Dendritic Loss Research Articles

Neurodegeneration, Mitochondria, and Antibiotics.

Neurodegenerative diseases are characterized by the progressive loss of neurons, synapses, dendrites, and myelin in the central and/or peripheral nervous system. Actual therapeutic options for patients are scarce and merely palliative. Although they affect millions of patients worldwide, the molecular mechanisms underlying these conditions remain unclear. Mitochondrial dysfunction is generally found in neurodegenerative diseases and is believed to be involved in the pathomechanisms of these disorders. Therefore, therapies aiming to improve mitochondrial function are promising approaches for neurodegeneration. Although mitochondrial-targeted treatments are limited, new research findings have unraveled the therapeutic potential of several groups of antibiotics. These drugs possess pleiotropic effects beyond their anti-microbial activity, such as anti-inflammatory or mitochondrial enhancer function. In this review, we will discuss the controversial use of antibiotics as potential therapies in neurodegenerative diseases.

Blocking osteopontin expression attenuates neuroinflammation and mitigates LPS-induced depressive-like behavior in mice

IntroductionNeuroinflammation plays an important role in the development of major depressive disorder (MDD). Osteopontin (OPN) is one of the key molecules involved in neuroinflammation. We demonstrate here for the first time a key role of OPN in lipopolysaccharide (LPS)-induced depressive-like behavioral syndrome. MethodsSystemic administration of LPS (5 mg/kg) mimics distinct depressive-like behavior, which could significantly upregulate OPN expression in microglia/macrophage in the hippocampus. The neurobehavioral assessments, quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR), Western blot, immunofluorescent staining, flow cytometry cell staining and Golgi staining were performed. ResultsSimilar to fluoxetine treatment (the positive control), OPN knockdown with shRNA lentivirus markedly reversed LPS-induced depressive-like behavior. Moreover, knockdown of OPN suppressed LPS-induced proinflammatory cytokine expression, microglial activation, dendritic spines loss, as well as unregulated PSD-95 and BDNF in the hippocampus. ConclusionWe demonstrated that targeting OPN expression in microglia/macrophage might help to rescue LPS-induced depressive-like behavior. The underlying mechanism may relate to the modulation of neuroinflammation, BDNF signaling and synaptic structural complexity.

Depressive-like Behavior Is Accompanied by Prefrontal Cortical Innate Immune Fatigue and Dendritic Spine Losses after HIV-1 Tat and Morphine Exposure.

Opioid use disorder (OUD) and HIV are comorbid epidemics that can increase depression. HIV and the viral protein Tat can directly induce neuronal injury within reward and emotionality brain circuitry, including the prefrontal cortex (PFC). Such damage involves both excitotoxic mechanisms and more indirect pathways through neuroinflammation, both of which can be worsened by opioid co-exposure. To assess whether excitotoxicity and/or neuroinflammation might drive depressive behaviors in persons infected with HIV (PWH) and those who use opioids, male mice were exposed to HIV-1 Tat for eight weeks, given escalating doses of morphine during the last two weeks, and assessed for depressive-like behavior. Tat expression decreased sucrose consumption and adaptability, whereas morphine administration increased chow consumption and exacerbated Tat-induced decreases in nesting and burrowing-activities associated with well-being. Across all treatment groups, depressive-like behavior correlated with increased proinflammatory cytokines in the PFC. Nevertheless, supporting the theory that innate immune responses adapt to chronic Tat exposure, most proinflammatory cytokines were unaffected by Tat or morphine. Further, Tat increased PFC levels of the anti-inflammatory cytokine IL-10, which were exacerbated by morphine administration. Tat, but not morphine, decreased dendritic spine density on layer V pyramidal neurons in the anterior cingulate. Together, our findings suggest that HIV-1 Tat and morphine differentially induce depressive-like behaviors associated with increased neuroinflammation, synaptic losses, and immune fatigue within the PFC.

Vanadium improves memory and spatial learning and protects the pyramidal cells of the hippocampus in juvenile hydrocephalic mice.

