Memory reconsolidation may be disrupted by a distractor stimulus presented during reactivation

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.

Dual-step pharmacological intervention for traumatic-like memories: implications from D-cycloserine and cannabidiol or clonidine in male and female rats

RATIONALE

Therapeutic approaches to mitigating traumatic memories have often faced resistance. Exploring safe reconsolidation blockers, drugs capable of reducing the emotional valence of the memory upon brief retrieval and reactivation, emerges as a promising pharmacological strategy. Towards this objective, preclinical investigations should focus on aversive memories resulting in maladaptive outcomes and consider sex-related differences to enhance their translatability.

OBJECTIVES

After selecting a relatively high training magnitude leading to the formation of a more intense and generalized fear memory in adult female and male rats, we investigated whether two clinically approved drugs disrupting its reconsolidation remain effective.

RESULTS

We found resistant reconsolidation impairment by the α2-adrenergic receptor agonist clonidine or cannabidiol, a major non-psychotomimetic Cannabis sativa component. However, pre-retrieval administration of D-cycloserine, a partial agonist at the glycine-binding site of the N-methyl-D-aspartate (NMDA) receptor complex, facilitated their impairing effects on reconsolidation. A similar reconsolidation blockade by clonidine or cannabidiol was achieved following exposure to a non-conditioned but generalized context after D-cycloserine administration. This suggests that sufficient memory destabilization can accompany generalized fear expression. Combining clonidine with cannabidiol without potentiating memory destabilization by D-cycloserine was ineffective.

CONCLUSIONS

These findings highlight the importance of NMDA receptor signaling in memory destabilization and underscore the efficacy of a dual-step pharmacological intervention in attenuating traumatic-like memories, even in a context different from the original learning environment.

Reminder-dependent alterations in long-term declarative memory expression

The reminder of a previously-learned memory can render that memory vulnerable to disruption or change in expression. Such memory alterations have been viewed as supportive of the framework of memory reconsolidation. However, alternative interpretations and inconsistencies in the replication of fundamental findings have raised questions particularly in the domain of human declarative memory. Here we present a series of related experiments, all of which involve the learning of a declarative memory, followed 1-2 days later by memory reminder. Post-reminder learning of interfering material did result in modulation of subsequent recall at test, but the precise manifestation of that interference effect differed across experiments. With post-reminder performance of a visuospatial task, a quantitative impairment in test recall performance was observed within a visual list-learning paradigm, but not in a foreign vocabulary learning paradigm. These results support the existence of reminder-induced memory processes that can lead to the alteration of subsequent memory performance by interfering tasks. However, it remains unclear whether these effects are reflective of modulation or impairment of the putative memory reconsolidation process.

Cathodal transcranial direct current stimulation on the prefrontal cortex applied after reactivation attenuates fear memories and prevent reinstatement after extinction

BACKGROUND

In the last decade, pharmacological strategies targeting reconsolidation after memory retrieval have shown promising efforts to attenuate persistent memories and overcome fear recovery. However, most reconsolidation inhibiting agents have not been approved for human testing. While non-invasive neuromodulation can be considered an alternative approach to pharmacological treatments, there is a lack of evidence about the efficacy of these technologies when modifying memory traces via reactivation/reconsolidation mechanism.

OBJECTIVE

In this study, we evaluate the effect of cathodal (c-tDCS) and anodal (a-DCS) transcranial direct current stimulation applied after memory reactivation and extinction in rats.

METHODS

Male Wistar rats were randomly assigned into three groups: one sham group, one anodal tDCS group, and one cathodal tDCS group (500 μA, 20 min). Reconsolidation and extinction of fear memories were evaluated using a contextual fear conditioning.

RESULTS

Our results showed that c-tDCS and a-tDCS after memory reactivation can attenuate mild fear memories. However, only c-tDCS stimulation prevented both fear expression under strong fear learning and fear recovery after a reinstatement protocol without modification of learning rate or extinction retrieval. Nevertheless, the remote memories were resistant to modification through this type of neuromodulation. Our results are discussed considering the interaction between intrinsic excitability promoted by learning and memory retrieval and the electric field applied during tDCS.

