Influence of Pre-reproductive Maternal Enrichment on Coping Response to Stress and Expression of c-Fos and Glucocorticoid Receptors in Adolescent Offspring

An enriched maternal environment and stereotypies of sows differentially affect the neuro-epigenome of brain regions related to emotionality in their piglets

Epigenetic mechanisms are important modulators of neurodevelopmental outcomes in the offspring of animals challenged during pregnancy. Pregnant sows living in a confined environment are challenged with stress and lack of stimulation which may result in the expression of stereotypies (repetitive behaviours without an apparent function). Little attention has been devoted to the postnatal effects of maternal stereotypies in the offspring. We investigated how the environment and stereotypies of pregnant sows affected the neuro-epigenome of their piglets. We focused on the amygdala, frontal cortex, and hippocampus, brain regions related to emotionality, learning, memory, and stress response. Differentially methylated regions (DMRs) were investigated in these brain regions of male piglets born from sows kept in an enriched vs a barren environment. Within the latter group of piglets, we compared the brain methylomes of piglets born from sows expressing stereotypies vs sows not expressing stereotypies. DMRs emerged in each comparison. While the epigenome of the hippocampus and frontal cortex of piglets is mainly affected by the maternal environment, the epigenome of the amygdala is mainly affected by maternal stereotypies. The molecular pathways and mechanisms triggered in the brains of piglets by maternal environment or stereotypies are different, which is reflected on the differential gene function associated to the DMRs found in each piglets' brain region . The present study is the first to investigate the neuro-epigenomic effects of maternal enrichment in pigs' offspring and the first to investigate the neuro-epigenomic effects of maternal stereotypies in the offspring of a mammal.

Environmental Enrichment Protects against Neurotoxic Effects of Lipopolysaccharide: A Comprehensive Overview

Neuroinflammation is a pathophysiological condition associated with damage to the nervous system. Maternal immune activation and early immune activation have adverse effects on the development of the nervous system and cognitive functions. Neuroinflammation during adulthood leads to neurodegenerative diseases. Lipopolysaccharide (LPS) is used in preclinical research to mimic neurotoxic effects leading to systemic inflammation. Environmental enrichment (EE) has been reported to cause a wide range of beneficial changes in the brain. Based on the above, the purpose of the present review is to describe the effects of exposure to EE paradigms in counteracting LPS-induced neuroinflammation throughout the lifespan. Up to October 2022, a methodical search of studies in the literature, using the PubMed and Scopus databases, was performed, focusing on exposure to LPS, as an inflammatory mediator, and to EE paradigms in preclinical murine models. On the basis of the inclusion criteria, 22 articles were considered and analyzed in the present review. EE exerts sex- and age-dependent neuroprotective and therapeutic effects in animals exposed to the neurotoxic action of LPS. EE’s beneficial effects are present throughout the various ages of life. A healthy lifestyle and stimulating environments are essential to counteract the damages induced by neurotoxic exposure to LPS.

Multigenerational effects of paternal spatial training are lasting in the F1 and F2 male offspring

Recent studies on intergenerational transmission of learning and memory performances demonstrated that parental spatial training before fertilization could facilitate learning and memory in the offspring, but many questions remain unclarified. Essential issues regarding whether and how long the effects of parental training in a task can last in several generations, and whether learning a task repeated in the successive generations can enhance a load of multigenerational effects. In the present study, the spatial performances of F1 and F2 generations of male offspring of fathers or grandfathers spatially trained in the Morris Water Maze were evaluated and compared with the performance of a control sample matched for age and sex. Further, to investigate the memory process in F1 and F2 male offspring, brain-derived neurotrophic factor (BDNF), p-ERK1/2 and acetylated histone 3 lysine 14 (H3K14) expression levels in the hippocampus were analyzed. The findings showed that paternal training reduced escape latencies and increased time spent in the target quadrant by F1 and F2 male offspring. Besides, paternal spatial training repeated in two generations did not enhance the beneficial effects on offspring's spatial performances. These findings were supported by neurobiologic data showing that paternal training increased BDNF and p-ERK1/2 in the hippocampus of F1 and F2 male offspring. Furthermore, the hippocampal level of acetylated H3K14 increased in the offspring of spatially trained fathers, reinforcing the hypothesis that the augmented histone acetylation might play an essential role in the inheritance of spatial competence.

