Estrogen receptor beta signaling enhances extinction memory recall for heroin-conditioned cues in a sex- and region-specific manner.

Return to use, or relapse, is a major challenge in the treatment of opioid use disorder (OUD). Relapse can be precipitated by several factors, including exposure to drug-conditioned cues. Identifying successful treatments to mitigate cue-induced relapse has been challenging, perhaps due to extinction memory recall (EMR) deficits. Previously, inhibition of estradiol (E2) signaling in the basolateral amygdala (BLA) impaired heroin-cue EMR. This effect was recapitulated by antagonism of BLA estrogen receptors (ER) in a sex-specific manner such that blocking ERα in males, but ERß in females, impaired EMR. However, it is unclear whether increased E2 signaling, in the BLA or systemically, enhances heroin-cue EMR. We hypothesized that ERß agonism would enhance heroin-cue EMR in a sex- and region-specific manner. To determine the capacity of E2 signaling to improve EMR, we pharmacologically manipulated ERß across several translationally designed experiments. First, male and female rats acquired heroin or sucrose self-administration. Next, during a cued extinction session, we administered diarylpropionitrile (DPN, an ERß agonist) and tested anxiety-like behavior on an open field. Subsequently, we assessed EMR in a cue-induced reinstatement test and, finally, measured ERß expression in several brain regions. Across all experiments, females took more heroin and sucrose than males and had greater responses during heroin-cued extinction. Administration of DPN in the BLA enhanced EMR in females only, driven by ERß's impacts on memory consolidation. Interestingly, however, systemic DPN administration improved EMR for heroin cues in both sexes across several different tests, but did not impact sucrose-cue EMR. Immunohistochemical analysis of ERß expression across several different brain regions showed that females only had greater expression of ERß in the basal nucleus of the BLA. Here, in several preclinical experiments, we demonstrated that ERß agonism enhances heroin-cue EMR and has potential utility in combatting cue-induced relapse.

Reducing FKBP51 Expression in the Ventral Hippocampus Decreases Auditory Fear Conditioning in Male Rats.

Fear conditioning evokes a physiologic release of glucocorticoids that assists learning. As a cochaperone in the glucocorticoid receptor complex, FKBP51 modulates stress-induced glucocorticoid signaling and may influence conditioned fear responses. This study combines molecular and behavioral approaches to examine whether locally reducing FKBP51 expression in the ventral hippocampus is sufficient to affect fear-related behaviors. We hypothesized that reducing FKBP51 expression in the VH would increase glucocorticoid signaling to alter auditory fear conditioning. Adult male rats were injected with an adeno-associated virus (AAV) vector expressing short hairpin - RNAs (shRNA) targeting FKBP5 into the ventral hippocampus to reduce FKBP5 levels or a control AAV. Infusion of FKBP5-shRNA into the ventral hippocampus decreased auditory fear acquisition and recall. Although animals injected with FKBP5-shRNA showed less freezing during extinction recall, the difference was due to a reduced fear recall rather than improved extinction. Reducing ventral hippocampus FKBP51 did not affect exploratory behavior in either the open field test or the elevated zero maze test but did increase passive behavior in the forced swim test, suggesting that the reduction in auditory fear recall was not due to more active responses to acute stress. Furthermore, lower ventral hippocampus FKBP51 levels did not alter corticosterone release in response to restraint stress, suggesting that the reduced fear recall was not due to lower corticosterone release. Our findings suggest FKBP51 in the ventral hippocampus plays a selective role in modulating fear-learning processes and passive behavioral responses to acute stress rather than hypothalamic-pituitary-adrenal axis reactivity or exploratory responses.

Modulation of contextual fear acquisition and extinction by acute and chronic relaxin-3 receptor (RXFP3) activation in the rat retrosplenial cortex.

