Structural and functional plasticity of dendritic spines - root or result of behavior?

The neuroplastic brain: current breakthroughs and emerging frontiers

Neuroplasticity, the brain's capacity to reorganize itself by forming new neural connections, is central to modern neuroscience. Once believed to occur only during early development, research now shows that plasticity continues throughout the lifespan, supporting learning, memory, and recovery from injury or disease. Substantial progress has been made in understanding the mechanisms underlying neuroplasticity and their therapeutic applications. This overview article examines synaptic plasticity, structural remodeling, neurogenesis, and functional reorganization, highlighting both adaptive (beneficial) and maladaptive (harmful) processes across different life stages. Recent strategies to harness neuroplasticity, ranging from pharmacological agents and lifestyle interventions to cutting-edge technologies like brain-computer interfaces (BCIs) and targeted neuromodulation are evaluated in light of current empirical evidence. Contradictory findings in the literature are addressed, and methodological limitations that hamper widespread clinical adoption are discussed. The ethical and societal implications of deploying novel neuroplasticity-based interventions, including issues of equitable access, data privacy, and the blurred line between treatment and enhancement, are then explored in a structured manner. By integrating mechanistic insights, empirical data, and ethical considerations, the aim is to provide a comprehensive and balanced perspective for researchers, clinicians, and policymakers working to optimize brain health across diverse populations.

Habituation to novel stimuli alters hippocampal plasticity associated with morphine tolerance in male Wistar rats

Chronic morphine exposure affects neuroplasticity in the hippocampus, a key area for learning and memory. Since, novelty exploration influence rodent hippocampal plasticity, the aim of this study was to investigate the effects of habituation to novel contexts and odors on hippocampal plasticity in morphine-tolerant rats. For this purpose, neurogenesis markers, dendritic spine density and mRNA levels for various genes encoding neurotrophic factors were evaluated in the hippocampus tissue (ventral, vH vs. dorsal, dH) of male rats. Habituation to the new environment was established using animal models of morphine tolerance. Following multiple exposures to a novel context (open field habituation, OFH) or a series of novel odors (odor habituation, OH), markers (Ki67 or DCX) associated with neurogenesis were found to be lower in the morphine-tolerant rats that underwent habituation than the non-habituated morphine-tolerant rats, with specific regions (dH, vH), being differently influenced by specific type of habituation (OFH, OH, respectively). Further results showed subregion and habituation specific effects on the number of dendritic spines per spine type or levels of neurotropic factors including BDNF and TrkB mRNA levels in the dH and vH in morphine-tolerant rats that underwent habituation as compared to the non-habituated morphine-tolerant rats. We provide new evidence that habituation to novel contexts and novel odors appears to affect hippocampal plasticity in morphine-tolerant rats and that pro-plasticity molecules appear to mediate habituation effects on morphine tolerance plasticity.

Phosphorylation of NLGN4X Regulates Spinogenesis and Synaptic Function

Neuroligins (NLGNs) are a family of postsynaptic adhesion molecules that bind to their presynaptic partners, neurexins, facilitating the formation and maintenance of synapses. In humans, there are five genes encoding NLGNs (NLGN1-3, NLGN4X, and NLGN4Y), with NLGN1-3 having highly conserved counterparts in rodents, allowing these genes to be studied with high confidence of translational validity in mouse models. Human NLGN4X and 4Y were often assumed to serve similar functions because they share a 97% sequence homology, whereas mouse NLGN4-like is quite divergent. Many NLGN-mediated synaptic effects are modulated through post-translation modifications, which exert temporal and spatial control. In this report, we characterize a conserved phosphorylation site, serine 712, on NLGN4X and 4Y. Despite serine 712 being located in a highly conserved region between NLGN4X and 4Y, we observed kinase specificity. PKA exclusively phosphorylates NLGN4X S712, whereas Cdk5 phosphorylates S712 on both NLGN4X and 4Y. NLGN4X S712 phosphorylation regulated spine density, with phosphorylation reducing mature mushroom spines and unphosphorylated S712 increasing spines and enhancing miniature excitatory postsynaptic current frequency.

Repetitive concussions promote microglia-mediated engulfment of presynaptic excitatory input associated with cognitive dysfunction

Concussions are a current health concern and account for the vast majority of head trauma. While symptoms after a single impact are usually transient, repetitive concussions, as often occur in sports, are responsible for persistent acute and chronic deficits. Here, we used a model of bilateral midline-centered concussions in mice to show that repetitive concussions selectively induce impairments in learning ability compared to single-impact injuries. Since microglial cells and their activation are considered key factors in degenerative pathology after brain trauma, we examined their structure and function after single and repetitive concussions in the cortex underlying the concussions and in the hippocampus. We found that only repetitive concussions led to a significant long-lasting structural activation of microglia and an increase in microglia-mediated engulfment of presynaptic excitatory synapses, while the elimination of inhibitory synapses was not altered. Since the density of excitatory input did not change during the 6-week study period, we hypothesize that there is a turnover of excitatory synapses following repetitive concussion that can be compensated for, anatomically but not behaviorally.

Stress Molecular Signaling in Interaction With Cognition

Exposure to stressful life events is associated with a high risk of developing psychiatric disorders with a wide variety of symptoms. Cognitive symptoms in stress-related psychiatric disorders can be particularly challenging to understand, both for those experiencing them and for health care providers. To gain insights, it is important to capture stress-induced structural, epigenomic, transcriptomic, and proteomic changes in relevant brain regions such as the amygdala, hippocampus, locus coeruleus, and prefrontal cortex that result in long-lasting alterations in brain function. In this review, we will emphasize a subset of stress molecular mechanisms that alter neuroplasticity, neurogenesis, and balance between excitatory and inhibitory neurons. Then, we discuss how to identify genetic risk factors that may accelerate stress-driven or stress-induced cognitive impairment. Despite the development of new technologies such as single-cell resolution sequencing, our understanding of the molecular effects of stress in the brain remains to be deepened. A better understanding of the diversity of stress effects in different brain regions and cell types is a prerequisite to open new avenues for mechanism-informed prevention and treatment of stress-related cognitive symptoms.

Guilu Erxian Jiao remodels dendritic spine morphology through activation of the hippocampal TRPC6-CaMKIV-CREB signaling pathway and suppresses fear memory generalization in rats with post-traumatic stress disorder

ETHNOPHARMACOLOGICAL RELEVANCE

Guilu Erxian Jiao (GLEXJ) is a renowned traditional Chinese herbal formula used to tonify the kidney. It is employed to treat psychiatric disorders, and alleviate memory impairment, cognitive dysfunction, and behavioral disorders. Modern pharmacological studies have demonstrated GLEXJ's ability to significantly inhibit the fear response in post-traumatic stress disorder (PTSD) and facilitate the extinction of fear memory. However, the underlying pharmacological mechanisms remain elusive.

AIM OF THE STUDY

Fear memory generalization, a fundamental characteristic of PTSD, remains poorly understood, and optimal pharmacological treatments are lacking. This study aimed to investigate GLEXJ's inhibitory effects on fear memory generalization in PTSD rats and elucidate its underlying mechanisms.

MATERIALS AND METHODS

PTSD rats were induced using the single prolonged stress and electrical stimulation (SPS&S) protocol and treated with GLEXJ or paroxetine (PRX). Fear memory generalization was assessed using a contextual fear memory test. Hippocampal dendritic spine morphology was analyzed using Golgi-Cox staining. The chemical composition of GLEXJ was determined using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Network pharmacology was employed to predict GLEXJ's therapeutic mechanism in PTSD treatment. Western blotting and immunofluorescence were used to measure indicators of the transient receptor potential channel 6 (TRPC6)-mediated calcium/calmodulin-dependent protein kinase IV-cAMP response element-binding protein (CaMKIV-CREB) signaling pathway. In vitro, TRPC6 was suppressed in rat adrenal pheochromocytoma (PC12) cells using lentiviral vectors, and phalloidin staining was employed to examine changes in Fibros actin (F-actin), elucidating the mechanistic effects of GLEXJ-containing serum.

RESULTS

GLEXJ significantly mitigated fear memory generalization in PTSD rats, even with repeated stress exposure. It also alleviated abnormal hippocampal dendritic spine morphology. Network pharmacology analysis confirmed that GLEXJ was closely related to the Ca2+ signaling pathway in PTSD treatment. PTSD rats exhibited disrupted TRPC6-mediated CaMKIV-CREB signaling and impaired synaptic plasticity. GLEXJ upregulated TRPC6 expression, reactivated the CaMKIV-CREB pathway, and promoted synaptic remodeling. In vitro studies confirmed that TRPC6 suppression reduced F-actin levels while GLEXJ-containing serum increased TRPC6 expression and F-actin content.

