Prenatal stress produces more behavioral alterations than maternal separation in the elevated plus-maze and in the elevated T-maze

Prenatal stress impacts foetal neurodevelopment: Temporal windows of gestational vulnerability

Prenatal maternal stressors ranging in severity from everyday occurrences/hassles to the experience of traumatic events negatively impact neurodevelopment, increasing the risk for the onset of psychopathology in the offspring. Notably, the timing of prenatal stress exposure plays a critical role in determining the nature and severity of subsequent neurodevelopmental outcomes. In this review, we evaluate the empirical evidence regarding temporal windows of heightened vulnerability to prenatal stress with respect to motor, cognitive, language, and behavioural development in both human and animal studies. We also explore potential temporal windows whereby several mechanisms may mediate prenatal stress-induced neurodevelopmental effects, namely, excessive hypothalamic-pituitary-adrenal axis activity, altered serotonin signalling and sympathetic-adrenal-medullary system, changes in placental function, immune system dysregulation, and alterations of the gut microbiota. While broadly defined developmental windows are apparent for specific psychopathological outcomes, inconsistencies arise when more complex cognitive and behavioural outcomes are considered. Novel approaches to track molecular markers reflective of the underlying aetiologies throughout gestation to identify tractable biomolecular signatures corresponding to critical vulnerability periods are urgently required.

Effects of acute maternal stress induced by predator cues on spatial learning and memory of offspring in the subterranean rodent Ctenomys talarum

One of the main selection pressures to which animals are exposed in nature is predation, which affects a wide variety of biological traits. When the mother experiences this stressor during pregnancy and/or lactation, behavioral and physiological responses may be triggered in the offspring as well. Thus, in order to broaden and deepen knowledge on the transgenerational effects of predation stress, we evaluated how maternal stress experienced during pregnancy and/or lactation affects the spatial abilities of progeny at the onset of adulthood in the subterranean rodent Ctenomys talarum. The results showed that, contrary to what was observed in other rodent species, maternal exposure to predator cues during pregnancy and lactation did not negatively affect the spatial abilities of the offspring, even registering some minor positive effects. Concomitantly, no effects of predatory cues on physiological parameters associated with stress were observed in the progeny. This difference in results between the present study and previous works on maternal stress highlights the importance of considering the species to be evaluated (strain, age and origin-wild or captive-) and the type of stressor used (artificial or natural, intensity of exposure) in the evaluation of the possible transgenerational effects of maternal stress.

Sex differences in the vulnerability of the hippocampus to prenatal stress

Distressing events during pregnancy that engage activity of the body's endocrine stress response have been linked with later life cognitive deficits in offspring and associated with developmental changes in cognitive-controlling neural regions. Interestingly, prenatal stress (PS)-induced alterations have shown some sex specificity. Here, we review the literature of animal studies examining sex-specific effect of physical PS on the function and structure of the hippocampus as hippocampal impairments likely underlie PS-associated deficits in learning and memory. Furthermore, the connectivity between the hypothalamic-pituitary-adrenal (HPA) axis and the hippocampus as well as the heavy presence of glucocorticoid receptors (GRs) in the hippocampus suggests this structure plays an important role in modulation of activity within stress circuitry in a sex-specific pattern. We hope that better understanding of sex-specific, PS-related hippocampal impairment will assist in uncovering the molecular mechanisms behind sex-based risk factors in PS populations across development, and perhaps contribute to greater precision in management of cognitive disturbances in this vulnerable population.

Effects of personality on assessments of anxiety and cognition

Individual variation in responses to commonly used tests of anxiety and spatial memory is often reported. While this variation is frequently considered to be 'noise', evidence suggests that it is, at least partially, related to consistent individual differences in behavioral responses (i.e., personality). The same tests used to assess anxiety are often used to profile personality traits, but personality differences are rarely considered when testing treatment differences in anxiety. Focusing on the rat literature, we describe fundamental principles involved in anxiety and spatial memory tests and we discuss how personality differences and housing conditions can influence behavioral responses in these tests. We propose that an opportunity exists to increase stress resiliency in environmentally sensitive individuals by providing environmental enrichment. We conclude by discussing different approaches to incorporating personality measures into the design and analysis of future studies; given the potential that variation masks research outcomes, we suggest that a strategy which considers the individual and its housing can contribute to improving research reproducibility.

Early environmental enrichment prevents cognitive impairments and developing addictive behaviours in a mouse model of prenatal psychological and physical stress

Environmental enrichment (EE) has shown remarkable effects in improving cognition and addictive behaviour. We tested whether EE could help recover from prenatal stress exposure. Mature Swiss Webster male and virgin female mice were placed together until vaginal plugs were detectable. Next, pregnant rodents were randomized into the control, physically and psychologically stressed groups. The application of stress was initiated on the 10th day of pregnancy and persisted for a week to induce stress in the mice. Open field and elevated plus-maze (EPM) tests were utilized as explorative and anxiety assays, respectively. A passive avoidance shuttle-box test was carried out to check anxiety-modulated behaviour. Morris water maze (MWM) test was undertaken to evaluate spatial learning and memory. Conditioned place preference (CPP) test was selected for evaluation of tendency to morphine consumption. Our results showed that prenatal stress elevated anxiety-like behaviour in the offspring which EE could significantly alleviate after weaning. We also found a higher preference for morphine use in the physical stress and psychological stress offspring group. However, no difference was observed among the genders. Application of EE for the stress group improved several parameters of the cognitive behaviour significantly. Although prenatal stress can lead to detrimental behavioural and cognitive outcomes, it can in part be relieved by early exposure to EE. However, some outcomes linked to prenatal stress exposure may not be diminished by EE therapy. In light of such irreversible effects, large-scale preventive actions promoting avoidance from stress during pregnancy should be advised.