CONCLUSION

These results point out some of the boundary conditions influencing the efficacy of tDCS in fear attenuation and open new ways for the development of noninvasive interventions aimed to control fear-related disorders via reconsolidation.

Hippocampus and cortex are involved in the retrieval of a spatial memory under full and partial cue availability

Retaking routes after a period of time usually occurs in an environment which has suffered from spatial configuration modifications. Thus, the original visual stimuli that allowed us to establish cognitive mapping using an allocentric strategy during the acquisition phase may not remain physically identical at the time of retrieval. However, in the standard experimental paradigms the cues are typically maintained constant. In this study, we explored memory retrieval with spatial modifications from learning in the Morris Water Maze. We trained rats on a reference memory protocol with five cues placed on black curtains that surrounded the pool, and seven days later, we tested memory retrieval under different conditions: maintenance of the five cues, removal of two and four of them, and the addition of three extra ones. Under full-cue and partial cue-conditions, rats showed successful memory retrieval, whereas adding extra cues resulted in impaired retrieval. Furthermore, we assessed brain oxidative metabolism through cytochrome c oxidase (CCO) histochemistry and found that, under full- and partial-cue conditions, there is an enhancement of the hippocampal, prefrontal, retrosplenial, parietal, and rhinal cortex metabolism. Rats that failed to retrieve spatial information in the extra cues condition showed similar or lower CCO activity than controls across many limbic areas. It is suggested that the presence of a partial portion of visual stimuli from learning makes it possible to reactivate the entire memory trace, but extra spatial information hinders retrieval, making it difficult to disengage the novel information from the older knowledge and establish a contextual generalization.

Nimodipine improves cortical efficiency during working memory in healthy subjects

The L-type calcium channel gene, CACNA1C, is a validated risk gene for schizophrenia and the target of calcium channel blockers. Carriers of the risk-associated genotype (rs1006737 A allele) have increased frontal cortical activity during working memory and higher CACNA1C mRNA expression in the prefrontal cortex. The aim of this study was to determine how the brain-penetrant calcium channel blocker, nimodipine, changes brain activity during working memory and other cognitive and emotional processes. We conducted a double-blind randomized cross-over pharmacoMRI study of a single 60 mg dose of oral nimodipine solution and matching placebo in healthy men, prospectively genotyped for rs1006737. With performance unchanged, nimodipine significantly decreased frontal cortical activity by 39.1% and parietal cortical activity by 42.8% during the N-back task (2-back > 0-back contrast; PFWE < 0.05; n = 28). Higher peripheral nimodipine concentrations were correlated with a greater decrease in activation in the frontal cortex. Carriers of the risk-associated allele, A (n = 14), had a greater decrease in frontal cortical activation during working memory compared to non-risk allele carriers. No differences in brain activation were found between nimodipine and placebo for other tasks. Future studies should be conducted to test if the decreased cortical brain activity after nimodipine is associated with improved working memory performance in patients with schizophrenia, particularly those who carry the risk-associated genotype. Furthermore, changes in cortical activity during working memory may be a useful biomarker in future trials of L-type calcium channel blockers.

An acute seizure prior to memory reactivation transiently impairs associative memory performance in C57BL/6J mice

