Aged rats: Sex differences and responses to chronic stress

The effect of late-life environmental enrichment on stress and anxiety: The role of sex and age-related differences in coping with aversive stimuli

Anxiety significantly diminishes the quality of life in older adults, and the drugs used for its treatment often come with risky side effects. Non-pharmacological protocols could be valuable, but more research is needed in this area. Environmental enrichment induces positive effects on anxiety-like behavior in young and adult animals; whether the same happens in aged animals is still elusive. The aged brain undergoes changes that contribute to make it "fragile" and consequently even mild, potentially positive stimuli can trigger dyshomeostasis, worsening rather than ameliorating functioning. Here, by combining behavioral analysis and measurement of serum and brain corticosterone levels, we show that late-life environmental enrichment can induce eustress or distress, depending on sex and hypothalamic-pituitary-adrenal axis function. These findings pave the way for optimizing outcomes and minimizing undesired effects in the clinical setting, underscoring the need to overcome the limits of gender medicine and emphasizing the crucial role of individually tailored therapies.

Limited effects of dehydration on object discrimination in the novel object recognition paradigm in young and middle-aged male and female rats

Dehydration is associated with impaired cognitive function in humans. Limited animal research also suggests that disruptions in fluid homeostasis impair performance in cognitive tasks. We previously demonstrated that extracellular dehydration impaired performance in the novel object recognition memory test in a sex and gonadal hormone specific manner. The experiments in this report were designed to further characterize the behavioral effects of dehydration on cognitive function in male and female rats. In Experiment 1, we tested whether dehydration during the training trial in the novel object recognition paradigm would impact performance, while euhydrated, in the test trial. Regardless of hydration status during training, all groups spent more time investigating the novel object during the test trial. In Experiment 2, we tested whether aging exacerbated dehydration-induced impairments on test trial performance. Although aged animals spent less time investigating the objects and had reduced activity levels, all groups spent more time investigating the novel object, compared to the original object, during the test trial. Aged animals also had reduced water intake after water deprivation and, unlike the young adult rats, there was no sex difference in water intake. Together these results, in combination with our previous findings, suggest that disruptions in fluid homeostasis have limited effects on performance in the novel object recognition test and may only impact performance after specific types of fluid manipulations.

Sex differences in neuroimmunoendocrine communication. Involvement on longevity

Endocrine, nervous, and immune systems work coordinately to maintain the global homeostasis of the organism. They show sex differences in their functions that, in turn, contribute to sex differences beyond reproductive function. Females display a better control of the energetic metabolism and improved neuroprotection and have more antioxidant defenses and a better inflammatory status than males, which is associated with a more robust immune response than that of males. These differences are present from the early stages of life, being more relevant in adulthood and influencing the aging trajectory in each sex and may contribute to the different life lifespan between sexes.

Prolactin and glucocorticoid receptors in the prefrontal cortex are associated with anxiety-like behavior in prenatally stressed adolescent offspring rats

Prenatal stress (PS) causes anxiety in mothers and their offspring and chewing is a commonly observed behavior during maternal stress. Prolactin (PRL) is an anti-anxiety factor that suppresses the hypothalamic-pituitary-adrenal axis. Here, we studied the roles of PRL, corticosterone (CORT), and their receptors in PS-induced anxiety-like behavior in dams and their offspring. We further investigated whether chewing during maternal stress could prevent PS-induced harmful consequences. Pregnant rats were randomly divided into PS, PS + chewing, and control groups. Anxiety-like behaviors of dams and their adolescent offspring were assessed using the open field test and elevated plus maze. Serum levels of PRL and CORT were measured by ELISA. Expression of mRNA and protein of PRLR and glucocorticoid receptor (GR) in the prefrontal cortex (PFC) were evaluated by qRT-PCR and western blotting, respectively. Compared to the control rats, dams and their female offspring, but not male offspring, in the PS group showed increased anxiety-like behaviors. The PS-affected rats had a lower serum PRL level and increased PRLR expression in the PFC. In contrast, these rats had a higher serum CORT level and decreased GR expression in the PFC. Chewing ameliorated anxiety-like behaviors and counteracted stress-induced changes in serum PRL and CORT, as well as the expression of their receptors in the PFC. Conclusion: PS-induced anxiety-like behavior is associated with changes in the serum levels of PRL and CORT and expression of their receptors in the PFC. Moreover, chewing blunts the hormonal and receptor changes and may serve as an effective stress-coping method for preventing PS-induced anxiety-like behavior.

Sex differences in cognition following variations in endocrine status

Spatial memory, mediated primarily by the hippocampus, is responsible for orientation in space and retrieval of information regarding location of objects and places in an animal's environment. Since the hippocampus is dense with steroid hormone receptors and is capable of robust neuroplasticity, it is not surprising that changes in spatial memory performance occur following a variety of endocrine alterations. Here, we review cognitive changes in both spatial and nonspatial memory tasks following manipulations of the hypothalamic-pituitary-adrenal and gonadal axes and after exposure to endocrine disruptors in rodents. Chronic stress impairs male performance on numerous behavioral cognitive tasks and enhances or does not impact female cognitive function. Sex-dependent changes in cognition following stress are influenced by both organizational and activational effects of estrogen and vary depending on the developmental age of the stress exposure, but responses to gonadal hormones in adulthood are more similar than different in the sexes. Also discussed are possible underlying neural mechanisms for these steroid hormone-dependent, cognitive effects. Bisphenol A (BPA), an endocrine disruptor, given at low levels during adolescent development, impairs spatial memory in adolescent male and female rats and object recognition memory in adulthood. BPA's negative effects on memory may be mediated through alterations in dendritic spine density in areas that mediate these cognitive tasks. In summary, this review discusses the evidence that endocrine status of an animal (presence or absence of stress hormones, gonadal hormones, or endocrine disruptors) impacts cognitive function and, at times, in a sex-specific manner.

Object recognition tasks in rats: Does sex matter?

Novelty recognition tasks based on object exploration are frequently used for the evaluation of cognitive abilities and investigation of neurobiological and molecular aspects of memory in rodents. This is an interesting approach because variations of the object recognition tasks focus on different aspects of the memory events such as novelty, location, context, and combinations of these elements. Nevertheless, as in most animal neuroscience research, female subjects are underrepresented in object recognition studies. When studies include females, the particularities of this sex are not always considered. For example, appropriate controls for manipulations conducted exclusively in females (such as estrous cycle verification) are not included. In addition, interpretation of data is often based on standardizations conducted with male subjects. Despite that, females are frequently reported as deficient and unable to adequately perform some memory tests. Thus, our study aims to review studies that describe similarities and differences between male and female performances in the different variations of object recognition tasks. In summary, although females are commonly described with deficits and the articles emphasize sex differences, most published data reveal similar performances when sexes are compared.

Challenges in the use of animal models and perspectives for a translational view of stress and psychopathologies

The neurobiology and development of treatments for stress-related neuropsychiatric disorders rely heavily on animal models. However, the complexity of these disorders makes it difficult to model them entirely, so only specific features of human psychopathology are emulated and these models should be used with great caution. Importantly, the effects of stress depend on multiple factors, like duration, context of exposure, and individual variability. Here we present a review on pre-clinical studies of stress-related disorders, especially those developed to model posttraumatic stress disorder, major depression, and anxiety. Animal models provide relevant evidence of the underpinnings of these disorders, as long as face, construct, and predictive validities are fulfilled. The translational challenges faced by scholars include reductionism and anthropomorphic/anthropocentric interpretation of the results instead of a more naturalistic and evolutionary understanding of animal behavior that must be overcome to offer a meaningful model. Other limitations are low statistical power of analysis, poor evaluation of individual variability, sex differences, and possible conflicting effects of stressors depending on specific windows in the lifespan.

