Structural plasticity of dendritic spines: the underlying mechanisms and its dysregulation in brain disorders

Glutamatergic synaptic plasticity in medial vestibular nuclei during vestibular compensation

Vestibular compensation, the spontaneous recovery from vestibular dysfunction following unilateral vestibular loss, serves as a valuable model for investigating post-lesion plasticity in the adult central nervous system. Elucidating the mechanisms underlying vestibular compensation also offers promising therapeutic avenues for treating vestibular disorders. While most studies have focused on the dynamics of GABAergic synaptic plasticity and intrinsic cellular adaptations in the ipsilesional medial vestibular nucleus (MVN) after unilateral labyrinthectomy (UL), the role of glutamatergic synaptic plasticity in this process remains largely unexplored. Here, we employed Golgi staining, immunofluorescence, whole-cell patch-clamp recordings, and behavioral assessments to examine the structural and functional dynamics of glutamatergic synapses during vestibular compensation. Our results reveal rapid structural and functional plasticity of glutamatergic transmission in response to UL. Specifically, dendritic spine density and morphology in the ipsilesional MVN recovered to baseline levels within 6 to 24 h post-UL. Furthermore, UL-induced postsynaptic depression of glutamatergic synaptic strength, reflected by a reduced AMPA/NMDA ratio, was reversed within 24 h, likely due to an upregulation of Ca2+-permeable AMPA receptors. In contrast, presynaptic glutamate release probability, as indicated by a reduced frequency of spontaneous excitatory postsynaptic currents, was not fully compensated during this period. These results suggest that while presynaptic properties recover more slowly in ipsilesional MVN neurons following UL, postsynaptic glutamatergic transmission undergoes rapid structural and functional reorganization. The findings highlight glutamatergic synaptic plasticity as a critical driver for vestibular compensation and suggest that pharmacological interventions targeting these mechanisms may accelerate functional recovery, offering potential therapeutic avenues for vestibular disorders.

The ROCK Inhibitor Fasudil and Sertraline Share Morphological and Molecular Effects in the Hippocampus of Chronically Stressed Rats: Exploring Common Antidepressant Pathways by Network Pharmacology

Despite the widespread use of selective serotonin reuptake inhibitors like sertraline, the intricate molecular mechanisms underlying major depression and the therapeutic efficacy of these treatments remain not fully elucidated. Building on our preliminary findings, this study investigates the antidepressant effects of fasudil, a Rho-associated protein kinase (ROCK) inhibitor typically utilized as a vasodilator and antispasmodic, and compares its effects with those of sertraline using a chronic restraint stress model in rats. Specifically, we examined the effects of chronic administration on dendritic spine density, key molecular survival pathways, and miRNA levels in the hippocampus. Adult male Sprague-Dawley rats were administered sertraline, fasudil (10 mg/kg/day), or saline over 14 days, with a subset experiencing daily restraint stress. Our findings demonstrate that both sertraline and fasudil effectively prevented stress-induced reductions in dendritic spine density and miR-138 levels in the rat hippocampus. Additionally, by employing a network pharmacology approach, we explored the converging molecular pathways influenced by both drugs, facilitating the identification of novel molecular targets and pathways implicated in the pathophysiology of depression and its treatment. Pharmacoinformatic analysis revealed common signaling cascades and critical proteins that may potentially underlie the observed pharmacological effects, contributing to a paradigm shift in understanding depression by integrating drug repurposing and network pharmacology, offering valuable insights into the underlying mechanisms of depression and the antidepressant effect from a new network-based paradigm rather than focusing solely on a single protein target.

Molecular Mechanisms of Propofol-Induced Cognitive Impairment: Suppression of Critical Hippocampal Pathways

Propofol, a commonly used anesthetic, is known to cause postoperative cognitive dysfunction (POCD), particularly after prolonged or high-dose administration. Its effects on neural remodeling in the hippocampal region, which is vital for cognitive function, remain poorly understood. This study employs single-cell RNA sequencing (scRNA-seq) and high-throughput transcriptomic analysis to elucidate the molecular mechanisms by which propofol impairs hippocampal neural remodeling. Our findings indicate that propofol suppresses the (5-Hydroxytryptamine Receptor 1A/Glutamate Receptor 2/Phosphoinositide 3-Kinase Regulatory Subunit 1) HTR1A/GRIA2/PIK3R1 signaling pathway, contributing to cognitive dysfunction in mice. In vitro experiments reveal that propofol treatment reduces the expression of HTR1A/GRIA2/PIK3R1-related factors, decreases neuronal activity and synaptic plasticity, and increases apoptosis and inflammation. In vivo experiments demonstrate significant impairments in spatial memory and learning abilities in mice treated with propofol. These results provide new insights into the long-term effects of anesthetic drugs and offer a scientific basis for their judicious use in clinical practice. The study highlights potential strategies and targets for preventing and treating POCD, emphasizing the importance of understanding the molecular mechanisms underlying anesthetic-induced cognitive dysfunction.

Maternal Exposure of SD Rats to Benzo[a]Pyrene Impairs Neurobehavior and Hippocampal Synaptic Ultrastructure in Offspring via Downregulating Synaptic-Associated Factors

Benzo[a]pyrene (B[a]P) is a carcinogenic contaminant widely present in the environment. Recently, increasing studies have paid attention to the developmental neurotoxicity of B[a]P in offspring in their early life stages; however, the underlying molecular mechanisms have not been clearly elucidated. In this study, we aimed to evaluate the effects of prenatal B[a]P exposure on neurobehavior of pups during their brain growth spurt (BGS) period and also explore the potential underlying mechanisms. Pregnant Sprague-Dawley (SD) rats were intraperitoneally exposed to 0, 10, 20, or 40 mg/kg-bw B[a]P for three consecutive days during embryonic days 17-19. The physiological development index of pups was observed, and a series of neurobehavioral tests assessing sensory and motor maturation were performed. The complexity of dendritic branches and the basal dendritic spine density of CA1 pyramidal neurons were examined using Golgi-Cox staining during PND 1-14. In addition, the mRNA and protein expression levels of hippocampal BDNF, SYP, Arc, PSD-95, DNMT1, and DNMT3a, and the level of 5-mC were detected using RT-qPCR, Western blotting, or immunohistochemical staining, respectively. We noted that prenatal B[a]P exposure induced body weight loss and neurobehavioral impairments in the early life stages. Furthermore, this study firstly revealed that maternal exposure to B[a]P impaired the dendritic arborization and complexity of pyramidal neurons in the hippocampus CA1 subfield in offspring during the early postnatal period, and the damage of B[a]P to basal dendritic spine density was also observed in a dose-dependent manner. Correspondingly, maternal exposure to B[a]P markedly reduced BDNF, Arc, SYP, and PSD-95 mRNA and protein levels in the offspring hippocampus. Meanwhile, the levels of hippocampal DNMT1, DNMT3a, and 5-mC significantly increased in the offspring prenatally exposed to B[a]P. In summary, this study firstly demonstrated that maternal B[a]P exposure induced neurobehavioral deficits by destroying the hippocampal synaptic ultrastructure, which was possibly associated with the downregulation of BDNF, Arc, SYP, and PSD95 in the hippocampus through increased DNMTs-mediated DNA methylation in offspring during the BGS period.

The impact of purine nucleosides on neuroplasticity in the adult brain

Neuroplasticity refers to the nervous system's ability to adapt and reorganize its cell structures and neuronal networks in response to internal and external stimuli. In adults, this process involves neurogenesis, synaptogenesis, and synaptic and neurochemical plasticity. Several studies have reported the significant impact of the purinergic system on neuroplasticity modulation. And, there is considerable evidence supporting the role of purine nucleosides, such as adenosine, inosine, and guanosine, in this process. This review presents extensive research on how these nucleosides enhance the neuroplasticity of the adult central nervous system, particularly in response to damage. The mechanisms through which these nucleosides exert their effects involve complex interactions with various receptors and signaling pathways. Adenosine's influence on neurogenesis involves interactions with adenosine receptors, specifically A1R and A2AR. A1R activation appears to inhibit neuronal differentiation and promote astrogliogenesis, while A2AR activation supports neurogenesis, neuritogenesis, and synaptic plasticity. Inosine and guanosine positively impact cell proliferation, neurogenesis, and neuritogenesis. Inosine seems to modulate extracellular adenosine levels, and guanosine might act through interactions between purinergic and glutamatergic systems. Additionally, the review discusses the potential therapeutic implications of purinergic signaling in neurodegenerative and neuropsychiatric diseases, emphasizing the importance of these nucleosides in the neuroplasticity of brain function and recovery.

Cholinesterase Inhibitor Reveals Synergistic Potential for Neural Stem Cell-Based Therapy in the 5xFAD Mouse Model of Alzheimer's Disease

Background and Objectives

Stem cell therapy shows great promise for treating Alzheimer's disease (AD). Cholinesterase inhibitors (ChEIs) like donepezil are well-established for alleviating AD symptoms. This study aimed to determine if combining ChEI treatment with stem cell therapy could improve therapeutic outcomes.

