Hippocampal Dendritic Spine Density Research Articles

Upregulation of cholinergic modulators Lypd6 and Lypd6b associated with autism drives anxiety and cognitive decline

Intellectual disability and autistic features are associated with chromosome region 2q23.q23.2 duplication carrying LYPD6 and LYPD6B genes. Here, we analyzed LYPD6 and LYPD6B expression in patients with different neuropsychiatric disorders. Increased LYPD6 and LYPD6B expression was revealed in autism and other disorders. To study possible consequences of Lypd6 and Lypd6b overexpression in the brain, we used a mouse model with intracerebroventricular delivery of recombinant analogs of these proteins. A two-week infusion evoked significant memory impairment and acute stress. Both modulators downregulated hippocampal and amygdala dendritic spine density. No changes in synaptic plasticity were observed. Intracerebroventricular administration by both proteins downregulated hippocampal expression of Lypd6, Lypd6b, and α7 nicotinic acetylcholine receptor (nAChR). Similar to Lypd6, Lypd6b targeted different nAChR subtypes in the brain with preferential inhibition of α7- and α4β2-nAChRs. Thus, increased Lypd6 and Lypd6b level in the brain are linked to cholinergic system depression, neuronal atrophy, memory decline, and anxiety.

Melatonin mitigates cisplatin-induced cognitive impairment in rats and improves hippocampal dendritic spine density.

Cisplatin-induced cognitive impairment (chemobrain) affects a considerable percentage of cancer patients and has no established pharmacological treatment. Chemobrain can be associated with neuroinflammation and oxidative stress. Melatonin, a pineal hormone, is known to have antioxidant, anti-inflammatory and neuroprotective potential. In this study, we investigated cisplatin-induced cognitive impairment in rats and whether melatonin can improve or reverse this impairment. Behavioral testing involved measuring working memory using the novel location recognition test (NLRT) under conditions of cisplatin or cisplatin + melatonin treatment, followed by the collection of rats' brains. The brains were subsequently stained with Golgi-Cox stain and then the hippocampus area CA3 of each one was examined, and dendritic spine density was calculated. Treatment with cisplatin resulted in deficits in the rats' performance in the NLRT (P < 0.05). These deficits were prevented by the coadministration of melatonin (P < 0.05). Cisplatin also reduced the density of dendritic spines in the hippocampus (P < 0.0001), specifically CA3 area, while the coadministration of melatonin significantly reversed this reduction (P < 0.001). This study showed that melatonin can ameliorate cisplatin-induced spatial memory deficits and dendritic spines density abnormalities in rats. Given that melatonin is a safe and wildly used supplement, it is feasible to explore its use as a palliative intervention in cancer treatment.

Caspase‐dependent Apoptosis Inhibition Improves Cognitive Function in Myocardial Infarction Rats

AbstractBackgroundCognitive impairment was frequently found following myocardial infarction (MI). Apoptosis, particularly in the hippocampal area, has been proposed as a mechanism involving in the cognitive impairment through the initiation of brain cell death and subsequently dendritic spine loss. The hypothesis of this study is that the inhibition of apoptosis using a pan‐caspase inhibitor (Z‐VAD‐FMK) improves hippocampal dependent cognitive function in MI rats via attenuating brain apoptosis and dendritic spine lossMethodMale Wistar rats were divided into sham operation or permanent left anterior descending coronary artery ligation‐induced MI. After one week, MI rats with LVEF less than 50% were randomly assigned to one of three interventions: (1) MI‐vehicle (DMSO), (2) Enalapril as a positive control (10 mg/kg/day, PO), and (3) A pan‐caspase inhibitor (Z‐VAD‐FMK, 1 mg/kg/day, IP). All rats received the intervention for 4 weeks, then cardiac function and hippocampal‐dependent cognitive function were assessed before they were sacrificed. Hippocampal dendritic spine density and apoptotic protein expression were determined.ResultMI‐vehicle rats exhibited cardiac dysfunction (as shown by a decrease in %LVEF), cognitive impairment (as shown by decreased %preference of novel object recognition), and hippocampal dendritic spine loss. Furthermore, our data showed that apoptosis was significantly increased (as shown by increased cleaved‐caspase 3/Pro‐caspase 3 levels) in MI‐vehicle rats, compared with the sham rats (as shown in Figure). Treatment with Z‐VAD‐FMK and enalapril equally improved cardiac function, cognitive function, and increased hippocampal dendritic spine density, compared with the MI‐vehicle rats. Z‐VAD‐FMK demonstrated a greater benefit in reducing apoptosis than enalapril in the brain of MI rats.ConclusionApoptosis inhibitor shared similar efficacy with enalapril in improving cognitive function through suppressing brain apoptosis and restoring hippocampal dendritic spine density in MI rats.

