Differential recruitment of brain circuits during fear extinction in non-stressed compared to stress resilient animals.

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.

Accelerating the Biodegradation of Poly(lactic acid) through the Inclusion of Plant Fibers: A Review of Recent Advances.

As the global demand for plastics continues to grow, plastic waste is accumulating at an alarming rate with negative effects on the natural environment. The industrially compostable biopolymer poly(lactic acid) (PLA) is therefore being adopted for use in many applications, but the degradation of this material is slow under many end-of-life conditions. This Perspective explores the feasibility of accelerating the degradation of PLA through the formation of PLA-plant fiber composites. Topics include: (a) key properties of PLA, plant-based fibers, and biocomposites; (b) mechanisms of both hydrolytic degradation and biodegradation of PLA-fiber composites; (c) end-of-life degradation of PLA and PLA-plant fiber composites in aerobic and anaerobic conditions, relevant to compost, soil and seawater (aerobic), and landfills (anaerobic); and (d) sustainability and environmental impact of PLA and PLA-plant fiber composites, as evaluated using life cycle assessment. Additional degradation modes, including thermal and photodegradation, which are relevant during processing and use, have been omitted for clarity, as have other types of PLA biocomposites. Multiple studies have shown that the addition of some types of plant fibers to PLA (to form PLA biocomposites) accelerates both water transport in the material and hydrolysis, presenting a possible avenue for improving the end-of-life degradation of these materials. To facilitate the continued development of materials with enhanced biodegradability, we identify a need to implement testing protocols that can distinguish between different degradation mechanisms.

Sex differences in electrophysiological properties and voltage-gated ion channel expression in the paraventricular thalamic nucleus following repeated stress.

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.

Hemicellulose Films from Curaua Fibers (Ananas erectifolius): Extraction and Thermal and Mechanical Characterization.

With growing environmental concerns over synthetic polymers, natural polymeric materials, such as hemicellulose, are considered a good sustainable alternative. Curaua fibers could be an excellent source of biopolymer as they have a relatively high hemicellulose content (15 wt%) and only a small amount of lignin (7 wt%). In this work, hemicellulose was extracted by an alkaline medium using KOH and the influence of the alkali concentration, temperature, and time was studied. A hemicellulose film was produced by water casting and its mechanical, thermal, and morphological properties were characterized. The results show that the best method, which resulted in the highest hemicellulose yield and lowest contamination from lignin, was using 10% (w/v) KOH concentration, 25 °C, and time of 3 h. The hemicellulose film exhibited better thermal stability and elongation at break than other polymeric films. It also exhibited lower rigidity and higher flexibility than other biodegradable polymers, including polylactic acid (PLA) and polyhydroxybutyrate (PHB).

Arc-Mediated Plasticity in the Paraventricular Thalamic Nucleus Promotes Habituation to Stress.

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.

FTY720 (Fingolimod), a modulator of sphingosine-1-phosphate receptors, increases baseline hypothalamic-pituitary adrenal axis activity and alters behaviors relevant to affect and anxiety.

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.

Sex differences in stress-induced sleep deficits.

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.

Passive Coping Strategies During Repeated Social Defeat Are Associated With Long-Lasting Changes in Sleep in Rats.

Exposure to severe stress has immediate and prolonged neuropsychiatric consequences and increases the risk of developing Posttraumatic Stress Disorder (PTSD). Importantly, PTSD develops in only a subset of individuals after exposure to a traumatic event, with the understanding of this selective vulnerability being very limited. Individuals who go on to develop PTSD after a traumatic experience typically demonstrate sleep disturbances including persistent insomnia and recurrent trauma-related nightmares. We previously established a repeated social defeat paradigm in which rats segregate into either passively or actively coping subpopulations, and we found that this distinction correlates with measures of vulnerability or resilience to stress. In this study, we examined differences between these two behavioral phenotypes in sleep changes resulting from repeated social defeat stress. Our data indicate that, compared to control and actively coping rats, passively coping rats have less slow-wave sleep (SWS) for at least 2 weeks after the end of a series of exposures to social defeat. Furthermore, resilient rats show less exaggerated motor activation at awakenings from rapid eye movement (REM) sleep and less fragmentation of REM sleep compared to control and passively coping rats. Together, these data associate a passive coping strategy in response to repeated social defeat stress with persisting sleep disturbances. Conversely, an active coping strategy may be associated with resilience to sleep disturbances. These findings may have both prognostic and therapeutic applications to stress-associated neuropsychiatric disorders, including PTSD.

