The Brown Norway rat displays enhanced stress-induced ACTH reactivity at day 18 after 24-h maternal deprivation at day 3

Maternal regulation of the infant's hypothalamic-pituitary-adrenal axis stress response: Seymour 'Gig' Levine's legacy to neuroendocrinology

Thirty years ago, Seymour 'Gig' Levine published a serendipitous, yet, seminal finding with respect to the regulatory role of maternal presence on the corticosterone stress response of neonatal rats during the developmental period known as the stress hyporesponsive period. At the same time, his group of students also investigated the stress response of infant monkeys with respect to maternal separation, as a means of understanding the stress to the primary caregiver resulting from disruptions of attachment. Gig and his group of students and collaborators, mainly in the USA and the Netherlands, investigated how initial social relationships buffer the stress response of nonhuman primates and rodent infants. His work in rodents involved determining how prolonged deprivation of maternal care disinhibits the stress response of neonates and how maternal behaviours regulate specific aspects of the hypothalamic-pituitary-adrenal axis. Maternal deprivation for 24 hours was useful for determining the importance of nutrition in suppressing the corticosterone stress response, whereas anogenital licking and grooming inhibited stress-induced adrenocortoctrophic hormone release, with the combination of both behaviours preventing the effects of maternal deprivation on the central hypothalamic stress response. Levine's group also studied the consequences of maternal deprivation on basal and stress-induced activity of the hypothalamic-pituitary-adrenal axis in juveniles and the persistent effects of the replacement of maternal behaviours on these parameters. Gig's legacy allowed many groups around the world to use the 24-hour maternal deprivation paradigm as an animal model of vulnerability and resilience to stress-related psychiatric disorders, as well as in studies of the neurobiological underpinnings of disruption of the mother-infant relationship and loss of parental care, a highly prevalent condition in humans. This review pays homage to a great scientist and mentor, whose discoveries paved the way for the understanding of how early social relationsships build resilience or lead to susceptibility to emotional disorders later in life.

The Effects of Maternal Deprivation on the Hippocampal Structure in Adult Rats

Objectives:

To examine the ultrastructural effects of maternal deprivation during developmental periods of limbi-chypothalamo-pituitary-adrenal system on hippocampal dendritic structures in adult rats.

Methods:

The experiments were carried out with male and female wistar rats in our department. The rats were mated and, after birth, the pups were divided into four groups. The first group (control group) pups remained undisturbed with their dam until postweaning day 22. Maternal deprived groups were separated from their dams for 24 hours at postnatal day 4, 9 and 18. The subjects were provided with food and water ad libitum until 3-months-of-age. At the third month, the rats were transcardially perfused, samples were taken from CA1 and CA3 regions of the hippocampus. Tissues were prepared for electron microscopy.

Results:

When the data were analyzed, there were no differences between male and female rats in both ultrastructure and semiquantitative analysis of axodendritic synapses. The ultrastructure of Group 1 was seen as normal while in the second Group some neurons nuclear envelope made deep invagination into the nucleus. Additionally, axodendritic synapses were found normal. In Group 3, micrographs and axodendritic synapses were showed normal structure. However, in Group 4 in some neurons invaginations were seen similar to Group 2. Axodendritic synapses were found to be normal.

Conclusion:

These experiments establish that MD in rats produces slight ultrastructural changes and decreases the number of synapses in CA1 and CA3 subregions of the hippocampus.

Neuroendocrine responses to social isolation and paternal deprivation at different postnatal ages in Mandarin voles

Neonatal isolation and paternal deprivation have long lasting effects on the behavior and neuroendocrine system at adulthood. Whether these effects at adulthood are induced by neonatal changes in relevant neuroendocrine parameters lead by these early-life social experiences is not well understood. Whether monogamous rodents exhibit a stress hypo-responsive period (SHRP) also remains unclear. Using the monogamous mandarin vole, we found that 30 min of isolation did not affect levels of corticosterone (CORT) and adrenocorticotropin (ACTH) at postnatal days 8, 10, and 12 displaying a SHRP, but increased these at postnatal days 4, 14, 16, and 18. Isolation increased vasopressin (AVP)-ir neurons in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) from postnatal days 4 to 12, and up-regulated oxytocin (OT)-ir neurons in the PVN at postnatal days 4 and 8 and SON at postnatal day 4. Paternally deprived pups showed increase in ACTH and CORT after 30 min of social isolation from postnatal days 8 to 14, increase in AVP-ir neurons in the PVN from postnatal days 10 to 14, reduction in OT-ir neurons in the PVN from postnatal days 10 to 14 and in the SON at postnatal days 12 and 14. These results indicate that monogamous mandarin voles display a short SHRP which can be disrupted by paternal deprivation. Central AVP and OT levels may also be altered by paternal deprivation and social isolation. We propose that changes in these neuroendocrine parameters induced by early-life social experiences such as those tested here persist and result.

