Effects of stress during pregnancy and lactation on offspring

A line of research is delving in a revealing way into the effects of maternal stress during pregnancy and breastfeeding on her sons or daughters.

The work has been carried out for more than two decades in the Perinatal Neurodevelopmental Programming laboratory coordinated by Marta Antonelli, a researcher at the National Scientific and Technical Research Council (CONICET) at the “Professor Eduardo De Robertis” Institute of Cellular Biology and Neurosciences (IBCN, dependent on CONICET and the University of Buenos Aires (UBA)).

Antonelli and his colleagues study prenatal stress and its effects on offspring at the behavioural and molecular level, based on tests with animal models.

More recently, they have begun to conduct studies on humans (based on a project with colleagues in Germany) while also starting to work on a new model of early stress linked to child abuse. The aim of this research is to design preventive strategies focused on mitigating or reversing the negative effects that maternal stress during pregnancy and lactation can have on children.

“By working on mouse models, specifically rats, we were able to prove that if mothers are subjected to stressful situations during pregnancy, over time these crystallize into deleterious effects on the offspring, which can be detected both at a behavioral and biochemical level, through different molecular markers,” explains Antonelli.

The method used to stress the mothers is what is called “movement restriction”, in which the pregnant mother is placed in an acrylic tube on days 14 to 21 of gestation. This limitation of movement produces chronic stress in the mother, which influences the offspring during gestation and then also during the lactation stage.

They have also tested reversal strategies, which involve raising the offspring of stressed mothers during pregnancy by non-stressed mothers (cross-fostering). They observed that these offspring did not develop the same symptoms as those raised by stressed mothers.

“This confirmed to us that, beyond the effects that maternal stress has on offspring in utero, one of the keys to understanding the effects of maternal stress on offspring lies in the bond that mothers establish with their offspring during breastfeeding,” says Antonelli.

Towards the study of child abuse

The verification, through various tests in experimental models, of the importance of the bond between mothers and offspring during the lactation stage, led the team led by Antonelli to investigate the effects of child abuse using the model of “environmental impoverishment”, which consists, fundamentally, in reducing the amount of resources that the mother has available for nest construction. This task is undertaken by Jazmín Grillo Balboa and Ailén Colapietro, both CONICET doctoral fellows at the IBCN under the direction of Antonelli and with the co-direction of Mariela Chertoff and Silvina Diaz.

Jazmín Grillo Balboa joined the laboratory in 2018, when she was still studying for a degree in Biology, to work on prenatal stress. At the beginning of her doctoral fellowship, she began to develop a model of child abuse in rats under the direction of María Eugenia Pallarés. “What we wanted to do was explore another type of stress in early life and see how it affects the infant throughout their life. My line of research focuses on studying how anxiety behaviors emerge during adulthood in animals abused in childhood,” says the fellow.

According to Antonelli, reducing the size of the nest causes mothers to become stressed and unable to care for their offspring properly, which leads to more fragmented and violent behaviour towards their offspring: “They shake them, do not pay attention to them and spend less time nursing. This has important neurobehavioral consequences for the offspring,” says the researcher.

Grillo Balboa’s doctoral thesis project also aims to observe what happens in certain areas of the mother’s brain, linked to maternal behavior, when they are stressed; a phenomenon that has been little investigated so far. This task is carried out in collaboration with Chertoff, a CONICET researcher at the Institute of Biological Chemistry of the Faculty of Exact and Natural Sciences (IQUIBICEN, CONICET-UBA) and an expert in early adversities, as well as in molecular and epigenetic techniques.

Chertoff works with mouse models of early malnutrition. “In these models we see some consequences very similar to those observed in prenatal stress, such as increased anxiety and depression in the offspring. Based on this situation, what we do is use an enriched environment strategy to lower and improve anxiety levels and we see that behaviors normalize in those animals that suffered malnutrition during development. In adulthood, many of the behaviors approach normal, after having been in an enriched environment, which is an environment in which they have more space, greater social interaction and more opportunity to play. The changes observed at the behavioral level also have a correlation at the molecular level,” says Chertoff.

Colapietro’s doctoral project focuses on understanding the effects of stress from child abuse on the generation of new neurons in the dentate gyrus of the hippocampus, which is the brain structure associated with depression, in juvenile rats.

“The objective of my doctoral project is to see the effects of the child abuse model on offspring during the juvenile or prepubertal stage, because it is an early stage of development, equivalent to childhood in humans, which has been little explored. The idea is to characterize at a molecular, biochemical and behavioral level what happens in offspring who suffered child abuse. The intention, in the future, is to provide more information to be able to develop interventions before the onset of psychopathologies in adulthood,” says Colapietro.

Silvina Diaz, co-director of Colapietro, CONICET researcher at the Institute of Biosciences, Biotechnology and Translational Biology (IB3, FCEN, UBA) and specialist in experimental neurogenesis, stresses that for this type of research it is essential to build models, tests or paradigms that work well in animals and that can represent similar situations in humans, “although it will never be the same.” These are tools that must be refined and adapted -continues the researcher-. The nest for rats is critical for good lactation; having a good nest is synonymous with being able to protect their offspring, with feeling safe. If you want to transfer the study to humans you have to look for the parallel, which obviously has nothing to do with the size of the ‘nest’ but with other factors.” In this sense, Diaz highlights the studies that Antonelli carries out with humans in Germany: “It is important to reach the study with people, given that it is often difficult to see the applicability of what we investigate in laboratories in animal models. Researching with clinical patients closes the circle.”

Jasmine Grillo Balboa works at the microscope, while Ailen Colapietro discusses the results with Marta Antonelli. (Photo: CONICET / Andres De Angelis. CC BY 2.5 AR)

Clinical experiences in prenatal stress in Germany

Antonelli also made progress in conducting clinical studies on prenatal stress: “The goal was always to develop ways to prevent the repercussions that maternal stress can have on children, so it was necessary to see what happened in humans,” says the scientist.

To this end, Antonelli contacted a group of colleagues from Germany, who work at a hospital affiliated with the Technical University of Munich (TUM).

The study involved a group of pregnant mothers who gave their consent to participate in the research. Based on a ten-question test, they were divided between stressed and non-stressed. Once this distinction was established, analyses were carried out to determine the state of the autonomic nervous system, while hair samples were taken to measure cortisol levels (a hormone released in response to stress). This analysis was carried out by Bibiana Fabre, from the Department of Endocrinology at the Hospital de Clínicas of the University of Buenos Aires. Once the child was born, a saliva sample was taken to perform epigenetic studies.

“After two years, we called them back together and gave the child the Baileys test, which assesses their cognitive, motor and linguistic development. At the same time, we took a new saliva sample, with the aim of measuring DNA methylation levels, which is an epigenetic marker of gene modulation. In the comparison, we found alterations in the children of stressed mothers that did not appear in the children of mothers who had not shown signs of stress during pregnancy,” she says.

Epigenetics refers to hereditary changes, the result of interaction with the environment, which do not involve alterations in the DNA sequence but rather behave as chemical marks that can activate or silence certain genes. In this case, the research seeks to understand what changes produced in mothers by stressful situations can be inherited by their children.

A preventive project is currently underway in Germany in which stressed mothers are enrolled in a yoga and meditation programme, with the aim of preventing this stress from affecting their children.

It is estimated that approximately 22 to 25 percent of pregnant women suffer from some type of stress. This is a very high figure. Being able to provide new prevention methods will help to build a healthier society, as Antonelli points out. (Source: Miguel Faigón / CONICET). CC BY 2.5 AR)