Extinction Of Conditioned Fear Research Articles

Transcranial focused ultrasound stimulation in the infralimbic cortex facilitates extinction of conditioned fear in rats

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.

Accelerated neurodegeneration of basal forebrain cholinergic neurons in HIV-1 gp120 transgenic mice: Critical role of the p75 neurotrophin receptor

Human Immunodeficiency Virus-1 (HIV) infection of the brain induces HIV-associated neurocognitive disorders (HAND). The set of molecular events employed by HIV to drive cognitive impairments in people living with HIV are diverse and remain not completely understood. We have shown that the HIV envelope protein gp120 promotes loss of synapses and decreases performance on cognitive tasks through the p75 neurotrophin receptor (p75NTR). This receptor is abundant on cholinergic neurons of the basal forebrain and contributes to cognitive impairment in various neurological disorders. In this study, we examined cholinergic neurons of gp120 transgenic (gp120tg) mice for signs of degeneration. We observed that the number of choline acetyltransferase-expressing cells is decreased in old (12–14-month-old) gp120tg mice when compared to age matched wild type. In the same animals, we observed an increase in the levels of pro-nerve growth factor, a ligand of p75NTR, as well as a disruption of consolidation of extinction of conditioned fear, a behavior regulated by cholinergic neurons of the basal forebrain. Both biochemical and behavioral outcomes of gp120tg mice were rescued by the deletion of the p75NTR gene, strongly supporting the role that this receptor plays in the neurotoxic effects of gp120. These data indicate that future p75NTR-directed pharmacotherapies could provide an adjunct therapy against synaptic simplification caused by HIV.

Modulation of learning safety signals by acute stress: paraventricular thalamus and prefrontal inhibition

Distinguishing between cues predicting safety and danger is crucial for survival. Impaired learning of safety cues is a central characteristic of anxiety-related disorders. Despite recent advances in dissecting the neural circuitry underlying the formation and extinction of conditioned fear, the neuronal basis mediating safety learning remains elusive. Here, we showed that safety learning reduces the responses of paraventricular thalamus (PVT) neurons to safety cues, while activation of these neurons controls both the formation and expression of safety memory. Additionally, the PVT preferentially activates prefrontal cortex somatostatin interneurons (SOM-INs), which subsequently inhibit parvalbumin interneurons (PV-INs) to modulate safety memory. Importantly, we demonstrate that acute stress impairs the expression of safety learning, and this impairment can be mitigated when the PVT is inhibited, indicating PVT mediates the stress effect. Altogether, our findings provide insights into the mechanism by which acute stress modulates safety learning.

The sexually divergent cFos activation map of fear extinction

ObjectivePost-traumatic stress disorder (PTSD) is a neuropsychiatric disorder that can develop after experiencing or witnessing a traumatic event. Exposure therapy is a common treatment for PTSD, but it has varying levels of efficacy depending on sex. In this study, we aimed to compare the sexual dimorphism in brain activation during the extinction of fear conditioning in male and female rats by detecting the c-fos levels in the whole brain. MethodsThirty-two rats (Male: n = 16; Female: n = 16) were randomly separated into the extinction group as well as the non-extinction group, and fear conditioning was followed by extinction and non-extinction, respectively. Subsequently, brain sections from the sacrificed animal were performed immunofluorescence and the collected data were analyzed by repeated two-way ANOVAs as well as Pearson Correlation Coefficient. ResultsOur findings showed that most brain areas activated during extinction were similar in both male and female rats, except for the reuniens thalamic nucleus and ventral hippocampi. Furthermore, we found differences in the correlation between c-fos activation levels and freezing behavior during extinction between male and female rats. Specifically, in male rats, c-fos activation in the anterior cingulate cortex was negatively correlated with the freezing level, while c-fos activation in the retrosplenial granular cortex was positively correlated with the freezing level; but in female rats did not exhibit any correlation between c-fos activation and freezing level. Finally, the functional connectivity analysis revealed differences in the neural networks involved in extinction learning between male and female rats. In male rats, the infralimbic cortex and insular cortex, anterior cingulate cortex and retrosplenial granular cortex, and dorsal dentate gyrus and dCA3 were strongly correlated after extinction. In female rats, prelimbic cortex and basolateral amygdala, insular cortex and dCA3, and anterior cingulate cortex and dCA1 were significantly correlated. ConclusionThese results suggest divergent neural networks involved in extinction learning in male and female rats and provide a clue for improving the clinical treatment of exposure therapy based on the sexual difference.

Age-specific sex effects in extinction of conditioned fear in rodents.

