Post-weaning Environmental Enrichment Research Articles

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

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

Local CRF and oxytocin receptors correlate with female experience-driven avoidance change and hippocampal neuronal plasticity

Understanding how experiences affect females' behaviors and neuronal plasticity is essential for uncovering the mechanism of neurodevelopmental disorders. The study explored how neonatal maternal deprivation (MD) and post-weaning environmental enrichment (EE) impacted the CA1 and DG's neuronal plasticity in the dorsal hippocampus, and its relationships with passive avoidance, local corticotrophin-releasing factor (CRF) levels, and oxytocin receptor (OTR) levels in female BALB/c mice. The results showed that MD damaged passive avoidance induced by foot shock and hotness, and EE restored it partially. In the CA1, MD raised CRF levels and OTR levels. Parallelly, MD increased synaptic connection levels but reduced the branches' numbers of pyramidal neurons. Meanwhile, in the DG, MD increased OTR levels but lowered CRF levels, DNA levels, and spine densities. EE did not change the CA1 and DG's CRF and OTR levels. However, EE added DG's dendrites of granular cells. The additive of MD and EE raised CA1's synaptophysin and DG's postsynaptic density protein-95 and OTR levels, and meanwhile, shaped avoidance behaviors primarily similar to the control. The results suggest that experience-driven avoidance change and hippocampal neuronal plasticity are associated with local CRF and OTR levels in female mice.

Experiences Shape Hippocampal Neuron Morphology and the Local Levels of CRHR1 and OTR.

The dorsal hippocampus is involved in behavioral avoidance regulation. It is unclear how experiences such as the neonatal stress of maternal deprivation (MD) and post-weaning environmental enrichment (EE) affect avoidance behavior and the dorsal hippocampal parameters, including neuronal morphology, corticotrophin-releasing hormone (CRH) signaling, and oxytocin receptor (OTR) level. In male BALB/c mice, we found that MD impaired avoidance behavior in the step-on test compared to non-MD and EE rearing conditions could alleviate that partially. MD increased neuronal branches in the CA1 but decreased synaptic connection levels in the CA2, CA3, and DG. Meanwhile, MD increased the CA1's OTR levels, which negatively correlated with nucleus densities. MD also increased the CA1's and CA2's CRH levels, which positively correlated with CRHR1 levels. However, MD statistically elevated the CA3's CRH receptor 1 (CRHR1) levels, which negatively correlated with nucleus densities and, probably, synaptic connection levels in the CA3. The additive effects of MD and EE maintained similar CRH levels and CRHR1 levels as well as OTR levels in the hippocampal areas as the additive of non-MD and non-EE. However, the presence of MD and EE still decreased the CA1's neuronal branches and the CA2's and DG's synaptic connection levels. The study illustrates how MD and EE affect avoidance behaviors, hippocampal neuron morphology, and CRH and OTR levels. The results indicate that the late-life environmental improvement partially restores the alterations in dorsal hippocampal areas induced by early life stress.

Effects of maternal deprivation and environmental enrichment on anxiety-like and depression-like behaviors correlate with oxytocin system and CRH level in the medial-lateral habenula

The medial-lateral habenula (LHbM)’s role in anxiety and depression behaviors in female mice remains unclear. Here, we used neonatal maternal deprivation (MD) and post-weaning environmental enrichment (EE) to treat female BALB/c offspring and checked anxiety-like and depression-like behaviors as well as the corticotropin-releasing hormone (CRH), oxytocin receptor (OTR), estrogen receptor-beta (ERβ) levels in their LHbM at adulthood. We found that MD enhanced state anxiety-like behaviors in the elevated plus-maze test, and EE caused trait anxiety-like behaviors in the open field test and depression-like behaviors in the tail suspension test. The immunochemistry showed that MD reduced OT immunoreactive neuron numbers in the hypothalamic paraventricular nucleus but increased OTR levels in the LHbM; EE increased CRH levels in the LHbM but decreased OTR levels in the LHbM. The additive effects of EE and MD maintained the behavioral parameters, OT-ir neuronal numbers, CRH levels, and OTR levels similar to the additive of non-MD and non-EE. The correlation analysis showed that CRH levels correlated with synaptic connection levels, OTR levels correlated with nucleus densities, and ERβ levels correlated with Nissl body levels and body weights in female mice. Neither MD nor EE affected ERβ levels in the LHbM. Together, the study revealed the relationships between behaviors and neuroendocrine and neuronal alterations in female LHbM and the effects of experiences including MD and EE on them.