Sex-dependent effects of pair bond interruption on anxiety- and depression-like behaviors in adult mandarin voles

Stable and positive social bonds are pretty vital to the development of animals. Instability and disruptions of social bonds, such as maternal separation and social isolation, always produce disastrous influence on physiology, neuroendocrine and behaviors. Pair bond is one of the most important social bonds in adulthood. But the different effects of pair bond interruption between males and females are rarely studied. In the present study, the monogamous mandarin voles (Microtus mandarinus) were used to confirm the time window of pair bond formation. After that, voles were separated from their partner for 1 or 2 weeks. Then anxiety- and depression-like behaviors were investigated by using open field test, light-dark box test, tail suspension test and forced swimming test, respectively. The results showed that: (1) cohabitation for 5 days is sufficient and necessary for mandarin voles to form pair bond; (2) loss of partner is always crucial for the effects of pair bond interruption, while social isolation works in certain behavioral tests.; (3) pair bond interruption for 2 weeks significantly increased the level of anxiety and depression in adult males, but not female mandarin voles. Overall, this research suggested that loss of partner plays a key role in pair bond interruption in male mandarin voles.

Sexual dimorphism in maternally separated rats: effects of repeated homotypic stress on gastrointestinal motor functions

Experiencing stressful events during early life has been considered as a risk factor for development of functional gastrointestinal disorders in adulthood. This study aimed to investigate the sex-related differences in stress-induced gastrointestinal (GI) dysmotility in rats exposed to neonatal maternal separation (MS). Newborn pups were removed from mothers for 180 min from postnatal day-1 to day-14. Experiments were performed in male and female offsprings at adulthood. Elevated plus maze (EPM) test was used to assess MS-induced anxiety-like behaviors. Ninety minute of restraint stress was applied for once or 5 consecutive days for acute stress (AS) or repeated homotypic stress (RHS), respectively. Measurement of fecal output (FO) and gastric emptying (GE), and hypothalamic microdialysis were performed. Both in males and females, MS produced anxiety-like behaviors. AS delayed GE and increased FO in all groups. In RHS-loaded MS females, AS-induced alterations in GE and FO were restored, however, no adaptation was observed in male counterparts. Regardless of sex and neonatal stress experience, AS significantly increased corticotropin-releasing factor (CRF) release from paraventricular nucleus of hypothalamus, whereas females were found more susceptible than males. Following RHS, AS-induced elevations in CRF release were attenuated only in MS females, but not in males. Both females and males seem to be prone to AS-induced alterations in hypothalamic CRF system and in GI motor functions. Neonatal MS disturbs chronic stress coping mechanisms in males. Conversely, females are likely to circumvent the deleterious effects of neonatal MS on GI functions through developing a habituation to prolonged stressed conditions.

Stereotypy and spontaneous alternation in deer mice and its response to anti-adenosinergic intervention

Repetitive behavioral phenotypes are a trait of several neuropsychiatric disorders, including obsessive-compulsive disorder (OCD). Such behaviors are typified by complex interactions between cognitive and neurobiological processes which most likely contribute to the suboptimal treatment responses often observed. To this end, exploration of the adenosinergic system may be useful, since adenosine-receptor modulation has previously shown promise to restore control over voluntary behavior and improve cognition in patients presenting with motor repetition. Here, we employed the deer mouse (Peromyscus maniculatus bairdii) model of compulsive-like behavioral persistence, seeking to investigate possible associations between stereotypic motor behavior and cognitive flexibility as measured in the T-maze continuous alternation task (T-CAT). The effect of istradefylline, a selective adenosine A_2A receptor antagonist at two doses (10 and 20 mg kg^-1  day^-1 ) on the expression of stereotypy and T-CAT performance in high (H) and non-(N) stereotypical animals, was investigated in comparison to a control intervention (six groups; n = 8 or 9 per group). No correlation between H behavior and T-CAT performance was found. However, H but not N animals presented with istradefylline-sensitive spontaneous alternation and stereotypy, in that istradefylline at both doses significantly improved the spontaneous alternation scores and attenuated the stereotypical expression of H animals. Thus, evidence is presented that anti-adenosinergic drug action improves repetitive behavior and spontaneous alternation in stereotypical deer mice, putatively pointing to a shared psychobiological construct underlying naturalistic stereotypy and alterations in cognitive flexibility in deer mice.

Auraptene exerts protective effects on maternal separation stress-induced changes in behavior, hippocampus, heart and serum of mice

Early life stress is associated with various complications. Auraptene has significant antioxidant and anti-inflammatory effects. This study aimed to assess the probable underlying mechanisms that mediate changes in the behavior, hippocampus, heart and serum in the mouse model of maternal separation (MS) stress. We evaluated the possible protective effects of auraptene in these changes focusing on inflammatory response and oxidative state. Mice were treated with auraptene (5, 10, and 50 mg/kg). In addition, anxiety-like behaviors were evaluated using behavioral tests; including open field test (OFT) and elevated plus maze (EPM). Hippocampus and heart samples were assessed histopathologically. Levels of malondialdehyde (MDA) and antioxidant capacity, as well as nitrite levels, were measured in serum, heart, and hippocampal tissues. Moreover, gene expression of inflammatory markers (Il-1β and Tlr-4) was evaluated in the heart and hippocampus. Results showed that auraptene reversed the negative effects of MS on behavior (increased time spent in central zone of the OFT and time and entries to the open arms of the EPM). Auraptene mitigated adverse effects of MS on the hippocampus (increased diameter and decreased percentage of dark neurons in the CA3 area). Accordingly, auraptene decreased MDA and nitrite levels and increased the antioxidant capacity in serum, and hippocampal samples. However, we observed different effects for different doses of auraptene in the heart samples. We concluded that MS is associated with anxiety-like behavior and cellular/molecular modifications in the heart, hippocampus and serum. We found that auraptene exerted protective effects against these negative effects of MS in mouse.

