Increase In Spine Density Research Articles

Time-lapse imaging of identified granule cells in the mouse dentate gyrus after entorhinal lesion in vitro reveals heterogeneous cellular responses to denervation.

Denervation of neurons is a network consequence of brain injury. The effects of denervation on neurons can be readily studied in vitro using organotypic slice cultures of entorhinal cortex and hippocampus. Following transection of the entorhino-dentate projection, granule cells (GCs) are denervated and show on average a transient loss of spines on their denervated distal dendrites but not on their non-denervated proximal dendrites. In the present study, we addressed the question how single GCs and their denervated and non-denervated segments react to entorhinal denervation. Local adeno-associated virus (AAV)-injections were employed to transduce dentate GCs with tdTomato and entorhinal projection neurons with EGFP. This made it possible to visualize both innervating entorhinal fibers and their target neurons and to identify dendritic segments located in the "entorhinal" and the "hippocampal" zone of the dentate gyrus. Confocal time-lapse imaging was used to image distal and proximal segments of single GCs after entorhinal denervation. Time-matched non-denervated cultures served as controls. In line with previous reports, average dendritic spine loss was ~30% (2-4 days post-lesion) in the denervated zone. However, individual GCs showed considerable variability in their response to denervation in both layers, and both decreases as well as increases in spine density were observed at the single cell level. Based on the standard deviations and the effect sizes observed in this study, a computer simulation yielded recommendations for the minimum number of neurons that should be analyzed in future studies using the entorhinal in vitro denervation model.

The Alzheimer's Disease Risk Gene CD2AP Functions in Dendritic Spines by Remodeling F-Actin.

CD2-associated protein (CD2AP) was identified as a genetic risk factor for late-onset Alzheimer's disease (LOAD). However, it is unclear how CD2AP contributes to LOAD synaptic dysfunction underlying AD memory deficits. We have shown that loss of CD2AP function increases β-amyloid (Aβ) endocytic production, but it is unknown whether it contributes to synapse dysfunction. As CD2AP is an actin-binding protein, it may also function in F-actin-rich dendritic spines, which are the excitatory postsynaptic compartments. Here, we demonstrate that CD2AP colocalizes with F-actin in dendritic spines of primary mouse cortical neurons of both sexes. Cell-autonomous depletion of CD2AP specifically reduces spine density and volume, resulting in a functional decrease in synapse formation and neuronal network activity. Postsynaptic reexpression of CD2AP, but not blocking Aβ production, is sufficient to rescue spine density. CD2AP overexpression increases spine density, volume, and synapse formation, while a rare LOAD CD2AP mutation induces aberrant F-actin spine-like protrusions without functional synapses. CD2AP controls postsynaptic actin turnover, with the LOAD mutation in CD2AP decreasing F-actin dynamicity. Our data support that CD2AP risk variants could contribute to LOAD synapse dysfunction by disrupting spine formation and growth by deregulating actin dynamics.

Autophagy defects at weaning impair complement-dependent synaptic pruning and induce behavior deficits

Autophagy is crucial for synaptic plasticity and the architecture of dendritic spines. However, the role of autophagy in schizophrenia (SCZ) and the mechanisms through which it affects synaptic function remain unclear. In this study, we identified 995 single nucleotide polymorphisms (SNPs) across 19 autophagy-related genes that are associated with SCZ. Gene Set Enrichment Analysis (GSEA) of data from the Gene Expression Omnibus public database revealed defective autophagy in patients with SCZ. Using a maternal immune activation (MIA) rat model, we observed that autophagy was downregulated during the weaning period, and early-life activation of autophagy with rapamycin restored abnormal behaviors and electrophysiological deficits in adult rats. Additionally, inhibition of autophagy with 3-Methyladenine (3-MA) during the weaning period resulted in aberrant behaviors, abnormal electrophysiology, increased spine density, and reduced microglia-mediated synaptic pruning. Furthermore, 3-MA treatment significantly decreased the expression and synaptosomal content of complement, impaired the recognition of C3b and CR3, indicating that autophagy deficiency disrupts complement-mediated synaptic pruning. Our findings provide evidence for a significant association between SCZ and defective autophagy, highlighting a previously underappreciated role of autophagy in regulating the synaptic and behavioral deficits induced by MIA.

