Effects of high fat or high sucrose diet on behavioral-response to social defeat stress in mice.

Stress increases risk for psychopathology, and diet may moderate the impact of stress on mental health. A "Western" diet has been linked to psychopathology in humans; animal studies also show that diet can influence negative valence behavior in the presence or absence of stress, but findings are inconsistent. Contradictions in existing studies may result from differences in macronutrient content of diets and presence of metabolic syndrome. The present study exposed mice to 10 days of high fat or high sucrose diet concurrent with social defeat stress exposure and examined negative valence behavior at acute (30 days) time points after stress/diet exposure. Predictably, stress increased negative valence behavior in the social interaction, open field, elevated zero maze, and tail suspension tests at the acute time point. While most stress-induced behaviors normalized after the 30-day recovery period, social avoidance was still highly significant for stress-exposed mice, supporting the hypothesis that avoidance of a trauma-related cue persists beyond non-specific anxiety-like behaviors. Supporting the hypothesis that an unhealthy diet contributes to psychopathology, non-stressed mice fed high fat or high sucrose diets spent less time exploring the center of the open field. This effect was no longer present after a 30-day recovery. Intriguingly, mice previously fed either high fat or high sucrose diets exhibited increased rearing behavior in the elevated zero maze 30 days post stress and diet exposure. This finding could be evidence that short-term diet administration can initiate a long-term increase in risk-assessment behavior.

Animal Models of PTSD: A Critical Review.

The goals of animal research in post-traumatic stress disorder (PTSD) include better understanding the neurophysiological etiology of PTSD, identifying potential targets for novel pharmacotherapies, and screening drugs for their potential use as PTSD treatment in humans. Diagnosis of PTSD relies on a patient interview and, as evidenced by changes to the diagnostic criteria in the DSM-5, an adequate description of this disorder in humans is a moving target. Therefore, it may seem insurmountable to model the construct of PTSD in animals such as rodents. Fortunately, the neural circuitry involved in fear and anxiety, thought to be essential to the etiology of PTSD in humans, is highly conserved throughout evolution. Furthermore, many symptoms can be modeled using behavioral tests that have face, construct, and predictive validity. Because PTSD is precipitated by a definite traumatic experience, animal models can simulate the induction of PTSD, and test causal factors with longitudinal designs. Accordingly, several animal models of physical and psychological trauma have been established. This review discusses the widely used animal models of PTSD in rodents, and overviews their strengths and weaknesses in terms of face, construct, and predictive validity.

Overexpression of Forebrain CRH During Early Life Increases Trauma Susceptibility in Adulthood.

Although early-life stress is a significant risk factor for developing anxiety disorders, including posttraumatic stress disorder (PTSD), the underlying mechanisms are unclear. Corticotropin releasing hormone (CRH) is disrupted in individuals with PTSD and early-life stress and hence may mediate the effects of early-life stress on PTSD risk. We hypothesized that CRH hyper-signaling in the forebrain during early development is sufficient to increase response to trauma in adulthood. To test this hypothesis, we induced transient, forebrain-specific, CRH overexpression during early-life (pre-puberty, CRHOEdev) in double-mutant mice (Camk2a-rtta2 × tetO-Crh) and tested their behavioral and gene expression responses to the predator stress model of PTSD in adulthood. In one cohort of CRHOEdev exposed and unexposed mice, avoidance and arousal behaviors were examined 7-15 days after exposure to predator stress. In another cohort, gene expression changes in Crhr1, Crhr2, and Fkbp51 in forebrain of CRHOEdev exposed and unexposed mice were examined 7 days after predator stress. CRHOEdev induced robust increases in startle reactivity and reductions in startle inhibition independently of predator stress in both male and female mice. Avoidance behaviors after predator stress were highly dependent on sex and CRHOEdev exposure. Whereas stressed females exhibited robust avoidance responses that were not altered by CRHOEdev, males developed significant avoidance only when exposed to both CRHOEdev and stress. Quantitative real-time-PCR analysis indicated that CRHOEdev unexposed males exhibit significant changes in Crhr2 expression in the amygdala and bed nucleus stria terminalis in response to stress, whereas males exposed to CRHOEdev did not. Similar to CRHOEdev males, females exhibited no significant Crhr2 gene expression changes in response to stress. Cortical Fkbp51 expression was also significantly reduced by stress and CRHOEdev exposure in males, but not in females. These findings indicate that forebrain CRH hyper-signaling in early-life is sufficient to increase enduring effects of adult trauma and attenuate Crhr2 expression changes in response to stress in males. These data support growing evidence for significant sex differences in response to trauma, and support further study of CRHR2 as a candidate mechanism for PTSD risk.

