Reduction In Dendritic Spine Density Research Articles

Increased gene dosage of RFWD2 causes autistic-like behaviors and aberrant synaptic formation and function in mice.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social interactions, communication deficits and repetitive behaviors. A study of autistic human subjects has identified RFWD2 as a susceptibility gene for autism, and autistic patients have 3 copies of the RFWD2 gene. The role of RFWD2 as an E3 ligase in neuronal functions, and its contribution to the pathophysiology of ASD, remain unknown. We generated RFWD2 knockin mice to model the human autistic condition of high gene dosage of RFWD2. We found that heterozygous knockin (Rfwd2+/-) male mice exhibited the core symptoms of autism. Rfwd2+/- male mice showed deficits in social interaction and communication, increased repetitive and anxiety-like behavior, and spatial memory deficits, whereas Rfwd2+/- female mice showed subtle deficits in social communication and spatial memory but were normal in anxiety-like, repetitive, and social behaviors. These autistic-like behaviors in males were accompanied by a reduction in dendritic spine density and abnormal synaptic function on layer II/III pyramidal neurons in the prelimbic area of the medial prefrontal cortex (mPFC), as well as decreased expression of synaptic proteins. Impaired social behaviors in Rfwd2+/- male mice were rescued by the expression of ETV5, one of the major substrates of RFWD2, in the mPFC. These findings indicate an important role of RFWD2 in the pathogenesis of autism.

Liraglutide Reduces Alcohol Consumption, Anxiety, Memory Impairment, and Synapse Loss in Alcohol Dependent Mice.

Glucagon-like peptide 1 (GLP-1) analogues have been commercialized for the management of type 2 diabetes. Recent studies have underscored GLP-1's role as a modulator of alcohol-related behavior. However, the role of the GLP-1 analogue liraglutide on alcohol-withdrawal responses have not been fully elucidated. Liraglutide binds to the G-protein-coupled receptor and activates an adenylyl cyclase and the associated classic growth factor signaling pathway, which acts growth factor-like and neuroprotective properties. The underlying neurobiological mechanisms of liraglutide on alcohol withdrawal remains unknown. This study endeavored to explore the effects of liraglutide on the emotion and memory ability of alcohol-withdrawal mice, and synaptic morphology in the medial prefrontal cortex (mPFC) and the hippocampus (HP), and thus affects the relapse-like drinking of alcohol-withdrawal mice. The alcohol-withdrawal group was reintroduced to a 20% v/v alcohol and water through the two-bottle choice for four consecutive days, a period referred to as alcohol re-drinking. Male C57BL/6J mice were exposed to a regimen of 20% alcohol and water for a duration of 6 weeks. This regimen established the two-bottle choice model of alcohol exposure. Learning capabilities, memory proficiency, and anxiety-like behavior were evaluated using the Morris water maze, open field, and elevated plus maze paradigms. Furthermore, synaptic morphology and the levels of synaptic transport-related proteins were assessed via Golgi staining and Western Blot analysis after a two-week alcohol deprivation period. Alcohol re-drinking of alcohol-withdrawal mice was also evaluated using a two-bottle choice paradigm. Our findings indicate that liraglutide can substantially decrease alcohol consumption and preference (p < 0.05) in the alcohol group and enhance learning and memory performance (p < 0.01), as well as alleviate anxiety-like behavior (p < 0.01) of alcohol-withdrawal mice. Alcohol consumption led to a reduction in dendritic spine density in the mPFC and HP, which was restored to normal levels by liraglutide (p < 0.001). Furthermore, liraglutide was found to augment the levels of synaptic transport-related proteins in mice subjected to alcohol withdrawal (p < 0.01). The study findings corroborate that liraglutide has the potential to mitigate alcohol consumption and ameliorate the memory impairments and anxiety induced by alcohol withdrawal. The therapeutic efficacy of liraglutide might be attributed to its role in counteracting synapse loss in the mPFC and HP regions and thus prevented relapse-like drinking in alcohol-withdrawal mice.

Engeletin alleviates depression-like phenotype by increasing synaptic plasticity via the BDNF-TrkB-mTORC1 signalling pathway.

