Effects of environmental enrichment on anxiety responses, spatial memory and cytochrome c oxidase activity in adult rats

Looks like home: numerosity, but not spatial frequency guides preference in zebrafish larvae (Danio rerio)

Despite their young age, zebrafish larvae have a well-developed visual system and can distinguish between different visual stimuli. First, we investigated if the first visual surroundings the larvae experience during the first days after hatching shape their habitat preference. Indeed, these animals seem to "imprint" on the first surroundings they see and select visual stimuli accordingly at 7 days post fertilization (dpf). In particular, if zebrafish larvae experience a bar background just after hatching, they later on prefer bars over white stimuli, and vice versa. We then used this acquired preference for bars to investigate innate numerical abilities. We wanted to specifically test if the zebrafish larvae show real numerical abilities or if they rely on a lower-level mechanism-i.e. spatial frequency-to discriminate between two different numerosities. When we matched the spatial frequency in stimuli with different numbers of bars, the larvae reliably selected the higher numerosity. A previous study has ruled out that 7 dpf zebrafish larvae use convex hull, cumulative surface area and density to choose between two numerosities. Therefore, our results indicate that zebrafish larvae rely on real numerical abilities rather than other cues, including spatial frequency, when spontaneously comparing two sets with different numbers of bars.

Environmental enrichment enhances the antidepressant effect of ketamine and ameliorates spatial memory deficits in adult rats

Ketamine is a rapid-acting antidepressant associated with various cognitive side effects. To mitigate these side effects while enhancing efficacy, it can be co-administered with other antidepressants. In our study, we adopted a similar strategy by combining ketamine with environmental enrichment, a potent sensory-motor paradigm, in adult male Wistar rats. We divided the animals into four groups based on a combination of housing conditions and ketamine versus vehicle injections. The groups included those housed in standard cages or an enriched environment for 50 days, which encompassed a 13-day-long behavioral testing period. Each group received either two doses of ketamine (20 mg/kg, IP) or saline as a vehicle. We tested the animals in the novel object recognition test (NORT), forced swim test (FST), open field test (OFT), elevated plus maze (EPM), and Morris water maze (MWM), which was followed by ex vivo c-Fos immunohistochemistry. We observed that combining environmental enrichment with ketamine led to a synergistic antidepressant effect. Environmental enrichment also ameliorated the spatial memory deficits caused by ketamine in the MWM. There was enhanced neuronal activity in the habenula of the enrichment only group following the probe trial of the MWM. In contrast, no differential activity was observed in enriched animals that received ketamine injections. The present study showed how environmental enrichment can enhance the antidepressant properties of ketamine while reducing some of its side effects, highlighting the potential of combining pharmacological and sensory-motor manipulations in the treatment of mood disorders.

Evaluation of different methods of environmental enrichment to control anxiety in dogs undergoing hemilaminectomy after acute intervertebral disc extrusion: a randomized double-blinded study

Objective

The goal of this randomized, double-blinded, placebo-controlled study was to evaluate the effect of environmental enrichment (EE) on post-operative pain and anxiety in dogs following hemilaminectomy for acute intervertebral disc extrusion (IVDE).

Methods

Twenty healthy client-owned dogs undergoing a hemilaminectomy for IVDE with the same immediate post-operative analgesia protocol were randomly assigned to either the EE or standard environment (SE) group post-operatively. Recovery was achieved in an intensive care room (SE) or a separate quiet room (EE) equipped with white noise and classical music. EE dogs were also exposed to dog-appeasing pheromones, essential oil scents, and positive human interactions and were provided meals through food toys. A blinded evaluator assessed all dogs using the modified Glasgow Composite Pain Scale (mGCPS) on presentation and at several time points post-operatively. A rescue injection of the opioid methadone was given to the dogs with an mGCPS score of ≥5/20. Dogs received the antidepressant trazodone when anxious behaviors (5 mg/kg) were observed. The mGCPS scores, the latencies to receive the first methadone and trazodone doses and to eat the first meal, the number of methadone and trazodone doses, and the number of meals ingested in the first 24 and 48 h post-surgery were compared using Wilcoxon tests, and Benjamini-Hochberg correction for false discovery rate was applied.

Results

Although median mGCPS scores did not differ between the groups, compared to SE dogs (n = 10), EE dogs (n = 6) received trazodone earlier (p = 0.019), were administered fewer methadone injections at 24 h (p = 0.043), and ate more at 48 h post-surgery (p = 0.007). Therefore, EE and anti-anxiety medications could be beneficial in improving the wellbeing of dogs post-operatively.