CONCLUSIONS

GLEXJ activates CaMKIV-CREB signaling by upregulating TRPC6 in the hippocampus of PTSD rats, leading to the positive modulation of dendritic spine morphology and synaptic remodeling. This mechanism contributes to the attenuation of fear memory generalization. Given the limitations of current PTSD treatments, these findings offer potential avenues for developing more effective therapeutic strategies.

The Dose-Dependent Effects of Fluorocitrate on the Metabolism and Activity of Astrocytes and Neurons

BACKGROUND

Fluorocitrate (FC) ranging from 5 μM to 5 mM is often used as a specific metabolic inhibitor of the astrocytes to study astrocytic functions. Whether FC at such concentrations may affect neuronal metabolism and function in vivo remains unclear.

METHODS

We examined the effects of FC on the ATP levels and Ca2+ activity of the astrocytes and neurons in the motor cortices of living mice using two-photon microscopy.

RESULTS

We found that 25 μM and 250 μM of FC decreased the intracellular ATP levels and Ca2+ activity in the astrocytes in the motor cortex. Equally, 250 μM of FC, but not 25 μM of FC, reduced the intracellular ATP levels in the dendritic processes of the layer 5 pyramidal neurons. However, 25 μM of FC increased the neuronal Ca2+ activity, whereas ≥250 μM of FC decreased it. To test whether the differential effects of FC on neuronal Ca2+ activity reflect the direct effect of FC on the neurons or its indirect effect on the astrocytes, we used the CNO-hM3Dq chemogenetic approach to block astrocytic Ca2+ activity and examined the effect of FC. In the absence of astrocytic Ca2+ activity, 25 μM of FC still increased and ≥250 μM of FC reduced the dendritic Ca2+ activity of the neurons, respectively, suggesting a direct effect of 250 μM of FC on inhibiting neuronal Ca2+ activity. Further, 250 μM, but not 25 μM, of FC increased the size of the dendritic spines over 2 h.

CONCLUSIONS

Our findings suggest that FC at high concentrations (≥250 μM) is not a specific inhibitor of astrocytic functions, as it directly affects neuronal metabolism and synaptic plasticity in vivo.

Buyang huanwu decoction improves synaptic plasticity of ischemic stroke by regulating the cAMP/PKA/CREB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Ischemic stroke is an acute central nervous system disease that poses a threat to human health. It induces a series of severe pathological mechanisms, ultimately leading to neuronal cell death in the brain due to local ischemia and hypoxia. Buyang Huanwu decoction (BYHWD), as a representative formula for treating ischemic stroke, has shown good therapeutic effects in stroke patients.

AIM OF THE STUDY

This study aimed to explore the mechanism of BYHWD in promoting neural remodeling after ischemic stroke from the perspective of neuronal synaptic plasticity, based on the cAMP/PKA/CREB signaling pathway.

MATERIALS AND METHODS

A modified suture technique was employed to establish a rat model of MCAO. The rats were divided into sham, model, and BYHWD (20 g/kg) groups. After the corresponding intervention, rat brains from each group were collected. TMT quantitative proteomics technology was employed for the research. Following proteomics studies, we investigated the mechanism of BYHWD in the intervention of ischemic stroke through animal experiments and cell experiments. The experimental animals were divided into sham, model, and BYHWD (5 g/kg, 10 g/kg, and 20 g/kg) groups. Infarct volume and severity of brain injury were measured by TTC staining. HE staining was utilized to evaluate alterations in tissue morphology. The Golgi staining was used to observe changes in cell body, dendrites, and dendritic spines. Transmission electron microscopy was used to observe the ultrastructure of synapses in the cortex and hippocampus. TUNEL staining was conducted to identify apoptotic neurons. Meanwhile, a stable and reliable (OGD/R) SH-SY5Y cell model was established. The effect of BYHWD-containing serum on SH-SY5Y cell viability was measured by CCK-8 kit. The apoptosis situation of SH-SY5Y cells was determined by Annexin V-FITC/PI. Immunofluorescence was employed to measure the fluorescence intensity of synaptic-related factors Syt1, Psd95, and Syn1. Synaptic plasticity pathways were assessed by using RT-qPCR and Western blot to determine the expression levels of cAMP, Psd95, Prkacb, Creb1/p-Creb1, BDNF, Shank2, Syn1, Syt1, Bcl-2, Bcl-2/Bax mRNA and proteins.

RESULTS

After treatment with BYHWD, notable alterations were detected in the signaling pathways linked to synaptic plasticity and the cAMP signaling pathway-related targets among the intervention targets. This trend of change was also reflected in other bioinformatics analyses, indicating the important role of synaptic plasticity changes before and after modeling and drug intervention. The results of vivo and vitro experiments showed that BYHWD improved local pathological changes, and reduced cerebral infarct volume, and neurological function scores in MCAO rats. It increased dendritic spine density, improved synaptic structural plasticity, and had a certain neuroprotective effect. BYHWD increased the postsynaptic membrane thickness, synaptic interface curvature, and synaptic quantity. 10% BYHWD-containing serum was determined as the optimal concentration for treatment. 10% BYHWD-containing serum significantly reduced the overall apoptotic rate of (OGD/R) SH-SY5Y cells. Immunofluorescence experiments demonstrated that 10% BYHWD-containing serum could improve synaptic plasticity and increase the relative expression levels of synaptic-related proteins Syt1, Psd95, and Syn1. BYHWD and decoction-containing serum upregulated the mRNA and protein expression levels in (OGD/R) SH-SY5Y cells and MCAO rats, suggesting its ability to improve damaged neuronal synaptic plasticity and enhance transmission efficiency, which might be achieved through the regulation of the cAMP/PKA/CREB pathway.

CONCLUSIONS

This study may provide a basis for clinical medication by elucidating the underlying experimental evidence for the promotion of neural plasticity after ischemic stroke by BYHWD.

JRM-28, a Novel HDAC2 Inhibitor, Upregulates Plasticity-Associated Proteins in Hippocampal Neurons and Enhances Morphological Plasticity via Activation of CREB: Implications for Alzheimer's Disease

Enhancement of neuronal plasticity by small-molecule therapeutics protects cognitive skills and also ameliorates progressive neurodegenerative pathologies like Alzheimer's disease (AD) and dementia. One such compound, a novel histone deacetylase 2 (HDAC2) inhibitor named JRM-28, was shown here to enhance dendritic strength, augment spine density, and upregulate post-synaptic neurotransmission in hippocampal neurons. The molecular basis for this effect correlates with JRM-28-induced upregulation of the transcription of cAMP response element-binding protein(CREB), induction of its transcriptional activity, and subsequent stimulation of expressions of CREB-dependent plasticity-associated genes, such as those encoding N-methyl-D-aspartate (NMDA) receptor subunit NR2A and the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluR1. Specifically, JRM-28 stimulated the NMDA- and AMPA-receptor-sensitive ionotropic calcium influx in hippocampal neurons. Interestingly, JRM-28 did not induce NMDA- and AMPA-sensitive calcium influx in hippocampal neurons once the expression of CREB was knocked down by creb siRNA, suggesting the critical role of CREB in JRM-28-mediated upregulation of synaptic plasticity. Finally, JRM-28 upregulated CREB mRNA, CREB-dependent plasticity-associated markers, and ionotropic calcium influx in iPSC-derived AD human neurons, indicating its therapeutic implications in the amelioration of AD pathologies.

Lasting effects of adolescent social instability stress on dendritic morphology in the nucleus accumbens in female and male Long Evans rats

Social instability stress (SS) in adolescence in rats leads to long-lasting changes in social behaviour and reward-related behaviour relative to control rats. Given the role of the nucleus accumbens (NAc) in such behaviours, we investigated the morphology of medium spiny neurons (MSNs), which are most neurons in the NAc, in adult female and male rats exposed to SS in adolescence. Irrespective of sex, SS rats had increased number of dendritic spines in both the core and shell regions of the NAc (2.3 % and 18.1 % increase, respectively). In the core, SS rats had a 16 % reduction in the total dendritic lengths of MSNs, whereas in the shell, SS rats had a greater dendritic length closer to the soma, and particularly in SS female rats, whereas the opposite was found farther from the soma (SS 10.6 % > CTL overall). Although the extent to which such structural changes may underlie the enduring effects of SS in adolescence requires investigation, the results add to evidence that changes to the social environment in adolescence can determine adult neuronal structural.

Cognitive dysfunction induced by cranial radiotherapy: mechanisms and therapeutic methods

Cranial radiotherapy can damage normal brain tissues, inducing cognitive dysfunction in patients. Radiotherapy-induced cognitive dysfunction is associated with hippocampal injury, white matter damage and microvascular injury. In this study, the mechanisms of cognitive dysfunction induced by cranial radiotherapy and combined chemoradiotherapy are reviewed, and the advances in therapeutic methods for radiotherapy-induced brain injury are summarized. The mechanisms of radiotherapy-induced brain injury include a decline of neurogenesis, impairment of neurons and glial cells, vascular injury, oxidative stress and DNA damage, cell death, and inflammatory response. Disruption of the bloodbrain barrier (BBB) increases the exposure of the brain to chemotherapeutic agents, thus exacerbating radiotherapy-induced brain damage. The current methods used to prevent radiotherapy-induced brain injury mainly include precision radiotherapy, stem cell transplantation, and treatment with neuroprotective drugs. The combined application of precision radiotherapy and neuroprotective drugs, including antioxidants, anti-inflammatory agents and other drugs, might exert better neuroprotective effects. To resolve the issues of neuroprotective drugs, such as difficulty in crossing the BBB, nanoenzymes and drug delivery nano-systems could be applied in the future.

