Distribution of map2 in hippocampus and cerebellum of young and old rats by quantitative immunohistochemistry

How do neurons age? A focused review on the aging of the microtubular cytoskeleton

Aging is the leading risk factor for Alzheimer's disease and other neurodegenerative diseases. We now understand that a breakdown in the neuronal cytoskeleton, mainly underpinned by protein modifications leading to the destabilization of microtubules, is central to the pathogenesis of Alzheimer's disease. This is accompanied by morphological defects across the somatodendritic compartment, axon, and synapse. However, knowledge of what occurs to the microtubule cytoskeleton and morphology of the neuron during physiological aging is comparatively poor. Several recent studies have suggested that there is an age-related increase in the phosphorylation of the key microtubule stabilizing protein tau, a modification, which is known to destabilize the cytoskeleton in Alzheimer's disease. This indicates that the cytoskeleton and potentially other neuronal structures reliant on the cytoskeleton become functionally compromised during normal physiological aging. The current literature shows age-related reductions in synaptic spine density and shifts in synaptic spine conformation which might explain age-related synaptic functional deficits. However, knowledge of what occurs to the microtubular and actin cytoskeleton, with increasing age is extremely limited. When considering the somatodendritic compartment, a regression in dendrites and loss of dendritic length and volume is reported whilst a reduction in soma volume/size is often seen. However, research into cytoskeletal change is limited to a handful of studies demonstrating reductions in and mislocalizations of microtubule-associated proteins with just one study directly exploring the integrity of the microtubules. In the axon, an increase in axonal diameter and age-related appearance of swellings is reported but like the dendrites, just one study investigates the microtubules directly with others reporting loss or mislocalization of microtubule-associated proteins. Though these are the general trends reported, there are clear disparities between model organisms and brain regions that are worthy of further investigation. Additionally, longitudinal studies of neuronal/cytoskeletal aging should also investigate whether these age-related changes contribute not just to vulnerability to disease but also to the decline in nervous system function and behavioral output that all organisms experience. This will highlight the utility, if any, of cytoskeletal fortification for the promotion of healthy neuronal aging and potential protection against age-related neurodegenerative disease. This review seeks to summarize what is currently known about the physiological aging of the neuron and microtubular cytoskeleton in the hope of uncovering mechanisms underpinning age-related risk to disease.

Considering impact of age and sex on cardiac cytoskeletal components

The cardiac cytoskeletal components are integral to cardiomyocyte function and are responsible for contraction, sustaining cell structure, and providing scaffolding to direct signaling. Cytoskeletal components have been implicated in cardiac pathology; however, less attention has been paid to age-related modifications of cardiac cytoskeletal components and how these contribute to dysfunction with increased age. Moreover, significant sex differences in cardiac aging have been identified, but we still lack a complete understanding to the mechanisms behind these differences. This review summarizes what is known about how key cardiomyocyte cytoskeletal components are modified because of age, as well as reported sex-specific differences. Thorough consideration of both age and sex as integral players in cytoskeletal function may reveal potential avenues for more personalized therapeutics.

Age-Dependent Regulation of Dendritic Spine Density and Protein Expression in Mir324 KO Mice

Dendritic spines are small, dynamic protrusions along the dendrite that comprise more than 90% of excitatory connections in the brain, making them essential sites for neuronal communication. These synaptic sites change throughout the process of development, reducing in density and shifting morphology as synapses are refined. One important class of dendritic spine regulators is microRNA (miRNA), small-noncoding RNAs that post-transcriptionally regulate gene expression. Several studies suggest that miRNA-324-5p regulates dendritic spine formation. In addition, we have previously shown that miR-324-5p plays a role in seizure and long-term potentiation, both of which involve dendritic spine changes. In this study, we aimed to characterize the role of miRNA-324-5p in developmental spine regulation by assessing the effect of Mir324 knockout (KO) on dendritic spine density and expression of a subset of dendritic proteins at select developmental time points. We show that miR-324-5p expression is developmentally regulated and peaks at 4 weeks of age. We demonstrate that loss of miR-324-5p expression leads to differential changes in both target protein expression and spine density at different time points during development, disrupting the pattern of spine density changes and leading to a premature loss of dendritic spines in KO mice, which is compensated later. Our findings indicate that miR-324-5p plays a role in synaptic refinement across development. Additionally, our data illustrate the importance of context in the study of miRNA, as regulation by and/or of miRNA can vary dramatically across development and in disease.

Age-dependent regulation of dendritic spine density and protein expression in Mir324 KO mice

Dendritic spines are small, dynamic protrusions along the dendrite that comprise more than 90% of excitatory connections in the brain, making them essential sites for neuronal communication. These synaptic sites change throughout the process of development, reducing in density and shifting morphology as synapses are refined. One important class of dendritic spine regulators is microRNA (miRNA), small noncoding RNAs that post-transcriptionally regulate gene expression. Several studies suggest that miRNA-324-5p regulates dendritic spine formation. In addition, we have previously shown that miR-324-5p plays a role in seizure and long-term potentiation, both of which involve dendritic spine changes. In this study, we aimed to characterize the role of miRNA-324-5p in developmental spine regulation by assessing the effect of Mir324 knockout (KO) on dendritic spine density and expression of a subset of dendritic proteins at select developmental time points. We show that miR-324-5p expression is developmentally regulated and peaks at four weeks of age. We demonstrate that loss of miR-324-5p expression leads to differential changes in both target protein expression and spine density at different time points during development, disrupting the pattern of spine density changes and leading to a premature loss of dendritic spines in KO mice, which is compensated later. Our findings indicate that miR-324-5p plays a role in synaptic refinement across development. Additionally, our data illustrate the importance of context in the study of miRNA, as regulation by and/or of miRNA can vary dramatically across development and in disease.

Brain transplantation of genetically corrected Sanfilippo type B neural stem cells induces partial cross-correction of the disease

Sanfilippo syndrome type B (mucopolysaccharidosis type IIIB) is a recessive genetic disorder that severely affects the brain due to a deficiency in the enzyme α-N-acetylglucosaminidase (NAGLU), leading to intra-lysosomal accumulation of partially degraded heparan sulfate. There are no effective treatments for this disorder. In this project, we carried out an ex vivo correction of neural stem cells derived from Naglu -/- mice (iNSCs) induced pluripotent stem cells (iPSC) using a modified enzyme in which human NAGLU is fused to an insulin-like growth factor II receptor binding peptide in order to improve enzyme uptake. After brain transplantation of corrected iNSCs into Naglu -/- mice and long-term evaluation of their impact, we successfully detected NAGLU-IGFII activity in all transplanted animals. We found decreased lysosomal accumulation and reduced astrocytosis and microglial activation throughout transplanted brains. We also identified a novel neuropathological phenotype in untreated Naglu -/- brains with decreased levels of the neuronal marker Map2 and accumulation of synaptophysin-positive aggregates. Upon transplantation, we restored levels of Map2 expression and significantly reduced formation of synaptophysin-positive aggregates. Our findings suggest that genetically engineered iNSCs can be used to effectively deliver the missing enzyme to the brain and treat Sanfilippo type B-associated neuropathology.

