Depression involves multiple mental problems, including low mood, inability to experience pleasure and emotional, cognitive and behavioral problems. It has a lifetime prevalence of ~15% in the... Show moreDepression involves multiple mental problems, including low mood, inability to experience pleasure and emotional, cognitive and behavioral problems. It has a lifetime prevalence of ~15% in the Dutch population, striking women twice as often as men. The disorder often comprises persisting disturbances in the neuroendocrine stress system, the hypothalamic- pituitary-adrenal (HPA) axis, including disregulation of its end-hormone cortisol. Cortisol normally stimulates emotional, cognitive and behavioral processes in order to cope with a stressor and promotes recovery, learning and memory. This thesis describes the identification of a specific genetic variant of the mineralocorticoid receptor (MR), one of the two receptors for cortisol, which protects against depression. MR transcript expression was found to be lower in postmortem limbic brain regions of depressed patients compared to non-depressed subjects. In addition, a specific and common MR gene variant was identified that results in higher MR expression in vitro. This same variant was found to associate with personality characteristics that predict the risk of depression later in life and with a lower risk of depression itself. All associations were found only in women and not in men. To conclude, the MR is an important determinant of resilience; increased MR expression seems to be protective against depression. Show less
Schizophrenia is a devastating mental disorder characterized by a hyperactive dopamine system and deregulated stress system. Human studies have suggested that the schizophrenia symptoms precipitate... Show moreSchizophrenia is a devastating mental disorder characterized by a hyperactive dopamine system and deregulated stress system. Human studies have suggested that the schizophrenia symptoms precipitate if a hyperactive dopaminergic genotype interacts with adverse life experiences that activate the stress system. To examine this gene-by-environment interaction, we exposed rats genetically-selected for enhanced apomorphine susceptibility to two stress-provoking life events, poor maternal care early-in-life, and isolation rearing later-in-life. This promoted the development of schizophrenia endophenotypes. Our experiments involved two complementary steps: First, we focused on the immediate endocrine adaptations to maternal separation in common rats. It is known that a single episode of prolonged maternal separation slowly increases corticosterone levels in the neonate rat. We discovered that if the pups had been previously exposed to maternal separation, this rise in corticosterone was abolished, suggesting that the pups had learned to predict the return of the dam. While readily adapting to repeated maternal absence, the pups, surprisingly, stayed alert and displayed a rapid response to an acute stressor. We then investigated whether pup__s stress responsiveness was influenced by the context of maternal separation. It appeared that the experience of being kept in isolation in a novel environment during repeated maternal separation, rather than the maternal absence per se, caused priming of the amygdala fear pathway, with lasting consequences for the responsiveness of the neuroendocrine and behavioral stress system. These endocrine and behavioral alterations, caused by early-life stress experience, consisted of schizophrenia-like phenotypes. Second, we sought to investigate the interplay of such early-life stress experience with schizophrenia genetic predisposition and/or later-life social stress experience. Thus, we were able to test the three-hit (cumulative stress) and the developmental mismatch hypotheses. The former states that exposure to earlylife adversity and later-life psychosocial stressors, superimposed on genetic susceptibility, result in a severe schizophrenia-like phenotype. The latter proposes that experiences early-in-life program the developing brain in preparation for the future. In the case of genetically-predisposed apomorphine susceptible rats (schizophrenia-susceptible), we provide strong evidence for the three-hit hypothesis. In the case of the nongenetically selected Wistar rats, the mismatch hypothesis is supported since the outcome of early-life stress often negatively interacted with the pre-puberty social context. In agreement with the three-hit hypothesis of schizophrenia, we conclude from the current experiments that early-life stress experience in interaction with highly reactive dopaminergic alleles, leads to amygdala priming that, together with additional stressors, precipitate schizophrenia. Show less
Recent studies have suggested that the fetus is capable of exhibiting a stress response to intrauterine needling, resulting in alterations in fetal stress hormone levels. Intrauterine transfusions... Show moreRecent studies have suggested that the fetus is capable of exhibiting a stress response to intrauterine needling, resulting in alterations in fetal stress hormone levels. Intrauterine transfusions are performed by inserting a needle either in the umbilical cord root at the placental surface (PCI), or in the intrahepatic portion of the umbilical vein (IHV). Aim of our study was to test the hypothesis that fetal hormonal changes during intrauterine transfusion are more pronounced when the needle is inserted in the fetal abdomen. Furthermore we aimed to evaluate the effect of fetal analgesia with remifentanil on the fetal stress hormone changes. Exploring the hemodynamic changes following a noxious stimulus, we saw no differences in transfusions through the IHV or the PCI. Remifentanil did not influence the stress hormone changes. We concluded that the stress hormone changes are independent of both site of transfusion and the use of remifentanil. Our results do not confirm nor deny that the fetus is capable to react to a potential painful stimulus, or to show signs of stress or even pain. However, previous research has suggested that presumably painful fetal conditions can lead to alterations in stress reactions after birth. This phenomenon is called ‘fetal programming’. Fetal programming could possibly lead to life-long changes in stress responses and even to increased susceptibility for certain diseases. With the current understanding of fetal pain and fetal analgesia we would advocate the following: 1. Fetal analgesia for invasive procedures should be provided from at least 20 weeks gestation onwards 2. All invasive fetal procedures warrant fetal analgesia, but in procedures involving more than just a single puncture with a thin needle it is obligatory. 3. Analgesics should be given intravenously to the mother. The drug of choice should be ultra-short working (like remifentanil) therefore minimising possible undesirable side-effects to both fetus and mother. Show less
Human epidemiology and animal studies have convincingly shown the long-lasting impact of early life experiences on the development of individual differences in stress responsiveness in later life.... Show moreHuman epidemiology and animal studies have convincingly shown the long-lasting impact of early life experiences on the development of individual differences in stress responsiveness in later life. The interplay between genes and environment underlies this phenomenon.We provide an overview of studies investigating the impact of early life experiences on the development of individual differences in neuroendocrine stress responsiveness in adulthood and address (1) impact of environment on later stress phenotypes, (2) role of genetic factors in modulating the outcome of environment, and (3) role of nonshared environmental experience in the outcome of gene x environment interplays. We present original findings where we investigated the influence of nonshared experiences in terms of individual differences in maternal care received, on the development of stress phenotype in later life in rats.Environmental influences in early life exert powerful effects on later stress phenotypes, but they do not always lead to expression of diseases. Heterogeneity in response is explained by the role of particular genetic factors in modulating the influence of environment. Nonshared experiences are important in the outcome of gene x environment interplays in humans. We show that nonshared experiences acquired through within-litter variation in maternal care in rats predict the stress phenotype of the offspring.The outcome of early experience is not deterministic and depends on several environmental and genetic factors interacting in an intricate manner to support stress adaptation. The degree of "match" and "mismatch" between early and later life environments predicts resilience and vulnerability to stress-related diseases, respectively. Show less