Androgens Enhance Recognition Memory and Dendritic Spine Density in the Hippocampus and Prefrontal Cortex of Ovariectomized Female Rats

Estrogen replacement has been repeatedly shown to enhance memory and increase dendritic spine density in the hippocampus and prefrontal cortex of ovariectomized (OVX) female rats. Given the potential deleterious effects of chronic estrogen administration, the present study assessed cognitive function using recognition memory tasks and measured dendritic spine density in the CA1 region of the hippocampus and medial prefrontal cortex after subchronic androgen replacement to adult OVX female rats. All androgens enhanced recognition memory in OVX rats, but object placement (OP) and object recognition (OR) results differed. Only testosterone enhanced OR. Testosterone had no effect on OP while dehydroepiandrosterone (DHEA), dihydrotestosterone (DHT) and androstenedione (AD) enhanced OP. Dendritic spine density was increased by both TP and DHEA in both brain areas (DHT and AD were not tested). Lastly, we used the aromatase inhibitor, letrozole, to discriminate between potential androgenic and estrogenic effects of androgens on behavior. Letrozole alone did not alter recognition memory in OVX rats and did not block the effects of either TP or DHEA on recognition memory suggesting that effects were mediated via androgenic mechanisms. The present results expand previous information on gonadal hormone actions and show that, in addition to estrogens, androgens also improve memory and increase spine density in brains of OVX female rats. While requiring further investigation, these observations provide a basis for therapeutic interventions in the treatment of menopausal, age or disease related memory loss.

Differences in learning and memory between middle-aged female and male rats

We observed differences in cognitive functions between middle-aged female and male Wistar rats. Both (like youngsters) discriminated new versus familiar objects, showing similar short- and long-term memory (STM and LTM, respectively). Only females show robust LTM for new location of an object. Both successfully form LTM of inhibitory avoidance, though males appeared to be amnesic for memory persistence. Habituation, locomotion, horizontal exploration, "stereotypies," fear, and anxiety-like behavior were similar for both, while vertical exploration was significantly higher in middle-aged and younger females. Therefore, sex-dependent differences in some cognitive functions and behaviors must be considered when designing and interpreting learning and memory studies.

The nonhuman primate hypothalamo-pituitary-adrenal axis is an orchestrator of programming-aging interactions: role of nutrition

Developmental programming alters life-course multi-organ function and significantly affects life-course health. Recently, interest has developed in how programming may influence the rate of aging. This review describes interactions of nutrition and programming-aging interactions in hypothalamo-pituitary-adrenal (HPA) development and function from fetal development to old age. A full picture of these interactions requires data on levels of HPA activity relating to the hypothalamic, adrenal cortical, circulating blood, and peripheral cortisol metabolism. Data are provided from studies on our baboon, nonhuman primate model both across the normal life course and in offspring of maternal baboons who were moderately undernourished by a global 30% diet reduction during pregnancy and lactation. Sex differences in offspring outcomes in response to similar challenges are described. The data clearly show programming of increased HPA axis activity by moderate maternal undernutrition. Increased postnatal circulating cortisol concentrations are related to accelerated aging of the brain and cardiovascular systems. Future studies should address peripheral cortisol production and the influence of aging advantage in females. These data support the view that the HPA is an orchestrator of interactions of programming-aging mechanisms.

Sex differences in body composition, metabolism-related hormones, and energy homeostasis during aging in Wistar rats

Aging affects the body composition and balance of energy metabolism. Here, we collected in a single work several physiological parameters to show how aging and sex differences can influence energy homeostasis. Body mass index (BMI), Lee index, glucose tolerance, glycemia, and lipidogram in fasting were measured in male and female Wistar rats at the ages of 2, 6, 9, 12, and 18 months. We also measured the lipid profile, free fatty acids, glycerol, glycemia, leptin, adiponectin, insulin, corticosterone (CORT), prolactin (PRL), thyroid stimulated hormone, and triiodothyronine (T3) in 3- and 18-month-old rats of both sexes, fed ad libitum. Animals were classified as obese beginning at 2 months in males and 6 months in females. Aged male rats showed hyperglycemia and glucose intolerance compared to young males and old females. In the ad libitum condition, the 18-month males presented higher serum levels of triglycerides, total cholesterol, and free fatty acids than females. The 18-month-old females had higher PRL and CORT concentration than males, but insulin and T3 were higher in 18-month-old males than females. Our work demonstrated that aging processes on energy metabolism in rats is sex specific, with a better lipid profile and glucose tolerance in aged females.

Roles for androgens in mediating the sex differences of neuroendocrine and behavioral stress responses

Estradiol and testosterone are powerful steroid hormones that impact brain function in numerous ways. During development, these hormones can act to program the adult brain in a male or female direction. During adulthood, gonadal steroid hormones can activate or inhibit brain regions to modulate adult functions. Sex differences in behavioral and neuroendocrine (i.e., hypothalamic pituitary adrenal (HPA) axis) responses to stress arise as a result of these organizational and activational actions. The sex differences that are present in the HPA and behavioral responses to stress are particularly important considering their role in maintaining homeostasis. Furthermore, dysregulation of these systems can underlie the sex biases in risk for complex, stress-related diseases that are found in humans. Although many studies have explored the role of estrogen and estrogen receptors in mediating sex differences in stress-related behaviors and HPA function, much less consideration has been given to the role of androgens. While circulating androgens can act by binding and activating androgen receptors, they can also act by metabolism to estrogenic molecules to impact estrogen signaling in the brain and periphery. This review focuses on androgens as an important hormone for modulating the HPA axis and behaviors throughout life and for setting up sex differences in key stress regulatory systems that could impact risk for disease in adulthood. In particular, impacts of androgens on neuropeptide systems known to play key roles in HPA and behavioral responses to stress (corticotropin-releasing factor, vasopressin, and oxytocin) are discussed. A greater knowledge of androgen action in the brain is key to understanding the neurobiology of stress in both sexes.

Hypothalamus-pituitary-adrenal axis imbalance and inflammation contribute to sex differences in separation- and restraint-induced depression

Whether social contact contributes to the underlying mechanisms of depression and the observed sex differences is unclear. In this study, we subjected young male and female mice to separation- and restraint-induced stress for 4 weeks and assessed behaviors, neurotransmitter levels, hormones, and inflammatory cytokines. Results showed that, compared with controls, male mice exposed to stress displayed significant decreases in body weight and sucrose preference after 1 week. In the fourth week, they exhibited a higher degree of anxiety (open field test) and depressive-like behavior (forced swim test). Moreover, the males showed significant decreases in monoamine neurotransmitters, including norepinephrine and dopamine in striatum, and an increase in pro-inflammatory cytokines, such as tumor necrosis factor α and interleukin 1β in serum. In contrast, females showed persistent loss of weight during stress and displayed significant decreases in sucrose preference after stress. Importantly, the females but not males showed activation of the hypothalamus-pituitary-adrenal (HPA) axis, with significantly higher levels adrenocorticotropic hormone. Additionally, mRNA level of c-fos and AVP showed there was significant interaction between stress and sex. Finally, we conclude that an imbalance of the HPA axis and inflammation might be important contributors to sex differences in separation/restraint-induced depressive behavior and that changes might be mediated by c-fos and AVP.