Duality in recognition memory deficits in APPswe/PS1dE9 mice

Effects of post weaning environmental enrichment (EE) on episodic memory was studied in 2-month-old APPswe/PS1dE9 (APP/PS1) mouse model of Alzheimer's disease METHOD: The basic protocol for post weaning EE and tests for episodic memory were adapted from previously established procedures. The experiments were conducted on WT and APP/PS1 male mice. In this study we demonstrate that object recognition memory is intact, however, object in place memory is impaired in APP/PS1 mice during the preplaque stages of disease pathogenesis at 2 months of age. We further demonstrate that post weaning EE ameliorates object in place memory, however, lead to deficits in object recognition memory. Our results indicate that 2-month-old APP/PS1 mice displays deficits within recognition memory selectively sparing the familiarity component of recognition. Furthermore, benefits of EE are biased towards context based recognition task in APP/PS1 mice.

Influence of environmental enrichment on the volume of brain regions sensitive to early life stress by maternal separation in rats.

Exposure to maternal separation (MS) in rodents may have long-lasting consequences for the structure and function of several brain regions, eventually associated with alterations in cognition and emotion later in life. Post-weaning environmental enrichment (EE) has been reported to ameliorate the detrimental effects of exposure to early life stress mainly in the hippocampus. In vivo magnetic resonance imaging (MRI) was applied to evaluate possible volumetric changes in the dorsal and ventral hippocampus, the medial prefrontal cortex and the dorsal striatum of 90-day-old male rats after daily MS for 240 min from postnatal days 2-21. No significant volume changes were found in the selected brain regions in MS animals as compared with an age-matched control group. However, additional groups of control and MS animals with EE from days 21-60 showed significant volume increases in the medial prefrontal cortex and the ventral hippocampus as compared to the groups without EE. In addition, general hemispheric asymmetry was found in the volume of the brain regions measured. Our results demonstrate that EE could have differential effects depending on previous exposure to MS and on the development of brain lateralization.

Post-weaning Environmental Enrichment in Male CD-1 Mice: Impact on Social Behaviors, Corticosterone Levels and Prefrontal Cytokine Expression in Adulthood.

Environmental enrichment is typically associated with enhanced well-being, improved cognitive function and stress resilience. However, in some instances grouping adult male mice in enriched conditions promoted a stressful environment, which resulted in elevated endocrine, monoamine and inflammatory outcomes in response to subsequent stressor exposure. The current investigation examined whether raising male mice in an enriched environment (EE) would modulate social and anxiety-like behaviors in early adulthood and influence brain expression of pro-inflammatory cytokines and brain-derived neurotrophic factor (BDNF). Immediately after weaning (postnatal day [PD] 21), CD-1 male mice were housed with their siblings (3/cage) for 6 weeks in an EE or a standard (SE) environment. Body weights and aggressive interactions were monitored weekly. Social avoidance behaviors in the social interaction test and anxiety-like behaviors in the elevated-plus maze were examined in early adulthood. Ninety minutes following the behavioral tests, mice were sacrificed and a blood sample and the prefrontal cortex (PFC) were collected for the determination of plasma corticosterone levels as well as cytokine and BDNF mRNA expression. Mice raised in an EE exhibited more wounds and gained less weight than mice housed in a SE. Enriched mice also spent a greater amount of time in proximity of a social target in the social interaction test and made fewer transitions into the closed arms of the elevated-plus maze. Interestingly, the elevated plasma corticosterone and upregulated prefrontal interleukin (IL)-1β expression observed after the social interaction test among the SE mice were not apparent among those housed in an EE. Enrichment also increased prefrontal BDNF expression, especially among mice that experienced the social interaction test. These results suggest that although raising male mice in an EE may elicit aggressive interactions between sibling cage-mates (as indicated by a high number of wounds), this environment also enhances social behaviors and limits the corticosterone and cytokine impacts of mild social stressors encountered in early adulthood.

