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Adolescents, both human and nonhuman, exhibit impairments in the extinction of learned fear, an effect that is exacerbated, at least in rodents, by exposure to chronic stress. However, we have little understanding of the mechanisms underlying this effect. Therefore, here, we examined whether corticosterone exposure, a model of chronic stress, alters the expression of inhibitory neurons expressing parvalbumin (PV) in the basolateral amygdala and prefrontal cortex, two brain regions that have been implicated in fear extinction memories, in adolescent rats. We also examined the expression of perineuronal nets (PNNs), extracellular matrix structures that encompass inhibitory interneurons, in these two regions. These structures might render fear memories resistant to extinction by applying a structural "brake" on the plasticity of fear memories. Corticosterone-exposed adolescent rats exhibited poor extinction retention, as in past work, and were also found to have reduced percentage of PV-positive cells surrounded by PNNs in the basolateral amygdala. PV cells and PNNs were unaffected by corticosterone exposure in the prefrontal cortex. Our results suggest that the altered function of amygdala interneurons may be associated with the impaired extinction performance in stress-exposed adolescent rats. [ABSTRACT FROM AUTHOR]

The mammalian dopamine system exhibits notable diversity, with dopamine neurons forming functionally distinct and nonoverlapping subpopulations based on their projection targets. Dopamine neurons have crucial roles in mediating not only reward processing, but also threat and safety learning. Distinct dopaminergic circuits encode prediction errors for threats as well as absence of threats, which are critical dopamine signals for driving associative threat and safety learning, respectively. Dopamine neurons that encode salience also project to brain regions underlying threat and safety learning, and are likely involved in these forms of learning. Dopamine neurons mediate threat and safety learning through their projections to the amygdala, medial prefrontal cortex, and striatum. These distinct dopaminergic circuits mediate different phases of associative learning and memory for threats and safety. The ability to learn from experience that certain cues and situations are associated with threats or safety is crucial for survival and adaptive behavior. Understanding the neural substrates of threat and safety learning has high clinical significance because deficits in these forms of learning characterize anxiety disorders. Traditionally, dopamine neurons were thought to uniformly support reward learning by signaling reward prediction errors. However, the dopamine system is functionally more diverse than was initially appreciated and is also critical for processing threat and safety. In this review, I highlight recent studies demonstrating that dopamine neurons generate prediction errors for threat and safety, and describe how dopamine projections to the amygdala, medial prefrontal cortex (mPFC), and striatum regulate associative threat and safety learning. [ABSTRACT FROM AUTHOR]

• Female rats show faster and more effective trauma extinction than males. • Shock reminder reactivates fear memory only in male rats. • Ultrasonic vocalizations mirror fear behavior profiles in both sexes. • Study underscores the need for female inclusion in preclinical PTSD research. Post-Traumatic Stress Disorder (PTSD) is a complex psychiatric condition arising from traumatic experiences, marked by abnormal fear memories. Despite women are twice as likely as men to develop PTSD, the biological mechanisms underlying this disparity remain inadequately explored, particularly in preclinical studies involving female subjects. Previous research shows that female rats exhibit active fear responses, while males display passive behaviors. Additionally, sex differences in ultrasonic vocalizations (USVs) during fear conditioning have been observed, indicating varying emotional responses. Here, we validated a traumatic stress model consisting of footshock exposure paired with social isolation − originally developed in male rats − on females for the first time, focusing on sex differences in fear memory expression, retention and extinction. Our findings reveal that only during trauma exposure, males predominantly exhibited passive responses, whereas females demonstrated more active responses, despite both sexes emitting similar numbers of alarm USVs. Females also showed lower levels of freezing and USV emissions throughout extinction sessions and displayed a higher extinction rate compared to males. Notably, only males displayed a conditioned fear response when triggered by a single mild stressor. These findings highlight sex differences in trauma responses and fear memory processes. The study emphasizes the importance of incorporating 22-kHz USV evaluations along with other behavioral metrics for a comprehensive understanding of fear memory. This research contributes to the existing literature on traumatic stress models as well as underscores the necessity of including female subjects in preclinical studies to better inform treatment and prevention strategies tailored to both sexes. [ABSTRACT FROM AUTHOR]

Post-traumatic stress disorder (PTSD) is a debilitating neuropsychiatric condition closely linked to neuroinflammation, with a higher prevalence in women. Cannabidiol (CBD), a non-psychoactive cannabinoid, has shown promise as a potential treatment for PTSD. In this study, we used a PTSD model in which female rats were subjected to a severe foot shock followed by contextual situational reminders (SRs). Testing was conducted one month after exposure. The rats received daily CBD injections for three weeks during the SRs, from days 7 to 28. Two days after the final SR, the rats underwent five extinction trials, followed by the forced swim test (FST). After a five-day rest period, the rats were sacrificed, and brain tissues from the medial prefrontal cortex (mPFC) and ventral subiculum (vSUB) were analyzed for inflammatory markers. Chronic CBD treatment reversed impairments in fear extinction caused by shock and SR. It also reduced learned helplessness in the FST and decreased the upregulation of mPFC-il1β induced by shock and SRs. Additionally, exposure to shock and SRs downregulated mPFC-il6 while upregulating vSUB-il6. CBD treatment further downregulated il6 expression in the vSUB compared to the vehicle groups. Our findings show that CBD effectively inhibited the development of PTSD-like behaviors and suppressed neuroinflammation in the mPFC. [ABSTRACT FROM AUTHOR]

We conducted a meta-analysis and qualitative review on the randomized controlled trials investigating the effects of transcranial direct current stimulation and transcranial magnetic stimulation on fear extinction and the return of fear in non-primate animals and humans. The meta-analysis was conducted by searching PubMed, Web of science, PsycINFO, and Cochrane Library and extracting fear response in the active and sham groups in the randomized controlled trials. The pooled effect size was quantified by Hedges' g using a three-level meta-analytic model in R. We identified 18 articles on the tDCS effect and 5 articles on the TMS effect, with 466 animal subjects and 621 human subjects. Our findings show that tDCS of the prefrontal cortex significantly inhibit fear retrieval in animal models (Hedges' g = -0.50). In human studies, TMS targeting the dorsolateral/ventromedial prefrontal cortex has an inhibiting effect on the return of fear (Hedges' g = -0.24). The limited number of studies and the heterogeneous designs of the selected studies made cross-study and cross-species comparison difficult. Our findings shed light on the optimal non-invasive brain stimulation protocols for targeting the neural circuitry of threat extinction in humans. [ABSTRACT FROM AUTHOR]

Background and Purpose: Post-traumatic stress disorder (PTSD) is a type of psychotic illness that can occur after traumatic events such as war, childhood abuse, rape, natural disasters like earthquakes, and other unfortunate life events. These stresses can damage different brain areas, leading to behavioral changes associated with these regions. Chronic stress increases the activity of microglial cells, resulting in the loss of dendritic spines in the medial prefrontal cortex and hippocampus. Additionally, memory formation is impaired after stress exposure, leading to the inability to replace new memories with previous disturbing ones. The pathophysiology of PTSD involves changes in specific anatomical regions and circuits of the brain. Damage to the prefrontal cortex (PFC) can hinder the ability to forget inappropriate and disturbing memories. The PFC plays a crucial role in the brain's physiological response, providing the necessary functions to create calm, rational, and flexible responses. Studies have shown that acute stress weakens the prefrontal cortex. Medications for psychotic disorders have side effects, and there is a risk of relapse in some patients. Finding new treatment methods with greater benefits and minimal side effects is essential. Exercise, as an adjunctive treatment, may improve the structural and functional changes caused by stress. Materials and Methods: In this experiment, Wistar male laboratory rats and a single prolonged stress animal model were used as valid models for PTSD induction. Following a 4-week exercise intervention on a treadmill (forced exercise at moderate intensity) — the first two weeks at a speed of 10 m/min for half an hour a day and the second two weeks at a speed of 15 m/min for half an hour a day, 5 days per week — cognitive memory and fear extinction were evaluated using behavioral tests (ORMT and Extinction). The animals were then euthanized under deep anesthesia with ketamine and xylazine. The brains were removed, and the hippocampus was fixed for histological studies using the Golgi staining method. The prefrontal cortex was also frozen at -80°C for BDNF measurement. Results: The results of this study showed that rats suffering from PTSD exhibited a decrease in fear extinction (the ability to forget disturbing memories), an increase in freezing behavior, a reduction in cognitive memory, a decrease in BDNF levels in the prefrontal cortex, and a reduction in dendritic branches. The selected exercise program significantly improved behavioral deficits (cognitive memory and fear extinction) and reduced freezing behavior as a measure of fear. Additionally, BDNF levels in the prefrontal cortex increased, and a relative increase in dendritic branches in the hippocampus was observed after the exercise protocol. Conclusion: A regular 4-week course of moderate-intensity exercise can improve the structural and functional damage caused by stress in an animal model of PTSD, particularly in the hippocampus and prefrontal cortex, as well as ameliorate deficits in cognitive memory and reduce fear responses.

