The impact of environmental enrichment in laboratory rats--behavioural and neurochemical aspects

Need for gender-specific pre-analytical testing: the dark side of the moon in laboratory testing

Many international organisations encourage studies in a sex-gender perspective. However, research with a gender perspective presents a high degree of complexity, and the inclusion of sex-gender variable in experiments presents many methodological questions, the majority of which are still neglected. Overcoming these issues is fundamental to avoid erroneous results. Here, pre-analytical aspects of the research, such as study design, choice of utilised specimens, sample collection and processing, animal models of diseases, and the observer's role, are discussed. Artefacts in this stage of research could affect the predictive value of all analyses. Furthermore, the standardisation of research subjects according to their lifestyles and, if female, to their life phase and menses or oestrous cycle, is urgent to harmonise research worldwide. A sex-gender-specific attention to pre-analytical aspects could produce a decrease in the time for translation from the bench to bedside. Furthermore, sex-gender-specific pre-clinical pharmacological testing will enable adequate assessment of pharmacokinetic and pharmacodynamic actions of drugs and will enable, where appropriate, an adequate gender-specific clinical development plan. Therefore, sex-gender-specific pre-clinical research will increase the gender equity of care and will produce more evidence-based medicine.

A novel unbiased counting method for the quantification of synapses in the mouse brain

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We describe a novel method for synapse quantification using electron microscopy.

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Nissl-stained vibratome sections allowed accurate brain region identification.

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Automatic microscope stage shifts using custom-made software excluded observer bias.

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The method showed altered synaptic features after environmental enrichment.

Background

The numerical density of synapses and their ultrastructural features are best assessed with electron microscopy. Counting is done within counting frames placed on a pair of sections (disector technique). But this requires that the thin sections are taken from comparable brain regions and the disectors are placed in a uniform random fashion. Small brain areas like the polymorph layer of the mouse dentate gyrus are difficult to encounter, and manually moving the microscope stage for placing the micrographs seems arbitrary.

New method

Here the polymorph layer was approximated with 20 μm thin, Nissl-stained vibratome sections. The subsequent vibratome section was processed for electron microscopy and serially thin sectioned. The microscope stage was moved using a random number generator, placing at least 20 disectors onto a pair of sections. The numerical synapse density, the numerical density of dense-core vesicles, and other ultrastructural features were compared between mice that had been kept in an enriched environment and mice kept under standard housing conditions.

Results

Environmental enrichment significantly decreased the numerical density of dense-core vesicles and synaptic cleft widths within the polymorph layer, associated with behavioral improvement in the Morris water maze, a hippocampus-dependent task of spatial learning and memory.

Comparison with existing methods

This procedure was easy to handle and enabled us to produce thin sections in small, defined brain areas. Furthermore, placing the disectors with random numbers excluded observer bias.

Conclusions

Our procedure provides an uncomplicated way of assessing numerical densities in small brain areas in an unbiased manner.

Transformation of cortical and hippocampal neural circuit by environmental enrichment

It has been half a century since brain volume enlargement was first reported in animals reared in an enriched environment (EE). As EE animals show improved memory task performance, exposure to EE has been a useful model system for studying the effects of experience on brain plasticity. We review EE-induced neural changes in the cerebral cortex and hippocampus focusing mainly on works published in the recent decade. The review is organized in three large domains of changes: anatomical, electrophysiological, and molecular changes. Finally, we discuss open issues and future outlook toward better understanding of EE-induced neural changes.

Behavioral testing-related changes in the expression of Synapsin I and glucocorticoid receptors in standard and enriched aged Wistar rats

Our aim was to assess the changes in the Synapsin I and glucocorticoid receptor (GR) expression induced by behavioral testing in the dorsal and ventral hippocampi of standard and enriched aged Wistar rats. The environmental enrichment (EE) was carried out 3h/day over a period of two months and then, the rats were tested in the elevated zero-maze (EZM) and radial-arm water maze (RAWM). Behavioral results showed that, even at an advanced age, EE was able to reduce anxiety-related behaviors and improve the performance in the RAWM. Regarding the neurobiological data, Synapsin I expression in the dorsal CA3, but not in the ventral, was enhanced both in enriched and standard rats when they performed the behavioral testing. Interestingly, the EE exposure was enough to increase Synapsin I in the ventral CA3. The analysis of GR in the dorsal hippocampus showed an increase of this receptor in the dDG both in enriched and standard rats when they performed the behavioral testing, whereas in the dCA1 and dCA3, the effect of the testing depended on the previous housing condition. In the ventral region, we found that the effects of EE were higher because on the one hand, the GR expression induced by the behavioral testing was enhanced in the dSUB, vCA1 and vCA3 when the rats were previously enriched and on the other hand, EE, regardless of the behavioral testing, increased the GR expression in the vDG and vSUB. Therefore, our results suggest that the effect of the behavioral testing on the neurobiological mechanisms studied is different depending on the previous housing condition of aged rats.

Environmental enrichment and the sensory brain: the role of enrichment in remediating brain injury

The brain's life-long capacity for experience-dependent plasticity allows adaptation to new environments or to changes in the environment, and to changes in internal brain states such as occurs in brain damage. Since the initial discovery by Hebb (1947) that environmental enrichment (EE) was able to confer improvements in cognitive behavior, EE has been investigated as a powerful form of experience-dependent plasticity. Animal studies have shown that exposure to EE results in a number of molecular and morphological alterations, which are thought to underpin changes in neuronal function and ultimately, behavior. These consequences of EE make it ideally suited for investigation into its use as a potential therapy after neurological disorders, such as traumatic brain injury (TBI). In this review, we aim to first briefly discuss the effects of EE on behavior and neuronal function, followed by a review of the underlying molecular and structural changes that account for EE-dependent plasticity in the normal (uninjured) adult brain. We then extend this review to specifically address the role of EE in the treatment of experimental TBI, where we will discuss the demonstrated sensorimotor and cognitive benefits associated with exposure to EE, and their possible mechanisms. Finally, we will explore the use of EE-based rehabilitation in the treatment of human TBI patients, highlighting the remaining questions regarding the effects of EE.

