CREB Regulates Experience-Dependent Spine Formation and Enlargement in Mouse Barrel Cortex

Hippocampal Crhr1 conditional gene knockout ameliorated the depression-like behavior and pathological damage in male offspring mice caused by chronic stress during pregnancy

Numerous studies have demonstrated that chronic stress during pregnancy (CSDP) can induce depression and hippocampal damage in offspring. It has also been observed that high levels of corticotropin-releasing hormone (CRH) can damage hippocampal neurons, and intraperitoneal injection of a corticotropin releasing hormone receptor 1 (CRHR1) antagonist decreases depression-like behavior and hippocampal neuronal damage in a mouse depression model. However, whether CSDP causes hippocampal damage and depression in offspring through the interaction of CRH and hippocampal CRHR1 remains unknown and warrants further investigation. Therefore, hippocampal Crhr1 conditional gene knockout mice and C57/BL6J mice were used to study these questions. Depression-related indexs in male offspring mice were examined using the forced swim test (FST), sucrose preference test (SPT), tail suspension test (TST) and open field test (OFT). Serum CRH levels were measured by enzyme-linked immunosorbent assay (ELISA). Golgi-Cox staining was used to examine the morphological changes of hippocampal neuronal dendrites. Neuronal apoptosis in the hippocampal CA3 regions was detected by terminal deoxynucleotidy transferase dUTP nick end labeling (TUNEL) staining. The levels of mammalian target of rapamycin (mTOR), phosphorylated mTOR (p-mTOR) and protein kinase B (AKT) proteins were measured by Western blot analysis. This study showed that CSDP induces depression-like behavior, hippocampal neuronal dendrite damage and apoptosis in male offspring mice. Conditional gene knockout of hippocampal Crhr1 in mice reduced CSDP-induced depression-like behavior, hippocampal neuronal dendrite damage and apoptosis in male offspring, and counteracted the CSDP-induced decreased expression of p-Akt and mTOR activity in male offspring hippocampus. These findings demonstrated that CSDP might inhibit the Akt/mTOR pathway by increasing the levels of CRH, leading to increased CRH-mediated activation of hippocampal CRHR1, thereby inducing synaptic impairment and apoptosis in hippocampal neurons, which in turn leads to depression-like behavior in offspring.

Microglia-mediated calcium-permeable AMPAR accumulation in the nucleus accumbens drives hyperlocomotion during cocaine withdrawal

During withdrawal from cocaine, calcium permeable-AMPA receptors (CP-AMPAR) progressively accumulate in nucleus accumbens (NAc) synapses, a phenomenon linked to behavioral sensitization and drug-seeking. Recently, it has been suggested that neuroimmune alterations might promote aberrant changes in synaptic plasticity, thus contributing to substance abuse-related behaviors. Here, we investigated the role of microglia in NAc neuroadaptations after withdrawal from cocaine-induced conditioned place preference (CPP). We depleted microglia using PLX5622-supplemented diet during cocaine withdrawal, and after the place preference test, we measured dendritic spine density and the presence of CP-AMPAR in the NAc shell. Microglia depletion prevented cocaine-induced changes in dendritic spines and CP-AMPAR accumulation. Furthermore, microglia depletion prevented conditioned hyperlocomotion without affecting drug-context associative memory. Microglia displayed fewer number of branches, resulting in a reduced arborization area and microglia control domain at late withdrawal. Our results suggest that microglia are necessary for the synaptic adaptations in NAc synapses during cocaine withdrawal and therefore represent a promising therapeutic target for relapse prevention.

The Pleiotropic Face of CREB Family Transcription Factors

cAMP responsive element-binding protein (CREB) is one of the most intensively studied phosphorylation-dependent transcription factors that provide evolutionarily conserved mechanisms of differential gene expression in vertebrates and invertebrates. Many cellular protein kinases that function downstream of distinct cell surface receptors are responsible for the activation of CREB. Upon functional dimerization of the activated CREB to cis-acting cAMP responsive elements within the promoters of target genes, it facilitates signal-dependent gene expression. From the discovery of CREB, which is ubiquitously expressed, it has been proven to be involved in a variety of cellular processes that include cell proliferation, adaptation, survival, differentiation, and physiology, through the control of target gene expression. In this review, we highlight the essential roles of CREB proteins in the nervous system, the immune system, cancer development, hepatic physiology, and cardiovascular function and further discuss a wide range of CREB-associated diseases and molecular mechanisms underlying the pathogenesis of these diseases.

