Gender-related qualitative differences in baseline and post-stress anxiety responses are not reflected in the incidence of criterion-based PTSD-like behaviour patterns

Stress-enhanced ethanol drinking does not increase sensitivity to the effects of a CRF-R1 antagonist on ethanol intake in male and female mice

Research confirms that stress is associated with alcohol drinking and relapse in males and females and that there are sex differences in the alcohol-related adaptations of stress pathways. The predator stress (PS) model of traumatic stress produces an increase in alcohol drinking or self-administration in a subpopulation of rodents, so it is utilized as an animal model of comorbid alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD). Previous work determined that sensitivity to PS-enhanced drinking produced sex differences in proteins related to stress-regulating systems in the medial prefrontal cortex and hippocampus. The present studies examined whether male and female C57BL/6J mice differ in sensitivity to the ability of the corticotropin releasing factor receptor 1 antagonist CP-376395 to decrease PS-enhanced drinking. In control studies, CP-376395 doses of 5, 10, and 20 mg/kg dose-dependently decreased 4-h ethanol drinking. Next, CP-376395 doses of 5 and 10 mg/kg were tested for effects on ethanol drinking in mice with differential sensitivity to PS-enhanced drinking. Subgroups of "Sensitive" and "Resilient" male and female mice were identified based on changes in ethanol intake in an unrestricted-access ethanol-drinking procedure following four exposures to PS (dirty rat bedding). During the first 2 h post-injection of CP-376395, both doses significantly decreased ethanol licks versus vehicle in the females, with no significant interaction between subgroups, whereas the 10 mg/kg dose significantly decreased ethanol licks versus vehicle in the "Resilient" males. Thus, sensitivity to the suppressive effect of CP-376395 on stress-induced ethanol intake was greater in females versus males, whereas sensitivity and resilience to PS-enhanced drinking produced differential sensitivity to the ability of CP-376395 to decrease ethanol drinking only in male mice. Our results argue against greater efficacy of CRF-R1's ability to decrease ethanol intake in subjects with traumatic stress-enhanced ethanol drinking.

The epigenetic changes are affected by sex and valproic acid treatment in a rat model of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) presents distinct sex-specific differences in both symptom expression and treatment outcomes, with the underlying biological mechanisms still remain unclear. Epigenetic modifications, particularly histone acetylation, have been increasingly recognized as critical factors in the pathophysiology of PTSD. Valproic acid (VPA), a potent histone deacetylase (HDAC) inhibitor, has shown promise in modulating epigenetic responses and improving therapeutic outcomes is PTSD, though its effect may differ between sexes. This study aimed to explore the sex-specific epigenetic changes in response to trauma and the impact of VPA treatment in a rat model of PTSD induced by predator scent stress. Sprague-Dawley rats of both sexes were randomly assigned to stressed and non-stressed groups and treated with either VPA (100 mg/kg) or vehicle. Anxiety levels were assessed using the elevated plus maze, followed by analysis of histone H3 and H4 acetylation, HDAC activity, and c-fos expression in the hippocampus. Our findings revealed that traumatic stress led to increased freezing time and anxiety levels, with more pronounced effects observed in females. Additionally, we have identified sex-specific differences in hippocampal epigenetic modifications; stressed females exhibited higher H3 acetylation, and VPA-treated stressed males showed increased H4 acetylation. These results highlight the importance of considering sex differences in the epigenetic mechanism underlying PTSD and suggest that personalized therapeutic approaches may be necessary to address these complexities.

Chronic sleep restriction during juvenility alters hedonic and anxiety-like behaviours in a sex-dependent fashion in adolescent Wistar rats

Chronic reduction of sleep time in children and adolescents has been related to increased incidence of anxiety and depression. In rats, protocols of protracted sleep deprivation or chronic sleep restriction (CSR) are considered a stressor. In previous studies we showed that post-weaning CSR in male rats induces anxiety-like behaviour and changes in neurotransmission in emotion-related brain areas. In the present study we examined whether the effects of this adversity are sex-dependent. Twenty-two litters, containing four males and four females were distributed into control (CTL) and CSR groups. CSR began on postnatal day (PND) 21 and lasted for 21 days; each day the animals were placed onto small platforms immersed in water for 18 h and were allowed to sleep freely in their home-cages for the remaining 6 h. Throughout the CSR, all animals underwent the sucrose splash test once/week to assess their self-care and hedonic behaviours. Body weight was measured on PNDs 21 and 42. At the end of CSR period, the adolescents were allowed to sleep freely for 2 days, after which, behavioural tests began. Within each litter, one male and one female (pair) were not tested and provided blood and brain for determination of basal corticosterone (CORT) levels and hippocampal BDNF. One pair was tested in the sucrose preference test (SPT), one pair on the elevated plus maze (EPM) and one pair in the forced swim test (FST). CORT was measured after all conditions. CSR impaired self-care behaviour and body weight gain in males and females and increased relative adrenal weight only in males. There were no changes in sucrose intake in the SPT; CSR females displayed less immobility in the FST and CSR males displayed more anxiety-like behaviour in the EPM. CORT levels were similar between CTL and CSR males, whilst lower in CSR females than CTL ones in all experimental conditions. No changes in BDNF levels were detected in the dorsal hippocampus of CSR rats. The results indicate that CSR impaired self-care behaviour in both sexes, but only males displayed anxiety-like behaviour, whilst sleep recovery in females appeared to normalise their behaviour.

Combination of UPLC-Q-TOF/MS and network pharmacology to reveal the mechanism of Chaihu-jia-Longgu-Muli decoction for treating vertigo with anxiety disorder

Chaihu-jia-Longgu-Muli decoction (CLMD) has been proven clinically effective in treating vertigo with anxiety disorder. However, the mechanism is not clear. This study aimed to explore the mechanism of CLMD in treating vertigo with anxiety disorder based on ultra-performance liquid chromatography-quadrupole time-of-flight/mass spectrometry (UPLC-Q-TOF/MS) and network pharmacology. UPLC-Q-TOF/MS was performed to identify the compounds in blood and the targets of compounds of CLMD in vertigo and anxiety were searched using databases. A protein-protein interaction network was built to screen the core targets. The core targets were analyzed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. In addition, the vertigo with anxiety rat model was used to verify the results. A total of 22 compounds were absorbed into the blood. Eighty-one potential targets associated with CLMD for vertigo with anxiety disorder were identified through network pharmacological analysis. Subsequently, GO and KEGG analysis showed that CLMD treatment for vertigo with anxiety disorder is associated with neurotransmitter levels and other pertinent physiological processes. The results of the animal experiments showed that CLMD decreased the levels of serotonin, norepinephrine and dopamine, alleviating the symptoms of vertigo and anxiety disorder in model rats. The study revealed CLMD could alleviate vertigo and anxiety symptoms through reducing the levels of neurotransmitters.

Changes in the hippocampal level of tau but not beta-amyloid may mediate anxiety-like behavior improvement ensuing from exercise in diabetic female rats

BACKGROUND

In the present study, we investigated the effect of high-intensity interval training (HIIT) on cognitive behaviors in female rats with a high-fat diet + streptozotocin (STZ)-induced type 2 diabetes.

METHODS

Twenty-four female rats were divided into four groups randomly (n = 6): control (C), control + exercise (Co + EX), diabetes mellitus (type 2) (T2D), and diabetes mellitus + exercise (T2D + EX). Diabetes was induced by a two-month high-fat diet and a single dose of STZ (35 mg/kg) in the T2D and T2D + EX groups. The Co + EX and T2D + EX groups performed HIIT for eight weeks (five sessions per week, running on a treadmill at 80-100% of VMax, 4-10 intervals). Elevated plus maze (EPM) and open field test (OFT) were used for assessing anxiety-like behaviors, and passive avoidance test (PAT) and Morris water maze (MWM) were applied for evaluating learning and memory. The hippocampal levels of beta-amyloid (Aβ) and Tau were also assessed using Western blot.

RESULTS

An increase in fasting blood glucose (FBG), hippocampal level of Tau, and a decrease in the percentage of open arm time (%OAT) as an index of anxiety-like behavior were seen in the female diabetic rats which could be reversed by HIIT. In addition, T2D led to a significant decrease in rearing and grooming in the OFT. No significant difference among groups was seen for the latency time in the PAT and learning and memory in the MWM.

