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

Early life adversities, psychopathologies and novel pharmacological strategies

Exposure to adversities during early life stages (early life adversities - ELA), ranging from pregnancy to adolescence, represents a major risk factor for the vulnerability to mental disorders. Hence, it is important to understand the molecular and functional underpinning of such relationship, in order to develop strategies aimed at reducing the psychopathologic burden associated with ELA, which may eventually lead to a significant improvement in clinical practice. In this review, we will initially recapitulate clinical and preclinical evidence supporting the link between ELA and psychopathology and we will primarily discuss the main biological mechanisms that have been described as potential mediators of the effects of ELA on the psychopathologic risk, including the role for genetic factors as well as sex differences. The knowledge emerging from these studies may be instrumental for the development of novel therapeutic strategies aimed not only at correcting the deficits that emerge from ELA exposure, but also in preventing the manifestation of a full-blown psychopathologic condition. With this respect, we will specifically focus on adolescence as a key time frame for disease onset as well as for early therapeutic intervention. We believe that incorporating clinical and preclinical research data in the context of early life adversities can be instrumental to elucidate the mechanisms contributing to the risk for psychopathology or that may promote resilience. This will ultimately allow the identification of 'at risk' individuals who may benefit from specific forms of interventions that, by interfering with disease trajectories, could result in more benign clinical outcomes.

Boosting decision-making in rat models of early-life adversity with environmental enrichment and intranasal oxytocin

Impaired decision-making constitutes a fundamental issue in numerous psychiatric disorders. Extensive research has established that early life adversity (ELA) increases vulnerability to psychiatric disorders later in life. ELA in human neonates is associated with changes in cognitive, emotional, as well as reward-related processing. Maternal separation (MS) is an established animal model of ELA and has been shown to be associated with decision-making deficits. On the other hand, enriched environment (EE) and intranasal oxytocin (OT) administration have been demonstrated to have beneficial effects on decision-making in humans or animals. Given these considerations, our investigation sought to explore the impact of brief exposure to EE and intranasal OT administration on the decision-making abilities of adolescent rats that had experienced MS during infancy. The experimental protocol involved subjecting rat pups to the MS regimen for 180 min per day from postnatal day (PND) 1 to PND 21. Then, from PND 22 to PND 34, the rats were exposed to EE and/or received intranasal OT (2 μg/μl) for seven days. The assessment of decision-making abilities, using a rat gambling task (RGT), commenced during adolescence. Our findings revealed that MS led to impaired decision-making and a decreased percentage of advantageous choices. However, exposure to brief EE or intranasal OT administration mitigated the deficits induced by MS and improved the decision-making skills of maternally-separated rats. Furthermore, combination of these treatments did not yield additional benefits. These results suggest that EE and OT may hold promise as therapeutic interventions to enhance certain aspects of cognitive performance.

A single 24 h maternal separation at PND 9 promotes behavioral resilience of female C57BL/6J mice and the possible role of hippocampal Homer1a

Early life stress (ELS) has been thought to increase vulnerability to developing psychiatric disorders later in life, while some researchers have found that adversity early in life may promote stress resilience. Studies investigating the resilient effect of maternal separation (MS) are still relatively few, and the underlying mechanisms remain unknown. In the current study, the effect of a single 24 h MS paradigm at postnatal day 9 (PND 9) in female C57BL/6J mice was investigated by assessing behavioral performance in middle adolescence. We demonstrated that, mice in MS group displayed decreased anxiety-like behavior and increased exploratory behavior than controls in the open field test and elevated plus maze test. Furthermore, MS mice exhibited improved hippocampal-dependent spatial learning in the Morris water maze test. This performance indicated behavioral resilience to early life stress. The protein expression levels of Homer1 isoforms, which are implicated in a variety of neuropsychiatric disorders, were evaluated using Western blot analysis. A significant increase in hippocampal Homer1a protein expression was observed immediately after MS, which subsequently decreased until adolescence (PND 27-42), when a significant increase was observed again. This distinctive change of hippocampal Homer1a protein expression pattern indicated that hippocampal Homer1a might play a role in behavioral resilience to MS in female C57BL/6J mice. In conclusion, this study demonstrated that exposure to a single 24 h MS at PND 9 promoted behavioral resilience of female C57BL/6J mice in middle adolescence. This behavioral resilience might be related to increased expression of hippocampal Homer1a.