Increased basolateral amygdala metabolic activity during flavor familiarization: an experimental study

BACKGROUND

Novel flavors elicit a cautious neophobic response which is attenuated as the flavor becomes familiar and safe. The attenuation of neophobia reveals the formation of a safe memory. Previous lesion studies in rats have reported that basolateral amygdala integrity is required for taste neophobia, but not neophobia to flavor, i.e., taste linked to an odorous component. Accordingly, immunohistochemical analyses show that novel tastes induced higher basolateral amygdala activity when compared to familiar ones. However, a different role of basolateral amygdala in flavor attenuation of neophobia is suggested by lesion studies using a vinegar solution. Studies assessing basolateral amygdala activity during flavor attenuation of neophobia are lacking. Thus, we quantified cytochrome oxidase as an index of basolateral amygdala activity along the first and second vinegar exposures in order to assess flavor neophobia and attenuation of neophobia.

METHODS

We exposed adult male Wistar rats either once or twice to a 3% cider vinegar solution or water, and compared the basolateral amygdala, piriform cortex and caudate putamen brain metabolic activity using cytochrome c-oxidase histochemistry.

RESULTS

We found increased flavor intake and cytochrome c-oxidase histochemistry activity during the second exposure in basolateral amygdala, but not in the piriform cortex and caudate/putamen.

CONCLUSIONS

The main finding of the study is that BLA metabolic activity was higher in the group exposed to a familiar vinegar solution than in the groups exposed to either water or a novel vinegar solution.

Preterm rat survival is enhanced by gestational environmental enrichment

Throughout the last decade, the estimated global human preterm birth rate was 10.6 %, with higher rates in Asia, South America, and Africa. Preterm individuals, even in adulthood, are more likely to develop cardiorespiratory, renal, and metabolic disorders. On the other hand, when experimental animals are housed in an enriched environment during gestation, the development of the progeny in utero is accelerated, compared to standard housing conditions. By terminating gestation one and a half days before parturition, we investigated whether environmental enrichment restricted to gestation may have an impact on progeny survival. Our results demonstrate that the gestational enriched environment tripled the rat´s offspring survival, which was associated with decreased expression of anxiety-like behaviors in the pregnant mother. Sex of the offspring was not a factor in determining survival. We discuss the effect of increased secretion of various trophic factors and hormones induced by the enriched environment on progeny survival.

Changes in Stereotypies: Effects over Time and over Generations

Simple Summary

Herein, we propose that there should be discussion about the function and effects of stereotypies in relation to the time during which they are shown. In the first stages, stereotypies may help animals deal with challenges. However, behavior can potentially alter the brain, impairing its function due the absence of a diverse repertory, and change brain connections, neurophysiology and later neuroanatomy. The neuroanatomical changes in individuals showing stereotypies could be an effect rather than a cause of the stereotypy. As a consequence, studies showing different outcomes for animal welfare from stereotypy expression could be due to variation in a timeline of expression. Stereotypies are widely used as an animal welfare indicator, and their expression can tell us about psychological states. However, there are questions about the longer-term consequences if animals express stereotypies: do the stereotypies help in coping? During the prenatal period, stereotypic behavior expressed by the mother can change the phenotype of the offspring, especially regarding emotionality, one mechanism acting via methylation in the limbic system in the brain. Are individuals that show stereotypies for shorter or longer periods all better adjusted, and hence have better welfare, or is the later welfare of some worse than that of individuals that do not show the behavior?

Abstract

Stereotypies comprise a wide range of repeated and apparently functionless behaviors that develop in individuals whose neural condition or environment results in poor welfare. While stereotypies are an indicator of poor welfare at the time of occurrence, they may have various consequences. Environmental enrichment modifies causal factors and reduces the occurrence of stereotypies, providing evidence that stereotypies are an indicator of poor welfare. However, stereotypy occurrence and consequences change over time. Furthermore, there are complex direct and epigenetic effects when mother mammals that are kept in negative conditions do or do not show stereotypies. It is proposed that, when trying to deal with challenging situations, stereotypies might initially help animals to cope. After further time in the conditions, the performance of the stereotypy may impair brain function and change brain connections, neurophysiology and eventually neuroanatomy. It is possible that reported neuroanatomical changes are an effect of the stereotypy rather than a cause.

