Neurobiological effects of neonatal maternal separation and post-weaning environmental enrichment

Sensitive Periods of Emotion Regulation: Influences of Parental Care on Frontoamygdala Circuitry and Plasticity

Early caregiving experiences play a central role in shaping emotional development, stress physiology, and refinement of limbic circuitry. Converging evidence across species delineates a sensitive period of heightened neuroplasticity when frontoamygdala circuitry is especially amenable to caregiver inputs early in life. During this period, parental buffering regulates emotional behaviors and stress physiology as emotion regulation circuitry continues to mature. By contrast, disorganized or poor quality caregiving has profound and lasting consequences on the maturation of frontoamygdala circuitry essential for emotion regulation, even following termination of this early life stressor (e.g., adoption from orphanage). This article highlights how interactions between caregiving experiences and the biological state of the developing brain have broad implications for long-term health.

Plasticity of the Maternal Brain Across the Lifespan

Maternal behavior is dynamic and highly sensitive to experiential and contextual factors. In this review, this plasticity will be explored, with a focus on how experiences of females occurring from the time of fetal development through to adulthood impact maternal behavior and the maternal brain. Variation in postpartum maternal behavior is dependent on estrogen sensitivity within the medial preoptic area of the hypothalamus and activation within mesolimbic dopamine neurons. This review will discuss how experiences across the lifespan alter the function of these systems and the multigenerational consequences of these neuroendocrine and behavioral changes. These studies, based primarily on the examination of maternal behavior in laboratory rodents and nonhuman primates, provide mechanistic insights relevant to our understanding of human maternal behavior and to the mechanisms of lifelong plasticity.

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

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

Differential effects of tianeptine on the dorsal hippocampal volume of rats submitted to maternal separation followed by chronic unpredictable stress in adulthood

Early maternal separation (MS) may produce lasting effects in the dorsal hippocampus (DH) that can change its response to chronic stress in adulthood. Chronic stress affects DH morphology and function, but tianeptine (an anti-depressant) can reverse the stress-induced morphological impairments. Morphologic alterations of hippocampus can affect contextual memory. Therefore, we evaluated the effect of tianeptine in MS and chronically stressed rats on: 1) volume of the DH and its areas using stereology and 2) hippocampal-dependent memory using a fear conditioning test. Male Wistar rats were subjected to daily MS for 4.5 h between postnatal days (PND) 1-21, or to animal facility rearing (AFR). Between (PND) days 50 and 74, rats were exposed to chronic unpredictable stress and were treated daily with tianeptine (10 mg/kg) or vehicle, providing eight groups: AFR-unstressed/vehicle (n = 5 for stereology, n = 18 for fear conditioning test); AFR unstressed/tianeptine (n = 6 and n = 10); AFR-chronic stress/vehicle (n = 6 and n = 14); AFR-chronic stress/tianeptine (n = 6 and n = 10), MS-unstressed/vehicle (n = 5 and n = 19), MS-unstressed/tianeptine (n = 6 and n = 10), MS-chronic stress/vehicle (n = 6 and n = 18), and MS-chronic stress/tianeptine (n = 6 and n = 10). MS-chronic stress/tianeptine rats showed a diminished CA1 area than the corresponding MS-unstressed/tianeptine rats. The combination of stressors produced a freezing response similar to those of the control group during postconditioning. During retrieval, MS led to a diminished freezing response compared to the AFR-unstressed groups. Tianeptine had no effect on freezing behavior. Our results show that tianeptine can affect the CA1 area volume differently depending on the nature and quantity of stressors but cannot alter freezing to context.

Effects of swimming exercise on morphine-induced reward and behavioral sensitization in maternally-separated rat pups in the conditioned place preference procedure

This study was designed to examine the effects of swimming exercise during adolescence on morphine-induced conditioned place preference (CPP) and behavioral sensitization in maternally separated male and female rat pups. Male Wistar rats were allowed to mate with female virgin Wistar rats. Pups were separated from the dam daily for 180min during postnatal days 2-14. All pups were weaned on day 21.The exercising pups were allowed to swim (60min/d, five days per a week, for 30days) during adolescence. Then, rat pups were tested for behavioral sensitization and the CPP induced by morphine. Maternal separation produced a significant increase in morphine-induced CPP in both sexes, behavioral sensitization in male pups and tolerance to morphine-induced motor activity in female pups. Swimmer pups separated from the dam exhibited a decrease in morphine-induced CPP in both sexes and behavioral sensitization in male pups than those of their control pups. The present results have shown that swimming exercise during adolescence may exert a protective effect against morphine-induced reward and behavioral sensitization in adult male and female rats following maternal separation.