Hydrocephalus is a neurological condition known to cause learning and memory disabilities due to its damaging effect on the hippocampal neurons, especially pyramidal neurons. Vanadium at low doses has been observed to improve learning and memory abilities in neurological disorders but it is uncertain whether such protection will be provided in hydrocephalus. We investigated the morphology of hippocampal pyramidal neurons and neurobehavior in vanadium-treated and control juvenile hydrocephalic mice. Hydrocephalus was induced by intra-cisternal injection of sterile-kaolin into juvenile mice which were then allocated into 4 groups of 10 pups each, with one group serving as an untreated hydrocephalic control while others were treated with 0.15, 0.3 and 3 mg/kg i.p of vanadium compound respectively, starting 7 days post-induction for 28 days. Non-hydrocephalic sham controls (n = 10) were sham operated without any treatment. Mice were weighed before dosing and sacrifice. Y-maze, Morris Water Maze and Novel Object Recognition tests were carried out before the sacrifice, the brains harvested, and processed for Cresyl Violet and immunohistochemistry for neurons (NeuN) and astrocytes (GFAP). The pyramidal neurons of the CA1 and CA3 regions of the hippocampus were assessed qualitatively and quantitatively. Data were analyzed using GraphPad prism 8. Escape latencies of vanadium-treated groups were significantly shorter (45.30 ± 26.30 s, 46.50 ± 26.35 s, 42.99 ± 18.44 s) than untreated group (62.06 ± 24.02 s) suggesting improvements in learning abilities. Time spent in the correct quadrant was significantly shorter in the untreated group (21.19 ± 4.15 s) compared to control (34.15 ± 9.44 s) and 3 mg/kg vanadium-treated group (34.35 ± 9.74 s). Recognition index and mean % alternation were lowest in untreated group (p = 0.0431, p=0.0158) suggesting memory impairments, with insignificant improvements in vanadium-treated groups. NeuN immuno-stained CA1 revealed loss of apical dendrites of the pyramidal cells in untreated hydrocephalus group relative to control and a gradual reversal attempt in the vanadium-treated groups. Astrocytic activation (GFAP stain) in the untreated hydrocephalus group were attenuated in the vanadium-treated groups under the GFAP stain. Pyknotic index in CA1 pyramidal layer of untreated (18.82 ± 2.59) and 0.15mg/kg vanadium-treated groups (18.14 ± 5.92) were significantly higher than control (11.11 ± 0.93; p = 0.0205, p = 0.0373) while there was no significant difference in CA3 pyknotic index across all groups. Our results suggest that vanadium has a dose-dependent protective effect on the pyramidal cells of the hippocampus and on memory and spatial learning functions in juvenile hydrocephalic mice.

Mitotherapy restores hippocampal mitochondrial function and cognitive impairment in aged male rats subjected to chronic mild stress.

This study aimed to determine the effects of mitotherapy on learning and memory and hippocampal kynurenine (Kyn) pathway, mitochondria function, and dendritic arborization and spines density in aged rats subjected to chronic mild stress. Twenty-eight male Wistar rats (22 months old( were randomly divided into Aged, Aged + Mit, Aged + Stress, and Aged + Stress + Mit groups. Aged rats in the stress groups were subjected to different stressors for 28 days. The Aged + Mit and Aged + stress + Mit groups were treated with intracerebroventricular injection (10µl) of fresh mitochondria harvested from the young rats' brains, and other groups received 10µl mitochondria storage buffer. Spatial and episodic-like memories were assessed via the Barnes maze and novel object recognition tests. Indoleamine 2,3-dioxygenase (IDO) expression and activity, Kyn, Tryptophan (TRY), ATP levels, and mitochondrial membrane potential (MMP) were measured in the hippocampus region. Golgi-Cox staining was also performed to assess the dendritic branching pattern and dendritic spines in the hippocampal CA1 subfield. The results showed that mitotherapy markedly improved both spatial and episodic memories in the Aged + Stress + Mit group compared to the Aged + Stress. Moreover, mitotherapy decreased IDO protein expression and activity and Kyn levels, while it increased ATP levels and improved MMP in the hippocampus of the Aged + Stress + Mit group. Besides, mitotherapy restored dendritic atrophy and loss of spine density in the hippocampal neurons of the stress-exposed aged rats. These findings provide evidence for the therapeutic effect of mitotherapy against stress-induced cognitive deterioration in aged rats by improving hippocampal mitochondrialfunction and modulation of the Kyn pathway.

