Extracellular Vesicles and Endocannabinoid Signaling in Patients with COVID-19.

Introduction: Endocannabinoids in COVID-19 have immunomodulatory and anti-inflammatory properties but the functional role and the regulation of endocannabinoid signaling in this pandemic disorder is controversial. To exercise their biologic function, endocannabinoids need to travel across the intercellular space and within the blood stream to reach their target cells. How the lipophilic endocannabinoids are transported in the vascular system and how these hydrophobic compounds cross cell membranes is still unclear. Extracellular vesicles (EVs) are released and incorporated by many cell types including immune cells. EVs are small lipid-membrane covered particles and contain RNA, lipids and proteins. They play an important role in intercellular communication by transporting these signaling molecules from their cells of origin to specific target cells. EVs may represent ideal transport vehicles for lipophilic signaling molecules like endocannabinoids and this effect could also be evident in COVID-19. Materials and Methods: We measured the endocannabinoids anandamide, 2-AG, SEA, PEA and OEA in patients with COVID-19 in EVs and plasma. RNA sequencing of microRNAs (miRNAs) derived from EVs (EV-miRNAs) and mRNA transcripts from blood cells was used for the construction of signaling networks reflecting endocannabinoid and miRNA communication by EVs to target immune cells. Results: With the exception of anandamide, endocannabinoid concentrations were significantly enriched in EVs in comparison to plasma and increased with disease severity. No enrichment in EVs was seen for the more hydrophilic steroid hormones cortisol and testosterone. High EV-endocannabinoid concentrations were associated with downregulation of CNR2 (CB2) by upregulated EV-miRNA miR-146a-5p and upregulation of MGLL by downregulated EV-miR-199a-5p and EV-miR-370-5p suggesting counterregulatory effects. In contrast, low EV-levels of anandamide were associated with upregulation of CNR1 by downregulation of EV-miR-30c-5p and miR-26a-5p along with inhibition of FAAH. Immunologically active molecules in immune cells regulated by endocannabinoid signaling included VEGFA, GNAI2, IGF1, BDNF, IGF1R and CREB1 and CCND1 among others. Discussion and Conclusions: EVs carry immunologically functional endocannabinoids in COVID-19 along with miRNAs which may regulate the expression of mRNA transcripts involved in the regulation of endocannabinoid signaling and metabolism. This mechanism could fine-tune and adapt endocannabinoid effects in recipient cells in relationship to the present biological context.

Stress in adolescence as a first hit in stress-related disease development: Timing and context are crucial.

The two-hit stress model predicts that exposure to stress at two different time-points in life may increase or decrease the risk of developing stress-related disorders later in life. Most studies based on the two-hit stress model have investigated early postnatal stress as the first hit with adult stress as the second hit. Adolescence, however, represents another highly sensitive developmental window during which exposure to stressful events may affect programming outcomes following exposure to stress in adulthood. Here, we discuss the programming effects of different types of stressors (social and nonsocial) occurring during adolescence (first hit) and how such stressors affect the responsiveness toward an additional stressor occurring during adulthood (second hit) in rodents. We then provide a comprehensive overview of the potential mechanisms underlying interindividual and sex differences in the resilience/susceptibility to developing stress-related disorders later in life when stress is experienced in two different life stages.

Enhancing Psychological Interventions for Post-Traumatic Stress Disorder (PTSD) Treatment with Memory Influencing Drugs.

Post-traumatic stress disorder (PTSD) is a chronic psychiatric disease resulting from the experience or witnessing of traumatic events. Persistent PTSD symptoms impair patients' daily quality of life, jeopardizing sleep, mood, sociability, and arousal. Recommended psychological or pharmacological interventions are effective only in a small portion of patients and often lead to relapse. Thus, there is a critical need to address a lack of advancement in the treatment of PTSD. The combination of psychological interventions, aimed at facilitating the extinction of the traumatic memory, and pharmacological medications, represents a promising tool for PTSD treatment. Timely use of psychotherapy in conjunction with pharmacological treatments, rather than monotherapy, could thus determine a synergistic effect by potentiating the effects of psychological interventions. In such a scenario, drugs that modulate cognitive processes involved in the development and/or persistence of post-traumatic symptomatology could be of great help to improve the outcome of psychotherapies and patients' prognosis. The purpose of the present article is to review the current data available from clinical trials on combined pharmacological treatments with psychological interventions in PTSD therapy. An overview of findings from animal studies that prompted clinical research is also discussed.

