Dendritic vulnerability in neurodegenerative disease: insights from analyses of cortical pyramidal neurons in transgenic mouse models

Morphology and synapse topography optimize linear encoding of synapse numbers in Drosophila looming responsive descending neurons

Synapses are often precisely organized on dendritic arbors, yet the role of synaptic topography in dendritic integration remains poorly understood. Utilizing electron microscopy (EM) connectomics we investigate synaptic topography in Drosophila melanogaster looming circuits, focusing on retinotopically tuned visual projection neurons (VPNs) that synapse onto descending neurons (DNs). Synapses of a given VPN type project to non-overlapping regions on DN dendrites. Within these spatially constrained clusters, synapses are not retinotopically organized, but instead adopt near random distributions. To investigate how this organization strategy impacts DN integration, we developed multicompartment models of DNs fitted to experimental data and using precise EM morphologies and synapse locations. We find that DN dendrite morphologies normalize EPSP amplitudes of individual synaptic inputs and that near random distributions of synapses ensure linear encoding of synapse numbers from individual VPNs. These findings illuminate how synaptic topography influences dendritic integration and suggest that linear encoding of synapse numbers may be a default strategy established through connectivity and passive neuron properties, upon which active properties and plasticity can then tune as needed.

Synaptic alterations associated with disrupted sensory encoding in a mouse model of tauopathy

Synapse loss is currently the best biological correlate of cognitive decline in Alzheimer's disease and other tauopathies. Synapses seem to be highly vulnerable to tau-mediated disruption in neurodegenerative tauopathies. However, it is unclear how and when this leads to alterations in function related to the progression of tauopathy and neurodegeneration. We used the well-characterized rTg4510 mouse model of tauopathy at 5-6 months and 7-8 months of age, respectively, to study the functional impact of cortical synapse loss. The earlier age was used as a model of prodromal tauopathy, with the later age corresponding to more advanced tau pathology and presumed progression of neurodegeneration. Analysis of synaptic protein expression in the somatosensory cortex showed significant reductions in synaptic proteins and NMDA and AMPA receptor subunit expression in rTg4510 mice. Surprisingly, in vitro whole-cell patch clamp electrophysiology from putative pyramidal neurons in layer 2/3 of the somatosensory cortex suggested no functional alterations in layer 4 to layer 2/3 synaptic transmission at 5-6 months. From these same neurons, however, there were alterations in dendritic structure, with increased branching proximal to the soma in rTg4510 neurons. Therefore, in vivo whole-cell patch clamp recordings were utilized to investigate synaptic function and integration in putative pyramidal neurons in layer 2/3 of the somatosensory cortex. These recordings revealed a significant increase in the peak response to synaptically driven sensory stimulation-evoked activity and a loss of temporal fidelity of the evoked signal to the input stimulus in rTg4510 neurons. Together, these data suggest that loss of synapses, changes in receptor expression and dendritic restructuring may lead to alterations in synaptic integration at a network level. Understanding these compensatory processes could identify targets to help delay symptomatic onset of dementia.

Impaired long-range excitatory time scale predicts abnormal neural oscillations and cognitive deficits in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the most common form of dementia, progressively impairing cognitive abilities. While neuroimaging studies have revealed functional abnormalities in AD, how these relate to aberrant neuronal circuit mechanisms remains unclear. Using magnetoencephalography imaging we documented abnormal local neural synchrony patterns in patients with AD. To identify global abnormal biophysical mechanisms underlying the spatial and spectral electrophysiological patterns in AD, we estimated the parameters of a biophysical spectral graph model (SGM).

METHODS

SGM is an analytic neural mass model that describes how long-range fiber projections in the brain mediate the excitatory and inhibitory activity of local neuronal subpopulations. Unlike other coupled neuronal mass models, the SGM is linear, available in closed-form, and parameterized by a small set of biophysical interpretable global parameters. This facilitates their rapid and unambiguous inference which we performed here on a well-characterized clinical population of patients with AD (N = 88, age = 62.73 +/- 8.64 years) and a cohort of age-matched controls (N = 88, age = 65.07 +/- 9.92 years).

RESULTS

Patients with AD showed significantly elevated long-range excitatory neuronal time scales, local excitatory neuronal time scales and local inhibitory neural synaptic strength. The long-range excitatory time scale had a larger effect size, compared to local excitatory time scale and inhibitory synaptic strength and contributed highest for the accurate classification of patients with AD from controls. Furthermore, increased long-range time scale was associated with greater deficits in global cognition.

CONCLUSIONS

These results demonstrate that long-range excitatory time scale of neuronal activity, despite being a global measure, is a key determinant in the local spectral signatures and cognition in the human brain, and how it might be a parsimonious factor underlying altered neuronal activity in AD. Our findings provide new insights into mechanistic links between abnormal local spectral signatures and global connectivity measures in AD.

Exercise Intervention for Alzheimer's Disease: Unraveling Neurobiological Mechanisms and Assessing Effects

Alzheimer's disease (AD) is a progressive neurodegenerative disease and a major cause of age-related dementia, characterized by cognitive dysfunction and memory impairment. The underlying causes include the accumulation of beta-amyloid protein (Aβ) in the brain, abnormal phosphorylation, and aggregation of tau protein within nerve cells, as well as neuronal damage and death. Currently, there is no cure for AD with drug therapy. Non-pharmacological interventions such as exercise have been widely used to treat AD, but the specific molecular and biological mechanisms are not well understood. In this narrative review, we integrate the biology of AD and summarize the knowledge of the molecular, neural, and physiological mechanisms underlying exercise-induced improvements in AD progression. We discuss various exercise interventions used in AD and show that exercise directly or indirectly affects the brain by regulating crosstalk mechanisms between peripheral organs and the brain, including "bone-brain crosstalk", "muscle-brain crosstalk", and "gut-brain crosstalk". We also summarize the potential role of artificial intelligence and neuroimaging technologies in exercise interventions for AD. We emphasize that moderate-intensity, regular, long-term exercise may improve the progression of Alzheimer's disease through various molecular and biological pathways, with multimodal exercise providing greater benefits. Through in-depth exploration of the molecular and biological mechanisms and effects of exercise interventions in improving AD progression, this review aims to contribute to the existing knowledge base and provide insights into new therapeutic strategies for managing AD.

Impaired long-range excitatory time scale predicts abnormal neural oscillations and cognitive deficits in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, progressively impairing memory and cognition. While neuroimaging studies have revealed functional abnormalities in AD, how these relate to aberrant neuronal circuit mechanisms remains unclear. Using magnetoencephalography imaging we documented abnormal local neural synchrony patterns in patients with AD. To identify abnormal biophysical mechanisms underlying these abnormal electrophysiological patterns, we estimated the parameters of a spectral graph-theory model (SGM). SGM is an analytic model that describes how long-range fiber projections in the brain mediate the excitatory and inhibitory activity of local neuronal subpopulations. The long-range excitatory time scale was associated with greater deficits in global cognition and was able to distinguish AD patients from controls with high accuracy. These results demonstrate that long-range excitatory time scale of neuronal activity, despite being a global measure, is a key determinant in the spatiospectral signatures and cognition in AD.

Impaired long-range excitatory time scale predicts abnormal neural oscillations and cognitive deficits in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, progressively impairing memory and cognition. While neuroimaging studies have revealed functional abnormalities in AD, how these relate to aberrant neuronal circuit mechanisms remains unclear. Using magnetoencephalography imaging we documented abnormal local neural synchrony patterns in patients with AD. To identify abnormal biophysical mechanisms underlying these abnormal electrophysiological patterns, we estimated the parameters of a spectral graph-theory model (SGM). SGM is an analytic model that describes how long-range fiber projections in the brain mediate the excitatory and inhibitory activity of local neuronal subpopulations. The long-range excitatory time scale was associated with greater deficits in global cognition and was able to distinguish AD patients from controls with high accuracy. These results demonstrate that long-range excitatory time scale of neuronal activity, despite being a global measure, is a key determinant in the spatiospectral signatures and cognition in AD.