Introduction: Fear extinction is a fundamental component of exposure-based therapies for anxiety-related disorders. The renewal of fear in a different context after extinction highlights the importance of contextual factors. In this study, we aimed to investigate the causal role of the left inferior frontal gyrus (LiFG) in the context-dependency of fear extinction learning via administration of transcranial direct current stimulation (tDCS) over this area. Methods: 180 healthy subjects were assigned to 9 groups: 3 tDCS conditions (anodal, cathodal, and sham) × 3 context combinations (AAA, ABA, and ABB). The fear conditioning/extinction task was conducted over three consecutive days: acquisition, extinction learning, and extinction recall. tDCS (2 mA, 10min) was administered during the extinction learning phase over the LiFG via a 4-electrode montage. Skin conductance response (SCR) data and self-report assessments were collected. Results: During the extinction learning phase, groups with excitability-enhancing anodal tDCS showed a significantly higher fear response to the threat cues compared to cathodal and sham stimulation conditions, irrespective of contextual factors. This effect was stable until the extinction recall phase. Additionally, excitability-reducing cathodal tDCS caused a significant decrease of the response difference between the threat and safety cues during the extinction recall phase. The self-report assessments showed no significant differences between the conditions throughout the experiment. Conclusion: Independent of the context, excitability enhancement of the LiFG did impair fear extinction, and led to preservation of fear memory. In contrast, excitability reduction of this area enhanced fear extinction retention. These findings imply that the LiFG plays a role in the fear extinction network, which seems to be however context-independent.

The role of the cerebellum in emotional control has gained increasing interest, with studies showing it is involved in fear learning and memory in both humans and rodents. This review will focus on the contributions of the cerebellum to the extinction of learned fear responses. Extinction of fearful memories is critical for adaptive behaviour, and is clinically relevant to anxiety disorders such as post-traumatic stress disorder, in which deficits in extinction processes are thought to occur. We present evidence that supports cerebellar involvement in fear extinction, from rodent studies that investigate molecular mechanisms and functional connectivity with other brain regions of the known fear extinction network, to fMRI studies in humans. This evidence is considered in relation to the theoretical framework that the cerebellum is involved in the formation and updating of internal models of the inner and outer world by detecting errors between predicted and actual outcomes. In the case of fear conditioning, these internal models are thought to predict the occurrence of an aversive unconditioned stimulus (US), and when the aversive US is unexpectedly omitted during extinction learning the cerebellum uses prediction errors to update the internal model. Differences between human and rodent studies are highlighted to help inform future work. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background and Purpose: Post-traumatic stress disorder (PTSD) is a type of psychotic illness that can occur after traumatic events such as war, childhood abuse, rape, natural disasters like earthquakes, and other unfortunate life events. These stresses can damage different brain areas, leading to behavioral changes associated with these regions. Chronic stress increases the activity of microglial cells, resulting in the loss of dendritic spines in the medial prefrontal cortex and hippocampus. Additionally, memory formation is impaired after stress exposure, leading to the inability to replace new memories with previous disturbing ones. The pathophysiology of PTSD involves changes in specific anatomical regions and circuits of the brain. Damage to the prefrontal cortex (PFC) can hinder the ability to forget inappropriate and disturbing memories. The PFC plays a crucial role in the brain's physiological response, providing the necessary functions to create calm, rational, and flexible responses. Studies have shown that acute stress weakens the prefrontal cortex. Medications for psychotic disorders have side effects, and there is a risk of relapse in some patients. Finding new treatment methods with greater benefits and minimal side effects is essential. Exercise, as an adjunctive treatment, may improve the structural and functional changes caused by stress. Materials and Methods: In this experiment, Wistar male laboratory rats and a single prolonged stress animal model were used as valid models for PTSD induction. Following a 4-week exercise intervention on a treadmill (forced exercise at moderate intensity) — the first two weeks at a speed of 10 m/min for half an hour a day and the second two weeks at a speed of 15 m/min for half an hour a day, 5 days per week — cognitive memory and fear extinction were evaluated using behavioral tests (ORMT and Extinction). The animals were then euthanized under deep anesthesia with ketamine and xylazine. The brains were removed, and the hippocampus was fixed for histological studies using the Golgi staining method. The prefrontal cortex was also frozen at -80°C for BDNF measurement. Results: The results of this study showed that rats suffering from PTSD exhibited a decrease in fear extinction (the ability to forget disturbing memories), an increase in freezing behavior, a reduction in cognitive memory, a decrease in BDNF levels in the prefrontal cortex, and a reduction in dendritic branches. The selected exercise program significantly improved behavioral deficits (cognitive memory and fear extinction) and reduced freezing behavior as a measure of fear. Additionally, BDNF levels in the prefrontal cortex increased, and a relative increase in dendritic branches in the hippocampus was observed after the exercise protocol. Conclusion: A regular 4-week course of moderate-intensity exercise can improve the structural and functional damage caused by stress in an animal model of PTSD, particularly in the hippocampus and prefrontal cortex, as well as ameliorate deficits in cognitive memory and reduce fear responses. [ABSTRACT FROM AUTHOR]

Exposure treatment involves systematic confrontation with fear-inducing stimuli, effectively reducing fear and anxiety. However, a significant number of clients still experience a return of fear (ROF) after treatment. This study investigates whether incorporating an approach component during fear extinction, a laboratory exposure analog, could mitigate this return of fear. Furthermore, we explored the underlying mechanisms by drawing on predictions from the inhibitory learning theory and the reflective-impulsive model of behavior. In a within-subjects design, we compared instructed active approach of a stimulus during extinction to more passive non-avoidance. Contrary to expectations, our findings revealed that performing approach behavior during extinction did not reduce ROF when compared to non-avoidance. Furthermore, valence and action tendencies, which were potential mechanisms based on the reflective-impulsive model of behavior, remained unaltered. Still, a noteworthy discovery emerged in the form of increased threat expectancies for the approached stimulus during extinction, suggesting a heightened level of expectancy violation, as predicted on the basis of the inhibitory learning theory. These findings offer valuable insights into the intricate relationship between approach behavior, ROF, and underlying mechanisms, highlighting the need for further research to assess the potential benefits of emphasizing approach in exposure treatment. [ABSTRACT FROM AUTHOR]