Methods

Neural stem cells (NSCs) were injected into the hippocampus of the 5xFAD AD mice using a stereotactic technique. Following this, donepezil or a placebo was administered for one month. We assessed behavioral improvements, survival and health of the grafts, and changes in synaptic density.

Results

The AD mice demonstrated cognitive impairment in both the Morris water maze and novel object recognition tests. In groups receiving stem cell therapy, donepezil enhanced the survival and neuronal differentiation of grafted NSCs, promoting the establishment of synaptic connections with the host brain. The combined treatment with donepezil and NSC transplantation more effectively increased synaptic density and improved behavioral performance in AD mice compared to NSC transplantation alone.

Conclusion

Combining ChEIs with NSC transplantation produces synergistic effects in AD treatment. This approach highlights the potential of integrating these therapies to develop more effective strategies for managing Alzheimer's disease.

Neuronal connectivity, behavioral, and transcriptional alterations associated with the loss of MARK2

Neuronal connectivity is essential for adaptive brain responses and can be modulated by dendritic spine plasticity and the intrinsic excitability of individual neurons. Dysregulation of these processes can lead to aberrant neuronal activity, which has been associated with numerous neurological disorders including autism, epilepsy, and Alzheimer's disease. Nonetheless, the molecular mechanisms underlying abnormal neuronal connectivity remain unclear. We previously found that the serine/threonine kinase Microtubule Affinity Regulating Kinase 2 (MARK2), also known as Partitioning Defective 1b (Par1b), is important for the formation of dendritic spines in vitro. However, despite its genetic association with several neurological disorders, the in vivo impact of MARK2 on neuronal connectivity and cognitive functions remains unclear. Here, we demonstrate that the loss of MARK2 in vivo results in changes to dendritic spine morphology, which in turn leads to a decrease in excitatory synaptic transmission. Additionally, the loss of MARK2 produces substantial impairments in learning and memory, reduced anxiety, and defective social behavior. Notably, MARK2 deficiency results in heightened seizure susceptibility. Consistent with this observation, electrophysiological analysis of hippocampal slices indicates underlying neuronal hyperexcitability in MARK2-deficient neurons. Finally, RNAseq analysis reveals transcriptional changes in genes regulating synaptic transmission and ion homeostasis. These results underscore the in vivo role of MARK2 in governing synaptic connectivity, neuronal excitability, and cognitive functions.

L-methionine and the L-type Ca2+ channel agonist BAY K 8644 collaboratively contribute to the reduction of depressive-like behavior in mice

The L-type Ca2+ channel (LTCC, also known as Cav1,2) is involved in the regulation of key neuronal functions, such as dendritic information integration, cell survival, and neuronal gene expression. Clinical studies have shown an association between L-type calcium channels and the onset of depression, although the precise mechanisms remain unclear. The development of depression results from a combination of environmental and genetic factors. DNA methylation, a significant epigenetic modification, plays a regulatory role in the pathogenesis of psychiatric disorders such as posttraumatic stress disorder (PTSD), depression, and autism. In our study, we observed reduced Dnmt3a expression levels in the hippocampal DG region of mice with LPS-induced depression compared to control mice. The antidepressant Venlafaxine was able to increase Dnmt3a expression levels. Conversely, Bay K 8644, an agonist of the L-type Ca2+ channel, partially ameliorated depression-like behaviors but did not elevate Dnmt3a expression levels. Furthermore, when we manipulated DNA methylation levels during Bay K 8644 intervention in depression-like models, we found that enhancing the expression of Dnmt3a could improve LPS-induced depression/anxiety-like behaviors, while inhibiting DNA methylation exacerbated anxiety-like behaviors, the combined use of BAY K 8644 and L-methionine can better improve depressive-like behavior. These findings indicate that DNA methylation plays a role in the regulation of depression-like behaviors by the L-type Ca2+ channel, and further research is needed to elucidate the interactions between DNA methylation and L-type Ca2+ channels.

Circadian-Dependent Intermittent Fasting Influences Ischemic Tolerance and Dendritic Spine Remodeling

BACKGROUND

Preconditioning by intermittent fasting is linked to improved cognition and motor function, and enhanced recovery after stroke. Although the duration of fasting was shown to elicit different levels of neuroprotection after ischemic stroke, the impact of time of fasting with respect to the circadian cycles remains unexplored.

METHODS

Cohorts of mice were subjected to a daily 16-hour fast, either during the dark phase (active-phase intermittent fasting) or the light phase (inactive-phase intermittent fasting) or were fed ad libitum. Following a 6-week dietary regimen, mice were subjected to transient focal cerebral ischemia and underwent behavioral functional assessment. Brain samples were collected for RNA sequencing and histopathologic analyses.

RESULTS

Active-phase intermittent fasting cohort exhibited better poststroke motor and cognitive recovery as well as reduced infarction, in contrast to inactive-phase intermittent fasting cohort, when compared with ad libitum cohort. In addition, protection of dendritic spine density/morphology and increased expression of postsynaptic density protein-95 were observed in the active-phase intermittent fasting.

CONCLUSIONS

These findings indicate that the time of daily fasting is an important factor in inducing ischemic tolerance by intermittent fasting.

Differential expression of genes in the RhoA/ROCK pathway in the hippocampus and cortex following intermittent hypoxia and high-intensity interval training

Structural neuroplasticity such as neurite extension and dendritic spine dynamics is enhanced by brain-derived neurotrophic factor (BDNF) and impaired by types of inhibitory molecules that induce growth cone collapse and actin depolymerization, for example, myelin-associated inhibitors, chondroitin sulfate proteoglycans, and negative guidance molecules. These inhibitory molecules can activate RhoA/rho-associated coiled-coil containing protein kinase (ROCK) signaling (known to restrict structural plasticity). Intermittent hypoxia (IH) and high-intensity interval training (HIIT) are known to upregulate BDNF that is associated with improvements in learning and memory and greater functional recovery following neural insults. We investigated whether the RhoA/ROCK signaling pathway is also modulated by IH and HIIT in the hippocampus, cortex, and lumbar spinal cord of male Wistar rats. The gene expression of 25 RhoA/ROCK signaling pathway components was determined following IH, HIIT, or IH combined with HIIT (30 min/day, 5 days/wk, 6 wk). IH included 10 3-min bouts that alternated between hypoxia (15% O2) and normoxia. HIIT included 10 3-min bouts alternating between treadmill speeds of 50 cm·s-1 and 15 cm·s-1. In the hippocampus, IH and HIIT significantly downregulated Acan and NgR2 mRNA that are involved in the inhibition of neuroplasticity. However, IH and IH + HIIT significantly upregulated Lingo-1 and NgR3 in the cortex. This is the first time IH and HIIT have been linked to the modulation of plasticity-inhibiting pathways. These results provide a fundamental step toward elucidating the interplay between the neurotrophic and inhibitory mechanisms involved in experience-driven neural plasticity that will aid in optimizing physiological interventions for the treatment of cognitive decline or neurorehabilitation.NEW & NOTEWORTHY Intermittent hypoxia (IH) and high-intensity interval training (HIIT) enhance neuroplasticity and upregulate neurotrophic factors in the central nervous system (CNS). We provide evidence that IH and IH + HIIT also have the capacity to regulate genes involved in the RhoA/ROCK signaling pathway that is known to restrict structural plasticity in the CNS. This provides a new mechanistic insight into how these interventions may enhance hippocampal-related plasticity and facilitate learning, memory, and neuroregeneration.

Therapeutic benefits of central LH receptor agonism in the APP/PS1 AD model involve trophic and immune regulation and are reproductive status dependent

The mechanisms that underly reproductive hormone effects on cognition, neuronal plasticity, and AD risk, particularly in relation to gonadotropin LH receptor (LHCGR) signaling, remain poorly understood. To address this gap in knowledge and clarify the impact of circulating steroid hormones on the therapeutic effects of CNS LHCGR activation, we delivered the LHCGR agonist human chorionic gonadotropin (hCG) intracerebroventricularly (ICV) and evaluated functional, structural, plasticity-related signaling cascades, Aβ pathology, and transcriptome differences in reproductively intact and ovariectomized (OVX) APP/PS1 AD female mice. Here we demonstrate that CNS hCG delivery restored function to wild-type levels only in OVX APP/PS1 mice. Spine density was increased in all hCG treated groups independently of reproductive status. Notably, increases in BDNF signaling and cognition, were selectively upregulated only in the OVX hCG-treated group. RNA sequencing analyses identified a significant increase in peripheral myeloid and pro-inflammatory genes within the hippocampi of the OVX group that were completely reversed by hCG treatment, identifying a potential mechanism underlying the selective therapeutic effect of LHCGR activation. Interestingly, in intact mice, hCG administration mimicked the effects of gonadectomy. Together, our findings indicate that CNS LHCGR agonism in the post-menopausal context is beneficial through trophic and immune mechanisms. Our findings also underscore the presence of a steroid-LHCGR mechanistic interaction that is unexplored yet potentially meaningful to fully understand "post-menopausal" brain function and CNS hormone treatment response.

