Regulate Fear Memory Research Articles

Context and Time Regulate Fear Memory Consolidation and Reconsolidation in the Basolateral Amygdala Complex.

It is widely accepted that fear memories are consolidated through protein synthesis-dependent changes in the basolateral amygdala complex (BLA). However, recent studies show that protein synthesis is not required to consolidate the memory of a new dangerous experience when it is similar to a prior experience. Here, we examined whether the protein synthesis requirement for consolidating the new experience varies with its spatial and temporal distance from the prior experience. Female and male rats were conditioned to fear a stimulus (S1, e.g., light) paired with shock in stage 1 and a second stimulus (S2, e.g., tone) that preceded additional S1-shock pairings (S2-S1-shock) in stage 2. The latter stage was followed by a BLA infusion of a protein synthesis inhibitor, cycloheximide, or vehicle. Subsequent testing with S2 revealed that protein synthesis in the BLA was not required to consolidate fear to S2 when the training stages occurred 48 h apart in the same context; was required when they were separated by 14 d or occurred in different contexts; but was again not required if S1 was re-presented after the delay or in the different context. Similarly, protein synthesis in the BLA was not required to reconsolidate fear to S2 when the training stages occurred 48 h apart but was required when they occurred 14 d apart. Thus, the protein synthesis requirement for consolidating/reconsolidating fear memories in the BLA is determined by similarity between present and past experiences, the time and place in which they occur, and reminders of the past experiences.

Sleep-wake dependent hippocampal regulation of fear memory

The hippocampus (HPC) plays a pivotal role in fear learning and memory. Our two recent studies suggest that rapid eye movement (REM) sleep via the HPC downregulates fear memory consolidation and promotes fear extinction. However, it is not clear whether and how the dorsal and the ventral HPC regulates fear memory differently; and how the HPC in wake regulates fear memory. By chemogenetic stimulating in the HPC directly and its afferent entorhinal cortex that selectively activated the HPC in REM sleep for 3-6 h post-fear-acquisition, we found that HPC activation in REM sleep consolidated fear extinction memory. In particular, dorsal HPC (dHPC) stimulation in REM sleep virtually eliminated fear memory by enhancing fear extinction and reducing fear memory consolidation. By contrast, chemogenetic stimulating HPC afferent the supramammillary nucleus (SUM) induced 3-hr wake with HPC activation impaired fear extinction. Finally, desipramine (DMI) injection that selectively eliminated REM sleep for >6 h impaired fear extinction. Our results demonstrate that the HPC is critical for fear memory regulation; and wake HPC and REM sleep HPC have an opposite role in fear extinction of respective impairment and consolidation.

DHHC2 regulates fear memory formation, LTP, and AKAP150 signaling in the hippocampus

Palmitoyl acyltransferases (PATs) have been suggested to be involved in learning and memory. However, the underlying mechanisms have not yet been fully elucidated. Here, we found that the activity of DHHC2 was upregulated in the hippocampus after fear conditioning, and DHHC2 knockdown impaired fear induced memory and long-term potentiation (LTP). Additionally, the activity of DHHC2 and its synaptic expression were increased after high frequency stimulation (HFS) or glycine treatment. Importantly, fear learning selectively augmented the palmitoylation level of AKAP150, not PSD-95, and this effect was abolished by DHHC2 knockdown. Furthermore, 2-bromopalmitic acid (2-BP), a palmitoylation inhibitor, attenuated the increased palmitoylation level of AKAP150 and the interaction between AKAP150 and PSD-95 induced by HFS. Lastly, DHHC2 knockdown reduced the phosphorylation level of GluA1 at Ser845, and also induced an impairment of LTP in the hippocampus. Our results suggest that DHHC2 plays a critical role in regulating fear memory via AKAP150 signaling.