Manipulation of radixin phosphorylation in the nucleus accumbens core modulates risky choice behavior

Ezrin-Radixin-Moesin (ERM) proteins are actin-binding proteins that contribute to morphological changes in dendritic spines. Despite their significant role in regulating spine structure, the role of ERM proteins in the nucleus accumbnes (NAcc) is not well known, especially in in the context of risk-reward decision-making. Here, we measured the relationship between synaptic excitation and inhibition (E/I ratio) from medium spiny neurons in the NAcc core obtained in the rat after a rat gambling task (rGT). Then, after surgery of a phosphomimetic pseudo-active mutant form of radixin (Rdx-T564D) in the NAcc core, we examined its role in synaptic plasticity and the accompanying risk-choice behavior in rGT. We found that basal E/I ratio in the NAcc core was higher in risk-averse rats than risk-seeking rats. However, it was significantly reduced in risk-averse rats similar to that in risk-seeking rats in the presence of Rdx-T564D in the NAcc core. Furthermore, the head sizes of spines were shifted in risk-averse rats expressing Rdx-T564D in the NAcc core, similar to those observed in risk-seeking rats. The effects of Rdx-T564D in risk-averse rats were again manifested as behavioral changes, with reduced selection of optimal choices and increased selection of disadvantageous ones. In this study, we demonstrated that manipulation of radixin phosphorylation status in the NAcc core can alter glutamatergic synaptic transmission and spine structure at this site, as well as risk choice behaviors in the rGT. These novel findings illustrate that radixin in the NAcc core plays a significant role in determining risk preference during the rGT.

Suppression of neuronal AMPKβ2 isoform impairs recognition memory and synaptic plasticity

AMP-activated protein kinase (AMPK) is an αβγ heterotrimer protein kinase that functions as a molecular sensor to maintain energy homeostasis. Accumulating evidence suggests a role of AMPK signaling in the regulation of synaptic plasticity and cognitive function; however, isoform-specific roles of AMPK in the central nervous system (CNS) remain elusive. Regulation of the AMPK activities has focused on the manipulation of the α or γ subunit. Meanwhile, accumulating evidence indicates that the β subunit is critical for sensing nutrients such as fatty acids and glycogen to control AMPK activity. Here, we generated transgenic mice with conditional suppression of either AMPKβ1 or β2 in neurons and characterized potential isoform-specific roles of AMPKβ in cognitive function and underlying mechanisms. We found that AMPKβ2 (but not β1) suppression resulted in impaired recognition memory, reduced hippocampal synaptic plasticity, and altered structure of hippocampal postsynaptic densities and dendritic spines. Our study implicates a role for the AMPKβ2 isoform in the regulation of synaptic and cognitive function.

Cognitive synaptopathy: synaptic and dendritic spine dysfunction in age-related cognitive disorders

Cognitive impairment is a leading component of several neurodegenerative and neurodevelopmental diseases, profoundly impacting on the individual, the family, and society at large. Cognitive pathologies are driven by a multiplicity of factors, from genetic mutations and genetic risk factors, neurotransmitter-associated dysfunction, abnormal connectomics at the level of local neuronal circuits and broader brain networks, to environmental influences able to modulate some of the endogenous factors. Otherwise healthy older adults can be expected to experience some degree of mild cognitive impairment, some of which fall into the category of subjective cognitive deficits in clinical practice, while many neurodevelopmental and neurodegenerative diseases course with more profound alterations of cognition, particularly within the spectrum of the dementias. Our knowledge of the underlying neuropathological mechanisms at the root of this ample palette of clinical entities is far from complete. This review looks at current knowledge on synaptic modifications in the context of cognitive function along healthy ageing and cognitive dysfunction in disease, providing insight into differential diagnostic elements in the wide range of synapse alterations, from those associated with the mild cognitive changes of physiological senescence to the more profound abnormalities occurring at advanced clinical stages of dementia. I propose the term "cognitive synaptopathy" to encompass the wide spectrum of synaptic pathologies associated with higher brain function disorders.

Endocrine disrupting effects on morphological synaptic plasticity

Neural regulation of the homeostasis depends on healthy synaptic function. Adaptation of synaptic functions to physiological needs manifests in various forms of synaptic plasticity (SP), regulated by the normal hormonal regulatory circuits. During the past several decades, the hormonal regulation of animal and human organisms have become targets of thousands of chemicals that have the potential to act as agonists or antagonists of the endogenous hormones. As the action mechanism of these endocrine disrupting chemicals (EDCs) came into the focus of research, a growing number of studies suggest that one of the regulatory avenues of hormones, the morphological form of SP, may well be a neural mechanism affected by EDCs. The present review discusses known and potential effects of some of the best known EDCs on morphological synaptic plasticity (MSP). We highlight molecular mechanisms altered by EDCs and indicate the growing need for more research in this area of neuroendocrinology.

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

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

Synthesis of geometrically realistic and watertight neuronal ultrastructure manifolds for in silico modeling

Understanding the intracellular dynamics of brain cells entails performing three-dimensional molecular simulations incorporating ultrastructural models that can capture cellular membrane geometries at nanometer scales. While there is an abundance of neuronal morphologies available online, e.g. from NeuroMorpho.Org, converting those fairly abstract point-and-diameter representations into geometrically realistic and simulation-ready, i.e. watertight, manifolds is challenging. Many neuronal mesh reconstruction methods have been proposed; however, their resulting meshes are either biologically unplausible or non-watertight. We present an effective and unconditionally robust method capable of generating geometrically realistic and watertight surface manifolds of spiny cortical neurons from their morphological descriptions. The robustness of our method is assessed based on a mixed dataset of cortical neurons with a wide variety of morphological classes. The implementation is seamlessly extended and applied to synthetic astrocytic morphologies that are also plausibly biological in detail. Resulting meshes are ultimately used to create volumetric meshes with tetrahedral domains to perform scalable in silico reaction-diffusion simulations for revealing cellular structure-function relationships. Availability and implementation: Our method is implemented in NeuroMorphoVis, a neuroscience-specific open source Blender add-on, making it freely accessible for neuroscience researchers.

The Effects of Sevoflurane and Aβ Interaction on CA1 Dendritic Spine Dynamics and MEGF10-Related Astrocytic Synapse Engulfment

General anesthetics may accelerate the neuropathological changes related to Alzheimer's disease (AD), of which amyloid beta (Aβ)-induced toxicity is one of the main causes. However, the interaction of general anesthetics with different Aβ-isoforms remains unclear. In this study, we investigated the effects of sevoflurane (0.4 and 1.2 maximal alveolar concentration (MAC)) on four Aβ species-induced changes on dendritic spine density (DSD) in hippocampal brain slices of Thy1-eGFP mice and multiple epidermal growth factor-like domains 10 (MEGF10)-related astrocyte-mediated synaptic engulfment in hippocampal brain slices of C57BL/6 mice. We found that both sevoflurane and Aβ downregulated CA1-dendritic spines. Moreover, compared with either sevoflurane or Aβ alone, pre-treatment with Aβ isoforms followed by sevoflurane application in general further enhanced spine loss. This enhancement was related to MEGF10-related astrocyte-dependent synaptic engulfment, only in AβpE3 + 1.2 MAC sevoflurane and 3NTyrAβ + 1.2 MAC sevoflurane condition. In addition, removal of sevoflurane alleviated spine loss in Aβ + sevoflurane. In summary, these results suggest that both synapses and astrocytes are sensitive targets for sevoflurane; in the presence of 3NTyrAβ, 1.2 MAC sevoflurane alleviated astrocyte-mediated synaptic engulfment and exerted a lasting effect on dendritic spine remodeling.

Cognitive integrity in Non-Demented Individuals with Alzheimer's Neuropathology is associated with preservation and remodeling of dendritic spines

INTRODUCTION

Individuals referred to as Non-Demented with Alzheimer's Neuropathology (NDAN) exhibit cognitive resilience despite presenting Alzheimer's disease (AD) histopathological signs. Investigating the mechanisms behind this resilience may unveil crucial insights into AD resistance.

METHODS

DiI labeling technique was used to analyze dendritic spine morphology in control (CTRL), AD, and NDAN post mortem frontal cortex, particularly focusing on spine types near and far from amyloid beta (Aβ) plaques.