Microtubule-modulating Agents in the Fight Against Neurodegeneration: Will it ever Work?

The microtubule skeleton plays an essential role in nerve cells as the most important structural determinant of morphology and as a highway for axonal transport processes. Many neurodegenerative diseases are characterized by changes in the structure and organization of microtubules and microtubule-regulating proteins such as the microtubule-associated protein tau, which exhibits characteristic changes in a whole class of diseases collectively referred to as tauopathies. Changes in the dynamics of microtubules appear to occur early under neurodegenerative conditions and are also likely to contribute to age-related dysfunction of neurons. Thus, modulating microtubule dynamics and correcting impaired microtubule stability can be a useful neuroprotective strategy to counteract the disruption of the microtubule system in disease and aging. In this article, we review current microtubule- directed approaches for the treatment of neurodegenerative diseases with microtubules as a drug target, tau as a drug target, and post-translational modifications as potential modifiers of the microtubule system. We discuss limitations of the approaches that can be traced back to the rather unspecific mechanism of action, which causes undesirable side effects in non-neuronal cell types or which are due to the disruption of non-microtubule-related interactions. We also develop some thoughts on how the specificity of the approaches can be improved and what further targets could be used for modulating substances.

CLPP deficiency ameliorates neurodegeneration caused by impaired mitochondrial protein synthesis

Mitochondria are essential organelles found in every eukaryotic cell, required to convert food into usable energy. Therefore, it is not surprising that mutations in either mtDNA or nuclear DNA-encoded genes of mitochondrial proteins cause diseases affecting the oxidative phosphorylation system, which are heterogeneous from a clinical, genetic, biochemical and molecular perspective and can affect patients at any age. Despite all this, it is surprising that our understanding of the mechanisms governing mitochondrial gene expression and its associated pathologies remain superficial and therapeutic interventions largely unexplored. We recently showed that loss of the mitochondrial matrix protease caseinolytic protease proteolytic subunit (CLPP) ameliorates phenotypes in cells characterized by defects in oxidative phosphorylation maintenance. Here, we build upon this finding by showing that CLPP depletion is indeed beneficial in vivo for various types of neuronal populations, including Purkinje cells in the cerebellum and cortical and hippocampal neurons in the forebrain, as it strongly improves distinct phenotypes of mitochondria encephalopathy, driven by the deficiency of the mitochondrial aspartyl tRNA synthase DARS2. In the absence of CLPP, neurodegeneration of DARS2-deficient neurons is delayed as they present milder oxidative phosphorylation dysfunction. This in turn leads to a decreased neuroinflammatory response and significantly improved motor functions in both double-deficient models (Purkinje cell-specific or forebrain neuron-specific Dars2/Clpp double knockout mice). We propose that diminished turnover of respiratory complex I caused by the loss of CLPP is behind the improved phenotype in Dars2/Clpp double knockout animals, even though this intervention might not restore respiratory complex I activity but rather improve mitochondrial cristae morphology or help maintain the NAD+/NADH ratio inside mitochondria. These results also open the possibility of targeting CLPP activity in many other mitochondrial encephalopathies characterized by respiratory complex I instability.

NLRP1 inflammasome involves in learning and memory impairments and neuronal damages during aging process in mice

Background

Brain aging is an important risk factor in many human diseases, such as Alzheimer’s disease (AD). The production of excess reactive oxygen species (ROS) mediated by nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) and the maturation of inflammatory cytokines caused by activation of the NOD-like receptor protein 1 (NLRP1) inflammasome play central roles in promoting brain aging. However, it is still unclear when and how the neuroinflammation appears in the brain during aging process.

Methods

In this study, we observed the alterations of learning and memory impairments, neuronal damage, NLRP1 inflammasome activation, ROS production and NOX2 expression in the young 6-month-old (6 M) mice, presenile 16 M mice, and older 20 M and 24 M mice.

Results

The results indicated that, compared to 6 M mice, the locomotor activity, learning and memory abilities were slightly decreased in 16 M mice, and were significantly decreased in 20 M and 24 M mice, especially in the 24 M mice. The pathological results also showed that there were no significant neuronal damages in 6 M and 16 M mice, while there were obvious neuronal damages in 20 M and 24 M mice, especially in the 24 M group. Consistent with the behavioral and histological changes in the older mice, the activity of β-galactosidase (β-gal), the levels of ROS and IL-1β, and the expressions of NLRP1, ASC, caspase-1, NOX2, p47phox and p22phox were significantly increased in the cortex and hippocampus in the older 20 M and 24 M mice.

Conclusion

Our study suggested that NLRP1 inflammasome activation may be closely involved in aging-related neuronal damage and may be an important target for preventing brain aging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12993-021-00185-x.

Impact of Alcohol Abuse on Susceptibility to Rare Neurodegenerative Diseases

Despite the prevalence and well-recognized adverse effects of prenatal alcohol exposure and alcohol use disorder in the causation of numerous diseases, their potential roles in the etiology of neurodegenerative diseases remain poorly characterized. This is especially true of the rare neurodegenerative diseases, for which small population sizes make it difficult to conduct broad studies of specific etiological factors. Nonetheless, alcohol has potent and long-lasting effects on neurodegenerative substrates, at both the cellular and systems levels. This review highlights the general effects of alcohol in the brain that contribute to neurodegeneration across diseases, and then focuses on specific diseases in which alcohol exposure is likely to play a major role. These specific diseases include dementias (alcohol-induced, frontotemporal, and Korsakoff syndrome), ataxias (cerebellar and frontal), and Niemann-Pick disease (primarily a Type B variant and Type C). We conclude that there is ample evidence to support a role of alcohol abuse in the etiology of these diseases, but more work is needed to identify the primary mechanisms of alcohol's effects.

