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

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

D-Pinitol mitigates post-traumatic stress disorder-like behaviors induced by single prolonged stress in mice through mineralocorticoid receptor antagonism

Post-traumatic stress disorder (PTSD) is a mental illness that can occur in individuals who have experienced trauma. Current treatments for PTSD, typically serotonin reuptake inhibitors, have limited effectiveness for patients and often cause serious adverse effects. Therefore, a novel class of treatment with better pharmacological profile is necessary. D-Pinitol has been reported to be effective for depression and anxiety disorders, but there are no reports associated with PTSD. In the present study, we investigated the effects of D-pinitol in a mouse model of PTSD induced by a single prolonged stress (SPS) protocol. We examined the therapeutic effects of D-pinitol on emotional and cognitive impairments in the SPS mouse model. We also investigated the effects of D-pinitol on fear memory formation. Mineralocorticoid receptor transactivation assay, Western blot, and quantitative PCR were employed to investigate how D-pinitol exerts its pharmacological activities. D-Pinitol ameliorated PTSD-like behaviors in a SPS mouse model. D-Pinitol also normalized the increased mRNA expression levels and protein levels of the mineralocorticoid receptor in the amygdala. A mineralocorticoid receptor agonist reversed the effects of D-pinitol on fear extinction and recall, and the antagonistic property of D-pinitol against the mineralocorticoid receptor was confirmed in vitro. Our findings suggest that D-pinitol could serve as a potential therapeutic agent for PTSD due to its antagonistic effect on the mineralocorticoid receptor.

Fear extinction is impaired in aged rats

Normal aging is accompanied by broad loss of cognitive function in humans and rodents, including declines in cognitive flexibility. In extinction, a conditional stimulus (CS) that was previously paired with a footshock is presented alone. This procedure reliably reduces conditional freezing behavior in young adult rats. Here, we aimed to investigate how normal aging affects extinction learning. Using young (3 months) and aged (20 months) male and female Long Evans rats, we compared extinction (using 20 CS-alone presentations) to a no extinction control (equal exposure to the conditioning chamber without CS presentations) following delay fear conditioning. We found that young animals in the extinction group showed a decrease in freezing following extinction; aged animals did not. We next examined changes in neural activity using expression of the immediate early gene zif268. In young animals, extinction corresponded with decreased expression of zif268 in the basolateral amygdala and anterior retrosplenial cortex; this was not observed in aged animals. Further, aged animals showed increased zif268 expression in each region examined, suggesting that dysfunction in neural activity precedes cognitive deficits. These results demonstrate that aging impacts both extinction learning and neural activity.

The effect of social anxiety on threat acquisition and extinction: a systematic review and meta-analysis

Although exposure-based therapy has been found to be effective at alleviating symptoms of social anxiety disorder, it often does not lead to full remission, and relapse after treatment is common. Exposure therapy is based on theoretical principles of extinction of conditioned fear responses. However, there are inconsistencies in findings across experiments that have investigated the effect of social anxiety on threat conditioning and extinction processes. This systematic review and meta-analysis aimed to examine whether elevated levels of social anxiety are associated with abnormalities in threat conditioning and extinction processes. A second aim was to examine the sensitivity of various study designs and characteristics to detect social anxiety-related differences in threat conditioning and extinction. A systematic search was conducted, which identified twenty-three experiments for inclusion in the review. The findings did not demonstrate compelling evidence that high levels of social anxiety are associated with atypical threat conditioning or extinction. Further, when systematically examining the data, there was no convincing support that the use of a particular psychophysiological measure, subjective rating, or experimental parameter yields more consistent associations between social anxiety and conditioning processes during threat acquisition or extinction. Meta-analyses demonstrated that during threat extinction, the use of anxiety ratings as a dependent variable, socially relevant unconditioned stimuli, and a higher reinforcement schedule produced more detectable effects of social anxiety on compromised extinction processes compared to any other dependent variable (subjective or physiological) or experimental parameter. Overall, the results of this study suggest that social anxiety is not reliably related to deficits in conditioning and extinction processes in the context of laboratory-based Pavlovian conditioning paradigms.

Resurgence of ethanol seeking following voluntary abstinence produced by nondrug differential reinforcement of other behavior

Resurgence refers to the relapse of a target behavior following the worsening of a source of alternative reinforcement that was made available during response elimination. Most laboratory analyses of resurgence have used a combination of extinction and alternative reinforcement to reduce target behavior. In contingency-management treatments for alcohol use disorder, however, alcohol use is not placed on extinction. Instead, participants voluntarily abstain from alcohol use to access nondrug alternative reinforcers. Inasmuch, additional laboratory research on resurgence following voluntary abstinence is warranted. The present experiment evaluated resurgence of rats' ethanol seeking following voluntary abstinence produced by differential reinforcement of other behavior (DRO). Lever pressing produced ethanol reinforcers during baseline phases. During DRO phases, lever pressing continued to produce ethanol and food reinforcers were delivered according to resetting DRO schedules. Ethanol and food reinforcers were suspended during resurgence test phases to evaluate resurgence following voluntary abstinence. Lever pressing was elevated during baseline phases and occurred at near-zero rates during DRO phases. During the resurgence test phases, lever pressing increased, despite that it no longer produced ethanol. The procedure introduced here may help researchers better understand the variables that affect voluntary abstinence from ethanol seeking and resurgence following voluntary abstinence.

Colonic butyrate administration modulates fear memory but not the acute stress response in men: A randomized, triple-blind, placebo-controlled trial

Short-chain fatty acids (SCFAs) are produced in the colon following bacterial fermentation of dietary fiber and are important microbiota-gut-brain messengers. However, their mechanistic role in modulating psychobiological processes that underlie the development of stress- and anxiety-related disorders is scarcely studied in humans. We have previously shown that colonic administration of a SCFA mixture (acetate, propionate, butyrate) lowers the cortisol response to stress in healthy participants, but does not impact fear conditioning and extinction. To disentangle the effects of the three main SCFAs, we examined whether butyrate alone would similarly modulate these psychobiological responses in a randomized, triple-blind, placebo-controlled intervention study in 71 healthy male participants (Mage = 25.2, MBMI = 22.7 [n = 35 butyrate group, n = 36 placebo group]). Colon-delivery capsules with pH-dependent coating were used to administer 5.28 g of butyrate or placebo daily for one week. Butyrate administration significantly increased serum butyrate concentrations without modulating serum acetate or propionate, nor fecal SCFAs. Butyrate administration also significantly modulated fear memory at the subjective but not physiological levels. Contrary to expectations, no changes in subjective nor neuroendocrine responses to acute stress were evident between the treatment groups from pre- to post-intervention. We conclude that colonic butyrate administration alone is not sufficient to modulate psychobiological stress responses, unlike administration of a SCFA mixture. The influence of colonic and systemic butyrate on fear memory and the persistence of fear extinction should be further systematically investigated in future studies.

Enhancing fear extinction

Gradually reducing a source of fear during extinction treatments may weaken negative memories in the long term.