RESULTS

NDAN subjects displayed a higher spine density in regions distant from Aβ plaques versus AD patients. In distal areas from the plaques, NDAN individuals exhibited more immature spines, while AD patients had a prevalence of mature spines. Additionally, our examination of levels of Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1), a protein associated with synaptic plasticity and AD, showed significantly lower expression in AD versus NDAN and CTRL.

DISCUSSION

These results suggest that NDAN individuals undergo synaptic remodeling, potentially facilitated by Pin1, serving as a compensatory mechanism to preserve cognitive function despite AD pathology.

HIGHLIGHTS

Spine density is reduced near Aβ plaques compared to the distal area in CTRL, AD, and NDAN dendrites. NDAN shows higher spine density than AD in areas far from Aβ plaques. Far from Aβ plaques, NDAN has a higher density of immature spines, AD a higher density of mature spines. AD individuals show significantly lower levels of Pin1 compared to NDAN and CTRL.

Unlocking the age-old secrets of reward and substance use

Although substance use is widespread across the lifespan from early adolescence to older adulthood, the prevalence of substance use disorder (SUD) differs between age groups. These age differences in SUD rates necessitate an investigation into how age moderates reward sensitivity, and consequently influences the risks and consequences related to substance use. This theoretical review integrates evidence from the literature to address the dynamic interplay between age and reward in the context of substance use. Overall, increasing evidence demonstrates that age moderates reward sensitivity and underlying reward system neurobiology. Reward sensitivity undergoes a non-linear trajectory across the lifespan. Low levels of reward sensitivity are associated with childhood and late adulthood. In contrast, high levels are associated with early to late adolescence, followed by a decline in the twenties. These fluctuations in reward sensitivity across the lifespan contribute to complex associations with substance use. This lends support to adolescence and young adulthood as vulnerable periods for the risk of subsequent SUD. More empirical research is needed to investigate reward sensitivity during SUD maintenance and recovery. Future research should also involve larger sample sizes and encompass a broader range of age groups, including older adults.

Targeting terminal pathway reduces brain complement activation, amyloid load and synapse loss, and improves cognition in a mouse model of dementia

Complement is dysregulated in the brain in Alzheimer's Disease and in mouse models of Alzheimer's disease. Each of the complement derived effectors, opsonins, anaphylatoxins and membrane attack complex (MAC), have been implicated as drivers of disease but their relative contributions remain unclarified. Here we have focussed on the MAC, a lytic and pro-inflammatory effector, in the AppNL-G-F mouse amyloidopathy model. To test the role of MAC, we back-crossed to generate AppNL-G-F mice deficient in C7, an essential MAC component. C7 deficiency ablated MAC formation, reduced synapse loss and amyloid load and improved cognition compared to complement-sufficient AppNL-G-F mice at 8-10 months age. Adding back C7 caused increased MAC formation in brain and an acute loss of synapses in C7-deficient AppNL-G-F mice. To explore whether C7 was a viable therapeutic target, a C7-blocking monoclonal antibody was administered systemically for one month in AppNL-G-F mice aged 8-9 months. Treatment reduced brain MAC and amyloid deposition, increased synapse density and improved cognitive performance compared to isotype control-treated AppNL-G-F mice. The findings implicate MAC as a driver of pathology and highlight the potential for complement inhibition at the level of MAC as a therapy in Alzheimer's disease.

Polystyrene microplastics induced disturbances in neuronal arborization and dendritic spine density in mice prefrontal cortex

An increasing use of plastics in daily life leads to the accumulation of microplastics (MPs) in the environment, posing a serious threat to the ecosystem, including humans. It has been reported that MPs cause neurotoxicity, but the deleterious effect of polystyrene (PS) MPs on neuronal cytoarchitectural morphology in the prefrontal cortex (PFC) region of mice brain remains to be established. In the present study, Swiss albino male mice were orally exposed to 0.1, 1, and 10 ppm PS-MPs for 28 days. After exposure, we found a significant accumulation of PS-MPs with a decreased number of Nissl bodies in the PFC region of the entire treated group compared to the control. Morphometric analysis in the PFC neurons using Golgi-Cox staining accompanied by Sholl analysis showed a significant reduction in basal dendritic length, dendritic intersections, nodes, and number of intersections at seventh branch order in PFC neurons of 1 ppm treated PS-MPs. In neurons of 0.1 ppm treated mice, we found only decrease in the number of intersections at the seventh branch order. While 10 ppm treated neurons decreased in basal dendritic length, dendritic intersections, followed by the number of intersections at the third and seventh branch order were observed. As well, spine density on the apical secondary branches along with mRNA level of BDNF was significantly reduced in all the PS-MPs treated PFC neurons, mainly at 1 ppm versus control. These results suggest that PS-MPs exposure affects overall basal neuronal arborization, with the highest levels at 1 and 10 ppm, followed by 0.1 ppm treated neurons, which may be related to the down-regulation of BDNF expression in PFC.

Conditioned morphine tolerance promotes neurogenesis, dendritic remodelling and pro-plasticity molecules in the adult rat hippocampus

Structural neuroplasticity of the hippocampus in the form of neurogenesis and dendritic remodelling underlying morphine tolerance is still less known. Therefore, in this study, we aimed to assess whether unconditioned- and conditioned-morphine tolerance can trigger structural neuroplasticity in the dorsal and ventral parts of the adult male rat hippocampus. Evaluation of the levels of neurogenesis markers (Ki67 and DCX) by immunohistochemistry shows that conditioned morphine tolerance is sufficient to increase the baseline topographic level of hippocampal neurogenesis in adult rats. Dendritic spine visualization by Golgi staining shows that the behavioural testing paradigms themselves are sufficient to trigger the hippocampus subregion-specific changes in the dendritic remodelling along the apical dendrites of hippocampal CA1 pyramidal neurons and dentate granule cells in adult rats. Quantitative reverse transcription polymerase chain reaction of Bdnf, Trkb, Rac-1 and RhoA mRNA levels as pro-plasticity molecules, shows that the conditioned morphine tolerance is effective in changing Bdnf and RhoA mRNA levels in the ventral hippocampus of adult rats. In summary, we demonstrate that the acquisition of morphine tolerance promotes adult neurogenesis, dendritic remodelling and pro-plasticity molecules such as Bdnf/Trkb in the rat hippocampus. Indeed, the structural neuroplasticity of the hippocampus may underlie the newly formed aberrant memory and could provide the initial basis for understanding the neurobiological mechanisms of morphine-tolerance plasticity in the hippocampus.

Ketamine Produces Antidepressant Effects by Inhibiting Histone Deacetylases and Upregulating Hippocampal Brain-Derived Neurotrophic Factor Levels in a Diisopropyl Fluorophosphate-Based Rat Model of Gulf War Illness

Approximately one-third of Gulf War veterans suffer from Gulf War Illness (GWI), which encompasses mood disorders and depressive symptoms. Deployment-related exposure to organophosphate compounds has been associated with GWI development. Epigenetic modifications have been reported in GWI veterans. We previously showed that epigenetic histone dysregulations were associated with decreased brain-derived neurotrophic factor (BDNF) expression in a GWI rat model. GWI has no effective therapies. Ketamine (KET) has recently been approved by the Food and Drug Administration for therapy-resistant depression. Interestingly, BDNF upregulation underlies KET's antidepressant effect in GWI-related depression. Here, we investigated whether KET's effect on histone mechanisms signals BDNF upregulations in GWI. Male Sprague-Dawley rats were injected once daily with diisopropyl fluorophosphate (DFP; 0.5 mg/kg, s.c., 5 days). At 6 months following DFP exposure, KET (10 mg/kg, i.p.) was injected, and brains were dissected 24 hours later. Western blotting was used for protein expression, and epigenetic studies used chromatin immunoprecipitation methods. Dil staining was conducted for assessing dendritic spines. Our results indicated that an antidepressant dose of KET inhibited the upregulation of histone deacetylase (HDAC) enzymes in DFP rats. Furthermore, KET restored acetylated histone occupancy at the Bdnf promoter IV and induced BDNF protein expression in DFP rats. Finally, KET treatment also increased the spine density and altered the spine diversity with increased T-type and decreased S-type spines in DFP rats. Given these findings, we propose that KET's actions involve the inhibition of HDAC expression, upregulation of BDNF, and dendritic modifications that together ameliorates the pathologic synaptic plasticity and exerts an antidepressant effect in DFP rats. SIGNIFICANCE STATEMENT: This study offers evidence supporting the involvement of epigenetic histone pathways in the antidepressant effects of ketamine (KET) in a rat model of Gulf War Illness (GWI)-like depression. This effect is achieved through the modulation of histone acetylation at the Bdnf promoter, resulting in elevated brain-derived neurotrophic factor expression and subsequent dendritic remodeling in the hippocampus. These findings underscore the rationale for considering KET as a potential candidate for clinical trials aimed at managing GWI-related depression.

