Bidirectional Dysregulation of AMPA Receptor-Mediated Synaptic Transmission and Plasticity in Brain Disorders

Cognitive Impairment and Synaptic Dysfunction in Cardiovascular Disorders: The New Frontiers of the Heart-Brain Axis

Within the central nervous system, synaptic plasticity, fundamental to processes like learning and memory, is largely driven by activity-dependent changes in synaptic strength. This plasticity often manifests as long-term potentiation (LTP) and long-term depression (LTD), which are bidirectional modulations of synaptic efficacy. Strong epidemiological and experimental evidence show that the heart-brain axis could be severely compromised by both neurological and cardiovascular disorders. Particularly, cardiovascular disorders, such as heart failure, hypertension, obesity, diabetes and insulin resistance, and arrhythmias, may lead to cognitive impairment, a condition known as cardiogenic dementia. Herein, we review the available knowledge on the synaptic and molecular mechanisms by which cardiogenic dementia may arise and describe how LTP and/or LTD induction and maintenance may be compromised in the CA1 region of the hippocampus by heart failure, metabolic syndrome, and arrhythmias. We also discuss the emerging evidence that endothelial dysfunction may contribute to directly altering hippocampal LTP by impairing the synaptically induced activation of the endothelial nitric oxide synthase. A better understanding of how CV disorders impact on the proper function of central synapses will shed novel light on the molecular underpinnings of cardiogenic dementia, thereby providing a new perspective for more specific pharmacological treatments.

Ellagic Acid Reverses Alterations in the Expression of AMPA Receptor and Its Scaffolding Proteins in the Cerebral Cortex and Memory Decline in STZ-sporadic Alzheimer' s Disease Mouse Model

RATIONALE

Alzheimer's disease (AD), an age-dependent devastating neuropsychiatric disorder, is a leading cause of learning, memory and intellectual disabilities. Current therapeutic approaches for the amelioration of the anomalies of AD are not effective.

OBJECTIVE

In the present study, the molecular mechanisms underlying sporadic AD (sAD), the memory related behavioral analysis and neuroprotective effects of Ellagic acid (EA) were investigated.

METHOD

sAD mouse model was developed by intracerebroventricular (ICV) injection of Streptozotocin (STZ). The efficacy of EA, a naturally occurring polyphenol, in amelioration of anomalies associated with sAD was assessed. EA was administered once daily for 28 days at a dose of 75 mg/kg body weight followed by neurobehavioral, biochemical, molecular and neuronal count analysis to delineate the mode of action of EA.

RESULT

The ICV injection of STZ in mice significantly increased the expression of AD biomarkers in addition to enhanced oxidative stress. A decline in the discrimination index in Novel Object Recognition Test was observed indicating the compromise of recognition memory in AD. Studies on the expression of genes involved in synaptic plasticity reveal the dysregulation of the α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) of the glutamate and its scaffolding proteins in the postsynaptic density and thereby synaptic plasticity in AD. ICV-STZ led to significant upregulation of apoptotic markers which led to decrease in neuronal density of the cerebral cortex. EA significantly reversed the above and improved anomalies of sAD.

CONCLUSION

EA was observed to profoundly modulate the genes involved in AD pathophysiology, restored antioxidant enzymes activity, reduced lipid peroxidation and neuronal loss in the sAD brain. Further, EA was observed to effectively modulate the genes involved in apoptosis and synaptic plasticity. Therefore, EA possesses promising anti-AD properties, which may improve AD-associated anomalies by modulating synaptic plasticity via AMPAR signaling.

The activity-regulated cytoskeleton-associated protein (Arc) functions in a cell type- and sex-specific manner in the adult nucleus accumbens to regulate non-contingent cocaine behaviors

Repeated cocaine use produces adaptations in brain function that contribute to long-lasting behaviors associated with cocaine use disorder (CUD). In rodents, the activity-regulated cytoskeleton-associated protein (Arc) can regulate glutamatergic synaptic transmission, and cocaine regulates Arc expression and subcellular localization in multiple brain regions, including the nucleus accumbens (NAc)-a brain region linked to CUD-related behavior. We show here that repeated, non-contingent cocaine administration in global Arc KO male mice produced a dramatic hypersensitization of cocaine locomotor responses and drug experience-dependent sensitization of conditioned place preference (CPP). In contrast to the global Arc KO mice, viral-mediated reduction of Arc in the adult male, but not female, NAc (shArcNAc) reduced both CPP and cocaine-induced locomotor activity, but without altering basal miniature or evoked glutamatergic synaptic transmission. Interestingly, cell type-specific knockdown of Arc in D1 dopamine receptor-expressing NAc neurons reduced cocaine-induced locomotor sensitization, but not cocaine CPP; whereas, Arc knockdown in D2 dopamine receptor-expressing NAc neurons reduced cocaine CPP, but not cocaine-induced locomotion. Taken together, our findings reveal that global, developmental loss of Arc produces hypersensitized cocaine responses; however, these effects cannot be explained by Arc's function in the adult mouse NAc since Arc is required in a cell type- and sex-specific manner to support cocaine-context associations and locomotor responses.

