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

Enriched Environment Induces Sex-Specific Changes in the Adult Neurogenesis, Cytokine and miRNA Expression in Rat Hippocampus

An enriched environment stimulates adult hippocampal plasticity, but the exact cellular and molecular mechanisms are complex, and thus a matter of debate. We studied the behavior and hippocampal neurogenesis in adult male and female Wistar rats that were housed in an enriched environment (EE) for two months. Both EE males and females performed better than control animals in a Barnes maze, meaning that EE enhances spatial memory. However, the expression levels of neurogenesis markers KI67, DCX, Nestin, and Syn1 increased only in EE females, while in EE males only KI67 and BDNF were higher than in the corresponding control. The number of DCX+ neurons on brain slices increased in the dentate gyrus of EE females only, i.e., the level of adult hippocampal neurogenesis was increased in female but not in male rats. The level of anti-inflammatory IL-10 and signaling pathway components was upregulated in EE females. Of 84 miRNAs tested, in the hippocampi of EE female rats we detected upregulation in the expression levels of 12 miRNAs related to neuronal differentiation and morphogenesis, while in EE males four miRNAs were upregulated and involved in the regulation of cell proliferation/differentiation, and one was downregulated and associated with the stimulation of proliferation. Taken altogether, our results point to sex-specific differences in adult hippocampal plasticity, IL-10 expression, and miRNA profiles induced by an enriched environment.

Restricted cafeteria feeding and treadmill exercise improved body composition, metabolic profile and exploratory behavior in obese male rats

The aim of this study was to evaluate, in male Long-Evans rats, whether a restricted-cafeteria diet (CAFR), based on a 30% calorie restriction vs continuous ad libitum cafeteria (CAF) fed animals, administered alone or in combination with moderate treadmill exercise (12 m/min, 35 min, 5 days/week for 8 weeks), was able to ameliorate obesity and the associated risk factors induced by CAF feeding for 18 weeks and to examine the changes in circadian locomotor activity, hypothalamic-pituitary-adrenal (HPA) axis functionality, and stress response elicited by this dietary pattern. In addition to the expected increase in body weight and adiposity, and the development of metabolic dysregulations compatible with Metabolic Syndrome, CAF intake resulted in a sedentary profile assessed by the home-cage activity test, reduced baseline HPA axis activity through decreased corticosterone levels, and boosted exploratory behavior. Both CAFR alone and in combination with exercise reduced abdominal adiposity and hypercholesterolemia compared to CAF. Exercise increased baseline locomotor activity in the home-cage in all dietary groups, boosted exploratory behavior in STD and CAF, partially decreased anxiety-like behavior in CAF and CAFR, but did not affect HPA axis-related parameters.

Investigating the role of environmental enrichment initiated in adolescence against the detrimental effects of chronic unpredictable stress in adulthood: Sex-specific differences in behavioral and neuroendocrinological findings

Environmental Enrichment (EE) improves cognitive function and enhances brain plasticity, while chronic stress increases emotionality, impairs learning and memory, and has adverse effects on brain anatomy and biochemistry. We explored the beneficial role of environmental enrichment initiated in adolescence against the negative outcomes of Chronic Unpredictable Stress (CUS) during adulthood on emotional behavior, cognitive function, as well as somatic and neuroendocrine markers in both sexes. Adolescent Wistar rats housed either in enriched or standard housing conditions for 10 weeks. On postnatal day 66, a subgroup from each housing condition was daily exposed to a 4-week stress protocol. Following stress, adult rats underwent behavioral testing to evaluate anxiety, exploration/locomotor activity, depressive-like behavior and spatial learning/memory. Upon completion of behavioral testing, animals were exposed to a 10-m stressful event to test the neuroendocrine response to acute stress. CUS decreased body weight gain and increased adrenal weight. Some stress-induced behavioral adverse effects were sex-specific since learning impairments were limited to males while depressive-like behavior to females. EE housing protected against CUS-related behavioral deficits and body weight loss. Exposure to CUS affected the neuroendocrine response of males to acute stress as revealed by the increased corticosterone levels. Our findings highlight the significant role of EE in adolescence as a protective factor against the negative effects of stress and underline the importance of inclusion of both sexes in animal studies.

Environmental enrichment as a strategy: Attenuates the anxiety and memory impairment in social isolation stress

BACKGROUND

Social isolation (SI) early in life produces behavioral and cognitive abnormalities. On the contrary, environmental enrichment (EE) offers beneficial effects on brain plasticity and development. This study was designed to examine how EE affects memory functions, anxiety level, and the expression levels of memory/anxiety-related genes such as NR2A, NR2B, BDNF, and cFos in the hippocampus of socially isolated rats.