Maternal separation prior to neonatal hypoxia-ischemia: Impact on emotional aspects of behavior and markers of synaptic plasticity in hippocampus

Exposure to early-life stress is associated with long-term alterations in brain and behavior, and may aggravate the outcome of neurological insults. This study aimed at investigating the possible interaction between maternal separation, a model of early stress, and subsequent neonatal hypoxia-ischemia on emotional behavior and markers of synaptic plasticity in hippocampus. Therefore, rat pups (N=60) were maternally separated for a prolonged (MS 180min) or a brief (MS 15min) period during the first six postnatal days, while a control group was left undisturbed. Hypoxia-ischemia was applied to a subgroup of each rearing condition on postnatal day 7. Emotional behavior was examined at three months of age and included assessments of anxiety (elevated plus maze), depression-like behavior (forced swimming) and spontaneous exploration (open field). Synaptic plasticity was evaluated based on BDNF and synaptophysin expression in CA3 and dentate gyrus hippocampal regions. We found that neonatal hypoxia-ischemia caused increased levels of anxiety, depression-like behavior and locomotor activity (ambulation). Higher anxiety levels were also seen in maternally separated rats (MS180min) compared to non-maternally separated rats, but prolonged maternal separation prior to HI did not potentiate the HI-associated effect. No differences among the three rearing conditions were found regarding depression-like behavior or ambulation. Immunohistochemical evaluation of synaptophysin revealed that both prolonged maternal separation (MS180min) and neonatal hypoxia-ischemia significantly reduced its expression in the CA3 and dentate gyrus. Decreases in synaptophysin expression in these areas were not exacerbated in rats that were maternally separated for a prolonged period prior to HI. Regarding BDNF expression, we found a significant decrease in immunoreactivity only in the hypoxic-ischemic rats that were subjected to the prolonged maternal separation paradigm. The above findings suggest that early-life stress prior to neonatal hypoxia-ischemia leads to significant alterations in synaptic plasticity of the dorsal hippocampus during adulthood, but does not exacerbate HI-related changes in emotional behavior.

Cognitive Dysfunction in Major Depressive Disorder. A Translational Review in Animal Models of the Disease

Major Depressive Disorder (MDD) is the most common psychiatric disease, affecting millions of people worldwide. In addition to the well-defined depressive symptoms, patients suffering from MDD consistently complain about cognitive disturbances, significantly exacerbating the burden of this illness. Among cognitive symptoms, impairments in attention, working memory, learning and memory or executive functions are often reported. However, available data about the heterogeneity of MDD patients and magnitude of cognitive symptoms through the different phases of MDD remain difficult to summarize. Thus, the first part of this review briefly overviewed clinical studies, focusing on the cognitive dysfunctions depending on the MDD type. As animal models are essential translational tools for underpinning the mechanisms of cognitive deficits in MDD, the second part of this review synthetized preclinical studies observing cognitive deficits in different rodent models of anxiety/depression. For each cognitive domain, we determined whether deficits could be shared across models. Particularly, we established whether specific stress-related procedures or unspecific criteria (such as species, sex or age) could segregate common cognitive alteration across models. Finally, the role of adult hippocampal neurogenesis in rodents in cognitive dysfunctions during MDD state was also discussed.