Hypersensitivity to sertraline in the absence of hippocampal 5-HT1AR and 5-HTT gene expression changes following paternal corticosterone treatment.

The male germ line is capable of transmitting a legacy of stress exposure to the next generation of offspring. This transgenerational process manifests by altering offspring affective behaviours, cognition and metabolism. Paternal early life trauma causes hippocampal serotonergic dysregulation in male offspring. We previously showed a transgenerational modification to male offspring anxiety-like behaviours by treatment of adult male breeders with corticosterone (CORT) prior to mating. In the present study, we used offspring from our paternal CORT model and characterised offspring serotonergic function by examining their responses to the 5HT1AR agonist, 8-OH-DPAT, and the selective serotonin reuptake inhibitor, sertraline. We also examined whether post-weaning environmental enrichment, a paradigm well-known to modulate serotonergic signalling in the brain, had the capacity to normalise the anxiety phenotype of male offspring. Finally, we assessed gene expression levels of 5HT1AR and serotonin transporter in the offspring hippocampus to determine whether deficits in gene transcription contributed to the male-only anxiety phenotype. We report that male and female offspring of CORT-treated fathers are hypersensitive to sertraline but have normal hypothermic responses to 8-OH-DPAT. No deficits in htr1a and sert were found in association with paternal CORT treatment, and environmental enrichment did not rescue the anxiety phenotype of male offspring on the elevated-plus maze. These findings indicate that varying forms of paternal stress exert different effects on offspring brain serotonergic function.

Amygdala - and serum - neurotrophic factor levels depend on rearing condition in male rats.

Early life experiences could determine brain and behavioral development. Neurotrophic factors are likely to mediate the effects of the experience on brain structures and function. Brain-derived neurotrophic factor (BDNF) plays a central role in psychiatric disorders. To investigate the effects of early rearing condition on the amygdala - and serum - BDNF levels, we reared male Wistar rats from weaning (postnatal days 21) to adulthood (postnatal days 119) in three different rearing conditions: (1) enriched, (2) standard and (3) isolated. We found that long-term post-weaning environmental enrichment leads to lower amygdala - and serum - BDNF levels as well as lower brain weights. Grouped rearing in standard laboratory cages enhanced body weight. Thus, early rearing condition might play a crucial role in adult healthiness by predetermining individual BDNF profiles.

Environmental enrichment normalizes hippocampal timing coding in a malformed hippocampus.

Neurodevelopmental insults leading to malformations of cortical development (MCD) are a common cause of psychiatric disorders, learning impairments and epilepsy. In the methylazoxymethanol (MAM) model of MCDs, animals have impairments in spatial cognition that, remarkably, are improved by post-weaning environmental enrichment (EE). To establish how EE impacts network-level mechanisms of spatial cognition, hippocampal in vivo single unit recordings were performed in freely moving animals in an open arena. We took a generalized linear modeling approach to extract fine spike timing (FST) characteristics and related these to place cell fidelity used as a surrogate of spatial cognition. We find that MAM disrupts FST and place-modulated rate coding in hippocampal CA1 and that EE improves many FST parameters towards normal. Moreover, FST parameters predict spatial coherence of neurons, suggesting that mechanisms determining altered FST are responsible for impaired cognition in MCDs. This suggests that FST parameters could represent a therapeutic target to improve cognition even in the context of a brain that develops with a structural abnormality.

Post-weaning Environmental Enrichment, But Not Chronic Maternal Isolation, Enhanced Ethanol Intake during Periadolescence and Early Adulthood.