Environmental determinants of behavioural responses to short-term stress in rats: Evidence for inhibitory effect of ambient landmarks

Behavioural responses to stress occur in an environment-dependent manner. Complex environments require flexible behavioural coping strategies and chronic stress usually generates psychomotor inhibition. Here, we examine if short-term stress also exerts an inhibitory effect on novelty-seeking, exploratory behaviours. Rats underwent acute restraint stress or were left undisturbed, and their neuroendocrine and behavioural responses were assessed at short- and long-term time points. Animals were individually tested in the open field task (OFT) and the corridor field task (CFT) with and without a central object for free exploration and novelty seeking behaviour. Stress-related psychomotor alterations were measured by path speed, path length, number of stops and thigmotaxis in both tasks. Short-term stress activated the hypothalamic-pituitary-adrenal axis causing elevated plasma corticosterone levels. Stress also impacted psychomotor functions in terms of motivational changes (higher speed and longer path) only in the central-object variations of the OFT and CFT. Moreover, stress-induced emotional alterations were manifested by a higher number of stops and thigmotactic behaviour only in the central-object condition. These findings suggest that environmental landmarks determine the type and direction of exploratory behaviour under transient stress.

A long-term cyclic plus tonic regimen of 17β-estradiol improves the ability to handle a high spatial working memory load in ovariectomized middle-aged female rats

The influence of estrogens on modifying cognition has been extensively studied, revealing that a wide array of factors can significantly impact cognition, including, but not limited to, subject age, estrogen exposure duration, administration mode, estrogen formulation, stress history, and progestogen presence. Less known is whether long-term, extended exposure to estrogens would benefit or otherwise impact cognition. The present study examined the effects of 17β-estradiol (E2) exposure for seven months, beginning in late adulthood and continuing into middle age, using a regimen of cyclic exposure (bi-monthly subcutaneous injection of 10 μg E2), or Cyclic+Tonic exposure (bi-monthly subcutaneous injection of 10 μg E2 + Silastic capsules of E2) in ovariectomized female Fischer-344-CDF rats. Subjects were tested on a battery of learning and memory tasks. All groups learned the water radial-arm maze (WRAM) and Morris water maze tasks in a similar fashion, regardless of hormone treatment regimen. In the asymptotic phase of the WRAM, rats administered a Cyclic+Tonic E2 regimen showed enhanced performance when working memory was taxed compared to Vehicle and Cyclic E2 groups. Assessment of spatial memory on object placement and object recognition was not possible due to insufficient exploration of objects; however, the Cyclic+Tonic group showed increased total time spent exploring all objects compared to Vehicle-treated animals. Overall, these data demonstrate that long-term Cyclic+Tonic E2 exposure can result in some long-term cognitive benefits, at least in the spatial working memory domain, in a surgically menopausal rat model.

Corticotropin-Releasing Factor-Producing Cells in the Paraventricular Nucleus of the Hypothalamus and Extended Amygdala Show Age-Dependent FOS and FOSB/DeltaFOSB Immunoreactivity in Acute and Chronic Stress Models in the Rat

Corticotropin-releasing factor (CRF) immunoreactive (ir) neurons of the paraventricular nucleus of the hypothalamus (PVN) play pivotal role in the coordination of stress response. CRF-producing cells in the central nucleus of amygdala (CeA) and oval division of the bed nucleus of stria terminalis (BNSTov) are also involved in stress adaptation and mood control. Immediate early gene products, subunits of the transcription factor activator protein 1 (AP1) are commonly used as acute (FOS) and/or chronic (FOSB/deltaFOSB) markers for the neuronal activity in stress research. It is well known that the course of aging affects stress adaptation, but little is known about the aging-related stress sensitivity of CRF neurons. To the best of our knowledge, the stress-induced neuronal activity of CRF neurons in the course of aging in acute and chronic stress models was not studied systematically yet. Therefore, the aim of the present study was to quantify the acute restraint stress (ARS) and chronic variable mild stress (CVMS) evoked neuronal activity in CRF cells of the PVN, CeA, and BNSTov using triple-label immunofluorescence throughout the whole lifespan in the rat. We hypothesized that the FOS and FOSB content of CRF cells upon ARS or CVMS decreases with age. Our results showed that the FOS and FOSB response to ARS declined with age in the PVN-CRF cells. BNSTov and CeA CRF cells did not show remarkable stress-induced elevation of these markers neither in ARS, nor in CVMS. Exposure to CVMS resulted in an age-independent significant increase of FOSB/delta FOSB immunosignal in PVN-CRF neurons. Unexpectedly, we detected a remarkable stress-independent FOSB/deltaFOSB signal in CeA- and BNSTov-CRF cells that declined with the course of aging. In summary, PVN-CRF cells show decreasing acute stress sensitivity (i.e., FOS and FOSB immunoreactivity) with the course of aging, while their (FOSB/deltaFOSB) responsivity to chronic challenge is maintained till senescence. Stress exposure does not affect the occurrence of the examined Fos gene products in CeA- and BNSTov-CRF cells remarkably suggesting that their contribution to stress adaptation response does not require AP1-controlled transcriptional changes.

Multiple prenatal stresses increase sexual dimorphism in adult offspring behavior

INTRODUCTION

Maternal gestational stress and immune activation have independently been associated with affective and neurodevelopmental disorders across the lifespan. We investigated whether rats exposed to prenatal maternal stressors (PNMS) consisting of psychological stress, interleukin (IL)-1β or both (two-hit stress) during critical developmental windows displayed a behavioral phenotype representative of these conditions.

METHODS

Long-Evans dams were exposed to psychological stressors consisting of restraint stress and forced swimming from gestational day (GD)12 to 18 or to no stress (controls). From GD17 until day of delivery, these same animals were injected with saline or IL-1β as a second hit and immune stressor (5 μg/day, intraperitoneally). The behavior of F1 offspring adults was tested on the open field test, elevated plus maze and affective exploration task on postnatal days (P)90, 100 and 110 respectively.

RESULTS

The effects of PNMS differed depending on the specific testing environment and potentially the age at assessment, especially in female offspring. Both locomotion and anxiety-like behavioral measures were susceptible to PNMS effects. In females, psychological stress increased anxiety-like behavior, whereas IL-1β had an opposite effect, inducing exploration and risk-taking behavior on the open field test and the elevated plus maze. When present, interactions between both stressors limited the anxiogenic effect of psychological stress on its own. In contrast, prenatal psychological stress increased anxiety-like behavior in adult males overall. A similar anxiogenic effect of IL-1β was only found on the open field test while the Stress*IL-1β interaction appeared to limit the effect of either alone. Contrarily, the PNMS effects on anxiety-like behavior on the affective exploration task were highly similar between both sexes. Analysis of males and females together revealed an additive effect of Stress and IL-1β on the number of exits from the refuge, a measure of risk assessment and thus correlated with anxiety.

CONCLUSION

PNMS affected offspring adult behavior in a sex-dependent manner. Effects on females were more variable, whereas psychological stress mostly induced anxiety-like behavior in males. These data highlight the sexual dimorphism in vulnerability to prenatal stressors. Maternal or stress-induced programming of the stress response and neuroinflammation may play an important role in mediating stress effects on offspring adult behavior.

