Sleep alterations following exposure to stress predict fear-associated memory impairments in a rodent model of PTSD.

Sleep abnormalities, such as insomnia, nightmares, hyper-arousal, and difficulty initiating or maintaining sleep, are diagnostic criteria of posttraumatic stress disorder (PTSD). The vivid dream state, rapid eye movement (REM) sleep, has been implicated in processing emotional memories. We have hypothesized that REM sleep is maladaptive in those suffering from PTSD. However, the precise neurobiological mechanisms regulating sleep disturbances following trauma exposure are poorly understood. Using single prolonged stress (SPS), a well-validated rodent model of PTSD, we measured sleep alterations in response to stressor exposure and over a subsequent 7-day isolation period during which the PTSD-like phenotype develops. SPS resulted in acute increases in REM sleep and transition to REM sleep, and decreased waking in addition to alterations in sleep architecture. The severity of the PTSD-like phenotype was later assessed by measuring freezing levels on a fear-associated memory test. Interestingly, the change in REM sleep following SPS was significantly correlated with freezing behavior during extinction recall assessed more than a week later. Reductions in theta (4-10 Hz) and sigma (10-15 Hz) band power during transition to REM sleep also correlated with impaired fear-associated memory processing. These data reveal that changes in REM sleep, transition to REM sleep, waking, and theta and sigma power may serve as sleep biomarkers to identify individuals with increased susceptibility to PTSD following trauma exposure.

Prospective Measurement of Skin Conductance Response during Trauma Interview Predicts Future PTSD Severity in Trauma Exposed Children.

Previous cross-sectional studies have shown that sympathetic nervous system (SNS) arousal is positively associated with posttraumatic stress disorder (PTSD) symptoms in children with trauma exposure. One of the ways that SNS activity is measured is through skin conductance response (SCR), which has been shown to predict future PTSD severity in adults. In this study, we explored the utility of a novel, low-cost mobile SCR device, eSense, to predict future PTSD symptom severity in trauma exposed children. We recruited children (N=43, age 9 years at initial visit) for a longitudinal study in which SCR was recorded at baseline visit, and PTSD symptoms were assessed two years later. Results indicated an interaction between SCR and trauma exposure, such that children with lower trauma exposure who demonstrated greater SCR reported higher PTSD severity two years later. This association remained significant even after controlling for baseline PTSD symptoms. Children with higher levels of trauma exposure did not show this association, potentially due to ceiling effects of PTSD symptoms. Together these findings suggest the utility of SCR as a biomarker for predicting trauma related disorders in children, and that it may be a valuable tool in clinical interventions targeting sympathetic arousal.

Altered locus coeruleus-norepinephrine function following single prolonged stress.

Data from preclinical and clinical studies have implicated the norepinephrine system in the development and maintenance of post-traumatic stress disorder. The primary source of norepinephrine in the forebrain is the locus coeruleus (LC); however, LC activity cannot be directly measured in humans, and previous research has often relied upon peripheral measures of norepinephrine to infer changes in central LC-norepinephrine function. To directly assess LC-norepinephrine function, we measured single-unit activity of LC neurons in a validated rat model of post-traumatic stress disorder - single prolonged stress (SPS). We also examined tyrosine hydroxylase mRNA levels in the LC of SPS and control rats as an index of norepinephrine utilisation. For electrophysiological recordings, 92 LC neurons were identified from 19 rats (SPS, 12; control, 7), and spontaneous and evoked responses to a noxious event (paw compression) were recorded. Baseline and restraint stress-evoked tyrosine hydroxylase mRNA expression levels were measured in SPS and control rats (n = 16 per group) in a separate experiment. SPS rats showed lower spontaneous activity but higher evoked responses, leading to an enhanced signal-to-noise ratio of LC neurons, accompanied by impaired recovery from post-stimulus inhibition. In concert, tyrosine hydroxylase mRNA expression in the LC of SPS rats tended to be lower at baseline, but was exaggerated following restraint stress. These data demonstrate persistent changes in LC function following stress/trauma in a rat model of post-traumatic stress, as measured by differences in both the electrophysiological properties of LC neurons and tyrosine hydroxylase mRNA transcription.

Single prolonged stress disrupts retention of extinguished fear in rats.

