Long-term Environmental Enrichment Normalizes Schizophrenia-like Abnormalities and Promotes Hippocampal Slc6a4 Promoter Demethylation in Mice Submitted to a Two-hit Model

Here, we explored the impact of prolonged environmental enrichment (EE) on behavioral, neurochemical, and epigenetic changes in the serotonin transporter gene in mice subjected to a two-hit schizophrenia model. The methodology involved administering the viral mimetic PolyI:C to neonatal Swiss mice as a first hit during postnatal days (PND) 5-7, or a sterile saline solution as a control. At PND21, mice were randomly assigned either to standard environment (SE) or EE housing conditions. Between PND35-44, the PolyI:C-treated group was submitted to various unpredictable stressors, constituting the second hit. Behavioral assessments were conducted on PND70, immediately after the final EE exposure. Following the completion of behavioral assessments, we evaluated the expression of proteins in the hippocampus that are indicative of microglial activation, such as Iba-1, as well as related to neurogenesis, including doublecortin (Dcx). We also performed methylation analysis on the serotonin transporter gene (Slc6a4) to investigate alterations in serotonin signaling. The findings revealed that EE for 50 days mitigated sensorimotor gating deficits and working memory impairments in two-hit mice and enhanced their locomotor and exploratory behaviors. EE also normalized the overexpression of hippocampal Iba-1 and increased the expression of hippocampal Dcx. Additionally, we observed hippocampal demethylation of the Slc6a4 gene in the EE-exposed two-hit group, indicating epigenetic reprogramming. These results contribute to the growing body of evidence supporting the protective effects of long-term EE in counteracting behavioral disruptions caused by the two-hit schizophrenia model, pointing to enhanced neurogenesis, diminished microglial activation, and epigenetic modifications of serotonergic pathways as underlying mechanisms.

New therapeutics for the prevention or amelioration of fetal alcohol spectrum disorders: a narrative review of the preclinical literature

Background: Ethanol consumption during pregnancy induces enduring detrimental effects in the offspring, manifesting as a spectrum of symptoms collectively termed as Fetal Alcohol Spectrum Disorders (FASD). Presently, there is a scarcity of treatments for FASD.Objectives: To analyze current literature, emphasizing evidence derived from preclinical models, that could potentially inform therapeutic interventions for FASD.Methods: A narrative review was conducted focusing on four prospective treatments: nutritional supplements, antioxidants, anti-inflammatory compounds and environmental enrichment. The review also highlights innovative therapeutic strategies applied during early (e.g. folate administration, postnatal days 4-9) or late (e.g. NOX2 inhibitors given after weaning) postnatal stages that resulted in significant improvements in behavioral responses during adolescence (a critical period marked by the emergence of mental health issues in humans).Results: Our findings underscore the value of treatments centered around nutritional supplementation or environmental enrichment, aimed at mitigating oxidative stress and inflammation, implying shared mechanisms in FASD pathogenesis. Moreover, the review spotlights emerging evidence pertaining to the involvement of novel molecular components with potential pharmacological targets (such as NOX2, MCP1/CCR2, PPARJ, and PDE1).Conclusions: Preclinical studies have identified oxidative imbalance and neuroinflammation as relevant pathological mechanisms induced by prenatal ethanol exposure. The relevance of these mechanisms, which exhibit positive feedback loop mechanisms, appear to peak during early development and decreases in adulthood. These findings provide a framework for the future development of therapeutic avenues in the development of specific clinical treatments for FASD.

Exploring the role of environmental enrichment and early life adversity on emotional development

Early life adversity has been linked with a higher probability of developing behavioral impairments and environmental manipulation is a strategy that may reduce the negative effects of exposure to adversity in early life. Here, we focused on exploring the influence of environmental enrichment (EE) as a protective factor in the context of early life adversity. We hypothesized that 24 hours of maternal deprivation (MD), in the second week of life, could induce anxiety-like behavior alterations and that exposure to EE could induce resilience to these behaviors due to alterations in the serotonergic system. Male Wistar rats were exposed to MD, on postnatal days 11 and 13, and to EE, after weaning. In adulthood, we performed a series of behavioral tests for fear, anxiety, and locomotor activity. We also measured the levels of serotonin in the amygdala and dorsal raphe nucleus. Our results revealed that MD does not impact fear behavior or the levels of serotonin, while EE decreases locomotor activity in a novel environment and enhances exploration in the predator odor test. EE also decreases serotonin in the amygdala and increases its turnover rate levels. Our findings provide insights into the critical timeframe during which stress exposure impacts the development and confirm that exposure to EE has an independent and protective effect for anxiety-like behaviors later in life.

Investigating the impact of environmental enrichment on proteome and neurotransmitter-related profiles in an animal model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder associated with behavioral and cognitive impairments. Unfortunately, the drugs the Food and Drug Administration currently approved for AD have shown low effectiveness in delaying the progression of the disease. The focus has shifted to non-pharmacological interventions (NPIs) because of the challenges associated with pharmacological treatments for AD. One such intervention is environmental enrichment (EE), which has been reported to restore cognitive decline associated with AD effectively. However, the therapeutic mechanisms by which EE improves symptoms associated with AD remain unclear. Therefore, this study aimed to reveal the mechanisms underlying the alleviating effects of EE on AD symptoms using histological, proteomic, and neurotransmitter-related analyses. Wild-type (WT) and 5XFAD mice were maintained in standard housing or EE conditions for 4 weeks. First, we confirmed the mitigating effects of EE on cognitive impairment in an AD animal model. Then, histological analysis revealed that EE reduced Aβ accumulation, neuroinflammation, neuronal death, and synaptic loss in the AD brain. Moreover, proteomic analysis by liquid chromatography-tandem mass spectrometry showed that EE enhanced synapse- and neurotransmitter-related networks and upregulated synapse- and neurotransmitter-related proteins in the AD brain. Furthermore, neurotransmitter-related analyses showed an increase in acetylcholine and serotonin concentrations as well as a decrease in polyamine concentration in the frontal cortex and hippocampus of 5XFAD mice raised under EE conditions. Our findings demonstrate that EE restores cognitive impairment by alleviating AD pathology and regulating synapse-related proteins and neurotransmitters. Our study provided neurological evidence for the application of NPIs in treating AD.

Environmental enrichment: a systematic review on the effect of a changing spatial complexity on hippocampal neurogenesis and plasticity in rodents, with considerations for translation to urban and built environments for humans

Introduction

Hippocampal neurogenesis is critical for improving learning, memory, and spatial navigation. Inhabiting and navigating spatial complexity is key to stimulating adult hippocampal neurogenesis (AHN) in rodents because they share similar hippocampal neuroplasticity characteristics with humans. AHN in humans has recently been found to persist until the tenth decade of life, but it declines with aging and is influenced by environmental enrichment. This systematic review investigated the impact of spatial complexity on neurogenesis and hippocampal plasticity in rodents, and discussed the translatability of these findings to human interventions.

Methods

Comprehensive searches were conducted on three databases in English: PubMed, Web of Science, and Scopus. All literature published until December 2023 was screened and assessed for eligibility. A total of 32 studies with original data were included, and the process is reported in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement and checklist.