Effects of early adolescent environmental enrichment on cognitive dysfunction, prefrontal cortex development, and inflammatory cytokines after early life stress

Early postnatal stress such as maternal separation causes cognitive dysfunction later in life, including working memory deficits that are largely mediated by the prefrontal cortex. Maternal separation in male rats also yields a loss of parvalbumin-containing prefrontal cortex interneurons in adolescence, which may occur via inflammatory or oxidative stress mechanisms. Environmental enrichment can prevent several effects of maternal separation; however, effects of enrichment on prefrontal cortex development are not well understood. Here, we report that enrichment prevented cognitive dysfunction in maternally separated males and females, and prevented elevated circulating pro-inflammatory cytokines that was evident in maternally separated males, but not females. However, enrichment did not prevent parvalbumin loss or adolescent measures of oxidative stress. Significant correlations indicated that adolescents with higher oxidative damage and less prefrontal cortex parvalbumin in adolescence committed more errors on the win-shift task; therefore, maternal separation may affect cognitive dysfunction via aberrant interneuron development. © 2015 Wiley Periodicals, Inc. Dev Psychobiol 58: 482-491, 2016.

Environmental Enrichment Increases Glucocorticoid Receptors and Decreases GluA2 and Protein Kinase M Zeta (PKMζ) Trafficking During Chronic Stress: A Protective Mechanism?

Environmental enrichment (EE) housing paradigms have long been shown beneficial for brain function involving neural growth and activity, learning and memory capacity, and for developing stress resiliency. The expression of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluA2, which is important for synaptic plasticity and memory, is increased with corticosterone (CORT), undermining synaptic plasticity and memory. Thus, we determined the effect of EE and stress on modulating GluA2 expression in Sprague-Dawley male rats. Several markers were evaluated which include: plasma CORT, the glucocorticoid receptor (GR), GluA2, and the atypical protein kinase M zeta (PKMζ). For 1 week standard-(ST) or EE-housed animals were treated with one of the following four conditions: (1) no stress; (2) acute stress (forced swim test, FST; on day 7); (3) chronic restraint stress (6 h/day for 7 days); and (4) chronic + acute stress (restraint stress 6 h/day for 7 days + FST on day 7). Hippocampi were collected on day 7. Our results show that EE animals had reduced time immobile on the FST across all conditions. After chronic + acute stress EE animals showed increased GR levels with no change in synaptic GluA2/PKMζ. ST-housed animals showed the reverse pattern with decreased GR levels and a significant increase in synaptic GluA2/PKMζ. These results suggest that EE produces an adaptive response to chronic stress allowing for increased GR levels, which lowers neuronal excitability reducing GluA2/PKMζ trafficking. We discuss this EE adaptive response to stress as a potential underlying mechanism that is protective for retaining synaptic plasticity and memory function.

Environmental enrichment does not reverse the effects of maternal deprivation on NMDAR and Balb/c mice behaviors

Early adverse life experiences have been associated with anxiety-like behavior and memory impairment. N-methyl-d-aspartate receptors (NMDARs) play an important role in brain development. Enriched environments are known to positively influence emotional and cognitive functions in the brain. We examined the effects of maternal deprivation (MD) on NMDAR subunits in the hippocampus, locomotor activity, anxiety behaviors, and learning-memory performance of Balb/c mice. We also examined whether these effects could be reversed by raising the offspring in an enriched environment. The mice were separated from their mothers for a single 24h episode on postnatal day (PND) 9. The mice were weaned on day 21 and were housed under either standard (SE) or enriched (EE) environmental conditions. Emotional behaviors and cognitive processes of mice were evaluated using an open field (OF) test, an elevated plus maze (EPM) test, and a Morris water-maze (MWM). NMDAR subunits (GluN1, GluN2A, and GluN2B) mRNA expression levels in the hippocampus were examined by real-time PCR. In OF, MD had no effect on horizontal locomotor activity. MD increased anxiety-like behaviors in the EPM and decreased spatial learning performance in MWM; however, these effects were not reversed by EE. MD (in SE and EE conditions) increased GluN1, GluN2A, and GluN2B mRNA expressions in the hippocampus. In conclusion, MD led to the deterioration of the emotional and cognitive processes during adulthood. Moreover, environmental enrichment did not reverse the deleterious effects of the MD on emotional and cognitive functions and increased the NMDAR levels.