Regional Differences of the Impact of Healthy Aging on Myeloarchitecture at 7T

AbstractBackgroundCortical gray matter (cGM) loss in healthy aging has been well documented by volumetric MRI. Less well known though is if this age‐related cGM loss is layer‐specific or diffuse. Benefiting from the higher resolution at 7T and the close relationship between cortical cyto‐ and myeloarchitecture (1) this project used a newly developed technique for the differentiation between heavily (layers IV‐VI) and sparsely (layers I‐III) myelinated cortical layers to investigate this question.MethodThe 7T MP2Rage images (TR/TE/TI1/TI2=5000/2.45/900/2750 ms, 0.7x0.7x0.7mm) of 45 healthy controls (age: 19‐75, f/m=23/22) from the ATAG data repository (http://doi.org/10.5061/dryad.fb41s) were used for this project and the following contrasts generated: 1. T1 weighted image (UNI). 2. T1 relaxation image (T1map). 3. Inv1/Inv2 ratio map (In1/In2 ratio). After skull‐stripping and intensity calibration a fourth contrast (UNI/T1map ratio) was calculated. The UNI was segmented in SPM and a binary cortical rim mask calculated. With these four contrasts as input K‐means clustering was used to identify 6 clusters within this mask: CSF cluster, CSF/cGM transition cluster, WM cluster, WM/cGM transition cluster, heavily myelinated cGM cluster (hcGM) and sparsely myelinated cGM cluster (scGM) (Figure 1). The hGM and scGM maps were warped into a common space with SPM’s DARTEL. SPM was used to compare hcGM and scGM differences of young adults (n=27, 19‐27 years) with that of older adults (n=18, 42‐75 years).ResultFigure 2 shows that hcGM loss was restricted to the mid‐posterior cingulate and parahippocampal gyrus. Age‐related scGM loss was more diffuse and affected mesial prefrontal, opercular cortex and superior temporal gyrus.ConclusionAge related cGM loss affects sparsely and heavily myelinated layers differently. The heavily myelinated posterior cingulate belongs to the late myelinating structures. The hcGM loss there is consistent with the “last in, first out” hypothesis. The scGM loss in the mesial prefrontal, opercular, superior temporal region affects sparsely myelinated layers I‐III that are known to have a high synaptic density (1) indicating that it is probably mostly driven by dendritic loss. Although preliminary, the data presented here indicate that this new technique might provide a better insight into the nature of GM loss in healthy and abnormal aging.1. Neuroimage 2019;197:716‐741

Novel insights into neuronal and vascular damage glaucoma

AbstractDespite decades of clinical and basic research, we still do not understand the factors that cause retinal ganglion cell death and loss of vision in glaucoma patients. This keynote lecture will provide insights into new mechanisms that lead to early neuronal and neurovascular dysregulation in glaucoma. Several pathological changes associated with retinal ganglion cell damage will be discussed including dendritic retraction and synapse loss, metabolic deficits, and loss of neurovascular coupling. The role of pericytes in retinal capillary function will be presented, including newly identified inter‐pericyte tunnelling nanotubes, and their impact on retinal ganglion cell viability. These new data will highlight therapeutic opportunities to alleviate key pathological processes and restore visual function in glaucoma and other optic neuropathies.

Acid Sphingomyelinase Inhibitor, Imipramine, Reduces Hippocampal Neuronal Death after Traumatic Brain Injury

Traumatic brain injury (TBI) broadly degrades the normal function of the brain after a bump, blow, or jolt to the head. TBI leads to the aggravation of pre-existing brain dysfunction and promotes neurotoxic cascades that involve processes such as oxidative stress, loss of dendritic arborization, and zinc accumulation. Acid sphingomyelinase (ASMase) is an enzyme that hydrolyzes sphingomyelin to ceramide in cells. Under normal conditions, ceramide plays an important role in various physiological functions, such as differentiation and apoptosis. However, under pathological conditions, excessive ceramide production is toxic and activates the neuronal-death pathway. Therefore, we hypothesized that the inhibition of ASMase activity by imipramine would reduce ceramide formation and thus prevent TBI-induced neuronal death. To test our hypothesis, an ASMase inhibitor, imipramine (10 mg/kg, i.p.), was administrated to rats immediately after TBI. Based on the results of this study, we confirmed that imipramine significantly reduced ceramide formation, dendritic loss, oxidative stress, and neuronal death in the TBI-imipramine group compared with the TBI-vehicle group. Additionally, we validated that imipramine prevented TBI-induced cognitive dysfunction and the modified neurological severity score. Consequently, we suggest that ASMase inhibition may be a promising therapeutic strategy to reduce hippocampal neuronal death after TBI.

