Although female rats are typically less aggressive than male rats, lactating females will vigorously defend their nests and pups against an intruder. Much attention has been directed at the consequences of this aggression on the intruder and less on the consequences for the mother and her subsequent interactions with her pups. Here, we exposed resident Sprague-Dawley dams to the resident-intruder paradigm twice daily for five consecutive days, beginning when the dam's (RES) pups were 7 days old, to assess social stress effects on maternal behavior and neurobiology. Controls were dams that had time-matched (TMC) separation from their pups but were not exposed to intruders, and naïve moms which were never separated nor exposed to an intruder (CTL). We assessed the dam's subsequent behavior and interactions with her pups on Day 1 and Day 5, and Fos expression after Day 5 in select regions of the prefrontal cortex, amygdala, hypothalamus and periaqueductal gray of the midbrain. In separate cohorts, after pups were weaned, the dams underwent restraint stress and plasma corticosterone assayed. PCA analysis of the dam's behaviors identified three components: normal self-focused behaviors; nurturing behaviors and rough non-nurturing behaviors. Relative to CTL, RES dams exhibited more disrupted behaviors towards their pups, including, rough transport, stepping on pups, and flinging/tossing pups around the cage. In contrast, TMC Dams showed some, but fewer changes relative to CTL, suggesting that separation from pups alone does not account for all disrupted behavior in RES dams. The bulk of these behavioral effects occurred in the first 5-10 min after reunion with the pups and were seen on both the first and fifth day of testing. Of the brain regions examined, the prefrontal cortex was activated by both the defeat/intruder stress (RES) and separation stress (TMC), whereas the dorsal PAG was activated specifically by the defeat/intruder stress. The medial and basolateral amygdala exhibited differential neuronal activity between the RES defeat/intruder-exposed dams and the other two groups. The RES moms exhibited an insufficient adrenocortical response to acute restraint stress. The results suggest that amygdala-dPAG activity is important for dissociating disrupted maternal care in RES (due to defense of the nest against an intruder) from simple pup separation, both of which activate the mPFC. The experience of repeatedly defending the nest may induce subsequent disruptions in HPA responses. The amygdala-dPAG pathway may regulate aspects of stress and emotional regulation exhibited by mothers who defend their offspring against intruders.

Glucocorticoid receptors (GRs) regulate transcription to reduce inflammatory processes, modulate neuron function, and influence behavior. However, the precise loci bound by GRs that are critically important for these effects have not been fully determined. Here, we deleted the GR binding site near the sphingosine-1-phosphate receptor 3 (S1PR3) gene using a CRISPR/Cas9 approach in rats (S1PR3GRE-/GRE- rats). Socially defeated S1PR3GRE-/GRE- males displayed increased inflammatory markers and reduced sociability compared to defeated wild-type (WT) controls. Similar effects were observed in non-stressed females, indicating a greater dependence on the regulation of S1PR3 by GRs in females. Coherent neural activity between the locus coeruleus (LC) and medial prefrontal cortex (mPFC) was increased in defeated S1PR3GRE-/GRE- males whereas increases were observed in non-stressed S1PR3GRE-/GRE females. Chemogenetically inhibiting mPFC-projecting LC neurons during defeat increased subsequent social interaction in WT and S1PR3GRE-/GRE- males. Together, these findings demonstrate that GR-induced S1PR3 mitigates inflammatory processes and promotes resilience by reducing coherent neural activity between the LC and mPFC and may be an important mechanism through which the effects of stress in females can be mitigated.

Research primarily in civilian samples supports bidirectional relations between daytime factors and trauma-related nightmare (TRN) reports. This study tested the relations of daytime negative affect and event-related stress with nightly occurrence and characteristics of TRNs in a sample of Veterans with and without posttraumatic stress disorder (PTSD). We studied 27 U.S. combat-exposed veterans who completed prompts across 7 days of an ecological momentary assessment protocol, assessing daytime negative affect and event-related stress. Each morning, they also reported whether they had a TRN and, if so, the level of disturbance and vividness. Over 100 morning reports were collected. Approximately half of this sample (55%) reported at least one TRN across the study week, with TRNs reported only by participants with current PTSD. In multilevel logistic regression models, higher average negative affect was associated with greater odds of having TRNs. While negative affect and event-related stress on a given day were not prospectively associated with TRNs later that night, a TRN occurrence was associated with greater next-day negative affect and event-related stress. In contrast to findings found in civilian populations, daytime negative affect and stress during the day were not associated with subsequent TRN occurrences in this veteran sample. Instead, there was evidence for a cumulative effect of negative affect on TRN occurrence, potentially driven by experiencing TRNs. Therefore, targeting TRNs specifically could have a positive impact on reducing this self-maintaining nightmare cycle.