Environmental enrichment and brain repair: harnessing the therapeutic effects of cognitive stimulation and physical activity to enhance experience-dependent plasticity

Environmental enrichment (EE) increases levels of novelty and complexity, inducing enhanced sensory, cognitive and motor stimulation. In wild-type rodents, EE has been found to have a range of effects, such as enhancing experience-dependent cellular plasticity and cognitive performance, relative to standard-housed controls. Whilst environmental enrichment is of course a relative term, dependent on the nature of control environmental conditions, epidemiological studies suggest that EE has direct clinical relevance to a range of neurological and psychiatric disorders. EE has been demonstrated to induce beneficial effects in animal models of a wide variety of brain disorders. The first evidence of beneficial effects of EE in a genetically targeted animal model was generated using Huntington's disease transgenic mice. Subsequent studies found that EE was also therapeutic in mouse models of Alzheimer's disease, consistent with epidemiological studies of relevant environmental modifiers. EE has also been found to ameliorate behavioural, cellular and molecular deficits in animal models of various neurological and psychiatric disorders, including Parkinson's disease, stroke, traumatic brain injury, epilepsy, multiple sclerosis, depression, schizophrenia and autism spectrum disorders. This review will focus on the effects of EE observed in animal models of neurodegenerative brain diseases, at molecular, cellular and behavioural levels. The proposal that EE may act synergistically with other approaches, such as drug and cell therapies, to facilitate brain repair will be discussed. I will also discuss the therapeutic potential of 'enviromimetics', drugs which mimic or enhance the therapeutic effects of cognitive activity and physical exercise, for both neuroprotection and brain repair.

Environmental rearing effects on impulsivity and reward sensitivity

Previous research has indicated that rearing in an enriched environment may promote self-control in an impulsive choice task. To further assess the effects of rearing environment on impulsivity, 2 experiments examined locomotor activity, impulsive action, impulsive choice, and different aspects of reward sensitivity and discrimination. In Experiment 1, rats reared in isolated or enriched conditions were tested on an impulsive choice procedure with a smaller-sooner versus a larger-later reward, revealing that the isolated rats valued the smaller-sooner reward more than the enriched rats. A subsequent reward challenge was presented in which the delay to the 2 rewards was the same but the magnitude difference remained. The enriched rats did not choose the larger reward as often as the isolated rats, reflecting poorer reward discrimination. Impulsive action was assessed using a differential-reinforcement-of-low-rate task, which revealed deficits in the enriched rats. In Experiment 2, rats reared in isolated, standard, or enriched conditions were tested on reward contrast and reward magnitude sensitivity procedures. The rats were presented with 2 levers that delivered different magnitudes of food on variable interval 30-s schedules. Across all tests, the enriched and social rats displayed more generalized responding to the small-reward lever, but a similar response to the large-reward lever, compared with the isolated rats. This confirmed the results of Experiment 1, indicating poorer reward discrimination in the enriched condition compared with the isolated condition. The results suggest that enrichment may moderate reward generalization/discrimination processes through alterations in incentive motivational processes.

Enhancing offspring hypothalamic-pituitary-adrenal (HPA) regulation via systematic novelty exposure: the influence of maternal HPA function

In the rat, repeated brief exposures to novelty early in life can induce long-lasting enhancements in adult cognitive, social, emotional, and neuroendocrine function. Family-to-family variations in these intervention effects on adult offspring are predicted by the mother’s ability to mount a rapid corticosterone (CORT) response to the onset of an acute stressor. Here, in Long-Evans rats, we investigated whether neonatal and adulthood novelty exposure, each individually and in combination, can enhance offspring hypothalamic-pituitary-adrenal (HPA) regulation. Using a 2 × 2 within-litter design, one half of each litter were exposed to a relatively novel non-home environment for 3-min (Neo_Novel) daily during infancy (PND 1–21) and the other half of the litter remained in the home cage (Neo_Home); we further exposed half of these two groups to early adulthood (PND 54–63) novelty exposure in an open field and the remaining siblings stayed in their home cages. Two aspects of HPA regulation were assessed: the ability to maintain a low level of resting CORT (CORTB) and the ability to mount a large rapid CORT response (CORTE) to the onset of an acute stressor. Assessment of adult offspring’s ability to regulate HPA regulation began at 370 days of age. We further investigated whether the novelty exposure effects on offspring HPA regulation are sensitive to the context of maternal HPA regulation by assessing maternal HPA regulation similarly beginning 7 days after her pups were weaned. We found that at the population level, rats receiving neonatal, but not early adulthood exposure or both, showed a greater rapid CORTE than their home-staying siblings. At the individual family level, these novelty effects are positively associated with maternal CORTE. These results suggest that early experience of novelty can enhance the offspring’s ability to mount a rapid response to environmental challenge and the success of such early life intervention is critically dependent upon the context of maternal HPA regulation.

Pre-reproductive maternal enrichment influences offspring developmental trajectories: motor behavior and neurotrophin expression

Environmental enrichment is usually applied immediately after weaning or in adulthood, with strong effects on CNS anatomy and behavior. To examine the hypothesis that a pre-reproductive environmental enrichment of females could affect the motor development of their offspring, female rats were reared in an enriched environment from weaning to sexual maturity, while other female rats used as controls were reared under standard conditions. Following mating with standard-reared males, all females were housed individually. To evaluate the eventual transgenerational influence of positive pre-reproductive maternal experiences, postural and motor development of male pups was analyzed from birth to weaning. Moreover, expression of Brain Derived Neurotrophic Factor and Nerve Growth Factor in different brain regions was evaluated at birth and weaning. Pre-reproductive environmental enrichment of females affected the offspring motor development, as indicated by the earlier acquisition of complex motor abilities displayed by the pups of enriched females. The earlier acquisition of motor abilities was associated with enhanced neurotrophin levels in striatum and cerebellum. In conclusion, maternal positive experiences were transgenerationally transmitted, and influenced offspring phenotype at both behavioral and biochemical levels.

Individual differences in impulsive and risky choice: effects of environmental rearing conditions

The present experiment investigated early-rearing environment modulation of individual differences in impulsive and risky choice. Rats were reared in an isolated condition (IC; n=12), in which they lived alone without novel stimuli, or an enriched condition (EC; n=11), in which they lived among conspecifics with novel stimuli. The impulsive choice task involved choices between smaller-sooner (SS) versus larger-later (LL) rewards. The risky choice task involved choices between certain-smaller (C-S) versus uncertain-larger (U-L) rewards. Following choice testing, incentive motivation to work for food was measured using a progressive ratio task and correlated with choice behavior. HPLC analyses were conducted to determine how monoamine concentrations within the prefrontal cortex (PFC) and nucleus accumbens (NAC) related to behavior in different tasks. IC rats were more impulsive than EC rats, but they did not differ in risky choice behavior. However, choice behavior across tasks was significantly correlated (i.e., the more impulsive rats were also riskier). There were no group differences in monoamine levels, but noradrenergic and serotonergic concentrations were significantly correlated with impulsive and risky choice. Furthermore, serotonin and norepinephrine concentrations in the NAC significantly correlated with incentive motivation and the timing of the reward delays within the choice tasks. These results suggest a role for domain general processes in impulsive and risky choice and indicate the importance of the NAC and/or PFC in timing, reward processing, and choice behavior.