Anandamide and 2-arachidonoylglycerol differentially modulate autistic-like traits in a genetic model of autism based on FMR1 deletion in rats.

Autism spectrum disorder (ASD) has a multifactorial etiology. Major efforts are underway to understand the neurobiological bases of ASD and to develop efficacious treatment strategies. Recently, the use of cannabinoid compounds in children with neurodevelopmental disorders including ASD has received increasing attention. Beyond anecdotal reports of efficacy, however, there is limited current evidence supporting such an intervention and the clinical studies currently available have intrinsic limitations that make the interpretation of the findings challenging. Furthermore, as the mechanisms underlying the beneficial effects of cannabinoid compounds in neurodevelopmental disorders are still largely unknown, the use of drugs targeting the endocannabinoid system remains controversial. Here, we studied the role of endocannabinoid neurotransmission in the autistic-like traits displayed by the recently validated Fmr1-Δexon 8 rat model of autism. Fmr1-Δexon 8 rats showed reduced anandamide levels in the hippocampus and increased 2-arachidonoylglycerol (2-AG) content in the amygdala. Systemic and intra-hippocampal potentiation of anandamide tone through administration of the anandamide hydrolysis inhibitor URB597 ameliorated the cognitive deficits displayed by Fmr1-Δexon 8 rats along development, as assessed through the novel object and social discrimination tasks. Moreover, blockade of amygdalar 2-AG signaling through intra-amygdala administration of the CB1 receptor antagonist SR141716A prevented the altered sociability displayed by Fmr1-Δexon 8 rats. These findings demonstrate that anandamide and 2-AG differentially modulate specific autistic-like traits in Fmr1-Δexon 8 rats in a brain region-specific manner, suggesting that fine changes in endocannabinoid mechanisms contribute to ASD-related behavioral phenotypes.

Prenatal stress induces a depressive-like phenotype in adolescent rats: The key role of TGF-ß1 pathway.

Stressful experiences early in life, especially in the prenatal period, can increase the risk to develop depression during adolescence. However, there may be important qualitative and quantitative differences in outcome of prenatal stress (PNS), where some individuals exposed to PNS are vulnerable and develop a depressive-like phenotype, while others appear to be resilient. PNS exposure, a well-established rat model of early life stress, is known to increase vulnerability to depression and a recent study demonstrated a strong interaction between transforming growth factor-ß1 (TGF-ß1) gene and PNS in the pathogenesis of depression. Moreover, it is well-known that the exposure to early life stress experiences induces brain oxidative damage by increasing nitric oxide levels and decreasing antioxidant factors. In the present work, we examined the role of TGF-ß1 pathway in an animal model of adolescent depression induced by PNS obtained by exposing pregnant females to a stressful condition during the last week of gestation. We performed behavioral tests to identify vulnerable or resilient subjects in the obtained litters (postnatal day, PND > 35) and we carried out molecular analyses on hippocampus, a brain area with a key role in the pathogenesis of depression. We found that female, but not male, PNS adolescent rats exhibited a depressive-like behavior in forced swim test (FST), whereas both male and female PNS rats showed a deficit of recognition memory as assessed by novel object recognition test (NOR). Interestingly, we found an increased expression of type 2 TGF-ß1 receptor (TGFß-R2) in the hippocampus of both male and female resilient PNS rats, with higher plasma TGF-ß1 levels in male, but not in female, PNS rats. Furthermore, PNS induced the activation of oxidative stress pathways by increasing inducible nitric oxide synthase (iNOS), NADPH oxidase 1 (NOX1) and NOX2 levels in the hippocampus of both male and female PNS adolescent rats. Our data suggest that high levels of TGF-ß1 and its receptor TGFß-R2 can significantly increase the resiliency of adolescent rats to PNS, suggesting that TGF-ß1 pathway might represent a novel pharmacological target to prevent adolescent depression in rats.