Major depressive disorder is one of the most prevalent psychiatric diseases, and up to 30-40% of patients remain symptomatic despite treatment. Novel therapies are sorely needed, and animal models may be used to elucidate fundamental neurobiological processes that contribute to human disease states. We conducted a systematic review of current preclinical approaches to investigating treatment resistance with the goal of describing a path forward for improving our understanding of treatment resistant depression.We conducted a broad literature search to identify studies relevant to the preclinical investigation of treatment resistant depression. We followed PRISMA (Preferred Reporting Items for Systemic Reviews and Meta-Analyses) guidelines and included all relevant studies.We identified 467 studies in our initial search. Of these studies, we included 69 in our systematic review after applying our inclusion/exclusion criteria. We identified 10 broad strategies for investigating treatment resistance in animal models. Stress hormone administration was the most commonly used model, and the most common behavioral test was the forced swim test.We systematically identified and reviewed current approaches for gaining insight into the neurobiology underlying treatment resistant depression using animal models. Each approach has its advantages and disadvantages, but all require careful consideration of their potential limitations regarding therapeutic translation. An enhanced understanding of treatment resistant depression is sorely needed given the burden of disease and lack of effective therapies.

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

It is well established that glucocorticoid receptors (GRs) bind DNA, regulate gene expression, reduce inflammatory processes, and modulate behavior. However, the precise loci bound by GRs that are necessary for these effects are not fully understood. Here, we deleted the GR binding site near the sphingosine-1-phospate receptor 3 gene using a CRISPR/Cas9 approach (S1PR3GR-/GR- rats). Defeated S1PR3GR-/GR- males displayed increased inflammatory markers and social anxiety-like behavior. Similar effects were observed in non-stressed females, indicating a greater dependence for GR-induced S1PR3 in females. Coherent neural activity between the locus coeruleus (LC) and medial prefrontal cortex (mPFC) was increased in S1PR3GR-/GR- males following 7 defeats. Chemogenetically inhibiting mPFC-projecting LC neurons during defeat increased subsequent social interaction in wild-type and S1PR3GR-/GR- males. Together, these findings demonstrate that GR-induced S1PR3 promotes resilience by mitigating stress-induced inflammatory processes and LC-mPFC coherence.One Sentence Summary Glucocorticoid receptor-induced expression of sphingosine-1- phosphate receptor 3 reduces social anxiety-like behavior by mitigating stress-induced inflammatory processes and coherent neural activity between the locus coeruleus and medial prefrontal cortex.### Competing Interest StatementThe authors have declared no competing interest.

Psychological stress poses a risk for sleep disturbances. Importantly, trauma-exposed individuals who develop posttraumatic stress disorder (PTSD) frequently report insomnia and recurrent nightmares. Clinical studies have provided insight into the mechanisms of these sleep disturbances. We review polysomnographic findings in PTSD and identify analogous measures that have been made in animal models of PTSD. There is a rich empirical and theoretical literature on rapid eye movement sleep (REMS) substrates of insomnia and nightmares, with an emphasis on REMS fragmentation. For future investigations of stress-induced sleep changes, we recommend a focus on tonic, phasic and other microarchitectural REMS measures. Power spectral density analysis of the sleep EEG should also be utilized. Animal models with high construct validity can provide insight into gender and time following stressor exposure as moderating variables. Ultimately, preclinical studies with translational potential will lead to improved treatment for stress-related sleep disturbances.

Delirium is a common, morbid, and costly syndrome that is closely linked to Alzheimer's disease (AD) and AD-related dementias (ADRD) as a risk factor and outcome. Human studies of delirium have advanced our knowledge of delirium incidence and prevalence, risk factors, biomarkers, outcomes, prevention, and management. However, understanding of delirium neurobiology remains limited. Preclinical and translational models for delirium, while challenging to develop, could advance our knowledge of delirium neurobiology and inform the development of new prevention and treatment approaches. We discuss the use of preclinical and translational animal models in delirium, focusing on (1) a review of current animal models, (2) challenges and strategies for replicating elements of human delirium in animals, and (3) the utility of biofluid, neurophysiology, and neuroimaging translational markers in animals. We conclude with recommendations for the development and validation of preclinical and translational models for delirium, with the goal of advancing awareness in this important field.