Simvastatin ameliorates synaptic plasticity impairment in chronic mild stress-induced depressed mice by modulating hippocampal NMDA receptor.

In our previous study, we showed simvastatin exerts an antidepressant effect and inhibits neuroinflammation. Given the role of synaptic impairment in depression development, we investigate the effect of simvastatin on synaptic plasticity in depression and the related mechanisms. Electrophysiological analysis, Golgi staining, and transmission electron microscope were performed to analyze the effect of simvastatin on synaptic impairment in depression. In addition, the localization and reactivity of N-methyl-D-aspartate receptor (NMDAR) subunits and the downstream signaling were investigated to explore the mechanism of simvastatin's effect on synaptic plasticity. Simvastatin ameliorated the reduction of the magnitude of long-term potentiation (LTP) in Schaffer collateral-CA1, restored hippocampal dendritic spine density loss, improved the number of spine synapses, reversed the reduction in BrdU-positive cells in chronic mild stress (CMS)-induced depressed mice, and ameliorated NMDA-induced neurotoxicity in hippocampal neurons. Dysfunction of NMDAR activity in the hippocampus is associated with depression. Simvastatin treatment reversed the surface expression and phosphorylation changes of NMDAR subunits in NMDA-treated hippocampal neurons and depressed mice. In addition, simvastatin further increased the levels of mature BDNF, activating TrkB-Akt-mTOR signaling, which is critical for synaptic plasticity. These findings suggest that simvastatin can improve the dysfunction of NMDAR and ameliorate hippocampal synaptic plasticity impairment in depressed mice.

Metformin Exerted Neuroprotective Effects on Cognition in Rats with Trastuzumap‐Induced Brain Toxicity

AbstractBackgroundTrastuzumap (Trz) is effectively used for breast cancer patients to improve health status and reduce mortality rate. Nevertheless, several studies reported its adverse effect on brain toxicity. To date, the mechanisms of Trz‐induced brain toxicity are not fully understood. Metformin is a generic prescribed drug for type 2 diabetes mellitus, while in the past decade it also used for attenuating the adverse effects of chemotherapy. However, the effects of metformin on brain mitochondrial function, hippocampal microglial function, hippocampal synaptic plasticity, and cognitive function in Trz‐induced brain toxicity have never been investigated.MethodEighteen male Wistar rats were randomly divided into two groups; control group (0.9% NSS, intraperitoneal (i.p.) injection, n = 8) and Trz‐treated group (4 mg/kg for 7 days, i.p. injection, n = 16). Then, Trz‐treated rats were divided into two subgroups (n = 6/ subgroup) to receive either vehicle (0.9% NSS, daily via oral gavage) or metformin (250 mg/kg/day for 7 days, daily via oral gavage). At the end of experiment protocol, cognitive function was measured, and brains were obtained for further molecular investigation.ResultTrz‐treated rats demonstrated an increase of mitochondrial ROS production, increased mean fluorescence intensity of ionized calcium binding adaptor molecule 1 (Iba1), decreased hippocampal dendritic spine density, decreased preferent index in novel object location (NOL) and novel object recognition (NOR) test (p&lt;0.05, Figure 1A‐F). Metformin‐treated in Trz‐rats reversed the adverse effect of Trz by attenuated mitochondrial ROS production, decreased mean fluorescence intensity of Iba1, increased hippocampal dendritic spine density, as well as increased preferent index in NOL and NOR test (p&lt;0.05, Figure 1A‐F).ConclusionTrz‐induced brain toxicity as indicated by brain mitochondrial dysfunction, decreased hippocampal microglial function, impaired hippocampal synaptic plasticity, and cognitive dysfunction, while metformin alleviated those deleterious effects. The findings in this study emphasize the roles of metformin against Trz‐induced brain toxicity and strengthen

Increased Expression of Kif11/Kinesin‐5 mRNA Offsets Cognitive Deficits In An Alzheimer’s Mouse Model, Blocks Aβ‐Mediated Decreases in Long‐Term Potentiation and Spine Density, and is Associated With Better Cognitive Performance in Alzheimer’s Patients

