Unconditioned- and Conditioned- Stimuli Induce Differential Memory Reconsolidation and β-AR-Dependent CREB Activation

Windows of change: Revisiting temporal and molecular dynamics of memory reconsolidation and persistence

Retrieval can bring memories to a labile state, creating a window to modify its content during reconsolidation. Numerous studies have investigated this period to elucidate reconsolidation mechanisms, understand long-term memory persistence, and develop therapeutic strategies for memory-related psychiatric disorders. However, the temporal dynamics of post-retrieval memory processes have been largely overlooked, leading to mixed findings and hindering the development of targeted interventions. This review discusses retrieval-related cellular and molecular events and how they develop in series and parallel across time. Emerging evidence suggests that some mechanisms triggered after fear memory retrieval can influence either reconsolidation or persistence in different time windows. The temporal boundaries of these post-retrieval processes are still unclear. Further research integrating behavioral and molecular approaches to a deeper understanding of reconsolidation and persistence temporal dynamics is essential to address current debates, including which system/pathway offers the most effective therapeutic window of opportunity.

How Fear Memory is Updated: From Reconsolidation to Extinction?

Post-traumatic stress disorder (PTSD) is a psychiatric disorder caused by traumatic past experiences, rooted in the neurocircuits of fear memory formation. Memory processes include encoding, storing, and recalling to forgetting, suggesting the potential to erase fear memories through timely interventions. Conventional strategies such as medications or electroconvulsive therapy often fail to provide permanent relief and come with significant side-effects. This review explores how fear memory may be erased, particularly focusing on the mnemonic phases of reconsolidation and extinction. Reconsolidation strengthens memory, while extinction weakens it. Interfering with memory reconsolidation could diminish the fear response. Alternatively, the extinction of acquired memory could reduce the fear memory response. This review summarizes experimental animal models of PTSD, examines the nature and epidemiology of reconsolidation to extinction, and discusses current behavioral therapy aimed at transforming fear memories to treat PTSD. In sum, understanding how fear memory updates holds significant promise for PTSD treatment.

An Expanded Narrative Review of Neurotransmitters on Alzheimer's Disease: The Role of Therapeutic Interventions on Neurotransmission

Alzheimer's disease (AD) is a progressive neurodegenerative disease. The accumulation of amyloid-β (Aβ) plaques and tau neurofibrillary tangles are the key players responsible for the pathogenesis of the disease. The accumulation of Aβ plaques and tau affect the balance in chemical neurotransmitters in the brain. Thus, the current review examined the role of neurotransmitters in the pathogenesis of Alzheimer's disease and discusses the alterations in the neurochemical activity and cross talk with their receptors and transporters. In the presence of Aβ plaques and neurofibrillary tangles, changes may occur in the expression of neuronal receptors which in turn triggers excessive release of glutamate into the synaptic cleft contributing to cell death and neuronal damage. The GABAergic system may also be affected by AD pathology in a similar way. In addition, decreased receptors in the cholinergic system and dysfunction in the dopamine neurotransmission of AD pathology may also contribute to the damage to cognitive function. Moreover, the presence of deficiencies in noradrenergic neurons within the locus coeruleus in AD suggests that noradrenergic stimulation could be useful in addressing its pathophysiology. The regulation of melatonin, known for its effectiveness in enhancing cognitive function and preventing Aβ accumulation, along with the involvement of the serotonergic system and histaminergic system in cognition and memory, becomes remarkable for promoting neurotransmission in AD. Additionally, nitric oxide and adenosine-based therapeutic approaches play a protective role in AD by preventing neuroinflammation. Overall, neurotransmitter-based therapeutic strategies emerge as pivotal for addressing neurotransmitter homeostasis and neurotransmission in the context of AD. This review discussed the potential for neurotransmitter-based drugs to be effective in slowing and correcting the neurodegenerative processes in AD by targeting the neurochemical imbalance in the brain. Therefore, neurotransmitter-based drugs could serve as a future therapeutic strategy to tackle AD.