The locus coeruleus (LC)-norepinephrine system is a stress responsive system that regulates arousal and cognitive functions through extensive projections, including to the prefrontal cortex. LC-cortical circuits are activated by stressors, and this activation is thought to contribute to stress-induced impairments in executive function. Because corticotropin-releasing factor (CRF) is a mediator of stress-induced LC activation, we examined the effects of CRF administered into the LC of male and female rats on network activity of two functionally distinct regions of the PFC, the medial PFC (mPFC) and the orbitofrontal cortex (OFC). Network activity, measured as local field potentials, was recorded in awake animals before and after intra-LC infusion of aCSF or CRF (2 or 20 ng). CRF had qualitatively distinct effects on network activity in males and females with respect to dose, region and timecourse. CRF (20 ng) produced a prominent theta oscillation (7-9 Hz) selectively in female rats shortly after LC infusion and 20 min later. In contrast, in male rats, CRF (2 and 20 ng) decreased the amplitude of power in the 4-6 Hz range in the mPFC 10 min after injection. Lastly, CRF (20 ng) increased mPFC-OFC coherence in females and decreased mPFC-OFC coherence in males. In sum, these results show sex differences in CRF modulation of the LC-norepinephrine system that regulates prefrontal cortical networks, which may underlie sex differences in cognitive and behavioral responses to stress.

Introduction: Cortisol plays a critical role in the biological link between stress and health outcomes. It is frequently investigated in the association between socioeconomic stress and morbidity, and the hypothesized biological mechanism by which socioeconomic stress and cortisol impact health is through chronically elevated systemic inflammation. This research is relevant to individuals with sickle cell disease (SCD) for several reasons. First, up to 40% of children and adolescents with SCD are impacted by neighborhood poverty. Furthermore, individuals with SCD are faced with significant disease-related morbidities, such as chronic and acute pain, renal injury, and cerebrovascular disease that are further complicated by elevated inflammatory markers. Finally, cortisol is heavily understudied in this population, with no research investigating socioeconomic or inflammatory correlates. The purpose of this study was to investigate plasma cortisol and its association with neighborhood-level socioeconomic factors (income and poverty) and immunomodulatory cytokines (IL-6, IL-10), among individuals with SCD. Method: Plasma from individuals with SCD within Children's Hospital of Philadelphia (CHOP) and University of Pennsylvania School of Medicine (Penn Medicine) BioBanks were identified. A cortisol radioimmunoassay was used to determine plasma cortisol levels. The Olink immune response panel was used to measure plasma levels of 92 proteins involved in inflammatory pathways. Home address collected from electronic health records was used to determine neighborhood census tract geoid, which was then used to collect data on median neighborhood income and percentage of families living in poverty from the 2020 American Census Survey. Bivariate and multivariate analyses were conducted across 4 subgroups in the total sample: pediatric patients, adult patients, SCA (HbSS/HbSß 0), and other SCD genotypes (HbSC/HbSß +). Control samples (healthy and sickle cell trait; n = 22) without neighborhood information were also available for comparison. Results: Fifty-four independent outpatient samples were identified after excluding duplicates and siblings. Twenty-seven samples were from children and adolescents receiving pediatric care at CHOP (Range age = .8 to 21; Mage= 13.6, SD = 5.3; 51.9% female, 74.1% SCA) and 27 samples were from adults receiving care at Penn Medicine (Range age = 19 to 56; Mage= 35.8, SD = 10.1; 51.9% female, 51.9% SCA). There were no significant differences in cortisol levels across each subgroup ( Mpeds= 16.6, SDpeds = 6.2; Madult= 13.4, SDadult = 6.9; MSCA= 15.1, SDSCA = 7.1; MSCD= 14.9, SDSCD = 6.3). Neighborhood income and poverty did not differ across pediatric and adult patients, and income did not differ across SCD types. However, neighborhood poverty was lower among patients with SCA ( M = 13.9; SD = 11.9) relative to other SCD genotypes ( M = 21.7; SD = 13.5; p = .041). Bivariate Spearman analyses found that neighborhood variables were not correlated with cortisol or cytokines in the total sample or subgroups. Yet, multivariate analyses controlling for sex and time of blood draw showed a positive main effect for patient age ( p = .019) and a significant age by poverty interaction ( p = .041) predicting cortisol among pediatric patients. Cortisol levels were higher with age, yet the association among poverty and cortisol was strongest in younger patients. Analyses also showed a sex*poverty interaction among pediatric patients that approached significance ( p = .081), such that poverty only predicted cortisol in male patients. There were no significant differences for immunomodulatory cytokines across each SCD subgroups; however, IL-6 and IL-10 were elevated in patients with SCA relative to healthy controls ( p IL6 = .021; p IL10 = .003). Bivariate Spearman correlations showed that cortisol was positively related to IL-6 (rho [ρ]= .38, p = .027) and IL-10 (ρ= .34, p = .048) among patients with SCA. There were no additional significant bivariate or multivariate effects. Conclusion: Neighborhood factors likely have downstream effects on the biological stress response and inflammation in SCD. Further research must be conducted to elucidate concurrent and prospective associations among neighborhood socioeconomic factors, stress-related cortisol response, and inflammatory outcomes when extending this work to investigate the impact of stress on SCD morbidity and mortality.