Clinical research has linked post-traumatic stress disorder (PTSD) with deficits in fear extinction. However, it is not clear whether these deficits result from stress-related changes in the acquisition or retention of extinction or in the regulation of extinction memories by context, for example. In this study, we used the single prolonged stress (SPS) animal model of PTSD and fear conditioning procedures to examine the effects of prior traumatic stress on the acquisition, retention, and context-specificity of extinction. SPS administered one week prior to fear conditioning had no effect on the acquisition of fear conditioning or extinction but disrupted the retention of extinction memories for both contextual and cued fear. This SPS effect required a post-stress incubation period to manifest. The results demonstrate that SPS disrupts extinction retention, leading to enhanced fear renewal; further research is needed to identify the neurobiological processes through which SPS induces these effects.

Unconditioned freezing is enhanced in an appetitive context: implications for the contextual dependency of unconditioned fear.

It has been well established that expression of conditioned fear is context independent, but the context dependency of unconditioned fear expression has rarely been explored. A recent study reported that unconditioned freezing in rats is enhanced in a familiar context, which suggests that unconditioned fear expression can be modulated by contextual processing. In order to further explore this possibility we examined unconditioned freezing in novel, familiar, and appetitive contexts; and attempted to identify brain regions critical for context-related changes in unconditioned freezing by measuring c-Fos mRNA levels in emotional circuits. Unconditioned freezing was enhanced in the appetitive context, and this enhancement was accompanied by increased c-Fos mRNA expression in the medial amygdala and hippocampus, but attenuated expression in the medial prefrontal cortex. In the appetitive context, expectation of a reward coupled with detection of threat may have enhanced unconditioned fear expression, which suggests that unconditioned fear expression can be modulated by contextual factors. Context-related expectancy mismatch may explain the enhancement of unconditioned fear expression seen in this study and warrants further examination.

Research With Refugees and Vulnerable Populations in a Post-COVID World: Challenges and Opportunities.

At the Stress, Trauma and Anxiety Research Clinic (STARC) at Wayne State University in Detroit, we are currently amid data collection for a longitudinal prospective study of Syrian refugee children and their parents. Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, our goal is to understand the impact of exposure to war trauma and the stress of migration on symptoms of posttraumatic stress disorder, anxiety, and depression, as well as the neurobiological, epigenetic, and environmental correlates of risk and resilience. Like many research groups around the world, the COVID-19 pandemic brought our work to a screeching halt. Researchers who, like us, were engaged in human subjects research were left grappling with the question of how to continue their work while ensuring the safety of both research staff and participants, and while maintaining scientific integrity. In March 2020, our institution halted all in-person human subjects research that did not have direct benefits to participants, which continued until October, when research activity was resumed subject to implementation of modified procedures. Over the past 2 years, we have pivoted, adapted, and flexed, ultimately making changes that have allowed us to continue successful data collection throughout the pandemic. This article will discuss the specific challenges of working with ethnically minoritized and immigrant populations during the pandemic, the adaptations that we implemented to enable safe and effective data collection, as well as the new knowledge that we can apply to future research protocols.

Maternal Separation Induces Sex-Specific Differences in Sensitivity to Traumatic Stress.

Post-traumatic stress disorder (PTSD) is a debilitating psychiatric disorder with a high economic burden. Two risk factors for increasing the chances of developing PTSD are sex (being female) and early life stress. These risk factors suggest that early life stress-induced changes and sex differences in emotional circuits and neuroendocrinological systems lead to susceptibility to traumatic stress. Exploring mechanisms via which stress leads to specific effects can be accomplished in animal models, but reliable animal models that allow for an examination of how early life stress interacts with sex to increase susceptibility to traumatic stress is lacking. To address this, we examined the effects of early life stress [using the maternal separation (MS) model] and late adolescence/early adult traumatic stress [using the single prolonged stress (SPS) model] on startle reactivity, anxiety-like behavior in the open field (OF), and basal corticosterone levels in male and female rats. Female rats exposed to MS and SPS (MS/SPS) showed enhanced startle reactivity relative to MS/control female rats. Enhanced startle reactivity was not observed in MS/SPS male rats. Instead, non-maternally separated male rats that were exposed to SPS showed enhanced startle reactivity relative to controls. Female rats had enhanced locomotor activity in the OF and higher basal corticosterone levels in comparison to males, but measures in the OF and basal corticosterone were not affected by MS or SPS. Overall the results suggest that the combined MS and SPS models can be used to explore how changes in maternal care during infancy lead to sex differences in sensitivity to the effects of traumatic stress as adolescents and adults.

