Untangling the Influences of Voluntary Running,Environmental Complexity,Social Housing and Stress on Adult Hippocampal Neurogenesis

Environmental enrichment (EE) exerts powerful effects on brain physiology, and is widely used as an experimental and therapeutic tool. Typical EE paradigms are multifactorial, incorporating elements of physical exercise, environmental complexity, social interactions and stress, however the specific contributions of these variables have not been separable using conventional housing paradigms. Here, we evaluated the impacts of these individual variables on adult hippocampal neurogenesis by using a novel “Alternating EE” paradigm. For 4 weeks, adult male CD1 mice were alternated daily between two enriched environments; by comparing groups that differed in one of their two environments, the individual and combinatorial effects of EE variables could be resolved. The Alternating EE paradigm revealed that (1) voluntary running for 3 days/week was sufficient to increase both mitotic and post-mitotic stages of hippocampal neurogenesis, confirming the central importance of exercise; (2) a complex environment (comprised of both social interactions and rotated inanimate objects) had no effect on neurogenesis itself, but enhanced depolarization-induced c-Fos expression (attributable to social interactions) and buffered stress-induced plasma corticosterone levels (attributable to inanimate objects); and (3) neither social isolation, group housing, nor chronically increased levels of plasma corticosterone had a prolonged impact on neurogenesis. Mouse strain, handling and type of running apparatus were tested and excluded as potential confounding factors. These findings provide valuable insights into the relative effects of key EE variables on adult neurogenesis, and this “Alternating EE” paradigm represents a useful tool for exploring the contributions of individual EE variables to mechanisms of neural plasticity.     

Effects of Enriched Environment on COX-2, Leptin and Eicosanoids in a Mouse Model of Breast Cancer

Cyclooxygenase-2 (COX-2) and adipokines have been implicated in breast cancer. This study investigated a possible link between COX-2 and adipokines in the development of mammary tumors. A model of environmental enrichment (EE), known to reduce tumor growth was used for a syngeneic murine model of mammary carcinoma. 3-week-old, female C57BL/6 mice were housed in standard environment (SE) or EE cages for 9 weeks and transplanted orthotopically with syngeneic EO771 adenocarcinoma cells into the right inguinal mammary fat pad. EE housing influenced mammary gland development with a decrease in COX-2 expressing cells and enhanced side-branching and advanced development of alveolar structures of the mammary gland. Tumor volume and weight were decreased in EE housed mice and were associated with a reduction in COX-2 and Ki67 levels, and an increase in caspase-3 levels. In tumors of SE mice, high COX-2 expression correlated with enhanced leptin detection. Non-tumor-bearing EE mice showed a significant increase in adiponectin levels but no change in those of leptin, F₂-isoprostanes, PGF_2α, IL-6, TNF-α, PAI-1, and MCP-1 levels. Both tumor-bearing groups (SE and EE housing) had increased resistin, IL-6, TNF-α, PAI-1 and MCP-1 levels irrespective of the different housing environment demonstrating higher inflammatory response due to the presence of the tumor. This study demonstrates that EE housing influenced normal mammary gland development and inhibited mammary tumor growth resulting in a marked decrease in intratumoral COX-2 activity and an increase in the plasma ratio of adiponectin/leptin levels.     

Enrichment devices for nonhuman primates

There has been in recent years a substantial increase in the variety of enhancement devices available for nonhuman primates in captivity, and the task of properly outfitting a housing unit can be daunting. Researchers continue to investigate the specific impact and importance of environmental enrichment, but it is generally accepted that increasing the complexity of the environment for the mental and physical stimulation of nonhuman primates is beneficial to their health and contentment, and enrichment is now a standard component of primate husbandry.     

Responses to Environmental Enrichment Differ with Sex and Genotype in a Transgenic Mouse Model of Huntington's Disease

Background

Environmental enrichment (EE) in laboratory animals improves neurological function and motor/cognitive performance, and is proposed as a strategy for treating neurodegenerative diseases. EE has been investigated in the R6/2 mouse model of Huntington''s disease (HD), where increased social interaction, sensory stimulation, exploration, and physical activity improved survival. We have also shown previously that HD patients and R6/2 mice have disrupted circadian rhythms, treatment of which may improve cognition, general health, and survival.

