Synaptic AMPA receptor plasticity and behavior

Potential mechanism of Qinggong Shoutao pill alleviating age-associated memory decline based on integration strategy

CONTEXT

Qinggong Shoutao Wan (QGSTW) is a pill used as a traditional medicine to treat age-associated memory decline (AAMI). However, its potential mechanisms are unclear.

OBJECTIVE

This study elucidates the possible mechanisms of QGSTW in treating AAMI.

MATERIALS AND METHODS

Network pharmacology and molecular docking approaches were utilized to identify the potential pathway by which QGSTW alleviates AAMI. C57BL/6J mice were divided randomly into control, model, and QGSTW groups. A mouse model of AAMI was established by d-galactose, and the pathways that QGSTW acts on to ameliorate AAMI were determined by ELISA, immunofluorescence staining and Western blotting after treatment with d-gal (100 mg/kg) and QGSTW (20 mL/kg) for 12 weeks.

RESULTS

Network pharmacology demonstrated that the targets of the active components were significantly enriched in the cAMP signaling pathway. AKT1, FOS, GRIN2B, and GRIN1 were the core target proteins. QGSTW treatment increased the discrimination index from -16.92 ± 7.06 to 23.88 ± 15.94% in the novel location test and from -19.54 ± 5.71 to 17.55 ± 6.73% in the novel object recognition test. ELISA showed that QGSTW could increase the levels of cAMP. Western blot analysis revealed that QGSTW could upregulate the expression of PKA, CREB, c-Fos, GluN1, GluA1, CaMKII-α, and SYN. Immunostaining revealed that the expression of SYN was decreased in the CA1 and DG.

DISCUSSION AND CONCLUSIONS

This study not only provides new insights into the mechanism of QGSTW in the treatment of AAMI but also provides important information and new research ideas for the discovery of traditional Chinese medicine compounds that can treat AAMI.

Synapse-specific structural plasticity that protects and refines local circuits during LTP and LTD

Synapses form trillions of connections in the brain. Long-term potentiation (LTP) and long-term depression (LTD) are cellular mechanisms vital for learning that modify the strength and structure of synapses. Three-dimensional reconstruction from serial section electron microscopy reveals three distinct pre- to post-synaptic arrangements: strong active zones (AZs) with tightly docked vesicles, weak AZs with loose or non-docked vesicles, and nascent zones (NZs) with a postsynaptic density but no presynaptic vesicles. Importantly, LTP can be temporarily saturated preventing further increases in synaptic strength. At the onset of LTP, vesicles are recruited to NZs, converting them to AZs. During recovery of LTP from saturation (1-4 h), new NZs form, especially on spines where AZs are most enlarged by LTP. Sentinel spines contain smooth endoplasmic reticulum (SER), have the largest synapses and form clusters with smaller spines lacking SER after LTP recovers. We propose a model whereby NZ plasticity provides synapse-specific AZ expansion during LTP and loss of weak AZs that drive synapse shrinkage during LTD. Spine clusters become functionally engaged during LTP or disassembled during LTD. Saturation of LTP or LTD probably acts to protect recently formed memories from ongoing plasticity and may account for the advantage of spaced over massed learning. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Roles of AMPA receptors in social behaviors

As a crucial player in excitatory synaptic transmission, AMPA receptors (AMPARs) contribute to the formation, regulation, and expression of social behaviors. AMPAR modifications have been associated with naturalistic social behaviors, such as aggression, sociability, and social memory, but are also noted in brain diseases featuring impaired social behavior. Understanding the role of AMPARs in social behaviors is timely to reveal therapeutic targets for treating social impairment in disorders, such as autism spectrum disorder and schizophrenia. In this review, we will discuss the contribution of the molecular composition, function, and plasticity of AMPARs to social behaviors. The impact of targeting AMPARs in treating brain disorders will also be discussed.

Protein Kinase C (PKC) in Neurological Health: Implications for Alzheimer's Disease and Chronic Alcohol Consumption

Protein kinase C (PKC) is a diverse enzyme family crucial for cell signalling in various organs. Its dysregulation is linked to numerous diseases, including cancer, cardiovascular disorders, and neurological problems. In the brain, PKC plays pivotal roles in synaptic plasticity, learning, memory, and neuronal survival. Specifically, PKC's involvement in Alzheimer's Disease (AD) pathogenesis is of significant interest. The dysregulation of PKC signalling has been linked to neurological disorders, including AD. This review elucidates PKC's pivotal role in neurological health, particularly its implications in AD pathogenesis and chronic alcohol addiction. AD, characterised by neurodegeneration, implicates PKC dysregulation in synaptic dysfunction and cognitive decline. Conversely, chronic alcohol consumption elicits neural adaptations intertwined with PKC signalling, exacerbating addictive behaviours. By unravelling PKC's involvement in these afflictions, potential therapeutic avenues emerge, offering promise for ameliorating their debilitating effects. This review navigates the complex interplay between PKC, AD pathology, and alcohol addiction, illuminating pathways for future neurotherapeutic interventions.

miRNAs in treatment-resistant depression: a systematic review

BACKGROUND

Treatment-resistant depression (TRD) is a condition in a subset of depressed patients characterized by resistance to antidepressant medications. The global prevalence of TRD has been steadily increasing, yet significant advancements in its diagnosis and treatment remain elusive despite extensive research efforts. The precise underlying pathogenic mechanisms are still not fully understood. Epigenetic mechanisms play a vital role in a wide range of diseases. In recent years, investigators have increasingly focused on the regulatory roles of miRNAs in the onset and progression of TRD. miRNAs are a class of noncoding RNA molecules that regulate the translation and degradation of their target mRNAs via interaction, making the exploration of their functions in TRD essential for elucidating their pathogenic mechanisms.

METHODS AND RESULTS

A systematic search was conducted in four databases, namely PubMed, Web of Science, Cochrane Library, and Embase, focusing on studies related to treatment-resistant depression and miRNAs. The search was performed using terms individually or in combination, such as "treatment-resistant depression," "medication-resistant depression," and "miRNAs." The selected articles were reviewed and collated, covering the time period from the inception of each database to the end of February 2024. We found that miRNAs play a crucial role in the pathophysiology of TRD through three main aspects: 1) involvement in miRNA-mediated inflammatory responses (including miR-155, miR-345-5p, miR-146a, and miR-146a-5p); 2) influence on 5-HT transport processes (including miR-674,miR-708, and miR-133a); and 3) regulation of synaptic plasticity (including has-miR-335-5p,has-miR- 1292-3p, let-7b, and let-7c). Investigating the differential expression and interactions of these miRNAs could contribute to a deeper understanding of the molecular mechanisms underlying TRD.

CONCLUSIONS

miRNAs might play a pivotal role in the pathogenesis of TRD. Gaining a deeper understanding of the roles and interrelations of miRNAs in TRD will contribute to elucidating disease pathogenesis and potentially provide avenues for the development of novel diagnostic and therapeutic strategies.

Gain-of-function and loss-of-function variants in GRIA3 lead to distinct neurodevelopmental phenotypes

AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors (AMPARs) mediate fast excitatory neurotransmission in the brain. AMPARs form by homo- or heteromeric assembly of subunits encoded by the GRIA1-GRIA4 genes, of which only GRIA3 is X-chromosomal. Increasing numbers of GRIA3 missense variants are reported in patients with neurodevelopmental disorders (NDD), but only a few have been examined functionally. Here, we evaluated the impact on AMPAR function of one frameshift and 43 rare missense GRIA3 variants identified in patients with NDD by electrophysiological assays. Thirty-one variants alter receptor function and show loss-of-function or gain-of-function properties, whereas 13 appeared neutral. We collected detailed clinical data from 25 patients (from 23 families) harbouring 17 of these variants. All patients had global developmental impairment, mostly moderate (9/25) or severe (12/25). Twelve patients had seizures, including focal motor (6/12), unknown onset motor (4/12), focal impaired awareness (1/12), (atypical) absence (2/12), myoclonic (5/12) and generalized tonic-clonic (1/12) or atonic (1/12) seizures. The epilepsy syndrome was classified as developmental and epileptic encephalopathy in eight patients, developmental encephalopathy without seizures in 13 patients, and intellectual disability with epilepsy in four patients. Limb muscular hypotonia was reported in 13/25, and hypertonia in 10/25. Movement disorders were reported in 14/25, with hyperekplexia or non-epileptic erratic myoclonus being the most prevalent feature (8/25). Correlating receptor functional phenotype with clinical features revealed clinical features for GRIA3-associated NDDs and distinct NDD phenotypes for loss-of-function and gain-of-function variants. Gain-of-function variants were associated with more severe outcomes: patients were younger at the time of seizure onset (median age: 1 month), hypertonic and more often had movement disorders, including hyperekplexia. Patients with loss-of-function variants were older at the time of seizure onset (median age: 16 months), hypotonic and had sleeping disturbances. Loss-of-function and gain-of-function variants were disease-causing in both sexes but affected males often carried de novo or hemizygous loss-of-function variants inherited from healthy mothers, whereas affected females had mostly de novo heterozygous gain-of-function variants.