Major depressive disorder (MDD) is a severe mental disorder associated with high rates of morbidity and mortality. Current first-line pharmacotherapies for MDD are based on enhancement of monoaminergic neurotransmission, but these antidepressants are still insufficient and produce significant side-effects. Consequently, the development of novel antidepressants and therapeutic targets is desired. Engeletin, a natural Smilax glabra rhizomilax derivative, is a compound with proven efficacy in treating ischemic stroke, yet its therapeutic effects and mechanisms for depression remain unexplored. The effects of engeletin were assessed in the forced swimming test (FST) and tail suspension test (TST) in mice. Engeletin was also investigated in the chronic restraint stress (CRS) mouse model of depression with fluoxetine (FLX) as the positive control. Changes in prefrontal cortex (PFC) spine density, synaptic plasticity-linked protein expressions and the brain-derived neurotrophic factor (BDNF)-tyrosine kinase B (TrkB)- mammalian target of rapamycin complex 1 (mTORC1) signalling pathway after chronic stress and engeletin treatment were then investigated. The TrkB and mTORC1 selective inhibitors, ANA-12 and rapamycin, respectively, were utilized to assess the engeletin's antidepressive mechanisms. Our data shows that engeletin exhibited antidepressant-like activity in the FST and TST in mice without affecting locomotor activity. Furthermore, it exhibited efficiency against the depression of CRS model. Moreover, it enhanced the BDNF-TrkB-mTORC1 pathway in the PFC during CRS and altered the reduction in dendritic spine density and levels of synaptic plasticity-linked protein induced by CRS. In conclusion, engeletin has antidepressant activity via activation of the BDNF-TrkB-mTORC1 signalling pathway and upregulation of PFC synaptic plasticity.

Morphological and transcriptomic analyses of stem cell-derived cortical neurons reveal mechanisms underlying synaptic dysfunction in schizophrenia

BackgroundPostmortem studies in schizophrenia consistently show reduced dendritic spines in the cerebral cortex but the mechanistic underpinnings of these deficits remain unknown. Recent genome-wide association studies and exome sequencing investigations implicate synaptic genes and processes in the disease biology of schizophrenia.MethodsWe generated human cortical pyramidal neurons by differentiating iPSCs of seven schizophrenia patients and seven healthy subjects, quantified dendritic spines and synapses in different cortical neuron subtypes, and carried out transcriptomic studies to identify differentially regulated genes and aberrant cellular processes in schizophrenia.ResultsCortical neurons expressing layer III marker CUX1, but not those expressing layer V marker CTIP2, showed significant reduction in dendritic spine density in schizophrenia, mirroring findings in postmortem studies. Transcriptomic experiments in iPSC-derived cortical neurons showed that differentially expressed genes in schizophrenia were enriched for genes implicated in schizophrenia in genome-wide association and exome sequencing studies. Moreover, most of the differentially expressed genes implicated in schizophrenia genetic studies had lower expression levels in schizophrenia cortical neurons. Network analysis of differentially expressed genes led to identification of NRXN3 as a hub gene, and follow-up experiments showed specific reduction of the NRXN3 204 isoform in schizophrenia neurons. Furthermore, overexpression of the NRXN3 204 isoform in schizophrenia neurons rescued the spine and synapse deficits in the cortical neurons while knockdown of NRXN3 204 in healthy neurons phenocopied spine and synapse deficits seen in schizophrenia cortical neurons. The antipsychotic clozapine increased expression of the NRXN3 204 isoform in schizophrenia cortical neurons and rescued the spine and synapse density deficits.ConclusionsTaken together, our findings in iPSC-derived cortical neurons recapitulate cell type-specific findings in postmortem studies in schizophrenia and have led to the identification of a specific isoform of NRXN3 that modulates synaptic deficits in schizophrenia neurons.

Long-term potentiation and spatial memory training stimulate the hippocampal expression of RyR2 calcium release channels.