Impact of housing conditions on social behavior, neuroimmune markers, and oxytocin receptor expression in aged male and female Fischer 344 rats

Aging is associated with a substantial decline in social behavior, whereas positive social interaction can improve overall health in aged individuals. In laboratory rodents, manipulations of the social environment across the lifespan have been shown to affect social behavior. Therefore, we examined the effects of long-term (5-6 weeks) housing conditions (alone, with one adult, or with two adults) on social behavior and the expression of neuroinflammation-related genes as well as oxytocin receptor (OXTR) gene expression in brain areas associated with social behavior regulation in aged male and female Fischer (F) 344 rats. Single-housed males and females exhibited increased social investigation, relative to pair-housed rats (one aged and one adult). Triple-housed (one aged and two adults) aged males exhibited lower levels of social investigation, relative to triple-housed aged females. Aged females were more socially active that their male counterparts. Although social housing condition significantly affected social behavior in males, it had no impact on cytokine gene expression in the paraventricular nucleus of hypothalamus (PVN), bed nucleus of the stria terminalis (BNST) or medial amygdala (MeA). However, in triple-housed aged females, who exhibited social behavior comparable to their single- and pair-housed counterparts, there was a significant increase in the expression of IL-1β and IL-6 mRNA in the MeA. No changes in cytokine gene expression were observed in the PVN or BNST, indicating that the increased expression of cytokines in the MeA was not a result of a generalized increase in neuroinflammation. Single-housed males and females exhibited elevated OXTR gene expression in the BNST. Taken together, these data indicate that manipulations of the social environment in late aging significantly influenced social interactions with a novel partner and gene expression in social behavior circuits and that these effects are sex-specific.

Stress: Influence of sex, reproductive status and gender

Emerging evidence from the preclinical and human research suggests sex differences in response to different types of stress exposure, and that developmental timing, reproductive status, and biological sex are important factors influencing the degree of HPA activation/function. Here we review data regarding: i) sex differences in behavioral and neural responses to uncontrollable and controllable stressors; ii) distinct trajectories of behavioral development and HPA-axis function in male and female rats following adolescent stress exposure; iii) normative changes in behavior and dopamine function in early postpartum rats; iv) aberrant HPA-axis function and its link to abnormal behaviors in two independent, preclinical mouse models of postpartum depression; and, v) data indicating that gender, in addition to sex, is an important determinant of stress reactivity in humans. Based on these findings, we conclude it will be important for future studies to investigate the short and long-term effects of a wide variety of stressors, how these effects may differ according to developmental timing and in relation to gonadal function, the relationship between aberrant HPA-axis activity during the postpartum and mood disorders, and influences of both sex and gender on stress reactivity in humans.

On the Role of Testosterone in Anxiety-Like Behavior Across Life in Experimental Rodents

Testosterone affects brain functions and might explain some of the observed behavioral sex differences. Animal models may help in elucidating the possible involvement of sex hormones in these sex differences. The effects of testosterone have been intensively investigated, especially in anxiety models. Numerous experiments have brought inconsistent results with either anxiolytic or anxiogenic effects. Besides methodological variations, contradictory findings might be explained by the divergent metabolism of testosterone and its recognition by neurons during prenatal and postnatal development. Gonadectomy and subsequent supplementation have been used to study the role of sex hormones. However, the variable duration of hypogonadism might affect the outcomes and the effect of long-term androgen deficiency is understudied. Testosterone can be metabolized to dihydrotestosterone strengthening the androgen signaling, but also to estradiol converting the androgen to estrogen activity. Moreover, some metabolites of testosterone can modulate γ-aminobutyric acid and serotonergic neurotransmission. Here we review the currently available experimental data in experimental rodents on the effects of testosterone on anxiety during development. Based on the experimental results, females are generally less anxious than males from puberty to middle-age. The anxiety-like behavior of females and males is likely influenced by early organizational effects, but might be modified by activational effects of testosterone and its metabolites. The effects of sex hormones leading to anxiogenesis or anxiolysis depend on factors affecting hormonal status including age. The biological and several technical issues make the study of effects of testosterone on anxiety very complex and should be taken into account when interpreting experimental results.

Behavioral effects of early life maternal trauma witness in rats

BACKGROUND

Earlier, we have reported that post-traumatic stress disorder (PTSD)-like behaviors developed in rats that witnessed their cage mates undergo repeated traumatic stress. More recently, we published that early life physical traumatic stress leads to later life depression-like behaviors in rats. Whether early life trauma witness causes later life PTSD-like behaviors is not known. Also unclear are sex-specific stress-induced behavioral variations in later life. The early life witness component of stress is an important aspect of stress-induced psychopathologies and must be investigated.

OBJECTIVE

Here, we have examined the impact of early life repeated witnessing of traumatic events by pups from post-natal day (PND) 21-PND27, on later life behaviors at PND60, and the behavioral impact of postpartum traumatic stress in female rats.

METHODS

We used a modified version of rodent social defeat model to induce postpartum stress in female rats and trauma witness stress in pups. One female Sprague-Dawley rat (intruder) was introduced into the cage of an aggressive Long-Evans male rat (resident). The encounter between the two resulted in attacks between the female rat and the Long-Evans male rat. Three exposures of social defeat (attacks) were given for 7 consecutive days. The social defeat traumatic events were witnessed by 6 pups (offspring of the intruder female rat, PND21-27), placed in six separate enclosures surrounding the cage. The objective of this experiment was three-fold: 1) to test later life behavioral effects in pups from witnessing maternal defeat, 2) to examine gender susceptibility of pups in maternal defeat witness-induced behaviors, 3) to test behavioral effect in female rats 24h after receiving the last social defeat exposure.

RESULTS

We observed that while anxiety-like behavior assessed in open-field and elevated plus-maze tests, was not affected in male or female rats upon witnessing repeated maternal traumatic stress, depression-like behavior in forced-swim test was observed at PND60 in both male and female rats, with greater effect in male rats. No change was observed in learning and memory functions using radial arm water maze test in both male and female rats. Interestingly, socially defeated female rats (dams: mother of the pups) developed both anxiety and depression-like behavior with no change in learning-memory function when compared to control female rats.

CONCLUSIONS

Our findings suggest that early life maternal stress witness history leads to depression-like behavior in both male and female adult rats, and dams developed both anxiety and depression-like behaviors.

No effect of testosterone on behavior in aged Wistar rats

In men, aging is accompanied by a gradual decline in androgen secretion. Studies suggest beneficial effects of endogenous and exogenous testosterone on affective behavior and cognitive functions. The aim of this study was to describe behavioral and cognitive sex differences and to analyze the effects of long-term androgen deficiency in aged male rats. Thirty-months old rats divided into three groups (males, females and males gonadectomized as young adults) underwent a battery of behavioral tests assessing locomotor activity, anxiety, memory, anhedonia, sociability and depression-like behavior. No major effect of gonadectomy was found in any of the analyzed behavioral measures in male rats. The only consistent sex difference was confirmed in depression-like behavior with longer immobility time observed in males. In an interventional experiment, a single dose of testosterone had no effect on gonadectomized male and female rats in the forced swim test. In contrast to previous studies this comprehensive behavioral phenotyping of aged rats revealed no major role of endogenous testosterone. Based on our results long-term hypogonadism does not alter the behavior of aged male rats, neither does acute testosterone treatment. Whether these findings have any consequences on androgen replacement therapy in aged men remains to be elucidated.

Sex differences and sex hormones in anxiety-like behavior of aging rats

Sex differences in the prevalence of affective disorders might be attributable to different sex hormone milieu. The effects of short-term sex hormone deficiency on behavior, especially on anxiety have been studied in numerous animal experiments, mainly on young adult rats and mice. However, sex differences in aged animals and the effects of long-term hypogonadism are understudied. The aim of our study was to analyze sex differences in anxiety-like behavior in aged rats and to prove whether they can be attributed to endogenous sex hormone production in males. A battery of tests was performed to assess anxiety-like behavior in aged female, male and gonadectomized male rats castrated before puberty. In addition, the aged gonadectomized male rats were treated with a single injection of estradiol or testosterone or supplemented with estradiol for two-weeks. Female rats displayed a less anxious behavior than male rats in most of the conducted behavioral tests except the light-dark box. Long-term androgen deficiency decreased the sex difference in anxiety either partially (open field, PhenoTyper cage) or completely (elevated plus maze). Neither single injection of sex hormones, nor two-week supplementation of estradiol in gonadectomized aged male rats significantly affected their anxiety-like behavior in the elevated plus maze. In conclusion, our results confirm sex differences in anxiety in aged rats likely mediated by endogenous testosterone production in males. Whether long-term supplementation with exogenous sex hormones could affect anxiety-like behavior in elderly individuals remains to be elucidated.