The differential effects of brief environmental enrichment following social isolation in rats

Environmental enrichment (EE) in rodents is associated with a wide range of physiological, affective, and cognitive benefits. A seemingly opposite housing condition, social isolation (SI), is used as a rodent model of stress, negatively affecting several neurobiological mechanisms and hampering cognitive performance. Experimental designs that involve switching between these housing conditions produced mixed results. We evaluated different behavioral and cognitive effects of brief EE following long-term, SI-induced stress. We revealed the influence of enrichment after 30 days of isolation on behavioral despair, anxiety-like behavior, and spatial working memory in adult male Wistar rats and found a substantial anxiolytic effect in the experimental (SI to EE) group. Interestingly, rats exposed to EE also showed increased behavioral despair compared with the control (continuous SI) group. There was no difference in spatial working memory performance at the end of a 5-day water Y-maze (WYM) test. However, the SI to EE animals displayed better memory performance in the first 2 days of the WYM, indicating faster learning. In line with this difference, we recorded significantly more c-Fos-immunopositive (c-Fos+) cells in the retrosplenial and perirhinal cortices of the SI to EE animals. The lateral and basolateral nuclei of the amygdala showed no such difference. These results suggest that brief enrichment following isolation stress leads to differential results in affective and cognitive systems.

Environmental enrichment: dissociated effects between physical activity and changing environmental complexity on anxiety and neurogenesis in adult male Balb/C mice

Several factors, including environmental modifications, stimulate neuroplasticity. One type of neuroplasticity consists in the generation of new neurons in the dentate gyrus of the hippocampus. Neurogenesis is modulated by environmental enrichment (ENR, tunnels plus running wheel) and affected by the time of exposure to ENR. Despite the wide use of ENR to stimulate neuroplasticity, the degree to which ENR variations modeled by temporally changing the level of environmental complexity affect hippocampal neurogenesis and anxiety is still unclear. Thus, we investigated the effects of five housing conditions on young adult male Balb/C mice exposed for 42 days. The groups were as follows: standard conditions without ENR, constant ENR complexity, gradual increase of ENR complexity followed by a gradual decrease of ENR complexity, gradual increase of ENR complexity followed by constant ENR complexity, and constant ENR complexity followed by a gradual decrease of ENR complexity. On day 44, mice were exposed to the elevated plus-maze to evaluate anxiety. Further, we analyzed neurogenesis and quantified corticosterone levels. In an additional experiment, we explored the effect of voluntary physical activity on anxiety, neurogenesis, and corticosterone during the variations in ENR complexity. Our results showed that any change in ENR complexity over time reduced anxiety. Also, voluntary physical activity alone or in the context of a complex environment increased doublecortin cell maturation in the granular cell layer of the hippocampus. Finally, our study supports that physical activity acts proneurogenic, whereas any change in environmental complexity decreases anxiety-like behavior. However, the decrease in corticosterone levels elicited by physical activity was lower than the decrease produced by the decrement in environmental complexity.

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.

Short-Term Environmental Enrichment is a Stronger Modulator of Brain Glial Cells and Cervical Lymph Node T Cell Subtypes than Exercise or Combined Exercise and Enrichment

Physical exercise (PE) and environmental enrichment (EE) can modulate immunity. However, the differential effects of short-term PE, EE, and PE + EE on neuroimmune mechanisms during normal aging has not been elucidated. Hence, a cohort of 3-, 8-, and 13-month-old immunologically unchallenged C57BL/6 wild-type mice were randomly assigned to either Control, PE, EE, or PE + EE groups and provided with either no treatment, a running wheel, a variety of plastic and wooden objects alone or in combination with a running wheel for seven weeks, respectively. Immunohistochemistry and 8-color flow cytometry were used to determine the numbers of dentate gyrus glial cells, and the proportions of CD4+ and CD8+ T cell numbers and their subsets from cervical lymph nodes, respectively. An increase in the number of IBA1+ microglia in the dentate gyrus at 5 and 10 months was observed after EE, while PE and PE + EE increased it only at 10 months. No change in astroglia number in comparison to controls were observed in any of the treatment groups. Also, all treatments induced significant differences in the proportion of specific T cell subsets, i.e., CD4+ and CD8+ T naïve (TN), central memory (TCM), and effector memory (TEM) cells. Our results suggest that in the short-term, EE is a stronger modulator of microglial and peripheral T cell subset numbers than PE and PE + EE, and the combination of short-term PE and EE has no additive effects.

Recovering Spatial Information through Reactivation: Brain Oxidative Metabolism Involvement in Males and Females

Memory involves a complex network system of interconnected brain areas in which labile trace memories are transformed into enduring ones and reorganized in a time-dependant manner. Although it has been observed that remote memories are less prone to destabilizing, they can become fragile and lead to behavioural decline. We explored the behavioural outcomes of male and female rats in response to the reactivation of a previously acquired allocentric spatial reference memory, under conditions in which animals have shown a retrieval decay. In addition, we assessed their brain metabolic activity through cytochrome c oxidase (CCO) histochemistry. Our results show that a spatial memory amnesia-like behaviour with a time interval of 45 days can be recovered after re-exposure to the environmental configuration with the reinforced contingencies. Moreover, we observed that, following reactivation, male rats reveal a decrease in metabolic activity in septal nuclei and thalamic structures, whereas female rats add a metabolic reduction in the hippocampus, amygdala, mPFC, and retrosplenial, parietal and rhinal cortices, suggesting that they efficiently employ these brain areas when reactivation a memory that has suffered a decay with time. Finally, although male and female rats perform the behavioural task equally, we found sex differences at the brain metabolism level, revealing the differential contribution of brain limbic system energy demands by sex, even when their performance is similar. In conclusion, our work provides behavioural and brain data about remote spatial retrieval and memory reactivation processes.