Glucocorticoid- β-adrenoceptors interactions in the infralimbic cortex in acquisition and consolidation of auditory fear memory extinction in rats

This study investigated the interactive effect of glucocorticoid and β-adrenoceptors in the infralimbic (IL) cortex on the acquisition and consolidation of fear extinction in rats' auditory fear conditioning (AFC) task. On day 1, rats underwent habituation for 9 min (12 tones, 10 s, 4 kHz, 80 dB, without footshock). On day 2 (conditioning), rats received 3 mild electrical footshocks (US; 2 s, 0.5 mA) paired with the auditory-conditioned stimulus (CS; tone: 30 s, 4 kHz, 80 dB). On days 3–5 (Ext 1–3), rats received 15 tones with no footshock in the test box. Intra-IL injection of corticosterone (CORT, 20 ng/0.5 μl per side) before Ext 1 and after Ext 1–2, respectively, facilitated the acquisition and consolidation of fear memory extinction. Intra-IL injection of the β2-adrenoceptor agonist clenbuterol (CLEN, 50 ng/0.5 μl per side) inhibited, but the β-adrenoceptor antagonist propranolol (PROP, 500 ng/0.5 μl per side) enhanced the facilitatory effects of CORT on fear memory extinction. CORT injection before the acquisition of fear extinction increased p-ERK levels in the IL. Co-injection of CORT with CLEN increased, but PROP decreased p-ERK activities. CORT injection after the consolidation of fear extinction increased p-CREB in the IL. Co-injection of CORT with CLEN increased, but PROP reduced p-CREB activities. Our findings show that corticosterone facilitates the acquisition and consolidation of fear memory extinction. GRs and β-adrenoceptors in the IL jointly regulate fear memory extinction via ERK and CREB signaling pathways. This pre-clinical animal study may highlight the effect of GRs and β-adrenoceptors of the IL cortex in regulating fear memory processes in fear-related disorders such as PTSD.

(2R,6R)-hydroxynorketamine targeting the basolateral amygdala regulates fear memory

(2R,6R)-Hydroxynorketamine (HNK), a ketamine metabolite, has been proposed as an ideal next-generation antidepressant due to its rapid-acting and long-lasting antidepression-relevant actions. Interestingly, recent studies have shown that (2R,6R)-HNK may have diverse impacts on memory formation. However, its effect on fear memory extinction is still unknown. In the present study, we assessed the effects of (2R,6R)-HNK on synaptic transmission and plasticity in the basolateral amygdala (BLA) and explored its actions on auditory fear memory extinction. Adult male C57BL/6J mice were used in this study. The extracellular electrophysiological recording was conducted to assay synaptic transmission and plasticity. The auditory fear conditioning paradigm was performed to test fear extinction. The results showed that (2R,6R)-HNK at 30 mg/kg increased the number of c-fos-positive cells in the BLA. Moreover, (2R,6R)-HNK enhanced the induction and maintenance of long-term potentiation (LTP) in the BLA in a dose-dependent manner (at 1, 10, and 30 mg/kg). In addition, (2R,6R)-HNK at 30 mg/kg and directly slice perfusion of (2R,6R)-HNK enhanced BLA synaptic transmission. Furthermore, intra-BLA application and systemic administration of (2R,6R)-HNK reduced the retrieval of recent fear memory and decreased the retrieval of remote fear memory. Both local and systemic (2R,6R)-HNK also inhibited the spontaneous recovery of remote fear memory. Taken together, these results indicated that (2R,6R)-HNK could regulate BLA synaptic transmission and plasticity and act through the BLA to modulate fear memory. The results revealed that (2R,6R)-HNK may be a potential drug to treat posttraumatic stress disorder (PTSD) patients.