Results

The studies evaluated various models of spatial complexity in rodents, including environmental enrichment, changes to in-cage elements, complex layouts, and navigational mazes featuring novelty and intermittent complexity. A regression equation was formulated to synthesize key factors influencing neurogenesis, such as duration, physical activity, frequency of changes, diversity of complexity, age, living space size, and temperature.

Conclusion

Findings underscore the cognitive benefits of spatial complexity interventions and inform future translational research from rodents to humans. Home-cage enrichment and models like the Hamlet complex maze and the Marlau cage offer insight into how architectural design and urban navigational complexity can impact neurogenesis in humans. In-space changing complexity, with and without physical activity, is effective for stimulating neurogenesis. While evidence on intermittent spatial complexity in humans is limited, data from the COVID-19 pandemic lockdowns provide preliminary evidence. Existing equations relating rodent and human ages may allow for the translation of enrichment protocol durations from rodents to humans.

Social isolation and post-weaning environmental enrichment effects on rat emotional behavior and serotonergic system

Social isolation (SI) is related to adverse neurobehavioral effects and neurochemical changes when it occurs early in development. On the other hand, environmental enrichment (EE) is associated with a reduction in anxiety-like and depression-like behavior, as well as an increase in serotonin (5-HT) levels in the prefrontal cortex and hippocampus in rodents. This study systematically reviewed the effects of SI and EE on emotional behavior and serotonergic system components in rats after weaning. Primary experimental studies that used subgroups of rats subjected to SI, EE, and normal social conditions after weaning were considered eligible. Studies that used transgenic rodents, ex vivo studies, in vitro studies, human research, or in silico studies were ineligible. Two authors completed searches in Medline/PubMed, LILACS, Scopus, Web of Science, EMBASE, and Open Gray. The Kappa index was calculated to assess agreement between reviewers and assess study quality. The results showed that the animals exposed to EE showed better adaptation to a new environment. Furthermore, EE increased 5-HT levels in the hippocampus and prefrontal cortex of rodents. Thus, it appears that an EE during the critical period of development may reduce anxiety/depression-like behaviors, as well as increase long-term neurotransmitter response.

Environmental Enrichment in Stroke Research: an Update

Environmental enrichment (EE) refers to different forms of stimulation, where the environment is designed to improve the levels of sensory, cognitive, and motor stimuli, inducing stroke recovery in animal models. Stroke is a leading cause of mortality and neurological disability among older adults, hence the importance of developing strategies to improve recovery for such patients. This review provides an update on recent findings, compiling information regarding the parameters affected by EE exposure in both preclinical and clinical studies. During stroke recovery, EE exposure has been shown to improve both the cognitive and locomotor aspects, inducing important neuroplastic alterations, increased angiogenesis and neurogenesis, and modified gene expression, among other effects. There is a need for further research in this field, particularly in those aspects where the evidence is inconclusive. Moreover, it is necessary refine and adapt the EE paradigms for application in human patients.

Immersive virtual reality-based rehabilitation for subacute stroke: a randomized controlled trial

OBJECTIVE

Few effective treatments improve upper extremity (UE) function after stroke. Immersive virtual reality (imVR) is a novel and promising strategy for stroke UE recovery. We assessed the extent to which imVR-based UE rehabilitation can augment conventional treatment and explored changes in brain functional connectivity (FC) that were related to the rehabilitation.

METHODS

An assessor-blinded, parallel-group randomized controlled trial was performed with 40 subjects randomly assigned to either imVR or Control group (1:1 allocation), each receiving rehabilitation 5 times per week for 3 weeks. Subjects in the imVR received both imVR and conventional rehabilitation, while those in the Control received conventional rehabilitation only. Our primary and secondary outcomes were the Fugl-Meyer assessment's upper extremity subscale (FMA-UE) and the Barthel Index (BI), respectively. Both intention-to-treat (ITT) and per-protocol (PP) analyses were performed to assess the effectiveness of the trial. For both the FMA-UE/BI, a one-way analysis of covariance (ANCOVA) model was used, with the FMA-UE/BI at post-intervention or at follow-up, respectively, as the dependent variable, the two groups as the independent variable, baseline FMA-UE/BI, age, sex, site, time since onset, hypertension and diabetes as covariates.

RESULTS

Both ITT and PP analyses demonstrated the effectiveness of imVR-based rehabilitation. The FMA-UE score was greater in the imVR compared with the Control at the post-intervention (mean difference: 9.1 (95% CI 1.6, 16.6); P = 0.019) and follow-up (mean difference:11.5 (95% CI 1.9, 21.0); P = 0.020). The results were consistent for BI scores. Moreover, brain FC analysis found that the motor function improvements were associated with a change in degree in ipsilesional premotor cortex and ipsilesional dorsolateral prefrontal cortex immediately following the intervention and in ipsilesional visual region and ipsilesional middle frontal gyrus after the 12-week follow-up.

CONCLUSIONS

ImVR-based rehabilitation is an effective tool that can improve the recovery of UE functional capabilities of subacute stroke patients when added to standard care. These improvements were associated with distinctive brain changes at two post-stroke timepoints. The study results will benefit future patients with stroke and provide evidence for a promising new method of stroke rehabilitation.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT03086889.

Environmental enrichment promotes adaptive responding during tests of behavioral regulation in male heterogeneous stock rats

Organisms must regulate their behavior flexibly in the face of environmental challenges. Failure can lead to a host of maladaptive behavioral traits associated with a range of neuropsychiatric disorders, including attention deficit hyperactivity disorder, autism, and substance use disorders. This maladaptive dysregulation of behavior is influenced by genetic and environmental factors. For example, environmental enrichment produces beneficial neurobehavioral effects in animal models of such disorders. The present study determined the effects of environmental enrichment on a range of measures related to behavioral regulation using a large cohort of male, outbred heterogeneous stock (HS) rats as subjects. Subjects were reared from late adolescence onwards either in pairs in standard housing with minimal enrichment (n = 200) or in groups of 16 in a highly enriched environment consisting of a large multi-level cage filled with toys, running wheels, and shelters (n = 64). Rats were subjected to a battery of tests, including: (i) locomotor response to novelty, (ii) light reinforcement, (iii) social reinforcement, (iv) reaction time, (v) a patch-depletion foraging test, (vi) Pavlovian conditioned approach, (vii) conditioned reinforcement, and (viii) cocaine conditioned cue preference. Results indicated that rats housed in the enriched environment were able to filter out irrelevant stimuli more effectively and thereby regulate their behavior more efficiently than standard-housing rats. The dramatic impact of environmental enrichment suggests that behavioral studies using standard housing conditions may not generalize to more complex environments that may be more ethologically relevant.

Structural enrichment attenuates colitis-associated colon cancer

Colorectal cancer (CRC) is a major public health concern and disproportionately impacts racial/ethnic minority populations in the US. Animal models are helpful in examining human health disparities because many stress-induced human health conditions can be recapitulated using mouse models. Azoxymethane (AOM)/ dextran sodium sulfate (DSS) treatment can be used to model colitis-associated cancers. While colitis-associated cancers account for only 2% of colon cancers, the AOM/DSS model is useful for examining links between inflammation, immunity, and colon cancer. Mice were housed in enriched and impoverished environments for 1-month prior to behavioral testing. Following behavioral testing the mice were subjected to the AOM/DSS model. While our analysis revealed no significant behavioral variances between the impoverished and enriched housing conditions, we found significant effects in tumorigenesis. Enriched mice had fewer tumors and smaller tumor volumes compared to impoverished mice. African Americans are at higher risk for early onset colorectal cancers in part due to social economic status. Furthermore, housing conditions and environment may reflect social economic status. Research aimed at understanding links between social economic status and colorectal cancer progression is important for eliminating disparities in health outcomes.