Astrocytic plasticity as a possible mediator of the cognitive improvements after environmental enrichment in aged rats

Currently, little is known about the effect of environmental enrichment (EE) on astrocytic plasticity, especially during aging. Given the newly discovered role of the astrocytes in regulating the synaptic transmission and thereby, the cognitive functions, we aimed to study the impact of EE on the performance in a spatial memory task and on the number and morphology of GFAP immunopositive cells in the dorsal hippocampus. After two months of EE (3 h/per day), the animals were tested in the Radial-Arm Water Maze (RAWM) for four days, with six daily trials. Next, we analyzed the changes in the GFAP immunopositive cells in CA1, CA3 and Dentate Gyrus (DG). Behavioral results showed that, even in advanced ages, EE improved the performance in a spatial memory task. Also, we found that aged rats submitted to EE had more GFAP immunopositive cells in the DG and more complex astrocytes, revealed by Sholl analysis, in all hippocampal subfields with respect to the other experimental conditions. Interestingly, the learning of a spatial memory task produced more morphological complexity and higher levels of GFAP immunopositive cells with regard to a standard control group, but not at the same level of the enriched groups. Thus, it is possible that the plastic changes found in the hippocampal astrocytes after EE are involved in a brain reserve to cope with age-related cognitive impairments.

Free access to running wheels abolishes hyperphagia in human growth hormone transgenic rats

Obesity is a major health problem, and increased food intake and decreased physical activity are considered as two major factors causing obesity. Previous studies show that voluntary exercise in a running wheel decreases not only body weight but also food intake of rats. We previously produced human growth hormone transgenic (TG) rats, which are characterized by severe hyperphagia and obesity. To gain more insight into the effects on physical activity to food consumption and obesity, we examined whether voluntary running wheel exercise causes inhibition of hyperphagia and alteration of body composition in TG rats. Free access to running wheels completely abolished hyperphagia in TG rats, and this effect persisted for many weeks as far as the running wheel is accessible. Unexpectedly, though the running distances of TG rats were significantly less than those of wild type rats, it was sufficient to normalize their food consumption. This raises the possibility that rearing environment, which enables them to access to a running wheel freely, rather than the amounts of physical exercises is more important for the maintenance of proper food intake.

The effects of prenatal cocaine, post-weaning housing and sex on conditioned place preference in adolescent rats

RATIONALE

Gestational exposure to cocaine now affects several million people including adolescents and young adults. Whether prenatal drug exposures alter an individual's tendency to take and/or abuse drugs is still a matter of debate.

OBJECTIVES

This study sought to answer the question "Does prenatal exposure to cocaine, in a dose-response fashion, alter the rewarding effects of cocaine using a conditioned place preference (CPP) procedure during adolescence in the rat?" Further, we wanted to assess the possible sex differences and the role of being raised in an enriched versus impoverished environment.

METHODS

Virgin female Sprague-Dawley rats were dosed daily with cocaine at 30 mg/kg (C30), 60 mg/kg (C60), or vehicle intragastrically prior to mating and throughout gestation. Pups were culled, fostered and, on postnatal day (PND) 23, placed into isolation cages or enriched cages with three same-sex littermates and stimulus objects. On PND43-47, CPP was determined across a range of cocaine doses.

RESULTS

C30 exposure increased sensitivity to the rewarding effects of cocaine in adolescent males, and being raised in an enriched environment further enhanced this effect. Rats exposed to C60 resembled the controls in cocaine CPP. Overall, females were modestly affected by prenatal cocaine and enrichment.

CONCLUSIONS

These data support the unique sensitivity of males to the effects of gestational cocaine, that moderate prenatal cocaine doses produce greater effects on developing reward circuits than high doses and that housing condition interacts with prenatal treatment and sex such that enrichment increases cocaine CPP mostly in adolescent males prenatally exposed to moderate cocaine doses.

Comprehensive behavioural analysis of Long Evans and Sprague-Dawley rats reveals differential effects of housing conditions on tests relevant to neuropsychiatric disorders

Genetic (G) and environmental (E) manipulations are known to alter behavioural outcomes in rodents, however many animal models of neuropsychiatric disorders only use a restricted selection of strain and housing conditions. The aim of this study was to examine GxE interactions comparing two outbred rat strains, which were housed in either standard or enriched cages. The strains selected were the albino Sprague-Dawley rat, commonly used for animal models, and the other was the pigmented Long Evans rat, which is frequently used in cognitive studies. Rats were assessed using a comprehensive behavioural test battery and included well-established tests frequently employed to examine animal models of neuropsychiatric diseases, measuring aspects of anxiety, exploration, sensorimotor gating and cognition. Selective strain and housing effects were observed on a number of tests. These included increased locomotion and reduced pre-pulse inhibition in Long Evans rats compared to Sprague Dawley rats; and rats housed in enriched cages had reduced anxiety-like behaviour compared to standard housed rats. Long Evans rats required fewer sessions than Sprague Dawley rats to learn operant tasks, including a signal detection task and reversal learning. Furthermore, Long Evans rats housed in enriched cages acquired simple operant tasks faster than standard housed Long Evans rats. Cognitive phenotypes in animal models of neuropsychiatric disorders would benefit from using strain and housing conditions where there is greater potential for both enhancement and deficits in performance.

Individual differences in the forced swimming test and the effect of environmental enrichment: searching for an interaction

Animals with low and high immobility in the forced swimming test (FST) differ in a number of neurobehavioral factors. A growing body of evidence suggests that the exposure to enriched environments mediates a number of changes in the brain. Therefore, we studied if animals' individuality can somehow modulate the response to environmental stimuli. Male rats were classified according to their immobility time scores in the FST test session as animals with low, medium or high immobility. Then, rats from groups with low and high immobility were randomly distributed in two groups to be reared in different housing conditions (i.e., enriched and standard conditions) during 8weeks. Animals were subjected to the open field test (OFT) before and 6weeks after the start of housing protocol. Rats with high immobility in the FST also showed high ambulation and high rearing time in the first OFT. Such findings were not observed in the second OFT. Conversely, an effect of environmental enrichment was found in the second OFT where enriched animals showed lower ambulation and higher grooming time than the standard control group. Rats were sacrificed after the housing protocol and neurochemical content and/or gene expression were studied in three different brain regions: the prefrontal cortex, the hippocampus and the nucleus accumbens. Rats with low immobility showed significantly higher accumbal 5-HT levels than animals with high immobility, whereas no neurochemical differences were observed between enriched and standard animals. Regarding expression data, however, an effect of enrichment on accumbal corticotropin-releasing factor (CRF) and its receptor 1 (CRFR1) levels was observed, and such effect depended on immobility levels. Thus, our results not only allowed us to identify a number of differences between animals with low and high immobility or animals housed in standard and enriched conditions, but also suggested that animals' individuality modulated in some way the response to environmental stimuli.