Mapping Molecular Interaction Interface Between Diaphanous Formin-2 and Neuron-Specific Drebrin A

Actin cytoskeleton is critical for neuronal shape and function. Drebrin and formins are key regulators of neuronal actin networks. Neuron-specific drebrin A is highly enriched in dendritic spines (postsynaptic terminals) of mature excitatory neurons. Decreased levels of drebrin in dendritic spines is a hallmark of Alzheimer's disease, epilepsy, and other complex disorders, which calls for better understanding of its regulatory functions. Drebrin A was previously shown to inhibit actin nucleation and bundling by the diaphanous formin-2 (mDia2) - an actin nucleator that is involved in the initiation of dendritic spines. Characterization of the molecular binding interface between mDia2 and drebrin is necessary to better understand the functional consequences of this interaction and its biological relevance. Prior work suggested a multi-pronged interface between mDia2 and drebrin, which involves both N-terminal and C-terminal regions of the drebrin molecule. Here we used mass spectrometry analysis, deletion mutagenesis, and an array of synthetic peptides of neuronal drebrin A to map its formin-binding interface. The mDia2-interacting interface on drebrin was narrowed down to three highly conserved 9-16 residue sequences that were used to identify some of the key residues involved in this interaction. Deletion of the C-terminal region of drebrin greatly reduces its binding to mDia2 and the extent of its inhibition of formin-driven actin assembly. Moreover, our experiments with formins from different subfamilies showed that drebrin is a specific rather than general inhibitor of these proteins. This work contributes to a molecular level understanding of the formin-drebrin interaction and will help to unravel its biological significance.

Stabilizing Immature Dendritic Spines in the Auditory Cortex: A Key Mechanism for mTORC1-Mediated Enhancement of Long-Term Fear Memories

Mammalian target of rapamycin (mTOR) pathway has emerged as a key molecular mechanism underlying memory processes. Although mTOR inhibition is known to block memory processes, it remains elusive whether and how an enhancement of mTOR signaling may improve memory processes. Here we found in male mice that the administration of VO-OHpic, an inhibitor of the phosphatase and tensin homolog (PTEN) that negatively modulates AKT-mTOR pathway, enhanced auditory fear memory for days and weeks, while it left short-term memory unchanged. Memory enhancement was associated with a long-lasting increase in immature-type dendritic spines of pyramidal neurons into the auditory cortex. The persistence of spine remodeling over time arose by the interplay between PTEN inhibition and memory processes, as VO-OHpic induced only a transient immature spine growth in the somatosensory cortex, a region not involved in long-term auditory memory. Both the potentiation of fear memories and increase in immature spines were hampered by rapamycin, a selective inhibitor of mTORC1. These data revealed that memory can be potentiated over time by the administration of a selective PTEN inhibitor. In addition to disclosing new information on the cellular mechanisms underlying long-term memory maintenance, our study provides new insights on the molecular processes that aid enhancing memories over time.SIGNIFICANCE STATEMENT The neuronal mechanisms that may help improve the maintenance of long-term memories are still elusive. The inhibition of mammalian-target of rapamycin (mTOR) signaling shows that this pathway plays a crucial role in synaptic plasticity and memory formation. However, whether its activation may strengthen long-term memory storage is unclear. We assessed the consequences of positive modulation of AKT-mTOR pathway obtained by VO-OHpic administration, a phosphatase and tensin homolog inhibitor, on memory retention and underlying synaptic modifications. We found that mTOR activation greatly enhanced memory maintenance for weeks by producing a long-lasting increase of immature-type dendritic spines in pyramidal neurons of the auditory cortex. These results offer new insights on the cellular and molecular mechanisms that can aid enhancing memories over time.

IGF2 prevents dopaminergic neuronal loss and decreases intracellular alpha-synuclein accumulation in Parkinson's disease models

Parkinson's disease (PD) is the second most common late-onset neurodegenerative disease and the predominant cause of movement problems. PD is characterized by motor control impairment by extensive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). This selective dopaminergic neuronal loss is in part triggered by intracellular protein inclusions called Lewy bodies, which are composed mainly of misfolded alpha-synuclein (α-syn) protein. We previously reported insulin-like growth factor 2 (IGF2) as a key protein downregulated in PD patients. Here we demonstrated that IGF2 treatment or IGF2 overexpression reduced the α-syn aggregates and their toxicity by IGF2 receptor (IGF2R) activation in cellular PD models. Also, we observed IGF2 and its interaction with IGF2R enhance the α-syn secretion. To determine the possible IGF2 neuroprotective effect in vivo we used a gene therapy approach in an idiopathic PD model based on α-syn preformed fibrils intracerebral injection. IGF2 gene therapy revealed a significantly preventing of motor impairment in idiopathic PD model. Moreover, IGF2 expression prevents dopaminergic neuronal loss in the SN together with a decrease in α-syn accumulation (phospho-α-syn levels) in the striatum and SN brain region. Furthermore, the IGF2 neuroprotective effect was associated with the prevention of synaptic spines loss in dopaminergic neurons in vivo. The possible mechanism of IGF2 in cell survival effect could be associated with the decrease of the intracellular accumulation of α-syn and the improvement of dopaminergic synaptic function. Our results identify to IGF2 as a relevant factor for the prevention of α-syn toxicity in both in vitro and preclinical PD models.

Development programming: Stress during gestation alters offspring development in sheep

Inappropriate management practices of domestic animals during pregnancy can be potential stressors, resulting in complex behavioural, physiological and neurological consequences in the developing offspring. Some of these consequences can last into adulthood or propagate to subsequent generations. We systematically summarized the results of different experimental patterns using artificially increased maternal glucocorticoid levels or prenatal maternal physiological stress paradigms, mediators between prenatal maternal stress (PMS) and programming effects in the offspring and the effects of PMS on offspring phenotypes in sheep. PMS can impair birthweight, regulate the development of the hypothalamic-pituitary-adrenal axis, modify behavioural patterns and cognitive abilities and alter gene expression and brain morphology in offspring. Further research should focus on the effects of programming on gene expression, immune function, gut microbiome, sex-specific effects and maternal behaviour of offspring, especially comparative studies of gestational periods when PMS is applied, continual studies of programming effects on offspring and treatment strategies that effectively reverse the detrimental programming effects of prenatal stress.

Impact of a pyridazine derivative on tripartite synapse ultrastructure in hippocampus: a three-dimensional analysis

Introduction

We previously discovered a pyridazine derivative compound series that can improve cognitive functions in mouse models of Alzheimer's disease. One of the advanced compounds from this series, LDN/OSU-0215111-M3, was selected as the preclinical development candidate. This compound activates local protein translation at the perisynaptic astrocytic process (PAP) and enhances synaptic plasticity sequentially. While biochemical evidence supports the hypothesis that the compound enhances the structural plasticity of the tripartite synapse, its direct structural impact has not been investigated.

Methods

Volume electron microscopy was used to study the hippocampal tripartite synapse three-dimensional structure in 3-month-old wild-type FVB/NJ mice after LDN/OSU-0215111-M3 treatment.

Results

LDN/OSU-0215111-M3 increased the size of tertiary apical dendrites, the volume of mushroom spines, the proportion of mushroom spines containing spine apparatus, and alterations in the spine distribution across the surface area of tertiary dendrites. Compound also increased the number of the PAP interacting with the mushroom spines as well as the size of the PAP in contact with the spines. Furthermore, proteomic analysis of the isolated synaptic terminals indicated an increase in dendritic and synaptic proteins as well as suggested a possible involvement of the phospholipase D signaling pathway. To further validate that LDN/OSU-0215111-M3 altered synaptic function, electrophysiological studies showed increased long-term potentiation following compound treatment.

Discussion

This study provides direct evidence that pyridazine derivatives enhance the structural and functional plasticity of the tripartite synapse.

Microglia in Alzheimer's disease: pathogenesis, mechanisms, and therapeutic potentials

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by protein aggregation in the brain. Recent studies have revealed the critical role of microglia in AD pathogenesis. This review provides a comprehensive summary of the current understanding of microglial involvement in AD, focusing on genetic determinants, phenotypic state, phagocytic capacity, neuroinflammatory response, and impact on synaptic plasticity and neuronal regulation. Furthermore, recent developments in drug discovery targeting microglia in AD are reviewed, highlighting potential avenues for therapeutic intervention. This review emphasizes the essential role of microglia in AD and provides insights into potential treatments.