MATERIALS AND METHODS

Wistar albino male rats (n = 40) were separated into the five groups: Standard cage (SC), SI, EE, SI + SC, and SI + EE group. For each group, eight rats were housed, either grouped or isolated, in a standard or 3-week EE, respectively. Morris water maze test (MWMT) was used for measuring the learning and memory function. Elevated plus maze (EPM) and open field (OF) were used for the evaluation of anxiety behavior. Blood corticosterone level was evaluated by the ELISA method. The expression levels of genes were measured by the RT-PCR method.

RESULTS

Results showed that EE increased memory performance in the SI group (p < 0.05). SI caused anxiety while EE improved anxiety behavior (p < 0.05). There was no significant difference between the groups in the OF test. Corticosterone levels did not change between groups. BDNF expression level was downregulated in EE and SI + SC compared with the SC group (respectively; p = 0.012; p = 0.011). NR2A, NR2B, and cFos expression levels did not change between groups significantly.

CONCLUSIONS

SI impaired memory performance while EE has beneficial effects on memory in socially isolated rats. EE alone was insufficient to cause alterations in the memory performance. The therapeutic effects of EE became strengthened while applied together with stress protocol. Together with improving the effectiveness of memory function, EE has the potential to decrease anxiety behavior. EE seemed to be the reason for decreasing in BDNF.

Environmental Enrichment Sex-dependently Rescues Memory Impairment in FABP5 KO Mice Not Mediated by Brain-Derived Neurotrophic Factor

Fatty acid-binding proteins (FABPs) are intracellular carriers of bioactive lipids and play a role in the trafficking of endocannabinoids as well as polyunsaturated fatty acids. Mice lacking the FABP5 gene have memory impairments. Environmental enrichment is a potent manipulation known to rescue or improve memory performance. The extent to which the memory impairments in FABP5 knockout (KO) mice can be rescued or improved through environmental conditions remains to be understood. To address this, we raised wild type (WT) and FABP5 KO mice in either socially isolated or environmental enrichment conditions during adolescence. Once in adulthood, mice were tested for Novel Object Recognition (NOR), T-maze, and Morris Water Maze (MWM) to evaluate memory performance. Mice were then euthanized to assess hippocampal brain-dervied neurotrophic factor (BDNF) concentrations. MWM results showed that male FABP5 KO mice performed worse compared to WT counterparts. Male and female mice raised in an enriched environment improved performance regardless of genotype. Results on the NOR test showed that male FABP5 KO mice displayed lower object recognition compared to WT counterparts across both environments. No differences of genotype or environment were seen in female mice. T maze findings showed that impaired performance in socially isolated FABP5 KO mice. Adolescent environmental enrichment rescued this deficit in male, but not female, FABP5 KO mice. Lastly, environmental enrichment increased hippocampal BDNF levels in male WT mice only. Our results corroborate the previously observed role of the FABP5 gene on memory performance and identify an important interaction with the environment during adolescence.

Neurotrophic Factors and Brain Health in Children with Overweight and Obesity: The Role of Cardiorespiratory Fitness

ABSTRACTNeurotrophic factors and cardiorespiratory fitness are both considered important in developmental trajectories but their link to brain health remains poorly understood. The aims of the study were to examine whether levels of plasma-derived neurotrophic factors were associated with brain health indicators in children with overweight or obesity; and to test whether these associations were moderated by cardiorespiratory fitness. 100 children (41% girls) were included in this analysis. Plasma levels of brain-derived neurotrophic factor, insulin-like growth factor-1, vascular endothelial growth factor A, and epidermal growth factor were determined by XMap technology. Academic performance and executive function were assessed using validated neuropsychological tests. Hippocampal volume was measured using magnetic resonance imaging. Cardiorespiratory fitness was assessed using the 20-m Shuttle Run Test. Insulin-like growth factor-1 was positively associated with cognitive flexibility. Stratified analyses by fitness categories (i.e., unfit vs. fit) showed that brain-derived neurotrophic factor was positively associated with right posterior hippocampal volume in fit children, and epidermal growth factor was negatively associated with right hippocampal, and right anterior hippocampal volumes in their unfit peers, with a moderating role of cardiorespiratory fitness in these associations. However, all these significant associations disappeared after correction for multiple comparisons. The association between neurotrophic factors and brain health indicators in children with overweight/obesity was neither strong nor consistent. These results could help enhance our understanding of determinants of brain health in children with overweight/obesity.Trial registration: ClinicalTrials.gov identifier: NCT02295072..