Individuals with highly superior autobiographical memory do not show enhanced creative thinking.

Creative ideas are thought to result from flexible recombination of concepts from memory. A growing number of behavioural and neuroscientific studies provide evidence of a link between episodic memory and divergent thinking; however, little is known about the potential contributions of autobiographical memory to creative ideation. To provide a novel perspective on this issue, we assessed measures of divergent and convergent creative thinking in a cohort (n = 14) of rare individuals showing Highly Superior Autobiographical Memory (HSAM). The HSAM cohort completed memory tasks in addition to a battery of creativity measures, including the Alternative Uses Task, Consequences Task and Remote Associates Task. We performed statistical analyses to establish whether there were any significant differences between HSAM and controls (n = 28) across these measures. Although HSAM participants were superior in the recall of autobiographical events compared to controls, we observed no overall difference between the groups in relation to the creativity measures. These findings suggest that the constructive episodic processes relevant to creative thinking are not enhanced in individuals with HSAM, perhaps because they are compulsively and narrowly focused on consolidation and retrieval of autobiographical events.

Co-Ultramicronized Palmitoylethanolamide/Luteolin Restores Oligodendrocyte Homeostasis via Peroxisome Proliferator-Activated Receptor-α in an In Vitro Model of Alzheimer's Disease.

Oligodendrocytes are cells fundamental for brain functions as they form the myelin sheath and feed axons. They perform these critical functions thanks to the cooperation with other glial cells, mainly astrocytes. The astrocyte/oligodendrocyte crosstalk needs numerous mediators and receptors, such as peroxisome proliferator-activated receptors (PPARs). PPAR agonists promote oligodendrocyte precursor cells (OPCs) maturation in myelinating oligodendrocytes. In the Alzheimer's disease brain, deposition of beta-amyloid (Aß) has been linked to several alterations, including astrogliosis and changes in OPCs maturation. However, very little is known about the molecular mechanisms. Here, we investigated for the first time the maturation of OPCs co-cultured with astrocytes in an in vitro model of Aß1-42 toxicity. We also tested the potential beneficial effect of the anti-inflammatory and neuroprotective composite palmitoylethanolamide and luteolin (co-ultra PEALut), which is known to engage the isoform alfa of the PPARs. Our results show that Aß1-42 triggers astrocyte reactivity and inflammation and reduces the levels of growth factors important for OPCs maturation. Oligodendrocytes indeed show low cell surface area and few arborizations. Co-ultra PEALut counteracts the Aß1-42-induced inflammation and astrocyte reactivity preserving the morphology of co-cultured oligodendrocytes through a mechanism that in some cases involves PPAR-α. This is the first evidence of the negative effects exerted by Aß1-42 on astrocyte/oligodendrocyte crosstalk and discloses a never-explored co-ultra PEALut ability in restoring oligodendrocyte homeostasis.

Circadian regulation of memory under stress: Endocannabinoids matter.

Organisms ranging from plants to higher mammals have developed 24-hour oscillation rhythms to optimize physiology to environmental changes and regulate a plethora of neuroendocrine and behavioral processes, including neurotransmitter and hormone regulation, stress response and learning and memory function. Compelling evidence indicates that a wide array of memory processes is strongly influenced by stress- and emotional arousal-activated neurobiological systems, including the endocannabinoid system which has been extensively shown to play an integral role in mediating stress effects on memory. Here, we review findings showing how circadian rhythms and time-of-day influence stress systems and memory performance. We report evidence of circadian regulation of memory under stress, focusing on the role of the endocannabinoid system and highlighting its circadian rhythmicity. Our discussion illustrates how the endocannabinoid system mediates stress effects on memory in a circadian-dependent fashion. We suggest that endocannabinoids might regulate molecular mechanisms that control memory function under circadian and stress influence, with potential important clinical implications for both neurodevelopmental disorders and psychiatric conditions involving memory impairments.

Basolateral amygdala activation enhances object recognition memory by inhibiting anterior insular cortex activity.