CONCLUSIONS

HIIT could improve anxiety-like behavior at least in part through changes in hippocampal levels of Tau.

Effect of combination fluoxetine and exercise on prefrontal BDNF, anxiety-like behavior and fear extinction in a female rat model of post-traumatic stress disorder (PTSD): a comparison with male animals

Despite significant differences between men and women in the symptoms of PTSD and the response to therapeutic interventions, most PTSD studies have been done on male subjects. Continuing our previous study in male rats, this study aimed at better understanding the effect of a combination therapy of exercise with fluoxetine on female PTSD rats. The results were then compared with our past findings in male animals. Female adult Wistar rats subjected to PTSD were treated with moderate treadmill exercise or fluoxetine, or a combination of both. PTSD was induced by the single prolonged stress (SPS) model. Elevated plus-maze (EPM), serum and prefrontal BDNF, and fear extinctions were evaluated. The results showed that exercise plus fluoxetine decreased anxiety-like behavior, improved fear extinction, and increased BDNF changes in female rats. The effects of exercise alone were comparable with those of combination therapy except that combination therapy was more effective on OAT (open arm entry). The majority of results in female rats, except for those of prefrontal BDNF, 4th extinction, and OAT, were similar to those of male rats as shown in our previous study. According to our findings, exercise as a safe and cost-effective intervention can be considered as a complementary efficient option for PTSD treatment in both sexes. To achieve better treatment outcomes in PTSD patient, considering sex differences is recommended.

Chronic rapid eye movement sleep restriction during juvenility has long-term effects on anxiety-like behaviour and neurotransmission of male Wistar rats

Modernity imposes a toll on the sleep time of young population, with concomitant increase in symptoms of anxiety and depression. Whether there is a causal relationship between these events are only now being experimentally tested in humans and rodents. In a previous study, we showed that chronic sleep deprivation in juvenile-adolescent male rats led to increased anxiety-like behaviour and changes in noradrenaline and serotonin in the amygdala and hippocampus. In the present study we investigated whether early chronic sleep restriction affects emotional behaviour, stress response and neurochemistry in adulthood. From 21 to 42 days of age, Wistar male rats were submitted to sleep restriction by the multiple platform method or allowed to sleep freely. Forty-five days after this period, rats were tested in the elevated plus maze (EPM) and blood samples were collected from non-tested rats or 30 and 60 min after the EPM for determination of plasma corticosterone levels. Levels of monoamines were determined in the frontal cortex, hippocampus, amygdala and hypothalamus 60 min after the EPM. Sleep restriction resulted in increased anxiety-like behaviour, decreased noradrenaline levels in the amygdala and dopamine levels in the ventral hippocampus. Anxiety index was positively correlated with increased serotonin metabolism in the frontal cortex and greater dopamine metabolism in the ventral hippocampus, and negatively correlated with dopamine levels in the ventral hippocampus. These results suggest that sleep restriction in juvenility and adolescence induces persistent changes in emotional behaviour in adult male rats and that levels of anxiety are correlated with increased serotonin and dopamine metabolism in specific brain areas.

Activation of Estrogen Receptor β in the Lateral Habenula Improves Ovariectomy-Induced Anxiety-Like Behavior in Rats

Background

Loss of estrogen due to menopause or ovarian resection is involved in the development of anxiety, which negatively impacts work productivity and quality of life. Estrogen modulates mood by binding to estrogen receptors in the brain. Estrogen receptor beta (ERβ) is highly expressed in the lateral habenula (LHb), a key site for controlling the activities of dopaminergic neurons in the ventral tegmental area (VTA) and serotoninergic neurons in the dorsal raphe nucleus (DRN) that are known to be involved in anxiety.

Methods

In this study, we examined the role of LHb in the anxiolytic-like effect of estrogen in ovariectomized (OVX) rats. The establishment of OVX anxiety model was validated in behavioral tests, including elevated plus maze (EPM) and mirror chamber maze (MCM) tasks. The expression of c-Fos in the LHb neurons was analyzed by immunohistochemistry, and monoamine neurotransmitter levels in related nuclei were analyzed using high-performance liquid chromatography (HPLC).

Results

Estrogen-treated OVX rats showed a lower degree of anxiety-like behavior than OVX rats. OVX rats showed anxiety-like behavior and low monoamine levels in the DRN and VTA compared with sham operated and estrogen-treated OVX rats. c-Fos expression in the LHb was higher than that in the sham operated and estrogen-treated OVX rats. Intra-LHb injection of the ERβ-selective agonist diarylprepionitrile (DPN) reduced expression of c-Fos (a neuronal activity marker) and anxiety-like behavior in OVX rats, but not in normal rats, as evidenced by increased time spent in EPM open areas and the MCM mirror chamber. These changes coincided with higher levels of serotonin and dopamine in the DRN and higher dopamine levels in the VTA in OVX rats receiving intra-LHb DPN compared with those receiving vehicle injection.

Conclusion

These results suggest that OVX-induced anxiety-like behavior may be associated with increased LHb activity. DPN may inhibit LHb activity to improve anxiety-like behavior in OVX rats by increasing monoamine neurotransmitter levels in the DRN and VTA.

The bee venom active compound melittin protects against bicuculline-induced seizures and hippocampal astrocyte activation in rats

Epilepsy is a chronic neuropathology characterized by an abnormal hyperactivity of neurons that generate recurrent, spontaneous, paradoxical and synchronized nerve impulses, leading or not to seizures. This neurological disorder affects around 70 million individuals worldwide. Pharmacoresistance is observed in about 30% of the patients and long-term use of antiepileptics may induce serious side effects. Thus, there is an interest in the study of the therapeutic potential of bioactive substances isolated from natural products in the treatment of epilepsy. Arthropod venoms contain neurotoxins that have high affinity for molecular structures in the neural tissue such as receptors, transporters and ion channels both in glial and neuronal membranes. This study evaluated the potential neuroprotective effect of melittin (MEL), an active compound of bee venom, in the bicuculline-induced seizure model (BIC) in rats. Male Wistar rats (3 months, 250-300 g) were submitted to surgery for the implantation of a unilateral cannula in the lateral ventricle. After the recovery period, rats received a microinjection of saline solution or MEL (0.1 mg per animal). Firstly, rats were evaluated in the open field (20 min) and in the elevated plus maze (5 min) tests after received microinjection of saline or MEL. After, 30 min later animals received BIC (100 mg/ml) or saline, and their behaviors were analyzed for 20 min in the open field according to a seizure scale. At the end, rats were euthanized, brains collected and processed to glial fibrillary acidic protein (GFAP) immunohistochemistry evaluation. No changes were observed in MEL-treated rats in the open field and elevated plus maze. However, 90% of MEL-treated animals were protected against seizures induced by BIC. There was an increase in the latency for the onset of seizures, accompanied by a reduction of GFAP-immunoreactivity cells in the dentate gyrus and CA1. Thus, our study suggests that MEL has an anticonvulsant potential, and further studies are needed to elucidate the mechanisms involved in this action.

Short Juvenile Stress Has No Long-Lasting Effects on Anxiety-Like Behavior, Object Recognition Memory, or Gross Brain Morphology but Affects Dendritic Spines in the Hippocampus in Male Rats

PURPOSE

During the juvenile stage, such areas as the hippocampus and corpus callosum (CC) are still immature and sensitive to stress exposure. The present study investigated whether two different types of stressors in the juvenile stage of life have a long-lasting impact on behavior and biological outcomes in adult rats.

METHODS

Male juvenile rats were exposed to restraint or predator stress on postnatal day 25 (P25) for 3 days. Thirty-two days later (P60-74), behavioral and biological analyses were conducted. The behavioral analysis included measures of anxiety-like behavior and recognition memory. The biological analysis investigated gross cerebral morphology, based on volume analysis of the CC and hippocampus, perirhinal cortex thickness, and dendritic spine density.

RESULTS

Neither restraint stress nor predator stress affected anxiety-like behavior or object recognition memory in adulthood. Body weight and adrenal gland weight were unaffected by both types of stress. Overall, volumetric measures of the CC and hippocampus were not significant, with no changes in perirhinal cortex thickness. Spine density in the medial prefrontal cortex also was unaffected, but a decrease in dendritic spine density was found in the hippocampus in response to restraint stress and an increase to predator stress.

