Fear Conditioning Research Articles

Gender-stereotypical attribution of fear and fearlessness in preschool children.

Fear and fearlessness are two distinct emotional responses that can occur when a person faces a potentially dangerous situation. These responses seem to be linked to gender stereotypes (fearful female and fearless male). This study examines whether preschool children attribute fear and fearlessness stereotypically in relation to gender and whether their attributions vary as a function of age and gender. One hundred and twenty children (60 boys and 60 girls) aged 3, 4 and 5 years participated in this study. We examined children's gender-stereotypical performance through emotional scenarios and drawing tasks involving fear and fearlessness conditions. The results showed that children's performance was equally stereotypical in the two conditions. An age effect was found: children's gender stereotypical attributions increased with age. The results showed no differences in children's stereotypical performance in regards to their gender and task type (emotional scenarios and drawing tasks). The significance and implications of these findings are discussed in the context of gender-emotion stereotypes.

The clinically relevant MEK inhibitor mirdametinib combined with D-cycloserine and prediction error disrupts fear memory in PTSD models

This study establishes mirdametinib as the first MEK inhibitor that can undergo clinical development for psychiatric indications such as post-traumatic stress disorder (PTSD). PTSD is characterized by persistent traumatic memories with limited effective treatment options. A body of evidence suggests that memory storage is dynamic and constantly updated through post-retrieval modification a process termed reconsolidation. Although ERK/MAPK signaling plays a central role in fear memory consolidation, no clinically translatable MEK inhibitor has been tested in experimental models or in clinical trials to disrupt this process. Furthermore, there is need to develop pharmacological and behavioral strategies to labilize the memory to make it susceptible for disruption. Here, we disrupted fear memory reconsolidation with the clinically relevant MEK inhibitor mirdametinib in C57BL/6 mice and tested memory destabilization strategies using an auditory fear conditioning paradigm, with drugs administered following reactivation of memory. We found prediction error effective in labilizing weak fear memory and combined D-cycloserine (DCS) and predication error effective in labilizing strong fear memory. Mirdametinib disrupted the weak fear memory and reduced ERK phosphorylation in lateral amygdala when coupled with prediction error at the time of memory reactivation but required coordinated combination of DCS, prediction error and mirdametinib to disrupt strong fear memory. Barnes maze spatial memory test and open field test revealed that mirdametinib did not affect retrieval of other forms (spatial) of long-term memory and locomotor activity. Furthermore, the effect of mirdametinib was specific to reconsolidation as it had no effect on fear memory when given without reactivation. These translational findings identify a new drug that can be adapted for the treatment of PTSD.

Knockout of AMPA receptor binding protein Neuron-specific gene 2 (NSG2) enhances associative learning and cognitive flexibility

The vast majority of gene mutations and/or gene knockouts result in either no observable changes, or significant deficits in molecular, cellular, or organismal function. However, in a small number of cases, mutant animal models display enhancements in specific behaviors such as learning and memory. To date, most gene deletions shown to enhance cognitive ability generally affect a limited number of pathways such as NMDA receptor- and translation-dependent plasticity, or GABA receptor- and potassium channel-mediated inhibition. While endolysosomal trafficking of AMPA receptors is a critical mediator of synaptic plasticity, mutations in genes that affect AMPAR trafficking either have no effect or are deleterious for synaptic plasticity, learning and memory. NSG2 is one of the three-member family of Neuron-specific genes (NSG1-3), which have been shown to regulate endolysosomal trafficking of a number of proteins critical for neuronal function, including AMPAR subunits (GluA1-2). Based on these findings and the largely universal expression throughout mammalian brain, we predicted that genetic knockout of NSG2 would result in significant impairments across multiple behavioral modalities including motor, affective, and learning/memory paradigms. However, in the current study we show that loss of NSG2 had highly selective effects on associative learning and memory, leaving motor and affective behaviors intact. For instance, NSG2 KO animals performed equivalent to wild-type C57Bl/6n mice on rotarod and Catwalk motor tasks, and did not display alterations in anxiety-like behavior on open field and elevated zero maze tasks. However, NSG2 KO animals demonstrated enhanced recall in the Morris water maze, accelerated reversal learning in a touch-screen task, and accelerated acquisition and enhanced recall on a Trace Fear Conditioning task. Together, these data point to a specific involvement of NSG2 on multiple types of associative learning, and expand the repertoire of pathways that can be targeted for cognitive enhancement.