Environmental enrichment improves cognitive function, learning, memory and anxiety-related behaviours in rodent models of dementia: Implications for future study

Environmental enrichment (EE) is a process of brain stimulation by modifying the surroundings, for example, by changing the sensory, social, or physical conditions. Rodents have been used in such experimental strategies through exposure to diverse physical, social, and exploration conditions. The present study conducted an extensive analysis of the existing literature surrounding the impact of EE on dementia rodent models. The review emphasised the two principal aspects that are very closely related to dementia: cognitive function (learning and memory) as well as psychological factors (anxiety-related behaviours such as phobias and unrealistic worries). Also highlighted were the mechanisms involved in the rodent models of dementia showing EE effects. Two search engines, PubMed and Science Direct, were used for data collection using the following keywords: environmental enrichment, dementia, rodent model, cognitive performance, and anxiety-related behaviour. Fifty-five articles were chosen depending on the criteria for inclusion and exclusion. The rodent models with dementia demonstrated improved learning and memory in the form of hampered inflammatory responses, enhanced neuronal plasticity, and sustained neuronal activity. EE housing also prevented memory impairment through the prevention of amyloid beta (Aβ) seeding formation, an early stage of Aβ plaque formation. The rodents subjected to EE were observed to present increased exploratory activity and exert less anxiety-related behaviour, compared to those in standard housing. However, some studies have proposed that EE intervention through exercise would be too mild to counteract the anxiety-related behaviour and risk assessment behaviour deficits in the Alzheimer's disease rodent model. Future studies should be conducted on old-aged rodents and the duration of EE exposure that would elicit the greatest benefits since the existing studies have been conducted on a range of ages and EE durations. In summary, EE had a considerable effect on dementia rodent models, with the most evident being improved cognitive function.

Gestational environmental enrichment prevents chronic social stress induced anxiety- and ethanol-related behaviors in offspring

Epidemiological surveys have shown a strong relationship between maternal stress and offspring's mood disorders. Growing evidence suggested that environmental enrichment (EE) improves cognitive function in models of psychiatric and neurological disorders. However, the potential protective effects of gestational EE on social stress-elicited mood disorders in offspring have not been studied. Knowing that the undeveloped brain is more sensitive to gestational environmental stimuli, we hypothesized that initiating cognitive stimulation, during gestation, would protect against social stress-induced behavioral alterations in adulthood. Therefore, the present study aimed to investigate the effects of gestational EE on social stress-elicited anxiety- and ethanol-related behaviors in adult offspring. EE consisted of free access, of dams, to tubular devices of different shapes, colors, and sizes that were changed regularly. After birth and weaning, young adult offspring were exposed to 19 days of social stress and anxiety-like behavior was evaluated by elevated plus maze, open field, and marbles burying tests. The two-bottle choice (TBC) drinking paradigm was used to assess stress-induced ethanol intake. Results showed that gestational EE prevented social stress-elicited anxiogenic-like effects with no differences in spontaneous locomotor activity. Moreover, in the TBC paradigm, mice pre-exposed to EE consistently showed a significantly decreased consumption and preference for ethanol with no effects on tastants' intakes. Interestingly, gestational EE increased serum BDNF levels, which showed a correlation with measures of anxiety- and ethanol-related behaviors. These findings indicate that some neurodevelopmental changes associated with prenatal EE may counteract adult social stress-induced behavioral alterations through a BDNF mechanism. Therefore, we propose that gestational EE has significant protective and beneficial effects on social stress-induced cognitive impairment. It can also alleviate anxiety-like behavior and subsequent excessive alcohol consumption.

Memantine and SKF82958 but not an enriched environment modulate naloxone-precipitated morphine abstinence syndrome without affecting hippocampal tPA mRNA levels in rats

There is accumulating evidence supporting the involvement of tissue-plasminogen activator (tPA) in the mechanisms underlying the effects of morphine and an enriched environment. This study was designed to investigate possible interactive roles of the glutamatergic and the dopaminergic systems regarding hippocampal tPA in the neurobiology of morphine dependence. For this purpose, Wistar albino rats, housed in either a standard- (SE) or an enriched environment (EE) were implanted subcutaneously with morphine (150 mg base) or placebo pellets. Behavioral and somatic signs of morphine abstinence precipitated by an opioid-receptor antagonist naloxone (1 mg/kg, i.p.) 72 h after the pellet implantation were observed individually for 15 min in all groups. Memantine (10 mg/kg i.p.), an antagonist of N-methyl-D-aspartic acid class of glutamatergic receptor-subtype decreased teeth-chattering, ptosis, diarrhea and the loss of body weight. SKF82958 (1 mg/kg, i.p.), a dopamine D1-receptor agonist decreased jumping and ptosis but increased rearing and loss of body weight. On the other hand, co-administration of SKF82958 with memantine prevented some of their effects that occur when administered alone at the same doses. Furthermore, the EE did not change the intensity of morphine abstinence. The level of hippocampal tPA mRNA was found to be lower in the SE morphine abstinence group than in the placebo group and close to the EE morphine abstinence group, whereas there was no significant alteration of its level in the memantine or SKF82958 groups. These findings suggest that the interaction between the glutamatergic and the dopaminergic systems may be an important component of the neurobiology of morphine dependence, and the role of tPA in this interaction should be further investigated.

Vulnerability of Spatial Pattern Separation in 5xFAD Alzheimer's Disease Mouse Model

Background

Alzheimer's disease (AD) is the most common cause of dementia and remains incurable. This age-related neurodegenerative disease is characterized by an early decline in episodic and spatial memory associated with progressive disruption of the hippocampal functioning. Recent clinical evidence suggests that impairment of the spatial pattern separation (SPS) function, which enables the encoding and storage of episodic spatial information, may be an indicator of the early stages of AD.

Objective

The aim of our study was to characterize SPS performance at a prodromal stage in 5xFAD transgenic mouse model of AD.

Methods

Behavioral performance of male wild-type (WT) and 5xFAD mice (n = 14 per group) was assessed from the age of 4 months in two validated paradigms of SPS function either based on spontaneous exploration of objects or on the use of a touchscreen system.

Results

Compared with age-matched WT littermates, a mild deficit in SPS function was observed in the object recognition task in 5xFAD mice, whereas both groups showed similar performance in the touchscreen-based task. These results were observed in the absence of changes in locomotor activity or anxiety-like behavior that could have interfered with the tasks assessing SPS function.

Conclusions

Our results indicate an early vulnerability of the SPS function in 5xFAD mice in the paradigm based on spontaneous exploration of objects. Our work opens up the possibility of examining the early neurobiological processes involved in the decline of episodic memory and may help to propose new therapeutic strategies in the context of AD.