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

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

Effects of environmental enrichment on behavioral deficits and alterations in hippocampal BDNF induced by prenatal exposure to morphine in juvenile rats

Prenatal morphine exposure throughout pregnancy can induce a series of neurobehavioral and neurochemical disturbances by affecting central nervous system development. This study was designed to investigate the effects of an enriched environment on behavioral deficits and changes in hippocampal brain-derived neurotrophic factor (BDNF) levels induced by prenatal morphine in rats. On pregnancy days 11-18, female Wistar rats were randomly injected twice daily with saline or morphine. Offspring were weaned on postnatal day (PND) 21. They were subjected to a standard rearing environment or an enriched environment on PNDs 22-50. On PNDs 51-57, the behavioral responses including anxiety and depression-like behaviors, and passive avoidance memory as well as hippocampal BDNF levels were investigated. The light/dark (L/D) box and elevated plus maze (EPM) were used for the study of anxiety, forced swimming test (FST) was used to assess depression-like behavior and passive avoidance task was used to evaluate learning and memory. Prenatal morphine exposure caused a reduction in time spent in the EPM open arms and a reduction in time spent in the lit side of the L/D box. It also decreased step-through latency and increased time spent in the dark side of passive avoidance task. Prenatal morphine exposure also reduced immobility time and increased swimming time in FST. Postnatal rearing in an enriched environment counteracted with behavioral deficits in the EPM and passive avoidance task, but not in the L/D box. This suggests that exposure to an enriched environment during adolescence period alters anxiety profile in a task-specific manner. Prenatal morphine exposure reduced hippocampal BDNF levels, but enriched environment significantly increased BDNF levels in both saline- and morphine-exposed groups. Our results demonstrate that exposure to an enriched environment alleviates behavioral deficits induced by prenatal morphine exposure and up-regulates the decreased levels of BDNF. BDNF may contribute to the beneficial effects of an enriched environment on prenatal morphine-exposed to rats.

Influence of environmental enrichment vs. time-of-day on behavioral repertoire of male albino Swiss mice

Environmental enrichment (EE) is a non-pharmacological manipulation that promotes diverse forms of benefits in the central nervous system of captive animals. It is thought that EE influences animal behavior in a specie-(strain)-specific manner. Since rodents in general present different behaviors during distinct periods of the day, in this study we aimed to investigate the influence of time-of-day on behavioral repertoire of Swiss mice that reared in EE. Forty male Swiss mice (21days old) were housed in standard (SC) or enriched conditions (EC) for 60days. Behavioral assessments were conducted during the light phase (in presence of light) or dark phase (in absence of light) in the following tasks: open field, object recognition and elevated plus maze. First, we observed that the locomotor and exploratory activities are distinct between SC and EC groups only during the light phase. Second, we observed that "self-protective behaviors" were increased in EC group only when mice were tested during the light phase. However, "less defensive behaviors" were not affected by both housing conditions and time-of-day. Third, we showed that the performance of EE animals in object recognition task was improved in both light and dark conditions. Our findings highlight that EE-induced alterations in exploratory and emotional behaviors are just evident during light conditions. However, EE-induced cognitive benefits are remarkable even during dark conditions, when exploratory and emotional behaviors were similar between groups.

Environmental enrichment models a naturalistic form of maternal separation and shapes the anxiety response patterns of offspring

Environmental enrichment (EE) mimics positive life experiences by providing enhanced social and physical stimulation. Placement into EE following weaning, or in later life, confers beneficial outcomes on both emotional and cognitive processes. However, anxiety-like behavior is also reported, particularly in rats exposed to enhanced housing during early development. Notably, the quality of maternal behavior affects stress regulation and emotional stability in offspring, yet the impact of environmental context on maternal care has not been thoroughly evaluated, or are the influences of EE on their offspring understood. To investigate the role of EE on these factors we analyzed the details of mother-neonate interactions, and juvenile offspring performance on several anxiety measures. Additionally, we evaluated neurochemical differences (i.e. serotonin, corticosterone, GABA, glutamate) in prefrontal cortex and hippocampus as a function of EE, Communal Nesting (CN) and Standard Care (SC). Although EE dams spent significantly less time on the nest and had lower nursing frequencies compared to SC dams, there were no differences in maternal licking/grooming. In offspring, EE increased GLUR1 level and GABA concentrations in the prefrontal cortex of both juvenile male and female rats. A similar pattern for glutamate was only observed in males. Although EE offspring spent less time on the open arms of the elevated plus maze and had faster escape latencies in a light-dark test, there were no other indications of anxiety-like behavior on these measures or when engaged in social interaction with a conspecific. In the wild, rats live in complicated and variable environments. Consequently dams must leave their nest to defend and forage, limiting their duration of direct contact. EE exposure in early development may mimic this naturalistic maternal separation, shaping parental behavior and offspring resiliency to stressors.