Male rats emit aversive 44-kHz ultrasonic vocalizations during prolonged Pavlovian fear conditioning.

Rats are believed to communicate their emotional state by emitting two distinct types of ultrasonic vocalizations. The first is long '22-kHz' vocalizations (>300 ms, <32-kHz) with constant frequency, signaling aversive states, and the second is short '50-kHz' calls (<150 ms, >32 kHz), often frequency-modulated, in appetitive situations. Here, we describe aversive vocalizations emitted at a higher pitch by male Wistar and spontaneously hypertensive rats (SHR) in an intensified aversive state - prolonged fear conditioning. These calls, which we named '44-kHz' vocalizations, are long (>150 ms), generally at a constant frequency (usually within 35-50-kHz range) and have an overall spectrographic image similar to 22-kHz calls. Some 44-kHz vocalizations are comprised of both 22-kHz-like and 44-kHz-like elements. Furthermore, two separate clustering methods confirmed that these 44-kHz calls can be separated from other vocalizations. We observed 44-kHz calls to be associated with freezing behavior during fear conditioning training, during which they constituted up to 19.4% of all calls and most of them appeared next to each other forming uniform groups of vocalizations (bouts). We also show that some of rats' responses to the playback of 44-kHz calls were more akin to that of aversive calls, for example, heart rate changes, whereas other responses were at an intermediate level between aversive and appetitive calls. Our results suggest that rats have a wider vocal repertoire than previously believed, and current definitions of major call types may require reevaluation. We hope that future investigations of 44-kHz calls in rat models of human diseases will contribute to expanding our understanding and therapeutic strategies related to human psychiatric conditions.

REM disruption and REM vagal activity predict extinction recall in trauma-exposed individuals.

Accumulating evidence suggests that rapid eye movement sleep (REM) supports the consolidation of extinction memory. REM is disrupted in posttraumatic stress disorder (PTSD), and REM abnormalities after traumatic events increase the risk of developing PTSD. Therefore, it was hypothesized that abnormal REM in trauma-exposed individuals may pave the way for PTSD by interfering with the processing of extinction memory. In addition, PTSD patients display reduced vagal activity. Vagal activity contributes to the strengthening of memories, including fear extinction memory, and recent studies show that the role of vagus in memory processing extends to memory consolidation during sleep. Therefore, it is plausible that reduced vagal activity during sleep in trauma-exposed individuals may be an additional mechanism that impairs extinction memory consolidation. However, to date, the contribution of sleep vagal activity to the consolidation of extinction memory or any emotional memory has not been investigated. Trauma-exposed individuals (n = 113) underwent a 2-day fear conditioning and extinction protocol. Conditioning and extinction learning phases were followed by extinction recall 24 h later. The association of extinction recall with REM characteristics and REM vagal activity (indexed as heart rate variability) during the intervening consolidation night was examined. Consistent with our hypotheses, REM disruption was associated with poorer physiological and explicit extinction memory. Furthermore, higher vagal activity during REM was associated with better explicit extinction memory, and physiological extinction memory in males. These findings support the notion that abnormal REM, including reduced REM vagal activity, may contribute to PTSD by impairing the consolidation of extinction memory.

Agmatine diminishes behavioral and endocrine alterations in a rat model of post-traumatic stress disorder.

Post-traumatic stress disorder (PTSD), is a severe anxiety disorder characterized by associative fear conditioning. Single prolonged stress (SPS) is a widely accepted reliable animal model to stimulate PTSD. Agmatine is an endogenous neuromodulator of stress; however, its effect on PTSD remains to be investigated. This study explored the role of agmatine in Conditioned Fear Response (CFR) in PTSD and highlighted how imidazoline receptors contribute to effect of agmatine. Intra-cerebroventricular (icv) surgery was done in order to facilitate drug administration. Animals were subjected to SPS. Agmatine and the involvement of Imidazoline receptors (I1 and I2) were assessed for their effect in fear conditioning apparatus. During weeks 1, 2, and 3, in CFR, agmatine (40 µg/rat, icv) showed significantly decreased freezing time as compared to other doses of agmatine (10 and 20 µg/rat, icv). Imidazoline (I1 and I2) receptor agonists Moxonidine (25 µg/rat, icv) and 2-BFI, (10 µg/rat, icv) respectively, at their sub-effective doses, with a submaximal dose of agmatine (20 µg/rat, icv) significantly decreased the altered freezing time during weeks 1, 2 and 3 compared to SPS animals. Moreover, the effective dose of agmatine (40 µg/rat, icv) with imidazoline (I1 and I2) receptor antagonists Efaroxan (10 µg/rat, icv) and Idazoxan (4 µg/rat, icv) respectively does not show a significant effect on freezing. Agmatine and its combination with I1 and I2 agonists, normalized the altered freezing behavior due to SPS during CFR projecting its strong therapeutic implication for CFR in SPS induced-PTSD.