The retrosplenial cortex (RSC) plays a central role in processing contextual fear conditioning. In addition to corticocortical and thalamocortical projections, the RSC receives subcortical inputs, including a substantial projection from the nucleus incertus in the pontine tegmentum. This GABAergic projection contains the neuropeptide, relaxin-3 (RLN3), which inhibits target neurons via its Gi/o-protein-coupled receptor, RXFP3. To assess this peptidergic system role in contextual fear conditioning, we bilaterally injected the RSC of adult rats with an adeno-associated-virus (AAV), expressing the chimeric RXFP3 agonist R3/I5 or a control AAV, and subjected them to contextual fear conditioning. The R3/I5 injected rats did not display any major differences to control-injected and naïve rats but displayed a significantly delayed extinction. Subsequently, we employed acute bilateral injections of the specific RXFP3 agonist peptide, RXFP3-Analogue 2 (A2), into RSC. While the administration of A2 before each extinction trial had no impact on the extinction process, treatment with A2 before each acquisition trial resulted in delayed extinction. In related anatomical studies, we detected an enrichment of RLN3-immunoreactive nerve fibers in deep layers of the RSC, and a higher level of co-localization of RXFP3 mRNA with vesicular GABA transporter (vGAT) mRNA than with vesicular glutamate transporter-1 (vGLUT1) mRNA across the RSC, consistent with an effect of RLN3/RXFP3 signalling on the intrinsic, inhibitory circuits within the RSC. These findings suggest that contextual conditioning processes in the RSC involve, in part, RLN3 afferent modulation of local inhibitory neurons that provides a stronger memory acquisition which, in turn, retards the extinction process.

Sex differences in extinction and reinstatement of nicotine discrimination in rats: The effects of reinforcer devaluation.

Nicotine functions effectively as an interoceptive operant discriminative stimulus (SD) that sets the occasion for voluntarily emitted behavior to be reinforced by biologically relevant outcomes (e.g., food). This has been demonstrated primarily with male rats. Far less is known about nicotine's operant SD functions in female rats. There are no reports of sex differences in extinction and recovery of the SD functions of nicotine, which may elucidate smoking cessation and relapse. In view of this, eight male and eight female rats were trained to nose poke differentially among quasirandomly intermixed sessions of food reinforcement variable interval (VI-30 s) and nonreinforcement in a go/no-go across session one-manipulanda operant drug discrimination procedure. For half the rats, presession administration of nicotine (0.30 mg/kg, subcutaneous) occasioned reinforcement sessions of nose pokes (i.e., SD); for the remaining rats, it occasioned nonreinforcement (SΔ). Saline sessions occasioned the opposite contingencies. Training was conducted first under feeding restriction and then under free feeding, which was then followed by extinction sessions that were also conducted with free feeding. During discrimination training, response rates for females did not differ from males when conducted under restricted feeding but did so during training and later extinction conducted under free feeding. Females also exhibited greater reinstatement of responding under the nicotine SD but not the SΔ. These data provide additional evidence for sex differences in rats with the discriminative stimulus functions of nicotine under low, but not high, food-drive states-and may have implications for sex/gender differences in smoking cessation and relapse. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

A large-scale c-Fos brain mapping study on extinction of cocaine-primed reinstatement.

Individuals with cocaine addiction can experience many craving episodes and subsequent relapses, which represents the main obstacle to recovery. Craving is often favored when abstinent individuals ingest a small dose of cocaine, encounter cues associated with drug use or are exposed to stressors. Using a cocaine-primed reinstatement model in rat, we recently showed that cocaine-conditioned interoceptive cues can be extinguished with repeated cocaine priming in the absence of drug reinforcement, a phenomenon we called extinction of cocaine priming. Here, we applied a large-scale c-Fos brain mapping approach following extinction of cocaine priming in male rats to identify brain regions implicated in processing the conditioned interoceptive stimuli of cocaine priming. We found that cocaine-primed reinstatement is associated with increased c-Fos expression in key brain regions (e.g., dorsal and ventral striatum, several prefrontal areas and insular cortex), while its extinction mostly disengages them. Moreover, while reinstatement behavior was correlated with insular and accumbal activation, extinction of cocaine priming implicated parts of the ventral pallidum, the mediodorsal thalamus and the median raphe. These brain patterns of activation and inhibition suggest that after repeated priming, interoceptive signals lose their conditioned discriminative properties and that action-outcome associations systems are mobilized in search for new contingencies, a brain state that may predispose to rapid relapse.

An investigation of the role of estradiol in fear reduction during a single session of exposure therapy.