Microglial activation in the medial prefrontal cortex after remote fear recall participates in the regulation of auditory fear extinction

Excessive or inappropriate fear responses can lead to anxiety-related disorders, such as post-traumatic stress disorder (PTSD). Studies have shown that microglial activation occurs after fear conditioning and that microglial inhibition impacts fear memory. However, the role of microglia in fear memory recall remains unclear. In this study, we investigated the activated profiles of microglia after the recall of remote-cued fear memory and the role of activated microglia in the extinction of remote-cued fear in adult male C57BL/6 mice. The results revealed that the expression of the microglia marker Iba1 increased in the medial prefrontal cortex (mPFC) at 10 min and 1 h following remote-cued fear recall, which was accompanied by amoeboid morphology. Inhibiting microglial activation through PLX3397 treatment before remote fear recall did not affect recall, reconsolidation, or regular extinction but facilitated recall-extinction and mitigated spontaneous recovery. Moreover, our results demonstrated reduced co-expression of Iba1 and postsynaptic density protein 95 (PSD95) in the mPFC, along with decreases in the p-PI3K/PI3K ratio, p-Akt/Akt ratio, and KLF4 expression after PLX3397 treatment. Our results suggest that microglial activation after remote fear recall impedes fear extinction through the pruning of synapses in the mPFC, accompanied by alterations in the expression of the PI3K/AKT/KLF4 pathway. This finding can help elucidate the mechanism involved in remote fear extinction, contributing to the theoretical foundation for the intervention and treatment of PTSD.

Phosphodiesterase 4 inhibition after retrieval switches the memory fate favoring extinction instead of reconsolidation

Phosphodiesterase 4 (PDE4), an enzyme expressed in the dorsal hippocampus (DH), hydrolyzes the cAMP, limiting the PKA-induced CREB phosphorylation (pCREB) and BDNF expression. Depending on the brain region, PKA and pCREB mediate reconsolidation or extinction, whereas BDNF is mainly related to extinction facilitation. The mechanisms underpinning the switch between reconsolidation and extinction are relatively unknown. Here, we tested the hypothesis that PDE4 might control these processes. We showed in Wistar rats submitted to contextual fear conditioning that PDE4 inhibition with roflumilast (ROF) within the DH, after a short retrieval, did not change freezing behavior after one day (TestA1). After 10 days, the ROF-treated group significantly reduced the expression of freezing behavior. This effect depended on retrieval, Test A1 exposure, and reinstated after a remainder foot shock, suggesting an extinction facilitation. The ROF effect depended on PKA after retrieval or, protein synthesis after Test A1. After retrieval, ROF treatment did not change the pCREB/CREB ratio in the DH. It enhanced proBDNF expression without changing pre-proBDNF or mature BDNF in the DH after Test A1. The results suggest that the inhibition of PDE4 in the DH after a short retrieval changes the memory sensibility from reconsolidation to extinction via regulating proBDNF expression.

A PAM of the α1A-Adrenergic receptor rescues biomarker, long-term potentiation, and cognitive deficits in Alzheimer's disease mouse models without effects on blood pressure

α1-Adrenergic Receptors (ARs) regulate the sympathetic nervous system by the binding of norepinephrine (NE) and epinephrine (Epi) through different subtypes (α1A, α1B, α1D). α1A-AR activation is hypothesized to be memory forming and cognitive enhancing but drug development has been stagnant due to unwanted side effects on blood pressure. We recently reported the pharmacological characterization of the first positive allosteric modulator (PAM) for the α1A-AR with predictive pro-cognitive and memory properties. In this report, we now demonstrate the in vivo characteristics of Compound 3 (Cmpd-3) in two genetically-different Alzheimer's Disease (AD) mouse models. Drug metabolism and pharmacokinetic studies indicate sufficient brain penetrance and rapid uptake into the brain with low to moderate clearance, and a favorable inhibition profile against the major cytochrome p450 enzymes. Oral administration of Cmpd-3 (3-9 mg/kg QD) can fully rescue long-term potentiation defects and AD biomarker profile (amyloid β-40, 42) within 3 months of dosing to levels that were non-significant from WT controls and which outperformed donepezil (1 mg/kg QD). There were also significant effects on paired pulse facilitation and cognitive behavior. Long-term and high-dose in vivo studies with Cmpd-3 revealed no effects on blood pressure. Our results suggest that Cmpd-3 can maintain lasting therapeutic levels and efficacy with disease modifying effects with a once per day dosing regimen in AD mouse models with no observed side effects.