Memory persistence induced by environmental enrichment is dependent on different brain structures

Environmental enrichment (EE) has been demonstrated to have a beneficial effect on different functions of the central nervous system in several mammal species, being used to improve behavior and cell damage in various neurological and psychiatric diseases. However, little has been investigated on the effect of EE in healthy animals, particularly regarding its impact on memory persistence and the brain structures involved. Therefore, here we verified in male Wistar rats that contextual fear conditioning (CFC) memory persistence, tested 28 days after the CFC training session, was facilitated by 5 weeks of exposure to EE, with no effect in groups tested 7 or 14 days after CFC training. However, a two-week exposure to EE did not affect memory persistence. Moreover, we investigated the role of specific brain regions in mediating the effect of EE on memory persistence. We conducted inactivation experiments using the GABAergic agonist Muscimol to target the basolateral amygdala (BLA), medial prefrontal cortex (mPFC), and CA1 region of the hippocampus (CA1). Inactivation of the BLA immediately and 12 h after CFC training impaired the effect of EE on memory persistence. Similarly, inactivation of the CA1 region and mPFC 12 h after training, but not immediately, also impaired the effect of EE on memory persistence. These results have important scientific implications as they shed new light on the effect of an enriched environment on memory persistence and the brain structures involved, thereby helping elucidate how an environment rich in experiences can modify the persistence of learned information.

Role of environmental enrichment on social interaction, anxiety, locomotion, and memory in Wistar rats under chronic methylphenidate intake

Introduction

Chronic use of various compounds can have long-lasting effects on animal behavior, and some of these effects can be influenced by the environment. Many environmental enrichment protocols have the potential to induce behavioral changes.

Aim

The aim of the present study was to investigate how environmental enrichment can mitigate the effects of chronic methylphenidate consumption on the behavior of Wistar rats.

Methods

The animals were housed for 20 days under either an environmental enrichment protocol (which included tubes of different shapes) or standard housing conditions. After seven days, half of the rats received 13 days of oral administration of methylphenidate (2 mg/kg). After seven days, the rats underwent behavioral tests, including the elevated plus maze (anxiety), open field (locomotion), object-in-place recognition test (spatial memory), and a test for social interaction (social behavior).

Results

The results showed that the enriched environmental condition reversed the enhanced time in the open arms of the elevated plus maze induced by methylphenidate (F[1,43] = 4.275, p = 0.045). Methylphenidate also enhanced exploratory rearing in the open field (F[1,43] = 4.663, p = 0.036) and the time spent in the open area of the open field (H[3] = 8.786, p = 0.032). The enriched environment mitigated the inhibition of social interaction with peers induced by methylphenidate (H[3] = 16.755, p  < 0.001) as well as the preference for single exploratory behavior (H[3] = 9.041, p = 0.029).

Discussion

These findings suggest that environmental enrichment can counteract some of the effects of methylphenidate. These results are relevant for the clinical treatment of the long-lasting secondary effects associated with methylphenidate pharmacological treatment.

Brief environmental enrichment elicits metaplasticity on the insular cortex in vivo and reduces the strength of conditioned taste aversion

Environmental enrichment (EE) is known to improve memory and cognition and modulate the impact of aversive stimuli in animals, promoting the development of resilience to stressful situations. Likewise, it is known that EE can modulate synaptic plasticity as is the case of long-term potentiation (LTP). These findings have been described initially in ex vivo preparations, suggesting that the effects of EE are the result of an early modification of the synaptic excitability and transmission. In this regard, it is known that metaplasticity refers to the persistent modification, by previous activity, in the ability to induce synaptic plasticity. Our previous studies have shown that prior training in conditioned taste aversion (CTA) prevents the subsequent induction of LTP in the projection from the basolateral nucleus of the amygdala (Bla) to the insular cortex (IC) in vivo. In addition, we have shown that CTA extinction allows the induction but not the maintenance of IC-LTP of the Bla-IC pathway. Recently, we also showed that prior exposure to environmental enrichment for three weeks reduces the strength of CTA, restoring the brain-derived neurotrophic factor (BDNF) levels in the IC. The present study aimed to analyze the effects of brief exposure to an enriched environment on the strength of aversive memory, as well as on the in vivo IC-LTP. To do so, adult rats were exposed for seven days to an EE, either before CTA training or LTP induction in the Bla-IC pathway. Our results demonstrate that a seven-day exposure to an enriched environment attenuates the aversive response to a strong CTA and allows the induction but not the maintenance of LTP in the insular cortex. These findings provide evidence that metaplastic regulation in a neocortical region takes part in the mechanisms through which brief exposure to enriched environments attenuates an aversive response.

The effects of environmental enrichment on voluntary physical activity and muscle mass gain in growing rats

Introduction: Environmental enrichment (EE) for rodents involves housing conditions that facilitate enhanced sensory, cognitive, and motor stimulation relative to standard housing conditions. A recent study suggested that EE induces muscle hypertrophy. However, it remains unclear whether muscle hypertrophy in EE is associated with voluntary physical activity, and the characteristics of muscle adaptation to EE remain unclarified. Therefore, this study investigated whether muscle adaptation to EE is associated with voluntary physical activity, and assessed the changes in the muscle fiber-type distribution and fiber-type-specific cross-sectional area in response to EE. Methods: Wistar rats (6 weeks of age) were randomly assigned to either the standard environment group (n = 10) or the EE group (n = 10). The voluntary physical activity of rats housed in EE conditions was measured using a recently developed three-axis accelerometer. After exposure to the standard or enriched environment for 30 days, the tibialis anterior, extensor digitorum longus, soleus, plantaris, and gastrocnemius muscles were removed and weighed. Immunohistochemistry analysis was performed on the surface (anterior) and deep (posterior) areas of the tibialis anterior and soleus muscles. Results and discussion: The EE group showed increased voluntary physical activity during the dark period compared with the standard environment group (p = 0.005). EE induced muscle mass gain in the soleus muscle (p = 0.002) and increased the slow-twitch muscle fiber cross-sectional area of the soleus muscle (p = 0.025). EE also increased the distribution of high-oxidative type IIa fibers of the surface area (p = 0.001) and type I fibers of the deep area (p = 0.037) of the tibialis anterior muscle. These findings suggest that EE is an effective approach to induce slow-twitch muscle fiber hypertrophy through increased daily voluntary physical activity.

Reduction of restricted repetitive behavior by environmental enrichment: Potential neurobiological mechanisms

Restricted repetitive behaviors (RRB) are one of two diagnostic criteria for autism spectrum disorder and common in other neurodevelopmental and psychiatric disorders. The term restricted repetitive behavior refers to a wide variety of inflexible patterns of behavior including stereotypy, self-injury, restricted interests, insistence on sameness, and ritualistic and compulsive behavior. However, despite their prevalence in clinical populations, their underlying causes remain poorly understood hampering the development of effective treatments. Intriguingly, numerous animal studies have demonstrated that these behaviors are reduced by rearing in enriched environments (EE). Understanding the processes responsible for the attenuation of repetitive behaviors by EE should offer insights into potential therapeutic approaches, as well as shed light on the underlying neurobiology of repetitive behaviors. This review summarizes the current knowledge of the relationship between EE and RRB and discusses potential mechanisms for EE's attenuation of RRB based on the broader EE literature. Existing gaps in the literature and future directions are also discussed.

Environmental modifications to rehabilitate social behavior deficits after acquired brain injury: What is the evidence?

