Sleep in prenatally restraint stressed rats, a model of mixed anxiety-depressive disorder

Animal models of maternal depression for monitoring neurodevelopmental changes occurring in dams and offspring

Depression is one of the most prevalent and life-threatening forms of mental illness affecting about 20% of the population. Depressive disorder as a biochemical phenomenon, was first recognized in the mid-20^th century of research, however the etiology of this disease is still not well understood. Although the need to investigate depressive disorders has emerged from the needs of clinical practice, there are many preclinical studies, which brought new insights into this field of research. During experimental work it was crucial to develop appropriate animal models, where the neurohumoral mechanism was similar to humans. In the past decades, several animal models of maternal depression have been developed. We describe the three most popular rodent models of maternal depression which are based on 1. stress prior to gestation, 2. prenatal stress and 3. early life stress. The above-mentioned animal models appear to fulfill many criteria for a relevant animal model of depression; they alter the regulation of the HPA, induce signs of depression-like behavior and several antidepressant treatments can reverse the state induced by maternal stress. Although, they are not able to model all aspects of maternal depression, they are useful models for monitoring neurodevelopmental changes occurring in dams and offspring.

Perinatal Programming of Circadian Clock-Stress Crosstalk

An intact communication between circadian clocks and the stress system is important for maintaining physiological homeostasis under resting conditions and in response to external stimuli. There is accumulating evidence for a reciprocal interaction between both-from the systemic to the molecular level. Disruption of this interaction by external factors such as shiftwork, jetlag, or chronic stress increases the risk of developing metabolic, immune, or mood disorders. From experiments in rodents, we know that both systems maturate during the perinatal period. During that time, exogenous factors such as stress or alterations in the external photoperiod may critically affect-or program-physiological functions later in life. This developmental programming process has been attributed to maternal stress signals reaching the embryo, which lastingly change gene expression through the induction of epigenetic mechanisms. Despite the well-known function of the adult circadian system in temporal coordination of physiology and behavior, the role of maternal and embryonic circadian clocks during pregnancy and postnatal development is still poorly defined. A better understanding of the circadian-stress crosstalk at different periods of development may help to improve stress resistance and devise preventive and therapeutic strategies against chronic stress-associated disorders.

Sleep patterning changes in a prenatal stress model of depression

Clinical depression is accompanied by changes in sleep patterning, which is controlled in a circadian fashion. It is thus desirable that animal models of depression mirror such diurnally-specific state alterations, along with other behavioral and physiological changes. We previously found several changes in behavior indicative of a depression-like phenotype in offspring of rats subjected to repeated, variable prenatal stress (PNS), including increased locomotor activity during specific periods of the circadian cycle. We, therefore, investigated whether PNS rats also exhibit alterations in sleep/wakefulness behavior around the change from light-to-dark phase. Control and PNS Sprague-Dawley rats were implanted with electrodes for continuous monitoring of electroencephalic activity used to determine behavioral state. The distribution of slow-wave sleep (SWS), rapid eye movement sleep (REMS) and wakefulness was compared for periods before and after lights were turned off, between baseline conditions and after exposure to an acute stressor. Both REMS and SWS amounts were increased in PNS rats relative to control animals in the beginning of the dark phase. REMS changes were due to an increase in REMS bout number, rather than in bout duration. During this circadian time period, we did not find any sex differences in the state changes. These results indicate that PNS affects baseline sleep patterning in both male and female rats around active-phase onset.

Early-life experiences and the development of adult diseases with a focus on mental illness: The Human Birth Theory

In mammals, early adverse experiences, including mother-pup interactions, shape the response of an individual to chronic stress or to stress-related diseases during adult life. This has led to the elaboration of the theory of the developmental origins of health and disease, in particular adult diseases such as cardiovascular and metabolic disorders. In addition, in humans, as stated by Massimo Fagioli's Human Birth Theory, birth is healthy and equal for all individuals, so that mental illness develop exclusively in the postnatal period because of the quality of the relationship in the first year of life. Thus, this review focuses on the importance of programming during the early developmental period on the manifestation of adult diseases in both animal models and humans. Considering the obvious differences between animals and humans we cannot systematically move from animal models to humans. Consequently, in the first part of this review, we will discuss how animal models can be used to dissect the influence of adverse events occurring during the prenatal and postnatal periods on the developmental trajectories of the offspring, and in the second part, we will discuss the role of postnatal critical periods on the development of mental diseases in humans. Epigenetic mechanisms that cause reversible modifications in gene expression, driving the development of a pathological phenotype in response to a negative early postnatal environment, may lie at the core of this programming, thereby providing potential new therapeutic targets. The concept of the Human Birth Theory leads to a comprehension of the mental illness as a pathology of the human relationship immediately after birth and during the first year of life.

Transgenerational Transmission of Stress Pathology

Abstract. The impact of the environment early in life on long-term outcomes is well known. Stressful experiences during pre- and postnatal development can modulate the genetic programming of specific brain circuits underlying emotional and cognitive aspects of behavioral adaptation to stressful experiences later in life. Furthermore, there is documented evidence for gene-environment interactions in the context of early-life stress. Identical gene variants can be associated with different phenotypes depending on environmental factors. DNA methylation, an enzymatically-catalyzed modification of the DNA, is the mechanism through which phenotypes are regulated. The dynamics and plasticity of epigenetic mechanisms can have short-term, long-term, or transgenerational consequences. In epigenetic research, rodent models have targeted several behavioral and emotional phenotypes. These models have contributed significantly to our understanding of the environmental regulation of the developmental brain in early life. This review will highlight studies with rats and mice on epigenetic processes in fetal programming of stress-related mental disorders.