The spike-timing-dependent plasticity of VIP interneurons in motor cortex

The plasticity of inhibitory interneurons (INs) plays an important role in the organization and maintenance of cortical microcircuits. Given the many different IN types, there is an even greater diversity in synapse-type-specific plasticity learning rules at excitatory to excitatory (E→I), I→E, and I→I synapses. I→I synapses play a key disinhibitory role in cortical circuits. Because they typically target other INs, vasoactive intestinal peptide (VIP) INs are often featured in I→I→E disinhibition, which upregulates activity in nearby excitatory neurons. VIP IN dysregulation may thus lead to neuropathologies such as epilepsy. In spite of the important activity regulatory role of VIP INs, their long-term plasticity has not been described. Therefore, we characterized the phenomenology of spike-timing-dependent plasticity (STDP) at inputs and outputs of genetically defined VIP INs. Using a combination of whole-cell recording, 2-photon microscopy, and optogenetics, we explored I→I STDP at layer 2/3 (L2/3) VIP IN outputs onto L5 Martinotti cells (MCs) and basket cells (BCs). We found that VIP IN→MC synapses underwent causal long-term depression (LTD) that was presynaptically expressed. VIP IN→BC connections, however, did not undergo any detectable plasticity. Conversely, using extracellular stimulation, we explored E→I STDP at inputs to VIP INs which revealed long-term potentiation (LTP) for both causal and acausal timings. Taken together, our results demonstrate that VIP INs possess synapse-type-specific learning rules at their inputs and outputs. This suggests the possibility of harnessing VIP IN long-term plasticity to control activity-related neuropathologies such as epilepsy.

Aβ peptide enhances GluA1 internalization via lipid rafts in Alzheimer's-related hippocampal LTP dysfunction

Amyloid β (Aβ) is a central contributor to neuronal damage and cognitive impairment in Alzheimer's disease (AD). Aβ disrupts AMPA receptor-mediated synaptic plasticity, a key factor in early AD progression. Numerous studies propose that Aβ oligomers hinder synaptic plasticity, particularly long-term potentiation (LTP), by disrupting GluA1 (encoded by GRIA1) function, although the precise mechanism remains unclear. In this study, we demonstrate that Aβ mediates the accumulation of GM1 ganglioside in lipid raft domains of cultured cells, and GluA1 exhibits preferential localization in lipid rafts via direct binding to GM1. Aβ enhances the raft localization of GluA1 by increasing GM1 in these areas. Additionally, chemical LTP stimulation induces lipid raft-dependent GluA1 internalization in Aβ-treated neurons, resulting in reduced cell surface and postsynaptic expression of GluA1. Consistent with this, disrupting lipid rafts and GluA1 localization in rafts rescues Aβ-mediated suppression of hippocampal LTP. These findings unveil a novel functional deficit in GluA1 trafficking induced by Aβ, providing new insights into the mechanism underlying AD-associated cognitive dysfunction.

The concept of resilience to Alzheimer's Disease: current definitions and cellular and molecular mechanisms

Some individuals are able to maintain their cognitive abilities despite the presence of significant Alzheimer's Disease (AD) neuropathological changes. This discrepancy between cognition and pathology has been labeled as resilience and has evolved into a widely debated concept. External factors such as cognitive stimulation are associated with resilience to AD, but the exact cellular and molecular underpinnings are not completely understood. In this review, we discuss the current definitions used in the field, highlight the translational approaches used to investigate resilience to AD and summarize the underlying cellular and molecular substrates of resilience that have been derived from human and animal studies, which have received more and more attention in the last few years. From these studies the picture emerges that resilient individuals are different from AD patients in terms of specific pathological species and their cellular reaction to AD pathology, which possibly helps to maintain cognition up to a certain tipping point. Studying these rare resilient individuals can be of great importance as it could pave the way to novel therapeutic avenues for AD.

Overnight neuronal plasticity and adaptation to emotional distress

Expressions such as 'sleep on it' refer to the resolution of distressing experiences across a night of sound sleep. Sleep is an active state during which the brain reorganizes the synaptic connections that form memories. This Perspective proposes a model of how sleep modifies emotional memory traces. Sleep-dependent reorganization occurs through neurophysiological events in neurochemical contexts that determine the fates of synapses to grow, to survive or to be pruned. We discuss how low levels of acetylcholine during non-rapid eye movement sleep and low levels of noradrenaline during rapid eye movement sleep provide a unique window of opportunity for plasticity in neuronal representations of emotional memories that resolves the associated distress. We integrate sleep-facilitated adaptation over three levels: experience and behaviour, neuronal circuits, and synaptic events. The model generates testable hypotheses for how failed sleep-dependent adaptation to emotional distress is key to mental disorders, notably disorders of anxiety, depression and post-traumatic stress with the common aetiology of insomnia.

Maternal exposure to deltamethrin during pregnancy and lactation impairs neurodevelopment of male offspring

Deltamethrin (DM) is a highly effective and widely used pyrethroid pesticide. It is an environmental factor affecting public and occupational health and exerts direct toxic effects on the central nervous system. As the major target organs for neurotoxicity of DM, the hippocampus and the cerebellum are critical to the learning and motor function. Pregnant Wistar rats were randomly divided into four groups and gavaged at doses of 0, 1, 4or 10 mg/kg/d DM from gestational day (GD) 0 to postnatal day (PN) 21. The PC12 cells were selected to further verify the regulatory mechanisms of DM on the neurodevelopmental injury. We found that maternal exposure to DM caused learning, memory and motor dysfunction in male offspring. Maternal exposure to DM induced the decrease in the density of hippocampal dendritic spines in male offspring through the reduced expression of M1 mAchRs, which in turn reduced the mediated AKT/mTOR signaling pathway, contributing to the inhibition of dynamic changes of GluA1. Meanwhile, DM exposure inhibited the BDNF/TrkB signaling pathway, thereby reducing phosphorylation of stathmin and impairing cerebellar purkinje cell dendrite growth and development. Taken together, maternal exposure to DM during pregnancy and lactation could impair neurodevelopment of male offspring.

SynGAP regulates synaptic plasticity and cognition independently of its catalytic activity

SynGAP is an abundant synaptic GTPase-activating protein (GAP) critical for synaptic plasticity, learning, memory, and cognition. Mutations in SYNGAP1 in humans result in intellectual disability, autistic-like behaviors, and epilepsy. Heterozygous Syngap1-knockout mice display deficits in synaptic plasticity, learning, and memory and exhibit seizures. It is unclear whether SynGAP imparts structural properties at synapses independently of its GAP activity. Here, we report that inactivating mutations within the GAP domain do not inhibit synaptic plasticity or cause behavioral deficits. Instead, SynGAP modulates synaptic strength by physically competing with the AMPA-receptor-TARP excitatory receptor complex in the formation of molecular condensates with synaptic scaffolding proteins. These results have major implications for developing therapeutic treatments for SYNGAP1-related neurodevelopmental disorders.

Novel crosstalk mechanisms between GluA3 and Epac2 in synaptic plasticity and memory in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease which accounts for the most cases of dementia worldwide. Impaired memory, including acquisition, consolidation, and retrieval, is one of the hallmarks in AD. At the cellular level, dysregulated synaptic plasticity partly due to reduced long-term potentiation (LTP) and enhanced long-term depression (LTD) underlies the memory deficits in AD. GluA3 containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are one of key receptors involved in rapid neurotransmission and synaptic plasticity. Recent studies revealed a novel form of GluA3 involved in neuronal plasticity that is dependent on cyclic adenosine monophosphate (cAMP), rather than N-methyl-d-aspartate (NMDA). However, this cAMP-dependent GluA3 pathway is specifically and significantly impaired by amyloid beta (Aβ), a pathological marker of AD. cAMP is a key second messenger that plays an important role in modulating memory and synaptic plasticity. We previously reported that exchange protein directly activated by cAMP 2 (Epac2), acting as a main cAMP effector, plays a specific and time-limited role in memory retrieval. From electrophysiological perspective, Epac2 facilities the maintenance of LTP, a cellular event closely associated with memory retrieval. Additionally, Epac2 was found to be involved in the GluA3-mediated plasticity. In this review, we comprehensively summarize current knowledge regarding the specific roles of GluA3 and Epac2 in synaptic plasticity and memory, and their potential association with AD.