Introduction: Neuronal Ca2+ signals generated through the activation of Ca2+-induced Ca2+ release in response to activity-generated Ca2+ influx play a significant role in hippocampal synaptic plasticity, spatial learning, and memory. We and others have previously reported that diverse stimulation protocols, or different memory-inducing procedures, enhance the expression of endoplasmic reticulum-resident Ca2+ release channels in rat primary hippocampal neuronal cells or hippocampal tissue. Methods and Results: Here, we report that induction of long-term potentiation (LTP) by Theta burst stimulation protocols of the CA3-CA1 hippocampal synapse increased the mRNA and protein levels of type-2 Ryanodine Receptor (RyR2) Ca2+ release channels in rat hippocampal slices. Suppression of RyR channel activity (1 h preincubation with 20 μM ryanodine) abolished both LTP induction and the enhanced expression of these channels; it also promoted an increase in the surface expression of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits GluR1 and GluR2 and caused a moderate but significant reduction of dendritic spine density. In addition, training rats in the Morris water maze induced memory consolidation, which lasted for several days after the end of the training period, accompanied by an increase in the mRNA levels and the protein content of the RyR2 channel isoform. Discussion: We confirm in this work that LTP induction by TBS protocols requires functional RyR channels. We propose that the increments in the protein content of RyR2 Ca2+ release channels, induced by LTP or spatial memory training, play a significant role in hippocampal synaptic plasticity and spatial memory consolidation.

17⍺-Estradiol Protects against HIV-1 Tat-Induced Endolysosome Dysfunction and Dendritic Impairments in Neurons.

HIV-1 Tat continues to play an important role in the development of HIV-associated neurocognitive disorders (HAND), which persist in 15-55% of people living with HIV even with virological control. In the brain, Tat is present on neurons, where Tat exerts direct neuronal damaging effects by, at least in part, disrupting endolysosome functions, a pathological feature present in HAND. In this study, we determined the protective effects of 17α-estradiol (17αE2), the predominant form of estrogen in the brain, against Tat-induced endolysosome dysfunction and dendritic impairment in primary cultured hippocampal neurons. We demonstrated that pre-treatment with 17αE2 protected against Tat-induced endolysosome dysfunction and reduction in dendritic spine density. Estrogen receptor alpha (ERα) knockdown impairs the ability of 17αE2 to protect against Tat-induced endolysosome dysfunction and reduction in dendritic spine density. Furthermore, over-expressing an ERα mutant that fails to localize on endolysosomes impairs 17αE2's protective effects against Tat-induced endolysosome dysfunction and reduction in dendritic spine density. Our findings demonstrate that 17αE2 protects against Tat-induced neuronal injury via a novel ERα-mediated and endolysosome-dependent pathway, and such a finding might lead to the development of novel adjunct therapeutics against HAND.

Cellular and molecular mechanisms of stress-induced memory impairment

Exposure to stressful conditions plays a critical role in brain processes, including neural plasticity, synaptic transmission, and cognitive functions. Since memory-related brain regions, the hippocampus (Hip), the amygdala, and the prefrontal cortex, express high glucocorticoid receptors (GRs), these areas are the potential targets of stress hormones. Stress affects memory encoding, consolidation, and retrieval, which may depend on many factors such as the type, duration, the intensity of the stressor or the brain region. Here, this review mainly focused on the mechanisms involved in stress-induced memory impairment. Acute/chronic stress induces structural and functional changes in neurons and glial cells. Dendritic arborization, reduction of dendritic spine density, and alteration in glutamatergic-mediated synaptic transmission via N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors are mechanisms that stress affect long-term memory formation. Exposure to acute or chronic stress could interplay with multiple neurotransmitter signaling, modulating the neuronal circuits involved in memory impairment or state-dependent learning. Stress hormones also modulate the expression of microRNAs in the specific brain regions responsible for stress-induced behaviors. Because of expressing GRs in astrocytes and microglial cells, stress could affect the morphology, structure, and functions of these glial cells in memory-related brain regions. Astrocytes play a crucial role in stress-induced aversive or fear memory formation. Over-activation of the microglial cells enhances the release of inflammatory cytokines, which results in neuronal injury. Stress has a prominent role in cognitive decline to induces memory problems, particularly in older adults. Due to the issue’s importance, here the provided overview attempted to address the question of how stress alters neuronal epigenetic regulators, synaptic transmissions, and glial activity in the brain.

Dendritic spine loss in epileptogenic Type II focal cortical dysplasia: Role of enhanced classical complement pathway activation.