Evaluating the Neuroprotective Potential of Novel Benzodioxole Derivatives in Parkinson's Disease via AMPA Receptor Modulation

Parkinson's disease (PD) is a significant health issue because it gradually damages the nervous system. α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors play a significant role in the development of PD. The current investigation employed hybrid benzodioxole-propanamide (BDZ-P) compounds to get information on AMPA receptors, analyze their biochemical and biophysical properties, and assess their neuroprotective effects. Examining the biophysical characteristics of all the subunits of the AMPA receptor offers insights into the impact of BDZ-P on the desensitization and deactivation rate. It demonstrates a partial improvement in the locomotor capacities in a mouse model of Parkinson's disease. In addition, the in vivo experiment assessed the locomotor activity by utilizing the open-field test. Our findings demonstrated that BDZ-P7 stands out with its remarkable potency, inhibiting the GluA2 subunit nearly 8-fold with an IC50 of 3.03 μM, GluA1/2 by 7.5-fold with an IC50 of 3.14 μM, GluA2/3 by nearly 7-fold with an IC50 of 3.19 μM, and GluA1 by 6.5-fold with an IC50 of 3.2 μM, significantly impacting the desensitization and deactivation rate of the AMPA receptor. BDZ-P7 showed an in vivo impact of partially reinstating locomotor abilities in a mouse model of PD. The results above suggest that the BDZ-P7 compounds show great promise as top contenders for the development of novel neuroprotective therapies.

Endoplasmic reticulum stress and its role in various neurodegenerative diseases

The Endoplasmic reticulum (ER), a critical cellular organelle, maintains cellular homeostasis by regulating calcium levels and orchestrating essential functions such as protein synthesis, folding, and lipid production. A pivotal aspect of ER function is its role in protein quality control. When misfolded proteins accumulate within the ER due to factors like protein folding chaperone dysfunction, toxicity, oxidative stress, or inflammation, it triggers the Unfolded protein response (UPR). The UPR involves the activation of chaperones like calnexin, calreticulin, glucose-regulating protein 78 (GRP78), and Glucose-regulating protein 94 (GRP94), along with oxidoreductases like protein disulphide isomerases (PDIs). Cells employ the Endoplasmic reticulum-associated degradation (ERAD) mechanism to counteract protein misfolding. ERAD disruption causes the detachment of GRP78 from transmembrane proteins, initiating a cascade involving Inositol-requiring kinase/endoribonuclease 1 (IRE1), Activating transcription factor 6 (ATF6), and Protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathways. The accumulation and deposition of misfolded proteins within the cell are hallmarks of numerous neurodegenerative diseases. These aberrant proteins disrupt normal neuronal signalling and contribute to impaired cellular homeostasis, including oxidative stress and compromised protein degradation pathways. In essence, ER stress is defined as the cellular response to the accumulation of misfolded proteins in the endoplasmic reticulum, encompassing a series of signalling pathways and molecular events that aim to restore cellular homeostasis. This comprehensive review explores ER stress and its profound implications for the pathogenesis and progression of neurodegenerative diseases.

E-Cigarette Exposure Alters Neuroinflammation Gene and Protein Expression in a Murine Model: Insights from Perinatally Exposed Offspring and Post-Birth Mothers

The use of E-cigarettes, often considered a safer alternative to traditional smoking, has been associated with high rates of cellular toxicity, genetic alterations, and inflammation. Neuroinflammatory impacts of cigarette smoking during pregnancy have been associated with increased risks of adverse childhood health outcomes; however, it is still relatively unknown if the same propensity is conferred on offspring by maternal vaping during gestation. Results from our previous mouse inhalation studies suggest such a connection. In this earlier study, pregnant C57BL/6 mice were exposed daily to inhaled E-cig aerosols (i.e., propylene glycol and vegetable glycerin, [PG/VG]), with or without nicotine (16 mg/mL) by whole-body inhalation throughout gestation (3 h/d; 5 d/week; total ~3-week) and continuing postnatally from post-natal day (PND) 4-21. As neuroinflammation is involved in the dysregulation of glucose homeostasis and weight gain, this study aimed to explore genes associated with these pathways in 1-mo.-old offspring (equivalent in humans to 12-18 years of age). Results in the offspring demonstrated a significant increase in glucose metabolism protein levels in both treatment groups compared to filtered air controls. Gene expression analysis in the hypothalamus of 1 mo. old offspring exposed perinatally to E-cig aerosols, with and without nicotine, revealed significantly increased gene expression changes in multiple genes associated with neuroinflammation. In a second proof-of-principal parallel study employing the same experimental design, we shifted our focus to the hippocampus of the postpartum mothers. We targeted the mRNA levels of several neurotrophic factors (NTFs) indicative of neuroinflammation. While there were suggestive changes in mRNA expression in this study, levels failed to reach statistical significance. These studies highlight the need for ongoing research on E-cig-induced alterations in neuroinflammatory pathways.

Synthesis of [11C]BIIB104, an α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic-Acid-Positive Allosteric Modulator, and Evaluation of the Bio-Distribution in Non-Human Primate Brains Using Positron Emission Tomography

The aim of this study was to measure the brain penetrance and kinetics of BIIB104, a first-in-class AMPA receptor potentiator developed for cognitive impairment associated with schizophrenia. It was recently halted in phase 2 clinical development, and there are a lack of tools to directly measure AMPA receptor engagement. To achieve this, the drug candidate was radiolabeled with carbon-11, and its brain penetrance and kinetics were measured in non-human primates via dynamic PET scans. Radiolabeling was achieved through a three-step nucleophilic [11C]cyanation reaction in one pot, resulting in the high radioactivity and radiochemical purity (>99%) of [11C]BIIB104. The study found that [11C]BIIB104 entered the non-human primate brains at 4-5% ID at peak, with a homogeneous distribution. However, a mild regional heterogeneity was observed in the thalamus. The lack of conclusive evidence for a change in regional values after BIIB104 dosing suggests that any specific binding component of BIIB104 is negligible compared to the free and non-specific components in the living brain. Overall, the study demonstrated high brain uptake with minor variability in [11C]BIIB104 distribution across various brain regions, its kinetics were consistent with those of passive diffusion, and the dominating components were the free concentration and non-specific binding. This information is valuable for understanding the potential effects and mechanisms of BIIB104 in the brain.