Chondroitin 4-O-sulfation regulates hippocampal perineuronal nets and social memory

Glycan alterations are associated with aging, neuropsychiatric, and neurodegenerative diseases, although the contributions of specific glycan structures to emotion and cognitive functions remain largely unknown. Here, we used a combination of chemistry and neurobiology to show that 4-O-sulfated chondroitin sulfate (CS) polysaccharides are critical regulators of perineuronal nets (PNNs) and synapse development in the mouse hippocampus, thereby affecting anxiety and cognitive abilities such as social memory. Brain-specific deletion of CS 4-O-sulfation in mice increased PNN densities in the area CA2 (cornu ammonis 2), leading to imbalanced excitatory-to-inhibitory synaptic ratios, reduced CREB activation, elevated anxiety, and social memory dysfunction. The impairments in PNN densities, CREB activity, and social memory were recapitulated by selective ablation of CS 4-O-sulfation in the CA2 region during adulthood. Notably, enzymatic pruning of the excess PNNs reduced anxiety levels and restored social memory, while chemical manipulation of CS 4-O-sulfation levels reversibly modulated PNN densities surrounding hippocampal neurons and the balance of excitatory and inhibitory synapses. These findings reveal key roles for CS 4-O-sulfation in adult brain plasticity, social memory, and anxiety regulation, and they suggest that targeting CS 4-O-sulfation may represent a strategy to address neuropsychiatric and neurodegenerative diseases associated with social cognitive dysfunction.

Immunotherapy with Cleavage-Specific 12A12mAb Reduces the Tau Cleavage in Visual Cortex and Improves Visuo-Spatial Recognition Memory in Tg2576 AD Mouse Model

Tau-targeted immunotherapy is a promising approach for treatment of Alzheimer's disease (AD). Beyond cognitive decline, AD features visual deficits consistent with the manifestation of Amyloid β-protein (Aβ) plaques and neurofibrillary tangles (NFT) in the eyes and higher visual centers, both in animal models and affected subjects. We reported that 12A12-a monoclonal cleavage-specific antibody (mAb) which in vivo neutralizes the neurotoxic, N-terminal 20-22 kDa tau fragment(s)-significantly reduces the retinal accumulation in Tg(HuAPP695Swe)2576 mice of both tau and APP/Aβ pathologies correlated with local inflammation and synaptic deterioration. Here, we report the occurrence of N-terminal tau cleavage in the primary visual cortex (V1 area) and the beneficial effect of 12A12mAb treatment on phenotype-associated visuo-spatial deficits in this AD animal model. We found out that non-invasive administration of 12 A12mAb markedly reduced the pathological accumulation of both truncated tau and Aβ in the V1 area, correlated to significant improvement in visual recognition memory performance along with local increase in two direct readouts of cortical synaptic plasticity, including the dendritic spine density and the expression level of activity-regulated cytoskeleton protein Arc/Arg3.1. Translation of these findings to clinical therapeutic interventions could offer an innovative tau-directed opportunity to delay or halt the visual impairments occurring during AD progression.

Transcranial Magnetic Stimulation Exerts "Rejuvenation" Effects on Corticostriatal Synapses after Partial Dopamine Depletion

BACKGROUND

In experimental models of Parkinson's disease (PD), different degrees of degeneration to the nigrostriatal pathway produce distinct profiles of synaptic alterations that depend on progressive changes in N-methyl-D-aspartate receptors (NMDAR)-mediated functions. Repetitive transcranial magnetic stimulation (rTMS) induces modifications in glutamatergic and dopaminergic systems, suggesting that it may have an impact on glutamatergic synapses modulated by dopamine neurotransmission. However, no studies have so far explored the mechanisms of rTMS effects at early stages of PD.

OBJECTIVES

We tested the hypothesis that in vivo application of rTMS with intermittent theta-burst stimulation (iTBS) pattern alleviates corticostriatal dysfunctions by modulating NMDAR-dependent plasticity in a rat model of early parkinsonism.