Prenatal heat stress effects on gestation and postnatal behavior in kid goats

Consequences of heat stress during pregnancy can affect the normal development of the offspring. In the present experiment, 30 Murciano-Granadina dairy goats (41.8 ± 5.7 kg) were exposed to 2 thermal environments varying in temperature-humidity index (THI) from 12 days before mating to 45 days of gestation. The environmental conditions were: gestation under thermal-neutral (TN; THI = 71 ± 3); and gestation under heat stress (HS; THI = 85 ± 3) conditions. At 27 ± 4 days old, female kids exposed to in utero TN (IUTN; n = 16) or in utero HS (IUHS; n = 10) were subjected to 2 tests: arena test (AT) and novel object test (NOT), the latter was repeated at 3 months of age. Additionally, 8 months after birth, a subset of IUTH and IUHS growing goats (n = 8 each; 16.8 ± 3.4 kg BW) were exposed to 2 environmental conditions in 2 consecutive periods: a basal thermal-neutral period (THI = 72 ± 3) for 7 days, and a heat-stress period (THI = 87 ± 2) for 21 days. In both periods, feeding, resting, posture, and thermally-associated behaviors were recorded. The gestation length was shortened by 3 days in GHS goats. In the AT, IUHS kids showed a lower number of sniffs (P < 0.01) compared to IUTN. In the NOT, IUHS kids also tended to show a lower number of sniffs (P = 0.09). During heat exposure, IUTN and IUHS growing goats spent more time resting and exhibited more heat-stress related behaviors such as panting and drinking (P < 0.001); however, no differences were observed between both groups. In conclusion, heat stress during the first third of pregnancy shortened gestation length and influenced the exploratory behavior of the kids in the early life. However, behavior responses to heat stress during the adulthood were not affected by the in utero thermal treatment.

Prenatal immobilization stress and postnatal maternal separation cause differential neuroendocrine responses to fasting stress in adult male rats

Prenatal immobilization stress (PNS) and postnatal maternal separation (MS180) are two widely used rodent models of early-life stress (ELS) that affect the hypothalamus-pituitary-adrenal (HPA) axis, cause behavioral alterations, and affect glucose tolerance in adults. We compared anxiety-like behavior, coping strategies, and HPA axis activity in PNS and MS180 adult (4-month-old) male rats and assessed their glucose tolerance and HPA axis response after mild fasting stress. Both PNS and MS180 induced a passive coping strategy in the forced swimming test, without affecting anxiety-like behavior in the elevated plus-maze. Moreover, both PNS and MS180 increased the hypothalamic corticotropin-releasing hormone expression; however, only MS180 increased the circulating corticosterone levels. Both early life stressors increased fasting glucose levels and this effect was significantly higher in PNS rats. MS180 rats showed impaired glucose tolerance 120 min after intravenous glucose administration, whereas PNS rats displayed an efficient homeostatic response. Moreover, MS180 rats showed higher circulating corticosteroid levels in response to fasting stress (overnight fasting, 12 hr), which were restored after glucose administration. In conclusion, early exposure to postnatal MS180, unlike PNS, increases the HPA axis response to moderate fasting stress, indicating a differential perception of fasting as a stressor in these two ELS models.

Environmental enrichment effects after early stress on behavior and functional brain networks in adult rats

Early life stress is associated with long-term and pervasive adverse effects on neuroendocrine development, affecting normal cognitive and emotional development. Experimental manipulations like environmental enrichment (EE) may potentially reverse the effects of early life stress induced by maternal separation (MS) paradigm in rodents. However, the functional brain networks involved in the effects of EE after prolonged exposure to MS have not yet been investigated. In order to evaluate possible changes in brain functional connectivity induced by EE after MS, quantitative cytochrome c oxidase (CCO) histochemistry was applied to determine regional brain oxidative metabolism in adult male rats. Unexpectedly, results show that prolonged MS during the entire weaning period did not cause any detrimental effects on spatial learning and memory, including depressive-like behavior evaluated in the forced-swim test, and decreased anxiety-like behavior. However, EE seemed to alter anxiety- and depression-like behaviors in both control and MS groups, but improved spatial memory in the latter groups. Analysis of brain CCO activity showed significantly lower metabolic capacity in most brain regions selected in EE groups probably associated with chronic stress, but no effects of MS on brain metabolic capacity. In addition, principal component analysis of CCO activity revealed increased large-scale functional brain connectivity comprising at least three main networks affected by EE in both MS and control groups. Moreover, EE induced a pattern of functional brain connectivity associated with stress and anxiety-like behavior as compared with non-enriched groups. In conclusion, EE had differential effects on cognition and emotional behavior irrespective of exposure to MS. In view of the remarkable effects of EE on brain function and behavior, implementation of rodent housing conditions should be optimized by evaluating the balance between scientific validity and animal welfare.

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.

Resilience priming: Translational models for understanding resiliency and adaptation to early life adversity

Despite the increasing attention to early life adversity and its long-term consequences on health, behavior, and the etiology of neurodevelopmental disorders, our understanding of the adaptations and interventions that promote resiliency and rescue against such insults are underexplored. Specifically, investigations of the perinatal period often focus on negative events/outcomes. In contrast, positive experiences (i.e. enrichment/parental care//healthy nutrition) favorably influence development of the nervous and endocrine systems. Moreover, some stressors result in adaptations and demonstrations of later-life resiliency. This review explores the underlying mechanisms of neuroplasticity that follow some of these early life experiences and translates them into ideas for interventions in pediatric settings. The emerging role of the gut microbiome in mediating stress susceptibility is also discussed. Since many negative outcomes of early experiences are known, it is time to identify mechanisms and mediators that promote resiliency against them. These range from enrichment, quality parental care, dietary interventions and those that target the gut microbiota.