Lotusine ameliorates propionic acid-induced autism spectrum disorder-like behavior in mice by activating D1 dopamine receptor in medial prefrontal cortex

Autism spectrum disorder (ASD) is a multifaceted neuropsychiatric condition for which effective drug therapy for core clinical symptoms remains elusive. Lotusine, known for its neuroprotective properties in the treatment of neurological disorders, holds potential in addressing ASD. Nevertheless, its specific efficacy in ASD remains uncertain. This study aims to investigate the therapeutic potential of lotusine in ASD and elucidate the underlying molecular mechanisms. We induced an ASD mouse model through intracerebroventricular-propionic acid (ICV-PPA) injection for 7 days, followed by lotusine administration for 5 days. The efficacy of lotusine was evaluated through a battery of behavioral tests, including the three-chamber social test. The underlying mechanisms of lotusine action in ameliorating ASD-like behavior were investigated in the medial prefrontal cortex (mPFC) using whole-cell patch-clamp recordings, western blotting, immunofluorescence staining, molecular docking, and cellular thermal shift assay. The efficacy and mechanisms of lotusine were further validated in vitro. Lotusine effectively alleviated social deficits induced by ICV-PPA injection in mice by counteracting the reduction in miniature excitatory postsynaptic current frequency within the mPFC. Moreover, lotusine enhanced neuronal activity and ameliorated α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor dysfunction in ICV-PPA infusion mice by upregulating c-fos, p-GluA1 Ser 845, and p-GluA1 Ser 831 protein levels within the mPFC. Our findings also suggest that lotusine may exert its effects through modulation of the D1 dopamine receptor (DRD1). Furthermore, the rescuing effects of lotusine were nullified by a DRD1 antagonist in PC12 cells. In summary, our results revealed that lotusine ameliorates ASD-like behavior through targeted modulation of DRD1, ultimately enhancing excitatory synaptic transmission. These findings highlight the potential of lotusine as a nutritional supplement in the treatment of ASD.

Copine-6 is a Ca2+ sensor for activity-induced AMPA receptor exocytosis

The recruitment of synaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors underlies the strengthening of neuronal connectivity during learning and memory. This process is triggered by N-methyl-D-aspartate (NMDA) receptor-dependent postsynaptic Ca2+ influx. Synaptotagmin (Syt)-1 and -7 have been proposed as Ca2+ sensors for AMPA receptor exocytosis but are functionally redundant. Here, we identify a cytosolic C2 domain-containing Ca2+-binding protein, Copine-6, that forms a complex with AMPA receptors. Loss of Copine-6 expression impairs activity-induced exocytosis of AMPA receptors in primary neurons, which is rescued by wild-type Copine-6 but not Ca2+-binding mutants. In contrast, Copine-6 loss of function does not affect steady-state expression or tetrodotoxin-induced synaptic upscaling of surface AMPA receptors. Loss of Syt-1/Syt-7 significantly reduces Copine-6 protein expression. Interestingly, overexpression of wild-type Copine-6, but not the Ca2+-binding mutants, restores activity-dependent exocytosis of AMPA receptors in Syt-1/Syt-7 double-knockdown neurons. We conclude that Copine-6 is a postsynaptic Ca2+ sensor that mediates AMPA receptor exocytosis during synaptic potentiation.

Impairments of Spatial Memory and N-methyl-d-aspartate Receptors and Their Postsynaptic Signaling Molecules in the Hippocampus of Developing Rats Induced by As, Pb, and Mn Mixture Exposure

Exposure to metal mixtures is recognized as a real-life scenario, needing novel studies that can assess their complex effects on brain development. There is still a significant public health concern associated with chronic low levels of metal exposure. In contrast to other metals, these three metals (As, Pb, and Mn) are commonly found in various environmental and industrial contexts. In addition to additive or synergistic interactions, concurrent exposure to this metal mixture may also have neurotoxic effects that differ from those caused by exposure to single components. The NMDA receptor and several important signaling proteins are involved in learning, memory, and synaptic plasticity in the hippocampus, including CaMKII, postsynaptic density protein-95 (PSD-95), synaptic Ras GTPase activating protein (SynGAP), a negative regulator of Ras-MAPK activity, and CREB. We hypothesized that alterations in the above molecular players may contribute to metal mixture developmental neurotoxicity. Thus, the aim of this study was to investigate the effect of these metals and their mixture at low doses (As 4 mg, Pb 4 mg, and Mn 10 mg/kg bw/p.o) on NMDA receptors and their postsynaptic signaling proteins during developing periods (GD6 to PD59) of the rat brain. Rats exposed to As, Pb, and Mn individually or at the same doses in a triple-metal mixture (MM) showed impairments in learning and memory functions in comparison to the control group rats. Declined protein expressions of NR2A, PSD-95, p- CaMKII, and pCREB were observed in the metal mix-exposed rats, while the expression of SynGAP was found to be enhanced in the hippocampus as compared to the controls on PD60. Thereby, our data suggest that alterations in the NMDA receptor complex and postsynaptic signaling proteins could explain the cognitive dysfunctions caused by metal-mixture-induced developmental neurotoxicity in rats. These outcomes indicate that incessant metal mixture exposure may have detrimental consequences on brain development.

Promising new pharmacological targets for depression: The search for efficacy

Pharmacological treatment of major depressive disorder (MDD) still relies on the use of serotonergic drugs, despite their limited efficacy. A few mechanistically new drugs have been developed in recent years, but many fail in clinical trials. Several hypotheses have been proposed to explain MDD pathophysiology, indicating that physiological processes such as neuroplasticity, circadian rhythms, and metabolism are potential targets. Here, we review the current state of pharmacological treatments for MDD, as well as the preclinical and clinical evidence for an antidepressant effect of molecules that target non-serotonergic systems. We offer some insights into the challenges facing the development of new antidepressant drugs, and the prospect of finding more effectiveness for each target discussed.

Differential regulation of tetramerization of the AMPA receptor glutamate-gated ion channel by auxiliary subunits

α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) auxiliary subunits are specialized, nontransient binding partners of AMPARs that modulate AMPAR channel gating properties and pharmacology, as well as their biogenesis and trafficking. The most well-characterized families of auxiliary subunits are transmembrane AMPAR regulatory proteins (TARPs), cornichon homologs (CNIHs), and the more recently discovered GSG1-L. These auxiliary subunits can promote or reduce surface expression of AMPARs (composed of GluA1-4 subunits) in neurons, thereby impacting their functional role in membrane signaling. Here, we show that CNIH-2 enhances the tetramerization of WT and mutant AMPARs, presumably by increasing the overall stability of the tetrameric complex, an effect that is mainly mediated by interactions with the transmembrane domain of the receptor. We also find CNIH-2 and CNIH-3 show receptor subunit-specific actions in this regard with CNIH-2 enhancing both GluA1 and GluA2 tetramerization, whereas CNIH-3 only weakly enhances GluA1 tetramerization. These results are consistent with the proposed role of CNIHs as endoplasmic reticulum cargo transporters for AMPARs. In contrast, TARP γ-2, TARP γ-8, and GSG1-L have no or negligible effect on AMPAR tetramerization. On the other hand, TARP γ-2 can enhance receptor tetramerization but only when directly fused with the receptor at a maximal stoichiometry. Notably, surface expression of functional AMPARs was enhanced by CNIH-2 to a greater extent than TARP γ-2, suggesting that this distinction aids in maturation and membrane expression. These experiments define a functional distinction between CNIHs and other auxiliary subunits in the regulation of AMPAR biogenesis.