LT-102, an AMPA receptor potentiator, alleviates depression-like behavior and synaptic plasticity impairments in prefrontal cortex induced by sleep deprivation

BackgroundSleep loss is closely related to the onset and development of depression, and the mechanisms involved may include impaired synaptic plasticity. Considering the important role of glutamate α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs) in synaptic plasticity as well as depression, we introduce LT-102, a novel AMPARs potentiator, to evaluate the potential of LT-102 in treating sleep deprivation-induced depression-like behaviors. MethodsWe conducted a comprehensive behavioral assessment to evaluate the effects of LT-102 on depression-like symptoms in male C57BL/6J mice. This assessment included the open field test to measure general locomotor activity and anxiety-like behavior, the forced swimming test and tail suspension test to assess despair behaviors indicative of depressive states, and the sucrose preference test to quantify anhedonia, a core symptom of depression. Furthermore, to explore the impact of LT-102 on synaptic plasticity, we utilized a combination of Western blot analysis to detect protein expression levels, Golgi-Cox staining to visualize neuronal morphology, and immunofluorescence to examine the localization of synaptic proteins. Additionally, we utilized primary cortical neurons to delineate the signaling pathway modulated by LT-102. ResultsTreatment with LT-102 significantly reduced depression-like behaviors associated with sleep deprivation. Quantitative Western blot (WB) analysis revealed a significant increase in GluA1 phosphorylation in the prefrontal cortex (PFC), triggering the Ca2+/calmodulin-dependent protein kinase II/cAMP response element-binding protein/brain-derived neurotrophic factor (CaMKII/CREB/BDNF) and forkhead box protein P2/postsynaptic density protein 95 (FoxP2/PSD95) signaling pathways. Immunofluorescence imaging confirmed that LT-102 treatment increased spine density and co-labeling of PSD95 and vesicular glutamate transporter 1 (VGLUT1) in the PFC, reversing the reductions typically observed following sleep deprivation. Golgi staining further validated these results, showing a substantial increase in neuronal dendritic spine density in sleep-deprived mice treated with LT-102. Mechanistically, application of LT-102 to primary cortical neurons, resulted in elevated levels of phosphorylated AKT (p-AKT) and phosphorylated glycogen synthase kinase-3 beta (p-GSK3β), key downstream molecules in the BDNF signaling pathway, which in turn upregulated FoxP2 and PSD95 expression. LimitationsIn our study, we chose to exclusively use male mice to eliminate potential influences of the estrous cycle on behavior and physiology. As there is no widely accepted positive drug control for sleep deprivation studies, we did not include one in our research. ConclusionOur results suggest that LT-102 is a promising therapeutic agent for counteracting depression-like behaviors and synaptic plasticity deficits induced by sleep deprivation, primarily through the activation of CaMKII/CREB/BDNF and AKT/GSK3β/FoxP2/PSD95 signaling pathways.

Reducing Filamin A Restores Cortical Synaptic Connectivity and Early Social Communication Following Cellular Mosaicism in Autism Spectrum Disorder Pathways.

Communication in the form of nonverbal, social vocalization, or crying is evolutionary conserved in mammals and is impaired early in human infants that are later diagnosed with autism spectrum disorder (ASD). Defects in infant vocalization have been proposed as an early sign of ASD that may exacerbate ASD development. However, the neural mechanisms associated with early communicative deficits in ASD are not known. Here, we expressed a constitutively active mutant of Rheb (RhebS16H), which is known to upregulate two ASD core pathways, mTOR complex 1 (mTORC1) and ERK1/2, in Layer (L) 2/3 pyramidal neurons of the neocortex of mice of either sex. We found that cellular mosaic expression of RhebS16H in L2/3 pyramidal neurons altered the production of isolation calls from neonatal mice. This was accompanied by an expected misplacement of neurons and dendrite overgrowth, along with an unexpected increase in spine density and length, which was associated with increased excitatory synaptic activity. This contrasted with the known decrease in spine density in RhebS16H neurons of 1-month-old mice. Reducing the levels of the actin cross-linking and adaptor protein filamin A (FLNA), known to be increased downstream of ERK1/2, attenuated dendrite overgrowth and fully restored spine properties, synaptic connectivity, and the production of pup isolation calls. These findings suggest that upper-layer cortical pyramidal neurons contribute to communicative deficits in a condition known to affect two core ASD pathways and that these mechanisms are regulated by FLNA.