Exposure to nonylphenol in early life causes behavioural deficits related with autism spectrum disorders in rats

Early-life exposure to environmental endocrine disruptors (EDCs) is a potential risk factor for autism spectrum disorder (ASD). Exposure to nonylphenol (NP), a typical EDC, is known to cause some long-term behavioural abnormalities. Moreover, these abnormal behaviours are the most frequent psychiatric co-morbidities in ASD. However, the direct evidence for the link between NP exposure in early life and ASD-like behavioural phenotypes is still missing. In the present study, typical ASD-like behaviours induced by valproic acid treatment were considered as a positive behavioural control. We investigated impacts on social behaviours following early-life exposure to NP, and explored effects of this exposure on neuronal dendritic spines, mitochondria function, oxidative stress, and endoplasmic reticulum (ER) stress. Furthermore, primary cultured rat neurons were employed as in vitro model to evaluate changes in dendritic spine caused by exposure to NP, and oxidative stress and ER stress were specifically modulated to further explore their roles in these changes. Our results indicated rats exposed to NP in early life showed mild ASD-like behaviours. Moreover, we also found the activation of ER stress triggered by oxidative stress may contribute to dendritic spine decrease and synaptic dysfunction, which may underlie neurobehavioural abnormalities induced by early-life exposure to NP.

Mesenchymal-derived extracellular vesicles enhance microglia-mediated synapse remodeling after cortical injury in aging Rhesus monkeys

Understanding the microglial neuro-immune interactions in the primate brain is vital to developing therapeutics for cortical injury, such as stroke or traumatic brain injury. Our previous work showed that mesenchymal-derived extracellular vesicles (MSC-EVs) enhanced motor recovery in aged rhesus monkeys following injury of primary motor cortex (M1), by promoting homeostatic ramified microglia, reducing injury-related neuronal hyperexcitability, and enhancing synaptic plasticity in perilesional cortices. A focal lesion was induced via surgical ablation of pial blood vessels over lying the cortical hand representation of M1 of aged female rhesus monkeys, that received intravenous infusions of either vehicle (veh) or EVs 24 h and again 14 days post-injury. The current study used this same cohort to address how these injury- and recovery-associated changes relate to structural and molecular interactions between microglia and neuronal synapses. Using multi-labeling immunohistochemistry, high-resolution microscopy, and gene expression analysis, we quantified co-expression of synaptic markers (VGLUTs, GLURs, VGAT, GABARs), microglia markers (Iba1, P2RY12), and C1q, a complement pathway protein for microglia-mediated synapse phagocytosis, in perilesional M1 and premotor cortices (PMC). We compared this lesion cohort to age-matched non-lesion controls (ctr). Our findings revealed a lesion-related loss of excitatory synapses in perilesional areas, which was ameliorated by EV treatment. Further, we found region-dependent effects of EVs on microglia and C1q expression. In perilesional M1, EV treatment and enhanced functional recovery were associated with increased expression of C1q + hypertrophic microglia, which are thought to have a role in debris-clearance and anti-inflammatory functions. In PMC, EV treatment was associated with decreased C1q + synaptic tagging and microglia-spine contacts. Our results suggest that EV treatment may enhance synaptic plasticity via clearance of acute damage in perilesional M1, and thereby preventing chronic inflammation and excessive synaptic loss in PMC. These mechanisms may act to preserve synaptic cortical motor networks and a balanced normative M1/PMC synaptic function to support functional recovery after injury.

Neuronal properties of pyramidal cells in lateral prefrontal cortex of the aging rhesus monkey brain are associated with performance deficits on spatial working memory but not executive function

Age-related declines in cognitive abilities occur as early as middle-age in humans and rhesus monkeys. Specifically, performance by aged individuals on tasks of executive function (EF) and working memory (WM) is characterized by greater frequency of errors, shorter memory spans, increased frequency of perseverative responses, impaired use of feedback and reduced speed of processing. However, how aging precisely differentially impacts specific aspects of these cognitive functions and the distinct brain areas mediating cognition are not well understood. The prefrontal cortex (PFC) is known to mediate EF and WM and is an area that shows a vulnerability to age-related alterations in neuronal morphology. In the current study, we show that performance on EF and WM tasks exhibited significant changes with age, and these impairments correlate with changes in biophysical properties of layer 3 (L3) pyramidal neurons in lateral LPFC (LPFC). Specifically, there was a significant age-related increase in excitability of L3 LPFC pyramidal neurons, consistent with previous studies. Further, this age-related hyperexcitability of LPFC neurons was significantly correlated with age-related decline on a task of WM, but not an EF task. The current study characterizes age-related performance on tasks of WM and EF and provides insight into the neural substrates that may underlie changes in both WM and EF with age.

Neuronal properties of pyramidal cells in lateral prefrontal cortex of the aging rhesus monkey brain are associated with performance deficits on spatial working memory but not executive function

Age-related declines in cognitive abilities occur as early as middle-age in humans and rhesus monkeys. Specifically, performance by aged individuals on tasks of executive function (EF) and working memory (WM) is characterized by greater frequency of errors, shorter memory spans, increased frequency of perseverative responses, impaired use of feedback and reduced speed of processing. However, how aging precisely differentially impacts specific aspects of these cognitive functions and the distinct brain areas mediating cognition are not well understood. The prefrontal cortex (PFC) is known to mediate EF and WM and is an area that shows a vulnerability to age-related alterations in neuronal morphology. In the current study, we show that performance on EF and WM tasks exhibited significant changes with age and these impairments correlate with changes in biophysical properties of L3 pyramidal neurons in lateral LPFC (LPFC). Specifically, there was a significant age-related increase in excitability of Layer 3 LPFC pyramidal neurons, consistent with previous studies. Further, this age-related hyperexcitability of LPFC neurons was significantly correlated with age-related decline on a task of WM, but not an EF task. The current study characterizes age-related performance on tasks of WM and EF and provides insight into the neural substrates that may underlie changes in both WM and EF with age.

Techniques to Render Dendritic Spines Visible in the Microscope

A tiny detail visible on certain neurons at the limit of resolution in light microscopy went in 130 years of neuroscience research through a dazzling career from suspicious staining artifact to what we recognize today as a complex postsynaptic molecular machine: the dendritic spine.This chapter deals with techniques to make spines visible. The original technique, Golgi silver staining, is still being used today. Electron microscopy and automated field ion beam scanning electron microscopy are ultrahigh resolution techniques, albeit specialized. Other methods are intracellular injection, uptake of dyes, and recently the exploitation of genetically modified animals in which certain neurons express fluorescent protein in all their processes, including the nooks and crannies of their dendritic spines.

Neurodegenerative Diseases: From Dysproteostasis, Altered Calcium Signalosome to Selective Neuronal Vulnerability to AAV-Mediated Gene Therapy

Despite intense research into the multifaceted etiology of neurodegenerative diseases (ND), they remain incurable. Here we provide a brief overview of several major ND and explore novel therapeutic approaches. Although the cause (s) of ND are not fully understood, the accumulation of misfolded/aggregated proteins in the brain is a common pathological feature. This aggregation may initiate disruption of Ca⁺⁺ signaling, which is an early pathological event leading to altered dendritic structure, neuronal dysfunction, and cell death. Presently, ND gene therapies remain unidimensional, elusive, and limited to modifying one pathological feature while ignoring others. Considering the complexity of signaling cascades in ND, we discuss emerging therapeutic concepts and suggest that deciphering the molecular mechanisms involved in dendritic pathology may broaden the phenotypic spectrum of ND treatment. An innovative multiplexed gene transfer strategy that employs silencing and/or over-expressing multiple effectors could preserve vulnerable neurons before they are lost. Such therapeutic approaches may extend brain health span and ameliorate burdensome chronic disease states.

Retinoic acid-induced protein 14 controls dendritic spine dynamics associated with depressive-like behaviors

Dendritic spines are the central postsynaptic machinery that determines synaptic function. The F-actin within dendritic spines regulates their dynamic formation and elimination. Rai14 is an F-actin-regulating protein with a membrane-shaping function. Here, we identified the roles of Rai14 for the regulation of dendritic spine dynamics associated with stress-induced depressive-like behaviors. Rai14-deficient neurons exhibit reduced dendritic spine density in the Rai14^+/- mouse brain, resulting in impaired functional synaptic activity. Rai14 was protected from degradation by complex formation with Tara, and accumulated in the dendritic spine neck, thereby enhancing spine maintenance. Concurrently, Rai14 deficiency in mice altered gene expression profile relevant to depressive conditions and increased depressive-like behaviors. Moreover, Rai14 expression was reduced in the prefrontal cortex of the mouse stress model, which was blocked by antidepressant treatment. Thus, we propose that Rai14-dependent regulation of dendritic spines may underlie the plastic changes of neuronal connections relevant to depressive-like behaviors.