Conditioned fear selectively increases the perception and neural processing of respiratory stimuli relative to somatosensory stimuli

Interoception is crucial to the experience of bodily complaints in chronic conditions. Fear can distort the perception of sensations like breathlessness and pain, yet few studies investigated the effects of conditioned fear on both self-report and neural processing of these sensations. In the current study, we conditioned fear of neutral female faces in healthy adults, pairing certain faces (CS+) with an aversive scream. In Experiment 1, we delivered paired inspiratory occlusions during the viewing of the faces. We collected self-reported intensity and unpleasantness of occlusions, and measured N1 and P2 amplitudes of the respiratory-related evoked potential (RREP) in the electroencephalogram, as well as neural gating (the ratio of N1 response to the second over the first occlusion, S2/S1). Skin conductance and self-reported fear increased in response to CS+ faces, and perception of occlusions increased during fear conditioning (FC) relative to baseline, with higher unpleasantness and RREP amplitudes during CS+ relative to CS- trials. We found no effects on neural gating. In Experiment 2, we used the same FC protocol, and delivered paired electrocutaneous pulses during the viewing of the faces. We measured intensity/unpleasantness, fear, N1/P2 amplitudes of the somatosensory evoked potential (SEP), and neural gating. While skin conductance and fear increased, no perceptual effects were found. Unexpectedly, SEP amplitudes decreased and neural gating increased during FC, likely due to habituation. The current results indicate that FC increases the perception and neural processing of respiratory stimuli specifically, consistent with previous literature on respiratory psychophysiology and fearful states.

The effects of crocin on fear condition memory impairment caused by morphine in relation to gene expression of amygdala HSP70, HSP90 and NF-kB

BackgroundSome studies have shown that morphine causes memory impairment through different mechanisms. The roles of inflammation/NF-κB and BDNF/TrkB/CREB pathways are significant in the memory deficits caused by morphine. Aim: In this study, the effect of crocin on the impairment of fear memory caused by morphine was investigated, and the expression of HSP70, HSP90, and NF-kB genes that play an important role in memory in male Wistar rats was measured. Material and methodThe fear conditioning test was used to check the fear memory of rats, and total Freezing time was considered as an index of memory. Rats (96 Wistar rats) were randomly divided into 12 groups. The rats were injected with saline (1 ml/kg) or different doses of morphine (0.5, 2.5, and 5 mg/kg) 5 min after injection of saline (1 ml/kg) or subthreshold doses of crocin (60 mg/kg). Real-time PCR method was used for HSP70, HSP90, and NF-kB gene expression in the Amygdala. ResultAdministration of morphine 5 mg/kg decreased the total freezing and increased the latency freezing (P < 0.001). Also, the results showed that crocin 60 mg/kg reduced memory impairment induced by morphine. Real-time PCR analysis showed that morphine 5 mg/kg significantly increased the expression of the HSP70, HSP90, and NF-kB genes. However, the subthreshold dose of crocin (60 mg/kg) reduced the increase in gene expression. ConclusionThe study showed that morphine impacts memory and boosts gene expression of HSP70, HSP90, and NF-kB, while crocin could potentially reverse this effect by regulating these amygdala genes, suggesting avenues for future research.