Perinatal environmental enrichment changes anxiety-like behaviours in mice and produces similar intergenerational benefits in offspring

Environmental enrichment implemented in early life is able to induce long-term changes in gene expression, synaptic function and behavioural responses. In this study, we evaluated the adult behavioural effects of perinatal environment enrichment in male and female mice (PEE), as well as the males and females of PEE male offspring (OPEE). For this purpose, animals were submitted to the following battery of behavioural analyses: elevated plus maze, open field test, light-dark box and novelty suppression feeding test. The frontal cortex and ventral hippocampus of PEE mice were collected for the evaluation of the expression of gamma-aminobutyric acid (GABA)-related genes. The PEE animals showed an increase in exploratory activity, associated with a reduction in anxiety-like behaviours on the elevated plus maze; this effect was mainly observed in males. Additionally, the male OPEE showed a reduction in anxiety-like behaviours on the elevated plus maze, mainly observed in a reduction of risk assessment-related behaviours. The PEE male mice also showed reduced expression of Gabra3 in the ventral hippocampus when compared to the control group. These results demonstrate that perinatal environmental enrichment promotes a reduction in anxiety-like behaviour that can be transferred intergenerationally.

One day away from mum has lifelong consequences on brain and behaviour

This chapter presents a brief overview of attachment theory and discusses the importance of the neonatal period in shaping an individual's physiological and behavioural responses to stress later in life, with a focus on the role of the parent-infant relationship, particularly in rodents. In rodents, the role of maternal behaviours goes far beyond nutrition, thermoregulation and excretion, acting as hidden regulators of the pup's physiology and development. In this review, we will discuss the inhibitory role of specific maternal behaviours on the ACTH and corticosterone (CORT) stress response. The interest of our group to explore the long-term consequences of maternal deprivation for 24 h (DEP) at different ages (3 days and 11 days) in rats was sparked by its opposite effects on ACTH and CORT levels. In early adulthood, DEP3 animals (males and females alike) show greater negative impact on affective behaviours and stress related parameters than DEP11, indicating that the latter is more resilient in tests of anxiety-like behaviour. These findings create an opportunity to explore the neurobiological underpinnings of vulnerability and resilience to stress-related disorders. The chapter also provides a brief historical overview and highlights the relevance of attachment theory, and how DEP helps to understand the effects of childhood parental loss as a risk factor for depression, schizophrenia, and PTSD in both childhood and adulthood. Furthermore, we present the concept of environmental enrichment (EE), its effects on stress responses and related behavioural changes and its benefits for rats previously subjected to DEP, along with the clinical implications of DEP and EE.

The impact of environmental factors during maternal separation on the behaviors of adolescent C57BL/6 mice

Neonatal maternal separation is a widely used method to construct an early-life stress model in rodents. In this method, pups are separated from their mothers for several hours every day during the first 2 weeks of life, which results in adverse early-life events. It is a known fact that maternal separation can exert a significant impact on the behavior and psychological health, such as anxiety and depression, in adolescent offspring. However, environmental conditions during maternal separation can differ such as the presence of other animals or by placing pups in a different dam. To investigate the differential effects of various conditions of maternal separation on the behavior of adolescent mice, we created the following groups: (1) iMS group: pups were moved to an isolated room with no other adult mice in a nearby cage, (2) eDam group: the pups randomly exchanged their dams, (3) OF group: pups were shifted to another cage with the bedding material containing maternal odor (olfactory stimulation), and (4) MS group: pups were shifted to another vivarium. From postnatal day (PND) 2-20 (i.e., 19 consecutive days), pups were separated from the dam daily for 4 h and exposed to various environments (MS, iMS, eDam, and OF) or were left undisturbed [control (CON) group]. A series of behavioral assessments were conducted to evaluate locomotion, anxiety, recognition, learning, and memory in adolescent offspring. The results showed that neonatal maternal separation led to impaired recognition memory, motor coordination, and motor skill learning across all groups. However, the iMS group exhibited anxiety-like behavior in the elevated plus maze test and enhanced the extinction of fear memory in the auditory fear conditioning test. The OF and eDam groups displayed partially recovered short-term working memory in the Y-maze test but exhibited opposite exploratory behaviors. The OF group spent more time in the center, while the eDam group spent less time. These findings demonstrated that exposure to different environmental conditions during maternal separation causes behavioral alterations in adolescent offspring, providing a potential explanation for the variation in behavioral phenotypes observed in the early-life stress models.