AbstractBackgroundInteractions between the Aβ with intra‐ and extra‐cellular molecules disrupt neuronal structures and functions, leading to cognitive dysfunction in Alzheimer’s disease (AD). We previously have shown that Aβ competitively inhibits the microtubule motor protein KIF11 (Kinesin‐5/Eg5), which regulates microtubule dynamics, cellular trafficking, neuronal migration, and neuronal structures important for learning and memory. In vitro cell culture and ex vivo electrophysiology experiments later revealed that the inhibition of KIF11 by Aβ underlies multiple phenotypes associated with AD, including decreases in LTP, breakdown of the microtubule network, and deficits in neurotransmitter receptor localization and function. Here we aimed to determine whether increased Kif11 expression overrides phenotypes associated with AD.MethodsKif11 overexpressing mice were crossed with the 5xFAD mouse model of AD to generate 5xFAD mice that overexposes Kif11. Learning and memory of these mice was measured through the performance of 6‐8 month old mice in the radial‐arm water maze and LTP was measured by the fEPSP response to high‐frequency stimulation of the CA1 region in hippocampal slices of our transgenic mice. Primary rat neurons were transiently transfected to express human APP harboring the Swedish mutation (APPswe) with or without Kif11 overexpression to determine whether increased Kif11 expression affects Aβ‐mediated decreases in dendritic spine, We then evaluated cognitive function in amyloid positive individuals in the ROS/MAP study with their KIF11 mRNA expression in 4 brain regions, the DLPFC (N = 939), PCC (N = 527), and the CN (N = 715).ResultsKIF11 overexpression overrides Aβ toxicity and rescues Aβ‐mediated decreases in LTP in hippocampal slices and dendritic spine density in cultured neurons. Furthermore, we found that spatial and working memory deficits were prevented in a 5xFAD Alzheimer’s mouse model that overexpresses Kif11. Analyses of RNAseq data from human participants in the Religious Order Study and Memory and Aging (ROS/MAP) revealed that higher KIF11 expression in AD patients correlated with better cognitive performance.ConclusionKIF11 is essential for maintaining synaptic structures and functions critical for learning and memory in AD, and preventing or overriding the inhibitory interaction of Aβ with Kif11 could be a promising therapeutic target for multiple AD phenotypes.

MAC28 Attenuates Neurodegeneration and Restores Cognitive Function via Reducing Peripheral Insulin Resistance, Neuroinflammation, Brain Oxidative Stress, Amyloid‐β Deposition, and Loss of Dendritic Spines in High‐Fat Diet‐induced Obese Rats

AbstractBackgroundLong‐term high‐fat diet (HFD) consumption induces not only peripheral insulin resistance with low‐grade systemic inflammation, but also neuroinflammation and subsequent brain pathologies including neurodegeneration, which can lead to cognitive impairment (1). MAC28, a novel mono‐carbonyl analogue of curcumin, was recently identified as a novel MD‐2 inhibitor, and has been shown to attenuate systemic inflammation (2). However, the effects of MAC 28 on the neuroinflammation, neurodegeneration and cognitive function in the HFD‐induced obese rats have never been studied.MethodMale Wistar rats were fed either a normal diet (ND; n = 8) or HFD (n = 40) for 16 weeks. At week 13, ND‐fed rats were orally administered a vehicle for 4 weeks, while HFD‐fed rats were randomly divided into 5 groups (n = 8/group). Each subgroup was orally administrated either vehicle, 10mg/kg/day of MAC 28, 20mg/kg/day of MAC 28, 40mg/kg/day of MAC 28 or 300 mg/kg/day of metformin for 4 weeks. At the end of experimental protocol, the novel object location (NOL) test was examined in each rat. Brains were rapidly removed to determine brain TLR4‐MD‐2 signaling pathway, inflammatory cytokines, brain oxidative stress, dendritic spine density, amyloid and tau pathology.ResultHFD‐fed rats developed obesity with peripheral insulin resistance. Neuroinflammation was observed in HFD‐fed rats, as evidenced by increased expressions of hippocampal MD‐2, TLR4 and TNF‐α levels. In addition, HFD‐fed rats not only increased the levels of brain MDA, hippocampal amyloid‐β/APP ratio, but also reduced hippocampal dendritic spine density, resulting in cognitive decline. Although all doses of MAC 28 and metformin attenuated peripheral insulin resistance, brain pathologies and cognitive impairment, MAC 28 (20mg/kg/day and 40mg/kg/day) and metformin had the highest efficacy in attenuating peripheral insulin resistance, brain inflammation, brain oxidative stress, amyloid‐β deposition and improving dendritic spines, resulting in restoring cognitive function (P &lt; 0.05, Figure 1).ConclusionThese findings suggest that an obvious neuroprotective effect of MD‐2 inhibitor may be the potential strategy for attenuating neurodegenerative disorders in the obese‐insulin resistant condition.