Extracellular zinc regulates contextual fear memory formation in male rats through MMP-BDNF-TrkB pathway in dorsal hippocampus and basolateral amygdala

Large amount of zinc (100 µM even up to 300 µM) is released from the nerve terminals in response to high frequency neuronal stimulation in certain brain regions including hippocampus and amygdala. However, its precise pharmacological effect is poorly understood. Here, we investigated the role of extracellular zinc (endogenous zinc) and exogenous zinc in memory formation using contextual fear conditioning (CFC) model. Male Sprague Dawley rats were trained for fear conditioning followed by in vivo microdialysis for collection of microdialysate samples from CA1 and CA3 regions of hippocampus and basolateral amygdala (BLA). Extracellular zinc chelator CaEDTA, BDNF scavenger TrkB-Fc, exogenous 7,8-DHF and matrix metalloproteinases (MMP) inhibitor were infused into the CA1 and CA3 regions of hippocampus and BLA after CFC. Different doses of exogenous zinc hydroaspartate were administered intraperitoneally immediately after CFC. We found that CFC increased the level of extracellular zinc in the hippocampus and BLA. Infusing the CaEDTA, TrkB-Fc and MMP inhibitor into the CA1 and CA3 regions of hippocampus and BLA disrupted the fear memory formation. Furthermore, administration of TrKB agonist 7,8-DHF reversed the inhibitory effect of CaEDTA on fear memory formation, suggesting that extracellular zinc may regulate fear memory formation via the BDNF-TrKB pathway. We also found that high dose of exogenous zinc hydroaspartate supplementation increased extracellular zinc levels in brain and enhanced fear memory formation. Altogether, these findings indicate that extracellular zinc may participate in formation of contextual fear memory through MMP-BDNF-TrkB pathway in the hippocampus and BLA.

Neuronal activity in the dorsal dentate gyrus during extinction regulates fear memory extinction and renewal

Memory extinction and renewal are major factors that limits the efficacy of exposure therapy. The dorsal dentate gyrus (dDG) plays a crucial role in spatial memory, and epigenetic modifications in the dDG play an important role in fear memory renewal. However, whether dDG activity regulates fear memory extinction and renewal remains unclear. In this study, we showed that an extinction procedure that prevents fear memory renewal (extinction within the reconsolidation window) leads to increased c-fos expression in the dDG. Chemicogenetic activation of dDG excitatory neurons during extinction training elevated fear memory extinction and prevented renewal, whereas inhibition of dDG excitatory neurons inhibited fear memory extinction. We also demonstrated that inhibiting fear engram cells (neurons active during fear acquisition) during extinction training inhibits fear memory extinction. Therefore, dDG activity during fear extinction plays an important role in fear memory extinction and renewal.

Cerebellar modulation of memory encoding in the periaqueductal grey and fear behaviour.

The pivotal role of the periaqueductal grey (PAG) in fear learning is reinforced by the identification of neurons in male rat ventrolateral PAG (vlPAG) that encode fear memory through signalling the onset and offset of an auditory-conditioned stimulus during presentation of the unreinforced conditioned tone (CS+) during retrieval. Some units only display CS+ onset or offset responses, and the two signals differ in extinction sensitivity, suggesting that they are independent of each other. In addition, understanding cerebellar contributions to survival circuits is advanced by the discovery that (i) reversible inactivation of the medial cerebellar nucleus (MCN) during fear consolidation leads in subsequent retrieval to (a) disruption of the temporal precision of vlPAG offset, but not onset responses to CS+, and (b) an increase in duration of freezing behaviour. And (ii) chemogenetic manipulation of the MCN-vlPAG projection during fear acquisition (a) reduces the occurrence of fear-related ultrasonic vocalisations, and (b) during subsequent retrieval, slows the extinction rate of fear-related freezing. These findings show that the cerebellum is part of the survival network that regulates fear memory processes at multiple timescales and in multiple ways, raising the possibility that dysfunctional interactions in the cerebellar-survival network may underlie fear-related disorders and comorbidities.

Plexin-A1 expression in the inhibitory neurons of infralimbic cortex regulates the specificity of fear memory in male mice.