Research suggests that estradiol may moderate fear extinction. It is unclear whether these results generalize to exposure therapy. The aim of the current study was to determine whether estradiol moderates outcomes in exposure therapy among women with anxiety disorders. Participants were 35 women with a primary diagnosis of an anxiety disorder who participated in the study as part of routine care at an anxiety specialty clinic. Endogenous estradiol was assessed via saliva. They provided subjective distress ratings before (pre) and after (post) an exposure session, as well as after a brief delay (recall). Contrary to predictions, there were no significant differences in exposure outcomes between the high and low estradiol groups. However, among participants with primary obsessive-compulsive disorder (OCD), results were partially consistent with the hypotheses. Women with lower estradiol initially demonstrated more improvement in subjective distress from pre- to post-exposure, but after the delay, significantly greater distress (attenuated extinction recall). Results suggest that women with lower estradiol may respond less favorably to exposure therapy for OCD relative to women with higher estradiol. These findings await replication in larger samples with longer recall delays. Should replication occur, these results may inform the use of estradiol to augment exposure therapy.

Distinct engrams control fear and extinction memory.

Memories are stored in engram cells, which are necessary and sufficient for memory recall. Recalling a memory might undergo reconsolidation or extinction. It has been suggested that the original memory engram is reactivated during reconsolidation so that memory can be updated. Conversely, during extinction training, a new memory is formed that suppresses the original engram. Nonetheless, it is unknown whether extinction creates a new engram or modifies the original fear engram. In this study, we utilized the Daun02 procedure, which uses c-Fos-lacZ rats to induce apoptosis of strongly activated neurons and examine whether a new memory trace emerges as a result of a short or long reactivation, or if these processes rely on modifications within the original engram located in the basolateral amygdala (BLA) and infralimbic (IL) cortex. By eliminating neurons activated during consolidation and reactivation, we observed significant impacts on fear memory, highlighting the importance of the BLA engram in these processes. Although we were unable to show any impact when removing the neurons activated after the test of a previously extinguished memory in the BLA, disrupting the IL extinction engram reactivated the aversive memory that was suppressed by the extinction memory. Thus, we demonstrated that the IL cortex plays a crucial role in the network involved in extinction, and disrupting this specific node alone is sufficient to impair extinction behavior. Additionally, our findings indicate that extinction memories rely on the formation of a new memory, supporting the theory that extinction memories rely on the formation of a new memory, whereas the reconsolidation process reactivates the same original memory trace.

Focused ultrasound stimulation of infralimbic cortex attenuates reinstatement of methamphetamine-induced conditioned place preference in rats.

Methamphetamine (MA) use disorder poses significant challenges to both the affected individuals and society. Current non-drug therapies like transcranial direct-current stimulation and transcranial magnetic stimulation have limitations due to their invasive nature and limited reach to deeper brain areas. Transcranial focused ultrasound (FUS) is gaining attention as a noninvasive option with precise spatial targeting, able to affect deeper areas of the brain. This research focused on assessing the effectiveness of FUS in influencing the infralimbic cortex (IL) to prevent the recurrence of MA-seeking behavior, using the conditioned place preference (CPP) method in rats. The study involved twenty male Sprague-Dawley rats. Neuronal activation by FUS was first examined via electromyography (EMG). Rats received alternately with MA or saline, and confined to one of two distinctive compartments in a three compartment apparatus over a 4-day period. After CPP test, extinction, the first reinstatement, and extinction again, FUS was applied to IL prior to the second MA priming-induced reinstatement. Safety assessments were conducted through locomotor and histological function examinations. EMG data confirmed the effectiveness of FUS in activating neurons. Significant attenuation of reinstatement of MA CPP was found, along with successful targeting of the IL region, confirmed through acoustic field scanning, c-Fos immunohistochemistry, and Evans blue dye staining. No damage to brain tissue or impaired locomotor activity was observed. The results of the study indicate that applying FUS to the IL markedly reduced the recurrence of MA seeking behavior, without harming brain tissue or impairing motor skills. This suggests that FUS could be a promising method for treating MA use disorder, with the infralimbic cortex being an effective target for FUS in preventing MA relapse.

Neurocognitive mechanisms of mental imagery-based disgust learning.

