Do early-life events permanently alter behavioral and hormonal responses to stressors?

Chronic stress during prepubertal development: immediate and long-lasting effects on arterial blood pressure and anxiety-related behavior

The present work was undertaken to study the immediate and long-lasting effects of environmental stress during prepubertal life in rats with inherited stress-induced arterial hypertension (ISIAH) and normotensive Wistar rats on blood pressure (BP) levels and anxiety-related behavior. Two models of chronic stress (21-32 postnatal days) were used: repeated handling (HS) and unpredictable stress (US) of daily exposures to a variety of mild physical or psychoemotional stressors. Rats were tested just after the end of the chronic stress period and then at the age of 4 months. Chronic prepubertal stress did not affect the basal or stress-induced BP levels in young or adult Wistar rats. In ISIAH rats, chronic stress during the early phase of hypertension development did not accelerate its formation and did not augment its manifestation in adults. Moreover, the basal BP was decreased in young and adult ISIAH rats exposed to HS or US as compared to the age-matched controls. No long-lasting effect on BP elevation under acute stress in adults was found. Plasma corticosterone levels at resting and acute stress conditions were not changed in adult rats that had experienced prepubertal stress. Hypertensive rats proved to be less anxious in the elevated plus-maze test. The immediate effects of chronic stress were similar in the two rat strains: HS had an anxiolytic action while US stimulated anxiety. Long-lasting consequences depended on the rat strain: the anxiolytic effect of HS was retained in Wistar rats and US caused a greater anxiety in adult ISIAH rats. The data do not evidence that symptoms of anxiety are related to the development and maintenance of stress-sensitive arterial hypertension in ISIAH rats.

Developmental neurobiology of childhood stress and trauma

Severe early stress and maltreatment produces a cascade of events that have the potential to alter brain development. The first stage of the cascade involves the stress-induced programming of the glucocorticoid, noradrenergic, and vasopressin-oxytocin stress response systems to augment stress responses. These neurohumors then produce effects on neurogenesis, synaptic overproduction and pruning, and myelination during specific sensitive periods. Major consequences include reduced size of the mid-portions of the corpus callosum; attenuated development of the left neocortex, hippocampus, and amygdala along with abnormal frontotemporal electrical activity; and reduced functional activity of the cerebellar vermis. These alterations, in turn, provide the neurobiological framework through which early abuse increases the risk of developing post-traumatic stress disorder (PTSD), depression, symptoms of attention-deficit/hyperactivity, borderline personality disorder, dissociative identity disorder, and substance abuse.

Inactivation of the GR in the nervous system affects energy accumulation

The homeostatic regulation of body weight protects the organism from the negative consequences of starvation and obesity. Glucocorticoids (GCs) modulate this regulation, although the underlying mechanisms remain unclear. To address the role of central GRs in the regulation of energy balance, we studied mice in which GRs have selectively been inactivated in the nervous system. Mutant mice display marked growth retardation. During suckling age this is associated with normal fat deposition causing a 60% temporary increase of percent body fat, compared with control littermates. After weaning, fat and protein depositions are reduced so that adults are both smaller and leaner than their controls. Decreased food intake and, after weaning, reduced metabolic efficiency account for these developmental disturbances. Plasma levels of leptin and insulin, two important energy balance regulators, are elevated in young mutants but normal in adults. Leptin/body fat ratio is higher at all ages, suggesting disturbed control of circulating leptin as a consequence of chronically elevated GC levels in mutant animals. Adult mutants display increased hypothalamic CRH and NPY levels, but peptide levels of melanin concentrating hormone and Orexin A and B are unchanged. The increased levels of plasma GCs and hypothalamic CRH may act as catabolic signals most likely leading to persistently reduced energy accumulation.

Gene-environment interplay in relation to emotional and behavioral disturbance

The conceptual and methodological issues involved in the study of gene-environment correlations (rGE) and interactions (GxE) are discussed in historical context. Quantitative genetic findings are considered with respect to rGE and GxE in relation to emotional and behavioral disturbance. Key conceptual and substantive implications are outlined in relation to both genetic and environmental risk mediation, with a brief note on evolutionary considerations.

Adrenocorticotropin and cortisol responses to a naloxone challenge and risk of alcoholism

BACKGROUND

Because abnormalities in opioid neurotransmission appear to underlie some of the inherited risk for alcoholism, we examined the effects of naloxone, an opioid antagonist, on corticotropin and cortisol responses in nonalcoholic subjects differentiated by paternal history of alcoholism.

METHODS

Placebo-controlled, balanced, within-subject design involving 2 test days over a period of 3 to 7 days. Thirty-six subjects (67% male; 53% paternal-history-positive; mean age = 25.0 years) were screened to exclude substance abuse or dependence. Subjects received intravenous naloxone 125 microg/kg or placebo, with sessions in random order. Plasma corticotropin and cortisol were measured for up to 120 min post infusion.