Functional effects of haemoglobin can be rescued by haptoglobin in an in vitro model of subarachnoid haemorrhage

During subarachnoid haemorrhage, a blood clot forms in the subarachnoid space releasing extracellular haemoglobin (Hb), which causes oxidative damage and cell death in surrounding tissues. High rates of disability and cognitive decline in SAH survivors are attributed to loss of neurons and functional connections during secondary brain injury. Haptoglobin sequesters Hb for clearance, but this scavenging system is overwhelmed after a haemorrhage. Whilst exogenous haptoglobin application can attenuate cytotoxicity of Hb in vitro and in vivo, the functional effects of sub-lethal Hb concentrations on surviving neurons and whether cellular function can be protected with haptoglobin treatment remain unclear. Here we use cultured neurons to investigate neuronal health and function across a range of Hb concentrations to establish the thresholds for cellular damage and investigate synaptic function. Hb impairs ATP concentrations and cytoskeletal structure. At clinically relevant but sub-lethal Hb concentrations, we find that synaptic AMPAR-driven currents are reduced, accompanied by a reduction in GluA1 subunit expression. Haptoglobin co-application can prevent these deficits by scavenging free Hb to reduce it to sub-threshold concentrations and does not need to be present at stoichiometric amounts to achieve efficacy. Haptoglobin itself does not impair measures of neuronal health and function at any concentration tested. Our data highlight a role for Hb in modifying synaptic function in surviving neurons, which may link to impaired cognition or plasticity after SAH and support the development of haptoglobin as a therapy for subarachnoid haemorrhage.

Chronic exposure to inorganic arsenic and fluoride induces redox imbalance, inhibits the transsulfuration pathway, and alters glutamate receptor expression in the brain, resulting in memory impairment in adult male mouse offspring

Exposure to toxic elements in drinking water, such as arsenic (As) and fluoride (F), starts at gestation and has been associated with memory and learning deficits in children. Studies in which rodents underwent mechanistic single exposure to As or F showed that the neurotoxic effects are associated with their capacity to disrupt redox balance, mainly by diminishing glutathione (GSH) levels, altering glutamate disposal, and altering glutamate receptor expression, which disrupts synaptic transmission. Elevated levels of As and F are common in groundwater worldwide. To explore the neurotoxicity of chronic exposure to As and F in drinking water, pregnant CD-1 mice were exposed to 2 mg/L As (sodium arsenite) and 25 mg/L F (sodium fluoride) alone or in combination. The male litter continued to receive exposure up to 30 or 90 days after birth. The effects of chronic exposure on GSH levels, transsulfuration pathway enzymatic activity, expression of cysteine/cystine transporters, glutamate transporters, and ionotropic glutamate receptor subunits as well as behavioral performance in the object recognition memory task were assessed. Combined exposure resulted in a significant reduction in GSH levels in the cortex and hippocampus at different times, decreased transsulfuration pathway enzyme activity, as well as diminished xCT protein expression. Altered glutamate receptor expression in the cortex and hippocampus and decreased transaminase enzyme activity were observed. These molecular alterations were associated with memory impairment in the object recognition task, which relies on these brain regions.

Pathophysiological mechanism and natural preventive and therapeutic strategies of Alzheimer's disease

Alzheimer's disease (AD) is characterized by the presence of two types of protein deposits in the brain, amyloid plaques and neurofibrillary tangles. The first one are dense deposits of beta amyloid protein, the second one are dense deposits of the protein tau. These proteins are present in all of our brains, but in AD they act unusually, leading to neuronal degeneration. This review will provide an overview of the AD, including the role of amyloid beta and tau, and mechanisms that lead to the formation of plaques and tangles. The review will also cover the existing researches that have focused on the inhibition of amyloid beta formation, cholinesterase, tau hyperphosphorylation, the pathogenic mechanisms of apoE4, and GSK-3 as a solution that could be used to slow or prevent the disease.

Structural mobility tunes signalling of the GluA1 AMPA glutamate receptor

AMPA glutamate receptors (AMPARs), the primary mediators of excitatory neurotransmission in the brain, are either GluA2 subunit-containing and thus Ca2+-impermeable, or GluA2-lacking and Ca2+-permeable1. Despite their prominent expression throughout interneurons and glia, their role in long-term potentiation and their involvement in a range of neuropathologies2, structural information for GluA2-lacking receptors is currently absent. Here we determine and characterize cryo-electron microscopy structures of the GluA1 homotetramer, fully occupied with TARPγ3 auxiliary subunits (GluA1/γ3). The gating core of both resting and open-state GluA1/γ3 closely resembles GluA2-containing receptors. However, the sequence-diverse N-terminal domains (NTDs) give rise to a highly mobile assembly, enabling domain swapping and subunit re-alignments in the ligand-binding domain tier that are pronounced in desensitized states. These transitions underlie the unique kinetic properties of GluA1. A GluA2 mutant (F231A) increasing NTD dynamics phenocopies this behaviour, and exhibits reduced synaptic responses, reflecting the anchoring function of the AMPAR NTD at the synapse. Together, this work underscores how the subunit-diverse NTDs determine subunit arrangement, gating properties and ultimately synaptic signalling efficiency among AMPAR subtypes.

Electrophysiological Assessment of Newly Synthesized 2,3-Benzodiazepine Derivatives for Inhibiting the AMPA Receptor Channel

Three major subtypes of ionotropic receptors regulate glutamatergic synaptic transmission, one of which is α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPARs). They are tetrameric, cation-permeable ionotropic glutamate receptors found across the brain. Abnormalities in AMPA receptor trafficking and synaptic assembly are linked to cognitive decline and neurological diseases such as Alzheimer's, Parkinson's, and Huntington's. The present study will investigate the effects of four novel 2,3-benzodiazepine derivatives on AMPA receptor subunits by comparing their effects on synaptic responses, desensitization, and deactivation rate in human embryonic kidney cells (HEK293T) recombinant AMPAR subunits using whole-cell patch-clamp electrophysiology. All four 2,3-BDZ compounds showed inhibitory activity against all the homomeric and heteromeric subunits tested. While the desensitization and deactivation rates in 2,3-BDZ-1 and 2,3-BDZ-2 decreased and increased, respectively, in the other two compounds (i.e., 2,3-BDZ-3 and 2,3-BDZ-4), there was no change in the desensitization or deactivation rates. These results contribute to a better understanding of AMPARs by identifying potential 2,3-BDZ drugs that demonstrate inhibitory effects on the AMPAR subunits.

Cofilin overactivation improves hippocampus-dependent short-term memory

Many living organisms of the animal kingdom have the fundamental ability to form and retrieve memories. Most information is initially stored as short-term memory, which is then converted to a more stable long-term memory through a process called memory consolidation. At the neuronal level, synaptic plasticity is crucial for memory storage. It includes the formation of new spines, as well as the modification of existing spines, thereby tuning and shaping synaptic efficacy. Cofilin critically contributes to memory processes as upon activation, it regulates the shape of dendritic spines by targeting actin filaments. We previously found that prolonged activation of cofilin in hippocampal neurons attenuated the formation of long-term object-location memories. Because the modification of spine shape and structure is also essential for short-term memory formation, we determined whether overactivation of hippocampal cofilin also influences the formation of short-term memories. To this end, mice were either injected with an adeno-associated virus expressing catalytically active cofilin, or an eGFP control, in the hippocampus. We show for the first time that cofilin overactivation improves short-term memory formation in the object-location memory task, without affecting anxiety-like behavior. Surprisingly, we found no effect of cofilin overactivation on AMPA receptor expression levels. Altogether, while cofilin overactivation might negatively impact the formation of long-lasting memories, it may benefit short-term plasticity.

Regulation of the Ca2+ Channel CaV1.2 Supports Spatial Memory and Its Flexibility and LTD

Widespread release of norepinephrine (NE) throughout the forebrain fosters learning and memory via adrenergic receptor (AR) signaling, but the molecular mechanisms are largely unknown. The β2 AR and its downstream effectors, the trimeric stimulatory Gs-protein, adenylyl cyclase (AC), and the cAMP-dependent protein kinase A (PKA), form a unique signaling complex with the L-type Ca2+ channel (LTCC) CaV1.2. Phosphorylation of CaV1.2 by PKA on Ser1928 is required for the upregulation of Ca2+ influx on β2 AR stimulation and long-term potentiation induced by prolonged theta-tetanus (PTT-LTP) but not LTP induced by two 1-s-long 100-Hz tetani. However, the function of Ser1928 phosphorylation in vivo is unknown. Here, we show that S1928A knock-in (KI) mice of both sexes, which lack PTT-LTP, express deficiencies during initial consolidation of spatial memory. Especially striking is the effect of this mutation on cognitive flexibility as tested by reversal learning. Mechanistically, long-term depression (LTD) has been implicated in reversal learning. It is abrogated in male and female S1928A knock-in mice and by β2 AR antagonists and peptides that displace β2 AR from CaV1.2. This work identifies CaV1.2 as a critical molecular locus that regulates synaptic plasticity, spatial memory and its reversal, and LTD.SIGNIFICANCE STATEMENT We show that phosphorylation of the Ca2+ channel CaV1.2 on Ser1928 is important for consolidation of spatial memory and especially its reversal, and long-term depression (LTD). Identification of Ser1928 as critical for LTD and reversal learning supports the model that LTD underlies flexibility of reference memory.