Disgust imagery represents a potential pathological mechanism for disgust-related disorders. However, it remains controversial as to whether disgust can be conditioned with disgust-evoking mental imagery serving as the unconditioned stimulus (US). Therefore, we examined this using a conditioned learning paradigm in combination with event-related potential (ERP) analysis in 35 healthy college students. The results indicated that the initial neutral face (conditioned stimulus, CS+) became more disgust-evoking, unpleasant, and arousing after pairing with disgust-evoking imagery (disgust CS+), compared to pairing with neutral (neutral CS+) and no (CS-) imagery. Moreover, we observed that mental imagery-based disgust conditioning was resistant to extinction. While the disgust CS + evoked larger P3 and late positive potential amplitudes than CS- during acquisition, no significant differences were found between disgust CS+ and neutral CS+, indicating a dissociation between self-reported and neurophysiological responses. Future studies may additionally acquire facial EMG as an implicit index of conditioned disgust. This study provides the first neurobiological evidence that associative disgust learning can occur without aversive physical stimuli, with implications for understanding how disgust-related disorders may manifest or deteriorate without external perceptual aversive experiences, such as in obsessive-compulsive disorder (OCD).

Is disgust more resistant to extinction than fear? A meta-analytic review of laboratory paradigms.

Disgust can be acquired via evaluative conditioning; a process by which a neutral stimulus (conditioned stimulus; CS) comes to be evaluated as disgusting due to its pairing with an inherently disgusting stimulus (unconditioned stimulus; US). Research has shown that conditioned disgust responses are resistant to extinction which may have implications for disorders (i.e., contamination-based obsessive-compulsive disorder, specific phobias, and post-traumatic stress disorder) in which heightened disgust has been implicated. Importantly, extinction is the primary mechanism by which exposure therapies are thought to achieve symptom reduction for these disorders. Exposure therapies were originally modeled on fear extinction, whereas disgust extinction was largely overlooked until recently. Accordingly, differences in the degree to which learned disgust and fear can be attenuated via extinction learning remains unclear. The present investigation was a meta-analysis directly comparing the degree of extinction of conditioned disgust (n = 14) and conditioned fear (n = 14) in laboratory paradigms. Extinction was operationalized as the standardized mean difference (SMD) in evaluative ratings between the CS+ (the CS paired with the US) and CS- (the unpaired CS) after extinction training. Results of a subgroup analysis indicated that disgust (SMD = 0.52) was significantly more resistant to extinction than fear (SMD = 0.37). Additionally, a series of meta-regression analyses indicated that extinction was not influenced by important study characteristics (e.g., sex, age, number of conditioning and extinction trials). The findings suggest that extinction-based approaches may be less effective at attenuating learned disgust and research is needed to better optimize treatments for disgust-related disorders.

N-acetylcysteine attenuates accumbal core neuronal activity in response to morphine in the reinstatement of morphine CPP in morphine extinguished rats.

Numerous studies have suggested that N-acetylcysteine (NAC), has the potential to suppress drug craving in people with substance use disorder and reduce drug-seeking behaviors in animals. The nucleus accumbens (NAc) plays a crucial role in the brain's reward system, with the nucleus accumbens core (NAcore) specifically implicated in compulsive drug seeking and relapse. In this study, we aimed to explore the impact of subchronic NAC administration during the extinction period and acute NAC administration on the electrical activity of NAcore neurons in response to a priming dose of morphine in rats subjected to extinction from morphine-induced place preference (CPP).We conducted single-unit recordings in anesthetized rats on the reinstatement day, following the establishment of morphine-induced conditioned place preference (7 mg/kg, s.c., 3 days), and subsequent drug-free extinction. In the subchronically NAC-treated groups, rats received daily injections of either NAC (50 mg/kg; i.p.) or saline during the extinction period. On the reinstatement day, we recorded the spontaneous activity of NAcore neurons for 15 min, administered a priming dose of morphine, and continued recording for an additional 45 min. While morphine excited most recorded neurons in saline-treated rats, it failed to alter firing rates in NAC-treated rats that had received NAC during the extinction period. For acutely NAC-treated animals, we recorded the baseline activity of NAcore neurons for 10 min before administering a single injection of either NAC (50 mg/kg; i.p.) or saline in rats with no treatment during the extinction. Following 30 min of recording and a priming dose of morphine (1 mg/kg, s.c.), the recording continued for an additional 30 min. The firing activity of NAcore neurons did not show significant changes after morphine or NAC injection. In conclusion, our findings emphasize that daily NAC administration during the extinction period significantly attenuates the morphine-induced increase in firing rates of NAcore neurons during the reinstatement of morphine CPP. However, acute NAC injection does not produce the same effect. These results suggest that modulating glutamate transmission through daily NAC during extinction may effectively inhibit the morphine place preference following the excitatory effects of morphine on NAcore neurons.