H7N7 viral infection elicits pronounced, sex-specific neuroinflammatory responses in vitro.

Influenza A virus (IAV) infection can increase the risk of neuroinflammation, and subsequent neurodegenerative diseases. Certain IAV strains, such as avian H7N7 subtype, possess neurotropic properties, enabling them to directly invade the brain parenchyma and infect neurons and glia cells. Host sex significantly influences the severity of IAV infections. Studies indicate that females of the reproductive age exhibit stronger innate and adaptive immune responses to IAVs compared to males. This heightened immune response correlates with increased morbidity and mortality, and potential neuronal damage in females. Understanding the sex-specific neurotropism of IAV and associated mechanisms leading to adverse neurological outcomes is essential. Our study reveals that primary hippocampal cultures from female mice show heightened interferon-β and pro-inflammatory chemokine secretion following neurotropic IAV infection. We observed sex-specific differences in microglia activation: both sexes showed a transition into a hyper-ramified state, but only male-derived microglia exhibited an increase in amoeboid-shaped cells. These disparities extended to alterations in neuronal morphology. Neurons derived from female mice displayed increased spine density within 24 h post-infection, while no significant change was observed in male cultures. This aligns with sex-specific differences in microglial synaptic pruning. Data suggest that amoeboid-shaped microglia preferentially target postsynaptic terminals, potentially reducing neuronal hyperexcitability. Conversely, hyper-ramified microglia may focus on presynaptic terminals, potentially limiting viral spread. In conclusion, our findings underscore the utility of primary hippocampal cultures, incorporating microglia, as an effective model to study sex-specific, virus-induced effects on brain-resident cells.

The administration of Cerebrolysin elicits neuroprotective and neurorepair effects in an animal model of type 1 diabetes mellitus

Diabetes mellitus (DM) is a metabolic disorder impacting cerebral function. The administration of Streptozotocin (STZ) is a well-known animal model of insulinopenic type 1 DM in rats. STZ-induced DM results in a myriad of alteration in the periphery and central nervous system (CNS). Cerebrolysin (CBL) is a neuropeptide preparation that promotes synaptic and neuronal plasticity in various animal models. In all cases, CBL was administered when the model was established. This research aims to investigate the neuroprotective and neurorepair effect of CBL on the cytoarchitecture of neurons and spine density in pyramidal neurons of the prefrontal (PFC) and the CA1 region of the dorsal hippocampus, as well as spheroidal neurons of the dentate gyrus (DG), in STZ-induced DM. In the first experimental condition, STZ and CBL are administered at the same time to evaluate the potential preventive effect of CBL. In the second experimental condition, CBL was administered two months after establishing the DM model to measure the potential neurorepair effect of CBL. STZ-induced hyperglycemia remained unaltered by the administration of CBL in both experimental conditions. In the first experimental condition, CBL treatment preserved the neuronal morphology in PFC layer 3, PFC layer 5 and the DG of the hippocampus, while also maintaining spine density in the PFC-3, DG and CA1 hippocampus. Furthermore, CBL induced neurorepair in neurons within the PFC-3, PFC-5 and CA1 regions of the hippocampus, along with an increase in spine density in the PFC-3, DG and CA1 hippocampus. These findings suggest that CBL´s effects on neuroplasticity could be observed before or after the damage was evident.