Microbe-Immune-Stress Interactions Impact Behaviour during Postnatal Development

Decades of research have established the role of microbiota-brain communication in behaviour and brain function. Studies have shown that microbiota composition and diversity are influenced by a variety of factors including host genetics, diet, and other environmental exposures, with implications for the immunological and neurobiological development of the host organism. To further understand early-life interactions between environment, genetic factors, the microbiome and the central nervous system, we investigated the impact of postnatal stress in C57Bl/6 wild type and T-cell deficient mice on microbe-brain interactions and behaviour. Mice were exposed to immune challenge with lipopolysaccharide (LPS) at postnatal day (P) 3 and maternal separation at P9 (16 h overnight). Behavioural assessment of growth and development as well as behaviour (righting reflex, ultrasonic vocalizations in response to brief maternal separation, open field, sociability, and grooming) was conducted. Microbiota diversity and composition of fecal samples collected at P24 revealed reduced alpha diversity in T-cell-deficient mice as well as genotype- and stress-related taxa. Notably, integrated analyses of microbiota and behaviour in the context of immunocompromise revealed key behavioural related taxa that may be important to brain development. These findings are important to determining the influence of genetic and environmental factors on gut microbiota and advances our understanding microbiome-brain signaling pathways on neurodevelopment and behaviour.

Investigating the role of environmental enrichment initiated in adolescence against the detrimental effects of chronic unpredictable stress in adulthood: Sex-specific differences in behavioral and neuroendocrinological findings

Environmental Enrichment (EE) improves cognitive function and enhances brain plasticity, while chronic stress increases emotionality, impairs learning and memory, and has adverse effects on brain anatomy and biochemistry. We explored the beneficial role of environmental enrichment initiated in adolescence against the negative outcomes of Chronic Unpredictable Stress (CUS) during adulthood on emotional behavior, cognitive function, as well as somatic and neuroendocrine markers in both sexes. Adolescent Wistar rats housed either in enriched or standard housing conditions for 10 weeks. On postnatal day 66, a subgroup from each housing condition was daily exposed to a 4-week stress protocol. Following stress, adult rats underwent behavioral testing to evaluate anxiety, exploration/locomotor activity, depressive-like behavior and spatial learning/memory. Upon completion of behavioral testing, animals were exposed to a 10-m stressful event to test the neuroendocrine response to acute stress. CUS decreased body weight gain and increased adrenal weight. Some stress-induced behavioral adverse effects were sex-specific since learning impairments were limited to males while depressive-like behavior to females. EE housing protected against CUS-related behavioral deficits and body weight loss. Exposure to CUS affected the neuroendocrine response of males to acute stress as revealed by the increased corticosterone levels. Our findings highlight the significant role of EE in adolescence as a protective factor against the negative effects of stress and underline the importance of inclusion of both sexes in animal studies.

Effects of early life adversities upon memory processes and cognition in rodent models

Exposure to stressors in early postnatal life induces long-lasting modifications in brainfunction.Thisplasticity,an essential characteristic of the brain that enables adaptation to the environment, may also induce impairments in some psychophysiological functions, including learning and memory. Early life stress (ELS) has long-term effects on thehypothalamic-pituitary-adrenal axisresponse to stressors, and has been reported to lead toneuroinflammation,altered levelsof neurotrophic factors, modifications inneurogenesis andsynaptic plasticity,with changes in neurotransmitter systems and network functioning. In this review, we focus on early postnatal stress in animal models and their effects on learning and memory.Many studies have reported ELS-induced impairments in different types of memories, including spatial memory, fear memory, recognition (both for objects and social) memory, working memory and reversal learning. Studies are not always in agreement, however, no effects, or sometimes facilitation, being reported, depending on the nature and intensity of the early intervention, as well as the age when the outcome was evaluated and the sex of the animals. When considering processes occurring after consolidation, related with memory maintenance or modification, there are a very reduced number of reports. Future studies addressing the mechanisms underlying memory changes for ELS should shed some light on the understanding of the different effects induced by stressors of different types and intensities on cognitive functions.

Providing Environmental Enrichment without Altering Behavior in Male and Female Wistar Rats (Rattus norvegicus)

In research using animal models, subjects are commonly maintained under standard housing conditions, mainly because of the idea that enhancing welfare conditions could alter experimental data. Another common practice in many laboratories relates to the preponderant use of males. Several reasons justifying this practice include the rapid hormonal and endocrine change in females, which may require a higher number of female animals to achieve more homogenous groups, thereby creating a dilemma with the reduction principle in animal research. In past decades, a relationship between enriched environments and enhanced cognitive functions has been reported in rats, but many of those enriched environmental protocols were not systematically or rigorously studied, leading to unexpected effects on behavior. Here we report the effects of 4 types of housing conditions (standard, structural changes, exercise, and foraging) in Wistar rats on anxiety (elevated plus maze), exploratory (open field), and stress vulnerability (forced swim test) responses. Sex was used as a blocking factor. Data show no effect of housing conditions on anxiety and exploratory behaviors, but do show an effect on stress responses. These results suggest the possibility of using a protocol for environmental enrichment without concern about altering experimental data. From this stand, new ways to enhance animal welfare in research laboratories could be designed and implemented.