Using unconditioned responses to predict fear acquisition, fear extinction learning, and extinction retention patterns: Sex hormone status matters.

Following a traumatic event, fear dysregulation can increase the likelihood of developing post-traumatic stress disorder (PTSD). This psychopathology is twice as prevalent in women than in men. High physiological reactivity following trauma may be an early risk indicator for the development of PTSD. Elevated physiological reactivity and low estradiol levels have individually been associated with higher fear acquisition and/or lower extinction retention. Thus, sex hormone status may also modulate fear regulation abilities. However, it is unknown whether these two vulnerability factors interact to modulate fear learning and regulation. Using a fear conditioning and extinction protocol, we examined whether physiological reactivity to the aversive stimulus during fear acquisition training predicted fear responses during fear learning, extinction learning, and extinction retention. We verified whether these associations differed according to sex hormone status. Seventy-seven non-clinical participants were recruited including oral contraceptive users (n = 18), early follicular women (n = 20, [low estradiol]), mid-cycle women (n = 20, [high estradiol]), and men (n = 19). Participants underwent a three-day fear conditioning and extinction protocol (day 1: fear acquisition training; day 2: extinction training; day 3: retention test). Skin conductance responses were recorded. In early follicular women, physiological reactivity predicted conditioned and extinguished stimulus fear responses during all phases. For the remaining women, this effect was only present during fear learning and extinction learning. These findings highlight the importance of considering physiological reactivity and sex hormone status following a traumatic event. This knowledge could aid in the early identification of those at higher risk of developing PTSD.

Hydrocortisone Differentially Affects Reinstatement of Pain-related Responses in Patients With Chronic Back Pain and Healthy Volunteers.

Despite the crucial role of effective and sustained extinction of conditioned pain-related fear in cognitive-behavioral treatment approaches for chronic pain, experimental research on extinction memory retrieval in chronic pain remains scarce. In healthy populations, extinction efficacy of fear memory is affected by stress. Therefore, we investigated the effects of oral hydrocortisone administration on the reinstatement of pain-related associations in 57 patients with non-specific chronic back pain (CBP) and 59 healthy control (HC) participants in a differential pain-related conditioning paradigm within a placebo-controlled, randomized, and double-blind design. Participants' skin conductance responses indicate hydrocortisone-induced reinstatement effects in HCs but no observable reinstatement in HCs receiving placebo treatment. Interestingly, these effects were reversed in patients with CBP, that is, reinstatement responses were only observed in the placebo and not in the hydrocortisone group. Our findings corroborate previous evidence of stress-induced effects on extinction efficacy and reinstatement of fear memory in HCs, extending them into the pain context, and call for more research to clarify the role of stress in fear extinction and return of fear phenomena possibly contributing to treatment failure in chronic pain treatment. PERSPECTIVE: Opposing effects in HCs and patients with non-specific CBP may be associated with changes in the patients' stress systems. These findings could be of relevance to optimizing psychological, extinction-based treatment approaches.

Inhibition of Estradiol Signaling in the Basolateral Amygdala Impairs Extinction Memory Recall for Heroin-Conditioned Cues in a Sex-Specific Manner.

INTRODUCTION: Relapse is a major treatment barrier for opioid use disorder. Environmental cues become associated with the rewarding effects of opioids and can precipitate relapse, even after numerous unreinforced cue presentations, due to deficits in extinction memory recall (EMR). Estradiol (E2) modulates EMR of fear-related cues, but it is unknown whether E2 impacts EMR of reward cues and what brain region(s) are responsible for E2s effects. Here, we hypothesize that inhibition of E2 signaling in the basolateral amygdala (BLA) will impair EMR of a heroin-associated cue in both male and female rats. METHODS: We pharmacologically manipulated E2 signaling to characterize the role of E2 in the BLA on heroin-cue EMR. Following heroin self-administration, during which a light/tone cue was co-presented with each heroin infusion, rats underwent cued extinction to extinguish the conditioned association between the light/tone and heroin. During extinction, E2 signaling in the BLA was blocked by an aromatase inhibitor or specific estrogen receptor (ER) antagonists. The next day, subjects underwent a cued test to assess heroin-cue EMR. RESULTS: In both experiments, females took more heroin than males (mg/kg) and had higher operant responding during cued extinction. Inhibition of E2 synthesis in the BLA impaired heroin-cue EMR in both sexes. Notably, E2s actions are mediated by different ER mechanisms, ERα in males but ERß in females. CONCLUSIONS: This study is the first to demonstrate a behavioral role for centrally-produced E2 in the BLA and that E2 also impacts EMR of reward-associated stimuli in both sexes.

