Regulation of AMPAR expression by microRNAs

(2R, 6R)-hydroxynorketamine ameliorates PTSD-like behaviors during the reconsolidation phase of fear memory in rats by modulating the VGF/BDNF/GluA1 signaling pathway in the hippocampus

RATIONALE

Fear memory, a fundamental symptom of post-traumatic stress disorder (PTSD), is improved by (2R, 6R)-hydroxynorketamine ((2R, 6R)-HNK) administration. However, the phase of fear memory in which the injected drug is the most effective at mitigating PTSD-like effects remains unknown.

OBJECTIVE

This study aimed to explore the effects of (2 R, 6 R)-HNK administration during three phases [acquisition (AP), reconsolidation (RP), and extinction (EP)] on PTSD-like behaviors in single prolonged stress (SPS) and contextual fear conditioning (CFC) rat models. The effects of VGF-inducible type of nerve growth factor (VGF), brain-derived neurotrophic factor (BDNF), and GluA1 on hippocampus (HIP) expression were also explored.

METHODS

SPS and CFC (SPSC) were used to establish a PTSD rat model. After lateral ventricle injection of 5 μL (2 R, 6 R)-HNK (0.5 nmol). Anxiety-depression-like behaviors were assessed in rats by the open field test (OFT) and elevated plus maze test (EPMT). Situational fear responses were evaluated in rodents by freezing behavior test (FBT) test. In addition, GluA1, VGF, and BDNF were assessed in the hippocampus by Western blot assay (WB) and Immunohistochemistry assay (IF).

RESULTS

SPSC procedure induced PTSD-like behaviors. The SPSC group had decreased spontaneous exploratory behavior and increased fear response. The (2R, 6R)-HNK group showed improved SPSC-induced reduction in GluA1, VGF, and BDNF levels in the HIP. During RP, anxiety and fear avoidance behaviors were alleviated, and the protein levels of GluA1, VGF, and BDNF in the HIP were restored. In contrast, no significant improvement was noted during AP and EP.

CONCLUSIONS

(2R,6R)-HNK modulates the VGF/BDNF/GluA1 signaling pathway in the hippocampus and improves PTSD-like behaviors during the reconsolidation phase of fear memory in rats, which may provide a new target for the clinical treatment and prevention of fear-related disorders such as PTSD.

Dopamine D2 Receptor Activation Blocks GluA2/ROS Positive Feedback Loop to Alienate Chronic-Migraine-Associated Pain Sensitization

Chronic migraine is a disabling disorder without effective therapeutic medicine. AMPA receptors have been proven to be essential to pathological pain and headaches, but the related regulatory mechanisms in chronic migraine have not yet been explored. In this study, we found that the level of surface GluA2 was reduced in chronic migraine rats. Tat-GluR23Y (a GluA2 endocytosis inhibitor) reduced calcium inward flow and weakened synaptic structures, thus alleviating migraine-like pain sensitization. In addition, the inhibition of GluA2 endocytosis reduced the calcium influx and alleviated mitochondrial calcium overload and ROS generation in primary neurons. Furthermore, our results showed that ROS can induce allodynia and GluA2 endocytosis in rats, thus promoting migraine-like pain sensitization. In our previous study, the dopamine D2 receptor was identified as a potential target in the treatment of chronic migraine, and here we found that dopamine D2 receptor activation suppressed chronic-migraine-related pain sensitization through blocking the GluA2/ROS positive feedback loop in vivo and in vitro. Additionally, ligustrazine, a core component of ligusticum chuanxiong, was shown to target the dopamine D2 receptor, thereby alleviating ROS production and abnormal nociception in CM rats. This study provides valuable insight into the treatment of chronic migraine.

Molecular Mechanisms of AMPA Receptor Trafficking in the Nervous System

Synaptic plasticity enhances or reduces connections between neurons, affecting learning and memory. Postsynaptic AMPARs mediate greater than 90% of the rapid excitatory synaptic transmission in glutamatergic neurons. The number and subunit composition of AMPARs are fundamental to synaptic plasticity and the formation of entire neural networks. Accordingly, the insertion and functionalization of AMPARs at the postsynaptic membrane have become a core issue related to neural circuit formation and information processing in the central nervous system. In this review, we summarize current knowledge regarding the related mechanisms of AMPAR expression and trafficking. The proteins related to AMPAR trafficking are discussed in detail, including vesicle-related proteins, cytoskeletal proteins, synaptic proteins, and protein kinases. Furthermore, significant emphasis was placed on the pivotal role of the actin cytoskeleton, which spans throughout the entire transport process in AMPAR transport, indicating that the actin cytoskeleton may serve as a fundamental basis for AMPAR trafficking. Additionally, we summarize the proteases involved in AMPAR post-translational modifications. Moreover, we provide an overview of AMPAR transport and localization to the postsynaptic membrane. Understanding the assembly, trafficking, and dynamic synaptic expression mechanisms of AMPAR may provide valuable insights into the cognitive decline associated with neurodegenerative diseases.