Diminished Value Discrimination in Obsessive-Compulsive Disorder: A Prospect Theory Model of Decision-Making Under Risk.

Introduction: It has been hypothesized that people diagnosed with anxiety and obsessive-compulsive disorder (OCD) exhibit behavioral aberrations when faced with the potential for negative outcomes, but the specific cognitive aspects of decision-making that may be altered have not been systematically studied in clinical populations. Here, we studied decision-making in a clinical cohort using a task that allows for examination of the decision weights and values associated with different choice outcomes. Methods: Patients diagnosed with OCD (n = 10), generalized anxiety disorder (n = 15), social anxiety disorder (n = 14), and healthy controls (n = 20) were given a decision-making task and choices were modeled using a cumulative prospect theory framework. Results: We found OCD patients to have lower value discrimination than controls, as well as less optimal performance on the task, an effect that was mostly driven by trials with only positive outcomes. Discussion: Our results shed light on the cognitive processes that drive altered decision-making under risk in OCD. Specifically, they demonstrate that OCD patients have diminished sensitivity to positive outcomes, which might be associated with risk aversion and altered learning of gain. These findings also extend prior reports, suggesting that altered cognitive processing during decision-making is linked to altered perception of value, but not probability, in these patients.

D-Cycloserine Facilitates Reversal in an Animal Model of Post-traumatic Stress Disorder.

Many psychiatric disorders are associated with cognitive dysfunction that is ineffectively treated by existing pharmacotherapies and which may contribute to poor real-world functioning. D-cycloserine (DCS) is a partial N-methyl-D-aspartate (NMDA) agonist that has attracted attention because of its cognitive enhancing properties, including in people with post-traumatic stress disorder (PTSD). Here, we examined the effect of DCS on reversal learning - a type of cognitive flexibility - following exposure to single prolonged stress (SPS), a rodent model of PTSD. Male Sprague Dawley rats (n = 64) were trained to press levers in an operant chamber, matched for performance and assigned to SPS or control (unstressed) groups. Following SPS, rats received three additional lever press sessions, followed by a side bias test on day three. One day later they learned a response discrimination rule (press left or right lever, opposite to side bias) and on a subsequent day were trained (and tested) for reversal to the opposite lever. DCS (15 mg/kg) or vehicle was administered 30 minutes prior to the reversal session. No between-group differences were found in acquisition or retrieval of the initial rule, but a significant drug x stress interaction on response discrimination reversal indicated that DCS had a greater beneficial effect on SPS rats' cognitive flexibility than it did on performance in controls. These findings add to a growing literature on the beneficial effects of DCS for treating a wide variety of deficits that develop following exposure to extreme stress and may have implications for the development of novel pharmacotherapies for PTSD.

Severe, multimodal stress exposure induces PTSD-like characteristics in a mouse model of single prolonged stress.

Appropriate animal models of posttraumatic stress disorder (PTSD) are needed because human studies remain limited in their ability to probe the underlying neurobiology of PTSD. Although the single prolonged stress (SPS) model is an established rat model of PTSD, the development of a similarly-validated mouse model emphasizes the benefits and cross-species utility of rodent PTSD models and offers unique methodological advantages to that of the rat. Therefore, the aims of this study were to develop and describe a SPS model for mice and to provide data that support current mechanisms relevant to PTSD. The mouse single prolonged stress (mSPS) paradigm, involves exposing C57Bl/6 mice to a series of severe, multimodal stressors, including 2h restraint, 10 min group forced swim, exposure to soiled rat bedding scent, and exposure to ether until unconsciousness. Following a 7-day undisturbed period, mice were tested for cue-induced fear behavior, effects of paroxetine on cue-induced fear behavior, extinction retention of a previously extinguished fear memory, dexamethasone suppression of corticosterone (CORT) response, dorsal hippocampal glucocorticoid receptor protein and mRNA expression, and prefrontal cortex glutamate levels. Exposure to mSPS enhanced cue-induced fear, which was attenuated by oral paroxetine treatment. mSPS also disrupted extinction retention, enhanced suppression of stress-induced CORT response, increased mRNA expression of dorsal hippocampal glucocorticoid receptors and decreased prefrontal cortex glutamate levels. These data suggest that the mSPS model is a translationally-relevant model for future PTSD research with strong face, construct, and predictive validity. In summary, mSPS models characteristics relevant to PTSD and this severe, multimodal stress modifies fear learning in mice that coincides with changes in the hypothalamo-pituitary-adrenal (HPA) axis, brain glucocorticoid systems, and glutamatergic signaling in the prefrontal cortex.