Genes underlying positive influence of prenatal environmental enrichment and negative influence of prenatal earthquake simulation and corrective influence of Chinese herbal medicine on rat offspring: Irf7 and Ninj2

BACKGROUND

Prenatal environmental enrichment (EE) has been proven to positively affect but prenatal stress negatively influence the physiological and psychological processes in animals, whose trans-generational genetic mechanism remains unclearly defined. We aimed to investigate and find out key genes underlying the positive-negative effects derived from prenatal interventions.

MATERIALS AND METHODS

Pregnant rats were randomized into EE group (EEG), earthquake simulation group (ESG), herbal group (HG) received herbal supplements in feed after earthquake simulation, and control group (CG).

RESULTS

Light Box Defecation Test (LBDT) showed EEG offspring presented less fecal pellets than CG offspring, ESG's more than CG's, and HG's less than ESG (p's<0.05). Open-field Test (OFT) score of EEG was higher than CG offspring, of ESG's was lower than CG's, and HG's higher than ESG's. Irf7 and Ninj were screened, which were up-regulated in EEG, down-regulated in ESG (FC<0.5), and were neutralized in HG. Prenatal EE could positively promote the nervous system development, prenatal earthquake simulation could retard the nervous system development and Chinese herbal remedy (JKSQW) which could correct the retardation.

CONCLUSION

The negative-positive prenatal effect could contribute to altered gene expression of Irf7 and Ninj2 which also could play a key role in the improving function of JKSQW for the kidneys.

Behavioral effects of different enriched environments in mice treated with the cholinergic agonist PNU-282987

Environmental enrichment is an experimental model in which rodents are housed in complex environments that favor lower levels of anxiety-like behavior. PNU-282987 (PNU) is a α7 nicotinic acetylcholine receptor agonist with beneficial effects on learning though its effects on anxiety are unclear. Our main aim was to carry out a study of its effects in NMRI (n=96) mice reared in different environments: environmental enrichment (EE), Marlau™ cages (MC) and standard environment (SE). After a 4-month period, mice received acute treatment of PNU (2.5, 5 and 10mg/kg) and were evaluated in the elevated plus-maze (EPM) and hole-board (HB). In the EPM, both EE and MC reared mice showed an increase in percentage of entries into open arms while those from EE group differed from SE in time spent on open arms. Mice treated with 2.5 and 10 mg/kg of PNU devoted less time to rearing into open arms. In the HB task, MC mice displayed higher exploratory activity reflected in more head-dips (HD) during the first minute than EE and SE, whereas EE displayed low exploration levels reflected in total HD (5 min). Further research is needed in order to clarify the behavioral effects of this nicotinic agonist in interaction with different environmental conditions. This article is part of a Special Issue entitled: insert SI title.

Increased physical activity is not enough to recover astrocytic population from dark-rearing. Synergy with multisensory enrichment is required

Elimination of sensory inputs (deprivation) modifies the properties of the sensory cortex and serves as a model for studying plasticity during postnatal development. Many studies on the effects of deprivation have been performed in the visual cortex using dark-rearing as a visual deprivation model. It induces changes in all cellular and molecular components, including astrocytes, which play an important role in the development, maintenance, and plasticity of the cortex, mediated by cytokines which have been termed angioglioneurins. When one sense is deprived, a compensatory mechanism called cross-modal plasticity increases performance in the remaining senses. Environmental enrichment is so far the best-known method to compensate sensorial deprivation. The aim of this work is to study the effects of exercise alone, and of an enriched environment combined with exercise, on astroglial population in order to observe the effects of exercise by itself, or the potential synergistic effect during the rat visual system development. Pregnant Sprague-Dawley rats were raised in one of the following rearing conditions: in total darkness and enriched environment conditions with physical exercise, and in total darkness with voluntary physical exercise. Astrocytic density was estimated by immunohistochemistry for S-100β protein and quantifications were performed in layer IV. The somatosensorial cortex barrel field was also studied as control. Our main result shows that an enriched environment combined with voluntary physical exercise manages to reverse the negative effects induced by darkness over the astroglial population of both the visual and the somatosensory cortices. On the other hand, exercise alone only produces effects upon the astroglial population of the somatosensory cortex, and less so when combined with an enriched environment.

Acetyltransferases (HATs) as targets for neurological therapeutics

The acetylation of histone and non-histone proteins controls a great deal of cellular functions, thereby affecting the entire organism, including the brain. Acetylation modifications are mediated through histone acetyltransferases (HAT) and deacetylases (HDAC), and the balance of these enzymes regulates neuronal homeostasis, maintaining the pre-existing acetyl marks responsible for the global chromatin structure, as well as regulating specific dynamic acetyl marks that respond to changes and facilitate neurons to encode and strengthen long-term events in the brain circuitry (e.g., memory formation). Unfortunately, the dysfunction of these finely-tuned regulations might lead to pathological conditions, and the deregulation of the HAT/HDAC balance has been implicated in neurological disorders. During the last decade, research has focused on HDAC inhibitors that induce a histone hyperacetylated state to compensate acetylation deficits. The use of these inhibitors as a therapeutic option was efficient in several animal models of neurological disorders. The elaboration of new cell-permeant HAT activators opens a new era of research on acetylation regulation. Although pathological animal models have not been tested yet, HAT activator molecules have already proven to be beneficial in ameliorating brain functions associated with learning and memory, and adult neurogenesis in wild-type animals. Thus, HAT activator molecules contribute to an exciting area of research.

Interaction of genotype and environment: effect of strain and housing conditions on cognitive behavior in rodent models of schizophrenia

Schizophrenia is associated with many genetic and environmental risk factors and there is growing evidence that the interactions between genetic and environmental "hits" are critical for disease onset. Animal models of schizophrenia have traditionally used specific strain and housing conditions to test potential risk factors. As the field moves towards testing gene (G) x environment (E) interactions the impact of these choices should be considered. Given the surge of research focused on cognitive deficits, we have examined studies of cognition in rodents from the perspective of GxE interactions, in which strain or housing manipulations have been varied. Behavior is clearly altered by these factors, yet few animal models of schizophrenia have investigated cognitive deficits using different strain and housing conditions. It is important to recognise the large variation in behavior observed when using different strain and housing combinations because GxE interactions may mask or exacerbate cognitive outcomes. Further consideration will improve our understanding of GxE interactions and the underlying neurobiology of cognitive impairments in neuropsychiatric disorders.

