720 restored the loss of NeuN/Fox-3 IF in pyramidal CA1 and granule DG cell layers produced by CIE, but there was no restoration in CA3. Application of KT-5720 during EWD failed to significantly alter levels of NeuN IF, implying that ethanol exposure activates protein kinases that, in part, mediate the effects of EWD. KT-5720 application during EWD also restored thionine staining in CA1, suggesting kinase regulation of both neurons and non-neuronal cells. These data demonstrate that CIE exposure alters protein kinase activity to promote ethanol withdrawal-associated loss of NeuN/Fox-3 and highlight the influence of kinase signaling on distinct cell types in the developing hippocampus.

Cerebral vascular burden on hippocampal subfields in first-onset drug-naïve subjects with late-onset depression

BACKGROUND

Although there is substantial evidence of associations between frontal-striatal circuits and cerebral vascular burden in late-onset depression (LOD), relationships between vascular burden and hippocampal subfields are not clear. The purpose of this study was to investigate relationships between cerebral vascular burden and hippocampal subfield volume in LOD patients.

METHODS

Fifty subjects with LOD and 50 group-matched healthy control subjects underwent magnetic resonance imaging scanning. Hippocampal subfields volumes were measured and compared between the groups. In addition, association patterns between white matter hyperintensity (WMH) volumes, clinical measures and hippocampal subfield volumes were investigated in the LOD group.

RESULTS

Subjects with LOD exhibited significant hippocampal volume reductions in the total hippocampus, cornu ammonis (CA) 1 and 3 and dentate gyrus (DG) areas compared with healthy subjects. Total WMH volume was negatively correlated with left total hippocampal volume and CA1 in the LOD group. In addition, depression severity was negatively associated with left and right CA3 volumes in the LOD group.

LIMITATION

Our findings of distinctive relationships between WMH and hippocampal subfields demonstrate a simple correlation, but do not prove causation CONCLUSION: This study is the first to elaborate distinctive association patterns between hippocampal subfield volumes and cerebral vascular burden in LOD. These structural changes in the hippocampal CA1, CA3 and DG areas might be at the core of the underlying neurobiological mechanisms of hippocampal dysfunction in LOD. However, longitudinal studies will be needed to identify the mechanisms of these structural changes.

Severity and timing: How prenatal stress exposure affects glial developmental, emotional behavioural and plasma neurosteroid responses in guinea pig offspring

Prenatal stress has been associated with a variety of developmental changes in offspring, notably those associated with brain development and subsequent risk for neuropathologies later in life. Recently, the importance of the timing and the severity of the stressor during pregnancy has been emphasized with neurosteroids including allopregnanolone implicated in the regulation of stress and also for endogenous neuroprotection in offspring. Prenatal stress was induced using strobe light exposure in pregnant guinea pigs (term 71days) in three defined stress exposure groups (Gestational Age (GA)35-65, GA50-65 and GA60-65). Stress was induced for 2h (9-11am) every 5days via strobe light exposure. A fetal cohort were euthanased at term with fetal brains and plasma collected. Anxiety-like behaviour was evaluated at 18 days of age in a separate cohort of offspring with brains and plasma collected at 21days of age. Markers for mature oligodendrocytes and reactive astrocytes were measured in the CA1 region of the hippocampus and the subcortical white matter. The neurosteroid allopregnanolone was measured by radioimmunoassay in offspring plasma. In the CA1 region of the hippocampus, fetuses from all stress groups showed reduced expression of mature oligodendrocytes and reactive astrocytes. By juvenility, all male stress exposure groups had recovered to levels of unaffected controls with the exception of the GA35-65 stress group. In juvenile females, mature oligodendrocyte marker expression was reduced in all stress groups and reactive astrocyte expression was reduced in the GA35-65 and GA60-65 stress groups by juvenility. Increased reactive astrocyte expression was also apparent in the subcortical white matter in both sexes both at term and at juvenility. Prenatally stressed offspring spent less time exploring in the object exploration test and also entered the inner zone of the open field less than controls at 18days of age. Circulating allopregnanolone concentrations were significantly reduced in GA35-65 and GA 60-65 stress exposed fetuses with those in the GA35-65 stress group remaining reduced by juvenility. This study has shown the effects of differing levels of prenatal stress severity and timing on glial development, emotional behaviour and plasma allopregnanolone concentrations in offspring.

Dopamine D2 receptor availability is linked to hippocampal-caudate functional connectivity and episodic memory

D1 and D2 dopamine receptors (D1DRs and D2DRs) may contribute differently to various aspects of memory and cognition. The D1DR system has been linked to functions supported by the prefrontal cortex. By contrast, the role of the D2DR system is less clear, although it has been hypothesized that D2DRs make a specific contribution to hippocampus-based cognitive functions. Here we present results from 181 healthy adults between 64 and 68 y of age who underwent comprehensive assessment of episodic memory, working memory, and processing speed, along with MRI and D2DR assessment with [(11)C]raclopride and PET. Caudate D2DR availability was positively associated with episodic memory but not with working memory or speed. Whole-brain analyses further revealed a relation between hippocampal D2DR availability and episodic memory. Hippocampal and caudate D2DR availability were interrelated, and functional MRI-based resting-state functional connectivity between the ventral caudate and medial temporal cortex increased as a function of caudate D2DR availability. Collectively, these findings indicate that D2DRs make a specific contribution to hippocampus-based cognition by influencing striatal and hippocampal regions, and their interactions.