Line- and sex-dependent effects of juvenile stress on contextual fear- and anxiety-related behavior in high- and low-alcohol-preferring mouse lines

Juvenile stress (JS) is a known risk factor for the development of alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD), both of which are frequently co-morbid. Data suggest there may be common, genetically-influenced biological responses to stress that contribute to the development of both AUD and PTSD. The present study investigated the impact of JS on contextual fear learning and extinction, as well as corticosterone (CORT) responses before and after JS, before and after contextual fear conditioning (CFC), and after fear extinction in male and female high-alcohol-preferring (HAP2) and low-alcohol-preferring (LAP2) mouse lines. We also measured unconditioned anxiety-related behavior in the light-dark-transition test before CFC. HAP2 and LAP2 mice did not differ in fear acquisition, but HAP2 mice showed faster fear extinction compared to LAP2 mice. No effects of JS were seen in HAP2 mice, whereas in LAP2 mice, JS reduced fear acquisition in males and facilitated fear extinction in females. Females showed greater fear-related behavior relative to males, regardless of subgroup. HAP2 males demonstrated more anxiolytic-like responses than LAP2 males and LAP2 females demonstrated more anxiolytic-like responses than LAP2 males in the light-dark transition test. HAP2 and LAP2 mice did not differ in CORT during the juvenile stage; however, adult LAP2 mice showed greater CORT levels than HAP2 mice at baseline and after CFC and extinction testing. These findings build upon prior work in these unique mouse lines that differ in genetic propensity toward alcohol preference and provide new information regarding contextual fear learning and extinction mechanisms theorized to contribute to co-morbid AUD and PTSD.

The 5-HT2A, 5-HT5A, and 5-HT6 serotonergic receptors in the medial prefrontal cortex behave differently in extinction learning: Does social support play a role?

Studies on the social modulation of fear have revealed that in social species, individuals in a distressed state show better recovery from aversive experiences when accompanied - referred to as social buffering. However, the underlying mechanisms remain unknown, hindering the understanding of such an approach. Our previous data showed that the presence of a conspecific during the extinction task inhibited the retrieval of fear memory without affecting the extinction memory in the retention test. Here, we investigate the role of serotonergic receptors (5-HTRs), specifically 5-HT2A, 5-HT5A, and 5-HT6 in the medial prefrontal cortex (mPFC), In the retention of extinction after the extinction task, in the absence or presence of social support. Extinction training was conducted on 60-day-old male Wistar rats either alone or with a conspecific (a familiar cagemate, non-fearful). The antagonists for these receptors were administered directly into the mPFC immediately after the extinction training. The results indicate that blocking 5-HT5A (SB-699551-10 μg/side) and 5-HT6 (SB-271046A - 10 μg/side) receptors in the mPFC impairs the consolidation of CFC in the social support group. Interestingly, blocking 5-HT2A receptors (R65777 - 4 μg/side) in the mPFC led to impaired CFC specifically in the group undergoing extinction training alone. These findings contribute to a better understanding of brain mechanisms and neuromodulation associated with social support during an extinction protocol. They are consistent with previously published research, suggesting that the extinction of contextual fear conditioning with social support involves distinct neuromodulatory processes compared to when extinction training is conducted alone.

DNA G-Quadruplex Is a Transcriptional Control Device That Regulates Memory

The conformational state of DNA fine-tunes the transcriptional rate and abundance of RNA. Here, we report that G-quadruplex DNA (G4-DNA) accumulates in neurons, in an experience-dependent manner, and that this is required for the transient silencing and activation of genes that are critically involved in learning and memory in male C57/BL6 mice. In addition, site-specific resolution of G4-DNA by dCas9-mediated deposition of the helicase DHX36 impairs fear extinction memory. Dynamic DNA structure states therefore represent a key molecular mechanism underlying memory consolidation.One-Sentence Summary: G4-DNA is a molecular switch that enables the temporal regulation of the gene expression underlying the formation of fear extinction memory.

Renewal in human fear conditioning: A systematic review and meta-analysis

Renewal is a 'return of fear' manipulation in human fear conditioning to investigate learning processes underlying anxiety and trauma. Even though renewal paradigms are widely used, no study has compared the strength of different renewal paradigms. We conduct a systematic review (N = 80) and meta-analysis (N = 23) of human fear conditioning studies assessing renewal. Our analysis shows that the classic ABA design is the most effective paradigm, compared to ABC and ABBA designs. We present evidence that conducting extinction in multiple contexts and increasing the similarity between acquisition and extinction contexts reduce renewal. Furthermore, we show that additional cues can be used as safety and 'protection from extinction' cues. The review shows that alcohol weakens the extinction process and that older adults appear less sensitive to context changes and thus show less renewal. The large variability in approaches to study renewal in humans suggests that standardisation of fear conditioning procedures across laboratories would be of great benefit to the field.

Effects of cannabidiol on fear conditioning in anxiety disorders: decreased threat expectation during retention, but no enhanced fear re-extinction

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.

Psilocybin analog 4-OH-DiPT enhances fear extinction and GABAergic inhibition of principal neurons in the basolateral amygdala

Psychedelics such as psilocybin show great promise for the treatment of depression and PTSD, but their long duration of action poses practical limitations for patient access. 4-OH-DiPT is a fast-acting and shorter-lasting derivative of psilocybin. Here we characterized the pharmacological profile of 4-OH-DiPT and examined its impact on fear extinction learning as well as a potential mechanism of action. First, we profiled 4-OH-DiPT at all 12 human 5-HT GPCRs. 4-OH-DiPT showed strongest agonist activity at all three 5-HT2A/2B/2C receptors with near full agonist activity at 5-HT2A. Notably, 4-OH-DiPT had comparable activity at mouse and human 5-HT2A/2B/2C receptors. In a fear extinction paradigm, 4-OH-DiPT significantly reduced freezing responses to conditioned cues in a dose-dependent manner with a greater potency in female mice than male mice. Female mice that received 4-OH-DiPT before extinction training had reduced avoidance behaviors several days later in the light dark box, elevated plus maze and novelty-suppressed feeding test compared to controls, while male mice did not show significant differences. 4-OH-DiPT produced robust increases in spontaneous inhibitory postsynaptic currents (sIPSCs) in basolateral amygdala (BLA) principal neurons and action potential firing in BLA interneurons in a 5-HT2A-dependent manner. RNAscope demonstrates that Htr2a mRNA is expressed predominantly in BLA GABA interneurons, Htr2c mRNA is expressed in both GABA interneurons and principal neurons, while Htr2b mRNA is absent in the BLA. Our findings suggest that 4-OH-DiPT activates BLA interneurons via the 5-HT2A receptor to enhance GABAergic inhibition of BLA principal neurons, which provides a potential mechanism for suppressing learned fear.

Impaired extinction of cocaine seeking in HIV-infected mice is accompanied by peripheral and central immune dysregulation

Substance use disorders (SUDs) are highly comorbid with HIV infection, necessitating an understanding of the interactive effects of drug exposure and HIV. The relationship between HIV infection and cocaine use disorder is likely bidirectional, with cocaine use directly impacting immune function while HIV infection alters addiction-related behavior. To better characterize the neurobehavioral and immune consequences of HIV infection and cocaine exposure, this study utilizes a humanized mouse model to investigate the outcomes of HIV-1 infection on cocaine-related behaviors in a conditioned place preference (CPP) model, and the interactive effects of cocaine and HIV infection on peripheral and central nervous system inflammation. HIV infection selectively impairs cocaine CPP extinction without effecting reinstatement or cocaine seeking under conflict. Behavioral alterations are accompanied by immune changes in HIV infected mice, including increased prefrontal cortex astrocyte immunoreactivity and brain-region specific effects on microglia number and reactivity. Peripheral immune system changes are observed in human cytokines, including HIV-induced reductions in human TNFα, and cocaine and HIV interactions on GM-CSF levels. Together these data provide new insights into the unique neurobehavioral outcomes of HIV infection and cocaine exposure and how they interact to effect immune responses.