MARK1 regulates dendritic spine morphogenesis and cognitive functions in vivo

Dendritic spines play a pivotal role in synaptic communication and are crucial for learning and memory processes. Abnormalities in spine morphology and plasticity are observed in neurodevelopmental and neuropsychiatric disorders, yet the underlying signaling mechanisms remain poorly understood. The microtubule affinity regulating kinase 1 (MARK1) has been implicated in neurodevelopmental disorders, and the MARK1 gene shows accelerated evolution in the human lineage suggesting a role in cognition. However, the in vivo role of MARK1 in synaptogenesis and cognitive functions remains unknown. Here we show that forebrain-specific conditional knockout (cKO) of Mark1 in mice causes defects in dendritic spine morphogenesis in hippocampal CA1 pyramidal neurons with a significant reduction in spine density. In addition, we found loss of MARK1 causes synaptic accumulation of GKAP and GluA2. Furthermore, we found that MARK1 cKO mice show defects in spatial learning in the Morris water maze and reduced anxiety-like behaviors in the elevated plus maze. Taken together, our data show a novel role for MARK1 in regulating dendritic spine morphogenesis and cognitive functions in vivo.

Rab11 regulates autophagy at dendritic spines in an mTOR- and NMDA-dependent manner

Synaptic plasticity is a process that shapes neuronal connections during neurodevelopment and learning and memory. Autophagy is a mechanism that allows the cell to degrade its unnecessary or dysfunctional components. Autophagosomes appear at dendritic spines in response to plasticity-inducing stimuli. Autophagy defects contribute to altered dendritic spine development, autistic-like behavior in mice, and neurological disease. While several studies have explored the involvement of autophagy in synaptic plasticity, the initial steps of the emergence of autophagosomes at the postsynapse remain unknown. Here, we demonstrate a postsynaptic association of autophagy-related protein 9A (Atg9A), known to be involved in the early stages of autophagosome formation, with Rab11, a small GTPase that regulates endosomal trafficking. Rab11 activity was necessary to maintain Atg9A-positive structures at dendritic spines. Inhibition of mTOR increased Rab11 and Atg9A interaction and increased the emergence of LC3 positive vesicles, an autophagosome membrane-associated protein marker, in dendritic spines when coupled to NMDA receptor stimulation. Dendritic spines with newly formed LC3+ vesicles were more resistant to NMDA-induced morphologic change. Rab11 DN overexpression suppressed appearance of LC3+ vesicles. Collectively, these results suggest that initiation of autophagy in dendritic spines depends on neuronal activity and Rab11a-dependent Atg9A interaction that is regulated by mTOR activity.

Differential regulations of neural activity and survival in primary cortical neurons by PFOA or PFHpA

Perfluorinated compounds (PFCs), organofluoride compounds comprising carbon-fluorine and carbon-carbon bonds, are used as water and oil repellents in textiles and pharmaceutical tablets; however, they are associated with potential neurotoxic effects. Moreover, the impact of PFCs on neuronal survival, activity, and regulation within the brain remains unclear. Additionally, the mechanisms through which PFCs induce neuronal toxicity are not well-understood because of the paucity of data. This study elucidates that perfluorooctanoic acid (PFOA) and perfluoroheptanoic acid (PFHpA) exert differential effects on the survival and activity of primary cortical neurons. Although PFOA triggers apoptosis in cortical neurons, PFHpA does not exhibit this effect. Instead, PFHpA modifies dendritic spine morphogenesis and synapse formation in primary cortical neuronal cultures, additionally enhancing neural activity and synaptic transmission. This research uncovers a novel mechanism through which PFCs (PFHpA and PFOA) cause distinct alterations in dendritic spine morphogenesis and synaptic activity, shedding light on the molecular basis for the atypical behaviors noted following PFC exposure. Understanding the distinct effects of PFHpA and PFOA could guide regulatory policies on PFC usage and inform clinical approaches to mitigate their neurotoxic effects, especially in vulnerable population.

The LH receptor regulates hippocampal spatial memory and restores dendritic spine density in ovariectomized APP/PS1 AD mice

Activation of the luteinizing hormone receptor (LHCGR) rescues spatial memory function and spine density losses associated with gonadectomy and high circulating gonadotropin levels in females. However, whether this extends to the AD brain or the mechanisms that underlie these benefits remain unknown. To address this question, we delivered the LHCGR agonist human chorionic gonadotropin (hCG) intracerebroventricularly (ICV), under reproductively intact and ovariectomized conditions to mimic the post-menopausal state in the APP/PS1mouse brain. Cognitive function was tested using the Morris water maze task, and hippocampal dendritic spine density, Aβ pathology, and signaling changes associated with these endpoints were determined to address mechanisms. Here we show that central LHCGR activation restored function in ovariectomized APP/PS1 female mice to wild-type levels without altering Aβ pathology. LHCGR activation increased hippocampal dendritic spine density regardless of reproductive status, and this was mediated by BDNF-dependent and independent signaling. We also show that ovariectomy in the APP/PS1 brain elicits an increase in peripherally derived pro-inflammatory genes which are inhibited by LHCGR activation. This may mediate reproductive status specific effects of LHCGR agonism on cognitive function and BDNF expression. Together, this work highlights the relevance of the LHCGR on cognition and its therapeutic potential in the "menopausal" AD brain.

Neuronal connectivity, behavioral, and transcriptional alterations associated with the loss of MARK2

Neuronal connectivity is essential for adaptive brain responses and can be modulated by dendritic spine plasticity and the intrinsic excitability of individual neurons. Dysregulation of these processes can lead to aberrant neuronal activity, which has been associated with numerous neurological disorders including autism, epilepsy, and Alzheimer's disease. Nonetheless, the molecular mechanisms underlying aberrant neuronal connectivity remains unclear. We previously found that the serine/threonine kinase Microtubule Affinity Regulating Kinase 2 (MARK2), also known as Partitioning Defective 1b (Par1b), is important for the formation of dendritic spines in vitro. However, despite its genetic association with several neurological disorders, the in vivo impact of MARK2 on neuronal connectivity and cognitive functions remains unclear. Here, we demonstrate that loss of MARK2 in vivo results in changes to dendritic spine morphology, which in turn leads to a decrease in excitatory synaptic transmission. Additionally, loss of MARK2 produces substantial impairments in learning and memory, anxiety, and social behavior. Notably, MARK2 deficiency results in heightened seizure susceptibility. Consistent with this observation, RNAseq analysis reveals transcriptional changes in genes regulating synaptic transmission and ion homeostasis. These findings underscore the in vivo role of MARK2 in governing synaptic connectivity, cognitive functions, and seizure susceptibility.

MARK1 regulates dendritic spine morphogenesis and cognitive functions in vivo

Dendritic spines play a pivotal role in synaptic communication and are crucial for learning and memory processes. Abnormalities in spine morphology and plasticity are observed in neurodevelopmental and neuropsychiatric disorders, yet the underlying signaling mechanisms remain poorly understood. The microtubule affinity regulating kinase 1 (MARK1) has been implicated in neurodevelopmental disorders, and the MARK1 gene shows accelerated evolution in the human lineage suggesting a role in cognition. However, the in vivo role of MARK1 in synaptogenesis and cognitive functions remains unknown. Here we show that forebrain-specific conditional knockout (cKO) of Mark1 causes defects in dendritic spine morphogenesis in hippocampal CA1 pyramidal neurons with a significant reduction in spine density. In addition, we found that MARK1 cKO mice show defects in spatial learning in the Morris Water Maze and reduced anxiety-like behaviors in the Elevated Plus Maze. Furthermore, we found loss of MARK1 causes synaptic accumulation of GKAP and GluR2. Taken together, our data show a novel role for MARK1 in regulating dendritic spine morphogenesis and cognitive functions in vivo .

Blue Native PAGE-Antibody Shift in Conjunction with Mass Spectrometry to Reveal Protein Subcomplexes: Detection of a Cerebellar α1/α6-Subunits Containing γ-Aminobutyric Acid Type A Receptor Subtype

The pentameric γ-Aminobutyric acid type A receptors (GABA_ARs) are ligand-gated ion channels that mediate the majority of inhibitory neurotransmission in the brain. In the cerebellum, the two main receptor subtypes are the 2α1/2β/γ and 2α6/2β/δ subunits. In the present study, an interaction proteomics workflow was used to reveal additional subtypes that contain both α1 and α6 subunits. Immunoprecipitation of the α6 subunit from mouse brain cerebellar extract co-purified the α1 subunit. In line with this, pre-incubation of the cerebellar extract with anti-α6 antibodies and analysis by blue native gel electrophoresis mass-shifted part of the α1 complexes, indicative of the existence of an α1α6-containing receptor. Subsequent mass spectrometry of the blue native gel showed the α1α6-containing receptor subtype to exist in two main forms, i.e., with or without Neuroligin-2. Immunocytochemistry on a cerebellar granule cell culture revealed co-localization of α6 and α1 in post-synaptic puncta that apposed the presynaptic marker protein Vesicular GABA transporter, indicative of the presence of this synaptic GABA_AR subtype.

