Melatonin alters neuronal architecture and increases cysteine-rich protein 1 signaling in the male mouse hippocampus.

Neuronal plasticity describes changes in structure, function, and connections of neurons. The hippocampus, in particular, has been shown to exhibit considerable plasticity regarding both physiological and morphological functions. Melatonin, a hormone released by the pineal gland, promotes cell survival and dendrite maturation of neurons in the newborn brain and protects against neurological disorders. In this study, we investigated the effect of exogenous melatonin on neuronal architecture and its possible mechanism in the hippocampus of adult male C57BL/6 mice. Melatonin treatment significantly increased the total length and complexity of dendrites in the apical and basal cornu ammonis (CA) 1 and in the dentate gyrus in mouse hippocampi. Spine density in CA1 apical dendrites was increased, but no significant differences in other subregions were observed. In primary cultured hippocampal neurons, the length and arborization of neurites were significantly augmented by melatonin treatment. Additionally, western blot and immunohistochemical analyses in both in vivo and in vitro systems revealed significant increases in the level of cysteine-rich protein 1 (crp-1) protein, which is known to be involved in dendritic branching in mouse hippocampal neurons after melatonin treatment. Our results suggest that exogenous melatonin leads to significant alterations of neuronal micromorphometry in the adult hippocampus, possibly via crp-1 signaling.

Ultrastructural Alterations in Granular Neurons of the Dentate Fascia Caused by Intrahippocampal Injection of Beta-Amyloid 1-42.

The deposition of beta-amyloid (Aß) in the brain is detected in Alzheimer's disease and during ageing. Until now, ultrastructural studies of changes caused by Aß in the dentate gyrus are very scarce. The effects of Aß 1-42 injection into the CA1 field of rat hippocampus were studied by electron microscopy. In 2 weeks after injection of aggregated Aß in low concentrations, destructive changes were seen in the structure of dentate gyrus cells, which consisted in a decrease in the number of dentate gyrus neurons and axo-dendritic synapses. These changes were accompanied by enlargement of the endoplasmic reticulum cisterns and widening of the active zones of synapses. Thus, injection of aggregated Aß 1-42 into the hippocampus led to irreversible (a decrease in the number of neurons and axo-dendritic synapses, agglutination of synthetic vesicles) and adaptive changes (an increase in the sizes of endoplasmic reticulum cisterns and active zones of synapses) in dentate gyrus neurons aimed at the maintenance of functional activity of the nervous system.

Granule Cell Ensembles in Mouse Dentate Gyrus Rapidly Upregulate the Plasticity-Related Protein Synaptopodin after Exploration Behavior.

The plasticity-related protein Synaptopodin (SP) has been implicated in neuronal plasticity. SP is targeted to dendritic spines and the axon initial segment, where it organizes the endoplasmic reticulum (ER) into the spine apparatus and the cisternal organelle, respectively. Here, we report an inducible third localization of SP in the somata of activated granule cell ensembles in mouse dentate gyrus. Using immunofluorescence and fluorescence in situ hybridization, we observed a subpopulation of mature granule cells (~1-2%) exhibiting perinuclear SP protein and a strong somatic SP mRNA signal. Double immunofluorescence labeling for Arc demonstrated that ~ 75% of these somatic SP-positive cells are also Arc-positive. Placement of mice into a novel environment caused a rapid (~2-4 h) induction of Arc, SP mRNA, and SP protein in exploration-induced granule cell ensembles. Lesion experiments showed that this induction requires input from the entorhinal cortex. Somatic SP colocalized with α-Actinin2, a known binding partner of SP. Finally, ultrastructural analysis revealed SP immunoprecipitate on dense plates linking cytoplasmic and perinuclear ER cisterns; these structures were absent in granule cells of SP-deficient mice. Our data implicate SP in the formation of contextual representations in the dentate gyrus and the behaviorally induced reorganization of cytoplasmic and perinuclear ER.

Testosterone administration increases synaptic density in the gyrus dentatus of old mice independently of physical exercise.