NCMP-18. NEUROLOGICAL SEQUELAE IN THE ID8 OVARIAN CANCER MOUSE MODEL: P38/JNK MAPK INHIBITION AS A POTENTIAL THERAPEUTIC FOR CANCER-RELATED COGNITIVE IMPAIRMENTS AND CHEMOTHERAPY-INDUCED PERIPHERAL NEUROPATHY

Abstract OBJECTIVES Chemotherapy-related cognitive impairment (CRCI) and chemotherapy-induced peripheral neuropathy (CIPN) are neurological sequelae of platinum-based chemotherapy. To examine the contribution of cancer itself and additional neurological impairment with chemotherapy, we used the ID8 syngeneic ovarian cancer mouse model and assessed cognition and hyperalgesia +/- cisplatin treatment. We examined the effect of p38 and c-JUN N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) inhibition on cisplatin-induced neuronal damage. METHODS B6 female mice were injected with 107 ID8 cells or 0.9% saline, i.p. Mice received cisplatin (2.3 m¬¬¬g/kg/day, i.p.) or 0.9% saline (OvT+CIS, OvT+VEH, respectively) for 5d, followed by 5d of rest for two cycles. Cognition was assessed longitudinally at 69d by the open field test (OFT), novel object recognition (NOR) at 75d and 104d, and novel place recognition (NPR) at 106d post-ID8 implantation. Hyperalgesia was assessed at 113d. Primary mouse and rat hippocampal neurons were pre-treated with VX-745 or SP600125, followed by cisplatin, and neuronal morphology was assessed. RESULTS OvT+VEH mice had detectable abdominal tumors 90d post-implantation. At 75d, OvT+VEH and OvT+CIS had impairments in NOR, with discrimination ratios (DR)= 0.52, 0.51, respectively. OvT+VEH showed trending differences vs. OvT+CIS (DR=0.39, DR=0.62, p=0.079) on NOR on 104d, and impairments on NPR on 106d (DR=0.41, DR=0.63, p=0.03). Cisplatin decreased mechanical (p< 0.05) and cold hyperalgesia (p< 0.07, n.s.) in OvT+CIS vs. OvT+VEH. VX-745 and SP600125 pre-treatment in mouse and rat hippocampal neurons prevented cisplatin-induced dendritic branching and spine density loss (p< 0.05). DISCUSSION While cisplatin transiently increased anxiogenic behavior, cognitive impairments, and hyperalgesia in OvT+CIS, these deficits persisted longitudinally in OvT+VEH, suggesting ovarian cancer may evoke sensory and progressive neurocognitive deficits in the absence of chemotherapy. Future studies will address hyperalgesia and cognitive differences between healthy control and ovarian cancer mice +/- cisplatin, and whether VX-745 and SP600125 administration ameliorates CRCI/CIPN in this model.

Dendritic Branching of Retinal Ganglion Cells as a Biomarker of Glaucomatous Optic Neuropathy and Alzheimer’s Disease and a Target of Neuroprotective Therapy

Irreversible damage to the structure of axons and death of the retinal ganglion cell (RGC) soma in primary open-angle glaucoma (POAG) and Alzheimer’s disease (AD) develop against the background of the already existing clinical manifestation, which is preceded by a slow period of progressive loss of synapses and dendrites of the RGCs. Recent studies have shown that the integrity of the RGC’s dendritic branching can serve as both a target of neuroprotective therapy and a sensitive marker of retinal degeneration in AD and glaucoma. To develop methods of complex neuroprotective therapy, it is necessary to substantiate the targets and tactics of affecting the dendritic tree of the RGCs, the remodeling of which, according to modern concepts, can be closely and antagonistically related to the regeneration of the axon after its damage in trauma and neurodegenerative diseases. RGCs are highly capable of functional modification. Currently, it has been proven that the use of neuroprotective drugs and neurotrophins is promising for maintaining the adaptive plasticity of RGCs and restoring their synaptic contacts at the level of the retina and brain. Understanding the features of the adaptive plasticity of RGCs in AD and glaucoma will make it possible to use technologies to activate the internal potential of neuronal remodeling, including the modification of dendritic branching of RGCs and regeneration of their axons, in the preclinical stages of these diseases. Increasing knowledge about the sequence and mechanisms of early events in the retina’s inner plexiform layer will contribute to the development of targeted neuroprotective therapy and new technologies to detect early POAG, AD, and, possibly, other systemic and local neurodegenerative conditions.

High B-value diffusion tensor imaging for early detection of hippocampal microstructural alteration in a mouse model of multiple sclerosis