Unpredictable chronic prenatal stress and manifestation of generalized anxiety and panic in rat's offspring

Often the manifestation of anxiety cannot be explained by known environmental or hereditary factors. With this perspective, it has been reported that prenatal stress may lead to emotional disturbances in the offspring. However, studies relating prenatal stress to anxiety are controversial and generally the stressors used do not mimicks the reality experienced by mothers. Thus, this investigation evaluated the effects of an unpredictable chronic stress scheme applied in one of the three gestational weeks of rats on the manifestation of generalized anxiety and panic disorder in the progeny (males), analyzing, respectively, the avoidances and escapes in the elevated T-maze, at the 1st, 3rd or 6th month of progeny life. Control offspring showed increased generalized anxiety disorder and reduced panic at 6 months. The effects of prenatal stress depended on the gestational week where it occurred and on the progeny age: during the 1st gestational week the generalized anxiety decreased in 6 month old rats. Animals in the 3rd month, prenatally stressed during the last gestational week, showed anxiogenesis and panicogenesis, but effects reverted at the 6th month, when they presented anxiolysis and no changes related to panic. Together the results show that not only the gestational period in which the aversive experience occurred was important, but the age of the evaluated progeny, since the type and the intensity of behaviors related to anxiety may vary with the developmental stage. For the model of stress used in the present study, the effects of prenatal stress were more prominent when the exposure occurred during the 3rd gestational week in rats.

Mild Prenatal Stress Causes Emotional and Brain Structural Modifications in Rats of Both Sexes

Stress or high levels of glucocorticoids (GCs) during developmental periods is known to induce persistent effects in the neuroendocrine circuits that control stress response, which may underlie individuals’ increased risk for developing neuropsychiatric conditions later in life, such as anxiety or depression. We developed a rat model (Wistar han) of mild exposure to unpredictable prenatal stress (PS), which consists in a 4-h stressor administered three times per week on a random basis; stressors include strobe lights, noise and restrain. Pregnant dams subjected to this protocol present disrupted circadian corticosterone secretion and increased corticosterone secretion upon acute stress exposure. Regarding progeny, both young adult (2 months old) male and female rats present increased levels of circulating corticosterone and hyperactivity of the hypothalamus-pituitary-adrenal axis to acute stress exposure. Both sexes present anxious- and depressive-like behaviors, shown by the decreased time spent in the open arms of the elevated plus maze (EPM) and in the light side of the light-dark box (LDB), and by increased immobility time in the forced swim test, respectively. Interestingly, these results were accompanied by structural modifications of the bed nucleus of stria terminalis (BNST) and hippocampus, as well as decreased norepinephrine and dopamine levels in the BNST, and serotonin levels in the hippocampus. In summary, we characterize a new model of mild PS, and show that stressful events during pregnancy can lead to long-lasting structural and neurochemical effects in the offspring, which affect behavior in adulthood.

Social dominance predicts hippocampal glucocorticoid receptor recruitment and resilience to prenatal adversity

The developing fetus is highly sensitive to prenatal stress, which may alter Hypothalamic-Pituitary-Adrenal (HPA) axis programming and increase the risk of behavioral disorders. There is high variability among the human population, wherein many offspring of stressed pregnancies display resilience to adversity, while the remainder displays vulnerability. In order to identify biological substrates mediating between resilience or vulnerability to prenatal adversity, we exposed stress-resistant Dominant (Dom) and stress-sensitive Submissive (Sub) mice to mild prenatal restraint stress (PRS, 45 min on gestational days (GD) 15, 16 and 17). We hypothesized that PRS would differentially alter prenatal programming of limbic regions regulating the HPA axis and affect among Dom and Sub offspring. Indeed, PRS increased Sub offspring’s serum corticosterone, and exaggerated their anxiety- and depressive-like behavior, while Dom offspring remained resilient to the hormonal and behavioral consequences of PRS. Moreover, PRS exposure markedly facilitated glucocorticoid receptor (GR) recruitment to the hippocampus among Dom mice in response to restraint stress, which may be responsible for their resilience to stressful challenge. These findings suggest proclivity to adaptive or maladaptive prenatal programming of hippocampal GR recruitment to be inheritable and predictable by social dominance or submissiveness.

Impact of social separation during pregnancy on the manifestation of defensive behaviors related to generalized anxiety and panic throughout offspring development

The multiple insecurities, anatomical, physiological and psychological changes arising from the gestational period can generate an overload of stress in the mother and cause disturbances in the offspring, affecting it throughout its development. The existing analysis linking prenatal stress and offspring’s anxiety have divergent results, being limited as to gestational week, type of stressor and age of progeny’s assessment. Social separation has been described as a stressor that causes increase in anxiety. Thus, the present study evaluated the effects of social separation applied in one of the three gestational weeks of rat dams on the manifestation of the defensive behaviors related to generalized anxiety disorder and panic in the Elevated T Maze of the male progeny in three stages of development (1, 3 or 6 months of life). It was found, in the offspring of grouped (control) dams, increased behaviors associated with generalized anxiety disorder and a reduction of panic-like behaviors throughout development. For animals whose dams were socially separated during pregnancy, the most critical period of exposure was the 2^nd gestational week, which affected the acquisition of aversive memory, demonstrated by the impairment on learning of avoidances of the offspring in all ages evaluated. Stressor exposure in this week also increased the avoidances, related to generalized anxiety of progeny in the 1^st month and decreased escapes, related to panic in the 3^rd month of life and, at the age of 6 months old, an inverse situation, with the reduction of the defensive behaviors associated to generalized anxiety disorder. The results show that, when assessing effects of prenatal stress on the manifestation of anxiety, not only the period of exposure is important, but also the age of offspring assessed.

Bumetanide treatment during early development rescues maternal separation-induced susceptibility to stress

Stress is a major risk factor for psychiatric disorders, such as depression, posttraumatic stress disorder, and schizophrenia. Early life stress, such as maternal separation, can have long-term effects on the development of the central nervous system and pathogenesis of psychiatric disorders. In the present study, we found that maternal separation increased the susceptibility to stress in adolescent rats, increased the expression of Na+/K+/2Cl- cotransporter 1 (NKCC1) on postnatal day 14, and increased the expression of K+/2Cl- cotransporter 2 (KCC2) and γ-aminobutyric acid A (GABAA) receptor subunits on postnatal day 40 in the hippocampus. NKCC1 inhibition by the U.S. Food and Drug Administration-approved drug bumetanide during the first two postnatal weeks rescued the depressive- and anxiety-like behavior that was induced by maternal separation and decreased the expression of NKCC1, KCC2 and GABAA receptor α1 and β2,3 subunits in the hippocampus. Bumetanide treatment during early development did not adversely affect body weight or normal behaviors in naive rats, or affect serum osmolality in adult rats. These results suggest that bumetanide treatment during early development may prevent the maternal separation-induced susceptibility to stress and impairments in GABAergic transmission in the hippocampus.

