Plasticity In Hippocampal Neurons Research Articles

The SNX17-Retriever endosomal recycling pathway is a key regulator of synaptic function and plasticity in hippocampal neurons

The insertion and removal of integral membrane proteins is a key mechanism for the regulation of synaptic function. Once surface proteins are internalized, they can either be routed to lysosomes for degradation or can be recycled back to the cell surface. Two recycling protein complexes - the SNX27-Retromer complex and the recently discovered SNX17-Retriever complex - are the main drivers in recycling internalized cargoes in non-neuronal cells. In neurons, the SNX27-Retromer pathway has been shown to regulate surface expression of AMPA-type glutamate receptors (AMPARs) during long-term potentiation (LTP), but almost nothing is known regarding the role of the SNX17-Retriever pathway at synapses. Here, using cultured hippocampal neurons, we demonstrate that the SNX17-Retriever pathway localizes to both synaptic and extra-synaptic sites and that RNAi-mediated disruption of this pathway leads to the functional and structural loss of excitatory synapses. Moreover, we find that synaptic stimulation leads to the recruitment of SNX17 to synaptic sites in a manner that depends on Ca2+ influx through NMDARs, activation of CaMKII, and Retriever complex binding. Knockdown of either SNX17 or the Retriever subunit DSCR3 prevents structural plasticity of dendritic spines during LTP. Finally, this loss of structural plasticity is associated with altered traffcking of the cell adhesion molecule β1 Integrin, which is a SNX17 cargo in non-neuronal cells and as we show, in neurons as well. Additionally, SNX17-Retriever is shown to not play a role in AMPAR recycling. Preliminary studies suggest that SNX27 and SNX17 sort distinct cargos in neurons, suggesting that these two recycling pathways each play important, but unique, roles at synaptic sites. National Institute of Neurological Disorders and Stroke (NINDS) of the National Institutes of Health (NIH) under award numbers R01-NS129198 to L.S. Weisman and M.A. Sutton, R01-NS099340 and R01- NS064015 to L.S. Weisman, R01-NS097498 to M.A. Sutton, and R21-NS125449, and R01-NS116008 to S. Iwase, by the National Institute of Mental Health (NIMH) of the NIH under award number R21-MH127485 to S. Iwase. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

L-DOPA ameliorates hippocampus-based mitochondria respiratory dysfunction caused by GCI/R injury

Mitochondrial dysmorphology/dysfunction follow global cerebral ischemia-reperfusion (GCI/R) injury, leading to neuronal death. Our previous researches demonstrated that Levodopa (L-DOPA) improves learning and memory impairment in GCI/R rats by increasing synaptic plasticity of hippocampal neurons. This study investigates if L-DOPA, used in Parkinson's disease treatment, alleviates GCI/R-induced cell death by enhancing mitochondrial quality. Metabolomics and transcriptomic results showed that GCI/R damage affected the Tricarboxylic acid (TCA) cycle in the hippocampus. The results of this study show that L-DOPA stabilized mitochondrial membrane potential and ultrastructure in hippocampus of GCI/R rats, increased dopamine level in hippocampus, decreased succinic acid level, and stabilized Ca2+ level in CA1 subregion of hippocampus. As a precursor of dopamine, L-DOPA is presumed to improves mitochondrial function in hippocampus of GCI/R rats. However, dopamine cannot cross the blood-brain barrier, so L-DOPA is used in clinical therapy to supplement dopamine. In this investigation, OGD/R models were established in isolated mouse hippocampal neurons (HT22) and primary rat hippocampal neurons. Notably, dopamine exhibited a multifaceted impact, demonstrating inhibition of mitochondrial reactive oxygen species (mitoROS) production, stabilization of mitochondrial membrane potential and Ca2+ level, facilitation of TCA circulation, promotion of aerobic respiratory metabolism, and downregulation of succinic acid-related gene expression. Consistency between in vitro and in vivo results underscores dopamine's significant neuroprotective role in mitigating mitochondrial dysfunction following global cerebral hypoxia and ischemia injury. Supplement dopamine may represent a promising therapy to the cognitive impairment caused by GCI/R injury.