Enhanced hippocampal LTP but normal NMDA receptor and AMPA receptor function in a rat model of CDKL5 deficiency disorder

BackgroundMutations in the X-linked gene cyclin-dependent kinase-like 5 (CDKL5) cause a severe neurological disorder characterised by early-onset epileptic seizures, autism and intellectual disability (ID). Impaired hippocampal function has been implicated in other models of monogenic forms of autism spectrum disorders and ID and is often linked to epilepsy and behavioural abnormalities. Many individuals with CDKL5 deficiency disorder (CDD) have null mutations and complete loss of CDKL5 protein, therefore in the current study we used a Cdkl5−/y rat model to elucidate the impact of CDKL5 loss on cellular excitability and synaptic function of CA1 pyramidal cells (PCs). We hypothesised abnormal pre and/or post synaptic function and plasticity would be observed in the hippocampus of Cdkl5−/y rats.MethodsTo allow cross-species comparisons of phenotypes associated with the loss of CDKL5, we generated a loss of function mutation in exon 8 of the rat Cdkl5 gene and assessed the impact of the loss of CDLK5 using a combination of extracellular and whole-cell electrophysiological recordings, biochemistry, and histology.ResultsOur results indicate that CA1 hippocampal long-term potentiation (LTP) is enhanced in slices prepared from juvenile, but not adult, Cdkl5−/y rats. Enhanced LTP does not result from changes in NMDA receptor function or subunit expression as these remain unaltered throughout development. Furthermore, Ca2+ permeable AMPA receptor mediated currents are unchanged in Cdkl5−/y rats. We observe reduced mEPSC frequency accompanied by increased spine density in basal dendrites of CA1 PCs, however we find no evidence supporting an increase in silent synapses when assessed using a minimal stimulation protocol in slices. Additionally, we found no change in paired-pulse ratio, consistent with normal release probability at Schaffer collateral to CA1 PC synapses.ConclusionsOur data indicate a role for CDKL5 in hippocampal synaptic function and raise the possibility that altered intracellular signalling rather than synaptic deficits contribute to the altered plasticity.LimitationsThis study has focussed on the electrophysiological and anatomical properties of hippocampal CA1 PCs across early postnatal development. Studies involving other brain regions, older animals and behavioural phenotypes associated with the loss of CDKL5 are needed to understand the pathophysiology of CDD.

TAF15 downregulation contributes to the benefits of physical training on dendritic spines and working memory in aged mice.

Moderate physical training has been shown to hinder age-related memory decline. While the benefits of physical training on hippocampal memory function are well-documented, little is known about its impact on working memory, which is linked to the prelimbic cortex (PrL), one major subdivision of the prefrontal cortex. Here, we examined the effects of physical training on spatial working memory in a well-established animal model of physical training, starting at 16 months of age and continuing for 5 months (running wheel 1 h/day and 5 days/week). This training strategy improved spatial working memory in aged mice (22-month-old), which was accompanied by an increased spine density and a lower TAF15 expression in the PrL. Specifically, physical training affected both thin and mushroom-type spines on PrL pyramidal cells, and prevented age-related loss of spines on selective segments of apical dendritic branches. Correlation analysis revealed that increased TAF15-expression was detrimental to the dendritic spines. However, physical training downregulated TAF15 expression in the PrL, preserving the dendritic spines on PrL pyramidal cells and improving working memory in trained aged mice. When TAF15 was overexpressed in the PrL via a viral approach, the benefits of physical training on the dendritic spines and working memory were abolished. These data suggest that physical training at a moderate pace might downregulate TAF15 expression in the PrL, which favors the dendritic spines on PrL pyramidal cells, thereby improving spatial working memory.

MET receptor tyrosine kinase promotes the generation of functional synapses in adult cortical circuits.

JOURNAL/nrgr/04.03/01300535-202505000-00026/figure1/v/2024-07-28T173839Z/r/image-tiff Loss of synapse and functional connectivity in brain circuits is associated with aging and neurodegeneration, however, few molecular mechanisms are known to intrinsically promote synaptogenesis or enhance synapse function. We have previously shown that MET receptor tyrosine kinase in the developing cortical circuits promotes dendritic growth and dendritic spine morphogenesis. To investigate whether enhancing MET in adult cortex has synapse regenerating potential, we created a knockin mouse line, in which the human MET gene expression and signaling can be turned on in adult (10-12 months) cortical neurons through doxycycline-containing chow. We found that similar to the developing brain, turning on MET signaling in the adult cortex activates small GTPases and increases spine density in prefrontal projection neurons. These findings are further corroborated by increased synaptic activity and transient generation of immature silent synapses. Prolonged MET signaling resulted in an increased α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/N-methyl-D-aspartate (AMPA/NMDA) receptor current ratio, indicative of enhanced synaptic function and connectivity. Our data reveal that enhancing MET signaling could be an interventional approach to promote synaptogenesis and preserve functional connectivity in the adult brain. These findings may have implications for regenerative therapy in aging and neurodegeneration conditions.