Social behavior deficits are a common, debilitating consequence of traumatic brain injury and stroke, particularly when sustained during childhood. Numerous factors influence the manifestation of social problems after acquired brain injuries, raising the question of whether environmental manipulations can minimize or prevent such deficits. Here, we examine both clinical and preclinical evidence addressing this question, with a particular focus on environmental enrichment paradigms and differing housing conditions. We aimed to understand whether environmental manipulations can ameliorate injury-induced social behavior deficits. In summary, promising data from experimental models supports a beneficial role of environmental enrichment on social behavior. However, limited studies have considered social outcomes in the chronic setting, and few studies have addressed the social context specifically as an important component of the post-injury environment. Clinically, limited high-caliber evidence supports the use of specific interventions for social deficits after acquired brain injuries. An improved understanding of how the post-injury environment interacts with the injured brain, particularly during development, is needed to validate the implementation of rehabilitative interventions that involve manipulating an individuals' environment.

The systemic effects of the enriched environment on the conditioned fear reaction

In this review, a hypothesis is proposed to explain the beneficial effect of an enriched environment (EE) on the conditioned fear reaction (CFR) from the perspective of a functional system of behavioral control. According to the hypothesis, the EE affects all behavioral act components, including the processing of sensory information, memory, motivational and reinforcing systems, and motor activities, which weakens the CFR. Animals raised in the EE have effects that are comparable to those of context (CTX) and CS pre-exposures at latent inhibition. An abundance of stimuli in the EE and constant contact with them provide the formation of CS-noUS and CTX-noUS connections that later, during CFR learning, slow down and diminish fear. The EE also contributes to faster processing of information and habituation to it. As a result, many stimuli in the context lose their significance, and subjects simply ignore them. And finally, the EE affects the motivational and reinforcing brain mechanisms, induces an impairment of search activity, and worsens memory consolidation, which leads to a reduction of CFR.

MSK1 is required for the beneficial synaptic and cognitive effects of enriched experience across the lifespan

Positive experiences, such as social interaction, cognitive training and physical exercise, have been shown to ameliorate some of the harms to cognition associated with ageing. Animal models of positive interventions, commonly known as environmental enrichment, strongly influence neuronal morphology and synaptic function and enhance cognitive performance. While the profound structural and functional benefits of enrichment have been appreciated for decades, little is known as to how the environment influences neurons to respond and adapt to these positive sensory experiences. We show that adult and aged male wild-type mice that underwent a 10-week environmental enrichment protocol demonstrated improved performance in a variety of behavioural tasks, including those testing spatial working and spatial reference memory, and an enhancement in hippocampal LTP. Aged animals in particular benefitted from enrichment, performing spatial memory tasks at levels similar to healthy adult mice. Many of these benefits, including in gene expression, were absent in mice with a mutation in an enzyme, MSK1, which is activated by BDNF, a growth factor implicated in rodent and human cognition. We conclude that enrichment is beneficial across the lifespan and that MSK1 is required for the full extent of these experience-induced improvements of cognitive abilities, synaptic plasticity and gene expression.

The influence of long-term housing in enriched environment on behavior of normal rats and subjected to neonatal pro-inflammatory challenge

It is well known that neonatal pro-inflammatory challenge (NPC) acquire a predisposition to the development of a number of neuropsychiatric diseases: depression, anxiety disorders, autism, attention deficit hyperactivity disorder. Symptoms of these diseases can manifest themselves in adulthood and adolescent after repeated exposure to negative influences. Preventing the development of the negative consequences of NPC is one of the main tasks for researchers. The exposure to an enriched environment (EE) was shown to have anxiolytic, anti-depressive, and pro-cognitive effects. The present work was aimed to investigate the effects of the long-term EE on anxious-depressive and conditioned fear behavior in normal male and female rats and subjected to NPC. The NPC was induced by subcutaneous administration of lipopolysaccharide (LPS, 50 μg/kg) on 3d and 5th PNDs. The control animals received saline (SAL). The rats were placed in the EE from 25 to 120 PND. Animals housed in the standard conditions (STAND) served as controls. In adult female and male rats of the STAND groups, LPS did not affect the anxiety, depressive-like behavior and conditioned fear. The EE increased motor and search activity in males and females. In the open field, the EE reduced anxiety in males of the SAL and LPS groups and in females of SAL groups compared to the STAND housed animals. In the elevated plus maze, the EE decreased anxiety only in males of the SAL group. In the sucrose preference test, the EE did not change sucrose consumption in males and females of SAL and LPS groups, while, in the forced swimming test, the EE reduced depressive-like behavior in females of both SAL and LPS groups. The enrichment decreased the contextual conditioned fear in male and female of SAL groups, but not of the LPS group, and did not affect the cue conditioned fear. The corticosterone reactivity to the forced swimming stress increased in males of the EE groups. The basal level of IL-1beta in blood serum decreased in males of the SAL-EE group. Thus, the EE reduced anxiety in males, depressive-like behavior in females, and contextual conditioned fear in males and females compared to the STAND housed animals. Although the NPC did not affect these behaviors in the STAND groups, LPS prevented the beneficial EE effects on anxiety and conditioned fear. The opposing effects of LPS were dependent on sex and type of testing.

Molecular mechanisms underlying the neuroprotection of environmental enrichment in Parkinson's disease

Parkinson's disease is the most common movement disorder, affecting about 1% of the population over the age of 60 years. Parkinson's disease is characterized clinically by resting tremor, bradykinesia, rigidity and postural instability, as a result of the progressive loss of nigrostriatal dopaminergic neurons. In addition to this neuronal cell loss, Parkinson's disease is characterized by the accumulation of intracellular protein aggregates, Lewy bodies and Lewy neurites, composed primarily of the protein α-synuclein. Although it was first described almost 200 years ago, there are no disease-modifying drugs to treat patients with Parkinson's disease. In addition to conventional therapies, non-pharmacological treatment strategies are under investigation in patients and animal models of neurodegenerative disorders. Among such strategies, environmental enrichment, comprising physical exercise, cognitive stimulus, and social interactions, has been assessed in preclinical models of Parkinson's disease. Environmental enrichment can cause structural and functional changes in the brain and promote neurogenesis and dendritic growth by modifying gene expression, enhancing the expression of neurotrophic factors and modulating neurotransmission. In this review article, we focus on the current knowledge about the molecular mechanisms underlying environmental enrichment neuroprotection in Parkinson's disease, highlighting its influence on the dopaminergic, cholinergic, glutamatergic and GABAergic systems, as well as the involvement of neurotrophic factors. We describe experimental pre-clinical data showing how environmental enrichment can act as a modulator in a neurochemical and behavioral context in different animal models of Parkinson's disease, highlighting the potential of environmental enrichment as an additional strategy in the management and prevention of this complex disease.

Postnatal environmental enrichment enhances memory through distinct neural mechanisms in healthy and trisomic female mice

Stimulating lifestyles have powerful effects on cognitive abilities, especially when they are experienced early in life. Cognitive therapies are widely used to improve cognitive impairment due to intellectual disability, aging, and neurodegeneration, however the underlying neural mechanisms are poorly understood. We investigated the neural correlates of memory amelioration produced by postnatal environmental enrichment (EE) in diploid mice and the Ts65Dn mouse model of Down syndrome (trisomy 21). We recorded neural activities in brain structures key for memory processing, the hippocampus and the prefrontal cortex, during rest, sleep and memory performance in mice reared in non-enriched or enriched environments. Enriched wild-type animals exhibited enhanced neural synchrony in the hippocampus across different brain states (increased gamma oscillations, theta-gamma coupling, sleep ripples). Trisomic females showed increased theta and gamma rhythms in the hippocampus and prefrontal cortex across different brain states along with enlarged ripples and disrupted circuit gamma signals that were associated with memory deficits. These pathological activities were attenuated in their trisomic EE-reared peers. Our results suggest distinct neural mechanisms for the generation and rescue of healthy and pathological brain synchrony, respectively, by EE and put forward hippocampal-prefrontal hypersynchrony and miscommunication as major targets underlying the beneficial effects of EE in intellectual disability.