The cytoplasmic localization of ADNP through 14-3-3 promotes sex-dependent neuronal morphogenesis, cortical connectivity, and calcium signaling

Defective neuritogenesis is a contributing pathogenic mechanism underlying a variety of neurodevelopmental disorders. Single gene mutations in activity-dependent neuroprotective protein (ADNP) are the most frequent among autism spectrum disorders (ASDs) leading to the ADNP syndrome. Previous studies showed that during neuritogenesis, Adnp localizes to the cytoplasm/neurites, and Adnp knockdown inhibits neuritogenesis in culture. Here, we hypothesized that Adnp is localized in the cytoplasm during neurite formation and that this process is mediated by 14-3-3. Indeed, applying the 14-3-3 inhibitor, difopein, blocked Adnp cytoplasmic localization. Furthermore, co-immunoprecipitations showed that Adnp bound 14-3-3 proteins and proteomic analysis identified several potential phosphorylation-dependent Adnp/14-3-3 binding sites. We further discovered that knockdown of Adnp using in utero electroporation of mouse layer 2/3 pyramidal neurons in the somatosensory cortex led to previously unreported changes in neurite formation beginning at P0. Defects were sustained throughout development, the most notable included increased basal dendrite number and axon length. Paralleling the observed morphological aberrations, ex vivo calcium imaging revealed that Adnp deficient neurons had greater and more frequent spontaneous calcium influx in female mice. GRAPHIC, a novel synaptic tracing technology substantiated this finding, revealing increased interhemispheric connectivity between female Adnp deficient layer 2/3 pyramidal neurons. We conclude that Adnp is localized to the cytoplasm by 14-3-3 proteins, where it regulates neurite formation, maturation, and functional cortical connectivity significantly building on our current understanding of Adnp function and the etiology of ADNP syndrome.

Re-evaluation of the risks to public health related to the presence of bisphenol A (BPA) in foodstuffs

In 2015, EFSA established a temporary tolerable daily intake (t-TDI) for BPA of 4 μg/kg body weight (bw) per day. In 2016, the European Commission mandated EFSA to re-evaluate the risks to public health from the presence of BPA in foodstuffs and to establish a tolerable daily intake (TDI). For this re-evaluation, a pre-established protocol was used that had undergone public consultation. The CEP Panel concluded that it is Unlikely to Very Unlikely that BPA presents a genotoxic hazard through a direct mechanism. Taking into consideration the evidence from animal data and support from human observational studies, the immune system was identified as most sensitive to BPA exposure. An effect on Th17 cells in mice was identified as the critical effect; these cells are pivotal in cellular immune mechanisms and involved in the development of inflammatory conditions, including autoimmunity and lung inflammation. A reference point (RP) of 8.2 ng/kg bw per day, expressed as human equivalent dose, was identified for the critical effect. Uncertainty analysis assessed a probability of 57-73% that the lowest estimated Benchmark Dose (BMD) for other health effects was below the RP based on Th17 cells. In view of this, the CEP Panel judged that an additional uncertainty factor (UF) of 2 was needed for establishing the TDI. Applying an overall UF of 50 to the RP, a TDI of 0.2 ng BPA/kg bw per day was established. Comparison of this TDI with the dietary exposure estimates from the 2015 EFSA opinion showed that both the mean and the 95th percentile dietary exposures in all age groups exceeded the TDI by two to three orders of magnitude. Even considering the uncertainty in the exposure assessment, the exceedance being so large, the CEP Panel concluded that there is a health concern from dietary BPA exposure.

The effects of regular swimming exercise and melatonin on the neurons localized in the striatum of hemiparkinsonian rats

Parkinson's disease is a progressive neurodegenerative movement disorder. We aimed to investigate the effects of regular swimming exercise and melatonin applied in the 6-Hydroxydopamine-induced Parkinson's disease rats by analysing dendritic spine of striatal neurons. Twenty-four male Wistar albino rats were used. 6-Hydroxydopamine unilaterally injected four (control, exercise, melatonin and exercise + melatonin) groups were included in the study. Tyrosine hydroxylase expression was detected by immunohistochemistry. Neurons and structures were identified from three-dimensional images by Neurolucida software. There was not any apparent difference for tyrosine hydroxylase positive neurons in the substantia nigra pars compacta and fibres in the striatum between the lesion sides of hemiparkinsonian groups. The treatment groups blocked the apomorphine-induced increase in rotations compared to the control group. In stepping test, the treatment groups prevented the loss of stepping in the contralateral side of hemiparkinsonian groups. The melatonin mostly had a positive effect on motor activity tests. In morphological analyses, the 6-Hydroxydopamine-induced lesion led to the reduction of the total dendritic length and number of branches. In the treatment groups, the reduction of the dendritic parameters was not observed. 6-Hydroxydopamine lesion led to a decrease in the total spine density, spine densities of thin and mushroom types. The exercise and melatonin treatments prevented the loss of spine density. The exercise treatment prevented the loss of spine density of mushroom type spines. The melatonin treatment blocked the loss of spine density of stubby type. In conclusion, these results provide evidence for effective additional protective therapeutic strategies for Parkinson's disease. In conclusion, results from the current study provide evidence for swimming exercise and melatonin as a promising candidate for effective additional protective strategies for PD.

Dendritic spine loss deep in the neocortex and dendrite distortion with diffusion disturbances occur early in experimental pneumococcal meningitis

Introduction

Streptococcus pneumoniae (pneumococcus) meningitis is a serious disease with substantial lethality and long-term disability in survivors. Loss of synaptic staining in the superficial layers of the neocortex in rodent models and in humans, and pneumolysin (a major pneumococcal toxin)-dependent dendritic spine collapse in brain slices have been described. It remains unclear how deep in the neocortex more discrete changes are present, how soon after disease onset these changes occur, and whether other properties of dendrites are also affected.

Methods

Using a mouse model of pneumococcal meningitis, we studied changes in the neocortex shortly (3-6 h) after the onset of clinical symptoms via modified Golgi-Cox silver staining.

Results

Dendritic changes were present in areas with otherwise unchanged cell numbers and no signs of necrosis or other apparent neuronal pathology. Mature dendritic spines were reduced in the pyramidal neurons running through layers 1-5. Additionally, spine morphology changes (swelling, spine neck distortion), were also observed in the deeper layers 4 and 5 of the neocortex. Immature spines (filopodia) remained unchanged between groups, as well as the dendritic arborization of the analyzed neurons. In a third of the animals with meningitis, massive mechanical distortion of the primary dendrites of most of the pyramidal neurons through layers 1-5 was observed. This distortion was reproduced in acute brain slices after exposure to pneumolysin-containing bacterial lysates (S. pneumoniae D39 strain), but not to lysates of pneumolysin-deficient bacteria, which we explain by the tissue remodeling effect of the toxin. Experimental mechanical dendrite distortion in primary neural cultures demonstrated diminished FRAP diffusion of neuronally-expressed enhanced green fluorescent protein (eGFP), indicative of disturbed dendritic diffusion.

Discussion

Our work extends earlier knowledge of synaptic loss in the superficial cortical layers during meningitis to deeper layers. These changes occurred surprisingly early in the course of the disease, substantially limiting the effective therapeutic window. Methodologically, we demonstrate that the dendritic spine collapse readout is a highly reliable and early marker of neural damage in pneumococcal meningitis models, allowing for reduction of the total number of animals used per a group due to much lower variation among animals.

Dendritic Spines: Synaptogenesis and Synaptic Pruning for the Developmental Organization of Brain Circuits

Synaptic overproduction and elimination is a regular developmental event in the mammalian brain. In the cerebral cortex, synaptic overproduction is almost exclusively correlated with glutamatergic synapses located on dendritic spines. Therefore, analysis of changes in spine density on different parts of the dendritic tree in identified classes of principal neurons could provide insight into developmental reorganization of specific microcircuits.The activity-dependent stabilization and selective elimination of the initially overproduced synapses is a major mechanism for generating diversity of neural connections beyond their genetic determination. The largest number of overproduced synapses was found in the monkey and human cerebral cortex. The highest (exceeding adult values by two- to threefold) and most protracted overproduction (up to third decade of life) was described for associative layer IIIC pyramidal neurons in the human dorsolateral prefrontal cortex.Therefore, the highest proportion and extraordinarily extended phase of synaptic spine overproduction is a hallmark of neural circuitry in human higher-order associative areas. This indicates that microcircuits processing the most complex human cognitive functions have the highest level of developmental plasticity. This finding is the backbone for understanding the effect of environmental impact on the development of the most complex, human-specific cognitive and emotional capacities, and on the late onset of human-specific neuropsychiatric disorders, such as autism and schizophrenia.

Enhanced activity of Alzheimer disease-associated variant of protein kinase Cα drives cognitive decline in a mouse model

Exquisitely tuned activity of protein kinase C (PKC) isozymes is essential to maintaining cellular homeostasis. Whereas loss-of-function mutations are generally associated with cancer, gain-of-function variants in one isozyme, PKCα, are associated with Alzheimer's disease (AD). Here we show that the enhanced activity of one variant, PKCα M489V, is sufficient to rewire the brain phosphoproteome, drive synaptic degeneration, and impair cognition in a mouse model. This variant causes a modest 30% increase in catalytic activity without altering on/off activation dynamics or stability, underscoring that enhanced catalytic activity is sufficient to drive the biochemical, cellular, and ultimately cognitive effects observed. Analysis of hippocampal neurons from PKCα M489V mice reveals enhanced amyloid-β-induced synaptic depression and reduced spine density compared to wild-type mice. Behavioral studies reveal that this mutation alone is sufficient to impair cognition, and, when coupled to a mouse model of AD, further accelerates cognitive decline. The druggability of protein kinases positions PKCα as a promising therapeutic target in AD.