Several studies have highlighted the value of diffusion tensor imaging (DTI) with strong diffusion weighting to reveal white matter microstructural lesions, but data in gray matter (GM) remains scarce. Herein, the effects of b-values combined with different numbers of diffusion-encoding directions (NDIRs) on DTI metrics to capture the normal hippocampal microstructure and its early alterations were investigated in a mouse model of multiple sclerosis (experimental autoimmune encephalomyelitis [EAE]). Two initial DTI datasets (B2700-43Dir acquired with b = 2700 s.mm−2 and NDIR = 43; B1000-22Dir acquired with b = 1000 s.mm−2 and NDIR = 22) were collected from 18 normal and 18 EAE mice at 4.7 T. Three additional datasets (B2700-22Dir, B2700-12Dir and B1000-12Dir) were extracted from the initial datasets. In healthy mice, we found a significant influence of b-values and NDIR on all DTI metrics. Confronting unsupervised hippocampal layers classification to the true anatomical classification highlighted the remarkable discrimination of the molecular layer with B2700-43Dir compared with the other datasets. Only DTI from the B2700 datasets captured the dendritic loss occurring in the molecular layer of EAE mice. Our findings stress the needs for both high b-values and sufficient NDIR to achieve a GM DTI with more biologically meaningful correlations, though DTI-metrics should be interpreted with caution in these settings.

Egr2 contributes to age-dependent vulnerability to sevoflurane-induced cognitive deficits in mice.

Sevoflurane inhalation is prone to initiate cognitive deficits in infants. The early growth response-2 (Egr-2) gene is DNA-binding transcription factor, involving in cognitive function. In this study we explored the molecular mechanisms underlying the vulnerability to cognitive deficits after sevoflurane administration. Six-day-old (young) and 6-week-old (early adult) mice received anesthesia with 3% sevoflurane for 2 h daily for 3 days. We showed that multiple exposures of sevoflurane induced significant learning ability impairment in young but not early adult mice, assessed in Morris water maze test on postnatal days 65. The integrated differential expression analysis revealed distinct transcription responses of Egr family members in the hippocampus of the young and early adult mice after sevoflurane administration. Particularly, Egr2 was significantly upregulated after sevoflurane exposure only in young mice. Microinjection of Egr2 shRNA recombinant adeno-associated virus into the dentate gyrus alleviated sevoflurane-induced cognitive deficits, and abolished sevoflurane-induced dendritic spins loss and BDNF downregulation in young mice. On the contrary, microinjection of the Egr2 overexpression virus in the dentate gyrus aggravated learning ability impairment induced by sevoflurane in young mice but not early adult mice. Furthermore, we revealed that sevoflurane markedly upregulated the nuclear factors of activated T-cells NFATC1 and NFATC2 in young mice, which were involved in Egr2 regulation. In conclusion, Egr2 serves as a critical factor for age-dependent vulnerability to sevoflurane-induced cognitive deficits.

Dual role of low frequency magnetic field on neuroinflammation induced dendritic trimming and memory impairment on rat model of sporadic Alzheimer’s disease

Gliosis and dendritic loss is reported to be secondary to the amyloid beta (Aß) and hyperphosphorylated tau (hp‐tau) production in Alzheimer’s disease(AD) brain. STZ administration is reported to induce sporadic AD. Previous clinical or preclinical studies on effect of rTMS treatment in AD patients or APP23 mice showed cognitive improvement alone or as adjuvant therapy along‐with amelioration of the glial aggravation in the hippocampus. However, studies on the effect of magnetic field stimulation on the gliosis related dendritic trimming in animal models of sporadic AD is elusive. Therefore, in the present study we have looked in to the effect of extremely low frequency magnetic field stimulation (ELF‐MF; 17.96µT, 50Hz, 2hr/day) for one month post‐injection of STZ (bilateral, 3mg/kg). Total 45 animals were (ethical no. 937/IAEC/2016) randomly divided into five groups: Control, Sham, AD, Sham+MF and AD+MF. After assessing retention of spatial and avoidance memory using Morris water maze and passive avoidance step down test on 30th day, animals were sacrificed and tissues processed for oxidative stress and immunofluorescence, Golgi‐Cox staining. Behavioural analysis revealed spatial memory improvement with no effect on the avoidance memory loss in AD+MF group as compared to AD group. We also found significant decrease in superoxide dismutase, catalase, GSH and increase in malon‐di‐aldehyde (MDA) in AD group. ELF‐MF treatment only reduced MDA level in hippocampus and frontal cortex. GFAP, IBA‐1 and hp‐tau (ser356) positive cells were found to be reduced in AD+MF group, as compared to all groups except Control. Sholl analysis revealed partial improvement of reduction in the number of intersection, bifurcation and length in basal and apical dendrite in the AD group after ELF‐MF treatment in CA3 layer. These findings suggests dual role of ELF‐MF exposure on STZ model of AD showing improvement of spatial memory by reducing the gliosis induced dendritic loss. However, inability to manage oxidative stress due to STZ, which may lead to avoidance memory deficit even after exposure period of one month.