Restoration of Polyamine Metabolic Patterns in In Vivo and In Vitro Model of Ischemic Stroke following Human Mesenchymal Stem Cell Treatment

We investigated changes in PA levels by the treatment of human bone-marrow-derived mesenchymal stem cells (hBM-MSCs) in ischemic stroke in rat brain model and in cultured neuronal SH-SY5Y cells exposed to oxygen-glucose deprivation (OGD). In ischemic rat model, transient middle cerebral artery occlusion (MCAo) was performed for 2 h, followed by intravenous transplantation of hBM-MSCs or phosphate-buffered saline (PBS) the day following MCAo. Metabolic profiling analysis of PAs was examined in brains from three groups: control rats, PBS-treated MCAo rats (MCAo), and hBM-MSCs-treated MCAo rats (MCAo + hBM-MSCs). In ischemic cell model, SH-SY5Y cells were exposed to OGD for 24 h, treated with hBM-MSCs (OGD + hBM-MSCs) prior to continued aerobic incubation, and then samples were collected after coculture for 72 h. In the in vivo MCAo ischemic model, levels of some PAs in brain samples of the MCAo and MCAo + hBM-MSCs groups were significantly different from those of the control group. In particular, putrescine, cadaverine, and spermidine in brain tissues of the MCAo + hBM-MSCs group were significantly reduced in comparison to those in the MCAo group. In the in vitro OGD system, N¹-acetylspermidine, spermidine, N¹-acetylspermine, and spermine in cells of the OGD + hBM-MSCs group were significantly reduced compared to those of OGD group.

Ethanol Stimulates Endoplasmic Reticulum Inositol Triphosphate and Sigma Receptors to Promote Withdrawal-Associated Loss of Neuron-Specific Nuclear Protein/Fox-3

BACKGROUND

Prior studies demonstrate that ethanol (EtOH) exposure induces the release of intracellular calcium (CA(2+) ) in modulation of γ-aminobutyric acid-ergic tone and produces concomitant alterations in sigma (σ)-1 protein expression that may contribute to the development EtOH dependence. However, the influence of CA(2+) released from endoplasmic reticulum (ER)-bound inositol triphosphate (IP3) and σ-1 receptors in regulating hippocampal function has yet to be delineated.

METHODS

Rat hippocampal explants were subjected to chronic intermittent EtOH (CIE) exposure with or without the addition of IP3 inhibitor xestospongin C (0 to 0.5 μM) or σ-1 receptor antagonist BD-1047 (0 to 80 μM). Hippocampal viability was assessed via immunohistochemical labeling of neuron-specific nuclear protein (NeuN)/Fox-3 in CA1, CA3, and dentate gyrus (DG) subregions.

RESULTS

Exposure to CIE produced consistent and significant decreases of NeuN/Fox-3 in each primary cell layer of the hippocampal formation. Co-exposure to xestospongin reversed these effects in the CA1 subregion and significantly attenuated these effects in the CA3 and DG regions. Xestospongin application also significantly increased NeuN/Fox-3 immunofluorescence in EtOH-naïve hippocampi. Co-exposure to 20 μM BD-1047 also reversed the loss of NeuN/Fox-3 during CIE exposure in each hippocampal cell layer, whereas exposure to 80 μM BD-1047 did not alter NeuN/Fox-3 in EtOH-treated hippocampi. By contrast, 80 μM BD-1047 application significantly increased NeuN/Fox-3 immunofluorescence in EtOH-naïve hippocampi in each subregion.

CONCLUSIONS

These data suggest that EtOH stimulates ER IP3 and σ-1 receptors to promote hippocampal loss of NeuN/Fox-3 during CIE.

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.

Selective neuronal vulnerability of human hippocampal CA1 neurons: lesion evolution, temporal course, and pattern of hippocampal damage in diffusion-weighted MR imaging

The CA1 (cornu ammonis) region of hippocampus is selectively vulnerable to a variety of metabolic and cytotoxic insults, which is mirrored in a delayed neuronal death of CA1 neurons. The basis and mechanisms of this regional susceptibility of CA1 neurons are poorly understood, and the correlates in human diseases affecting the hippocampus are not clear. Adopting a translational approach, the lesion evolution, temporal course, pattern of diffusion changes, and damage in hippocampal CA1 in acute neurologic disorders were studied using high-resolution magnetic resonance imaging. In patients with hippocampal ischemia (n=50), limbic encephalitis (n=30), after status epilepticus (n=17), and transient global amnesia (n=53), the CA1 region was selectively affected compared with other CA regions of the hippocampus. CA1 neurons exhibited a maximum decrease of apparent diffusion coefficient (ADC) 48 to 72 hours after the insult, irrespective of the nature of the insult. Hypoxic-ischemic insults led to a significant lower ADC suggesting that the ischemic insult results in a stronger impairment of cellular metabolism. The evolution of diffusion changes show that CA1 diffusion lesions mirror the delayed time course of the pathophysiologic cascade typically observed in animal models. Studying the imaging correlates of hippocampal damage in humans provides valuable insight into the pathophysiology and neurobiology of the hippocampus.