RESULTS

Corticotropin responses at baseline and following naloxone did not differ by paternal history of alcoholism; however, paternal-history-positive subjects exhibited greater cortisol concentrations at baseline, and at 15 and 30 min after naloxone administration. Paternal-history-positive subjects also had an earlier and greater peak cortisol response to naloxone and a nonsignificant trend for a greater area under the cortisol time curve than paternal-history-negative subjects.

CONCLUSIONS

These findings suggest that individuals with greater vulnerability to alcoholism may have altered Hypothalamic-pituitary axis (HPA) dynamics, a finding that is consistent with a growing body of data on the role of opioidergic neurotransmission in the inherited risk of alcoholism.

The influence of handling and isolation postweaning on open field, exploratory and maternal behavior of female rats

Fifty-three black-hooded female rats, raised from the 28th to the 128th day of life under four types of environmental conditions differing in social and handling factors, had their behavioral performance evaluated in eight tests involving exploration of a complex environment (EX) in two open field (OF) tests and in three pup-retrieving tests. These tests were held before, during and after the period of lactation of their first brood. Females differed from (previously studied) males in that environmental raising conditions had a much smaller influence, especially during the lactation period. Nevertheless, females raised in isolation tended to remain for longer times inside a protected den in the exploration tests and to have greater locomotion in the open field. Previous handling allowed a greater exploration during the first contact with the novel complex environment as well as greater activity in the open field. The presence of small pups drastically reduced the exploratory motivation, but the presence of pups more than 20 days old tended to increase it. Maternal behavior evaluated in the pup retrieval test and in the test of time for the female to leave the nest side of the double box system was markedly refractory to previous environmental influences.

Maternal behavior in F344/N and LEW/N rats. Effects on carrageenan-induced inflammatory reactivity and body weight

Inbred Fischer (F344/N) and Lewis (LEW/N) rats differ on a myriad of behavioral and physiological endpoints, such as inflammatory, startle and drug responsivity. These differences point to underlying genetic differences between the strains. However, genetic models of hypertension have shown the importance of the maternal environment in the development of high blood pressure, suggesting that maternal influences might also play a role in adult phenotypes of the LEW/N and F344/N strains. This was tested in the present series of experiments in which the effects of crossfostering on carrageenan-induced inflammation and on body weight were examined in the two strains. Following the demonstration that the two strains differed in maternal behavior (Experiment 1), which was independent of the pup being reared (Experiment 2), crossfostered and in-fostered pups from the LEW/N and F344/N strains were injected with carrageenan (at 60 days of age) and subsequently assessed for the accumulation of exudate in response to the injection. Body weights were also monitored from birth through 60 days of age. Although crossfostering affected body weight of the two strains, specifically, reducing weights in LEW/N pups reared by F344/N dams and increasing weights of F344/N pups reared by LEW/N dams, crossfostering did not affect inflammatory reactivity to carrageenan. Specifically, LEW/N pups had a greater level of exudate than F344/N pups, independent of the conditions under which they were reared, suggesting that differences in the inflammatory response between these two strains are under a high degree of genetic control. These results were discussed in terms of genetic factors mediating the early form of immune reactivity induced by carrageenan.

Salivary cortisol concentrations before and after carbon-dioxide inhalations in children

BACKGROUND

Considerable research implicates over-activity of the hypothalamic-pituitary adrenal axis in the pathophysiology of adult mood and anxiety disorders. The current study evaluates the association between salivary cortisol concentrations and response to carbon-dioxide inhalation in children and adolescents with anxiety disorders, mood disorders, or no psychiatric illness. The central question was whether response to carbon-dioxide inhalation is associated with levels of hypothalamic-pituitary adrenal axis activation. If confirmed, this would relate hypothalamic-pituitary adrenal axis activation in juveniles, as in adults, and response to a well-studied respiratory procedure.

METHODS

Serial salivary cortisol samples were examined in 98 subjects (ages 9-17 years), including 62 subjects with an anxiety and/or mood disorder and 36 nonpsychiatrically ill comparisons. Samples were obtained upon arrival at the laboratory, following a tilt test, then before and immediately after a standard 5% carbon dioxide inhalation procedure.

RESULTS

Salivary cortisol levels pre-carbon-dioxide inhalation were significantly higher in patients sensitive to the anxiogenic effects of carbon dioxide (n = 20) than in patients who did not respond to carbon dioxide (n = 42) and in healthy subjects, none of whom were sensitive to carbon dioxide (n = 36); cortisol concentrations in the latter two groups were indistinguishable. Salivary cortisol did not increase during carbon-dioxide inhalation, irrespective of diagnostic group or degree of reactivity to the procedure.