This study analyzed ethanol intake in male and female Wistar rats exposed to maternal separation (MS) during infancy (postnatal days 1–21, PD1–21) and environmental enrichment (EE) during adolescence (PD 21–42). Previous work revealed that MS enhances ethanol consumption during adulthood. It is still unknown if a similar effect is found during adolescence. Several studies, in turn, have revealed that EE reverses stress experiences, and reduces ethanol consumption and reinforcement; although others reported greater ethanol intake after EE. The interactive effects between these treatments upon ethanol’s effects and intake have yet to be explored. We assessed chronic ethanol intake and preference (12 two-bottle daily sessions, spread across 30 days, 1st session on PD46) in rats exposed to MS and EE. The main finding was that male – but not female – rats that had been exposed to EE consumed more ethanol than controls given standard housing, an effect that was not affected by MS. Subsequent experiments assessed several factors associated with heightened ethanol consumption in males exposed to MS and EE; namely taste aversive conditioning and hypnotic-sedative consequences of ethanol. We also measured anxiety response in the light-dark box and in the elevated plus maze tests; and exploratory patterns of novel stimuli and behaviors indicative of risk assessment and risk-taking, via a modified version of the concentric square field (CSF) test. Aversive conditioning, hypnosis and sleep time were similar in males exposed or not to EE. EE males, however, exhibited heightened exploration of novel stimuli and greater risk taking behaviors in the CSF test. It is likely that the promoting effect of EE upon ethanol intake was due to these effects upon exploratory and risk-taking behaviors.

Post-weaning environmental enrichment improves BDNF response of adult male rats

The environment could have long lasting effects on the individual phenotype through developmental plasticity. Early environmental enrichment exerts profound biological effects, most of which are quite beneficial ones. To explore the enduring effects of rearing condition quality on BDNF11BDNF: Brain-derived neurotrophic factor. responses, we reared male Wistar rats from weaning to young-adulthood in three different environmental conditions: 1. Enriched 2. Standard, and 3. Isolated. Then, at the age of 16 weeks, 10 rats from each group were randomly chosen and allocated to six common mix cages. They were kept together for 14 weeks. At the end of the experiment, each rat received ten inescapable foot-shocks. Twelve hours later, the BDNF contents of the amygdala and CA1 sub-region of the dorsal hippocampus were measured. The serum BDNF levels, hematocrit values as well as brain and testis weights were also measured. Results showed that the environmental enrichment led to stronger dorsal hippocampal BDNF response and higher serum BDNF levels, while rats from standard laboratory condition showed higher amygdala BDNF response. Also, enriched animals showed higher brain weight compared to isolation reared rats as well as higher testis weight and hematocrit value compared to animals reared in standard laboratory condition. Rats showed less body weights in isolated condition. In conclusion, the BDNF profile of enriched animals might represent the neurobiological correlate of resilience phenotype under a stressful situation.

Neurobiological effects of neonatal maternal separation and post-weaning environmental enrichment

Throughout the lifespan, the brain has a considerable degree of plasticity and can be strongly influenced by sensory input from the outside environment. Given the importance of the environment in the regulation of the brain structure, behavior and physiology, the aim of the present work was to analyze the effects of different environmental qualities during two critical ontogenic periods (early life and peripuberty) on behavior and hippocampal physiology. Male Wistar rats were separated from their mothers for 4.5h daily during the first 3 weeks of life. They were weaned on day 21 and housed under either standard or enriched conditions. At 60 d of age, all animals were then housed in same-treatment groups, two per cage, until testing began on day 74. Emotional and cognitive responses were tested using the open field, novel object recognition test and step-down inhibitory avoidance learning. In the dorsal hippocampus, glucocorticoid receptor expression and neuronal activity were examined by immunoreactivity. Grooming behavior in the open field was found to be significantly lower in maternally separated animals, but post-weaning environmental enrichment completely reversed this tendency. Inhibitory avoidance but not object recognition memory was impaired in maternally separated animals, suggesting that early maternal separation alters learning and memory in a task-specific manner. Again, environmental enrichment reversed the effects of maternal separation on the inhibitory avoidance task. Even though maternal separation did not significantly affect Fos and glucocorticoid receptor (GR) expression, environmental enrichment increased both Fos expression in the total hippocampal area and also the overall number of GR positive cells per hippocampal area, mainly due to the changes in CA1. These findings suggest that differential rearing is a useful procedure to study behavioral and physiological plasticity in response to early experience and that, although the effects of adverse experience early in life such as maternal separation can persist until adulthood, some of them can be compensated by early favorable environments, possibly through nervous system plasticity.