Alterations in cognitive flexibility in a rat model of post-traumatic stress disorder.

Exposure to stressful or traumatic events is associated with increased vulnerability to post-traumatic stress disorder (PTSD). This vulnerability may be partly mediated by effects of stress on the prefrontal cortex (PFC) and associated circuitry. The PFC mediates critical cognitive functions, including cognitive flexibility, which reflects an organism's ability to adaptively alter behavior in light of changing contingencies. Prior work suggests that chronic or acute stress exerts complex effects on different forms of cognitive flexibility, via actions on the PFC. Similarly, PFC dysfunction is reported in PTSD, as are executive function deficits. Animal models that permit study of the effects of stress/trauma on cognitive flexibility may be useful in illuminating ways in which stress-linked cognitive changes contribute to PTSD. Here, we examined the behavioral effects of a rodent model of PTSD - single prolonged stress (SPS) - on performance of two forms of cognitive flexibility: reversal learning and strategy set-shifting. SPS did not impair acquisition of either a response or visual-cue discrimination but did cause slight impairments in the retrieval of the visual-cue rule. During response discrimination reversal, SPS rats made more perseverative errors. In comparison, during set-shifting from the visual-cue to response discrimination, SPS rats did not show enhanced perseveration, but did display increased never-reinforced errors, indicative of impairment in selecting a novel strategy. These data demonstrate that SPS leads to a complex and intriguing pattern of deficits in flexible responding and suggest that impairments in executive functioning associated with PTSD could, in part, be a neuro-cognitive consequence of trauma exposure.

The effect of chronic phenytoin administration on single prolonged stress induced extinction retention deficits and glucocorticoid upregulation in the rat medial prefrontal cortex.

RATIONALE: Post-traumatic stress disorder (PTSD) is a chronic, debilitating disorder. Only two pharmacological agents are approved for PTSD treatment, and they often do not address the full range of symptoms nor are they equally effective in all cases. Animal models of PTSD are critical for understanding the neurobiology involved and for identification of novel therapeutic targets. Using the rodent PTSD model, single prolonged stress (SPS), we have implicated aberrant excitatory neural transmission and glucocorticoid receptor (GR) upregulation in the medial prefrontal cortex (mPFC) and hippocampus (HPC) in fear memory abnormalities associated with PTSD. OBJECTIVE: The objective of this study is to examine the potential protective effect of antiepileptic phenytoin (PHE) administration on SPS-induced extinction retention deficits and GR expression. METHODS: Forty-eight SPS-treated male Sprague Dawley rats or controls were administered PHE (40, 20 mg/kg, vehicle) for 7 days following SPS stressors; then, fear conditioning, extinction, and extinction retention were tested. RESULTS: Fear conditioning and extinction were unaffected by SPS or PHE, but SPS impaired extinction retention, and both doses of PHE rescued this impairment. Similarly, SPS increased GR expression in the mPFC and dorsal HPC, and PHE prevented SPS-induced GR upregulation in the mPFC. CONCLUSIONS: These data demonstrate that PHE administration can prevent the development of extinction retention deficits and upregulation of GR. PHE exerts inhibitory effects on voltage-gated sodium channels and decreases excitatory neural transmission via glutamate antagonism. If glutamate hyperactivity in the days following SPS contributes to SPS-induced deficits, then these data may suggest that the glutamatergic system constitutes a target for secondary prevention.

Early handling attenuates enhancement of glucocorticoid receptors in the prefrontal cortex in an animal model of post-traumatic stress disorder.