Single cell molecular alterations reveal target cells and pathways of conditioned fear memory

OBJECTIVES

Recent evidence indicates that hippocampus is important for conditioned fear memory (CFM). Though few studies consider the roles of various cell types' contribution to such a process, as well as the accompanying transcriptome changes during this process. The purpose of this study was to explore the transcriptional regulatory genes and the targeted cells that are altered by CFM reconsolidation.

METHODS

A fear conditioning experiment was established on adult male C57 mice, after day 3 tone-cued CFM reconsolidation test, hippocampus cells were dissociated. Using single cell RNA sequencing (scRNA-seq) technique, alterations of transcriptional genes expression were detected and cell cluster analysis were performed and compared with those in sham group.

RESULTS

Seven non-neuronal and eight neuronal cell clusters (including four known neurons and four newly identified neuronal subtypes) has been explored. Among them, CA subtype 1 has characteristic gene markers of Ttr and Ptgds, which is speculated to be the outcome of acute stress and promotes the production of CFM. The results of KEGG pathway enrichment indicate the differences in the expression of certain molecular protein functional subunits in long-term potentiation (LTP) pathway between two types of neurons (DG and CA1) and astrocytes, thus providing a new transcriptional perspective for the role of hippocampus in the CFM reconsolidation. More importantly, the correlation between the reconsolidation of CFM and neurodegenerative diseases-linked genes is substantiated by the results from cell-cell interactions and KEGG pathway enrichment. Further analysis shows that the reconsolidation of CFM inhibits the risk-factor genes App and ApoE in Alzheimer's Disease (AD) and activates the protective gene Lrp1.

CONCLUSIONS

This study reports the transcriptional genes expression changes of hippocampal cells driven by CFM, which confirm the involvement of LTP pathway and suggest the possibility of CFM-like behavior in preventing AD. However, the current research is limited to normal C57 mice, and further studies on AD model mice are needed to prove this preliminary conclusion.

Characterization of a novel positive allosteric modulator of the α1A-Adrenergic receptor

α1-Adrenergic Receptors (ARs) are G-protein Coupled Receptors (GPCRs) that regulate the sympathetic nervous system via the binding and activation of norepinephrine (NE) and epinephrine (Epi). α1-ARs control various aspects of neurotransmission, cognition, cardiovascular functions as well as other organ systems. However, therapeutic drug development for these receptors, particularly agonists, has been stagnant due to unwanted effects on blood pressure regulation. We report the synthesis and characterization of the first positive allosteric modulator (PAM) for the α1-AR based upon the derivation of the α1A-AR selective imidazoline agonist, cirazoline. Compound 3 (Cmpd-3) binds the α1A-AR with high and low affinity sites (0.13pM; 54 ​nM) typical of GPCR agonists, and reverts to a single low affinity site of 100 ​nM upon the addition of GTP. Comparison of Cmpd-3 versus other orthosteric α1A-AR-selective imidazoline ligands reveal unique properties that are consistent with a type I PAM. Cmpd-3 is both conformationally and ligand-selective for the α1A-AR subtype. In competition binding studies, Cmpd-3 potentiates NE-binding at the α1A-AR only on the high affinity state of NE with no effect on the Epi-bound α1A-AR. Moreover, Cmpd-3 demonstrates signaling-bias and potentiates the NE-mediated cAMP response of the α1A-AR at nM concentrations with no effects on the NE-mediated inositol phosphate response. There are no effects of Cmpd-3 on the signaling at the α1B- or α1D-AR subtypes. Cmpd-3 displays characteristics of a pure PAM with no intrinsic agonist properties. Specific derivation of Cmpd-3 at the R1 ortho-position recapitulated PAM characteristics. Our results characterize the first PAM for the α1-AR and holds promise for a first-in-class therapeutic to treat various diseases without the side effect of increasing blood pressure intrinsic to classical orthosteric agonists.