Multi-biological activity assessment and phytochemical characterization of an aqueous extract of the Cymbopogon citratus grown in Palestine

BACKGROUND

Plants have historically been a rich source of medicinal compounds, with many modern pharmaceuticals derived from botanical origins. In contemporary healthcare, there is a resurgence in utilizing botanical substances as recognized medicinal agents. This study delved into understanding the phytochemical makeup and the multifaceted biological activities of an aqueous extract from Cymbopogon citratus (C. citratus). The investigated activities were its effect on AMPA receptors, antioxidant capacity, anti-lipase, anti-α-amylase actions, cytotoxicity, and antimicrobial properties.

METHODS

The extract of C. citratus received a comprehensive investigation, which included the study of its phytochemical composition, assessment of its antioxidant and anti-lipase properties, evaluation of its capacity to inhibit α-amylase, analysis of its impact on cell viability, and assessment of its antimicrobial activity. The approaches are used to clarify the complex physiological and biochemical characteristics.

RESULTS

The results were compelling; receptor kinetics had a marked impact, notably on the GluA2 subunit. Regarding its medicinal potential, the extract demonstrated potent antioxidant and anti-diabetic activities with IC50 values of 15.13 and 101.14 µg/mL, respectively. Additionally, it displayed significant inhibitory effects on the lipase enzyme and showed cytotoxicity against the Hep3B cancer cell line, with IC50 values of 144.35 and 148.37 µg/mL. In contrast, its effects on the normal LX-2 cell line were minimal, indicating selectivity.

CONCLUSION

The aqueous extract of C. citratus shows promising therapeutic properties. The findings advocate for further research into its compounds for potential isolation, purification, and in-depth pharmacological studies, especially in areas like nervous system disorders, diabetes, obesity, and combating oxidative stress.

Glutamate Receptor Dysregulation and Platelet Glutamate Dynamics in Alzheimer's and Parkinson's Diseases: Insights into Current Medications

Two of the most prevalent neurodegenerative disorders (NDDs), Alzheimer's disease (AD) and Parkinson's disease (PD), present significant challenges to healthcare systems worldwide. While the etiologies of AD and PD differ, both diseases share commonalities in synaptic dysfunction, thereby focusing attention on the role of neurotransmitters. The possible functions that platelets may play in neurodegenerative illnesses including PD and AD are becoming more acknowledged. In AD, platelets have been investigated for their ability to generate amyloid-ß (Aß) peptides, contributing to the formation of neurotoxic plaques. Moreover, platelets are considered biomarkers for early AD diagnosis. In PD, platelets have been studied for their involvement in oxidative stress and mitochondrial dysfunction, which are key factors in the disease's pathogenesis. Emerging research shows that platelets, which release glutamate upon activation, also play a role in these disorders. Decreased glutamate uptake in platelets has been observed in Alzheimer's and Parkinson's patients, pointing to a systemic dysfunction in glutamate handling. This paper aims to elucidate the critical role that glutamate receptors play in the pathophysiology of both AD and PD. Utilizing data from clinical trials, animal models, and cellular studies, we reviewed how glutamate receptors dysfunction contributes to neurodegenerative (ND) processes such as excitotoxicity, synaptic loss, and cognitive impairment. The paper also reviews all current medications including glutamate receptor antagonists for AD and PD, highlighting their mode of action and limitations. A deeper understanding of glutamate receptor involvement including its systemic regulation by platelets could open new avenues for more effective treatments, potentially slowing disease progression and improving patient outcomes.

Parkinson's disease, epilepsy, and amyotrophic lateral sclerosis-emerging role of AMPA and kainate subtypes of ionotropic glutamate receptors

Ionotropic glutamate receptors (iGluRs) mediate the majority of excitatory neurotransmission and are implicated in various neurological disorders. In this review, we discuss the role of the two fastest iGluRs subtypes, namely, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate receptors, in the pathogenesis and treatment of Parkinson's disease, epilepsy, and amyotrophic lateral sclerosis. Although both AMPA and kainate receptors represent promising therapeutic targets for the treatment of these diseases, many of their antagonists show adverse side effects. Further studies of factors affecting the selective subunit expression and trafficking of AMPA and kainate receptors, and a reasonable approach to their regulation by the recently identified novel compounds remain promising directions for pharmacological research.