Testosterone and physical exercise administration have been shown to affect hippocampal morphology in adult rodents. In aged animals, similar data are only available after physical exercise. In this work we used ultrastructural quantitative morphometry to investigate the effect of testosterone administration on the hippocampal synapses of old mice, either alone or in combination with aerobic physical exercise. The inner molecular layer of the hippocampal dentate gyrus (IMLDG) and the molecular stratum of Ammon's horn 1 neurons (SMCA1) were investigated in 27-month-old male Balb/c mice randomly allocated to one of four experimental conditions (five mice each): sedentary control (C), testosterone administration (10 mg/kg once a week, TA), treadmill training (30 min a day, five days a week for 4 weeks at belt speed 8 m/min, 0% incline, TT) and testosterone administration plus treadmill training (TTTA). At the end of a four-week period, hippocampi were excised, fixed, and processed by ethanol phosphotungstic acid procedure to contrast synapses. The following variables were measured in electron micrographs: number of synapses/µm3 of tissue (Nv), total area of contact zones/µm3 of tissue (Sv), average area of the synaptic contact zone (S), and percentage of perforated synapses (%PS). ANOVA showed a statistically significant main effect of experimental condition for Nv and Sv in IMLDG, and for Sv in SMCA1 (p ≤ 0.003). The S and %PS were similar within group in ANOVA. Post-hoc analysis revealed a significant (p < 0.05) increase of Sv vs. C in SMCA1 and IMLDG after TT and TA, respectively. In IMLDG, Nv was significantly increased vs. C and TT after both TA and TTTA. Overall, results showed that testosterone increases synaptic density in IMLDG of old mice independently of physical exercise or changes in synaptic size. Instead, synaptic density in SMCA1 was only sensitive to physical exercise. These findings show that exogenous testosterone administration exerts a positive effect of on synapses in selected areas of the old mouse hippocampus.

Axonal Anatomy Optimizes Spatial Encoding in the Rat Entorhinal-Dentate System: A Computational Study.

OBJECTIVE: The network architecture connecting neural regions is defined by the organization and anatomical properties of the projecting axons, but its contributions to neural encoding and system function are difficult to study experimentally. METHODS: Using a large-scale, spiking neuronal network model of rat dentate gyrus, the role of the anatomy of the entorhinal-dentate axonal projection was evaluated in the context of spatial encoding by incorporating grid cell activity to provide physiological, spatially-correlated input. The dorso-ventral extents of the entorhinal axon terminal fields were varied to generate different feedforward architectures, and the resulting spatial representations and spatial information scores of the network were evaluated. Position was decoded from the population activity using a point process filter to investigate the contributions of network architecture on spatial encoding. RESULTS: The model predicted the emergence of anatomical gradients within the dentate gyrus for place field size and spatial information along its dorso-ventral axis, which were dependent on the extents of the entorhinal axon terminal fields. The decoding results revealed an optimal performance at an axon terminal field extent of 2 mm that lies within the biological range. CONCLUSION: The axonal anatomy mediates a tradeoff between encoding multiple place field sizes or achieving a high spatial information score, and the combination of both properties is necessary to maximize spatial encoding by a network. SIGNIFICANCE: In total, this paper establishes a mechanistic neuronal network model that, in concert with information-theoretic and statistical methods, can be used to investigate how lower level properties contribute to higher level function.

Reactive Astrogliosis in an Experimental Model of Fibromyalgia: Effect of Dexmedetomidine.

To our knowledge, this is the first study which investigates the induction of neuroinflammation in rats using an acidic-saline model of fibromyalgia. It is well known that the hippocampus has a fundamental role in pain perception, and astrocytes play a crucial role in pain signaling. Our aim is to evaluate the ability of dexmedetomidine to attenuate the inflammatory responses induced in astrocytes. In a group of healthy rats, induction of chronic muscle pain by intramuscular injection of 100 µL of acidic saline on days 0 and 5 resulted in peripheral sensitization (measured using the von Frey test) and significant (p < 0.05) increases in IL-1ß (160.2 ± 1.1 to 335.2 ± 1.8), IL-6 (100.1 ± 1.4 to 202.4 ± 1.1), and TNF-α (60.0 ± 0.7 to 115.5 ± 1). Light and electron microscopy revealed degenerative changes in the hippocampus and reactive astrogliosis. Immunohistochemistry showed increased expression of glial fibrillary acid protein and inducible nitric oxide synthase. Surprisingly, treatment with a single dose of an α2-adrenergic agonist, dexmedetomidine (5 µg/kg i.p.), attenuated these changes. This trial suggests that dexmedetomidine possibly directly acts on astrocytes, and a peripheral action is also suggested.