Group 1 mGlu-family proteins promote neuroadaptation to ethanol and withdrawal-associated hippocampal damage

BACKGROUND

Group 1 mGlu-family proteins (i.e., mGlu) consist of mGlu1 and mGlu5 and their activity may influence voluntary ethanol intake. The present studies sought to examine the influence of these receptors on the development of ethanol dependence using in vitro and in vivo models of chronic, intermittent ethanol (CIE).

METHODS

Rat hippocampal explants were exposed to CIE with or without the addition of mGlu1 antagonist (7-hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester (CPCCOEt; 0.5, 1, and 3μM) or mGlu5 antagonist (E)-2-methyl-6-styryl-pyridine (SIB-1893; 20, 100, and 200μM) to assess sparing of withdrawal-induced cytotoxicity. In a separate study, adult male rats were administered CIE with or without the addition of oral administration of group 1 mGlu antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP; 3mg/kg). Blood ethanol levels (BELs) were determined at 0930h on Day 2 of Weeks 1, 2, and 3. Withdrawal behavior was monitored during Day 6 of the third consecutive withdrawal.

RESULTS

CIE produced significant hippocampal cytotoxicity. These effects were attenuated by co-exposure to CPCCOEt (3μM) with ethanol in the CA3. By contrast, these effects were blocked by SIB-1893 (20μM) in each primary cell layer. Oral administration of MPEP with ethanol significantly attenuated behavioral effects of subsequent withdrawal and reduced BELs.

CONCLUSIONS

These data demonstrate that ethanol activates group 1 mGlu-family proteins to promote withdrawal-associated cytotoxicity in vitro and physical dependence in vivo. These findings suggest that group 1 mGlu-family proteins may be therapeutic targets for treatment of alcohol use disorders.

Neuroprotective and Functional Improvement Effects of Methylene Blue in Global Cerebral Ischemia

Transient global cerebral ischemia (GCI) causes delayed neuronal cell death in the vulnerable hippocampus CA1 subfield, as well as behavioral deficits. Ischemia reperfusion (I/R) produces excessive reactive oxygen species and plays a key role in brain injury. The mitochondrial electron respiratory chain is the main cellular source of free radical generation, and dysfunction of mitochondria has a significant impact on the neuronal cell death in ischemic brain. The aim of the present study is to investigate the potential beneficial effects of methylene blue (MB) in a four-vessel occlusion (4VO) GCI model on adult male rats. MB was delivered at a dose of 0.5 mg/kg/day for 7 days, through a mini-pump implanted subcutaneously after GCI. We first found that MB significantly improved ischemic neuronal survival in the hippocampal CA1 region as measured by cresyl violet staining as well as NeuN staining. We also found that MB has the ability to rescue ischemia-induced decreases of cytochrome c oxidase activity and ATP generation in the CA1 region following I/R. Further analysis with labeling of MitoTracker® Red revealed that the depolarization of mitochondrial membrane potential (MMP) was markedly attenuated following MB treatment. In addition, the induction of caspase-3, caspase-8, and caspase-9 activities and the increased numbers of TUNEL-positive cells of the CA1 region were significantly reduced by MB application. Correspondingly, Barnes maze tests showed that the deterioration of spatial learning and memory performance following GCI was significantly improved in the MB-treatment group compared to the ischemic control group. In summary, our study suggests that MB may be a promising therapeutic agent targeting neuronal cell death and cognitive deficits following transient global cerebral ischemia.

The hippocampus in aging and disease: From plasticity to vulnerability

The hippocampus has a pivotal role in learning and in the formation and consolidation of memory and is critically involved in the regulation of emotion, fear, anxiety, and stress. Studies of the hippocampus have been central to the study of memory in humans and in recent years, the regional specialization and organization of hippocampal functions have been elucidated in experimental models and in human neurological and psychiatric diseases. The hippocampus has long been considered a classic model for the study of neuroplasticity as many examples of synaptic plasticity such as long-term potentiation and -depression have been identified and demonstrated in hippocampal circuits. Neuroplasticity is the ability to adapt and reorganize the structure or function to internal or external stimuli and occurs at the cellular, population, network or behavioral level and is reflected in the cytological and network architecture as well as in intrinsic properties of hippocampal neurons and circuits. The high degree of hippocampal neuroplasticity might, however, be also negatively reflected in the pronounced vulnerability of the hippocampus to deleterious conditions such as ischemia, epilepsy, chronic stress, neurodegeneration and aging targeting hippocampal structure and function and leading to cognitive deficits. Considering this framework of plasticity and vulnerability, we here review basic principles of hippocampal anatomy and neuroplasticity on various levels as well as recent findings regarding the functional organization of the hippocampus in light of the regional vulnerability in Alzheimer's disease, ischemia, epilepsy, neuroinflammation and aging.

Hypoglycemia-induced alterations in hippocampal intrinsic rhythms: Decreased inhibition, increased excitation, seizures and spreading depression

Seizures are the most common clinical presentation of severe hypoglycemia, usually as a side effect of insulin treatment for juvenile onset type 1 diabetes mellitus and advanced type 2 diabetes. We used the mouse thick hippocampal slice preparation to study the pathophysiology of hypoglycemia-induced seizures and the effects of severe glucose depletion on the isolated hippocampal rhythms from the CA3 circuitry.