5 Hz of repetitive transcranial magnetic stimulation improves cognition and induces modifications in hippocampal neurogenesis in adult female Swiss Webster mice

Adult hippocampal neurogenesis is regulated by several stimuli to promote the creation of a reserve that may facilitate coping with environmental challenges. In this regard, repetitive transcranial magnetic stimulation (rTMS), a neuromodulation therapy, came to our attention because in clinical studies it reverts behavioral and cognitive alterations related to changes in brain plasticity. Some preclinical studies emphasize the need to understand the underlying mechanism of rTMS to induce behavioral modifications. In this study, we investigated the effects of rTMS on cognition, neurogenic-associated modifications, and neuronal activation in the hippocampus of female Swiss Webster mice. We applied 5 Hz of rTMS twice a day for 14 days. Three days later, mice were exposed to the behavioral battery. Then, brains were collected and immunostained for Ki67-positive cells, doublecortin-positive (DCX+)-cells, calbindin, c-Fos and FosB/Delta-FosB in the dentate gyrus. Also, we analyzed mossy fibers and CA3 with calbindin immunostaining. Mice exposed to rTMS exhibited cognitive improvement, an increased number of proliferative cells, DCX cells, DCX cells with complex dendrite morphology, c-Fos and immunoreactivity of FosB/Delta-FosB in the granular cell layer. The volume of the granular cell layer, mossy fibers and CA3 in rTMS mice also increased. Interestingly, cognitive improvement correlated with DCX cells with complex dendrite morphology. Also, those DCX cells and calbindin immunoreactivity correlated with c-Fos in the granular cell layer. Our results suggest that 5 Hz of rTMS applied twice a day modify cell proliferation, doublecortin cells, mossy fibers and enhance cognitive behavior in healthy female Swiss Webster mice.

The role of enriched environment in neural development and repair

In addition to genetic information, environmental factors play an important role in the structure and function of nervous system and the occurrence and development of some nervous system diseases. Enriched environment (EE) can not only promote normal neural development through enhancing neuroplasticity but also play a nerve repair role in restoring functional activities during CNS injury by morphological and cellular and molecular adaptations in the brain. Different stages of development after birth respond to the environment to varying degrees. Therefore, we systematically review the pro-developmental and anti-stress value of EE during pregnancy, pre-weaning, and “adolescence” and analyze the difference in the effects of EE and its sub-components, especially with physical exercise. In our exploration of potential mechanisms that promote neurodevelopment, we have found that not all sub-components exert maximum value throughout the developmental phase, such as animals that do not respond to physical activity before weaning, and that EE is not superior to its sub-components in all respects. EE affects the developing and adult brain, resulting in some neuroplastic changes in the microscopic and macroscopic anatomy, finally contributing to enhanced learning and memory capacity. These positive promoting influences are particularly prominent regarding neural repair after neurobiological disorders. Taking cerebral ischemia as an example, we analyzed the molecular mediators of EE promoting repair from various dimensions. We found that EE does not always lead to positive effects on nerve repair, such as infarct size. In view of the classic issues such as standardization and relativity of EE have been thoroughly discussed, we finally focus on analyzing the essentiality of the time window of EE action and clinical translation in order to devote to the future research direction of EE and rapid and reasonable clinical application.

Survey on the Past Decade of Technology in Animal Enrichment: A Scoping Review

Simple Summary

Enrichment is important for supporting the well-being of captive animals. Enrichment increase animal quality of life through encouraging natural behaviours. As enrichment is shifting to a more centered role in animal care, technology is becoming increasingly accessible and is becoming embedded in animal enrichment in creative ways. This review explores the trends in technology usage in animal enrichment studies. Through pulling the past decade of technology enrichment work together, we discuss gaps such as needing to include a larger variety of species (extending passed mammals), ensuring enrichment designs focus primarily on the senses an animal uses to interact with the world rather than human senses, and encouraging similar study designs across animal contexts to allow for streamlined comparisons.

Abstract

Environmental enrichment is adding complexity to an environment that has a positive impact on a captive animal as a necessity of care. Computing technology is being rapidly weaved throughout the space in both enrichment devices as well as evaluating enrichment outcomes. In this article, we present a scoping review of 102 captive animal enrichment studies and propose a contextual lens for exploring current practices. We discuss the importance of directed growth in species inclusion, transitioning beyond anthro-centric designs, and utilizing shared methodologies.

Environmental Enrichment Facilitates Anxiety in Conflict-Based Tests but Inhibits Predator Threat-Induced Defensive Behaviour in Male Mice

INTRODUCTION

Environmental enrichment (EE) is a useful and sophisticated tool that improves rodents' well-being by stimulating social behaviour and cognitive, motor, and sensory functions. Exposure to EE induces neuroplasticity in different brain areas, including the limbic system, which has been implicated in the control of anxiety and fear. However, the effects of EE on ethologically relevant naturalistic behaviours, such as those displayed by prey in the presence of predators, remain largely unexplored.

MATERIAL AND METHODS

In the present study, we investigated anxiety- and panic attack-like behaviours in a predator (cat)-prey confrontation paradigm and compared them with those in classical assays, such as the elevated plus-maze (EPM), marble-burying, and open field tests (OFTs), using C57BL/6J male mice housed in enriched or standard environments for 6 weeks.

RESULTS

We observed that EE exposure caused enhancement of the levels of anxiety-like behaviours in the EPM and OFTs, increasing risk assessment (an anxiety-related response), and decreasing escape (a panic attack-like response) behaviours during exposure to the predator versus prey confrontation paradigm.

CONCLUSION

Taken together, our findings suggest that enriched external environments can modify the processing of fear- and anxiety-related stimuli in dangerous situations, changing the decision-making defensive strategy.

Use of prepubertal environment enrichment to prevent dopamine dysregulation in a neurodevelopmental rat model of schizophrenia risk

Here, we present a protocol for delivering environmental enrichment (EE) in discrete postnatal windows to prevent long-term dopamine neuron dysfunctions in a neurodevelopmental rat model of schizophrenia risk. We describe generation of the schizophrenia model through prenatal treatment of rats with methylazoxymethanol acetate (the MAM model) and the saline-treated controls. We then detail the 10-day or 20-day EE paradigms applied on male rats at different ages. This protocol also includes preparation of control groups in regular environment (RE) cages for comparison.

For complete details on the use and execution of this protocol, please refer to Zhu and Grace (2021).

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Protocol to deliver EE in postnatal windows of a rat model of schizophrenia risk

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Detailed description of supplies and procedures to construct EE boxes

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Details of animal loading/offloading, cage maintenance, and design of control groups

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Expected electrophysiological outcomes and troubleshooting of common pitfalls

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.