Early life stress due to repeated maternal separation alters the working memory acquisition brain functional network

Unfortunately, adverse environments in early life are frequently found in most human populations. Early life stress leads to diverse cognitive impairments, some of them related to learning and memory and executive functions such as working memory (WM). We employ an animal model of early stress using repeated maternal separation (MS) for 4 h a day on 21 consecutive days, pre-weaning. In adulthood, we tested their spatial WM using the Morris water maze. MS subjects showed a marked delay in the acquisition of the task. In addition, we explored brain energy oxidative metabolism and found an increase in cytochrome c oxidase (CCO) activity in the cingulate cortex, anterior thalamus, and supramammillary areas, indicating an intense effort to successfully solve the WM task. However, decreased CCO activity was found in the medial-medial mammillary nucleus in MS animals, which would partially explain the delayed acquisition of the WM task. Further studies are needed to explore the long-term alterations produced by early stress. LAY SUMMARY A stressful environment caused by the separation of baby rats from the mother for several hours a day in the first stages of postnatal life can be devastating to brain cells, making them look for alternative sources of energy, among other changes. These alterations in brain functional networks would lead to cognitive impairments such as the delayed acquisition of new learning and strategies.

Environmental enrichment alters neurobehavioral development following maternal immune activation in mice offspring with epilepsy

Epilepsy is a chronic brain disease affecting millions of people worldwide. Anxiety-related disorders and cognitive deficits are common in patients with epilepsy. Previous studies have shown that maternal infection/immune activation renders children more vulnerable to neurological disorders later in life. Environmental enrichment has been suggested to improve seizures, anxiety, and cognitive impairment in animal models. The present study aimed to explore the effects of environmental enrichment on seizure scores, anxiety-like behavior, and cognitive deficits following maternal immune activation in offspring with epilepsy. Pregnant mice were treated with lipopolysaccharides-(LPS) or vehicle, and offspring were housed in normal or enriched environments during early adolescence to adulthood. To induce epilepsy, adult male and female offspring were treated with Pentylenetetrazol-(PTZ), and then anxiety-like behavior and cognitive functions were assessed. Tumor-necrosis-factor (TNF)-α and interleukin (IL) 10 were measured in the hippocampus of offspring. Maternal immune activation sex-dependently increased seizure scores in PTZ-treated offspring. Significant increases in anxiety-like behavior, cognitive impairment, and hippocampal TNF-α and IL-10 were also found following maternal immune activation in PTZ-treated offspring. However, there was no sex difference in these behavioral abnormalities in offspring. Environmental enrichment reversed the effects of maternal immune activation on behavioral and inflammatory parameters in PTZ-treated offspring. Overall, the present findings highlight the adverse effects of prenatal maternal immune activation on seizure susceptibility and psychiatric comorbidities in offspring. This study suggests that environmental enrichment may be used as a potential treatment approach for behavioral abnormalities following maternal immune activation in PTZ-treated offspring.

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.

Neurobehavioral Effects of Restricted and Unpredictable Environmental Enrichment in Rats

To study how motivational factors modulate experience-dependent neurobehavioral plasticity, we modify a protocol of environmental enrichment (EE) in rats. We assumed that the benefits derived from EE might vary according to the level of incentive salience attributed to it. To enhance the rewarding properties of EE, access to the EE cage varied randomly from 2 to 48 h for 30 days (REE). The REE group was enriched only 50% of the time and was compared to standard housing and continuous EE (CEE) groups. As behavioral readout, we analyzed the spontaneous activity and the ultrasonic vocalizations (USVs) within the EE cage weekly, and in the open field test at the end of the experiment. In the cage, REE increased the utilization of materials, physical activity, and the rate of appetitive USVs. In the OF, the CEE-induced enhancements in novelty habituation and social signaling were equaled by the REE. At the neural level, we measured the expression of genes related to neural plasticity and epigenetic regulations in different brain regions. In the dorsal striatum and hippocampus, REE upregulated the expression of the brain-derived neurotrophic factor, its tropomyosin kinase B receptor, and the DNA methyltransferase 3A. Altogether, our results suggest that the higher activity within the cage and the augmented incentive motivation provoked by the REE boosted its neurobehavioral effects equaling or surpassing those observed in the CEE condition. As constant exposures to treatments or stimulating environments are virtually impossible for humans, restricted EE protocols would have greater translational value than traditional ones.