Age-specific sex effects in extinction of conditioned fear in rodents.

Dissociable role of the basolateral complex of the amygdala in the acquisition and extinction of conditioned fear following reproductive experience in female rats

In female rats and humans, reproductive experience (i.e., pregnancy) alters the behavioral, hormonal and molecular substrates of fear extinction. Here, we assessed whether the role of a central neural substrate of fear extinction, the basolateral amygdala (BLA), also changes following reproductive experience. Nulliparous (virgin) and primiparous (one prior pregnancy) female rats received infusions of the GABAA agonist, muscimol, to temporarily inactivate the BLA prior to fear conditioning or extinction training. In follow up experiments, the BLA was also inactivated immediately after extinction training. BLA inactivation impaired the acquisition and expression of conditioned fear in both nulliparous and primiparous rats. In nulliparous rats, BLA inactivation prior to or immediately after extinction training impaired extinction retention. In contrast, in primiparous rats, BLA inactivation prior to or immediately after extinction training did not impair extinction retention, despite suppressing freezing during extinction training. These results suggest that, consistent with past findings in males, the BLA is a central component of the neural circuitry of fear acquisition and its extinction in virgin female rats. However, after pregnancy, female rats no longer depend on the BLA to extinguish fear, despite requiring the BLA to acquire conditioned fear. Given that fear extinction forms the basis of exposure therapy for anxiety disorders in humans, the present findings may have clinical implications. To improve the efficacy of exposure therapy for anxiety disorders, we may need to target different mechanisms in females dependent on their reproductive history.

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. PerspectiveOpposing 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.

The effects of a dual orexin receptor antagonist on fear extinction memory and sleep in mice: Implications for exposure therapy

Extinction of conditioned fear is considered a fundamental process in the recovery from posttraumatic stress disorder and anxiety disorders. Sleep, especially rapid-eye-movement (REM) sleep, has been implicated in promoting extinction memory. The orexin system contributes to the regulation of sleep and wakefulness and emotional behaviors. In rodents, administrations of an orexin receptor antagonist following fear extinction training enhanced consolidation of extinction memory. Although orexin antagonists increase sleep, including REM sleep, the possible contribution of sleep to the effects of orexin antagonists on extinction memory has not been examined. Therefore, this study examined the effects of suvorexant, a dual orexin receptor antagonist, on extinction memory and sleep and their associations in mice. C57BL/6 mice underwent sleep recording for 24 h before and after contextual fear conditioning with footshocks and extinction learning during the early light phase or early dark phase. Mice were systemically injected with either 25 mg/kg of suvorexant or vehicle immediately after the extinction session. We found that suvorexant neither altered sleep nor improved extinction memory recall compared with vehicle. The higher percentages of REM sleep during the post-extinction dark phase were associated with lower extinction memory recall and greater freezing responses to the fear context. Results also indicate that animals did not reach complete extinction of fear with the fear extinction training protocol used in this study. These findings suggest that promoting REM sleep may not enhance fear extinction memory when extinction of fear is incomplete.

Developmental changes in functional connectivity between the prefrontal cortex and amygdala following fear extinction

The amygdala and prefrontal cortex (PFC) undergo dramatic changes in structure, function, and regional connectivity in early life, ultimately stabilizing in early adulthood. Pathways between these two structures underlie many forms of emotional learning, including the extinction of conditioned fear. Here we sought to characterize changes in extinction-related medial PFC (mPFC) → amygdala functional connectivity across development that might explain adolescent impairments in extinction. The retrograde tracer Fluorogold was infused into the amygdala of postnatal day (P)22–23 (juvenile), P31-32 (adolescent), or ≥ P69 (adult) rats, which were then exposed to fear conditioning and extinction training. Brains were collected following extinction or context exposure and processed for expression of pMAPK (as a marker of learning-dependent plasticity) in prelimbic (PL) and infralimbic (IL) amygdala-projecting neurons. Consistent with previous findings, amygdala-projecting mPFC neurons were located primarily in layers (L)II/III and V of the mPFC. We noted that mPFC LII/III projected predominantly to the ipsilateral basolateral amygdala, whereas LV projected bilaterally and targeted multiple amygdalar nuclei. Extinction was not associated with changes in extinction-related plasticity in the PL-amygdala pathways in any age group. No changes were seen in LII/III of the IL, but extinction-related plasticity in LV amygdala-projecting IL neurons decreased linearly across development. These findings suggest that extinction-related functional connectivity between the IL and the amygdala undergoes fundamental changes across development that may contribute to alterations in fear suppression across development.