The Long-Term Pannexin 1 Ablation Produces Structural and Functional Modifications in Hippocampal Neurons

Enhanced activity and overexpression of Pannexin 1 (Panx1) channels contribute to neuronal pathologies such as epilepsy and Alzheimer's disease (AD). The Panx1 channel ablation alters the hippocampus's glutamatergic neurotransmission, synaptic plasticity, and memory flexibility. Nevertheless, Panx1-knockout (Panx1-KO) mice still retain the ability to learn, suggesting that compensatory mechanisms stabilize their neuronal activity. Here, we show that the absence of Panx1 in the adult brain promotes a series of structural and functional modifications in the Panx1-KO hippocampal synapses, preserving spontaneous activity. Compared to the wild-type (WT) condition, the adult hippocampal neurons of Panx1-KO mice exhibit enhanced excitability, a more complex dendritic branching, enhanced spine maturation, and an increased proportion of multiple synaptic contacts. These modifications seem to rely on the actin-cytoskeleton dynamics as an increase in the actin polymerization and an imbalance between the Rac1 and the RhoA GTPase activities were observed in Panx1-KO brain tissues. Our findings highlight a novel interaction between Panx1 channels, actin, and Rho GTPases, which appear to be relevant for synapse stability.

Insight into the Effects of High-Altitude Hypoxic Exposure on Learning and Memory

The earth land area is heterogeneous in terms of elevation; about 45% of its land area belongs to higher elevation with altitude above 500 meters compared to sea level. In most cases, oxygen concentration decreases as altitude increases. Thus, high-altitude hypoxic stress is commonly faced by residents in areas with an average elevation exceeding 2500 meters and those who have just entered the plateau. High-altitude hypoxia significantly affects advanced neurobehaviors including learning and memory (L&M). Hippocampus, the integration center of L&M, could be the most crucial target affected by high-altitude hypoxia exposure. Based on these points, this review thoroughly discussed the relationship between high-altitude hypoxia and L&M impairment, in terms of hippocampal neuron apoptosis and dysfunction, neuronal oxidative stress disorder, neurotransmitters and related receptors, and nerve cell energy metabolism disorder, which is of great significance to find potential targets for medical intervention. Studies illustrate that the mechanism of L&M damaged by high-altitude hypoxia should be further investigated based on the entire review of issues related to this topic.

Patchouli alcohol as a selective estrogen receptor β agonist ameliorates AD-like pathology of APP/PS1 model mice

Clinical evidence shows that postmenpausal women are almost twice as likely to develop Alzheimer's disease (AD) as men of the same age, and estrogen is closely related to the occurrence of AD. Estrogen receptor (ER) α is mainly expressed in the mammary gland and other reproductive organs like uterus while ERβ is largely distributed in the hippocampus and cardiovascular system, suggesting that ERβ selective agonist is a valuable drug against neurodegenerative diseases with low tendency in inducing cancers of breast and other reproductive organs. In this study we identified a natural product patchouli alcohol (PTA) as a selective ERβ agonist which improved the cognitive defects in female APP/PS1 mice, and explore the underlying mechanisms. Six-month-old female APP/PS1 mice were administered PTA (20, 40 mg · kg-1 · d-1, i.g.) for 90 days. We first demonstrated that PTA bound to ERβ with a dissociation constant (KD) of 288.9 ± 35.14 nM in microscale thermophoresis. Then we showed that PTA administration dose-dependently ameliorated cognitive defects evaluated in Morris water maze and Y-maze testes. Furthermore, PTA administration reduced amyloid plaque deposition in the hippocampus by promoting microglial phagocytosis; PTA administration improved synaptic integrity through enhancing BDNF/TrkB/CREB signaling, ameliorated oxidative stress by Catalase level, and regulated Bcl-2 family proteins in the hippocampus. The therapeutic effects of PTA were also observed in vitro: PTA (5, 10, 20 μM) dose-dependently increased phagocytosis of o-FAM-Aβ42 in primary microglia and BV2 cells through enhancing ERβ/TLR4 signaling; PTA treatment ameliorated o-Aβ25-35-induced reduction of synapse-related proteins VAMP2 and PSD95 in primary neurons through enhancing ERβ/BDNF/TrkB/CREB pathways; PTA treatment alleviated o-Aβ25-35-induced oxidative stress in primary neurons through targeting ERβ and increasing Catalase expression. Together, this study has addressed the efficacy of selective ERβ agonist in the amelioration of AD and highlighted the potential of PTA as a drug lead compound against the disease.

Reelin cells and sex-dependent synaptopathology in autism following postnatal immune activation

BACKGROUND AND PURPOSE

Autism spectrum disorders (ASD) are heterogeneous neurodevelopmental disorders with considerably increased risk in male infants born preterm and with neonatal infection. Here, we investigated the role of postnatal immune activation on hippocampal synaptopathology by targeting Reelin+ cells in mice with ASD-like behaviours.

EXPERIMENTAL APPROACH

C57/Bl6 mouse pups of both sexes received lipopolysaccharide (LPS, 1 mg·kg-1 ) on postnatal day (P) 5. At P45, animal behaviour was examined by marble burying and sociability test, followed by ex vivo brain MRI diffusion kurtosis imaging (DKI). Hippocampal synaptogenesis, number and morphology of Reelin+ cells, and mRNA expression of trans-synaptic genes, including neurexin-3, neuroligin-1, and cell-adhesion molecule nectin-1, were analysed at P12 and P45.

KEY RESULTS

Social withdrawal and increased stereotypic activities in males were related to increased mean diffusivity on MRI-DKI and overgrowth in hippocampus together with retention of long-thin immature synapses on apical dendrites, decreased volume and number of Reelin+ cells as well as reduced expression of trans-synaptic and cell-adhesion molecules.

CONCLUSION AND IMPLICATIONS

The study provides new insights into sex-dependent mechanisms that may underlie ASD-like behaviour in males following postnatal immune activation. We identify GABAergic interneurons as core components of dysmaturation of excitatory synapses in the hippocampus following postnatal infection and provide cellular and molecular substrates for the MRI findings with translational value.

Impaired learning and memory generated by hyperthyroidism is rescued by restoration of AMPA and NMDA receptors function

Hyperthyroidism has been identified as a risk factor for cognitive disorders. The hippocampus is a key brain region associated with cognitive function, among which excitatory synapse transmission plays an important role in the process of learning and memory. However, the mechanism by which hyperthyroidism leads to cognitive dysfunction through a synaptic mechanism remains unknown. We investigated the synaptic mechanisms in the effects of hyperthyroidism in an animal model that involved repeated injection of triiodothyronine (T3). These mice displayed impaired learning and memory in the Novel object recognition test, Y-maze test, and Morris Water Maze test, as well as elevated anxiety in the elevated plus maze. Mature dendritic spines in the hippocampal CA1 region of hyperthyroid mice were significantly decreased, accompanied by decreased level of AMPA- and NMDA-type glutamate receptors in the hippocampus. In primary cultured hippocampal neurons, levels of AMPA- and NMDA-type glutamate receptors also decreased and whole-cell patch-clamp recording revealed that excitatory synaptic function was obviously attenuated after T3 treatment. Notably, pharmacological activation of AMPAR or NMDAR by intraperitoneal injection of CX546, an AMPAR agonist, or NMDA, an NMDAR agonist can restore excitatory synaptic function and corrected impaired learning and memory deficit in hyperthyroid mice. Together, our findings uncovered a previously unrecognized AMPAR and NMDAR-dependent mechanism involved in regulating hippocampal excitatory synaptic transmission and learning and memory disorders in hyperthyroidism.

NMDA receptors mediate synaptic plasticity impairment of hippocampal neurons due to arsenic exposure

Endemic arsenism is a worldwide health problem. Chronic arsenic exposure results in cognitive dysfunction due to arsenic and its metabolites accumulating in hippocampus. As the cellular basis of cognition, synaptic plasticity is pivotal in arsenic-induced cognitive dysfunction. N-methyl-D-aspartate receptors (NMDARs) serve physiological functions in synaptic transmission. However, excessive NMDARs activity contributes to exitotoxicity and synaptic plasticity impairment. Here, we provide an overview of the mechanisms that NMDARs and their downstream signaling pathways mediate synaptic plasticity impairment due to arsenic exposure in hippocampal neurons, ways of arsenic exerting on NMDARs, as well as the potential therapeutic targets except for water improvement.