Use of pattern recognition in photoacoustic imaging to identify neuronal ensembles in the prefrontal cortex of rats undergoing conditioned fear learning

Use of pattern recognition in photoacoustic imaging to identify neuronal ensembles in the prefrontal cortex of rats undergoing conditioned fear learning

Deficits in prosodic speech-in-noise recognition in schizophrenia patients and its association with psychiatric symptoms

BackgroundUncertainty in speech perception and emotional disturbances are intertwined with psychiatric symptoms. How prosody embedded in target speech affects speech-in-noise recognition (SR) and is related to psychiatric symptoms in patients with schizophrenia (SCHs) remains unclear. This study aimed to examine the neural substrates of prosodic SR deficits and their associations with psychiatric symptom dimensions in patients with schizophrenia.MethodsFifty-four SCHs and 59 healthy control participants (HCs) completed the SR task (participants were required to identify the contents of the target pseudo-sentences expressed in neutral, happy, sad, angry, fearful, and disgusted prosody by actors), positive and negative syndrome scale (PANSS) assessment, and magnetic resonance imaging scanning. We examined the deficits of the six prosodic SRs in schizophrenia patients and their associations with brain gray matter volume (GMV) and psychiatric symptoms.ResultsNegative emotional (sad, angry, fearful, and disgusted) prosodies of the target sentences worsened SR across groups. Both participant groups had equal SR between the neutral and happy prosody conditions. Compared to the anger and disgusted conditions, SCHs and HCs had better SR under sad and fearful conditions. Better prosodic SR was associated with shorter duration and lower local shimmer of target sentences. A partial least squares (PLS) component of GMV (covering 47 brain regions with group differences) was associated with six prosodic SRs. The happy SR was associated with the PANSS total, negative, and general scores, adjusting for covariates.ConclusionsNegative emotional prosodies of the target sentences dampened the recognition of the target sentences. The prosodic SR abnormalities in SCHs were associated with not only brain GMV reductions in the regions involved in the processing of sensorimotor, speech, and emotion but also with negative and general psychiatric symptoms. These findings suggest the possibility of improving negative symptoms by improving a happy SR in schizophrenia patients based on neuroplasticity.

Post-conditioning sleep deprivation facilitates delay and trace fear memory extinction

Trace and delay auditory fear conditioning involve different memory association strategies based on working memory involvement; however, their differences in long-term processing through sleep and extinction training remain unclear. While females often exhibit more persistent fear, complicating psychiatric treatment, most studies have primarily focused on how sleep affects initial recall in male mice. We investigated the three-way interaction between tests (trace vs. delay), sleep states, and sex during initial recall, extinction, and post-extinction remote recall. A six-hour post-conditioning sleep deprivation (SD) did not affect freezing behavior during the following day’s extinction training of delay fear memory. However, during post-extinction remote recall of delay fear memory, SD prevented spontaneous recovery in males and reduced persistent freezing in females. In contrast, SD rapidly facilitated extinction of trace fear memory. In summary, SD enhances extinction both in the short-term and long-term, depending on the conditioning protocol. These findings highlight the importance of long-term assessments to explore interactions among emotional memory, sleep, and sex differences, with implications for individualized mechanisms underlying post-traumatic stress disorder (PTSD) and its treatments.

Temporal Ablation of the Ciliary Protein IFT88 Alters Normal Brainwave Patterns.

The primary cilium is a hair-like organelle that hosts molecular machinery for various developmental and homeostatic signaling pathways. Its alteration can cause rare ciliopathies such as the Bardet-Biedl and Joubert syndromes, but is also linked to Alzheimer's disease, clinical depression, and autism spectrum disorder. These afflictions are caused by disturbances in a wide variety of genes but a common phenotype amongst them is cognitive impairment. While cilia-mediated neural function has been widely examined in early neurodevelopment, their function in the adult brain is not well understood. To help elucidate the role of cilia in neural activity, we temporally induced the ablation of IFT88, a gene encoding the intraflagellar transport 88 protein which is neccessary for ciliogenesis, in adult mice before performing memory-related behavioral assays and electroencephalogram/electromyogram (EEG/EMG) recordings. Inducible IFT88 KO mice exhibited severe learning deficits in trace fear conditioning and Morris water maze tests. They had strongly affected brainwave activity both under isoflurane induced anesthesia and during normal activity. And additionally, inducible IFT88 KO mice had altered sleep architecture and attenuated phase-amplitude coupling, a process that underlies learning and memory formation. These results highlight the growing significance of primary cilia for healthy neural function in the adult brain.

Ketamine differentially affects implicit and explicit memory processes in rats.