Animal models of depression and neuroplasticity: assessing drug action in relation to behavior and neurogenesis

Depression is among the most prevalent forms of mental illness and a major cause of morbidity worldwide. Diagnosis of depression is mainly based on symptomatic criteria, and the heterogeneity of the disease suggests that multiple different biological mechanisms may underlie its etiology. Animal models have been important for recent advances in experimental neuroscience, including modeling of human mood disorders, such as depression and anxiety. Over the past few decades, a number of stress and neurobiochemical models have been developed as primary efficacy measures in depression trials, which are paving the way for the discovery of novel therapeutic targets. Recent data indicates that stress-related mood disorders have influence on neuroplasticity and adult neurogenesis. In this chapter, several currently available animal models are presented as powerful tools for both mechanistic studies into the neurobiology of the antidepressant response and for drug discovery.

Early life stress paradigms in rodents: potential animal models of depression?

RATIONALE

While human depressive illness is indeed uniquely human, many of its symptoms may be modeled in rodents. Based on human etiology, the assumption has been made that depression-like behavior in rats and mice can be modulated by some of the powerful early life programming effects that are known to occur after manipulations in the first weeks of life.

OBJECTIVE

Here we review the evidence that is available in literature for early life manipulation as risk factors for the development of depression-like symptoms such as anhedonia, passive coping strategies, and neuroendocrine changes. Early life paradigms that were evaluated include early handling, separation, and deprivation protocols, as well as enriched and impoverished environments. We have also included a small number of stress-related pharmacological models.

RESULTS

We find that for most early life paradigms per se, the actual validity for depression is limited. A number of models have not been tested with respect to classical depression-like behaviors, while in many cases, the outcome of such experiments is variable and depends on strain and additional factors.

CONCLUSION

Because programming effects confer vulnerability rather than disease, a number of paradigms hold promise for usefulness in depression research, in combination with the proper genetic background and adult life challenges.

Brain development under stress: hypotheses of glucocorticoid actions revisited

One of the conundrums in today's stress research is why some individuals flourish and others perish under similar stressful conditions. It is recognized that this individual variability in adaptation to stress depends on the outcome of the interaction of genetic and cognitive/emotional inputs in which glucocorticoid hormones and receptors play a crucial role. Hence one approach towards understanding individual variation in stress coping is how glucocorticoid actions can change from protective to harmful. To address this question we focus on four hypotheses that are connected and not mutual exclusive. First, the classical Glucocorticoid Cascade Hypothesis, in which the inability to cope with chronic stress causes a vicious cycle of excess glucocorticoid and downregulation of glucocorticoid receptors (GR) in the hippocampus triggering a feed-forward cascade of degeneration and disease. Second, the Balance Hypothesis, which takes also the limbic mineralocorticoid receptors (MR) into account and proposes that an integral limbic MR:GR imbalance is causal to altered processing of information in circuits underlying fear, reward, social behaviour and resilience, dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and impairment of behavioural adaptation. The MR:GR balance is altered by gene variants of these receptor complexes and experience-related factors, which can induce lasting epigenetic changes in the expression of these receptors. A particular potent epigenetic stimulus is the maternal environment which is fundamental for the Maternal Mediation Hypothesis. The outcome of perinatal gene x environment interaction, and thus of MR:GR-mediated functions depends however, on the degree of 'matching' with environmental demands in later life. The Predictive Adaptation Hypothesis therefore presents a conceptual framework to examine the role of glucocorticoids in understanding individual phenotypic differences in stress-related behaviours over the lifespan.

Opposite effects of early maternal deprivation on neurogenesis in male versus female rats

Background

Major depression is more prevalent in women than in men. The underlying neurobiological mechanisms are not well understood, but recent data shows that hippocampal volume reductions in depressed women occur only when depression is preceded by an early life stressor. This underlines the potential importance of early life stress, at least in women, for the vulnerability to develop depression. Perinatal stress exposure in rodents affects critical periods of brain development that persistently alter structural, emotional and neuroendocrine parameters in adult offspring. Moreover, stress inhibits adult hippocampal neurogenesis, a form of structural plasticity that has been implicated a.o. in antidepressant action and is highly abundant early postnatally. We here tested the hypothesis that early life stress differentially affects hippocampal structural plasticity in female versus male offspring.