Maintaining appropriate levels of fear memory specificity is crucial for individual's survival and mental health, whereas overgeneralized fear commonly occurs in neuropsychiatric disorders, including posttraumatic stress disorder and generalized anxiety disorder. However, the molecular mechanisms regulating fear memory specificity remain poorly understood. The medial prefrontal cortex (mPFC) is considered as a key brain region in fear memory regulation. Previous transcriptomic studies have identified that plexin-A1, a transmembrane receptor critical for axon development, was downregulated in the mPFC after fear memory training. In this study, we identified that learning-induced downregulation of the mRNA and protein levels of plexin-A1 specifically occurred in the inhibitory but not excitatory neurons in the infralimbic cortex (IL) of mPFC. Further studies of plexin-A1 by virus-mediated over-expression of functional mutants selectively in the IL inhibitory neurons revealed the critical roles of plexin-A1 for regulating memory specificity and anxiety. Moreover, our findings revealed that plexin-A1 regulated the distribution of glutamic acid decarboxylase 67, a GABA synthetase, which in turn modulated the activity of IL and its downstream brain regions. Collectively, our findings elucidate the molecular modifier of IL inhibitory neurons in regulating memory specificity and anxiety, and provide candidates for developing therapeutic strategies for the prevention or treatment of a series of fear generalization-related neuropsychiatric disorders.

Rac1 Signaling in Amygdala Astrocytes Regulates Fear Memory Acquisition and Retrieval.

The importance of astrocytes in behavior control is increasingly appreciated, but little is known about the effects of their dynamic activity in regulating learning and memory. In the present study, we constructed AAVs of photoactivatable and photoinactivatable Ras-related C3 botulinum toxin substrate 1 (Rac1) under the mGFAP promoter, which enabled the manipulation of Rac1 activity in astrocytes by optical stimulation in free-moving mice. We found that both up-regulation and down-regulation of astrocytic Rac1 activity in the basolateral amygdala (BLA) attenuated memory acquisition in a fear conditioning mouse model. Meanwhile, neuronal activation in the BLA induced by memory acquisition was inhibited under both the up- and down-regulation of astrocytic Rac1 activity during training. In terms of the impact on fear memory retrieval, we found both up- and down-regulation of BLA astrocytic Rac1 activity impaired memory retrieval of fear conditioning and memory retrieval-induced neuronal activation. Notably, the effect of astrocytic Rac1 on memory retrieval was reversible. Our results demonstrate that the normal activity of astrocytic Rac1 is necessary for the activation of neurons and memory formation. Both activation and inactivation of astrocytic Rac1 activity in the BLA reduced the excitability of neurons, and thereby impaired fear memory acquisition and retrieval.

Temporary inactivation of the infralimbic cortex impairs while the blockade of its dopamine D2 receptors enhances auditory fear extinction in rats

Fear extinction is defined as decline in conditioned fear responses that occurs with repeated and non-reinforced exposure to a feared conditioned stimulus. Experimental evidence suggests that the extinction of fear memory requires the integration of the medial prefrontal cortex (mPFC); nevertheless, the role of its sub-regions in regulating the expression and extinction of auditory fear has been rarely addressed in literature. The present study examined the roles of the infra-limbic (IL) and pre-limbic (PL) regions of the mPFC in the expression and extinction of auditory fear by temporally deactivating these regions using lidocaine (10 μg/0.5 μl) before training male Wistar rats in auditory fear-conditioning tasks. The results showed increased freezing levels and impaired extinction through deactivating the IL rather than the PL cortex. Given the role of the dopaminergic pathways in regulating fear memory, this study also investigated the role of D2 receptors located in the IL cortex in fear extinction. Fear extinction was improved in an inverted U-shape pattern through the intra-IL infusion of 15.125, 31.25, 62.5, 125, 250 and 500 ng/0.5 μl of the D2 receptor antagonist sulpiride. In other words, the moderate doses, i.e. 31.25, 62.5, 125, 250 ng/0.5 μl, enhanced auditory fear extinction, whereas the lowest and highest doses, i.e. 15.125 and 500 ng/0.5 μl, were ineffective. These findings demonstrated the key roles of the IL cortex and its dopamine D2 receptors in regulating auditory fear in rats.