Mir155hg Accelerates Hippocampal Neuron Injury in Convulsive Status Epilepticus by Inhibiting Microglial Phagocytosis.

Convulsive status epilepticus (CSE) is a common critical neurological condition that can lead to irreversible hippocampal neuron damage and cognitive dysfunction. Multiple studies have demonstrated the critical roles that long non-coding RNA Mir155hg plays in a variety of diseases. However, less is known about the function and mechanism of Mir155hg in CSE. Here we investigate and elucidate the mechanism underlying the contribution of Mir155hg to CSE-induced hippocampal neuron injury. By applying high-throughput sequencing, we examined the expression of differentially expressed genes in normal and CSE rats. Subsequent RT-qPCR enabled us to measure the level of Mir155hg in rat hippocampal tissue. Targeted knockdown of Mir155hg was achieved by the AAV9 virus. Additionally, we utilized HE and Tunel staining to evaluate neuronal injury. Immunofluorescence (IF), Golgi staining, and brain path clamping were also used to detect the synaptic plasticity of hippocampal neurons. Finally, through IF staining and Sholl analysis, we assessed the degree of microglial phagocytic function. It was found that the expression of Mir155hg was elevated in CSE rats. HE and Tunel staining results showed that Mir155hg knockdown suppressed the hippocampal neuron loss and apoptosis followed CSE. IF, Golgi staining and brain path clamp data found that Mir155hg knockdown enhanced neuronal synaptic plasticity. The results from IF staining and Sholl analysis showed that Mir155hg knockdown enhanced microglial phagocytosis. Our findings suggest that Mir155hg promotes CSE-induced hippocampal neuron injury by inhibiting microglial phagocytosis.

Bergamot essential oil improves CUMS-induced depression-like behaviour in rats by protecting the plasticity of hippocampal neurons.

Bergamot essential oil (BEO) is an extract of the bergamot fruit with significant neuroprotective effect. This study was to investigate the effects and the underlying mechanism of BEO in mitigating depression. GC-MS were used to identify its constituents. Antidepressive properties of BEO were evaluated by sucrose preference test (SPT), force swimming test (FST) and open field test (OFT). Nissl staining was used to determine the number of Nissl bodies in hippocampus (HIPP) of rats. Changes in HIPP dendritic length and dendritic spine density were detected by Golgi-Cox staining. Immunohistochemistry and Western blot were used to detect the postsynaptic density protein-95 (PSD-95) and synaptophysin (SYP) in the HIPP of rats. The enzyme-linked immunosorbent assay was used to determine the 5-hydroxytryptamine (5-HT), insulin-like growth factor 1 (IGF-1) and interleukin-1β (IL-1β) in the HIPP, serum and cerebrospinal fluid (CSF) of rats. Inhaled BEO significantly improved depressive behaviour in chronic unpredictable mild stress (CUMS) rats. BEO increased Nissl bodies, dendritic length and spine density, PSD-95 and SYP protein in the HIPP. Additionally, BEO upregulated serum 5-HT, serum and CSF IGF-1, while downregulating serum IL-1β. Collectively, inhaled BEO mitigates depression by protecting the plasticity of hippocampal neurons, hence, providing novel insights into treatment of depression.

Long non‐coding RNA CASC15 enhances learning and memory in mice by promoting synaptic plasticity in hippocampal neurons

AbstractAlzheimer's disease (AD) is a debilitating systemic disorder that has a detrimental impact on the overall well‐being of individuals. Emerging research suggests that long non‐coding RNAs play a role in neural development and function. Nevertheless, the precise relationship between lncRNAs and Alzheimer's disease remains uncertain. The authors' recent discoveries have uncovered an unconventional mechanism involving the regulation of synaptic plasticity and the functioning of the hippocampal fragile X mental retardation protein 1 (FMR1)—neurotrophin 3 (NTF3) pathway, which is mediated by cancer susceptibility candidate 15 (CASC15). Subsequently, functional rescue experiments were performed to illustrate the efficient delivery of exosomes harboring a significant amount of 2610307p16Rik transcripts, which is the murine equivalent of human CASC15, to the hippocampal region of mice. This resulted in significant improvements in synaptic morphological plasticity and cognitive function in APP/PS1 mice. Given the pivotal involvement of CASC15 in synaptic plasticity and the distinctive regulatory mechanisms of the CASC15‐FMR1‐NTF3 axis, CASC15 emerges as a promising biomarker for Alzheimer's disease and may even possess potential as a feasible therapeutic target.