MDMA-assisted psychotherapy has shown potential as an effective treatment for post-traumatic stress disorder (PTSD). Preclinical studies involving rodents have demonstrated that MDMA can facilitate the extinction of fear memories. It has been noted that MDMA impacts oxytocin neurons and pro-inflammatory cytokines. Thus, the aim of this study was to explore the role of oxytocinergic signaling and neuroinflammatory markers in the therapeutic effects of MDMA. To achieve this, male rats were subjected to a model of PTSD involving exposure to shock and situational reminders. MDMA was microinjected into the medial prefrontal cortex (mPFC) before extinction training, followed by behavioral tests assessing activity levels, anxiety, and social function. Our findings indicate that MDMA treatment facilitated fear extinction and mitigated the shock-induced increase in freezing, as well as deficits in social behavior. Shock exposure led to altered expression of the gene coding for OXT-R and neuroinflammation in the mPFC and basolateral amygdala (BLA), which were restored by MDMA treatment. Importantly, the OXT-R antagonist L-368,899 prevented MDMA's therapeutic effects on extinction and freezing behavior. In conclusion, MDMA's therapeutic effects in the PTSD model are associated with alterations in OXT-R expression and neuroinflammation, and MDMA's effects on extinction and anxiety may be mediated by oxytocinergic signaling. [ABSTRACT FROM AUTHOR]

Objective: Anorexia nervosa (AN) is a pernicious psychiatric disorder which is principally characterized by a fear of weight gain. Notwithstanding the centrality of fear in the psychopathology of AN, controlled assessments of negative valence systems are lacking. Herein we assess fear conditioning in adolescent females with AN. Method: Adolescent girls (Mage = 14.6 years, ±1.57) with DSM‐5 diagnoses of AN (N = 25) and age‐matched control girls (Mage = 14.8 years, ±1.46) with no DSM‐5 diagnoses (N = 25) completed structured clinical interviews and participated in a classical three‐phase Pavlovian fear conditioning paradigm. Participants with comorbid anxiety disorders were excluded. Skin conductance response (SCR) was measured, alongside self‐reported fear, valence, and fear expectancy ratings. Results: Both groups demonstrated significant differential acquisition across all four measures. Regarding group comparisons, no differences emerged for self‐reported fear, valence, and fear expectancy ratings during acquisition, although for SCR, those with AN demonstrated reduced physiological arousal relative to controls. Both groups demonstrated significant differential extinction for unconditioned stimuli (US) expectancy, self‐report fear, and self‐report valence. No statistically significant group differences were evident during extinction to the conditioned stimuli (CS)+, on any outcome measure. However, controls reported more positive valence to the CS− than those with AN. Conclusions: Contrary to our hypotheses, our preliminary assessment did not find support for elevated fear responding among adolescent girls with AN with regards to fear acquisition or extinction. These data suggest that AN in adolescent girls may not be associated with a heightened propensity to acquire fear, but conversely, may suggest that exposure treatments for AN may be helpful, since extinction learning is intact in AN. Public significance: AN is characterized by fear‐related symptoms, including food and weight‐related fear, and behavioral avoidance, yet controlled studies assessing fear learning are limited. Our preliminary assessment of adolescent AN indicates no abnormalities in fear learning among adolescents with AN. These findings may inform existing mechanistic models of AN psychopathology, and the development of exposure‐based treatments for AN. [ABSTRACT FROM AUTHOR]

Fear extinction is a fundamental component of exposure-based therapies for anxiety-related disorders. The renewal of fear in a different context after extinction highlights the importance of contextual factors. In this study, we aimed to investigate the causal role of the left inferior frontal gyrus (LiFG) in the context-dependency of fear extinction learning via administration of transcranial direct current stimulation (tDCS) over this area. 180 healthy subjects were assigned to 9 groups: 3 tDCS conditions (anodal, cathodal, and sham) × 3 context combinations (AAA, ABA, and ABB). The fear conditioning/extinction task was conducted over three consecutive days: acquisition, extinction learning, and extinction recall. tDCS (2 mA, 10min) was administered during the extinction learning phase over the LiFG via a 4-electrode montage. Skin conductance response (SCR) data and self-report assessments were collected. During the extinction learning phase, groups with excitability-enhancing anodal tDCS showed a significantly higher fear response to the threat cues compared to cathodal and sham stimulation conditions, irrespective of contextual factors. This effect was stable until the extinction recall phase. Additionally, excitability-reducing cathodal tDCS caused a significant decrease of the response difference between the threat and safety cues during the extinction recall phase. The self-report assessments showed no significant differences between the conditions throughout the experiment. Independent of the context, excitability enhancement of the LiFG did impair fear extinction, and led to preservation of fear memory. In contrast, excitability reduction of this area enhanced fear extinction retention. These findings imply that the LiFG plays a role in the fear extinction network, which seems to be however context-independent. • Using multiple contextual conditions and tDCS to assess the role of the left inferior frontal gyrus in fear extinction. • tDCS over the left inferior frontal gyrus affected fear extinction independent of context. • tDCS polarity determined the directionality of effects on extinction, and recall. [ABSTRACT FROM AUTHOR]

‘Abstract: The basolateral amygdala (BLA) is a dynamic brain region involved in emotional experiences and subject to long-term plasticity. The BLA also modulates activity, plasticity, and related behaviors associated with other brain regions, including the mPFC and hippocampus. Accordingly, intra-BLA plasticity can be expected to alter both BLA-dependent behaviors and behaviors mediated by other brain regions. Lasting intra-BLA plasticity may be considered a form of metaplasticity, since it will affect subsequent plasticity and response to challenges later on. Activity within the BLA is tightly modulated by GABAergic interneurons, and thus inducing lasting alteration of GABAergic modulation of principal neurons may have an impactful metaplastic effect on BLA functioning. Previously, we demonstrated that intra-BLA knockdown (KD) of neurofascin (NF) reduced GABAergic synapses exclusively at the axon initial segment (AIS). Here, by reducing the expression of the tyrosine kinase receptor ephrin A7 (EphA7), we selectively impaired the modulatory function of a different subpopulation of interneurons, specifically targeting the soma and proximal dendrites of principal neurons. This perturbation induced an expected reduction in the spontaneous inhibitory synaptic input and an increase in the excitatory spontaneous synaptic activity, most probably due to the reduction of inhibitory tone. Moreover, this increased synaptic activity was followed by a reduction in intrinsic excitability. While intra-BLA NF-KD resulted in impaired extinction learning, without increased symptoms of anxiety, intra-BLA reduction of EphA7 expression resulted in increased symptoms of anxiety, as measured in the elevated plus maze, but without affecting fear conditioning or extinction learning. These results confirm the role of the BLA and intra-BLA metaplasticity in stress-induced increased anxiety symptoms and in impaired fear extinction learning but reveals a difference in intra-BLA mechanisms involved. The results also confirm the contribution of GABAergic interneurons to these effects but indicate selective roles for different subpopulations of intra-BLA interneurons.

Abstract Background Fear memory extinction is closely related to insomnia. Repetitive transcranial magnetic stimulation (rTMS) is safe and effective for treating insomnia disorder (ID), and it has been shown to be an efficient method for modulating fear extinction. However, whether rTMS can improve fear extinction memory in ID patients remains to be studied. In this study, we specifically aim to (1) show that 1 Hz rTMS stimulation could improve fear extinction memory in ID patients and (2) examine whether changes in sleep mediate this impact. Methods and design We propose a parallel group randomised controlled trial of 62 ID participants who meet the inclusion criteria. Participants will be assigned to a real rTMS group or a sham rTMS group. The allocation ratio will be 1:1, with 31 subjects in each group. Interventions will be administered five times per week over a 4-week period. The assessments will take place at baseline (week 0), post-intervention (week 4), and 8-week follow-up (week 8). The primary outcome measure of this study will be the mean change in the Pittsburgh Sleep Quality Index (PSQI) scores from baseline to post-intervention at week 4. The secondary outcome measures include the mean change in skin conductance response (SCR), fear expectation during fear extinction, Insomnia Severity Index (ISI), Zung Self-Rating Anxiety Scale (SAS), and the Zung Self-Rating Depression Scale (SDS). Discussion This study will be the first examination of the impact of rTMS on fear memory extinction in ID patients. Trial registration Chinese Clinical Trials Register ChiCTR2300076097. Registered on 25 September 2021.