A Critical Role of Mitochondria in BDNF-Associated Synaptic Plasticity After One-Week Vortioxetine Treatment.

Background: Preclinical studies have indicated that antidepressant effect of vortioxetine involves increased synaptic plasticity and promotion of spine maturation. Mitochondria dysfunction may contribute to the pathophysiological basis of major depressive disorder. Taking into consideration that vortioxetine increases spine number and dendritic branching in hippocampus CA1 faster than fluoxetine, we hypothesize that new spines induced by vortioxetine can rapidly form functional synapses by mitochondrial support, accompanied by increased brain-derived neurotrophic factor signaling. Methods: Rats were treated for 1 week with vortioxetine or fluoxetine at pharmacologically relevant doses. Number of synapses and mitochondria in hippocampus CA1 were quantified by electron microscopy. Brain-derived neurotrophic factor protein levels were visualized with immunohistochemistry. Gene and protein expression of synapse and mitochondria-related markers were investigated with real-time quantitative polymerase chain reaction and immunoblotting. Results: Vortioxetine increased number of synapses and mitochondria significantly, whereas fluoxetine had no effect after 1-week dosing. BDNF levels in hippocampus DG and CA1 were significantly higher after vortioxetine treatment. Gene expression levels of Rac1 after vortioxetine treatment were significantly increased. There was a tendency towards increased gene expression levels of Drp1 and protein levels of Rac1. However, both gene and protein levels of c-Fos were significantly decreased. Furthermore, there was a significant positive correlation between BDNF levels and mitochondria and synapse numbers. Conclusion: Our results imply that mitochondria play a critical role in synaptic plasticity accompanied by increased BDNF levels. Rapid changes in BDNF levels and synaptic/mitochondria plasticity of hippocampus following vortioxetine compared with fluoxetine may be ascribed to vortioxetine's modulation of serotonin receptors.

Neuroadaptations in the dentate gyrus following contextual cued reinstatement of methamphetamine seeking.

Abstinence from unregulated methamphetamine self-administration increases hippocampal dependent, context-driven reinstatement of methamphetamine seeking. The current study tested the hypothesis that alterations in the functional properties of granule cell neurons (GCNs) in the dentate gyrus (DG) of the hippocampus in concert with altered expression of synaptic plasticity-related proteins and ultrastructural changes in the DG are associated with enhanced context-driven methamphetamine-seeking behavior. Whole-cell patch-clamp recordings were performed in acute brain slices from methamphetamine naïve (controls) and methamphetamine experienced animals (during acute withdrawal, during abstinence, after extinction and after reinstatement). Spontaneous excitatory postsynaptic currents (sEPSCs) and intrinsic excitability were recorded from GCNs. Reinstatement of methamphetamine seeking increased sEPSC frequency and produced larger amplitude responses in GCNs compared to controls and all other groups. Reinstatement of methamphetamine seeking reduced spiking capability in GCNs compared to controls, and all other groups, as indicated by reduced intrinsic spiking elicited by increasing current injections, membrane resistance and fast after hyperpolarization. In rats that reinstated methamphetamine seeking, these altered electrophysiological properties of GCNs were associated with enhanced expression of Fos, GluN2A subunits and PSD95 and reduced expression of GABAA subunits in the DG and enhanced expression of synaptic PSD in the molecular layer. The alterations in functional properties of GCNs and plasticity related proteins in the DG paralleled with no changes in structure of microglial cells in the DG. Taken together, our results demonstrate that enhanced reinstatement of methamphetamine seeking results in alterations in intrinsic spiking and spontaneous glutamatergic synaptic transmission in the GCNs and concomitant increases in neuronal activation of GCNs, and expression of GluNs and decreases in GABAA subunits that may contribute to the altered synaptic connectivity-neuronal circuitry-and activity in the hippocampus, and enhance propensity for relapse.

Uhrf2 deletion impairs the formation of hippocampus-dependent memory by changing the structure of the dentate gyrus.