Principal Findings

We show that 24 h of maternal deprivation (MD) at PND3 affects hippocampal structural plasticity at PND21 in a sex-dependent manner. Neurogenesis was significantly increased in male but decreased in female offspring after MD. Since no other structural changes were found in granule cell layer volume, newborn cell survival or proliferation rate, astrocyte number or gliogenesis, this indicates that MD elicits specific changes in subsets of differentiating cells and differentially affects immature neurons. The MD induced sex-specific effects on neurogenesis cannot be explained by differences in maternal care.

Conclusions

Our data shows that early environment has a critical influence on establishing sex differences in neural plasticity and supports the concept that the setpoint for neurogenesis may be determined during perinatal life. It is tempting to speculate that a reduced level of neurogenesis, secondary to early stress exposure, may contribute to maladaptation of the HPA axis and possibly to the increased vulnerability of women to stress-related disorders.

Hypothalamic-pituitary-adrenal axis activity of newborn mice rapidly desensitizes to repeated maternal absence but becomes highly responsive to novelty

In CD1 mice we investigated the hypothalamic-pituitary-adrenal (HPA) axis response to maternal separation for 8 h daily from postnatal d 3 to 5. At d 3 a slow separation-induced corticosterone response developed that peaked after 8 h, and the pups became responsive to stressors. On the second and third day, the response to 8 h separation rapidly attenuated, whereas the response to novelty did not, a pattern reflected by the hypothalamic c-fos mRNA response. If maternal separation and exposure to novelty were combined, then after the third such daily exposure, the sensitivity to the stressor was further enhanced. Meanwhile, basal corticosterone and ACTH levels were persistently suppressed 16 h after pups were reunited with their mothers. To explain the HPA axis desensitization after repeated separation, we found that circulating ghrelin levels increased and glucose levels decreased after all periods of maternal separation, ruling out a role of altered metabolism. Glucocorticoid feedback was not involved either because a glucocorticoid receptor antagonist amplified the corticosterone response after the first but became ineffective after the third separation. In contrast, a mineralocorticoid receptor antagonist decreased and increased corticosterone levels after the first and third period of separation, respectively. In conclusion, the newborn's HPA axis readily desensitizes to repeated daily maternal separation, but continues to respond to novelty in a manner influenced by a central mineralocorticoid receptor- rather than glucocorticoid receptor-mediated mechanism.

Differential development of stress system (re)activity at weaning dependent on time of disruption of maternal care

Maternal deprivation, a separation of mother and pups for 24 h in the first weeks of life has long-lasting consequences for the glucocorticoid stress system in rats. We examined in male CD1 mice whether the postnatal day (pnd) of deprivation determines the (re)activity of the stress system at weaning under basal and novelty stress conditions. Maternal deprivation was only effective when applied within the stress hypo-responsive period (SHRP) between pnds 1 and 12, but not on pnd 13. Maternal deprivation (i) early in the SHRP (pnd 3) resulted in lower hippocampal GR mRNA expression together with a prolonged corticosterone response to stress; while (ii) late in the SHRP (pnd 8) the amplitude of the ACTH response to stress was enhanced. (iii) Strikingly, the effects of the double deprivation (pnds 3 and 8) were not additive: sustained, stress non-responsive high plasma ACTH concentrations with corticosterone indistinguishable from control animals coincided with a lower expression of hippocampal MR and GR mRNA. These results present species-specific effects (mouse versus rat) of an adverse early life event on HPA axis regulation at weaning. A subsequent deprivation experience interferes with the effects of earlier deprivation. We conclude that the developmental stage of the organism determines the vulnerability for the detrimental effects of maternal deprivation and the organization of the stress system in adolescence.

Effects of maternal deprivation of CD1 mice on performance in the water maze and swim stress

Rat pups subjected to a single 24h maternal deprivation show altered stress responsiveness and cognitive performance in the water maze in adulthood. Here we show in 6-month-old male CD1 mice (deprived 24h at postnatal day 8) an initial impairment in reversal learning: relocating the platform revealed perseverance in search for the former location. Spatial learning, long-term memory and swim-induced corticosterone responses were not affected. We conclude that reduced flexibility is a subtle long-lasting behavioural change induced by maternal deprivation.

Maternal deprivation in the early versus late postnatal period differentially affects growth and stress-induced corticosterone responses in adolescent rats