Duration of Environmental Enrichment Determines Astrocyte Number and Cervical Lymph Node T Lymphocyte Proportions but Not the Microglial Number in Middle-Aged C57BL/6 Mice

Environmental enrichment (EE) has been shown to modulate behavior and immunity. We recently reported that both short and long-term EE enhance baseline locomotion and alleviate depressive-like behavior, but only long-term EE affects locomotion adversely in a threatening environment and enhances anxiety-like behavior in middle-age mice. We have now investigated whether the observed changes in behavior after short- and long-term EE were associated with underlying immune changes. Hence, at the end of behavioral testing, mice were sacrificed, and brains and cervical lymph nodes were collected to investigate the differential effects of the duration of EE (short- and long-term) on the number of immunopositive glial cells in the dentate gyrus, CA1, CA2, and CA3 regions of the hippocampus and proportions of T cell subsets in the cervical lymph nodes using immunohistochemistry and flow cytometry, respectively. EE, regardless of duration, caused an increase in microglia number within the dentate gyrus, CA1 and CA3 hippocampal regions, but only long-term EE increased astrocytes number within the dentate gyrus and CA3 hippocampal regions. A significantly higher proportion of CD8⁺ naive T cells was observed after long-term EE vs. short-term EE. No significant differences were observed in the proportion of central memory and effector memory T cells or early activated CD25⁺ cells between any of the test groups. Our results suggest that EE, irrespective of duration, enhances the numbers of microglia, but long-term EE is required to modify astrocyte number and peripheral T cell proportions in middle-aged mice. Our findings provide new insights into the therapeutic effects of EE on various brain disorders, which may be at least partly mediated by glial and neuroimmune modulation.

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

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

Environmental Impoverishment, Aging, and Reduction in Mastication Affect Mouse Innate Repertoire to Explore Novel Environments and to Assess Risk

Studies indicate that inhibition of adequate masticatory function, due to soft diet, occlusal disharmony, or molar losses affects the cognitive behavior of rodents. However, no study has tested the effects on new environments exploration and risk assessment coupled with a combination of masticatory function rehabilitation and environmental enrichment. In the present report, we tested the hypothesis that age, environment, and masticatory changes may interact and alter exploratory patterns of locomotor activity and mice preferences in an open field (OF) arena. As OF arenas are widely used to measure anxiety-like behavior in rats and mice. We examined in an open arena, the exploratory and locomotor activities of mature (6-month-old; 6M), late mature (12-month-old; 12M), and aged (18-month-old; 18M) mice, subjected to distinct masticatory regimens and environments. Three different regimens of masticatory activity were used: continuous normal mastication with hard pellets (HD); normal mastication followed by reduced mastication with equal periods of pellets followed by soft powder – HD/SD; or rehabilitated masticatory activity with equal periods of HD, followed by powder, followed by pellets – HD/SD/HD). Under each diet regimen, half of the individuals were raised in standard cages [impoverished environment (IE)] and the other half in enriched cages [enriched environment (EE)]. Animals behavior on the open field (OF) task were recorded by webcam and analyzed with Any Maze software (Stöelting). The locomotor and exploratory activities in OF task declined with age, and this was particularly evident in 18M HD EE mice. Although all groups kept their preference by the peripheral zone, the outcomes were significantly influenced by interactions between environment, age, and diet. Independent of diet regime, 6M young mice maintained in an EE where voluntary exercise apparatus is available, revealed significant less body weight than all other groups. Although body weight differences were minimized as age progressed, 18M EE group revealed intragroup significant influence of diet regimens. We suggest that long life environmental enrichment reduces the tendency to avoid open/lit spaces (OF) and this is particularly influenced by masticatory activity. These measurements may be useful in discussions of anxiety-related tasks.