Environmental enrichment in female rodents: considerations in the effects on behavior and biochemical markers

Environmental enrichment (EE) exposes laboratory animals to novelty and complexity through alterations in the physical and social environment, which lead to enhanced sensory, cognitive and physical stimulation. Housing rodents in an EE is a highly recommended practice by governing bodies regulating animal welfare due to a growing body of evidence suggesting its benefits on rodents' wellbeing and the more naturalistic environment that such housing conditions provide. However, most paradigms and hypotheses rely on information currently available from studies performed on male subjects and the information regarding the effects of EE on female rodents' behavior and physiology is limited. Given the variety of EE paradigms described, it is increasingly difficult to ascertain the benefits or possible consequences of enriched housing strategies in females, let alone aid at establishing standardized environments in rodents. This review evaluates the female rodent literature that has examined the outcome of EE on behavior and neurochemistry and aims at identifying key elements to be addressed by future studies. Specifically, results from cognitive behavioral tests as well as commonly used tests of emotionality will be discussed, while also evaluating their relation to changes in neurochemistry and hormones brought on by various EE paradigms. Lastly, the impact of maternal enrichment on both offspring and maternal behavior and physiology will be reviewed.

Reconsidering the evolution of brain, cognition, and behavior in birds and mammals

Despite decades of research, some of the most basic issues concerning the extraordinarily complex brains and behavior of birds and mammals, such as the factors responsible for the diversity of brain size and composition, are still unclear. This is partly due to a number of conceptual and methodological issues. Determining species and group differences in brain composition requires accounting for the presence of taxon-cerebrotypes and the use of precise statistical methods. The role of allometry in determining brain variables should be revised. In particular, bird and mammalian brains appear to have evolved in response to a variety of selective pressures influencing both brain size and composition. “Brain” and “cognition” are indeed meta-variables, made up of the variables that are ecologically relevant and evolutionarily selected. External indicators of species differences in cognition and behavior are limited by the complexity of these differences. Indeed, behavioral differences between species and individuals are caused by cognitive and affective components. Although intra-species variability forms the basis of species evolution, some of the mechanisms underlying individual differences in brain and behavior appear to differ from those between species. While many issues have persisted over the years because of a lack of appropriate data or methods to test them; several fallacies, particularly those related to the human brain, reflect scientists' preconceptions. The theoretical framework on the evolution of brain, cognition, and behavior in birds and mammals should be reconsidered with these biases in mind.

Environmental enrichment improves novel object recognition and enhances agonistic behavior in male mice

Environmental enrichment (EE) is an experimental paradigm in which rodents are housed in complex environments containing objects that provide stimulation, the effects of which are expected to improve the welfare of these subjects. EE has been shown to considerably improve learning and memory in rodents. However, knowledge about the effects of EE on social interaction is generally limited and rather controversial. Thus, our aim was to evaluate both novel object recognition and agonistic behavior in NMRI mice receiving EE, hypothesizing enhanced cognition and slightly enhanced agonistic interaction upon EE rearing. During a 4-week period half the mice (n = 16) were exposed to EE and the other half (n = 16) remained in a standard environment (SE). On PND 56-57, animals performed the object recognition test, in which recognition memory was measured using a discrimination index. The social interaction test consisted of an encounter between an experimental animal and a standard opponent. Results indicated that EE mice explored the new object for longer periods than SE animals (P < .05). During social encounters, EE mice devoted more time to sociability and agonistic behavior (P < .05) than their non-EE counterparts. In conclusion, EE has been shown to improve object recognition and increase agonistic behavior in adolescent/early adulthood mice. In the future we intend to extend this study on a longitudinal basis in order to assess in more depth the effect of EE and the consistency of the above-mentioned observations in NMRI mice.

Environmental enrichment influences brain cytokine variations elicited by social defeat in mice

Environmental enrichment may protect against some of the adverse behavioural and biological effects of stressors. However, unlike the effects seen in some species, among male mice housed in groups, enrichment may alter social stability, encourage competition and aggression, and thus promote the establishment of a stressful environment. A potent psychosocial stressor such as social defeat in mice promotes brain neurochemical changes as well as pro-inflammatory cytokine variations in the prefrontal cortex (PFC) and hippocampus. The present investigation demonstrated that enrichment in group-housed male mice, even in the relatively nonaggressive, although highly anxious BALB/cByJ strain encouraged the effects of a repeated social defeat stressor experienced 4 weeks later, especially with respect to corticosterone as well as hippocampal corticotropin-releasing hormone (CRH) and interleukin (IL)-6 variations. Moreover, within the hippocampus, enrichment itself was accompanied by modest reductions in the expression of the IL-1β receptor (IL-1r1). Thus, it seems that living in an enriched environment among group-housed male mice might promote a stressful environment that enhances basal hippocampal CRH and cytokine variations and increased vulnerability to further changes upon subsequent exposure to a social stressor.

Age-dependent effects of environmental enrichment on brain networks and spatial memory in Wistar rats

We assessed the effect of 3h of environmental enrichment (EE) exposure per day started at different ages (3 and 18months old) on the performance in a spatial memory task and on brain regions involved in the spatial learning (SPL) process using the principal component analysis (PCA). The animals were tested in the four-arm radial water maze (4-RAWM) for 4days, with six daily trials. We used cytochrome c oxidase (COx) histochemistry to determine the brain oxidative metabolic changes related to age, SPL and EE. Behavioural results showed that the enriched groups, regardless of their age, achieved better performance in the spatial task. Interestingly, in the case of the distance travelled in the 4-RAWM, the effect of the EE was dependent on the age, so the young enriched group travelled a shorter distance compared to the aged enriched group. Respect to COx histochemistry results, we found that different brain mechanisms are triggered in aged rats to solve the spatial task, compared to young rats. PCA revealed the same brain functional network in both age groups, but the contribution of the brain regions involved in this network was slightly different depending on the age of the rats. Thus, in the aged group, brain regions involved in anxiety-like behaviour, such as the amygdala or the bed nucleus of the stria terminalis had more relevance; whereas in the young enriched group the frontal and the hippocampal subregions had more contribution.

Alleviation of chronic neuropathic pain by environmental enrichment in mice well after the establishment of chronic pain

Background

In animal models, the impact of social and environmental manipulations on chronic pain have been investigated in short term studies where enrichment was implemented prior to or concurrently with the injury. The focus of this study was to evaluate the impact of environmental enrichment or impoverishment in mice three months after induction of chronic neuropathic pain.