Effects of HIV gp120 on Neuroinflammation in Immunodeficient vs. Immunocompetent States

HIV affects 37 million people worldwide, 25-69% of which develop HIV-associated neurocognitive disorders (HAND) regardless of antiviral treatment. HIV infection of the brain decreases cognitive function, disrupts/impairs learning and memory, and reduces quality of life for those affected. HIV-induced neuroinflammation has been associated with viral proteins such as gp120 and Tat, which remain elevated in the CNS even in patients with low peripheral viremia counts. In this study, we examined the effects of gp120 on neuroinflammation in immunodeficient vs. immunocompetent states by examining neuroinflammatory markers in gp120tg mice with or without systemic immunodeficiency caused by murine retroviral administration (LP-BM5 murine AIDS). Changes in inflammatory cytokine/chemokine mRNA expression was complex and dependent upon expression of gp120 protein, immunodeficiency status, brain region (hippocampus, frontal lobe, or striatum), and age. Gp120 expression reduced hippocampal synaptophysin expression but did not affect animals' learning/memory on the spontaneous T-maze test in our experimental conditions. Our results emphasize the critical role of the neuroinflammatory micro-environment and the peripheral immune system context in which gp120 acts. Multiple factors, particularly system-level differences in the immune response of different brain regions, need to be considered when developing treatment for HAND. Graphical Abstract.

Modulation of the p75 neurotrophin receptor suppresses age-related basal forebrain cholinergic neuron degeneration

Age-related degeneration of basal forebrain cholinergic neurons (BFCNs) is linked to cognitive impairment. The p75 neurotrophin receptor (p75^NTR) has been proposed to mediate neuronal degeneration in aging. Therefore, we tested the hypothesis that modifying p75^NTR function would prevent or reverse aging-related neuronal degeneration using LM11A-31, a small molecule p75^NTR modulator that downregulates degenerative and upregulates trophic receptor-associated signaling. Morphological analysis in mice showed loss of BFCN area detectable by 18 months of age. Oral administration of LM11A-31 from age 15 to 18 months resulted in a dose-related preservation of BFCN area and one month of treatment from 17 to 18 months also preserved cell area. To evaluate reversal of established neuronal atrophy, animals were treated from 21 to 25 months of age. Treatment was associated with an increase of cell size to a mean area larger than that observed at 18 months, accompanied by increases in mean MS/VDB neurite length, as well as increased cholinergic fiber density and synaptophysin pre-synaptic marker levels in the hippocampus. These findings support the idea that modulation of p75^NTR activity can prevent and potentially reverse age-associated BFCN degeneration. Moreover, this may be achieved therapeutically with orally bioavailable agents such as LM11A-31.

Ginsenoside Rg1 protects against neuronal degeneration induced by chronic dexamethasone treatment by inhibiting NLRP-1 inflammasomes in mice

Glucocorticoids (GCs) are known to alter neuronal plasticity, impair learning and memory and play important roles in the generation and progression of Alzheimer's disease. There are no effective drug options for preventing neuronal injury induced by chronic GC exposure. Ginsenoside Rg1 (Rg1) is a steroidal saponin found in ginseng. The present study investigated the neuroprotective effect of Rg1 on neuroinflammation damage induced by chronic dexamethasone (5 mg/kg for 28 days) exposure in male mice. Our results showed that Rg1 (2 and 4 mg/kg) treatment increased spontaneous motor activity and exploratory behavior in an open field test, and increased the number of entries into the new object zone in a novel object recognition test. Moreover, Rg1 (2 and 4 mg/kg) treatment significantly alleviated neuronal degeneration and increased MAP2 expression in the frontal cortex and hippocampus. Additionally, inhibition of NLRP-1 inflammasomes was also involved in the mechanisms underlying the effect of Rg1 on GC-induced neuronal injury. We found that Rg1 (2 and 4 mg/kg) treatment increased the expression of glucocorticosteroid receptor and decreased the expression of NLRP-1, ASC, caspase-1, caspase-5, IL-1β and IL-18 in the hippocampus in male mice. The present study indicates that Rg1 may have protective effects on neuroinflammation and neuronal injury induced by chronic GC exposure.

Chronic glucocorticoid exposure activates BK-NLRP1 signal involving in hippocampal neuron damage

BACKGROUND

Neuroinflammation mediated by NLRP1 (nucleotide-binding oligomerization domain (NOD)-like receptor protein 1) inflammasome plays an important role in many neurological diseases such as Parkinson's disease (PD) and Alzheimer's disease (AD). Our previous studies showed that chronic glucocorticoid (GC) exposure increased brain inflammation via NLRP1 inflammasome and induce neurodegeneration. However, little is known about the mechanism of chronic GC exposure on NLRP1 inflammasome activation in hippocampal neurons.

METHODS

Hippocampal neurons damage was assessed by LDH kit and Hoechst 33258 staining. The expression of microtubule-associated protein 2 (MAP2), inflammasome complex protein (NLRP1, ASC and caspase-1), inflammatory cytokines (IL-1β), and large-conductance Ca²⁺ and voltage-activated K⁺ channel (BK channels) protein was detected by Western blot. The inflammatory cytokines (IL-1β and IL-18) were examined by ELISA kit. The mRNA levels of NLRP1, IL-1β, and BK were detected by real-time PCR. BK channel currents were recorded by whole-cell patch-clamp technology. Measurement of [K⁺]_i was performed by ion-selective electrode (ISE) technology.

RESULTS

Chronic dexamethasone (DEX) treatment significantly increased LDH release and neuronal apoptosis and decreased expression of MAP2. The mechanistic studies revealed that chronic DEX exposure significantly increased the expression of NLRP1, ASC, caspase-1, IL-1β, L-18, and BK protein and NLRP1, IL-1β and BK mRNA levels in hippocampal neurons. Further studies showed that DEX exposure results in the increase of BK channel currents, with the subsequent K⁺ efflux and a low concentration of intracellular K⁺, which involved in activation of NLRP1 inflammasome. Moreover, these effects of chronic DEX exposure could be blocked by specific BK channel inhibitor iberiotoxin (IbTx).

CONCLUSION

Our findings suggest that chronic GC exposure may increase neuroinflammation via activation of BK-NLRP1 signal pathway and promote hippocampal neurons damage, which may be involved in the development and progression of AD.

Cannabidiol reduces neuroinflammation and promotes neuroplasticity and functional recovery after brain ischemia

This study investigated the effects of cannabidiol (CBD), a non-psychotomimetic phytochemical present in Cannabis sativa, on the cognitive and emotional impairments induced by bilateral common carotid artery occlusion (BCCAO) in mice. Using a multi-tiered behavioral testing battery during 21days, we found that BCCAO mice exhibited long-lasting functional deficits reflected by increase in anxiety-like behavior (day 9), memory impairments (days 12-18) and despair-like behavior (day 21). Short-term CBD 10mg/kg treatment prevented the cognitive and emotional impairments, attenuated hippocampal neurodegeneration and white matter (WM) injury, and reduced glial response that were induced by BCCAO. In addition, ischemic mice treated with CBD exhibited an increase in the hippocampal brain derived neurotrophic factor (BDNF) protein levels. CBD also stimulated neurogenesis and promoted dendritic restructuring in the hippocampus of BCCAO animals. Collectively, the present results demonstrate that short-term CBD treatment results in global functional recovery in ischemic mice and impacts multiple and distinct targets involved in the pathophysiology of brain ischemic injury.