Dendritic spines are the postsynaptic sites for most excitatory glutamatergic synapses. We previously demonstrated a severe spine loss and synaptic reorganization in human neocortices presenting Type II focal cortical dysplasia (FCD), a developmental malformation and frequent cause of drug-resistant focal epilepsy. We extend the findings, investigating the potential role of complement components C1q and C3 in synaptic pruning imbalance. Data from Type II FCD were compared with those obtained in focal epilepsies with different etiologies. Neocortical tissues were collected from 20 subjects, mainly adults with a mean age at surgery of 31 years, admitted to epilepsy surgery with a neuropathological diagnosis of: cryptogenic, temporal lobe epilepsy with hippocampal sclerosis, and Type IIa/b FCD. Dendritic spine density quantitation, evaluated in a previous paper using Golgi impregnation, was available in a subgroup. Immunohistochemistry, in situ hybridization, electron microscopy, and organotypic cultures were utilized to study complement/microglial activation patterns. FCD Type II samples presenting dendritic spine loss were characterized by an activation of the classical complement pathway and microglial reactivity. In the same samples, a close relationship between microglial cells and dendritic segments/synapses was found. These features were consistently observed in Type IIb FCD and in 1 of 3 Type IIa cases. In other patient groups and in perilesional areas outside the dysplasia, not presenting spine loss, these features were not observed. In vitro treatment with complement proteins of organotypic slices of cortical tissue with no sign of FCD induced a reduction in dendritic spine density. These data suggest that dysregulation of the complement system plays a role in microglia-mediated spine loss. This mechanism, known to be involved in the removal of redundant synapses during development, is likely reactivated in Type II FCD, particularly in Type IIb; local treatment with anticomplement drugs could in principle modify the course of disease in these patients.

Transcriptomic analysis in the striatum reveals the involvement of Nurr1 in the social behavior of prenatally valproic acid-exposed male mice

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that exhibits neurobehavioral deficits characterized by abnormalities in social interactions, deficits in communication as well as restricted interests, and repetitive behaviors. The basal ganglia is one of the brain regions implicated as dysfunctional in ASD. In particular, the defects in corticostriatal function have been reported to be involved in the pathogenesis of ASD. Surface deformation of the striatum in the brains of patients with ASD and their correlation with behavioral symptoms was reported in magnetic resonance imaging (MRI) studies. We demonstrated that prenatal valproic acid (VPA) exposure induced synaptic and molecular changes and decreased neuronal activity in the striatum. Using RNA sequencing (RNA-Seq), we analyzed transcriptome alterations in striatal tissues from 10-week-old prenatally VPA-exposed BALB/c male mice. Among the upregulated genes, Nurr1 was significantly upregulated in striatal tissues from prenatally VPA-exposed mice. Viral knockdown of Nurr1 by shRNA significantly rescued the reduction in dendritic spine density and the number of mature dendritic spines in the striatum and markedly improved social deficits in prenatally VPA-exposed mice. In addition, treatment with amodiaquine, which is a known ligand for Nurr1, mimicked the social deficits and synaptic abnormalities in saline-exposed mice as observed in prenatally VPA-exposed mice. Furthermore, PatDp+/− mice, a commonly used ASD genetic mouse model, also showed increased levels of Nurr1 in the striatum. Taken together, these results suggest that the increase in Nurr1 expression in the striatum is a mechanism related to the changes in synaptic deficits and behavioral phenotypes of the VPA-induced ASD mouse model.

Transient reduction in dendritic spine density in brain-specific profilin1 mutant mice is associated with behavioral deficits.

Actin filaments form the backbone of dendritic spines, the postsynaptic compartment of most excitatory synapses in the brain. Spine density changes affect brain function, and postsynaptic actin defects have been implicated in various neuropathies. It is mandatory to identify the actin regulators that control spine density. Based on previous studies, we hypothesized a role for the actin regulator profilin1 in spine formation. We report reduced hippocampal spine density in juvenile profilin1 mutant mice together with impairments in memory formation and reduced ultrasonic communication during active social behavior. Our results, therefore, underline a previously suggested function of profilin1 in controlling spine formation and behavior in juvenile mice.

Hippocampal Excitatory Synaptic Transmission and Plasticity Are Differentially Altered during Postnatal Development by Loss of the X-Linked Intellectual Disability Protein Oligophrenin-1.