The gut microbiome regulates the increases in depressive-type behaviors and in inflammatory processes in the ventral hippocampus of stress vulnerable rats.

Chronic exposure to stress is associated with increased incidence of depression, generalized anxiety, and PTSD. However, stress induces vulnerability to such disorders only in a sub-population of individuals, as others remain resilient. Inflammation has emerged as a putative mechanism for promoting stress vulnerability. Using a rodent model of social defeat, we have previously shown that rats with short-defeat latencies (SL/vulnerable rats) show increased anxiety- and depression-like behaviors, and these behaviors are mediated by inflammation in the ventral hippocampus. The other half of socially defeated rats show long-latencies to defeat (LL/resilient) and are similar to controls. Because gut microbiota are important activators of inflammatory substances, we assessed the role of the gut microbiome in mediating vulnerability to repeated social defeat stress. We analyzed the fecal microbiome of control, SL/vulnerable, and LL/resilient rats using shotgun metagenome sequencing and observed increased expression of immune-modulating microbiota, such as Clostridia, in SL/vulnerable rats. We then tested the importance of gut microbiota to the SL/vulnerable phenotype. In otherwise naive rats treated with microbiota from SL/vulnerable rats, there was higher microglial density and IL-1ß expression in the vHPC, and higher depression-like behaviors relative to rats that received microbiota from LL/resilient rats, non-stressed control rats, or vehicle-treated rats. However, anxiety-like behavior during social interaction was not altered by transplant of the microbiome of SL/vulnerable rats into non-stressed rats. Taken together, the results suggest the gut microbiome contributes to the depression-like behavior and inflammatory processes in the vHPC of stress vulnerable individuals.

The effects of early life adversity on growth, maturation, and steroid hormones in male and female rats.

Early life adversity is a risk factor for psychiatric disorders, yet the mechanisms by which adversity increases this risk are still being delineated. Here, we used a limited bedding and nesting (LBN) manipulation in rats that models a low resource environment to examine effects on growth, developmental milestones, and endocrine endpoints. In LBN, dams and pups, from pups' postnatal days 2-9, are exposed to an environment where dams lack proper materials to build a nest. This manipulation is compared to control housing conditions, where rat dams have access to ample nesting materials and enrichment throughout pups' development. We found that the LBN condition altered maternal care, increasing pup-directed behaviors while reducing self-care. This, perhaps compensatory, increase in nursing and attention to pups did not mitigate against changes in metabolism, as LBN reduced weight gain in both sexes and this effect persisted into adulthood. Although adult stress hormone levels in both sexes and vaginal opening and estrous cycle length in females were not disrupted, there was other evidence of endocrine dysregulation. Compared to controls, LBN rats of both sexes had shortened anogenital distances, indicating reduced androgen exposure. LBN males also had higher plasma estradiol levels in adulthood. This combination of results suggests that LBN causes a demasculinizing effect in males that could contribute to lasting changes in the brain and behavior. Importantly, alterations in metabolic and endocrine systems due to early life adversity could be one mechanism by which stress early in life increases risk for later disease.

Sphingosine-1-phosphate receptor 3 in the medial prefrontal cortex promotes stress resilience by reducing inflammatory processes.

Stress can promote the development of psychiatric disorders, though some individuals are more vulnerable to stress compared to others who are more resilient. Here we show that the sphingosine-1-phosphate receptor 3 (S1PR3) in the medial prefrontal cortex (mPFC) of rats regulates resilience to chronic social defeat stress. S1PR3 expression is elevated in the mPFC of resilient compared to vulnerable and control rats. Virally-mediated over-expression of S1PR3 in the mPFC produces a resilient phenotype whereas its knock-down produces a vulnerable phenotype, characterized by increased anxiety- and depressive-like behaviors, and these effects are mediated by TNFα. Furthermore, we show that S1PR3 mRNA in blood is reduced in veterans with PTSD compared to combat-exposed control subjects and its expression negatively correlates with symptom severity. Together, these data identify S1PR3 as a regulator of stress resilience and reveal sphingolipid receptors as important substrates of relevance to stress-related psychiatric disorders.