Role of adult hippocampal neurogenesis in stress resilience

There is a growing appreciation that adult hippocampal neurogenesis plays a role in emotional and cognitive processes related to psychiatric disorders. Although many studies have investigated the effects of stress on adult hippocampal neurogenesis, most have not focused on whether stress-induced changes in neurogenesis occur specifically in animals that are more resilient or more susceptible to the behavioural and neuroendocrine effects of stress. Thus, in the present review we explore whether there is a clear relationship between stress-induced changes in adult hippocampal neurogenesis, stress resilience and antidepressant-induced recovery from stress-induced changes in behaviour. Exposure to different stressors is known to reduce adult hippocampal neurogenesis, but some stressors have also been shown to exert opposite effects. Ablation of neurogenesis does not lead to a depressive phenotype, but it can enhance responsiveness to stress and affect stress susceptibility. Monoaminergic-targeted antidepressants, environmental enrichment and adrenalectomy are beneficial for reversing stress-induced changes in behaviour and have been shown to do so in a neurogenesis-dependant manner. In addition, stress and antidepressants can affect hippocampal neurogenesis, preferentially in the ventral hippocampus. Together, these data show that adult hippocampal neurogenesis may play a role in the neuroendocrine and behavioural responses to stress, although it is not yet fully clear under which circumstances neurogenesis promotes resilience or susceptibility to stress. It will be important that future studies carefully examine how adult hippocampal neurogenesis can contribute to stress resilience/susceptibility so that it may be appropriately exploited for the development of new and more effective treatments for stress-related psychiatric disorders.

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Ablation of adult hippocampal NG can affect stress susceptibility.

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Increased hippocampal NG is associated with both susceptibility and resilience.

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Adult hippocampal NG can influence stress-induced alterations in HPA-axis activity.

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Behavioural effects of some but not all antidepressants are neurogenesis-dependent.

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Stress and antidepressants can affect NG preferentially in the ventral hippocampus.

Environmental enrichment mitigates the sex-specific effects of gestational inflammation on social engagement and the hypothalamic pituitary adrenal axis-feedback system

Modest environmental enrichment (EE) is well recognized to protect and rescue the brain from the consequences of a variety of insults. Although animal models of maternal immune activation (MIA) are associated with several neurodevelopmental impairments in both the behavioral and cognitive functioning of offspring, the impact of EE in protecting or reversing these effects has not been fully evaluated. In the present study, female Sprague-Dawley rats were randomized into EE (pair-housed in a large multi-level cage with toys, tubes and ramps) or animal care control (ACC; pair-housed in standard cages) conditions. Each pair was bred, following assignment to their housing condition, and administered 100μg/kg of lipopolysaccharide (LPS) on gestational day 11. After birth, and until the end of the study, offspring were maintained in their respective housing conditions. EE protected against both the social and hypothalamic pituitary adrenal axis consequences of MIA in juvenile male rats, but surprisingly not against the spatial discrimination deficits or accompanying decrease in glutamate levels within the hippocampus (as measured via LCMS-MS). Based on these preliminary results, the mechanisms that underlie the sex-specific consequences that follow MIA appear to be dependent on environmental context. Together, this work highlights the importance of environmental complexity in the prevention of neurodevelopmental deficits following MIA.