Distribution of Aquaporin-4 channels in hippocampus and prefrontal cortex in mk-801-treated balb/c mice

Functional disorders of the glymphatic system and Aquaporin-4 (AQP-4) channels take part in the pathophysiology of neurodegenerative disease. The aim of this study was to describe the distribution of AQP-4 channels in the prefrontal cortex and hippocampus in a mouse model of NMDA receptor blocking agent-induced schizophrenia-like behavior model. NMDA receptor antagonist MK-801 was used to produce the experimental schizophrenia model. MK-801 injections were administered for eleven days to Balb/c mice intraperitoneally. Beginning from the sixth day of injection, the spatial learning and memory of the mice were tested by the Morris water maze (MWM) task. A group of mice was injected with MK-801 for ten days without the MWM task. Hippocampus and prefrontal specimens were collected from this group. Tissue samples were stained immunohistochemically and AQP-4 channels were examined by electron microscope. Time to find the platform was significantly longer at MK-801 injected group than the control group at the MWM task. Also, time spent at the target quadrant by the MK-801 group was shorter compared to the control group. AQP-4 expression increased significantly at MK-801 group glial cells, neuronal perikaryon, perineuronal and pericapillary spaces. In the MK-801 group, there was remarkable damage in neurons and glial cells. Increased AQP-4 channel expression and neurodegeneration at the MK-801 group induced with schizophrenia-like behavior model. MK-801 induced NMDA receptor blockade causes a decline in cognitive and memory functions. Increased AQP-4 expression at the prefrontal cortex and hippocampus to elicit and transport products of synaptic neurotransmitters and end metabolites is suggested.

Environmental enrichment and intranasal oxytocin administration reverse maternal separation-induced impairments of prosocial choice behavior

Adverse early life experiences influence behavioral and physiological functions and increase vulnerability to neuropsychiatric disorders. Maternal separation (MS) is an established animal model that reproduces the features of chronic stress or adverse experiences during early life. Previous studies have been shown that MS may lead to impairments of social behaviors. Here, we investigated the effects of MS on mutual reward preferences in a double T-maze prosocial choice task. Since enriched environment (EE) and intranasal oxytocin (OT) administration have beneficial effects on cognition and social behaviors, in the present study we tested whether these treatments, alone or in combination, would affect prosocial behavior of rats which underwent MS during infancy. Rat pups underwent MS paradigm for 180 min/day from postnatal day (PND) 1-21. From PND 22-34, rats were exposed to an EE and/or received intranasal OT (2 μg/μl, 7 days). Hence, the 8 groups consisted of control (CTRL), MS, CTRL+EE, CTRL+OT and the saline groups. Assessment of prosocial choice behavior was started in adolescence. MS impaired prosocial choice behavior and reduced mutual reward preferences. Getting exposed to EE and intranasal OT administration could overcome MS-induced deficits and promoted mutual reward preferences of MS rats. Combination of short-term EE and OT strengthened prosocial behavior. Obtained results showed that EE and OT may be considered as profitable therapeutic approaches for promoting some aspects of social behavior.

Effects of short environmental enrichment on early-life adversity induced cognitive alternations in adolescent rats

Early-life experiences, including parental care, affect cognitive performance later in life. Being exposed to early-life maternal separation (MS) increases susceptibility to stress-related psychopathology. Previous studies suggest that MS could induce learning and memory impairments. Since enriched environment (EE) provides more opportunities for exploration and social interaction, in the present study we evaluated the effects of a short EE paradigm with a duration of 13 days on cognitive abilities of maternally separated rats (MS; 180 min/day, postnatal day (PND) 1-21) during adolescence in four experimental groups: Control, Control+EE, MS, and MS+EE. Plasma corticosterone (CORT) and brain-derived neurotrophic factor (BDNF) levels were also measured in experimental animals. We also studied the induction of long-term potentiation (LTP) in the slices of hippocampal CA1 area. The behavioral and electrophysiological assessments were started at PND 35. MS caused higher basal CORT levels in plasma and impaired spatial learning, memory, and social interaction. LTP induction was also impaired in MS rats and plasma BDNF levels were reduced in these animals. MS also induced more anxiety-like behavior. Short EE reduced plasma CORT levels had the potential to improve locomotor activity and anxiety-like behavior in MS+EE rats and reversed MS-induced impairments of spatial learning, memory, and social behavior. LTP induction and plasma BDNF levels were also enhanced in MS+EE rats. We concluded that short EE might be considered as a therapeutic strategy for promoting cognition.