Background Habituation to repeated stress refers to a progressive reduction in the stress response following multiple exposures to the same, predictable stressor. We previously demonstrated that the posterior division of the paraventricular thalamic nucleus (pPVT) nucleus regulates habituation to 5 days of repeated restraint stress in male rats. Compared to males, female rats display impaired habituation to 5 days of restraint. To better understand how activity of pPVT neurons is differentially impacted in stressed males and females, we examined the electrophysiological properties of pPVT neurons under baseline conditions or following restraint. Methods Adult male and female rats were exposed to no stress (handling only), a single period of 30 min restraint or 5 daily exposures to 30 min restraint. 24 h later, pPVT tissue was prepared for recordings. Results We report here that spontaneous excitatory post-synaptic current (sEPSC) amplitude was increased in males, but not females, following restraint. Furthermore, resting membrane potential of pPVT neurons was more depolarized in males. This may be partially due to reduced potassium leakage in restrained males as input resistance was increased in male, but not female, rats 24 h following 1 or 5 days of 30-min restraint. Reduced potassium efflux during action potential firing also occurred in males following a single restraint as action potential half-width was increased following a single restraint. Restraint had limited effects on electrophysiological properties in females, although the mRNA for 10 voltage-gated ion channel subunits was altered in the pPVT of female rats. Conclusions The results suggest that restraint-induced changes in pPVT activation promote habituation in males. These findings are the first to describe a sexual dimorphism in stress-induced electrophysiological properties and voltage-gated ion channel expression in the pPVT. These results may explain, at least in part, why habituation to 5 days of restraint is disrupted in female rats.

AbstractStudy ObjectivesSelf-reported sleep disturbance has been established as a risk factor and predictor for posttraumatic stress disorder (PTSD); however, less is known about the relationship between objective sleep and PTSD symptom clusters, and the specific role of hyperarousal. The present study examined the relationships between sleep continuity and architecture on PTSD symptom clusters.MethodsParticipants underwent two in-laboratory sleep studies to assess sleep continuity and architecture. They also completed the Clinician-Administered PTSD-IV scale and the Structured Clinical Interview for the DSM-IV to assess for PTSD diagnosis and other psychiatric disorders.ResultsSleep continuity (i.e. total sleep time, sleep efficiency percent, wake after sleep onset, sleep latency) was significantly related to PTSD Cluster B (reexperiencing) symptom severity (R2 = .27, p < .001). Sleep architecture, specifically Stage N1 sleep, was significantly associated with PTSD Cluster B (t = 2.98, p = .004), C (Avoidance; t = 3.11, p = .003), and D (Hyperarosual; t = 3.79, p < .001) symptom severity independently of Stages N2, N3, and REM sleep. REM sleep variables (i.e. REM latency, number of REM periods) significantly predicted Cluster D symptoms (R2 = .17, p = .002).ConclusionsThese data provide evidence for a relationship between objective sleep and PTSD clusters, showing that processes active during Stage N1 sleep may contribute to PTSD symptomatology in civilians and veterans. Further, these data suggest that arousal mechanisms active during REM sleep may also contribute to PTSD hyperarousal symptoms.This paper is part of the War, Trauma, and Sleep Across the Lifespan Collection. This collection is sponsored by the Sleep Research Society.