CONCLUSION

Short-term and daily restraint and predator stress during the juvenile stage had no long-lasting effects on anxiety-like behavior, object memory, volume of the CC or hippocampus, or perirhinal cortex thickness, but a decrease in dendritic spine density was found in the hippocampus. These findings suggest that different types of stressors have different impacts on microstructures in the brain without affecting behavior or the gross morphology of stress-sensitive brain areas.

Inducible Nitric Oxide Synthase Inhibition in the Medial Prefrontal Cortex Attenuates the Anxiogenic-Like Effect of Acute Restraint Stress via CB1 Receptors

Stress exposure can result in several proinflammatory alterations in the brain, including overexpression of the inducible isoform of nitric oxide synthase (iNOS) in the medial prefrontal cortex (mPFC). These changes may be involved in the development of many psychiatric conditions. However, it is unknown if iNOS in mPFC plays a significant role in stress-induced behavioral changes. The endocannabinoid (ECB) system is also influenced by stress. Its activation seems to be a counter regulatory mechanism to prevent or decrease the stress-mediated neuroinflammatory consequences. However, it is unclear if the ECB system and iNOS interact to influence stress consequences. This study aimed to test the hypothesis that the anti-stress effect of iNOS inhibition in mPFC involves the local ECB system, particularly the CB₁ cannabinoid receptors. Male Wistar rats with guide cannula aimed at the mPFC were submitted to acute restraint stress (RS) for 2 h. In the following morning, rats received bilateral microinjections of vehicle, AM251 (CB₁ antagonist; 100 pmol), and/or 1400W (iNOS selective inhibitor; 10^-4, 10^-3, or 10^-2 nmol) into the prelimbic area of mPFC (PL-mPFC) before being tested in the elevated plus-maze (EPM). iNOS inhibition by 1400W prevented the anxiogenic-like effect observed in animals submitted to RS. The drug did not promote behavior changes in naive animals, demonstrating a stress-dependent effect. The 1400W-anti-stress effect was prevented by local pretreatment with AM251. Our data suggest that iNOS inhibition may facilitate the local endocannabinoid signaling, attenuating stress effects.

Sex differences in risk behavior parameters in adolescent mice: Relationship with brain-derived neurotrophic factor in the medial prefrontal cortex

Adolescence is as a period of development characterized by impulsive and risk-seeking behaviors. Risk behaviors (RB) involves exposure to dangerous or negative consequences to achieve goal-directed behaviors, such as reward-seeking. On the other hand, risk aversion/assessment behaviors allow the individual to gather information or avoid potentially threatening situations. Evidence has suggested that both behavioral processes, RB and risk assessment (RA), may have sex-differences. However, sex-specific behavioral patterns implicated in RB and RA are not fully understood. To address that, we investigated sex differences in risk-behavioral parameters in a decision-making task developed for rodents. In addition, we investigated the potential role of sex-dependent differences in gene expression of brain-derived neurotrophic factor (BDNF) exon IV in the medial prefrontal cortex (mPFC), which has been implicated to mediate PFC-related behavioral dysfunctions. Male and female C57BL/6J adolescent mice were evaluated in the elevated plus-maze (EPM) to assess anxiety-like behaviors and in the predator-odor risk taking (PORT) task. The PORT task is a decision-making paradigm in which a conflict between the motivation towards reward pursuit and the threat elicited by predatory olfactory cues (coyote urine) is explored. After behavioral testing, animals were euthanized and BDNF exon IV gene expression was measured by RT-qPCR. Comparative and correlational analyses for behavioral and molecular parameters were performed for both sexes. We observed that female mice spent more time exploring the middle chamber of the PORT apparatus in the aversive condition, which is an indicative of avoidance behavior. Female mice also had a higher latency to collect the reward than male mice and presented less time exploring the open arms of the EPM. BDNF exon IV gene expression was higher among females, and there was a positive correlation between the BDNF and PORT behavioral parameters. Our findings suggest sex-dependent effects in the PORT task. Females presented higher RA and avoidance behavior profile and expressed higher levels of BDNF exon IV in the mPFC. Moreover, higher BDNF expression was correlated with RA behaviors, which suggests that adolescent females tend to evaluate the risks more than adolescent males and that BDNF gene expression may be mediating decision-making processes.

Effect of treadmill exercise on serum corticosterone, serum and hippocampal BDNF, hippocampal apoptosis and anxiety behavior in an ovariectomized rat model of post-traumatic stress disorder (PTSD)

There is a sex difference in vulnerability to PTSD and in response to therapeutic interventions. Since relation between gonadal hormones and PTSD has been revealed, this study aimed to understand the severity of PTSD-induced impairments after ovarian hormone deficiency and the influence of exercise on PTSD accompanied by ovarian hormone deficiency. Female adult Wistar rats were subjected to ovariectomy, PTSD, or combination ovariectomy plus PTSD. Twenty days after ovariectomy, PTSD was induced by single prolonged stress (SPS) model. The exercise started 14 days after SPS and continued for 4 weeks. Thirty minutes moderate treadmill exercise was planned for 5 days per week. On day 65, after assessing rats using the elevated plus-maze (EPM) test, corticosterone, BDNF, and apoptotic markers were tested. p < 0.05 was considered as significant level. The results showed that ovariectomy worsened the effect of SPS on hippocampal BDNF and led to greater increase in serum corticosterone and hippocampal caspase 3 and BAX in SPS rats. Also, ovariectomy exacerbated anxiety-like behavior in SPS rats. Exercise improved the alterations of hippocampal BDNF, corticosterone, caspase 3, and BAX in SPS ovariectomized rats. However, exercise had no statistically significant effect on anxiety-like behavior in this group. According to the results, exercise is effective to attenuate SPS-induced impairments in molecular and cellular responses even when the condition becomes more complicated due to ovarian hormone deficiency. However, exercise alone cannot help to improve behavior impairments in PTSD combined with an ovarian hormone deficiency. Therefore, exercise could likely be considered as a complementary intervention to strengthen other treatments.

Increased mGlu5 mRNA expression in BLA glutamate neurons facilitates resilience to the long-term effects of a single predator scent stress exposure

Post-traumatic stress disorder (PTSD) develops in a subset of individuals exposed to a trauma with core features being increased anxiety and impaired fear extinction. To model the heterogeneity of PTSD behavioral responses, we exposed male Sprague-Dawley rats to predator scent stress once for 10 min and then assessed anxiety-like behavior 7 days later using the elevated plus maze and acoustic startle response. Rats displaying anxiety-like behavior in both tasks were classified as stress Susceptible, and rats exhibiting behavior no different from un-exposed Controls were classified as stress Resilient. In Resilient rats, we previously found increased mRNA expression of mGlu5 in the amygdala and prefrontal cortex (PFC) and CB1 in the amygdala. Here, we performed fluorescent in situ hybridization (FISH) to determine the subregion and cell-type-specific expression of these genes in Resilient rats 3 weeks after TMT exposure. Resilient rats displayed increased mGlu5 mRNA expression in the basolateral amygdala (BLA) and the infralimbic and prelimbic regions of the PFC and increased BLA CB1 mRNA. These increases were limited to glutamatergic cells. To test the necessity of mGlu5 for attenuating TMT-conditioned contextual fear 3 weeks after TMT conditioning, intra-BLA infusions of the mGlu5 negative allosteric modulator MTEP were administered prior to context re-exposure. In TMT-exposed Resilient rats, but not Controls, MTEP increased freezing on the day of administration, which extinguished over two additional un-drugged sessions. These results suggest that increased mGlu5 expression in BLA glutamate neurons contributes to the behavioral flexibility observed in stress-Resilient animals by facilitating a capacity for extinguishing contextual fear associations.

Early life stress alters emotional learning in a sex- and age-dependent manner with no impact on emotional behaviors

Neonatal adversity can impact neurodevelopmental trajectories. This study examined the long-term effects of maternal deprivation on day 9 (DEP9), associated or not to a stressor (saline injection [SAL]), on contextual fear conditioning (Experiment 1) and emotional behaviors (Experiment 2) in Wistar rats. Whole litters were either assigned to DEP9 or control groups, and on day 10, half of the litters in each group received an SAL or not (NSAL). DEP9-SAL male adolescents showed the longest freezing time and DEP9 adult males froze more than females. Females exhibited less anxiety-like behavior than males; DEP9-SAL females spent more time in the open arms and DEP9 males visited less the extremity of the open arm in the elevated plus maze. Early life stress increased conditioned and innate fear in males, but not in females, indicating a clear sexual dimorphism in the response to potentially threatening stimuli.