Early life stress and serotonin transporter gene variation interact to affect the transcription of the glucocorticoid and mineralocorticoid receptors, and the co-chaperone FKBP5, in the adult rat brain

The short allelic variant of the serotonin transporter (5-HTT) promoter-linked polymorphic region (5-HTTLPR) has been associated with the etiology of major depression by interaction with early life stress (ELS). A frequently observed endophenotype in depression is the abnormal regulation of levels of stress hormones such as glucocorticoids. It is hypothesized that altered central glucocorticoid influence on stress-related behavior and memory processes could underlie the depressogenic interaction of 5-HTTLPR and ELS. One possible mechanism could be the altered expression of the genes encoding the glucocorticoid and mineralocorticoid receptors (GR, MR) and their inhibitory regulator FK506-binding protein 51 (FKBP5) in stress-related forebrain areas. To test this notion, we exposed heterozygous (5-HTT^+/−) and homozygous (5-HTT^−/−) serotonin transporter knockout rats and their wildtype littermates (5-HTT^+/+) to daily 3 h maternal separations from postnatal day 2 to 14. In the medial prefrontal cortex (mPFC) and hippocampus of the adult male offspring, we found that GR, MR, and FKBP5 mRNA levels were affected by ELS × 5-HTT genotype interaction. Specifically, 5-HTT^+/+ rats exposed to ELS showed decreased GR and FKBP5 mRNA in the dorsal and ventral mPFC, respectively. In contrast, 5-HTT^+/− rats showed increased MR mRNA levels in the hippocampus and 5-HTT^−/− rats showed increased FKBP5 mRNA in the ventral mPFC after ELS exposure. These findings indicate that 5-HTT genotype determines the specific adaptation of GR, MR, and FKBP5 expression in response to early life adversity. Therefore, altered extra-hypothalamic glucocorticoid signaling should be considered to play a role in the depressogenic interaction of ELS and 5-HTTLPR.

Long-term effects of maternal deprivation on the neuronal soma area in the rat neocortex

Early separation of rat pups from their mothers (separatio a matrem) is considered and accepted as an animal model of perinatal stress. Adult rats, separated early postnatally from their mothers, are developing long-lasting changes in the brain and neuroendocrine system, corresponding to the findings observed in schizophrenia and affective disorders. With the aim to investigate the morphological changes in this animal model we exposed 9-day-old (P9) Wistar rats to a 24 h maternal deprivation (MD). At young adult age rats were sacrificed for morphometric analysis and their brains were compared with the control group bred under the same conditions, but without MD. Rats exposed to MD had a 28% smaller cell soma area in the prefrontal cortex (PFCX), 30% in retrosplenial cortex (RSCX), and 15% in motor cortex (MCX) compared to the controls. No difference was observed in the expression of glial fibrillary acidic protein in the neocortex of MD rats compared to the control group. The results of this study demonstrate that stress in early life has a long-term effect on neuronal soma size in cingulate and retrosplenial cortex and is potentially interesting as these structures play an important role in cognition.

Modulation of early stress-induced neurobiological changes: a review of behavioural and pharmacological interventions in animal models

Childhood adversity alters the predisposition to psychiatric disorders later in life. Those with psychiatric conditions and a history of early adversity exhibit a higher incidence of treatment resistance compared with individuals with no such history. Modulation of the influence early stress exerts over neurobiology may help to prevent the development of psychiatric disorders in some cases, while attenuating the extent of treatment resistance in those with established psychiatric disorders. This review aims to critically evaluate the ability of behavioural, environmental and pharmacologic interventions to modulate neurobiological changes induced by early stress in animal models. Databases were systematically searched to locate literature relevant to this review. Early adversity was defined as stress that resulted from manipulation of the mother-infant relationship. Analysis was restricted to animal models to enable characterisation of how a given intervention altered specific neurobiological changes induced by early stress. A wide variety of changes in neurobiology due to early stress are amenable to intervention. Behavioural interventions in childhood, exercise in adolescence and administration of epigenetic-modifying drugs throughout life appear to best modulate cellar and behavioural alterations induced by childhood adversity. Other pharmacotherapies, such as endocannabinoid system modulators, anti-inflammatories and antidepressants can also influence these neurobiological and behavioural changes that result from early stress, although findings are less consistent at present and require further investigation. Further work is required to examine the influence that behavioural interventions, exercise and epigenetic-modifying drugs exert over alterations that occur following childhood stress in human studies, before possible translational into clinical practice is possible.