Ovariectomy and chronic stress lead toward leptin resistance in the satiety centers and insulin resistance in the hippocampus of Sprague-Dawley rats

Aim

To evaluate the changes in the expression level of gonadal steroid, insulin, and leptin receptors in the brain of adult Sprague-Dawley female rats due to ovariectomy and/or chronic stress.

Methods

Sixteen-week-old ovariectomized and non-ovariectomized female Sprague-Dawley rats were divided in two groups and exposed to three 10-day-sessions of sham or chronic stress. After the last stress-session the brains were collected and free-floating immunohistochemical staining was performed using androgen (AR), progesterone (PR), estrogen-β (ER-β), insulin (IR-α), and leptin receptor (ObR) antibodies. The level of receptors expression was analyzed in hypothalamic (HTH), cortical (CTX), dopaminergic (VTA/SNC), and hippocampal regions (HIPP).

Results

Ovariectomy downregulated AR in the hypothalamic satiety centers and hippocampus. It prevented or attenuated the stress-specific upregulation of AR in these regions. The main difference in stress response between non-ovariectomized and ovariectomized females was in PR level. Ovariectomized ones had increased PR level in the HTH, VTA, and HIPP. Combination of stressors pushed the hypothalamic satiety centers toward the rise of ObR and susceptibility to leptin resistance. When exposed to combined stressors, the HIPP, SNC and piriform cortex upregulated the expression of IR-α and the possibility to develop insulin resistance.

Conclusion

Ovariectomy exacerbates the effect of chronic stress by preventing gonadal receptor-specific stress response reflected in the upregulation of AR in the satiety and hippocampal regions, while stress after ovariectomy usually raises PR. The final outcome of inadequate stress response is reflected in the upregulation of ObR in the satiety centers and IR-α in the regions susceptible to early neurodegeneration. We discussed the possibility of stress induced metabolic changes under conditions of hormone deprivation.

Sex differences in psychotomimetic-induced behaviours in rats

Animal model studies using equal numbers of males and females are sparse in psychiatry research. Given the marked sex differences observed in psychiatric disorders, such as schizophrenia, using both males and females in research studies is an important requirement. Thus the aim of this study was to examine sex differences in psychotomimetic-induced behavioural deficits relevant to psychosis. We therefore compared the acute effect of amphetamine or phencyclidine on locomotor activity and prepulse inhibition in adult male and female Sprague-Dawley rats. The results of this study were that: (1) amphetamine-induced distance travelled was greater in female rats than in male rats, (2) phencyclidine-induced locomotor hyperactivity was similar in male and female rats; (3) there were no sex differences in amphetamine- or phencyclidine-induced disruption of prepulse inhibition; (4) male rats had an increased startle response after amphetamine. These findings suggest that sensitivity to amphetamine, but not phencyclidine, differs between male and female rats, and that this sex difference is selective to locomotor hyperactivity and startle, but not prepulse inhibition. This study used two widely-used, validated preclinical assays relevant to psychosis; the results of this study have implications for psychiatry research, particularly for disorders where marked sex differences in onset and symptomology are observed.

Sex Differences in Stress and Group Housing Effects on the Number of Newly Proliferated Cells and Neuroblasts in Middle-Aged Dentate Gyrus

Sex differences in stress and coping responses have been frequently documented in aged people, while whether such differences in aged people may appear at the middle age are unknown. This study was undertaken to study the impact of acute stress and social interaction on early neurogenesis in the dentate gyrus (DG) and hippocampus-related memory in two sexes of middle-aged mice. The number of newly proliferated cells, neuroblasts in DG, the object recognition and location memory in 9-month-old male and female C57BL/6N mice were assessed under baseline conditions as well as following an acute stressor regimen and group housing. Three conspecific companions, serving as "the housing group," were used to model the social interaction throughout the stressor regimen. Males had lower numbers of newly proliferated cells and neuroblasts under baseline conditions as compared to females. The stressor regimen caused rapid decreases in the number of newly proliferated cells and neuroblasts in female DG but no obvious changes were observed in male DG. Group housing, regardless of companions' age, prevented the stress-induced decreases in the number of newly proliferated cells and neuroblasts in female DG. In contrast, the presence of young or age-matched companions potentiated the stress effect in males by decreasing the number of newly proliferated cells and neuroblasts. Finally, neither the stressor regimen nor group housing affected mouse performances in the object recognition and location memory in either sex. These findings, taken together, provide evidence to support a notion that middle-aged females appear to demonstrate more stress susceptibility on early neurogenesis in DG as compared to middle-aged males, although the hippocampus-related memory performances are comparable and not affected by stress in these males and females. Experiencing stress, middle-aged females are more prone to benefit from social interaction as compared to middle-aged males in this regard. We suggest, accordingly, that involving social interaction may afford a therapeutic advance in preventing stress-produced decreases in early neurogenesis in middle-aged females' DG.

Disruption of the Glutamate-Glutamine Cycle Involving Astrocytes in an Animal Model of Depression for Males and Females

Background: Women are twice as likely as men to develop major depression. The brain mechanisms underlying this sex disparity are not clear. Disruption of the glutamate–glutamine cycle has been implicated in psychiatric disturbances. This study identifies sex-based impairments in the glutamate–glutamine cycle involving astrocytes using an animal model of depression.

Methods: Male and female adult Long-Evans rats were exposed to chronic social defeat stress (CSDS) for 21 days, using a modified resident-intruder paradigm. Territorial aggression was used for males and maternal aggression was used for females to induce depressive-like deficits for intruders. The depressive-like phenotype was assessed with intake for saccharin solution, weight gain, estrous cycle, and corticosterone (CORT). Behaviors displayed by the intruders during daily encounters with residents were characterized. Rats with daily handling were used as controls for each sex. Ten days after the last encounter, both the intruders and controls were subjected to a no-net-flux in vivo microdialysis to assess glutamate accumulation and extracellular glutamine in the nucleus accumbens (NAc). The contralateral hemispheres were used for determining changes in astrocytic markers, including glial fibrillary acidic protein (GFAP) and glutamate transporter-1 (GLT-1).

Results: Both male and female intruders reduced saccharin intake over the course of CSDS, compared to their pre-stress period and to their respective controls. Male intruders exhibited submissive/defensive behaviors to territorial aggression by receiving sideways threats and bites. These males showed reductions in striatal GLT-1 and spontaneous glutamine in the NAc, compared to controls. Female intruders exhibited isolated behaviors to maternal aggression, including immobility, rearing, and selfgrooming. Their non-reproductive days were extended. Also, they showed reductions in prefrontal and accumbal GFAP⁺ cells and prefrontal GLT-1, compared to controls. When 10 μM of glutamate was infused, these females showed a significant accumulation of glutamate compared to controls. Infusions of glutamate reduced extracellular glutamine for both male and female intruders compared to their respective controls.

Conclusion: Twenty-one days of territorial or maternal aggression produced a depressive-like phenotype and impaired astrocytes in both male and female intruders. Disruption of the glutamate–glutamine cycle in the PFC-striatal network may be linked to depressive-like deficits more in females than in males.