A rigorous behavioral testing platform for the assessment of radiation-induced neurological outcomes.

Behavioral testing is a popular and reliable method of neurocognitive assessment of rodents but the lack of standard operating procedures has led to a high variation of protocols in use. Therefore, there exists a strong need to standardize protocols for a combined behavioral platform in order to maintain consistency across institutions and assist newcomers in the field. This paper provides details on the methodology of several behavioral tasks which have been validated in identifying radiation induced cognitive impairment as well as provide guidance on timescales and best practices. The cognitive assessments outlined here are optimized for rodent studies and either target learning and memory (open field task, object in updated location, novel object recognition, object in place, and temporal order) or mood and cognition (social interaction, elevated plus maze, light dark box, forced swim test, and fear extinction). We have utilized this platform successfully in evaluating cognitive injury induced by various radiation types, doses, fractionation schedules and also with ultra-high dose rate FLASH radiotherapy. Recommended materials and software are provided as well as advice on methods of data analysis. In this way a comprehensive behavioral platform is described with broad applicability to assess cognitive endpoints critical to therapeutic outcome.

Differential Roles of Oxytocin Receptors in the Prefrontal Cortex and Nucleus Accumbens on Cocaine Self-Administration and Reinstatement of Cued Cocaine Seeking in Male Rats.

BACKGROUND: Little is known about the specific roles of cortical and accumbal oxytocin receptors in drug use disorders. To better understand the importance of the endogenous oxytocin system in cocaine relapse behavior, we developed an adeno-associated viral vector-expressing short hairpin (sh) RNAs to selectively degrade the rat oxytocin receptor (OxyR) mRNA in vivo. METHODS: Male (Sprague-Dawley) rats received bilateral infusions of the shRNA for the oxytocin receptor (shOxyR) or an shRNA control virus into the prefrontal cortex (PFC) or the nucleus accumbens core (NAc). Rats self-administered cocaine on an escalating FR ratio for 14 days, lever responding was extinguished, and rats were tested for cued and cocaine-primed reinstatement of drug seeking. RESULTS: OxyR knockdown in the PFC delayed the acquisition of lever pressing on an fixed ratio 1 schedule of reinforcement. All rats eventually acquired the same level of lever pressing and discrimination, and there were no differences in extinction. OxyR knockdown in the NAc had no effect during acquisition. In both the PFC and NAc, the shOxyR decreased cued reinstatement relative to shRNA control virus but was without effect during drug-primed reinstatement. OxyR knockdown in the PFC increased chamber activity during a social interaction task. CONCLUSIONS: This study provides critical new information about how endogenous OxyRs function to affect drug seeking in response to different precipitators of relapse. The tool developed to knockdown OxyRs in rat could provide important new insights that aid development of oxytocin-based therapeutics to reduce return-to-use episodes in people with substance use disorder and other neuropsychiatric disorders.

Synapse-Enriched m6A-Modified Malat1 Interacts with the Novel m6A Reader, DPYSL2, and Is Required for Fear-Extinction Memory.

The RNA modification N6-methyladenosine (m6A) regulates the interaction between RNA and various RNA binding proteins within the nucleus and other subcellular compartments and has recently been shown to be involved in experience-dependent plasticity, learning, and memory. Using m6A RNA-sequencing, we have discovered a distinct population of learning-related m6A- modified RNAs at the synapse, which includes the long noncoding RNA metastasis-associated lung adenocarcinoma transcript 1 (Malat1). RNA immunoprecipitation and mass spectrometry revealed 12 new synapse-specific learning-induced m6A readers in the mPFC of male C57/BL6 mice, with m6A-modified Malat1 binding to a subset of these, including CYFIP2 and DPYSL2. In addition, a cell type- and synapse-specific, and state-dependent, reduction of m6A on Malat1 impairs fear-extinction memory; an effect that likely occurs through a disruption in the interaction between Malat1 and DPYSL2 and an associated decrease in dendritic spine formation. These findings highlight the critical role of m6A in regulating the functional state of RNA during the consolidation of fear-extinction memory, and expand the repertoire of experience-dependent m6A readers in the synaptic compartment.SIGNIFICANCE STATEMENT We have discovered that learning-induced m6A-modified RNA (including the long noncoding RNA, Malat1) accumulates in the synaptic compartment. We have identified several new m6A readers that are associated with fear extinction learning and demonstrate a causal relationship between m6A-modified Malat1 and the formation of fear-extinction memory. These findings highlight the role of m6A in regulating the functional state of an RNA during memory formation and expand the repertoire of experience-dependent m6A readers in the synaptic compartment.