Periodic maternal deprivation (MD) in the early postnatal period leads to permanently altered responsibility of the hypothalamus-pituitary-adrenocortical (HPA) axis to various types of stress. However, no reports appear to have described the effect of periodic MD under different conditions on growth of the developing rat and responsibility of the HPA axis to immobilization stress in adolescent rats. Furthermore, although body weight changes are known to affect stress responsibility, their relationship under periodic MD is not clear. The present study therefore used 4 different types of periodic MD: for 12 h/day from postnatal day (P)1 to P6 (12E group); for 3 h/day from P1 to P6 (3E group); for 12 h/day from P16 to P21 (12L group); and for 3 h/day from P16 to P21 (3L group). Mean body weights were less in the 3E and 12E groups than in the control group until at least 9 weeks old, although body weight gain in the 3L and 12L groups was only transiently affected. Stress-induced corticosterone levels in the 3E and 12E groups did not return to basal levels until at least 330 min after the termination of stress, while temporal variations of stress-induced corticosterone levels did not differ significantly between the 3L, 12L and control groups. Periodic MD in the first postnatal week affected growth of developing rats and responsibility of the HPA axis to immobilization stress in adolescent rats, and the extent of this modification was larger with MD for 12 h/day than with MD for 3 h/day. Conversely, periodic MD from P16 to P21 had little effect. Periodic MD in the postnatal period induces long-term effects on growth and stress responsibility of the HPA axis. Furthermore, a critical age of the pup at the time of MD exists as well as a critical length of MD for inducing these effects.

Early maternal deprivation retards neurodevelopment in Wistar rats

A single 24 h period of maternal deprivation (MD) in rats has been shown to induce, in adulthood, a number of abnormalities in brain and behaviour that also occur in patients with schizophrenia. However, the short-term behavioural effects of MD have not been studied in detail. Since patients with schizophrenia are characterized by a retardation of normal development, we aimed in the present study to investigate the development of control rats and rats that were exposed to MD on postnatal day 9. Compared to control animals, MD rats showed (1) a reduction in body weight, (2) an increased in reversal latency in negative geotaxis, (3) a delayed eye opening, (4) a delayed emergence of walking and rearing; and (5) a delayed emergence of the behavioural response to amphetamine (amph). On the other hand, MD and control rats responded similarly to the non-competitive NMDA antagonist MK801. These data clearly show that early MD delays development, especially of the dopaminergic system and confirm our hypothesis that MD may represent an interesting animal model for the neurodevelopmental hypothesis of schizophrenia.

The impact of early trauma and recent life-events on symptom severity in patients with conversion disorder

Although the presence of psychological stress factors in the evolution of conversion symptoms forms an important criterion for the DSM-IV diagnosis of conversion disorder, little is known about the nature and timing of these stress factors. Fifty-four patients with conversion disorder and 50 control patients with an affective disorder were screened for life events experienced in the year before the symptom onset. Conversion patients did not differ from control patients in the number or severity of life events, but showed a significant relation between the recent life events and the severity of conversion symptoms. Especially life events with respect to work and relationships contributed to this effect. These results remained when controlling for the previously found effects of childhood traumatization on the severity of conversion symptoms. The findings imply that conversion symptoms may be elicited by a complex of early and later negative life events and that traditional unifactorial trauma-theories of conversion disorder should be replaced by multifactorial stress models.

Effect of early life stress on serotonin responses in the hippocampus of young adult rats

In this study, we investigated the effects of early life stress on several aspects of serotonin (5-HT) transmission in hippocampus, later on in life. Three-day-old rats were subjected to 24-hour maternal deprivation or control treatment. Maternal deprivation is known to activate the hypothalamo-pituitary-adrenal axis, resulting in increased corticosterone levels at a time-point in life when the axis is particularly insensitive to most stressful stimuli. When these animals had matured to 3 months of age, functional responses to 5-HT as well as 5-HT1A-receptor mRNA expression were examined. Also, indices for hypothalamo-pituitary-adrenal function were studied in the adult state, including hippocampal mRNA expression for the mineralocorticoid and the glucocorticoid receptor. Resting membrane potential of CA1 pyramidal neurons was significantly depolarized in animals earlier subjected to maternal deprivation compared to the controls. Despite this depolarized resting potential, hyperpolarizing responses induced by 5-HT in CA1 pyramidal neurons from deprived compared to non-deprived rats were attenuated. This attenuation in 5-HT response was not accompanied by changes in mRNA expression of the 5-HT1A-receptor. Maternal deprivation was not found to change any of the neuroendocrine parameters investigated once animals had matured. We conclude that maternal deprivation can alter specific aspects of hippocampal 5-HT transmission later on in life, possibly by post-translational modification of the 5-HT1A-receptor or changes in the 5-HT1A-receptor signal transduction pathway.

Pituitary-adrenal responses to standard and low-dose dexamethasone suppression tests in adult survivors of child abuse

BACKGROUND

Previous studies indicate that adverse childhood events are associated with persistent changes in corticotropin-releasing factor neuronal systems. Our aim was to determine whether altered glucocorticoid feedback mediates the neuroendocrine sequelae of childhood trauma.