Sex differences in chronic stress effects on cognition in rodents

Chronic stress causes deleterious changes in physiological function in systems ranging from neural cells in culture to laboratory rodents, sub-human primates and humans. It is notable, however, that the vast majority of research in this area has been conducted in males. In this review, we provide information about chronic stress effects on cognition in female rodents and contrast it with responses in male rodents. In general, females show cognitive resilience to chronic stressors which impair male cognitive function using spatial tasks including the radial arm maze, radial arm water maze, Morris water maze, Y-maze and object placement. Moreover, stress often enhances female performance in some of these cognitive tasks. Memory in females is not affected by stress in non-spatial memory tasks like recognition memory and temporal order recognition memory while males show impaired memory following stress. We discuss possible bases for these sex-dependent differences including the use of different strategies by the sexes to solve cognitive tasks. Whether the sex differences result from changes in non-mnemonic factors is also considered. Sex-dependent differences in alcohol and drug influences on stress responses are also described. Finally, the role of neurally derived estradiol in driving sex differences and providing resilience to stress in females is shown. The importance of determining the nature and extent of sex differences in stress responses is that such differences may provide vital information for understanding why some stress related diseases have different incidence rates between the sexes and for developing novel therapeutic treatments.

Delayed restraint procedure enhances cognitive recovery of spatial function after fimbria-fornix transection

PURPOSE

To i) evaluate the effect of a restraint procedure (7 days, 2 h/day) on place learning after fimbria-fornix transection (FF), ii) investigate effects of early vs. late administration of restraint, and iii) establish effects of the restraint procedure on expression of brain derived neurotrophic factor (BDNF) in prefrontal cortex and hippocampus.

METHODS

Fifty rats subjected to FF or sham surgery and divided into groups exposed to restraint immediately (early restraint) or 21 days (late restraint) after surgery were trained to acquire an allocentric place learning task. In parallel, 29 animals were subjected to FF or sham surgery and an identical restraint procedure in order to measure concentrations of BDNF and corticosterone.

RESULTS

The performance of the sham operated rats was positively affected by the late restraint. In FF-lesioned animals, the late restraint significantly improved task performance compared to the lesioned group with no restraint, while the early restraint was associated with a negative impact on task acquisition. Biochemical analysis after restraint procedure revealed a lesion-induced upregulation of BDNF in FF animals.

CONCLUSIONS

The improved task performance of lesioned animals suggests a therapeutic effect of this manipulation, independent of BDNF. This effect is sensitive to the temporal administration of treatment.

Administration of Lactobacillus helveticus NS8 improves behavioral, cognitive, and biochemical aberrations caused by chronic restraint stress

Increasing numbers of studies have suggested that the gut microbiota is involved in the pathophysiology of stress-related disorders. Chronic stress can cause behavioral, cognitive, biochemical, and gut microbiota aberrations. Gut bacteria can communicate with the host through the microbiota-gut-brain axis (which mainly includes the immune, neuroendocrine, and neural pathways) to influence brain and behavior. It is hypothesized that administration of probiotics can improve chronic-stress-induced depression. In order to examine this hypothesis, the chronic restraint stress depression model was established in this study. Adult specific pathogen free (SPF) Sprague-Dawley rats were subjected to 21 days of restraint stress followed by behavioral testing (including the sucrose preference test (SPT), elevated-plus maze test, open-field test (OFT), object recognition test (ORT), and object placement test (OPT)) and biochemical analysis. Supplemental Lactobacillus helveticus NS8 was provided every day during stress until the end of experiment, and selective serotonin reuptake inhibitor (SSRI) citalopram (CIT) served as a positive control. Results showed that L. helveticus NS8 improved chronic restraint stress-induced behavioral (anxiety and depression) and cognitive dysfunction, showing an effect similar to and better than that of CIT. L. helveticus NS8 also resulted in lower plasma corticosterone (CORT) and adrenocorticotropic hormone (ACTH) levels, higher plasma interleukin-10 (IL-10) levels, restored hippocampal serotonin (5-HT) and norepinephrine (NE) levels, and more hippocampal brain-derived neurotrophic factor (BDNF) mRNA expression than in chronic stress rats. Taken together, these results indicate an anti-depressant effect of L. helveticus NS8 in rats subjected to chronic restraint stress depression and that this effect could be due to the microbiota-gut-brain axis. They also suggest the therapeutic potential of L. helveticus NS8 in stress-related and possibly other kinds of depression.

Sex differences and stress across the lifespan

Sex differences in stress responses can be found at all stages of life and are related to both the organizational and activational effects of gonadal hormones and to genes on the sex chromosomes. As stress dysregulation is the most common feature across neuropsychiatric diseases, sex differences in how these pathways develop and mature may predict sex-specific periods of vulnerability to disruption and increased disease risk or resilience across the lifespan. The aging brain is also at risk to the effects of stress, where the rapid decline of gonadal hormones in women combined with cellular aging processes promote sex biases in stress dysregulation. In this Review, we discuss potential underlying mechanisms driving sex differences in stress responses and their relevance to disease. Although stress is involved in a much broader range of diseases than neuropsychiatric ones, we highlight here this area and its examples across the lifespan.

Doxorubicin and cyclophosphamide induce cognitive dysfunction and activate the ERK and AKT signaling pathways

Chemotherapy is associated with long-term cognitive deficits in breast cancer survivors. Studies suggest that these impairments result in the loss of cognitive reserve and/or induce a premature aging of the brain. This study has been aimed to determine the potential underlying mechanisms that induce cognitive impairments by chemotherapeutic agents commonly used in breast cancer. Intact and ovariectomized (OVX) female rats were treated intravenously with either saline or a combination of cyclophosphamide (40 mg/kg) and doxorubicin (4 mg/kg). All subjects were tested for anxiety, locomotor activity, working, visual and spatial memory consecutively. Although anxiety and visual memory were not affected, chemotherapy significantly decreased locomotor activity and impaired working and spatial memory in female rats, independent of their hormonal status. The cognitive deficits observed are hippocampal dependent. Therefore, as a first step to identity the potential signaling pathways involved in this cognitive dysfunction, the protein levels of extracellular signal-regulated kinase 1/2 (Erk1/2), Akt (neuroprotectant) BDNF and (structural protein) PSD95 in hippocampal lysates were measured. Erk1/2 and Akt pathways are known to modulate synaptic plasticity, neuronal survival, aging and cancer. We found an increased activation of Erk1/2 and Akt as well as an increase in the protein levels of PSD95 in OVX female rodents. However, OVX females had a higher overall BDNF level, independent of chemotherapy. These studies provide additional evidence that commonly used chemotherapeutic agents affect cognitive function and impact synaptic plasticity/aging molecules which may be part of the underlying biology explaining cognitive change and can be potential therapeutic targets.

Aging, glucocorticoids and developmental programming

Glucocorticoids are pleiotropic regulators of multiple cell types with critical roles in physiological systems that change across the life-course. Although glucocorticoids have been associated with aging, available data on the aging trajectory in basal circulating glucocorticoids are conflicting. A literature search reveals sparse life-course data. We evaluated (1) the profile of basal circulating corticosterone across the life-course from weaning (postnatal day-PND 21), young adult PND 110, adult PND 450, mature adult PND 650 to aged phase PND 850 in a well-characterized homogeneous rat colony to determine existence of significant changes in trajectory in the second half of life; (2) sex differences; and (3) whether developmental programming of offspring by exposure to maternal obesity during development alters the later-life circulating corticosterone trajectory. We identified (1) a fall in corticosterone between PND 450 and 650 in both males and females (p < 0.05) and (2) higher female than male concentrations (p < 0.05). (3) Using our five life-course time-point data set, corticosterone fell at a similar age but from higher levels in male and female offspring of obese mothers. In all four groups studied, there was a second half of life fall in corticosterone. Higher corticosterone levels in offspring of obese mothers may play a role in their shorter life-span, but the age-associated fall occurs at a similar time to control offspring. Although even more life-course time-points would be useful, a five life-course time-point analysis provides important new information on normative and programmed aging of circulating corticosterone.