Methodology/Principal Findings

We examined the effects of EE on the behavioral phenotype and circadian activity of R6/2 mice. Our mice are typically housed in an “enriched” environment, so the EE that the mice received was in addition to these enhanced housing conditions. Mice were either kept in their home cages or exposed daily to the EE (a large playground box containing running wheels and other toys). The “home cage” and “playground” groups were subdivided into “handling” (stimulated throughout the experimental period) and “no-handling” groups. All mice were assessed for survival, body weight, and cognitive performance in the Morris water maze (MWM). Mice in the playground groups were more active throughout the enrichment period than home cage mice. Furthermore, R6/2 mice in the EE/no-handling groups had better survival than those in the home cage/no-handling groups. Sex differences were seen in response to EE. Handling was detrimental to R6/2 female mice, but EE increased the body weight of male R6/2 and WT mice in the handling group. EE combined with handling significantly improved MWM performance in female, but not male, R6/2 mice.

Conclusions/Significance

We show that even when mice are living in an enriched home cage, further EE had beneficial effects. However, the improvements in cognition and survival vary with sex and genotype. These results indicate that EE may improve the quality of life of HD patients, but we suggest that EE as a therapy should be tailored to individuals.     

Improving housing conditions for laboratory mice: a review of "environmental enrichment"

Laboratory animal facilities have been designed to provide a standard environment where animals can be kept in good physical health at the same time as economic and ergonomic considerations are met. Recognizing the potential welfare problem associated with behavioural restriction in such housing systems, a number of attempts have been made to improve this environment, generally described under the term "environmental enrichment". Modifications of cages for mice usually consist of providing material for nest building and structures which can serve as hiding places and/or for climbing. We have reviewed 40 studies carried out between 1987 and 2000, in which preferences as well as the effect of housing modifications have been studied. Mice will work for access to nesting material and make use of this material to make nests in which they rest. They prefer a more complex cage to the standard cage and will also work for access to cages with shelter and raised platforms. On the basis of present knowledge, it is recommended that mice should have access to nesting material. Strategies for future research are outlined in the article.     

Comparison of survival rates in four inbred mouse strains under different housing conditions: effects of environmental enrichment

Housing conditions can affect the well-being of laboratory animals and thereby affect the outcomes of experiments. The appropriate environment is essential for the expression of natural behavior in animals. Here, we compared survival rates in four inbred mouse strains maintained under three different environmental conditions. Three mouse strains (C57BL/6J, C3H/HeN, and DBA/2J) housed under environmental enrichment (EE) conditions showed improved survival; however, EE did not alter the survival rate of the fourth strain, BALB/c. None of the strains showed significant differences in body weights or plasma corticosterone levels in the three environmental conditions. For BALB/c mice, the rates of debility were higher in the EE group. Interestingly, for C57BL/6J and C3H/HeN mice, the incidence of animals with alopecia was significantly lower in the EE groups than in the control group. It is possible that the enriched environment provided greater opportunities for sheltering in a secure location in which to avoid interactions with other mice. The cloth mat flooring used for the EE group was bitten and chewed by the mice. Our findings suggest that depending on the mouse strains different responses to EE are caused with regard to health and survival rates. The results of this study provide basic data for further studies on EE.     

Differential Regulation of the Variations Induced by Environmental Richness in Adult Neurogenesis as a Function of Time: A Dual Birthdating Analysis

Adult hippocampal neurogenesis (AHN) augments after environmental enrichment (EE) and it has been related to some of the anxiolytic, antidepressant and neuroprotective effects of EE. Indeed, it has been suggested that EE specifically modulates hippocampal neurogenic cell populations over the course of time. Here we have used dual-birthdating to study two subpopulations of newborn neuron in mice (Mus musculus): those born at the beginning and at the end of enrichment. In this way, we demonstrate that while short-term cell survival is upregulated after an initial 1 week period of enrichment in 2 month old female mice, after long-term enrichment (2 months) neither cell proliferation nor the survival of the younger newly born cell populations are distinguishable from that observed in non-enriched control mice. In addition, we show that the survival of older newborn neurons alone (i.e. those born at the beginning of the enrichment) is higher than in controls, due to the significantly lower levels of cell death. Indeed, these parameters are rapidly adjusted to the sudden cessation of the EE conditions. These findings suggest both an early selective, long-lasting effect of EE on the neurons born in the initial stages of enrichment, and a quick response when the environment again becomes impoverished. Therefore, EE induces differential effects on distinct subpopulations of newborn neurons depending on the age of the immature cells and on the duration of the EE itself. The interaction of these two parameters constitutes a new, specific regulation of these neurogenic populations that might account for the long-term enrichment''s behavioral effects.     