Memory deficits significantly decrease an individual's quality of life and are a pervasive comorbidity of epilepsy. Despite the various distinct processes of memory, the majority of epilepsy research has focused on seizures during the encoding phase of memory, therefore the effects of a seizure on other memory processes is relatively unknown. In the present study, we investigated how a single seizure affects memory reactivation in C57BL/6J adult mice using an associative conditioning paradigm. Initially, mice were trained to associate a tone (conditioned stimulus), with the presence of a shock (unconditioned stimulus). Flurothyl was then administered 1 h before, 1 h after, or 6 h before a memory reactivation trial. The learned association was then assessed by presenting a conditioned stimulus in a new context 24 h or 1 wk after memory reactivation. We found that mice receiving a seizure 1 h prior to reactivation exhibited a deficit in memory 24 h later but not 1 wk later. When mice were administered a seizure 6 h before or 1 h after reactivation, there were no differences in memory between seizure and control animals. Altogether, our study indicates that an acute seizure during memory reactivation leads to a temporary deficit in associative memory in adult mice. These findings suggest that the cognitive impact of a seizure may depend on the timing of the seizure relative to the memory process that is active.

Shifting from fear to safety through deconditioning-update

Aversive memories are at the heart of psychiatric disorders such as phobias and post-traumatic stress disorder (PTSD). Here, we present a new behavioral approach in rats that robustly attenuates aversive memories. This method consists of ‘deconditioning’ animals previously trained to associate a tone with a strong footshock by replacing it with a much weaker one during memory retrieval. Our results indicate that deconditioning-update is more effective than traditional extinction in reducing fear responses; moreover, such effects are long lasting and resistant to renewal and spontaneous recovery. Remarkably, this strategy overcame important boundary conditions for memory updating, such as remote or very strong traumatic memories. The same beneficial effect was found in other types of fear-related memories. Deconditioning was mediated by L-type voltage-gated calcium channels and is consistent with computational accounts of mismatch-induced memory updating. Our results suggest that shifting from fear to safety through deconditioning-update is a promising approach to attenuate traumatic memories.

Resistance to fear memory destabilization triggers exaggerated emotional-like responses following memory reactivation

Fear memory reactivation does not always lead to memory destabilization-reconsolidation. For instance, fear memories formed following withdrawal from chronic ethanol consumption or a stressful event are less likely to become destabilized after reactivation, with the effect of recall of these memories on the affective state still requiring elucidation. Here, we investigated the negative emotional-like responses following fear memory reactivation in ethanol-withdrawn (ETOH) rats by focusing on the possible role played by destabilization. Our findings indicated that ETOH rats displayed an increased freezing in a novel context and an anxiogenic-like response in the elevated plus maze (EPM) following memory reactivation, whereas the behavior of CON animals was not affected. The destabilization blockade by pre-reactivation nimodipine (16 mg/kg, s.c) administration promoted in CON animals a similar behavior in the EPM and in a novel environment as that exhibited by ETOH rats after the reminder. Moreover, facilitating destabilization by pre-reactivation d-cycloserine (5 mg/kg, i.p) administration prevented the emotional-like disturbances observed in ETOH rats. Finally, using restraint stress, which is also an inductor of a fear memory resistant to destabilization, an increased fear response in an unconditioned environment and an anxiogenic-like state was also found after the presentation of the fear reminder in stressed rats. Our results suggest that, in the context of resistant fear memories, the occurrence of destabilization influences how animals respond to subsequent environmental challenges following reactivation.

Resilience and Vulnerability to Trauma: Early Life Interventions Modulate Aversive Memory Reconsolidation in the Dorsal Hippocampus