Need for gender-specific pre-analytical testing: the dark side of the moon in laboratory testing

Many international organisations encourage studies in a sex-gender perspective. However, research with a gender perspective presents a high degree of complexity, and the inclusion of sex-gender variable in experiments presents many methodological questions, the majority of which are still neglected. Overcoming these issues is fundamental to avoid erroneous results. Here, pre-analytical aspects of the research, such as study design, choice of utilised specimens, sample collection and processing, animal models of diseases, and the observer's role, are discussed. Artefacts in this stage of research could affect the predictive value of all analyses. Furthermore, the standardisation of research subjects according to their lifestyles and, if female, to their life phase and menses or oestrous cycle, is urgent to harmonise research worldwide. A sex-gender-specific attention to pre-analytical aspects could produce a decrease in the time for translation from the bench to bedside. Furthermore, sex-gender-specific pre-clinical pharmacological testing will enable adequate assessment of pharmacokinetic and pharmacodynamic actions of drugs and will enable, where appropriate, an adequate gender-specific clinical development plan. Therefore, sex-gender-specific pre-clinical research will increase the gender equity of care and will produce more evidence-based medicine.

Behavioral and locomotor measurements using an open field activity monitoring system for skeletal muscle diseases

The open field activity monitoring system comprehensively assesses locomotor and behavioral activity levels of mice. It is a useful tool for assessing locomotive impairment in animal models of neuromuscular disease and efficacy of therapeutic drugs that may improve locomotion and/or muscle function. The open field activity measurement provides a different measure than muscle strength, which is commonly assessed by grip strength measurements. It can also show how drugs may affect other body systems as well when used with additional outcome measures. In addition, measures such as total distance traveled mirror the 6 min walk test, a clinical trial outcome measure. However, open field activity monitoring is also associated with significant challenges: Open field activity measurements vary according to animal strain, age, sex, and circadian rhythm. In addition, room temperature, humidity, lighting, noise, and even odor can affect assessment outcomes. Overall, this manuscript provides a well-tested and standardized open field activity SOP for preclinical trials in animal models of neuromuscular diseases. We provide a discussion of important considerations, typical results, data analysis, and detail the strengths and weaknesses of open field testing. In addition, we provide recommendations for optimal study design when using open field activity in a preclinical trial.

Two weeks of predatory stress induces anxiety-like behavior with co-morbid depressive-like behavior in adult male mice

Psychological stress can have devastating and lasting effects on a variety of behaviors, especially those associated with mental illnesses such as anxiety and depression. Animal models of chronic stress are frequently used to elucidate the mechanisms underlying the relationship between stress and mental health disorders and to develop improved treatment options. The current study expands upon a novel chronic stress paradigm for mice: predatory stress. The predatory stress model incorporates the natural predator-prey relationship that exists among rats and mice and allows for greater interaction between the animals, in turn increasing the extent of the stressful experience. In this study, we evaluated the behavioral effects of exposure to 15 days of predatory stress on an array of behavioral indices. Up to 2 weeks after the end of stress, adult male mice showed an increase of anxiety-like behaviors as measured by the open field and social interaction tests. Animals also expressed an increase in depressive-like behavior in the sucrose preference test. Notably, performance on the novel object recognition task, a memory test, improved after predatory stress. Taken as a whole, our results indicate that 15 exposures to this innovative predatory stress paradigm are sufficient to elicit robust anxiety-like behaviors with evidence of co-morbid depressive-like behavior, as well as changes in cognitive behavior in male mice.

Xanthohumol improved cognitive flexibility in young mice

The protein palmitoylation cycle has been shown to be important for protein signaling and synaptic plasticity. Data from our lab showed a change in the palmitoylation status of certain proteins with age. A greater percentage of the NMDA receptor subunits GluN2A and GluN2B, along with Fyn and PSD95 proteins, were palmitoylated in the old mice. The higher level of protein palmitoylation was also associated with poorer learning scores. Xanthohumol is a prenylated flavonoid that has been shown to increase beta-oxidation in the livers of rodents, decreasing circulating free fatty acids in the serum. What is not known is whether the application of xanthohumol could influence the palmitoylation status of proteins. In this study, young and old mice were fed a diet supplemented with xanthohumol for 8 weeks. Spatial memory was assessed with the Morris water maze and protein palmitoylation quantified. The young xanthohumol-treated mice showed a significant improvement in cognitive flexibility. However, this appeared to be associated with the young control mice, on a defined, phytoestrogen-deficient diet, performing as poorly as the old mice and xanthohumol reversing this effect. The old mice receiving xanthohumol did not significantly improve their learning scores. Xanthohumol treatment was unable to affect the palmitoylation of NMDA receptor subunits and associated proteins assessed in this study. This evidence suggests that xanthohumol may play a role in improving cognitive flexability in young animals, but it appears to be ineffective in adjusting the palmitoylation status of neuronal proteins in aged individuals.

Emotionality modulates the effect of chronic stress on feeding behaviour in birds

Chronic stress is a long-lasting negative emotional state that induces negative consequences on animals' psycho-physiological state. This study aimed at assessing whether unpredictable and repeated negative stimuli (URNS) influence feeding behaviour in quail. Sixty-four quail were exposed to URNS from day 17 to 40, while 64 quail were undisturbed. Two lines divergently selected on their inherent emotionality were used to assess the effect of genetic factors on the sensitivity to URNS. All quail were submitted to a sequential feeding procedure (using two diets of different energetic values) which placed them in a contrasting situation. Behavioural tests were performed to assess the emotional reactivity of the two lines. Results confirmed that differences exist between them and that their emotional reactivity was enhanced by URNS. Diet preferences, motivation and daily intake were also measured. URNS did not change the preferences for the hypercaloric diet compared to the hypocaloric diet in choice tests, but they reduced daily intakes in both lines. Motivations for each diet were differently affected by URNS: they decreased the motivation to eat the hypercaloric diet in quail selected for their low inherent fearfulness whereas they increased the motivation to eat the hypocaloric diet in quail selected for their high inherent fearfulness, which suggested a devaluation process in the former and a compensatory behaviour in the later. Growth was furthermore reduced and laying delayed by URNS in both lines. In conclusion, the exposure to URNS induced interesting changes in feeding behaviour added with an increase in emotional reactivity and an alteration of production parameters. This confirms that both lines of quail experienced a chronic stress state. However differences in feed motivation and emotional reactivity between lines under chronic stress suggested that they experienced different emotional state and use different ways to cope with it depending on their genetic background.