CONCLUSIONS

The current data resemble data from studies of laboratory-induced panic among adult patients. In both groups, activation of the hypothalamic-pituitary adrenal axis is associated with the response to a standardized stressor. Similarly, as in adults, carbon-dioxide inhalation in juveniles does not produce a significant change in hypothalamic-pituitary adrenal axis activation.

Adolescent life events as predictors of adult depression

BACKGROUND

Among adults, life events predict future episodes of major depression as well as a range of anxiety disorders. While studies have begun to examine this issue in adolescents, few studies rely upon prospective epidemiological designs to document relationships between adolescent life events and adult major depression.

METHOD

An epidemiologically-selected sample of 776 young people living in Upstate New York received DSM-based psychiatric assessments and an assessment of life events in 1986. Psychopathology was again assessed in 1992. The current study examined the predictive relationship between life events in 1986 and depression as well as anxiety in 1992, controlling for depression/anxiety in 1986.

RESULTS

Adolescent life events predicted an increased risk for major depression diagnosis in adulthood. When analyzed continuously, an association emerged with symptoms of major depression as well as with symptoms of generalized anxiety disorder. However, this association with generalized anxiety disorder was limited to females.

CONCLUSIONS

Life events in adolescence predict risk for major depression during early adulthood.

Immediate and long-lasting effects of chronic stress in the prepubertal age on the startle reflex

The immediate and long-lasting effects of two models of chronic stress during the prepubertal period of life (21-32 days) on the acoustic startle response (ASR) were studied in outbred Wistar normotensives and rats with inherited stress-induced arterial hypertension (ISIAH) derived from them. Chronic variable stress (CVS) and repeated handling were used as chronic treatment. The obtained data showed a significantly attenuated ASR and a greater magnitude of prepulse inhibition (PPI) in juvenile and adult ISIAH compared to Wistar rats. The immediate effects of prolonged stress on the ASR were genotype-dependent. Young ISIAH rats exposed to both types of prepubertal stimulation had higher ASR than the age-matched controls. No significant stress-induced changes in the ASR were found in young Wistar rats. The long-lasting consequences of prolonged prepubertal stress were similar in the two strains and were determined by the specificity of stress stimulation: chronic handling had no effect on the ASR, while CVS enhanced it. The long-lasting effect of CVS experienced in prepubertal life appears to produce ASR changes similar to those seen in patients with posttraumatic stress disorder (PTSD). The magnitude of PPI increased from early age to adulthood and it was tolerant to environmental influences. The two rat strains did not differ in the rate of short-term habituation to repeated acoustic stimuli, which was unaffected by prepubertal stress. Evidence was obtained indicating that genetic and environmental background in childhood may contribute to the truncation of the startle response.

Parental stress as a predictor of wheezing in infancy: a prospective birth-cohort study

The role of stress in the pathogenesis of childhood wheeze remains controversial. Caretaker stress might influence wheeze through stress-induced behavioral changes in caregivers (e.g., smoking, breast-feeding) or biologic processes impacting infant development (e.g., immune response, susceptibility to lower respiratory infections). The influence of caregiver stress on wheeze in infancy was studied in a genetically predisposed prospective birth-cohort (n = 496). Caregiver-perceived stress and wheeze in the children were ascertained bimonthly from the first 2 to 3 mo of life. Greater levels of caregiver-perceived stress at 2 to 3 mo was associated with increased risk of subsequent repeated wheeze among the children during the first 14 mo of life (RR, 1.6; 95% CI, 1.3 to 1.9). Caregiver-perceived stress remained significant (RR, 1.4; 95% CI, 1.1 to 1.9) when controlling for factors potentially associated with both stress and wheeze (parental asthma, socioeconomic status, birth weight, and race/ethnicity) as well as mediators through which stress might influence wheeze (maternal smoking, breast-feeding, indoor allergen exposures, and lower respiratory infections). Furthermore, caregiver stress prospectively predicted wheeze in the infants, whereas wheeze in the children did not predict subsequent caregiver stress. The effect of caregiver stress on early childhood wheeze was independent of caregiver smoking and breast-feeding behaviors, as well as allergen exposure, birth weight, and lower respiratory infections. These findings suggest a more direct mechanism may be operating between stress and wheeze in early childhood. Stress may contribute significantly to the population burden of preventable childhood respiratory illness.