Avenanthramide-C Activates Nrf2/ARE Pathway and Inhibiting Ferroptosis Pathway to Improve Cognitive Dysfunction in Aging Rats

Postoperative neurocognitive impairment (POCD) is a common complication after surgery and anesthesia, especially in elderly patients. Avenanthramide-C (AVC) test is a vascular endothelial cell adhesion molecule inhibitor with strong anti-inflammatory and antioxidant effects. The aim of this study was to investigate the effect and mechanism of AVC on POCD in aged rats to clarify the effect of AVC on POCD in aged rats. The aging rat model was established by continuous 200 mg/kg propofol anesthesia. Repeated propofol anesthesia could severely impair spatial learning ability, memory and cognitive function, and could promote hippocampal apoptosis, oxidative stress injury, neuroinflammation and ferroptosis in aging rats. In addition, AVC not only improved cognitive dysfunction, but also significantly inhibited apoptosis, neuroinflammatory response, ferroptosis and oxidative stress level in the hippocampus of aging rats induced by repeated anesthesia. Further mechanistic studies manifested that the above protective effects of AVC on aging rats induced by repeated propofol anesthesia may be achieved by activating Nrf2/ARE pathway activity. AVC pretreatment has a preventive effect on cognitive dysfunction induced by repeated propofol anesthesia in aging rats, and the preventive effect of AVC may be realized by activating the Nrf2/ARE signaling pathway activity. Our results demonstrate that AVC preconditioning reduces postoperative neuronal loss and neuroinflammation, activates the Nrf2/ARE pathway, reduces oxidative stress injury, and improves POCD in aged rats.

Therapeutic Potential and Limitation of Serotonin Type 7 Receptor Modulation

Although a number of mood-stabilising atypical antipsychotics and antidepressants modulate serotonin type 7 receptor (5-HT7), the detailed contributions of 5-HT7 function to clinical efficacy and pathophysiology have not been fully understood. The mood-stabilising antipsychotic agent, lurasidone, and the serotonin partial agonist reuptake inhibitor, vortioxetine, exhibit higher binding affinity to 5-HT7 than other conventional antipsychotics and antidepressants. To date, the initially expected rapid onset of antidepressant effects-in comparison with conventional antidepressants or mood-stabilising antipsychotics-due to 5-HT7 inhibition has not been observed with lurasidone and vortioxetine; however, several clinical studies suggest that 5-HT7 inhibition likely contributes to quality of life of patients with schizophrenia and mood disorders via the improvement of cognition. Furthermore, recent preclinical studies reported that 5-HT7 inhibition might mitigate antipsychotic-induced weight gain and metabolic complication by blocking other monoamine receptors. Further preclinical studies for the development of 5-HT7 modulation against neurodevelopmental disorders and neurodegenerative diseases have been ongoing. To date, various findings from various preclinical studies indicate the possibility that 5-HT7 modifications can provide two independent strategies. The first is that 5-HT7 inhibition ameliorates the dysfunction of inter-neuronal transmission in mature networks. The other is that activation of 5-HT7 can improve transmission dysfunction due to microstructure abnormality in the neurotransmission network-which could be unaffected by conventional therapeutic agents-via modulating intracellular signalling during the neurodevelopmental stage or via loss of neural networks with aging. This review attempts to describe the current and novel clinical applications of 5-HT7 modulation based on preclinical findings.

The Anaesthetics Isoflurane and Xenon Reverse the Synaptotoxic Effects of Aβ1-42 on Megf10-Dependent Astrocytic Synapse Elimination and Spine Density in Ex Vivo Hippocampal Brain Slices

It has been hypothesised that inhalational anaesthetics such as isoflurane (Iso) may trigger the pathogenesis of Alzheimer's disease (AD), while the gaseous anaesthetic xenon (Xe) exhibits many features of a putative neuroprotective agent. Loss of synapses is regarded as one key cause of dementia in AD. Multiple EGF-like domains 10 (MEGF10) is one of the phagocytic receptors which assists the elimination of synapses by astrocytes. Here, we investigated how β-amyloid peptide 1-42 (Aβ_1-42), Iso and Xe interact with MEGF10-dependent synapse elimination. Murine cultured astrocytes as well as cortical and hippocampal ex vivo brain slices were treated with either Aβ_1-42, Iso or Xe and the combination of Aβ_1-42 with either Iso or Xe. We quantified MEGF10 expression in astrocytes and dendritic spine density (DSD) in slices. In brain slices of wild type and AAV-induced MEGF10 knock-down mice, antibodies against astrocytes (GFAP), pre- (synaptophysin) and postsynaptic (PSD95) components were used for co-localization analyses by means of immunofluorescence-imaging and 3D rendering techniques. Aβ_1-42 elevated pre- and postsynaptic components inside astrocytes and decreased DSD. The combined application with either Iso or Xe reversed these effects. In the presence of Aβ_1-42 both anaesthetics decreased MEGF10 expression. AAV-induced knock-down of MEGF10 reduced the pre- and postsynaptic marker inside astrocytes. The presented data suggest Iso and Xe are able to reverse the Aβ_1-42-induced enhancement of synaptic elimination in ex vivo hippocampal brain slices, presumably through MEGF10 downregulation.

The effect and safety of constraint-induced movement therapy for post-stroke motor dysfunction: a meta-analysis and trial sequential analysis

Background

Due to motor function insufficiency, patients with post-stroke motor dysfunction (PSMD) have limitations in performing an activity, feel restricted during social participation, and feel impaired in their quality of life. Constraint-induced movement therapy (CIMT) is a neurorehabilitation technique, but its effectiveness on PSMD after stroke still remains controversial.

Objective

This meta-analysis and trial sequential analysis (TSA) aimed to comprehensively evaluate the effect and safety of CIMT for PSMD.

Methods

Four electronic databases were searched from their inception to 1 January 2023 to identify randomized controlled trials (RCTs) investigating the effectiveness of CIMT for PSMD. Two reviewers independently extracted the data and assessed the risk of bias and reporting quality. The primary outcome was a motor activity log for the amount of use (MAL-AOU) and the quality of movement (MAL-QOM). RevMan 5.4, Statistical Package for Social Sciences (SPSS) 25.0, and STATA 13.0 software were used for statistical analysis. The certainty of the evidence was appraised using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) system. We also performed the TSA to assess the reliability of the evidence.

Results

A total of 44 eligible RCTs were included. Our results showed that CIMT combined with conventional rehabilitation (CR) was superior to CR in improving MAL-AOU and MAL-QOM scores. The results of TSA indicated that the above evidence was reliable. Subgroup analysis demonstrated that CIMT (≥6 h per day or duration ≤ 20 days) combined with CR was more effective than CR. Meanwhile, both CIMT and modified CIMT (mCIMT) combined with CR were more efficient than CR at all stages of stroke. No severe CIMT-related adverse events occurred.

Conclusion

CIMT may be an optional and safe rehabilitation therapy to improve PSMD. However, due to limited studies, the optimal protocol of CIMT for PSMD was undetermined, and more RCTs are required for further exploration.

Clinical trial registration

https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=143490, identifier: CRD42019143490.

Electrophysiology of Dendritic Spines: Information Processing, Dynamic Compartmentalization, and Synaptic Plasticity

For many years, synaptic transmission was considered as information transfer between presynaptic neuron and postsynaptic cell. At the synaptic level, it was thought that dendritic arbors were only receiving and integrating all information flow sent along to the soma, while axons were primarily responsible for point-to-point information transfer. However, it is important to highlight that dendritic spines play a crucial role as postsynaptic components in central nervous system (CNS) synapses, not only integrating and filtering signals to the soma but also facilitating diverse connections with axons from many different sources. The majority of excitatory connections from presynaptic axonal terminals occurs on postsynaptic spines, although a subset of GABAergic synapses also targets spine heads. Several studies have shown the vast heterogeneous morphological, biochemical, and functional features of dendritic spines related to synaptic processing. In this chapter (adding to the relevant data on the biophysics of spines described in Chap. 1 of this book), we address the up-to-date functional dendritic characteristics assessed through electrophysiological approaches, including backpropagating action potentials (bAPs) and synaptic potentials mediated in dendritic and spine compartmentalization, as well as describing the temporal and spatial dynamics of glutamate receptors in the spines related to synaptic plasticity.