Cellular and molecular mechanisms of immunomodulation in the brain through environmental enrichment

Recent studies on environmental enrichment (EE) have shown cytokines, cellular immune components [e.g., T lymphocytes, natural killer (NK) cells], and glial cells in causal relationship to EE in bringing out changes to neurobiology and behavior. The purpose of this review is to evaluate these neuroimmune mechanisms associated with neurobiological and behavioral changes in response to different EE methods. We systematically reviewed common research databases. After applying all inclusion and exclusion criteria, 328 articles remained for this review. Physical exercise (PE), a form of EE, elicits anti-inflammatory and neuromodulatory effects through interaction with several immune pathways including interleukin (IL)-6 secretion from muscle fibers, reduced expression of Toll-like receptors on monocytes and macrophages, reduced secretion of adipokines, modulation of hippocampal T cells, priming of microglia, and upregulation of mitogen-activated protein kinase phosphatase-1 in central nervous system. In contrast, immunomodulatory roles of other enrichment methods are not studied extensively. Nonetheless, studies showing reduction in the expression of IL-1β and tumor necrosis factor-α in response to enrichment with novel objects and accessories suggest anti-inflammatory effects of novel environment. Likewise, social enrichment, though considered a necessity for healthy behavior, results in immunosuppression in socially defeated animals. This has been attributed to reduction in T lymphocytes, NK cells and IL-10 in subordinate animals. EE through sensory stimuli has been investigated to a lesser extent and the effect on immune factors has not been evaluated yet. Discovery of this multidimensional relationship between immune system, brain functioning, and EE has paved a way toward formulating environ-immuno therapies for treating psychiatric illnesses with minimal use of pharmacotherapy. While the immunomodulatory role of PE has been evaluated extensively, more research is required to investigate neuroimmune changes associated with other enrichment methods.

Sex-dependent effects of an early life treatment in rats that increases maternal care: vulnerability or resilience?

Early life stress (ELS) in rodents has profound long-term effects that are partially mediated by changes in maternal care. ELS not only induces “detrimental” effects in adulthood, increasing psychopathology, but also promotes resilience to further stressors. In Long-Evans rats, we evaluated a combination of two procedures as a model of ELS: restriction of bedding during the first post-natal days and exposure to a “substitute” mother. The maternal care of biological and “substitute” mothers was measured. The male and female offspring were evaluated during adulthood in several contexts. Anxiety was measured by the elevated plus-maze (EPM), acoustic startle response (ASR) and forced swim test (FST). In other group of animals, novelty-seeking was measured (activity in an inescapable novel environment, preference for novel environments and exploration of novel objects). Plasmatic ACTH and corticosterone in basal conditions and in response to stress were also measured. Cognitive impulsivity was assessed by a delay-discounting paradigm, and impulsive action, attention and compulsive-like behavior by a five choice serial reaction time task (5CSRTT). ELS decreased pup body weight and increased the care of the biological mother; however, the “substitute” mother did not exhibit overt maltreatment. A mixture of “detrimental” and “beneficial” effects was shown. In the 5CSRTT, attention was impaired in both genders, and in females, ELS increased compulsive-like behavior. Novel object exploration was only increased by ELS in males, but the preference for novel spaces decreased in both genders. Baseline anxiety (EPM and ASR) and recognition memory were not affected. Unexpectedly, ELS decreased the ACTH response to novelty and swim stress and increased active coping in the FST in both genders. Cognitive impulsivity was decreased only in females, but impulsive action was not affected. The enhancement in maternal care may “buffer” the effects of ELS in a context-dependent manner.