Adult hippocampal neurogenesis is a lifelong process that involves the integration of newborn neurons into the hippocampal network, and plays a role in cognitive function and the modulation of mood-related behavior. Here, we sought to address the impact of chemogenetic activation of adult hippocampal progenitors on distinct stages of progenitor development, including quiescent stem cell activation, progenitor turnover, differentiation and morphological maturation. We find that hM3Dq-DREADD-mediated activation of nestin-positive adult hippocampal progenitors recruits quiescent stem cells, enhances progenitor proliferation, increases doublecortin-positive newborn neuron number, accompanied by an acceleration of differentiation and morphological maturation, associated with increased dendritic complexity. Behavioral analysis indicated anxiolytic behavioral responses in transgenic mice subjected to chemogenetic activation of adult hippocampal progenitors at timepoints when newborn neurons are predicted to integrate into the mature hippocampal network. Furthermore, we noted an enhanced fear memory extinction on a contextual fear memory learning task in transgenic mice subjected to chemogenetic activation of adult hippocampal progenitors. Our findings indicate that hM3Dq-DREAD-mediated chemogenetic activation of adult hippocampal progenitors impacts distinct aspects of hippocampal neurogenesis, associated with the regulation of anxiety-like behavior and fear memory extinction.

Background and purpose: Unpredictable stressors cause changes in behavioral parameters such as motor and exploratory behaviors, feeding, and sexual and anxiety behaviors. Stress leads to the release of corticosteroids and, as a result, causes dysfunction in different parts of the nervous system. A decrease in the synaptic levels of serotonin or norepinephrine in different parts of the brain such as the prefrontal cortex and a decrease in BDNF production in the hippocampus may also contribute to stress-related complications. Posttraumatic stress disorder occurs in some people after facing a severe stressful event. In PTSD, the activity and function of many physiological systems are disturbed. Fluoxetine, or Prozac, is used to treat neurological disorders such as depression and anxiety and inhibits the reuptake of serotonin by the serotonin transporter (SERT) in neurons. Some studies have shown that females respond better to SSRI antidepressants than males, which may be due to the interaction between estrogenic and serotonergic pathways. BDNF is a member of the neurotrophin family and is expressed in several tissues and cells such as the brain and blood. Its role in several mental disorders, such as depression, anxiety, eating disorders, and PTSD, has been identified. SPS (single prolonged stress) as an animal model of PTSD decreases the mRNA expression of BDNF in hippocampus rats and causes anxiety-like behaviors. The role of gender differences in the effect of antidepressants and clinical interventions in psychotic diseases is also discussed. Sex hormones in women affect the pharmacokinetics and efficacy of antidepressants. Women respond better to fluoxetine than men during reproductive years. Considering the different results regarding the effectiveness of effective drugs in the treatment of psychotic diseases in both sexes, in this study, we aim to investigate the response of male and female rats exposed to stress to the trial of fluoxetine. Materials and methods: In this experimental study, Wistar male and female rats with an average weight of 200-250 grams were used (56 animals, 8 groups of 7). The selection of the number of animals was based on previous studies in this field. After the drug intervention period, and fear and anxiety suppression test, the animals were killed under deep anesthesia, and a blood sample was collected to prepare serum to measure BDNF and corticosterone levels (using the Eliza kit of Germany Zelbio Company and according to the kit protocol). All experiments were performed according to the laboratory animal protocol of Mazandaran University of Medical Sciences. The work steps are as follows: 1. Creation of PTSD through SPS was done in three stages, 2. Drug intervention: the drug dose for all groups is 10 mg/kg/day for 4 weeks dissolved in drinking water, 3. Evaluation of anxiety-like behaviors with the light-dark box (L/D BOX), 4. Evaluation of the ability to forget painful memories with the fear silence test, 5. Measurement of BDNF and corticosterone in serum by Eliza method. Results: In this study, it was observed that male and female rats that were exposed to single prolonged stress showed a decrease in fear extinction an increase in anxiety-like behaviors in the dark-light box test, and an increase in serum corticosterone. Fluoxetine led to an increase in the percentage of fear extinction, a decrease in the Entrance Latency in the light area, the Time in the Light Compartment, the number of rearing, and a decrease in serum corticosterone significantly in both sexes(P

Fear-related disorders, including post-traumatic stress disorder (PTSD), and anxiety disorders are pervasive psychiatric conditions marked by persistent fear, stemming from its dysregulated acquisition and extinction. The primary treatment for these disorders, exposure therapy (ET), relies heavily on fear extinction (FE) principles. Adolescence, a vulnerable period for developing psychiatric disorders, is characterized by neurobiological changes in the fear circuitry, leading to impaired FE and increased susceptibility to relapse following ET. Ketamine, known for relieving anxiety and reducing PTSD symptoms, influences fear-related learning processes and synaptic plasticity across the fear circuitry. Our study aimed to investigate the effects of ketamine (10 mg/kg) on FE in adolescent male C57 BL/6 mice at the behavioral and molecular levels. We analyzed the protein and gene expression of synaptic plasticity markers in the hippocampus (HPC) and prefrontal cortex (PFC) and sought to identify neural correlates associated with ketamine's effects on adolescent extinction learning. Ketamine ameliorated FE in the adolescent males, likely affecting the consolidation and/or recall of extinction memory. Ketamine also increased the Akt and mTOR activity and the GluA1 and GluN2A levels in the HPC and upregulated BDNF exon IV mRNA expression in the HPC and PFC of the fear-extinguished mice. Furthermore, ketamine increased the c-Fos expression in specific brain regions, including the ventral HPC (vHPC) and the left infralimbic ventromedial PFC (IL vmPFC). Providing a comprehensive exploration of ketamine's mechanisms in adolescent FE, our study suggests that ketamine's effects on FE in adolescent males are associated with the activation of hippocampal Akt-mTOR-GluA1 signaling, with the vHPC and the left IL vmPFC as the proposed neural correlates. [ABSTRACT FROM AUTHOR]

Background: Laboratory paradigms are widely used to study fear learning in posttraumatic stress disorder (PTSD). Recent basic science models demonstrate that, during fear learning, patterns of activity in large neuronal ensembles for the conditioned stimuli (CS) begin to reinstate neural activity patterns for the unconditioned stimuli (US), suggesting a direct way of quantifying fear memory strength for the CS. Here, we translate this concept to human neuroimaging and test the impact of post-learning dopaminergic neurotransmission on fear memory strength during fear acquisition, extinction, and recall among women with PTSD in a re-analysis of previously reported data. Methods: Participants (N = 79) completed a context-dependent fear acquisition and extinction task on day 1 and extinction recall tests 24 h later. We decoded activity patterns in large-scale functional networks for the US, then applied this decoder to activity patterns toward the CS on day 1 and day 2. Results: US decoder output for the CS+ increased during acquisition and decreased during extinction in networks traditionally implicated in human fear learning. The strength of US neural reactivation also predicted individuals skin conductance responses. Participants randomized to receive L-DOPA (n = 43) following extinction on day 1 demonstrated less US neural reactivation on day 2 relative to the placebo group (n = 28). Conclusion: These results support neural reactivation as a measure of memory strength between competing memories of threat and safety and further demonstrate the role of dopaminergic neurotransmission in the consolidation of fear extinction memories. [ABSTRACT FROM AUTHOR]

Understanding why only a subset of trauma-exposed individuals develop posttraumatic stress disorder is critical for advancing clinical strategies. A few behavioral (deficits in fear extinction) and biological (blunted glucocorticoid levels, small hippocampal size, and rapid-eye-movement sleep [REMS] disturbances) traits have been identified as potential vulnerability factors. However, whether and to what extent these traits are interrelated and whether one of them could causally engender the others are not known. In a genetically selected rat model of reduced corticosterone responsiveness to stress, we explored posttraumatic stress disorder–related biobehavioral traits using ex vivo magnetic resonance imaging, cued fear conditioning, and polysomnographic recordings combined with in vivo photometric measurements. We showed that genetic selection for blunted glucocorticoid responsiveness led to a correlated multitrait response, including impaired fear extinction (observed in males but not in females), small hippocampal volume, and REMS disturbances, supporting their interrelatedness. Fear extinction deficits and concomitant disruptions in REMS could be normalized through postextinction corticosterone administration, causally implicating glucocorticoid deficiency in two core posttraumatic stress disorder–related risk factors and manifestations. Furthermore, reduced REMS was accompanied by higher norepinephrine levels in the hippocampal dentate gyrus that were also reversed by postextinction corticosterone treatment. Our results indicate a predominant role for glucocorticoid deficiency over the contribution of reduced hippocampal volume in engendering both REMS alterations and associated deficits in fear extinction consolidation, and they causally implicate blunted glucocorticoids in sustaining neurophysiological disturbances that lead to fear extinction deficits. [ABSTRACT FROM AUTHOR]