Ketamine, a non-competitive NMDA receptor antagonist, produces antidepressant effects at subanesthetic doses. The therapeutic effect, however, is often accompanied by cognitive side effects, including memory impairments. Yet, the specific effects of ketamine on different processes of implicit and explicit memory remain to be elucidated. We examined the effect of an antidepressant dose of ketamine (10mg/kg, IP) on the encoding, retrieval, and modulation processes of fear memory and spatial memory in adult Wistar rats. Ketamine was administered before the fear acquisition, retrieval, or extinction procedures in a Pavlovian fear conditioning task. In another set of experiments, it was administered before the training, probe trial, or reversal training phases of the Morris Water Maze (MWM). The antidepressant dose of ketamine partially impaired fear extinction when administered before the acquisition or retrieval. In contrast, it facilitated memory modulation and decreased the escape latency in the first day of reversal training in the MWM when administered before the training or reversal training sessions. Encoding or retrieval performance in either type of memory was not affected. These findings show that ketamine does not impair the acquisition or retrieval processes of cued fear or spatial memory; but exerts differential effects on memory modulation of these implicit and explicit memory paradigms, by disrupting fear extinction and facilitating reversal spatial learning.

4-Methoxycinnamic acid ameliorates post-traumatic stress disorder-like behavior in mice by antagonizing the CRF type 1 receptor

AimsPosttraumatic stress disorder (PTSD) is a debilitating neuropsychiatric illness caused by traumatic or life-threatening events and manifesting as various symptoms, including intrusive re-experiences of trauma, avoidance behaviors, hyperarousal, and negative changes in perception and mood. Main methodsCurrent monoamine-based medications commonly exhibit limited efficacy and significant side effects, which hamper their clinical utility. To address this unmet need, we explored 4-methoxycinnamic acid (4-MCA) as a potential novel treatment for PTSD in a single prolonged stress (SPS)-induced animal model. Key findingsAdministration of 4-MCA (3 and 10 mg/kg, p.o.) significantly mitigated anxiety-like behaviors, alleviated depression-like behaviors, and improved cognitive function in an SPS-treated PTSD mouse model. Further, 4-MCA treatment effectively rectified the fear extinction deficits in the fear conditioning test. Molecular analyses revealed that 4-MCA normalized the elevated corticotropin-releasing hormone (CRH) levels as well as the phosphorylation of protein kinase A (PKA) and cAMP response element-binding protein (CREB) in the amygdala, a pivotal region for fear memory formation. Co-administration of 4-MCA and the CRFR1 antagonist antalarmin at subeffective doses facilitated fear memory extinction. SignificanceThese findings suggest that 4-MCA alleviates SPS-induced PTSD-like behaviors by regulating the CRH-CRFR1-PKA-CREB signaling pathway in the amygdala, and that 4-MCA may be a potential candidate for future PTSD treatment.

Long-term exposure to excessive norepinephrine in the brain induces tau aggregation, neuronal death, and cognitive deficits in early tau transgenic mice.

Alzheimer's disease (AD) is marked by the presence of intraneuronal neurofibrillary tangles (NFTs), which are primarily composed of hyperphosphorylated tau protein. The locus coeruleus (LC), the brain's main source of norepinephrine (NE), is one of the earliest regions to develop NFTs and experience neurodegeneration in AD. While LC-derived NE plays beneficial roles in cognition, emotion, locomotion, and the sleep-wake cycle, its impact on tau pathology is unclear. To explore this relationship, we administered intraperitoneal injections of either N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4), a selective neurotoxin for noradrenergic neurons, or reboxetine (RBX), a norepinephrine reuptake inhibitor, to decrease or increase NE levels, respectively, in early tau transgenic mice expressing mutant human P301L tau (ADLPTau) for two months. Only the RBX-treated mice exhibited cognitive deficits, as evidenced by their performance in the Y-maze, novel object recognition, and contextual fear conditioning tests. Immunohistochemical analysis revealed increased hyperphosphorylated tau aggregates in the LC and hippocampus of the RBX-treated mice. Furthermore, neuronal apoptosis was observed in the hippocampal CA1 region of these mice. Western blotting showed that RBX injections led to the overactivation of tau kinases PKA and GSK3β, resulting in hyperphosphorylated tau, neuronal loss, and cognitive impairments. Consistent with these findings, human brain organoids exposed to higher NE concentrations also displayed elevated hyperphosphorylated tau and increased activity of the same tau kinases. These findings suggest that excessive NE exposure accelerates tau pathology by overactivating the tau kinases. Thus, modulating NE levels in the brain via the LC-NE system could be a potential therapeutic strategy for tau-related AD.