Environmental Enrichment Results in Both Brain Connectivity Efficiency and Selective Improvement in Different Behavioral Tasks

Exposure to environmental enrichment (EE) has been a useful model for studying the effects of experience on brain plasticity, but to date, few is known about the impact of this condition on the brain functional networks that probably underlies the multiple behavioral improvements. Hence, we assessed the effect of an EE protocol in adult Wistar rats on the performance in several behavioral tasks testing different domains (Open field (OP): locomotor activity; Elevated-zero maze (EZM): anxiety-related behaviors; 5-choice serial reaction time task (5-CSRTT): attentional processes; 4-arm radial water maze (4-RAWM): spatial memory) in order to check its effectiveness in a wide range of functions. After this, we analyzed the functional brain connectivity underlying each experimental condition through cytochrome C oxidase (COx) histochemistry. Our EE protocol reduced both locomotor activity in the OP and anxiety-related behaviors in the EZM. On the other hand, enriched rats showed more accuracy in the 4-RAWM, whereas 5-CSRTT performance was not significantly ameliorated by EE condition. In relation to COx functional connectivity, we found that EE reduced the number of strong positive correlations both in basal and training conditions, suggesting a modulating effect on specific brain connections. Our results suggest that EE seems to have a selective effect on specific brain regions, such as prefrontal cortex and hippocampus, leading to a more efficient brain connectivity.

Why are maternally separated females inflexible? Brain activity pattern of COx and c-Fos

Subjects' early life events will affect them later in life. When these events are stressful, such as child abuse in humans or repeated maternal separation in rodents, subjects can show some behavioral and brain alterations. This study used young adult female Wistar rats that were maternally raised (AFR), maternally separated from post-natal day (PND) 1 to PND10 (MS10), or maternally separated from PND1 to PND21 (MS21), in order to assess the effects of maternal separation (MS) on spatial learning and memory, as well as cognitive flexibility, using the Morris Water Maze (MWM). We performed quantitative cytochrome oxidase (COx) histochemistry on selected brain areas in order to identify whether maternal separation affects brain energy metabolism. We also performed c-Fos immunohistochemistry on the medial prefrontal cortex (mPFC), thalamus, and hippocampus to explore whether this immediate early gene activity was altered in stressed subjects. We obtained a similar spatial learning pattern in maternally raised and maternally separated subjects on the reference memory task, but only the controls were flexible enough to solve the reversal learning successfully. Separated groups showed less c-Fos activity in the mPFC and less complex neural networks on COx.

Effects of Environmental Enrichment on Doublecortin and BDNF Expression along the Dorso-Ventral Axis of the Dentate Gyrus

Adult hippocampal neurogenesis (AHN) in the dentate gyrus is known to respond to environmental enrichment, chronic stress, and many other factors. The function of AHN may vary across the septo-temporal axis of the hippocampus, as different subdivisions are responsible for different functions. The dorsal pole regulates cognitive-related behaviors, while the ventral pole mediates mood-related responses through the hypothalamic-pituitary-adrenal (HPA) axis. In this study, we investigate different methods of quantifying the effect of environmental enrichment on AHN in the dorsal and ventral parts of the dentate gyrus (dDG and vDG). To this purpose, 11-week-old female CD-1 mice were assigned for 8 days to one of two conditions: the Environmental Enrichment (E) group received (i) running wheels, (ii) larger cages, (iii) plastic tunnels, and (iv) bedding with male urine, while the Control (C) group received standard housing. Dorsal CA (Cornu Ammonis) and DG regions were larger in the E than the C animals. Distance run linearly predicted the volume of the dorsal hippocampus, as well as of the intermediate and ventral CA regions. In the dDG, the amount of Doublecortin (DCX) immunoreactivity was significantly higher in E than in C mice. Surprisingly, this pattern was the opposite in the vDG (C > E). Real-time PCR measurement of Dcx mRNA and DCX protein analysis using ELISA showed the same pattern. Brain Derived Neurotrophic Factor (BDNF) immunoreactivity and mRNA displayed no difference between E and C, suggesting that upregulation of DCX was not caused by changes in BDNF levels. BDNF levels were higher in vDG than in dDG, as measured by both methods. Bdnf expression in vDG correlated positively with the distance run by individual E mice. The similarity in the patterns of immunoreactivity, mRNA and protein for differential DCX expression and for BDNF distribution suggests that the latter two methods might be effective tools for more rapid quantification of AHN.

Environmental enrichment enhances cognitive flexibility in C57BL/6 mice on a touchscreen reversal learning task

Environmental enrichment (EE) is any positive modification of the 'standard housing' (SH) conditions in which laboratory animals are typically held, usually involving increased opportunity for cognitive stimulation and physical activity. EE has been reported to enhance baseline performance of wild-type animals on traditional cognitive behavioural tasks. Recently, touchscreen operant testing chambers have emerged as a way of performing rodent cognitive assays, providing greater reproducibility, translatability and automatability. Cognitive tests in touchscreen chambers are performed over numerous trials and thus experimenters have the power to detect subtle enhancements in performance. We used touchscreens to analyse the effects of EE on reversal learning, visual discrimination and hippocampal-dependent spatial pattern separation and working memory. We hypothesized that EE would enhance the performance of mice on cognitive touchscreen tasks. Our hypothesis was partially supported in that EE induced enhancements in cognitive flexibility as observed in visual discrimination and reversal learning improvements. However, no other significant effects of EE on cognitive performance were observed. EE decreased the activity level of mice in the touchscreen chambers, which may influence the enrichment level of the animals. Although we did not see enhancements on all hypothesized parameters, our testing paradigm is capable of detecting EE-induced improved cognitive flexibility in mice, which has implications for both understanding the mechanisms of EE and improving screening of putative cognitive-enhancing therapeutics.