Stress-induced NLRP3 inflammasome activation negatively regulates fear memory in mice

BackgroundPersistent inflammation dysregulation and cognitive decline have been associated with several trauma- and stress-related disorders such as posttraumatic stress disorder (PTSD) and anxiety disorder. Despite the abundant discoveries of neuroinflammation in such disorders, the underlying mechanisms still remain unclear.MethodWild-type and Nlrp3−/− mice were exposed to the electric foot shocks in the contextual fear memory paradigm. Three hours after the electric foot shocks, activation of the NLRP3 inflammasome was investigated through immunoblotting and ELISA. Microglia were isolated and analyzed by quantitative real-time PCR. Hippocampal tissues were collected 3 h and 72 h after the electric foot shocks and subjected to RNA sequencing. MCC950 was administrated to mice via intraperitoneal (i.p.) injection. Interleukin-1 receptor antagonist (IL-ra) and interleukin-1β (IL-1β) were delivered via intracerebroventricular (i.c.v.) infusion. Contextual fear responses of mice were tested on 4 consecutive days (test days 1-4) starting at 48 h after the electric foot shocks. Anxiety-like behaviors were examined by elevated plus maze and open-field test.ResultsWe demonstrated that, in the contextual fear memory paradigm, the NLRP3 inflammasome was activated 3 h after electric foot shocks. We also found an upregulation in toll-like receptor and RIG-I-like receptor signaling, and a decrease in postsynaptic density (PSD) related proteins, such as PSD95 and Shank proteins, in the hippocampus 72 h after the electric foot shocks, indicating an association between neuroinflammation and PSD protein loss after stress encounter. Meanwhile, Nlrp3 knockout could significantly prevent both neuroinflammation and loss of PSD-related proteins, suggesting a possible protective role of NLRP3 deletion during this process. For further studies, we demonstrated that both genetic knockout and pharmaceutical inhibition of the NLRP3 inflammasome remarkably enhanced the extinction of contextual fear memory and attenuated anxiety-like behavior caused by electric foot shocks. Moreover, cytokine IL-1β administration inhibited the extinction of contextual fear memory. Meanwhile, IL-1ra significantly enhanced the extinction of contextual fear memory and attenuated anxiety-like behavior.ConclusionTaken together, our data revealed the pivotal role of NLRP3 inflammasome activation in the regulation of fear memory and the development of PTSD and anxiety disorder, providing a novel target for the clinical treatment of such disorders.

IQGAP1/ERK regulates fear memory formation via histone posttranslational modifications induced by HDAC2.

Epigenetic mechanisms of learning and memory are particularly interesting topics in neuroscience that have recently been investigated. As shown in our previous study, IQGAP1, a scaffolding protein of MAPK, is involved in fear memory through interactions with GluN2A-containing NMDA receptors and the ERK1/2 cascade. However, researchers have not determined whether histone posttranslational modifications are regulated by the IQGAP1/ERK signaling pathway. We performed in vivo studies using IQGAP1-/- and IQGAP1+/+ mice to provide insights into the specific functions of IQGAP1 in memory processes and the precise mechanisms underlying its regulatory effects. IQGAP1-/- mice exhibited impaired fear memory, decreased levels of phosphorylated ERK1/2 and histone H3S10, decreased acetylation of H3K14, and decreased c-Fos expression in the hippocampus compared to IQGAP1+/+ mice after fear conditioning. HDAC2 was significantly enriched at the c-fos gene promoter in IQGAP1-/- mice. Correspondingly, the disruption of the epigenetic regulation induced by ERK1/2 signaling through an intra-hippocampal injection of the MEK antagonist U0126 or GluN2A-selective pharmacological antagonist NVP-AAM077 blocked context-dependent memory formation, while no changes were observed after treatment with the GluN2B-selective antagonist Ro25-6981. The administration of SAHA, a non-specific HDAC inhibitor, or knock-down of HDAC2 with shHDAC2-AAV in the dorsal hippocampus significantly rescued the impaired fear memory formation, H3S10 phosphorylation, H3K14 acetylation, and c-Fos expression in IQGAP1-/- mice. Thus, we postulated that the IQGAP1/ERK-dependent mechanism regulating histone posttranslational modifications via HDAC2 potentially underlies memory formation.