ZIP9 mediates the effects of DHT on learning, memory and hippocampal synaptic plasticity of male Tfm and APP/PS1 mice.

Androgens are closely associated with functions of hippocampal learning, memory, and synaptic plasticity. The zinc transporter ZIP9 (SLC39A9) regulates androgen effects as a binding site distinct from the androgen receptor (AR). However, it is still unclear whether androgens regulate their functions in hippocampus of mice through ZIP9. Compared with wild-type (WT) male mice, we found that AR-deficient male testicular feminization mutation (Tfm) mice with low androgen levels had learning and memory impairment, decreased expression of hippocampal synaptic proteins PSD95, drebrin, SYP, and dendritic spine density. Dihydrotestosterone (DHT) supplementation significantly improved these conditions in Tfm male mice, although the beneficial effects disappeared after hippocampal ZIP9 knockdown. To explore the underlying mechanism, we first detected the phosphorylation of ERK1/2 and eIF4E in the hippocampus and found that it was lower in Tfm male mice than in WT male mice, it upregulated with DHT supplementation, and it downregulated after hippocampal ZIP9 knockdown. Next, we found that the expression of PSD95, p-ERK1/2, and p-eIF4E increased in DHT-treated mouse hippocampal neuron HT22 cells, and ZIP9 knockdown or overexpression inhibited or further enhanced these effects. Using the ERK1/2 specific inhibitor SCH772984 and eIF4E specific inhibitor eFT508, we found that DHT activated ERK1/2 through ZIP9, resulting in eIF4E phosphorylation, thus promoting PSD95 protein expression in HT22 cells. Finally, we found that ZIP9 mediated the effects of DHT on the expression of synaptic proteins PSD95, drebrin, SYP, and dendritic spine density in the hippocampus of APP/PS1 mice through the ERK1/2-eIF4E pathway and affected learning and memory. This study demonstrated that androgen affected learning and memory in mice through ZIP9, providing new experimental evidence for improvement in learning and memory in Alzheimer's disease with androgen supplementation.

Whole-Transcriptome Analysis of Repeated Low-Level Sarin-Exposed Rat Hippocampus and Identification of Cerna Networks to Investigate the Mechanism of Sarin-Induced Cognitive Impairment.

Sarin is a potent organophosphorus nerve agent that causes cognitive dysfunction, but its underlying molecular mechanisms are poorly understood. In this study, a rat model of repeated low-level sarin exposure was established using the subcutaneous injection of 0.4 × LD50 for 21 consecutive days. Sarin-exposed rats showed persistent learning and memory impairment and reduced hippocampal dendritic spine density. A whole-transcriptome analysis was applied to study the mechanism of sarin-induced cognitive impairment, and a total of 1035 differentially expressed mRNA (DEmRNA), including 44 DEmiRNA, 305 DElncRNA, and 412 DEcircRNA, were found in the hippocampus of sarin-treated rats. According to Gene Ontology (GO) annotation, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, and Protein-Protein Interaction (PPI) analysis, these DERNAs were mainly involved in neuronal synaptic plasticity and were related to the pathogenesis of neurodegenerative diseases. The circRNA/lncRNA-miRNA-mRNA ceRNA network was constructed, in which Circ_Fmn1, miR-741-3p, miR-764-3p, miR-871-3p, KIF1A, PTPN11, SYN1, and MT-CO3 formed one circuit, and Circ_Cacna1c, miR-10b-5p, miR-18a-5p, CACNA1C, PRKCD, and RASGRP1 constituted another circuit. The balance between the two circuits was crucial for maintaining synaptic plasticity and may be the regulatory mechanism by which sarin causes cognitive impairment. Our study reveals the ceRNA regulation mechanism of sarin exposure for the first time and provides new insights into the molecular mechanisms of other organophosphorus toxicants.