Selecting antidepressants according to a drug-by-environment interaction: A comparison of fluoxetine and minocycline effects in mice living either in enriched or stressful conditions

Selective serotonin reuptake inhibitors (SSRIs) are the first-line treatment for major depressive disorder. It has been recently proposed that these drugs, by enhancing neural plasticity, amplify the influences of the living conditions on mood. Consequently, SSRI outcome depends on the quality of the environment, improving symptomatology mainly in individuals living in favorable conditions. In adverse conditions, drugs with a different mechanism of action might have higher efficacy. The antibiotic minocycline, with neuroprotective and anti-inflammatory properties, has been recently proposed as a novel potential antidepressant treatment. To explore the drug-by-environment interaction, we compared the effects on depressive-like behavior and neural plasticity of the SSRI fluoxetine and minocycline in enriched and stressful conditions. We first exposed C57BL/6 adult female mice to 14 days of chronic unpredictable mild stress to induce a depressive-like profile. Afterward, mice received vehicle, fluoxetine, or minocycline for 21 days, while exposed to either enriched or stressful conditions. During the first five days, fluoxetine led to an improvement in enrichment but not in stress. By contrast, minocycline led to an improvement in both conditions. After 21 days, all groups showed a significant improvement in enrichment while fluoxetine worsened the depressive like behavior in stress. The effects of the drugs on neural plasticity, measured as long-term potentiation, were also environment-dependent. Overall, we show that the environment affects fluoxetine but not minocycline outcome, indicating that the latter represents a potential alternative to SSRIs to treat depressed patients living in adverse conditions. From a translation perspective, our finding call for considering the drug-by-environment interaction to select the most effective pharmacological treatment.

Behavioral impact of experience based on environmental enrichment: Influence of age and duration of exposure in male NMRI mice

Prior studies have suggested that short periods of exposure to environmental enrichment (EE) in rodents induce physiological and behavioral effects. In the present study, our aim was to evaluate if the impact of experiences based on EE could be modulated by the age of onset and the developmental period of exposure. NMRI male mice (n = 64) were exposed to EE or standard environment (SE) and behavioral changes (anxiety, exploration, memory and social interaction) were evaluated. Groups compared were: (a) SE: exposure to SE on post-natal day (PND) 28 and lasting 6 months; (b) EE-6: exposure to EE on PND 28 and lasting 6 months; (c) EE-4: exposure to EE on PND 91 and lasting 4 months; (d) EE-2: exposure to EE on PND 154 and lasting 2 months. Results indicated that in the hole-board task the decrease in exploratory behavior reached significance when EE was initiated at adolescence whereas anxiolytic effects in the elevated plus-maze tend to diminish after a longer period of EE. No significant effects of EE on aggressive behavior or novel object recognition were obtained. Taking these results into account, further studies are needed in order to determine the possible modulating role of age and duration of exposure to enriched environments on behavior. Results obtained could explain some discrepancies reported in previous studies, providing new evidence that could contribute to the design of future research related to the benefits of complex and enriched environments.

Differential impact of stress and environmental enrichment on corticolimbic circuits

Stress exposure can produce profound changes in physiology and behavior that can impair health and well-being. Of note, stress exposure is linked to anxiety disorders and depression in humans. The widespread impact of these disorders warrants investigation into treatments to mitigate the harmful effects of stress. Pharmacological treatments fail to help many with these disorders, so recent work has focused on non-pharmacological alternatives. One of the most promising of these alternatives is environmental enrichment (EE). In rodents, EE includes social, physical, and cognitive stimulation for the animal, in the form of larger cages, running wheels, and toys. EE successfully reduces the maladaptive effects of various stressors, both as treatment and prophylaxis. While we know that EE can have beneficial effects under stress conditions, the morphological and molecular mechanisms underlying these behavioral effects are still not well understood. EE is known to alter neurogenesis, dendrite development, and expression of neurotrophic growth factors, effects that vary by type of enrichment, age, and sex. To add to this complexity, EE has differential effects in different brain regions. Understanding how EE exerts its protective effects on morphological and molecular levels could hold the key to developing more targeted pharmacological treatments. In this review, we summarize the literature on the morphological and molecular consequences of EE and stress in key emotional regulatory pathways in the brain, the hippocampus, prefrontal cortex, and amygdala. The similarities and differences among these regions provide some insight into stress-EE interaction that may be exploited in future efforts toward prevention of, and intervention in, stress-related diseases.

Concurrent environmental enrichment and chronic restraint stress: Effects on innate anxiety and depressive-like behavior in male adolescent mice

Adolescence is a period that exhibits both vulnerability and adaptation to environmental stimulus. This study explored the co-existence effect of environmental enrichment (EE) and restraint stress (RS) on innate anxiety and depressive-like behavior in adolescent mice. Male ICR mice were treated with daily EE and RS (4 h/d or 8 h/d) for 2 or 4 weeks from early adolescence (postnatal day 30) and emotional behaviors were evaluated 24 h after the end of treatment. 4 weeks of 8 h RS treatment decreased immobility time in forced swimming test, demonstrating an antidepressant-like effect. For 2 weeks of treatment, 8 h RS significantly reduced the time spent in the lighted compartment of the light-dark box, indicating an increased anxiety level. These results show that under the present experimental design, RS treatment with different duration could have different effect on mice emotion-related behavior, but there was no interaction between EE and RS.

Collective Behavior in Wild Zebrafish

Anthropogenic change is expected to alter environments at alarming rates. To predict the impact of modified environments on social behavior, we must study the relationship between environmental features and collective behavior in a genetically tractable model, zebrafish (Danio rerio). Here, we conducted a field study to examine the relationship between salient environmental features and collective behavior in four populations of zebrafish. We found zebrafish in flowing water formed volatile groups, whereas those in still water had more consistent membership and leadership. Groups in fast-flowing water were large (up to 2000 fish) and tightly knit with short nearest neighbor distances, whereas group sizes were smaller (11 fish/group) with more space between individual fish in still and slow-flowing water. These observations point to a possible profound role of water flow in influencing collective behavior in wild zebrafish.

Environmental Enrichment and Physical Exercise Attenuate the Depressive-Like Effects Induced by Social Isolation Stress in Rats

We assessed the antidepressant-like effects of environmental enrichment (EE) and physical exercise (PE) compared with the selective serotonin reuptake inhibitor fluoxetine against the depression-related neurobehavioral alterations induced by postweaning social isolation (SI) in rats. After 1 month of SI, rats were submitted to PE (treadmill), EE, or fluoxetine (10 mg/kg), which were compared with naïve SI and group-housed rats. After 1 month, behavior was analyzed in the open field (OFT), the sucrose preference (SPT), and the forced swimming (FST) tests. Afterward, the hippocampal serotonin contents, its metabolite, and turnover were measured. SI induced a depression-related phenotype characterized by a marginal bodyweight gain, anxiety, anhedonia, behavioral despair, and alterations of serotonin metabolism. EE produced the widest and largest antidepressive-like effect, followed by PE and fluoxetine, which were almost equivalent. The treatments, however, affected differentially the neurobehavioral domains investigated. EE exerted its largest effect on anhedonia and was the only treatment inducing anxiolytic-like effects. Fluoxetine, in contrast, produced its largest effect on serotonin metabolism, followed by its anti-behavioral despair action. PE was a middle-ground treatment with broader behavioral outcomes than fluoxetine, but ineffective to reverse the serotonergic alterations induced by SI. The most responsive test to the treatments was the FST, followed closely by the SPT. Although OFT locomotion and body weight varied considerably between groups, they were barely responsive to PE and fluoxetine. From a translational standpoint, our data suggest that exercise and recreational activities may have broader health benefits than antidepressants to overcome confinement and the consequences of chronic stress.