Tanshinone IIA Regulates Synaptic Plasticity in Mg2+-Free-Induced Epileptic Hippocampal Neurons via the PI3K/Akt Signaling Pathway.

Tanshinone IIA (TSIIA) is an element of the effective ingredients of Salvia miltiorrhiza Bunge (Labiatae), exhibits a significant therapeutic effect in brain neuroprotection. The focus of this study was the examination of synaptic plasticity of in Mg2+-free-induced epileptic hippocampus neurons and how TSIIA protects against it. The purity of the primary hippocampal neurons extracted from Sprague Dawley rats was assessed within 24 hours by microtubule-associated protein (MAP2) immunofluorescence staining. A hippocampal neuron model for Mg2+-free-induced spontaneous recurrent epileptiform discharge was developed, five experimental groups were then randomized: blank (Blank), model (Model), TSIIA (TSIIA, 20 µM), LY294002 (LY294002, 25 µM), and TSIIA+LY294002 (TSIIA+LY294002, 20 µM+25 µM). FIJI software was used to examine variations of neurite complexity, total length of hippocampal neurons, number of primary dendrites and density of dendritic spines. Developmental regulation brain protein (Drebrin) and brain-derived neurotrophic factor (BDNF) expression was evaluated using immunofluorescence staining and the relative expression of phospho-protein kinase B (p-Akt)/Akt, BDNF, synaptophysin (SYN) and postsynaptic density 95 (PSD-95) determined by Western blot. In contrast to the model group, TSIIA drastically reduced damage to synaptic plasticity of hippocampal neurons caused by epilepsy (p < 0.05). The TSIIA group showed a significant increase in the relative expression of PSD-95, SYN, BDNF, and p-Akt/Akt (p < 0.01). TSIIA was effective in reducing harm to the synaptic plasticity of hippocampal neurons induced by persistent status epilepticus, with the possible mechanism being regulation of the phosphatidylinositol 3-kinase 56 (PI3K)/Akt signaling pathway.

MKK3 K329 Mutation Attenuates Diabetes-Associated Cognitive Dysfunction by Blocking the MKK3-RAGE Interaction and Inhibiting Neuroinflammation.

The receptor for advanced glycation end products (RAGE) contributes to diabetes-associated cognitive dysfunction (DACD) through the interaction of its C-terminal AAs 2-5 with mitogen-activated protein kinase kinase 3 (MKK3). However, the associated MKK3 binding site is unknown. Here, db/db mice were used as a model for type 2 diabetes. GST pull-down assays and AutoDock Vina simulations were conducted to identify the key RAGE binding site in MKK3. This binding site was mutated to investigate its effects on DACD and to elucidate the underlying mechanisms. The interaction of MKK3 and RAGE, the levels of inflammatory factors, and the activation of microglia and astrocytes were tested. Synaptic morphology and plasticity in hippocampal neurons were assessed via electrophysiological recordings and Golgi staining. Behavioral tests were used to assess cognitive function. In this study, MKK3 bound directly to RAGE via its lysine 329 (K329), leading to the activation of the nuclear factor-κB (NF-κB) signaling pathway, which in turn triggered neuroinflammation and synaptic dysfunction, and ultimately contributed to DACD. MKK3 mutation at K329 reversed synaptic dysfunction and cognitive deficits by downregulating the NF-κB signaling pathway and inhibiting neuroinflammation. These results confirm that neuroinflammation and synaptic dysfunction in the hippocampus rely on the direct binding of MKK3 and RAGE. We conclude that MKK3 K329 binding to C-terminal RAGE (ct-RAGE) is a key mechanism by which neuroinflammation and synaptic dysfunction are induced in the hippocampus. This study presents a novel mechanism for DACD and proposes a novel therapeutic avenue for neuroprotection in DACD.

Changes in structural plasticity of hippocampal neurons in an animal model of multiple sclerosis.