Neurobiological effects of neonatal maternal separation and post-weaning environmental enrichment

Throughout the lifespan, the brain has a considerable degree of plasticity and can be strongly influenced by sensory input from the outside environment. Given the importance of the environment in the regulation of the brain structure, behavior and physiology, the aim of the present work was to analyze the effects of different environmental qualities during two critical ontogenic periods (early life and peripuberty) on behavior and hippocampal physiology.Male Wistar rats were separated from their mothers for 4.5h daily during the first 3 weeks of life. They were weaned on day 21 and housed under either standard or enriched conditions. At 60 d of age, all animals were then housed in same-treatment groups, two per cage, until testing began on day 74. Emotional and cognitive responses were tested using the open field, novel object recognition test and step-down inhibitory avoidance learning. In the dorsal hippocampus, glucocorticoid receptor expression and neuronal activity were examined by immunoreactivity.Grooming behavior in the open field was found to be significantly lower in maternally separated animals, but post-weaning environmental enrichment completely reversed this tendency. Inhibitory avoidance but not object recognition memory was impaired in maternally separated animals, suggesting that early maternal separation alters learning and memory in a task-specific manner. Again, environmental enrichment reversed the effects of maternal separation on the inhibitory avoidance task. Even though maternal separation did not significantly affect Fos and glucocorticoid receptor (GR) expression, environmental enrichment increased both Fos expression in the total hippocampal area and also the overall number of GR positive cells per hippocampal area, mainly due to the changes in CA1.These findings suggest that differential rearing is a useful procedure to study behavioral and physiological plasticity in response to early experience and that, although the effects of adverse experience early in life such as maternal separation can persist until adulthood, some of them can be compensated by early favorable environments, possibly through nervous system plasticity.

Post-weaning environmental enrichment alters affective responses and interacts with behavioral testing to alter nNOS immunoreactivity

Challenging early life events can dramatically affect mental health and wellbeing. Childhood trauma and neglect can increase the risk for developing depressive, anxiety, and substance abuse disorders. Early maternal separation in rodents has been extensively studied and induces long-lasting alterations in affective and stress responses. However, other developmental periods (e.g., the pubertal period) comprise a critical window whereby social and environmental complexity can exert lasting changes on the brain and behavior. In this study, we tested whether early life environmental complexity impacts affective responses, aggressive behaviors, and expression of neuronal nitric oxide synthase (nNOS), the synthetic enzyme for nitric oxide, in adulthood. Mice were weaned into social+nonsocial enrichment, social only enrichment, or standard (isolated) laboratory environments and were tested in open field, elevated plus maze, forced swim, and resident–intruder aggression tests 60days later. Social+nonsocial enrichment reduced locomotor behavior and anxiety-like responses in the open field and reduced depressive-like responses in the forced swim test. Social housing increased open arm exploration in the elevated plus maze. Both social+nonsocial enrichment and social housing only reduced aggressive behaviors compared with isolation. Social+nonsocial enrichment also increased body mass gain throughout the study. Finally, socially-housed mice had reduced corticosterone concentrations compared with social+nonsocial-enriched mice. Behavioral testing reduced nNOS-positive neurons in the basolateral amygdala and the ventral lateral septum, but not in the social+nonsocial-enriched mice, suggesting that environmental complexity may buffer the brain against some environmental perturbations.

Hippocampal neurochemistry is involved in the behavioural effects of neonatal maternal separation and their reversal by post-weaning environmental enrichment: A magnetic resonance study

Exposure to early life stress results in behavioural changes, and these dysfunctions may persist throughout adulthood. In this study, we investigated whether hippocampus volume and neurochemical changes were involved in the appearance of these effects in the maternal separation (MS) animal model using the noninvasive techniques of structural magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). Sprague–Dawley rats exposed to MS for 180 min from postnatal days (PND) 2–14 demonstrated decreased sucrose preference, increased immobility in the forced swimming test (FST), and impaired memory in the Morris water maze in adulthood. Environmental enrichment (EE) (PND 21–60) could ameliorate the effects of MS on sucrose preference and learning and memory but not on immobility in the FST. In addition, EE significantly increased N-acetylaspartate (NAA) of MS animals. However, we did not find an effect of MS or EE on hippocampal volume. These results indicate the involvement of hippocampal neurochemistry in the behavioural changes that result from early stressful life events and their modification by post-weaning EE. Thus changes in NAA, as a measure of neuronal integrity, appear to be a sensitive correlate of these behavioural effects.

