Effects of multiple brief exposures to trauma-associated cues on traumatized resilient and vulnerable rats

Maternal deprivation causes CaMKII downregulation and modulates glutamate, norepinephrine and serotonin in limbic brain areas in a rat model of single prolonged stress

BACKGROUND

Early life stress is a major risk factor for later development of psychiatric disorders, including post-traumatic stress disorder (PTSD). An intricate relationship exists between various neurotransmitters (such as glutamate, norepinephrine or serotonin), calcium/calmodulin-dependent protein kinase II (CaMKII), as an important regulator of glutamatergic synaptic function, and PTSD. Here, we developed a double-hit model to investigate the interaction of maternal deprivation (MD) as an early life stress model and single prolonged stress (SPS) as a PTSD model at the behavioral and molecular levels.

METHODS

Male Wistar rats exposed to these stress paradigms were subjected to a comprehensive behavioral analysis. In hippocampal synaptosomes we investigated neurotransmitter release and glutamate concentration. The expression of CaMKII and the content of monoamines were determined in selected brain regions. Brain-derived neurotrophic factor (BDNF) mRNA was quantified by radioactive in situ hybridization.

RESULTS

We report a distinct behavioral phenotype in the double-hit group. Double-hit and SPS groups had decreased hippocampal presynaptic glutamatergic function. In hippocampus, double-hit stress caused a decrease in autophosphorylation of CaMKII. In prefrontal cortex, both SPS and double-hit stress had a similar effect on CaMKII autophosphorylation. Double-hit stress, rather than SPS, affected the norepinephrine and serotonin levels in prefrontal cortex, and suppressed BDNF gene expression in prefrontal cortex and hippocampus.

LIMITATIONS

The study was conducted in male rats only. The affected brain regions cannot be restricted to hippocampus, prefrontal cortex and amygdala.

CONCLUSION

Double-hit stress caused more pronounced and distinct behavioral, molecular and functional changes, compared to MD or SPS alone.

Proust and involuntary retrieval

Proust was undoubtedly a pioneer in exploring cognitive processes engaged in memory. The analysis of the episode of the madeleine, as well as the study of Proust's statements on the goals of his work, clearly reveal the visionary side of this author. Long before several concepts entered into mainstream scientific thought, Proust proposed, among other things, that recall was a reconstruction, that a sensory cue could provoke a memory recall, and that we should distinguish between voluntary and involuntary memory. Through numerous episodes of "involuntary reminiscence" scattered throughout his work, Proust illustrates a particular form of autobiographic memory recall: a recall that does not involve consciousness and whose starting point is an emotion provoked by a specific cue. This recall, which leads, according to Proust, to a more intense revival of the memory than voluntary recall, has only reached prominence in cognitive science more than 80 years later. Additionaly, Proust underlined the determinant role that emotion may have in this particular form of recall. On the other hand, studies on animals have shown that the presentation of a retrieval cue could induce emotional reactions followed by a facilitation of the memory retrieval associated with the cue. The existence of these data, which support Proust's proposals, should encourage the neuroscience community to further explore, in humans and animals, this form of cue elicited emotion that initiated involuntary recall of autobiographical memory.

Potential resilience treatments for orangutans (Pongo spp.): Lessons from a scoping review of interventions in humans and other animals

Wild orangutans (Pongo spp.) rescued from human-wildlife conflict must be adequately rehabilitated before being returned to the wild. It is essential that released orangutans are able to cope with stressful challenges such as food scarcity, navigating unfamiliar environments, and regaining independence from human support. Although practical skills are taught to orangutans in rehabilitation centres, post-release survival rates are low. Psychological resilience, or the ability to 'bounce back' from stress, may be a key missing piece of the puzzle. However, there is very little knowledge about species-appropriate interventions which could help captive orangutans increase resilience to stress. This scoping review summarises and critically analyses existing human and non-human animal resilience literature and provides suggestions for the development of interventions for orangutans in rehabilitation. Three scientific databases were searched in 2021 and 2023, resulting in 63 human studies and 266 non-human animal studies. The first section brings together human resilience interventions, identifying common themes and assessing the applicability of human interventions to orangutans in rehabilitation. The second section groups animal interventions into categories of direct stress, separation stress, environmental conditions, social stress, and exercise. In each category, interventions are critically analysed to evaluate their potential for orangutans in rehabilitation. The results show that mild and manageable forms of intervention have the greatest potential benefit with the least amount of risk. The study concludes by emphasising the need for further investigation and experimentation, to develop appropriate interventions and measure their effect on the post-release survival rate of orangutans.