Effects of separation and separation with supplemental stroking in BALb/c infant mice

The purpose of this pilot study was to investigate selected stress, immune, and growth consequences of maternal separation and separation with supplemental stroking in neonatal BALB/c infant mice and their dams. Three groups of 5 litters each (7 pups per litter) were studied. Control litters were undisturbed. Separated litters experienced 3 h of daily maternal deprivation on postnatal days 6 to 10. Separated/stroked litters were separated also, but for 2 h, which was then followed by 1 h of stroking with a wet paintbrush to simulate maternal tactile stimulation. After the experimental period, all animals were returned to the nest and left undisturbed for 5 additional days. One pup from each litter was sacrificed on postnatal days 6, 8, 10, and 15. Spleens and thymuses were removed, weighed, and homogenized for cell sorting, cytokine analysis, and proliferation studies. Blood was drawn for corticosterone levels and hematocrit. Hematocrits and thymus weights were lower in separated mice, suggesting decreased growth and protein synthesis. Separated/stroked pups had increased splenic proliferation responses to conconavalin A and phytohemagglutinin at day 15. Separated dams' proliferative response to ConA was lower than control dams at day 15. Day 15 decreases in thymic CD8 cells occurred in pups, with an increased thymic H:S ratio in separated pups. CD90 cells were higher at day 15 in separated/stroked pups as were CD25s at day 10 in spleen and thymus. However, gene expression of cytokines was not measurable in spleen and thymic cells, with the exception of gamma-IFN in separated/stroked animals. Pooled organ homogenates were used in this preliminary work, and further studies are needed to more precisely analyze the stress, immune, and growth effects of these interventions.

Genetic basis of anxiety-like behaviour: a critical review

The way genetic and/or environmental factors influence psychiatric disorders is an enduring question in the field of human psychiatric diseases. Anxiety-related disorders provide a relevant example of how such an interaction is involved in the aetiology of a psychiatric disease. In this paper we review the literature on that subject, reporting data derived from human and rodent studies. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of anxiety, including inbred mice, selected lines, multiple marker strains, or knockout mice and review data reporting environmental components influencing anxiety-related behaviours. We conclude that anxiety is a complex behaviour, underlined not only by genetic or environmental factors but also by multiple interactions between these two factors.

The neonatal glucocorticoid treatment-produced long-term changes of the pituitary-adrenal function and brain corticosteroid receptors in rats

Two distinct periods of sensitivity to elevated glucocorticoid hormone levels during postnatal development of the pituitary-adrenal axis were studied. Wistar rats were injected subcutaneously (s.c.) with cortisol (1 mg/kg) on postnatal days 1-5 or 14-18. The steroid treatment during the first postnatal week resulted in a decrease of the morning basal and stress-induced plasma corticosterone levels in 30 day-old male rats, as well as in rats that were injected with cortisol on the third postnatal week. Stress-induced corticosterone levels in 90-day old cortisol-treated rats were determined in blood samples drawn from the tail vein before the restraint stress, immediately after the 20-min long stress, then 60 and 180 min afterwards. Only the rats treated with cortisol during the third week showed a prolonged stress-induced corticosterone secretion, with the highest corticosterone level in 180 min after the restraint stress. The early neonatal cortisol treatment had no effect on (3)H-corticosterone binding in all studied brain areas of the 90-day old rats. The rats treated with cortisol at the 14-17th postnatal days showed a significantly lower (3)H-corticosterone binding in the frontal cortex, hippocampus, and hypothalamus. These findings suggest that the third week of life in rats is more sensitive to elevated levels of corticosterone than the first one. The high level of glucocorticoids at this period has long-term effects on the efficiency of the negative feedback mechanisms provided by hypothalamus-pituitary-adrenal axis.

Local brain functional activity following early deprivation: a study of postinstitutionalized Romanian orphans

Early global deprivation of institutionalized children may result in persistent specific cognitive and behavioral deficits. In order to examine brain dysfunction underlying these deficits, we have applied positron emission tomography using 2-deoxy-2-[(18)F]fluoro-D-glucose in 10 children (6 males, 4 females, mean age 8.8 years) adopted from Romanian orphanages. Using statistical parametric mapping (SPM), the pattern of brain glucose metabolism in the orphans was compared to the patterns obtained from two control groups: (i) a group of 17 normal adults (9 males, 8 females, mean age 27.6 years) and (ii) a group of 7 children (5 males and 2 females, mean age 10.7 years) with medically refractory focal epilepsy, but normal glucose metabolism pattern in the contralateral hemisphere. Consistent with previous studies of children adopted from Romanian orphanages, neuropsychological assessment of Romanian orphans in the present study showed mild neurocognitive impairment, impulsivity, and attention and social deficits. Comparing the normalized glucose metabolic rates to those of normal adults, the Romanian orphans showed significantly decreased metabolism bilaterally in the orbital frontal gyrus, the infralimbic prefrontal cortex, the medial temporal structures (amygdala and head of hippocampus), the lateral temporal cortex, and the brain stem. These findings were confirmed using a region-of-interest approach. SPM analysis showed significantly decreased glucose metabolism in the same brain regions comparing the orphans to the nonepileptic hemisphere of the childhood epilepsy controls. Dysfunction of these brain regions may result from the stress of early global deprivation and may be involved in the long-term cognitive and behavioral deficits displayed by some Romanian orphans.