Neuroplasticity: Insights from Patients Harboring Gliomas

Neuroplasticity is the ability of the brain to reorganize itself during normal development and in response to illness. Recent advances in neuroimaging and direct cortical stimulation in human subjects have given neuroscientists a window into the timing and functional anatomy of brain networks underlying this dynamic process. This review will discuss the current knowledge about the mechanisms underlying neuroplasticity, with a particular emphasis on reorganization following CNS pathology. First, traditional mechanisms of neuroplasticity, most relevant to learning and memory, will be addressed, followed by a review of adaptive mechanisms in response to pathology, particularly the recruitment of perilesional cortical regions and unmasking of latent connections. Next, we discuss the utility and limitations of various investigative techniques, such as direct electrocortical stimulation (DES), functional magnetic resonance imaging (fMRI), corticocortical evoked potential (CCEP), and diffusion tensor imaging (DTI). Finally, the clinical utility of these results will be highlighted as well as possible future studies aimed at better understanding of the plastic potential of the brain with the ultimate goal of improving quality of life for patients with neurologic injury.

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

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

Age-dependent increase of blood-brain barrier permeability and neuron-binding autoantibodies in S100B knockout mice

S100B is a calcium-sensor protein that impacts multiple signal transduction pathways. It is widely considered to be an important biomarker for several neuronal diseases as well as blood-brain barrier (BBB) breakdown. In this report, we demonstrate a BBB deficiency in mice that lack S100B through detection of leaked Immunoglobulin G (IgG) in the brain parenchyma. IgG leaks and IgG-binding to selected neurons were observed in S100B knockout (S100BKO) mice at 6 months of age but not at 3 months. By 9 months, IgG leaks persisted and the density of IgG-bound neurons increased significantly. These results reveal a chronic increase in BBB permeability upon aging in S100BKO mice for the first time. Moreover, coincident with the increase in IgG-bound neurons, autoantibodies targeting brain proteins were detected in the serum via western blots. These events were concurrent with compromise of neurons, increase of activated microglia and lack of astrocytic activation as evidenced by decreased expression of microtubule-associated protein type 2 (MAP2), elevated number of CD68 positive cells and unaltered expression of glial fibrillary acidic protein (GFAP) respectively. Results suggest a key role for S100B in maintaining BBB functional integrity and, further, propose the S100BKO mouse as a valuable model system to explore the link between chronic functional compromise of the BBB, generation of brain-reactive autoantibodies and neuronal dysfunctions.

Chronic glucocorticoids exposure enhances neurodegeneration in the frontal cortex and hippocampus via NLRP-1 inflammasome activation in male mice

Neuroinflammation plays an important role in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD) and depression. Chronic glucocorticoids (GCs) exposure has deleterious effects on the structure and function of neurons and is associated with development and progression of AD. However, little is known about the proinflammatory effects of chronic GCs exposure on neurodegeneration in brain. Therefore, the aim of this study was to evaluate the effects of chronic dexamethasone (DEX) treatment (5mg/kg, s.c. for 7, 14, 21 and 28 days) on behavior, neurodegeneration and neuroinflammatory parameters of nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 1 (NLRP-1) inflammasome in male mice. The results showed that DEX treatment for 21 and 28 days significantly reduced the spontaneous motor activity and exploratory behavior of the mice. In addition, these mice showed significant neurodegeneration and a decrease of microtubule-associated protein 2 (MAP2) in the frontal cortex and hippocampus CA3. DEX treatment for 7, 14, 21 and 28 days significantly decreased the mRNA and protein expression of glucocorticoid receptor (GR). Moreover, DEX treatment for 21 and 28 days significantly increased the proteins expression of NLRP-1, Caspase-1, Caspase-5, apoptosis associated speck-like protein (ASC), nuclear factor-κB (NF-κB), p-NF-κB, interleukin-1β (IL-1β), IL-18 and IL-6 in the frontal cortex and hippocampus brain tissue. DEX treatment for 28 days also significantly increased the mRNA expression levels of NLRP-1, Caspase-1, ASC and IL-1β. These results suggest that chronic GCs exposure may increase brain inflammation via NLRP-1 inflammasome activation and induce neurodegeneration.

Microtubule Dynamics in Neuronal Development, Plasticity, and Neurodegeneration

Neurons are the basic information-processing units of the nervous system. In fulfilling their task, they establish a structural polarity with an axon that can be over a meter long and dendrites with a complex arbor, which can harbor ten-thousands of spines. Microtubules and their associated proteins play important roles during the development of neuronal morphology, the plasticity of neurons, and neurodegenerative processes. They are dynamic structures, which can quickly adapt to changes in the environment and establish a structural scaffold with high local variations in composition and stability. This review presents a comprehensive overview about the role of microtubules and their dynamic behavior during the formation and maturation of processes and spines in the healthy brain, during aging and under neurodegenerative conditions. The review ends with a discussion of microtubule-targeted therapies as a perspective for the supportive treatment of neurodegenerative disorders.

Establishment of Lipofection Protocol for Efficient miR-21 Transfection into Cortical Neurons In Vitro

Dysregulated microRNAs in neurons could cause many nervous system diseases. The therapeutic manipulation of these pathogenic microRNAs necessitates novel, efficient delivery systems to facilitate microRNA modulators targeting neurons with minimal off-target effects. The study aimed to establish a lipofection protocol to upregulate expression levels of miR-21 in neurons under different conditions, including different serum-free medium, transfection conditions, and reagent concentration, by evaluating the expression levels of miR-21 and neuron injury. The expression levels of miR-21 were higher in neurons transfected by Neurobasal-A than by DMEM. Expression levels of miR-21 were already the highest at the ratio RNAiMAX:miR-21 = 3:5, but the increase of RNAiMAX's concentration had not caused the further upregulation of expression level of miR-21. Neuron injury was condition dependent and dose dependent after transfection. Compared to S-Neurobasal groups, neurons have a smaller injury in N-Neurobasal groups, and compared to ratios RNAiMAX:miR-21 = 4:5, 5:5, neuron injury was smaller at ratios of RNAiMAX:miR-21 = 1:5, 2:5, 3:5. Without the pretreatment of starvation in vitro, the lipofection protocol was that RNAiMAX/miR-21 agomir complexes were diluted in Neurobasal-A at the ratio of RNAiMAX:miR-21 = 3:5.