Propranolol versus Other Selected Drugs in the Treatment of Various Types of Anxiety or Stress, with Particular Reference to Stage Fright and Post-Traumatic Stress Disorder

Propranolol, a non-cardioselective β1,2 blocker, is most commonly recognised for its application in the therapy of various cardiovascular conditions, such as hypertension, coronary artery disease, and tachyarrhythmias. However, due to its ability to cross the blood-brain barrier and affinity towards multiple macromolecules, not only adrenoreceptors, it has also found application in other fields. For example, it is one of the very few medications successfully applied in the treatment of stage fright. This review focuses on the application of propranolol in the treatment of various types of anxiety and stress, with particular reference to stage fright and post-traumatic stress disorder (PTSD). Both mechanisms of action as well as comparison with other therapies are presented. As those indications for propranolol are, in most countries, considered off-label, this review aims to gather information that can be useful while making a decision about the choice of propranolol as a drug in the treatment of those mental conditions.

Effects of propranolol on the modification of trauma memory reconsolidation in PTSD patients: A systematic review and meta-analysis

Post-traumatic stress disorder (PTSD) develops after an exposure to a life-threatening event and is characterized by intrusive memories. According to memory reconsolidation theory retrieval of memory under certain conditions leads to its labilization and subsequent re-storage which could be disrupted by drugs. Propranolol has been the most commonly investigated drug for memory reconsolidation therapy in clinical trials. Intervention with propranolol have shown mixed results in PTSD patients with some studies showing improvement in symptoms while other failing to replicate these findings. We conducted a systematic review and meta-analysis to determine the efficacy of trauma memory disruption by propranolol on PTSD symptoms and physiological responses in PTSD patients. 3224 publications were assessed for eligibility. Seven studies on effects of propranolol on PTSD symptoms and 3 studies on effects of propranolol on physiological responses were incorporated in the meta-analyses. Overall, results indicate that propranolol did not show a beneficial effect on PTSD symptoms (standardized mean difference: 1.29; 95% CI = -2.16 - 0.17). Similarly, propranolol did not influence skin conductance (standardized mean difference: 0.77; 95% CI = -1.85 - 0.31) or EMG response (standardized mean difference: 0.16; 95% CI = -0.65 - 0.33). However, propranolol significantly reduced heart rate after trauma memory recall compared to placebo (standardized mean difference: 0.67; 95% CI = -1.27 to -0.07). This study finds a lack of evidence for the efficacy of propranolol on traumatic memory disruption, in PTSD patients, to recommend its routine clinical use. However, a high level of heterogeneity, variation in propranolol dosage and inadequate sample sizes mean that these findings require cautious interpretation.

Diverse therapeutic developments for post-traumatic stress disorder (PTSD) indicate common mechanisms of memory modulation

Post-traumatic stress disorder (PTSD), characterized by abnormally persistent and distressing memories, is a chronic debilitating condition in need of new treatment options. Current treatment guidelines recommend psychotherapy as first line management with only two drugs, sertraline and paroxetine, approved by U.S. Food and Drug Administration (FDA) for treatment of PTSD. These drugs have limited efficacy as they only reduce symptoms related to depression and anxiety without producing permanent remission. PTSD remains a significant public health problem with high morbidity and mortality requiring major advances in therapeutics. Early evidence has emerged for the beneficial effects of psychedelics particularly in combination with psychotherapy for management of PTSD, including psilocybin, MDMA, LSD, cannabinoids, ayahuasca and ketamine. MDMA and psilocybin reduce barrier to therapy by increasing trust between therapist and patient, thus allowing for modification of trauma related memories. Furthermore, research into the memory reconsolidation mechanisms has allowed for identification of various pharmacological targets to disrupt abnormally persistent memories. A number of pre-clinical and clinical studies have investigated novel and re-purposed pharmacological agents to disrupt fear memory in PTSD. Novel therapeutic approaches like neuropeptide Y, oxytocin, cannabinoids and neuroactive steroids have also shown potential for PTSD treatment. Here, we focus on the role of fear memory in the pathophysiology of PTSD and propose that many of these new therapeutic strategies produce benefits through the effect on fear memory. Evaluation of recent research findings suggests that while a number of drugs have shown promising results in preclinical studies and pilot clinical trials, the evidence from large scale clinical trials would be needed for these drugs to be incorporated in clinical practice.