METHODS AND RESULTS

Dropping the glucose perfusate concentration from the standard 10 mM to 1 mM produced epileptiform activity in 14/16 of the slices. Seizure-like events (SLEs) originated in the CA3 region and then spread into the CA1 region. Following the SLE, a spreading-depression (SD)-like event occurred (12/16 slices) with irreversible synaptic failure in the CA1 region (8/12 slices). CA3 SD-like events followed ~30 s after the SD-like event in the CA1 region. Less commonly, SD-like events originated in the CA3 region (4/12). Additionally, prior to the onset of the SLE in the CA3 area, there was decreased GABA correlated baseline SPW activity (bSPW), while there was increased large-amplitude sharp wave (LASW) activity, thought to originate from synchronous pyramidal cell firing. CA3 pyramidal cells displayed progressive tonic depolarization prior to the seizure which was resistant to synaptic transmission blockade. The initiation of hypoglycemic seizures and SD was prevented by AMPA/kainate or NMDA receptor blockade.

CONCLUSIONS

Severe glucose depletion induces rapid changes initiated in the intrinsic CA3 rhythms of the hippocampus including depressed inhibition and enhanced excitation, which may underlie the mechanisms of seizure generation and delayed spreading depression.

Complement C1q-C3-associated synaptic changes in multiple sclerosis hippocampus

OBJECTIVE

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system, leading to memory impairment in up to 65% of patients. Memory dysfunction in MS has been associated with loss of synapses in the hippocampus, but its molecular basis is unknown. Accumulating evidence suggests that components of the complement system, C1q and C3, can mediate elimination of synapses.

METHODS

To investigate the involvement of complement in synaptic changes in MS, gene and protein expression and localization of C1q and C3 were analyzed in relation to neuropathological changes in myelinated and demyelinated hippocampi from postmortem MS brains. Findings were compared to hippocampi of Alzheimer disease (AD) and non-neurological controls.

RESULTS

C1q expression and C3 activation were increased in myelinated and demyelinated MS hippocampi, mainly in the CA3/2 and CA1 subfields, which also showed a marked decrease in synaptic density and increased neuronal staining for the mitochondrial heat shock protein 70 (mtHSP70) stress marker. Neurons were the major source of C1q mRNA. C1q protein and activated C3 localized at synapses within human leukocyte antigen-positive cell processes and lysosomes, suggesting engulfment of complement-tagged synapses by microglia. A significant association (p < 0.0001) between the density of C1q and synaptophysin-positive synapses or mtHSP70 was seen in myelinated MS hippocampi, further pointing toward a link between the complement pathway and synaptic changes. In contrast to AD, MS hippocampi were consistently negative for the terminal complement activation complex C5b9.

INTERPRETATION

These data support a role for the C1q-C3 complement axis in synaptic alterations in the MS hippocampus.

Ethanol withdrawal is required to produce persisting N-methyl-D-aspartate receptor-dependent hippocampal cytotoxicity during chronic intermittent ethanol exposure

Chronic intermittent ethanol consumption is associated with neurodegeneration and cognitive deficits in preclinical laboratory animals and in the clinical population. While previous work suggests a role for neuroadaptations in the N-methyl-D-aspartate (NMDA) receptor in the development of ethanol dependence and manifestation of withdrawal, the relative roles of ethanol exposure and ethanol withdrawal in producing these effects have not been fully characterized. To examine underlying cytotoxic mechanisms associated with CIE exposure, organotypic hippocampal slices were exposed to 1–3 cycles of ethanol (50 mM) in cell culture medium for 5 days, followed by 24-hours of ethanol withdrawal in which a portion of slices were exposed to competitive NMDA receptor antagonist (2R)-amino-5-phosphonovaleric acid (APV; 40 µM). Cytotoxicity was assessed using immunohistochemical labeling of neuron specific nuclear protein (NeuN; Fox-3), a marker of mature neurons, and thionine (2%) staining of Nissl bodies. Multiple cycles of CIE produced neurotoxicity, as reflected in persisting losses of neuron NeuN immunoreactivity and thionine staining in each of the primary cell layers of the hippocampal formation. Hippocampi aged in vitro were significantly more sensitive to the toxic effects of multiple CIEs than were non-aged hippocampi. This effect was not demonstrated in slices exposed to continuous ethanol, in the absence of withdrawal, or to a single exposure/withdrawal regimen. Exposure to APV significantly attenuated the cytotoxicity observed in the primary cell layers of the hippocampus. The present findings suggest that ethanol withdrawal is required to produce NMDA receptor-dependent hippocampal cytotoxicity, particularly in the aging hippocampus in vitro.