Neuralized1-Mediated CPEB3 Ubiquitination in the Spinal Dorsal Horn Contributes to the Pathogenesis of Neuropathic Pain in Rats

Compelling evidence has shown that Neuralized1 (Neurl1) facilitates hippocampal-dependent memory storage by modulating cytoplasmic polyadenylation element-binding protein 3 (CPEB3)-dependent protein synthesis. In the current study, we investigated the role of Neurl1 in the pathogenesis of neuropathic pain and the underlying mechanisms. The neuropathic pain was evaluated by lumbar 5 spinal nerve ligation (SNL) in rats. Immunofluorescence staining, Western blotting, qRT-PCR, and coimmunoprecipitation (Co-IP) were performed to investigate the underlying mechanisms. Our results showed that SNL led to an increase of Neurl1 in the spinal dorsal horn. Spinal microinjection of AAV-EGFP-Neurl1 shRNA alleviated mechanical allodynia; decreased the level of CPEB3 ubiquitination; inhibited the production of GluA1, GluA2, and PSD95; and reduced GluA1-containing AMPA receptors in the membrane of the dorsal horn following SNL. Knockdown of spinal CPEB3 decreased the production of GluA1, GluA2, and PSD95 in the dorsal horn and attenuated abnormal pain after SNL. Overexpression of Neurl1 in the dorsal horn resulted in pain-related hypersensitivity in naïve rats; raised the level of CPEB3 ubiquitination; increased the production of GluA1, GluA2, and PSD95; and augmented GluA1-containing AMPA receptors in the membrane in the dorsal horn. Moreover, spinal Neurl1 overexpression-induced mechanical allodynia in naïve rats was partially reversed by repeated intrathecal injections of CPEB3 siRNA. Collectively, our results suggest that SNL-induced upregulation of Neurl1 through CPEB3 ubiquitination-dependent production of GluA1, GluA2, and PSD95 in the dorsal horn contributes to the pathogenesis of neuropathic pain in rats. Targeting spinal Neurl1 might be a promising therapeutic strategy for the treatment of neuropathic pain.

Nigella sativa Oil Improves Motor Skill Learning of Albino Mice: In Vivo and In Silico Investigations

Experimental evidences demonstrated that Nigella sativa oil (NSO) can restore neuronal integrities and processes by increasing the neuronal density, decreasing apoptosis, preventing inflammatory processes, and improving the neurogenic cells in the hippocampus. This refurbishment enhances the learning process and memory. The antioxidant defense mechanism of NSO slows down the process of neurodegeneration and motor deficit. The present study aimed to investigate the effects of NSO on motor skill learning using the single pellet reaching task method on Swiss albino mice, followed by in silico studies. Mice (total of 16) were randomly divided into the control group and treatment group (n = 8). The treatment group received 1 ml/kg b.w. NSO orally once daily for 7 days, and a control group received 1 ml/kg normal saline instead of NSO in a similar manner. The average success rate due to ingestion of NSO in the treatment group mice increased significantly (P < 0.05) compared to controlled mice. Molecular docking analysis revealed that thymoquinone, carvacrol, thymohydroquinone, p-cymene, and t-anethole have binding affinities for the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA-R) that ranges from (-5.1 to -6.2) kcal/mol, which is comparable to the reference ligand glutamic acid binding affinity with AMPA-R (-6.6 kcal/mol). Thymoquinone and carvacrol formed hydrogen bonds with AMPA receptor at TYR61, SER142, and SER143 residues, comparable to the binding affinity of glutamic acid. ADMET analysis reported that all the compounds have higher bioavailability (>90%) and can cross the BBB easily (logBB> 0.3). Based on our experimental data and in silico report, we concluded that the enhanced motor skill learning effects of NSO are due to presence of potent antioxidants-thymoquinone and carvacrol-which might serve as AMPA receptor agonists. These phytoconstituents may play role in synaptic strengthening and promote experience-dependent motor skill learning.

KCTD13-mediated ubiquitination and degradation of GluN1 regulates excitatory synaptic transmission and seizure susceptibility

Temporal lobe epilepsy (TLE) is the most common and severe form of epilepsy in adults; however, its underlying pathomechanisms remain elusive. Dysregulation of ubiquitination is increasingly recognized to contribute to the development and maintenance of epilepsy. Herein, we observed for the first time that potassium channel tetramerization domain containing 13 (KCTD13) protein, a substrate-specific adapter for cullin3-based E3 ubiquitin ligase, was markedly down-regulated in the brain tissue of patients with TLE. In a TLE mouse model, the protein expression of KCTD13 dynamically changed during epileptogenesis. Knockdown of KCTD13 in the mouse hippocampus significantly enhanced seizure susceptibility and severity, whereas overexpression of KCTD13 showed the opposite effect. Mechanistically, GluN1, an obligatory subunit of N-methyl-D-aspartic acid receptors (NMDARs), was identified as a potential substrate protein of KCTD13. Further investigation revealed that KCTD13 facilitates lysine-48-linked polyubiquitination of GluN1 and its degradation through the ubiquitin-proteasome pathway. Besides, the lysine residue 860 of GluN1 is the main ubiquitin site. Importantly, dysregulation of KCTD13 affected membrane expression of glutamate receptors and impaired glutamate synaptic transmission. Systemic administration of the NMDAR inhibitor memantine significantly rescued the epileptic phenotype aggravated by KCTD13 knockdown. In conclusion, our results demonstrated an unrecognized pathway of KCTD13-GluN1 in epilepsy, suggesting KCTD13 as a potential neuroprotective therapeutic target for epilepsy.