Stathmin Regulates Spatiotemporal Variation in the Memory Loop in Single-Prolonged Stress Rats.

Posttraumatic stress disorder (PTSD) is closely related to brain structures of the memory loop such as the hippocampus, amygdala, and medial prefrontal cortex (mPFC). The fear gene stathmin plays an important role in regulating fear memory. However, whether the fear gene stathmin is related to fear memory loop anomalies caused by PTSD is unclear. A single-prolonged stress (SPS) rat model of PTSD was constructed. Wistar rats were randomly divided into 5 groups: the control group, SPS 1-day group, SPS 4-day group, SPS 7-day group, and SPS 14-day group. Then, we measured the protein and mRNA expression of stathmin, p-stathmin (Ser16, Ser25, Ser38, and Ser63), β-tubulin, and MAP-1B in the hippocampus, amygdala, and mPFC in the 5 groups by immunohistochemistry, Western blotting, and qRT-PCR. The expression of the stathmin protein in the hippocampus, mPFC, and amygdala of the rat memory loop decreased gradually in the SPS 1-day group, the SPS 4-day group, and the SPS 7-day group, in which it was the lowest, and then increased. The trend of the expression of stathmin mRNA in the three areas of the memory loop was consistent with the trend of the expression of the stathmin protein. The trend of the protein expression of p-stathmin (Ser25 and Ser38) was opposite of that of stathmin; it reached a peak on the 7th day, and then decreased in the hippocampus. The protein expression of p-stathmin (Ser63) showed the same trend in the mPFC. The protein and mRNA expression of β-tubulin and MAP-1B was consistent with that of p-stathmin; it reached a peak on the 7th day, and then decreased in the rat hippocampus, mPFC, and amygdala. Stathmin in the memory loop, especially in the hippocampus, regulates microtubule structure through its phosphorylation at Ser25 and Ser38 and thereby participates in the mediation of fear memory abnormalities in PTSD.

Continuous exposure to α-glycosyl isoquercitrin from developmental stages to adulthood is necessary for facilitating fear extinction learning in rats.

We previously reported that exposure to α-glycosyl isoquercitrin (AGIQ) from the fetal stage to adulthood facilitated fear extinction learning in rats. The present study investigated the specific AGIQ exposure period sufficient for inducing this behavioral effect. Rats were dietarily exposed to 0.5% AGIQ from the postweaning stage to adulthood (PW-AGIQ), the fetal stage to postweaning stage (DEV-AGIQ), or the fetal stage to adulthood (WP-AGIQ). Fear memory, anxiety-like behavior, and object recognition memory were assessed during adulthood. Fear extinction learning was exclusively facilitated in the WP-AGIQ rats. Synaptic plasticity-related genes showed a similar pattern of constitutive expression changes in the hippocampal dentate gyrus and prelimbic medial prefrontal cortex (mPFC) between the DEV-AGIQ and WP-AGIQ rats. However, WP-AGIQ rats revealed more genes constitutively upregulated in the infralimbic mPFC and amygdala than DEV-AGIQ rats, as well as FOS-immunoreactive(+) neurons constitutively increased in the infralimbic cortex. Ninety minutes after the last fear extinction trial, many synaptic plasticity-related genes (encoding Ephs/Ephrins, glutamate receptors/transporters, and immediate-early gene proteins and their regulator, extracellular signal-regulated kinase 2 [ERK2]) were upregulated in the dentate gyrus and amygdala in WP-AGIQ rats. Additionally, WP-AGIQ rats exhibited increased phosphorylated ERK1/2+ neurons in both the prelimbic and infralimbic cortices. These results suggest that AGIQ exposure from the fetal stage to adulthood is necessary for facilitating fear extinction learning. Furthermore, constitutive and learning-dependent upregulation of synaptic plasticity-related genes/molecules may be differentially involved in brain regions that regulate fear memory. Thus, new learning-related neural circuits for facilitating fear extinction can be established in the mPFC.