Distinct sex-dependent effects of maternal preconception nicotine and enrichment on the early development of rat offspring brain and behavior

Developmental nicotine exposure is harmful to offspring. Whereas much is known about the consequences of prenatal nicotine exposure, relatively little is understood about how maternal preconception nicotine impacts the next generation. Positive experiences, such as environmental enrichment/complexity, have considerable potential to improve developmental outcomes and even treat and prevent drug addiction. Therefore, the current study sought to identify how maternal exposure to moderate levels of nicotine prior to conception impacts offspring development, and if the presumably negative consequence of nicotine could be reversed by concurrent exposure to an enriched environment. We treated female Long Evans rats with nicotine in their drinking water (15 mg nicotine salt/L) for seven weeks while residing in either standard or enriched conditions. Both experiences occurred exclusively prior to mating. Nicotine exposure reduced dam fertility by ~20% (p = .06). Females reared their own litters, and offspring were tested in two assessments of early development: negative geotaxis and open field. Offspring were euthanized at weaning (P21), and their brains were processed with Golgi-Cox solution to allow quantification of dendritic spine density. Results indicate that neither maternal nicotine or enrichment had an impact on maternal care, but male offspring were impaired at negative geotaxis due to maternal nicotine, female offspring showed altered open field exploration due to maternal enrichment, and offspring of both sexes had increased spine density in OFC due to maternal enrichment. Therefore, this experiment provides novel insights into the unique, sex-dependent consequences of maternal preconception nicotine and enrichment on the early development of rat behavior and brain.

Maternal spatial training before fertilization improves the spatial learning process in female offspring

Recent results of our team showed that parental spatial training before fertilization improves the offspring's spatial memory. However, the process of spatial learning (short-term/working and long-term memories, mnesic consolidation and procedures) in the offspring has not been fully clarified yet. Therefore, this study aimed at specifically analyzing whether maternal learning of a spatial task before fertilization can impact on the process of spatial learning in the female offspring. In the present study, 8-week-old female Wistar rats that had been spatially trained (or not) in the Morris Water Maze (MWM) were mated with conspecific standard-reared male rats, and their 4-week-old female offspring were spatially tested in the same MWM to evaluate their learning and memory processes. Results showed that the female offspring of trained mothers significantly displayed lower escape latencies, higher swimming speed, shorter total distance swum, longer percentage of time spent in the target quadrant and better localization memory in comparison to the female offspring of not trained mothers. Further, MWM performances of mothers trained and their female offspring significantly correlated. These findings indicate that the maternal spatial training before fertilization improves the spatial learning and memory consolidation process of the female offspring.

Pre-reproductive Parental Enriching Experiences Influence Progeny's Developmental Trajectories

While the positive effects of environmental enrichment (EE) applied after weaning, in adulthood, during aging, or even in the presence of brain damage have been widely described, the transgenerational effects of pre-reproductive EE have been less examined. And yet, this issue is remarkable given that parental environmental experience may imprint offspring’s phenotype over generations through many epigenetic processes. Interactions between individual and environment take place lifelong even before conception. In fact, the environment pre-reproductively experienced by the mother and/or the father exerts a substantial impact on neural development and motor and cognitive performances of the offspring, even if not directly exposed to social, cognitive, physical and/or motor enrichment. Furthermore, pre-reproductive parental enrichment exerts a transgenerational impact on coping response to stress as well as on the social behavior of the offspring. Among the effects of pre-reproductive parental EE, a potentiation of the maternal care and a decrease in global methylation levels in the frontal cortex and hippocampus of the progeny have been described. Finally, pre-reproductive EE modifies different pathways of neuromodulation in the brain of the offspring (involving brain-derived neurotrophic factor, oxytocin and glucocorticoid receptors). The present review highlights the importance of pre-reproductive parental enrichment in altering the performances not only of animals directly experiencing it, but also of their progeny, thus opening the way to new hypotheses on the inheritance mechanisms of behavioral traits.