Mitochondria in neurodegeneration

The brain is one of the most energetically demanding tissues in the human body, and mitochondrial pathology is strongly implicated in chronic neurodegenerative diseases. In contrast to acute brain injuries in which bioenergetics and cell death play dominant roles, studies modeling familial neurodegeneration implicate a more complex and nuanced relationship involving the entire mitochondrial life cycle. Recent literature on mitochondrial mechanisms in Parkinson's disease, Alzheimer's disease, frontotemporal dementia, Huntington's disease, and amyotrophic lateral sclerosis is reviewed with an emphasis on mitochondrial quality control, transport and synaptodendritic calcium homeostasis. Potential neuroprotective interventions include targeting the mitochondrial kinase PTEN-induced kinase 1 (PINK1), which plays a role in regulating not only multiple facets of mitochondrial biology, but also neuronal morphogenesis and dendritic arborization.

Structural Plasticity of the Hippocampus in Neurodegenerative Diseases

Neuroplasticity is the capacity of neural networks in the brain to alter through development and rearrangement. It can be classified as structural and functional plasticity. The hippocampus is more susceptible to neuroplasticity as compared to other brain regions. Structural modifications in the hippocampus underpin several neurodegenerative diseases that exhibit cognitive and emotional dysregulation. This article reviews the findings of several preclinical and clinical studies about the role of structural plasticity in the hippocampus in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. In this study, literature was surveyed using Google Scholar, PubMed, Web of Science, and Scopus, to review the mechanisms that underlie the alterations in the structural plasticity of the hippocampus in neurodegenerative diseases. This review summarizes the role of structural plasticity in the hippocampus for the etiopathogenesis of neurodegenerative diseases and identifies the current focus and gaps in knowledge about hippocampal dysfunctions. Ultimately, this information will be useful to propel future mechanistic and therapeutic research in neurodegenerative diseases.

Adolescent Ethanol Exposure Alters Cholinergic Function and Apical Dendritic Branching Within the Orbital Frontal Cortex

During adolescence, heavy binge-like ethanol consumption can lead to frontocortical structural and functional impairments. These impairments are likely driven by adolescence being a critical time point for maturation of brain regions associated with higher-order cognitive functioning. Rodent models of heavy binge-like ethanol exposure show consistent disruptions to the typical development of the prefrontal cortex (PFC). All deep cortical layers receive cholinergic projections that originate from the Nucleus basalis of Meynert (NbM) complex. These cholinergic projections are highly involved in learning, memory, and attention. Adolescent intermittent ethanol exposure (AIE) induces cholinergic dysfunction as a result of an epigenetic suppression of the genes that drive the cholinergic phenotype. The current study used a model of AIE to assess structural and functional changes to the frontal cortex and NbM following binge-like ethanol exposure in adolescence. Western blot analysis revealed long-term disruptions of the cholinergic circuit following AIE: choline acetyltransferase (ChAT) was suppressed in the NbM and vesicular acetylcholine transporter (VAChT) was suppressed in the orbitofrontal cortex (OFC). In vivo microdialysis for acetylcholine efflux during a spatial memory task determined changes in cholinergic modulation within the PFC following AIE. However, AIE spared performance on the spatial memory task and on an operant reversal task. In a second study, Golgi-Cox staining determined that AIE increased apical dendritic complexity in the OFC, with sex influencing whether the increase in branching occurred near or away from the soma. Spine density or maturity was not affected, likely compensating for a disruption in neurotransmitter function following AIE.

Single-neuron dynamical effects of dendritic pruning implicated in aging and neurodegeneration: towards a measure of neuronal reserve

Aging is a main risk factor for neurodegenerative disorders including Alzheimer's disease. It is often accompanied by reduced cognitive functions, gray-matter volume, and dendritic integrity. Although age-related brain structural changes have been observed across multiple scales, their functional implications remain largely unknown. Here we simulate the aging effects on neuronal morphology as dendritic pruning and characterize its dynamical implications. Utilizing a detailed computational modeling approach, we simulate the dynamics of digitally reconstructed neurons obtained from Neuromorpho.org. We show that dendritic pruning affects neuronal integrity: firing rate is reduced, causing a reduction in energy consumption, energy efficiency, and dynamic range. Pruned neurons require less energy but their function is often impaired, which can explain the diminished ability to distinguish between similar experiences (pattern separation) in older people. Our measures indicate that the resilience of neuronal dynamics is neuron-specific, heterogeneous, and strongly affected by dendritic topology and the position of the soma. Based on the emergent neuronal dynamics, we propose to classify the effects of dendritic deterioration, and put forward a topological measure of “neuronal reserve” that quantifies the resilience of neuronal dynamics to dendritic pruning. Moreover, our findings suggest that increasing dendritic excitability could partially mitigate the dynamical effects of aging.

Fibroblast Growth Factor 9 Stimulates Neuronal Length Through NF-kB Signaling in Striatal Cell Huntington's Disease Models

Proper development of neuronal cells is important for brain functions, and impairment of neuronal development may lead to neuronal disorders, implying that improvement in neuronal development may be a therapeutic direction for these diseases. Huntington's disease (HD) is a neurodegenerative disease characterized by impairment of neuronal structures, ultimately leading to neuronal death and dysfunctions of the central nervous system. Based on previous studies, fibroblast growth factor 9 (FGF9) may provide neuroprotective functions in HD, and FGFs may enhance neuronal development and neurite outgrowth. However, whether FGF9 can provide neuronal protective functions through improvement of neuronal morphology in HD is still unclear. Here, we study the effects of FGF9 on neuronal length in HD and attempt to understand the related working mechanisms. Taking advantage of striatal cell lines from HD knock-in mice, we found that FGF9 increases total neuronal length and upregulates several structural and synaptic proteins under HD conditions. In addition, activation of nuclear factor kappa B (NF-kB) signaling by FGF9 was observed to be significant in HD cells, and blockage of NF-kB leads to suppression of these structural and synaptic proteins induced by FGF9, suggesting the involvement of NF-kB signaling in these effects of FGF9. Taken these results together, FGF9 may enhance total neuronal length through upregulation of NF-kB signaling, and this mechanism could serve as an important mechanism for neuroprotective functions of FGF9 in HD.

FGF9 induces neurite outgrowth upon ERK signaling in knock-in striatal Huntington's disease cells

AIMS

Huntington's disease (HD) is a neurodegenerative disease that causes deficits in neurite outgrowth, which suggests that enhancement of neurite outgrowth is a potential direction by which to improve HD. Our previous publications showed that fibroblast growth factor 9 (FGF9) provides anti-apoptosis and anti-oxidative functions in striatal cell models of HD through the extracellular signal-regulated kinases (ERK) pathway, and FGF9 also stimulates cytoskeletons to enhance neurite outgrowth via nuclear factor kappa B (NF-kB) signaling. In this study, we further demonstrate the importance of the ERK pathway for the neurite outgrowth induced by FGF9 in HD striatal models.

MATERIALS AND METHODS

FGF9 was treated with ERK (U0126) or NF-kB (BAY11-7082) inhibitors in STHdh^Q7/Q7 and STHdh^Q111/Q111 striatal knock-in cell lines to examine neurite outgrowth, cytoskeletal markers, and synaptic proteins via immunofluorescence staining and Western blotting. NF-kB activity was analyzed by NF-kB promoter reporter assay.

KEY FINDINGS

Here, we show that suppression of ERK signaling significantly inhibits FGF9-induced neurite outgrowth, cytoskeletal markers, and synaptic proteins in HD striatal cells. In addition, we also show suppression of ERK signaling significantly decreases FGF9-induced NF-kB activation, whereas suppression of NF-kB does not decrease FGF9-induced ERK signaling. These results suggest that FGF9 activates ERK signaling first, stimulates NF-kB upregulation, and then enhances neurite outgrowth in HD striatal cells.

SIGNIFICANCE

We elucidate the more detailed mechanisms of neurite outgrowth enhanced by FGF9 in these HD striatal cells. This study may provide insights into targeting neurite outgrowth for HD therapy.

Diffusion Tensor Imaging in Preclinical and Human Studies of Huntington's Disease: What Have we Learned so Far?

BACKGROUND

Huntington's Disease is an irreversible neurodegenerative disease characterized by the progressive deterioration of specific brain nerve cells. The current evaluation of cellular and physiological events in patients with HD relies on the development of transgenic animal models. To explore such events in vivo, diffusion tensor imaging has been developed to examine the early macro and microstructural changes in brain tissue. However, the gap in diffusion tensor imaging findings between animal models and clinical studies and the lack of microstructural confirmation by histological methods has questioned the validity of this method.