Regulatory Modulations and Dendritic Arborization in the Mouse Hippocampus Following Gulf War Toxicant Exposure

Gulf War illness (GWI) is a chronic multi‐symptom syndrome which affects approximately 30% of the nearly 700,000 Veterans who were deployed to the Persian Gulf from 1990 to 1991. These Veterans have reported experiencing a variety of symptoms including difficulties with learning and memory, depression and anxiety, and increased incidence of neurodegenerative diseases. Evidence suggests that combined exposure to both reversible and irreversible acetylcholinesterase (AChE) inhibitors is a likely risk factor. We modeled Gulf War exposure in male C57Bl/6J mice with three AChE inhibitors that have been implicated as causative agents for GWI: pyridostigmine bromide (PB), the anti‐sarin prophylactic; chlorpyrifos (CPF), an organophosphate insecticide; and N,N‐diethyl‐m‐toluamide (DEET), a common insect repellent. Previously, we reported acute hippocampal gene expression changes following 10 d of toxicant exposure, including significant downregulation of several neuronal immediate early genes (IEGs) such as Arc, Egr1, and Nr4a1, as well as hippocampal‐dependent memory impairment in a Y‐maze task. Arc is predominantly expressed in cortical and hippocampal neurons and is critical for long‐term potentiation (LTP) and stabilization of synaptic plasticity. IEGs such as Arc and Egr1 have also been suggested to play a role in determining the risk of developing major depressive disorder, which is often comorbid with GWI. Here, we quantified Arc protein expression in granule cells of the dentate gyrus with IHC at 2‐4 h post‐exposure and examined the effects of treatment with a neuroprotective Nrf2 activator, tert‐butylhydroquinone (tBHQ), at 14 weeks post‐exposure. Additionally, mice were either placed in a novel enriched environment for 5 min or kept in their home cage to evaluate induced Arc expression in granule cells at 4 h post‐exposure. We also assessed dendritic arborization, important in connectivity, in granule cells by measuring dendritic lengths and spine densities with Golgi staining at 12 weeks post‐exposure. We hypothesized that toxicant‐exposed mice would have fewer Arc+ granule cells in the dentate gyrus and show reductions in both basal and induced Arc expression at 4 h post‐exposure. We also hypothesized that exposed mice would display dendritic arbor reduction and loss of spines in granule cells at the chronic timepoint, and that this effect would be reversed by antioxidant treatment. Preliminary results indicate that Arc protein expression is decreased in granule cells of exposed mice at the acute but not chronic timepoint. Dendritic arbor complexity was significantly reduced at the chronic phase in exposed mice but improved when treated with 1% tBHQ formulated food pellets. Our results suggest that IEGs may only be dysregulated immediately following exposure but could contribute to long‐term detrimental effects on hippocampal neuroplasticity, which may be improved with antioxidant treatment.

Neurite density and free water concentration are associated with synaptic density in the hippocampus as assessed through NODDI and [C‐11]UCB‐J PET

AbstractBackgroundNeurite Orientation Dispersion and Density Imaging (NODDI), derived through multi‐shell diffusion MRI, allows for the estimation of markers pertaining to multiple distinct components of neural tissue microstructure. Lower neurite density index (NDI), lower orientation dispersion index (ODI), and higher volume fraction of isotropic water (Viso), have all been significantly associated with biomarkers of AD pathology, as well as increase diagnostic model predictability. Recent studies employing [C‐11]UCB‐J PET to study synaptic vesicle glycoprotein 2A (SV2A) have found strong reductions in individuals with AD. Here we explore regional associations between cortical tissue microstructure (indexed by NODDI) and synaptic density (measured through [C‐11]UCB‐J PET). We hypothesize that increased NDI and ODI, and decreased Viso will associate with higher [C‐11]UCB‐J binding.MethodParticipants (N=24) included cognitively unimpaired and impaired older adults (Table 1) from the Wisconsin Alzheimer’s Disease Research Center who underwent [C‐11]UCB‐J PET and multi‐shell diffusion MRI. NODDI measures (including NDI, ODI, and Viso) were estimated and [11‐C]UCB‐J binding was quantified by calculating distribution volume ratios (DVR) using SRTM2 with the whole cerebellum as a reference region. Pearson correlations were conducted within Desikan‐Killiany‐derived regions of interest (ROI) including the hippocampus, entorhinal cortex, and parahippocampal gyrus, regions previously associated with altered NODDI metrics and [C‐11]UCB‐J binding in the AD population.ResultSignificant associations were found between [C‐11]UCB‐J DVR and both NDI and Viso in the hippocampus (NDI: r = 0.45, p=0.047; Viso: r = ‐0.46, p = 0.043). A trend was identified between [C‐11]UCB‐J DVR and ODI in the parahippocampus (r = 0.39, p = 0.098). No significant associations or trends were found in the entorhinal cortex.ConclusionThis preliminary analysis identified associations between increased synaptic density and metrics of cortical tissue microstructure. Both NDI and Viso were correlated with [C‐11]UCB‐J DVR in the hippocampus, indicating dendritic complexity and synaptic density are possibly linked. Future analyses will include more participants, determine whether hippocampal [C‐11]UCB‐J DVR in addition to NODDI may increase diagnostic model predictability, as well as estimate the temporal progression of synaptic and dendritic loss in AD.