Noradrenergic activation of the basolateral amygdala (BLA) by emotional arousal enhances different forms of recognition memory via functional interactions with the insular cortex (IC). Human neuroimaging studies have revealed that the anterior IC (aIC), as part of the salience network, is dynamically regulated during arousing situations. Emotional stimulation first rapidly increases aIC activity but suppresses it in a delayed fashion. Here, we investigated in male Sprague-Dawley rats whether the BLA influence on recognition memory is associated with an increase or suppression of aIC activity during the postlearning consolidation period. We first employed anterograde and retrograde viral tracing and found that the BLA sends dense monosynaptic projections to the aIC. Memory-enhancing norepinephrine administration into the BLA following an object training experience suppressed aIC activity 1 h later, as determined by a reduced expression of the phosphorylated form of the transcription factor cAMP response element-binding (pCREB) protein and neuronal activity marker c-Fos. In contrast, the number of perisomatic γ-aminobutyric acid (GABA)ergic inhibitory synapses per pCREB-positive neuron was significantly increased, suggesting a dynamic up-regulation of GABAergic tone. In support of this possibility, pharmacological inhibition of aIC activity with a GABAergic agonist during consolidation enhanced object recognition memory. Norepinephrine administration into the BLA did not affect neuronal activity within the posterior IC, which receives sparse innervation from the BLA. The evidence that noradrenergic activation of the BLA enhances the consolidation of object recognition memory via a mechanism involving a suppression of aIC activity provides insight into the broader brain network dynamics underlying emotional regulation of memory.

Perinatal supplementation with omega-3 fatty acids corrects the aberrant social and cognitive traits observed in a genetic model of autism based on FMR1 deletion in rats.

Background and objective: Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder for which no treatments exist. Fragile X syndrome (FXS) is the most common form of inherited mental retardation and the most frequent monogenic cause of ASD. Given the lack of pharmacological treatments for ASD, increasing interest is devoted to non-pharmacological approaches, including dietary interventions. Omega-3 polyunsaturated fatty acids (PUFAs) are critical for neurobehavioraldevelopment. This study had two aims: 1. To validatethe recently developed Fmr1-Δexon 8 rat model of FXS; 2. To assess the impact of omega-3 PUFAs dietary supplementation during pregnancy and lactation on the altered behavior displayed by Fmr1-Δexon 8 rats.Methods: Female Fmr1-Δexon 8 and wild-type Sprague-Dawley rats were fed with either an omega-3 PUFAs enriched diet or with an isocaloric control diet during pregnancy and lactation. Behavioral experiments were carried out on the infant (Postnatal days (PNDs) 9 and 13), juvenile (PND 35) and adult (PND 90) male offspring.Results: Fmr1-Δexon 8 pups showed hypolocomotion, reduced ultrasonic vocalizations (USVs) emission and impaired social discrimination compared to wild-type controls. Juvenile and adult Fmr1-Δexon 8 rats showed deficits in the social and cognitive domains, that were counteracted by perinatal omega-3 PUFAs supplementation.Conclusion: Our results support the validity of the Fmr1-Δexon 8 rat model to mimic key autistic-like features and support an important role of omega-3 PUFAs during of neurodevelopment. Although the mechanisms underlying the beneficial effects of omega-3 PUFAs supplementation in ASD needs to be clarified, this dietary intervention holds promise to mitigate core and comorbid autistic features.

Hippocampal glucocorticoid target genes associated with enhancement of memory consolidation.