Estrogens are neuroprotective factors for hypertensive encephalopathy

Estrogens are neuroprotective factors for brain diseases, including hypertensive encephalopathy. In particular, the hippocampus is highly damaged by high blood pressure, with several hippocampus functions being altered in humans and animal models of hypertension. Working with a genetic model of primary hypertension, the spontaneously hypertensive rat (SHR), we have shown that SHR present decreased dentate gyrus neurogenesis, astrogliosis, low expression of brain derived neurotrophic factor (BDNF), decreased number of neurons in the hilus of the dentate gyrus, increased basal levels of the estrogen-synthesizing enzyme aromatase, and atrophic dendritic arbor with low spine density in the CA1 region compared to normotensive Wistar Kyoto (WKY) ratsl. Changes also occur in the hypothalamus of SHR, with increased expression of the hypertensinogenic peptide arginine vasopressin (AVP) and its V1b receptor. Following chronic estradiol treatment, SHR show decreased blood pressure, enhanced hippocampus neurogenesis, decreased the reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus, increased neuronal number in the hilus of the dentate gyrus, further increased the hyperexpression of aromatase and replaced spine number with remodeling of the dendritic arbor of the CA1 region. We have detected by qPCR the estradiol receptors ERα and ERβ in hippocampus from both SHR and WKY rats, suggesting direct effects of estradiol on brain cells. We hypothesize that a combination of exogenously given estrogens plus those locally synthesized by estradiol-stimulated aromatase may better alleviate the hippocampal and hypothalamic encephalopathy of SHR. This article is part of a Special Issue entitled "Sex steroids and brain disorders".

Electroosmotic perfusion of tissue: sampling the extracellular space and quantitative assessment of membrane-bound enzyme activity in organotypic hippocampal slice cultures

This review covers recent advances in sampling fluid from the extracellular space of brain tissue by electroosmosis (EO). Two techniques, EO sampling with a single fused-silica capillary and EO push-pull perfusion, have been developed. These tools were used to investigate the function of membrane-bound enzymes with outward-facing active sites, or ectoenzymes, in modulating the activity of the neuropeptides leu-enkephalin and galanin in organotypic-hippocampal-slice cultures (OHSCs). In addition, the approach was used to determine the endogenous concentration of a thiol, cysteamine, in OHSCs. We have also investigated the degradation of coenzyme A in the extracellular space. The approach provides information on ectoenzyme activity, including Michaelis constants, in tissue, which, as far as we are aware, has not been done before. On the basis of computational evidence, EO push-pull perfusion can distinguish ectoenzyme activity with a ~100 μm spatial resolution, which is important for studies of enzyme kinetics in adjacent regions of the rat hippocampus.

D-serine-induced inactivation of NMDA receptors in cultured rat hippocampal neurons expressing NR2A subunits is Ca2+-dependent

AIMS

Our previous studies indicate that glycine can inhibit N-methyl-D-aspartate receptor (NMDAR) responses induced by high concentrations of NMDA in rat hippocampal neurons. The present study was designed to observe whether D-serine induces inactivation of NMDARs in cultured rat hippocampal neurons and to investigate the underlying mechanisms of this effect.

METHODS

Cell culture, whole-cell patch-clamp electrophysiology, Ca(2+) imaging, immunohistochemistry, and Western blot analysis were used.

RESULTS

We found that the peak current and Ca(2+) influx evoked by 30 μM NMDA were increased by co-application of D-serine, but those evoked by 300 μM NMDA were reduced dose-dependently by co-application of D-serine. However, the inhibitory effect of D-serine on NMDAR responses was reversed by ZnCl2 (30 nM), an inhibitor of the NR2A subunit, but was less influenced by ifenprodil (10 μM), an NR2B inhibitor. In addition, the inhibitory effect of D-serine was not detected in young hippocampal neurons that expressed less of the NR2A subunits and reversed in the presence of 10 mM BAPTA.

CONCLUSIONS

D-serine can also induce inactivation of NMDARs, the NR2A subunit is required for the induction of this effect, and this inactivation is Ca(2+)-dependent in nature. This action of D-serine is hypothesized to play a neuroprotective role upon a sustained large glutamate insult to the brain.

Hippocampal sclerosis in dementia, epilepsy, and ischemic injury: differential vulnerability of hippocampal subfields

Severe neuronal loss in the hippocampus, that is, hippocampal sclerosis (HS), can be seen in 3 main clinical contexts: dementia (particularly frontotemporal lobar degeneration [FTLD]), temporal lobe epilepsy (TLE), and hippocampal ischemic injury (H-I). It has been suggested that shared pathogenetic mechanisms may underlie selective vulnerability of the hippocampal subfields such as the CA1 in these conditions. We determined the extent of neuronal loss in cases of HS-FTLD (n=14), HS-TLE (n=35), and H-I (n=20). Immunohistochemistry for zinc transporter 3 was used to help define the CA3/CA2 border in the routinely processed human autopsy tissue samples. The subiculum was involved in 57% of HS-FTLD, 10% of H-I, and 0% of HS-TLE cases (p<0.0001). The CA regions other than CA1 were involved in 57% of HS-TLE, 30% of H-I, and 0% of HS-FTLD cases (p=0.0003). The distal third of CA1 was involved in 79% of HS-FTLD, 35% of H-I, and 37% of HS-TLE cases (p=0.02). The distal third of CA1 was the only area involved in 29% of HS-FTLD, 3% of HS-TLE, and 0% of H-I cases (p=0.019). The proximal-middle CA1 was the only area affected in 50% of H-I, 29% of HS-TLE, and 0% of HS-FTLD cases (p=0.004). These findings support heterogeneity in the pathogenesis of HS.