Ubiquitin-like with PHD and ring finger domains 2 (Uhrf2) is distributed in many brain regions, including the cortex and hippocampus. Decreased Uhrf2 expression is involved in neurodegenerative disease. A recent study showed Uhrf2 deletion impaired spatial memory; however, the mechanism remains elusive. In our study, we determined that Uhrf2+/- and Uhrf2-/- mice had significant learning and memory deficiencies in contextual fear conditioning (CFC) and the novel place recognition test but not in the novel object recognition test. Interestingly, there were no changes in the Uhrf2 protein levels in the hippocampus of C57BL6 mice after CFC training, which suggests Uhrf2 in adult mice may not be related to the formation of CFC long-term memory. Based on Nissl staining, Uhrf2 deletion caused neuropathological changes specifically in the crest of the dentate gyrus (DG), such as cell swelling, a vague outline and confused boundary; however, no changes were identified in the medial prefrontal cortex (mPFC). Transmission electron microscope assay further indicated a series of abnormal ultrastructure changes in neurons and glia in the DG crest. These results suggested that Uhrf2 deletion selectively blocked the development of the DG crest and impaired hippocampus-dependent learning and memory. Our study will facilitate a better understanding of the role of Uhrf2 protein in the central nervous system.

Immature morphological properties in subcellular-scale structures in the dentate gyrus of Schnurri-2 knockout mice: a model for schizophrenia and intellectual disability.

Accumulating evidence suggests that subcellular-scale structures such as dendritic spine and mitochondria may be involved in the pathogenesis/pathophysiology of schizophrenia and intellectual disability. Previously, we proposed mice lacking Schnurri-2 (Shn2; also called major histocompatibility complex [MHC]-binding protein 2 [MBP-2], or human immunodeficiency virus type I enhancer binding protein 2 [HIVEP2]) as a schizophrenia and intellectual disability model with mild chronic inflammation. In the mutants' brains, there are increases in C4b and C1q genes, which are considered to mediate synapse elimination during postnatal development. However, morphological properties of subcellular-scale structures such as dendritic spine in Shn2 knockout (KO) mice remain unknown. In this study, we conducted three-dimensional morphological analyses in subcellular-scale structures in dentate gyrus granule cells of Shn2 KO mice by serial block-face scanning electron microscopy. Shn2 KO mice showed immature dendritic spine morphology characterized by increases in spine length and decreases in spine diameter. There was a non-significant tendency toward decrease in spine density of Shn2 KO mice over wild-type mice, and spine volume was indistinguishable between genotypes. Shn2 KO mice exhibited a significant reduction in GluR1 expression and a nominally significant decrease in SV2 expression, while PSD95 expression had a non-significant tendency to decrease in Shn2 KO mice. There were significant decreases in dendrite diameter, nuclear volume, and the number of constricted mitochondria in the mutants. Additionally, neuronal density was elevated in Shn2 KO mice. These results suggest that Shn2 KO mice serve as a unique tool for investigating morphological abnormalities of subcellular-scale structures in schizophrenia, intellectual disability, and its related disorders.

L-type VDCCs participate in behavioral-LTP and memory retention.

Although L-type voltage-dependent calcium channels (VDCCs) have been reported to display different even contrary actions on cognitive functions and long-term potentiation (LTP) formation, there is little information regarding the role of L-type VDCCs in behavioral LTP, a learning-induced LTP model, in the intact brain of freely behaving animals. Here we investigated the effects of verapamil, a non-selective blocker of L-type VDCCs, on behavioral LTP and cognitive functions. Population spikes (PS) were recorded by using electrophysiological methods to examine the role of verapamil in behavioral LTP in the hippocampal dentate gyrus (DG) region. Y-maze assay was used to evaluate the effects of verapamil on learning and memory. Electron microscope was used to observe the changes on synaptic ultrastructural morphology in hippocampal DG area. We found that intrahippocampal verapamil treatments had no significant changes on the PS amplitude during a 90min recordings period. However, intrahippocampal applications of verapamil, including pre- or post-training, reduced behavioral LTP magnitude and memory retention but did not prevent the induction of behavioral LTP and the acquisition of learning. The saline group with behaving trainings showed obvious increases in the number of smile synapses, the length of active zones and the thickness of postsynaptic density as compared to the baseline group, but verapamil with pre-training treatment almost returned these changes to the baseline levels except for the synaptic interface curvature. In conclusion, our results suggest that L-type VDCCs may only contribute to the magnitude of behavioral LTP and the memory maintenance with an activity-independent relationship. L-type VDCCs may be critical to new information long-term storage rather than acquisition in hippocampus.