Early life experiences program lifelong responses to stress. In agreement, resilience and vulnerability to psychopathologies, such as posttraumatic stress disorder (PTSD), have been suggested to depend on the early background. New therapies have targeted memory reconsolidation as a strategy to modify the emotional valence of traumatic memories. Here, we used animal models to study the molecular mechanism through which early experiences may later affect aversive memory reconsolidation. Handling (H)—separation of pups from dams for 10 min—or maternal separation (MS) — 3-h separation—were performed from PDN1–10, using non-handled (NH) litters as controls. Adult males were trained in a contextual fear conditioning (CFC) task; 24 h later, a short reactivation session was conducted in the conditioned or in a novel context, followed by administration of midazolam 3 mg/kg i.p. (mdz), known to disturb reconsolidation, or vehicle; a test session was performed 24 h after. The immunocontent of relevant proteins was studied 15 and 60 min after memory reactivation in the dorsal hippocampus (dHc) and basolateral amygdala complex (BLA). Mdz-treated controls (NH) showed decreased freezing to the conditioned context, consistent with reconsolidation impairment, but H and MS were resistant to labilization. Additionally, MS males showed increased freezing to the novel context, suggesting fear generalization; H rats showed lower freezing than the other groups, in accordance with previous suggestions of reduced emotionality facing adversities. Increased levels of Zif268, GluN2B, β-actin and polyubiquitination found in the BLA of all groups suggest that memory reconsolidation was triggered. In the dHc, only NH showed increased Zif268 levels after memory retrieval; also, a delay in ERK1/2 activation was found in H and MS animals. We showed here that reconsolidation of a contextual fear memory is insensitive to interference by a GABAergic drug in adult male rats exposed to different neonatal experiences; surprisingly, we found no differences in the reconsolidation process in the BLA, but the dHc appears to suffer temporal desynchronization in the engagement of reconsolidation. Our results support a hippocampal-dependent mechanism for reconsolidation resistance in models of early experiences, which aligns with current hypotheses for the etiology of PTSD.

Temporal Flexibility of Systems Consolidation and the Synaptic Occupancy/Reset Theory (SORT): Cues About the Nature of the Engram

The ability to adapt to new situations involves behavioral changes expressed either from an innate repertoire, or by acquiring experience through memory consolidation mechanisms, by far a much richer and flexible source of adaptation. Memory formation consists of two interrelated processes that take place at different spatial and temporal scales, Synaptic Consolidation, local plastic changes in the recruited neurons, and Systems Consolidation, a process of gradual reorganization of the explicit/declarative memory trace between hippocampus and the neocortex. In this review, we summarize some converging experimental results from our lab that support a normal temporal framework of memory systems consolidation as measured both from the anatomical and the psychological points of view, and propose a hypothetical model that explains these findings while predicting other phenomena. Then, the same experimental design was repeated interposing additional tasks between the training and the remote test to verify for any interference: we found that (a) when the animals were subject to a succession of new learnings, systems consolidation was accelerated, with the disengagement of the hippocampus taking place before the natural time point of this functional switch, but (b) when a few reactivation sessions reexposed the animal to the training context without the shock, systems consolidation was delayed, with the hippocampus prolonging its involvement in retrieval. We hypothesize that new learning recruits from a fixed number of plastic synapses in the CA1 area to store the engram index, while reconsolidation lead to a different outcome, in which additional synapses are made available. The first situation implies the need of a reset mechanism in order to free synapses needed for further learning, and explains the acceleration observed under intense learning activity, while the delay might be explained by a different process, able to generate extra free synapses: depending on the cognitive demands, it deals either with a fixed or a variable pool of available synapses. The Synaptic Occupancy/Reset Theory (SORT) emerged as an explanation for the temporal flexibility of systems consolidation, to encompass the two different dynamics of explicit memories, as well as to bridge both synaptic and systems consolidation in one single mechanism.

Different temporal windows for CB1 receptor involvement in contextual fear memory destabilisation in the amygdala and hippocampus