Structural plasticity is critical for the functional diversity of neurons in the brain. Experimental autoimmune encephalomyelitis (EAE) is the most commonly used model for multiple sclerosis (MS), successfully mimicking its key pathological features (inflammation, demyelination, axonal loss, and gliosis) and clinical symptoms (motor and non-motor dysfunctions). Recent studies have demonstrated the importance of synaptic plasticity in EAE pathogenesis. In the present study, we investigated the features of behavioral alteration and hippocampal structural plasticity in EAE-affected mice in the early phase (11 days post-immunization, DPI) and chronic phase (28 DPI). EAE-affected mice exhibited hippocampus-related behavioral dysfunction in the open field test during both early and chronic phases. Dendritic complexity was largely affected in the cornu ammonis 1 (CA1) and CA3 apical and dentate gyrus (DG) subregions of the hippocampus during the chronic phase, while this effect was only noted in the CA1 apical subregion in the early phase. Moreover, dendritic spine density was reduced in the hippocampal CA1 and CA3 apical/basal and DG subregions in the early phase of EAE, but only reduced in the DG subregion during the chronic phase. Furthermore, mRNA levels of proinflammatory cytokines ( Il1β, Tnfα, and Ifnγ) and glial cell markers ( Gfap and Cd68) were significantly increased, whereas the expression of activity-regulated cytoskeleton-associated protein (ARC) was reduced during the chronic phase. Similarly, exposure to the aforementioned cytokines in primary cultures of hippocampal neurons reduced dendritic complexity and ARC expression. Primary cultures of hippocampal neurons also showed significantly reduced extracellular signal-regulated kinase (ERK) phosphorylation upon treatment with proinflammatory cytokines. Collectively, these results suggest that autoimmune neuroinflammation alters structural plasticity in the hippocampus, possibly through the ERK-ARC pathway, indicating that this alteration may be associated with hippocampal dysfunctions in EAE.

Neuronal plasticity in hippocampal neurons due to chronic mild stress and after stress removal in postnatal chicks.

The avian dorsomedial surface of the cerebral hemisphere is occupied by the hippocampal complex (HCC), which plays an important role in learning, memory, cognitive functions, and regulating instinctive behavior patterns. The objective of the study was to evaluate the effect of chronic mild stress (CMS) in 4, 6, and 8 weeks and after chronic stress removal (CSR) in 6 and 8 weeks, on neuronal plasticity in HCC neurons of chicks through the Golgi-Cox technique. Further, behavioral study and open field test were conducted to test of exploration or of anxiety. The study revealed that the length of CMS and CSR groups shows a similar pattern as in nonstressed (NS) chicks, while weight shows nonsignificant decrease due to CMS as compared to NS and after CSR. The behavioral test depicts that the CMS group took more time to reach the food as compared to the NS and CSR groups. Due to CMS, the dendritic field of multipolar neurons shows significant decrease in 4 weeks, but in 6- and 8-week-old chicks, the multipolar, pyramidal, and stellate neurons depict significant decrease, whereas after CSR all neurons show significant increase in 8-week-old chicks. In 4- and 8-week-old chicks, all neurons depict significant decrease in their spine number, whereas in 6 weeks only multipolar neurons show significant decrease, but after CSR significant increase in 8-week-old chicks was observed. The study revealed that HCC shows continuous neuronal plasticity, which plays a significant role in normalizing and re-establishing the homeostasis in animals to survive.

Design of Ultrapotent Genetically Encoded Inhibitors ofKv4.2 for Gating Neural Plasticity.