Decreased surface expression of the δ subunit of the GABAA receptor contributes to reduced tonic inhibition in dentate granule cells in a mouse model of fragile X syndrome.

While numerous changes in the GABA system have been identified in models of Fragile X Syndrome (FXS), alterations in subunits of the GABAA receptors (GABAARs) that mediate tonic inhibition are particularly intriguing. Considering the key role of tonic inhibition in controlling neuronal excitability, reduced tonic inhibition could contribute to FXS-associated disorders such as hyperactivity, hypersensitivity, and increased seizure susceptibility. The current study has focused on the expression and function of the δ subunit of the GABAAR, a major subunit involved in tonic inhibition, in granule cells of the dentate gyrus in the Fmr1 knockout (KO) mouse model of FXS. Electrophysiological studies of dentate granule cells revealed a marked, nearly four-fold, decrease in tonic inhibition in the Fmr1 KO mice, as well as reduced effects of two δ subunit-preferring pharmacological agents, THIP and DS2, supporting the suggestion that δ subunit-containing GABAARs are compromised in the Fmr1 KO mice. Immunohistochemistry demonstrated a small but statistically significant decrease in δ subunit labeling in the molecular layer of the dentate gyrus in Fmr1 KO mice compared to wildtype (WT) littermates. The discrepancy between the large deficits in GABA-mediated tonic inhibition in granule cells in the Fmr1 KO mice and only modest reductions in immunolabeling of the δ subunit led to studies of surface expression of the δ subunit. Cross-linking experiments followed by Western blot analysis demonstrated a small, non-significant decrease in total δ subunit protein in the hippocampus of Fmr1 KO mice, but a four-fold decrease in surface expression of the δ subunit in these mice. No significant changes were observed in total or surface expression of the α4 subunit protein, a major partner of the δ subunit in the forebrain. Postembedding immunogold labeling for the δ subunit demonstrated a large, three-fold, decrease in the number of symmetric synapses with immunolabeling at perisynaptic locations in Fmr1 KO mice. While α4 immunogold particles were also reduced at perisynaptic locations in the Fmr1 KO mice, the labeling was increased at synaptic sites. Together these findings suggest that, in the dentate gyrus, altered surface expression of the δ subunit, rather than a decrease in δ subunit expression alone, could be limiting δ subunit-mediated tonic inhibition in this model of FXS. Finding ways to increase surface expression of the δ subunit of the GABAAR could be a novel approach to treatment of hyperexcitability-related alterations in FXS.

Assessment of Hippocampal Dendritic Complexity in Aged Mice Using the Golgi-Cox Method.

Dendritic spines are the protuberances from the neuronal dendritic shafts that contain  excitatory synapses. The morphological and branching variations of the neuronal dendrites within the hippocampus are implicated in cognition and memory formation. There are several approaches to Golgi staining, all of which have been useful for determining the morphological characteristics of dendritic arbors and produce a clear background. The present Golgi-Cox method, (a slight variation of the protocol that is provided with a commercial Golgi staining kit), was designed to assess how a relatively low dose of the chemotherapeutic drug 5-flurouracil (5-Fu) would affect dendritic morphology, the number of spines, and the complexity of arborization within the hippocampus. The 5-Fu significantly modulated the dendritic complexity and decreased the spine density throughout the hippocampus in a region-specific manner. The data presented show that the Golgi staining method effectively stained the mature neurons in the CA1, the CA3, and the dentate gyrus (DG) of the hippocampus. This protocol reports the details for each step so that other researchers can reliably stain tissue throughout the brain with high quality results and minimal troubleshooting.

P2X7 Receptors Drive Spine Synapse Plasticity in the Learned Helplessness Model of Depression.