Psilocybin facilitates fear extinction in mice by promoting hippocampal neuroplasticity.

Posttraumatic stress disorder (PTSD) and depression are highly comorbid. Psilocybin exerts substantial therapeutic effects on depression by promoting neuroplasticity. Fear extinction is a key process in the mechanism of first-line exposure-based therapies for PTSD. We hypothesized that psilocybin would facilitate fear extinction by promoting hippocampal neuroplasticity. First, we assessed the effects of psilocybin on percentage of freezing time in an auditory cued fear conditioning (FC) and fear extinction paradigm in mice. Psilocybin was administered 30 min before extinction training. Fear extinction testing was performed on the first day; fear extinction retrieval and fear renewal were tested on the sixth and seventh days, respectively. Furthermore, we verified the effect of psilocybin on hippocampal neuroplasticity using Golgi staining for the dendritic complexity and spine density, Western blotting for the protein levels of brain derived neurotrophic factor (BDNF) and mechanistic target of rapamycin (mTOR), and immunofluorescence staining for the numbers of doublecortin (DCX)- and bromodeoxyuridine (BrdU)-positive cells. A single dose of psilocybin (2.5 mg/kg, i.p.) reduced the increase in the percentage of freezing time induced by FC at 24 h, 6th day and 7th day after administration. In terms of structural neuroplasticity, psilocybin rescued the decrease in hippocampal dendritic complexity and spine density induced by FC; in terms of neuroplasticity related proteins, psilocybin rescued the decrease in the protein levels of hippocampal BDNF and mTOR induced by FC; in terms of neurogenesis, psilocybin rescued the decrease in the numbers of DCX- and BrdU-positive cells in the hippocampal dentate gyrus induced by FC. A single dose of psilocybin facilitated rapid and sustained fear extinction; this effect might be partially mediated by the promotion of hippocampal neuroplasticity. This study indicates that psilocybin may be a useful adjunct to exposure-based therapies for PTSD and other mental disorders characterized by failure of fear extinction.

Increased Brain-Derived Neurotrophic Factor and Hippocampal Dendritic Spine Density Are Associated with the Rapid Antidepressant-like Effect of Iron-citalopram and Iron-Imipramine Combinations in Mice

Iron supplementation previously demonstrated antidepressant-like effects in post-partum rats. The present study evaluates the possible synergistic antidepressant effect of sub-therapeutic dose of iron co-administered with citalopram or imipramine in female Institute of Cancer Research mice. Depression-like symptoms were induced in the forced swim (FST), tail suspension (TST), and open space swim (OSST) tests while open field test (OFT) was used to assess locomotor activity. Mice (n = 8) received iron (0.8–7.2 mg/kg), citalopram (3–30 mg/kg), imipramine (3–30 mg/kg), desferrioxamine (50 mg/kg) or saline in the single treatment phase of each model and subsequently a sub-therapeutic dose of iron co-administered with citalopram or imipramine. Assessment of serum brain derived neurotrophic factor (BDNF) and dendritic spine density was done using ELISA and Golgi staining techniques respectively. Iron, citalopram and imipramine, unlike desferrioxamine, reduced immobility score in the TST, FST and OSST without affecting locomotor activity, suggesting antidepressant-like effect. Sub-therapeutic dose of iron in combination with citalopram or imipramine further enhanced the antidepressant-like effect, producing a more rapid effect when compared to the iron, citalopram or imipramine alone. Iron, citalopram and imipramine or their combinations increased serum BDNF concentration, hippocampal neuronal count and dendritic spine densities. Our study provides experimental evidence that iron has antidepressant-like effect and sub-therapeutic dose of iron combined with citalopram or imipramine produces more rapid antidepressant-like effect. We further show that iron alone or its combination with citalopram or imipramine attenuates the neuronal loss associated with depressive conditions, increases dendritic spines density and BDNF levels. These finding suggest iron-induced neuronal plasticity in the mice brain.

Seasonal differences in the morphology and spine density of hippocampal neurons in wild ground squirrels.