Association of Cognitive Deficit with Glutamate and Insulin Signaling in a Rat Model of Parkinson's Disease

Cognitive deficit is a frequent non-motor symptom in Parkinson's disease (PD) with an unclear pathogenesis. Recent research indicates possible involvement of insulin resistance and glutamate excitotoxicity in PD development. We investigated cognitive performance and the brain glutamate and insulin signaling in a rat model of PD induced by bilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA). Cognitive functions were assessed with Passive Avoidance (PA) and Morris Water Maze (MWM) tests. The expression of tyrosine hydroxylase (TH) and proteins involved in insulin (insulin receptor - IR, phosphoinositide 3 kinase - pI3K, extracellular signal-regulated kinases-ERK) and glutamate receptor (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptos-AMPAR, N-methyl-D-aspartate receptor - NMDAR) signaling was assessed in the hippocampus (HPC), hypothalamus (HPT) and striatum (S) by immunofluorescence, Western blot and enzyme-linked immunosorbent assay (ELISA). Three months after 6-OHDA treatment, cognitive deficit was accompanied by decreased AMPAR activity and TH levels (HPC, S), while levels of the proteins involved in insulin signaling remained largely unchanged. Spearman's rank correlation revealed a strong positive correlation for pAMPAR-PA (S), pNMDAR-pI3K (HPC) and pNMDAR-IR (all regions). Additionally, a positive correlation was found for TH-ERK and TH-pI3K, and a negative one for TH-MWM/errors and pI3K-MWM/time (S). These results suggest a possible association between brain glutamate (but not insulin) signaling dysfunction and cognitive deficit in a rat PD model, detected three months after 6-OHDA treatment.

Crosstalk between biochemical signalling network architecture and trafficking governs AMPAR dynamics in synaptic plasticity

Synaptic plasticity involves modification of both biochemical and structural components of neurons. Many studies have revealed that the change in the number density of the glutamatergic receptor AMPAR at the synapse is proportional to synaptic weight update; an increase in AMPAR corresponds to strengthening of synapses while a decrease in AMPAR density weakens synaptic connections. The dynamics of AMPAR are thought to be regulated by upstream signalling, primarily the calcium-CaMKII pathway, trafficking to and from the synapse, and influx from extrasynaptic sources. Previous work in the field of deterministic modelling of CaMKII dynamics has assumed bistable kinetics, while experiments and rule-based modelling have revealed that CaMKII dynamics can be either monostable or ultrasensitive. This raises the following question: how does the choice of model assumptions involving CaMKII dynamics influence AMPAR dynamics at the synapse? To answer this question, we have developed a set of models using compartmental ordinary differential equations to systematically investigate contributions of different signalling and trafficking variations, along with their coupled effects, on AMPAR dynamics at the synaptic site. We find that the properties of the model including network architecture describing different stability features of CaMKII and parameters that capture the endocytosis and exocytosis of AMPAR significantly affect the integration of fast upstream species by slower downstream species. Furthermore, we predict that the model outcome, as determined by bound AMPAR at the synaptic site, depends on (1) the choice of signalling model (bistable CaMKII or monostable CaMKII dynamics), (2) trafficking versus influx contributions and (3) frequency of stimulus. KEY POINTS: The density of AMPA receptors (AMPARs) at the postsynaptic density of the synapse provides a readout of synaptic plasticity, which involves crosstalk between complex biochemical signalling networks including CaMKII dynamics and trafficking pathways including exocytosis and endocytosis. Here we build a model that integrates CaMKII dynamics and AMPAR trafficking to explore this crosstalk. We compare different models of CaMKII that result in monostable or bistable kinetics and their impact on AMPAR dynamics. Our results show that AMPAR density depends on the coupling between aspects of biochemical signalling and trafficking. Specifically, assumptions regarding CaMKII dynamics and its stability features can alter AMPAR density at the synapse. Our model also predicts that the kinetics of trafficking versus influx of AMPAR from the extrasynaptic space can further impact AMPAR density. Thus, the contributions of both signalling and trafficking should be considered in computational models.

Phosphoproteomic dysregulation in Huntington's disease mice is rescued by environmental enrichment

Huntington's disease is a fatal autosomal-dominant neurodegenerative disorder, characterized by neuronal cell dysfunction and loss, primarily in the striatum, cortex and hippocampus, causing motor, cognitive and psychiatric impairments. Unfortunately, no treatments are yet available to modify the progression of the disease. Recent evidence from Huntington's disease mouse models suggests that protein phosphorylation (catalysed by kinases and hydrolysed by phosphatases) might be dysregulated, making this major post-translational modification a potential area of interest to find novel therapeutic targets. Furthermore, environmental enrichment, used to model an active lifestyle in preclinical models, has been shown to alleviate Huntington's disease-related motor and cognitive symptoms. However, the molecular mechanisms leading to these therapeutic effects are still largely unknown. In this study, we applied a phosphoproteomics approach combined with proteomic analyses on brain samples from pre-motor symptomatic R6/1 Huntington's disease male mice and their wild-type littermates, after being housed either in environmental enrichment conditions, or in standard housing conditions from 4 to 8 weeks of age (n = 6 per group). We hypothesized that protein phosphorylation dysregulations occur prior to motor onset in this mouse model, in two highly affected brain regions, the striatum and hippocampus. Furthermore, we hypothesized that these phosphoproteome alterations are rescued by environmental enrichment. When comparing 8-week-old Huntington's disease mice and wild-type mice in standard housing conditions, our analysis revealed 229 differentially phosphorylated peptides in the striatum, compared with only 15 differentially phosphorylated peptides in the hippocampus (statistical thresholds fold discovery rate 0.05, fold change 1.5). At the same disease stage, minor differences were found in protein levels, with 24 and 22 proteins dysregulated in the striatum and hippocampus, respectively. Notably, we found no differences in striatal protein phosphorylation and protein expression when comparing Huntington's disease mice and their wild-type littermates in environmentally enriched conditions. In the hippocampus, only four peptides were differentially phosphorylated between the two genotypes under environmentally enriched conditions, and 22 proteins were differentially expressed. Together, our data indicates that protein phosphorylation dysregulations occur in the striatum of Huntington's disease mice, prior to motor symptoms, and that the kinases and phosphatases leading to these changes in protein phosphorylation might be viable drug targets to consider for this disorder. Furthermore, we show that an early environmental intervention was able to rescue the changes observed in protein expression and phosphorylation in the striatum of Huntington's disease mice and might underlie the beneficial effects of environmental enrichment, thus identifying novel therapeutic targets.