Apparent reconsolidation interference without generalized amnesia

Memories remain dynamic after consolidation, and when reactivated, they can be rendered vulnerable to various pharmacological agents that disrupt the later expression of memory (i.e., amnesia). Such drug-induced post-reactivation amnesia has traditionally been studied in AAA experimental designs, where a memory is initially created for a stimulus A (be it a singular cue or a context) and later reactivated and tested through exposure to the exact same stimulus. Using a contextual fear conditioning procedure in rats and midazolam as amnestic agent, we recently demonstrated that drug-induced amnesia can also be obtained when memories are reactivated through exposure to a generalization stimulus (GS, context B) and later tested for that same generalization stimulus (ABB design). However, this amnestic intervention leaves fear expression intact when at test animals are instead presented with the original training stimulus (ABA design) or a novel generalization stimulus (ABC design). The underlying mechanisms of post-reactivation memory malleability and of MDZ-induced amnesia for a generalization context remain largely unknown. Here, we evaluated whether, like typical CS-mediated (or AAA) post-reactivation amnesia, GS-mediated (ABB) post-reactivation amnesia displays key features of a destabilization-based phenomenon. We first show that ABB post-reactivation amnesia is critically dependent on prediction error at the time of memory reactivation and provide evidence for its temporally graded nature. In line with the known role of GluN2B-NMDA receptor activation in memory destabilization, we further demonstrate that pre-reactivation administration of ifenprodil, a selective antagonist of GluN2B-NMDA receptors, prevents MDZ-induced ABB amnesia. In sum, our data reveal that ABB MDZ-induced post-reactivation amnesia exhibits the hallmark features of a destabilization-dependent phenomenon. Implication of our findings for a reconsolidation-based account of post-reactivation amnesia are discussed.

Propranolol-induced inhibition of unconditioned stimulus-reactivated fear memory prevents the return of fear in humans

Fear memories can be reactivated by a fear-associated conditioned stimulus (CS) or unconditioned stimulus (US) and then undergo reconsolidation. Propranolol administration during CS retrieval-induced reconsolidation can impair fear memory that is specific to the reactivated CS. However, from a practical perspective, the US is often associated with multiple CSs, and each CS can induce a fear response. The present study sought to develop and test a US-based memory retrieval interference procedure with propranolol to disrupt the original fear memory and eliminate all CS-associated fear responses in humans. We recruited 127 young healthy volunteers and conducted three experiments. All of the subjects acquired fear conditioning, after which they received the β-adrenergic receptor antagonist propranolol (40 mg) or placebo (vitamin C) and were exposed to the US or CS to reactivate the original fear memory. Fear responses were measured. Oral propranolol administration 1 h before US retrieval significantly decreased subsequent fear responses and disrupted associations between all CSs and the US. However, propranolol administration before CS retrieval only inhibited the fear memory that was related to the reactivated CS. Moreover, the propranolol-induced inhibition of fear memory reconsolidation that was retrieved by the US had a relatively long-lasting effect (at least 2 weeks) and was also effective for remote fear memory. These findings indicate that the US-based memory retrieval interference procedure with propranolol can permanently decrease the fear response and prevent the return of fear for all CSs in humans. This procedure may open new avenues for treating fear-related disorders.

Downregulation of miR-200c stabilizes XIAP mRNA and contributes to invasion and lung metastasis of bladder cancer

Our previous studies have demonstrated that XIAP promotes bladder cancer metastasis through upregulating RhoGDIβ/MMP-2 pathway. However, the molecular mechanisms leading to the XIAP upregulation was unclear. In current studies, we found that XIAP was overexpressed in human high grade BCs, high metastatic human BCs, and in mouse invasive BCs. Mechanistic studies indicated that XIAP overexpression in the highly metastatic T24T cells was due to increased mRNA stability of XIAP that was mediated by downregulated miR-200c. Moreover, the downregulated miR-200c was due to CREB inactivation, while miR-200c downregulation reduced its binding to the 3’-UTR region of XIAP mRNA. Collectively, our results demonstrate the molecular basis leading to XIAP overexpression and its crucial role in BC invasion.

Retrieval-Extinction and Relapse Prevention: Rewriting Maladaptive Drug Memories?