MicroRNAs in Myocarditis-Review of the Preclinical In Vivo Trials

Myocarditis is an inflammatory heart disease with viruses as the most common cause. Regardless of multiple studies that have recently been conducted, the diagnostic options still need to be improved. Although endomyocardial biopsy is known as a diagnostic gold standard, it is invasive and, thus, only sometimes performed. Novel techniques of cardiac magnetic resonance are not readily available. Therapy in viral infections is based mainly on symptomatic treatment, while steroids and intravenous immunoglobulins are used in autoimmune myocarditis. The effectiveness of neither of these methods has been explicitly proven to date. Therefore, novel diagnostic and therapeutic strategies are highly needed. MiRNAs are small, non-coding molecules that regulate fundamental cell functions, including differentiation, metabolism, and apoptosis. They present altered levels in different diseases, including myocarditis. Numerous studies investigating the role of miRNAs in myocarditis have already been conducted. In this review, we discussed only the original preclinical in vivo research. We eventually included 30 studies relevant to the discussed area. The altered miRNA levels have been observed, including upregulation and downregulation of different miRNAs in the mice models of myocarditis. Furthermore, the administration of mimics or inhibitors of particular miRNAs was shown to significantly influence inflammation, morphology, and function of the heart and overall survival. Finally, some studies presented prospective advantages in vaccine development.

Ethanol-induced AMPA alterations are mediated by mGLU5 receptors through miRNA upregulation in hippocampal slices

Prenatal alcohol exposure (PAE) affects neuronal networks and brain development causing a range of physical, cognitive and behavioural disorders in newborns that persist into adulthood. The array of consequences associated with PAE can be grouped under the umbrella-term 'fetal alcohol spectrum disorders' (FASD). Unfortunately, there is no cure for FASD as the molecular mechanisms underlying this pathology are still unknown. We have recently demonstrated that chronic EtOH exposure, followed by withdrawal, induces a significant decrease in AMPA receptor (AMPAR) expression and function in developing hippocampus in vitro. Here, we explored the EtOH-dependent pathways leading to hippocampal AMPAR suppression. Organotypic hippocampal slices (2 days in cultures) were exposed to EtOH (150 mM) for 7 days followed by 24 h EtOH withdrawal. Then, the slices were analysed by means of RT-PCR for miRNA content, western blotting for AMPA and NMDA related-synaptic proteins expression in postsynaptic compartment and electrophysiology to record electrical properties from CA1 pyramidal neurons. We observed that EtOH induces a significant downregulation of postsynaptic AMPA and NMDA subunits and relative scaffolding protein expression and, accordingly, a decrease of AMPA-mediated neurotransmission. Simultaneously, we found that chronic EtOH induced-upregulation of miRNA 137 and 501-3p and decreased AMPA-mediated neurotransmission are prevented by application of the selective mGlu5 antagonist MPEP during EtOH withdrawal. Our data indicate mGlu5 via miRNA137 and 501-3p expression as key factors in the regulation of AMPAergic neurotransmission that may contribute, at least in part, to the pathogenesis of FASD.

Exogenous AMPA downregulates gamma-frequency network oscillation in CA3 of rat hippocampal slices

Pharmacologically-induced persistent hippocampal γ oscillation in area CA3 requires activation of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs). However, we demonstrated that exogenous AMPA dose-dependently inhibited carbachol (CCH)-induced γ oscillation in the CA3 area of rat hippocampal slices, but the underlying mechanism is not clear. Application of AMPARs antagonist NBQX (1 μM) did not affect γ oscillation power (γ power), nor AMPA-mediated γ power reduction. At 3 μM, NBQX had no effect on γ power but largely blocked AMPA-mediated γ power reduction. Ca2+-permeable AMPA receptor (CP-AMPAR) antagonist IEM1460 or CaMKK inhibitor STO-609 but not CaMKIIα inhibitor KN93 enhanced γ power, indicating that activation of CP-AMPAR or CaMKK negatively modulated CCH-induced γ oscillation. Either CP-AMPAR antagonist or CaMKK inhibitor alone did not affected AMPA-mediated γ power reduction, but co-administration of IEM1460 and NBQX (1 μM) largely prevented AMPA-mediated downregulation of γ suggesting that CP-AMPARs and CI-AMPARs are involved in AMPA downregulation of γ oscillation. The recurrent excitation recorded at CA3 stratum pyramidale was significantly reduced by AMPA application. Our results indicate that AMPA downregulation of γ oscillation may be related to the reduced recurrent excitation within CA3 local neuronal network due to rapid CI-AMPAR and CP-AMPAR activation.

The many faces of the AMPA-type ionotropic glutamate receptor

Knowledge of the biology of ionotropic glutamate receptors (iGluRs) is a prerequisite for any student of the neurosciences. But yet, half a century ago, the situation was quite different. There was fierce debate on whether simple amino acids, such as l-glutamic acid (L-Glu), should even be considered as putative neurotransmitter candidates that drive excitatory synaptic signaling in the vertebrate brain. Organic chemist, Jeff Watkins, and physiologist, Dick Evans, were amongst the pioneering scientists who shed light on these tribulations. By combining their technical expertise, they performed foundational work that explained that the actions of L-Glu were, in fact, mediated by a family of ion-channels that they named NMDA-, AMPA- and kainate-selective iGluRs. To celebrate and reflect upon their seminal work, Neuropharmacology has commissioned a series of issues that are dedicated to each member of the Glutamate receptor superfamily that includes both ionotropic and metabotropic classes. This issue brings together nine timely reviews from researchers whose work has brought renewed focus on AMPA receptors (AMPARs), the predominant neurotransmitter receptor at central synapses. Together with the larger collection of papers on other GluR family members, these issues highlight that the excitement, passion, and clarity that Watkins and Evans brought to the study of iGluRs is unlikely to fade as we move into a new era on this most interesting of ion-channel families.