Modulation of the Hypothalamic-Pituitary-Adrenal Axis by Early Life Stress Exposure

Exposure to stress during critical periods in development can have severe long-term consequences, increasing overall risk on psychopathology. One of the key stress response systems mediating these long-term effects of stress is the hypothalamic-pituitary-adrenal (HPA) axis; a cascade of central and peripheral events resulting in the release of corticosteroids from the adrenal glands. Activation of the HPA-axis affects brain functioning to ensure a proper behavioral response to the stressor, but stress-induced (mal)adaptation of the HPA-axis' functional maturation may provide a mechanistic basis for the altered stress susceptibility later in life. Development of the HPA-axis and the brain regions involved in its regulation starts prenatally and continues after birth, and is protected by several mechanisms preventing corticosteroid over-exposure to the maturing brain. Nevertheless, early life stress (ELS) exposure has been reported to have numerous consequences on HPA-axis function in adulthood, affecting both its basal and stress-induced activity. According to the match/mismatch theory, encountering ELS prepares an organism for similar ("matching") adversities during adulthood, while a mismatching environment results in an increased susceptibility to psychopathology, indicating that ELS can exert either beneficial or disadvantageous effects depending on the environmental context. Here, we review studies investigating the mechanistic underpinnings of the ELS-induced alterations in the structural and functional development of the HPA-axis and its key external regulators (amygdala, hippocampus, and prefrontal cortex). The effects of ELS appear highly dependent on the developmental time window affected, the sex of the offspring, and the developmental stage at which effects are assessed. Albeit by distinct mechanisms, ELS induced by prenatal stressors, maternal separation, or the limited nesting model inducing fragmented maternal care, typically results in HPA-axis hyper-reactivity in adulthood, as also found in major depression. This hyper-activity is related to increased corticotrophin-releasing hormone signaling and impaired glucocorticoid receptor-mediated negative feedback. In contrast, initial evidence for HPA-axis hypo-reactivity is observed for early social deprivation, potentially reflecting the abnormal HPA-axis function as observed in post-traumatic stress disorder, and future studies should investigate its neural/neuroendocrine foundation in further detail. Interestingly, experiencing additional (chronic) stress in adulthood seems to normalize these alterations in HPA-axis function, supporting the match/mismatch theory.

Effects of hesperidin on formaldehyde-induced toxicity in pregnant rats

This experimental study aimed to investigate the protective effect of a bioflavonoid, hesperidin (HP), on formaldehyde (FA)-related pathophysiological and behavioral outcomes in pregnant rats and developmental aspects in their offspring. Female Wistar rats were subjected to perigestational exposure to FA (2 mg/kg/day per os) with a concomitant treatment with HP (50 mg/kg/day per os). Pregnant rats were weighed throughout gestation and tested in two behavioral paradigms (elevated plus-maze and open field) at gestational days (GD) 1, 10 and 19 to evaluate the anxiety-like behavior and locomotive alterations. Another subset of rats was decapitated at GD19 to determine the hematological profile along with cortisol, 17β-estradiol, and progesterone plasma levels. Reproductive and fetal measures and observations were also performed to check for developmental deformities. Significant body weight loss, hemato-immune decline, hormonal changes, anxiety and lethargy signs, locomotor disabilities, reproductive failure and fetal weight decrease were observed in FA-exposed rats. Treatment with HP alleviated the reproductive and fetal weight defects. Its behavioral benefits were only seen at GD1 and 10. This flavanone ameliorated some hematological parameters, decreased cortisol levels and increased 17β-estradiol rates. A potential preventive impact of HP was found against FA toxicity in pregnant rats.

Effects of natural enrichment materials on stress, memory and exploratory behavior in mice

Environmental enrichment is an essential component of laboratory animal housing that allows animals to engage in natural behaviors in an otherwise artificial setting. Previous research by the authors suggested that, compared with synthetic enrichment materials, natural materials were associated with lower stress levels in mice. Here, the authors compare the effects of different enrichment materials on stress, memory and exploratory behavior in Swiss Webster mice. Mice that were provided with natural enrichment materials had lower stress levels, better memory and greater exploratory behavior than did mice provided with synthetic enrichment materials or with no enrichment materials. These findings suggest that provision of natural enrichment materials can improve well-being of laboratory mice.

Concordance and incongruence in preclinical anxiety models: Systematic review and meta-analyses

Rodent defense behavior assays have been widely used as preclinical models of anxiety to study possibly therapeutic anxiety-reducing interventions. However, some proposed anxiety-modulating factors - genes, drugs and stressors - have had discordant effects across different studies. To reconcile the effect sizes of purported anxiety factors, we conducted systematic review and meta-analyses of the literature on ten anxiety-linked interventions, as examined in the elevated plus maze, open field and light-dark box assays. Diazepam, 5-HT1A receptor gene knockout and overexpression, SERT gene knockout and overexpression, pain, restraint, social isolation, corticotropin-releasing hormone and Crhr1 were selected for review. Eight interventions had statistically significant effects on rodent anxiety, while Htr1a overexpression and Crh knockout did not. Evidence for publication bias was found in the diazepam, Htt knockout, and social isolation literatures. The Htr1a and Crhr1 results indicate a disconnect between preclinical science and clinical research. Furthermore, the meta-analytic data confirmed that genetic SERT anxiety effects were paradoxical in the context of the clinical use of SERT inhibitors to reduce anxiety.

Laboratory environment and bio-medical experience: the impact of administration technique on the quality of immune-behavior data results in stress experience

Introduction: Often in an experiment, the control group and the intact group are not identified because most scientists neglect the fact that the sets of manipulation as technical administrations may be considered as an undesirable stress on the clarity of the data obtained from a scientific research specifically if it focuses on studying the effects of stress.