Enhanced Spine Stability and Survival Lead to Increases in Dendritic Spine Density as an Early Response to Local Alpha-Synuclein Overexpression in Mouse Prefrontal Cortex

Lewy Body Dementias (LBD), including Parkinson’s disease dementia and Dementia with Lewy Bodies, are characterized by widespread accumulation of intracellular alpha-Synuclein protein deposits in regions beyond the brainstem, including in the cortex. However, the impact of local pathology in the cortex is unknown. To investigate this, we employed viral overexpression of human alpha-Synuclein protein targeting the mouse prefrontal cortex (PFC). We then used in vivo 2-photon microscopy to image awake head-fixed mice via an implanted chronic cranial window to assess the early consequences of alpha-Synuclein overexpression in the weeks following overexpression. We imaged apical tufts of Layer V pyramidal neurons in the PFC of Thy1-YFP transgenic mice at 1-week intervals from 1 to 2 weeks before and 9 weeks following viral overexpression, allowing analysis of dynamic changes in dendritic spines. We found an increase in the relative dendritic spine density following local overexpression of alpha-Synuclein, beginning at 5 weeks post-injection, and persisting for the remainder of the study. We found that alpha-Synuclein overexpression led to an increased percentage and longevity of newly-persistent spines, without significant changes in the total density of newly formed or eliminated spines. A follow-up study utilizing confocal microscopy revealed that the increased spine density is found in cortical cells within the alpha-Synuclein injection site, but negative for alpha-Synuclein phosphorylation at Serine-129, highlighting the potential for effects of dose and local circuits on spine survival. These findings have important implications for the physiological role and early pathological stages of alpha-Synuclein in the cortex.Graphical

Ludwigia octovalvis (Jacq.) P.H. Raven extract improves memory performance in mice with chronic kidney disease

BackgroundChronic kidney disease (CKD) is a significant global health concern often accompanied by cognitive impairment in affected patients. Ludwigia octovalvis extract (LOE) is a traditional medicine widely used for various conditions, including renal disease and its associated complications. However, the pharmacological effects and underlying mechanisms of LOE on CKD remain unclear. MethodsAdult male mice underwent a 4-week oral adenine-induced CKD model, followed by daily administration of either a vehicle, losartan, or LOE for 1 to 2 months. A battery of behavioral tests was conducted to examine CKD-associated cognitive impairments. Additionally, RNA sequencing, Golgi staining, and immunohistochemistry were performed to decipher the underlying mechanisms. ResultsNeither losartan nor LOE supplementation could reverse adenine-induced kidney damage. However, during behavioral tests, both losartan and LOE treatments improved memory performance in mice without affecting emotional status and general locomotor activity. Transcriptome profiling and histological analyses revealed altered dendritic arborization and increased spine density of dentate granule cells, along with augmented adult hippocampal neurogenesis, contributing to the improved memory performance of mice treated with LOE. ConclusionOur study provides comprehensive neurobehavioral and molecular evidence supporting the potential use of LOE for future CKD-associated memory dysfunction treatment.

Interplay between hippocampal TACR3 and systemic testosterone in regulating anxiety-associated synaptic plasticity