Reconsolidation is a process in which re-exposure to a reminder causes a previously acquired memory to undergo a process of destabilisation followed by subsequent restabilisation. Different molecular mechanisms have been postulated for destabilisation in the amygdala and hippocampus, including CB1 receptor activation, protein degradation and AMPA receptor exchange; however, most of the amygdala studies have used pre-reexposure interventions, while those in the hippocampus have usually performed them after reexposure. To test whether the temporal window for destabilisation is similar across both structures, we trained Lister Hooded rats in a contextual fear conditioning task, and 1 day later performed memory reexposure followed by injection of either the NMDA antagonist MK-801 (0.1 mg/kg) or saline in order to block reconsolidation. In parallel, we also performed local injections of either the CB1 antagonist SR141716A or its vehicle in the hippocampus or in the amygdala, either immediately before or immediately after reactivation. Infusion of SR141716A in the hippocampus prevented the reconsolidation-blocking effect of MK-801 when performed after reexposure, but not before it. In the amygdala, meanwhile, pre-reexposure infusions of SR141716A impaired reconsolidation blockade by MK-801, although the time-dependency of this effect was not as clear as in the hippocampus. Our results suggest the temporal windows for CB1-receptor-mediated memory destabilisation during reconsolidation vary between brain structures. Whether this reflects different time windows for engagement of these structures or different roles played by CB1 receptors in destabilisation across structures remains an open question for future studies.

Avoidance Behavior Prevents Modification of Fear Memory During Reconsolidation

Several studies have revealed that fear recovery is prevented when extinction training is conducted after retrieval of a fear memory. Postretrieval extinction training is related to modification of memory during reconsolidation. Providing new information during reconsolidation can modify the original memory. We propose that avoidance behavior is a relevant factor that prevents subjects from obtaining new safety information during reconsolidation. Postretrieval extinction training without avoidance behavior reduced the fear response to conditioned stimulus and prevented spontaneous recovery in the current study, which corresponded with previous studies. Under the condition of postretrieval extinction training with avoidance behavior, the fear response was not reduced as much as it was in the condition without avoidance. It is possible that avoidance behavior prevents receiving new safety information during postretrieval extinction training.

Calcium/calmodulin-dependent kinase II and memory destabilization: a new role in memory maintenance

In this review, we discuss the poorly explored role of calcium/calmodulin-dependent protein kinase II (CaMKII) in memory maintenance, and its influence on memory destabilization. After a brief review on CaMKII and memory destabilization, we present critical pieces of evidence suggesting that CaMKII activity increases retrieval-induced memory destabilization. We then proceed to propose two potential molecular pathways to explain the association between CaMKII activation and increased memory destabilization. This review will pinpoint gaps in our knowledge and discuss some 'controversial' observations, establishing the basis for new experiments on the role of CaMKII in memory reconsolidation. The role of CaMKII in memory destabilization is of great clinical relevance. Still, because of the lack of scientific literature on the subject, more basic science research is necessary to pursue this pathway as a clinical tool.

Periodical reactivation under the effect of caffeine attenuates fear memory expression in rats

In the last decade, several studies have shown that fear memories can be attenuated by interfering with reconsolidation. However, most of the pharmacological agents used in preclinical studies cannot be administered to humans. Caffeine is one of the world’s most popular psychoactive drugs and its effects on cognitive and mood states are well documented. Nevertheless, the influence of caffeine administration on fear memory processing is not as clear. We employed contextual fear conditioning in rats and acute caffeine administration under a standard memory reconsolidation protocol or periodical memory reactivation. Additionally, potential rewarding/aversion and anxiety effects induced by caffeine were evaluated by conditioning place preference or open field, respectively. Caffeine administration was able to attenuate weak fear memories in a standard memory reconsolidation protocol; however, periodical memory reactivation under caffeine effect was necessary to attenuate strong and remote memories. Moreover, caffeine promoted conditioned place preference and anxiolytic-like behavior, suggesting that caffeine weakens the initial learning during reactivation through counterconditioning mechanisms. Thus, our study shows that rewarding and anxiolytic effects of caffeine during fear reactivation can change the emotional valence of fear memory. It brings a new promising pharmacological approach based on drugs widely used such as caffeine to treat fear-related disorders.