Quantifying Levels of Dopaminergic Neuron Morphological Alteration and Degeneration in Caenorhabditis elegans.

Dopamine neuron loss is involved in the pathology of Parkinson's Disease (PD), a highly prevalent neurodegenerative disorder affecting over 10 million people worldwide. Since many details about PD etiology remain unknown, studies investigating genetic and environmental contributors to PD are needed to discover methods of prevention, management, and treatment. Proper characterization of dopaminergic neuronal loss may be relevant not only to PD research, but to other increasingly prevalent neurodegenerative disorders. There are established genetic and chemical models of dopaminergic neurodegeneration in the Caenorhabditis elegans model system, with easy visualization of neurobiology supported by the nematodes' transparency and invariant neuronal architecture. In particular, hermaphroditic C. elegans' dopaminergic neuron morphological changes can be visualized using strains with fluorescent reporters driven by cell-specific promotors such as the dat-1 dopamine transporter gene, which is expressed exclusively in their eight dopaminergic neurons. With the capabilities of this model system and the appropriate technology, many laboratories have studied dopaminergic neurodegeneration. However, there is little consistency in the way the data is analyzed and much of the present literature uses binary scoring analyses that capture the presence of degeneration but not the full details of the progression of neuron loss. Here, we introduce a universal scoring system to assess morphological changes and degeneration in C. elegans' cephalic neuron dendrites. This seven-point scale allows for analysis across a full range of dendrite morphology, ranging from healthy neurons to complete dendrite loss, and considering morphological details including kinks, branching, blebs, and breaks. With this scoring system, researchers can quantify subtle age-related changes as well as more dramatic chemical-induced changes. Finally, we provide a practice set of images with commentary that can be used to train, calibrate, and assess the scoring consistency of researchers new to this method. This should improve within- and between- laboratory consistency, increasing rigor and reproducibility.

Quantifying Levels of Dopaminergic Neuron Morphological Alteration and Degeneration in <em>Caenorhabditis elegans</em>

Dopamine neuron loss is involved in the pathology of Parkinson's Disease (PD), a highly prevalent neurodegenerative disorder affecting over 10 million people worldwide. Since many details about PD etiology remain unknown, studies investigating genetic and environmental contributors to PD are needed to discover methods of prevention, management, and treatment. Proper characterization of dopaminergic neuronal loss may be relevant not only to PD research, but to other increasingly prevalent neurodegenerative disorders. There are established genetic and chemical models of dopaminergic neurodegeneration in the Caenorhabditis elegans model system, with easy visualization of neurobiology supported by the nematodes' transparency and invariant neuronal architecture. In particular, hermaphroditic C. elegans' dopaminergic neuron morphological changes can be visualized using strains with fluorescent reporters driven by cell-specific promotors such as the dat-1 dopamine transporter gene, which is expressed exclusively in their eight dopaminergic neurons. With the capabilities of this model system and the appropriate technology, many laboratories have studied dopaminergic neurodegeneration. However, there is little consistency in the way the data is analyzed and much of the present literature uses binary scoring analyses that capture the presence of degeneration but not the full details of the progression of neuron loss. Here, we introduce a universal scoring system to assess morphological changes and degeneration in C. elegans' cephalic neuron dendrites. This seven-point scale allows for analysis across a full range of dendrite morphology, ranging from healthy neurons to complete dendrite loss, and considering morphological details including kinks, branching, blebs, and breaks. With this scoring system, researchers can quantify subtle age-related changes as well as more dramatic chemical-induced changes. Finally, we provide a practice set of images with commentary that can be used to train, calibrate, and assess the scoring consistency of researchers new to this method. This should improve within- and between- laboratory consistency, increasing rigor and reproducibility.