Sex differences in the medial prefrontal cortical glutamate system

BACKGROUND

Dysregulation in the prefrontal cortex underlies a variety of psychiatric illnesses, including substance use disorder, depression, and anxiety. Despite the established sex differences in prevalence and presentation of these illnesses, the neural mechanisms driving these differences are largely unexplored. Here, we investigate potential sex differences in glutamatergic transmission within the medial prefrontal cortex (mPFC). The goal of these experiments was to determine if there are baseline sex differences in transmission within this region that may underlie sex differences in diseases that involve dysregulation in the prefrontal cortex.

METHODS

Adult male and female C57Bl/6J mice were used for all experiments. Mice were killed and bilateral tissue samples were taken from the medial prefrontal cortex for western blotting. Both synaptosomal and total GluA1 and GluA2 levels were measured. In a second set of experiments, mice were killed and ex vivo slice electrophysiology was performed on prepared tissue from the medial prefrontal cortex. Spontaneous excitatory postsynaptic currents and rectification indices were measured.

RESULTS

Females exhibit higher levels of synaptosomal GluA1 and GluA2 in the mPFC compared to males. Despite similar trends, no statistically significant differences are seen in total levels of GluA1 and GluA2. Females also exhibit both a higher amplitude and higher frequency of spontaneous excitatory postsynaptic currents and greater inward rectification in the mPFC compared to males.

CONCLUSIONS

Overall, we conclude that there are sex differences in glutamatergic transmission in the mPFC. Our data suggest that females have higher levels of glutamatergic transmission in this region. This provides evidence that the development of sex-specific pharmacotherapies for various psychiatric diseases is important to create more effective treatments.

The upregulation of glutamate decarboxylase 67 against hippocampal excitability damage in male fetal rats by prenatal caffeine exposure

As a kind of xanthine alkaloid, caffeine is widely present in beverages, food, and analgesic drugs. Our previous studies have shown that prenatal caffeine exposure (PCE) can induce programmed hypersensitivity of the hypothalamic-pituitary-adrenal (HPA) axis in offspring rats, which is involved in developing many chronic adult diseases. The present study further examined the potential molecular mechanism and toxicity targets of hippocampal dysfunction, which might mediate the programmed hypersensitivity of the HPA axis in offspring. Pregnant rats were intragastrically administered with 0, 30, and 120 mg/kg/day caffeine from gestational days (GD) 9-20, and the fetal rats were extracted at GD20. Rat fetal hippocampal H19-7/IGF1R cell line was treated with caffeine, adenosine A2A receptor (A2AR) agonist (CGS-21680) or adenylate cyclase agonist (forskolin) plus caffeine. Compared with the control group, hippocampal neurons of male fetal rats by PCE displayed increased apoptosis and reduced synaptic plasticity, whereas glutamate decarboxylase 67 (GAD67) expression was increased. Moreover, the expression of A2AR was down-regulated, PCE inhibited the cAMP/PKA/CREB/BDNF/TrkB pathway. Furthermore, the results in vitro were consistent with the in vivo study. Both CGS21680 and forskolin could reverse the above alteration caused by caffeine. These results indicated that PCE inhibits the BDNF pathway and mediates the hippocampus's glutamate (Glu) excitotoxicity. The compensatory up-regulation of GAD67 unbalanced the Glu/gamma-aminobutyric acid (GABA)ergic output, leading to the impaired negative feedback to the hypothalamus and hypersensitivity of the HPA axis.

RNF220 is an E3 ubiquitin ligase for AMPA receptors to regulate synaptic transmission

The accurate expression of postsynaptic AMPA receptors (AMPARs) is critical for information processing in the brain, and ubiquitination is a key regulator for this biological process. However, the roles of E3 ubiquitin ligases in the regulation of AMPARs are poorly understood. Here, we find that RNF220 directly interacts with AMPARs to meditate their polyubiquitination, and RNF220 knockout specifically increases AMPAR protein levels, thereby enhancing basal synaptic activity while impairing synaptic plasticity. Moreover, depending on its E3 ubiquitin ligase activity, RNF220 represses AMPAR-mediated excitatory synaptic responses and their neuronal surface expression. Furthermore, learning and memory are altered in forebrain RNF220-deficient mice. In addition, two neuropathology-related RNF220 variants fail to repress excitatory synaptic activity because of the incapability to regulate AMPAR ubiquitination due to their attenuated interaction. Together, we identify RNF220 as an E3 ubiquitin ligase for AMPARs and establish its substantial role in excitatory synaptic transmission and brain function.