Neuropsin Expression Correlates with Dendritic Marker MAP2c Level in Different Brain Regions of Aging Mice

Neuropsin (NP) is a serine protease, implicated in synaptic plasticity and memory acquisition through cleavage of synaptic adhesion molecule, L1CAM. However, NP has not been explored during brain aging that entails drastic deterioration of plasticity and memory with selective regional vulnerability. Therefore, we have analysed the expression of NP and correlated with its function via analysis of endogenous cleavage of L1CAM and level of dendritic marker MAP2c in different regions of the aging mouse brain. While NP expression gradually decreased in the cerebral cortex during aging, it showed a sharp rise in both olfactory bulb and hippocampus in adult and thereafter declined in old age. NP expression was moderate in young medulla, but undetectable in midbrain and cerebellum. It was positively correlated with L1CAM cleavage and MAP2c level in different brain regions during aging. Taken together, our study shows age-dependent regional variation in NP expression and its positive correlation with MAP2c level, suggesting the involvement of NP in MAP2c mediated alterations in dendritic morphology during aging.

Reduction and the intracellular translocation of EphB2 in Tg2576 mice and the effects of β-amyloid

AIMS

EphB2 is a member of receptor tyrosine kinases (RTKs) family that is essential for the cell adhesion, neural crest migration, axon guidance and synaptogenesis in the nervous system. Recent studies show that preservation of EphB2 in a transgenic mouse model of Alzheimer's disease (AD) rescues the cognitive deficit, suggesting a crucial role of EphB2 in AD. However, the expression and distribution profiles of EphB2 in the early stage of AD have not been reported.

METHODS

Immunohistochemistry, immunoblot and immunofluorescence were used to analyse the level of EphB2 in Tg2576 mice at different ages and in cultured neurones with Aβ treatment at different times.

RESULTS

EphB2 was reduced in an age-dependent manner in the olfactory bulb and the hippocampus of Tg2576 mice. The decrease of EphB2 appeared earlier in the olfactory bulb than the hippocampus, and reduction of EphB2 appeared earlier than that of MAP2, a dendritic cytoskeleton marker. In the cortex, EphB2 displayed a significant translocation from the neuronal processes to the cell bodies with ageing. In primary hippocampal neuronal cultures, Aβ42 treatment also induced the decrement of EphB2 that was prior to the decline of MAP2.

CONCLUSIONS

Our findings provide the first evidence for an age- and region-dependent reduction and intracellular translocation of EphB2 in Tg2576 mice, and the foremost decrement of EphB2 in the olfactory bulb may represent an early sign of AD.

Gene expression patterns in the hippocampus during the development and aging of Glud1 (Glutamate Dehydrogenase 1) transgenic and wild type mice

Background

Extraneuronal levels of the neurotransmitter glutamate in brain rise during aging. This is thought to lead to synaptic dysfunction and neuronal injury or death. To study the effects of glutamate hyperactivity in brain, we created transgenic (Tg) mice in which the gene for glutamate dehydrogenase (Glud1) is over-expressed in neurons and in which such overexpression leads to excess synaptic release of glutamate. In this study, we analyzed whole genome expression in the hippocampus, a region important for learning and memory, of 10 day to 20 month old Glud1 and wild type (wt) mice.

Results

During development, maturation and aging, both Tg and wt exhibited decreases in the expression of genes related to neurogenesis, neuronal migration, growth, and process elongation, and increases in genes related to neuro-inflammation, voltage-gated channel activity, and regulation of synaptic transmission. Categories of genes that were differentially expressed in Tg vs. wt during development were: synaptic function, cytoskeleton, protein ubiquitination, and mitochondria; and, those differentially expressed during aging were: synaptic function, vesicle transport, calcium signaling, protein kinase activity, cytoskeleton, neuron projection, mitochondria, and protein ubiquitination. Overall, the effects of Glud1 overexpression on the hippocampus transcriptome were greater in the mature and aged than the young.

Conclusions

Glutamate hyperactivity caused gene expression changes in the hippocampus at all ages. Some of these changes may result in premature brain aging. The identification of these genomic expression differences is important in understanding the effects of glutamate dysregulation on neuronal function during aging or in neurodegenerative diseases.

Expression in the human brain of retinoic acid induced 1, a protein associated with neurobehavioural disorders

Retinoic acid induced 1 (RAI1) is a protein of uncertain mechanism of action which nevertheless has been the focus of attention because it is a major contributing factor in several human developmental disorders including Smith–Magenis and Potocki–Lupski syndromes. Further, RAI1 may be linked to adult neural disorders with developmental origins such as schizophrenia and autism. The protein has been extensively examined in the rodent but very little is known about its distribution in the human central nervous system. This study demonstrated the presence of RAI1 transcript in multiple regions of the human brain. The cellular expression of RAI1 protein in the human brain was found to be similar to that described in the mouse, with high levels in neurons, but not glia, of the dentate gyrus and cornus ammonis of the hippocampus. In the cerebellum, a second region of high expression, RAI1 was present in Purkinje cells, but not granule cells. RAI1 was also found in neurons of the occipital cortex. The expression of this retinoic acid-induced protein matched well in the hippocampus with expression of the retinoic acid receptors. The subcellular distribution of human neuronal RAI1 indicated its presence in both cytoplasm and nucleus. Overall, human RAI1 protein was found to be a highly expressed neuronal protein whose distribution matches well with its role in cognitive and motor skills.

Metabolism changes during aging in the hippocampus and striatum of glud1 (glutamate dehydrogenase 1) transgenic mice

The decline in neuronal function during aging may result from increases in extracellular glutamate (Glu), Glu-induced neurotoxicity, and altered mitochondrial metabolism. To study metabolic responses to persistently high levels of Glu at synapses during aging, we used transgenic (Tg) mice that over-express the enzyme Glu dehydrogenase (GDH) in brain neurons and release excess Glu in synapses. Mitochondrial GDH is important in amino acid and carbohydrate metabolism and in anaplerotic reactions. We monitored changes in nineteen neurochemicals in the hippocampus and striatum of adult, middle aged, and aged Tg and wild type (wt) mice, in vivo, using proton ((1)H) magnetic resonance spectroscopy. Significant differences between adult Tg and wt were higher Glu, N-acetyl aspartate (NAA), and NAA + NAA-Glu (NAAG) levels, and lower lactate in the Tg hippocampus and striatum than those of wt. During aging, consistent changes in Tg and wt hippocampus and striatum included increases in myo-inositol and NAAG. The levels of glutamine (Gln), a key neurochemical in the Gln-Glu cycle between neurons and astroglia, increased during aging in both the striatum and hippocampus of Tg mice, but only in the striatum of the wt mice. Age-related increases of Glu were observed only in the striatum of the Tg mice.