Frontopolar multifocal transcranial direct current stimulation reduces conditioned fear reactivity during extinction training: A pilot randomized controlled trial.

Exposure-based therapies for anxiety and related disorders are believed to depend on fear extinction learning and corresponding changes in extinction circuitry. Frontopolar multifocal transcranial direct current stimulation (tDCS) has been shown to improve therapeutic safety learning during in vivo exposure and may modulate functional connectivity of networks implicated in fear processing and inhibition. A pilot randomized controlled trial was completed to determine the effects of frontopolar tDCS on extinction learning and memory. Community volunteers (n = 35) completed a 3-day fear extinction paradigm with measurement of electrodermal activity. Participants were randomized (single-blind) to 20-min of sham (n = 17, 30 s. ramp in/out) or active (n = 18) frontopolar (anode over Fpz, 10-10 EEG) multifocal tDCS (20-min, 1.5 mA) prior to extinction training. Mixed ANOVAs revealed a significant group*trial effect on skin conductance response (SCR) to the conditioned stimulus (CS + ) during extinction training (p = 0.007, Cohen's d = 0.55). The effects of frontopolar tDCS were greatest during the first two extinction trials, suggesting that tDCS may have promoted fear inhibition prior to safety learning. Return of fear to the CS + during tests were comparable across conditions (ps > 0.50). These findings suggest that frontopolar tDCS may modulate the processing of threat cues and associated circuitry or promote the inhibition of fear. This has clear implications for the treatment of anxiety and related disorders with therapeutic exposure.

The Impacts of Sex Differences and Sex Hormones on Fear Extinction.

Fear extinction memories are strongly modulated by sex and hormonal status, but the exact mechanisms are still being discovered. In humans, there are some basal and task-related features in which male and female individuals differ in fear conditioning paradigms. However, analyses considering the effects of sex hormones demonstrate a role for estradiol in fear extinction memory consolidation. Translational studies are taking advantage of the convergent findings between species to understand the brain structures implicated. Nevertheless, the human brain is complex and the transfer of these findings into the clinics remains a challenge. The promising advances in the field together with the standardization of fear extinction methodologies in humans will benefit the design of new personalized therapies.

Role of sex hormones in the effects of sleep deprivation on methamphetamine reward memory.

Sleep deficiency is known as an important risk factor for relapse to drug abuse, especially for the powerful psychostimulant methamphetamine (METH). On the other hand, both drug addiction and sleep neurobiology are affected by sex hormones. We, therefore, aimed to examine the probable effects of sleep deprivation (SD) on methamphetamine (METH) reward memory in male and female rats. Moreover, we asked if sex hormones influence the effects of SD on METH reward memory. Adult male and female Wistar rats were divided into two main groups, sham and gonadectomized groups. Three weeks later, they were conditioned to receive METH (2 mg/kg, i.p.) in the conditioned place preference. METH reward memory was then reinstated following a 10-day extinction period. SD was induced for 72 h, either before or after extinction, in different groups. In gonadectomized animals, they daily received either subcutaneous administration of estrogen (5 µg/0.1 ml oil) or progesterone (2 mg/0.1 ml oil) or dihydrotestosterone (25 mg/0.1 ml oil) for thirteen days, from post-conditioning day to reinstatement session. We found that SD facilitated relapse to METH reward memory, depending on the time interval between SD and METH reinstatement. Furthermore, we found that estrogen and SD showed synergistic effects to facilitate METH reward memory, whereas testosterone and progesterone revealed inhibitory effects in the controls, but not in the SD, animals. Our findings would seem to suggest that sex hormones should be considered as determinant factors to manage METH abuse and relapse to METH seeking/taking behavior, especially for those with sleep deficiency.