MPP2 interacts with SK2 to rescue the excitability of glutamatergic neurons in the BLA and facilitate the extinction of conditioned fear in mice.

The basolateral amygdala (BLA) plays an integral role in anxiety disorders (such as post traumatic stress disorder) stem from dysregulated fear memory. The excitability of glutamatergic neurons in the BLA correlates with fear memory, and the afterhyperpolarization current (IAHP ) mediated by small-conductance calcium-activated potassium channel subtype 2 (SK2) dominates the excitability of glutamatergicneurons. This study aimed to explore the effect of MPP2 interacts with SK2 in the excitability of glutamatergic neurons in the BLA and the extinction of conditioned fear in mice. Fear memory was analyzed via freezing percentage. Western blotting and fluorescence quantitative PCR were used to determine the expression of protein and mRNA respectively. Electrophysiology was employed to measure the excitability of glutamatergic neurons and IAHP . Fear conditioning decreased the levels of synaptic SK2 channels in the BLA, which were restored following fear extinction. Notably, reduced expression of synaptic SK2 channels in the BLA during fear conditioning was caused by the increased activity of protein kinase A (PKA), while increased levels of synaptic SK2 channels in the BLA during fear extinction were mediated by interactions with membrane-palmitoylated protein 2 (MPP2). Our results revealed that MPP2 interacts with the SK2 channels and rescues the excitability of glutamatergic neurons by increasing the expression of synaptic SK2 channels in the BLA to promote the normalization of anxiety disorders and provide a new direction for the treatment.

Involvement of the GABAergic system in PTSD and its therapeutic significance.

The neurobiological mechanism of post-traumatic stress disorder (PTSD) is poorly understood. The inhibition of GABA neurons, especially in the amygdala, is crucial for the precise regulation of the consolidation, expression, and extinction of fear conditioning. The GABAergic system is involved in the pathophysiological process of PTSD, with several studies demonstrating that the function of the GABAergic system decreases in PTSD patients. This paper reviews the preclinical and clinical studies, neuroimaging techniques, and pharmacological studies of the GABAergic system in PTSD and summarizes the role of the GABAergic system in PTSD. Understanding the role of the GABAergic system in PTSD and searching for new drug targets will be helpful in the treatment of PTSD.

The effectiveness of extinction training in male rats: Temporal considerations and brain mechanisms

The extinction of conditioned fear is frequently used in laboratories as a model for human exposure therapy and is crucial for studies of posttraumatic stress disorder (PTSD). However, the efficacy of specific protocols can vary greatly, and the underlying brain mechanisms are not sufficiently clarified. To address this issue, variable starting time (one or twenty-eight days after fear conditioning) and extinction protocols were used, and the efficacy and durability of fear extinction were also studied. Changes in the behavior, stress hormone levels and neuronal activation patterns of stressed rats were analyzed. Conditioned fear was rapidly and efficiently extinguished by all the protocols investigated. However, when these extinction protocols were initiated one day after fear training, conditioned fear relapsed spontaneously four weeks later. In contrast, when extinction trials were started 28 days after conditioning, no relapse occurred. Hormone measurements taken by the end of extinction trials indicated that adrenocorticotropin, but not corticosterone responses reflected behavioral extinction without any sign of relapse. The last extinction training increased the activation of the medial prefrontal cortex and decreased the activation of the central and medial amygdala when extinction began one day after fear conditioning. By contrast, the activation of the basolateral amygdala and the entire hippocampus decreased by the last training session when extinction started 28 days after fear conditioning. Our findings show that extinction training can extinguish remote fear memories more effectively than recent ones, and that the brain mechanisms underlying remote and recent fear memory extinction differ. Laboratory models should also focus on a later time point to increase their translational value.

Inflammation shapes neural processing of interoceptive fear predictors during extinction learning in healthy humans