Endocrine disrupting chemicals affect the gonadotropin releasing hormone neuronal network

Endocrine disrupting chemicals have been shown to alter the pubertal process. The controlling levels of the Gonadotropin releasing hormone (GnRH) network involve GnRH itself, KiSS1, and the transcriptional regulators enhanced at puberty 1 (EAP1), Thyroid Transcription Factor 1 (TTF1), and Yin Yang 1 (YY1). While Genistein and Bisphenol A (BPA) have been shown to advance the advent of puberty, exposure to Dioxin delayed pubertal onset. Utilizing in vitro approaches, we observed that Genistein and BPA suppress inhibitory and activate stimulatory components of the GnRH network, while Dioxin exhibit an inhibitory effect at all regulatory hierarchical levels of the GnRH network. It repressed KiSS1, Gnrh, Ttf1 and Yy1 transcription via the xenobiotic response element (XRE), while EAP1 was not affected. Therefore, EDCs alter the neuroendocrine GnRH regulatory network at all hierarchical levels.

Involvement of α2-antiplasmin in dendritic growth of hippocampal neurons

The α2-Antiplasmin (α2AP) protein is known as a principal physiological inhibitor of plasmin, but we previously demonstrated that it acts as a regulatory factor for cellular functions independent of plasmin. α2AP is highly expressed in the hippocampus, suggesting a potential role for α2AP in hippocampal neuronal functions. However, the role for α2AP was unclear. This study is the first to investigate the involvement of α2AP in the dendritic growth of hippocampal neurons. The expression of microtubule-associated protein 2, which contributes to neurite initiation and neuronal growth, was lower in the neurons from α2AP⁻/⁻ mice than in the neurons from α2AP⁺/⁺ mice. Exogenous treatment with α2AP enhanced the microtubule-associated protein 2 expression, dendritic growth and filopodia formation in the neurons. This study also elucidated the mechanism underlying the α2AP-induced dendritic growth. Aprotinin, another plasmin inhibitor, had little effect on the dendritic growth of neurons, and α2AP induced its expression in the neurons from plaminogen⁻/⁻ mice. The activation of p38 MAPK was involved in the α2AP-induced dendritic growth. Therefore, our findings suggest that α2AP induces dendritic growth in hippocampal neurons through p38 MAPK activation, independent of plasmin, providing new insights into the role of α2AP in the CNS.

Capsaicin-induced activation of ERK1/2 and its involvement in GAP-43 expression and CGRP depletion in organotypically cultured DRG neurons

Low concentrations of capsaicin (CAP) stimulate and high concentrations of CAP can be toxic to the primary sensory neurons of the dorsal root ganglion (DRG). CAP induces the phosphorylation of extracellular signal-regulated protein kinases 1/2 (ERK1/2) in DRG neurons. The effect of the activation of ERK1/2 by different concentrations of CAP on growth-associated protein 43 (GAP-43) expression and calcitonin gene-related peptide (CGRP) depletion in DRG neurons remains unknown. In the present study, organotypic embryonic 15-day-old rat DRG explants were used to determine the effect of different concentrations of CAP on GAP-43 expression and CGRP depletion. The results showed that, compared to unstimulated control cultures, GAP-43 and pERK1/2 protein levels increased at a low concentration (2 μmol/L) of CAP and decreased at a higher concentration (10 μmol/L). The number of CGRP-immunoreactive (IR) migrating neurons also decreased in CAP-treated cultures. The increase in GAP-43 levels and CGRP depletion could be blocked by the administration of ERK1/2 inhibitor PD98059. The results of the present study imply that CAP at different concentrations has different effects on GAP-43 expression and CGRP depletion. These effects were involved in the activation of ERK1/2 in organotypically cultured DRG neurons stimulated with CAP. These data may provide new insights for further development potential therapeutic applications of CAP with moderate dose on neurogenic inflammation.

The effects of target skeletal muscle cells on dorsal root ganglion neuronal outgrowth and migration in vitro

Targets of neuronal innervations play a vital role in regulating the survival and differentiation of innervating neurotrophin-responsive neurons. During development, neurons extend axons to their targets, and then their survival become dependent on the trophic substances secreted by their target cells. Sensory endings were present on myoblasts, myotubes, and myofibers in all intrafusal bundles regardless of age. The interdependence of sensory neurons and skeletal muscle (SKM) cells during both embryonic development and the maintenance of the mature functional state has not been fully understood. In the present study, neuromuscular cocultures of organotypic dorsal root ganglion (DRG) explants and dissociate SKM cells were established. Using this culture system, the morphological relationship between DRG neurons and SKM cells, neurites growth and neuronal migration were investigated. The migrating neurons were determined by fluorescent labeling of microtubule-associated protein-2 (MAP-2) and neurofilament 200 (NF-200) or growth-associated protein 43 (GAP-43). The expression of NF-200 and GAP-43 and their mRNAs was evaluated by Western blot assay and real time-PCR analysis. The results reveal that DRG explants showed more dense neurites outgrowth in neuromuscular cocultures as compared with that in the culture of DRG explants alone. The number of total migrating neurons (the MAP-2-expressing neurons) and the percentage NF-200-immunoreactive (IR) and GAP-43-IR neurons increased significantly in the presence of SKM cells. The levels of NF-200 and GAP-43 and their mRNAs increased significantly in neuromuscular cocultures as compared with that in the culture of DRG explants alone. These results suggested that target SKM cells play an important role in regulating neuronal protein synthesis, promoting neuritis outgrowth and neuronal migration of DRG explants in vitro. These results not only provide new clues for a better understanding of the association of SKM cells with DRG sensory neurons during development, they may also have implications for axonal regeneration after nerve injury.

Expression of mRNAs for PPT, CGRP, NF-200, and MAP-2 in cocultures of dissociated DRG neurons and skeletal muscle cells in administration of NGF or NT-3

Both neurotrophins (NTs) and target skeletal muscle (SKM) cells are essential for the maintenance of the function of neurons and nerve-muscle communication. However, much less is known about the association of target SKM cells with distinct NTs on the expression of mRNAs for preprotachykinin (PPT), calcitonin-gene related peptide (CGRP), neurofilament 200 (NF-200), and microtubule associated protein 2 (MAP-2) in dorsal root ganglion (DRG) sensory neurons. In the present study, a neuromuscular coculture model of dissociated dorsal root ganglion (DRG) neurons and SKM cells was established. The morphology of DRG neurons and SKM cells in coculture was observed with an inverted phase contrast microscope. The effects of nerve growth factor (NGF) or neurotrophin-3 (NT-3) on the expression of mRNAs for PPT, CGRP, NF-200, and MAP-2 was analyzed by real time-PCR assay. The morphology of DRG neuronal cell bodies and SKM cells in neuromuscular coculture at different conditions was similar. The neurons presented evidence of dense neurite outgrowth in the presence of distinct NTs in neuromuscular cocultures. NGF and NT-3 increased mRNA levels of PPT, CGRP, and NF-200, but not MAP-2, in neuromuscular cocultures. These results offer new clues towards a better understanding of the association of target SKM cells with distinct NTs on the expression of mRNAs for PPT, CGRP, NF-200 and MAP-2, and implicate the association of target SKM cells and NTs with DRG sensory neuronal phenotypes.