Enhancement of the GluN2B subunit of glutamatergic NMDA receptors in rat brain areas after cocaine abstinence

BACKGROUND

Cocaine use disorder is associated with compulsive drug-seeking and drug-taking, whereas relapse may be induced by several factors, including stress, drug-related places, people, and cues. Recent observations strongly support the involvement of the N-methyl-D-aspartate (NMDA) receptors in cocaine use disorders and abstinence, whereas withdrawal in different environments may affect the intensification of relapse.

METHODS

The aim of this study was to examine the GluN2B subunit expression and its association with the postsynaptic density protein 95 (PSD95) in several brain structures in rats with a history of cocaine self-administration and housed either in an enriched environment or in an isolated condition. Furthermore, a selective antagonist of the GluN2B subunit-CP 101,606 (10 and 20 mg/kg) administered during exposure to cocaine or a drug-associated conditional stimulus (a cue) was used to evaluate seeking behavior in rats.

RESULTS

In rats previously self-administering cocaine, we observed an increase in the GluN2B expression in the total homogenate from the dorsal hippocampus under both enriched environment and isolation. Cocaine abstinence under isolation conditions increased the GluN2B and GluN2B/PSD95 complex levels in the PSD fraction of the prelimbic cortex in rats previously self-administering cocaine. Administration of CP 101,606 attenuated cue-induced cocaine-seeking behavior only in isolation-housed rats.

CONCLUSION

In summary, in this study we showed region-specific changes in both the expression of GluN2B subunit and NMDA receptor trafficking during cocaine abstinence under different housing conditions. Furthermore, we showed that the pharmacological blockade of the GluN2B subunit may be useful in attenuating cocaine-seeking behavior.

The impact of environmental and social factors on learning abilities: a meta-analysis

Since the 1950s, researchers have examined how differences in the social and asocial environment affect learning in rats, mice, and, more recently, a variety of other species. Despite this large body of research, little has been done to synthesize these findings and to examine if social and asocial environmental factors have consistent effects on cognitive abilities, and if so, what aspects of these factors have greater or lesser impact. Here, we conducted a systematic review and meta-analysis examining how different external environmental features, including the social environment, impact learning (both speed of acquisition and performance). Using 531 mean-differences from 176 published articles across 27 species (with studies on rats and mice being most prominent) we conducted phylogenetically corrected mixed-effects models that reveal: (i) an average absolute effect size |d| = 0.55 and directional effect size d = 0.34; (ii) interventions manipulating the asocial environment result in larger effects than social interventions alone; and (iii) the length of the intervention is a significant predictor of effect size, with longer interventions resulting in larger effects. Additionally, much of the variation in effect size remained unexplained, possibly suggesting that species differ widely in how they are affected by environmental interventions due to varying ecological and evolutionary histories. Overall our results suggest that social and asocial environmental factors do significantly affect learning, but these effects are highly variable and perhaps not always as predicted. Most notably, the type (social or asocial) and length of interventions are important in determining the strength of the effect.

Maternal separation impairs mother's cognition 1 month beyond the separation

OBJECTIVE

Separation of pups from their dam during the infancy not only has detrimental effects on the pups' brain but also affects dams' behavior. Postpartum stress may affect mothers' cognitive functions. In the present study, by using a 180-min day^-1 maternal separation (MS) paradigm, we assessed anxiety-like behavior and locomotor activity of rat dams which experienced separation from postnatal day (PND) 1 until weaning. We tried for the first time to clarify whether such separation impairs dam's performance in the Morris water maze.

METHOD

We assessed dams' behavior at three time points: 24 h, 1 week, and 1 month after weaning. Therefore, the six groups consisted of control (CTRL) 24 h, 1 week, and 1 month and MS 24 h, 1 week, and 1 month, which was allocated in this study.

RESULTS

Our results revealed that although MS-24 h and MS-1 week groups had intact locomotor activity, MS-1 month group showed less locomotor activity in the open field. Moreover, MS-induced anxiety-like behavior was more pronounced in MS-1 week and MS-1 month dams. Spatial learning and memory was also impaired only in MS-1 month dams.

CONCLUSION

We can conclude that MS induces cognitive impairments in dam that may appear not immediately after the separation but a few weeks after such stressful event.