The Kv4.2 potassium channel plays established roles in neuronal excitability, while also being implicated in plasticity. Current means to study the roles of Kv4.2 are limited, motivating us to design a genetically encoded membrane tethered Heteropodatoxin-2 (MetaPoda). We find that MetaPoda is an ultrapotent and selective gating-modifier of Kv4.2. We narrow its site of contact with the channel to two adjacent residues within the voltage sensitive domain (VSD) and, with docking simulations, suggest that the toxin binds the VSD from within the membrane. We also show that MetaPoda does not require an external linker of the channel for its activity. In neurons (obtained from female and male rat neonates), MetaPoda specifically, and potently, inhibits all Kv4 currents, leaving all other A-type currents unaffected. Inhibition of Kv4 in hippocampal neurons does not promote excessive excitability, as is expected from a simple potassium channel blocker. We do find that MetaPoda's prolonged expression (1 week) increases expression levels of the immediate early gene cFos and prevents potentiation. These findings argue for a major role of Kv4.2 in facilitating plasticity of hippocampal neurons. Lastly, we show that our engineering strategy is suitable for the swift engineering of another potent Kv4.2-selective membrane-tethered toxin, Phrixotoxin-1, denoted MetaPhix. Together, we provide two uniquely potent genetic tools to study Kv4.2 in neuronal excitability and plasticity.

Reversing Aging: Decline in Complex Olfactory Learning Can be Rectified by Restoring Intrinsic Plasticity of Hippocampal CA1 Pyramidal Neurons.

The acquisition of complex rules requires modifications in intrinsic plasticity of excitatory neurons within relevant brain areas. Olfactory discrimination (OD) rule learning occludes slow calcium-dependent potassium current (sIAHP ) in piriform cortex (PC) pyramidal neurons, which increases their intrinsic neuronal excitability. Similar learning-induced sIAHP changes are demonstrated in hippocampal CA1. The shutdown of sIAHP is mediated by the metabotropic activation of the kainate subtype glutamatergic receptor, GluK2. Here, the duration of training required for OD rule learning increased significantly as the mice matured and aged is first shown, which appears earlier in 5xFAD mice. At the cellular biophysical level, aging is accompanied by reduction in the post-burst AHP in these neurons, while neuronal excitability remains stable. This is in contrast to aging CA1 neurons that exhibit enhanced post-burst AHPs in previous reports. Kainate reduces post-burst AHP in adults, but not in aged PC neurons, whereas it reduces post-burst AHPs in hippocampal CA1 pyramidal neurons of both young and aged mice. Overexpression of GluK2 in CA1 neurons restores OD learning capabilities in aged wild-type and 5xFAD mice, to a level comparable to young adults. Activation of GluK2 receptors in selectively vulnerable neurons can prevent aging-related cognitive decline is suggested.

Dynamic regulation of BDNF gene expression by estradiol and lncRNA HOTAIR

Brain derived neurotrophic factor (BDNF) is a major neurotransmitter that controls growth and maintenance of neurons and its misregulation is linked to neurodegeneration and human diseases. Estradiol (E2) is well-known to regulate the process of differentiation and plasticity of hippocampal neurons. Here we examined the mechanisms of BDNF gene regulation under basal conditions and under stimuli such as E2. Our results demonstrated that BDNF expression is induced by E2 in vitro in HT22 cells (hippocampal neuronal cells) and in vivo (in ovariectomized mouse brain under E2-treatment). Using chromatin immunoprecipitation assay, we demonstrated that estrogen receptors (ERα, ERβ) were enriched at the BDNF promoter in presence of E2. Additionally, ER-coregulators (e.g., CBP/p300, MLL3), histone acetylation, H3K4-trimethylation, and RNA polymerase II levels were also elevated at the BDNF promoter in an E2-dependent manner. Additionally, under the basal conditions (in the absence of E2), the long noncoding RNA HOTAIR and its interacting partners PRC2 and LSD1 complexes binds to the promoter of BDNF and represses its expression. HOTAIR knockdown -relieves the repression resulting in elevation of BDNF expression. Further, levels of HOTAIR-interacting partners, EZH2 and LSD1 were reduced at the BDNF promoter upon HOTAIR-knockdown revealing that HOTAIR plays a regulatory role in BDNF gene expression by modulating promoter histone modifications. Additionally, we showed that E2 induced-BDNF expression is mediated by the displacement of silencing factors, EZH2 and LSD1 at BDNF promoter and subsequent recruitment of active transcription machinery. These results reveal the mechanisms of BDNF gene regulation under the basal condition and in presence of a positive regulator such as E2 in neuronal cells.

The Edible Seaweed Gelidium amansii Promotes Structural Plasticity of Hippocampal Neurons and Improves Scopolamine-Induced Learning and Memory Impairment in Mice.