Oligophrenin-1 (OPHN1) is a Rho-GTPase-activating protein (RhoGAP), whose mutations are associated with X-linked intellectual disability (XLID). OPHN1 is enriched at the synapse in both pre- and postsynaptic compartments, where it regulates the RhoA/ROCK/MLC2 signaling pathway, playing a critical role in cytoskeleton remodeling and vesicle recycling. Ophn1 knockout (KO) adult mice display some behavioral deficits in multiple tasks, reminiscent of some symptoms in the human pathology. We also previously reported a reduction in dendritic spine density in the adult hippocampus of KO mice. Yet the nature of the deficits occurring in these mice during postnatal development remains elusive. Here, we show that juvenile KO mice present normal basal synaptic transmission, but altered synaptic plasticity, with a selective impairment in long-term depression, but no change in long-term potentiation. This contrasts with the functional deficits that these mice display at the adult stage, as we found that both basal synaptic transmission and long-term potentiation are reduced at later stages, due to presynaptic alterations. In addition, the number of excitatory synapses in adult is increased, suggesting some unsuccessful compensation. Altogether, these results suggest that OPHN1 function at synapses is differentially affected during maturation of the brain, which provides some therapeutic opportunities for early intervention.

Distinct effects of interleukin-6 and interferon-γ on differentiating human cortical neurons

Translational evidence suggests that cytokines involved in maternal immune activation (MIA), such as interleukin-6 (IL-6) and interferon-γ (IFN-γ), can cross the placenta, injure fetal brain, and predispose to neuropsychiatric disorders. To elaborate developmental neuronal sequelae of MIA, we differentiated human pluripotent stem cells to cortical neurons over a two-month period, exposing them to IL-6 or IFN-γ. IL-6 impacted expression of genes regulating extracellular matrix, actin cytoskeleton and TGF-β signaling while IFN-γ impacted genes regulating antigen processing, major histocompatibility complex and endoplasmic reticulum biology. IL-6, but not IFN-γ, altered mitochondrial respiration while IFN-γ, but not IL-6, induced reduction in dendritic spine density. Pre-treatment with folic acid, which has known neuroprotective and anti-inflammatory properties, ameliorated IL-6 effects on mitochondrial respiration and IFN-γ effects on dendritic spine density. These findings suggest distinct mechanisms for how fetal IL-6 and IFN-γ exposure influence risk for neuropsychiatric disorders, and how folic acid can mitigate such risk.

Apoptosis inhibitor attenuates cardiac ischemia/reperfusion injury‐induced amyloid beta aggregation and dendritic spine loss in rats

Recently, several studies have reported the incidence of cognitive impairments in patients with acute myocardial infarction and heart failure. Mechanistically, dendritic spine loss in hippocampus, due to oxidative stress/inflammation induced apoptosis, is proposed as one of responsible mechanisms underlying cognitive impairments. However, the effects of z-vad, which is an apoptosis inhibitor, on brain pathologies following cardiac ischemia/reperfusion (I/R) injury have never been investigated. We hypothesized that z-vad alleviates brain damage in rats with cardiac I/R injury by reducing apoptosis, mitochondrial oxidative stress, and inflammation. Fifty-four male rats were subjected to either sham (n=6/group) or cardiac I/R operation (n=48). Rats in cardiac I/R group were divided into 4 groups (n=6-12/group) including 1) vehicle, 2) low-dose of z-vad (L-z-vad; 1.65 mg/kg), medium-dose of z-vad (M-z-vad; 3.3 mg/kg), and high-dose of z-vad (H-z-vad; 6.6 mg/kg). Treatments were intravenously injected to the rats at 15 min before ischemia. Then, rats were subjected to left anterior descending coronary artery ligation induced myocardial ischemia for 30 min, followed by 120 min of reperfusion. At the end of protocol, rats were sacrificed, and the brain was used to determine mitochondrial oxidative stress, inflammation, cell death pathways, blood brain barrier (BBB), Alzheimer's disease related proteins, and dendritic spine density. Cardiac I/R injury led to BBB breakdown, increased brain mitochondrial oxidative stress and apoptosis, as well as amyloid beta aggregation, tau hyperphosphorylation, and subsequent dendritic spine loss. Treatment with M-z-vad and H-z-vad reduced dendritic spine loss, tau hyperphosphorylation, and Bax/Bcl2 ratio. Additionally, the reduction of dendritic spine density was lowered in M-z-vad than H-z-vad group, since only M-z-vad attenuated mitochondrial oxidative stress, inflammation, amyloid beta aggregation, and cleaved-caspase 3 protein expression. For L-z-vad, we found that this treatment regimen showed no benefit on brain pathologies following cardiac I/R injury, implying that low dose of z-vad may be insufficient to exert neuroprotection (Figure 1). Moreover, all doses of z-vad did not decrease BBB breakdown after cardiac I/R injury. Pretreatment with medium dose of apoptosis inhibitor prevented amyloid beta aggregation and dendritic spine loss against cardiac I/R injury, possibly through reductions of mitochondrial oxidative stress, inflammation, and apoptosis.