Posttraumatic stress disorder (PTSD) is a widespread fear-related psychiatric affection associated with fear extinction impairments and important avoidance behaviors. Trauma-related exposure therapy is the current first-hand treatment for PTSD, yet it needs to be improved to shorten the time necessary to reach remission and increase responsiveness. Additional studies to decipher the neurobiological bases of extinction and effects on PTSD-like symptoms could therefore be of use. However, a PTSD-like animal model exhibiting pronounced PTSD-related phenotypes even after an extinction training directly linked to the fearful event is necessary. Thus, using a contextual fear conditioning model of PTSD, we increased the severity of stress during conditioning to search for effects on extinction acquisition and on pre- and post-extinction behaviors. During conditioning, mice received either two or four electrical shocks while a control group was constituted of mice only exposed to the context. Stressed mice exhibited important fear generalization, high fear reaction to the context and selective avoidance of a contextual reminder even after the extinction protocol. Increasing the number of footshocks did not induce major changes on these behaviors. [ABSTRACT FROM AUTHOR]

Rationale: Preclinical research suggests that pharmacologically elevating cannabinoid levels may attenuate fear memory expression and enhance fear extinction. Objectives: We studied the effects of cannabidiol (CBD) on fear memory expression and fear re-extinction in 69 patients with panic disorder with agoraphobia or with social anxiety disorder. Moderation by sex, diagnosis, and serotonergic antidepressant (AD) use was explored. Methods: A cued fear conditioning paradigm was applied before the first treatment session with 300 mg CBD/placebo augmented exposure therapy. Study medication was administered orally preceding 8 weekly sessions. Fear acquisition and suboptimal extinction took place prior to the first medication ingestion (T0). After the first medication ingestion (T1), we investigated effects on fear memory expression at retention and fear re-extinction. Subjective fear, shock expectancy, skin conductance, and startle responses to conditioned (CS+) and safety stimulus (CS−) were measured. Results: Across the sample, CBD reduced shock expectancy at retention under low and ambiguous threat of shock, but fear re-extinction at T1 was unaffected by CBD. However, in AD users, re-extinction of subjective fear was impaired in the CBD condition compared to placebo. In female AD users, CBD interfered with safety learning measured with fear-potentiated startle. Conclusions: The current findings provide no evidence for enhanced fear re-extinction by CBD. However, CBD acutely decreased threat expectation at retention, without affecting other indices of fear. More studies are needed to elucidate possible interactions with AD use and sex, as well as potential effects of CBD on threat expectancies. [ABSTRACT FROM AUTHOR]

Background and purpose: Unpredictable stressors cause changes in behavioral parameters such as motor and exploratory behaviors, feeding, and sexual and anxiety behaviors. Stress leads to the release of corticosteroids and, as a result, causes dysfunction in different parts of the nervous system. A decrease in the synaptic levels of serotonin or norepinephrine in different parts of the brain such as the prefrontal cortex and a decrease in BDNF production in the hippocampus may also contribute to stress-related complications. Posttraumatic stress disorder occurs in some people after facing a severe stressful event. In PTSD, the activity and function of many physiological systems are disturbed. Fluoxetine, or Prozac, is used to treat neurological disorders such as depression and anxiety and inhibits the reuptake of serotonin by the serotonin transporter (SERT) in neurons. Some studies have shown that females respond better to SSRI antidepressants than males, which may be due to the interaction between estrogenic and serotonergic pathways. BDNF is a member of the neurotrophin family and is expressed in several tissues and cells such as the brain and blood. Its role in several mental disorders, such as depression, anxiety, eating disorders, and PTSD, has been identified. SPS (single prolonged stress) as an animal model of PTSD decreases the mRNA expression of BDNF in hippocampus rats and causes anxiety-like behaviors. The role of gender differences in the effect of antidepressants and clinical interventions in psychotic diseases is also discussed. Sex hormones in women affect the pharmacokinetics and efficacy of antidepressants. Women respond better to fluoxetine than men during reproductive years. Considering the different results regarding the effectiveness of effective drugs in the treatment of psychotic diseases in both sexes, in this study, we aim to investigate the response of male and female rats exposed to stress to the trial of fluoxetine. Materials and methods: In this experimental study, Wistar male and female rats with an average weight of 200-250 grams were used (56 animals, 8 groups of 7). The selection of the number of animals was based on previous studies in this field. After the drug intervention period, and fear and anxiety suppression test, the animals were killed under deep anesthesia, and a blood sample was collected to prepare serum to measure BDNF and corticosterone levels (using the Eliza kit of Germany Zelbio Company and according to the kit protocol). All experiments were performed according to the laboratory animal protocol of Mazandaran University of Medical Sciences. The work steps are as follows: 1. Creation of PTSD through SPS was done in three stages, 2. Drug intervention: the drug dose for all groups is 10 mg/kg/day for 4 weeks dissolved in drinking water, 3. Evaluation of anxiety-like behaviors with the light-dark box (L/D BOX), 4. Evaluation of the ability to forget painful memories with the fear silence test, 5. Measurement of BDNF and corticosterone in serum by Eliza method. Results: In this study, it was observed that male and female rats that were exposed to single prolonged stress showed a decrease in fear extinction an increase in anxiety-like behaviors in the dark-light box test, and an increase in serum corticosterone. Fluoxetine led to an increase in the percentage of fear extinction, a decrease in the Entrance Latency in the light area, the Time in the Light Compartment, the number of rearing, and a decrease in serum corticosterone significantly in both sexes(P<0.05). The change in serum BDNF levels in both sexes before and after stress was not significant. Conclusion: The results of the study showed that exposure to stress leads to behavioral and biochemical damage in male and female rats. The use of fluoxetine 10 mg/kg for 4 weeks improved the damage caused by stress, but there was a significant difference in Response of both genders to the above treatment was not observed. [ABSTRACT FROM AUTHOR]

Background: The renin-angiotensin system has been identified as a potential therapeutic target for posttraumatic stress disorder, although its mechanisms are not well understood. Brain angiotensin type 2 receptors (AT2Rs) are a subtype of angiotensin II receptors located in stress and anxiety-related regions, including the medial prefrontal cortex (mPFC), but their function and mechanism in the mPFC remain unexplored. Therefore, we used a combination of imaging, cre/lox, and behavioral methods to investigate mPFC-AT2R–expressing neurons in fear and stess related behavior. Methods: To characterize mPFC-AT2R–expressing neurons in the mPFC, AT2R-Cre/tdTomato male and female mice were used for immunohistochemistry. mPFC brain sections were stained with glutamatergic or interneuron markers, and density of AT2R+ cells and colocalization with each marker were quantified. To assess fear-related behaviors in AT2R-flox mice, we selectively deleted AT2R from mPFC neurons using a Cre-expressing adeno-associated virus. Mice then underwent Pavlovian auditory fear conditioning, elevated plus maze, and open field testing. Results: Immunohistochemistry results revealed that AT2R was densely expressed throughout the mPFC and primarily expressed in somatostatin interneurons in a sex-dependent manner. Following fear conditioning, mPFC-AT2R Cre-lox deletion impaired extinction and increased exploratory behavior in female but not male mice, while locomotion was unaltered by mPFC-AT2R deletion in both sexes. Conclusions: These results identify mPFC-AT2R+ neurons as a novel subgroup of somatostatin interneurons and reveal their role in regulating fear learning in a sex-dependent manner, potentially offering insights into novel therapeutic targets for posttraumatic stress disorder.