TRPA1 involvement in depression- and anxiety-like behaviors in a progressive multiple sclerosis model in mice

Progressive multiple sclerosis (PMS) is a neurological disease associated with the development of depression and anxiety, but treatments available are unsatisfactory. The transient receptor potential ankyrin 1 (TRPA1) is a cationic channel activated by reactive compounds, and the blockage of this receptor can reduce depression- and anxiety-like behaviors in naive mice. Thus, we investigated the role of TRPA1 in depression- and anxiety-like behaviors in a PMS model in mice. PMS model was induced in C57BL/6 female mice by the experimental autoimmune encephalomyelitis (EAE). Nine days after the PMS-EAE induction, behavioral tests (tail suspension and elevated plus maze tests) were performed to verify the effects of sertraline (positive control), selective TRPA1 antagonist (A-967,079), and antioxidants (α-lipoic acid and apocynin). The prefrontal cortex and hippocampus were collected to evaluate biochemical and inflammatory markers. PMS-EAE induction did not cause locomotor changes but triggered depression- and anxiety-like behaviors, which were reversed by sertraline, A-967,079, α-lipoic acid, or apocynin treatments. The neuroinflammatory markers (AIF1, GFAP, IL-1β, IL-17, and TNF-α) were increased in mice's hippocampus. Moreover, this model did not alter TRPA1 RNA expression levels in the hippocampus but decrease TRPA1 levels in the prefrontal cortex. Moreover, PMS-EAE induced an increase in NADPH oxidase and superoxide dismutase activities and TRPA1 endogenous agonist levels (hydrogen peroxide and 4-hydroxynonenal). TRPA1 plays a fundamental role in depression- and anxiety-like behaviors in a PMS-EAE model; thus, it could be a possible pharmacological target for treating these symptoms in PMS.

Immune receptor toll-like receptor 4 contributes to stress-induced affective responses in a sex-specific manner

Stress activates innate immune Toll-like receptors (TLRs) and enhances susceptibility to depression, a condition that is more prevalent in females. The TLR4 receptor type is involved in inflammatory responses and its expression levels associate with depressive symptoms and their successful treatment. Yet, little preclinical research has examined the role of TLR4 in stress-induced affective responses to determine if these are sex-specific. One group per genotype of male and female Tlr4 knockout (KO) and wild type (WT) rats were exposed to predator odor in a place conditioning apparatus with others exposed to saline. Affective behaviors evaluated included distance traveled and center time in an open-field apparatus, sucrose preference and fluid intake in a two-bottle test, and conditioned place aversion to the odor-paired compartment. Predator odor exposed rats showed conditioned place aversion to the odor-paired compartment, demonstrating predator odor was aversive. Such exposure led to anhedonia (decreased sucrose preference) across genotypes and sex. Predator odor exposure decreased distance traveled, an effect that was greater in KO rats, especially in females. Tlr4 deletion also resulted in sex-specific effects on anxiety-like behavior. Compared to WTs, female KO rats showed lower center time after predator odor exposure whereas genotype did not affect this response in male rats. Across litters, fewer male KO and heterozygous rats and more WT rats were born whereas female rats showed the typical genotype distribution. Results suggest predator odor alters affective behaviors, consistent with the preclinical literature, and deletion of Tlr4 enhances some stress-induced affective responses, often in a sex-specific manner.

Chronic Escitalopram Treatment Does Not Alter the Effects of Neonatal Stress on Hippocampal BDNF Levels, 5-HT1A Expression and Emotional Behaviour of Male and Female Adolescent Rats

Early life stress is considered a risk factor for the development of long-term psychiatric disorders. Maternal deprivation (MD) is a useful paradigm to understand the neurobiological underpinnings of early stress-induced changes in neurodevelopment trajectory. The goal of the present study was to examine the effects of a chronic treatment with escitalopram (ESC) on the hippocampal levels of BDNF and neuropeptide Y (NPY), expression of serotonin type 1A receptor (5-HT1A), plasma corticosterone levels and emotional behaviours in male and female adolescent rats submitted to MD at 9 days of life (group DEP9) and challenged with a brief and mild stress (saline injection (SAL)) at the end of MD. Whole litters were kept with mothers (CTL) or submitted to MD (DEP9). Within each group, pups were stress-challenged (CTL-SAL and DEP9-SAL) or not (CTL-NSAL and DEP9-NSAL). ESC or vehicle treatments began at weaning and lasted 24 days, when animals were sacrificed for determination of neurobiological variables or submitted to a battery of tests for evaluation of emotional behaviours. The results showed that BDNF levels were higher in SAL-challenged males and in DEP9-SAL females, whereas 5-HT1A receptor expression was reduced in DEP9 males and in SAL-challenged females. There were no changes in NPY or corticosterone levels. In the forced swim test, SAL-challenged males and DEP9 females displayed less immobility and ESC only increased social motivation in males. The results indicated that neonatal stress led to sex-dependent changes in neurobiology and behaviour and that chronic ESC treatment had minor effects on these parameters.

Acquisition of remifentanil self-administration: Enhanced in female rats but no effect of adolescent stress exposure

Animal models of acquisition have been vital in shaping our understanding of vulnerability factors that influence susceptibility to drugs of abuse. Decades of research substantiates a number of biological, environmental, and behavioral factors that predict vulnerability - many of which have been important in the development of early intervention efforts in humans. The goal of the present study was to examine the acquisition of a synthetic opioid derivative in 66 adult male and female Long-Evans rats following histories of stress exposure during adolescence. Stress-exposed rats were subjected to a mild stress paradigm, which included alternating exposure to synthetic fox feces and physical restraint for eight days. Following stress induction and assessment, all rats were implanted with intravenous catheters in order to self-administer remifentanil (1 μm/kg/infusion) with no prior operant training. Acquisition of remifentanil self-administration was measured over 15 days. Findings indicate that regardless of stress condition, female rats acquired remifentanil self-administration sooner and emitted more active lever presses than males. Stress exposed animals exhibited increased anxiety-like response compared to the control group following exposure to stress, operationalized as decreased exploratory behavior on an Elevated Plus Maze. However, these effects were not expressed as significant differences in self-administration by stress. Together, these findings indicate that sex differences are evident in remifentanil self-administration.

The Neurochemical Effects of Prazosin Treatment on Fear Circuitry in a Rat Traumatic Stress Model

Objective

The timing of administration of pharmacologic agents is crucial in traumatic stress since they can either potentiate the original fear memory or may cause fear extinction depending on the phase of fear conditioning. Brain noradrenergic system has a role in fear conditioning. Data regarding the role of prazosin in traumatic stress are controversial.

Methods

In this study, we examined the effects of prazosin and the noradrenergic system in fear conditioning in a predator stress rat model. We evaluated the direct or indirect effects of stress and prazosin on noradrenaline (NA), gamma-aminobuytyric acid (GABA), glutamate, glycine levels and choline esterase activity in the amygdaloid complex, the dorsal hippocampus, the prefrontal cortex and the rostral pons.

Results

Our results demonstrated that prazosin might alleviate defensive behaviors and traumatic stress symptoms when given during the traumatic cue presentation in the stressed rats. However prazosin administration resulted in higher anxiety levels in non stressed rats when the neutral cue was presented.

Conclusion

Prazosin should be used in PTSD with caution because prazosin might exacerbate anxiety in non-traumatized subjects. However prazosin might as well alleviate stress responses very effectively. Stress induced changes included increased NA and GABA levels in the amygdaloid complex in our study, attributing noradrenaline a possible inhibitory role on fear acquisition. Acetylcholine also has a role in memory modulation in the brain. We also demonstrated increased choline esterase acitivity. Cholinergic modulation might be another target for indirect prazosin action which needs to be further studied.