Influence of Epoxidized Canola Oil (eCO) and Cellulose Nanocrystals (CNCs) on the Mechanical and Thermal Properties of Polyhydroxybutyrate (PHB)-Poly(lactic acid) (PLA) Blends.

Two major obstacles to utilizing polyhydroxybutyrate (PHB)-a biodegradable and biocompatible polymer-in commercial applications are its low tensile yield strength (<10 MPa) and elongation at break (~5%). In this work, we investigated the modification of the mechanical properties of PHB through the use of a variety of bio-derived additives. Poly(lactic acid) (PLA) and sugarcane-sourced cellulose nanocrystals (CNCs) were proposed as mechanical reinforcing elements, and epoxidized canola oil (eCO) was utilized as a green plasticizer. Zinc acetate was added to PHB and PLA blends in order to improve blending. Composites were mixed in a micro-extruder, and the resulting filaments were molded into 2-mm sheets utilizing a hot-press prior to characterization. The inclusion of the various additives was found to influence the crystallization process of PHB without affecting thermal stability. In general, the addition of PLA and, to a lesser degree, CNCs, resulted in an increase in the Young's modulus of the material, while the addition of eCO improved the strain at break. Overall, samples containing eCO and PLA (at concentrations of 10 wt %, and 25 wt %, respectively) demonstrated the best mechanical properties in terms of Young's modulus, tensile strength and strain at break.

Sex- and Age-dependent Effects of Orexin 1 Receptor Blockade on Open-Field Behavior and Neuronal Activity.

Adolescence is a sensitive and critical period in brain development where psychiatric disorders such as anxiety, depression and post-traumatic stress disorder are more likely to emerge following a stressful life event. Females are two times more likely to suffer from psychiatric disorders than males. Patients with these disorders show alterations in orexins (also called hypocretins), important neuropeptides that regulate arousal, wakefulness and the hypothalamic-pituitary-adrenal axis activity. Little is known on the role of orexins in mediating arousal behaviors in male and female rats during adolescence or adulthood. Here, we examine the influence of orexin 1 receptor blockade by SB334867 in open-field behavior in male and female rats during early adolescence (PND 31-33) or adulthood (PND 75-77). Animals were injected with 0 (vehicle), 1, 10, or 30 mg/kg SB334867 (i.p.). Thirty minutes later, they were placed in an open field, and behavior and neuronal activity (c-Fos) were assessed. In adolescent males, SB334867 significantly increased immobility in the 10 mg/kg group compared to vehicle. However, this increase in immobility in adolescent males was not observed in adolescent females. In contrast to adolescent males, adult males in the 10 mg/kg dose group showed the opposite effect on immobility compared to vehicle. These results indicate that 10 mg/kg dose of SB334867 has opposing effects in adolescent and adult males, but few effects in adolescent and adult females. Differences in functional networks between limbic regions may underlie these effects of orexin receptor blockade that are sex- and age-dependent in rats.

Sex differences in circuits activated by corticotropin releasing factor in rats.

Women are more likely than men to suffer from psychiatric disorders characterized by corticotropin releasing factor (CRF) hypersecretion, suggesting sex differences in CRF sensitivity. In rodents, sex differences in the sensitivity of specific brain regions to CRF have been identified. However, regions do not work in isolation, but rather form circuits to coordinate distinct responses to stressful events. Here we examined whether CRF activates different circuits in male and female rats. Following central administration of CRF or artificial cerebrospinal fluid (aCSF), neuronal activation in stress-related areas was assessed using cFOS. Functional connectivity was gauged by correlating the number of cFOS-positive cells between regions and then identifying differences within each sex in correlations for aCSF-treated and CRF-treated groups. This analysis revealed that CRF altered different circuits in males and females. As an example, CRF altered correlations involving the dorsal raphe in males and the bed nucleus of the stria terminalis in females, suggesting sex differences in stress-activated circuits controlling mood and anxiety. Next, plasma estradiol and progesterone levels were correlated with cFOS counts in females. Negative correlations between estradiol and neuronal activation in the regions within the extended amygdala were found in CRF-treated, but not aCSF-treated females. This result suggests that estrogens and CRF together modulate the fear and anxiety responses mediated by these regions. Collectively, these studies reveal sex differences in the way brain regions work together in response to CRF. These differences could drive different stress coping strategies in males and females, perhaps contributing to sex biases in psychopathology.