Background Habituation is defined as a progressive decline in response to repeated exposure to a familiar and predictable stimulus and is highly conserved across species. Disrupted habituation is a signature of posttraumatic stress disorder. In rodents, habituation is observed in neural, neuroendocrine, and behavioral responses to repeated exposure to predictable and moderately intense stress or restraint. We previously demonstrated that lesioning the posterior paraventricular thalamic nucleus (pPVT) impairs habituation. However, the underlying molecular mechanisms and specific neural connections among the pPVT and other brain regions that underlie habituation are unknown. Methods Behavioral and neuroendocrine habituation was assessed in adult male Sprague Dawley rats using the repeated restraint paradigm. Pan-neuronal and Cre-dependent DREADDs (designer receptors exclusively activated by designer drugs) were used to chemogenetically inhibit the pPVT and the subpopulation of pPVT neurons that project to the medial prefrontal cortex (mPFC), respectively. Activity-regulated cytoskeleton-associated protein (Arc) expression was knocked down in the pPVT using small interfering RNA. Structural plasticity of pPVT neurons was assessed using Golgi staining. Local field potential recordings were used to assess coherent neural activity between the pPVT and mPFC. The attentional set shifting task was used to assess mPFC-dependent behavior. Results Here, we show that Arc promotes habituation by increasing stress-induced spinogenesis in the pPVT, increasing coherent neural activity with the mPFC, and improving mPFC-mediated cognitive flexibility. Conclusions Our results demonstrate that Arc induction in the pPVT regulates habituation and mPFC function. Therapies that improve synaptic plasticity during posttraumatic stress disorder therapy may enhance habituation and the efficacy of posttraumatic stress disorder treatment.

Resilience to stressful life events has received considerable attention in both clinical and preclinical studies. A number of neural substrates have been identified as putatively mediating resilience to stress. However, there remains considerable diversity in how resilience is defined and studied. This article aims to examine how resilience is defined and conceptualized in social psychology, public health, and related fields, to better inform the understanding of stress resilience in the neurobiological context, and to differentiate resilience from other patterns of response to stressful experiences. An understanding of resilience through the lens of clinical and applied sciences is likely to lead to the identification of more robust and reproducible neural substrates, though many challenges remain.

Abstract Introduction Nightmare occurrences may, in part, result from prior-day arousal (e.g., the continuity hypothesis), and that they then influence next-day symptoms. Recent ecological momentary assessment (EMA) studies in samples of civilian trauma survivors found that elevated PTSD symptoms, pre-sleep cognitive arousal, and greater sleep onset latency predicted nightmare reports. This study adds to these works by using EMA in a sample of combat-exposed Veterans. Methods Data were analyzed from a study examining neurobiological and neuropsychological factors associated with PTSD in a sample of 27 combat-exposed OEF/OIF Veterans, with and without PTSD. Participants engaged in EMA for 6 days, with assessments across the day inquiring about mood, activity, and stressful events. Morning reports also included the consensus sleep diary and prompts on nightmare experiences. Those reporting nightmares were asked about nightmare disturbance and the level of replicability to a traumatic event (replays or symbolic/unrelated). Multi-level modeling analyses were used. Results A total of 113 morning reports were acquired, in which 40 included a report of having a nightmare and 73 did not. Main effects were found for baseline PTSD symptom severity (OR=1.13, p=0.02), prior day time spent alone (OR=0.01, p=0.01) and prior day level of distraction (OR=0.25, p=0.02) on morning reports of nightmares. However, when accounting for the previous night’s nightmare report (OR=15.9, p<0.001), these effects were no longer significant. No other effects on nightmare reports were observed. Additionally, no factors predicted replicability of nightmare content or level of nightmare disturbance. Regarding daytime impact, nightmare reports were associated with greater levels of stress associated with events later that day (OR=2.48, p=0.04). Conclusion Greater baseline PTSD symptom severity, less daytime spent alone, and greater daytime attentiveness were significant predictors of nightmare reports. While daily social interactions and attentiveness may be beneficial, these factors also may be associated with hypervigilance, a known risk for sleep disruption. However, these data also suggest that day-to-day levels of stress may have less influence when a chronic nightmare pattern is present. Support (if any) Defense Advanced Research Projects Agency under a grant from the U.S. Army Research Office (W911NF1010093). U.S. Department of Veterans Affairs, Veterans Health Administration (CSR&D- IK2 CX001874).