Chrysin restores memory deficit in hypothyroidism mice: Behavioral, neurochemical and computational approaches involving the neurotrophinergic system

Hypothyroidism is a condition that affects multiple systems, including the central nervous system, causing, for example, cognitive deficits closely related to Alzheimer's disease. The flavonoid chrysin is a natural compound associated with neuronal improvement in several experimental models. Here, we evaluated the effect of chrysin on cognitive impairment in hypothyroid female mice by exploring neuroplasticity. Hypothyroidism was induced by continuous exposure to 0.1% methimazole (MTZ) in drinking water for 31 days. On the 32nd day, the animals showed low plasma levels of thyroid hormones (hypothyroid mice) than the control group (euthyroid mice). Subsequently, mice were intragastrically administered with vehicle or chrysin (20 mg/kg) once a day for 28 consecutive days. At the end of the treatments, behavioral tests were performed: open-field test (OFT) and morris water maze (MWM). Then, the levels of neurotrophins (BDNF and NGF) in the hippocampus and prefrontal cortex were measured and tested the affinity of chrysin with neurotrophinergic receptors through molecular docking. Hypothyroid mice showed memory deficit in the MWM and reduced neurotrophins levels in the hippocampus and prefrontal cortex, meanwhile, the chrysin treatment was able to reversed the deficit of spatial memory function and increased the levels of BDNF in hipocamppus and NGF in both structures. Additionally, molecular docking analysis showed that chrysin potentially binds to the active site of the TrkA, TrkB, and p75NTR receptors. Together, these findings suggest that chrysin reversed behavioral and neurochemical alterations associated with memory deficit induced by hypothyroidism, possibly by modulating synaptic plasticity in the neurotrophinergic system.

Combined Neuroprotective Strategies Blocked Neurodegeneration and Improved Brain Function in Senescence-Accelerated Mice

Increase in the quality of life, combined with drug strategies, has been studied as possibilities for improving memory and delaying the onset of neurodegenerative diseases. A previous study published by the group of the authors has shown that microdose lithium and enriched environment can improve memory in both mice and humans. To elucidate this relationship better, this study aimed to evaluate whether the chronic combination of these two strategies could increase healthy aging in Senescence Accelerated Mouse-Prone 8 (SAMP8). Animals were submitted to either one or both of these strategies until the age of 10 months when they were anesthetized and killed and their hippocampus was extracted. The untreated SAMP-8 group exhibited worse memory and reduced neuronal density with greater neurodegeneration and increased amyloid-β plaque density compared with the control group. Moreover, significant alterations in proteins related to long-term potentiation, such as, synaptophysin and brain-derived neurotrophic factor (BDNF), were observed in this group. The strategies used in the study maintained long-term memory, reduced anxiety, and increased neuroprotection. Both strategies were efficient in reducing neurodegeneration and increasing parameters related to memory maintenance. In many experiments, the combination of the two strategies was more effective in improving healthy aging. This study sheds light on the combination of strategies that choose to improve the quality of life and drugs with low side effects. Moreover, it opens perspectives for a new field of study for healthy aging.

Long-Term Music Exposure Prevents Age-Related Cognitive Deficits in Rats Independently of Hippocampal Neurogenesis

Cognitive decline appears across aging. While some studies report beneficial effects of musical listening and practice on cognitive aging, the underlying neurobiological mechanisms remain unknown. This study aims to determine whether chronic (6 h/day, 3 times/week) and long-lasting (4-8 months) music exposure, initiated at middle age in rats (15 months old), can influence behavioral parameters sensitive to age effects and reduce age-related spatial memory decline in rats. Spontaneous locomotor, circadian rhythmic activity, and anxiety-like behavior as well as spatial working and reference memory were assessed in 14-month-old rats and then after 4 and 8 months of music exposure (19 and 23 months old, respectively). Spatial learning and reference memory data were followed up by considering cognitive status of animals prior to music exposure (14 months old) given by K-means clustering of individual Z-score. Hippocampal cell proliferation and brain-derived neurotrophic factor (BDNF) level in the hippocampus and frontal cortex were measured. Results show that music exposure differentially rescues age-related deficits in spatial navigation tasks according to its duration without affecting spontaneous locomotor, circadian rhythmic activity, and anxiety-like behavior. Hippocampal cell proliferation as well as hippocampal and frontal cortex BDNF levels was not affected by music across aging. Cognitive improvement by music in aging rats may require distinct neurobiological mechanisms than hippocampal cell proliferation and BDNF.