Seasonally reproducing small mammals often undergo changes in brain anatomy throughout the year. Much of the research on this seasonal neuroplasticity has focused on changes in hippocampus volume and neurogenesis, with relatively little attention paid to neuronal morphology. Here, we test for sex, season and sex-season interaction effects on hippocampal neuron morphology and dendritic spine density in a seasonally reproducing rodent: Richardson's ground squirrel (Urocitellus richardsonii). We quantified the morphology and spine densities of Golgi-stained pyramidal neurons and granule cells in the hippocampus and tested for differences between sexes and seasons with generalized linear models. Although we found no significant sex differences or sex-season interaction effects on any of our morphological measurements, there were significant differences in neuron morphology and spine density between breeding and non-breeding seasons. In the non-breeding season, ground squirrels had CA1 neurons with longer basal dendrites with more branches than in the breeding season. Non-breeding season animals also had higher apical and basal dendrite spine density in CA1 and CA3 neurons than breeding-season animals. Conversely, the spine densities of CA1 somata and granule cells were higher in breeding than in non-breeding season. These differences in neuron morphology and spine density between breeding and non-breeding seasons likely arise from a combination of activity levels, stress hormones, and photoperiod. Although the functional implications of seasonal changes in hippocampal neuron morphology and spine density are uncertain, our data suggest that ground squirrels may be a good model for understanding seasonal neuroplasticity in mammals.

Dose makes poison: Insights into the neurotoxicity of perinatal and juvenile exposure to environmental doses of 16 priority-controlled PAHs

Whether chronic exposure to environmental doses of polycyclic aromatic hydrocarbons (PAHs) can lead to neurotoxic effects is still unclear. Hence, the neurotoxic effects of perinatal and juvenile exposure to 16 priority-controlled PAHs were investigated. The mice were treated with 0, 0.5, 18.75, 50, 1875 μg/kg/day of PAHs corresponding to various population exposure concentrations from gestation to postnatal day 60. Urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) and hippocampal and cortical neurotransmitter levels were determined using liquid chromatography-tandem mass spectrometry. Typical indicators or outcome of neurotoxicity, including, spatial learning and memory ability, hippocampal long-term potentiation (LTP) and dendritic spine density were evaluated via Morris water maze tests, electrophysiological experiments and Golgi-Cox assays, respectively. The results showed that exposure to different levels of PAH could not increase oxidative DNA damage level. Mice exposed to 0.5, 50 and 1875 μg/kg/day PAHs had significantly longer escape latency than the control group only on the 1st day (p < 0.05). The number of platform crossings and the time spent in target quadrant were similar between the control and the PAHs-exposed mice. Compared with the control mice, only those exposed to 50 μg/kg/day PAHs had significantly lower LTP in hippocampal CA1 region and dendritic spine density in hippocampal DG region (p < 0.05). Except for serotonin, no significant difference in hippocampal and cortical neurotransmitter concentrations was observed between the control and PAHs-exposed groups. Taken together, perinatal and juvenile exposure to environmental doses of PAHs had no profound effect on spatial learning and memory abilities, hippocampal LTP, dendritic spines density, and neurotransmitter levels. These unexpected findings were quite different from previous in vivo studies which commonly used 2–3 orders of magnitude higher PAHs doses to treat animals. Thus, the environmental dose is a crucial reference for future toxicological research to reveal the actual toxic mechanisms and human health effects of PAHs exposure.

Activation of CNR1/PI3K/AKT Pathway by Tanshinone IIA Protects Hippocampal Neurons and Ameliorates Sleep Deprivation-Induced Cognitive Dysfunction in Rats

Sleep deprivation is commonplace in modern society, Short periods of continuous sleep deprivation (SD) may negatively affect brain and behavioral function and may lead to vehicle accidents and medical errors. Tanshinone IIA (Tan IIA) is an important lipid-soluble component of Salvia miltiorrhiza, which could exert neuroprotective effects. The aim of this study was to investigate the mechanism of neuroprotective effect of Tan IIA on acute sleep deprivation-induced cognitive dysfunction in rats. Tan IIA ameliorated behavioral abnormalities in sleep deprived rats, enhanced behavioral performance in WMW and NOR experiments, increased hippocampal dendritic spine density, and attenuated atrophic loss of hippocampal neurons. Tan IIA enhanced the expression of CB1, PI3K, AKT, STAT3 in rat hippocampus and down-regulated the expression ratio of Bax to Bcl-2. These effects were inhibited by cannabinoid receptor 1 antagonist (AM251). In conclusion, Tan IIA can play a neuroprotective role by activating the CNR1/PI3K/AKT signaling pathway to antagonize apoptosis in the hippocampus and improve sleep deprivation-induced spatial recognition and learning memory dysfunction in rats. Our study suggests that Tan IIA may be a candidate for the prevention of sleep deprivation-induced dysfunction in spatial recognition and learning memory.