KIF5B plays important roles in dendritic spine plasticity and dendritic localization of PSD95 and FMRP in the mouse cortex in vivo

Kinesin 1 (KIF5) is one major type of motor protein in neurons, but its members' function in the intact brain remains less studied. Using in vivo two-photon imaging, we find that conditional knockout of Kif5b (KIF5B cKO) in CaMKIIα-Cre-expressing neurons shows heightened turnover and lower stability of dendritic spines in layer 2/3 pyramidal neurons with reduced spine postsynaptic density protein 95 acquisition in the mouse cortex. Furthermore, the RNA-binding protein fragile X mental retardation protein (FMRP) is translocated to the proximity of newly formed spines several hours before the spine formation events in vivo in control mice, but this preceding transport of FMRP is abolished in KIF5B cKO mice. We further find that FMRP is localized closer to newly formed spines after fear extinction, but this learning-dependent localization is disrupted in KIF5B cKO mice. Our findings provide the crucial in vivo evidence that KIF5B is involved in the dendritic targeting of synaptic proteins that underlies dendritic spine plasticity.

Extinct and extant termites reveal the fidelity of behavior fossilization in amber

Fossils encompassing multiple individuals provide rare direct evidence of behavioral interactions among extinct organisms. However, the fossilization process can alter the spatial relationship between individuals and hinder behavioral reconstruction. Here, we report a Baltic amber inclusion preserving a female-male pair of the extinct termite species Electrotermes affinis. The head-to-abdomen contact in the fossilized pair resembles the tandem courtship behavior of extant termites, although their parallel body alignment differs from the linear alignment typical of tandem runs. To solve this inconsistency, we simulated the first stage of amber formation, the immobilization of captured organisms, by exposing living termite tandems to sticky surfaces. We found that the posture of the fossilized pair matches trapped tandems and differs from untrapped tandems. Thus, the fossilized pair likely is a tandem running pair, representing the direct evidence of the mating behavior of extinct termites. Furthermore, by comparing the postures of partners on a sticky surface and in the amber inclusion, we estimated that the male likely performed the leader role in the fossilized tandem. Our results demonstrate that past behavioral interactions can be reconstructed despite the spatial distortion of body poses during fossilization. Our taphonomic approach demonstrates how certain behaviors can be inferred from fossil occurrences.

Requisite role of dorsal raphé in contextual cocaine-memory reconsolidation

Memory reconsolidation is a process by which labile drug memories are restabilized in long-term memory stores, permitting their enduring control over drug-seeking behaviors. In the present study, we investigated the involvement of the dorsal raphé nuclei (DRN) in cocaine-memory reconsolidation. Sprague-Dawley rats (male, female) were trained to self-administer cocaine in a distinct environmental context to establish contextual drug memories. They then received extinction training in a different context. Next, the rats were re-exposed to the cocaine-predictive context for 15 min to reactivate their cocaine memories or remained in their home cages (no-reactivation control). Memory reactivation was sufficient to increase c-Fos expression, an index of neuronal activation, in the DRN, but not in the median raphé nuclei, during reconsolidation, compared to no reactivation. To determine whether DRN neuronal activity was necessary for cocaine-memory reconsolidation, rats received intra-DRN baclofen plus muscimol (BM; GABAB/A agonists) or vehicle microinfusions immediately after or 6 h after a memory reactivation session conducted with or without lever access. The effects of DRN functional inactivation on long-term memory strength, as indicated by the magnitude of context-induced cocaine seeking, were assessed 72 h later. Intra-DRN BM treatment immediately after memory reactivation with or without lever access attenuated subsequent context-induced cocaine-seeking behavior, independent of sex. Conversely, BM treatment in the adjacent periaqueductal gray (PAG) immediately after memory reactivation, or BM treatment in the DRN 6 h after memory reactivation, did not alter responding. Together, these findings indicate that the DRN plays a requisite role in maintaining cocaine-memory strength during reconsolidation.

Tackling Costly Fearful Avoidance Using Pavlovian Counterconditioning

Avoidance behavior constitutes a major transdiagnostic symptom that exacerbates anxiety. It hampers fear extinction and predicts poor therapy-outcome. Pavlovian counterconditioning with a reward could alleviate avoidance better than traditional extinction by reducing negative valence of the feared situation. However, previous studies are scarce and did not consider that pathological avoidance is often costly and typically evolves from an approach-avoidance conflict. Therefore, we used an approach-avoidance conflict paradigm to model effects of counterconditioning on costly avoidance (i.e., avoidance that leads to missing out on rewards). Results from our preregistered Bayesian Mixed Model analyses in 51 healthy participants (43 females) indicated that counterconditioning was more effective in reducing negative valuation and decreasing costly avoidance than traditional extinction. This study supports application of a simple counterconditioning technique, shows that its efficacy transfers to more complex avoidance situations, and suggests treatment may benefit from increasing reward drive in combination with extinction to overcome avoidance. Application in a clinical sample is a necessary next step to assess clinical utility of counterconditioning.

Effects of fentanyl and the adulterant levamisole on the rewarding and locomotor effects of methamphetamine in rats

BACKGROUND

People who use psychostimulant substances can be exposed to unknown adulterants, such as the synthetic opioid fentanyl (FEN) and the anthelmintic cholinergic agent levamisole (LEV). This work explores the rewarding and locomotor effects of methamphetamine (METH) in combination with FEN or LEV.

METHODS

We used adult male Wistar rats in the conditioned-place preference (CPP) paradigm (conditioning, extinction, and reinstatement phases) and in the open field test to study effective doses of METH, FEN, or LEV, or ineffective doses of METH+FEN or METH+LEV in combination.

RESULTS

METH and LEV, at 1mg/kg METH each, and 30µg/kg FEN produced CPP. Extinction to METH- or LEV-induced CPP occurred after eight saline injections, but it took 8-26 sessions to extinguish FEN-induced CPP. A challenge dose of 0.5mg/kg METH reinstated CPP. The same occurred with 15µg/kg FEN but not with 0.5 or 1mg/kg LEV. Training animals with ineffective doses of METH (0.01mg/kg) combined with either FEN (0.3µg/kg) or LEV (0.01mg/kg) produced CPP. Sub-effective doses of METH or FEN alone did not induce reinstatement after extinction. However, animals challenged with LEV, METH+FEN, or METH+LEV mixtures did it. Combining FEN (3µg/kg) with 0.1mg/kg METH increased locomotor activity.

CONCLUSION

Ineffective FEN and LEV doses mixed with METH produce effects larger than would be expected based on the effects of either drug alone. This outcome suggests a supra-additive interaction, which could increase the risk of developing a METH use disorder.

Multiple schedules of conjugate reinforcement and extinction: A translational model for assessing automatically reinforced behavior

This study evaluated the extent to which a conjugate reinforcement schedule (CONJ) involving a contingency between pedaling a stationary bike and viewing a preferred movie could serve as a translational preparation for the analysis of automatically reinforced behavior. In part, researchers examined whether providing participants with either an accurate or an inaccurate rule about the extinction (EXT) component of a multiple schedule (MULT) contributed to the development of control by the MULT (CONJ EXT) schedule. Results show schedule control emerged for four of five participants who received the accurate rule and none of the five participants who received the inaccurate rule. In addition, participants who received accurate rules typically increased pedaling during CONJ components that followed two consecutive EXT components, suggesting that they experienced deprivation for audio and visual stimulation generated by pedaling. These preliminary findings suggest that researchers could use this translational preparation to identify matched interventions for some automatically reinforced behavior.

Resurgence Following Higher or Lower Quality Alternative Reinforcement

Resurgence is a temporary increase in a previously suppressed target behavior following a worsening in reinforcement conditions. Previous studies have examined how higher rates or magnitudes of alternative reinforcement affect suppression of the target behavior and subsequent resurgence. However, there has been no investigation of the effects of higher versus lower qualities of alternative reinforcement on resurgence. Using a three-phase resurgence preparation with rats, the present experiments examined the effects of an alternative reinforcer that was of higher (Experiment 1) or lower (Experiment 2) quality than the reinforcer that had previously maintained the target behavior. The results of both experiments showed greater reductions in target behavior with a higher quality alternative reinforcer and larger increases in target responding when a higher quality alternative reinforcer was removed. Along with prior findings with higher rates and magnitudes of alternative reinforcement, these findings suggest that variations in reinforcer dimensions that increase the efficacy of alternative reinforcement also tend to increase resurgence when alternative reinforcement is removed. The results are discussed in terms of the resurgence as choice in context model and in terms of potential clinical implications.