Development and Validation of Arc Nanobodies: New Tools for Probing Arc Dynamics and Function

Activity-regulated cytoskeleton-associated (Arc) protein plays key roles in long-term synaptic plasticity, memory, and cognitive flexibility. However, an integral understanding of Arc mechanisms is lacking. Arc is proposed to function as an interaction hub in neuronal dendrites and the nucleus, yet Arc can also form retrovirus-like capsids with proposed roles in intercellular communication. Here, we sought to develop anti-Arc nanobodies (ArcNbs) as new tools for probing Arc dynamics and function. Six ArcNbs representing different clonal lines were selected from immunized alpaca. Immunoblotting with recombinant ArcNbs fused to a small ALFA-epitope tag demonstrated binding to recombinant Arc as well as endogenous Arc from rat cortical tissue. ALFA-tagged ArcNb also provided efficient immunoprecipitation of stimulus-induced Arc after carbachol-treatment of SH-SY5Y neuroblastoma cells and induction of long-term potentiation in the rat dentate gyrus in vivo. Epitope mapping showed that all Nbs recognize the Arc C-terminal region containing the retroviral Gag capsid homology domain, comprised of tandem N- and C-lobes. ArcNbs E5 and H11 selectively bound the N-lobe, which harbors a peptide ligand binding pocket specific to mammals. Four additional ArcNbs bound the region containing the C-lobe and C-terminal tail. For use as genetically encoded fluorescent intrabodies, we show that ArcNbs fused to mScarlet-I are uniformly expressed, without aggregation, in the cytoplasm and nucleus of HEK293FT cells. Finally, mScarlet-I-ArcNb H11 expressed as intrabody selectively bound the N-lobe and enabled co-immunoprecipitation of full-length intracellular Arc. ArcNbs are versatile tools for live-cell labeling and purification of Arc, and interrogation of Arc capsid domain specific functions.

Different Synaptic Plasticity After Physiological and Psychological Stress in the Anterior Insular Cortex in an Observational Fear Mouse Model

Post-traumatic stress disorder (PTSD) can be triggered not only in people who have personally experienced traumatic events but also in those who witness them. Physiological and psychological stress can have different effects on neural activity, but little is known about the underlying mechanisms. There is ample evidence that the insular cortex, especially the anterior insular cortex (aIC), is critical to both the sensory and emotional experience of pain. It is therefore worthwhile to explore the effects of direct and indirect stress on the synaptic plasticity of the aIC. Here, we used a mouse model of observational fear to mimic direct suffering (Demonstrator, DM) and witnessing (Observer, OB) of traumatic events. After observational fear training, using a 64-channel recording system, we showed that both DM and OB mice exhibited a decreased ratio of paired-pulse with intervals of 50 ms in the superficial layers of the aIC but not in the deep layers. We found that theta-burst stimulation (TBS)–induced long-term potentiation (LTP) in OB mice was significantly higher than in DM mice, and the recruitment of synaptic responses occurred only in OB mice. Compared with naive mice, OB mice showed stronger recruitment and higher amplitude in the superficial layers of the aIC. We also used low-frequency stimulation (LFS) to induce long-term depression (LTD). OB mice showed greater LTD in both the superficial and deep layers of the aIC than naive mice, but no significant difference was found between OB and DM mice. These results provide insights into the changes in synaptic plasticity in the aIC after physiological and psychological stress, and suggest that different types of stress may have different mechanisms. Furthermore, identification of the possible causes of the differences in stress could help treat stress-related disorders.

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

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

AMPA Receptor Function in Hypothalamic Synapses

AMPA receptors (AMPARs) are critical for mediating glutamatergic synaptic transmission and plasticity, thus playing a major role in the molecular machinery underlying cellular substrates of memory and learning. Their expression pattern, transport and regulatory mechanisms have been extensively studied in the hippocampus, but their functional properties in other brain regions remain poorly understood. Interestingly, electrophysiological and molecular evidence has confirmed a prominent role of AMPARs in the regulation of hypothalamic function. This review summarizes the existing evidence on AMPAR-mediated transmission in the hypothalamus, where they are believed to orchestrate the role of glutamatergic transmission in autonomous, neuroendocrine function, body homeostasis, and social behavior.

Substance abuse and neurotransmission

The number of people who suffer from a substance abuse disorder has continued to rise over the last decade; particularly, the number of drug-related overdose deaths has sharply increased during the COVID-19 pandemic. Converging lines of clinical observations, supported by imaging and neuropsychological performance testing, have demonstrated that substance abuse-induced dysregulation of neurotransmissions in the brain is critical for development and expression of the addictive properties of abused substances. Recent scientific advances have allowed for better understanding of the neurobiological processes that mediates drugs of abuse and addiction. This chapter presents the past classic concepts and the recent advances in our knowledge about how cocaine, amphetamines, opioids, alcohol, and nicotine alter multiple neurotransmitter systems, which contribute to the behaviors associated with each drug. Additionally, we discuss the interactive effects of HIV-1 or COVID-19 and substance abuse on neurotransmission and neurobiological pathways. Finally, we introduce therapeutic strategies for development of pharmacotherapies for substance abuse disorders.