A possible role of astrocytes in contextual memory retrieval: An analysis obtained using a quantitative framework

The hippocampus is central to our understanding of memory formation and retrieval. Its CA1 region is known for encoding contextual memory. Here, using a computational approach, which embeds existing physiological data, we propose a particular role of astrocytes in contextual memory retrieval. We provide a quantitative framework under which the astrocyte modulates the firing of a context-associated CA1 pyramidal neurons, resulting in a prominent tuning of neurons to a delta rhythm. Using the very framework, we further studied astrocytic function in the modulation of neuronal firing under pathological conditions, i.e., during astrocytic induction of epileptiform discharge in CA1 pyramidal neurons. Thus, we provide a quantitative framework that would aid understanding of the Schaffer collateral-CA1 tripartite synapse in health and disease.

Long-term ethanol and corticosterone co-exposure sensitize the hippocampal ca1 region pyramidal cells to insult during ethanol withdrawal in an NMDA GluN2B subunit-dependent manner

BACKGROUND

Chronic ethanol (EtOH) exposure produces neuroadaptations in NMDA receptor function and/or abundance and alterations in hypothalamic-pituitary-adrenal (HPA) axis functioning that contribute to neuronal excitation and neurotoxicity during ethanol withdrawal (EWD). Both EtOH and corticosterone (CORT) promote synthesis of polyamines, which allosterically potentiate NMDA receptor function at the GluN2B subunit. The current studies investigated the effect of 10-day EtOH and CORT co-exposure on toxicity during EWD in rat hippocampal explants and hypothesized that alterations in function and/or density of GluN2B subunits contribute to the toxicity.

METHODS

Organotypic hippocampal slice cultures were exposed to CORT (0.01-1.0 μM) during 10-day EtOH exposure (50 mM) and 1 day of EWD. EtOH-naïve cultures were exposed to CORT for 11 days. Additional cultures were exposed to a membrane impermeable form of CORT (BSA-CORT) with and without 10-day EtOH exposure and EWD. Cytotoxicity (uptake of propidium iodide) was assessed in the pyramidal cell layer of the CA1 region. Western blot analysis was employed to assess the density of GluN2B subunits following EtOH and CORT exposure.

RESULTS

EWD did not produce overt neurotoxicity. However, co-exposure to EtOH/EWD and CORT produced significant neurotoxicity in the CA1 region pyramidal cell layer. Ifenprodil, a GluN2B polyamine site antagonist, significantly reduced toxicity from EtOH and CORT (0.1 μM) co-exposure during EWD. However, Western blots did not reveal differences in GluN2B subunit density among groups. Exposure to BSA-CORT did not produce toxicity, suggesting that membrane-bound CORT receptors did not significantly contribute to the observed toxicity.

CONCLUSIONS

These data suggest that CORT and EtOH co-exposure result in increased function of polyamine-sensitive GluN2B subunits, but this toxicity does not appear dependent on the abundance of hippocampal NMDA GluN2B subunits or membrane-bound CORT receptor function.

Electroosmotic push-pull perfusion: description and application to qualitative analysis of the hydrolysis of exogenous galanin in organotypic hippocampal slice cultures

We demonstrate here a method that perfuses a small region of an organotypic hippocampal culture with a solution containing an enzyme substrate, a neuropeptide. Perfusate containing hydrolysis products is continually collected and subsequently analyzed for the products of the enzymatic degradation of the peptide substrate. The driving force for perfusion is an electric field. The fused silica capillaries used as "push" and "pull" or "source" and "collection" capillaries have a ζ-potential that is negative and greater in magnitude than the tissue's ζ-potential. Thus, depending on the magnitudes of particular dimensions, the electroosmotic flow in the capillaries augments the fluid velocity in the tissue. The flow rate is not directly measured; however, we determine it using a finite-element approach. We have determined the collection efficiency of the system using an all d-amino acid internal standard. The flow rates are low, in the nL/min range, and adjustable by controlling the current or voltage in the system. The collection efficiency of the d-amino acid peptide internal standard is variable, increasing with increased current and thus electroosmotic flow rate. The collection efficiency can be rationalized in the context of a Peclet number. Electroosmotic push-pull perfusion of the neuropeptide galanin (gal1-29) through the extracellular space of an organotypic hippocampal culture results in its hydrolysis by ectopeptidase reactions occurring in the extracellular space. The products of hydrolysis were identified by MALDI-MS. Experiments at two levels of current (8-12 μA and 19-40 μA) show that the probability of seeing hydrolysis products (apparently from aminopeptidases) is greater in the Cornu Ammonis area 3 (CA3) than in the Cornu Ammonis area 1 (CA1) in the higher current experiments. In the lower current experiments, shorter peptide products of aminopeptidases (gal13-29 to gal20-19) are seen with greater frequency in CA3 than in CA1 but there is no statistically significant difference for longer peptides (gal3-29 to gal12-29).