Response-dependent point loss and response force as disrupting operations on behavioral resistance to change in humans

Behavioral momentum theory (BMT) provides a theoretical and methodological framework for understanding how differentially maintained operant responding resists disruption. A common way to test operant resistance involves contingencies with suppressive effects, such as extinction or prefeeding. Other contingencies with known suppressive effects, such as response-cost procedures arranged as point-loss or increases in response force, remain untested as disruptive events within the BMT framework. In the present set of three experiments, responding of humans was maintained by point accumulation programmed according to a multiple variable-interval (VI) VI schedule with different reinforcement rates in either of two components. Subsequently, subtracting a point following each response (Experiment 1) or increasing the force required for the response to be registered (Experiments 2 and 3 decreased response rates, but responding was less disrupted in the component associated with the higher reinforcement rate. The point-loss contingency and increased response force similarly affected response rates by suppressing responding and human persistence, replicating previous findings with humans and nonhuman animals when other types of disruptive events (e.g., extinction and prefeeding) were investigated. The present findings moreover extend the generality of the effects of reinforcement rate on persistence, and thus BMT, extending the analysis of resistance to two well-known manipulations used to reduce responding in the experimental analysis of behavior.

The role of stimulus combinations in the repeated assessment of resurgence

The current study examined the role of stimulus combinations on the repeated assessment of resurgence. Using a within-session resurgence procedure, rats were exposed to different conditions, each with distinct stimulus combinations (AAA, ABA, ABB, ABC and AAB). Two arrangements of stimulus changes were compared: Experiment 1 involved changes in stimulus combinations every five sessions, while Experiment 2 implemented changes every session. Resurgence was observed in both experiments; however, Experiment 2 demonstrated more consistent and repeated resurgence when stimulus combinations changed every session. Notably, the ABA, ABB and ABC conditions showed the highest percentage of sessions in which resurgence was observed. Lastly, the current study extends the application of the within-session resurgence procedure to rats and auditory stimuli, providing a reliable method for assessing resurgence in single subjects under different variable conditions.

Evaluation of two physical guidance procedures in the treatment of pediatric feeding disorder

Children with pediatric feeding disorder may refuse to consume an adequate variety and/or volume of food to maintain expected growth. They can consume food but may actively or passively refuse, resulting in escape or avoidance of eating. Behavioral interventions like positive reinforcement with escape extinction can increase consumption. However, sometimes these interventions are insufficient, especially in treating passive refusal. In these cases, physical guidance may be used to prompt an open mouth to deposit food. Research indicates open-mouth prompts are effective and rated as acceptable. This study replicated an existing physical guidance procedure, the finger prompt, and compared its efficacy and acceptability with that of a spoon prompt. This study extended research by defining and measuring passive refusal as a dependent variable and assessing social validity among different stakeholders and times. Both prompts were effective in treating food refusal, and caregivers rated the finger prompt as more preferred.

Selective enhancement of fear extinction by inhibiting neuronal adenylyl cyclase 1 (AC1) in aged mice

Adenylyl cyclase 1 (AC1) is a selective subtype of ACs, which is selectively expressed in neurons. The activation of AC1 is activity-dependent, and AC1 plays an important role in cortical excitation that contributes to chronic pain and related emotional disorders. Previous studies have reported that human-used NB001 (hNB001, a selective AC1 inhibitor) produced analgesic effects in different animal models of chronic pain. However, the potential effects of hNB001 on learning and memory have been less investigated. In the present study, we found that hNB001 affected neither the induction nor the expression of trace fear, but selectively enhanced the relearning ability during the extinction in aged mice. By contrast, the same application of hNB001 did not affect recent, remote auditory fear memory, or remote fear extinction in either adult or aged mice. Furthermore, a single or consecutive 30-day oral administration of hNB001 did not affect acute nociceptive response, motor function, or anxiety-like behavior in either adult or aged mice. Our results are consistent with previous findings that inhibition of AC1 did not affect general sensory, emotional, and motor functions in adult mice, and provide strong evidence that inhibiting the activity of AC1 may be beneficial for certain forms of learning and memory in aged mice.

Differential recruitment of brain circuits during fear extinction in non-stressed compared to stress resilient animals

Dysfunctional fear responses in post-traumatic stress disorder (PTSD) may be partly explained by an inability to effectively extinguish fear responses elicited by trauma-related cues. However, only a subset of individuals exposed to traumatic stress develop PTSD. Therefore, studying fear extinction deficits in animal models of individual differences could help identify neural substrates underlying vulnerability or resilience to the effects of stress. We used a rat model of social defeat in which rats segregate into passively and actively coping rats. In previous work, we showed that passively coping rats exhibit disruptions in social interaction whereas actively coping rats do not display behaviors differently from controls, indicating their resilience. Here, adult male rats exposed to 7 days of social defeat were tested for fear extinction, retention of extinction, and persistence of retention using contextual fear and ethologically-relevant fear tests. Passively coping rats exhibited elevated freezing in response to the previously extinguished context. Analyses of cFos expressing cells across select brain regions showed high correlations within dorsal hippocampal subregions, while passively coping rats had high correlations between the dorsal hippocampus CA1 and the central and basolateral subregions of the amygdala. Importantly, although control and actively coping rats showed similar levels of behavioral extinction, there was little similarity between activated structures, suggesting stress resilience in response to chronic social defeat involves an adaptive differential recruitment of brain circuits to successfully extinguish fear memories.

Placoderms

For over 70 million years, during the Paleozoic, the placoderms (Greek for 'plated skin'), an extinct group of armoured fishes, were the most abundant and diverse vertebrates on our planet. Some of the first placoderm fossils discovered - such as Bothriolepis with its bone-covered pectoral fins - seemed so bizarre that they were thought to represent turtles or ancient beetles. All placoderms bear thick overlapping dermal plates around the head (called the 'head shield') and an area of the body covered in similar overlapping plates enveloping the pectoral to anal region (called the 'trunk-shield'). Placoderm fossils (Figure 1) are known from every continent on Earth ranging from the early Silurian (∼438 million years ago) to the end Devonian (∼359 million years ago) when they became extinct.

Targeting Human Glucocorticoid Receptors in Fear Learning: A Multiscale Integrated Approach to Study Functional Connectivity

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.

Fear extinction rescuing effects of dopamine and L-DOPA in the ventromedial prefrontal cortex

The ventromedial prefrontal cortex (vmPFC; rodent infralimbic cortex (IL)), is posited to be an important locus of fear extinction-facilitating effects of the dopamine (DA) bio-precursor, L-DOPA, but this hypothesis remains to be formally tested. Here, in a model of impaired fear extinction (the 129S1/SvImJ inbred mouse strain; S1), we monitored extracellular DA dynamics via in vivo microdialysis in IL during fear extinction and following L-DOPA administration. Systemic L-DOPA caused sustained elevation of extracellular DA levels in IL and increased neuronal activation in a subpopulation of IL neurons. Systemic L-DOPA enabled extinction learning and promoted extinction retention at one but not ten days after training. Conversely, direct microinfusion of DA into IL produced long-term fear extinction (an effect that was insensitive to ɑ-/ß-adrenoreceptor antagonism). However, intra-IL delivery of a D1-like or D2 receptor agonist did not facilitate extinction. Using ex vivo multi-electrode array IL neuronal recordings, along with ex vivo quantification of immediate early genes and DA receptor signalling markers in mPFC, we found evidence of reduced DA-evoked mPFC network responses in S1 as compared with extinction-competent C57BL/6J mice that were partially driven by D1 receptor activation. Together, our data demonstrate that locally increasing DA in IL is sufficient to produce lasting rescue of impaired extinction. The finding that systemic L-DOPA increased IL DA levels, but had only transient effects on extinction, suggests L-DOPA failed to reach a threshold level of IL DA or produced opposing behavioural effects in other brain regions. Collectively, our findings provide further insight into the neural basis of the extinction-promoting effects of DA and L-DOPA in a clinically relevant animal model, with possible implications for therapeutically targeting the DA system in anxiety and trauma-related disorders.