TIAM1-mediated synaptic plasticity underlies comorbid depression-like and ketamine antidepressant-like actions in chronic pain

Chronic pain often leads to depression, increasing patient suffering and worsening prognosis. While hyperactivity of the anterior cingulate cortex (ACC) appears to be critically involved, the molecular mechanisms underlying comorbid depressive symptoms in chronic pain remain elusive. T cell lymphoma invasion and metastasis 1 (Tiam1) is a Rac1 guanine nucleotide exchange factor (GEF) that promotes dendrite, spine, and synapse development during brain development. Here, we show that Tiam1 orchestrates synaptic structural and functional plasticity in ACC neurons via actin cytoskeleton reorganization and synaptic N-methyl-d-aspartate receptor (NMDAR) stabilization. This Tiam1-coordinated synaptic plasticity underpins ACC hyperactivity and drives chronic pain-induced depressive-like behaviors. Notably, administration of low-dose ketamine, an NMDAR antagonist emerging as a promising treatment for chronic pain and depression, induces sustained antidepressant-like effects in mouse models of chronic pain by blocking Tiam1-mediated maladaptive synaptic plasticity in ACC neurons. Our results reveal Tiam1 as a critical factor in the pathophysiology of chronic pain-induced depressive-like behaviors and the sustained antidepressant-like effects of ketamine.

Prenatal benzo[a]pyrene exposure impairs hippocampal synaptic plasticity and cognitive function in SD rat offspring during adolescence and adulthood via HDAC2-mediated histone deacetylation

Benzo[a]pyrene (B[a]P) is a widespread carcinogenic pollutant in the environment. Although previous studies have demonstrated the neurodevelopmental toxicity of B[a]P, the precise mechanisms underlying the neurotoxic effects induced by prenatal B[a]P exposure remain largely unknown. In the present study, pregnant Sprague-Dawley (SD) rats were injected intraperitoneally with 0, 10, 20, or 40 mg/kg-bw of B[a]P for three consecutive days on embryonic days 17-19. The learning and memory abilities of offspring were determined by Morris Water Maze (MWM) test, while the number of dendritic branches and the density of dendritic spines in hippocampal CA1 and DG regions were evaluated by Golgi-Cox staining at PND 45 and PND 75. The mRNA expression of BDNF, PSD-95, and SYP in offspring hippocampus were detected by qRT-PCR, and the protein expression of BDNF, PSD-95, SYP, HDAC2, acH3K9, and acH3K14 were measured by Western blotting or immunohistochemistry. CHIP-PCR was performed to further detect the levels of acH3K9 and acH3K14 in the promoter regions of BDNF and PSD-95 genes. Our results showed that rats prenatally exposed to B[a]P exhibited impaired spatial learning and memory abilities and the number of dendritic branches and the density of dendritic spines in the hippocampal CA1 and DG regions were significantly reduced during adolescence and adulthood. The expression of HDAC2 protein was significantly upregulated, while acH3K9, acH3K14, BDNF, PSD-95, and SYP protein levels were significantly downregulated in the hippocampus of B[a]P- exposed rats. In addition, CHIP results showed that prenatal B[a]P exposure markedly decreased the level of acH3K9 and acH3K14 in the promoter region of BDNF and PSD-95 gene in the hippocampus of PND 45 and PND 75 offspring. All of the results suggest that prenatal B[a]P exposure impairs cognitive function and hippocampal synaptic plasticity of offspring in adolescence and adulthood, and HDAC2-mediated histone deacetylation plays a crucial role in these deficits.

Aberrant cortical spine dynamics after concussive injury are reversed by integrated stress response inhibition

Traumatic brain injury (TBI) is a leading cause of long-term neurological disability in the world and the strongest environmental risk factor for the development of dementia. Even mild TBI (resulting from concussive injuries) is associated with a greater than twofold increase in the risk of dementia onset. Little is known about the cellular mechanisms responsible for the progression of long-lasting cognitive deficits. The integrated stress response (ISR), a phylogenetically conserved pathway involved in the cellular response to stress, is activated after TBI, and inhibition of the ISR-even weeks after injury-can reverse behavioral and cognitive deficits. However, the cellular mechanisms by which ISR inhibition restores cognition are unknown. Here, we used longitudinal two-photon imaging in vivo after concussive injury in mice to study dendritic spine dynamics in the parietal cortex, a brain region involved in working memory. Concussive injury profoundly altered spine dynamics measured up to a month after injury. Strikingly, brief pharmacological treatment with the drug-like small-molecule ISR inhibitor ISRIB entirely reversed structural changes measured in the parietal cortex and the associated working memory deficits. Thus, both neural and cognitive consequences of concussive injury are mediated in part by activation of the ISR and can be corrected by its inhibition. These findings suggest that targeting ISR activation could serve as a promising approach to the clinical treatment of chronic cognitive deficits after TBI.

Recent Advances on the Role of Brain-Derived Neurotrophic Factor (BDNF) in Neurodegenerative Diseases

Neurotrophins, such as brain-derived neurotrophic factor (BDNF), are essential for neuronal survival and growth. The signaling cascades initiated by BDNF and its receptor are the key regulators of synaptic plasticity, which plays important role in learning and memory formation. Changes in BDNF levels and signaling pathways have been identified in several neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease, and have been linked with the symptoms and course of these diseases. This review summarizes the current understanding of the role of BDNF in several neurodegenerative diseases, as well as the underlying molecular mechanism. The therapeutic potential of BDNF treatment is also discussed, in the hope of discovering new avenues for the treatment of neurodegenerative diseases.

Structural Plasticity of the Hippocampus in Neurodegenerative Diseases

Neuroplasticity is the capacity of neural networks in the brain to alter through development and rearrangement. It can be classified as structural and functional plasticity. The hippocampus is more susceptible to neuroplasticity as compared to other brain regions. Structural modifications in the hippocampus underpin several neurodegenerative diseases that exhibit cognitive and emotional dysregulation. This article reviews the findings of several preclinical and clinical studies about the role of structural plasticity in the hippocampus in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. In this study, literature was surveyed using Google Scholar, PubMed, Web of Science, and Scopus, to review the mechanisms that underlie the alterations in the structural plasticity of the hippocampus in neurodegenerative diseases. This review summarizes the role of structural plasticity in the hippocampus for the etiopathogenesis of neurodegenerative diseases and identifies the current focus and gaps in knowledge about hippocampal dysfunctions. Ultimately, this information will be useful to propel future mechanistic and therapeutic research in neurodegenerative diseases.

Common synaptic phenotypes arising from diverse mutations in the human NMDA receptor subunit GluN2A

Dominant mutations in the human gene GRIN2A, encoding NMDA receptor (NMDAR) subunit GluN2A, make a significant and growing contribution to the catalogue of published single-gene epilepsies. Understanding the disease mechanism in these epilepsy patients is complicated by the surprising diversity of effects that the mutations have on NMDARs. Here we have examined the cell-autonomous effect of five GluN2A mutations, 3 loss-of-function and 2 gain-of-function, on evoked NMDAR-mediated synaptic currents (NMDA-EPSCs) in CA1 pyramidal neurons in cultured hippocampal slices. Despite the mutants differing in their functional incorporation at synapses, prolonged NMDA-EPSC current decays (with only marginal changes in charge transfer) were a common effect for both gain- and loss-of-function mutants. Modelling NMDA-EPSCs with mutant properties in a CA1 neuron revealed that the effect of GRIN2A mutations can lead to abnormal temporal integration and spine calcium dynamics during trains of concerted synaptic activity. Investigations beyond establishing the molecular defects of GluN2A mutants are much needed to understand their impact on synaptic transmission.

The cell-autonomous effect of five severe loss- or gain-of-function GluN2A (NMDA receptor) mutations is assessed on evoked NMDAR-mediated synaptic currents in CA1 pyramidal neurons in cultured mouse hippocampal slices. Data and modelling suggest that mutant-like NMDA-EPSCs can lead to abnormal temporal summation and spine calcium dynamics.

More than Addiction—The Nucleus Accumbens Contribution to Development of Mental Disorders and Neurodegenerative Diseases

Stress and negative emotions evoked by social relationships and working conditions, frequently accompanied by the consumption of addictive substances, and metabolic and/or genetic predispositions, negatively affect brain function. One of the affected structures is nucleus accumbens (NAc). Although its function is commonly known to be associated with brain reword responses and addiction, a growing body of evidence also suggests its role in some mental disorders, such as depression and schizophrenia, as well as neurodegenerative diseases, such as Alzheimer’s, Huntington’s, and Parkinson’s. This may result from disintegration of the extensive connections based on numerous neurotransmitter systems, as well as impairment of some neuroplasticity mechanisms in the NAc. The consequences of NAc lesions are both morphological and functional. They include changes in the NAc’s volume, cell number, modifications of the neuronal dendritic tree and dendritic spines, and changes in the number of synapses. Alterations in the synaptic plasticity affect the efficiency of synaptic transmission. Modification of the number and structure of the receptors affects signaling pathways, the content of neuromodulators (e.g., BDNF) and transcription factors (e.g., pCREB, DeltaFosB, NFκB), and gene expression. Interestingly, changes in the NAc often have a different character and intensity compared to the changes observed in the other parts of the basal ganglia, in particular the dorsal striatum. In this review, we highlight the role of the NAc in various pathological processes in the context of its structural and functional damage, impaired connections with the other brain areas cooperating within functional systems, and progression of the pathological processes.