Tachykinin receptor 3 (TACR3) is a member of the tachykinin receptor family and falls within the rhodopsin subfamily. As a G protein-coupled receptor, it responds to neurokinin B (NKB), its high-affinity ligand. Dysfunctional TACR3 has been associated with pubertal failure and anxiety, yet the mechanisms underlying this remain unclear. Hence, we have investigated the relationship between TACR3 expression, anxiety, sex hormones, and synaptic plasticity in a rat model, which indicated that severe anxiety is linked to dampened TACR3 expression in the ventral hippocampus. TACR3 expression in female rats fluctuates during the estrous cycle, reflecting sensitivity to sex hormones. Indeed, in males, sexual development is associated with a substantial increase in hippocampal TACR3 expression, coinciding with elevated serum testosterone and a significant reduction in anxiety. TACR3 is predominantly expressed in the cell membrane, including the presynaptic compartment, and its modulation significantly influences synaptic activity. Inhibition of TACR3 activity provokes hyperactivation of CaMKII and enhanced AMPA receptor phosphorylation, associated with an increase in spine density. Using a multielectrode array, stronger cross-correlation of firing was evident among neurons following TACR3 inhibition, indicating enhanced connectivity. Deficient TACR3 activity in rats led to lower serum testosterone levels, as well as increased spine density and impaired long-term potentiation (LTP) in the dentate gyrus. Remarkably, aberrant expression of functional TACR3 in spines results in spine shrinkage and pruning, while expression of defective TACR3 increases spine density, size, and the magnitude of cross-correlation. The firing pattern in response to LTP induction was inadequate in neurons expressing defective TACR3, which could be rectified by treatment with testosterone. In conclusion, our study provides valuable insights into the intricate interplay between TACR3, sex hormones, anxiety, and synaptic plasticity. These findings highlight potential targets for therapeutic interventions to alleviate anxiety in individuals with TACR3 dysfunction and the implications of TACR3 in anxiety-related neural changes provide an avenue for future research in the field.

Vitamin B12-folic acid supplementation improves memory by altering mitochondrial dynamics, dendritic arborization, and neurodegeneration in old and amnesic male mice

Memory impairment during aging and amnesia is attributed to compromised mitochondrial dynamics and mitophagy and other mitochondrial quality control mechanisms. Mitochondrial dynamics involves the continuous process of fission and fusion of mitochondria within a cell and is a fundamental mechanism for regulating mitochondrial quality and function. An extensive range of potential nutritional supplements has been shown to improve mitochondrial health, synaptic plasticity, and cognitive functions. Previous findings revealed that supplementation of vitamin B12-folic acid reduces locomotor deficits and mitochondrial abnormalities but enhances mitochondrial and neuronal health. The present study aims to explore the impact of combined vitamin B12-folic acid supplementation on mitochondrial dynamics, neuronal health, and memory decline in old age and scopolamine-induced amnesia, which remains elusive. The results demonstrated that supplementation led to a noteworthy increase in recognition and spatial memory and expression of memory-related protein BDNF in old and amnesic mice. Moreover, the decrease in the fragmented mitochondrial number was validated by the downregulation of mitochondrial fission p-Drp1 (S616) protein and the increase in elongated mitochondria by the upregulation of mitochondrial fusion Mfn2 protein. The increased spine density and dendritic arborization in old and amnesic mice upon supplementation were confirmed by the enhanced expression level of PSD95 and synaptophysin. Furthermore, supplementation reduced ROS production, inhibited Caspase-3 activation, mitigated neurodegeneration, and enhanced mitochondrial membrane potential, ATP production, Vdac1 expression, myelination, in old and amnesic mice. Collectively, our findings imply that combined supplementation of vitamin B12-folic acid improves mitochondrial dynamics and neuronal health, and leads to recovery of memory during old age and amnesia.

The Q/R editing site of AMPA receptor GluA2 subunit acts as an epigenetic switch regulating dendritic spines, neurodegeneration and cognitive deficits in Alzheimer’s disease

BackgroundRNA editing at the Q/R site of GluA2 occurs with ~99% efficiency in the healthy brain, so that the majority of AMPARs contain GluA2(R) instead of the exonically encoded GluA2(Q). Reduced Q/R site editing increases AMPA receptor calcium permeability and leads to dendritic spine loss, neurodegeneration, seizures and learning impairments. Furthermore, GluA2 Q/R site editing is impaired in Alzheimer’s disease (AD), raising the possibility that unedited GluA2(Q)-containing AMPARs contribute to synapse loss and neurodegeneration in AD. If true, then inhibiting expression of unedited GluA2(Q), while maintaining expression of GluA2(R), may be a novel strategy of preventing synapse loss and neurodegeneration in AD.MethodsWe engineered mice with the ‘edited’ arginine codon (CGG) in place of the unedited glutamine codon (CAG) at position 607 of the Gria2 gene. We crossbred this line with the J20 mouse model of AD and conducted anatomical, electrophysiological and behavioural assays to determine the impact of eliminating unedited GluA2(Q) expression on AD-related phenotypes.ResultsEliminating unedited GluA2(Q) expression in AD mice prevented dendritic spine loss and hippocampal CA1 neurodegeneration as well as improved working and reference memory in the radial arm maze. These phenotypes were improved independently of Aβ pathology and ongoing seizure susceptibility. Surprisingly, our data also revealed increased spine density in non-AD mice with exonically encoded GluA2(R) as compared to their wild-type littermates, suggesting an unexpected and previously unknown role for unedited GluA2(Q) in regulating dendritic spines.ConclusionThe Q/R editing site of the AMPA receptor subunit GluA2 may act as an epigenetic switch that regulates dendritic spines, neurodegeneration and memory deficits in AD.