Nalmefene attenuates reinstatement of methamphetamine-seeking behavior in rats through group II metabotropic glutamate receptors (mGluR2/3)

Nalmefene, an analog to naltrexone, is an antagonist at the μ opioid receptor and a partial agonist at the κ opioid receptor. Both agents are approved for the treatment of alcohol use disorder and opioid addiction. Here, we evaluated the potential of nalmefene for treating psychostimulant dependence using a methamphetamine (METH) self-administration rat model. Rats were trained to press a lever for 0.02-mg intravenous METH infusions paired with drug-associated cues (light and tone) under a fixed ratio 1 schedule. After a 10-day METH self-administration acquisition phase, rats underwent extinction training. A reinstatement test was conducted after fulfilment of the extinction criterion under saline infusions. Re-exposure to METH-associated cues or a priming injection of METH (1.0 mg/kg, i.p.) significantly reinstated METH-seeking behaviors. Pretreatment with nalmefene (10 mg/kg, i.p.) immediately before reinstatement tests significantly attenuated the METH-seeking behaviors induced by both cues and METH priming injection. To investigate the mechanism of effect of nalmefene, we also tested the ability of a group II metabotropic glutamate receptors (mGluR2/3) antagonist, LY341495, to the ameliorating effects of nalmefene. Pretreatment with LY341495 (1.0 mg/kg, i.p.) before nalmefene administration antagonized the effect of nalmefene on reinstatement. LY341495 alone did not affect the reinstatement of lever pressing. We found that nalmefene attenuates METH-seeking behaviors during withdrawal, and this attenuation of reinstatement is mediated by the activation of mGluR2/3. The present findings suggest that nalmefene could decrease incentive motivation for drug use in psychostimulant dependence.

Effects of fisetin on ethanol-induced rewarding properties in mice

Background: Alcohol use disorder (AUD) is a chronic relapsing disorder associated with compulsive drinking of alcohol. Natural flavonoid fisetin affects a variety of transmitter systems relevant to AUD, such as aminobutyric acid, N-methyl-D-aspartate, and dopamine, as well as peroxisome proliferator-activated receptors.Objectives: This study investigated fisetin's impact on the motivational properties of ethanol using conditioned place preference (CPP) in mice (n = 50).Methods: Mice were conditioned with ethanol (2 g/kg, i.p.) or saline on alternating days for 8 consecutive days and were given intragastric (i.g.) fisetin (10, 20, or 30 mg/kg, i.g.), 45 min before ethanol conditioning. During extinction, physiological saline was injected to the control and ethanol groups, and fisetin was administered to the fisetin groups. To evaluate the effect of fisetin on the reinstatement of ethanol-induced CPP, fisetin was given 45 min before a priming dose of ethanol (0.4 g/kg, i.p.; reinstatement test day).Results: Fisetin decreased the acquisition of ethanol-induced CPP (30 mg/kg, p < .05) and accelerated extinction (20 and 30 mg/kg, p < .05). Furthermore, fisetin attenuated reinstatement of ethanol-induced CPP (30 mg/kg, p < .05).Conclusions: Fisetin appears to diminish the rewarding properties of ethanol, as indicated by its inhibitory effect and facilitation of extinction in ethanol-induced CPP. These findings imply a potential therapeutic application of fisetin in preventing ethanol-seeking behavior, promoting extinction, and reducing the risk of relapse.

Effect of instructions on the microstructure of human schedule performance

Three experiments examined the effect of instructions on human free-operant performance on random ratio (RR) and random interval (RI) schedules. Both rates of responding, and the microstructure of behavior, were explored to determine whether bout-initiation and within-bout responding may be controlled by different processes. The results demonstrated that responding in acquisition (Experiments 1 and 2) and extinction (Experiment 3) was impacted in line with given instructions. During acquisition, rates were higher on RR compared to RI for accurate and minimal instructions. During extinction, rates decreased when there were minimal instructions. However, instructions had a greater impact on within-bout responding, than they did on bout-initiation responding. Overall rates of responding, and within-bout rates, varied in line with the nature of the instructions, but bout-initiation responding did not (Experiments 1 and 2). Resistance to extinction was increased by instructions in terms of overall responding and within-bout rates, but not in terms of bout-initiation rates (Experiment 3). These data are consistent with the hypothesis that bout-initiation responding may be less impacted by instructions than within-bout responding, speculatively, the former is stimulus-driven, automatic/habitual, and less accessible to conscious processing. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

The effects of extinction and an explicitly unpaired treatment on the reinforcing properties of a Pavlovian conditioned stimulus

This series of experiments examined the effects of extinction and an explicitly unpaired treatment on the ability of a conditioned stimulus (CS) to function as a reinforcer. Rats were trained to lever press for food, exposed to pairings of a noise CS and food, and, finally, tested for their willingness to lever press for the CS in the absence of the food. Experiment 1 provided a demonstration of conditioned reinforcement (using controls that were only exposed to unpaired presentations of the CS and food) and showed that it was equivalent after one or four sessions of CS-food pairings. Experiments 2 and 3 showed that, after one session of CS-food pairings, repeated presentations of the CS alone reduced its reinforcing properties; but after four sessions of CS-food pairings, repeated presentations of the CS alone had no effect on these properties. Experiment 4 showed that, after four sessions of CS-food pairings, explicitly unpaired presentations of the CS and food completely undermined conditioned reinforcement. Finally, Experiment 5 provided within-experiment evidence that, after four sessions of CS-food pairings, the reinforcing properties of the CS were disrupted by explicitly unpaired presentations of the CS and food but spared by repeated presentations of the CS alone. Together, these findings indicate that the effectiveness of extinction in undermining the reinforcing properties of a CS depends on its level of conditioning; and that, where extinction fails to disrupt these properties, they are successfully undermined by an explicitly unpaired treatment. They are discussed with respect to findings in the literature on Pavlovian-to-instrumental transfer; and the Rescorla-Wagner model, which anticipates that an explicitly unpaired treatment will be more effective than extinction in reversing the effects of conditioning.

Evaluating the effects of counterconditioning, novelty-facilitated, and standard extinction on the spontaneous recovery of threat expectancy and conditioned stimulus valence

Extinction training has proved effective to diminish the expectancy of the aversive unconditioned stimulus (US). However, the negative valence of the conditioned stimulus (CS) may still stay intact. In fact, several studies have suggested that the CS negative valence may be a factor that promotes the return of fear. Our study focuses on the role of changes in the CS valence as a potential mechanism to reduce the spontaneous recovery of threat expectancies. To do that, we evaluated counterconditioning (CC), a technique aimed to reduce the CS negative valence by paring it with a positive stimulus and compared its efficacy to that of a novelty-facilitated extinction (NFE) and a standard extinction interventions. Using a 2-day protocol, participants first learned the relationship between a figure and an aversive sound, using a differential conditioning paradigm, and were then randomly assigned to one of three different groups. For the CC group, CS+ or cue A was paired with a positive US. The standard extinction group was exposed to cue A alone. For a third NFE group, cue A was followed by a neutral US. Finally, on the second day, spontaneous recovery was tested. Our findings did not provide evidence to suggest that CC could be more effective to prevent or reduce the return of threat expectancies or influence valence ratings when compared with NFE and standard extinction.