Background: Major depressive disorder is characterized by structural and functional abnormalities of cortical and limbic brain areas, including a decrease in spine synapse number in the dentate gyrus of the hippocampus. Recent studies highlighted that both genetic and pharmacological invalidation of the purinergic P2X7 receptor (P2rx7) leads to antidepressant-like phenotype in animal experiments; however, the impact of P2rx7 on depression-related structural changes in the hippocampus is not clarified yet. Methods: Effects of genetic deletion of P2rx7s on depressive-like behavior and spine synapse density in the dentate gyrus were investigated using the learned helplessness mouse model of depression. Results: We demonstrate that in wild-type animals, inescapable footshocks lead to learned helplessness behavior reflected in increased latency and number of escape failures to subsequent escapable footshocks. This behavior is accompanied with downregulation of mRNA encoding P2rx7 and decrease of spine synapse density in the dentate gyrus as determined by electron microscopic stereology. In addition, a decrease in synaptopodin but not in PSD95 and NR2B/GluN2B protein level was also observed under these conditions. Whereas the absence of P2rx7 was characterized by escape deficit, no learned helpless behavior is observed in these animals. Likewise, no decrease in spine synapse number and synaptopodin protein levels was detected in response to inescapable footshocks in P2rx7-deficient animals. Conclusion: Our findings suggest the endogenous activation of P2rx7s in the learned helplessness model of depression and decreased plasticity of spine synapses in P2rx7-deficient mice might explain the resistance of these animals to repeated stressful stimuli.

Epilepsy and intellectual disability linked protein Shrm4 interaction with GABABRs shapes inhibitory neurotransmission.

Shrm4, a protein expressed only in polarized tissues, is encoded by the KIAA1202 gene, whose mutations have been linked to epilepsy and intellectual disability. However, a physiological role for Shrm4 in the brain is yet to be established. Here, we report that Shrm4 is localized to synapses where it regulates dendritic spine morphology and interacts with the C terminus of GABAB receptors (GABABRs) to control their cell surface expression and intracellular trafficking via a dynein-dependent mechanism. Knockdown of Shrm4 in rat severely impairs GABABR activity causing increased anxiety-like behaviour and susceptibility to seizures. Moreover, Shrm4 influences hippocampal excitability by modulating tonic inhibition in dentate gyrus granule cells, in a process involving crosstalk between GABABRs and extrasynaptic δ-subunit-containing GABAARs. Our data highlights a role for Shrm4 in synaptogenesis and in maintaining GABABR-mediated inhibition, perturbation of which may be responsible for the involvement of Shrm4 in cognitive disorders and epilepsy.

Early developmental bisphenol-A exposure sex-independently impairs spatial memory by remodeling hippocampal dendritic architecture and synaptic transmission in rats.

Bisphenol-A (BPA, 4, 4'-isopropylidene-2-diphenol), a synthetic xenoestrogen that widely used in the production of polycarbonate plastics, has been reported to impair hippocampal development and function. Our previous study has shown that BPA exposure impairs Sprague-Dawley (SD) male hippocampal dendritic spine outgrowth. In this study, the sex-effect of chronic BPA exposure on spatial memory in SD male and female rats and the related synaptic mechanism were further investigated. We found that chronic BPA exposure impaired spatial memory in both SD male and female rats, suggesting a dysfunction of hippocampus without gender-specific effect. Further investigation indicated that BPA exposure causes significant impairment of dendrite and spine structure, manifested as decreased dendritic complexity, dendritic spine density and percentage of mushroom shaped spines in hippocampal CA1 and dentate gyrus (DG) neurons. Furthermore, a significant reduction in Arc expression was detected upon BPA exposure. Strikingly, BPA exposure significantly increased the mIPSC amplitude without altering the mEPSC amplitude or frequency, accompanied by increased GABAARß2/3 on postsynaptic membrane in cultured CA1 neurons. In summary, our study indicated that Arc, together with the increased surface GABAARß2/3, contributed to BPA induced spatial memory deficits, providing a novel molecular basis for BPA achieved brain impairment.

Age­dependent increase in the expression of antioxidant­like protein­1 in the gerbil hippocampus.

Antioxidant-like protein-1 (AOP-1) reduces the intracellular level of reactive oxygen species. In the present study, the age­related change in AOP­1 expression in the hippocampus among young, adult and aged gerbils was compared using western blot analysis and immunohistochemistry. The results demonstrated that the protein expression of AOP­1 was gradually and significantly increased in the hippocampus during the normal aging process. In addition, the age­dependent increase in AOP­1 immunoreactivity was also observed in pyramidal neurons of the hippocampus proper; however, in the dentate gyrus, AOP­1 immunoreactivity was not altered during the normal aging process. These results indicated that the expression of AOP­1 is significantly increased in the hippocampus proper, but not in the dentate gyrus, during the normal aging process.