Variance analysis as a method to predict the locus of plasticity at populations of non-uniform synapses

Our knowledge on synaptic transmission in the central nervous system has often been obtained by evoking synaptic responses to populations of synapses. Analysis of the variance in synaptic responses can be applied as a method to predict whether a change in synaptic responses is a consequence of altered presynaptic neurotransmitter release or postsynaptic receptors. However, variance analysis is based on binomial statistics, which assumes that synapses are uniform. In reality, synapses are far from uniform, which questions the reliability of variance analysis when applying this method to populations of synapses. To address this, we used an in silico model for evoked synaptic responses and compared variance analysis outcomes between populations of uniform versus non-uniform synapses. This simulation revealed that variance analysis produces similar results irrespectively of the grade of uniformity of synapses. We put this variance analysis to the test with an electrophysiology experiment using a model system for which the loci of plasticity are well established: the effect of amyloid-β on synapses. Variance analysis correctly predicted that postsynaptically produced amyloid-β triggered predominantly a loss of synapses and a minor reduction of postsynaptic currents in remaining synapses with little effect on presynaptic release probability. We propose that variance analysis can be reliably used to predict the locus of synaptic changes for populations of non-uniform synapses.

Long-Term Capsaicin Administration Ameliorates the Dysfunction and Astrogliosis of the Brain in Aged Mice with Missing Maxillary Molars

Tooth loss and decreased masticatory function reportedly affect cognitive function; tooth loss allegedly induces astrogliosis and aging of astrocytes in the hippocampus and hypothalamus, which is a response specific to the central nervous system owing to homeostasis in different brain regions. Capsaicin, a component of red peppers, has positive effects on brain disorders in mice. Decreased expression of transient receptor potential vanilloid 1, a receptor of capsaicin, is associated with the development of dementia. In this study, we investigated the effect of capsaicin administration in aged mice (C57BL/6N mice) with reduced masticatory function owing to the extraction of maxillary molars to investigate preventive/therapeutic methods for cognitive decline attributed to age-related masticatory function loss. The results demonstrated that mice with impaired masticatory function showed decreased motor and cognitive function at the behavioral level. At the genetic level, neuroinflammation, microglial activity, and astrogliosis, such as increased glial fibrillary acidic protein levels, were observed in the mouse brain. The mice with extracted molars fed on a diet containing capsaicin for 3 months demonstrated improved behavioral levels and astrogliosis, which suggest that capsaicin is useful in maintaining brain function in cases of poor oral function and prosthetic difficulties.

The effect of Lavandula Coronopifolia essential oil on the biophysical properties of desensitization and deactivation gating currents in ionotropic receptors

The rising incidence of cancer and the lack of effective therapeutic interventions for many neurological illnesses like Alzheimer's and epilepsy has prompted us to investigate the composition and effects of the Lavandula coronopifolia oil from Palestine on cancer cells and AMPA receptor subunits in the brain due to the vast range of beneficial properties of Lavandula coronopifolia essential oil (EO). GC/MS was used to analyze L. coronopifolia's EO chemistry. EO's cytotoxicity and biophysical effects on AMPA receptors were investigated using MTS and electrophysiological techniques. The GC-MS results revealed that L. coronopifolia EO has a high content of eucalyptol (77.23%), β-pinene (6.93%), and α-pinene (4.95%). The EO showed more significant antiproliferative selectivity activities against HepG2 cancer cell lines than HEK293T cell lines with IC₅₀ values of 58.51 and 133.22 µg/mL, respectively. The EO of L. coronopifolia affected AMPA receptor kinetics (desensitization and deactivation) and preferred homomeric GluA1 and heteromeric GluA1/A2 receptors. These findings indicate the potential therapeutic use of L. coronopifolia EO in the selective treatment of HepG2 cancer cell lines and neurodegenerative diseases.

Activity-Dependent Nr4a2 Induction Modulates Synaptic Expression of AMPA Receptors and Plasticity via a Ca2+/CRTC1/CREB Pathway

Transcription factors have a pivotal role in synaptic plasticity and the associated modification of neuronal networks required for memory formation and consolidation. The nuclear receptors subfamily 4 group A (Nr4a) have emerged as possible modulators of hippocampal synaptic plasticity and cognitive functions. However, the molecular and cellular mechanisms underlying Nr4a2-mediated hippocampal synaptic plasticity are not completely known. Here, we report that neuronal activity enhances Nr4a2 expression and function in cultured mouse hippocampal neurons (both sexes) by an ionotropic glutamate receptor/Ca2+/cAMP response element-binding protein/CREB-regulated transcription factor 1 (iGluR/Ca2+/CREB/CRTC1) pathway. Nr4a2 activation mediates BDNF production and increases expression of iGluRs, thereby affecting LTD at CA3-CA1 synapses in acute mouse hippocampal slices (both sexes). Together, our results indicate that the iGluR/Ca2+/CREB/CRTC1 pathway mediates activity-dependent expression of Nr4a2, which is involved in glutamatergic synaptic plasticity by increasing BDNF and synaptic GluA1-AMPARs. Therefore, Nr4a2 activation could be a therapeutic approach for brain disorders associated with dysregulated synaptic plasticity.SIGNIFICANCE STATEMENT A major factor that regulates fast excitatory synaptic transmission and plasticity is the modulation of synaptic AMPARs. However, despite decades of research, the underlying mechanisms of this modulation remain poorly understood. Our study identified a molecular pathway that links neuronal activity with AMPAR modulation and hippocampal synaptic plasticity through the activation of Nr4a2, a member of the nuclear receptor subfamily 4. Since several compounds have been described to activate Nr4a2, our study not only provides mechanistic insights into the molecular pathways related to hippocampal synaptic plasticity and learning, but also identifies Nr4a2 as a potential therapeutic target for pathologic conditions associated with dysregulation of glutamatergic synaptic function.

Urocanic acid facilitates acquisition of object recognition memory in mice

Trans-urocanic acid (UCA), an isomer of cis-UCA that is located in the skin, has recently been reported to have a role in short-term working memory and in the consolidation, reconsolidation and retrieval of long-term memory. However, its effect on memory acquisition remains unclear. In the present study, the effect of UCA on short-term and long-term memory acquisition in mice was investigated using novel object recognition (NOR) and object location recognition (OLR) protocols that each involved three stages: habituation, sampling and testing. UCA was intraperitoneally injected 0.5 h pre-sampling, and the discrimination index during subsequent testing was determined in NOR and OLR tasks. The results showed that 10 mg/kg UCA significantly facilitated short-term and long-term memory acquisition in both types of tasks. Furthermore, 30 mg/kg UCA significantly facilitated long-term memory acquisition in the NOR task and tended to facilitate long-term memory acquisition in the OLR tasks but did not facilitate short-term memory acquisition in either task. Additionally, the enhancing role of UCA on memory acquisition was not dependent on changes of nonspecific responses, e.g. exploratory behavior and locomotor activity. The current study suggests that UCA facilitates short-term and long-term recognition memory acquisition, which further extends the functional role of UCA in the brain function.