Microbial short-chain fatty acids regulate drug seeking and transcriptional control in a model of cocaine seeking

Cocaine use disorder represents a public health crisis with no FDA-approved medications for its treatment. A growing body of research has detailed the important connections between the brain and the resident population of bacteria in the gut, the gut microbiome, in psychiatric disease models. Acute depletion of gut bacteria results in enhanced reward in a mouse cocaine place preference model, and repletion of bacterially-derived short-chain fatty acid (SCFA) metabolites reverses this effect. However, the role of the gut microbiome and its metabolites in modulating cocaine-seeking behavior after prolonged abstinence is unknown. Given that relapse prevention is the most clinically challenging issue in treating substance use disorders, studies examining the effects of microbiome manipulations in relapse-relevant models are critical. Here, male Sprague-Dawley rats received either untreated water or antibiotics to deplete the gut microbiome and its metabolites. Rats were trained to self-administer cocaine and subjected to either within-session threshold testing to evaluate motivation for cocaine or 21 days of abstinence followed by a cue-induced cocaine-seeking task to model relapse behavior. Microbiome depletion did not affect cocaine acquisition on an fixed-ratio 1 schedule. However, microbiome-depleted rats exhibited significantly enhanced motivation for low dose cocaine on a within-session threshold task. Similarly, microbiome depletion increased cue-induced cocaine-seeking following prolonged abstinence and altered transcriptional regulation in the nucleus accumbens. In the absence of a normal microbiome, repletion of bacterially-derived SCFA metabolites reversed the behavioral and transcriptional changes associated with microbiome depletion. These findings suggest that gut bacteria, via their metabolites, are key regulators of drug-seeking behaviors, positioning the microbiome as a potential translational research target.

Inhibition of fatty acid binding protein-5 in the basolateral amygdala induces anxiolytic effects and accelerates fear memory extinction

RATIONALE

The endocannabinoid (eCB) system critically controls anxiety and fear-related behaviours. Anandamide (AEA), a prominent eCB ligand, is a hydrophobic lipid that requires chaperone proteins such as Fatty Acid Binding Proteins (FABPs) for intracellular transport. Intracellular AEA transport is necessary for degradation, so blocking FABP activity increases AEA neurotransmission.

OBJECTIVE

To investigate the effects of a novel FABP5 inhibitor (SBFI-103) in the basolateral amygdala (BLA) on anxiety and fear memory.

METHODS

We infused SBFI-103 (0.5 μg-5 μg) to the BLA of adult male Sprague Dawley rats and ran various anxiety and fear memory behavioural assays, neurophysiological recordings, and localized molecular signaling analyses. We also co-infused SBFI-103 with the AEA inhibitor, LEI-401 (3 μg and 10 μg) to investigate the potential role of AEA in these phenomena.

RESULTS

Acute intra-BLA administration of SBFI-103 produced strong anxiolytic effects across multiple behavioural tests. Furthermore, animals exhibited acute and long-term accelerated associative fear memory extinction following intra-BLA FABP5 inhibition. In addition, BLA FABP5 inhibition induced strong modulatory effects on putative PFC pyramidal neurons along with significantly increased gamma oscillation power. Finally, we observed local BLA changes in the phosphorylation activity of various anxiety- and fear memory-related molecular biomarkers in the PI3K/Akt and MAPK/Erk signaling pathways. At all three levels of analyses, we found the functional effects of SBFI-103 depend on availability of the AEA ligand.

CONCLUSIONS

These findings demonstrate a novel intra-BLA FABP5 signaling mechanism regulating anxiety and fear memory behaviours, neuronal activity states, local anxiety-related molecular pathways, and functional AEA modulation.

Blockade of the orexin-2 receptors within the ventral tegmental area facilitates the extinction and prevents the reinstatement of methamphetamine-seeking behavior

Repeated use of methamphetamine (METH) causes severe effects on the central nervous system, associated with an increased relapse rate. The orexinergic system is highly implicated in the reward circuitry and may be a promising target for treating psychostimulant dependency. The present study aimed to investigate the involvement of the orexin system, mainly the orexin-2 receptors (OX2R) in the ventral tegmental area (VTA) in the extinction and reinstatement of METH-seeking behavior using a conditioned place preference (CPP) paradigm. To this end, animals received METH (1 mg/kg; sc) for a 5-day conditioning period. Then, in the first set of experiments, different groups of rats were given intra-VTA TCS OX2 29 (1, 3, 10, or 30 nmol/0.3 μl DMSO) as an OX2R antagonist over a 10-day extinction period. In another experiment, after the extinction period, a different set of animals received a single dose of TCS OX2 29 (1, 3, 10, or 30 nmol) before the priming dose of METH (0.25 mg/kg; sc) on the reinstatement day. The results revealed that TCS OX2 29 (10 and 30 nmol) remarkably facilitated the extinction of rewarding properties of METH (P < 0.001 for both doses). Furthermore, TCS OX2 29 (3, 10, or 30 nmol) significantly suppressed the METH-induced reinstatement (3 nmol; P < 0.05, 10 nmol; P < 0.01, and 30 nmol; P < 0.001). In conclusion, the current study revealed that the orexinergic system, specifically the VTA OX2R, is involved in METH-seeking behaviors and that manipulation of this system can be considered a potential therapeutics in treating METH dependency.

Psilocybin facilitates fear extinction in mice by promoting hippocampal neuroplasticity

BACKGROUND

Posttraumatic stress disorder (PTSD) and depression are highly comorbid. Psilocybin exerts substantial therapeutic effects on depression by promoting neuroplasticity. Fear extinction is a key process in the mechanism of first-line exposure-based therapies for PTSD. We hypothesized that psilocybin would facilitate fear extinction by promoting hippocampal neuroplasticity.

METHODS

First, we assessed the effects of psilocybin on percentage of freezing time in an auditory cued fear conditioning (FC) and fear extinction paradigm in mice. Psilocybin was administered 30 min before extinction training. Fear extinction testing was performed on the first day; fear extinction retrieval and fear renewal were tested on the sixth and seventh days, respectively. Furthermore, we verified the effect of psilocybin on hippocampal neuroplasticity using Golgi staining for the dendritic complexity and spine density, Western blotting for the protein levels of brain derived neurotrophic factor (BDNF) and mechanistic target of rapamycin (mTOR), and immunofluorescence staining for the numbers of doublecortin (DCX)- and bromodeoxyuridine (BrdU)-positive cells.

RESULTS

A single dose of psilocybin (2.5 mg/kg, i.p.) reduced the increase in the percentage of freezing time induced by FC at 24 h, 6th day and 7th day after administration. In terms of structural neuroplasticity, psilocybin rescued the decrease in hippocampal dendritic complexity and spine density induced by FC; in terms of neuroplasticity related proteins, psilocybin rescued the decrease in the protein levels of hippocampal BDNF and mTOR induced by FC; in terms of neurogenesis, psilocybin rescued the decrease in the numbers of DCX- and BrdU-positive cells in the hippocampal dentate gyrus induced by FC.

CONCLUSIONS

A single dose of psilocybin facilitated rapid and sustained fear extinction; this effect might be partially mediated by the promotion of hippocampal neuroplasticity. This study indicates that psilocybin may be a useful adjunct to exposure-based therapies for PTSD and other mental disorders characterized by failure of fear extinction.