Maternal Deprivation in Rats Decreases the Expression of Interneuron Markers in the Neocortex and Hippocampus

Early life stress has profound effects on the development of the central nervous system. We exposed 9-day-old rat pups to a 24 h maternal deprivation (MD) and sacrificed them as young adults (60-day-old), with the aim to study the effects of early stress on forebrain circuitry. We estimated numbers of various immunohistochemically defined interneuron subpopulations in several neocortical regions and in the hippocampus. MD rats showed reduced numbers of parvalbumin-expressing interneurons in the CA1 region of the hippocampus and in the prefrontal cortex, compared with controls. Numbers of reelin-expressing and calretinin-expressing interneurons were also reduced in the CA1 and CA3 hippocampal areas, but unaltered in the neocortex of MD rats. The number of calbinin-expressing interneurons in the neocortex was similar in the MD rats compared with controls. We analyzed cell death in 15-day-old rats after MD and found no difference compared to control rats. Thus, our results more likely reflect the downregulation of markers than the actual loss of interneurons. To investigate synaptic activity in the hippocampus we immunostained for glutamatergic and inhibitory vesicular transporters. The number of inhibitory synapses was decreased in the CA1 and CA3 regions of the hippocampus in MD rats, with the normal number of excitatory synapses. Our results indicate complex, cell type-specific, and region-specific alterations in the inhibitory circuitry induced by maternal deprivation. Such alterations may underlie symptoms of MD at the behavioral level and possibly contribute to mechanisms by which early life stress causes neuropsychiatric disorders, such as schizophrenia.

Intranasal oxytocin administration facilitates the induction of long-term potentiation and promotes cognitive performance of maternally separated rats

Maternal separation (MS) is known to induce permanent changes in the central nervous system and is associated with increased levels of anxiety and cognitive impairments. The neuropeptide oxytocin (OT) has been implicated in a broad spectrum of social and nonsocial and behaviors. Since it plays a significant role in learning and memory and enhances synaptic plasticity, we hypothesized that OT may affect MS-induced changes in synaptic plasticity and cognitive performance. Rat pups underwent MS protocol for 180 min/day from postnatal day (PND) 1-21. OT was administered intranasally (2 μg/μl, 7 days) to control and MS groups from PND 22-34. Plasma corticosterone (CORT) levels, anxiety-like behavior, sociability, learning and memory were measured in adolescent rats. In addition, extracellular evoked field excitatory postsynaptic potentials (fEPSP) were also recorded from hippocampal slices. MS induced higher plasma CORT levels and impaired social interaction, learning and memory. Moreover, MS reduced locomotor activity and increased anxiety-like behavior. Intranasal OT could overcome MS-induced deficits and promoted sociability, learning and memory of MS rats. OT also enhanced locomotor activity in the open field and decreased anxiety-like behavior. Obtained results showed that long term potentiation (LTP) was not induced in MS animals. However, OT injection overcame the MS-induced impairment in LTP generation in CA1 area of the hippocampus.

Enriched environment enhances histone acetylation of NMDA receptor in the hippocampus and improves cognitive dysfunction in aged mice

The mechanisms of age-associated memory impairment may be associated with glutamate receptor function and chromatin modification. To observe the effect of an enriched environment on the cognitive function of mice with age-associated memory impairment, 3-month-old C57BL/6 male mice ("young" mice) were raised in a standard environment, while 24-month-old C57BL/6 male mice with memory impairment ("age-associated memory impairment" mice) were raised in either a standard environment or an enriched environment. The enriched environment included a variety of stimuli involving movement and sensation. A water maze test was then used to measure cognitive function in the mice. Furthermore, quantitative real-time polymerase chain reaction and western blot assays were used to detect right hippocampal GluN2B mRNA as well as protein expression of GluN2B and CREB binding protein in all mice. In addition, chromatin immunoprecipitation was used to measure the extent of histone acetylation of the hippocampal GluN2B gene promoters. Compared with the young mice, the water maze performance of age-associated memory impairment mice in the standard environment was significantly decreased. In addition, there were significantly lower levels of total histone acetylation and expression of CREB binding protein in the hippocampus of age-associated memory impairment mice in the standard environment compared with the young mice. There were also significantly lower levels of histone acetylation, protein expression, and mRNA expression of GluN2B in the hippocampus of these mice. In contrast, in the age-associated memory impairment mice with the enriched environment intervention, the water maze performance and molecular biological indexes were significantly improved. These data confirm that an enriched environment can improve cognitive dysfunction in age-associated memory impairment mice, and suggest that the mechanisms may be related to the increased expression of CREB binding protein and the increased degree of total histone acetylation in the hippocampus of age-associated memory impairment mice, which may cause the increase of histone acetylation of GluN2B gene promoter and the enhancement of GluN2B mRNA transcription and protein expression in hippocampus. The animal experiment was approved by the Animal Ethics Committee of Yangzhou University, China (approval No. 20170312001) in March 2017.