Neuron-derived extracellular vesicles contain synaptic proteins, promote spine formation, activate TrkB-mediated signalling and preserve neuronal complexity.

Extracellular vesicles (EVs) play an important role in intercellular communication as carriers of signalling molecules such as bioactive miRNAs, proteins and lipids. EVs are key players in the functioning of the central nervous system (CNS) by influencing synaptic events and modulating recipient neurons. However, the specific role of neuron-to-neuron communication via EVs is still not well understood.Here, we provide evidence that primary neurons uptake neuron-derived EVs in the soma, dendrites, and even in the dendritic spines, and carry synaptic proteins. Neuron-derived EVs increased spine density and promoted the phosphorylation of Akt and ribosomal protein S6 (RPS6), via TrkB-signalling, without impairing the neuronal network activity. Strikingly, EVs exerted a trophic effect on challenged nutrient-deprived neurons. Altogether, our results place EVs in the spotlight for synaptic plasticity modulation as well as a possible therapeutic tool to fight neurodegeneration.

Ankyrin B promotes developmental spine regulation in the mouse prefrontal cortex.

Postnatal regulation of dendritic spine formation and refinement in cortical pyramidal neurons is critical for excitatory/inhibitory balance in neocortical networks. Recent studies have identified a selective spine pruning mechanism in the mouse prefrontal cortex mediated by class 3 Semaphorins and the L1 cell adhesion molecules, neuron-glia related cell adhesion molecule, Close Homolog of L1, and L1. L1 cell adhesion molecules bind Ankyrin B, an actin-spectrin adaptor encoded by Ankyrin2, a high-confidence gene for autism spectrum disorder. In a new inducible mouse model (Nex1Cre-ERT2: Ank2flox: RCE), Ankyrin2 deletion in early postnatal pyramidal neurons increased spine density on apical dendrites in prefrontal cortex layer 2/3 of homozygous and heterozygous Ankyrin2-deficient mice. In contrast, Ankyrin2 deletion in adulthood had no effect on spine density. Sema3F-induced spine pruning was impaired in cortical neuron cultures from Ankyrin B-null mice and was rescued by re-expression of the 220kDa Ankyrin B isoform but not 440kDa Ankyrin B. Ankyrin B bound to neuron-glia related CAM at a cytoplasmic domain motif (FIGQY1231), and mutation to FIGQH inhibited binding, impairing Sema3F-induced spine pruning in neuronal cultures. Identification of a novel function for Ankyrin B in dendritic spine regulation provides insight into cortical circuit development, as well as potential molecular deficiencies in autism spectrum disorder.

Operant Training for Highly Palatable Food Alters Translating Messenger RNA in Nucleus Accumbens D2 Neurons and Reveals a Modulatory Role of Ncdn