Environmental enrichment of laboratory rodents: the answer depends on the question

Efforts to refine the care and use of animals in research have been ongoing for many years and have led to general standardization of rodent models, particularly with regard to animal housing, genetics, and health status. Concurrently, numerous informal practices and recommendations have been promulgated with the laudable intent of promoting general animal wellbeing through so-called enrichment of the cage environment. However, the variety of housing conditions fostered by efforts at environmental enrichment (EE) complicates the goal of establishing standardized or even defined environments for laboratory rodents. Many studies over the years have sought to determine whether or how various enrichment strategies affect the behavior and physiology of laboratory rodents. The findings, conclusions, and interpretations of these studies are mixed, particularly with regard to their application across rodent species, strains, genders, and ages; whether or how they affect the animals and the science; and, in some cases, whether the effects are positive, negative, or neutral in terms of animal wellbeing. Crucial issues related to the application of EE in research settings include its poorly defined effect on the animals, the potential for increased variability in the data, poor definition across labs and in publications, and potential for animal or scientific harm. The complexities, uncertainties, interpretational conundrums, varying conclusions, and lack of consensus in the EE literature warrant careful assessment of the benefits and liabilities associated with implementing such interventions. Reliance on evidence, professional judgment, and performance standards are crucial in the development of EE strategies.     

丰富环境对脑缺血再灌注小鼠神经细胞凋亡和XIAP基因表达的影响

该研究主要探讨丰富环境干预对脑缺血再灌注小鼠神经细胞凋亡的影响。实验采用健康雄性ICR 小鼠,随机分为丰富环境缺血组(IE)、标准环境缺血组(IS),同时分别设丰富环境假手术组(SE)、标准环境假手术组(SS)。通过双侧颈动脉重复结扎建立小鼠全脑缺血再灌注模型,分别在缺血后在丰富环境和标准环境饲养3 d或7 d 后,进行开场行为和水迷宫空间记忆行为检测;同时进行神经细胞损伤的组织学观测,并采用琼脂糖凝胶电泳技术分析DNA 片段化,用RT-PCR 检测X 染色体连锁的凋亡抑制蛋白（X-linked inhibitor of apoptosis protein,XIAP） mRNA的表达。结果表明,丰富环境干预能有效改善脑缺血导致的自发活动、探究行为减少和空间学习记忆能力减退,并对正常小鼠也有促进作用。缺血再灌注4 d的海马神经细胞损伤较严重,神经元密度显著减少,脑组织DNA 片段化明显增强,丰富环境作用使神经细胞损伤和DNA 片段化程度均有所减轻。同时丰富环境作用可抑制反复脑缺血再灌注导致的XIAP mRNA 表达下调。可见,丰富环境干预可改善脑缺血小鼠的自发活动、探究行为和空间学习记忆能力,该作用可能与其抑制神经细胞XIAP基因表达下调、减弱脑缺血再灌注诱导的神经细胞凋亡有关。     

Influence of different types of environmental enrichment on the behaviour of finishing pigs in two different housing systems: 3. Hanging toy versus rootable toy of the same material

This study aimed to assess the effects of (1) environmental enrichment with either straw bedding or a plastic toy and (2) the way in which the plastic toy was presented on the behaviour of finishing pigs in two different housing systems. One thousand and twenty four (Large White × Landrace) × Large White pigs were housed contemporarily in either a straw-based (ST) or fully slatted (FS) building from 35 kg to slaughter at 104 kg. In each building, half of the pens received additional environmental enrichment in the form of a hanging plastic toy. The remaining pens in the ST house were enriched only by the straw bedding. In the FS house, the remaining pens were provided with a rootable toy of the same plastic material presented on the floor of the pen. There was no significant effect of housing system on the level of manipulation of the hanging toy. Within the FS system, the level of manipulation of the hanging toy tended to be higher than that of the plastic toy presented on the floor (P = 0.052). Neither form of additional environmental enrichment provided a comparable level of occupation to that of straw bedding. In the absence of straw, more investigatory behaviours were directed towards both pen-mates (P < 0.001) and pen components (P < 0.001). Further study is required to identify functional forms of environmental enrichment in slatted systems to occupy pigs and prevent them from performing adverse behaviours.     

Modifications to husbandry and housing conditions of laboratory rodents for improved well-being

For a change to be considered enriching, the change must enhance animal welfare and improve biological functioning of the animals. A review of the literature shows that a consensus on the definition of changes constituting "environmental enrichment" has yet to be reached. For this reason, the results of studies on the effects of rodent enrichment are inconsistent. In many cases, changes have not been shown to be real improvements. However, enrichment is increasingly appreciated as a way to improve the well-being of rodents, providing them with opportunities for species-specific behaviors that might be available to them in the wild. Frequently defined as "change to the environment," enrichment can be as complex as devices (frequently termed "toys") or as simple as the provision of tissues from which mice readily construct nests. Nest making is a learned behavior in rats, and laboratory rats do show preferences for chewable objects in their environment. Rather than attempting a comprehensive review of the entire literature on environmental enrichment and its effects on rodent physiology and behavior, this paper focuses on husbandry and housing alterations that may improve the welfare of laboratory rodents. The effects of beneficial changes in housing and husbandry on rodent well-being and on experimental variability--and thus cost--are discussed. Areas that require more research are suggested. Also suggested are possible inexpensive and effective enrichment schemes for laboratory mice that might include reducing the cage floor space per mouse combined with providing nesting material.     