The role of ciliopathy-associated type 3 adenylyl cyclase in infanticidal behavior in virgin adult male mice

Virgin adult male mice often display killing of alien newborns, defined as infanticide, and this behavior is dependent on olfactory signaling. Olfactory perception is achieved by the main olfactory system (MOS) or vomeronasal system (VNS). Although it has been established that the VNS is crucial for infanticide in male mice, the role of the MOS in infanticide remains unknown. Herein, by producing lesions via ZnSO₄ perfusion and N-methyl-D-aspartic acid stereotactic injection, we demonstrated that the main olfactory epithelium (MOE), anterior olfactory nucleus (AON), or ventromedial hypothalamus (VMH) is crucial for infanticide in adult males. By using CRISPR-Cas9 coupled with adeno-associated viruses to induce specific knockdown of type 3 adenylyl cyclase (AC3) in these tissues, we further demonstrated that AC3, a ciliopathy-associated protein, in the MOE and the expression of related proteins in the AON or VMH are necessary for infanticidal behavior in virgin adult male mice.

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MOE lesions and knockdown of AC3 in the MOE result in abnormal infanticidal behavior

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The infanticidal behavior of male mice is impaired by lesioning of the AON or VMH

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AC3 knockdown in the AON or VMH affects the infanticidal behavior of male mice

Methylphenidate Restores Behavioral and Neuroplasticity Impairments in the Prenatal Nicotine Exposure Mouse Model of ADHD: Evidence for Involvement of AMPA Receptor Subunit Composition and Synaptic Spine Morphology in the Hippocampus

In ADHD treatment, methylphenidate (MPH) is the most frequently used medication. The present work provides evidence that MPH restored behavioral impairments and neuroplasticity due to changes in AMPAR subunit composition and distribution, as well as maturation of dendritic spines, in a prenatal nicotine exposure (PNE) ADHD mouse model. PNE animals and controls were given a single oral dose of MPH (1 mg/kg), and their behavior was tested for attention, hyperactivity, and working memory. Long-term potentiation (LTP) was induced and analyzed at the CA3/CA1 synapse in hippocampal slices taken from the same animals tested behaviorally, measuring fEPSPs and whole-cell patch-clamp EPSCs. By applying crosslinking and Western blots, we estimated the LTP effects on AMPAR subunit composition and distribution. The density and types of dendritic spines were quantified by using the Golgi staining method. MPH completely restored the behavioral impairments of PNE mice. Reduced LTP and AMPA-receptor-mediated EPSCs were also restored. EPSC amplitudes were tightly correlated with numbers of GluA1/GluA1 AMPA receptors at the cell surface. Finally, we found a lower density of dendritic spines in hippocampal pyramidal neurons in PNE mice, with a higher fraction of thin-type immature spines and a lower fraction of mushroom mature spines; the latter effect was also reversed by MPH.

Deletion of the Autism-Associated Protein SHANK3 Abolishes Structural Synaptic Plasticity after Brain Trauma

Autism spectrum disorders (ASDs) are characterized by repetitive behaviors and impairments of sociability and communication. About 1% of ASD cases are caused by mutations of SHANK3, a major scaffolding protein of the postsynaptic density. We studied the role of SHANK3 in plastic changes of excitatory synapses within the central nervous system by employing mild traumatic brain injury (mTBI) in WT and Shank3 knockout mice. In WT mice, mTBI triggered ipsi- and contralateral loss of hippocampal dendritic spines and excitatory synapses with a partial recovery over time. In contrast, no significant synaptic alterations were detected in Shank3∆11−/− mice, which showed fewer dendritic spines and excitatory synapses at baseline. In line, mTBI induced the upregulation of synaptic plasticity-related proteins Arc and p-cofilin only in WT mice. Interestingly, microglia proliferation was observed in WT mice after mTBI but not in Shank3∆11−/− mice. Finally, we detected TBI-induced increased fear memory at the behavioral level, whereas in Shank3∆11−/− animals, the already-enhanced fear memory levels increased only slightly after mTBI. Our data show the lack of structural synaptic plasticity in Shank3 knockout mice that might explain at least in part the rigidity of behaviors, problems in adjusting to new situations and cognitive deficits seen in ASDs.

Selective plasticity of callosal neurons in the adult contralesional cortex following murine traumatic brain injury

Traumatic brain injury (TBI) results in deficits that are often followed by recovery. The contralesional cortex can contribute to this process but how distinct contralesional neurons and circuits respond to injury remains to be determined. To unravel adaptations in the contralesional cortex, we used chronic in vivo two-photon imaging. We observed a general decrease in spine density with concomitant changes in spine dynamics over time. With retrograde co-labeling techniques, we showed that callosal neurons are uniquely affected by and responsive to TBI. To elucidate circuit connectivity, we used monosynaptic rabies tracing, clearing techniques and histology. We demonstrate that contralesional callosal neurons adapt their input circuitry by strengthening ipsilateral connections from pre-connected areas. Finally, functional in vivo two-photon imaging demonstrates that the restoration of pre-synaptic circuitry parallels the restoration of callosal activity patterns. Taken together our study thus delineates how callosal neurons structurally and functionally adapt following a contralateral murine TBI.

Which contralesional circuits adapt after traumatic brain injury (TBI) is unclear. Here the authors used in vivo imaging, retrograde labeling, rabies tracing, clearing and functional imaging to demonstrate that callosal neurons selectively adapt after TBI in mice.

Can biophysical models of dendritic spines be used to explore synaptic changes associated with addiction?

Effective treatments that prevent or reduce drug relapse vulnerability should be developed to relieve the high burden of drug addiction on society. This will only be possible by enhancing the understanding of the molecular mechanisms underlying the neurobiology of addiction. Recent experimental data have shown that dendritic spines, small protrusions from the dendrites that receive excitatory input, of spiny neurons in the nucleus accumbens exhibit morphological changes during drug exposure and withdrawal. Moreover, these changes relate to the characteristic drug-seeking behavior of addiction. However, due to the complexity of the dendritic spines, we do not yet fully understand the processes underlying their structural changes in response to different inputs. We propose that biophysical models can enhance the current understanding of these processes by incorporating different, and sometimes, discrepant experimental data to identify the shared underlying mechanisms and generate experimentally testable hypotheses. This review aims to give an up-to-date report on biophysical models of dendritic spines, focusing on those models that describe their shape changes, which are well-known to relate to learning and memory. Moreover, it examines how these models can enhance our understanding of the effect of the drugs and the synaptic changes during withdrawal, as well as during neurodegenerative disease progression such as Alzheimer's disease.

Logical fallacies and misinterpretations that hinder progress in translational addiction neuroscience

Substance use disorders (SUDs) are heterogeneous and complex, making the development of translationally predictive rodent and nonhuman primate models to uncover their neurobehavioral underpinnings difficult. Neuroscience-focused outcomes have become highly prevalent, and with this, the notion that SUDs are disorders of the brain embraced as a dominant theoretical orientation to understand SUD etiology and treatment. These efforts, however, have led to few efficacious pharmacotherapies, and in some cases (as with cocaine or methamphetamine), no pharmacotherapies have translated from preclinical models for clinical use. In this theoretical commentary, we first describe the development of animal models of substance use behaviors from a historical perspective. We then define and discuss three logical fallacies including 1) circular explanation, 2) affirming the consequent, and 3) reification that can apply to developed models. We then provide three case examples in which conceptual or logical issues exist in common methods (i.e., behavioral economic demand, escalation, and reinstatement). Alternative strategies to refocus behavioral models are suggested for the field to better bridge the translational divide between animal models, the clinical condition of SUDs, and current and future regulatory pathways for intervention development.

The Intriguing Contribution of Hippocampal Long-Term Depression to Spatial Learning and Long-Term Memory

Long-term potentiation (LTP) and long-term depression (LTD) comprise the principal cellular mechanisms that fulfill established criteria for the physiological correlates of learning and memory. Traditionally LTP, that increases synaptic weights, has been ascribed a prominent role in learning and memory whereas LTD, that decreases them, has often been relegated to the category of "counterpart to LTP" that serves to prevent saturation of synapses. In contradiction of these assumptions, studies over the last several years have provided functional evidence for distinct roles of LTD in specific aspects of hippocampus-dependent associative learning and information encoding. Furthermore, evidence of the experience-dependent "pruning" of excitatory synapses, the majority of which are located on dendritic spines, by means of LTD has been provided. In addition, reports exist of the temporal and physical restriction of LTP in dendritic compartments by means of LTD. Here, we discuss the role of LTD and LTP in experience-dependent information encoding based on empirical evidence derived from conjoint behavioral and electrophysiological studies conducted in behaving rodents. We pinpoint the close interrelation between structural modifications of dendritic spines and the occurrence of LTP and LTD. We report on findings that support that whereas LTP serves to acquire the general scheme of a spatial representation, LTD enables retention of content details. We argue that LTD contributes to learning by engaging in a functional interplay with LTP, rather than serving as its simple counterpart, or negator. We propose that similar spatial experiences that share elements of neuronal representations can be modified by means of LTD to enable pattern separation. Therewith, LTD plays a crucial role in the disambiguation of similar spatial representations and the prevention of generalization.