Alteration of Energy Metabolism and Antioxidative Processing in the Hippocampus of Rats Reared in Long-Term Environmental Enrichment

Environmental enrichment (EE) is a typical experimental method that promotes levels of novelty and complexity that enhance experience-dependent neuroplasticity and cognitive behavior function in laboratory animals. Early EE is associated with resilience in the face of later-life challenges. Since increased synaptic activity enhances endogenous neuronal antioxidant defenses, we hypothesized that long-term EE beginning at an early stage may alter the levels of oxidative stress. We investigated global protein expression and oxidative stress in hippocampal proteins from rats nurtured for a 6-month EE beginning in the prenatal period. The analysis of protein expression was carried out using 2-dimensional gel electrophoresis with matrix-associated laser desorption ionization time-of-flight mass spectrometry. Proteins with altered expression were involved in energy metabolism (phosphoglycerate mutase 1, α-enolase isoform 1, adenylate kinase 1, and triose phosphate isomerase) and antioxidant enzymes (superoxide dismutase 1, glutathione S-transferase ω type 1, peroxiredoxin 5, DJ-1, and glial maturation factor β). Using Western blot assays, some of the proteins with altered expression and NADPH oxidase 2 were confirmed to be decreased. Further confirmation was demonstrated with attenuated expression of 7,8-dihydro-8-oxo-deoxyguanine, a DNA oxidative stress marker, in the hippocampus of EE group rats. Our data demonstrate that a long-term EE program beginning in the prenatal and early postnatal phase of development modulates energy metabolism and reduced oxidant stress possibly through enhanced synaptic activity. We provide evidence that EE can be developed as a tool to protect the brain from oxidative stress-induced injury.

Influence of daily social stimulation on behavioral and physiological outcomes in an animal model of PTSD

INTRODUCTION

We have shown in previous work that acute episodes of predator exposure occurring in the context of chronic social instability produced PTSD-like sequelae in rats. Our animal model of PTSD contained two components: (1) acute trauma, immobilization of rats in close proximity to a cat twice in 10 days, and (2) chronic social instability, 31 days of randomized housing of cage cohorts. Here we tested the hypothesis that daily social stimulation would block the development of the PTSD-like sequelae.

METHODS

Beginning 24 h after the first cat exposure, adult male rats were given our established PTSD model, alone or in conjunction with daily social stimulation, in which all rats within a group interacted in a large apparatus for 2 h each day for the final 30 days of the PTSD regimen. All behavioral, for example, anxiety, memory, startle testing, and physiological assessments, for example, body growth, organ weights, and corticosterone levels, took place following completion of the psychosocial stress period.

RESULTS

Daily social stimulation blocked the expression of a subset of PTSD-like effects, including predator-based cued fear conditioning, enhanced startle response, heightened anxiety on the elevated plus maze and the stress-induced suppression of growth rate. We also found that social stimulation and psychosocial stress produced equivalent outcomes in some measures, including adrenal and heart hypertrophy, thymus atrophy, and a reduction in poststress corticosterone levels.

CONCLUSIONS

Daily exposure of rats to a highly social environment blocked the development of a subset of trauma-induced sequelae, particularly fear-related outcomes. It is notable that daily social stimulation normalized a subset, but not all, of the PTSD-like effects. We discuss our findings in the context of the literature demonstrating that social stimulation can counteract the adverse effects of traumatic stress on behavioral and physiological measures, as well as to produce its own stress-like outcomes.