Extending the developmental origins of disease model: Impact of preconception stress exposure on offspring neurodevelopment

The concept of the developmental origins of health and disease via prenatal programming has informed many etiologic models of health and development. Extensive experimental research in non-human animal models has revealed the impact of in utero exposure to stress on fetal development and neurodevelopment later in life. Stress exposure, however, is unlikely to occur de novo following conception, and pregnancy health is not independent of the health of the system prior to conception. For these reasons, the preconception period is emerging as an important new focus for research on adverse birth outcomes and offspring neurodevelopment. In this review, we summarize the existing evidence for the role of preconception stress exposure on pregnancy health and offspring neurodevelopment across species and discuss the implications of this model for addressing health disparities in obstetrics and offspring outcomes.

Effects of Physical Exercise on Cognitive Functioning and Wellbeing: Biological and Psychological Benefits

Much evidence shows that physical exercise (PE) is a strong gene modulator that induces structural and functional changes in the brain, determining enormous benefit on both cognitive functioning and wellbeing. PE is also a protective factor for neurodegeneration. However, it is unclear if such protection is granted through modifications to the biological mechanisms underlying neurodegeneration or through better compensation against attacks. This concise review addresses the biological and psychological positive effects of PE describing the results obtained on brain plasticity and epigenetic mechanisms in animal and human studies, in order to clarify how to maximize the positive effects of PE while avoiding negative consequences, as in the case of exercise addiction.

Coping with Stress During Aging: The Importance of a Resilient Brain

BACKGROUND

Resilience is the ability to achieve a positive outcome when we are in the face of adversity. It supposes an active resistance to adversity by coping mechanisms in which genetic, molecular, neural and environmental factors are involved. Resilience has been usually studied in early ages and few is known about it during aging.

METHODS

In this review, we will address the age-related changes in the brain mechanisms involved in regulating the stress response. Furthermore, using the EE paradigm, we analyse the resilient potential of this intervention and its neurobiological basis. In this case, we will focus on identifying the characteristics of a resilient brain (modifications in HPA structure and function, neurogenesis, specific neuron types, glia, neurotrophic factors, nitric oxide synthase or microRNAs, among others).

RESULTS

The evidence suggests that a healthy lifestyle has a crucial role to promote a resilient brain during aging. Along with the behavioral changes described, a better regulation of HPA axis, enhanced levels of postmitotic type-3 cells or changes in GABAergic neurotransmission are some of the brain mechanisms involved in resilience.

CONCLUSION

Future research should identify different biomarkers that increase the resistance to develop mood disorders and based on this knowledge, develop new potential therapeutic targets.

Effects of pre-reproductive maternal enrichment on maternal care, offspring's play behavior and oxytocinergic neurons

Potentiating social, cognitive, and sensorimotor stimulations the Environmental Enrichment (EE) increases levels of novelty and complexity experienced by individuals. Growing evidence demonstrates that parental EE experience, even occurring in the pre-reproductive phase, affects behavioral and neural developmental trajectories of the offspring. To discover how the accumulation of early maternal complex experiences may inform and shape the social behavior of the following generation, we examined the effects of pre-reproductive enrichment of dams (post-natal days 21-72) on the play performances of their male and female adolescent offspring. Furthermore, we examined the effects of pre-reproductive enrichment on maternal behavior (during post-partum days 1-10) and male intruder aggression (on post-partum day 11). Since oxytocin modulates maternal care, social bonding, and agonistic behavior, the number of oxytocinergic neurons of the paraventricular (PVN) and supraoptic (SON) nuclei was examined in both dams and offspring. Results revealed that enriched females exhibited higher levels of pup-oriented behaviors, especially Crouching, and initiated pup-retrieval more quickly than standard females after the maternal aggression test. Such behavioral peculiarities were accompanied by increased levels of oxytocinergic neurons in PVN and SON. Moreover, pre-reproductive maternal EE cross-generationally influenced the offspring according to sex. Indeed, male pups born to enriched females exhibited a reduced play fighting associated with a higher number of oxytocinergic neurons in SON in comparison to male pups born to standard-housed females. In conclusion, pre-reproductive EE to the mothers affects their maternal care and has a cross-generational impact on the social behavior of their offspring that do not directly experiences EE. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".