Forebrain-specific CRF overproduction during development is sufficient to induce enduring anxiety and startle abnormalities in adult mice.

Corticotropin releasing factor (CRF) regulates physiological and behavioral responses to stress. Trauma in early life or adulthood is associated with increased CRF in the cerebrospinal fluid and heightened anxiety. Genetic variance in CRF receptors is linked to altered risk for stress disorders. Thus, both heritable differences and environmentally induced changes in CRF neurotransmission across the lifespan may modulate anxiety traits. To test the hypothesis that CRF hypersignaling is sufficient to modify anxiety-related phenotypes (avoidance, startle, and conditioned fear), we induced transient forebrain-specific overexpression of CRF (CRFOE) in mice (1) during development to model early-life stress, (2) in adulthood to model adult-onset stress, or (3) across the entire postnatal lifespan to model heritable increases in CRF signaling. The consequences of these manipulations on CRF peptide levels and behavioral responses were examined in adulthood. We found that transient CRFOE during development decreased startle habituation and prepulse inhibition, and increased avoidance (particularly in females) recapitulating the behavioral effects of lifetime CRFOE despite lower CRF peptide levels at testing. In contrast, CRFOE limited to adulthood reduced contextual fear learning in females and increased startle reactivity in males but did not change avoidance or startle plasticity. These findings suggest that forebrain CRFOE limited to development is sufficient to induce enduring alterations in startle plasticity and anxiety, while forebrain CRFOE during adulthood results in a different phenotype profile. These findings suggest that startle circuits are particularly sensitive to forebrain CRFOE, and that the impact of CRFOE may be dependent on the time of exposure.

Escitalopram alters gene expression and HPA axis reactivity in rats following chronic overexpression of corticotropin-releasing factor from the central amygdala.

We have previously demonstrated that viral-mediated overexpression of corticotropin-releasing factor (CRF) within the central nucleus of the amygdala (CeA) reproduces many of the behavioral and endocrine consequences of chronic stress. The present experiment sought to determine whether administration of the selective serotonin reuptake inhibitor (SSRI) escitalopram reverses the adverse effects of CeA CRF overexpression. In a 2×2 design, adult male rats received bilateral infusions of a control lentivirus or a lentivirus in which a portion of the CRF promoter is used to drive increased expression of CRF peptide. Four weeks later, rats were then implanted with an Alzet minipump to deliver vehicle or 10mg/kg/day escitalopram for a 4-week period of time. The defensive withdrawal (DW) test of anxiety and the sucrose-preference test (SPT) of anhedonia were performed both before and after pump implantation. Additional post-implant behavioral tests included the elevated plus maze (EPM) and social interaction (SI) test. Following completion of behavioral testing, the dexamethasone/CRF test was performed to assess HPA axis reactivity. Brains were collected and expression of HPA axis-relevant transcripts were measured using in situ hybridization. Amygdalar CRF overexpression increased anxiety-like behavior in the DW test at week eight, which was only partially prevented by escitalopram. In both CRF-overexpressing and control groups, escitalopram decreased hippocampal CRF expression while increasing hypothalamic and hippocampal expression of the glucocorticoid receptor (GR). These gene expression changes were associated with a significant decrease in HPA axis reactivity in rats treated with escitalopram. Interestingly, escitalopram increased the rate of weight gain only in rats overexpressing CRF. Overall these data support our hypothesis that amygdalar CRF is critical in anxiety-like behavior; because the antidepressant was unable to reverse behavioral manifestations of CeA CRF-OE. This may be a potential animal model to study treatment-resistant psychopathologies.