Methods: This study was conducted in two parts using 40 male Wistar rats. The first part aimed to treat a group of rats by repeated injections i.p route (1 mL/kg) of placebo or NaCl (0.9%) and the other by direct oral administration of NaCl (0.9%). Both groups spent 1 h of jet air stress with stressed group. Our objective was to consider the effects that these manipulations would have on the validity of behavioral results (the elevated plus maze test, the open field, the light/dark box test) and immune data (immune cell count) during this stress experience. The second part was devoted to the measurement of ACTH, IL6, and CRP in these experimental groups.

Results: Unlike oral administration, repeated intra-peritoneal injections cause a significant increase of plasma obtained levels of the adrenocorticotropin hormone (ACTH), interleukin-6 (IL-6) and the C-reactive protein (CRP) using injections of placebo: NaCl 0.9% (1 mL/kg) and it may have side effect on significant immune and behavioral alterations data quality induced by 1 h of air jet in the animal’s cage identified by the leukocyte formula and behavioral tests.

Conclusion: In an experimental protocol conducted on animal models, it is essential to opt for painless techniques such as oral administration instead of painful injections to avoid confusion at the behavioral and immunological results from biomedical experiments specifically one that focuses on the stress study.

Effects of prenatal stress on anxiety-like behavior and nociceptive response in rats

We assess the anxiety-like behavior in the open field and elevated plus maze tests and measure the nociceptive response in the tail flick test following prenatal stress exposure in adult male and female Wistar rats. In both behavioral anxiety tests, prenatal stress increased the anxiety-like behavior in male PS rats, but not in females suggesting a strong sex-dependent anxiogenic effect. The tail flick results showed a hypersensitivity to pain in male and female PS rats with a subtle gender difference. These findings suggest that prenatal stress is an important risk factor for multiple mental disorders.

Changes induced by prenatal stress in behavior and brain morphology: can they be prevented or reversed?

This chapter presents a critical analysis of the behavioral alterations reported in the offspring of women exposed to stress and/or depression during pregnancy and the neurochemical and structural changes underlying them. Among the alterations attributed to prenatal stress in humans and experimental rats of both sexes is impaired regulation of the hypothalamic-pituitary-adrenal (HPA) axis, anxiety and exaggerated fear of novelty, and decreased social interaction. Learning and attention deficits are more prevalent in boys and male rats. Fear of novelty and anxiety are associated with enlargement of the amygdala and its corticotropin-releasing factor content, and decreased socialization, with lower oxytocin activity in the amygdala. Learning deficits are associated with a decrease in neurogenesis, dendritic complexity, and spine number in the dorsal hippocampus. Fostering prenatally stressed (PS) pups onto control mothers prevents the dysregulation of the HPA axis and heightened anxiety, indicating a role for postnatal factors in their etiology. By contrast, learning impairment and decreased socialization are not affected by this fostering procedure and are therefore prenatally mediated.In spite of their widespread use in depressed pregnant women, selective serotonin reuptake inhibitor (SSRI) antidepressants do not normalize the behavior of their children. When administered during gestation to stressed rats, SSRIs do not reduce anxiety or learning deficits in their offspring. Moreover, when given to unstressed mothers, SSRIs induce anxiety in the offspring. The detrimental effect of SSRIs may result from inhibition of the serotonin transporter exposing the brain to excess amounts of 5-hydroxytryptamine (5-HT) at a critical time during fetal development.

Sleep deprivation during late pregnancy produces hyperactivity and increased risk-taking behavior in offspring

Sleep deprivation in women resulting from their modern lifestyle, especially during pregnancy, is a serious concern as it can affect the health of the newborn. Anxiety disorders and cognitive deficits in the offspring are also on the rise. However, experimental studies on the effects of sleep loss during pregnancy, on emotional development and cognitive function of the newborn, are scanty in literature. In the current study, female rats were sleep-deprived for 5h by gentle handling, during the 6 days of the third trimester (days 14-19 of pregnancy). The effects of this sleep deprivation on anxiety-related behaviors of pups during their peri-adolescence age were studied using elevated plus maze (EPM). In addition to body weights of dams and offspring, the maternal behavior was also monitored. The weanlings of sleep-deprived dams showed heightened risk-taking behavior as they made increased explorations into the open arms of EPM. They also showed higher mobility in comparison to the control group. Though the body weights of sleep-deprived dams were comparable to those of the control group, their newborns had lower birth weight. Nevertheless, these pups gained weight and reached the control group values during the initial post-natal week. But after weaning, their rate of growth was lower than that of the control group. This is the first report providing evidences for the role of sleep during late pregnancy in shaping the neuropsychological development in offspring.

The effects of prenatal stocking densities on the fear responses and sociality of goat (Capra hircus) kids

Prenatal stress (stress experienced by a pregnant mother) and its effects on offspring have been comprehensively studied but relatively little research has been done on how prenatal social stress affects farm animals such as goats. Here, we use the operational description of ‘stress’ as “physical or perceived threats to homeostasis.” The aim of this study was to investigate the prenatal effects of different herd densities on the fear responses and sociality of goat kids. Pregnant Norwegian dairy goats were exposed to high, medium or low prenatal animal density treatments throughout gestation (1.0, 2.0 or 3.0 m² per animal, respectively). One kid per litter was subjected to two behavioral tests at 5 weeks of age. The ‘social test’ was applied to assess the fear responses, sociality and social recognition skills when presented with a familiar and unfamiliar kid and the ‘separation test’ assessed the behavioral coping skills when isolated. The results indicate goat kids from the highest prenatal density of 1.0 m² were more fearful than the kids from the lower prenatal densities (i.e. made more escape attempts (separation test: P < 0.001) and vocalizations (social test: P < 0.001; separation test: P < 0.001). This effect was more pronounced in females than males in the high density (vocalizations; social test: P < 0.001; separation test: P  =  0.001) and females were generally more social than males. However, goat kids did not differentiate between a familiar and an unfamiliar kid at 5 weeks of age and sociality was not affected by the prenatal density treatment. We conclude that high animal densities during pregnancy in goats produce offspring that have a higher level of fear, particularly in females. Behavioral changes in offspring that occur as an effect of prenatal stress are of high importance as many of the females are recruited to the breeding stock of dairy goats.