Environmental enrichment and its influence on rodent offspring and maternal behaviours, a scoping style review of indices of depression and anxiety

Environmental enrichment is a widely used experimental manipulation that consistently shows measurable effects on rodent behaviour across the lifespan. This scoping review assesses and thematically summarizes the literature of the past decade concerning the effects of environmental enrichment applied during sensitive developmental periods in rodent mothers and offspring. Maternal behaviours as well as maternal and offspring anxiety- and depressive-like behaviours are considered. Relevant terms were searched across five databases (Embase, MEDLINE, PsycINFO, PubMed, Web of Science) and articles were screened with inclusion and exclusion criteria. The remaining articles were thematically analysed. Our results suggest that a greater number of articles reviewed the impacts of environmental enrichment on offspring anxiety-like behaviour (n = 23) rather than on depressive-like behaviour (n = 11) or maternal caregiving behaviour (n = 12). Maternal anxiety- (n = 4) or depressive-like (n = 2) behaviours are not often evaluated for in enrichment studies. The main behavioural tests of anxiety that were reviewed include the elevated plus-maze, the open field test, and the light-dark box whereas those for depression included the forced swim test and the sucrose preference test. Our results yielded mixed findings and significant variation in behavioural responses across all tests. In mothers, trends of increased maternal care behaviours and decreased maternal depressive-like behaviours in enriched mothers were appreciated. Enrichment during the gestational period was identified as pivotal to creating behavioural change in mother subjects. In enriched offspring rodents, a trend towards decreased anxiety-like behaviours was observed most often. Potential confounds inherent in enrichment paradigms and relevant theories of enrichment and their relation to rodent behavioural tests are discussed.

Reverse translation of major depressive disorder symptoms: A framework for the behavioural phenotyping of putative biomarkers

BACKGROUND

Reverse translating putative biomarkers of depression from patients to animals is complex because Major Depressive Disorder (MDD) is a highly heterogenous condition. This review proposes an approach to reverse translation based on relating relevant bio-behavioural functions in laboratory rodents to MDD symptoms.

METHODS

This systematic review outlines symptom clusters assessed by psychometric tests of MDD and antidepressant treatment response including the Montgomery-Åsberg Depression Rating Scale, the Hamilton Depression Rating Scale, and the Beck Depression Inventory. Symptoms were related to relevant behavioural assays in laboratory rodents.

RESULTS

The resulting battery of tests includes passive coping, anxiety-like behaviours, sleep, caloric intake, cognition, psychomotor functions, hedonic reactivity and aversive learning. These assays are discussed alongside relevant clinical symptoms of MDD, providing a framework through which reverse translation of a biomarker can be interpreted.

LIMITATIONS

Certain aspects of MDD may not be quantified by tests in laboratory rodents, and their biological significance may not always be of clinical relevance.

CONCLUSIONS

Using this reverse translation approach, it is possible to clarify the functional significance of a putative biomarker in rodents and hence translate its contribution to specific clinical symptoms, or clusters of symptoms.

Attachment Dimensions and Spatial Navigation in Female College Students: The Role of Comfort With Closeness and Confidence in Others

There is preliminary evidence suggesting that hippocampal functioning is associated with attachment style. However, it is unknown if attachment is also associated with hippocampal-related cognitive function such as spatial learning and recall. This study aims to verify if attachment dimensions are associated with spatial learning and recall. Sixty-five female participants were recruited and were evaluated using the Adult Attachment Scale-R and tested on a virtual maze navigation task (VMT) at one moment (exploratory trial + 3 trials) and 24 h later (3 trials). There was a significant Moment × Trial × Close-Depend interaction for the outcome time, F(2,126) = 3.807, p = 0.025, with post hoc analysis indicating that the High Close-Depend group displayed significant improvements between Trial 1 and Trial 3 in the post-test assessment. Conversely, the Low Close-Depend group displayed significant improvements between Trial 1and Trial 3 but on the pre-test assessment. Furthermore, the Low Close-Depend group presented significant better performance in pre-test Trial 3 in comparison to the High Close-Depend group. Thereby, it seems that low comfort with proximity and trust in others is associated with reduced spatial recall, although spatial learning performance was actually superior in these participants. It is possible that reduced exposure to social interaction and meaningful relationships may be reduced in the Low Close-Depend group, leading to modifications in hippocampal function and, ultimately, reduced spatial recall. Oppositely, participants in the High Close-Depend group may not display typical spatial learning in the proposed task as they are more willing to freely explore the presented environment.