Levo-Stepholidine as a Potential Cognitive Enhancer: Insights into Executive Function and Memory Improvements

Background/Objectives: Levo-Stepholidine (l-SPD), a compound extracted from Chinese herbs, has the potential to treat psychotic disorders where cognitive deficits are a critical challenge. L-SPD displays a D1R agonism/D2R antagonism pharmacological profile, and its effect on cognitive function is still vague and lacks comprehensive study. Here, we investigated the impact of l-SPD on two core indexes of executive function, working memory and response inhibition, and learning and memory. Methods: Using a delayed alternation T-maze task (DAT), we investigated the impact of l-SPD on working memory, evaluated its effect on response inhibition using the stop-signal task (SST), and assessed the impact on learning and memory using trace fear conditioning in Sprague-Dawley rats. We further evaluated its effects on prefrontal glutamate receptor expression using western blot. Results: Rats receiving l-SPD made fewer errors in the T-maze, exhibited faster stop action in response to the stop signal, and showed longer-lasting memory retention. Molecular mechanism investigations reveal that l-SPD upregulates the expression of prefrontal glutamate receptors. These results demonstrate that l-SPD improves executive function and memory. Conclusions: Here, we show the enhancement effect of l-SPD on cognitive function, which provides essential implicants for the treatment of cognitive deficits, which is a critical unmet need in psychiatric care.

Dopamine release and dopamine-related gene expression in the amygdala are modulated by the gastrin-releasing peptide in opposite directions during stress-enhanced fear learning and extinction.

Fear extinction leads to a decrease of originally acquired fear responses after the threat is no longer present. Fear extinction is adaptive and critical for organism's survival, but deficits in extinction may lead to exaggerated fear in animals or post-traumatic stress disorder (PTSD) in humans. Dopamine has recently emerged as essential for fear extinction and PTSD, however the neural circuits serving this dopamine function are only beginning to be investigated, and the dopamine intracellular signaling pathways are unknown. We generated gastrin-releasing peptide gene knockout (Grp-/-) mice and found that they exhibit enhanced fear memory in a stress-enhanced fear learning (SEFL) paradigm, which combines stress exposure and fear extinction, two features critical for developing PTSD. Using in vivo fiber photometry to record dopamine signals, we found that the susceptibility of Grp-/- mice to SEFL is paralleled by an increase in basolateral amygdala (BLA) dopaminergic binding during fear conditioning and early extinction. Combined optogenetics and ex vivo electrophysiology showed an increase in presynaptic ventral tegmental area (VTA)-BLA connectivity in Grp-/- mice, demonstrating a role of dysregulated input from the VTA on BLA function in the absence of the GRP. When examining gene transcription using RNA-seq and qPCR, we discovered concerted down-regulation in dopamine-related genes in the BLA of Grp-/- mice following long-term SEFL memory recall that was not observed in naïve conditions. These experiments demonstrate that the GRP regulates dopamine function in stress-enhanced fear processing and identify the Grp as the first gene known to regulate dopaminergic control of fear extinction.

Iodine Deficiency Exacerbates Thyroidal and Neurological Effects of Developmental Perchlorate Exposure in the Neonatal and Adult Rat

Thyroid hormones (THs) require iodine for biosynthesis and play critical roles in brain development. Perchlorate is an environmental contaminant that reduces serum THs by blocking the uptake of iodine from the blood to the thyroid gland. Using a pregnant rodent model, we examined the impact of maternal exposure to perchlorate under conditions of dietary iodine deficiency (ID) on the brain and behavior of offspring. We observed modest reductions in thyroxine (T4) in the serum of dams and no effect on T4 in pup serum in response to maternal exposure to 300 ppm of perchlorate in the drinking water. Likewise, serum T4 was reduced in ID dams, but, as with perchlorate, no effects were evident in the pup. However, when ID was coupled with perchlorate, reductions in pup serum THs and transcriptional alterations in the thyroid gland and pup brain were detected. These observations were accompanied by reductions in the number of cortical inhibitory interneurons containing the calcium-binding protein parvalbumin (Pvalb). Alterations in Pvalb expression in the neonatal brain were associated with deficits in the prepulse inhibition of acoustic startle in adult male offspring and enhanced fear conditioning in females. These findings support and extend structural defects in the brain previously reported in this model. Further, they underscore the critical need to consider additional non-chemical stressors in the determination of hazards and risks posed by environmental contaminants that affect the thyroid system.