Diet-induced effects on neuronal and glial elements in the middle-aged rat hippocampus

Consumption of a high-fat and/or high-cholesterol diet can have detrimental effects on the brain. In the present study, dietary treatment with saturated fats, trans fats, or cholesterol to middle-aged Fischer 344 rats resulted in alterations to serum triglyceride and cholesterol levels, organ weights, and hippocampal morphology. Previously, we demonstrated that a 10% hydrogenated coconut oil and 2% cholesterol diet resulted in worse performance on the 12-day water radial arm maze, increased cholesterol and triglyceride levels, and decreased dendritic microtubule associated protein 2 (MAP2) staining in the hippocampus. The diets administered herein were used to examine components from the previous diet and further examine their effects on hippocampal morphology. Specifically, neuronal morphology, dendritic integrity, fatty acid metabolism, microgliosis, and blood vessel structure in the hippocampus and/or adjacent structures were explored. Our results indicate alterations to peripheral and neural systems following each of the diets.

Age-related decreases in SYN levels associated with increases in MAP-2, apoE, and GFAP levels in the rhesus macaque prefrontal cortex and hippocampus

Loss of synaptic integrity in the hippocampus and prefrontal cortex (PFC) may play an integral role in age-related cognitive decline. Previously, we showed age-related increases in the dendritic marker microtubule associated protein 2 (MAP-2) and the synaptic marker synaptophysin (SYN) in mice. Similarly, apolipoprotein E (apoE), involved in lipid transport and metabolism, and glial fibrillary acidic protein (GFAP), a glia specific marker, increase with age in rodents. In this study, we assessed whether these four proteins show similar age-related changes in a nonhuman primate, the rhesus macaque. Free-floating sections from the PFC and hippocampus from adult, middle-aged, and aged rhesus macaques were immunohistochemically labeled for MAP-2, SYN, apoE, and GFAP. Protein levels were measured as area occupied by fluorescence using confocal microscopy as well as by Western blot. In the PFC and hippocampus of adult and middle-aged animals, the levels of SYN, apoE, and GFAP immunoreactivity were comparable but there was a trend towards higher MAP-2 levels in middle-aged than adult animals. There was significantly less SYN and more MAP-2, apoE, and GFAP immunoreactivity in the PFC and hippocampus of aged animals compared to adult or middle-aged animals. Thus, the age-related changes in MAP-2, apoE, and GFAP levels were similar to those previously observed in rodents. On the other hand, the age-related changes in SYN levels were not, but were similar to those previously observed in the aging human brain. Taken together, these data emphasize the value of the rhesus macaque as a pragmatic translational model for human brain aging.

Melatonin attenuates the decrement of dendritic protein MAP-2 immuno-staining in the hippocampal CA1 and CA3 fields of the aging male rat

Neuronal death during brain aging results, at least in part, from the disruption of synaptic connectivity caused by oxidative stress. Synaptic elimination might be caused by increased instability of the neuronal processes. In vitro evidence shows that melatonin increases MAP-2 expression, a protein that improves the stability of the dendritic cytoskeleton, opening the possibility that melatonin could prevent synaptic elimination by increasing dendritic stability. One way to begin exploring this issue in vivo is to evaluate whether long-term melatonin treatment changes the intensity of MAP-2 immuno-staining in areas commonly afflicted by aging that are rich in dendritic processes. Accordingly, we evaluated the effects of administering melatonin for 6 or 12 months on the intensity of MAP-2 immuno-staining in the strata oriens and lucidum of the hippocampal CA1 and CA3 fields of aging male rats, through semi-quantitative densitometry. Melatonin treated rats showed a relative increment in the intensity of MAP-2 immuno-staining in both regions after 6 or 12 months of treatment, as compared with age matched control rats. Although melatonin untreated and treated rats showed a decrease of MAP-2 immuno-staining in the hippocampus with increasing age, such decrement was less pronounced following melatonin treatment. These findings were confirmed by qualitative Western blot analyses. The melatonin effect seems specific because MAP-2 staining in the primary somatosensory cortex was not affected by the treatment. Thus, chronic melatonin administration increases MAP-2 immuno-staining and attenuates its decay in the adult aging hippocampus. These results are compatible with the idea that melatonin could improve dendritic stability and thus diminish synaptic elimination in the aging brain.

c-fos gene expression is increased in the paraventricular hypothalamic nucleus of Sprague-Dawley rats with visceral pain induced by acetic acid without detectable changes of corticotrophin-releasing factor mRNA: a quantitative approach with an image analysis system

This study is the first of its kind to demonstrate that c-Fos immunoreactivity (ir) together with c-fos mRNA in their immediately adjacent tissue sections of a discrete brain region can be reliably measured. The c-fos gene expression in the paraventricular hypothalamic nucleus (PVN) of Sprague-Dawley rats for an animal model for visceral or somatovisceral pain induced by 2% acetic acid (AA) was used in this study. Specifically, c-fos mRNA signals were measured by quantitative autoradiography after in situ hybridization using c-fos oligodeoxynucleotide probe, and c-Fos-ir signals were represented by c-Fos immunostaining, as detected using c-Fos antibody in a regular immunohistochemistry. Signals from both c-Fos-ir and c-fos mRNA in the PVN were measured from their immediately adjacent cryostat sections. For the measurement of c-Fos-ir, it was carried out by reading 10 rectangles (1,000 microm(2)/rectangle) on each PVN section with c-Fos immunostaining. Specific signals were obtained from subtracting the nonspecific background signal from the total signals using a computer-assisted image analysis system. Results indicated that the AA treatment induced a significant increase of both c-Fos-ir and c-fos mRNA in the PVN. Interestingly, there was no increase of corticotrophin-releasing factor (CRF) mRNA expression in the PVN and central nucleus of the amygdala of Sprague-Dawley rats subjected to the AA treatment. In summary, this study has demonstrated that c-Fos-ir in the PVN with an anatomical resolution can be semiquantitatively measured after immunohistochemistry using an image analysis system, and that increased c-fos mRNA in the PVN 1 hr after the AA treatment is associated with no changes of the CRF mRNA expression.