Glucocorticoids enhance memory consolidation of emotionally arousing events via largely unknown molecular mechanisms. This glucocorticoid effect on the consolidation process also requires central noradrenergic neurotransmission. The intracellular pathways of these two stress mediators converge on two transcription factors: the glucocorticoid receptor (GR) and phosphorylated cAMP response element-binding protein (pCREB). We therefore investigated, in male rats, whether glucocorticoid effects on memory are associated with genomic interactions between the GR and pCREB in the hippocampus. In a two-by-two design, object exploration training or no training was combined with post-training administration of a memory-enhancing dose of corticosterone or vehicle. Genomic effects were studied by chromatin immunoprecipitation followed by sequencing (ChIP-seq) of GR and pCREB 45 min after training and transcriptome analysis after 3 hr. Corticosterone administration induced differential GR DNA-binding and regulation of target genes within the hippocampus, largely independent of training. Training alone did not result in long-term memory nor did it affect GR or pCREB DNA-binding and gene expression. No strong evidence was found for an interaction between GR and pCREB. Combination of the GR DNA-binding and transcriptome data identified a set of novel, likely direct, GR target genes that are candidate mediators of corticosterone effects on memory consolidation. Cell-specific expression of the identified target genes using single-cell expression data suggests that the effects of corticosterone reflect in part non-neuronal cells. Together, our data identified new GR targets associated with memory consolidation that reflect effects in both neuronal and non-neuronal cells.

Altered Hippocampal Resting-state Functional Connectivity in Highly Superior Autobiographical Memory.

Individuals with Highly Superior Autobiographical Memory (HSAM) provide the opportunity to investigate the neurobiological substrates of enhanced memory performance. While previous studies started to assess the neural correlates of memory retrieval in HSAM, here we assessed for the first time the intrinsic connectivity of a core memory region, the hippocampus, with the whole brain, in 8 HSAM subjects (HSAMs) and 21 controls during resting-state functional neuroimaging. We found in HSAMs vs. controls disrupted hippocampal resting-state functional connectivity (rsFC) with high-level control regions belonging to the saliency network (the anterior cingulate cortex and the left and right insulae), and to the ventral fronto-parietal attentional network (the temporo-parietal junction and the inferior frontal gyrus), also involved with salience detection. Conversely, HSAMs showed enhanced hippocampal rsFC with sensory regions along the fusiform gyrus and the inferior temporal cortex. This altered pattern of hippocampal rsFC might be interpreted as a reduced capability of HSAMs to discriminate and select salient information, with a subsequent increase in the probability to encode and consolidate sensory information irrespective of their task-relevancy. Ultimately, these findings provide evidence that HSAM might be paradoxically enabled by an altered hippocampal rsFC that bypasses regions involved with salience detection in favor of specialized sensory regions.

Sex-dependent Effects of the Drugs of Abuse Amphetamine and the Smart Drug 3,4-Methylenedioxypyrovalerone on Fear Memory Generalization in Rats.

In recent years there has been an increase in the development of new synthetic drugs, among which the "bath salt" 3,4-methylenedioxypyrovalerone (MDPV), a psychostimulant with a mechanism of action similar to those of cocaine and amphetamine, stands out. Drugs of abuse have been consistently shown to affect memory function in male rodents. We have recently shown that amphetamine and MDPV induce generalization of fear memory in an inhibitory avoidance discrimination task in male rats. Although abuse of illicit drugs is more prevalent in men than in women, several studies have demonstrated that females are more vulnerable to the effects of drugs of abuse than males and the effects caused by substance dependence on memory in females are still under-investigated. Thus, we examined the effects of subchronic amphetamine or MDPV administrations on memory in a contextual fear conditioning/generalization paradigm in adult male and female rats. Animals were given daily subchronic injections of the drugs, starting 6 days prior to the beginning of the behavioral procedures until the end of the paradigm. On day 1 of the experimental protocol, all rats were exposed to a safe context and, the day after, to a slightly different chamber where they received an unsignaled footshock. Twenty-four and forty-eight hours later, freezing behavior and emission of 22 kHz-ultrasonic vocalizations (USVs) were measured in the two different contexts to assess fear memory retention and generalization. Our results indicate that MDPV treatment altered freezing in both sexes, USVs were affected by amphetamine in males while by MDPV in females.

Highly superior autobiographical memory in aging: A single case study.