METHODS

Dorsolateral striatal spiny projection neurons (SPNs) activity was studied through ex vivo whole-cell patch-clamp recordings in corticostriatal slices obtained from 6-hydroxydopamine-lesioned rats, subjected to a single session (acute) of iTBS and tested for forelimb akinesia with the stepping test. Immunohistochemical analyses were performed to analyze morphological correlates of plasticity in SPNs.

RESULTS

Acute iTBS ameliorated limb akinesia and rescued corticostriatal long-term potentiation (LTP) in SPNs of partially lesioned rats. This effect was abolished by applying a selective inhibitor of GluN2B-subunit-containing NMDAR, suggesting that iTBS treatment could be associated with an enhanced activation of specific NMDAR subunits, which are major regulators of structural plasticity during synapse development. Morphological analyses of SPNs revealed that iTBS treatment reverted dendritic spine loss inducing a prevalence of thin-elongated spines in the biocytin-filled SPNs.

CONCLUSIONS

Taken together, our data identify that an acute iTBS treatment produces a series of plastic changes underlying striatal compensatory adaptation in the parkinsonian basal ganglia circuit. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Azadirachtin directly or indirectly affects the abundance of intestinal flora of Spodoptera litura and the energy conversion of intestinal contents mediates the energy balance of intestine-brain axis, and along with decreased expression CREB in the brain neurons

Azadirachtin is a good growth inhibitor for Lepidopteran larvae, but its effect on the brain neurons, intestinal flora and intestinal contents caused by the growth inhibition mechanism has not been reported yet. This study explored the mechanism of azadirachtin on the growth and development of Spodoptera litura larvae and brain neurons through three aspects: intestinal pathology observation, intestinal flora sequencing, and intestinal content analysis. The results showed that the treatment of azadirachtin led to the pathological changes in the structure of the midgut and the goblet cells in the intestinal wall cells to undergo apoptosis. Changes in the host environment of the intestinal flora lead to changes in the abundance value of the intestinal flora, showing an increase in the abundance value of harmful bacteria such as Sphingomonas and Enterococcus, as well as an increase in the abundance value of excellent flora such as Lactobacillus and Bifidobacterium. Changes in the abundance of intestinal flora will result in changes in intestinal contents and metabolites. The test results show that after azadirachtin treatment, the alkane compounds in the intestinal contents of the larvae are greatly reduced, and the number of the long carbon chain and multi-branched hydrocarbon compounds is increased, unsaturated fatty acids, silicon‑oxygen compounds and ethers. The production of similar substances indicates that azadirachtin has an inhibitory effect on digestive enzymes in the intestines, which results in the inhibition of substance absorption and energy transmission, and ultimately the inhibition of larval growth and brain neurons.

Passive immunotherapy for N-truncated tau ameliorates the cognitive deficits in two mouse Alzheimer's disease models

Clinical and neuropathological studies have shown that tau pathology better correlates with the severity of dementia than amyloid plaque burden, making tau an attractive target for the cure of Alzheimer's disease. We have explored whether passive immunization with the 12A12 monoclonal antibody (26-36aa of tau protein) could improve the Alzheimer's disease phenotype of two well-established mouse models, Tg2576 and 3xTg mice. 12A12 is a cleavage-specific monoclonal antibody which selectively binds the pathologically relevant neurotoxic NH226-230 fragment (i.e. NH2htau) of tau protein without cross-reacting with its full-length physiological form(s). We found out that intravenous administration of 12A12 monoclonal antibody into symptomatic (6 months old) animals: (i) reaches the hippocampus in its biologically active (antigen-binding competent) form and successfully neutralizes its target; (ii) reduces both pathological tau and amyloid precursor protein/amyloidβ metabolisms involved in early disease-associated synaptic deterioration; (iii) improves episodic-like type of learning/memory skills in hippocampal-based novel object recognition and object place recognition behavioural tasks; (iv) restores the specific up-regulation of the activity-regulated cytoskeleton-associated protein involved in consolidation of experience-dependent synaptic plasticity; (v) relieves the loss of dendritic spine connectivity in pyramidal hippocampal CA1 neurons; (vi) rescues the Alzheimer's disease-related electrophysiological deficits in hippocampal long-term potentiation at the CA3-CA1 synapses; and (vii) mitigates the neuroinflammatory response (reactive gliosis). These findings indicate that the 20-22 kDa NH2-terminal tau fragment is crucial target for Alzheimer's disease therapy and prospect immunotherapy with 12A12 monoclonal antibody as safe (normal tau-preserving), beneficial approach in contrasting the early Amyloidβ-dependent and independent neuropathological and cognitive alterations in affected subjects.