Environmental enrichment alters locomotor behaviour and ventricular volume in Mecp21lox mice

Rett syndrome (RTT) is an autistic spectrum developmental disorder associated with mutations in the X-linked Mecp2 gene, and severe behavioural and neuropathological deficits. In a mouse model of RTT (Mecp21lox), we examined whether environmental enrichment (EE) alters behavioural performance and regional brain volume. At weaning, Mecp21lox and control mice were assigned to enriched or standard housing. From postnatal day 29 to 43, mice were subjected to behavioural tasks measuring motor and cognitive performance. At postnatal day 44, volumes of whole brain, cerebellum, ventricles, and motor cortex were measured using magnetic resonance imaging. EE provided subtle improvements to locomotor activity and contextual fear conditioning in Mecp21lox mice. Additionally, EE reduced ventricular volumes, which correlated with improved locomotor activity, suggesting that neuroanatomical changes contribute to improved behaviour. Our results suggest that post-weaning EE may provide a non-invasive palliative treatment for RTT.

The effects of dietary fatty acid composition combined with environmental enrichment on brain and behavior in mice.

In this study we investigated the effects of dietary fatty acid (FA) composition combined with postweaning environmental enrichment on brain fatty acid composition and behavior in mice. There were three dietary conditions: a saturated fat group deficient in essential fatty acids, a group deficient in n-3 fatty acids only, and a control group containing both n-3 and n-6 fatty acids in a ratio of 0.27. Animals were fed these diets during pregnancy and lactation and after weaning. Brain fatty acid composition was determined on days 1, 9, 17 and 25 after birth and in adult animals at 3 months. At weaning two females from each litter were assigned randomly to either an enriched or standard environmental condition. After six weeks in these environments they were tested in the Morris water maze and open field. Adult percentages of 22:6n-3 were present in the brain within the first week after birth. These values were reduced by 50% in the n-3 deficient diet and by 80% in the saturated fat diet; adult animals on the saturated fat diet were also severely retarded in growth. Animals fed the saturated fat diet were initially slightly slower in locating the hidden platform in the Morris maze relative to the control group, but this was not apparent in the reversal learning phase; a cued learning task using a visible platform indicated that these effects did not appear to be related to differences in motor or motivational capacities. The n-3 deficient group did not differ from either the saturated fat group or the controls. All dietary groups showed beneficial effects of environmental enrichment in decreasing their latency to locate the hidden platform, and these effects appeared to be partially independent of the increased swimming speed of the enriched animals. Enriched animals in all groups showed less rearing activity in the open field and spent more time stationary; the animals fed saturated fat reared less and travelled shorter distances more slowly. In all cases the effects of diet and environment were additive, thereby providing little support for the hypothesis that dietary fatty acid composition would affect the animals' capacity to benefit from the functional effects of environmental enrichment.

Environmental enrichment and the behavioral effects of prenatal exposure to alcohol in rats

Animals exposed prenatally to alcohol (4 g/kg/day) via maternal peroral intubation or control offspring were reared after weaning either alone in standard steel/wire cages or in groups of eight, for 6 weeks. Rats exposed prenatally to alcohol and reared in isolation had a dysmetric stride length indicative of an ataxic gait. However, following postweaning environmental enrichment, prenatal alcohol-exposed rats showed no evidence of ataxia. In addition, the prenatal alcohol-exposed rats showed the same magnitude of improved Morris maze performance after enrichment as did the control offspring. These preliminary results suggest that postnatal environment can influence the expression of alcohol-related birth defects in rats, that rats exposed prenatally to alcohol can benefit from the effects of enriched postweaning environment and that postnatal factors can attenuate some of the deficits due to prenatal alcohol exposure.

Greater efficacy of preweaning than postweaning environmental enrichment on maze learning in adult rats

In order to assess the behavioural effects of environmental stimulation at different stages of development, two groups of rats were exposed to multisensory enrichment on days 10–24 (preweaning) or 25–39 (postweaning). Both groups had four 25-min sessions per day in a large cage with a variety of stimuli, in addition to 3 min of handling before each session. The mother of the preweaning group remained in the home cage during the stimulation sessions. A third group was maintained in a social condition. Testing in a Hebb-Williams maze started when the rats of the 3 groups were 100 days old. Error, latency and running time scores were lowest in the preweaning group.