CA1 Spike Timing is Impaired in the 129S Inbred Strain During Cognitive Tasks

A spontaneous mutation of the disrupted in schizophrenia 1 (Disc1) gene is carried by the 129S inbred mouse strain. Truncated DISC1 protein in 129S mouse synapses impairs the scaffolding of excitatory postsynaptic receptors and leads to progressive spine dysgenesis. In contrast, C57BL/6 inbred mice carry the wild-type Disc1 gene and exhibit more typical cognitive performance in spatial exploration and executive behavioral tests. Because of the innate Disc1 mutation, adult 129S inbred mice exhibit the behavioral phenotypes of outbred B6 Disc1 knockdown (Disc1^-/-) or Disc1-L-100P mutant strains. Recent studies in Disc1^-/- and L-100P mice have shown that impaired excitation-driven interneuron activity and low hippocampal theta power underlie the behavioral phenotypes that resemble human depression and schizophrenia. The current study compared the firing rate and connectivity profile of putative neurons in the CA1 of freely behaving inbred 129S and B6 mice, which have mutant and wild-type Disc1 genes, respectively. In cognitive behavioral tests, 129S mice had lower exploration scores than B6 mice. Furthermore, the mean firing rate for 129S putative pyramidal (pyr) cells and interneurons (int) was significantly lower than that for B6 CA1 neurons sampled during similar tasks. Analysis of pyr/int connectivity revealed a significant delay in synaptic transmission for 129S putative pairs. Sampled 129S pyr/int pairs also had lower detectability index scores than B6 putative pairs. Therefore, the spontaneous Disc1 mutation in the 129S strain attenuates the firing of putative pyr CA1 neurons and impairs spike timing fidelity during cognitive tasks.

Neuroadaptations and TGF-β signaling: emerging role in models of neuropsychiatric disorders

Neuropsychiatric diseases are manifested by maladaptive behavioral plasticity. Despite the greater understanding of the neuroplasticity underlying behavioral adaptations, pinpointing precise cellular mediators has remained elusive. This has stymied the development of pharmacological interventions to combat these disorders both at the level of progression and relapse. With increased knowledge on the putative role of the transforming growth factor (TGF- β) family of proteins in mediating diverse neuroadaptations, the influence of TGF-β signaling in regulating maladaptive cellular and behavioral plasticity underlying neuropsychiatric disorders is being increasingly elucidated. The current review is focused on what is currently known about the TGF-β signaling in the central nervous system in mediating cellular and behavioral plasticity related to neuropsychiatric manifestations.

Deciphering the mechanisms underlying brain alterations and cognitive impairment in congenital myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is a multisystemic and heterogeneous disorder caused by the expansion of CTG repeats in the 3' UTR of the myotonic dystrophy protein kinase (DMPK) gene. There is a congenital form (CDM1) of the disease characterized by severe hypotonia, respiratory insufficiency as well as developmental delays and intellectual disabilities. CDM1 infants manifest important brain structure abnormalities present from birth while, in contrast, older patients with adult-onset DM1 often present neurodegenerative features and milder progressive cognitive deficits. Promising therapies targeting central molecular mechanisms contributing to the symptoms of adult-onset DM1 are currently in development, but their relevance for treating cognitive impairment in CDM1, which seems to be a partially distinct neurodevelopmental disorder, remain to be elucidated. Here, we provide an update on the clinical presentation of CDM1 and review recent in vitro and in vivo models that have provided meaningful insights on its consequences in development, with a particular focus on the brain. We discuss how enhanced toxic gain-of-function of the mutated DMPK transcripts with larger CUG repeats and the resulting dysregulation of RNA-binding proteins may affect the developing cortex in utero. Because the methylation of CpG islets flanking the trinucleotide repeats has emerged as a strong biomarker of CDM1, we highlight the need to investigate the tissue-specific impacts of these chromatin modifications in the brain. Finally, we outline promising potential therapeutic treatments for CDM1 and propose future in vitro and in vivo models with great potential to shed light on this disease.

Functional Integrity of Synapses in the Central Nervous System of Cognitively Intact Individuals with High Alzheimer's Disease Neuropathology Is Associated with Absence of Synaptic Tau Oligomers

BACKGROUND

Certain individuals, here referred to as Non-Demented with Alzheimer Neuropathology (NDAN), do not show overt neurodegeneration (N-) and remain cognitively intact despite the presence of plaques (A+) and tangles (T+) that would normally be consistent with fully symptomatic Alzheimer's disease (AD).

OBJECTIVE

The existence of NDAN (A + T+N-) subjects suggests that the human brain utilizes intrinsic mechanisms that can naturally evade cognitive decline normally associated with the symptomatic stages of AD (A + T+N+). Deciphering the underlying mechanisms would prove relevant to develop complementing therapeutics to prevent progression of AD-related cognitive decline.

METHODS

Previously, we have reported that NDAN present with preserved neurogenesis and synaptic integrity paralleled by absence of amyloid oligomers at synapses. Using postmortem brain samples from age-matched control subjects, demented AD patients and NDAN individuals, we performed immunofluorescence, western blots, micro transplantation of synaptic membranes in Xenopus oocytes followed by twin electrode voltage clamp electrophysiology and fluorescence assisted single synaptosome-long term potentiation studies.

RESULTS

We report decreased tau oligomers at synapses in the brains of NDAN subjects. Furthermore, using novel approaches we report, for the first time, that such absence of tau oligomers at synapses is associated with synaptic functional integrity in NDAN subjects as compared to demented AD patients.

CONCLUSION

Overall, these results give further credence to tau oligomers as primary actors of synaptic destruction underscoring cognitive demise in AD and support their targeting as a viable therapeutic strategy for AD and related tauopathies.

Abnormal dendritic morphology in the cerebellum of cyclooxygenase-2- knockin mice

Prostaglandin E2 (PGE2) is a bioactive signalling molecule metabolized from the phospholipid membranes by the enzymatic activity of cycloxygenase-2 (COX-2). In the developing brain, COX-2 constitutively regulates the production of PGE2, which is important in neuronal development. However, abnormal COX-2/PGE2 signalling has been linked to neurodevelopmental disorders including autism spectrum disorders (ASDs). We have previously demonstrated that COX-2^- -KI mice show autism-related behaviours including social deficits, repetitive behaviours and anxious behaviours. COX-2-deficient mice also have deficits in pathways involved in synaptic transmission and dendritic spine formation. In this study, we use a Golgi-COX staining method to examine sex-dependent differences in dendritic and dendritic spine morphology in neurons of COX-2^- -KI mice cerebellum compared with wild-type (WT) matched controls at postnatal day 25 (P25). We show that COX-2^- -KI mice have increased dendritic arborization closer to the cell soma and increased dendritic looping. We also observed a sex-dependent effect of the COX-2^- -KI on dendritic thickness, dendritic spine density, dendritic spine morphology, and the expression of β-actin and the actin-binding protein spinophilin. Our findings show that changes in COX-2/PGE2 signalling lead to impaired morphology of dendrites and dendritic spines in a sex-dependant manner and may contribute the pathology of the cerebellum seen in individuals with ASD. This study provides further evidence that the COX-2^- -KI mouse model can be used to study a subset of ASD pathologies.

Neuroplasticity and Multilevel System of Connections Determine the Integrative Role of Nucleus Accumbens in the Brain Reward System

A growing body of evidence suggests that nucleus accumbens (NAc) plays a significant role not only in the physiological processes associated with reward and satisfaction but also in many diseases of the central nervous system. Summary of the current state of knowledge on the morphological and functional basis of such a diverse function of this structure may be a good starting point for further basic and clinical research. The NAc is a part of the brain reward system (BRS) characterized by multilevel organization, extensive connections, and several neurotransmitter systems. The unique role of NAc in the BRS is a result of: (1) hierarchical connections with the other brain areas, (2) a well-developed morphological and functional plasticity regulating short- and long-term synaptic potentiation and signalling pathways, (3) cooperation among several neurotransmitter systems, and (4) a supportive role of neuroglia involved in both physiological and pathological processes. Understanding the complex function of NAc is possible by combining the results of morphological studies with molecular, genetic, and behavioral data. In this review, we present the current views on the NAc function in physiological conditions, emphasizing the role of its connections, neuroplasticity processes, and neurotransmitter systems.