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.

Therapeutic potential of Nlrp1 inflammasome, Caspase-1, or Caspase-6 against Alzheimer disease cognitive impairment.

The sequential activation of Nucleotide-binding oligomerization domain, Leucine rich Repeat and Pyrin domain containing protein 1 (Nlrp1) inflammasome, Caspase-1 (Casp1), and Caspase-6 (Casp6) is implicated in primary human neuron cultures and Alzheimer Disease (AD) neurodegeneration. To validate the Nlrp1-Casp1-Casp6 pathway in vivo, the APPSwedish/Indiana J20 AD transgenic mouse model was generated on either a Nlrp1, Casp1 or Casp6 null genetic background and mice were studied at 4-5 months of age. Episodic memory deficits assessed with novel object recognition were normalized by genetic ablation of Nlrp1, Casp1, or Casp6 in J20 mice. Spatial learning deficits, assessed with the Barnes Maze, were normalized in genetically ablated J20, whereas memory recall was normalized in J20/Casp1-/- and J20/Casp6-/-, and improved in J20/Nlrp1-/- mice. Hippocampal CA1 dendritic spine density of the mushroom subtype was reduced in J20, and normalized in genetically ablated J20 mice. Reduced J20 hippocampal dentate gyrus and CA3 synaptophysin levels were normalized in genetically ablated J20. Increased Iba1+-microglia in the hippocampus and cortex of J20 brains were normalized by Casp1 and Casp6 ablation and reduced by Nlrp1 ablation. Increased pro-inflammatory cytokines, TNF-α and CXCL1, in the J20 hippocampus were normalized by Nlrp1 or Casp1 genetic ablation. CXCL1was also normalized by Casp6 genetic ablation. IFN-γ was increased and total amyloid β peptide was decreased in genetically ablated Nlrp1, Casp1 or Casp6 J20 hippocampi. We conclude that Nlrp1, Casp1, or Casp6 are implicated in AD-related cognitive impairment, inflammation, and amyloidogenesis. These results indicate that Nlrp1, Casp1, and Casp6 represent rational therapeutic targets against cognitive impairment and inflammation in AD.

Legumain knockout improves repeated corticosterone injection-induced depression-like emotional and cognitive deficits

Emotional and cognitive impairment has been recognized as a central feature of depression, which is closely related to hyperfunction of the hypothalamic-pituitary-adrenal (HPA) axis caused by down-regulation of glucocorticoid receptor (GR) expression in patients. A decrease in GR expression can cause pathological changes and lead to the impairment of synaptic plasticity. Legumain, a lysosomal cysteine protease, plays an important role in neurological diseases. It is reported that legumain activates the MAPK signaling pathway, which modifies the GR. Therefore, we hypothesize that regulation of the GR by legumain plays a crucial role in the pathological process of depression. The relationships between legumain, GR, synaptic plasticity and emotional and cognitive deficits were explored in this study. The results demonstrated that repeated corticosterone (CORT) injections (3 weeks) induced emotional and cognitive deficits in mice, based on behavioral experiments and the detection of synaptic plasticity. Furthermore, CORT injections decreased the expression of hippocampal synapse-related proteins, cell density and dendritic spine density in the hippocampus, accompanied by increased protein expression in the MAPK signaling pathway and decreased expression of the GR. In conclusion, our results demonstrated that legumain knockout up-regulated expression of the GR by reducing protein expression in the MAPK signaling pathway, thereby improving hippocampal synaptic plasticity as well as the emotional and cognitive impairment of model mice. This suggests that legumain may be an effective therapeutic target for emotional and cognitive deficits.

GABAA Alpha 2,3 Modulation Improves Select Phenotypes in a Mouse Model of Fragile X Syndrome.