BACKGROUND Habituation is defined as a progressive decline in response to repeated exposure to a familiar and predictable stimulus and is highly conserved across species. Disrupted habituation is a signature of post-traumatic stress disorder (PTSD). In rodents, habituation is observed in neural, neuroendocrine and behavioral responses to repeated exposure to the predictable and moderately intense stress or restraint. We previously demonstrated that lesions to the posterior division of the paraventricular thalamic nucleus (pPVT) impairs habituation. However, the underlying molecular mechanisms and specific neural connections among the pPVT and other brain regions that underlie habituation are unknown. METHODS Behavioral and neuroendocrine habituation was assessed in adult male Sprague-Dawley restraints using the repeated restraint paradigm. Pan neuronal and Cre-dependent Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) were used to chemogenetically inhibit the pPVT and the subpopulation of pPVT neurons that project to the medial prefrontal cortex (mPFC), respectively. Activity-regulated cytoskeleton-associated protein (Arc) expression was knocked down in the pPVT using siRNA directed towards Arc. Golgi staining was used to assess structural plasticity of pPVT neurons. Local field potential recordings were used to assess coherent neural activity between the pPVT and mPFC. The attentional set-shifting task was used to assess mPFC-dependent behavior. RESULTS Here, we show that Arc promotes habituation by increasing stress-induced spinogenesis in the pPVT, increasing coherent neural activity with the mPFC, and improving mPFC-mediated cognitive flexibility. CONCLUSION Our results demonstrate that Arc induction in the pPVT regulates habituation to repeated restraint and mPFC function. One Sentence Summary We demonstrate that Arc in the posterior division of the paraventricular thalamic nucleus promotes habituation to repeated stress by increasing dendritic spines.

EDITORIAL article Front. Integr. Neurosci., 17 August 2021 | https://doi.org/10.3389/fnint.2021.744147

Sleep disruptions are hallmarks in the pathophysiology of several stress-related disorders, including Major Depressive Disorder (MDD) and Post-Traumatic Stress Disorder (PTSD), both known to disproportionately affect female populations. Although previous studies have attempted to investigate disordered sleep in women, few studies have explored and compared how repeated stress affects sleep in both sexes in either human or animal models. We have previously shown that male rats exhibit behavioral and neuroendocrine habituation to 5 days of repeated restraint, whereas females do not; additional days of stress exposure are required to observe habituation in females. This study examined sex differences in sleep measures prior to, during, and after repeated restraint stress in adult male and female rats. Our data reveal that repeated stress increased time spent awake and decreased slow-wave sleep (SWS) and REM sleep (REMS) in females, and these effects persisted over 2 days of recovery. In contrast, the effects of stress on males were transient. These insomnia-like symptoms were accompanied by a greater number of exaggerated motor responses to waking from REMS in females, a phenotype similar to trauma-related nightmares. In sum, these data demonstrate that repeated stress produces disruptions in sleep that persist days after the stress is terminated in female rats. These disruptions in sleep produced by 5 days of repeated restraint may be due to their lack of habituation.

FTY720 (fingolimod) is an analog of sphingosine, a ubiquitous sphingolipid. Phosphorylated FTY720 (FTY720-P) non-selectively binds to sphingosine-1-phosphate receptors (S1PRs) and regulates multiple cellular processes including cell proliferation, inflammation, and vascular remodeling. We recently demonstrated that S1PR3 expression in the medial prefrontal cortex (mPFC) of rats promotes stress resilience and that S1PR3 expression in blood may serve as a biomarker for PTSD. Here we investigate the effects of FTY720 in regulating the stress response. We found that single and repeated intraperitoneal injections of FTY720 increased baseline plasma adrenocorticotropic hormone (ACTH) and corticosterone concentrations. FTY720 reduced social anxiety- and despair-like behavior as assessed by increased social interaction time and reduced time spent immobile in the Porsolt forced swim test. In blood, FTY720 administration reduced lymphocyte and reticulocyte counts, but raised erythrocyte counts. FTY720 also reduced mRNA of angiopoietin 1, endothelin 1, plasminogen, TgfB2, Pdgfa, and Mmp2 in the medial prefrontal cortex, suggesting that FTY720 reduced vascular remodeling. The antidepressant-like and anxiolytic-like effects of FTY720 may be attributed to reduced vascular remodeling as increased stress-induced blood vessel density in the brain contributes to behavior associated with vulnerability in rats. Together, these results demonstrate that FTY720 regulates baseline HPA axis activity but reduces social anxiety and despair, providing further evidence that S1PRs are important and novel regulators of stress-related functions.