Gelidium amansii has been gaining profound interest in East Asian countries due to its enormous commercial value for agar production and its extensive pharmacological properties. Previous studies have shown that the ethanol extract of Gelidium amansii (GAE) has promising neurotrophic effects in in vitro conditions. The present study aimed at investigating the protective effects of GAE against scopolamine-induced cognitive deficits and its modulatory effects on hippocampal plasticity in mice. For memory-related behavioral studies, the passive avoidance test and radial arm maze paradigm were conducted. The brain slices of the hippocampus CA1 neurons of experimental mice were then prepared to perform Golgi staining for analyzing spine density and its characteristic shape, and immunohistochemistry for assessing the expression of different pre- and postsynaptic proteins. Following oral administration of GAE (0.5 mg/g body weight), mice with memory deficits exhibited a significant increase in the latency time on the passive avoidance test and a decrease in the number of working and reference memory errors and latency time on the radial arm maze test. Microscopic observations of Golgi-impregnated tissue sections and immunohistochemistry of hippocampal slices showed that neurons from GAE-treated mice displayed higher spine density and spine dynamics, increased synaptic contact, and the recruitment of memory-associated proteins such as N-methyl-D-aspartate receptors (NR2A and NR2B) and postsynaptic density-95 (PSD-95) when compared with the control group. With these memory-protective functions and a modulatory role in underlying memory-related events, GAE could be a potential functional food and a promising source of pharmacological agents for the prevention and treatment of memory-related brain disorders.

Panoramic variation analysis of a family with neurodevelopmental disorders caused by biallelic loss-of-function variants in TMEM141, DDHD2, and LHFPL5.

Highly clinical and genetic heterogeneity of neurodevelopmental disorders presents a major challenge in clinical genetics and medicine. Panoramic variation analysis is imperative to analyze the disease phenotypes resulting from multilocus genomic variation. Here, a Pakistani family with parental consanguinity was presented, characterized with severe intellectual disability (ID), spastic paraplegia, and deafness. Homozygosity mapping, integrated single nucleotide polymorphism (SNP) array, whole-exome sequencing, and whole-genome sequencing were performed, and homozygous variants in TMEM141 (c.270G>A, p.Trp90*), DDHD2 (c.411+767_c.1249-327del), and LHFPL5 (c.250delC, p.Leu84*) were identified. A Tmem141p.Trp90*/p.Trp90* mouse model was generated. Behavioral studies showed impairments in learning ability and motor coordination. Brain slice electrophysiology and Golgi staining demonstrated deficient synaptic plasticity in hippocampal neurons and abnormal dendritic branching in cerebellar Purkinje cells. Transmission electron microscopy showed abnormal mitochondrial morphology. Furthermore, studies on a human in vitro neuronal model (SH-SY5Y cells) with stable shRNA-mediated knockdown of TMEM141 showed deleterious effect on bioenergetic function, possibly explaining the pathogenesis of replicated phenotypes in the cross-species mouse model. Conclusively, panoramic variation analysis revealed that multilocus genomic variations of TMEM141, DDHD2, and LHFPL5 together caused variable phenotypes in patient. Notably, the biallelic loss-of-function variants of TMEM141 were responsible for syndromic ID.

Sodium channel endocytosis drives axon initial segment plasticity.

Activity-dependent plasticity of the axon initial segment (AIS) endows neurons with the ability to adapt action potential output to changes in network activity. Action potential initiation at the AIS highly depends on the clustering of voltage-gated sodium channels, but the molecular mechanisms regulating their plasticity remain largely unknown. Here, we developed genetic tools to label endogenous sodium channels and their scaffolding protein, to reveal their nanoscale organization and longitudinally image AIS plasticity in hippocampal neurons in slices and primary cultures. We find that N-methyl-d-aspartate receptor activation causes both long-term synaptic depression and rapid internalization of AIS sodium channels within minutes. The clathrin-mediated endocytosis of sodium channels at the distal AIS increases the threshold for action potential generation. These data reveal a fundamental mechanism for rapid activity-dependent AIS reorganization and suggests that plasticity of intrinsic excitability shares conserved features with synaptic plasticity.