Fragile X syndrome (FXS) is the most common cause of inherited intellectual disability. FXS is caused by functional loss of the Fragile X Protein (FXP), also known as Fragile X Mental Retardation Protein (FMRP). In humans and animal models, loss of FXP leads to sensory hypersensitivity, increased susceptibility to seizures and cortical hyperactivity. Several components of the GABAergic system, the major inhibitory system in the brain, are dysregulated in FXS, and thus modulation of GABAergic transmission was suggested and tested as a treatment strategy. However, so far, clinical trials using broad spectrum GABAA or GABAB receptor-specific agonists have not yielded broad improvement of FXS phenotypes in humans. Here, we tested a more selective strategy in Fmr1 knockout (KO) mice using the experimental drug BAER-101, which is a selective GABAA α2/α3 agonist. Our results suggest that BAER-101 reduces hyperexcitability of cortical circuits, partially corrects increased frequency-specific baseline cortical EEG power, reduces susceptibility to audiogenic seizures and improves novel object memory. Other Fmr1 KO-specific phenotypes were not improved by the drug, such as increased hippocampal dendritic spine density, open field activity and marble burying. Overall, this work shows that BAER-101 improves select phenotypes in Fmr1 KO mice and encourages further studies into the efficacy of GABAA-receptor subunit-selective agonists for the treatment of FXS.

Kihito prevents corticosterone-induced brain dysfunctions in mice

Kihito (KIT; Gui Pi Tang) is a traditional herbal medicine that is used for treatment of neuropsychiatric disorders such as depression, anxiety, neurosis and insomnia in China and Japan. Recently, it has also been shown that KIT improves cognitive dysfunction in patients with Alzheimer's disease. In this study, to investigate the mechanisms underlying the effects of KIT on stress-induced brain dysfunctions such as a depressed state and memory impairment, we examined whether KIT prevents behavioral and neurophysiological abnormalities in mice treated chronically with corticosterone (CORT). CORT (40 mg/kg/day, s.c.) and KIT (1000 mg/kg/day, p.o.) were given to 7-week-old male ddY mice for 14 days. Twenty-four hours after the last treatment, depression-like behavior in the forced swim test, spatial memory in the Barnes maze test, cell survival and the number of new-born immature neurons, dendritic spine density and expression levels of mRNA for neurotrophic factors were analyzed. Depression-like behavior and spatial memory impairment were observed in CORT-treated mice without KIT treatment. Hippocampal cell survival, the number of hippocampal new-born immature neurons, hippocampal and accumbal dendritic spine density and mRNA levels for neurotrophic factors such as glial cell line-derived neurotrophic factor (GDNF) were decreased in CORT-treated mice without KIT treatment. KIT prevented CORT-induced depression-like behavior, spatial memory impairment, and decreases in hippocampal cell survival, the number of hippocampal new-born immature neurons, accumbal dendritic spine density and GDNF mRNA. KIT may ameliorate stress-induced brain dysfunctions via prevention of adverse effects of CORT on cell survival, new-born immature neurons, spine density and neurotrophic factors.

Long-Term Consequence of Non-neurotropic H3N2 Influenza A Virus Infection for the Progression of Alzheimer's Disease Symptoms.

Influenza viruses until today are a leading cause of worldwide severe pandemics and represent a major threat to human and animal health. Although the primary target of influenza viruses is the lung, infection may manifest with acute and even chronic neurological complications (e.g., status epilepticus, encephalopathies, and encephalitis) potentially increasing the long-term risk for neurodegenerative diseases. We previously described that a peripheral influenza A virus (IAV) infection caused by non-neurotropic H3N2 (maHK68) variant leads to long-term neuroinflammation and synapse loss together with impaired memory formation in young adult mice. Processes of neuroinflammation have been associated with neurodegenerative diseases such as Alzheimer’s disease (AD) and prolonged or excessive innate immune responses are considered a risk factor for AD. Here, the role of purely peripheral IAV infection for the development and progression of AD in a transgenic mouse model (APP/PS1) was investigated. At 2 months of age, mice were infected with H3N2 IAV and the detailed analysis of microglia morphology revealed neuroinflammation in the hippocampus already of 6 months old non-infected APP/PS1 mice together with impaired spatial learning, however, microglia activation, amyloid-β plaques load and cognitive impairments were even more pronounced in APP/PS1 mice upon H3N2 infection. Moreover, CA1 hippocampal dendritic spine density was reduced even at 120 dpi compared to wild-type and also to non-infected APP/PS1 mice, whereas neuronal cells number was not altered. These findings demonstrate that non-neurotropic H3N2 IAV infection as a peripheral immune stimulation may exacerbate AD symptoms possibly by triggering microglial hyperactivation.