METHODS

Standard and low-dose dexamethasone suppression tests (DST) were performed in women with a history of child abuse (n=19), child abuse and major depression (n=16), major depression and no childhood trauma (n=10), and no history of mental illness or childhood trauma (n=19). Secondary analysis with posttraumatic stress disorder (PTSD) as the organizing diagnosis was also conducted.

RESULTS

In the low-dose DST, depressed women with a history of abuse exhibited greater cortisol suppression than any comparator group and greater corticotropin suppression than healthy volunteers or nondepressed abuse survivors. There were no differences between nondepressed abuse survivors and healthy volunteers in the low-dose DST or between any subject groups in the standard DST. The PTSD analysis produced similar results.

CONCLUSIONS

Cortisol supersuppression is evident in psychiatrically ill trauma survivors, but not in nondepressed abuse survivors, indicating that enhanced glucocorticoid feedback is not an invariable consequence of childhood trauma but is more related to the resultant psychiatric illness in traumatized individuals.

Crossroads of corticotropin releasing hormone, corticosteroids and monoamines. About a biological interface between stress and depression

Mental disorders are frequently preceded by stressful events or situations. Depression is a typical case in point. This raises the question, is depression - or possibly better: are certain forms of depression - caused by stress? Can stress be a true pathogenic factor? Phrased differently: can stress destabilize neuronal systems in the central nervous system to such an extent that depressive symptoms are generated? This question is discussed with the corticotrophin releasing hormone (CRH) and MA systems and hypothalamic-pituitary-adrenal (HPA) axis as major foci. The following issues are explored: the effect of antidepressants on corticosteroid receptor gene expression; the behavioral sequellae of CRH administration; CRH disturbances in depression; the impact of early life adversity on the development of the CRH system and on stress reactivity; the interrelationships of stress hormones and monoaminergic (MA ergic) transmission and finally the therapeutic potential of CRH and cortisol antagonists. The available data suggest that CRH overdrive and cortisol overproduction may play a pathogenic role in the occurrence of certain types of depression, directly and/or indirectly, i.e. by induction or exacerbation of disturbances in MA ergic transmission. Stress should, thus, become a major focus of biological depression research.

Correlation between hippocampal BDNF mRNA expression and memory performance in senescent rats

Brain-derived neurotrophic factor (BDNF) has been suggested to be involved in memory processes. In the present study, the association between memory impairment at senescence and BDNF expression in the hippocampus was studied in 30-32-month-old Brown Norway rats, which had been maternally deprived early in life. These animals display a bimodal distribution in their spatial learning ability: rats are either non-impaired or impaired. BDNF mRNA expression in the hippocampus was compared between non-impaired and impaired rats. We measured BDNF mRNA expression in the hippocampus 3 h after training in the Morris water maze ('post-training') and at 1 month after training ('basal'). Non-impaired performers displayed a higher post-training BDNF mRNA level in the CA1 region than impaired rats. In addition, only in the non-impaired performers post-training BDNF mRNA levels in CA1 and dentate gyrus were increased as compared to basal levels. Thus, we have demonstrated that in senescent rats, hippocampal BDNF expression in response to water maze training is associated with memory performance.

Maternal deprivation increases 5-HT(1A) receptor expression in the CA1 and CA3 areas of senescent Brown Norway rats

Maternally-deprived male Brown Norway rats were classified as non-impaired or impaired according to their performance in the water maze when 3 and 30-32 months old. Age and spatial learning ability did not affect the pattern and density of hippocampal 5-HT(1A)-receptor mRNA in mother-reared control rats. However, senescent maternally-deprived rats with impaired spatial learning ability showed increased expression of 5-HT(1A)-receptor mRNA in the hippocampal CA1 (14%) and CA3 (13%) areas but not in the dentate gyrus.

Postnatal maternal deprivation produces long-lasting modifications of the stress response, feeding and stress-related behaviour in the rat

The hypothalamo-pituitary-adrenal (HPA) axis plays a central role both in the regulation of the stress response, and in the control of feeding behaviour. Sensitivity of the HPA axis to respond to stress varies both during ontogeny and between individuals, and can be altered by neonatal events. The aim of our experiments was to determine whether early events that affect the HPA axis could also induce persistent modifications in food intake (quantitatively and qualitatively), as well as alterations of anxiety-related behaviour. Twenty-four-hour maternal deprivation was introduced at two different periods of HPA maturation, on day 5 (DEP5) or day 14 (DEP14) after birth. Sequential measurements of plasma levels of adrenocorticotropin hormone (ACTH) and corticosterone showed that this deprivation altered the HPA axis of adults; the response to restraint stress was prolonged in DEP5 and a higher ACTH peak appeared in DEP14. The neonatal stress also produced long-lasting modifications of rat behaviour, as DEP14 adults became more anxious. Standard food intake decreased in both groups of deprived rats. Diet preferences also changed, as carbohydrate intake decreased in DEP5 rats. Corticosteroid receptor binding did not vary in the hippocampus of the deprived rats. The modifications of the stress response and the behaviour parameters could be due to the alteration of corticosteroid receptors in the hypothalamic paraventricular nucleus and/or corticotropin-releasing hormone or vasopressin function, but these parameters have yet to be determined. This early stress paradigm altering feeding behaviour could become an interesting model for research into human eating disorders.