Prenatal stress and subsequent exposure to chronic mild stress in rats; interdependent effects on emotional behavior and the serotonergic system

Exposure to prenatal stress (PS) can predispose individuals to the development of psychopathology later in life. We examined the effects of unpredictable chronic mild stress (CMS) exposure during adolescence on a background of PS in male and female Sprague-Dawley rats. PS induced more anxiety-like behavior in the elevated zero maze in both sexes, an effect that was normalized by subsequent exposure to CMS. Moreover, PS was associated with increased depression-like behavior in the forced swim test in males only. Conversely, sucrose intake was increased in PS males, whilst being decreased in females when consecutively exposed to PS and CMS. Hypothalamo-pituitary-adrenal (HPA) axis reactivity was affected in males only, with higher stress-induced plasma corticosterone levels after PS. Markedly, CMS normalized the effects of PS on elevated zero maze behavior as well as basal and stress-induced plasma corticosterone secretion. At the neurochemical level, both PS and CMS induced various sex-specific alterations in serotonin (5-HT) and tryptophan hydroxylase 2 (TPH2) immunoreactivity in the dorsal raphe nucleus, hippocampus and prefrontal cortex with, in line with the behavioral observations, more profound effects in male offspring. In conclusion, these findings show that prenatal maternal stress in Sprague-Dawley rats induces various anxiety- and depression-related behavioral and neuroendocrine changes, as well as alterations in central 5-HT and TPH2 function, predominantly in male offspring. Moreover, CMS exposure partially normalized the effects of previous PS experience, suggesting that the outcome of developmental stress exposure largely depends on the environmental conditions later in life and vice versa.

Strain-dependent effects of prenatal maternal immune activation on anxiety- and depression-like behaviors in offspring

There is converging evidence that prenatal maternal infection can increase the risk of occurrence of neuropsychiatric disorders like schizophrenia, autism, anxiety and depression in later life. Experimental studies have shown conflicting effects of prenatal maternal immune activation on anxiety-like behavior and hypothalamic-pituitary-adrenal (HPA) axis development in offspring. We investigated the effects of maternal immune activation during pregnancy on anxiety- and depression-like behaviors in pregnant mice and their offspring to determine whether these effects are dependent on strain. NMRI and C57BL/6 pregnant mice were treated with either saline or lipopolysaccharide on gestational day 17 and then interleukin (IL)-6 and corticosterone (COR) levels; anxiety or depression in the pregnant mice and their offspring were evaluated. The results indicate that maternal inflammation increased the levels of COR and anxiety-like behavior in NMRI pregnant mice, but not in C57BL/6 dams. Our data also demonstrate that maternal inflammation elevated the levels of anxiety-and depression-like behaviors in NMRI offspring on the elevated plus-maze, elevated zero-maze, tail suspension test and forced swimming test respectively, but not in the open field and light-dark box. In addition, we did not find any significant change in anxiety- and depression-like behaviors of adult C57BL/6 offspring. Our findings suggest that prenatal maternal immune activation can alter the HPA axis activity, anxiety- and depression-like behaviors in a strain- and task-dependent manner in offspring and further comprehensive studies are needed to prove the causal relationship between the findings found here and to validate their relevance to neuropsychiatric disorders in humans.

Quercetin alleviates predator stress-induced anxiety-like and brain oxidative signs in pregnant rats and immune count disturbance in their offspring

This study was performed in rats to investigate the effect of a psychogenic stress during late gestation on the immediate behavior and brain oxidative status in dams as well as on the immune cell counts in their offspring up to weaning. Besides, the ability of quercetin (a natural flavonoid) to prevent stress effects was evaluated. Quercetin was orally administered for 6 consecutive days before the pregnant rats were acutely exposed to predator stress on gestational day 19. Post-stress corticosterone level, brain oxidative stress parameters and anxiety-like behavior were assessed in dams, whereas immune cell counts were postnatally determined in both male and female pups. Predator stress caused an oxidative stress in the brain and elicited an elevation in plasma corticosterone with concomitant behavioral impairment in dams. Prenatally-stressed pups mainly showed a decrease in total leukocytes and lymphocytes along with monocytosis and granulocytosis, but these changes were sex-dependent throughout the postnatal period studied. Quercetin pretreatment blocked the stress-induced corticosterone release and alleviated the brain oxidative stress with the maternal anxiety measures being slightly attenuated, whereas its effects on the offspring immune cell counts were mostly revealed at birth. Our findings suggest that late gestational exposure to traumatic events may cause anxiety symptoms in dams, in which corticosterone and brain oxidative stress play a certain role, and trigger negative immune changes in the early postnatal life of progeny. Notably, quercetin intake before such adverse events seems to be beneficial against negative outcomes in both dams and offspring.

Interaction between neonatal allopregnanolone administration and early maternal separation: effects on adolescent and adult behaviors in male rat

Endogenous neurosteroid level fluctuations are related to several emotional and behavioral alterations. Neurosteroids also have important roles during neurodevelopment, with there being a relationship between modification of their levels in neurodevelopmental periods and behavioral alterations in adolescence and adulthood. Early maternal separation (EMS) is a stressful event that also alters neurodevelopment and adolescent and adult behaviors. The aim of the present study is to analyze the interaction between the effects of the neonatal alteration of allopregnanolone (AlloP), neurosteroid that increase its levels after acute stress presentation, and EMS on adolescent exploration and adult anxiety and sensorimotor gating in male rats. AlloP (10 mg/kg s.c.) was administrated between postnatal day 5 (PN5) and PN9, and a single 24-hour period of EMS was carried out on PN9. Exploration was analyzed at PN40 and PN60. At adult age (PN85), anxiety was tested by means of the elevated plus-maze test (EPM), and sensorimotor gating by means of prepulse inhibition test (PPI). PPI deterioration has been considered as a reliable indicator of diseases such as schizophrenia. Results showed that the previous neonatal AlloP administration neutralized the effects of EMS in the adolescent exploration (increase of traveled distance and decrease of head-dips). In adult age, an anxiolytic-like profile was observed as a consequence of EMS. Finally, EMS and neonatal AlloP disrupted PPI. Taken together, these data show the important role that physiological neonatal AlloP levels and stressful events play in neural development, adult behavior and vulnerability to neurodevelopmental disorders such as schizophrenia.