White to brown fat phenotypic switch induced by genetic and environmental activation of a hypothalamic-adipocyte axis

Living in an enriched environment with complex physical and social stimulation leads to improved cognitive and metabolic health. In white fat, enrichment induced the upregulation of the brown fat cell fate determining gene Prdm16, brown fat-specific markers, and genes involved in thermogenesis and β-adrenergic signaling. Moreover, pockets of cells with prototypical brown fat morphology and high UCP1 levels were observed in the white fat of enriched mice associated with resistance to diet-induced obesity. Hypothalamic overexpression of BDNF reproduced the enrichment-associated activation of the brown fat gene program and lean phenotype. Inhibition of BDNF signaling by genetic knockout or dominant-negative trkB reversed this phenotype. Our genetic and pharmacologic data suggest a mechanism whereby induction of hypothalamic BDNF expression in response to environmental stimuli leads to selective sympathoneural modulation of white fat to induce "browning" and increased energy dissipation.     

Potential for unintended consequences of environmental enrichment for laboratory animals and research results

Many aspects of the research animal's housing environment are controlled for quality and/or standardization. Of recent interest is the potential for environmental enrichment to have unexpected consequences such as unintended harm to the animal, or the introduction of variability into a study that may confound the experimental data. The effects of enrichment provided to nonhuman primates, rodents, and rabbits are described to illustrate that the effects can be numerous and may vary by strain and/or species. Examples of parameters measured where no change is detected are also included because this information provides an important counterpoint to studies that demonstrate an effect. In addition, this review of effects and noneffects serves as a reminder that the provision of enrichment should be evaluated in the context of the health of the animal and research goals on a case-by-case basis. It should also be kept in mind that the effects produced by enrichment are similar to those of other components of the animal's environment. Although it is unlikely that every possible environmental variable can be controlled both within and among research institutions, more detailed disclosure of the living environment of the subject animals in publications will allow for a better comparison of the findings and contribute to the broader knowledge base of the effects of enrichment.     

Novel function of Tau in regulating the effects of external stimuli on adult hippocampal neurogenesis

Tau is a microtubule‐associated neuronal protein found mainly in axons. However, its presence in dendrites and dendritic spines is particularly relevant due to its involvement in synaptic plasticity and neurodegeneration. Here, we show that Tau plays a novel in vivo role in the morphological and synaptic maturation of newborn hippocampal granule neurons under basal conditions. Furthermore, we reveal that Tau is involved in the selective cell death of immature granule neurons caused by acute stress. Also, Tau deficiency protects newborn neurons from the stress‐induced dendritic atrophy and loss of postsynaptic densities (PSDs). Strikingly, we also demonstrate that Tau regulates the increase in newborn neuron survival triggered by environmental enrichment (EE). Moreover, newborn granule neurons from Tau^?/? mice did not show any stimulatory effect of EE on dendritic development or on PSD generation. Thus, our data demonstrate that Tau^?/? mice show impairments in the maturation of newborn granule neurons under basal conditions and that they are insensitive to the modulation of adult hippocampal neurogenesis exerted by both stimulatory and detrimental stimuli.     

Enriched Environment Protects the Optic Nerve from Early Diabetes-Induced Damage in Adult Rats

Diabetic retinopathy is a leading cause of reduced visual acuity and acquired blindness. Axoglial alterations of the distal (close to the chiasm) optic nerve (ON) could be the first structural change of the visual pathway in streptozotocin (STZ)-induced diabetes in rats. We analyzed the effect of environmental enrichment on axoglial alterations of the ON provoked by experimental diabetes. For this purpose, three days after vehicle or STZ injection, animals were housed in enriched environment (EE) or remained in a standard environment (SE) for 6 weeks. Anterograde transport, retinal morphology, optic nerve axons (toluidine blue staining and phosphorylated neurofilament heavy immunoreactivity), microglia/macrophages (ionized calcium binding adaptor molecule 1 (Iba-1) immunoreactivity), astrocyte reactivity (glial fibrillary acid protein-immunostaining), myelin (myelin basic protein immunoreactivity), ultrastructure, and brain derived neurotrophic factor (BDNF) levels were assessed in non-diabetic and diabetic animals housed in SE or EE. No differences in retinal morphology or retinal ganglion cell number were observed among groups. EE housing which did not affect the STZ-induced weight loss and hyperglycemia, prevented a decrease in the anterograde transport from the retina to the superior colliculus, ON axon number, and phosphorylated neurofilament heavy immunoreactivity. Moreover, EE housing prevented an increase in Iba-1 immunoreactivity, and astrocyte reactivity, as well as ultrastructural myelin alterations in the ON distal portion at early stages of diabetes. In addition, EE housing avoided a decrease in BDNF levels induced by experimental diabetes. These results suggest that EE induced neuroprotection in the diabetic visual pathway.     