OBJECTIVE

This review explores white and grey matter ultrastructural changes associated to diffusion tensor imaging, as well as similarities and differences between preclinical and clinical Huntington's Disease studies.

METHODS

A comprehensive review of the literature using online-resources was performed (Pub- Med search).

RESULTS

Similar changes in fractional anisotropy as well as axial, radial and mean diffusivities were observed in white matter tracts across clinical and animal studies. However, comparative diffusion alterations in different grey matter structures were inconsistent between clinical and animal studies.

CONCLUSION

Diffusion tensor imaging can be related to specific structural anomalies in specific cellular populations. However, some differences between animal and clinical studies could derive from the contrasting neuroanatomy or connectivity across species. Such differences should be considered before generalizing preclinical results into the clinical practice. Moreover, current limitations of this technique to accurately represent complex multicellular events at the single micro scale are real. Future work applying complex diffusion models should be considered.

Dysregulated Plasma Membrane Turnover Underlying Dendritic Pathology in Neurodegenerative Diseases

Due to their enormous surface area compared to other cell types, neurons face unique challenges in properly handling supply and retrieval of the plasma membrane (PM)-a process termed PM turnover-in their distal areas. Because of the length and extensiveness of dendritic branches in neurons, the transport of materials needed for PM turnover from soma to distal dendrites will be inefficient and quite burdensome for somatic organelles. To meet local demands, PM turnover in dendrites most likely requires local cellular machinery, such as dendritic endocytic and secretory systems, dysregulation of which may result in dendritic pathology observed in various neurodegenerative diseases (NDs). Supporting this notion, a growing body of literature provides evidence to suggest the pathogenic contribution of dysregulated PM turnover to dendritic pathology in certain NDs. In this article, we present our perspective view that impaired dendritic endocytic and secretory systems may contribute to dendritic pathology by encumbering PM turnover in NDs.

Curcumin Attenuates Chronic Unpredictable Mild Stress-Induced Depressive-Like Behaviors via Restoring Changes in Oxidative Stress and the Activation of Nrf2 Signaling Pathway in Rats

Accumulating evidence has demonstrated that oxidative stress is associated with depression. Our present study aimed at investigating the antidepressant effect and the possible mechanisms of curcumin (CUR) in chronic unpredictable mild stress- (CUMS-) induced depression model in rats. After exposure to CUMS for four weeks, the rats showed depressive-like behavior, and the depressive-like behaviors in CUMS-treated rats were successfully corrected after administration of CUR. In addition, CUR could effectively decrease protein expression of oxidative stress markers (Nox2, 4-HNE, and MDA) and increase the activity of CAT. CUR treatment also reversed CUMS-induced inhibition of Nrf2-ARE signaling pathway, along with increasing the mRNA expression of NQO-1 and HO-1. Furthermore, the supplementation of CUR also increased the ratio of pCREB/CREB and synaptic-related protein (BDNF, PSD-95, and synaptophysin). In addition, CUR could effectively reverse CUMS-induced reduction of spine density and total dendritic length. In conclusion, the study revealed that CUR relieves depressive-like state through the mitigation of oxidative stress and the activation of Nrf2-ARE signaling pathway.

Assessing neuraxial microstructural changes in a transgenic mouse model of early stage Amyotrophic Lateral Sclerosis by ultra-high field MRI and diffusion tensor metrics

OBJECTIVE

Cell structural changes are one of the main features observed during the development of amyotrophic lateral sclerosis (ALS). In this work, we propose the use of diffusion tensor imaging (DTI) metrics to assess specific ultrastructural changes in the central nervous system during the early neurodegenerative stages of ALS.

METHODS

Ultra-high field MRI and DTI data at 17.6T were obtained from fixed, excised mouse brains, and spinal cords from ALS (G93A-SOD1) mice.

RESULTS

Changes in fractional anisotropy (FA) and linear, planar, and spherical anisotropy ratios (CL, CP, and CS, respectively) of the diffusion eigenvalues were measured in white matter (WM) and gray matter (GM) areas associated with early axonal degenerative processes (in both the brain and the spinal cord). Specifically, in WM structures (corpus callosum, corticospinal tract, and spinal cord funiculi) as the disease progressed, FA, CL, and CP values decreased, whereas CS values increased. In GM structures (prefrontal cortex, hippocampus, and central spinal cord) FA and CP decreased, whereas the CL and CS values were unchanged or slightly smaller. Histological studies of a fluorescent mice model (YFP, G93A-SOD1 mouse) corroborated the early alterations in neuronal morphology and axonal connectivity measured by DTI.

CONCLUSIONS

Changes in diffusion tensor shape were observed in this animal model at the early, nonsymptomatic stages of ALS. Further studies of CL, CP, and CS as imaging biomarkers should be undertaken to refine this neuroimaging tool for future clinical use in the detection of the early stages of ALS.

Advances in exogenous docosahexaenoic acid-containing phospholipids: Sources, positional isomerism, biological activities, and advantages

In recent years, docosahexaenoic acid-containing phospholipids (DHA-PLs) have attracted much attention because of theirs unique health benefits. Compared with other forms of docosahexaenoic acid (DHA), DHA-PLs possess superior biological effects (e.g., anticancer, lipid metabolism regulation, visual development, and brain and nervous system biochemical reactions), more intricate metabolism mechanisms, and a stronger attraction to consumer. The production of DHA-PLs is hampered by several challenges associated with the limited content of DHA-PLs in natural sources, incomplete utilization of by-products, few microorganisms for DHA-PLs production, high cost, and complex process of artificial preparation of DHA-PLs. In this article, the sources, biological activities, and commercial applications of DHA-PLs were summarized, with intensive discussions on advantages of DHA-PLs over DHA, isomerism of DHA in phospholipids (PLs), and brain health. The excellent biological characteristics of DHA-PLs are primarily concerned with DHA and PLs. The metabolic fate of different DHA-PLs varies from the position of DHA in PLs to polar groups in DHA-PLs. Overall, well understanding of DHA-PLs about their sources and characteristics is critical to accelerate the production of DHA-PLs, economically enhance the value of DHA-PLs, and improve the applicability of DHA-PLs and the acceptance of consumers.

The cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) targets the olfactory bulb region

Olfactory dysfunction is implicated in neurodegenerative disorders and typically manifests years before other symptoms. The cyanobacterial neurotoxin β-N-methylamino-l-alanine (BMAA) is suggested as a risk factor for neurodegenerative disease. Detection of BMAA in air filters has increased the concern that aerosolization may lead to human BMAA exposure through the air. The aim of this study was to determine if BMAA targets the olfactory system. Autoradiographic imaging showed a distinct localization of radioactivity in the right olfactory mucosa and bulb following a unilateral intranasal instillation of ³H-BMAA (0.018 µg) in mice, demonstrating a direct transfer of BMAA via the olfactory pathways to the brain circumventing the blood–brain barrier, which was confirmed by liquid scintillation. Treatment of mouse primary olfactory bulb cells with 100 µM BMAA for 24 h caused a disruption of the neurite network, formation of dendritic varicosities and reduced cell viability. The NMDA receptor antagonist MK-801 and the metabotropic glutamate receptor antagonist MCPG protected against the BMAA-induced alterations, demonstrating the importance of glutamatergic mechanisms. The ionotropic non-NMDA receptor antagonist CNQX prevented the BMAA-induced decrease of cell viability in mixed cultures containing both neuronal and glial cells, but not in cultures with neurons only, suggesting a role of neuron–glial interactions and glial AMPA receptors in the BMAA-induced toxicity. The results show that the olfactory region may be a target for BMAA following inhalation exposure. Further studies on the relations between environmental olfactory toxicants and neurodegenerative disorders are warranted.