Offline ventral subiculum-ventral striatum serial communication is required for spatial memory consolidation

The hippocampal formation is considered essential for spatial navigation. In particular, subicular projections have been suggested to carry spatial information from the hippocampus to the ventral striatum. However, possible cross-structural communication between these two brain regions in memory formation has thus far been unknown. By selectively silencing the subiculum-ventral striatum pathway we found that its activity after learning is crucial for spatial memory consolidation and learning-induced plasticity. These results provide new insight into the neural circuits underlying memory consolidation and establish a critical role for off-line cross-regional communication between hippocampus and ventral striatum to promote the storage of complex information.

Understanding the link between insulin resistance and Alzheimer's disease: Insights from animal models

Alzheimer's disease (AD) is a devastating neurodegenerative disease affecting millions of people worldwide. AD is characterized by a profound impairment of higher cognitive functions and still lacks any effective disease-modifying treatment. Defective insulin signaling has been implicated in AD pathophysiology, but the mechanisms underlying this process are not fully understood. Here, we review the molecular mechanisms underlying defective brain insulin signaling in rodent models of AD, and in a non-human primate (NHP) model of the disease that recapitulates features observed in AD brains. We further highlight similarities between the NHP and human brains and discuss why NHP models of AD are important to understand disease mechanisms and to improve the translation of effective therapies to humans. We discuss how studies using different animal models have contributed to elucidate the link between insulin resistance and AD.

Biphasic effect of abstinence duration following cocaine self-administration on spine morphology and plasticity-related proteins in prelimbic cortical neurons projecting to the nucleus accumbens core

Cocaine self-administration (SA) in rats dysregulates glutamatergic signaling in the prelimbic (PrL) cortex and glutamate release in the nucleus accumbens (NA) core, promoting cocaine seeking. PrL adaptations that affect relapse to drug seeking emerge during the first week of abstinence, switching from an early (2 h) hypoglutamatergic state to a later (7 days) hyperglutamatergic state. Different interventions that normalize glutamatergic signaling in PrL cortex at each timepoint are necessary to suppress relapse. We hypothesized that plasticity-related proteins that regulate glutamatergic neurotransmission as well as dendritic spine morphology would be biphasically regulated during these two phases of abstinence in PrL cortical neurons projecting to the NA core (PrL-NA core). A combinatorial viral approach was used to selectively label PrL-NA core neurons with an mCherry fluorescent reporter. Male rats underwent 2 weeks of cocaine SA or received yoked-saline infusions and were perfused either 2 h or 7 days after the final SA session. Confocal microscopy and 3D reconstruction analyses were performed for Fos and pCREB immunoreactivity (IR) in the nucleus of layer V PrL-NA core neurons and GluA1-IR and GluA2-IR in apical dendritic spines of the same neurons. Here, we show that cocaine SA decreased PrL-NA core spine head diameter, nuclear Fos-IR and pCREB-IR, and GluA1-IR and GluA2-IR in putative mushroom-type spines 2 h after the end of cocaine SA, whereas the opposite occurred following 1 week of abstinence. Our findings reveal biphasic, abstinence duration-dependent alterations in structural plasticity and relapse-related proteins in the PrL-NA core pathway after cocaine SA.

Permanent Whisker Removal Reduces the Density of c-Fos+ Cells and the Expression of Calbindin Protein, Disrupts Hippocampal Neurogenesis and Affects Spatial-Memory-Related Tasks