N-Cadherin Regulates GluA1-Mediated Depressive-Like Behavior in Adolescent Female Rat Offspring following Prenatal Stress

BACKGROUND

The incidence of depression is twice higher in women than in men, and gender differences in the prevalence rates first emerge around puberty. Prenatal stress (PS) induces gender-dependent depressive-like behavior in adolescent offspring, but the neuro-physiological mechanisms remain unclear. Our study aimed to investigate the possible neuro-physiological mechanisms of gender-dependent depressive-like behavior in PS adolescent offspring and further explored the possibility of treating depression in adolescent female rats.

METHODS

The pregnant rats were exposed to restraint stress in the third trimester for 7 days. The depressive-like behavior and the expression of N-cadherin and AMPARs in the hippocampus of adolescent offspring rats were assessed. 10 mg/kg AMPAR antagonist CNQX and 10 mg/kg N-cadherin antagonist ADH-1 were intraperitoneally injected into female adolescent offspring, respectively; 0.2 µg AMPAR agonist CX546 was administered to the dentate gyrus of male adolescent offspring to determine the role of N-cadherin-AMPARs in depressive-like behavior of the offspring following PS.

RESULTS

We found that PS increased N-cadherin expression, which upregulated GluA1 expression in the dentate gyrus, mediating depressive-like behavior in adolescent female rat offspring by reducing PSD-95. In addition, ADH-1 and CNQX improved depressive-like behavior in adolescent female offspring following PS. Furthermore, injection of the CX546 into the dentate gyrus induced depressive-like behavior in PS male offspring.

CONCLUSION

The gender-dependent expression of N-cadherin-GluA1 pathway in adolescent offspring in the dentate gyrus was the key factor in gender differences of depressive-like behavior following PS.

AMPA Receptors: A Key Piece in the Puzzle of Memory Retrieval

Retrieval constitutes a highly regulated and dynamic phase in memory processing. Its rapid temporal scales require a coordinated molecular chain of events at the synaptic level that support transient memory trace reactivation. AMPA receptors (AMPAR) drive the majority of excitatory transmission in the brain and its dynamic features match the singular fast timescales of memory retrieval. Here we provide a review on AMPAR contribution to memory retrieval regarding its dynamic movements along the synaptic compartments, its changes in receptor number and subunit composition that take place in activity dependent processes associated with retrieval. We highlight on the differential regulations exerted by AMPAR subunits in plasticity processes and its impact on memory recall.

Modulatory effects of photobiomodulation in the anterior cingulate cortex of diabetic rats

Anterior Cingulate Cortex (ACC) has a crucial contribution to higher order pain processing. Photobiomodulation (PBM) has being used as integrative medicine for pain treatment and for a variety of nervous system disorders. This study evaluated the effects of PBM in the ACC of diabetic rats. Type 1 diabetes was induced by a single dose of streptozotocin (85 mg/Kg). A total of ten sessions of PBM (pulsed gallium-arsenide laser, 904 nm, 9500 Hz, 6.23 J/cm²) was applied to the rat peripheral nervous system. Glial fibrillary acidic protein (GFAP), mu-opioid receptor (MOR), glutamate receptor 1 (GluR1), and glutamic acid decarboxylase (GAD65/67) protein level expression were analyzed in the ACC of diabetic rats treated with PBM. Our data revealed that PBM decreased 79.5% of GFAP protein levels in the ACC of STZ rats. Moreover, STZ + PBM rats had protein levels of MOR increased 14.7% in the ACC. Interestingly, STZ + PBM rats had a decrease in 70.7% of GluR1 protein level in the ACC. Additionally, PBM decreased 45.5% of GAD65/67 protein levels in the ACC of STZ rats.

Synaptic Reshaping and Neuronal Outcomes in the Temporal Lobe Epilepsy

Temporal lobe epilepsy (TLE) is one of the most common types of focal epilepsy, characterized by recurrent spontaneous seizures originating in the temporal lobe(s), with mesial TLE (mTLE) as the worst form of TLE, often associated with hippocampal sclerosis. Abnormal epileptiform discharges are the result, among others, of altered cell-to-cell communication in both chemical and electrical transmissions. Current knowledge about the neurobiology of TLE in human patients emerges from pathological studies of biopsy specimens isolated from the epileptogenic zone or, in a few more recent investigations, from living subjects using positron emission tomography (PET). To overcome limitations related to the use of human tissue, animal models are of great help as they allow the selection of homogeneous samples still presenting a more various scenario of the epileptic syndrome, the presence of a comparable control group, and the availability of a greater amount of tissue for in vitro/ex vivo investigations. This review provides an overview of the structural and functional alterations of synaptic connections in the brain of TLE/mTLE patients and animal models.

The emerging role of kainate receptor functional dysregulation in pain

Pain is a serious clinical challenge, and is associated with a significant reduction in quality of life and high financial costs for affected patients. Research efforts have been made to explore the etiological basis of pain to guide the future treatment of patients suffering from pain conditions. Findings from studies using KA (kainate) receptor agonist, antagonists and receptor knockout mice suggested that KA receptor dysregulation and dysfunction may govern both peripheral and central sensitization in the context of pain. Additional evidence showed that KA receptor dysfunction may disrupt the finely-tuned process of glutamic acid transmission, thereby contributing to the onset of a range of pathological contexts. In the present review, we summarized major findings in recent studies which examined the roles of KA receptor dysregulation in nociceptive transmission and in pain. This timely overview of current knowledge will help to provide a framework for future developing novel therapeutic strategies to manage pain.