Disrupted Timing of MET Signaling Derails the Developmental Maturation of Cortical Circuits and Leads to Altered Behavior in Mice

The molecular regulation of the temporal dynamics of circuit maturation is a key contributor to the emergence of normal structure-function relations. Developmental control of cortical MET receptor tyrosine kinase, expressed early postnatally in subpopulations of excitatory neurons, has a pronounced impact on the timing of glutamatergic synapse maturation and critical period plasticity. Here, we show that using a controllable overexpression (cto-Met) transgenic mouse, extending the duration of MET signaling after endogenous Met is switched off leads to altered molecular constitution of synaptic proteins, persistent activation of small GTPases Cdc42 and Rac1, and sustained inhibitory phosphorylation of cofilin. These molecular changes are accompanied by an increase in the density of immature dendritic spines, impaired cortical circuit maturation of prefrontal cortex layer 5 projection neurons, and altered laminar excitatory connectivity. Two photon in vivo imaging of dendritic spines reveals that cto-Met enhances de novo spine formation while inhibiting spine elimination. Extending MET signaling for two weeks in developing cortical circuits leads to pronounced repetitive activity and impaired social interactions in adult mice. Collectively, our data revealed that temporally controlled MET signaling as a critical mechanism for controlling cortical circuit development and emergence of normal behavior.

Mitochondria in Neuronal Health: From Energy Metabolism to Parkinson's Disease

Mitochondria are the main suppliers of neuronal adenosine triphosphate and play a critical role in brain energy metabolism. Mitochondria also serve as Ca²⁺ sinks and anabolic factories and are therefore essential for neuronal function and survival. Dysregulation of neuronal bioenergetics is increasingly implicated in neurodegenerative disorders, particularly Parkinson's disease. This review describes the role of mitochondria in energy metabolism under resting conditions and during synaptic transmission, and presents evidence for the contribution of neuronal mitochondrial dysfunction to Parkinson's disease.

Early Effects of Cyclophosphamide, Methotrexate, and 5-Fluorouracil on Neuronal Morphology and Hippocampal-Dependent Behavior in a Murine Model

Breast cancer (BC) is the most common cancer among women. Fortunately, BC survival rates have increased because the implementation of adjuvant chemotherapy leading to a growing population of survivors. However, chemotherapy-induced cognitive impairments (CICIs) affect up to 75% of BC survivors and may be driven by inflammation and oxidative stress. Chemotherapy-induced cognitive impairments can persist 20 years and hinder survivors' quality of life. To identify early effects of CMF administration in mice, we chose to evaluate adult female mice at 2-week postchemotherapy. Mice received weekly IP administration of CMF (or saline) for 4 weeks, completed behavioral testing, and were sacrificed 2 weeks following their final CMF injection. Behavioral results indicated long-term memory (LTM) impairments postchemotherapy, but did not reveal short-term memory deficits. Dendritic morphology and spine data found increases in overall spine density within CA1 basal and CA3 basal dendrites, but no changes in DG, CA1 apical, or CA3 apical dendrites. Further analysis revealed decreases in arborization across the hippocampus (DG, CA1 apical and basal, CA3 apical and basal). These physiological changes within the hippocampus correlate with our behavioral data indicating LTM impairments following CMF administration in female mice 2-week postchemotherapy. Hippocampal cytokine analysis identified decreases in IL-1α, IL-1β, IL-3, IL-10, and TNF-α levels.

The Protein Arginine Methyltransferase PRMT8 and Substrate G3BP1 Control Rac1-PAK1 Signaling and Actin Cytoskeleton for Dendritic Spine Maturation

Excitatory synapses of neurons are located on dendritic spines. Spine maturation is essential for the stability of synapses and memory consolidation, and overproduction of the immature filopodia is associated with brain disorders. The structure and function of synapses can be modulated by protein post-translational modification (PTM). Arginine methylation is a major PTM that regulates chromatin structure, transcription, and splicing within the nucleus. Here we find that the protein arginine methyltransferase PRMT8 is present at neuronal synapses and its expression is upregulated in the hippocampus when dendritic spine maturation occurs. Depletion of PRMT8 leads to overabundance of filopodia and mis-localization of excitatory synapses. Mechanistically, PRMT8 promotes dendritic spine morphology through methylation of the dendritic RNA-binding protein G3BP1 and suppression of the Rac1-PAK1 signaling pathway to control synaptic actin dynamics. Our findings unravel arginine methylation as a crucial regulatory mechanism for actin cytoskeleton during synapse development.

Microglial HIV-1 Expression: Role in HIV-1 Associated Neurocognitive Disorders

The persistence of HIV-1 viral reservoirs in the brain, despite treatment with combination antiretroviral therapy (cART), remains a critical roadblock for the development of a novel cure strategy for HIV-1. To enhance our understanding of viral reservoirs, two complementary studies were conducted to (1) evaluate the HIV-1 mRNA distribution pattern and major cell type expressing HIV-1 mRNA in the HIV-1 transgenic (Tg) rat, and (2) validate our findings by developing and critically testing a novel biological system to model active HIV-1 infection in the rat. First, a restricted, region-specific HIV-1 mRNA distribution pattern was observed in the HIV-1 Tg rat. Microglia were the predominant cell type expressing HIV-1 mRNA in the HIV-1 Tg rat. Second, we developed and critically tested a novel biological system to model key aspects of HIV-1 by infusing F344/N control rats with chimeric HIV (EcoHIV). In vitro, primary cultured microglia were treated with EcoHIV revealing prominent expression within 24 h of infection. In vivo, EcoHIV expression was observed seven days after stereotaxic injections. Following EcoHIV infection, microglia were the major cell type expressing HIV-1 mRNA, results that are consistent with observations in the HIV-1 Tg rat. Within eight weeks of infection, EcoHIV rats exhibited neurocognitive impairments and synaptic dysfunction, which may result from activation of the NogoA-NgR3/PirB-RhoA signaling pathway and/or neuroinflammation. Collectively, these studies enhance our understanding of HIV-1 viral reservoirs in the brain and offer a novel biological system to model HIV-associated neurocognitive disorders and associated comorbidities (i.e., drug abuse) in rats.

The multi-functional RNA-binding protein G3BP1 and its potential implication in neurodegenerative disease

Ras-GTPase-activating protein (GAP)-binding protein 1 (G3BP1) is a multi-functional protein that is best known for its role in the assembly and dynamics of stress granules. Recent studies have highlighted that G3BP1 also has other functions related to RNA metabolism. In the context of disease, G3BP1 has been therapeutically targeted in cancers because its over-expression is correlated with proliferation of cancerous cells and metastasis. However, evidence suggests that G3BP1 is essential for neuronal development and possibly neuronal maintenance. In this review, we will examine the many functions that are carried out by G3BP1 in the context of neurons and speculate how these functions are critical to the progression of neurodegenerative diseases. Additionally, we will highlight the similarities and differences between G3BP1 and the closely related protein G3BP2, which is frequently overlooked. Although G3BP1 and G3BP2 have both been deemed important for stress granule assembly, their roles may differ in other cellular pathways, some of which are specific to the CNS, and presents an opportunity for further exploration.

The Rac-GEF Tiam1 Promotes Dendrite and Synapse Stabilization of Dentate Granule Cells and Restricts Hippocampal-Dependent Memory Functions

The dentate gyrus (DG) controls information flow into the hippocampus and is critical for learning, memory, pattern separation, and spatial coding, while DG dysfunction is associated with neuropsychiatric disorders. Despite its importance, the molecular mechanisms regulating DG neural circuit assembly and function remain unclear. Here, we identify the Rac-GEF Tiam1 as an important regulator of DG development and associated memory processes. In the hippocampus, Tiam1 is predominantly expressed in the DG throughout life. Global deletion of Tiam1 in male mice results in DG granule cells with simplified dendritic arbors, reduced dendritic spine density, and diminished excitatory synaptic transmission. Notably, DG granule cell dendrites and synapses develop normally in Tiam1 KO mice, resembling WT mice at postnatal day 21 (P21), but fail to stabilize, leading to dendrite and synapse loss by P42. These results indicate that Tiam1 promotes DG granule cell dendrite and synapse stabilization late in development. Tiam1 loss also increases the survival, but not the production, of adult-born DG granule cells, possibly because of greater circuit integration as a result of decreased competition with mature granule cells for synaptic inputs. Strikingly, both male and female mice lacking Tiam1 exhibit enhanced contextual fear memory and context discrimination. Together, these results suggest that Tiam1 is a key regulator of DG granule cell stabilization and function within hippocampal circuits. Moreover, based on the enhanced memory phenotype of Tiam1 KO mice, Tiam1 may be a potential target for the treatment of disorders involving memory impairments.SIGNIFICANCE STATEMENT The dentate gyrus (DG) is important for learning, memory, pattern separation, and spatial navigation, and its dysfunction is associated with neuropsychiatric disorders. However, the molecular mechanisms controlling DG formation and function remain elusive. By characterizing mice lacking the Rac-GEF Tiam1, we demonstrate that Tiam1 promotes the stabilization of DG granule cell dendritic arbors, spines, and synapses, whereas it restricts the survival of adult-born DG granule cells, which compete with mature granule cells for synaptic integration. Notably, mice lacking Tiam1 also exhibit enhanced contextual fear memory and context discrimination. These findings establish Tiam1 as an essential regulator of DG granule cell development, and identify it as a possible therapeutic target for memory enhancement.