Transcriptome analysis of the effects of maternal fructose exposure during gestation and lactation on the cytoskeleton of offspring hippocampus

Excessive fructose consumption poses a public health concern. Maternal fructose overconsumption impairs offspring hippocampal function, indicating hippocampal sensitivity to fructose. The hippocampus is the vital for spatial learning and memory, and the cytoskeletal structure is crucial for hippocampal neuronal plasticity. The Rho GTPase is a key regulator of neuronal cytoskeleton formation, with RhoA protein governing neuronal growth and development. The RhoA/ROCK2 pathway affects myosin light chain phosphorylation, leading to cytoskeletal reorganization, actin cytoskeleton changes, and neurite retraction. However, the effects of maternal fructose exposure during gestation and lactation on the offspring's neural cytoskeleton remain unclear. We established maternal fructose exposure models during gestation and lactation, assessing fasting blood glucose levels in offspring confirm model effectiveness. Whole transcriptome sequencing examined offspring hippocampal developmental programming. Immunofluorescence and Western blot analyses assessed RhoA/ROCK2 pathway expression changes in the hippocampus, with PCR validating transcriptome sequencing results. Transcriptome sequencing identified 193 and 298 differentially expressed genes in the control, 13% fructose, and 40% fructose groups, respectively. GO and KEGG analyses revealed significant changes related to neural development, learning memory, and cytoskeleton in both fructose-exposed groups. GSEA indicated substantial cytoskeleton-related alterations in the offspring. Immunofluorescence demonstrated significant CRMP2 protein down-regulation in both fructose-exposed groups. Western blotting showed significantly higher expression of RhoA, ROCK2, p-ROCK2, and p-MLC2 in the fructose-exposed groups (P < 0.05). Maternal high-fructose exposure significantly impacts gene expression in offspring. These alterations may influence hippocampal neurodevelopment by up-regulating the RhoA/ROCK2 pathway, leading to cytoskeletal damage and axon growth inhibition.

A critical role for CaMKII in behavioral timescale synaptic plasticity in hippocampal CA1 pyramidal neurons.

Behavioral timescale synaptic plasticity (BTSP) is a type of non-Hebbian synaptic plasticity reported to underlie place field formation. Despite this important function, the molecular mechanisms underlying BTSP are poorly understood. The α-calcium-calmodulin-dependent protein kinase II (αCaMKII) is activated by synaptic transmission-mediated calcium influx, and its subsequent phosphorylation is central to synaptic plasticity. Because the activity of αCaMKII is known to outlast the event triggering phosphorylation, we hypothesized that it could mediate the extended timescale of BTSP. To examine the role of αCaMKII in BTSP, we performed whole-cell in vivo and in vitro recordings in CA1 pyramidal neurons from mice engineered with a point mutation at the autophosphorylation site (T286A) causing accelerated signaling kinetics. Here, we demonstrate a profound deficit in synaptic plasticity, strongly suggesting that αCaMKII signaling is required for BTSP. This study elucidates part of the molecular mechanism of BTSP and provides insight into the function of αCaMKII in place cell formation and ultimately learning and memory.

Gestational dexamethasone exposure impacts hippocampal excitatory synaptic transmission and learning and memory function with transgenerational effects.

The formation of learning and memory is regulated by synaptic plasticity in hippocampal neurons. Here we explored how gestational exposure to dexamethasone, a synthetic glucocorticoid commonly used in clinical practice, has lasting effects on offspring's learning and memory. Adult offspring rats of prenatal dexamethasone exposure (PDE) displayed significant impairments in novelty recognition and spatial learning memory, with some phenotypes maintained transgenerationally. PDE impaired synaptic transmission of hippocampal excitatory neurons in offspring of F1 to F3 generations, and abnormalities of neurotransmitters and receptors would impair synaptic plasticity and lead to impaired learning and memory, but these changes failed to carry over to offspring of F5 and F7 generations. Mechanistically, altered hippocampal miR-133a-3p-SIRT1-CDK5-NR2B signaling axis in PDE multigeneration caused inhibition of excitatory synaptic transmission, which might be related to oocyte-specific high expression and transmission of miR-133a-3p. Together, PDE affects hippocampal excitatory synaptic transmission, with lasting consequences across generations, and CDK5 in offspring's peripheral blood might be used as an early-warning marker for fetal-originated learning and memory impairment.