Biological ageing research in the Netherlands

After an introduction on the development of biological ageing research in the Netherlands during the past decades, 606 papers on aging published by Dutch institutes in the period 1991-2000, collected from PubMed, were analysed for their relevance to research into biological ageing. For the period 1996-2000, the total number of research papers on biological ageing amounted to 142, which accounts for 23% of all publications on ageing in that period. The number of publications per year did not change. On the basis of these papers and additional information provided by research groups a comprehensive overview of biological ageing research in the Netherlands is presented, together with an extensive literature list. Ageing of the central nervous system (CNS), of the endocrinological system and of the cardiovascular system are the topics most studied. It is concluded that general biological ageing research has not increased in the Netherlands over the last ten years, and that the infrastructure for basic biological ageing research in the Netherlands is weak.

Differential and age-dependent effects of maternal deprivation on the hypothalamic-pituitary-adrenal axis of brown norway rats from youth to senescence

In this study, the hypothesis was tested that infants deprived from maternal care show persistent changes in hypothalamic-pituitary-adrenal activity. For this purpose, we studied the effect of maternal deprivation in one cohort of the healthy ageing Brown Norway rat strain showing still more than 80% survival rate at 32 months of age. Three-day-old male Brown Norway rats were either maternally deprived for 24 h or remained with the dam. In 3, 12 and 30-32 months (young, adult, senescent) deprived rats and their nondeprived littermates (controls), we determined basal resting and stress-induced plasma adrenocorticotropic hormone (ACTH) and corticosterone as well as corticotropin releasing hormone (CRH) mRNA expression in the paraventricular nucleus (PVN) of the hypothalamus. Mineralocorticoid (MR) and glucocorticoid receptors (GR) in hippocampus and PVN were also assessed using in vitro cytosol binding and in situ hybridization. The effect of ageing per se showed that in the control nondeprived Brown Norway rats, basal corticosterone and ACTH concentrations did not change during life. However, with age, the corticosterone response to novelty stress became progressively attenuated, but prolonged, while there was an age-related increase in the ACTH response. CRH mRNA expression in PVN decreased with age. Hippocampal MR binding and MR mRNA expression in the dentate gyrus were reduced at senescence, as were the GR binding capacities in hippocampus and hypothalamus. Maternal deprivation did not affect survival rate, body weight, nor adrenal weight of the ageing Brown Norway rats. Basal corticosterone and ACTH levels were not affected by deprivation, except for a rise in basal corticosterone concentrations at 3 months. At this age, the corticosterone output in response to novelty was attenuated in the deprived rats. In contrast, a striking surge in novelty stress-induced corticosterone output occurred at midlife while, at senescence, the corticosterone and ACTH responses were attenuated again in the deprived animals, particularly after the more severe restraint stressor. CRH mRNA expression was reduced only during adulthood in the deprived animals. After maternal deprivation, the MR mRNA in dentate gyrus showed a transient midlife rise. GR binding in hypothalamus and hippocampus GR binding was reduced in young rats while, in the senescent deprived animals, a reduced GRmRNA expression was observed in PVN and hippocampal CA1. In conclusion, in the Brown Norway rat, ageing causes a progressive decline in corticosterone output after stress, which is paralleled at senescence by decreased MR and GR mRNA expression in hippocampus and hypothalamus. The long-term effects of maternal deprivation become manifest differently at different ages and depend on test conditions. The deprivation effect culminates in a midlife corticosterone surge and results at senescence in a strongly reduced corticosterone output.

The role of childhood trauma in the neurobiology of mood and anxiety disorders: preclinical and clinical studies

Epidemiologic studies indicate that children exposed to early adverse experiences are at increased risk for the development of depression, anxiety disorders, or both. Persistent sensitization of central nervous system (CNS) circuits as a consequence of early life stress, which are integrally involved in the regulation of stress and emotion, may represent the underlying biological substrate of an increased vulnerability to subsequent stress as well as to the development of depression and anxiety. A number of preclinical studies suggest that early life stress induces long-lived hyper(re)activity of corticotropin-releasing factor (CRF) systems as well as alterations in other neurotransmitter systems, resulting in increased stress responsiveness. Many of the findings from these preclinical studies are comparable to findings in adult patients with mood and anxiety disorders. Emerging evidence from clinical studies suggests that exposure to early life stress is associated with neurobiological changes in children and adults, which may underlie the increased risk of psychopathology. Current research is focused on strategies to prevent or reverse the detrimental effects of early life stress on the CNS. The identification of the neurobiological substrates of early adverse experience is of paramount importance for the development of novel treatments for children, adolescents, and adults.