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

BACKGROUND

Little is known about the specific roles of cortical and accumbal oxytocin receptors in drug use disorders. To better understand the importance of the endogenous oxytocin system in cocaine relapse behavior, we developed an adeno-associated viral vector-expressing short hairpin (sh) RNAs to selectively degrade the rat oxytocin receptor (OxyR) mRNA in vivo.

METHODS

Male (Sprague-Dawley) rats received bilateral infusions of the shRNA for the oxytocin receptor (shOxyR) or an shRNA control virus into the prefrontal cortex (PFC) or the nucleus accumbens core (NAc). Rats self-administered cocaine on an escalating FR ratio for 14 days, lever responding was extinguished, and rats were tested for cued and cocaine-primed reinstatement of drug seeking.

RESULTS

OxyR knockdown in the PFC delayed the acquisition of lever pressing on an fixed ratio 1 schedule of reinforcement. All rats eventually acquired the same level of lever pressing and discrimination, and there were no differences in extinction. OxyR knockdown in the NAc had no effect during acquisition. In both the PFC and NAc, the shOxyR decreased cued reinstatement relative to shRNA control virus but was without effect during drug-primed reinstatement. OxyR knockdown in the PFC increased chamber activity during a social interaction task.

CONCLUSIONS

This study provides critical new information about how endogenous OxyRs function to affect drug seeking in response to different precipitators of relapse. The tool developed to knockdown OxyRs in rat could provide important new insights that aid development of oxytocin-based therapeutics to reduce return-to-use episodes in people with substance use disorder and other neuropsychiatric disorders.

RTI-263, a biased neuropeptide S receptor agonist that retains an anxiolytic effect, attenuates cocaine-seeking behavior in rats

Neuropeptide S (NPS) is a neuromodulatory peptide that acts via a G protein-coupled receptor. Centrally administered NPS suppresses anxiety-like behaviors in rodents while producing a paradoxical increase in arousal. In addition, NPS increases drug-seeking behavior when administered during cue-induced reinstatement. Conversely, an NPS receptor (NPSR) antagonist, RTI-118, decreases cocaine-seeking behavior. A biased NPSR ligand, RTI-263, produces anxiolytic-like effects and has memory-enhancing effects similar to those of NPS but without the increase in arousal. In the present study, we show that RTI-263 decreased cocaine seeking by both male and female rats during cue-induced reinstatement. However, RTI-263 did not modulate the animals' behaviors during natural reward paradigms, such as palatable food intake, feeding during a fasting state, and cue-induced reinstatement of sucrose seeking. Therefore, NPSR biased agonists are a potential pharmacotherapy for substance use disorder because of the combined benefits of decreased drug seeking and the suppression of anxiety.

Impaired learning, memory, and extinction in posttraumatic stress disorder: translational meta-analysis of clinical and preclinical studies

Current evidence-based treatments for post-traumatic stress disorder (PTSD) are efficacious in only part of PTSD patients. Therefore, novel neurobiologically informed approaches are urgently needed. Clinical and translational neuroscience point to altered learning and memory processes as key in (models of) PTSD psychopathology. We extended this notion by clarifying at a meta-level (i) the role of information valence, i.e. neutral versus emotional/fearful, and (ii) comparability, as far as applicable, between clinical and preclinical phenotypes. We hypothesized that cross-species, neutral versus emotional/fearful information processing is, respectively, impaired and enhanced in PTSD. This preregistered meta-analysis involved a literature search on PTSD+Learning/Memory+Behavior, performed in PubMed. First, the effect of information valence was estimated with a random-effects meta-regression. The sources of variation were explored with a random forest-based analysis. The analyses included 92 clinical (N = 6732 humans) and 182 preclinical (N = 6834 animals) studies. A general impairment of learning, memory and extinction processes was observed in PTSD patients, regardless of information valence. Impaired neutral learning/memory and fear extinction were also present in animal models of PTSD. Yet, PTSD models enhanced fear/trauma memory in preclinical studies and PTSD impaired emotional memory in patients. Clinical data on fear/trauma memory was limited. Mnemonic phase and valence explained most variation in rodents but not humans. Impaired neutral learning/memory and fear extinction show stable cross-species PTSD phenotypes. These could be targeted for novel PTSD treatments, using information gained from neurobiological animal studies. We argue that apparent cross-species discrepancies in emotional/fearful memory deserve further in-depth study; until then, animal models targeting this phenotype should be applied with utmost care.

Relation among, trait anxiety, intolerance to uncertainty and early maltreatment experiences on fear discrimination learning and avoidance generalization online task

BACKGROUND AND OBJECTIVES

Early aversive experiences, which have been associated with elevated anxiety and intolerance of uncertainty (IUS), may contribute negatively to fear conditioning learning. The aim of the present study was to analyze the relation among individual differences in childhood maltreatment experiences, trait anxiety, and IUS in adulthood; and to determine how these variables could affect fear learning discrimination and avoidance generalization.

METHODS

We adapted an avoidance procedure in an online fear learning task. Two pictures of different lamp colors (CS+) were first associated with two aversive images (US), while a third color was not (CS-). Next, clicking a button during one CS + could effectively avoid the US (CS + av), but not during the other (CS + unav). Finally, avoidance generalization was tested to lamp colors that were between CS- and CS + av (safety dimension) and CS + av and CS + unav (avoidability dimension). With a sample of 67 participants, we measured ratings of relief, expectancy, and anxiety, as well as button presses and individual differences (STAI, IUS and MAES).

RESULTS

Aversive early experiences were positively related to trait anxiety and intolerance of uncertainty. The results of the task further suggested that maltreatment experience contributes to be more attentive to aversive signals, which could be implicated in leading to difficulties in discrimination learning.

LIMITATIONS

Online experiments implies some loss of control over subjects and environment that can threaten internal validity. Likewise, the commitment of participants may be low.

CONCLUSIONS

Results suggest that early aversive experience and anxiety could contribute to the development of IUS, which likely contributes to the development of avoidance behavior.

Cue-induced reinstatement of seeking behavior in male rats is independent from the rewarding value of the primary reinforcer: Effect of mGluR5 blockade

Environmental conditioning factors have a profound impact on alcohol-seeking behavior and the maintenance of alcohol use in individuals with alcohol dependence. Cues associated with alcohol, depending on the perceived value of the primary reinforcer, gain salience and can trigger relapse. This study investigates the correlation between the reward magnitude of the primary reinforcer and the reinstatement evoked by cues predictive of their availability in male rats. Rat self-administration procedures were used to test reinstatement, with reinforcers consisting of 10% alcohol, 10% sucrose, or 2% sodium chloride (NaCl) experienced under need-state conditions. The effect of MTEP ([(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine), a selective metabotropic glutamate receptor 5 (mGluR5) antagonist, on motivation and reinstatement behaviors was also evaluated. RESULTS: demonstrate that under Fixed Ratio 1 (FR1) schedule, the three reinforcers maintain operant responding with the following order of magnitude 10% sucrose >2% NaCl >10% alcohol > water. Under a progressive ratio (PR) schedule of reinforcement, rats exhibit a significantly higher breakpoint for 2% NaCl (under Na-depletion), followed by 10% sucrose and 10% alcohol. After extinction, a significant reinstatement is observed with the magnitude order of 10% sucrose >10% alcohol >2% NaCl. However, only re-exposure to alcohol-paired cues induced significant reinstatement of alcohol-seeking after 4 and 8 months. Treatment with MTEP significantly reduces reinstatement of responding across all reinforcers, with the strongest effect observed on alcohol-seeking. These findings suggest that mGluR5 plays a general role in controlling cue-reactivity, but the effect is prominent in the case of alcohol compared to natural rewards. In conclusion, the results demonstrate a remarkable dissociation between the rewarding magnitude of the primary reinforcer and its ability to trigger relapse upon presentation of a cue previously associated with it. Importantly, alcohol, despite having lower intrinsic motivational value compared to a natural reward (sucrose) or a consummatory stimulus experienced under need state conditions (NaCl), can elicit more robust and longer-term reinstatement of seeking responses. Finally, our data demonstrate a significant involvement of the mGluR5 system in the regulation of seeking behavior.