An Innovative Framework for Delivering Psychotherapy to Patients With Treatment-Resistant Posttraumatic Stress Disorder: Rationale for Interactive Motion-Assisted Therapy

Despite an array of evidence-based psychological treatments for patients with a posttraumatic stress disorder (PTSD), a majority of patients do not fully benefit from the potential of these therapies. In veterans with PTSD, up to two-thirds retain their diagnosis after psychotherapy and often their disorder is treatment-resistant, which calls for improvement of therapeutic approaches for this population. One of the factors hypothesized to underlie low response in PTSD treatment is high behavioral and cognitive avoidance to traumatic reminders. In the current paper we explore if a combination of personalized virtual reality, multi-sensory input, and walking during exposure can enhance treatment engagement, overcome avoidance, and thereby optimize treatment effectiveness. Virtual reality holds potential to increase presence and in-session attention and to facilitate memory retrieval. Multi-sensory input such as pictures and music can personalize this experience. Evidence for the positive effect of physical activity on fear extinction and associative thinking, as well as embodied cognition theories, provide a rationale for decreased avoidance by literally approaching cues of the traumatic memories. A dual-attention task further facilitates new learning and reconsolidation. These strategies have been combined in an innovative framework for trauma-focused psychotherapy, named Multi-modular Motion-assisted Memory Desensitization and Reconsolidation (3MDR). In this innovative treatment the therapeutic setting is changed from the face-to-face sedentary position to a side-by-side activating context in which patients walk toward trauma-related images in a virtual environment. The framework of 3MDR has been designed as a boost for patients with treatment-resistant PTSD, which is illustrated by three case examples. The intervention is discussed in context of other advancements in treatment for treatment-resistant PTSD. Novel elements of this approach are activation, personalization and empowerment. While developed for veterans with PTSD who do not optimally respond to standardized treatments, this innovative framework holds potential to also be used for other patient populations and earlier stages of treatment for patients with PTSD.

Enhancement of extinction memory by pharmacological and behavioral interventions targeted to its reactivation

Extinction is a process that involves new learning that inhibits the expression of previously acquired memories. Although temporarily effective, extinction does not erase an original fear association. Since the extinction trace tends to fade over time, the original memory can resurge. On the other hand, strengthening effects have been described in several reconsolidation studies using different behavioral and pharmacological manipulations. In order to know whether an extinction memory can be strengthened by reactivation-based interventions in the contextual fear conditioning task, we began by replicating the classic phenomenon of spontaneous recovery to show that brief reexposure sessions can prevent the decay of the extinction trace over time in a long-lasting way. This fear attenuation was shown to depend both on L-type calcium channels and protein synthesis, which suggests a reconsolidation process behind the reactivation-induced strengthening effect. The extinction trace was also susceptible to enhancement by a post-reactivation infusion of a memory-enhancing drug (NaB), which was also able to prevent rapid fear reacquisition (savings). These findings point to new reactivation-based approaches able to strengthen an extinction memory to promote its persistence. The constructive interactions between extinction and reconsolidation may represent a promising novel approach in the realm of fear-related disorder treatments.

Interference Conditions of the Reconsolidation Process in Humans: The Role of Valence and Different Memory Systems

Following the presentation of a reminder, consolidated memories become reactivated followed by a process of re-stabilization, which is referred to as reconsolidation. The most common behavioral tool used to reveal this process is interference produced by new learning shortly after memory reactivation. Memory interference is defined as a decrease in memory retrieval, the effect is generated when new information impairs an acquired memory. In general, the target memory and the interference task used are the same. Here we investigated how different memory systems and/or their valence could produce memory reconsolidation interference. We showed that a reactivated neutral declarative memory could be interfered by new learning of a different neutral declarative memory. Then, we revealed that an aversive implicit memory could be interfered by the presentation of a reminder followed by a threatening social event. Finally, we showed that the reconsolidation of a neutral declarative memory is unaffected by the acquisition of an aversive implicit memory and conversely, this memory remains intact when the neutral declarative memory is used as interference. These results suggest that the interference of memory reconsolidation is effective when two task rely on the same memory system or both evoke negative valence.