Female early adult depression results in detrimental impacts on the behavioral performance and brain development in offspring

AIMS

The present study was to understand whether early adult depressive females implicated their offspring.

METHODS

Seven-week-old female mice were subject to chronic mild stress (CMS) to establish the animal model of depression. The behavioral performance of their offspring were tested via neonatal reflexes tests, hole-board test, and morris water maze test in different ages. Astrocyte number, hippocampal volume, and neurogenesis were analyzed via immunohistochemical blotting. Glucocorticoid receptor (GR) expression and serum cortisol levels were measured by western blotting and ELISA.

RESULTS

Female depressive mice had normal fertility, but their offspring had lowered neonatal survival rate and body weight from neonatal period to early adulthood. The offspring of female depressive mice exhibited the impairments of neonatal reflex attainment and memory, but had higher emotionality as adults. Furthermore, the astrocyte number, hippocampal volume, and neurogenesis were reduced in the offspring. However, the expressions of GR were increased in the hippocampus of offspring.

CONCLUSION

This study reveals that female early adult depressive mice have normal reproductive ability, but make long-term detrimental impacts on the behavioral performance and brain development of their offspring.

Neuroprotective effect of resveratrol against prenatal stress induced cognitive impairment and possible involvement of Na(+), K(+)-ATPase activity

Resveratrol, an active ingredient of red wine extracts, has been shown to exhibit neuroprotective effects in several experimental models. Hence in the present study, the protective effects of resveratrol on cognitive deficits induced by prenatal stress were evaluated in offspring, and the possible involvement of Na(+), K(+)-ATPase in learning deficits were explored. Pregnant rats were subjected to restraint stress during early or late gestational period. Another set of rats received resveratrol during the entire gestational period along with early or late gestational stress. The study parameters included various behavioral tests like open field test and Morris water maze test. At the end of the behavioral tests (on 40th postnatal day), the offspring were sacrificed, and their brain homogenate was subjected to Na(+), K(+)-ATPase estimation. Early and late gestational stress affected spatial learning and memory and prenatal resveratrol has reversed these cognitive deficits. The Na(+), K(+)-ATPase activity in the offspring brain homogenate was reduced in the late gestational stress group; however prenatal resveratrol treatment has not affected this activity. These data suggest the neuroprotective efficacy of resveratrol against prenatal stress induced cognitive impairment. Though late gestational stress involves Na(+), K(+)-ATPase activity in rat brain homogenate, this would not be the primary cause in prenatal stress-induced cognitive dysfunction.

Prenatal exposure to chronic mild stress increases corticosterone levels in the amniotic fluid and induces cognitive deficits in female offspring, improved by treatment with the antidepressant drug amitriptyline

Prenatal stress and associated in utero exposure to elevated levels of stress hormones can adversely affect the development of the central nervous system, thereby increasing the risk of mental illnesses in later life. Here, we examined the impact of prenatal exposure to chronic mild stress (CMS) on locomotion, anxiety-related behaviour, cognition and hippocampal serotonergic neurotransmission in juvenile and adult B6D2F2 mice, and whether antidepressant treatment in adulthood could reverse the observed behavioural disturbances. Pregnant B6D2F1 female mice were either subjected to CMS or left undisturbed until parturition. Three-week and 7-week-old male and female offspring were assessed in the open-field, novel object recognition and contextual fear conditioning tests. Hippocampal levels of serotonin and its major metabolite were then quantified using high-performance liquid chromatography. Some prenatally-stressed adult females were treated with amitriptyline (20mg/kg/day in drinking water) for 10 days, from the day prior to onset of behavioural testing. In a separate experiment, amniotic fluid was collected from stressed and non-stressed dams on gestational (G) days 13 and 18 to quantify levels of corticosterone. We found that prenatal CMS specifically impaired learning and memory performance in adult females. Amitriptyline elevated hippocampal serotonin levels and attenuated these cognitive deficits. Corticosterone levels in the amniotic fluid were increased by CMS on G13 but by G18, the levels in non-stressed dams reached those of stressed dams. These results suggest that female mice are particularly vulnerable to the adverse developmental effects of prenatal stress which can be improved by appropriate treatment strategies including antidepressants.

Basal anxiety-like behavior predicts differences in dendritic morphology in the medial prefrontal cortex in two strains of rats

Basal differences in the brain may account for why some individuals are more vulnerable to stress than others. Although trait anxiety behavior varies greatly in human populations, most animal models of anxiety disorders tend to focus on the development of anxiety after a stressful experience. In this study, adult male Sprague-Dawley and Lewis rats were grouped according to baseline anxiety-like behavior in the open field, measured by time spent and distance traveled in the center. Individuals that fell one standard deviation above and below the mean, approximately the top and bottom 15%, were selected for the Low and High Anxiety groups. Pyramidal neurons from layer II/III of the prelimbic region of the medial prefrontal cortex were iontophoretically loaded with Lucifer yellow dye and reconstructed. In both strains, animals in the High Anxiety group had smaller apical dendrites than those in the Low Anxiety group. No difference was found in basal dendrites. Sholl analysis revealed a strain difference in the distribution of dendritic material between anxiety groups. These results illustrate significant variability in dendritic morphology in the prefrontal cortex of healthy adult male rats prior to experimental manipulation that correlates with baseline levels of anxiety-like behavior.