Transcranial focused ultrasound (tFUS) neuromodulation emerges as a promising non-invasive approach for improving neurological conditions. Extinction of conditioned fear has served as a prime model for exposure-based therapies for anxiety disorders. We investigated whether tFUS stimulation to a critical brain area, the infralimbic subdivision of the prefrontal cortex (IL), could facilitate fear extinction using rats. In a series of experiments, tFUS was delivered to the IL of a freely-moving rat and compared to sham stimulation (tFUS vs. SHAM). Initially, Fos expression in the IL was measured shortly after the stimulation. The results show that Fos expression was significantly increased in the IL but not in the neighboring regions compared to SHAM. Subsequently, two groups of rats were subjected to fear conditioning, extinction, and retention while receiving stimulation during the extinction. Rats in the tFUS group froze significantly less than SHAM during both extinction and retention tests. Importantly, the reduced freezing in the tFUS group was not attributable to non-specific effect such as auditory noise, as both groups demonstrated a similar level of locomotive activity in an open field regardless of the stimulation condition. Finally, we replicated the procedure with a shortened conditioning-to-extinction interval (15 min) to induce immediate extinction deficit. The tFUS group showed a facilitated reduction in freezing during the extinction, which persisted in the subsequent retention session compared to SHAM. In summary, the current findings suggest that tFUS stimulation in the IL facilitates fear extinction, offering a potential therapeutic regimen for fear-related psychiatric disorders.

Abstract Aim Impairments in emotional memory are frequently observed in several mental disorders, highlighting their significance as potential therapeutic targets. Recent research on the cued fear conditioning model has elucidated the neural circuits involved in fear memory processing. However, contradictory findings have been reported concerning the role of dopamine and the impact of dopamine D2 receptor (D2R) antagonists. There is notably limited knowledge regarding the clinical utility of chronic D2R antagonist treatments. This study aimed to uncover how such treatments affect fear memory processing. Methods We utilized a cued fear conditioning rat model and conducted chronic haloperidol treatment for 14 days. Subsequently, to investigate the effect of chronic haloperidol treatment on fear‐conditioned memory expression and extinction, we observed freezing behavior under exposure to a conditioned stimulus for 14 days. Results Chronic haloperidol treatment suppressed freezing time on the fear memory expression. In contrast, a single haloperidol administration enhanced the freezing time on fear memory expression and delayed extinction. Conclusion The results of this study suggest that chronic administration of antipsychotic drugs affects fear memory processing differently from single‐dose administration. This indicates that the effects of chronic D2R antagonist treatment are distinct from the nonspecific effects of the drugs. This study provides fundamental insights that may contribute to our understanding of therapeutic mechanisms for fear memory disorders related to D2R in the future.

Post-traumatic stress disorder (PTSD) is a debilitating neuropsychiatric condition closely linked to neuroinflammation, with a higher prevalence in women. Cannabidiol (CBD), a non-psychoactive cannabinoid, has shown promise as a potential treatment for PTSD. In this study, we used a PTSD model in which female rats were subjected to a severe foot shock followed by contextual situational reminders (SRs). Testing was conducted one month after exposure. The rats received daily CBD injections for three weeks during the SRs, from days 7 to 28. Two days after the final SR, the rats underwent five extinction trials, followed by the forced swim test (FST). After a five-day rest period, the rats were sacrificed, and brain tissues from the medial prefrontal cortex (mPFC) and ventral subiculum (vSUB) were analyzed for inflammatory markers. Chronic CBD treatment reversed impairments in fear extinction caused by shock and SR. It also reduced learned helplessness in the FST and decreased the upregulation of mPFC-il1β induced by shock and SRs. Additionally, exposure to shock and SRs downregulated mPFC-il6 while upregulating vSUB-il6. CBD treatment further downregulated il6 expression in the vSUB compared to the vehicle groups. Our findings show that CBD effectively inhibited the development of PTSD-like behaviors and suppressed neuroinflammation in the mPFC.

Impaired extinction of fear memory is one of the most common symptoms in post‐traumatic stress disorder (PTSD), with limited therapeutic strategies due to the poor understanding of its underlying neural substrates. In this study, functional screening is performed and identified hyperactivity in the mediodorsal thalamic nucleus (MD) during fear extinction. Furthermore, the encoding patterns of the hyperactivated MD is investigated during persistent fear responses using multiple machine learning algorithms. The anterior cingulate cortex (ACC) is also identified as a functional downstream region of the MD that mediates the extinction of fear memory. The thalamocortical circuit is comprehensively analyzed and found that the MD‐ACC parvalbumin interneurons circuit is preferentially enhanced in PTSD mice, disrupting the local excitatory and inhibitory balance. It is found that decreased phosphorylation of the Kv3.2 channel contributed to the hyperactivated MD, primarily to the malfunctioning thalamocortical circuit. Using a lipid nanoparticle‐based RNA therapy strategy, channelopathy is corrected via a methoxylated siRNA targeting the protein phosphatase 6 catalytic subunit and restored fear memory extinction in PTSD mice. These findings highlight the function of the thalamocortical circuit in PTSD‐related impaired extinction of fear memory and provide therapeutic insights into Kv3.2‐targeted RNA therapy for PTSD. [ABSTRACT FROM AUTHOR]

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. • HPC activation in REM sleep consolidated fear extinction memory. • The dorsal HPC stimulation in REM sleep eliminated fear memory by enhancing fear extinction and reducing fear memory consolidation. • Wake HPC and REM HPC have an opposite role in fear extinction of respective impairment and consolidation. [ABSTRACT FROM AUTHOR]

Aim: Impairments in emotional memory are frequently observed in several mental disorders, highlighting their significance as potential therapeutic targets. Recent research on the cued fear conditioning model has elucidated the neural circuits involved in fear memory processing. However, contradictory findings have been reported concerning the role of dopamine and the impact of dopamine D2 receptor (D2R) antagonists. There is notably limited knowledge regarding the clinical utility of chronic D2R antagonist treatments. This study aimed to uncover how such treatments affect fear memory processing. Methods: We utilized a cued fear conditioning rat model and conducted chronic haloperidol treatment for 14 days. Subsequently, to investigate the effect of chronic haloperidol treatment on fear‐conditioned memory expression and extinction, we observed freezing behavior under exposure to a conditioned stimulus for 14 days. Results: Chronic haloperidol treatment suppressed freezing time on the fear memory expression. In contrast, a single haloperidol administration enhanced the freezing time on fear memory expression and delayed extinction. Conclusion: The results of this study suggest that chronic administration of antipsychotic drugs affects fear memory processing differently from single‐dose administration. This indicates that the effects of chronic D2R antagonist treatment are distinct from the nonspecific effects of the drugs. This study provides fundamental insights that may contribute to our understanding of therapeutic mechanisms for fear memory disorders related to D2R in the future. [ABSTRACT FROM AUTHOR]

Transcranial focused ultrasound (tFUS) neuromodulation emerges as a promising non-invasive approach for improving neurological conditions. Extinction of conditioned fear has served as a prime model for exposure-based therapies for anxiety disorders. We investigated whether tFUS stimulation to a critical brain area, the infralimbic subdivision of the prefrontal cortex (IL), could facilitate fear extinction using rats. In a series of experiments, tFUS was delivered to the IL of a freely-moving rat and compared to sham stimulation (tFUS vs. SHAM). Initially, Fos expression in the IL was measured shortly after the stimulation. The results show that Fos expression was significantly increased in the IL but not in the neighboring regions compared to SHAM. Subsequently, two groups of rats were subjected to fear conditioning, extinction, and retention while receiving stimulation during the extinction. Rats in the tFUS group froze significantly less than SHAM during both extinction and retention tests. Importantly, the reduced freezing in the tFUS group was not attributable to non-specific effect such as auditory noise, as both groups demonstrated a similar level of locomotive activity in an open field regardless of the stimulation condition. Finally, we replicated the procedure with a shortened conditioning-to-extinction interval (15 min) to induce immediate extinction deficit. The tFUS group showed a facilitated reduction in freezing during the extinction, which persisted in the subsequent retention session compared to SHAM. In summary, the current findings suggest that tFUS stimulation in the IL facilitates fear extinction, offering a potential therapeutic regimen for fear-related psychiatric disorders. • tFUS stimulation in the IL facilitates fear extinction. • tFUS stimulation promotes Fos expression in the IL. • tFUS stimulation ameliorates immediate extinction deficit. [ABSTRACT FROM AUTHOR]