Development and Validation of a Measurement System for Assessment of Energy Expenditure and Physical Activity in Prader-Willi Syndrome

CHEN, KONG Y., MING SUN, MERLIN G. BUTLER, TRAVIS THOMPSON, AND MICHAEL G. CARLSON. Development and validation of a measurement system for assessment of energy expenditure and physical activity in Prader—Willi syndrome. Obes Res. Objective: The morbid obesity associated with Prader—Willi syndrome (PWS) may result from either excessive energy intake or reduced energy expenditure (EE). In this report, we describe the development and validation of an Activity—Energy Measurement System (AEMS) to measure EE and physical activity components in an environment approximating free-living conditions. Research Methods and Procedures: The AEMS consists of a live-in, whole-room indirect calorimeter equipped with a novel force platform floor system to enable simultaneous measurements of EE, physical activity, and work efficiency during spontaneous activities and standardized exercises. Free-living physical activity and estimated free-living EE are measured using portable triaxial accelerometers individually calibrated in each subject during their stay in the AEMS. Results: Representative data from two PWS patients and two matched control (CTR) subjects displayed EE during their inactive lifestyles. Discussion: This combination of methods will allow the quantification of daily EE and its components, the amount and energy cost of physical activity, and the relationships between body composition and EE, in order to determine their roles in the development and maintenance of the morbid obesity in PWS.     

Exposure to environmental enrichment elicits differential hippocampal cell proliferation: role of individual responsiveness to anxiety

Environmental enrichment (EE) is a largely employed behavioral procedure in which animals are exposed to high stimulation compared with conventional housing conditions. Animal exposure to an EE exerts beneficial effects on the performance of different learning tasks and induces a number of behavioral, neurochemical, and neuroanatomical changes including hippocampal cell proliferation. However, the importance of voluntary interaction with the environment in these changes has not been clearly resolved yet. Moreover, the effects of a complex environment on animal emotionality still remains questionable and has not been explored in detail under conditions that allow unmasking individual responses among subjects in a group. The present study was aimed at exposing groups of rats to an EE, and analyzing individual differences in activity levels during EE sessions. We observed differences with respect to the activity level displayed by rats during the enriched sessions, which correlated with differences in the rate of hippocampal cell proliferation. It is suggested that exposure to EE may reduce anxiety-like behaviors and may elicit individual differences on emotional reactions positively linked with hippocampal neurogenesis and testosterone levels.     

Effect of environmental enrichment on morphology of deep layer III and layer V pyramidal cells of occipital cortex in oldest-old rat - A quantitative golgi cox study

Dendrites and dendritic spine density regress extensively during aging in rats housed under standard conditions (SC), which can be ameliorated by housing in the enriched environment (EE). This event is particularly pronounced on neurons where high rates of plasticity are conceivable, such as on projection neurons of archicortical regions of dentate gyrus'. However, effects of EE on neocortical projection neurons are still poorly understood. Therefore, we investigated the effect of EE housing on a deep layer III (L3) and layer V pyramidal cell (L5) morphology in the associative occipital neocortex of male Sprague-Dawley rats at 24 months of age. Rats were randomly distributed in two groups and reared under either SC (n=5) or EE conditions (n=6) for 26 days. In depth quantitative analysis of dendritic tree morphology and spine density on occipital projection neurons, from Golgi-Cox stained sections, showed similar trend in both EE occipital layers L3 and L5. Significant increase was found in total number of dendritic segments (L3 - 37.5 %, L5 - 33 %) and in dendritic diameter of intermediate segments (for more than 20 %), while increase in total spine number was around the level of significance (p>0.55; L3 - 30 %, L5 - 64 %). These findings suggest an outgrowth of new dendritic segments, When compared to archicortical region of dentate gyrus, effects of aging in the associative occipital cortex were less pronounced. Taken together, these findings suggest that structures being more affected by the aging process are more susceptible to the environmental enrichment in old age.