Maturation of newborn neurons predicts social memory persistence in mice

Memory transience is essential to gain cognitive flexibility. Recently, hippocampal neurogenesis is emerging as one of the mechanisms involved in the balance between persistence and forgetting. Social recognition memory (SRM) has its duration prolonged by neurogenesis. However, it is still to be determined whether boosting neurogenesis in distinct phases of SRM may favor forgetting over persistence. In the present study, we used enriched environment (EE) and memantine (MEM) to increase neurogenesis. SRM was ubiquitously prolonged by both, while EE after the memory acquisition did not favor forgetting. Interestingly, the proportion of newborn neurons with mature morphology in the dorsal hippocampus was higher in animals where persistence prevailed. Finally, one of the main factors for dendritic growth is the formation of cytoskeleton. We found that Latrunculin A, an inhibitor of actin polymerization, blunted the promnesic effect of EE. Altogether, our results indicate that the mechanisms triggered by EE to improve SRM are not limited to increasing the number of newborn neurons.

Mapping accumulative whole-brain activities during environmental enrichment with manganese-enhanced magnetic resonance imaging

An enriched environment (EE) provides multi-dimensional stimuli to the brain. EE exposure for days to months induces functional and structural neuroplasticity. In this study, manganese-enhanced magnetic resonance imaging (MEMRI) was used to map the accumulative whole-brain activities associated with a 7-day EE exposure in freely-moving adult male mice, followed by c-Fos immunochemical assessments. Relative to the mice residing in a standard environment (SE), the mice subjected to EE treatment had significantly enhanced regional MEMRI signal intensities in the prefrontal cortex, somatosensory cortices, basal ganglia, amygdala, motor thalamus, lateral hypothalamus, ventral hippocampus and midbrain dopaminergic areas at the end of the 7-day exposure, likely attributing to enhanced Mn²⁺ uptake/transport associated with brain activities at both the regional and macroscale network levels. Some of, but not all, the brain regions in the EE-treated mice showing enhanced MEMRI signal intensity had accompanying increases in c-Fos expression. The EE-treated mice were also found to have significantly increased overall amount of food consumption, decreased body weight gain and upregulated tyrosine hydroxylase (TH) expression in the midbrain dopaminergic areas. Taken together, these results demonstrated that the 7-day EE exposure was associated with elevated cumulative activities in the nigrostriatal, mesolimbic and corticostriatal circuits underpinning reward, motivation, cognition, motor control and appetite regulation. Such accumulative activities might have served as the substrate of EE-related neuroplasticity and the beneficial effects of EE treatment on neurological/psychiatric conditions including drug addiction, Parkinson's disease and eating disorder.

Socioeconomic status and brain injury in children born preterm: modifying neurodevelopmental outcome

Improved intensive care therapies have increased the survival of children born preterm. Yet, many preterm children experience long-term neurodevelopmental sequelae. Indeed, preterm birth remains a leading cause of lifelong neurodevelopmental disability globally, posing significant challenges to the child, family, and society. Neurodevelopmental disability in children born preterm is traditionally linked to acquired brain injuries such as white matter injury and to impaired brain maturation resulting from neonatal illness such as chronic lung disease. Socioeconomic status (SES) has long been recognized to contribute to variation in outcome in children born preterm. Recent brain imaging data in normative term-born cohorts suggest that lower SES itself predicts alterations in brain development, including the growth of the cerebral cortex and subcortical structures. Recent evidence in children born preterm suggests that the response to early-life brain injuries is modified by the socioeconomic circumstances of children and families. Exciting new data points to the potential of more favorable SES circumstances to mitigate the impact of neonatal brain injury. This review addresses emerging evidence suggesting that SES modifies the relationship between early-life exposures, brain injury, and neurodevelopmental outcomes in children born preterm. Better understanding these relationships opens new avenues for research with the ultimate goal of promoting optimal outcomes for those children born preterm at highest risk of neurodevelopmental consequence.

Effect of enriched environment and predictable chronic stress on spatial memory in adolescent rats: Predominant expression of BDNF, nNOS, and interestingly malondialdehyde in the right hippocampus

Little is known about the mechanisms that promote divergence of function between left and right in the hippocampus, which is most affected by external factors and critical for spatial memory. We investigated the levels of memory-related mediators in the left and right hippocampus and spatial memory in rats exposed to predictable chronic stress (PCS) and an enriched environment (EE) during adolescence. Twenty-eight-day-old Sprague-Dawley rats were divided into control (standard cages), PCS (15 min/day immobilization stress for four weeks), and EE (one hour/day environmentally enriched cages for four weeks) groups. After the applications, spatial memory was tested with the Morris water maze, and the serum levels of corticosterone were evaluated. The levels of brain-derived neurotrophic factor (BDNF) and neuronal nitric oxide synthase (nNOS), which are critical for synaptic plasticity; malondialdehyde (MDA; lipid-peroxidation indicator); protein carbonyl (protein-oxidation indicator); and superoxide dismutase (antioxidant enzyme) were evaluated in the left and right hippocampus. Corticosterone levels in both the PCS and EE groups did not change compared with control. In both the PCS and EE groups, spatial memory improved and BDNF was increased in both halves of the hippocampus, still there was an asymmetry. nNOS levels were increased in the dentate gyrus and CA1 regions of the right hippocampus in both PCS and EE groups. MDA levels were increased but PCO levels were decreased in the right hippocampus in both the PCS and EE groups, but SOD did not change in either half of the hippocampus. Our results suggest that both PCS and EE improved spatial memory by increasing BDNF and nNOS in the right hippocampus and that, interestingly; MDA could be the physiological signal molecule in the right hippocampus for spatial memory process.

The effect of environmental enrichment on behavioral variability depends on genotype, behavior, and type of enrichment

Non-genetic individuality in behavior, also termed intragenotypic variability, has been observed across many different organisms. A potential cause of intragenotypic variability is sensitivity to minute environmental differences during development, which are present even when major environmental parameters are kept constant. Animal enrichment paradigms often include the addition of environmental diversity, whether in the form of social interaction, novel objects or exploratory opportunities. Enrichment could plausibly affect intragenotypic variability in opposing ways: it could cause an increase in variability due to the increase in microenvironmental variation, or a decrease in variability due to elimination of aberrant behavior as animals are taken out of impoverished laboratory conditions. In order to test these hypothesis, we assayed five isogenic Drosophila melanogaster lines raised in control and mild enrichment conditions, and one isogenic line under both mild and intense enrichment conditions. We compared the mean and variability of six behavioral metrics between our enriched fly populations and the laboratory housing control. We found that enrichment often caused a small increase in variability across most of our behaviors, but that the ultimate effect of enrichment on both behavioral means and variabilities was highly dependent on genotype and its interaction with the particular enrichment treatment. Our results support previous work on enrichment that presents a highly variable picture of its effects on both behavior and physiology.