Like mother, like daughter: evidence for non-genomic transmission of parental behavior and stress responsivity

Considerable evidence demonstrates that the quality of the early environment influences patterns of development that, in turn, determine the health and productivity of the individual throughout their life span. However, the processes through which early life influences health are not clearly understood. Through the activation of the hypothalamo-pituitary-adrenal (HPA) axis and corticotropin-releasing hormone (CRH) pathways, prolonged or exaggerated responses to stress have profound effects on physiological and cognitive functions. Early maternal separation or handling of neonatal rats can program widespread and lifelong changes in various transmitter systems that regulate the HPA and CRH systems. Our studies show that a high level of maternal licking/grooming, and arched-back nursing correlates with reduced CRH mRNA expression and enhanced glucocorticoid negative feedback, and lower stress responses in the adult. This behavior is stably transmitted between generations and cross-fostering studies show that the offspring inherit the behavior from the nursing mother and not the biological mother. Such intergenerational transmission of maternal behavior is seen in rodents, primates and humans, and may underlie adaptive changes in the HPA axis. The neural basis of this inheritance pattern appears to reside in the central oxytocin system which determines features of maternal behavior. Through these various adaptive neural mechanisms the environmental demand on the mother is reflected in the quality of maternal care to her offspring. This, in turn, programs stress reactivity and maternal behavior patterns of the offspring. This not only determines certain health outcomes but also establishes the relationships between mother and offspring in the next generation. These findings suggest that for neurobiologists, the function of the family is an important level of analysis and the critical question is that of how environmental events regulate neural systems that mediate the expression of parental care.

Emotional reactivity in mice, a case of nongenetic heredity?

Nongenetic heredity cases have been described in man, as well as in animals, and relationships between parents and offspring seem to play an important role in this transmission. In mice, mothering type could be nongenetically heritable by a latent learning close to mechanism. As mothering style clearly influences emotional reactivity, this reactivity could be nongenetically transmitted over generations. To clarify this question, the mother's influence on adult offspring reactivity must be established (whatever its basis, genetic, social or other). Thus, two reciprocal F1 hybrids (CB6 from a BALB/c mother and B6C from a C57BL/6 mother) have been compared using an ethological analysis in animal tests of emotional reactivity such as the free exploration paradigm and the light/dark box. First results show a sharp influence of the mother's strain and that suggests an effect of mothering style. The offspring from C57BL/6 mothers display less reactivity in the free exploration paradigm than the offspring from BALB/c mothers. In the light/dark box, no difference has been found between the two hybrids. Moreover, the mother's influence is greater in males than in females.

Neonatal exposure to a novel environment enhances the effects of corticosterone on neuronal excitability and plasticity in adult hippocampus

Electrophysiological studies have shown that activation of glucocorticoids receptors (GRs) influences neuronal excitability and activity dependent synaptic plasticity. In developmental studies, early life stimulation such as neonatal handling results in an up-regulation of glucocorticoid-receptor (GR) binding in the hippocampus that persists into adulthood. It is, therefore, hypothesized that early environment-induced changes in receptor sensitivity to corticosterone (CORT) might have functional effects on adult neuronal excitability and synaptic plasticity. To test this hypothesis, we exposed rats daily from post-natal days 1-21 to a non-home environment for 3 min. When the animals became adults, we studied the effects of glucocorticoid hormone corticosterone (CORT) on population spike (PS) amplitude and long-term potentiation of population spikes (PS-LTP) in vitro in the hippocampal CA1 region following activation of the Schaffer collateral fibers. Bath application of CORT reduced PS amplitude and subsequent induction of PS-LTP. This inhibitory effect of CORT was significantly greater in the slices from the novelty exposed rats (Novel) than the control rats that remained in their home cage (Home). Inhibition of population spike amplitude during CORT perfusion was 28.0+/-5.3% of baseline in Novel slices, and 9.1+/-4.4% in Home slices. CORT pre-exposure (20 min) also inhibited the subsequent induction of PS-LTP in Novel slices by 57.7+/-17.7% and by 7.5+/-12.1% in Home slices. These results provide electrophysiological evidence that neonatal novelty exposure results in functional increases in receptor sensitivity to CORT that enhances the inhibitory effects of CORT on field CA1 neuronal excitability and plasticity.