Murine social stress results in long lasting voiding dysfunction.

Repeated exposure to social stress shifts the voiding phenotype in male mice leading to bladder wall remodeling and is associated with increased expression of the stress neuropeptide, corticotropin-releasing factor (CRF) in Barrington's nucleus neurons. In these studies, we set out to determine if the voiding phenotype could recover upon removal from the stressor. Male mice were exposed for 1h daily to an aggressor and the voiding phenotype was assessed at one month followed by randomization to three groups. One group underwent immediate sacrifice. Two groups were allowed a one month recovery from the social stress exposure with or without the addition of fluoxetine (1.2mg/ml) in their drinking water and repeat voiding patterns were measured prior to sacrifice. Social stress significantly increased bladder mass, bladder mass corrected for body weight, voided volumes, and decreased urinary frequency. The abnormal voiding phenotype persisted after a 1month recovery with no effect from the addition of fluoxetine. CRF mRNA in Barrington's nucleus was increased by social stress and remained elevated following recovery with no effect from the addition of fluoxetine. The mRNA and protein expression for the alpha 1 chains of type 1 and type III collagen was unchanged across all groups suggesting that changes in the extracellular matrix of the bladder are not responsible for the voiding phenotype. This persisting voiding dysfunction correlates with the persistent elevation of CRF mRNA expression in Barrington's nucleus.

Environmental and technical feasibility of cellulose nanocrystal manufacturing from sugarcane bagasse.

The environmental and technical feasibility of cellulose nanocrystal production from sugarcane bagasse fibers was evaluated. First, the life cycle assessment (LCA) is presented as a methodology to investigate the most feasible form of obtainment. The environmental impacts regarding climate change and water footprint were evaluated considering a gate-to-gate process and a functional unit of 1kg. The inventory data encompassed sugarcane plantation and pretreatment, bleaching and hydrolysis for bagasse generation. The twelve scenarios for extracting nanocrystals that were investigated consisted of treatment with sodium hydroxide or sodium chlorite followed by sulfuric acid hydrolysis. All products and processes were characterized by their yield and X-ray diffraction. As a result, all scenarios showed that the pretreatment stage was the most important contributor to the environmental impact. The comparison among the scenarios showed that nanocrystals produced by processes V - NaClO2/NaOH/H2SO4/30min/1x and IX - NaClO2/NaOH/HNO3/H2SO4/30min/1x presented low water consumption and minimal contributions to climate change. Therefore, considering the LCA, yield and crystallinity, the best processes were V and IX sequences. Finally, these cellulose nanocrystals were evaluated by their chemical composition, morphology and thermal stability, exhibiting hemicellulose and lignin removal, nanometric dimensions from 8 to 12nm, high crystallinity and low thermal stability.

Orexin 2 receptor regulation of the hypothalamic-pituitary-adrenal (HPA) response to acute and repeated stress.

Orexins are hypothalamic neuropeptides that have a documented role in mediating the acute stress response. However, their role in habituation to repeated stress, and the role of orexin receptors (OX1R and OX2R) in the stress response, has yet to be defined. Orexin neuronal activation and levels in the cerebrospinal fluid (CSF) were found to be stimulated with acute restraint, but were significantly reduced by day five of repeated restraint. As certain disease states such as panic disorder are associated with increased central orexin levels and failure to habituate to repeated stress, the effect of activating orexin signaling via Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) on the hypothalamic-pituitary-adrenal (HPA) response was evaluated after repeated restraint. While vehicle-treated rats displayed habituation of Adrenocorticotropic Hormone (ACTH) from day 1 to day 5 of restraint, stimulating orexins did not further increase ACTH beyond vehicle levels for either acute or repeated restraint. We delineated the roles of orexin receptors in acute and repeated stress using a selective OX2R antagonist (MK-1064). Pretreatment with MK-1064 reduced day 1 ACTH levels, but did not allow further habituation on day 5 compared with vehicle-treated rats, indicating that endogenous OX2R activity plays a role in acute stress, but not in habituation to repeated stress. However, in restrained rats with further stimulated orexins by DREADDs, MK-1064 decreased ACTH levels on day 5. Collectively, these results indicate that the OX2R plays a role in acute stress, and can prevent habituation to repeated stress under conditions of high orexin release.