Rostral intralaminar thalamic deep brain stimulation ameliorates memory deficits and dendritic regression in β-amyloid-infused rats

Rostral intralaminar thalamic deep brain stimulation (ILN-DBS) has been shown to enhance attention and cognition through neuronal activation and brain plasticity. We examined whether rostral ILN-DBS can also attenuate memory deficits and impaired synaptic plasticity and protect glutamatergic transmission in the rat intraventricular β-amyloid (Aβ) infusion model of Alzheimer's disease (AD). Spatial memory was tested in the Morris water maze (MWM), while structural synaptic plasticity and glutamatergic transmission strength were estimated by measuring dendritic spine densities in dye-injected neurons and tissue expression levels of postsynaptic density protein 95 (PSD-95) in medial prefrontal cortex (mPFC) and hippocampus. All these assessments were compared among the naïve control rats, AD rats, and AD rats with ILN-DBS. We found that a single rostral ILN-DBS treatment significantly improved MWM performance and reversed PSD-95 expression reductions in the mPFC and hippocampal region of Aβ-infused rats. In addition, ILN-DBS preserved dendritic spine densities on mPFC and hippocampal pyramidal neurons. In fact, MWM performance, PSD-95 expression levels, and dendritic spine densities did not differ between naïve control and rostral ILN-DBS treatment groups, indicating near complete amelioration of Aβ-induced spatial memory impairments and dendritic regression. These findings suggest that the ILN is critical for modulating glutamatergic transmission, neural plasticity, and spatial memory functions through widespread effects on distributed brain regions. Further, these findings provide a rationale for examining the therapeutic efficacy of ILN-DBS in AD patients.

Novel Positive Allosteric Modulators of Glutamate Transport Have Neuroprotective Properties in an in Vitro Excitotoxic Model

Dysfunction of excitatory amino acid transporters (EAATs) has been implicated in the pathogenesis of various neurological disorders, such as stroke, brain trauma, epilepsy, and several neurodegenerative disorders. EAAT2 is the main transporter subtype responsible for glutamate clearance in the brain, and plays a key role in regulating neurotransmission and preventing excitotoxicity. Therefore, compounds that increase the activity of EAAT2 have therapeutic potential for neuroprotection. In previous studies, we used virtual screening approaches to identify novel positive allosteric modulators (PAMs) of EAAT2. These compounds were shown to selectively increase the activity of EAAT2 and increase V_max of transport, without changing substrate affinity. In this work, our major effort was to investigate whether increasing the activity of EAAT2 by allosteric modulation would translate to neuroprotection in in vitro primary culture models of excitotoxicity. To investigate potential neuroprotective effects of one EAAT2 PAM, GT949, we subjected cultures to acute and prolonged excitotoxic insults by exogenous application of glutamate, or oxidative stress by application of hydrogen peroxide. GT949 administration did not result in neuroprotection in the oxidative stress model, likely due to damage of the glutamate transporters. However, GT949 displayed neuroprotective properties after acute and prolonged glutamate-mediated excitotoxicity. We propose that this compound prevents excess glutamate signaling by increasing the rate of glutamate clearance by EAAT2, thereby preventing excitotoxic damage and cell death. This novel class of compounds is therefore an innovative approach for neuroprotection with potential for translation in in vivo animal models of excitotoxicity.

Alzheimer's disease DNA methylome of pyramidal layers in frontal cortex: laser-assisted microdissection study

OBJECTIVE

To study DNA methylation patterns of cortical pyramidal layers susceptible to late-onset Alzheimer's disease (LOAD) neurodegeneration.

METHODS

Laser-assisted microdissection to select pyramidal layers' cells in frontal cortex of 32 human brains (18 LOAD) and Infinium DNA Methylation 450K analysis were performed to find differential methylated positions and regions, in addition to the corresponding gene set functional enrichment analyses.

RESULTS

Differential hypermethylation in several genomic regions and genes mainly in HOXA3, GSTP1, CXXC1-3 and BIN1. The functional enrichment analysis revealed genes significantly related to oxidative-stress and synapsis.

CONCLUSION

The present results indicate the differentially methylated genes related to neural projections, synapsis, oxidative stress and epigenetic regulator genes and represent the first epigenome of cortical pyramidal layers in LOAD.

Driven to decay: Excitability and synaptic abnormalities in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron (MN) disease and is clinically characterised by the death of corticospinal motor neurons (CSMNs), spinal and brainstem MNs and the degeneration of the corticospinal tract. Degeneration of CSMNs and MNs leads inexorably to muscle wastage and weakness, progressing to eventual death within 3-5 years of diagnosis. The CSMNs, located within layer V of the primary motor cortex, project axons constituting the corticospinal tract, forming synaptic connections with brainstem and spinal cord interneurons and MNs. Clinical ALS may be divided into familial (∼10% of cases) or sporadic (∼90% of cases), based on apparent random incidence. The emergence of transgenic murine models, expressing different ALS-associated mutations has accelerated our understanding of ALS pathogenesis, although precise mechanisms remain elusive. Multiple avenues of investigation suggest that cortical electrical abnormalities have pre-eminence in the pathophysiology of ALS. In addition, glutamate-mediated functional and structural alterations in both CSMNs and MNs are present in both sporadic and familial forms of ALS. This review aims to promulgate debate in the field with regard to the common aetiology of sporadic and familial ALS. A specific focus on a nexus point in ALS pathogenesis, namely, the synaptic and intrinsic hyperexcitability of CSMNs and MNs and alterations to their structure are comprehensively detailed. The association of extramotor dysfunction with neuronal structural/functional alterations will be discussed. Finally, the implications of the latest research on the dying-forward and dying-back controversy are considered.

Transgenic autoinhibition of p21-activated kinase exacerbates synaptic impairments and fronto-dependent behavioral deficits in an animal model of Alzheimer's disease

Defects in p21-activated kinase (PAK) lead to dendritic spine abnormalities and are sufficient to cause cognition impairment. The decrease in PAK in the brain of Alzheimer's disease (AD) patients is suspected to underlie synaptic and dendritic disturbances associated with its clinical expression, particularly with symptoms related to frontal cortex dysfunction. To investigate the role of PAK combined with Aβ and tau pathologies (3xTg-AD mice) in the frontal cortex, we generated a transgenic model of AD with a deficit in PAK activity (3xTg-AD-dnPAK mice). PAK inactivation had no effect on Aβ40 and Aβ42 levels, but increased the phosphorylation ratio of tau in detergent-insoluble protein fractions in the frontal cortex of 18-month-old heterozygous 3xTg-AD mice. Morphometric analyses of layer II/III pyramidal neurons in the frontal cortex showed that 3xTg-AD-dnPAK neurons exhibited significant dendritic attrition, lower spine density and longer spines compared to NonTg and 3xTg-AD mice. Finally, behavioral assessments revealed that 3xTg-AD-dnPAK mice exhibited pronounced anxious traits and disturbances in social behaviors, reminiscent of fronto-dependent symptoms observed in AD. Our results substantiate a critical role for PAK in the genesis of neuronal abnormalities in the frontal cortex underlying the emergence of psychiatric-like symptoms in AD.

Motor Areas Show Altered Dendritic Structure in an Amyotrophic Lateral Sclerosis Mouse Model

Objective: Motor neurons (MNs) die in amyotrophic lateral sclerosis (ALS), a clinically heterogeneous neurodegenerative disease of unknown etiology. In human or rodent studies, MN loss is preceded by increased excitability. As increased neuronal excitability correlates with structural changes in dendritic arbors and spines, we have examined longitudinal changes in dendritic structure in vulnerable neuron populations in a mouse model of familial ALS.

Methods: We used a modified Golgi-Cox staining method to determine the progressive changes in dendritic structure of hippocampal CA1 pyramidal neurons, striatal medium spiny neurons, and resistant (trochlear, IV) or susceptible (hypoglossal, XII; lumbar) MNs from brainstem and spinal cord of mice over-expressing the human SOD1^G93A (SOD1) mutation, in comparison to wild-type (WT) mice, at four postnatal (P) ages of 8–15, 28–35, 65–75, and 120 days.

Results: In SOD1 mice, dendritic changes occur at pre-symptomatic ages in both XII and spinal cord lumbar MNs. Spine loss without dendritic changes was present in striatal neurons from disease onset. Spine density increases were present at all ages studied in SOD1 XII MNs. Spine density increased in neonatal lumbar MNs, before decreasing to control levels by P28-35 and was decreased by P120. SOD1 XII MNs and lumbar MNs, but not trochlear MNs showed vacuolization from the same time-points. Trochlear MN dendrites were unchanged.

Interpretation: Dendritic structure and spine alterations correlate with the neuro-motor phenotype in ALS and with cognitive and extra-motor symptoms seen in patients. Prominent early changes in dendritic arbors and spines occur in susceptible cranial and spinal cord MNs, but are absent in MNs resistant to loss in ALS.

Dysregulation of LIMK-1/cofilin-1 pathway: A possible basis for alteration of neuronal morphology in experimental cerebral malaria

OBJECTIVE

Loss of cognition even after survival is the salient feature of cerebral malaria (CM). Currently, the fate of neuronal morphology is not studied at the ultrastructural level in CM. Recent studies suggest that maintenance of neuronal morphology and dendritic spine density (actin dynamics in particular) are essential for proper cognitive function. LIMK-1/cofilin-1 signaling pathway is known to be involved in the maintenance of actin dynamics through regulation of cofilin-1, and in executing learning and memory functions.