Estradiol increases dendritic length and spine density in CA1 neurons of the hippocampus of spontaneously hypertensive rats: a Golgi impregnation study

Increased neuronal vulnerability has been described in the brain of spontaneously hypertensive rats (SHR), models of primary hypertension. Previous data indicate that estradiol treatment corrects several dysfunctions of the hippocampus and hypothalamus of SHR. Considering this evidence we analyzed the dendritic arborization and spine density of the CA1 subfield in SHR and Wistar-Kyoto (WKY) normotensive rats with and without estradiol treatment. Five month old male SHR and WKY rats received single estradiol or cholesterol pellets (sham treatment) for 2 weeks. A substantial rise of circulating estradiol (>25 fold) and testicular atrophy was present in all estradiol-receiving rats. In both SHR and WKY rats, estradiol decreased blood pressure by ~20 mm Hg; however, a moderate hypertension persisted in SHR (164 mm Hg). Using a modified Golgi impregnation technique, apical and basal dendrites of the CA1 subfield were subjected to Sholl analysis. Spine density was also statistically analyzed. Apical dendritic length was significantly lower in SHR compared to WKY rats (p<0.01), whereas estradiol treatment increased dendritic length in the SHR group only (SHR vs SHR+estradiol; p<0.01). Apical dendritic length plotted against the shell distances 20-100, 120-200 and 220-300 μm, revealed that changes were more pronounced in the range 120-200 μm between SHR vs. WKY rats (p<0.05) and SHR vs. SHR+estradiol (p<0.05). Instead, basal dendrites were not significantly modified by hypertension or steroid treatment. Spine density of apical dendrites was lower in SHR than WKY (p<0.05) and was up-regulated in the SHR+estradiol group compared to the SHR group (p<0.001). Similar changes were obtained for basal dendritic spines. These data suggest that changes of neuronal processes in SHR are plastic events restorable by estradiol treatment. In conjunction with previous results, the present data reveal new targets of estradiol neuroprotection in the brain of hypertensive rats.

Polyamine modulation of NMDARs as a mechanism to reduce effects of alcohol dependence

Relapse and neurodegeneration are two of the major therapeutic targets in alcoholism. Fortuitously, the roles of glutamate/NMDA receptors (NMDARs) in withdrawal, conditioning and neurotoxicity mean that NMDAR inhibitors are potentially valuable for both targets. Preclinical studies further suggest that inhibitory modulators that specifically reduce the co-agonist effects of polyamines on NMDARs are potential non-toxic medications. Using agmatine as a lead compound, over 1000 novel compounds based loosely on this structure were synthesized using feedback from a molecular screen. A novel series of aryliminoguanidines with appropriate NMDAR activity in the molecular screen were discovered (US patent application filed 2007). The most potent and selective aryliminoguanidine, JR 220 [4- (chlorobenzylidenamino)- guanidine hydrochloride], has now been tested in a screening hierarchy for anti-relapse and neuroprotective activity, ranging from cell-based assay, through tissue culture to animal behavior. This hierarchy has been validated using drugs with known, or potential, clinical value at these targets (acamprosate (N-acetyl homotaurine), memantine and topiramate). JR220 was non-toxic and showed excellent activity in every screen with a potency 5-200x that of the FDA-approved anti-relapse agent, acamprosate. This chapter will present a review of the background and rationale for this approach and some of the findings garnered from this approach as well as patents targeting the glutamatergic system especially the NMDAR.

Temporal dependence of cysteine protease activation following excitotoxic hippocampal injury

Excitotoxic insults can lead to intracellular signaling cascades that contribute to cell death, in part by activation of proteases, phospholipases, and endonucleases. Cysteine proteases, such as calpains, are calcium (Ca(2+))-activated enzymes which degrade cytoskeletal proteins, including microtubule-associated proteins, tubulin, and spectrin, among others. The current study used the organotypic hippocampal slice culture model to examine whether pharmacologic inhibition of cysteine protease activity inhibits N-methyl-D-aspartate- (NMDA-) induced excitotoxic (20 μM NMDA) cell death and changes in synaptophysin immunoreactivity. Significant NMDA-induced cytotoxicity (as measured by propidium iodide [PI] uptake) was found in the CA1 region of the hippocampus at all timepoints examined (24, 72, 120 h), an effect significantly attenuated by co-exposure to the selective NMDA receptor antagonist DL-2-Amino-5-phosphonopentanoic acid (APV), but not MDL-28170, a potent cysteine protease inhibitor. Results indicated sparing of NMDA-induced loss of the synaptic vesicular protein synaptophysin in all regions of the hippocampus by MDL-28170, though only at early timepoints after injury. These results suggest Ca(2+)-dependent recruitment of cysteine proteases within 24h of excitotoxic insult, but activation of alternative cellular degrading mechanisms after 24h. Further, these data suggest that synaptophysin may be a substrate for calpains and related proteases.

Glucocorticoid and polyamine interactions in the plasticity of glutamatergic synapses that contribute to ethanol-associated dependence and neuronal injury

Stress contributes to the development of ethanol dependence and is also a consequence of dependence. However, the complexity of physiological interactions between activation of the hypothalamic-pituitary-adrenal (HPA) axis and ethanol itself is not well delineated. Emerging evidence derived from examination of corticotropin-releasing factor systems and glucocorticoid receptor systems in ethanol dependence suggests a role for pharmacological manipulation of the HPA axis in attenuating ethanol intake, though it is not clear how activation of the HPA axis may promote ethanol dependence or contribute to the neuroadaptative changes that accompany the development of dependence and the severity of ethanol withdrawal. This review examines the role that glucocorticoids, in particular, have in promoting ethanol-associated plasticity of glutamatergic synapses by influencing expression of endogenous linear polyamines and polyamine-sensitive polypeptide subunits of N-methyl-D-aspartate (NMDA)-type glutamate receptors. We provide evidence that interactions among glucocorticoid systems, polyamines and NMDA receptors are highly relevant to both the development of ethanol dependence and to behavioral and neuropathological sequelae associated with ethanol withdrawal. Examination of these issues is likely to be of critical importance not only in further elucidating the neurobiology of HPA axis dysregulation in ethanol dependence, but also with regard to identification of novel therapeutic targets that may be exploited in the treatment of ethanol dependence.