Corticotropin-releasing hormone and animal models of anxiety: gene-environment interactions

The study of the neural substrates underlying stress and anxiety has in recent years been enriched by a burgeoning pool of genetic information gathered from rodent studies. Two general approaches have been used to characterize the interaction of genetic and environmental factors in stress regulation: the evaluation of stress-related behavioral and endocrine responses in animals with targeted deletion or overexpression of specific genes and the evaluation of changes in central nervous system gene expression in response to environmental perturbations. We review recent studies that have used molecular biology and genetic engineering techniques such as in situ hybridization, transgenic animal, and antisense oligonucleotide gene-targeting methodologies to characterize the function of corticotropin-releasing hormone (CRH) system genes in stress. The effects of genetic manipulations of each element of the CRH system (CRH, its two receptors, and its binding protein) on stress-related responses are summarized. In addition, the effects of stress (acute, repeated, or developmental) on CRH system gene expression are described. The results from these studies indicate that experimentally engineered or stress-induced dysregulation of gene expression within the CRH system is associated with aberrant responses to environmental contingencies. These results are discussed in the context of how CRH system dysfunction might contribute to stress-related psychopathology and are presented in conjunction with clinical findings of CRH system dysregulation in psychiatric illness. Finally, future research strategies (i.e., high-throughput gene screening and novel gene-targeting methodologies) that may be used to gain a fuller understanding of how CRH system gene expression affects stress-related functioning are discussed.

Maternal deprivation affects behaviour from youth to senescence: amplification of individual differences in spatial learning and memory in senescent Brown Norway rats

Previous studies have shown that deprivation of the infant rat from maternal care has pronounced effects on the stress system during ontogeny. Here we test the hypothesis that 24 h of maternal deprivation at postnatal day 3 will cause persistent changes in behaviour. Spatial learning and memory of male Brown Norway rats deprived as infants were observed in the Morris water maze at 3, 12, 24 and 30-32 months of age (young, adult, aged, senescent). Their nondeprived mother-reared littermates served as controls. (i) With increasing age, water maze performance declined in deprived and nondeprived groups. However, once the task was learned the animals maintained their good performance during retest at later ages. (ii) Maternal deprivation delayed acquisition until adulthood and caused at every age a higher degree of persistent behaviour as judged from the performance of deprived rats' free swim trials and reversal trials. (iii) At senescence the mean performance in the water maze did not differ between the groups. Instead, the individual performance was strikingly different within each group. Senescent deprived rats were either nonimpaired or impaired with only a few animals showing an intermediate performance. Thus, a large group of animals ( approximately 40%) ages successfully as they are resistant to the effect of maternal deprivation. In contrast, the majority of the control animals displayed intermediate performance. Taken together, maternal deprivation has life-long consequences for behaviour and culminates at senescence in amplification of individual differences in learning ability rather than in a generalized deterioration of cognitive functions.

The impact of early adverse experiences on brain systems involved in the pathophysiology of anxiety and affective disorders

The relative contribution of genetic and environmental factors to the development of the major psychiatric disorders has long been debated. Recently, considerable attention has been given to the observations that adverse experiences early in life predispose individuals to the development of affective and anxiety disorders in adulthood. Corticotropin-releasing factor (CRF) is the central coordinator of the endocrinologic, autonomic, immunologic, and behavioral stress responses. When centrally administered, CRF produces many physiologic and behavioral changes reminiscent of both acute stress and depression. Moreover, CRF has also been implicated in the pathogenesis of a variety of anxiety disorders, mainly through CRF neurocircuits connecting the amygdala and the locus ceruleus. Clinical studies have provided convincing evidence for central CRF hypersecretion in depression, and, to a lesser extent, in some anxiety disorders. Evidence mainly from preclinical studies suggests that stress early in life results in persistent central CRF hyperactivity and increased stress reactivity in adulthood. Thus, genetic disposition coupled with early stress in critical phases of development may result in a phenotype that is neurobiologically vulnerable to stress and may lower an individual's threshold for developing depression and anxiety upon further stress exposure. This pathophysiologic model may provide novel approaches to the prevention and treatment of psychopathology associated with stress early in life.