Early appearance of developmental alterations in the dendritic tree of the hippocampal granule cells in the Ts65Dn model of Down syndrome

Down syndrome (DS), a genetic condition caused by triplication of chromosome 21, is characterized by alterations in various cognitive domains, including hippocampus-dependent memory functions, starting from early life stages. The major causes of intellectual disability in DS are prenatal neurogenesis alterations followed by impairment of dendritic development in early infancy. While there is evidence that the Ts65Dn mouse, the most widely used model of DS, exhibits dendritic alterations in adulthood, no studies are available regarding the onset of dendritic pathology. The goal of the current study was to establish whether this model exhibits early dendritic alterations in the hippocampus, a region whose function is severely damaged in DS. To this purpose, in Golgi-stained brains, we evaluated the dendritic arborization and dendritic spines of the granule cells of the hippocampal dentate gyrus in Ts65Dn mice aged 8 (P8) and 15 (P15) days. While P15 Ts65Dn mice exhibited a notably hypotrophic dendritic arbor and a reduced spine density, P8 mice exhibited a moderate reduction in the number of dendritic ramifications and no differences in spine density in comparison with their euploid counterparts. Both in P8 and P15 mice, spines were longer and had a longer neck, suggesting possible alterations in synaptic function. Moreover, P8 and P15 Ts65Dn mice had more thin spines and fewer stubby spines in comparison with euploid mice. Our study provides novel evidence on the onset of dendritic pathology, one of the causes of intellectual disability in DS, showing that it is already detectable in the dentate gyrus of Ts65Dn pups. This evidence strengthens the suitability of this model of DS as a tool to study dendritic pathology in DS and to test the efficacy of early therapeutic interventions aimed at ameliorating hippocampal development and, therefore, memory functions in children with DS.

Roles of palmitoylation in structural long-term synaptic plasticity

Long-term potentiation (LTP) and long-term depression (LTD) are important cellular mechanisms underlying learning and memory processes. N-Methyl-d-aspartate receptor (NMDAR)-dependent LTP and LTD play especially crucial roles in these functions, and their expression depends on changes in the number and single channel conductance of the major ionotropic glutamate receptor α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) located on the postsynaptic membrane. Structural changes in dendritic spines comprise the morphological platform and support for molecular changes in the execution of synaptic plasticity and memory storage. At the molecular level, spine morphology is directly determined by actin cytoskeleton organization within the spine and indirectly stabilized and consolidated by scaffold proteins at the spine head. Palmitoylation, as a uniquely reversible lipid modification with the ability to regulate protein membrane localization and trafficking, plays significant roles in the structural and functional regulation of LTP and LTD. Altered structural plasticity of dendritic spines is also considered a hallmark of neurodevelopmental disorders, while genetic evidence strongly links abnormal brain function to impaired palmitoylation. Numerous studies have indicated that palmitoylation contributes to morphological spine modifications. In this review, we have gathered data showing that the regulatory proteins that modulate the actin network and scaffold proteins related to AMPAR-mediated neurotransmission also undergo palmitoylation and play roles in modifying spine architecture during structural plasticity.

Chronic fluoxetine treatment impairs motivation and reward learning by affecting neuronal plasticity in the central amygdala

BACKGROUND AND PURPOSE

The therapeutic effects of fluoxetine are believed to be due to increasing neuronal plasticity and reversing some learning deficits. Nevertheless, a growing amount of evidence shows adverse effects of this drug on cognition and some forms of neuronal plasticity.

EXPERIMENTAL APPROACH

To study the effects of chronic fluoxetine treatment, we combine an automated assessment of motivation and learning in mice with an investigation of neuronal plasticity in the central amygdala and basolateral amygdala. We use immunohistochemistry to visualize neuronal types and perineuronal nets, along with DI staining to assess dendritic spine morphology. Gel zymography is used to test fluoxetine's impact on matrix metalloproteinase-9, an enzyme involved in synaptic plasticity.

KEY RESULTS

We show that chronic fluoxetine treatment in non-stressed mice increases perineuronal nets-dependent plasticity in the basolateral amygdala, while impairing MMP-9-dependent plasticity in the central amygdala. Further, we illustrate how the latter contributes to anhedonia and deficits of reward learning. Behavioural impairments are accompanied by alterations in morphology of dendritic spines in the central amygdala towards an immature state, most likely reflecting animals' inability to adapt. We strengthen the link between the adverse effects of fluoxetine and its influence on MMP-9 by showing that behaviour of MMP-9 knockout animals remains unaffected by the drug.

CONCLUSION AND IMPLICATIONS

Chronic fluoxetine treatment differentially affects various forms of neuronal plasticity, possibly explaining its opposing effects on brain and behaviour. These findings are of immediate clinical relevance since reported side effects of fluoxetine pose a potential threat to patients.

Current Limitations and Candidate Potential of 5-HT7 Receptor Antagonism in Psychiatric Pharmacotherapy

Several mood-stabilizing atypical antipsychotics and antidepressants weakly block serotonin (5-HT) receptor type-7 (5-HT7R); however, the contributions of 5-HT7R antagonism to clinical efficacy and pathophysiology are yet to be clarified. A novel mood-stabilizing antipsychotic agent, lurasidone exhibits predominant binding affinity to 5-HT7R when compared with other monoamine receptors. To date, we have failed to discover the superior clinical efficacy of lurasidone on schizophrenia, mood, or anxiety disorders when compared with conventional mood-stabilizing atypical antipsychotics; however, numerous preclinical findings have indicated the possible potential of 5-HT7R antagonism against several neuropsychiatric disorders, as well as the generation of novel therapeutic options that could not be expected with conventional atypical antipsychotics. Traditional experimental techniques, electrophysiology, and microdialysis have demonstrated that the effects of 5-HT receptor type-1A (5-HT1AR) and 5-HT7R on neurotransmission are in contrast, but the effect of 5-HT1AR is more predominant than that of 5-HT7R, resulting in an insufficient understanding of the 5-HT7R function in the field of psychopharmacology. Accumulating knowledge regarding the pharmacodynamic profiles of 5-HT7R suggests that 5-HT7R is one of the key players in the establishment and remodeling of neural development and cytoarchitecture during the early developmental stage to the mature brain, and dysfunction or modulation of 5-HT7R is linked to the pathogenesis/pathophysiology of neuropsychiatric and neurodevelopmental disorders. In this review, to explore candidate novel applications for the treatment of several neuropsychiatric disorders, including mood disorders, schizophrenia, and other cognitive disturbance disorders, we discuss perspectives of psychopharmacology regarding the effects of 5-HT7R antagonism on transmission and intracellular signaling systems, based on preclinical findings.

Orai1 Channels Are Essential for Amplification of Glutamate-Evoked Ca2+ Signals in Dendritic Spines to Regulate Working and Associative Memory

Store-operated Orai1 calcium channels function as highly Ca²⁺-selective ion channels and are broadly expressed in many tissues including the central nervous system, but their contributions to cognitive processing are largely unknown. Here, we report that many measures of synaptic, cellular, and behavioral models of learning are markedly attenuated in mice lacking Orai1 in forebrain excitatory neurons. Results with focal glutamate uncaging in hippocampal neurons support an essential role of Orai1 channels in amplifying NMDA-receptor-induced dendritic Ca²⁺ transients that drive activity-dependent spine morphogenesis and long-term potentiation at Schaffer collateral-CA1 synapses. Consistent with these signaling roles, mice lacking Orai1 in pyramidal neurons (but not interneurons) exhibit striking deficits in working and associative memory tasks. These findings identify Orai1 channels as essential regulators of dendritic spine Ca²⁺ signaling, synaptic plasticity, and cognition.

Severe childhood and adulthood stress associates with neocortical layer-specific reductions of mature spines in psychiatric disorders

Severe stress exposure causes the loss of dendritic spines on cortical pyramidal neurons and induces psychiatric-like symptoms in rodent models. These effects are strongest following early-life stress and are most persistent on apical dendrites. However, the long-term impacts and temporal effects of stress exposure on the human brain remain poorly understood. Using a novel postmortem cohort of psychiatric cases with severe stress experienced in childhood, adulthood, or no severe stress, and matched controls, we aimed to determine the impact of stress timing on pyramidal neuron structure in the human orbitofrontal cortex (OFC). We performed Golgi Cox staining and manually measured the morphology and density of over 22,000 dendritic spines on layer-specific pyramidal neuron apical dendrites. We also quantified glucocorticoid receptor mRNA and protein as a marker of stress dysregulation. Both childhood and adulthood stress were associated with large reductions in mature mushroom spine density (up to 56% loss) in both the superficial (II/III) and deeper layers (V) of the OFC. However, childhood stress caused more substantial reductions to both total and mature mushroom spines. No difference in glucocorticoid receptor mRNA and protein were seen between groups, although both negatively correlated with total spine density within the whole cohort. These findings indicate that severe stress, especially when experienced during childhood, persistently affects the fine morphological properties of neurons in the human OFC. This may impact on cell connectivity in this brain area, and at least partly explain the social and emotional symptoms that originate in the OFC in psychiatric disorders.