Visualizing Metal Content and Intracellular Distribution in Primary Hippocampal Neurons with Synchrotron X-Ray Fluorescence.

Increasing evidence suggests that metal dyshomeostasis plays an important role in human neurodegenerative diseases. Although distinctive metal distributions are described for mature hippocampus and cortex, much less is known about metal levels and intracellular distribution in individual hippocampal neuronal somata. To solve this problem, we conducted quantitative metal analyses utilizing synchrotron radiation X-Ray fluorescence on frozen hydrated primary cultured neurons derived from rat embryonic cortex (CTX) and two regions of the hippocampus: dentate gyrus (DG) and CA1. Comparing average metal contents showed that the most abundant metals were calcium, iron, and zinc, whereas metals such as copper and manganese were less than 10% of zinc. Average metal contents were generally similar when compared across neurons cultured from CTX, DG, and CA1, except for manganese that was larger in CA1. However, each metal showed a characteristic spatial distribution in individual neuronal somata. Zinc was uniformly distributed throughout the cytosol, with no evidence for the existence of previously identified zinc-enriched organelles, zincosomes. Calcium showed a peri-nuclear distribution consistent with accumulation in endoplasmic reticulum and/or mitochondria. Iron showed 2-3 distinct highly concentrated puncta only in peri-nuclear locations. Notwithstanding the small sample size, these analyses demonstrate that primary cultured neurons show characteristic metal signatures. The iron puncta probably represent iron-accumulating organelles, siderosomes. Thus, the metal distributions observed in mature brain structures are likely the result of both intrinsic neuronal factors that control cellular metal content and extrinsic factors related to the synaptic organization, function, and contacts formed and maintained in each region.

Traumatic Brain Injury Causes Aberrant Migration of Adult-Born Neurons in the Hippocampus.

Traumatic brain injury (TBI) promotes neural stem/progenitor cell (NSC) proliferation in an attempt to initiate innate repair mechanisms. However, all immature neurons in the CNS are required to migrate from their birthplace to their final destination to develop into functional neurons. Here we assessed the destination of adult-born neurons following TBI. We found that a large percentage of immature neurons migrated past their normal stopping site at the inner granular cell layer (GCL), and became misplaced in the outer GCL of the hippocampal dentate gyrus. The aberrant migration of adult-born neurons in the hippocampus occurred 48 hours after TBI, and lasted for 8 weeks, resulting in a great number of newly generated neurons misplaced in the outer GCL in the hippocampus. Those misplaced neurons were able to become mature and differentiate into granular neurons, but located ectopically in the outer GCL with reduced dendritic complexity after TBI. The adult-born neurons at the misplaced position may make wrong connections with inappropriate nearby targets in the pre-existing neural network. These results suggest that although stimulation of endogenous NSCs following TBI might offer new avenues for cell-based therapy, additional intervention is required to further enhance successful neurogenesis for repairing the damaged brain.

Resveratrol Reverses the Synaptic Plasticity Deficits in a Chronic Cerebral Hypoperfusion Rat Model.

BACKGROUND: Dementia is the most prevalent neurological disease in aged people. Chronic cerebral hypoperfusion (CCH) is one of the causes of vascular dementia (VaD) and is also an etiological factor for Alzheimer's disease (AD). However, effective therapy for those two diseases is still missing. Resveratrol is a polyphenol produced by plants that have multiple biological functions, such as increased life span and delay in the onset of diseases associated with aging. It is known supplement with resveratrol could exert neuroprotection against multiple injury factors induced neuronal death and degeneration, as well as the cognitive decline of CCH rat model. METHODS: The morris water maze was used to evaluate the learning and memory, electrophysiological recording was used to detect the synaptic plasticity, the Golgi staining was used to examine the change of dendritic spines, the western blot was used to detect the proteins levels. RESULTS: We reported that resveratrol pretreatment effectively restore the synaptic plasticity in CCH rats both functional and structural. We also found that the PKA-CREB activation may be a major player in resveratrol-mediated neuroprotection in CCH model. CONCLUSIONS: Our data provide the mechanistic evidence for the neuroprotective effects of resveratrol in vascular dementia.