METHODS

Using an experimental mouse model, we analyzed the behavioral parameters of asymptomatic mice with CM by performing a rapid murine coma and behavior scale experiment. We performed Golgi-Cox staining to assess neuronal morphology, dendritic spine density, and arborization in brain cortex subjected to Plasmodium berghei ANKA infection compared to asymptomatic, anemic, and control groups. We studied the neural gene expression pattern of LIMK-1, cofilin-1, and β-actin in all the experimental groups by semiquantitative and quantitative polymerase chain reaction followed by immunoblotting and immunofluorescence.

RESULTS

We observed significant loss of dendritic spine density, abnormal spine morphology, reduced dendritic arborization, and extensive dendritic varicosities in the cortical neurons of CM-infected brain. Furthermore, these observations correlated with diminished protein levels of LIMK-1, cofilin-1, phospho-cofilin-1, and β-actin in the whole brain lysates as well as formation of actin-cofilin rods in the brain sections of symptomatic mice with CM.

INTERPRETATION

Overall, our findings suggest that the altered neuronal morphology and dysregulation of LIMK-1/cofilin-1 pathway could affect the cognitive outcome after experimental CM. Therefore, this study could help to establish newer therapeutic strategies addressing long-term cognitive impairment after CM. Ann Neurol 2017;82:429-443.

Maternal autoimmune antibodies alter the dendritic arbor and spine numbers in the infragranular layers of the cortex

An association between maternal IgG antibodies reactive against proteins in fetal brain and an outcome of autism in the child has been identified. Using a mouse model of prenatal intraventricular administration of autism-specific maternal IgG, we demonstrated that these antibodies produce behavioral alterations similar to those in children with ASD. We previously demonstrated that these antibodies bind to radial glial stem cells (RG) and observed an increase in the number of divisions of translocating RG in the developing cortex. We also showed an alteration in brain size and as well as a generalized increased of neuronal volume in adult mice. Here, we used our intraventricular mouse model of antibody administration, followed by Golgi and Neurolucida analysis to demonstrate that during midstages of neurogenesis these maternal autism-specific antibodies produced a consistent decrease in the number of spines in the infragranular layers in the adult cortical areas analyzed. Specifically, in the frontal cortex basal dendrites of layer V neurons were decreased in length and volume, and both the total number of spines-mature and immature-and the spine density were lower than in the control neurons from the same region. Further, in the occipital cortex layer VI neurons presented with a decrease in the total number of spines and in the spine density in the apical dendrite, as well as decrease in the number of mature spines in the apical and basal dendrites. Interestingly, the time of exposure to these antibodies (E14.5) coincides with the generation of pyramidal neurons in layer V in the frontal cortex and in layer VI in the occipital cortex, following the normal rostro-caudal pattern of cortical cell generation. We recently demonstrated that one of the primary antigens recognized by these antibodies corresponds to stress-induced phosphoprotein 1 (STIP1). Here we hypothesize that the reduction in the access of newborn cells to STIP1 in the developing cortex may be responsible for the reduced dendritic arborization and number of spines we noted in the adult cortex.

Dendrite and spine modifications in autism and related neurodevelopmental disorders in patients and animal models

Dendrites and spines are the main neuronal structures receiving input from other neurons and glial cells. Dendritic and spine number, size, and morphology are some of the crucial factors determining how signals coming from individual synapses are integrated. Much remains to be understood about the characteristics of neuronal dendrites and dendritic spines in autism and related disorders. Although there have been many studies conducted using autism mouse models, few have been carried out using postmortem human tissue from patients. Available animal models of autism include those generated through genetic modifications and those non-genetic models of the disease. Here, we review how dendrite and spine morphology and number is affected in autism and related neurodevelopmental diseases, both in human, and genetic and non-genetic animal models of autism. Overall, data obtained from human and animal models point to a generalized reduction in the size and number, as well as an alteration of the morphology of dendrites; and an increase in spine densities with immature morphology, indicating a general spine immaturity state in autism. Additional human studies on dendrite and spine number and morphology in postmortem tissue are needed to understand the properties of these structures in the cerebral cortex of patients with autism. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 419-437, 2017.

Spatiotemporal expression of osteopontin in the striatum of rats subjected to the mitochondrial toxin 3-nitropropionic acid correlates with microcalcification

Our aim was to elucidate whether osteopontin (OPN) is involved in the onset of mineralisation and progression of extracellular calcification in striatal lesions due to mitochondrial toxin 3-nitropropionic acid exposure. OPN expression had two different patterns when observed using light microscopy. It was either localised to the Golgi complex in brain macrophages or had a small granular pattern scattered in the affected striatum. OPN labelling tended to increase in number and size over a 2-week period following the lesion. Ultrastructural investigations revealed that OPN is initially localised to degenerating mitochondria within distal dendrites, which were then progressively surrounded by profuse OPN on days 7–14. Electron probe microanalysis of OPN-positive and calcium-fixated neurites indicated that OPN accumulates selectively on the surfaces of degenerating calcifying dendrites, possibly via interactions between OPN and calcium. In addition, 3-dimensional reconstruction of OPN-positive neurites revealed that they are in direct contact with larger OPN-negative degenerating dendrites rather than with fragmented cell debris. Our overall results indicate that OPN expression is likely to correlate with the spatiotemporal progression of calcification in the affected striatum, and raise the possibility that OPN may play an important role in the initiation and progression of microcalcification in response to brain insults.

High plasticity of axonal pathology in Alzheimer's disease mouse models

Axonal dystrophies (AxDs) are swollen and tortuous neuronal processes that are associated with extracellular depositions of amyloid β (Aβ) and have been observed to contribute to synaptic alterations occurring in Alzheimer's disease. Understanding the temporal course of this axonal pathology is of high relevance to comprehend the progression of the disease over time. We performed a long-term in vivo study (up to 210 days of two-photon imaging) with two transgenic mouse models (dE9xGFP-M and APP-PS1xGFP-M). Interestingly, AxDs were formed only in a quarter of GFP-expressing axons near Aβ-plaques, which indicates a selective vulnerability. AxDs, especially those reaching larger sizes, had long lifetimes and appeared as highly plastic structures with large variations in size and shape and axonal sprouting over time. In the case of the APP-PS1 mouse only, the formation of new long axonal segments in dystrophic axons (re-growth phenomenon) was observed. Moreover, new AxDs could appear at the same point of the axon where a previous AxD had been located before disappearance (re-formation phenomenon). In addition, we observed that most AxDs were formed and developed during the imaging period, and numerous AxDs had already disappeared by the end of this time. This work is the first in vivo study analyzing quantitatively the high plasticity of the axonal pathology around Aβ plaques. We hypothesized that a therapeutically early prevention of Aβ plaque formation or their growth might halt disease progression and promote functional axon regeneration and the recovery of neural circuits.

Marked changes in dendritic structure and spine density precede significant neuronal death in vulnerable cortical pyramidal neuron populations in the SOD1(G93A) mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is characterised by the death of upper (corticospinal) and lower motor neurons (MNs) with progressive muscle weakness. This incurable disease is clinically heterogeneous and its aetiology remains unknown. Increased excitability of corticospinal MNs has been observed prior to symptoms in human and rodent studies. Increased excitability has been correlated with structural changes in neuronal dendritic arbors and spines for decades. Here, using a modified Golgi-Cox staining method, we have made the first longitudinal study examining the dendrites of pyramidal neurons from the motor cortex, medial pre-frontal cortex, somatosensory cortex and entorhinal cortex of hSOD1^G93A (SOD1) mice compared to wild-type (WT) littermate controls at postnatal (P) days 8–15, 28–35, 65–75 and 120. Progressive decreases in dendritic length and spine density commencing at pre-symptomatic ages (P8-15 or P28-35) were observed in layer V pyramidal neurons within the motor cortex and medial pre-frontal cortex of SOD1 mice compared to WT mice. Spine loss without concurrent dendritic pathology was present in the pyramidal neurons of the somatosensory cortex from disease-onset (P65-75). Our results from the SOD1 model suggest that dendritic and dendritic spine changes foreshadow and underpin the neuromotor phenotypes present in ALS and may contribute to the varied cognitive, executive function and extra-motor symptoms commonly seen in ALS patients. Determining if these phenomena are compensatory or maladaptive may help explain differential susceptibility of neurons to degeneration in ALS.