Methods

Thirty-four CD-1 seven to eight week-old male mice were used. Mice underwent surgery on the left leg under isoflurane anesthesia to induce the spared nerve injury model of neuropathic pain or sham condition. Mice were then randomly assigned to one of four groups: nerve injury with enriched environment (n = 9), nerve injury with impoverished environment (n = 8), sham surgery with enriched environment (n = 9), or sham surgery with impoverished environment (n = 8). The effects of environmental manipulations on mechanical (von Frey filaments) heat (hot plate) and cold (acetone test) cutaneous hypersensitivities, motor impairment (Rotarod), spontaneous exploratory behavior (open field test), anxiety-like behavior (elevated plus maze) and depression-like phenotype (tail suspension test) were assessed in neuropathic and control mice 1 and 2 months post-environmental change. Finally, the effect of the environment on spinal expression of the pro-nociceptive neuropeptides substance P and CGRP form the lumbar spinal cord collected at the end of the study was evaluated by tandem liquid chromatography mass spectrometry.

Results

Environmental enrichment attenuated nerve injury-induced hypersensitivity to mechanical and cold stimuli. In contrast, an impoverished environment exacerbated mechanical hypersensitivity. No antidepressant effects of enrichment were observed in animals with chronic neuropathic pain. Finally, environmental enrichment resulted lower SP and CGRP concentrations in neuropathic animals compared to impoverishment. These effects were all observed in animals that had been neuropathic for several months prior to intervention.

Conclusions

These results suggest that environmental factors could play an important role in the rehabilitation of chronic pain patients well after the establishment of chronic pain. Enrichment is a potentially inexpensive, safe and easily implemented non-pharmacological intervention for the treatment of chronic pain.

Effects of environmental enrichment on nicotine-induced sensitization and cross-sensitization to d-amphetamine in rats

INTRODUCTION

Research indicates that adolescent nicotine exposure may predispose individuals to use other psychostimulants later in adulthood, offering support for the incentive-sensitization theory of addiction. Preclinical studies testing the incentive-sensitization theory show that repeated nicotine exposure in adolescent rats can lead to an increased sensitivity to the motor stimulant effects of nicotine and other psychostimulants in adulthood. Although previous nicotine exposure can increase sensitivity to stimulant drugs, rats raised in enriched conditions (EC) show, decreased sensitivity to psychostimulant drugs compared to rats raised in isolation conditions (IC).

METHODS

We examined whether nicotine sensitization or cross-sensitization to d-amphetamine induced by adolescent nicotine exposure is altered by exposure to environmental enrichment. Adolescent EC and IC male rats received subcutaneous (s.c.) injections of saline or 0.4mg/kg of nicotine once daily for seven days. Thirty-five days following the last nicotine injection EC and IC animals were challenged with saline, nicotine (0.2 or 0.4mg/kg) or d-amphetamine (0.5 or 1.0mg/kg).

RESULTS

EC rats failed to show nicotine sensitization at either nicotine dose tested while IC rats showed nicotine sensitization following the 0.4mg/kg nicotine dose. EC rats also failed to show nicotine-induced cross-sensitization to the 0.5mg/kg dose of d-amphetamine while IC rats displayed cross-sensitization. However, EC rats did exhibit nicotine-induced cross-sensitization to the 1.0mg/kg dose of d-amphetamine.

CONCLUSION

These findings indicate that environmental enrichment can alter the ability of adolescent nicotine exposure to induce sensitization and cross-sensitization in adulthood and may be used as a protectant factor against adolescent nicotine exposure.

Traumatic brain injury and post-acute decline: what role does environmental enrichment play? A scoping review

Objectives: While a growing number of studies provide evidence of neural and cognitive decline in traumatic brain injury (TBI) survivors during the post-acute stages of injury, there is limited research as of yet on environmental factors that may influence this decline. The purposes of this paper, therefore, are to (1) examine evidence that environmental enrichment (EE) can influence long-term outcome following TBI, and (2) examine the nature of post-acute environments, whether they vary in degree of EE, and what impact these variations have on outcomes.

Methods: We conducted a scoping review to identify studies on EE in animals and humans, and post-discharge experiences that relate to barriers to recovery.

Results: One hundred and twenty-three articles that met inclusion criteria demonstrated the benefits of EE on brain and behavior in healthy and brain-injured animals and humans. Nineteen papers on post-discharge experiences revealed that variables such as insurance coverage, financial, and social support, home therapy, and transition from hospital to home, can have an impact on clinical outcomes.

Conclusion: There is evidence to suggest that lack of EE, whether from lack of resources or limited ability to engage in such environments, may play a role in post-acute cognitive and neural decline. Maximizing EE in the post-acute stages of TBI may improve long-term outcomes for the individual, their family and society.

The differential impact of social defeat on mice living in isolation or groups in an enriched environment: plasma corticosterone and monoamine variations

Social defeat in mice is a potent stressor that promotes the development of depressive- and anxiety-like behaviours, as well as variations of neuroendocrine and brain neurotransmitter activity. Although environmental enrichment may protect against some of the adverse behavioural and biological effects of social defeat, it seems that, among male group-housed mice maintained in an enriched environment (EE), aggressive behaviours may be more readily instigated, thus promoting distress and exacerbating psychopathological features. Thus, although an EE can potentially have numerous beneficial effects, these may depend on the general conditions in which mice were raised. It was observed in the current investigations that EE group-housed BALB/cByJ mice displayed increased anxiety-like behaviours compared to their counterparts maintained in a standard environment (SE). Furthermore, in response to social defeat, EE group-housed male mice exhibited decreased weight gain, exaggerated corticosterone elevations and altered hippocampal norepinephrine utilization compared to their SE counterparts. These effects were not apparent in the individually housed EE mice and, in fact, enrichment among these mice appeared to buffer against serotonin changes induced by social defeat. It is possible that some potentially beneficial effects of enrichment were precluded among group-housed mice, possibly owing to social disturbances that might occur in these conditions. In fact, even if social interaction is an essential feature of enrichment, it seems that some of the positive effects of this housing condition might be optimal when mice are housed individually, particularly with regard to buffering the effects of social defeat.