Efficacy of fluoxetine and (R,S)-ketamine in attenuating conditioned fear behaviors in male mice

Post-traumatic stress disorder (PTSD) is caused by exposure to a traumatic or stressful event. Symptoms related to this disorder include persistent re-experiencing of memories and fear of generalization. Current pharmacological treatments for PTSD are insufficient, with fewer than 30% of patients reporting symptom remission. This study aims to determine the efficacy of acute (R,S)-ketamine and chronic fluoxetine (FLX) in reducing fear memory and fear generalization. In rodents, fear conditioning (FC) is commonly used in the literature to induce behaviors related to symptoms of PTSD, and the open field test (OFT) can assess anxiety and fear generalization behaviors during the exploration of a novel environment. In this study, FC consisted of a white noise cue stimulus and 4 inescapable foot shocks. Treatments began 4 hours after FC. Fear and anxiety behaviors were recorded during re-exposure to the FC stimuli at 24 hours and 2 weeks. The OFT was conducted 1 day before the last FC re-exposure. Results support the combined use of acute ketamine and chronic FLX as a treatment for reducing behaviors indicative of fear memory during re-exposure at 2 weeks, but not behaviors indicative of anxiety and fear generalization in the OFT. FLX alone was most effective in reducing behaviors related to fear generalization. This study contributes to the existing literature on pharmacological treatment for fear and anxiety behaviors relating to fear memory and fear generalization. Continued research is necessary to replicate results, optimize treatment protocols, and investigate the molecular adaptations to trauma and treatment. Significance StatementUp to 6% of people in the United States will develop PTSD within their lifetime, and less than half of those individuals will find relief from their symptoms given the current therapeutic options. This study offers preliminary support for the efficacy of ketamine and FLX in reducing PTSD-like behaviors induced by fear-conditioning in mice. Compared with current standard treatments, the results of the current study indicate the potential for a more effective therapeutic option for those with stress-related disorders, such as PTSD.

D30 alleviates β2-microglobulin -facilitated neurotoxic microglial responses in isoflurane/surgery-induced cognitive dysfunction in aged mice

Post-operative cognitive dysfunction (POCD) is a common complication with no effective treatment in elderly patients. POCD and Alzheimer’s disease (AD), and many other cognitive diseases mostly involve neurotoxic microglia response, and recently, β2-microglobulin (B2M) has been suggested to play a pivotal role. A novel pyromeconic acid-styrene hybrid compound D30 was synthesized by our team and shown to be safe and effective in some neurodegenerative mouse models. Here we evaluated D30 on POCD and its potential mechanism. 14-18month-old male C57BL/6 mice were used to establish POCD through isoflurane anesthesia and surgery. Elderly patients’ plasmas were collected pre- and post-operatively. Primary mouse microglia were subjected to various stimulations in multiple experimental designs to imitate in vivo POCD-like conditions. Morris water maze, fear conditioning, western blot, immunofluorescent staining, and blood-brain-barrier (BBB) permeability were conducted in this study. D30 administration significantly improved learning and memory in aged mice following POCD. While neurotoxic M1 microglia cells were dramatically increased following POCD, manifested as morphologically changing into fewer and shorter branches, enlarged somatic areas, and upregulated expression of iNOS and C1q, Notably, following POCD, B2M was significantly upregulated in the plasma and the brain. D30 treatment significantly suppressed these pathological changes, by inhibiting the POCD-induced BBB breakdown while suppressing the surge of plasma B2M levels. D30 treatment suppressed POCD- induced surge of B2M and Aβ plaques in the brain, preserved adult hippocampal neurogenesis vulnerable to POCD. Furthermore, post-operative levels of B2M were significantly elevated over the preoperative levels in patients aged over 80 years and over. In parallel to mouse plasma after POCD, the post-operative patient plasma was also much more effective at activating M1 microglia. Of note, these POCD plasma-induced activation of M1 microglia were largely prevented by D30 treatment. Taken together, by inhibiting the surge of plasma B2M, protecting BBB integrity, and reducing inflammatory response, D30 protected aged mice from B2M-facilitated POCD.