Early stress and genetic influences on hypothalamic-pituitary-adrenal axis functioning in adulthood

During early development, environmental challenges set the stage for permanent changes in the functioning of the pituitary-adrenal stress response. Since these data have been reported almost exclusively in single rat strains the role of phenotypic and genotypic factors in shaping the stress response is relatively unknown. This study examined whether the phenotypic/genetic profile of the rat influences the long-term response to challenge after early exposure to stress. Two strains of Sprague-Dawley rats were used in this study: one is a stress-induced animal model of "learned helpless" (LH) behavior and the other a resistant strain developed through selective breeding. Stress-induced adrenocorticotropic hormone (ACTH) and corticosterone release was monitored in adult congenital learned helpless (cLH) rats and congenital non-learned helpless (cNLH) rats. The rats were exposed to cold stress or maternal deprivation (on either postnatal day 7 or day 21). After the early acute stress exposure, animals remained undisturbed until challenged in adulthood (day 90) with footshock stress. In cLH animals (adults) early cold stress (particularly after acute stress on postnatal day 21) and maternal deprivation stress resulted in an enhancement of stress-induced ACTH release compared to nonstressed cLH and cNLH controls. In contrast, adrenal responsiveness was generally suppressed in cLH animals that were acutely stressed with cold stress or maternal deprivation stress early in life. The above results suggest that the genetic/phenotypic profile of the animal is a determinant in the changes observed in the adult stress response after early exposure to stressors.

Persistent effects of maternal deprivation on HPA regulation can be reversed by feeding and stroking, but not by dexamethasone

Maternal deprivation of neonatal rats for 24 h has immediate and persistent effects on hypothalamic-pituitary-adrenal (HPA) regulation. Immediately after deprivation corticosterone (CORT) is elevated. The primary purpose of our experiments was to determine if, by preventing this CORT elevation, the persistent effects could be reversed. In experiment 1, pups were injected with dexamethasone at the onset of the 24-h deprivation period on postnatal day 11 to suppress the rise in CORT. In experiment 2 some aspects of maternal behaviour known to suppress CORT levels were mimicked during deprivation from postnatal days 11-12. The pups were either: (1) left undisturbed; (2) stroked periodically; or (3) stroked and episodically fed. At postnatal day 20 basal and stress-induced adrenocorticotrophic hormone (ACTH) and CORT levels were measured as well as brain mineralocorticoid (MR) and glucocorticoid receptors (GR). Neonatal rats receiving dexamethasone prior to the onset of the deprivation on day 11 did not differ on day 20 from deprived pups that were exposed to elevated CORT levels. There were no detectable changes in the non-deprived pups that were treated with dexamethasone. In contrast, feeding and stroking during the period of deprivation obliterated the persistent effects both with regard to the reduced ACTH response and the decreased GR mRNA in hippocampus and hypothalamus. Stroking alone appears to have no influence. In conclusion, the persistent reduction of the ACTH response to mild stress and the decrease of GR mRNA is not mediated by deprivation-induced elevations in CORT, but appears to be reversible by reinstating specific aspects of the dam's nurturing behaviour.

Early vs. late maternal deprivation differentially alters the endocrine and hypothalamic responses to stress

Twenty-four hours of maternal deprivation results in persistent changes in the ACTH response to mild stress. These effects are dependent on the age of the neonate at the time of deprivation. Pups that were separated from the dam at postnatal days (pnd) 3-4 showed an enhanced stress-induced ACTH response at age 20, while pups deprived at pnd 11-12 displayed an attenuated ACTH response to stress at that time. The present study was designed to test the hypothesis that the immediate effects of deprivation at pnd 3 vs. pnd 11 would provide an explanation for these paradoxical effects observed at day 20. For this purpose, we measured the basal and the stress-induced ACTH and corticosterone (CORT) response at days 4 and 12, following 24 h of maternal deprivation. Furthermore, we examined whether similar differences in c-fos and CRH mRNA expression in the paraventricular nucleus (PVN) accompanied the differences in response characteristics of ACTH at pnd 20. The results indicate that changes in the ACTH and CORT responses were minimal after 24 h of maternal deprivation at day 4, whereas these hormones were markedly elevated following deprivation at day 12. The persistent effects also showed age-dependency: pups deprived early showed at pnd 20 an exaggerated ACTH response. Late deprived juveniles exhibited an attenuated ACTH response to stress at pnd 20 while in both conditions the CORT response was not different from the non-deprived litter mates. These persistent endocrine changes were accompanied by the changes in the neural stress markers. The expressions of c-fos and CRH mRNA in the PVN were at pnd 20 significantly greater in their controls in early-deprived animals. The late deprived juveniles showed a reduced response in these neural markers. In conclusion, the persistent alterations in ACTH are reflected by changes in c-fos and CRH mRNA, but these changes in endocrine and in neural stress markers do not appear to be related to any of the hormonal changes that occur at the time of maternal deprivation.