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Fear extinction is a phenomenon that involves a gradual reduction in conditioned fear responses through repeated exposure to fear-inducing cues. Functional brain connectivity assessments, such as functional magnetic resonance imaging (fMRI), provide valuable insights into how brain regions communicate during these processes. Stress, a ubiquitous aspect of life, influences fear learning and extinction by changing the activity of the amygdala, prefrontal cortex, and hippocampus, leading to enhanced fear responses and/or impaired extinction. Glucocorticoid receptors (GRs) are key to the stress response and show a dual function in fear regulation: while they enhance the consolidation of fear memories, they also facilitate extinction. Accordingly, GR dysregulation is associated with anxiety and mood disorders. Recent advancements in cognitive neuroscience underscore the need for a comprehensive understanding that integrates perspectives from the molecular, cellular, and systems levels. In particular, neuropharmacology provides valuable insights into neurotransmitter and receptor systems, aiding the investigation of mechanisms underlying fear regulation and potential therapeutic targets. A notable player in this context is cortisol, a key stress hormone, which significantly influences both fear memory reconsolidation and extinction processes. Gaining a thorough understanding of these intricate interactions has implications in terms of addressing psychiatric disorders related to stress. This review sheds light on the complex interactions between cognitive processes, emotions, and their neural bases. In this endeavor, our aim is to reshape the comprehension of fear, stress, and their implications for emotional well-being, ultimately aiding in the development of therapeutic interventions. [ABSTRACT FROM AUTHOR]

The consequences of the COVID-19 pandemic have resulted in many disruptions to daily life, including an abrupt increase in social disconnection. As measures were put in place to combat the spread of COVID-19, people across the globe began living in states of limited social contact, fostering feelings of social isolation and loneliness. Previous literature suggests that these increases in social disconnection can have profound effects on both physical and mental health, perhaps especially in the case of fear disorders. The combination of feeling disconnected from others and the high level of daily threat experienced due to COVID-19 created conditions under which dysfunctional and persistent fears were especially likely to develop. Building on current understanding of the harmful effects of social disconnection on well-being in general as well as specific implications for fear, here we present findings from three preliminary investigations that are the first to directly examine the effects of loneliness on how fears are learned and maintained. The Results of this work show that loneliness impairs the process by which fears are extinguished, which is central to both the regulation of fear and treatment of fear disorders, and provide insight into potential avenues to mitigate such effects.

Background and purpose: Post-traumatic stress disorder (PTSD), a type of psychiatric disorder that occurs after exposure to traumatic events, is associated with anxiety and abnormality in the activity of hypothalamic-pituitary-adrenal axis and cognitive functions. Physical activity can improve symptoms of somatic and neuropsychiatric disorders; however, appropriate exercise intensity and duration are still in question. In the present study, the effects of high-intensity exercise on anxiety-like behaviors, fear extinction, serum insulin-like growth factor (IGF-1), brain-derived neurotrophic factor (BDNF), and expression of apoptosis-related genes were investigated in the prefrontal cortex of the rat PTSD model. Materials and methods: In this experimental study, single prolonged stress (SPS) was used to induce PTSD in adult male Wistar rats. After 10 days, the animals in the exercise groups were subjected to high-intensity treadmill exercise (20 m/min, 5 days/week) for four weeks. Next, anxiety-like behaviors and fear extinction were examined using open field and shuttle box tests, respectively. Thereafter, serum IGF-1 and brain BDNF were measured by ELISA kits; and expression of Bax, Bcl-2, and caspase-3 in the prefrontal cortex were measured by real-time PCR. Results: SPS rats showed increased anxiety and decreased fear extinction, serum IGF-1, and prefrontal BDNF compared to the control animals. In addition, SPS induced apoptosis by an increase in Bax and caspase-3 and a decrease in Bcl-2. High-intensity exercise reduced apoptosis and increased serum IGF-1 significantly (P

Here, we used RNA capture-seq to identify a large population of lncRNAs that are expressed in the infralimbic prefrontal cortex of adult male mice in response to fear-related learning. Combining these data with cell-type-specific ATAC-seq on neurons that had been selectively activated by fear extinction learning, we find inducible 434 lncRNAs that are derived from enhancer regions in the vicinity of protein-coding genes. In particular, we discover an experience-induced lncRNA we call ADRAM (activity-dependent lncRNA associated with memory) that acts as both a scaffold and a combinatorial guide to recruit the brain-enriched chaperone protein 14-3-3 to the promoter of the memory-associated immediate-early gene Nr4a2 and is required fear extinction memory. This study expands the lexicon of experience-dependent lncRNA activity in the brain and highlights enhancer-derived RNAs (eRNAs) as key players in the epigenomic regulation of gene expression associated with the formation of fear extinction memory.

Balanced fear supports human rational decision-making and useful behavioral responses. In contrast, overwhelming, persistent, and unbalanced fear can paralyze the individual and result in heightened anxiety, lack of cognitive flexibility, fear-based public compliance and serious mental health issues. Psychobiotics research has established that a healthy microbiome is required for balanced fear and mental health protection via control of fear extinction. The recent COVID-19 pandemic featured daily, persistent, fear-of-a-single-contagion conditioning on a global scale paired with various behavioral mandates (e.g., lockdowns of the healthy, required wearing of face masks in many locations including schools, isolation from environmental microbes and each other through the closure of beaches and parks, and restrictions on social gatherings including access to family members in hospitals and senior-assisted facilities). Such mandates degraded the human microbiome and isolated us from each other and useful environmental microbes. It also ignored the historic role of secondary bacterial pathogens in pandemic deaths. This narrative review examines how the institutional promotion of fear-of-a-single-contagion, lack of balanced risk communication, and appalling disregard of our fundamental nature (as majority-microbial human superorganisms) resulted in problems rather than solutions. This review illustrates that government-public health-media promotion of pervasive fear and microbiome-degrading behaviors: (1) increased public compliance, (2) reduced cognitive flexibility, and (3) increased risk of mental health conditions. However, a portion of the general public chose a healthier path through their increased consumption of microbiome- and immune-supportive supplements and fermented foods during and after the COVID-19 pandemic. For a healthier future, public health must follow the lead of this population to ensure that human freedom, rather than paralyzing fear, dominates our future.

Abstract Impaired extinction of fear memory is one of the most common symptoms in post‐traumatic stress disorder (PTSD), with limited therapeutic strategies due to the poor understanding of its underlying neural substrates. In this study, functional screening is performed and identified hyperactivity in the mediodorsal thalamic nucleus (MD) during fear extinction. Furthermore, the encoding patterns of the hyperactivated MD is investigated during persistent fear responses using multiple machine learning algorithms. The anterior cingulate cortex (ACC) is also identified as a functional downstream region of the MD that mediates the extinction of fear memory. The thalamocortical circuit is comprehensively analyzed and found that the MD‐ACC parvalbumin interneurons circuit is preferentially enhanced in PTSD mice, disrupting the local excitatory and inhibitory balance. It is found that decreased phosphorylation of the Kv3.2 channel contributed to the hyperactivated MD, primarily to the malfunctioning thalamocortical circuit. Using a lipid nanoparticle‐based RNA therapy strategy, channelopathy is corrected via a methoxylated siRNA targeting the protein phosphatase 6 catalytic subunit and restored fear memory extinction in PTSD mice. These findings highlight the function of the thalamocortical circuit in PTSD‐related impaired extinction of fear memory and provide therapeutic insights into Kv3.2‐targeted RNA therapy for PTSD.