High‐fat diet reduced dendritic spine density, but it did not affect cognitive function in spontaneous diabetic torii rats

Diabetes is a known risk factor for dementia, several factors are involved in the pathogenesis of diabetes including genetic predisposition, and high calorie diet consumption. We previously reported that long-term high-fat diet (HFD) consumption led to prediabetes, which associated with cognitive impairments. However, the effects of long-term HFD consumption on metabolic and brain function in genetically type 2 diabetes (T2DM) model have not been investigated. Therefore, we hypothesized that long-term HFD consumption aggravates metabolic and cognitive impairments in T2DM rats. Sixteen Spontaneous Diabetic Torii (SDT) rats, which is a genetically engineered T2DM rats, and eight wild type (WT) rats were used. At the age of 8 weeks old, SDT rats were divided into two dietary groups either normal diet or HFD feeding for 12 weeks. WT rats were received a normal diet entire the study. At 20 weeks old, metabolic parameters, the hippocampal dependent cognitive function using novel object location (NOL) test, and hippocampal dendritic spine density were determined. Our data demonstrated that, at 20 weeks old, SDT rats in both dietary groups exhibited their diabetic characters as indicated by hyperglycemia, hypoinsulinemia, and insulin insensitivity. HFD feeding did not aggravate diabetic status, but it significantly induced body weight gain, visceral fat deposition, hypertriglyceridemia, and hypercholesterolemia (as shown in Figure 1). Unexpectedly, hippocampal dependent cognitive impairments were not observed in both normal diet and HFD-fed SDT rats, when compared with WT rats (Figure 1). However, brain mitochondrial dysfunction and dendritic spine loss were observed in both dietary groups of SDT rats. Interestingly, the reduction of dendritic spine density was greater in HFD-fed SDT rats than normal diet-fed SDT rats (Figure 1). Long-term HFD consumption induced truncal obesity, dyslipidemia, and reduced dendritic spine density in SDT rats, but it did not affect hippocampal dependent cognitive function. It is possible that the duration of HFD feeding was insufficient to promote cognitive impairments in genetically T2DM rats.

Cannabidiol regulates CB1‐pSTAT3 signaling for neurite outgrowth, prolongs lifespan, and improves health span in Caenorhabditis elegans of Aβ pathology models

Cannabidiol (CBD), a phytocannabinoid from the Cannabis sativa plant, exhibits a broad spectrum of potential therapeutic properties for neurodegenerative diseases. An accumulation of amyloid-β (Aβ) protein is one of the most important neuropathology in neurodegenerative diseases like Alzheimer's disease (AD). Data on the effect of CBD on the amelioration of Aβ-induced neurite degeneration and its consequences of life and health spans is sparse. This study aimed to investigate the effects of CBD on neurite outgrowth in cells and lifespan and health span in Caenorhabditis elegans (C. elegans). In human SH-SY5Y neuronal cells, CBD prevented neurite lesion induced by Aβ1-42 and increased the expression of fatty acid amide hydrolase (FAAH) and cannabinoid receptor 1 (CB1R). Furthermore, CBD both protected the reduction of dendritic spine density and rescued the activity of synaptic Ca2+ /calmodulin-dependent protein kinase II (CaMKII) from Aβ1-42 toxicity in primary hippocampal neurons. In C. elegans, we used the transgenic CL2355 strain of C. elegans, which expresses the human Aβ peptide throughout the nervous system and found that CBD treatment extended lifespan and improved health span. The neuroprotective effect of CBD was further explored by observing the dopaminergic neurons using transgenic dat-1: GFP strains using the confocal microscope. This study shows that CBD prevents the neurite degeneration induced by Aβ, by a mechanism involving CB1R activation, and extends lifespan and improves health span in Aβ-overexpressing worms. Our findings support the potential therapeutic approach of CBD for the treatment of AD patients.