Prenatal transport stress, postnatal maternal behavior, and offspring sex differentially affect seizure susceptibility in young rats

Epilepsy is a heterogeneous and chronic neurological condition of undefined etiology in the majority of cases. Similarly, the pathogenesis of the unprovoked seizures that lead to epilepsy is not known. We are interested in the factors that modify inherent seizure susceptibility, with a particular focus on those occurring during the prenatal and early postnatal periods. Female Sprague-Dawley rats were bred in-house or transported during pregnancy at one of two gestational days (G9 or G16). The effects of transport stress, maternal behavior, and offspring sex were then examined in terms of how they were related to provoked seizure susceptibility to kainic acid (KA) or a model of febrile convulsions (FCs) on postnatal day 14 (P14). We also examined the pattern of neuronal activation in the hippocampus and amygdala as indicated by the density of FosB protein immunoreactivity (FosB-ir). Results demonstrated only a small and inconsistent effect of transport alone, suggesting that the groups differed slightly prior to experimental manipulations. However, the influence of maternal behaviors such as licking and grooming (LG), arched back nursing (ABN), and dam-off time (DO) exerted a much stronger effect on the offspring. Dams designated as high LG gave birth to smaller litters, had pups that weighed less, had greater seizure susceptibility and severity, and had more FosB-ir neurons predominantly in the ventral hippocampus and the medial subnucleus of the amygdala (MeA). We also found a sex-dependent effect such that P14 males were smaller than their female littermates and had a greater seizure susceptibility and severity. Taken together, these results suggest an impact of prenatal and postnatal factors, as well as sex, on seizure susceptibility in young animals.

Exposure to enriched environment decreases neurobehavioral deficits induced by neonatal glutamate toxicity

Environmental enrichment is a popular strategy to enhance motor and cognitive performance and to counteract the effects of various harmful stimuli. The protective effects of enriched environment have been shown in traumatic, ischemic and toxic nervous system lesions. Monosodium glutamate (MSG) is a commonly used taste enhancer causing excitotoxic effects when given in newborn animals. We have previously demonstrated that MSG leads to a delay in neurobehavioral development, as shown by the delayed appearance of neurological reflexes and maturation of motor coordination. In the present study we aimed at investigating whether environmental enrichment is able to decrease the neurobehavioral delay caused by neonatal MSG treatment. Newborn pups were treated with MSG subcutaneously on postnatal days 1, 5 and 9. For environmental enrichment, we placed rats in larger cages, supplemented with different toys that were altered daily. Normal control and enriched control rats received saline treatment only. Physical parameters such as weight, day of eye opening, incisor eruption and ear unfolding were recorded. Animals were observed for appearance of reflexes such as negative geotaxis, righting reflexes, fore- and hindlimb grasp, fore- and hindlimb placing, sensory reflexes and gait. In cases of negative geotaxis, surface righting and gait, the time to perform the reflex was also recorded daily. For examining motor coordination, we performed grid walking, footfault, rope suspension, rota-rod, inclined board and walk initiation tests. We found that enriched environment alone did not lead to marked alterations in the course of development. On the other hand, MSG treatment caused a slight delay in reflex development and a pronounced delay in weight gain and motor coordination maturation. This delay in most signs and tests could be reversed by enriched environment: MSG-treated pups kept under enriched conditions showed no weight retardation, no reflex delay in some signs and performed better in most coordination tests. These results show that environmental enrichment is able to decrease the neurobehavioral delay caused by neonatal excitotoxicity.

Behavioral and neurochemical characterization of maternal care effects on juvenile Sprague-Dawley rats

Maternal care represents a major constituent of early life environment and has the potential to modulate critical neurobehavioral responses to stress. The aim of the present study was to determine the effects of naturally occurring variations in maternal care on behavioral and neurochemical responses of juvenile Sprague-Dawley rats. A group of dams were classified based on their licking behavior in high and low licking-grooming mothers. Afterwards, the male offspring was tested in a series of behavioral tests: open field test (OFT), elevated plus maze (EPM) and forced swimming test (FST). Additionally, monoamine concentrations were determined post-mortem in three brain regions: hippocampus, ventral striatum and prefrontal cortex. Our findings suggest that maternal care variations have an effect on several anxiety-related behaviors in OFT and EPM but not in depression-like behaviors in FST. Such behavioral differences could be related to an increased DOPAC concentration and 5-HT turnover in prefrontal cortex. These evidences suggest that natural variations in maternal care modified some behavioral and neurochemical parameters related with anxiety and stress in this strain.