Maternal care, gene expression, and the transmission of individual differences in stress reactivity across generations

Naturally occurring variations in maternal care alter the expression of genes that regulate behavioral and endocrine responses to stress, as well as hippocampal synaptic development. These effects form the basis for the development of stable, individual differences in stress reactivity and certain forms of cognition. Maternal care also influences the maternal behavior of female offspring, an effect that appears to be related to oxytocin receptor gene expression, and which forms the basis for the intergenerational transmission of individual differences in stress reactivity. Patterns of maternal care that increase stress reactivity in offspring are enhanced by stressors imposed on the mother. These findings provide evidence for the importance of parental care as a mediator of the effects of environmental adversity on neural development.

Possible role of cortisol and dehydroepiandrosterone in human development and psychopathology

BACKGROUND

The characteristics of adrenal hormone secretion change markedly during infancy. Disturbances in basal levels may precipitate psychological dysfunction and are associated with psychopathology in young people.

AIMS

To relate three aspects of behavioural endocrinology: developmental changes in cortisol and dehydroepiandrosterone (DHEA), the role of these hormones in the psychopathology of young people, and the action of these steroids in the brain.

METHOD

A selective review from the human developmental, psychiatric and neurosciences literature.

RESULTS

There are developmentally mediated changes in brain sensitivity following excess exposure to cortisol. This may result in impairments of mental and behavioural function. DHEA and gonadal steroids may modulate the actions of cortisol.

CONCLUSIONS

Steroid hormones contribute to shaping behavioural function during early development and act as risk factors for psychopathology.

Variable foraging demand rearing: sustained elevations in cisternal cerebrospinal fluid corticotropin-releasing factor concentrations in adult primates

BACKGROUND

The authors previously reported elevated cerebrospinal fluid (CSF) corticotropin-releasing factor (CRF) concentrations in juvenile primates nursed by mothers undergoing experimentally imposed unpredictable foraging conditions in comparison to normally reared controls. The purpose of the present study was to determine if these changes would endure into young adulthood.

METHODS

Cisternal CSF samples were obtained from those unpredictably reared young adult primates who had been previously studied as juveniles and age-matched ad libitum normally reared controls. Samples were assayed for CSF CRF.

RESULTS

Concentrations of CSF CRF were significantly elevated in the unpredictably reared sample in comparison to the ad libitum-reared control group. A significant positive correlation was noted between juvenile and young adult CSF CRF values within the unpredictably reared cohort.

CONCLUSIONS

Disturbances of maternal-infant attachment processes have an enduring impact on primate CRF function into young adulthood. The CRF elevations following unpredictable maternal foraging conditions appear traitlike in nature.

Autonomic reactivity and psychopathology in middle childhood

BACKGROUND

Better indicators are needed for identifying children with early signs of developmental psychopathology.

AIMS

To identify measures of autonomic nervous system reactivity that discriminate children with internalising and externalising behavioural symptoms.

METHOD

A cross-sectional study of 122 children aged 6--7 years examined sympathetic and parasympathetic reactivity to standardised field-laboratory stressors as predictors of parent- and teacher-reported mental health symptoms.

RESULTS

Measures of autonomic reactivity discriminated between children with internalising behaviour problems, externalising behaviour problems and neither. Internalisers showed high reactivity relative to low-symptom children, principally in the parasympathetic branch, while externalisers showed low reactivity, in both autonomic branches.

CONCLUSIONS

School-age children with mental health symptoms showed a pattern of autonomic dimorphism in their reactivity to standardised challenges. This observation may be of use in early identification of children with presyndromal psychopathology.

Mice with targeted mutations of glucocorticoid and mineralocorticoid receptors: models for depression and anxiety?

Impaired corticosteroid receptor signaling is a key mechanism in the pathogenesis of stress-related psychiatric disorders such as depression and anxiety. Since in vivo expression and functional studies of corticosteroid receptors are not feasible in the human central nervous system, such analyses have to be done in animal models. Transgenic mice with mutations of corticosteroid receptors are promising tools, which allow us to investigate the role of these proteins in the pathogenesis of symptoms characteristic for depression and anxiety. This review summarizes the neuroendocrinological and behavioral findings that have been obtained in six different mouse strains with specific mutations that influence the expression or the function of the glucocorticoid or the mineralocorticoid receptor (MR). The analyses of these mice helped to define molecular concepts of how corticosteroid receptors regulate the activity of the hypothalamic-pituitary-adrenal (HPA) system. Furthermore, some of these mutant mice exhibited characteristic alterations in behavioral tests for anxiety and despair. However, so far, none of the mouse strains described here can be viewed as an animal model of a specific psychiatric disease defined by common diagnostic criteria. Using high throughput technologies for the identification of genes regulated by glucocorticoid receptor (GR) and MR in brain areas responsible for specific symptoms of stress-related disorders will yield potential new drug targets for the treatment of depression and anxiety.