Relationships between dietary macronutrients and adult neurogenesis in the regulation of energy metabolism

Of the environmental factors which have an impact on body weight, nutrients are most influential. Within normal limits, hypothalamic and related neuronal populations correct perturbations in energy metabolism, to return the body to its nutritional set-point, either through direct response to nutrients or indirectly via peripheral appetite signals. Excessive intake of certain macronutrients, such as simple carbohydrates and SFA, can lead to obesity and attendant metabolic dysfunction, also reflected in alterations in structural plasticity, and, intriguingly,neurogenesis, in some of these brain regions. Neurogenesis, previously thought to occur only in the embryo, is now known to take place in the adult brain, dependent on numerous stimulating and inhibiting factors, including dietary components. Because of classic associations between neurogenesis and the hippocampus, in learning and cognition, this brain region has also been the focus of attention in the study of links between diet and neurogenesis. Recently, however, a more complete picture of this relationship has been building: not only has the hypothalamus been shown to satisfy the criteria for a neurogenic niche, but appetite-related mediators, including circulating hormones, such as leptin and ghrelin, pro-inflammatory cytokines and the endocannabinoid intracellular messengers, are also being examined for their potential role in mediating neurogenic responses to macronutrients. The present review draws together these observations and investigates whether n-3 PUFA may exert their attenuating effects on body weight through the stimulation of adult neurogenesis. Exploration of the effects of nutraceuticals on neurogenic brain regions may encourage the development of new rational therapies in the fight against obesity.

Transgenerational epigenetic effects on brain functions

Psychiatric diseases are multifaceted disorders with complex etiology, recognized to have strong heritable components. Despite intense research efforts, genetic loci that substantially account for disease heritability have not yet been identified. Over the last several years, epigenetic processes have emerged as important factors for many brain diseases, and the discovery of epigenetic processes in germ cells has raised the possibility that they may contribute to disease heritability and disease risk. This review examines epigenetic mechanisms in complex diseases and summarizes the most illustrative examples of transgenerational epigenetic inheritance in mammals and their relevance for brain function. Environmental factors that can affect molecular processes and behavior in exposed individuals and their offspring, and their potential epigenetic underpinnings, are described. Possible routes and mechanisms of transgenerational transmission are proposed, and the major questions and challenges raised by this emerging field of research are considered.

Environmental enrichment during development decreases intravenous self-administration of methylphenidate at low unit doses in rats

Despite the efficacy and widespread use of methylphenidate (MPH) as a treatment modality for attention deficit hyperactivity disorder, clinical and preclinical findings indicate that it has abuse potential. Environmental enrichment reduces susceptibility to cocaine and amphetamine self-administration and decreases impulsive behavior, but its effects on MPH self-administration are unknown. The present experiments sought to determine the influence of environmental enrichment on MPH self-administration. Male rats were raised in an enriched condition (EC) or isolated condition (IC). They were trained to self-administer MPH (0.3 mg/kg/infusion) and then exposed to varying doses of MPH on either a fixed-ratio (experiment 1) or a progressive-ratio (experiment 2) schedule of reinforcement. EC rats earned significantly fewer infusions of MPH at low doses (0.03 and 0.056 mg/kg/infusion) compared with IC rats under both schedules; however, no differences were observed at high unit doses (0.1-1.0 mg/kg/infusion). During saline substitution at the end of MPH self-administration, EC rats also responded less for saline compared with IC rats, indicative of more rapid extinction. As with other stimulant drugs with different mechanisms of action, environmental enrichment during development protects against self-administration of MPH at low unit doses but not at high unit doses.

Brain hemispheric differences in the neurochemical effects of lead, prenatal stress, and the combination and their amelioration by behavioral experience

Brain lateralization, critical to mediation of cognitive functions and to "multitasking," is disrupted in conditions such as attention deficit disorder and schizophrenia. Both low-level lead (Pb) exposure and prenatal stress (PS) have been associated with mesocorticolimbic system-mediated executive-function cognitive and attention deficits. Mesocorticolimbic systems demonstrate significant laterality. Thus, altered brain lateralization could play a role in this behavioral toxicity. This study examined laterality of mesocorticolimbic monoamines (frontal cortex, nucleus accumbens, striatum, midbrain) and amino acids (frontal cortex) in male and female rats subjected to lifetime Pb exposure (0 or 50 ppm in drinking water), PS (restraint stress on gestational days 16-17), or the combination with and without repeated learning behavioral experience. Control males exhibited prominent laterality, particularly in midbrain and also in frontal cortex and striatum; females exhibited less laterality, and this was primarily striatal. Lateralized Pb ± PS induced neurotransmitter changes were assessed only in males because of limited sample sizes of Pb + PS females. In males, Pb ± PS changes occurred in left hemisphere of frontal cortex and right hemisphere of midbrain. Behavioral experience modified the laterality of Pb ± PS-induced neurotransmitter changes in a region-dependent manner. Notably, behavioral experience eliminated Pb ± PS neurotransmitter changes in males. These findings underscore the critical need to evaluate both sexes and brain hemispheres for the mechanistic understanding of sex-dependent differences in neuro- and behavioral toxicity. Furthermore, assessment of central nervous system mechanisms in the absence of behavioral experience, shown here for males, may constitute less relevant models of human health effects.

Differential effects of environmental enrichment, social-housing, and isolation-rearing on a rat gambling task: dissociations between impulsive action and risky decision-making

RATIONALE

Decision-making deficits, measured using the Iowa Gambling Task (IGT), are observed in many psychiatric populations. Additionally, evidence suggests that the environment also influences the development of these same disorders.

OBJECTIVE

To determine the direct influence of the environment on decision-making by utilizing the rat gambling task (rGT), a risky decision-making test modeled after the IGT.

METHODS

Male rats reared in isolation, in pairs, or in an enriched environment were trained on the rGT as adults. During the rGT, animals chose from four different options. The optimal strategy on the rGT and IGT is the same: to favor options associated with smaller immediate rewards and less punishment/loss. Impulsive action is also measured during rGT performance by recording the number of premature responses made, similar to the five-choice serial reaction time task.

RESULTS

Compared to pair-housed rats, isolated and environmentally enriched rats were slower at learning the optimal strategy. However, following training, only isolation-reared rats chose the disadvantageous options more often. Amphetamine altered decision-making on the rGT in socially housed animals, yet isolates were unaffected. Conversely, amphetamine increased premature responding similarly in all groups. This increase was attenuated by prior administration of a dopamine D(1) or D(2) antagonist; however, the ability of amphetamine to alter decision-making was not blocked by either drug.

CONCLUSIONS

Housing environment affects animals' ability to learn and perform a decision-making task. Additionally, amphetamine's effect on impulsive action appears to be mediated by the dopaminergic system, whereas its effect on risky decision-making may be mediated by other neurotransmitters.