Regulating fear memory

Neuroscience Treatment for anxiety and fear is often based on extinction training, but fear can spontaneously reappear even after successful initial treatment. Neuroscientists have discovered two different neuronal ensembles operating within the brain's hippocampal dentate gyrus: extinction neurons and fear engram neurons. Lacagnina et al. used optogenetics and neural tagging to identify, stimulate, and inhibit these different neuronal populations. They found that silencing fear engram neurons prevented spontaneous fear recovery, whereas silencing extinction neurons impaired the trained memory that suppresses fear (extinction retrieval). By contrast, stimulating fear engram neurons potentiated fear, whereas stimulating extinction neurons suppressed it. Nat. Neurosci. 22 , 753 (2019).

Androgen receptor is a negative regulator of contextual fear memory in male mice

Although sex-hormones have a well-documented role in memory formation, most literature has focused on estrogens, whereas the role of androgens and their receptor (the androgen receptor; AR) in fear memory is relatively unexplored. To address this gap, we used a transgenic mouse model of AR overexpression (CMV-AR) to determine if AR regulates fear memory, and if this effect can be reversed either by the removal of circulating androgens via gonadectomy, or by antagonising AR activity with flutamide. We found that AR overexpression results in reduced freezing in response to foot shock, and that this difference is reversed with both gonadectomy and flutamide treatment. Differences between genotypes were reinstated by testosterone replacement in gonadectomized mice, suggesting that reduced fear memory in mutants results from AR activation by testosterone and is not secondary to group differences in circulating testosterone. Potential transcriptional mechanisms by which CMV-AR exerts its effects on fear memory were assessed by quantitating the expression of memory-related genes in area CA1 of the hippocampus. Several genes that are altered with AR inhibition and activation, including genes that encode for the histone variant H2A.Z, cholinergic receptors, glutamate receptors, and brain-derived neurotrophic factor. Overall, our findings suggest that AR is a negative regulator of fear memory and identify potential gene targets through which AR may mediate this effect.

Change of Rin1 and Stathmin in the Animal Model of Traumatic Stresses.

The molecular mechanism of fear memory is poorly understood. Therefore, the pathogenesis of post-traumatic stress disorder (PTSD), whose symptom presentation can enhance fear memory, remains largely unclear. Recent studies with knockout animals have reported that Rin1 and stathmin regulate fear memory. Rin1 inhibits acquisition and promotes memory extinction, whereas stathmin regulates innate and basal fear. The aim of our study was to examine changes in the expression of Rin1 and stathmin in different animal models of stress, particluarly traumatic stress. We used three animal traumatic stresses: single prolonged stress (SPS, which is a rodent model of PTSD), an immobilization-stress (IM) and a Loud sound stress (LSS), to examine the change and uniqueness in Rin1/stathmin expression. Behavioral tests of SPS rats demonstrated increased anxiety and contextual fear-conditioning. They showed decreased long-term potentiation (LTP), as well as decreased stathmin and increased Rin1 expression in the hippocampus and the amygdala. Expression of the stathmin effector, tubulin, and downstream molecules Rin1, Rab5, and Abl, appeared to increase. Rin1 and EphA4 were endogenously coexpressed in primary neurons after SPS stimulation. IM rats exhibited increased anxiety behavior and enhanced fear-conditioning to contextual and auditory stimuli. Similar changes in expression of Rin1/stathmin were observed in IM rats whereas no changes were observed in rats exposed to a loud sound. These data suggest that changes in expression of the Rin1 and stathmin genes may be involved in rodents with SPS and IM stresses, which provide valuable insight into fear memories under abnormal conditions, particularly in PTSD.