Inflammation could impact on the formation and persistence of interoceptive fear and hypervigilance, with relevance to psychiatric disorders and chronic pain. To systematically analyze effects of inflammation on fear learning and extinction, we performed two complementary randomized, double-blind, placebo-controlled functional magnetic resonance imaging (fMRI) studies combining experimental endotoxemia as a translational model of acute systemic inflammation with a two-day multiple-threat fear conditioning paradigm involving interoceptive and exteroceptive unconditioned stimuli (US). Healthy volunteers (N = 95) were randomized to receive intravenous injections of either endotoxin (lipopolysaccharide, LPS; 0.4 ng/kg) or placebo prior to fear acquisition (study 1) or extinction training (study2). Treatment effects on behavioral and neural responses to conditioned stimuli (CS) predicting interoceptive or exteroceptive threat were assessed during fear learning and extinction phases, along with US valence ratings. Despite robust inflammatory and emotional responses triggered by LPS, no direct effects of inflammation on US ratings or on the formation or extinction of conditioned fear, as assessed with CS valence ratings, were observed. However, in the group treated with LPS prior to acquisition (i.e., study 1), we found enhanced neural responses to the interoceptive but not the exteroceptive CS in key regions of the central fear circuitry during extinction learning. After extinction, this group further showed enhanced negative valence ratings selectively for the interoceptive US during unexpected US re-exposure when compared to the placebo group. Together, inflammation during fear acquisition may promote the establishment of a more robust neural signature of the interoceptive fear memory trace, which may contribute to altered interoceptive pain perception. The fear extinction circuitry engaged during interoceptive fear memory processing may be particularly vulnerable to inflammation, with transdiagnostic implications for gut-brain mechanisms underlying disturbed interoception in psychiatric conditions and chronic visceral pain.

Involvement of D2-like dopaminergic receptors in contextual fear conditioning in female rats: influence of estrous cycle.

Introduction: Dopamine has been increasingly recognized as a key neurotransmitter regulating fear/anxiety states. Nevertheless, the influence of sex and estrous cycle differences on the role of dopamine in fear responses needs further investigation. We aimed to evaluate the effects of sulpiride (a dopaminergic D2-like receptor antagonist) on contextual fear conditioning in females while exploring the influence of the estrous cycle. Methods: First, using a contextual fear conditioning paradigm, we assessed potential differences in acquisition, expression, and extinction of the conditioned freezing response in male and female (split in proestrus/estrus and metestrus/diestrus) Wistar rats. In a second cohort, we evaluated the effects of sulpiride (20 and 40 mg/kg) on contextual conditioned fear in females during proestrus/estrus and metestrus/diestrus. Potential nonspecific effects were assessed in motor activity assays (catalepsy and open-field tests). Results: No sex differences nor estrous cycle effects on freezing behavior were observed during the fear conditioning phases. Sulpiride reduced freezing expression in female rats. Moreover, females during the proestrus/estrus phases of the estrous cycle were more sensitive to the effects of sulpiride than females in metestrus/diestrus. Sulpiride did not cause motor impairments. Discussion: Although no sex or estrous cycle differences were observed in basal conditioned fear expression and extinction, the estrous cycle seems to influence the effects of D2-like antagonists on contextual fear conditioning.

Sex Differences in the Effects of Cognitive Reappraisal Training on Conditioned Fear Responses

Sex differences in emotion regulation strategies may impact sex differences in affective disorders. Using cognitive reappraisal strategy in the discriminative task of conditioned fear was studied to understand how sex differences in emotion regulation impact on conditioned fear in men and women. College students with low cognitive reappraisal scores completed the task of conditioned fear during two days: acquisition and extinction at the first day, and re-extinction at the second day. The reappraisal training was carried out before conditioned fear task. The self-reported fear rating of the conditioned stimulus (CS) and US-expectancy in the conditioned fear (unconditioned stimulus, US) were analyzed. Results showed all subjects acquired conditional fear and successfully distinguished CS+ from CS-. Cognitive reappraisal significantly reduces the fear rating and improves the extinction of US-expectancy in both sexes, but the fear rating in female reappraisal group decreases more slowly than that in male reappraisal group, as well as the extinction of US-expectancy in woman requiring a longer time and more trials of extinction than that in men. For individuals with low cognitive reappraisal scores, cognitive reappraisal promotes the extinction of conditioned fear in both males and females. Because of the original gender difference of conditioned fear extinction and emotion regulation, the effect of cognitive reappraisal on conditioned fear is complex, which shows differently in influence speed and practice effect.

Impact of acute inflammation on the extinction of conditioned visceral pain-related fear in healthy humans

Impact of acute inflammation on the extinction of conditioned visceral pain-related fear in healthy humans

P105 Women with greater post-traumatic stress symptom severity and less disrupted sleep have improved fear extinction recall compared to men