Self-Regulatory Neuronal Mechanisms and Long-Term Challenges in Schizophrenia Treatment

Schizophrenia is a chronic and relapsing disorder that is characterized not only by delusions and hallucinations but also mainly by the progressive development of cognitive and social deficits. These deficits are related to impaired synaptic plasticity and impaired neurotransmission in the nervous system. Currently, technological innovations and medical advances make it possible to use various self-regulatory methods to improve impaired synaptic plasticity. To evaluate the therapeutic effect of various rehabilitation methods, we reviewed methods that modify synaptic plasticity and improve the cognitive and executive processes of patients with a diagnosis of schizophrenia. PubMed, Scopus, and Google Scholar bibliographic databases were searched with the keywords mentioned below. A total of 555 records were identified. Modern methods of schizophrenia therapy with neuroplastic potential, including neurofeedback, transcranial magnetic stimulation, transcranial direct current stimulation, vagus nerve stimulation, virtual reality therapy, and cognitive remediation therapy, were reviewed and analyzed. Since randomized controlled studies of long-term schizophrenia treatment do not exceed 2-3 years, and the pharmacological treatment itself has an incompletely estimated benefit-risk ratio, treatment methods based on other paradigms, including neuronal self-regulatory and neural plasticity mechanisms, should be considered. Methods available for monitoring neuroplastic effects in vivo (e.g., fMRI, neuropeptides in serum), as well as unfavorable parameters (e.g., features of the metabolic syndrome), enable individualized monitoring of the effectiveness of long-term treatment of schizophrenia.

Dynamics of AMPA receptors regulate epileptogenesis in patients with epilepsy

The excitatory glutamate α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) contribute to epileptogenesis. Thirty patients with epilepsy and 31 healthy controls are scanned using positron emission tomography with our recently developed radiotracer for AMPARs, [¹¹C]K-2, which measures the density of cell-surface AMPARs. In patients with focal-onset seizures, an increase in AMPAR trafficking augments the amplitude of abnormal gamma activity detected by electroencephalography. In contrast, patients with generalized-onset seizures exhibit a decrease in AMPARs coupled with increased amplitude of abnormal gamma activity. Patients with epilepsy had reduced AMPAR levels compared with healthy controls, and AMPARs are reduced in larger areas of the cortex in patients with generalized-onset seizures compared with those with focal-onset seizures. Thus, epileptic brain function can be regulated by the enhanced trafficking of AMPAR due to Hebbian plasticity with increased simultaneous neuronal firing and compensational downregulation of cell-surface AMPARs by the synaptic scaling.

Intravenous Injection of GluR2-3Y Inhibits Repeated Morphine-Primed Reinstatement of Drug Seeking in Rats

Studies have demonstrated that the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor is essential to drug addiction. In this study, we explored the influence of GluR2-3Y, an interfering peptide to prevent the endocytosis of AMPA receptors containing the GluR2 subunit, on morphine-seeking behavior in the rat self-administration model. After self-administration was established, the rats received intravenous injections of GluR2-3Y during the extinction sessions. There were no significant differences in both active and inactive pokes compared to the control group of rats that received GluR2-3S, indicating that GluR2-3Y has no significant influences on the extinction of morphine self-administration. The other two groups of rats were trained, extinguished, and reinstated by repeated morphine priming (respectively, called Prime 1, Prime 2, and Prime 3). Only one intravenous injection of GluR2-3Y was performed before Prime 1. Compared to the control group, GluR2-3Y did not affect Prime 1, but significantly attenuated the morphine-seeking behavior during repeated morphine-primed reinstatement, indicating an inhibitory after effect of GluR2-3Y on morphine-seeking behavior in rats. The long-term depression (LTD) in the nucleus accumbens (NAc) shell was also assessed. Pretreatment with GluR2-3Y altered the ability of LTD induction to the level of that in the naive group, while pretreatment with GluR2-3S had no effects on LTD. Our results demonstrated that the intravenous injection of GluR2-3Y, to block the endocytosis of AMPA receptors, inhibited the reinstatement of morphine-seeking behavior, which may be induced by modulating the neuronal plasticity in the NAc shell of rats.

Integration of reconfigurable microchannels into aligned three-dimensional neural networks for spatially controllable neuromodulation

Anisotropically organized neural networks are indispensable routes for functional connectivity in the brain, which remains largely unknown. While prevailing animal models require additional preparation and stimulation-applying devices and have exhibited limited capabilities regarding localized stimulation, no in vitro platform exists that permits spatiotemporal control of chemo-stimulation in anisotropic three-dimensional (3D) neural networks. We present the integration of microchannels seamlessly into a fibril-aligned 3D scaffold by adapting a single fabrication principle. We investigated the underlying physics of elastic microchannels' ridges and interfacial sol-gel transition of collagen under compression to determine a critical window of geometry and strain. We demonstrated the spatiotemporally resolved neuromodulation in an aligned 3D neural network by local deliveries of KCl and Ca²⁺ signal inhibitors, such as tetrodotoxin, nifedipine, and mibefradil, and also visualized Ca²⁺ signal propagation with a speed of ~3.7 μm/s. We anticipate that our technology will pave the way to elucidate functional connectivity and neurological diseases associated with transsynaptic propagation.

In the fast lane: Receptor trafficking during status epilepticus

Status epilepticus (SE) remains a significant cause of morbidity and mortality and often is refractory to standard first-line treatments. A rapid loss of synaptic inhibition and development of pharmacoresistance to benzodiazepines (BZDs) occurs early during SE, while NMDA and AMPA receptor antagonists remain effective treatments after BZDs have failed. Multimodal and subunit-selective receptor trafficking within minutes to an hour of SE involves GABA-A, NMDA, and AMPA receptors and contributes to shifts in the number and subunit composition of surface receptors with differential impacts on the physiology, pharmacology, and strength of GABAergic and glutamatergic currents at synaptic and extrasynaptic sites. During the first hour of SE, synaptic GABA-A receptors containing γ2 subunits move to the cell interior while extrasynaptic GABA-A receptors with δ subunits are preserved. Conversely, NMDA receptors containing N2B subunits are increased at synaptic and extrasynaptic sites, and homomeric GluA1 ("GluA2-lacking") calcium permeant AMPA receptor surface expression also is increased. Molecular mechanisms, largely driven by NMDA receptor or calcium permeant AMPA receptor activation early during circuit hyperactivity, regulate subunit-specific interactions with proteins involved with synaptic scaffolding, adaptin-AP2/clathrin-dependent endocytosis, endoplasmic reticulum (ER) retention, and endosomal recycling. Reviewed here is how SE-induced shifts in receptor subunit composition and surface representation increase the excitatory to inhibitory imbalance that sustains seizures and fuels excitotoxicity contributing to chronic sequela such as "spontaneous recurrent seizures" (SRS). A role for early multimodal therapy is suggested both for treatment of SE and for prevention of long-term comorbidities.

Cnih3 Deletion Dysregulates Dorsal Hippocampal Transcription across the Estrous Cycle

In females, the hippocampus, a critical brain region for coordination of learning, memory, and behavior, displays altered physiology and behavioral output across the estrous or menstrual cycle. However, the molecular effectors and cell types underlying these observed cyclic changes have only been partially characterized to date. Recently, profiling of mice null for the AMPA receptor trafficking gene Cnih3 have demonstrated estrous-dependent phenotypes in dorsal hippocampal synaptic plasticity, composition, and learning/memory. We therefore profiled dorsal hippocampal transcriptomes from female mice in each estrous cycle stage, and contrasted it with that of males, across wild-type (WT) and Cnih3 mutants. In wild types, we identified only subtle differences in gene expression between the sexes, while comparing estrous stages to one another revealed up to >1000 differentially expressed genes (DEGs). These estrous-responsive genes are especially enriched in gene markers of oligodendrocytes and the dentate gyrus, and in functional gene sets relating to estrogen response, potassium channels, and synaptic gene splicing. Surprisingly, Cnih3 knock-outs (KOs) showed far broader transcriptomic differences between estrous cycle stages and males. Moreover, Cnih3 knock-out drove subtle but extensive expression changes accentuating sex differential expression at diestrus and estrus. Altogether, our profiling highlights cell types and molecular systems potentially impacted by estrous-specific gene expression patterns in the adult dorsal hippocampus, enabling mechanistic hypothesis generation for future studies of sex-differential neuropsychiatric function and dysfunction. Moreover, these findings suggest an unrecognized role of Cnih3 in buffering against transcriptional effects of estrous, providing a candidate molecular mechanism to explain estrous-dependent phenotypes observed with Cnih3 loss.