Effects of neonatal handling on nociceptin/orphanin FQ and opioid peptide levels in female rats

Animals exposed to short periods of handling during the critical period of development, i.e., the first 21 days of life in rats, show attenuated neuroendocrine responses to stress in adult life. We have previously reported long-term changes in brain dynorphin (DYN) peptide levels in male Sprague-Dawley rats after neonatal handling. The purpose of this study was to investigate whether neonatal handling, 15-min individual separation from the mother during postnatal days 1-21, can induce long-term changes in DYNB, Met-enkephalin Arg(6)Phe(7) (MEAP) and nociceptin/orphanin FQ (N/OFQ) immunoreactive (ir) levels in female Sprague-Dawley rats. The peptides were measured in brain and pituitary gland 2 months after the handling procedure. The results reveal that handled (H) rats had increased ir levels of N/OFQ, DYNB and MEAP in the periaqueductal gray (PAG) as compared to nonhandled (NH) controls. Furthermore, H rats had decreased ir levels of DYNB in the frontal cortex and in the amygdala. In contrast to previous findings in male rats, DYNB levels were unaffected in areas related to the hypothalamo-pituitary-adrenal (HPA)-axis. The results indicate that a manipulation early in life can induce persistent neurochemical changes in the N/OFQ and opioid peptide system in female Sprague-Dawley rats.

Nature, nurture, and the disunity of knowledge

The Human Genome Project and the tools of modern molecular biology bring enormous promise for the understanding of human biology. Juxtaposed, however, is a conceptual stagnation reflected in the continued nature/nurture debate. More sophisticated models reflecting the inevitable interdependence of gene and environment are essential if we are to realize the potential offered by today's technological advances.

Pathways mediating sexual abuse and eating disturbance in children

OBJECTIVE

To examine the relationship between childhood maltreatment and eating disorders in a sample of children.

METHOD

Twenty 10-15-year-old female children who were receiving treatment following reported childhood sexual abuse and 20 age-matched controls were compared on a series of measures assessing eating disorder behaviors, body image concerns, substance use, mood, impulsive behavior, and self-concept.

RESULTS

Sexually abused children reported higher levels of eating disorder behaviors, impulsive behaviors, and drug abuse than controls. Furthermore, behavioral impulsivity provided the strongest mediational effect between a history of childhood sexual abuse and purging and restrictive dieting behavior. Drug use proved to be a significant secondary mediator of the childhood sexual abuse eating disorder behavior association.

DISCUSSION

These data support the hypothesis that childhood sexual abuse is related to disordered eating in children, and extend similar findings that have been previously reported with adults. Behavioral impulsivity and drug use appear to be significant mechanisms that influence eating disorder behavior following childhood sexual abuse.

Long-term biobehavioral effects of maternal separation in the rat: consistent or confusing?

Over the last decades of research there has been increasing interest in endocrine and behavioral effects of postnatal environmental manipulations. A manipulation procedure that has been widely used to date is that of maternal separation. Many studies have demonstrated that, in the rat, a single or repeated separation of the pups from the mother leads to acute as well as long-term effects on endocrinology and behavior. However, reviewing the literature shows that contrary findings for almost all parameters investigated can be found. A possible explanation for this inconsistency may be the fact that maternal separation has become a collective term for a variety of extremely different experimental manipulations. Therefore, this review aims at evaluating typical effects of maternal separation in the laboratory rat by categorizing different experimental procedures. We concentrate in particular on longterm behavioral effects, although a brief summary of neuroendocrine effects is also provided. In addition, important methodological issues of maternal separation studies are discussed as a possible source for inconsistent findings.

Parenting and its effects on children: on reading and misreading behavior genetics

There is clear evidence that parents can and do influence children. There is equally clear evidence that children's genetic makeup affects their own behavioral characteristics, and also influences the way they are treated by their parents. Twin and adoption studies provide a sound basis for estimating the strength of genetic effects, although heritability estimates for a given trait vary widely across samples, and no one estimate can be considered definitive. This chapter argues that knowing only the strength of genetic factors, however, is not a sufficient basis for estimating environmental ones and indeed, that attempts to do so can systematically underestimate parenting effects. Children's genetic predispositions and their parents' childrearing regimes are seen to be closely interwoven, and the ways in which they function jointly to affect children's development are explored.

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.