A comparison of the impact on neuronal transcriptome and cognition of rAAV5 transduction with three different doses in the mouse hippocampus.

Recombinant adeno-associated viruses (rAAVs) are widely used in genetic therapeutics. AAV5 has shown superior transduction efficiency, targeting neurons and glial cells in primate brains. Nonetheless, the comprehensive impact of AAV5 transduction on molecular and behavioral alterations remains unexplored. This study focuses on evaluating the effects of AAV5 transduction in the hippocampus, a critical region for memory formation and emotional processes. In this experiment, fluorescence-activated cell sorting (FACS) was utilized to isolate the mCherry-labeled pyramidal neurons in the hippocampus of CaMkIIα-cre mice following three different doses rAAV5-mCherry infusion after 3 weeks, which were then subjected to RNA sequencing (RNA-seq) to assess gene expression profiles. The cytokines concentration, mRNA expression, and glial response in hippocampi were confirmed by ELASA, digital droplet PCR and immunohistochemistry respectively. Locomotion and anxiety-like behaviors were elevated by Open Field Test and Elevated Plus Maze Test, while the Y-Maze were used to assessed spatial working memory. Recognition memory and fear responses were examined by the Novel Object Recognition Test and Fear Conditioning Test, respectively. We found that 2.88 × 1010 v.g rAAV5 transduction significantly upregulated genes related to the immune response and apoptosis, and downregulated genes associated with mitochondrial function and synaptic plasticity in hippocampal pyramidal neurons, while did not induce neuronal loss and gliosis compared with 2.88 × 109 v.g and 2.88 × 108 v.g. Furthermore, the same doses impaired working memory and contextual fear memory, without effects on locomotion and anxiety-related behaviors. Our findings highlight the detrimental impact of high-dose administration compared to median-dose or low-dose, resulting in increased neural vulnerability and impaired memory. Therefore, when considering the expression effectiveness of exogenous genes, it is crucial to also take potential side effects into account in clinical settings. However, the precise molecular mechanisms underlying these drawbacks of high-dose rAAV5-mCherry still require further investigation in future studies.

MiR-204-5p Plays a Critical Role in the Pathogenesis of Depression and Anti-depression Action of Venlafaxine in the Hippocampus of Mice

Background: Venlafaxine has been demonstrated to treat diseases such as social anxiety disorder and depression. Most of antidepressants including venlafaxine have a certain effect, but significant side effects. Therefore, it is necessary for us to research the development of novel antidepressants for effective treatment in practice. MicroRNA-204 (miR-204) is highly expressed in brain tissue, and plays a critical role in the synaptic plasticity of hippocampal neurons in rats. However, the underlying molecular mechanism of miR-204 remains unclear to date, this study aims to offer unique insights into depression and provide a theoretical basis for clinical physicians. A chronic social defeat stress (CSDS) was initially adopted for establishing a mice model of depression in this research and depression-like behaviors were evaluated by a series of behavioral experiments including the sucrose preference test (SPT), the tail suspension test (TST), the forced swim test (FST) and the social interaction test (SIT). Quantitative real-time reverse transcription PCR (qRT-PCR) was also conducted to test the expression levels of miR-204 and BDNF in the hippocampus of mice. Finally, gene interference of miR-204-5p was further adopted to test whether miR-204-5p played an effective role in the antidepressant effects of venlafaxine in mice. Our data implicated that CSDS significantly increased the miR-204-5p but not miR-204-3p levels in the hippocampus of mice. The treatment of venlafaxine obviously relieved depression- like behaviors of CSDS-induced mice. The usage of venlafaxine abolished the increasing effects on the expression of miR-204-5p but up-regulated the BDNF expression level in CSDS-exposured mice. More importantly, we found that genetic overexpression of miR-204-5p decreased the reverse effects of venlafaxine on depressive-like behaviors and genetic knockdown of hippocampal miR-204-5p relieved the depressive-like behaviors and neurogenesis in CSDS-induced mice. miR-204-5p played an effective role in the antidepressant effects of venlafaxine in CSDS-induced mice.