On making (and turning adaptive to) maladaptive aversive memories in laboratory rodents

Fear conditioning and avoidance tasks usually elicit adaptive aversive memories. Traumatic memories are more intense, generalized, inflexible, and resistant to attenuation via extinction- and reconsolidation-based strategies. Inducing and assessing these dysfunctional, maladaptive features in the laboratory are crucial to interrogating posttraumatic stress disorder's neurobiology and exploring innovative treatments. Here we analyze over 350 studies addressing this question in adult rats and mice. There is a growing interest in modeling several qualitative and quantitative memory changes by exposing already stressed animals to freezing- and avoidance-related tests or using a relatively high aversive training magnitude. Other options combine aversive/fearful tasks with post-acquisition or post-retrieval administration of one or more drugs provoking neurochemical or epigenetic alterations reported in the trauma aftermath. It is potentially instructive to integrate these procedures and incorporate the measurement of autonomic and endocrine parameters. Factors to consider when defining the organismic and procedural variables, partially neglected aspects (sex-dependent differences and recent vs. remote data comparison) and suggestions for future research (identifying reliable individual risk and treatment-response predictors) are discussed.

Searching for glycomic biomarkers for predicting resilience and vulnerability in a rat model of posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is triggered by traumatic events in 10-20% of exposed subjects. N-linked glycosylation, by modifying protein functions, may provide an important environmental link predicting vulnerability. Our goals were (1) to find alterations in plasma N-glycome predicting stress-vulnerability; (2) to investigate how trauma affects N-glycome in the plasma (PGP) and in three PTSD-related brain regions (prefrontal cortex, hippocampus and amygdala; BGP), hence, uncover specific targets for PTSD treatment. We examined male (1) controls, (2) traumatized vulnerable and (3) traumatized resilient rats both before and several weeks after electric footshock. Vulnerable and resilient groups were separated by z-score analysis of behavior. Higher freezing behavior and decreased social interest were detected in vulnerable groups compared to control and resilient rats. Innate anxiety did not predict vulnerability, but pretrauma levels of PGP10(FA1G1Ga1), PGP11(FA2G2), and PGP15(FA3G2) correlated positively with it, the last one being the most sensitive. Traumatic stress induced a shift from large, elaborate N-glycans toward simpler neutral structures in the plasma of all traumatized animals and specifically in the prefrontal cortex of vulnerable rats. In plasma trauma increased PGP17(A2G2S) level in vulnerable animals. In all three brain regions, BGP11(F(6)A2B) was more abundant in vulnerable rats, while most behavioral correlations occurred in the prefrontal cortex. In conclusion, we found N-glycans (especially PGP15(FA3G2)) in plasma as possible biomarkers of vulnerability to trauma that warrants further investigation. Posttrauma PGP17(A2G2S1) increase showed overlap with human results highlighting the utility and relevance of this animal model. Prefrontal cortex is a key site of trauma-induced glycosylation changes that could modulate the behavioral outcome.

Emotional remodeling with oxytocin durably rescues trauma-induced behavioral and neuro-morphological changes in rats: a promising treatment for PTSD

Recent evidence indicates that reactivated memories are malleable and can integrate new information upon their reactivation. We injected rats with oxytocin to investigate whether the delivery of a drug which dampens anxiety and fear before the reactivation of trauma memory decreases the emotional load of the original representation and durably alleviates PTSD-like symptoms. Rats exposed to the single prolonged stress (SPS) model of PTSD were classified 15 and 17 days later as either resilient or vulnerable to trauma on the basis of their anxiety and arousal scores. Following 2 other weeks, they received an intracerebral infusion of oxytocin (0.1 µg/1 µL) or saline 40 min before their trauma memory was reactivated by exposure to SPS reminders. PTSD-like symptoms and reactivity to PTSD-related cues were examined 3-14 days after oxytocin treatment. Results showed that vulnerable rats treated with saline exhibited a robust PTSD syndrome including increased anxiety and decreased arousal, as well as intense fear reactions to SPS sensory and contextual cues. Exposure to a combination of those cues resulted in c-fos hypo-activation and dendritic arbor retraction in prefrontal cortex and amygdala neurons, relative to resilient rats. Remarkably, 83% of vulnerable rats subjected to oxytocin-based emotional remodeling exhibited a resilient phenotype, and SPS-induced morphological alterations in prelimbic cortex and basolateral amygdala were eliminated. Our findings emphasize the translational potential of the present oxytocin-based emotional remodeling protocol which, when administered even long after the trauma, produces deep re-processing of traumatic memories and durable attenuation of the PTSD symptomatology.