BAF53b, a Neuron-Specific Nucleosome Remodeling Factor, Is Induced after Learning and Facilitates Long-Term Memory Consolidation.

Although epigenetic mechanisms of gene expression regulation have recently been implicated in memory consolidation and persistence, the role of nucleosome-remodeling is largely unexplored. Recent studies show that the functional loss of BAF53b, a postmitotic neuron-specific subunit of the BAF nucleosome-remodeling complex, results in the deficit of consolidation of hippocampus-dependent memory and cocaine-associated memory in the rodent brain. However, it is unclear whether BAF53b expression is regulated during memory formation and how BAF53b regulates fear memory in the amygdala, a key brain site for fear memory encoding and storage. To address these questions, we used viral vector approaches to either decrease or increase BAF53b function specifically in the lateral amygdala of adult mice in auditory fear conditioning paradigm. Knockdown of Baf53b before training disrupted long-term memory formation with no effect on short-term memory, basal synaptic transmission, and spine structures. We observed in our qPCR analysis that BAF53b was induced in the lateral amygdala neurons at the late consolidation phase after fear conditioning. Moreover, transient BAF53b overexpression led to persistently enhanced memory formation, which was accompanied by increase in thin-type spine density. Together, our results provide the evidence that BAF53b is induced after learning, and show that such increase of BAF53b level facilitates memory consolidation likely by regulating learning-related spine structural plasticity.SIGNIFICANCE STATEMENT Recent works in the rodent brain begin to link nucleosome remodeling-dependent epigenetic mechanism to memory consolidation. Here we show that BAF53b, an epigenetic factor involved in nucleosome remodeling, is induced in the lateral amygdala neurons at the late phase of consolidation after fear conditioning. Using specific gene knockdown or overexpression approaches, we identify the critical role of BAF53b in the lateral amygdala neurons for memory consolidation during long-term memory formation. Our results thus provide an idea about how nucleosome remodeling can be regulated during long-term memory formation and contributes to the permanent storage of associative fear memory in the lateral amygdala, which is relevant to fear and anxiety-related mental disorders.

Context and Auditory Fear are Differentially Regulated by HDAC3 Activity in the Lateral and Basal Subnuclei of the Amygdala.

Histone acetylation is a fundamental epigenetic mechanism that is dynamically regulated during memory formation. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) compete to modulate histone acetylation, allowing for rapid changes in acetylation in response to a learning event. HDACs are known to be powerful negative regulators of memory formation, but it is not clear whether this function depends on HDAC enzymatic activity per se. Here, we tested whether the enzymatic activity of an individual Class I HDAC, HDAC3, has a role in fear memory formation in subregions of the hippocampus and amygdala. We found that fear conditioning drove expression of the immediate early genes cFos and Nr4a2 in the hippocampus, which coincided with reduced HDAC3 occupancy at these promoters. Using a dominant-negative, deacetylase-dead point mutant virus (AAV-HDAC3(Y298H)-v5), we found that selectively blocking HDAC3 deacetylase activity in either the dorsal hippocampus or basal nucleus of the amygdala enhanced context fear without affecting tone fear. Blocking HDAC3 activity in the lateral nucleus of the amygdala, on the other hand, enhanced tone, but not context fear memory. These results show for the first time that the enzymatic activity of HDAC3 functions to negatively regulate fear memory formation. Further, HDAC3 activity regulates different aspects of fear memory in the basal and lateral subregions of the amygdala. Thus, the deacetylase activity of HDAC3 is a powerful negative regulator of fear memory formation in multiple subregions of the fear circuit.