Whilst countless studies have shown that aging is associated with cognitive decline in the general population, near to nothing is known about this association in elderly individuals naturally exhibiting enhanced memory capabilities. The identification of a 75 years old individual (GC) with highly superior autobiographical memory (HSAM), and his willingness to volunteer to our study over a period of five years, allowed us to investigate this issue in a single case study. At the age of 75 years, GC was screened for HSAM with the Public Events Quiz and the Random Dates Quiz, with a positive outcome. GC's memory performance was extraordinarily higher than normal-memory control subjects (>3 standard deviations), and comparable to a group of younger HSAM individuals (mean age of 32.5 years; Santangelo et al., 2018). GC underwent general neuropsychological (Mini-Mental State Examination), personality (Personality Assessment Inventory), and brain morphological (brain volumes and lesions) assessments, showing no deviation from normal ranges. To gain insight into the brain mechanisms underlying his memory performance, GC underwent functional brain imaging during the retrieval of memories associated with random dates. The latter were also rated in terms of reliving quality and emotional valence. Similar to younger HSAM individuals, GC's access to past memories recruited a wide network of prefrontal and temporo-parietal regions, especially during the recollection of memories associated with a lower reliving rating, suggesting a compensatory mechanism in HSAM. Increased activity in the insula was instead associated with emotionally-positive memories. Five years later, GC was tested again for HSAM and showed no sign of memory decline, whereby his memory performance was indistinguishable from the tests he performed five years earlier. GC's case suggests that highly superior memory performance can manifest without apparent decline in physiological aging. Implications of the current findings for the extant models of autobiographical memory are discussed.

Amphetamine Modulation of Long-Term Object Recognition Memory in Rats: Influence of Stress.

Amphetamine is a potent psychostimulant that increases brain monoamine levels. Extensive evidence demonstrated that norepinephrine is crucially involved in the regulation of memory consolidation for stressful experiences. Here, we investigated amphetamine effects on the consolidation of long-term recognition memory in rats exposed to different intensities of forced swim stress immediately after training. Furthermore, we evaluated whether such effects are dependent on the activation of the peripheral adrenergic system. To this aim, male adult Sprague Dawley rats were subjected to an object recognition task and intraperitoneally administered soon after training with amphetamine (0.5 or 1 mg/kg), or its corresponding vehicle. Rats were thereafter exposed to a mild (1 min, 25 ± 1°C) or strong (5 min, 19 ± 1°C) forced swim stress procedure. Recognition memory retention was assessed 24-h after training. Our findings showed that amphetamine enhances the consolidation of memory in rats subjected to mild stress condition, while it impairs long-term memory performance in rats exposed to strong stress. These dichotomic effects is dependent on stress-induced activation of the peripheral adrenergic response.

The neurochemistry of social reward during development: What have we learned from rodent models?

Social rewards are fundamental to survival and overall health. Several studies suggest that adequate social stimuli during early life are critical for developing appropriate socioemotional and cognitive skills, whereas adverse social experiences negatively affect the proper development of brain and behavior, by increasing the susceptibility to develop neuropsychiatric conditions. Therefore, a better understanding of the neural mechanisms underlying social interactions, and their rewarding components in particular, is an important challenge of current neuroscience research. In this context, preclinical research has a crucial role: Animal models allow to investigate the neurobiological aspects of social reward in order to shed light on possible neurochemical alterations causing aberrant social reward processing in neuropsychiatric diseases, and they allow to test the validity and safety of innovative therapeutic strategies. Here, we discuss preclinical research that has investigated the rewarding properties of two forms of social interaction that occur in different phases of the lifespan of mammals, that is, mother-infant interaction and social interactions with peers, by focusing on the main neurotransmitter systems mediating their rewarding components. Together, the research performed so far helped to elucidate the mechanisms of social reward and its psychobiological components throughout development, thus increasing our understanding of the neurobiological substrates sustaining social functioning in health conditions and social dysfunction in major psychiatric disorders.

Social Defeat Stress During Early Adolescence Confers Resilience Against a Single Episode of Prolonged Stress in Adult Rats.