Cell-type specific deletion of GABA(A)α1 in corticotropin-releasing factor-containing neurons enhances anxiety and disrupts fear extinction.

Corticotropin-releasing factor (CRF) is critical for the endocrine, autonomic, and behavioral responses to stressors, and it has been shown to modulate fear and anxiety. The CRF receptor is widely expressed across a variety of cell types, impeding progress toward understanding the contribution of specific CRF-containing neurons to fear dysregulation. We used a unique CRF-Cre driver transgenic mouse line to remove floxed GABA(A)α1 subunits specifically from CRF neurons [CRF-GABA(A)α1 KO]. This process resulted in mice with decreased GABA(A)α1 expression only in CRF neurons and increased CRF mRNA within the amygdala, bed nucleus of the stria terminalis (BNST) and paraventricular nucleus of the hypothalamus. These mice show normal locomotor and pain responses and no difference in depressive-like behavior or Pavlovian fear conditioning. However, CRF-GABA(A)α1 KO increased anxiety-like behavior and impaired extinction of conditioned fear, coincident with an increase in plasma corticosterone concentration. These behavioral impairments were rescued with systemic or BNST infusion of the CRF antagonist R121919. Infusion of Zolpidem, a GABA(A)α1-preferring benzodiazepine-site agonist, into the BNST of the CRF-GABA(A)α1 KO was ineffective at decreasing anxiety. Electrophysiological findings suggest a disruption in inhibitory current may play a role in these changes. These data indicate that disturbance of CRF containing GABA(A)α1 neurons causes increased anxiety and impaired fear extinction, both of which are symptoms diagnostic for anxiety disorders, such as posttraumatic stress disorder.

Chronic overexpression of corticotropin-releasing factor from the central amygdala produces HPA axis hyperactivity and behavioral anxiety associated with gene-expression changes in the hippocampus and paraventricular nucleus of the hypothalamus.

Environmental stress has been demonstrated to increase susceptibility for mood and anxiety disorders, and hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, the primary endocrine response to stress, is often observed in these patients. HPA axis activation is initiated by corticotropin-releasing factor (CRF) from the hypothalamus, leading to the hypothesis that hypothalamic CRF overexpression contributes to HPA axis hyperactivity in psychiatric patients. In addition, elevated CRF in cerebrospinal fluid is observed in mood and anxiety disorder patients, suggesting that CRF is also being overproduced from extrahypothalamic sources such as the central amygdala (CeA) and overactivity of the amygdala in neuroimaging studies is a consistent finding in anxiety and depression patients. Due to the importance of CRF and the amygdala in the etiology of stress-sensitive psychiatric disorders, the present study sought to further dissect the impact of CRF overexpression (OE) in the amygdala on downstream behavioral, endocrine, and gene-expression changes typically associated with chronic stress. To test the hypothesis that elevated CRF output from the amygdala would reproduce HPA axis hyperactivity and behavioral symptoms of chronic stress, we developed a lentiviral vector in which 3.0kb of the CRF promoter drives overexpression of CRF (LVCRFp3.0CRF). In adult male rats, Experiment-1 examined behavioral consequences of chronic CRF overexpression from the amygdala; the dexamethasone (Dex)/CRF test was used to measure HPA axis reactivity. Experiment-2 focused on HPA axis disruptions; the dexamethasone-suppression and CRF-stimulation tests as well as the Dex/CRF test were used. In both experiments, expression of HPA-axis related transcripts were assessed.