Susceptibility and Resilience to PTSD-Like Symptoms in Mice Are Associated with Opposite Dendritic Changes in the Prelimbic and Infralimbic Cortices Following Trauma

Post-traumatic stress disorder (PTSD) is triggered by exposure to traumatic events, but not everyone who experiences trauma develops this disorder. Like humans, PTSD-like symptoms develop in some laboratory rodents (susceptible individuals), while others express less or no symptoms (resilient individuals). Here, considering (i) the putative causal role of fear conditioning in PTSD development and (ii) the involvement of the medial prefrontal cortex (mPFC) in the regulation of conditioned fear response, we tested whether trauma-associated changes in the mPFC may discriminate stress-resilient from stress-susceptible mice. From data on avoidance behavior (as a major symptom), we found that trauma-exposed mice displayed a bimodal distribution in their step-through latency, with low avoider (stress-resilient) individuals and high avoider (stress-susceptible) individuals. Dendrites of Golgi-Cox-stained neurons were analyzed in two parts of the mPFC: the prelimbic (PrL) and infralimbic (IL) areas. In the resilient phenotype, the total number of dendrites decreased in the PrL and increased in the IL; however, it decreased only in the IL in the susceptible phenotype compared to controls. These findings demonstrate that the type of post-trauma morphological changes in the mPFC is associated with susceptibility or resilience to trauma-related symptoms.

Post Traumatic Stress Disorder and Substance Use Disorder as Two Pathologies Affecting Memory Reactivation: Implications for New Therapeutic Approaches

In the present review, we provide evidence indicating that although post traumatic stress disorder (PTSD) and substance use disorder (SUD) are two distinct pathologies with very different impacts on people affected by these chronic illnesses, they share numerous common characteristics, present high rates of co-morbidity, and may result from common physiological dysfunctions. We propose that these pathologies result from hyper reactivity to reminders, and thus should be considered as two disorders of memory, treated as such. We review the different possibilities to intervene on pathological memories such as extinction therapy and reconsolidation blockade. We also introduce new therapeutic avenues directly indicate by our recent proposal to replace the consolidation/reconsolidation hypothesis by the integration concept. State dependency and emotional remodeling are two innovative treatments that have already provided encouraging results. In summary, this review shows that the discovery of reactivation-dependent memory malleability has open new therapeutic avenues based on the reprocessing of pathological memories, which constitute promising approaches to treat PTSD and SUD.

Behavioral and Noradrenergic Sensitizations in Vulnerable Traumatized Rats Suggest Common Bases with Substance Use Disorders

The aim of the present study was to strengthen our hypothesis of a common physiological basis for post-traumatic stress disorder (PTSD) and substance use disorders. This paper investigates the possibility that rats exposed to a PTSD model exhibit noradrenergic and behavioral sensitization, as observed following repeated drugs of abuse injections. First, rats received a single prolonged stress (SPS), combining three consecutive stressors. They were then tested, 2 weeks after the trauma for PTSD-like symptoms to discriminate between vulnerable and resilient rats. When microdialysis was performed in the prelimbic cortex (Experiment 1), larger increases of noradrenaline (NA) release in response to amphetamine were observed in vulnerable rats when compared to control and resilient animals. Experiment 2 showed that trauma-vulnerable rats exhibited increases in locomotor activity relative to controls, in response to an exposure to trauma-associated cues. These data demonstrate that a single trauma exposure induces in vulnerable animals both, a noradrenergic sensitization evidenced within the prelimbic cortex and behavioral sensitization obtained after a physiologic activation of the noradrenergic system. However, Experiment 3 showed that when NA system was activated by amphetamine (1 mg/kg), a decrease in behavioral sensitization was obtained in vulnerable rats. We proposed that this decreased locomotor activity results from an additional stress-induced increased reactivity of mesocortical dopaminergic neurons, known to counteract the consequences of cortical noradrenergic release in rats. These results support our hypothesis that noradrenergic sensitization represents a common physiological basis, involved both in PTSD and drug addiction and suggest new common therapeutic approaches for these pathologies.

Single-Prolonged Stress: A Review of Two Decades of Progress in a Rodent Model of Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a common, costly, and often debilitating psychiatric condition. However, the biological mechanisms underlying this disease are still largely unknown or poorly understood. Considerable evidence indicates that PTSD results from dysfunction in highly-conserved brain systems involved in stress, anxiety, fear, and reward. Pre-clinical models of traumatic stress exposure are critical in defining the neurobiological mechanisms of PTSD, which will ultimately aid in the development of new treatments for PTSD. Single prolonged stress (SPS) is a pre-clinical model that displays behavioral, molecular, and physiological alterations that recapitulate many of the same alterations observed in PTSD, illustrating its validity and giving it utility as a model for investigating post-traumatic adaptations and pre-trauma risk and protective factors. In this manuscript, we review the present state of research using the SPS model, with the goals of (1) describing the utility of the SPS model as a tool for investigating post-trauma adaptations, (2) relating findings using the SPS model to findings in patients with PTSD, and (3) indicating research gaps and strategies to address them in order to improve our understanding of the pathophysiology of PTSD.