Rab7 reduces α-synuclein toxicity in rats and primary neurons

During the pathogenesis of Parkinson's disease (PD), aggregation of alpha-synuclein (αSyn) induces a vicious cycle of cellular impairments that lead to neurodegeneration. Consequently, removing toxic αSyn aggregates constitutes a plausible strategy against PD. In this work, we tested whether stimulating the autolysosomal degradation of αSyn aggregates through the Ras-related in brain 7 (Rab7) pathway can reverse αSyn-induced cellular impairment and prevent neurodegeneration in vivo. The disease-related A53T mutant of αSyn was expressed in primary neurons and in dopaminergic neurons of the rat brain simultaneously with wild type (WT) Rab7 or the T22N mutant as negative control. The cellular integrity was quantified by morphological and biochemical analyses. In primary neurons, WT Rab7 rescued the αSyn-induced loss of neurons and neurites. Furthermore, Rab7 decreased the amount of reactive oxygen species and the amount of Triton X-100 insoluble αSyn. In rat brain, WT Rab7 reduced αSyn-induced loss of dopaminergic axon terminals in the striatum and the loss of dopaminergic dendrites in the substantia nigra pars reticulata. Further, WT Rab7 lowered αSyn pathology as quantified by phosphorylated αSyn staining. Finally, WT Rab7 attenuated αSyn-induced DNA damage in primary neurons and rat brain. In brief, Rab7 reduced αSyn-induced pathology, ameliorated αSyn-induced neuronal degeneration, oxidative stress and DNA damage. These findings indicate that Rab7 is able to disrupt the vicious cycle of cellular impairment, αSyn pathology and neurodegeneration present in PD. Stimulation of Rab7 and the autolysosomal degradation pathway could therefore constitute a beneficial strategy for PD.

Complement C3 mediates early hippocampal neurodegeneration and memory impairment in experimental multiple sclerosis

Memory impairment is one of the disabling manifestations of multiple sclerosis (MS) possibly present from the early stages of the disease and for which there is no specific treatment. Hippocampal synaptic dysfunction and dendritic loss, associated with microglial activation, can underlie memory deficits, yet the molecular mechanisms driving such hippocampal neurodegeneration need to be elucidated. In early-stage experimental autoimmune encephalomyelitis (EAE) female mice, we assessed the expression level of molecules involved in microglia-neuron interactions within the dentate gyrus and found overexpression of genes of the complement pathway. Compared to sham immunized mice, the central element of the complement cascade, C3, showed the strongest and 10-fold upregulation, while there was no increase of downstream factors such as the terminal component C5. The combination of in situ hybridization with immunofluorescence showed that C3 transcripts were essentially produced by activated microglia. Pharmacological inhibition of C3 activity, by daily administration of rosmarinic acid, was sufficient to prevent early dendritic loss, microglia-mediated phagocytosis of synapses in the dentate gyrus, and memory impairment in EAE mice, while morphological markers of microglial activation were still observed. In line, when EAE was induced in C3 deficient mice (C3KO), dendrites and spines of the dentate gyrus as well as memory abilities were preserved. Altogether, these data highlight the central role of microglial C3 in early hippocampal neurodegeneration and memory impairment in EAE and, therefore, pave the way toward new neuroprotective strategies in MS to prevent cognitive deficit using complement inhibitors.

Subthreshold repetitive transcranial magnetic stimulation drives structural synaptic plasticity in the young and aged motor cortex

BackgroundRepetitive transcranial magnetic stimulation (rTMS) is a non-invasive tool commonly used to drive neural plasticity in the young adult and aged brain. Recent data from mouse models have shown that even at subthreshold intensities (0.12 T), rTMS can drive neuronal and glial plasticity in the motor cortex. However, the physiological mechanisms underlying subthreshold rTMS induced plasticity and whether these are altered with normal ageing are unclear. ObjectiveTo assess the effect of subthreshold rTMS, using the intermittent theta burst stimulation (iTBS) protocol on structural synaptic plasticity in the mouse motor cortex of young and aged mice. MethodsLongitudinal in vivo 2-photon microscopy was used to measure changes to the structural plasticity of pyramidal neuron dendritic spines in the motor cortex following a single train of subthreshold rTMS (in young adult and aged animals) or the same rTMS train administered on 4 consecutive days (in young adult animals only). Data were analysed with Bayesian hierarchical generalized linear regression models and interpreted with the aid of Bayes Factors (BF). ResultsWe found strong evidence (BF > 10) that subthreshold rTMS altered the rate of dendritic spine losses and gains, dependent on the number of stimulation sessions and that a single session of subthreshold rTMS was effective in driving structural synaptic plasticity in both young adult and aged mice. ConclusionThese findings provide further evidence that rTMS drives synaptic plasticity in the brain and uncovers structural synaptic plasticity as a key mechanism of subthreshold rTMS induced plasticity.