Construct and face validity of a new model for the three-hit theory of depression using PACAP mutant mice on CD1 background

Major depression is a common cause of chronic disability. Despite decades of efforts, no equivocally accepted animal model is available for studying depression. We tested the validity of a new model based on the three-hit concept of vulnerability and resilience. Genetic predisposition (hit 1, mutation of pituitary adenylate cyclase-activating polypeptide, PACAP gene), early-life adversity (hit 2, 180-min maternal deprivation, MD180) and chronic variable mild stress (hit 3, CVMS) were combined. Physical, endocrinological, behavioral and functional morphological tools were used to validate the model. Body- and adrenal weight changes as well as corticosterone titers proved that CVMS was effective. Forced swim test indicated increased depression in CVMS PACAP heterozygous (Hz) mice with MD180 history, accompanied by elevated anxiety level in marble burying test. Corticotropin-releasing factor neurons in the oval division of the bed nucleus of the stria terminalis showed increased FosB expression, which was refractive to CVMS exposure in wild-type and Hz mice. Urocortin1 neurons became over-active in CMVS-exposed PACAP knock out (KO) mice with MD180 history, suggesting the contribution of centrally projecting Edinger-Westphal nucleus to the reduced depression and anxiety level of stressed KO mice. Serotoninergic neurons of the dorsal raphe nucleus lost their adaptation ability to CVMS in MD180 mice. In conclusion, the construct and face validity criteria suggest that MD180 PACAP HZ mice on CD1 background upon CVMS may be used as a reliable model for the three-hit theory.

Altered brain network topology in left-behind children: A resting-state functional magnetic resonance imaging study

Whether a lack of direct parental care affects brain function in children is an important question, particularly in developing countries where hundreds of millions of children are left behind when their parents migrate for economic or political reasons. In this study, we investigated changes in the topological architectures of brain functional networks in left-behind children (LBC). Resting-state functional magnetic resonance imaging data were obtained from 26 LBC and 21 children living within their nuclear family (non-LBC). LBC showed a significant increase in the normalized characteristic path length (λ), suggesting a decrease in efficiency in information access, and altered nodal centralities in the fronto-limbic regions and motor and sensory systems. Moreover, a decreased nodal degree and the nodal betweenness of the right rectus gyrus were positively correlated with annual family income. The present study provides the first empirical evidence that suggests that a lack of direct parental care could affect brain functional development in children, particularly involving emotional networks.

The Regulation of GluN2A by Endogenous and Exogenous Regulators in the Central Nervous System

The NMDA receptor is the most widely studied ionotropic glutamate receptor, and it is central to many physiological and pathophysiological processes in the central nervous system. GluN2A is one of the two main types of GluN2 NMDA receptor subunits in the forebrain. The proper activity of GluN2A is important to brain function, as the abnormal regulation of GluN2A may induce some neuropsychiatric disorders. This review will examine the regulation of GluN2A by endogenous and exogenous regulators in the central nervous system.

Simvastatin enhances NMDA receptor GluN2B expression and phosphorylation of GluN2B and GluN2A through increased histone acetylation and Src signaling in hippocampal CA1 neurons

Simvastatin (SV) can improve cognitive deficits in Alzheimer's disease patients and mice. Herein, we report that the administration of SV (20 mg/kg) for 5 days in mice (SV-mice) or the treatment of slices with SV (10 μM) for 4 h (SV-slices) could increase the density of NMDA-evoked inward currents (INMDA) in hippocampal CA1 pyramidal cells, which were blocked by farnesol (FOH) that converts farnesyl pyrophosphate (FPP), but not geranylgeraniol (GGOH) that increases geranylgeranylpyrophosphate (GGPP). Sensitivity of INMDA to ifenprodil in SV-mice or SV-slices was significantly increased. The levels of hippocampal GluN2B and GluN2A or Src phosphorylation in SV-mice or SV-slices were higher than controls, which were sensitive to FOH. The Src inhibitor PP2 could inhibit the SV-enhanced phosphorylation of GluN2B and GluN2A and SV-augmented INMDA, but PI3K inhibitor LY294002 did not. The levels of GluN2B mRNA and protein were elevated in SV-mice, which was abolished by FOH, but not by GGOH or PP2. Furthermore, the histone H3K9 and H3K27 acetylation of GluN2B promoter was increased in SV-mice, which was suppressed by FOH rather than GGOH or PP2. In control mice and slices, the reduction of FPP by farnesyl transferase inhibitor could increase the levels of GluN2B expression, the histone H3K9 and H3K27 acetylation and enhance the phosphorylation of GluN2B, GluN2A and Src. The findings indicate that the administration of SV can enhance GluN2B expression and GluN2B and GluN2A phosphorylation leading to augmentation of NMDAR activity through reducing FPP to increase histone acetylation of GluN2B and Src signaling.