Prenatal exposure to koumine results in cognitive deficits and increased anxiety-like behavior in mice offspring

Koumine (KM) is a major alkaloid monomer in the traditional Chinese medicine herb Gelsemium elegans Benth that has exhibited therapeutic potential in clinical applications. However, the pharmacological toxicological mechanism of this drug has not been fully explored. The purpose of this study was to evaluate the impacts of KM administration at a therapeutic dose in offspring. On gestational day 0, mice were injected with KM once daily for 4 consecutive days. Male and female offspring were subjected to behavioral tests and neuropathological analyses from postnatal day 60. Prenatal KM exposure resulted in cognitive and memory impairments in the Morris water maze, Y-maze test, and novel object recognition test. The open field test and elevated plus maze test indicated that prenatal KM exposure induced anxiety-like behavior in offspring. Electrophysiological experiments demonstrated that KM exposure inhibited hippocampal long-term potentiation. Immunostaining for neurogenesis markers DCX and BrdU demonstrated that KM suppressed adult neurogenesis in the subgranular zone of the dentate gyrus. In addition, prenatal KM exposure induced a significant reduction in dendritic spine density in hippocampal neurons. Synaptic formation-related proteins were decreased in the KM group based on western blot. No sex differences in the effects of KM were observed. Collectively, our results indicate that prenatal KA exposure has detrimental neural effects on offspring. This study provides a preliminary preclinical toxicological assessment of the safety of KM use during pregnancy.

The potassium channel Kv4.2 regulates dendritic spine morphology, electroencephalographic characteristics and seizure susceptibility in mice

The voltage-gated potassium channel Kv4.2 is a critical regulator of dendritic excitability in the hippocampus and is crucial for dendritic signal integration. Kv4.2 mRNA and protein expression as well as function are reduced in several genetic and pharmacologically induced rodent models of epilepsy and autism. It is not known, however, whether reduced Kv4.2 is just an epiphenomenon or a disease-contributing cause of neuronal hyperexcitability and behavioral impairments in these neurological disorders. To address this question, we used male and female mice heterozygous for a Kv.2 deletion and adult-onset manipulation of hippocampal Kv4.2 expression in male mice to assess the role of Kv4.2 in regulating neuronal network excitability, morphology and anxiety-related behaviors. We observed a reduction in dendritic spine density and reduced proportions of thin and stubby spines but no changes in anxiety, overall activity, or retention of conditioned freezing memory in Kv4.2 heterozygous mice compared with wildtype littermates. Using EEG analyses, we showed elevated theta power and increased spike frequency in Kv4.2 heterozygous mice under basal conditions. In addition, the latency to onset of kainic acid-induced seizures was significantly shortened in Kv4.2 heterozygous mice compared with wildtype littermates, which was accompanied by a significant increase in theta power. By contrast, overexpressing Kv4.2 in wildtype mice through intrahippocampal injection of Kv4.2-expressing lentivirus delayed seizure onset and reduced EEG power. These results suggest that Kv4.2 is an important regulator of neuronal network excitability and dendritic spine morphology, but not anxiety-related behaviors. In the future, manipulation of Kv4.2 expression could be used to alter seizure susceptibility in epilepsy.

Pneumonia-induced endothelial amyloids reduce dendritic spine density in brain neurons