BACKGROUND: Changes in glucocorticoid receptors (GRs) have been implicated in the pathogenesis of stress related psychiatric disorders such as depression and post-traumatic stress disorder (PTSD). Abnormal adaptation of the stress-response system following traumatic stress can lead to an altered hypothalamic-pituitary-adrenal axis that may contribute to PTSD development. Indeed, elevated GR expression in the hippocampus and prefrontal cortex linked to PTSD-like characteristics have been reported in the validated animal model of PTSD, single-prolonged stress. These findings implicate increased levels of GRs in the development of post-traumatic psychopathology and suggest that exploration of GR-targeted interventions may have potential for PTSD prevention. Early handling during the neonatal phase alters GR expression and is proposed to confer resilience to stress. We therefore examined the effects of combined early handling and single prolonged stress treatments on GR expression. METHODS: Timed pregnant dams gave birth to pups that were subjected to early handling (n = 11) or control (n = 13) procedures during the neonatal phase. At postnatal day 45 animals underwent single prolonged stress or a control procedure. Rats were euthanized one day later and GR levels were assayed using western blot electrophoresis. RESULTS: Single prolonged stress exposure enhanced GR expression in the hippocampus and prefrontal cortex. Early handling treatment protected against single prolonged stress-induced enhancement of GR expression in the prefrontal cortex, but not in the hippocampus. CONCLUSIONS: These data are a first step in highlighting the importance of targeting GR systems in prevention/resilience and may suggest that preventive strategies targeting GR upregulation might be particularly effective when prefrontal rather than hippocampal GRs are the target.

CRH-stimulated cortisol release and food intake in healthy, non-obese adults.

BACKGROUND: There is considerable anecdotal and some scientific evidence that stress triggers eating behavior, but underlying physiological mechanisms remain uncertain. The hypothalamic-pituitary-adrenal (HPA) axis is a key mediator of physiological stress responses and may play a role in the link between stress and food intake. Cortisol responses to laboratory stressors predict consumption but it is unclear whether such responses mark a vulnerability to stress-related eating or whether cortisol directly stimulates eating in humans. METHODS: We infused healthy adults with corticotropin-releasing hormone (CRH) at a dose that is subjectively undetectable but elicits a robust endogenous cortisol response, and measured subsequent intake of snack foods, allowing analysis of HPA reactivity effects on food intake without the complex psychological effects of a stress paradigm. RESULTS: CRH elevated cortisol levels relative to placebo but did not impact subjective anxious distress. Subjects ate more following CRH than following placebo and peak cortisol response to CRH was strongly related to both caloric intake and total consumption. CONCLUSIONS: These data show that HPA axis reactivity to pharmacological stimulation predicts subsequent food intake and suggest that cortisol itself may directly stimulate food consumption in humans. Understanding the physiological mechanisms that underlie stress-related eating may prove useful in efforts to attack the public health crises created by obesity.

Single prolonged stress decreases glutamate, glutamine, and creatine concentrations in the rat medial prefrontal cortex.

Application of single prolonged stress (SPS) in rats induces changes in neuroendocrine function and arousal that are characteristic of post traumatic stress disorder (PTSD). PTSD, in humans, is associated with decreased neural activity in the prefrontal cortex, increased neural activity in the amygdala complex, and reduced neuronal integrity in the hippocampus. However, the extent to which SPS models these aspects of PTSD has not been established. In order to address this, we used high-resolution magic angle spinning proton magnetic resonance spectroscopy (HR-MAS (1)H MRS) ex vivo to assay levels of neurochemicals critical for energy metabolism (creatine and lactate), excitatory (glutamate and glutamine) and inhibitory (gamma amino butyric acid (GABA)) neurotransmission, and neuronal integrity (N-acetylaspartate (NAA)) in the medial prefrontal cortex (mPFC), amygdala complex, and hippocampus of SPS and control rats. Glutamate, glutamine, and creatine levels were decreased in the mPFC of SPS rats when compared to controls, which suggests decreased excitatory tone in this region. SPS did not alter the neurochemical profiles of either the hippocampus or amygdala. These data suggest that SPS selectively attenuates excitatory tone, without a disruption of neuronal integrity, in the mPFC.