Effects of enriched environment on alterations in the prefrontal cortex GFAP- and S100B-immunopositive astrocytes and behavioral deficits in MK-801-treated rats

A plethora of studies have indicated that enriched environment (EE) paradigm provokes plastic and morphological changes in astrocytes with accompanying increments of their density and positively affects the behavior of rodents. We also previously documented that EE could be employed to preclude several behavioral abnormalities, mainly cognitive deficits, attributed to postnatal N-methyl-d-aspartate (NMDA) receptor antagonist (MK-801) treatment, as a rodent model of schizophrenia (SCH) aspects. Given this, the current study quantitatively investigated the number of cells, presumed to be astrocytes, expressing two astroglia-associated proteins (S100B and glial fibrillary acidic protein (GFAP)) by immunohistochemistry in the prefrontal cortex (PFC), along with anxiety and passive avoidance (PA) learning behaviors by utilizing elevated plus maze (EPM) and shuttle-box tests, in MK-801-treated male wistar rats submitted to EE and non-EE rats. Following a treatment regime of sub-chronic MK-801 (1.0mg/kg i.p. daily for five consecutive days from postnatal day (P) 6), S-100B-positive cells and anxiety level were markedly increased, while the GFAP-positive cells and PA learning were notably attenuated. The trend of diminished GFAP-immunopositive cells and elevated S100B-immunostained cells in the PFC was reversed in the SCH-like rats by exposure of animals to EE, commencing from birth up to the time of experiments on P28-85. Additionally, EE exhibited an ameliorating effect on the behavioral abnormalities evoked by MK-801. Overall, present findings support that improper astrocyte functioning and behavioral changes, reminiscent of the many facets of SCH, occur consequential to repetitive administration of MK-801 and that raising rat pups in an EE mitigates these alterations.

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

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

Transgenerational Transmission of Stress Pathology

Abstract. The impact of the environment early in life on long-term outcomes is well known. Stressful experiences during pre- and postnatal development can modulate the genetic programming of specific brain circuits underlying emotional and cognitive aspects of behavioral adaptation to stressful experiences later in life. Furthermore, there is documented evidence for gene-environment interactions in the context of early-life stress. Identical gene variants can be associated with different phenotypes depending on environmental factors. DNA methylation, an enzymatically-catalyzed modification of the DNA, is the mechanism through which phenotypes are regulated. The dynamics and plasticity of epigenetic mechanisms can have short-term, long-term, or transgenerational consequences. In epigenetic research, rodent models have targeted several behavioral and emotional phenotypes. These models have contributed significantly to our understanding of the environmental regulation of the developmental brain in early life. This review will highlight studies with rats and mice on epigenetic processes in fetal programming of stress-related mental disorders.

Life-long environmental enrichment counteracts spatial learning, reference and working memory deficits in middle-aged rats subjected to perinatal asphyxia

Continuous environmental stimulation induced by exposure to enriched environment (EE) has yielded cognitive benefits in different models of brain injury. Perinatal asphyxia results from a lack of oxygen supply to the fetus and is associated with long-lasting neurological deficits. However, the effects of EE in middle-aged rats suffering perinatal asphyxia are unknown. Therefore, the aim of the present study was to assess whether life-long exposure to EE could counteract the cognitive and behavioral alterations in middle-aged asphyctic rats. Experimental groups consisted of rats born vaginally (CTL), by cesarean section (C+), or by C+ following 19 min of asphyxia at birth (PA). At weaning, rats were assigned to standard (SE) or enriched environment (EE) for 18 months. During the last month of housing, animals were submitted to a behavioral test battery including Elevated Plus Maze, Open Field, Novel Object Recognition and Morris water maze (MWM). Results showed that middle-aged asphyctic rats, reared in SE, exhibited an impaired performance in the spatial reference and working memory versions of the MWM. EE was able to counteract these cognitive impairments. Moreover, EE improved the spatial learning performance of middle-aged CTL and C+ rats. On the other hand, all groups reared in SE did not differ in locomotor activity and anxiety levels, while EE reduced locomotion and anxiety, regardless of birth condition. Recognition memory was altered neither by birth condition nor by housing environment. These results support the importance of environmental stimulation across the lifespan to prevent cognitive deficits induced by perinatal asphyxia.

PhenoWorld: a new paradigm to screen rodent behavior

Modeling depression in animals has inherent complexities that are augmented by intrinsic difficulties to measure the characteristic features of the disorder. Herein, we describe the PhenoWorld (PhW), a new setting in which groups of six rats lived in an ethological enriched environment, and have their feeding, locomotor activity, sleeping and social behavior automatically monitored. A battery of emotional and cognitive tests was used to characterize the behavioral phenotype of animals living in the PhW and in standard conditions (in groups of six and two rats), after exposure to an unpredictable chronic mild stress paradigm (uCMS) and antidepressants. Data reveal that animals living in the PhW displayed similar, but more striking, behavioral differences when exposed to uCMS, such as increased behavioral despair shown in the forced swimming test, resting/sleep behavior disturbances and reduced social interactions. Moreover, several PhW-cage behaviors, such as spontaneous will to go for food or exercise in running wheels, proved to be sensitive indicators of depressive-like behavior. In summary, this new ethological enriched paradigm adds significant discriminative power to screen depressive-like behavior, in particularly rodent's hedonic behavior.

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

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