Abstract Sleep has been found to play a key role in fear conditioning, extinction learning and extinction recall, the paradigm modelling the development, maintenance and treatment of anxiety disorders including post-traumatic stress disorder (PTSD), which are disorders commonly associated with sleep disturbances. Previous studies examining associations between sleep and fear or extinction processes predominately focused on objectively measured sleep architecture using polysomnography, and the majority of the research has been done in healthy populations. To date, little research has focused on subjective sleep measures and particularly in clinical populations including PTSD, which often experience subjectively poor sleep. Here we investigated whether subjective sleep disturbance, sleep onset latency, wake after sleep onset or sleep efficiency were related to fear conditioning, extinction learning or extinction recall in a large sample of individuals with a range of PTSD symptom severity and healthy controls. Overall, we did not find that sleep was associated with fear conditioning extinction learning or extinction recall. However, emerging evidence highlighting the critical role of sex in PTSD risk, fear conditioning processes, as well as in the sleep-fear conditioning relationship. Exploratory analyses examining sex-specific effects found that shorter sleep onset latency and greater sleep efficiency during the previous night were associated with improved extinction recall in women with higher PTSD symptom severity. This suggests that less time falling asleep and longer time asleep while in bed may be protective against the commonly observed impaired extinction recall in PTSD in highly symptomatic women, but is not relevant in men.

Facilitated extinction of conditioned fear responses by delta 9-tetrahyrdrocannabidol in humans: a pilot study.

We sought to determine whether acute delta 9-tetrahyrdrocannabidol (THC) administration would facilitate fear extinction in young occasional cannabis users, given that animal models indicate THC facilitates extinction learning, and recent studies indicate THC administration may also enhance threat memory extinction in humans. On each of the 2days, 24+hour THC-deprived participants were conditioned to fear visual stimuli in a delay conditioning and extinction paradigm. Both CS+ and CS- were faces of negative emotional valence, with the CS+ paired with mild electric shock. Throughout both conditioning and extinction paradigms, EEG was measured to quantify event-related potentials for these learning processes. Following conditioning, individuals, in a randomized and counter-balanced order, smoked either an active THC cigarette (26.25mg/2.7% THC) or a placebo marijuana cigarette (0.002% THC) on 1day and the opposite cigarette on the second day. After smoking, CS+ and CS- were presented without shock, resulting in extinction of conditioned fear. Relative to placebo, THC facilitated extinction of the conditioned response to the CS+, as reflected by reductions in late positive potential amplitude during extinction learning. The results indicate that acute THC administration may facilitate extinction of the conditioned fear response in humans.

Caffeine facilitates extinction of auditory fear conditioning inrats.

Caffeine is the most widely consumed psychostimulant drug which could affect learning and memory acting through central adenosine receptors. Although caffeine has been suggested to impair the acquisition and the expression of auditory fear conditioning, its effect on the extinction has not been elucidated. To address this issue, in the present study, we investigated whether caffeine affects the extinction of conditioned fear in an auditory fear conditioning paradigm. During conditioning, rats received pairings of auditory cues (conditioned stimulus, CS) and foot shocks (unconditioned stimulus). On the next day, the rats were intraperitoneally administrated saline or caffeine (5 or 10mg/kg) and then subjected to the extinction training, in which CSs were repeatedly presented without the foot shocks. Twenty-four hours later, the rats were re-exposed to the presentations of CSs (retrieval test). We found an acute caffeine administration dose-dependently decreased freezing rates during the presentations of CS in the extinction training. Furthermore, caffeine-treated animals showed lower conditioned freezing responses in the retrieval test. These findings suggest that caffeine facilitates the extinction of conditioned fear.

Nucleus reuniens inactivation does not impair consolidation or reconsolidation of fear extinction.

Recent data reveal that the thalamic nucleus reuniens (RE) has a critical role in the extinction of conditioned fear. Muscimol (MUS) infusions into the RE impair within-session extinction of conditioned freezing and result in poor long-term extinction memories in rats. Although this suggests that RE inactivation impairs extinction learning, it is also possible that it is involved in the consolidation of extinction memories. To examine this possibility, we examined the effects of RE inactivation on the consolidation and reconsolidation of fear extinction in male and female rats. Twenty-four hours after auditory fear conditioning, rats underwent an extinction procedure (45 CS-alone trials) in a novel context and were infused with saline (SAL) or MUS within minutes of the final extinction trial. Twenty-four hours later, conditioned freezing to the extinguished CS was assessed in the extinction context. Postextinction inactivation of the RE did not affect extinction retrieval. In a second experiment, rats underwent extinction training and, 24 h later, were presented with a single CS to reactivate the extinction memory; rats were infused with SAL or MUS immediately after the reactivation session. Pharmacological inactivation of the RE did not affect conditioned freezing measured in a drug-free retrieval test the following day. Importantly, we found in a subsequent test that MUS infusions immediately before retrieval testing increased conditioned freezing and impaired extinction retrieval, as we have previously reported. These results indicate that although RE inactivation impairs the expression of extinction, it does not impair either the consolidation or reconsolidation of extinction memories. We conclude that the RE may have a critical role in suppressing context-inappropriate fear memories in the extinction context.