Behavioral deficits and cellular damage following developmental ethanol exposure in rats are attenuated by CP-101,606, an NMDAR antagonist with unique NR2B specificity

NMDAR-mediated excitotoxicity has been implicated in some of the impairments following fetal ethanol exposure. Previous studies suggest that both neuronal cell death and some of the behavioral deficits can be reduced by NMDAR antagonism during withdrawal, including antagonism of a subpopulation of receptors containing NR2B subunits. To further investigate NR2B involvement, we selected a compound, CP-101,606 (CP) which binds selectively to NR2B/2B stoichiometries, for both in vitro and in vivo analyses. For the in vitro study, hippocampal explants were exposed to ethanol for 10 days and then 24 h following removal of ethanol, cellular damage was quantified via propidium iodide fluorescence. In vitro ethanol withdrawal-associated neurotoxicity was prevented by CP (10 and 25 nM). In vivo ethanol exposure was administered on PNDs 1-7 with CP administered 21 h following cessation. Activity (PNDs 20-21), motor skills (PNDs 31-33), and maze navigation (PNDs 43-44) were all susceptible to ethanol insult; treatment with CP (15 mg/kg) rescued these deficits. Our findings show that CP-101,606, a drug that blocks the NR2B/2B receptor, can reduce some of the damaging effects of "3rd trimester" alcohol exposure in our rodent model. Further work is clearly warranted on the neuroprotective potential of this drug in the developing brain.

Oxygen/glucose deprivation induces a reduction in synaptic AMPA receptors on hippocampal CA3 neurons mediated by mGluR1 and adenosine A3 receptors

Hippocampal CA1 pyramidal neurons are highly sensitive to ischemic damage, whereas neighboring CA3 pyramidal neurons are less susceptible. It is proposed that switching of AMPA receptor (AMPAR) subunits on CA1 neurons during an in vitro model of ischemia, oxygen/glucose deprivation (OGD), leads to an enhanced permeability of AMPARs to Ca(2+), resulting in delayed cell death. However, it is unclear whether the same mechanisms exist in CA3 neurons and whether this underlies the differential sensitivity to ischemia. Here, we investigated the consequences of OGD for AMPAR function in CA3 neurons using electrophysiological recordings in rat hippocampal slices. Following a 15 min OGD protocol, a substantial depression of AMPAR-mediated synaptic transmission was observed at CA3 associational/commissural and mossy fiber synapses but not CA1 Schaffer collateral synapses. The depression of synaptic transmission following OGD was prevented by metabotropic glutamate receptor 1 (mGluR1) or A(3) receptor antagonists, indicating a role for both glutamate and adenosine release. Inhibition of PLC, PKC, or chelation of intracellular Ca(2+) also prevented the depression of synaptic transmission. Inclusion of peptides to interrupt the interaction between GluA2 and PICK1 or dynamin and amphiphysin prevented the depression of transmission, suggesting a dynamin and PICK1-dependent internalization of AMPARs after OGD. We also show that a reduction in surface and total AMPAR protein levels after OGD was prevented by mGluR1 or A(3) receptor antagonists, indicating that AMPARs are degraded following internalization. Thus, we describe a novel mechanism for the removal of AMPARs in CA3 pyramidal neurons following OGD that has the potential to reduce excitotoxicity and promote neuroprotection.

Increase in blood-brain barrier permeability, oxidative stress, and activated microglia in a rat model of blast-induced traumatic brain injury

Traumatic brain injury (TBI) as a consequence of exposure to blast is increasingly prevalent in military populations, with the underlying pathophysiological mechanisms mostly unknown. In the present study, we utilized an air-driven shock tube to investigate the effects of blast exposure (120 kPa) on rat brains. Immediately following exposure to blast, neurological function was reduced. BBB permeability was measured using IgG antibody and evaluating its immunoreactivity in the brain. At 3 and 24 hr postexposure, there was a transient significant increase in IgG staining in the cortex. At 3 days postexposure, IgG immunoreactivity returned to control levels. Quantitative immunostaining was employed to determine the temporal course of brain oxidative stress following exposure to blast. Levels of 4-hydroxynonenal (4-HNE) and 3-nitrotyrosine (3-NT) were significantly increased at 3 hr postexposure and returned to control levels at 24 hr postexposure. The response of microglia to blast exposure was determined by autoradiographic localization of (3) H-PK11195 binding. At 5 days postexposure, increased binding was observed in the contralateral and ipsilateral dentate gyrus. These regions also displayed increased binding at 10 days postexposure; in addition to these regions there was increased binding in the contralateral ventral hippocampus and substantia nigra at this time point. By using antibodies against CD11b/c, microglia morphology characteristic of activated microglia was observed in the hippocampus and substantia nigra of animals exposed to blast. These results indicate that BBB breakdown, oxidative stress, and microglia activation likely play a role in the neuropathology associated with TBI as a result of blast exposure.