Early-life adverse experiences (first hit) lead to coping strategies that may confer resilience or vulnerability to later experienced stressful events (second hit) and the subsequent development of stress-related psychopathologies. Here, we investigated whether exposure to two stressors at different stages in life has long-term effects on emotional and cognitive capabilities, and whether the interaction between the two stressors influences stress resilience. Male rats were subjected to social defeat stress (SDS, first hit) in adolescence and to a single episode of prolonged stress (SPS, second hit) in adulthood. Behavioral outcomes, hippocampal expression of brain-derived neurotrophic factor, and plasma corticosterone levels were tested in adulthood. Rats exposed to both stressors exhibited resilience against the development of stress-induced alterations in emotional behaviors and spatial memory, but vulnerability to cued fear memory dysfunction. Rats subjected to both stressors demonstrated resilience against the SDS-induced alterations in hippocampal brain-derived neurotrophic factor expression and plasma corticosterone levels. SPS alone altered locomotion and spatial memory retention; these effects were absent in SDS-exposed rats later exposed to SPS. Our findings reveal that exposure to social stress during early adolescence influences the ability to cope with a second challenge experienced later in life.

A novel arousal-based individual screening reveals susceptibility and resilience to PTSD-like phenotypes in mice.

Translational animal models for studying post-traumatic stress disorder (PTSD) are valuable for elucidating the poorly understood neurobiology of this neuropsychiatric disorder. These models should encompass crucial features, including persistence of PTSD-like phenotypes triggered after exposure to a single traumatic event, trauma susceptibility/resilience and predictive validity. Here we propose a novel arousal-based individual screening (AIS) model that recapitulates all these features. The AIS model was designed by coupling the traumatization (24 h restraint) of C57BL/6 J mice with a novel individual screening. This screening consists of z-normalization of post-trauma changes in startle reactivity, which is a measure of arousal depending on neural circuits conserved across mammals. Through the AIS model, we identified susceptible mice showing long-lasting hyperarousal (up to 56 days post-trauma), and resilient mice showing normal arousal. Susceptible mice further showed persistent PTSD-like phenotypes including exaggerated fear reactivity and avoidance of trauma-related cue (up to 75 days post-trauma), increased avoidance-like behavior and social/cognitive impairment. Conversely, resilient mice adopted active coping strategies, behaving like control mice. We further uncovered novel transcriptional signatures driven by PTSD-related genes as well as dysfunction of hypothalamic-pituitary-adrenal axis, which corroborated the segregation in susceptible/resilient subpopulations obtained through the AIS model and correlated with trauma susceptibility/resilience. Impaired hippocampal synaptic plasticity was also observed in susceptible mice. Finally, chronic treatment with paroxetine ameliorated the PTSD-like phenotypes of susceptible mice. These findings indicate that the AIS model might be a new translational animal model for the study of crucial features of PTSD. It might shed light on the unclear PTSD neurobiology and identify new pharmacological targets for this difficult-to-treat disorder.

Ketamine anesthesia enhances fear memory consolidation via noradrenergic activation in the basolateral amygdala.

Trauma patients treated with ketamine during emergency care present aggravated early post- traumatic stress reaction which is highly predictive of post-traumatic stress disorder (PTSD) development and severity. The use of ketamine in the acute trauma phase may directly or indirectly interfere with neural processes of memory consolidation of the traumatic event, thus leading to the formation of maladaptive memories, a hallmark symptom of PTSD. We have recently shown that ketamine anesthesia, immediately after a traumatic event, enhances memory consolidation and leads to long-lasting alterations of social behavior in rats. Based on the evidence that ketamine induces a robust central and peripheral adrenergic/noradrenergic potentiation and that activation of this system is essential for the formation of memory for stressful events, we explored the possibility that the strong sympathomimetic action of ketamine might underlie its memory enhancing effects. We found that rats given immediate, but not delayed, post-training ketamine anesthesia (125 mg/kg) presented enhanced 48-h memory retention in an inhibitory avoidance task and that these effects were blocked by adrenal medullectomy, lesions of the locus coeruleus, systemic or intra-basolateral amygdala ß-adrenergic receptor antagonism. Thus, the memory enhancing effects of ketamine anesthesia are time-dependent and mediated by a combined peripheral-central sympathomimetic action. We elucidated a mechanism by which ketamine exacerbates acute post-traumatic reaction, possibly leading to development of PTSD symptomatology later in life. These findings will help guide for a better management of sedation/anesthesia in emergency care to promote the prophylaxis and reduce the risk of developing trauma-related disorders in trauma victims.