Reproductive experience alters the effects of diazepam and fluoxetine on anxiety-like behaviour, fear extinction, and corticosterone levels in female rats

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.

Extinction and reinstatement of methamphetamine-induced conditioned place preference in zebrafish

Conditioned place preference (CPP) paradigm in zebrafish has been used to measure drug reward, but there is limited research on CPP reinstatement to determine relapse vulnerability. The present study aimed to investigate extinction and reinstatement of methamphetamine (MA)-induced CPP in zebrafish and evaluate the model's predictive validity. Zebrafish received different doses of MA (0-60 mg/kg) during CPP training. The preferred dose of MA at 40 mg/kg was used for extinction via either confined or nonconfined procedures. The extinguished CPP was reinstated by administering a priming dose of MA (20 mg/kg) or various stressors. To assess persistent susceptibility to reinstatement, MA CPP and reinstatement were retested following 14 days of abstinence. In addition, the effects of SCH23390, naltrexone, and clonidine on MA CPP during acquisition, expression, or reinstatement phases were monitored. MA induced CPP in a dose-dependent manner. Both nonconfined and confined extinction procedures time-dependently reduced the time spent on the MA-paired side. A priming dose of MA, chasing stress, or yohimbine reinstated the extinguished CPP. After 14 days of abstinence, the MA CPP remained extinguished and was significantly reinstated by MA priming or chasing stress. Similar to the observations in rodents, SCH23390 suppressed the acquisition of MA CPP, naltrexone reduced the expression and MA priming-induced reinstatement, while clonidine prevented stress-induced reinstatement of MA CPP. This work expanded the zebrafish CPP paradigm to include extinction and reinstatement phases, demonstrating predictive validity and highlighting its potential as a valuable tool for exploring drug relapse.

The Role of Dorsal Raphe Nucleus Serotonergic Systems in Emotional Learning and Memory in Male BALB/c Mice

Selective serotonin reuptake inhibitors (SSRIs) are the first-line pharmacological treatment for a variety of anxiety-, trauma- and stressor-related disorders. Although they are efficacious, therapeutic improvements require several weeks of treatment and are often associated with an initial exacerbation of symptoms. The dorsal raphe nucleus (DR) has been proposed as an important target for the modulation of emotional responses and the therapeutic effects of SSRIs. Using a fear-conditioning paradigm we aimed to understand how SSRIs affect emotional learning and memory, and their effects on serotonergic circuitry. Adult male BALB/c mice were treated with vehicle (n = 16) or the SSRI fluoxetine (18 mg/kg/d) acutely (n = 16), or chronically (21d, n = 16), prior to fear conditioning. Treatment was stopped, and half of the mice (n = 8/treatment group) were exposed to cued fear memory recall 72 h later. Activation of DR serotonergic neurons during fear conditioning (Experiment 1) or fear memory recall (Experiment 2), was measured using dual-label immunohistochemistry for Tph2 and c-Fos. Acute and chronic fluoxetine treatment reduced associative fear learning without affecting memory recall and had opposite effects on anxiety-like behaviour. Acute fluoxetine decreased serotonergic activity in the DR, while chronic treatment led to serotonergic activity that was indistinguishable from that of control levels in DRD and DRV subpopulations. Chronic fluoxetine facilitated fear extinction, which was associated with rostral DRD inhibition. These findings provide further evidence that SSRIs can alter aspects of learning and memory processes and are consistent with a role for discrete populations of DR serotonergic neurons in regulating fear- and anxiety-related behaviours.

Fear extinction is regulated by the activity of long noncoding RNAs at the synapse

Long noncoding RNAs (lncRNAs) represent a multidimensional class of regulatory molecules that are involved in many aspects of brain function. Emerging evidence indicates that lncRNAs are localized to the synapse; however, a direct role for their activity in this subcellular compartment in memory formation has yet to be demonstrated. Using lncRNA capture-seq, we identified a specific set of lncRNAs that accumulate in the synaptic compartment within the infralimbic prefrontal cortex of adult male C57/Bl6 mice. Among these was a splice variant related to the stress-associated lncRNA, Gas5. RNA immunoprecipitation followed by mass spectrometry and single-molecule imaging revealed that this Gas5 isoform, in association with the RNA binding proteins G3BP2 and CAPRIN1, regulates the activity-dependent trafficking and clustering of RNA granules. In addition, we found that cell-type-specific, activity-dependent, and synapse-specific knockdown of the Gas5 variant led to impaired fear extinction memory. These findings identify a new mechanism of fear extinction that involves the dynamic interaction between local lncRNA activity and RNA condensates in the synaptic compartment.

Heterotypic Stressors Unmask Behavioral Influences of PMAT Deficiency in Mice

Certain life stressors having enduring physiological and behavioral consequences, in part by eliciting dramatic signaling shifts in monoamine neurotransmitters. High monoamine levels can overwhelm selective transporters like the serotonin transporter. This is when polyspecific transporters like plasma membrane monoamine transporter (PMAT, Slc29a4) are hypothesized to contribute most to monoaminergic signaling regulation. Here, we employed two distinct counterbalanced stressors-fear conditioning and swim stress-in mice to systematically determine how reductions in PMAT function affect heterotypic stressor responsivity. We hypothesized that male heterozygotes would exhibit augmented stressor responses relative to female heterozygotes. Decreased PMAT function enhanced context fear expression, an effect unexpectedly obscured by a sham stress condition. Impaired cued fear extinction retention and enhanced context fear expression in males were conversely unmasked by a sham swim condition. Abrogated corticosterone levels in male heterozygotes that underwent swim stress after context fear conditioning did not map onto any measured behaviors. In sum, male heterozygous mouse fear behaviors proved malleable in response to preceding stressor or sham stress exposure. Combined, these data indicate that reduced male PMAT function elicits a form of stress-responsive plasticity. Future studies should assess how PMAT is differentially affected across sexes and identify downstream consequences of the stress-shifted corticosterone dynamics.

Voluntary alcohol intake alters the motivation to seek intravenous oxycodone and neuronal activation during the reinstatement of oxycodone and sucrose seeking

Opioid-alcohol polysubstance use is prevalent and worsens treatment outcomes. Here we assessed whether co-consumption of oxycodone and alcohol influence the intake of one another, demand for oxycodone, and the neurocircuitry underlying cue-primed reinstatement of oxycodone-seeking. Male and female rats underwent oxycodone intravenous self-administration (IVSA) with homecage access to alcohol (20% v/v) and/or water immediately after the IVSA session. Next, economic demand for intravenous oxycodone was assessed while access to alcohol and/or water continued. Control rats self-administered sucrose followed by access to alcohol and/or water. Rats underwent a cue-primed reinstatement test and brains were processed for c-fos mRNA expression. While both sexes decreased oxycodone intake if they had access to alcohol, and decreased alcohol intake if they had access to oxycodone, only female oxycodone + alcohol rats exhibited decreased demand elasticity and increased cue-primed reinstatement. Alcohol consumption increased the number of basolateral and central amygdala neurons activated during sucrose and oxycodone reinstatement and the number of ventral and dorsal striatum neurons engaged by sucrose reinstatement. Nucleus accumbens shell dopamine 1 receptor expressing neurons displayed activation patterns consistent with oxycodone reinstatement. Thus, alcohol alters the motivation to seek oxycodone in a sex-dependent manner and the neural circuitry engaged by cue-primed reinstatement of sucrose and oxycodone-seeking.