Stress inhibits psychomotor performance differently in simple and complex open field environments

Stress affects psychomotor profiles and exploratory behavior in response to environmental features. Here we investigated psychomotor and exploratory patterns induced by stress in a simple open-field arena and a complex, multi-featured environment. Groups of rats underwent seven days of restraint stress or no-stress conditions and were individually tested in three versions of the ziggurat task (ZT) that varied according to environmental complexity. The hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis due to stress procedure was evaluated by the pre- and post-stress levels of circulating corticosterone (CORT). Horizontal activity, exploration, and motivation were measured by the number of fields entered, the time spent in the central fields, path length and speed, and stop duration. In addition, vertical exploratory behavior was measured by the times rats climbed onto ziggurats. Stress-induced psychomotor changes were indicated by reduced path length and path speed and increased duration of stops only within the complex arena of the ZT. Rats in stress groups also showed a significant decline in the vertical movements as measured by the number of climbing onto ziggurats. No stress-induced changes were revealed by the simple open-field arena. The exploratory patterns of stressed animals suggest psychomotor inhibition and reduced novelty-seeking behaviors in an environment-dependent manner. Thus, multi-featured arenas that require complex behavioral strategies are ideally suited to reveal the inhibitory effects of stress on psychomotor capabilities in rodents.

Disruption of reproductive aging in female and male rats by gestational exposure to estrogenic endocrine disruptors

Polychlorinated biphenyls (PCBs) are industrial contaminants and known endocrine-disrupting chemicals. Previous work has shown that gestational exposure to PCBs cause changes in reproductive neuroendocrine processes. Here we extended work farther down the life spectrum and tested the hypothesis that early life exposure to Aroclor 1221 (A1221), a mixture of primarily estrogenic PCBs, results in sexually dimorphic aging-associated alterations to reproductive parameters in rats, and gene expression changes in hypothalamic nuclei that regulate reproductive function. Pregnant Sprague Dawley rats were injected on gestational days 16 and 18 with vehicle (dimethylsulfoxide), A1221 (1 mg/kg), or estradiol benzoate (50 μg/kg). Developmental parameters, estrous cyclicity (females), and timing of reproductive senescence were monitored in the offspring through 9 months of age. Expression of 48 genes was measured in 3 hypothalamic nuclei: the anteroventral periventricular nucleus (AVPV), arcuate nucleus (ARC), and median eminence (females only) by real-time RT-PCR. Serum LH, testosterone, and estradiol were assayed in the same animals. In males, A1221 had no effects; however, prenatal estradiol benzoate increased serum estradiol, gene expression in the AVPV (1 gene), and ARC (2 genes) compared with controls. In females, estrous cycles were longer in the A1221-exposed females throughout the life cycle. Gene expression was not affected in the AVPV, but significant changes were caused by A1221 in the ARC and median eminence as a function of cycling status. Bionetwork analysis demonstrated fundamental differences in physiology and gene expression between cycling and acyclic females independent of treatment. Thus, gestational exposure to biologically relevant levels of estrogenic endocrine-disrupting chemicals has sexually dimorphic effects, with an altered transition to reproductive aging in female rats but relatively little effect in males.

Brain-derived neurotrophic factor-estrogen interactions in the hippocampal mossy fiber pathway: implications for normal brain function and disease

The neurotrophin brain-derived neurotrophic factor (BDNF) and the steroid hormone estrogen exhibit potent effects on hippocampal neurons during development and in adulthood. BDNF and estrogen have also been implicated in the etiology of diverse types of neurological disorders or psychiatric illnesses, or have been discussed as potentially important in treatment. Although both are typically studied independently, it has been suggested that BDNF mediates several of the effects of estrogen in the hippocampus, and that these interactions play a role in the normal brain as well as disease. Here we focus on the mossy fiber (MF) pathway of the hippocampus, a critical pathway in normal hippocampal function, and a prime example of a location where numerous studies support an interaction between BDNF and estrogen in the rodent brain. We first review the temporal and spatially regulated expression of BDNF and estrogen in the MFs, as well as their receptors. Then we consider the results of studies that suggest that 17β-estradiol alters hippocampal function by its influence on BDNF expression in the MF pathway. We also address the hypothesis that estrogen influences the hippocampus by mechanisms related not only to the mature form of BDNF, acting at trkB receptors, but also by regulating the precursor, proBDNF, acting at p75NTR. We suggest that the interactions between BDNF and 17β-estradiol in the MFs are potentially important in the normal function of the hippocampus, and have implications for sex differences in functions that depend on the MFs and in diseases where MF plasticity has been suggested to play an important role, Alzheimer's disease, epilepsy and addiction.

Age and sex affect spatial and emotional behaviors in rats: the role of repeated elevated plus maze test

The main objective of the study was to investigate the effects of age and sex differences on locomotor activity, learning and memory in rats. Another objective was to investigate whether repeated elevated plus maze tests induce anxiety in rats. Eighty Wistar rats were divided into eight groups according to their sex, age and anxiety status. Locomotor activity was assessed in open field. Repeated anxiety tests were performed in elevated plus maze. Spatial learning and memory were evaluated with the Morris water maze. All behavioral tests were recorded online and analyzed offline with an analytical software. Exploratory behavior was lower in anxiety-induced rats. Male rats had lower anxiety levels, locomotor activity and exploratory behavior compared to females. During the training period of Morris water maze latency to find platform, total distance traveled and average swimming speed decreased in all groups with repeated tests and young rats generally were faster than aged rats. During the probe trial, although the number of platform crossings was not affected, time spent in the platform zone was higher in the young groups compared to the aged groups. In conclusion, age and sex affect locomotor activity, learning and memory in different aspects.

Age-related deficits in spatial memory and hippocampal spines in virgin, female Fischer 344 rats

Effects of aging on memory and brain morphology were examined in aged, 21-month-old, and young, 4-month-old, Fischer 344 female rats. Spatial memory was assessed using the object placement task, and dendritic spine density was determined on pyramidal neurons in the hippocampus following Golgi impregnation. Consistent with previous studies, aged females showed poorer object placement performance than young subjects. Young subjects significantly discriminated the location of objects with a 1.5-hour intertrial delay while aged subjects did not. Spine density of basal dendrites on CA1 pyramidal cells was 16% lower in the aged subjects as compared to the young subjects. No differences in spine density were found between young and aged subjects in basal dendrites of CA1 or in either dendritic field of CA3 pyramidal neurons. Thus, decreased hippocampal CA1 dendritic spine density in aged rats may contribute to poorer spatial memory as compared to young rats. The possibility that the neuroplastic changes observed in this study may pertain only to female subjects having had a specific set of life experiences is discussed. Different factors, such as reproductive status, diet, and handling may contribute to neuroplasticity of the brain during aging; however, this view requires further examination.

Prenatal cocaine exposure increases anxiety, impairs cognitive function and increases dendritic spine density in adult rats: influence of sex

Cocaine exposure during pregnancy can impact brain development and have long-term behavioral consequences. The present study examined the lasting consequences of prenatal cocaine (PN-COC) exposure on the performance of cognitive tasks and dendritic spine density in adult male and female rats. From gestational day 8 to 20, dams were treated daily with 30 mg/kg (ip) of cocaine HCl or saline. At 62 days of age, offspring were tested consecutively for anxiety, locomotion, visual memory and spatial memory. PN-COC exposure significantly increased anxiety in both sexes. Object recognition (OR) and placement (OP) tasks were used to assess cognitive function. Behavioral tests consisted of an exploration trial (T1) and a recognition trial (T2) that were separated by an inter-trial delay of varying lengths. Male PN-COC subjects displayed significantly less time investigating new objects or object locations during T2 in both OR and OP tasks. By contrast, female PN-COC subjects exhibited impairments only in OR and only at the longest inter-trial delay interval. In addition, gestational cocaine increased dendritic spine density in the prefrontal cortex and nucleus accumbens in both genders, but only females had increased spine density in the CA1 region of the hippocampus. These data reveal that in-utero exposure to cocaine results in enduring alterations in anxiety, cognitive function and spine density in adulthood. Moreover, cognitive deficits were more profound in males than in females.