Hydroalcoholic extract of leaf of Arachis hypogaea L. (Fabaceae) did not induce toxic effects in the repeated-dose toxicity study in rats

Arachis hypogaea L. (peanut) leaf is traditionally used for the treatment of insomnia in Asia. However, studies describing the safety and toxicity profile for this plant preparation are limited. Thus, the goal of this study was to investigate the toxicity of peanut leaf hydroalcoholic extract (PLHE) repeated treatment. The extract was administered orally (100, 300 or 1000 mg/kg) in male and female Wistar rats for 28 days (OECD guideline 407). PLHE treatment did not cause mortality or weight variation in the animals. Also, there was no alteration on locomotor activity (open field test), motor coordination (rotarod test), or anxiety behaviour (elevated plus-maze test). Male rats had a reduction in relative liver weight (100 mg/kg) and an increase in total kidney weight (1000 mg/kg), but there was no change in biochemical and haematological parameters after PLHE treatment. Free extracellular double-stranded DNA (dsDNA) levels was also evaluated, but PLHE treatment did not increase this parameter in rat organs. Also, the dose of 1000 mg/kg of PLHE significantly increased the total thiols in the liver of females compared with the control animals. Thus, PLHE did not induce toxicity after repeated exposure for 28 days in rats.

Rodent models of post-traumatic stress disorder: behavioral assessment

Although the etiology and expression of psychiatric disorders are complex, mammals show biologically preserved behavioral and neurobiological responses to valent stimuli which underlie the use of rodent models of post-traumatic stress disorder (PTSD). PTSD is a complex phenotype that is difficult to model in rodents because it is diagnosed by patient interview and influenced by both environmental and genetic factors. However, given that PTSD results from traumatic experiences, rodent models can simulate stress induction and disorder development. By manipulating stress type, intensity, duration, and frequency, preclinical models reflect core PTSD phenotypes, measured through various behavioral assays. Paradigms precipitate the disorder by applying physical, social, and psychological stressors individually or in combination. This review discusses the methods used to trigger and evaluate PTSD-like phenotypes. It highlights studies employing each stress model and evaluates their translational efficacies against DSM-5, validity criteria, and criteria proposed by Yehuda and Antelman's commentary in 1993. This is intended to aid in paradigm selection by informing readers about rodent models, their benefits to the clinical community, challenges associated with the translational models, and opportunities for future work. To inform PTSD model validity and relevance to human psychopathology, we propose that models incorporate behavioral test batteries, individual differences, sex differences, strain and stock differences, early life stress effects, biomarkers, stringent success criteria for drug development, Research Domain Criteria, technological advances, and cross-species comparisons. We conclude that, despite the challenges, animal studies will be pivotal to advances in understanding PTSD and the neurobiology of stress.

The potential role of the HCN1 ion channel and BDNF-mTOR signaling pathways and synaptic transmission in the alleviation of PTSD

The function of the hyperpolarization-activated cyclic nucleotide-gated channel 1 (HCN1) and the expression of brain-derived neurotrophic factor (BDNF) may be involved in the pathogenesis of post-traumatic stress disorder (PTSD). This study aims to explore the role of the HCN1 channel, BDNF, and mTOR in the actions of PTSD and to examine whether synaptic transmission or plasticity is involved in the regulation of this disease. In the present study, rats were exposed to the single prolonged stress and electric foot shock (SPS&S) procedure, which can induce PTSD-like behaviors in rats. ZD7288 was administered by intracerebroventricular (i.c.v.) injection to one experimental group to inhibit the function of the HCN1 ion channel while 8-Br-cAMP was administered to another group to activate the function of the HCN1 ion channel. A series of behavioral tests and biochemical assessments of certain proteins (HCN1, BDNF, and pmTOR) and synaptic ultrastructure in the prefrontal cortex (PFC) and hippocampus (Hip) were then conducted. The SPS&S procedure induced apparent PTSD-like symptoms in rats. The administration of ZD7288 reduced the immobility time and escape latency time in the forced swim test (FST) and water maze test (WMT) with a decreased level of HCN1, upregulated BDNF-mTOR signaling pathways in the PFC and Hip, and synaptic ultrastructure changes in the PFC. In contrast, the administration of 8-Br-cAMP, which led to a higher level of HCN1 in PFC and Hip, resulted in a decreased number of entries to the open arms without significant change in total arm entries in the elevated plus maze test (EPMT) as well as a shorter center square distance and total distance in the open field test (OFT). Extended escape latency time was also observed in the WMT although there was no alteration of BDNF-mTOR signaling pathways and synaptic ultrastructure in the PFC and Hip. Overall, the inhibition of HCN1, which can alleviate PTSD-like behavior of rats by relieving depression and improving learning ability, may be related to the upregulated BDNF-mTOR signaling pathways and synaptic transmission.

Evaluation of the Effect of Prazosin Treatment on α-2c Adrenoceptor and Apoptosis Protein Levels in the Predator Scent-Induced Rat Model of Post-Traumatic Stress Disorder

The predator scent-induced (PSI) stress model is a rat model used to mimic post-traumatic stress disorder (PTSD) symptoms in humans. There is growing evidence that prazosin, which blocks α-1 and is approved by the FDA as an anti-hypertensive drug, can potentially be of use in the treatment of PTSD-related sleep disorders. The aim of this study was to investigate the role of prazosin treatment on behavioral parameters (freezing time, total transitions, and rearing frequency measured from the open field; anxiety index, total entries and time spent in open arms calculated from the elevated plus maze), apoptotic proteins and α-2c-AR in fear memory reconsolidation in the PSI stress rat model. We used western blot analysis to determine the effect of prazosin (0.5 mg/kg/ip) on α-2c-AR and apoptotic protein expression changes in the frontal cortex, hippocampus, and amygdala. It was determined that in the stress group, there was increased freezing time and anxiety index, and decreased rearing frequency, total transitions, total entries, and time spent in open arms compared to the control groups. Following PSI-stress, pro-apoptotic (bax) protein expression levels increased and α-2c AR and anti-apoptotic protein (bcl-2) levels decreased in investigated all brain regions. The majority of stress-induced changes were recovered with prazosin treatment. The results of our study may potentially be useful in understanding the effect of prazosin treatment, given the fact that the amygdala, frontal cortex, and hippocampus regions are affected for stress conditions.

Animal models of post-traumatic stress disorder and novel treatment targets

Understanding the neurobiological basis of post-traumatic stress disorder (PTSD) is fundamental to accurately diagnose this neuropathology and offer appropriate treatment options to patients. The lack of pharmacological effects, too often observed with the most currently used drugs, the selective serotonin reuptake inhibitors (SSRIs), makes even more urgent the discovery of new pharmacological approaches. Reliable animal models of PTSD are difficult to establish because of the present limited understanding of the PTSD heterogeneity and of the influence of various environmental factors that trigger the disorder in humans. We summarize knowledge on the most frequently investigated animal models of PTSD, focusing on both their behavioral and neurobiological features. Most of them can reproduce not only behavioral endophenotypes, including anxiety-like behaviors or fear-related avoidance, but also neurobiological alterations, such as glucocorticoid receptor hypersensitivity or amygdala hyperactivity. Among the various models analyzed, we focus on the social isolation mouse model, which reproduces some deficits observed in humans with PTSD, such as abnormal neurosteroid biosynthesis, changes in GABAA receptor subunit expression and lack of pharmacological response to benzodiazepines. Neurosteroid biosynthesis and its interaction with the endocannabinoid system are altered in PTSD and are promising neuronal targets to discover novel PTSD agents. In this regard, we discuss pharmacological interventions and we highlight exciting new developments in the fields of research for novel reliable PTSD biomarkers that may enable precise diagnosis of the disorder and more successful pharmacological treatments for PTSD patients.

Endocannabinoids and Fear-Related Behavior in Mice Selectively Bred for High or Low Alcohol Preference

Alcohol use disorders (AUDs) have a high incidence of co-morbidity with stress-related psychopathologies, such as post-traumatic stress disorder (PTSD). Genetic and pharmacological studies support a prominent role for the endocannabinoid system (ECS) in modulating stress-related behaviors relevant to AUDs and PTSD. Mouse lines selectively bred for high (HAP) and low (LAP) alcohol preference show reproducible differences in fear-potentiated startle (FPS), a model for PTSD-related behavior. The first experiment in this study assessed levels of the endocannabinoids, anandamide (AEA) and sn-2 arachidonylglycerol (2-AG), in the prefrontal cortex (PFC), amygdala (AMG), and hippocampus (HIP) of male and female HAP1 and LAP1 mice following the expression of FPS to determine whether ECS responses to conditioned-fear stress (FPS) were correlated with genetic propensity toward high or low alcohol preference. The second experiment examined effects of a cannabinoid receptor type 1 agonist (CP55940) and antagonist (rimonabant) on the expression of FPS in HAP1 and LAP1 male and female mice. The estrous cycle of females was monitored throughout the experiments to determine if the expression of FPS differed by stage of the cycle. FPS was greater in male and female HAP1 than LAP1 mice, as previously reported. In both experiments, LAP1 females in diestrus displayed greater FPS than LAP1 females in metestrus and estrus. In the AMG and HIP, AEA levels were greater in male fear-conditioned HAP1 mice than LAP1 mice. There were no line or sex differences in effects of CP55940 or rimonabant on the expression of FPS. However, surprisingly, evidence for anxiogenic effects of prior treatment with CP55940 were seen in all mice during the third drug-free FPS test. These findings suggest that genetic differences in ECS function in response to fear-conditioning stress may underlie differences in FPS expression in HAP1 and LAP1 selected lines.