Spatiotemporal Progression of Microcalcification in the Hippocampal CA1 Region following Transient Forebrain Ischemia in Rats: An Ultrastructural Study

Calcification in areas of neuronal degeneration is a common finding in several neuropathological disorders including ischemic insults. Here, we performed a detailed examination of the onset and spatiotemporal profile of calcification in the CA1 region of the hippocampus, where neuronal death has been observed after transient forebrain ischemia. Histopathological examinations showed very little alizarin red staining in the CA1 pyramidal cell layer until day 28 after reperfusion, while prominent alizarin red staining was detected in CA1 dendritic subfields, particularly in the stratum radiatum, by 14 days after reperfusion. Electron microscopy using the osmium/potassium dichromate method and electron probe microanalysis revealed selective calcium deposits within the mitochondria of degenerating dendrites at as early as 7 days after reperfusion, with subsequent complete mineralization occurring throughout the dendrites, which then coalesced to form larger mineral conglomerates with the adjacent calcifying neurites by 14 days after reperfusion. Large calcifying deposits were frequently observed at 28 days after reperfusion, when they were closely associated with or completely engulfed by astrocytes. In contrast, no prominent calcification was observed in the somata of CA1 pyramidal neurons showing the characteristic features of necrotic cell death after ischemia, although what appeared to be calcified mitochondria were noted in some degenerated neurons that became dark and condensed. Thus, our data indicate that intrahippocampal calcification after ischemic insults initially occurs within the mitochondria of degenerating dendrites, which leads to the extensive calcification that is associated with ischemic injuries. These findings suggest that in degenerating neurons, the calcified mitochondria in the dendrites, rather than in the somata, may serve as the nidus for further calcium precipitation in the ischemic hippocampus.

A Novel Form of Compensation in the Tg2576 Amyloid Mouse Model of Alzheimer's Disease

One century after its first description, pathology of Alzheimer’s disease (AD) is still poorly understood. Amyloid-related dendritic atrophy and membrane alterations of susceptible brain neurons in AD, and in animal models of AD are widely recognized. However, little effort has been made to study the potential effects of combined morphological and membrane alterations on signal transfer and synaptic integration in neurons that build up affected neural networks in AD. In this study spatial reconstructions and electrophysiological measurements of layer II/III pyramidal neurons of the somatosensory cortex from wild-type (WT) and transgenic (TG) human amyloid precursor protein (hAPP) overexpressing Tg2576 mice were used to build faithful segmental cable models of these neurons. Local synaptic activities were simulated in various points of the dendritic arbors and properties of subthreshold dendritic impulse propagation and predictors of synaptic input pattern recognition ability were quantified and compared in modeled WT and TG neurons. Despite the widespread dendritic degeneration and membrane alterations in mutant mouse neurons, surprisingly little, or no change was detected in steady-state and 50 Hz sinusoidal voltage transfers, current transfers, and local and propagation delays of PSPs traveling along dendrites of TG neurons. Synaptic input pattern recognition ability was also predicted to be unaltered in TG neurons in two different soma-dendritic membrane models investigated. Our simulations predict the way how subthreshold dendritic signaling and pattern recognition are preserved in TG neurons: amyloid-related membrane alterations compensate for the pathological effects that dendritic atrophy has on subthreshold dendritic signal transfer and integration in layer II/III somatosensory neurons of this hAPP mouse model for AD. Since neither propagation of single PSPs nor integration of multiple PSPs (pattern recognition) changes in TG neurons, we conclude that AD-related neuronal hyperexcitability cannot be accounted for by altered subthreshold dendritic signaling in these neurons but hyperexcitability is related to changes in active membrane properties and network connectivity.

PyramidalExplorer: A New Interactive Tool to Explore Morpho-Functional Relations of Human Pyramidal Neurons

This work presents PyramidalExplorer, a new tool to interactively explore and reveal the detailed organization of the microanatomy of pyramidal neurons with functionally related models. It consists of a set of functionalities that allow possible regional differences in the pyramidal cell architecture to be interactively discovered by combining quantitative morphological information about the structure of the cell with implemented functional models. The key contribution of this tool is the morpho-functional oriented design that allows the user to navigate within the 3D dataset, filter and perform Content-Based Retrieval operations. As a case study, we present a human pyramidal neuron with over 9000 dendritic spines in its apical and basal dendritic trees. Using PyramidalExplorer, we were able to find unexpected differential morphological attributes of dendritic spines in particular compartments of the neuron, revealing new aspects of the morpho-functional organization of the pyramidal neuron.

Image Informatics Strategies for Deciphering Neuronal Network Connectivity

Brain function relies on an intricate network of highly dynamic neuronal connections that rewires dramatically under the impulse of various external cues and pathological conditions. Amongst the neuronal structures that show morphological plasticity are neurites, synapses, dendritic spines and even nuclei. This structural remodelling is directly connected with functional changes such as intercellular communication and the associated calcium bursting behaviour. In vitro cultured neuronal networks are valuable models for studying these morpho-functional changes. Owing to the automation and standardization of both image acquisition and image analysis, it has become possible to extract statistically relevant readouts from such networks. Here, we focus on the current state-of-the-art in image informatics that enables quantitative microscopic interrogation of neuronal networks. We describe the major correlates of neuronal connectivity and present workflows for analysing them. Finally, we provide an outlook on the challenges that remain to be addressed, and discuss how imaging algorithms can be extended beyond in vitro imaging studies.

Comparative Histological Study on the Therapeutic Effect of Green Tea and Stem Cells in Alzheimer's Disease Complicating Experimentally Induced Diabetes

BACKGROUND AND OBJECTIVES

Alzheimer's disease (AD) is a devastating neurodegenerative disorder. Increasing evidence implicates diabetes mellitus (DM) as a risk factor for AD. Green tea (GT) has several beneficial effects attributed to its anti-oxidant phenolic compounds. Adipose tissue is a rich source of adipose-derived mesenchymal stem cells (ADSCs). This study was designed to evaluate and compare the possible therapeutic effect of green tea extract (GTE) and ADSCs on AD complicating induced DM in male rat.

METHODS

31 adult male albino rats were divided into 5 groups. Group I (Control), Group II received GTE, 50 mg/kg daily orally for 4 weeks, Group III received a single intraperitoneal injection of Streptozotocin (STZ), 50 mg/kg, Group IV: received STZ followed by GTE and Group V: received STZ followed by human ADSCs (hADSCs) intravenously.

RESULTS

Multiple acidophilic masses, deformed neurons, Congo red +ve masses and Caspase 3 +ve neurons were seen in group III, became few in group IV and occasional in group V. Multiple Prussian blue +ve cells were detected in group V. Some CD44 +ve cells were noticed in group III, became multiple in groups IV and V. The mean area of neurons exhibiting acidophilic cytoplasm, mean area of amyloid plaques and mean area % of Caspase 3 +ve cells indicated a significant increase in group III. The mean area % of CD44 +ve cells recorded a significant increase in group IV.

CONCLUSIONS

hADSCs exerted a more marked therapeutic effect on the neurodegenerative changes complicating DM and corresponding to AD.

Uncoupling phototoxicity-elicited neural dysmorphology and death by insidious function and selective impairment of Ran-binding protein 2 (Ranbp2)

Morphological disintegration of neurons is coupled invariably to neural death. In particular, disruption of outer segments of photoreceptor neurons triggers photoreceptor death regardless of the pathological stressors. We show that Ranbp2(-/-)::Tg-Ranbp2(CLDm-HA) mice with mutations in SUMO-binding motif (SBM) of cyclophilin-like domain (CLD) of Ran-binding protein 2 (Ranbp2) expressed in a null Ranbp2 background lack untoward effects in photoreceptors in the absence of light-stress. However, compared to wild type photoreceptors, light-stress elicits profound disintegration of outer segments of Ranbp2(-/-)::Tg-Ranbp2(CLDm-HA) with paradoxical age-dependent resistance of photoreceptors to death and genotype-independent activation of caspases. Ranbp2(-/-)::Tg-Ranbp2(CLDm-HA) exhibit photoreceptor death-independent changes in ubiquitin-proteasome system (UPS), but death-dependent increase of ubiquitin carrier protein 9(ubc9) levels. Hence, insidious functional impairment of SBM of Ranbp2's CLD promotes neuroprotection and uncoupling of photoreceptor degeneration and death against phototoxicity.