Orexins Mediate Sex Differences in the Stress Response and in Cognitive Flexibility.

BACKGROUND: Women are twice as likely as men to experience stress-related psychiatric disorders. The biological basis of these sex differences is poorly understood. Orexins are altered in anxious and depressed patients. Using a rat model of repeated stress, we examined whether orexins contribute to sex differences in outcomes relevant to stress-related psychiatric diseases. METHODS: Behavioral, neural, and endocrine habituation to repeated restraint stress and subsequent cognitive flexibility was examined in adult male and female rats. In parallel, orexin expression and activation were determined in both sexes, and chromatin immunoprecipitation was used to determine transcription factors acting at the orexin promoter. Designer receptors exclusively activated by designer drugs were used to inhibit orexin activation throughout repeated restraint to determine if the stress-related impairments in female rats could be reduced. RESULTS: Female rats exhibited impaired habituation to repeated restraint with subsequent deficits in cognitive flexibility compared with male rats. Increased orexin expression and activation were observed in female rats compared with male rats. The higher expression of orexin messenger RNA in female rats was due to actions of glucocorticoid receptors on the orexin promoter, as determined by chromatin immunoprecipitation. Inhibition of orexins using designer receptors exclusively activated by designer drugs in female rats throughout repeated restraint abolished their heightened hypothalamic-pituitary-adrenal responsivity and reduced stress-induced cognitive impairments. CONCLUSIONS: Orexins mediate the impairments in adaptations to repeated stress and in subsequent cognitive flexibility exhibited by female rats and provide evidence for a broader role for orexins in mediating functions relevant to stress-related psychiatric diseases.

Social isolation in adolescence alters behaviors in the forced swim and sucrose preference tests in female but not in male rats.

Social interactions in rodents are rewarding and motivating and social isolation is aversive. Accumulating evidence suggests that disruption of the social environment in adolescence has long-term effects on social interactions, on anxiety-like behavior and on stress reactivity. In previous work we showed that adolescent isolation produced increased reactivity to acute and to repeated stress in female rats, whereas lower corticosterone responses to acute stress and decreased anxiety-related behavior were noted in isolated males. These results indicate a sex specific impact on the effects of social stress in adolescence. However, little is known about whether social isolation impacts behaviors related to affect and whether it does so differently in male and female rats. The present study investigated the impact of adolescent social isolation from day 30-50 of age in male and female Sprague Dawley rats on behavior in the forced swim test at the end of adolescence and in adulthood and on behavior in the sucrose preference test in adulthood. Adult female rats that were isolated in adolescence exhibited increased climbing on the first and second day of the forced swim test and showed an increased preference for sucrose compared to adult females that were group-housed in adolescence. There were no effects in male rats. The results indicate that social isolation in adolescence produces a stable and active behavioral phenotype in adult female rats.

Orexins/hypocretins act in the posterior paraventricular thalamic nucleus during repeated stress to regulate facilitation to novel stress.

Orexins/hypocretins heavily innervate the posterior division of the paraventricular nucleus of the thalamus (pPVT), which expresses both orexin receptor types. The pPVT is important for adaptations to repeated stress, particularly the ability to facilitate to novel stress after repeated stress exposure. Here, we examined how orexins acting in the pPVT regulate facilitation of hypothalamic-pituitary-adrenal (HPA) responses to novel restraint after 4 d of repeated swim stress. Blockade of orexin receptors in the pPVT with SB334867 before novel restraint did not change the facilitated HPA response. However, blockade of orexin receptors before each of four daily swim exposures prevented the facilitated ACTH and facilitated hypothalamic c-Fos response to restraint as well as the repeated swim stress-induced increase in CRH mRNA in the paraventricular hypothalamus. These results suggest that orexin actions in the pPVT during the 4 d of swim, but not during restraint, are necessary for the facilitated HPA response to heterotypic restraint. Exposure to the fourth swim produced a shift in orexin1 receptors from membrane to cytosolic fractions. OrexinA also changed the firing patterns of pPVT cells to be more responsive in repeatedly swim stressed rats compared with nonstressed rats. Together, the results suggest that orexin actions in the pPVT, mediated by orexin1 receptors, are important for the ability to adapt to repeated stress.