A predator-based psychosocial stress animal model of PTSD in females: Influence of estrous phase and ovarian hormones

Traumatized women are more likely than traumatized men to develop post-traumatic stress disorder (PTSD). Still, the inclusion of females in animal models of PTSD has largely been avoided, likely due to the variable hormone profile of female rodents. Because a valid animal model of PTSD that incorporates females is still needed, we examined the influence of estrous stage and ovarian hormones on the female rat response to a predator-based psychosocial stress model of PTSD. Female Sprague-Dawley rats were exposed to psychosocial stress or control conditions for 31 days. Stressed rats were given two cat exposures and daily social instability; control rats were handled daily. Beginning on Day 32, rats underwent physiological or behavioral testing. In Experiment 1, vaginal smears were collected on days of the first and second cat exposures and each day of behavioral testing to determine estrous stage. In Experiments 2 and 3, ovariectomized or sham control rats were exposed to stress or control conditions. Then, they were given behavioral testing (Exp 2), or their hearts were isolated and subjected to ischemia/reperfusion on a Langendorff isolated heart system (Exp 3). Chronic stress increased anxiety-like behavior, irrespective of estrous stage or ovariectomy condition. Ovariectomized females displayed greater startle responses and anxiety-like behavior than sham rats. Stress had no impact on myocardial sensitivity to ischemic injury; however, ovariectomized females exhibited greater ischemia-induced infarction than sham rats. These findings suggest that ovarian hormones may prevent anxiety-like behavior and be cardioprotective in non-stressed controls, but they do not interact with chronic stress to influence the development of PTSD-like sequelae in female rats.

Modulation of Hippocampal Antioxidant Defense System in Chronically Stressed Rats by Lithium

This study examined the effects of lithium on gene expression and activity of the antioxidant enzymes copper zinc superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) in the hippocampus of chronically stressed rats. In addition, we examined the effects of lithium on anxiety behaviors, hippocampal concentrations of dopamine (DA) and malondialdehyde (MDA), protein levels of brain-derived neurotrophic factor (BDNF), tyrosine hydroxylase (TH), dopamine transporter (DAT), and catechol-O-methyltransferase (COMT), as well as activity of monoamine oxidase (MAO) in chronically stressed rats. The investigated parameters were quantified by real-time RT-PCR, Western blot analyses, and assays of enzyme activities. We found that lithium did not change gene expression of SOD1, CAT, GPx, and GR but decreased gene expression of SOD2 in chronically stressed rats. A very important result in this study was that lithium treatment decreased the enzyme activities of SOD1 and SOD2 but increased the enzyme activities of GPx and GR in stress condition, which indicates the control of redox balance. The reduced concentration of MDA confirms this. In addition, we found that lithium treatment decreased high protein levels of BDNF and DAT in chronically stressed rats to the level found in unstressed animals. Also, lithium treatment increased the expression of TH but decreased the enzyme activity of MAO B, which contributed to the increase of hippocampal concentration of DA in chronically stressed rats to the level of unstressed animals. Finally, lithium treatment in animals exposed to chronic stress increased the time spent in open arms. Lithium-induced modulation of hippocampal antioxidant status and attenuation of oxidative stress stabilized behavior in animals with high anxiety index. In addition, reduced oxidative stress was followed by the changes of both turnover of DA and levels of BDNF protein in chronically stressed rats treated with lithium. These findings may be important in preclinical research of the effects of lithium on oxidative stress level in pathological conditions.

Single Prolonged Stress as a Prospective Model for Posttraumatic Stress Disorder in Females

Sex plays an important role in susceptibility to stress triggered disorders. Posttraumatic Stress disorder (PTSD), a debilitating psychiatric disorder developed after exposure to a traumatic event, is two times more prevalent in women than men. However, the vast majority of animal models of PTSD, including single prolonged stress (SPS), were performed mostly with males. Here, we evaluated SPS as an appropriate PTSD model for females in terms of anxiety, depressive symptoms and changes in gene expression in the noradrenergic system in the brain. In addition, we examined intranasal neuropeptide Y (NPY) as a possible treatment in females. Female rats were subjected to SPS and given either intranasal NPY or vehicle in two separate experiments. In the first experiment, stressed females were compared to unstressed controls on forced swim test (FST) and for levels of expression of several genes in the locus coeruleus (LC) 12 days after SPS exposure. Using a separate cohort of animals, experiment two examined stressed females and unstressed controls on the elevated plus maze (EPM) and LC gene expression 7 days after SPS stressors. SPS led to increased anxiety-like behavior on EPM and depressive-like behavior on FST. Following FST, the rats displayed elevated tyrosine hydroxylase (TH), CRHR1 and Y1R mRNA levels in the LC, consistent with increased activation of the noradrenergic system. The expression level of these mRNAs was unchanged following EPM, except Y1R. Intranasal NPY at the doses shown to be effective in males, did not prevent development of depressive or anxiety-like behavior or molecular changes in the LC. The results indicate that while SPS could be an appropriate PTSD model for females, sex differences, such as response to NPY, are important to consider.

Maternal Deprivation Increases Anxiety- and Depressive-Like Behaviors in an Age-Dependent Fashion and Reduces Neuropeptide Y Expression in the Amygdala and Hippocampus of Male and Female Young Adult Rats

Maternal deprivation for 24 h produces an immediate increase in basal and stress-induced corticosterone (CORT) secretion. Given the impact of elevated CORT levels on brain development, the goal of the present study was to characterize the effects of maternal deprivation at postnatal days 3 (DEP3) or 11 (DEP11) on emotional behavior and neuropeptide Y immunoreactivity (NPY-ir) in the basolateral amygdala (BLA) and dorsal hippocampus (dHPC) of male and female rats. Litters were distributed in control non-deprived (CTL), DEP3, or DEP11 groups. In Experiment 1, within each litter, one male and one female were submitted to one of the following tests: novelty suppressed feeding (NSF), sucrose negative contrast test (SNCT), and forced swimming test (FST), between postnatal days 52 and 60. In Experiment 2, two males and two females per litter were exposed to the elevated plus maze and 1 h later, perfused for investigation of NPY-ir, on PND 52. The results showed that DEP3 rats displayed greater anxiety-like behavior in the NSF and EPM, compared to CTL and DEP11 counterparts. In the SNCT, DEP3 and DEP11 males showed less suppression of the lower sucrose concentration intake, whereas all females suppressed less than males. Both manipulated groups displayed more immobility in the FST, although this effect was greater in DEP3 than in DEP11 rats. NPY-ir was reduced in DEP3 and DEP11 males and females in the BLA, whereas in the dHPC, DEP3 males showed less NPY-ir than DEP11, which, in turn, presented less NPY-ir than CTL rats. Females showed less NPY-ir than males in both structures. Because the deprivation effects were more intense in DEP3 than in DEP11, in Experiment 3, the frequency of nursing posture, licking-grooming, and interaction with pups was assessed upon litter reunion with mothers. Mothers of DEP11 litters engaged more in anogenital licking than mothers of DEP3 litters. The present results indicate that maternal deprivation changed affective behavior with greater impact in the earlier age and reduced the expression of NPY in emotion-related brain areas. The age-dependent differential effects of deprivation on maternal behavior could, at least in part, explain the outcomes in young adult rats.