The role of ryanodine receptor type 3 in a mouse model of Alzheimer disease

Dysregulated endoplasmic reticulum (ER) calcium (Ca²⁺) signaling is reported to play an important role in Alzheimer disease (AD) pathogenesis. The role of ER Ca²⁺ release channels, the ryanodine receptors (RyanRs), has been extensively studied in AD models and RyanR expression and activity are upregulated in the brains of various familial AD (FAD) models. The objective of this study was to utilize a genetic approach to evaluate the importance of RyanR type 3 (RyanR3) in the context of AD pathology.

Motor cortex layer V pyramidal neurons exhibit dendritic regression, spine loss, and increased synaptic excitation in the presymptomatic hSOD1(G93A) mouse model of amyotrophic lateral sclerosis

Motor cortex layer V pyramidal neurons (LVPNs) regulate voluntary control of motor output and selectively degenerate (along with lower motor neurons) in amyotrophic lateral sclerosis. Using dye-filling and whole-cell patch clamping in brain slices, together with high-resolution spinning disk confocal z-stack mosaics, we characterized the earliest presymptomatic cortical LVPN morphologic and electrophysiological perturbations in hSOD1(G93A) (SOD1) mice to date. Apical dendritic regression occurred from postnatal day (P) 28, dendritic spine loss from P21, and increased EPSC frequency from P21 in SOD1 LVPNs. These findings demonstrate extensive early changes in motor cortex of the SOD1 mouse model, which thus recapitulates clinically relevant cortical pathophysiology more faithfully than previously thought.

Diversity of glutamatergic synaptic strength in lateral prefrontal versus primary visual cortices in the rhesus monkey

Understanding commonalities and differences in glutamatergic synaptic signaling is essential for understanding cortical functional diversity, especially in the highly complex primate brain. Previously, we have shown that spontaneous EPSCs differed markedly in layer 3 pyramidal neurons of two specialized cortical areas in the rhesus monkey, the high-order lateral prefrontal cortex (LPFC) and the primary visual cortex (V1). Here, we used patch-clamp recordings and confocal and electron microscopy to determine whether these distinct synaptic responses are due to differences in firing rates of presynaptic neurons and/or in the features of presynaptic or postsynaptic entities. As with spontaneous EPSCs, TTX-insensitive (action potential-independent) miniature EPSCs exhibited significantly higher frequency, greater amplitude, and slower kinetics in LPFC compared with V1 neurons. Consistent with these physiological differences, LPFC neurons possessed higher densities of spines, and the mean width of large spines was greater compared with those on V1 neurons. Axospinous synapses in layers 2-3 of LPFC had larger postsynaptic density surface areas and a higher proportion of large perforated synapses compared with V1. Axonal boutons in LPFC were also larger in volume and contained ∼ 1.6× more vesicles than did those in V1. Further, LPFC had a higher density of AMPA GluR2 receptor labeling than V1. The properties of spines and synaptic currents of individual layer 3 pyramidal neurons measured here were significantly correlated, consistent with the idea that significantly more frequent and larger synaptic currents are likely due to more numerous, larger, and more powerful synapses in LPFC compared with V1.

Selective dendritic susceptibility to bioenergetic, excitotoxic and redox perturbations in cortical neurons

Neurodegenerative and neurological disorders are often characterised by pathological changes to dendrites, in advance of neuronal death. Oxidative stress, energy deficits and excitotoxicity are implicated in many such disorders, suggesting a potential vulnerability of dendrites to these situations. Here we have studied dendritic vs. somatic responses of primary cortical neurons to these types of challenges in real-time.

Using a genetically encoded indicator of intracellular redox potential (Grx1-roGFP2) we found that, compared to the soma, dendritic regions exhibited more dramatic fluctuations in redox potential in response to sub-lethal ROS exposure, and existed in a basally more oxidised state. We also studied the responses of dendritic and somatic regions to excitotoxic NMDA receptor activity. Both dendritic and somatic regions experienced similar increases in cytoplasmic Ca²⁺. Interestingly, while mitochondrial Ca²⁺ uptake and initial mitochondrial depolarisation were similar in both regions, secondary delayed mitochondrial depolarisation was far weaker in dendrites, potentially as a result of less NADH depletion. Despite this, ATP levels were found to fall faster in dendritic regions. Finally we studied the responses of dendritic and somatic regions to energetically demanding action potential burst activity. Burst activity triggered PDH dephosphorylation, increases in oxygen consumption and cellular NADH:NAD ratio. Compared to somatic regions, dendritic regions exhibited a smaller degree of mitochondrial Ca²⁺ uptake, lower fold-induction of NADH and larger reduction in ATP levels. Collectively, these data reveal that dendritic regions of primary neurons are vulnerable to greater energetic and redox fluctuations than the cell body, which may contribute to disease-associated dendritic damage. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

•

Dendrites exhibit a greater shift in redox potential than the soma, following an oxidative insult.

•

Dendritic mitochondria depolarise less than somatic ones during excitotoxicity.

•

Nevertheless ATP falls faster in dendritic regions during excitotoxicity.

•

Energetically demanding AP bursting induces adaptive metabolic responses.

•

These responses are weaker in dendrites, and ATP levels are suppressed more strongly.

Early fear memory defects are associated with altered synaptic plasticity and molecular architecture in the TgCRND8 Alzheimer's disease mouse model

Alzheimer's disease (AD) is a complex and slowly progressing dementing disorder that results in neuronal and synaptic loss, deposition in brain of aberrantly folded proteins, and impairment of spatial and episodic memory. Most studies of mouse models of AD have employed analyses of cognitive status and assessment of amyloid burden, gliosis, and molecular pathology during disease progression. Here we sought to understand the behavioral, cellular, ultrastructural, and molecular changes that occur at a pathological stage equivalent to the early stages of human AD. We studied the TgCRND8 mouse, a model of aggressive AD amyloidosis, at an early stage of plaque pathology (3 months of age) in comparison to their wildtype littermates and assessed changes in cognition, neuron and spine structure, and expression of synaptic glutamate receptor proteins. We found that, at this age, TgCRND8 mice display substantial plaque deposition in the neocortex and hippocampus and impairment on cued and contextual memory tasks. Of particular interest, we also observed a significant decrease in the number of neurons in the hippocampus. Furthermore, analysis of CA1 neurons revealed significant changes in apical and basal dendritic spine types, as well as altered expression of GluN1 and GluA2 receptors. This change in molecular architecture within the hippocampus may reflect a rising representation of inherently less stable thin spine populations, which can cause cognitive decline. These changes, taken together with toxic insults from amyloid-β protein, may underlie the observed neuronal loss.

Altered synaptic structure in the hippocampus in a mouse model of Alzheimer's disease with soluble amyloid-β oligomers and no plaque pathology

Background

Mounting evidence suggests that soluble oligomers of amyloid-β (oAβ) represent the pertinent synaptotoxic form of Aβ in sporadic Alzheimer’s disease (AD); however, the mechanistic links between oAβ and synaptic degeneration remain elusive. Most in vivo experiments to date have been limited to examining the toxicity of oAβ in mouse models that also possess insoluble fibrillar Aβ (fAβ), and data generated from these models can lead to ambiguous interpretations. Our goal in the present study was to examine the effects of soluble oAβ on neuronal and synaptic structure in the amyloid precursor protein (APP) E693Q (“Dutch”) mouse model of AD, which develops intraneuronal accumulation of soluble oAβ with no detectable plaques in AD-relevant brain regions. We performed quantitative analyses of neuronal pathology, including dendrite morphology, spine density, and synapse ultrastructure in individual hippocampal CA1 neurons.

Results

When assessing neuronal morphology and complexity we observed significant alterations in apical but not in basal dendritic arbor length in Dutch mice compared to wild type. Moreover, Dutch mice exhibited a significant decrease in dendritic arborization with a decrease in dendritic length and number of intersections at 120 μm and 150 μm from the soma, respectively. We next examined synaptic parameters and found that while there were no differences in overall synaptic structure, Dutch mice displayed a significant reduction in the post-synaptic density (PSD) length of synapses on mushroom spines, in comparison to wild type littermates.

Conclusion

The structural alterations to individual neurons in Dutch mice along with the changes in larger dendritic spines support the Aβ oligomer hypothesis, which postulates that the early cognitive impairments that occur in AD are attributed to the accumulation of soluble oAβ first affecting at the synaptic level with subsequent structural disturbances and cellular degeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/1750-1326-9-41) contains supplementary material, which is available to authorized users.