Effects of environmental enrichment exposure on synaptic transmission and plasticity in the hippocampus

Exposure to an enriched environment (EE) is beneficial to the structure and function of the brain. The added sensory, social, and spatial complexity of the EE also improves cognitive functions such as memory in both healthy brains and damaged or diseased brains, yet the underlying neural mechanisms of these cognitive improvements are poorly understood. In particular, studies that have examined the effects of EE on cellular function in the hippocampus, a structure critical for memory storage, have produced somewhat confusing results. Experiments performed in ex vivo hippocampal slices have reported a variety of EE effects on synaptic transmission and plasticity in both CA1 and the dentate gyrus. However, together with data from in vivo recordings made during and after the EE treatment, the overall results suggest an evolution of changes in neuronal function in the hippocampus, whereby there is an early transient increase in cell activity and plasticity that gives rise to more subtle long-term enhancements in cellular and network function that may contribute to enhanced hippocampus-dependent cognition.

Mechanism of earthquake simulation as a prenatal stressor retarding rat offspring development and chinese medicine correcting the retardation: hormones and gene-expression alteration

We aimed to investigate the mechanism of shaking as a prenatal stressor impacting the development of the offspring and Chinese medicines correcting the alterations. Pregnant rats were randomized into earthquake simulation group (ESG), herbal group (HG) which received herbal supplements in feed after shaking, and control group (CG). Findings revealed body weight and open field test (OFT) score of ESG offspring were statistically inferior to the CG and HG offspring. The corticosterone levels of ESG were higher than those of CG but not than HG. The dopamine level of ESG was slightly lower than that of the CG and of HG was higher than that of ESG. The 5-HT of ESG was higher than CG and HG. The growth hormone level of the ESG was significantly lower than ESG but not than CG. Gene expression profile showed 81 genes upregulated and 39 genes downregulated in ESG versus CG, and 60 genes upregulated and 28 genes downregulated in ESG versus HG. Eighty-four genes were found differentially expressed in ESG versus CG comparison and were normalized in ESG versus HG. We conclude that maternal shaking negatively affected physical and nervous system development, with specific alterations in neurohormones and gene expression. Chinese herbal medicine reduced these negative outcomes.

How to improve housing conditions of laboratory animals: the possibilities of environmental refinement

Housing systems for captive animals have often been designed on the basis of economic and ergonomic considerations, such as equipment, costs, space, workload, ability to observe the animals and to maintain a certain degree of hygiene, with little or no consideration for animal welfare. Environmental refinement can be defined as any modification in the environment of captive animals that seeks to enhance the physical and psychological well-being of the animals by providing stimuli which meet the animals' species-specific needs. This article provides an overview of environmental factors that influence the well-being of captive animals with specific reference to the needs of the most common laboratory species. It is important to evaluate environmental refinement in terms of the benefit to the animal, by assessing the use of and preference for certain enrichment, the effect on behaviour, and the performance of species-typical behaviour on physiological parameters. It is also necessary to evaluate the impact of refinement on scientific outcome, including whether and how statistical power is affected. Communication and team work between animal welfare scientists, animal research scientists, institutional animal welfare officers, veterinarians and animal ethics committees, animal facility management and personnel, are essential for success.

Physiological and behavioural consequences of long-term moderate treadmill exercise

The benefits of long-term moderate exercise for health are widely accepted in humans, but few animal studies have been undertaken to characterize the effects of such activity on emotionality and responsiveness to stress. The present study describes the effects of long-term moderate forced treadmill training (36 weeks) on exploratory activity, anxiety-like behaviour, and the resting or stress levels of some physiological variables, including pituitary-adrenal (PA) hormones. Five-week-old male Sprague-Dawley rats were trained on the treadmill (TM) for 36 weeks, using a more moderate training (12m/min, 30min/day, 4-5 days/week) than that currently used in the literature. Two groups were used as controls: a non-handled sedentary (SED) group, receiving no manipulation, and a control (CON) group exposed to a stationary treadmill for the same amount of time as the TM group. In accordance with literature data, TM rats showed lower resting levels of glucose, triglycerides and cholesterol than the other two groups. The TM and CON groups both showed higher ambulation than the SED group in some behavioural tests, without evidence for altered anxiety. Resting levels of adrenocorticotropin (ACTH) and corticosterone did not differ among the groups, but a reduced ACTH response to both a novel environment (mild stressor) and an active escape-avoidance task (severe stressor) was observed in TM rats, whereas changes in corticosterone were modest. The results support the view that the physiological consequences of long-term moderate training are beneficial, including reduced PA responsiveness to stress, even though exercise training did not affect anxiety-like behaviour.

Effects of increased spatial complexity on behavioural development and task performance in Lister Hooded rats

Enhancing laboratory animal welfare, particularly in rodents, has been achieved through environmental enrichment in caging systems. Traditional enrichment such as adding objects has shown to impact development, reproductive and maternal performance as well as cognition. However, effects of increased spatial complexity as part of larger novel caging systems have not been investigated. While adoption of caging systems with increased spatial complexity seems uncontroversial from a welfare perspective, effects of such housing on the development and task performance of experimental animals remains unclear. In this study, we investigate differences in key behaviours and cognitive performance between Lister Hooded rats housed in traditional (single-shelf) cages (‘basic’) and those housed in larger cages with an additional shelf (‘enriched’). We found minor differences in maternal behaviour, such as nursing and offspring development. Further, we compared task performance in females, using a hippocampus-dependent task (T-maze) and a hippocampus-independent task (Novel Object Recognition, NOR). While in the T-maze no differences in either the rate of learning or probe trial performance were found, in the NOR task females housed in enriched cages performed better than those housed in basic cages. Our results show that increased spatial complexity does not significantly affect development and maternal performance but may enhance learning in females for a non-spatial task. Increased spatial complexity does not appear to have the same effects on behaviour and development as traditional enrichment. Thus, our results suggest no effect of housing conditions on the development of most behaviours in experimental animals housed in spatially enriched caging systems.

Large litters rearing changes brain expression of GLUT3 and acetylcholinesterase activity in adult rats

Effects of malnutrition in the brain are more pronounced during the period of growth spurt, corresponding to the suckling in rodents. Neuronal glucose transporter GLUT3 expression and acetylcholinesterase activity were studied in the brain of adult young rats (84 days old) suckled in litters formed by 6 (control group) or 12 pups (malnourished group). In the adult rats, brain weight, blood glucose levels and GLUT3 expression were decreased in malnourished group (5%, 18%, 58%, respectively, P<0.001, Student's t test) compared to the control. Increased activity of acetylcholinesterase was found in cerebral cortex homogenates and a significant interaction (P=0.019, ANOVA two-way, Tukey's test) was found between nutritional state and homogenate fraction. In summary, malnutrition during suckling period decreased GLUT3 expression and increased acetylcholinesterase activity in the rat brain that could contribute to possible cognitive deficits and changes of brain metabolic activity.