Addicted individuals are highly susceptible to relapse when exposed to drug-associated conditioned stimuli (CSs; "drug cues") even after extensive periods of abstinence. Until recently, these maladaptive emotional drug memories were believed to be permanent and resistant to change. The rediscovery of the phenomenon of memory reconsolidation-by which retrieval of the memory can, under certain conditions, destabilize the previously stable memory before it restabilizes in its new, updated form-has led to the hypothesis that it may be possible to disrupt the strong maladaptive drug-memories that trigger a relapse. Furthermore, recent work has suggested that extinction training "within the reconsolidation window" may lead to a long-term reduction in relapse without the requirement for pharmacological amnestic agents. However, this so-called "retrieval-extinction" effect has been inconsistently observed in the literature, leading some to speculate that rather than reflecting memory updating, it may be the product of facilitation of extinction. In this mini review article, we will focus on factors that might be responsible for the retrieval-extinction effects on preventing drug-seeking relapse and how inter-individual differences may influence this therapeutically promising effect. A better understanding of the psychological and neurobiological mechanisms underpinning the "retrieval-extinction" paradigm, and individual differences in boundary conditions, should provide insights with the potential to optimize the translation of "retrieval-extinction" to clinical populations.

Pi4KIIα Regulates Unconditioned Stimulus-Retrieval-Induced Fear Memory Reconsolidation through Endosomal Trafficking of AMPA Receptors

Targeting memory reconsolidation is an effective intervention for treating posttraumatic stress disorder (PTSD). Disrupting unconditioned stimulus (US)-retrieval-induced fear memory reconsolidation has become an effective therapeutic approach to attenuate fear memory, but the underlying molecular mechanisms remain unknown. Here, we report that US-retrieval-dependent increase in phosphatidylinositol 4-kinase IIα (Pi4KIIα) promotes early endosomal trafficking of AMPA receptors, leading to the enhancement of synaptic efficacy in basolateral amygdala (BLA) neurons. The inhibition of Pi4KIIα by an inhibitor or short hairpin RNA impaired contextual fear memory reconsolidation. This disruptive effect persisted for at least 2 weeks, which was restored by Pi4KIIα overexpression with TAT-Pi4KIIα. Furthermore, the blockade of early endosomal trafficking following US retrieval reduced synaptosomal membrane GluA1 levels and decreased subsequent fear expression. These data demonstrate that Pi4KIIα in the BLA is crucial for US-retrieval-induced fear memory reconsolidation, the inhibition of which might be an effective therapeutic strategy for treating PTSD.

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Unconditioned stimulus (US) retrieval induces a transient increase in Pi4KIIα expression

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Pi4KIIα regulates early endosomal trafficking of AMPARs during memory reconsolidation

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Pi4KIIα contributes to US-retrieval-induced synaptic enhancement in rat BLA

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Pi4KIIα inhibition after US retrieval impairs fear expression and shows long-term effects

Fear not: recent advances in understanding the neural basis of fear memories and implications for treatment development

Fear is a highly adaptive emotion that has evolved to promote survival and reproductive fitness. However, maladaptive expression of fear can lead to debilitating stressor-related and anxiety disorders such as post-traumatic stress disorder. Although the neural basis of fear has been extensively researched for several decades, recent technological advances in pharmacogenetics and optogenetics have allowed greater resolution in understanding the neural circuits that underlie fear. Alongside conceptual advances in the understanding of fear memory, this increased knowledge has clarified mechanisms for some currently available therapies for post-traumatic stress disorder and has identified new potential treatment targets.

Persistent Stress-Induced Neuroplastic Changes in the Locus Coeruleus/Norepinephrine System

Neural plasticity plays a critical role in mediating short- and long-term brain responses to environmental stimuli. A major effector of plasticity throughout many regions of the brain is stress. Activation of the locus coeruleus (LC) is a critical step in mediating the neuroendocrine and behavioral limbs of the stress response. During stressor exposure, activation of the hypothalamic-pituitary-adrenal axis promotes release of corticotropin-releasing factor in LC, where its signaling promotes a number of physiological and cellular changes. While the acute effects of stress on LC physiology have been described, its long-term effects are less clear. This review will describe how stress changes LC neuronal physiology, function, and morphology from a genetic, cellular, and neuronal circuitry/transmission perspective. Specifically, we describe morphological changes of LC neurons in response to stressful stimuli and signal transduction pathways underlying them. Also, we will review changes in excitatory glutamatergic synaptic transmission in LC neurons and possible stress-induced modifications of AMPA receptors. This review will also address stress-related behavioral adaptations and specific noradrenergic receptors responsible for them. Finally, we summarize the results of several human studies which suggest a link between stress, altered LC function, and pathogenesis of posttraumatic stress disorder.