BackgroundHighly palatable food triggers behavioral responses including strong motivation. These effects involve the reward system and dopamine neurons, which modulate neurons in the nucleus accumbens (NAc). The molecular mechanisms underlying the long-lasting effects of highly palatable food on feeding behavior are poorly understood. MethodsWe studied the effects of 2-week operant conditioning of mice with standard or isocaloric highly palatable food. We investigated the behavioral responses and dendritic spine modifications in the NAc. We compared the translating messenger RNA in NAc neurons identified by the type of dopamine receptors they express, depending on the kind of food and training. We tested the consequences of invalidation of an abundant downregulated gene, Ncdn. ResultsOperant conditioning for highly palatable food increased motivation for food even in well-fed mice. In wild-type mice, free choice between regular and highly palatable food increased weight compared with access to regular food only. Highly palatable food increased spine density in the NAc. In animals trained for highly palatable food, translating messenger RNAs were modified in NAc neurons expressing dopamine D2 receptors, mostly corresponding to striatal projection neurons, but not in neurons expressing D1 receptors. Knockout of Ncdn, an abundant downregulated gene, opposed the conditioning-induced changes in satiety-sensitive feeding behavior and apparent motivation for highly palatable food, suggesting that downregulation may be a compensatory mechanism. ConclusionsOur results emphasize the importance of messenger RNA alterations in D2 striatal projection neurons in the NAc in the behavioral consequences of highly palatable food conditioning and suggest a modulatory contribution of Ncdn downregulation.

Sialic Acid Enhanced the Antistress Capability under Challenging Situations by Increasing Synaptic Transmission

BackgroundIn early life, sialic acid (SA) plays a crucial role in neurodevelopment and neuronal function. However, it remains unclear whether and how SA supplementation in early life promotes behavioral response to stress in adolescence. ObjectivesThis study aimed to examine the effects and mechanisms of SA on the antistress capability under challenging situations. MethodsIn this study, C57BL/6 mice were daily supplemented with 1 μL SA solution/g body weight at the dose of 10 mg/kg/d from postnatal day (PND) 5–45. The antistress behaviors, including open field, elevated plus maze, forced swimming test, and tail suspension test, were performed at PND 46, PND 48, PND 50, and PND 52 to detect the antistress ability of SA, respectively. ResultsOur results showed that SA-treated mice were more active in facing challenging situations. The fiber photometry experiment showed that SA promoted the excitatory neuronal response in the medial prefrontal cortex (mPFC), which was extensively interconnected to stress. Besides, electrophysiological results revealed SA enhanced synaptic transmission rather than neuronal excitability of mPFC excitatory neurons. It was also supported by the increasing spine density of mPFC excitatory neurons. At the molecular amount, the SA elevated the transmitter release-related proteins of mPFC, including Synapsin 1 and vesicular glutamate transporter 1 (VGlut 1). Furthermore, SA supplementation enhanced synaptic transmission mainly by altering the kinetics of synaptic transmission. ConclusionsThe SA supplementation enhanced the response capability to stress under challenging situations, and the enhanced synaptic transmission of mPFC excitatory neurons may be the neurological basis of active response under challenging situations. In general, our findings suggested that SA supplementation in early life can promote stress resistance in adolescence.

Administration of the glutamate-modulating drug, riluzole, after stress prevents its delayed effects on the amygdala in male rats.

Extracellular glutamate levels are elevated across brain regions immediately after stress. Despite sharing common features in their genesis, the patterns of stress-induced plasticity that eventually take shape are strikingly different between these brain areas. While stress causes structural and functional deficits in the hippocampus, it has the opposite effect on the amygdala. Riluzole, an FDA-approved drug known to modulate glutamate release and facilitate glutamate clearance, prevents stress-induced deficits in the hippocampus. But whether the same drug is also effective in countering the opposite effects of stress in the amygdala remains unexplored. We addressed this question by using a rat model wherein even a single 2-h acute immobilization stress causes a delayed expression of anxiety-like behavior, 10 days later, alongside stronger excitatory synaptic connectivity in the basolateral amygdala (BLA). This temporal profile-several days separating the acute stressor and its delayed impact-allowed us to test if these effects can be prevented by administering riluzole in drinking water after acute stress. Poststress riluzole not only prevented the delayed increase in anxiety-like behavior on the elevated plus maze but also blocked the increase in spine density on BLA neurons 10 days later. Further, stress-induced increase in the frequency of miniature excitatory postsynaptic currents recorded in BLA slices, 10 days later, was also blocked by the same poststress riluzole administration. Together, these findings underscore the importance of therapeutic strategies, aimed at glutamate uptake and modulation, in correcting the delayed behavioral, physiological, and morphological effects of stress on the amygdala.