Facial vibrissae, commonly known as whiskers, are the main sensitive tactile system in rodents. Whisker stimulation triggers neuronal activity that promotes neural plasticity in the barrel cortex (BC) and helps create spatial maps in the adult hippocampus. Moreover, activity-dependent inputs and calcium homeostasis modulate adult neurogenesis. Therefore, the neuronal activity of the BC possibly regulates hippocampal functions and neurogenesis. To assess whether tactile information from facial whiskers may modulate hippocampal functions and neurogenesis, we permanently eliminated whiskers in CD1 male mice and analyzed the effects in cellular composition, molecular expression and memory processing in the adult hippocampus. Our data indicated that the permanent deprivation of whiskers reduced in 4-fold the density of c-Fos+ cells (a calcium-dependent immediate early gene) in cornu ammonis subfields (CA1, CA2 and CA3) and 4.5-fold the dentate gyrus (DG). A significant reduction in the expression of calcium-binding proteincalbindin-D_28k was also observed in granule cells of the DG. Notably, these changes coincided with an increase in apoptosis and a decrease in the proliferation of neural precursor cells in the DG, which ultimately reduced the number of Bromodeoxyuridine (BrdU)+NeuN+ mature neurons generated after whisker elimination. These abnormalities in the hippocampus were associated with a significant impairment of spatial memory and navigation skills. This is the first evidence indicating that tactile inputs from vibrissal follicles strongly modify the expression of c-Fos and calbindin in the DG, disrupt different aspects of hippocampal neurogenesis, and support the notion that spatial memory and navigation skills strongly require tactile information in the hippocampus.

AD-Related N-Terminal Truncated Tau Is Sufficient to Recapitulate In Vivo the Early Perturbations of Human Neuropathology: Implications for Immunotherapy

The NH₂tau 26-44 aa (i.e., NH₂htau) is the minimal biologically active moiety of longer 20-22-kDa NH₂-truncated form of human tau-a neurotoxic fragment mapping between 26 and 230 amino acids of full-length protein (htau40)-which is detectable in presynaptic terminals and peripheral CSF from patients suffering from AD and other non-AD neurodegenerative diseases. Nevertheless, whether its exogenous administration in healthy nontransgenic mice is able to elicit a neuropathological phenotype resembling human tauopathies has not been yet investigated. We explored the in vivo effects evoked by subchronic intracerebroventricular (i.c.v.) infusion of NH₂htau or its reverse counterpart into two lines of young (2-month-old) wild-type mice (C57BL/6 and B6SJL). Six days after its accumulation into hippocampal parenchyma, significant impairment in memory/learning performance was detected in NH₂htau-treated group in association with reduced synaptic connectivity and neuroinflammatory response. Compromised short-term plasticity in paired-pulse facilitation paradigm (PPF) was detected in the CA3/CA1 synapses from NH₂htau-impaired animals along with downregulation in calcineurin (CaN)-stimulated pCREB/c-Fos pathway(s). Importantly, these behavioral, synaptotoxic, and neuropathological effects were independent from the genetic background, occurred prior to frank neuronal loss, and were specific because no alterations were detected in the control group infused with its reverse counterpart. Finally, a 2.0-kDa peptide which biochemically and immunologically resembles the injected NH₂htau was endogenously detected in vivo, being present in hippocampal synaptosomal preparations from AD subjects. Given that the identification of the neurotoxic tau species is mandatory to develop a more effective tau-based immunological approach, our evidence can have important translational implications for cure of human tauopathies.

Entorhinal Cortex dysfunction can be rescued by inhibition of microglial RAGE in an Alzheimer's disease mouse model

The Entorhinal cortex (EC) has been implicated in the early stages of Alzheimer's disease (AD). In particular, spreading of neuronal dysfunction within the EC-Hippocampal network has been suggested. We have investigated the time course of EC dysfunction in the AD mouse model carrying human mutation of amyloid precursor protein (mhAPP) expressing human Aβ. We found that in mhAPP mice plasticity impairment is first observed in EC superficial layer and further affected with time. A selective impairment of LTP was observed in layer II horizontal connections of EC slices from 2 month old mhAPP mice, whereas at later stage of neurodegeneration (6 month) basal synaptic transmission and LTD were also affected. Accordingly, early synaptic deficit in the mhAPP mice were associated with a selective impairment in EC-dependent associative memory tasks. The introduction of the dominant-negative form of RAGE lacking RAGE signalling targeted to microglia (DNMSR) in mhAPP mice prevented synaptic and behavioural deficit, reducing the activation of stress related kinases (p38MAPK and JNK). Our results support the involvement of the EC in the development and progression of the synaptic and behavioural deficit during amyloid-dependent neurodegeneration and demonstrate that microglial RAGE activation in presence of Aβ-enriched environment contributes to the EC vulnerability.