Forgetting of what was once learned: Exploring the role of postsynaptic ionotropic glutamate receptors on memory formation, maintenance, and decay

Over the past years, extensive research in experimental cognitive neuroscience has provided a comprehensive understanding about the role of ionotropic glutamate receptor (IGluR)-dependent signaling underpinning postsynaptic plasticity induced by long-term potentiation (LTP), the leading cellular basis of long-term memory (LTM). However, despite the fact that iGluR-mediated postsynaptic plasticity regulates the formation and persistence of LTP and LTM, here we discuss the state-of-the-art regarding the mechanisms underpinning both LTP and LTM decay. First, we review the crucial roles that iGluRs play on memory encoding and stabilization. Second, we discuss the latest findings in forgetting considering hippocampal GluA2-AMPAR trafficking at postsynaptic sites as well as dendritic spine remodeling possibly involved in LTP decay. Third, on the role of retrieving consolidated LTMs, we discuss the mechanisms involved in memory destabilization that occurs followed reactivation that share striking similarities with the neurobiological basis of forgetting. Fourth, since different AMPAR subunits as well as postsynaptic scaffolding proteins undergo ubiquitination, the ubiquitin-proteasome system (UPS) is discussed in light of memory decay. In conclusion, we provide an integrated overview revealing some of the mechanisms determining memory forgetting that are mediated by iGluRs. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.

Blocking GluN2B subunits reverses the enhanced seizure susceptibility after prolonged febrile seizures with a wide therapeutic time-window

Febrile seizures (FSs), the most common type of convulsive events in infants, are closely associated with temporal lobe epilepsy (TLE) in adulthood. It is urgent to investigate how FSs promote epileptogenesis and find the potential therapeutic targets. In the present study, we showed that the phosphorylation of GluN2B Tyr1472 gradually reached peak level at 24h after prolonged FSs and remained elevated during 7days thereafter. IL-1β treatment alone, which in previous study mimicked the effect of prolonged FSs on adult seizure susceptibility, increased GluN2B Tyr1472 phosphorylation. Both IL-1 receptor antagonist (IL-1Ra) and IL-1R1 deletion were sufficient to reverse the prolonged FSs induced hyper-phosphorylation of GluN2B Tyr1472. GluN2B antagonist ifenprodil showed a wide therapeutic time-window (3days) to reverse the enhanced seizure susceptibility after prolonged FSs or IL-1β treatment. Our study demonstrated that GluN2B phosphorylation at Tyr1472 site mediated by the transient increase of IL-1β was involved in the enhanced adult seizure susceptibility after prolonged FSs, implicating GluN2B-containing NMDAR is a new potential drug target with a wide therapeutic time window to prevent epileptogenesis in patients with infantile FSs.

Forgetting of long-term memory requires activation of NMDA receptors, L-type voltage-dependent Ca2+ channels, and calcineurin

In the past decades, the cellular and molecular mechanisms underlying memory consolidation, reconsolidation, and extinction have been well characterized. However, the neurobiological underpinnings of forgetting processes remain to be elucidated. Here we used behavioral, pharmacological and electrophysiological approaches to explore mechanisms controlling forgetting. We found that post-acquisition chronic inhibition of the N-methyl-D-aspartate receptor (NMDAR), L-type voltage-dependent Ca²⁺ channel (LVDCC), and protein phosphatase calcineurin (CaN), maintains long-term object location memory that otherwise would have been forgotten. We further show that NMDAR activation is necessary to induce forgetting of object recognition memory. Studying the role of NMDAR activation in the decay of the early phase of long-term potentiation (E-LTP) in the hippocampus, we found that ifenprodil infused 30 min after LTP induction in vivo blocks the decay of CA1-evoked postsynaptic plasticity, suggesting that GluN2B-containing NMDARs activation are critical to promote LTP decay. Taken together, these findings indicate that a well-regulated forgetting process, initiated by Ca²⁺ influx through LVDCCs and GluN2B-NMDARs followed by CaN activation, controls the maintenance of hippocampal LTP and long-term memories over time.