The prevention and treatment of fear-related disorders in offspring affected by pregnancy stress remains challenging at clinic. Here, we examined the effects of gut microbiota of stressed pregnant rats on the fear extinction of their offsprings, and the potential mechanisms. We found that gut microbiota transplantation from rats with pregnancy stress to normal pregnant rats impaired fear extinction, induced microglial activation and synaptic phagocytosis, increased synapse loss in offsprings. Probiotics supplement during pregnancy stress partly normalized pregnancy stress-induced gut microbiota dysbiosis of pregnant rats, and promoted fear memory extinction, inhibited fear memory reappearance, and limited microglial activation and synaptic phagocytosis in offsprings. These data revealed that gut microbiota of stressed pregnant mother improved the development of fear-related disorders of offspring, which may be associated with microglial synaptic pruning.

Overview: Reproductive experience (pregnancy and motherhood) leads to long-term changes in the neurobiological and hormonal features of anxiety in rats and humans. The aim of this study was to examine whether reproductive experience alters the effects of two pharmacological treatments for anxiety, a benzodiazepine (diazepam) and a selective serotonin reuptake inhibitor (fluoxetine), on animal models of anxiety. Methods: In Experiment 1, virgin (n = 47) and age-matched mother (n = 50) rats at 1-month post-weaning were injected with diazepam (1.3 mg/kg or 1.7 mg/kg, i.p.) or vehicle, in the proestrus (high estradiol/progesterone/allopregnanolone) or metestrus (low estradiol/progesterone/allopregnanolone) phase of the estrous cycle 30 min prior to the elevated plus maze (EPM). In Experiment 2, virgin (n = 25) and mother rats (n = 20) were administered fluoxetine (10 mg/kg) or vehicle for 2 weeks prior to being tested on a Pavlovian fear conditioning and extinction protocol, and the EPM. Results: Replicating past research, in virgin rats, the low dose of diazepam produced anxiolytic-like effects in proestrus, but only the high dose was anxiolytic-like in metestrus. In contrast, in mother rats, both doses of diazepam were anxiolytic-like irrespective of estrous phase. Fluoxetine produced anxiogenic-like effects in virgin rats during fear extinction and the EPM, but had no behavioural effects in mothers. In contrast, fluoxetine increased plasma corticosterone levels measured 30-min post-EPM in mothers, but not virgin rats. Conclusions: Reproductive experience alters the dose responsivity and efficacy of common anti-anxiety medications in female rats. These findings highlight the importance of considering reproductive status in studies on anxiety and its treatment. [ABSTRACT FROM AUTHOR]

Background and purpose: Post-traumatic stress disorder (PTSD), a type of psychiatric disorder that occurs after exposure to traumatic events, is associated with anxiety and abnormality in the activity of hypothalamic-pituitary-adrenal axis and cognitive functions. Physical activity can improve symptoms of somatic and neuropsychiatric disorders; however, appropriate exercise intensity and duration are still in question. In the present study, the effects of high-intensity exercise on anxiety-like behaviors, fear extinction, serum insulin-like growth factor (IGF-1), brain-derived neurotrophic factor (BDNF), and expression of apoptosis-related genes were investigated in the prefrontal cortex of the rat PTSD model. Materials and methods: In this experimental study, single prolonged stress (SPS) was used to induce PTSD in adult male Wistar rats. After 10 days, the animals in the exercise groups were subjected to high-intensity treadmill exercise (20 m/min, 5 days/week) for four weeks. Next, anxiety-like behaviors and fear extinction were examined using open field and shuttle box tests, respectively. Thereafter, serum IGF-1 and brain BDNF were measured by ELISA kits; and expression of Bax, Bcl-2, and caspase-3 in the prefrontal cortex were measured by real-time PCR. Results: SPS rats showed increased anxiety and decreased fear extinction, serum IGF-1, and prefrontal BDNF compared to the control animals. In addition, SPS induced apoptosis by an increase in Bax and caspase-3 and a decrease in Bcl-2. High-intensity exercise reduced apoptosis and increased serum IGF-1 significantly (P<0.05). Conclusion: High-intensity exercise decreases anxiety-like behaviors by increasing serum IGF-1 and inhibiting apoptosis in the prefrontal cortex of PTSD rats. [ABSTRACT FROM AUTHOR]

Reminders of loved ones have long been avoided during extinction-based treatments because of their assumed status as safety signals, which, by inhibiting fear in the moment, impair the long-term outcomes of fear extinction. Yet, recent work has demonstrated that in contrast to standard safety signals, social support reminders actually enhance fear extinction and lead to lasting reduction of fear, suggesting that they may have beneficial effects during exposure therapy that have before-now been overlooked. Here, we argue for a revision of the assumption that social support is detrimental to fear extinction processes and propose that future work should focus on the potential of social support reminders to improve treatment outcomes in those with anxiety disorders.

MDMA-assisted psychotherapy has shown potential as an effective treatment for post-traumatic stress disorder (PTSD). Preclinical studies involving rodents have demonstrated that MDMA can facilitate the extinction of fear memories. It has been noted that MDMA impacts oxytocin neurons and pro-inflammatory cytokines. Thus, the aim of this study was to explore the role of oxytocinergic signaling and neuroinflammatory markers in the therapeutic effects of MDMA. To achieve this, male rats were subjected to a model of PTSD involving exposure to shock and situational reminders. MDMA was microinjected into the medial prefrontal cortex (mPFC) before extinction training, followed by behavioral tests assessing activity levels, anxiety, and social function. Our findings indicate that MDMA treatment facilitated fear extinction and mitigated the shock-induced increase in freezing, as well as deficits in social behavior. Shock exposure led to altered expression of the gene coding for OXT-R and neuroinflammation in the mPFC and basolateral amygdala (BLA), which were restored by MDMA treatment. Importantly, the OXT-R antagonist L-368,899 prevented MDMA’s therapeutic effects on extinction and freezing behavior. In conclusion, MDMA’s therapeutic effects in the PTSD model are associated with alterations in OXT-R expression and neuroinflammation, and MDMA’s effects on extinction and anxiety may be mediated by oxytocinergic signaling.

Fear-related disorders, including post-traumatic stress disorder (PTSD), and anxiety disorders are pervasive psychiatric conditions marked by persistent fear, stemming from its dysregulated acquisition and extinction. The primary treatment for these disorders, exposure therapy (ET), relies heavily on fear extinction (FE) principles. Adolescence, a vulnerable period for developing psychiatric disorders, is characterized by neurobiological changes in the fear circuitry, leading to impaired FE and increased susceptibility to relapse following ET. Ketamine, known for relieving anxiety and reducing PTSD symptoms, influences fear-related learning processes and synaptic plasticity across the fear circuitry. Our study aimed to investigate the effects of ketamine (10 mg/kg) on FE in adolescent male C57 BL/6 mice at the behavioral and molecular levels. We analyzed the protein and gene expression of synaptic plasticity markers in the hippocampus (HPC) and prefrontal cortex (PFC) and sought to identify neural correlates associated with ketamine’s effects on adolescent extinction learning. Ketamine ameliorated FE in the adolescent males, likely affecting the consolidation and/or recall of extinction memory. Ketamine also increased the Akt and mTOR activity and the GluA1 and GluN2A levels in the HPC and upregulated BDNF exon IV mRNA expression in the HPC and PFC of the fear-extinguished mice. Furthermore, ketamine increased the c-Fos expression in specific brain regions, including the ventral HPC (vHPC) and the left infralimbic ventromedial PFC (IL vmPFC). Providing a comprehensive exploration of ketamine’s mechanisms in adolescent FE, our study suggests that ketamine’s effects on FE in adolescent males are associated with the activation of hippocampal Akt-mTOR-GluA1 signaling, with the vHPC and the left IL vmPFC as the proposed neural correlates.