Glutamatergic neurotransmission: A potential pharmacotherapeutic target for the treatment of cognitive disorders

In the mammalian brain, glutamate is regarded to be the primary excitatory neurotransmitter due to its widespread distribution and wide range of metabolic functions. Glutamate plays key roles in regulating neurogenesis, synaptogenesis, neurite outgrowth, and neuron survival in the brain. Ionotropic and metabotropic glutamate receptors, neurotransmitters, neurotensin, neurosteroids, and others co-ordinately formulate a complex glutamatergic network in the brain that maintains optimal excitatory neurotransmission. Cognitive activities are potentially synchronized by the glutamatergic activities in the brain via restoring synaptic plasticity. Dysfunctional glutamate receptors and other glutamatergic components are responsible for the aberrant glutamatergic activity in the brain that cause cognitive impairments, loss of synaptic plasticity, and neuronal damage. Thus, controlling the brain's glutamatergic transmission and modifying glutamate receptor function could be a potential therapeutic strategy for cognitive disorders. Certain drugs that regulate glutamate receptor activities have shown therapeutic promise in improving cognitive functions in preclinical and clinical studies. However, several issues regarding precise functional information of glutamatergic activity are yet to be comprehensively understood. The present article discusses the scope of developing glutamatergic systems as prospective pharmacotherapeutic targets to treat cognitive disorders. Special attention has been given to recent developments, challenges, and future prospects.

Layer-specific distribution and expression pattern of AMPA- and NMDA-type glutamate receptors in the barrel field of the adult rat somatosensory cortex: a quantitative electron microscopic analysis

AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and NMDA (N-methyl-d-aspartate) glutamate receptors are driving forces for synaptic transmission and plasticity at neocortical synapses. However, their distribution pattern in the adult rat neocortex is largely unknown and was quantified using freeze fracture replication combined with postimmunogold-labeling. Both receptors were co-localized at layer (L)4 and L5 postsynaptic densities (PSDs). At L4 dendritic shaft and spine PSDs, the number of gold grains detecting AMPA was similar, whereas at L5 shaft PSDs AMPA-receptors outnumbered those on spine PSDs. Their number was significantly higher at L5 vs. L4 PSDs. At L4 and L5 dendritic shaft PSDs, the number of gold grains detecting GluN1 was ~2-fold higher than at spine PSDs. The number of gold grains detecting the GluN1-subunit was higher for both shaft and spine PSDs in L5 vs. L4. Both receptors showed a large variability in L4 and L5. A high correlation between the number of gold grains and PSD size for both receptors and targets was observed. Both receptors were distributed over the entire PSD but showed a layer- and target-specific distribution pattern. The layer- and target-specific distribution of AMPA and GluN1 glutamate receptors partially contribute to the observed functional differences in synaptic transmission and plasticity in the neocortex.

Non-Motor Symptoms of Parkinson's Disease: The Neurobiology of Early Psychiatric and Cognitive Dysfunction

Parkinson's disease (PD) is a progressive neurodegenerative disorder that has been recognized for over 200 years by its clinically dominant motor system impairment. There are prominent non-motor symptoms as well, and among these, psychiatric symptoms of depression and anxiety and cognitive impairment are common and can appear earlier than motor symptoms. Although the neurobiology underlying these particular PD-associated non-motor symptoms is not completely understood, the identification of PARK genes that contribute to hereditary and sporadic PD has enabled genetic models in animals that, in turn, have fostered ever deepening analyses of cells, synapses, circuits, and behaviors relevant to non-motor psychiatric and cognitive symptoms of human PD. Moreover, while it has long been recognized that inflammation is a prominent component of PD, recent studies demonstrate that brain-immune signaling crosstalk has significant modulatory effects on brain cell and synaptic function in the context of psychiatric symptoms. This review provides a focused update on such progress in understanding the neurobiology of PD-related non-motor psychiatric and cognitive symptoms.

Synapse Dysfunctions in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system (CNS) affecting nearly three million humans worldwide. In MS, cells of an auto-reactive immune system invade the brain and cause neuroinflammation. Neuroinflammation triggers a complex, multi-faceted harmful process not only in the white matter but also in the grey matter of the brain. In the grey matter, neuroinflammation causes synapse dysfunctions. Synapse dysfunctions in MS occur early and independent from white matter demyelination and are likely correlates of cognitive and mental symptoms in MS. Disturbed synapse/glia interactions and elevated neuroinflammatory signals play a central role. Glutamatergic excitotoxic synapse damage emerges as a major mechanism. We review synapse/glia communication under normal conditions and summarize how this communication becomes malfunctional during neuroinflammation in MS. We discuss mechanisms of how disturbed glia/synapse communication can lead to synapse dysfunctions, signaling dysbalance, and neurodegeneration in MS.

p85S6K sustains synaptic GluA1 to ameliorate cognitive deficits in Alzheimer's disease

BACKGROUND

Ribosomal protein S6 kinase 1 (S6K1) is a serine-threonine kinase that has two main isoforms: p70S6K (70-kDa isoform) and p85S6K (85-kDa isoform). p70S6K, with its upstream mammalian target of rapamycin (mTOR), has been shown to be involved in learning and memory and participate in the pathophysiology of Alzheimer's disease (AD). However, the function of p85S6K has long been neglected due to its high similarity to p70S6k. The role of p85S6K in learning and memory is still largely unknown.

METHODS

We fractionated the postsynaptic densities to illustrate the differential distribution of p85S6K and p70S6K. Coimmunoprecipitation was performed to unveil interactions between p85S6K and the GluA1 subunit of AMPA receptor. The roles of p85S6K in synaptic targeting of GluA1 and learning and memory were evaluated by specific knockdown or overexpression of p85S6K followed by a broad range of methodologies including immunofluorescence, Western blot, in situ proximity ligation assay, morphological staining and behavioral examination. Further, the expression level of p85S6K was measured in brains from AD patients and AD model mice.

RESULTS

p85S6K, but not p70S6K, was enriched in the postsynaptic densities. Moreover, knockdown of p85S6K resulted in defective spatial and recognition memory. In addition, p85S6K could interact with the GluA1 subunit of AMPA receptor through synapse-associated protein 97 and A-kinase anchoring protein 79/150. Mechanistic studies demonstrated that p85S6K could directly phosphorylate GluA1 at Ser845 and increase the amount of GluA1 in synapses, thus sustaining synaptic function and spine densities. Moreover, p85S6K was found to be specifically decreased in the synaptosomal compartment in the brains of AD patients and AD mice. Overexpression of p85S6K ameliorated the synaptic deficits and cognitive impairment in transgenic AD model mice.

CONCLUSIONS

These results strongly imply a significant role for p85S6K in maintaining synaptic and cognitive function by interacting with GluA1. The findings provide an insight into the rational targeting of p85S6K as a therapeutic potential for AD.

Inter-neuronal signaling mediated by small extracellular vesicles: wireless communication?

Conventional inter-neuronal communication conceptualizes the wired method of chemical synapses that physically connect pre-and post-synaptic neurons. In contrast, recent studies indicate that neurons also utilize synapse-independent, hence "wireless" broadcasting-type communications via small extracellular vesicles (EVs). Small EVs including exosomes are secreted vesicles released by cells and contain a variety of signaling molecules including mRNAs, miRNAs, lipids, and proteins. Small EVs are subsequently absorbed by local recipient cells via either membrane fusion or endocytic processes. Therefore, small EVs enable cells to exchange a "packet" of active biomolecules for communication purposes. It is now well established that central neurons also secrete and uptake small EVs, especially exosomes, a type of small EVs that are derived from the intraluminal vesicles of multivesicular bodies. Specific molecules carried by neuronal small EVs are shown to affect a variety of neuronal functions including axon guidance, synapse formation, synapse elimination, neuronal firing, and potentiation. Therefore, this type of volume transmission mediated by small EVs is thought to play important roles not only in activity-dependent changes in neuronal function but also in the maintenance and homeostatic control of local circuitry. In this review, we summarize recent discoveries, catalog neuronal small EV-specific biomolecules, and discuss the potential scope of small EV-mediated inter-neuronal signaling.

Evolutionarily conserved gene expression patterns for affective disorders revealed using cross-species brain transcriptomic analyses in humans, rats and zebrafish

Widespread, debilitating and often treatment-resistant, depression and other stress-related neuropsychiatric disorders represent an urgent unmet biomedical and societal problem. Although animal models of these disorders are commonly used to study stress pathogenesis, they are often difficult to translate across species into valuable and meaningful clinically relevant data. To address this problem, here we utilized several cross-species/cross-taxon approaches to identify potential evolutionarily conserved differentially expressed genes and their sets. We also assessed enrichment of these genes for transcription factors DNA-binding sites down- and up- stream from their genetic sequences. For this, we compared our own RNA-seq brain transcriptomic data obtained from chronically stressed rats and zebrafish with publicly available human transcriptomic data for patients with major depression and their respective healthy control groups. Utilizing these data from the three species, we next analyzed their differential gene expression, gene set enrichment and protein-protein interaction networks, combined with validated tools for data pooling. This approach allowed us to identify several key brain proteins (GRIA1, DLG1, CDH1, THRB, PLCG2, NGEF, IKZF1 and FEZF2) as promising, evolutionarily conserved and shared affective 'hub' protein targets, as well as to propose a novel gene set that may be used to further study affective pathogenesis. Overall, these approaches may advance cross-species brain transcriptomic analyses, and call for further cross-species studies into putative shared molecular mechanisms of affective pathogenesis.