Pseudomonas aeruginosa pneumonia elicits endothelial cell release of cytotoxic amyloids that can be recovered from the bronchoalveolar lavage and cerebrospinal fluids of critically ill patients. Introduction of these cytotoxic amyloids into the lateral ventricle impairs learning and memory in mice. However, it is unclear whether the amyloids of lung origin (1) are neurotropic, and (2) cause structural remodeling of hippocampal dendrites. Thus, we used electrophysiological studies in brain slices and structural analysis of post-mortem tissues obtained from animals exposed to endothelium-derived amyloids to assess these issues. The amyloids were administered via three different routes, by intracerebroventricular, intratracheal, and intraperitoneal injections. Synaptic long-term potentiation was abolished following intracerebroventricular amyloid injection. Fluorescence dialysis or Golgi-impregnation labeling showed reduced dendritic spine density and destabilized spines of hippocampal pyramidal neurons 4 weeks after intracerebroventricular amyloid injection. In comparison, endothelial amyloids introduced to the airway caused the most prominent dendritic spine density reduction, yet intraperitoneal injection of these amyloids did not affect spine density. Our findings indicate that infection-elicited lung endothelial amyloids are neurotropic and reduce neuronal dendritic spine density in vivo. Amyloids applied into the trachea may either be disseminated through the circulation and cross the blood-brain barrier to access the brain, initiate feed-forward amyloid transmissibility among cells of the blood-brain barrier or access the brain in other ways. Nevertheless, lung-derived amyloids suppress hippocampal signaling and cause injury to neuronal structure.

Nicotinamide attenuates the decrease in dendritic spine density in hippocampal primary neurons from 5xFAD mice, an Alzheimer\u2019s disease animal model

Alzheimer’s disease (AD) is the most common neurodegenerative disease characterized by memory loss and the presence of amyloid plaques and neurofibrillary tangles in the patients’ brains. In this study, we investigated the alterations in metabolite profiles of the hippocampal tissues from 6, 8, and 12 month-old wild-type (WT) and 5xfamiliar AD (5xFAD) mice, an AD mouse model harboring 5 early-onset familiar AD mutations, which shows memory loss from approximately 5 months of age, by exploiting the untargeted metabolomics profiling. We found that nicotinamide and adenosine monophosphate levels have been significantly decreased while lysophosphatidylcholine (LysoPC) (16:0), LysoPC (18:0), and lysophosphatidylethanolamine (LysoPE) (16:0) levels have been significantly increased in the hippocampi from 5xFAD mice at 8 months or 12 months of age, compared to those from age-matched wild-type mice. In the present study, we focused on the role of nicotinamide and examined if replenishment of nicotinamide exerts attenuating effects on the reduction in dendritic spine density in hippocampal primary neurons from 5xFAD mice. Treatment with nicotinamide attenuated the deficits in spine density in the hippocampal primary neurons derived from 5xFAD mice, indicating a potential role of nicotinamide in the pathogenesis of AD. Taken together, these findings suggest that the decreased hippocampal nicotinamide level could be linked with AD pathogenesis and be a useful therapeutic target for AD.

Csmd2 Is a Synaptic Transmembrane Protein that Interacts with PSD-95 and Is Required for Neuronal Maturation.

Mutations and copy number variants of the CUB and Sushi multiple domains 2 (CSMD2) gene are associated with neuropsychiatric disease. CSMD2 encodes a single-pass transmembrane protein with a large extracellular domain comprising repeats of CUB and Sushi domains. High expression of CSMD2 in the developing and mature brain suggests possible roles in neuron development or function, but the cellular functions of CSMD2 are not known. In this study, we show that mouse Csmd2 is expressed in excitatory and inhibitory neurons in the forebrain. Csmd2 protein exhibits a somatodendritic localization in the neocortex and hippocampus, with smaller puncta localizing to the neuropil. Using immunohistochemical and biochemical methods, we demonstrate that Csmd2 localizes to dendritic spines and is enriched in the postsynaptic density (PSD). Accordingly, we show that the cytoplasmic tail domain of Csmd2 interacts with synaptic scaffolding proteins of the membrane-associated guanylate kinase (MAGUK) family. The association between Csmd2 and MAGUK member PSD-95 is dependent on a PDZ-binding domain on the Csmd2 tail, which is also required for synaptic targeting of Csmd2. Finally, we show that knock-down of Csmd2 expression in hippocampal neuron cultures results in reduced complexity of dendritic arbors and deficits in dendritic spine density. Knock-down of Csmd2 in immature developing neurons results in reduced filopodia density, whereas Csmd2 knock-down in mature neurons causes significant reductions in dendritic spine density and dendrite complexity. Together, these results point toward a function for Csmd2 in development and maintenance of dendrites and synapses, which may account for its association with certain psychiatric disorders.