Competition and complementation between thymidine kinase-negative and wild-type herpes simplex virus during co-infection of mouse trigeminal ganglia

Laboratory strains of herpes simplex virus lacking thymidine kinase (TK) cannot replicate acutely to detectable levels in mouse trigeminal ganglia and do not reactivate from latency. However, many pathogenic clinical isolates that are resistant to the antiviral drug acyclovir are heterogeneous populations of TK-negative (TK(-)) and TK-positive (TK(+)) viruses. To recapitulate this in vivo, mice were infected with mixtures of wild-type virus and a recombinant TK(-) mutant in various ratios. Following co-infection, the replication, number of latent viral genomes and reactivation efficiency of TK(+) virus in trigeminal ganglia were reduced in a manner related to the amount of TK(-) virus in the inoculum. TK(+) virus did not always complement the acute replication or increase the number of latent viral genomes of TK(-) mutant in mouse ganglia. Even so, TK(+) virus could still confer the pathogenic phenotype to a TK(-) mutant, somehow providing sufficient TK activity in trans to permit a TK(-) mutant to reactivate from latently infected ganglia.

Cognition- and anxiety-related behavior, synaptophysin and MAP2 immunoreactivity in the adult rat treated with a single course of antenatal betamethasone

We investigated the effects of a single course of antenatal betamethasone on cognition- and anxiety-related behavior and synaptophysin and microtubule-associated protein 2 (MAP2) immunoreactivity in the adult rat hippocampus. On d 20 of gestation, pregnant rats were injected with either 1) 170 microg/kg body weight of betamethasone ("clinically equivalent dose," equivalent to 12 mg twice, 24 h apart); 2) half this dose; or 3) vehicle. Cognition- and anxiety-related behavior of the offspring was analyzed at an age of 5 mo using the Morris water maze, object recognition task, and open field test. Subsequently, synaptophysin and MAP2 immunoreactivity were measured in the hippocampus. We report no detrimental effects of antenatal betamethasone on cognition- and anxiety-related behavior and synaptophysin immunoreactivity in the adult rat. On the other hand, MAP2 immunoreactivity was decreased by betamethasone in males, suggesting a permanent impairment in the hippocampus. Interestingly, the lower dose appears to have less influence in terms of growth restriction, known to be associated with an increased risk of disease in adulthood. Further research might elucidate whether the betamethasone effect on hippocampal neurons persists later in life and could affect the aging process increasing the risk for neuropathology of the adult.

Sex-differences in age-related cognitive decline in C57BL/6J mice associated with increased brain microtubule-associated protein 2 and synaptophysin immunoreactivity

Understanding cognitive aging is becoming more important as the elderly population grows. Here, the effects of age and sex on learning and memory performance were compared in female and male young (3-4 months old) middle-aged (10-12 months old) and old (18-20 months old) wild-type C57BL/6J mice. Old males and females performed worse than young or middle-aged mice in novel location, but not novel object recognition tasks. Old mice, of both sexes, also showed impaired spatial water maze performance during training compared with young or middle-aged mice, however only old females failed to show robust spatial bias during probe trials. While there was no age-difference in passive avoidance performance for males, females showed an age-related decline. There was no difference in cognitive performance between young and middle-age mice of either sex on any task. Cognitive performance was associated with alterations in immunoreactivity of microtubule-associated protein 2-positive dendrites and synaptophysin-positive pre-synaptic terminals in hippocampal CA1, CA3, and dentate, entorhinal cortex, and central nucleus of amygdala. Overall, microtubule-associated protein 2 immunoreactivity was increased in old females compared with both young and middle-age females with no significant difference in males. In contrast, synaptophysin immunoreactivity increased from young to middle-age in females, and from middle-age to old in males; females had higher levels of synaptophysin immunoreactivity than males in middle-age only. Elevated levels of microtubule-associated protein 2 and synaptophysin may constitute a compensatory response to age-related functional decline in mice.

Immunocytochemical analysis of synaptic proteins provides new insights into diabetes-mediated plasticity in the rat hippocampus

The hippocampus, an important integration center for learning and memory in the mammalian brain, undergoes neurological changes in response to a variety of stimuli that are suggestive of ongoing synaptic reorganization. Accordingly, the aim of this study was to identify markers of synaptic plasticity using rapid and reliable techniques such as radioimmunocytochemistry and confocal microscopy, thereby providing a "birds-eye view" of the whole hippocampus under hypercorticosteronemic conditions. The regulation of microtubule-associated protein 2, synaptophysin and postsynaptic density-95 was examined in two different animal models of hypercorticosteronemia: corticosterone administration and streptozotocin-induced diabetes using both a short-term (1 week) and long-term (5 weeks) treatment. Glucocorticoids and/or hyperglycemia increased synaptophysin expression in CA1, CA3 and the dentate gyrus, regions that exhibit synaptic plasticity in response to glucocorticoid exposure. In these models, postsynaptic density-95 expression increased in the CA3 region, particularly in the diabetic rats, while microtubule-associated protein 2 exhibited more selective changes. Fluoro-Jade histochemistry did not detect neuronal damage, suggesting that glucocorticoids and/or hyperglycemia induce plastic and not irreversible neuronal changes at these time points. Collectively, these results demonstrate that changes in the expression and distribution of synaptic proteins provide another measure of synaptic plasticity in the rat hippocampus in response to glucocorticoid exposure, changes that may accompany or contribute to neuroanatomical, neurochemical, and behavioral changes observed in experimental models of type 1 diabetes.

Vitamin E Deficiency and Aging Effect on Expression Levels of GAP-43 and MAP-2 in Selected Areas of the Brain

The expression levels of GAP-43 and MAP-2, two proteins involved, respectively, in axonal and dendritic remodeling, in control adult (11 months), old (24 months), and vitamin E-deficient (11 months) rats were evaluated. mRNA levels were determined by means of a quantitative in situ hybridization procedure in subregions of hippocampus and cerebellum. Though a general trend can be observed indicating a reduction in GAP-43 expression in aging as compared to adult animals and an increase in vitamin E-deprived rats in comparison with adult animals, no statistically significant change was found in any region analyzed. In the same way, MAP-2 mRNA levels show an increase in vitamin E-deprived rats in comparison with other groups tested; only one variation was statistically significant, namely the increase in cerebellar cortex MAP-2 nRNA levels in vitamin E-deficient versus adult rats. These results suggest that oxidative stress and aging negatively affect neuroplasticity, showing different characteristics at the dendritic and axonal levels.

Uniform polarity microtubule assemblies imaged in native brain tissue by second-harmonic generation microscopy

Microtubule (MT) ensemble polarity is a diagnostic determinant of the structure and function of neuronal processes. Here, polarized MT structures are selectively imaged with second-harmonic generation (SHG) microscopy in native brain tissue. This SHG is found to colocalize with axons in both brain slices and cultured neurons. Because SHG arises only from noninversion symmetric structures, the uniform polarity of axonal MTs leads to the observed signal, whereas the mixed polarity in dendrites leads to destructive interference. SHG imaging provides a tool to investigate the kinetics and function of MT ensemble polarity in dynamic native brain tissue structures and other subcellular motility structures based on polarized MTs.