Sex differences in the traumatic stress response: PTSD symptoms in women recapitulated in female rats

Background

Post-traumatic stress disorder (PTSD) affects men and women differently. Not only are women twice as likely as men to develop PTSD, they experience different symptoms and comorbidities associated with PTSD. Yet the dearth of preclinical research on females leaves a notable gap in understanding the underlying neuropathology of this sex difference.

Methods

Using two standard measures of PTSD-like responses in rats, the acoustic startle response (ASR) and dexamethasone suppression test (DST), we tested the effects of traumatic stress in adult male and female rats using two rodent models of PTSD, single prolonged stress and predator exposure. We then examined the neural correlates underlying these responses with cFos and glucocorticoid receptor immunohistochemistry in brain regions implicated in the traumatic stress response.

Results

We now report that adult male and female rats across two models of PTSD show consistent sex-specific responses that recapitulate fundamental differences of PTSD in men and women. Trauma-exposed males showed the well-established hyper-responsive phenotype of enhanced ASR and exaggerated negative feedback control of the hypothalamic-pituitary-adrenal axis, while the same traumatic event had little effect on these same measures in females. Dramatic sex differences in how trauma affected cFos and glucocorticoid receptor expression in the brain lend further support to the idea that the trauma response of male and female rats is fundamentally different.

Conclusions

Two standard measures, ASR and DST, might suggest that females are resilient to the effects of traumatic stress, but other measures make it clear that females are not resilient, but simply respond differently to trauma. The next important question to answer is why. We conclude that males and females show fundamentally different responses to trauma that do not simply reflect differences in resilience. The divergent effects of trauma in the brains of males and females begin to shed light on the neurobiological underpinnings of these sex differences, paving the way for improved diagnostics and therapeutics that effectively treat both men and women.

Electronic supplementary material

The online version of this article (10.1186/s13293-018-0191-9) contains supplementary material, which is available to authorized users.

Association of 24 h maternal deprivation with a saline injection in the neonatal period alters adult stress response and brain monoamines in a sex-dependent fashion

Maternal deprivation (MD) disinhibits the adrenal glands, rendering them responsive to various stressors, including saline injection, and this increased corticosterone (CORT) response can last for as long as 2 h. In the present study, we tested the hypothesis that association of MD on day 11 with a saline injection would alter emotional behavior, CORT response, and brain monoamine levels, in male and female adult rats. Rats were submitted to the novelty suppressed feeding (NSF), the sucrose negative contrast test (SNCT), social investigation test (SIT), and the elevated plus maze (EPM). One quarter of each group was not tested (providing basal values of CORT and brain monoamines) and the remainder was decapitated 15, 45, or 75 min after the EPM, to assess CORT reactivity. Monoamine levels were determined in the hypothalamus (HPT), frontal cortex (FC), amygdala (AMY), ventral, and dorsal hippocampus (vHPC, dHPC, respectively). MD reduced food intake, in the home-cage, and latency to eat in the NSF in both sexes; females explored less the target animal in the SIT and explored more the open arms of the EPM than males; the CORT response to the EPM was greater in maternally-deprived males and females than in their control counterparts, and this response was further elevated in maternally-deprived females injected with saline. Regarding monoamine levels, females were less affected, showing isolated effects of the stressors, while in males, MD increased 5-HT levels in the HPT and decreased this monoamine in the FC, MD associated with saline reduced dopamine levels in all brain regions, except the HPT. MD at 11 days did not alter emotional behaviors in adult rats, but had an impact in neurobiological parameters associated with this class of behaviors. The impact of MD associated with saline on dopamine levels suggests that males may be vulnerable to motivation-related disorders.

Neonatal Stress Has a Long-Lasting Sex-Dependent Effect on Anxiety-Like Behavior and Neuronal Morphology in the Prefrontal Cortex and Hippocampus

The long-lasting effects of early stress on brain development have been well studied. Recent evidence indicates that males and females respond differently to the same stressor. We examined the chronic effects of daily maternal separation (MS) on behavior and cerebral morphology in both male and female rats. Cognitive and anxiety-like behaviors were evaluated, and neuroplastic changes in 2 subregions of the prefrontal cortex (dorsal agranular insular cortex [AID] and cingulate cortex [Cg3]) and hippocampus (CA1 and dentate gyrus) were measured in adult male and female rats. The animals were subjected to MS on postnatal day (P) 3-14 for 3 h per day. Cognitive and emotional behaviors were assessed in the object/context mismatch task, elevated plus maze, and locomotor activity test in early adulthood (P87-P95). Anatomical assessments were performed in the prefrontal cortex (i.e., cortical thickness and spine density) and hippocampus (i.e., spine density). Sex-dependent effects were observed. MS increased anxiety-related behavior only in males, whereas locomotor activity was higher in females, with no effects on cognition. MS decreased spine density in the AID and increased spine density in the CA1 area in males. Females exhibited an increase in spine density in the Cg3. Our findings confirm previous work that found that MS causes long-term behavioral and anatomical effects, and these effects were dependent on sex and the duration of MS stress.

Agomelatine protects against neuronal damage without preventing epileptogenesis in the kainate model of temporal lobe epilepsy

Recent studies about the novel antidepressant agomelatine, which is a mixed MT₁ and MT₂ melatonin receptor agonist and 5HT_2C serotonin receptor antagonist possessing an anticonvulsant and neuroprotective action, suggest that it may have potential to contribute against epileptogenesis and epilepsy-induced memory impairment. In order to ascertain whether protection of some brain structures could suppress epileptogenesis, in the present study, we evaluated the effect of chronic post-status treatment with agomelatine on epileptogenesis, behavioral and neuronal damage induced by kainate acid (KA) status epilepticus (SE). Agomelatine/vehicle treatment (40mg/kg, i.p.) started one hour after SE and continued up to 10weeks in Wistar rats. Latency for onset of spontaneous motor seizures (SMS) and their frequency was detected by a 24-h video-recording. Locomotor activity, anxiety and hippocampus-dependent spatial memory in open field (OF), elevated plus maze (EPM), light-dark test (LDT) and radial arm maze (RAM) test, respectively, were evaluated during the last two weeks after SE. Agomelatine significantly decreased the latency for onset of SMS and increased the seizure frequency during the 2nd and the 3rd week of treatment. The MT₁ and MT₂ receptor agonist and serotonin 5HT_2C receptor antagonist exacerbated the KA-induced hyperlocomotion and impulsive behavior and it was unable to prevent spatial memory impairment of epileptic rats. However, agomelatine induced a neuroprotection in the dorsal hippocampus, specifically in the CA1, septal CA2 and partially in the CA3c region, the hilus of the dentate gyrus, piriform cortex and septo-temporal and temporal basolateral amygdala. Our findings suggest that the beneficial impact against SE-induced neuronal loss exerted by agomelatine is not crucial for the suppression of epileptogenesis and its deleterious consequences in KA model of temporal lobe epilepsy.

Tactile stimulation during different developmental periods modifies hippocampal BDNF and GR, affecting memory and behavior in adult rats

Recent studies have shown that tactile stimulation (TS) in pups is able to prevent and/or minimize fear, anxiety behaviors, and addiction to psychostimulant drugs in adult rats. In these studies, animals have been exposed to handling from postnatal day (PND) 1-21. This study was designed to precisely establish which period of preweaning development has a greater influence of TS on neuronal development. After birth, male pups were exposed to TS from PND1-7, PND8-14, and PND15-21. In adulthood, the different periods of postnatal TS were assessed through behavioral, biochemical, and molecular assessments. Animals that received TS from PND8-14 showed lower anxiety-like symptoms, as observed by decreased anxiety index in elevated plus maze. This same TS period was able to improve rats' working memory by increasing the percentage of alternation rate in Y-maze, and induce better ability to cope with stressful situations, as showed in the defensive burying test by a reduced time of burying behavior. On the other hand, animals receiving TS in the first week of life showed longest cumulative burying time, which is directly related to increased anxiety-like behavior. Moreover, TS from PND8-14 showed lower corticosterone levels and better oxidative status, as observed by decreased lipid peroxidation and increased catalase activity in the hippocampus. Brain-derived neurotrophic factor (BDNF) immunocontent was increased in the hippocampus of animals receiving TS from PND8-14, while glucocorticoid receptors immunocontent was decreased in both TS_1-7 and TS_15-21 , but not TS_8-14 . To the best of our knowledge, this study is the first to show TS can be more efficient if applied over a focused period of neonatal development (PND8-14) and this beneficial influence can be reflected on reduced emotionality and increased ability to address stressful situations in adulthood. © 2016 Wiley Periodicals, Inc.