Glutamate receptor 4 as a fluid biomarker for the diagnosis of psychiatric disorders

Psychiatric disorders are widely underreported diseases, especially in their early stages. So far, there is no fluid biomarker to confirm the diagnosis of these disorders. Proteomics data suggest the synaptic protein glutamate receptor 4 (GluR4), part of the AMPA receptor, as a potential diagnostic biomarker of major depressive disorder (MDD). A novel sandwich ELISA was established and analytically validated to detect GluR4 in cerebrospinal fluid (CSF) samples. A total of 85 subjects diagnosed with MDD (n = 36), bipolar disorder (BD, n = 12), schizophrenia (SCZ, n = 12) and neurological controls (CON, n = 25) were analysed. The data exhibited a significant correlation (r = 0.74; CI:0.62 to 0.82; p < 0.0001) with the antibody-free multiple reaction monitoring (MRM) mass spectrometry (MS) data. CSF GluR4 levels were lower in MDD (p < 0.002) and BD (p = 0.012) than in CON. Moreover, subjects with SCZ described a trend towards lower levels than CON (p = 0.13). The novel GluR4 ELISA may favour the clinical application of this protein as a potential diagnostic biomarker of psychiatric disorders and may facilitate the understanding of the pathophysiological mechanisms behind these disorders.

A gain-of-function GRIA2 variant associated with neurodevelopmental delay and seizures: Functional characterization and targeted treatment

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors (AMPARs) are ligand-gated cationic channels formed from combinations of GluA1-4 subunits. Pathogenic variants of GRIA1-4 have been described in patients with developmental delay, intellectual disability, autism spectrum disorder, and seizures, with GRIA2 variants typically causing AMPAR loss of function. Here, we identify a novel, heterozygous de novo pathogenic missense mutation in GRIA2 (c.1928 C>T, p.A643V, NM_001083619.1) in a 1-year-old boy with epilepsy, developmental delay, and failure to thrive. We made patch-clamp recordings to compare the functional and pharmacological properties of variant and wild-type receptors expressed in HEK293 cells, with and without the transmembrane AMPAR regulatory protein γ2. This showed GluA2 A643V-containing AMPARs to exhibit a novel gain of function, with greatly slowed deactivation, markedly reduced desensitization, and increased glutamate sensitivity. Perampanel, an antiseizure AMPAR negative allosteric modulator, was able to fully block GluA2 A643V/γ2 currents, suggesting potential therapeutic efficacy. The subsequent introduction of perampanel to the patient's treatment regimen was associated with a marked reduction in seizure burden, a resolution of failure to thrive, and clear developmental gains. Our study reveals that GRIA2 disorder can be caused by a gain-of-function variant, and both predicts and suggests the therapeutic efficacy of perampanel. Perampanel may prove beneficial for patients with other gain-of-function GRIA variants.

The regulatory role of endoplasmic reticulum chaperone proteins in neurodevelopment

The endoplasmic reticulum (ER) is the largest tubular reticular organelle spanning the cell. As the main site of protein synthesis, Ca2+ homeostasis maintenance and lipid metabolism, the ER plays a variety of essential roles in eukaryotic cells, with ER molecular chaperones participate in all these processes. In recent years, it has been reported that the abnormal expression of ER chaperones often leads to a variety of neurodevelopmental disorders (NDDs), including abnormal neuronal migration, neuronal morphogenesis, and synaptic function. Neuronal development is a complex and precisely regulated process. Currently, the mechanism by which neural development is regulated at the ER level remains under investigation. Therefore, in this work, we reviewed the recent advances in the roles of ER chaperones in neural development and developmental disorders caused by the deficiency of these molecular chaperones.

Prolonged contextual fear memory in AMPA receptor palmitoylation-deficient mice

Long-lasting fear-related disorders depend on the excessive retention of traumatic fear memory. We previously showed that the palmitoylation-dependent removal of synaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors prevents hyperexcitation-based epileptic seizures and that AMPA receptor palmitoylation maintains neural network stability. In this study, AMPA receptor subunit GluA1 C-terminal palmitoylation-deficient (GluA1C811S) mice were subjected to comprehensive behavioral battery tests to further examine whether the mutation causes other neuropsychiatric disease-like symptoms. The behavioral analyses revealed that palmitoylation-deficiency in GluA1 is responsible for characteristic prolonged contextual fear memory formation, whereas GluA1C811S mice showed no impairment of anxiety-like behaviors at the basal state. In addition, fear generalization gradually increased in these mutant mice without affecting their cued fear. Furthermore, fear extinction training by repeated exposure of mice to conditioned stimuli had little effect on GluA1C811S mice, which is in line with augmentation of synaptic transmission in pyramidal neurons in the basolateral amygdala. In contrast, locomotion, sociability, depression-related behaviors, and spatial learning and memory were unaffected by the GluA1 non-palmitoylation mutation. These results indicate that impairment of AMPA receptor palmitoylation specifically causes posttraumatic stress disorder (PTSD)-like symptoms.

Membrane lipid rafts are required for AMPA receptor tyrosine phosphorylation

Membrane lipid rafts are sphingolipids and cholesterol-enriched membrane microdomains, which form a center for the interaction or assembly of palmitoylated signaling molecules, including Src family non-receptor type protein tyrosine kinases. Lipid rafts abundantly exist in neurons and function in the maintenance of synapses. Excitatory synaptic strength is largely controlled by the surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors in the mammalian brain. AMPA receptor endocytosis from the synaptic surface is regulated by phosphorylation of the GluA2 subunit at tyrosine 876 by Src family kinases. Here, I revealed that tyrosine phosphorylated GluA2 is concentrated in the lipid rafts fraction. Furthermore, stimulation-induced upregulation of GluA2 tyrosine phosphorylation is disrupted by the treatment of neurons with a cholesterol-depleting compound, filipin III. These results indicate the importance of lipid rafts as enzymatic reactive sites for AMPA receptor tyrosine phosphorylation and subsequent AMPA receptor internalization from the synaptic surface.

Willardiine and Its Synthetic Analogues: Biological Aspects and Implications in Peptide Chemistry of This Nucleobase Amino Acid

Willardiine is a nonprotein amino acid containing uracil, and thus classified as nucleobase amino acid or nucleoamino acid, that together with isowillardiine forms the family of uracilylalanines isolated more than six decades ago in higher plants. Willardiine acts as a partial agonist of ionotropic glutamate receptors and more in particular it agonizes the non-N-methyl-D-aspartate (non-NMDA) receptors of L-glutamate: ie. the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) and kainate receptors. Several analogues and derivatives of willardiine have been synthesised in the laboratory in the last decades and these compounds show different binding affinities for the non-NMDA receptors. More in detail, the willardiine analogues have been employed not only in the investigation of the structure of AMPA and kainate receptors, but also to evaluate the effects of receptor activation in the various brain regions. Remarkably, there are a number of neurological diseases determined by alterations in glutamate signaling, and thus, ligands for AMPA and kainate receptors deserve attention as potential neurodrugs. In fact, similar to willardiine its analogues often act as agonists of AMPA and kainate receptors. A particular importance should be recognized to willardiine and its thymine-based analogue AlaT also in the peptide chemistry field. In fact, besides the naturally-occurring short nucleopeptides isolated from plant sources, there are different examples in which this class of nucleoamino acids was investigated for nucleopeptide development. The applications are various ranging from the realization of nucleopeptide/DNA chimeras for diagnostic applications, and nucleoamino acid derivatization of proteins for facilitating protein-nucleic acid interaction, to nucleopeptide-nucleopeptide molecular recognition for nanotechnological applications. All the above aspects on both chemistry and biotechnological applications of willardine/willardine-analogues and nucleopeptide will be reviewed in this work.