Distinctive cardiac autonomic dysfunction following stress exposure in both sexes in an animal model of PTSD

It is unclear whether the poor autonomic flexibility or dysregulation observed in patients with posttraumatic stress disorder (PTSD) represents a pre-trauma vulnerability factor or results from exposure to trauma. We used an animal model of PTSD to assess the association between the behavioral response to predator scent stress (PSS) and the cardiac autonomic modulation in male and female rats. The rats were surgically implanted with radiotelemetry devices to measure their electrocardiograms and locomotor activity (LMA). Following baseline telemetric monitoring, the animals were exposed to PSS or sham-PSS. Continuous telemetric monitoring (24h/day sampling) was performed over the course of 7days. The electrocardiographic recordings were analyzed using the time- and frequency-domain indexes of heart rate variability (HRV). The behavioral response patterns were assessed using the elevated plus maze and acoustic startle response paradigms for the retrospective classification of individuals according to the PTSD-related cut-off behavioral criteria. During resting conditions, the male rats had significantly higher heart rates (HR) and lower HRV parameters than the female rats during both the active and inactive phases of the daily cycle. Immediately after PSS exposure, both the female and male rats demonstrated a robust increase in HR and a marked drop in HRV parameters, with a shift of sympathovagal balance towards sympathetic predominance. In both sexes, autonomic system habituation and recovery were selectively inhibited in the rats whose behavior was extremely disrupted after exposure to PSS. However, in the female rats, exposure to the PSS produced fewer EBR rats, with a more rapid recovery curve than that of the male rats. PSS did not induce changes to the circadian rhythm of the LMA. According to our results, PTSD can be conceptualized as a disorder that is related to failure-of-recovery mechanisms that impede the restitution of physiological homeostasis.

Long-term intracerebroventricular infusion of angiotensin II after kainate-induced status epilepticus: Effects on epileptogenesis, brain damage, and diurnal behavioral changes

Our previous studies revealed that Angiotensin (Ang) II has anticonvulsant effects in acute seizure models. However, data on its role in experimental models of epilepsy are missing. In the present study, we tested whether posttreatment with Ang II after kainate (KA)-induced status epilepticus (SE) can affect epileptogenesis, concomitant behavioral changes, and brain damage. The Wistar rats were intracerebroventricularly infused via osmotic mini-pumps with Ang II (1.52μg/μl/day for 28days) after SE. Spontaneous motor seizures (SMS) were video-recorded for up to three months. Locomotor activity, anxiety, and depression-like behavior were evaluated during the last week of drug infusion, while spatial memory was assessed during the 3rd month after SE. Angiotensin II decreased the latency for onset of the first SMS and increased the frequency of SMS two months after SE. The continuous peptide infusion exacerbated the KA-induced hyperactivity and caused depression-like behavior. The reduced anxiety of KA-treated rats was alleviated by Ang II exposure. The KA-induced deficit in the hippocampal-dependent spatial memory was not influenced by Ang II. However, Ang II partially prevented the neuronal damage in the hippocampus, specifically in the CA1 area. The role of AT1 and AT2 receptor activation in the effects of the octapeptide is discussed.

Stress during the gestational period modifies pups' emotionality parameters and favors preference for morphine in adolescent rats

Experimental animal studies have shown that early life periods are highly vulnerable to environmental factors, which may exert prolonged impact on HPA axis function and on subsequent neurochemical and behavioral responses in adulthood. Here we evaluated the influence of environmental stressful situations in two different early life stages on stress-related behaviors, and morphine-conditioned place preference (CPP), which is indicative of addiction. While in the gestational stress (Gest-S) dams were exposed to daily sessions of chronic mild stress (CMS) for 2 weeks, in the postnatal stress (post-NS) the offspring were exposed daily to neonatal isolation from postnatal day (PND) 2 to PND 9 for 60 min. Animals exposed to post-NS showed lesser anxiety in different behavioral paradigms (elevated plus maze-EPM and defensive burying test-DBT) as well as increased exploratory behavior (open-field task-OFT), and no preference for morphine in CPP. In contrast, animals exposed to Gest-S showed increased corticosterone plasma levels together with anxiety symptoms and greater preference for morphine following three days of drug withdrawal. Our findings indicate that the gestational period is critical for stress, whose effects may be manifest throughout life. On the other hand, post-NS can trigger neuroadaptations able to overcome emotional consequences of early life. We hypothesized that Gest-S is able to modify responses to opioids along adulthood, which may facilitate development of addiction to these drugs.

Beyond the HPA-axis: The role of the gonadal steroid hormone receptors in modulating stress-related responses in an animal model of PTSD

The hypothalamic-pituitary-adrenal (HPA) axis, which plays a major role in the response to stress, and the hypothalamic-pituitary-gonadal (HPG) axis are closely linked with the ability to inhibit the other. Testosterone, a product of the HPG, has many beneficial effects beyond its functions as a sex hormone including anti-anxiety properties. In this study we examined the effect of stress exposure on gonadal hormones, and their efficacy in modulating anxiety-like response in an animal model of PTSD. Male rats were exposed to predator scent stress, followed by analysis of brain expression of androgen receptor (AR) receptor and estrogen receptor α (ERα). The behavioral effects of immediate treatment with testosterone, testosterone receptor antagonist (flutamide) or vehicle were evaluated using the elevated plus-maze, acoustic startle response and trauma-cue response. Levels of circulating corticosterone and testosterone were also measured after treatment. The behavioral effects of delayed testosterone treatment were explored in the same manner. We report that animals whose behavior was extremely disrupted (EBR) selectively displayed significant down-regulation of AR and ERα in the hippocampus. Immediate treatment with flutamide or delayed treatment with testosterone significantly increased prevalence rates of minimal behavioral response (MBR) and decreased prevalence of EBR with favorable behavioral results. Testosterone levels were higher in control un-exposed animals, while corticosterone was higher in control exposed animals. This study suggests that gonadal steroid hormones are involved in the neurobiological response to predator scent stress and thus warrant further study as a potential therapeutic avenue for the treatment of anxiety-related disorders.

Sex differences in PTSD resilience and susceptibility: Challenges for animal models of fear learning

PTSD occurs in only a small fraction of trauma-exposed individuals, but risk is twice as high in women as in men. The neurobiological basis for this discrepancy is not known, but the identification of biological determinants of resilience and susceptibility in each sex could lead to more targeted preventions and treatments. Animal models are a useful tool for dissecting the circuits and mechanisms that underlie the brain's response to stress, but the vast majority of this work has been developed and conducted in males. The limited work that does incorporate female animals is often inconsistent across labs and does not broadly reflect human populations in terms of female susceptibility to PTSD-like behaviors. In this review, we suggest that interpreting male vs. female comparisons in these models be approached carefully, since common behavioral outcome measures may in fact reflect distinct neural processes. Moreover, since the factors that determine resilience and susceptibility are likely at least in part distinct in men and women, models that take a within-sex approach to response variability may be more useful in identifying critical mechanisms for manipulation.

Sex differences in the long-lasting effects of a single exposure to immobilization stress in rats

In male rats, a single exposure to a severe stressor such as immobilization (IMO) results in marked activation of the HPA axis and reduction of body weight gain. In addition, the HPA response to the same (homotypic) stressor is reduced, whereas the response to a different (heterotypic) stressor is enhanced for days. Although sex differences in the responsiveness of the HPA axis have been described, there are few studies about the influence of sex on long-lasting effects of stress. Thus, we have compared the consequences of a single exposure to IMO in male and female rats. Females showed a similar ACTH response to the first IMO associated with higher corticosterone, but they were more resistant than males to stress-induced loss of body weight. Unstressed females showed higher resting levels of ACTH and corticosterone, but they did not show the increase in the resting levels of HPA hormones observed in males on the day after IMO. During exposure to a different stressor (open-field) two days after IMO, enhanced corticosterone response and hypoactivity was observed in males, but not in females. Finally, a second exposure to IMO 8 days after the first one resulted in a reduction of the HPA response and of the negative impact on body weight as compared to the first exposure, and this protective effect was greater in females. In sum, IMO-exposed females showed a greater reduction of the response to a second IMO and appear to be more resistant than males to some of the negative impacts of IMO.