Variations in maternal care in infancy regulate the development of stress reactivity

Naturally occurring variations in maternal care in early postnatal life are associated with the development of individual differences in behavioral and hypothalamic-pituitary-adrenal responses to stress in the rat. These effects appear to be mediated by the influence of maternal licking/grooming on the development of central systems that serve to activate (corticotropin-releasing factor) or inhibit (gamma-aminobutyric acid) the expression of behavioral and endocrine responses to stress through effects on forebrain noradrenergic systems. Importantly, individual differences in maternal care are transmitted from mother to daughter, providing a mechanism for the behavioral transmission of individual differences in stress reactivity across generations.

Multilevel integrative analyses of human behavior: social neuroscience and the complementing nature of social and biological approaches

Social and biological explanations traditionally have been cast as incompatible, but advances in recent years have revealed a new view synthesized from these 2 very different levels of analysis. The authors review evidence underscoring the complementing nature of social and biological levels of analysis and how the 2 together can foster understanding of the mechanisms underlying complex behavior and the mind. Specifically, they review the utility of considering social influences on biological processes that are often viewed as outside the social domain including genetic constitution, gene expression, disease, and autonomic, neuroendocrine, and immune activity. This research underscores the unity of psychology and the importance of retaining multilevel integrative research that spans molar and molecular levels of analysis. Especially needed in the coming years is more research on the mechanisms linking social and biological events and processes.

Quantitative changes in reduced nicotinamide adenine dinucleotide phosphate-diaphorase-reactive neurons in the brain of Octodon degus after periodic maternal separation and early social isolation

The influence of preweaning maternal separation and postweaning social isolation on the development of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase-reactive neurons in prefrontal cortical areas, in subdivisions of the nucleus accumbens and in the corpus callosum was quantitatively investigated in the precocious rodent Octodon degus. Forty-five-day-old degus from three animal groups were compared: (i) degus that were reared under normal undisturbed social conditions; (ii) degus that were repeatedly separated from their mothers during the first three postnatal weeks and thereafter reared with their family; and (iii) degus that remained undisturbed with the family until weaning (postnatal day 21) and thereafter were reared in social isolation. Preweaning maternal separation led to a significant decrease in NADPH-diaphorase-containing neurons in the corpus callosum in both genders (down to 33%) compared with the social control group. No significant changes were found in the subregions of the medial prefrontal cortex and nucleus accumbens. Postweaning social isolation led to a reduced density of NADPH-diaphorase-containing neurons in the corpus callosum in both genders (down to 52%) compared with the social control group. Furthermore, in the precentral medial cortex of female pups, a significant reduction in NADPH-diaphorase-reactive neurons (down to 72%) was detectable. All other regions of the medial prefrontal cortex and the nucleus accumbens remained unchanged. The observed deprivation-induced changes may reflect either an excessive reduction in NADPH-diaphorase-positive neurons or a down-regulation of the enzyme in neurons that normally express it.Our results indicate a link between early adverse socio-emotional experience and the maturation of NADPH-reactive neurons. Further studies are required to analyse the functional implications of this experience-induced brain pathology.

Effects of early adverse experiences on brain structure and function: clinical implications

Child abuse is associated with markedly elevated rates of major depression and other psychiatric disorders in adulthood. This article reviews preclinical studies examining the effects of early stress, factors that modify the impact of these experiences, and neurobiological changes associated with major depression. Preclinical studies demonstrate that early stress can alter the development of the hypothalamic-pituitary-adrenal axis, hypothalamic and extrahypothalamic corticotropin releasing hormone, monoaminergic, and gamma-aminobutyric acid/benzodiazepine systems. Stress has also been shown to promote structural and functional alterations in brain regions similar to those seen in adults with depression. Emerging data suggest, however, that the long-term effects of early stress can be moderated by genetic factors and the quality of the subsequent caregiving environment. These effects also can be prevented or reversed with various pharmacologic interventions. Preclinical studies of early stress can provide valuable insights in understanding the pathophysiology and treatment of major depression. They also can provide an important tool to use to investigate interactions between genes and environments in determining an individual's sensitivity to stress. More research is needed to understand how inherent factors interact with experiences of abuse and other psychosocial factors to confer vulnerability to develop depression.

Postnatal handling alters the activation of stress-related neuronal circuitries

Postnatal handling, as a crucial early life experience, plays an essential role in the development of hypothalamo-pituitary-adrenal axis responses to stress. The impact of postnatal handling on the reactivity of stress-related neuronal circuitries was investigated in animals that were handled for the first 21 days of life and as adults they were exposed to physical (ether) or emotional (restraint) challenge. To assess neuronal activation we relied on the induction of immediate-early gene product c-Fos and analysed its spatial and temporal distribution at various time intervals after stress. Ether and restraint commonly activated parvocellular neurons in the hypothalamic paraventricular nucleus, and resulted in activation of brain areas providing stress-related information to the hypothalamic effector neurons and/or in regions governing autonomic and behavioural responses to stress. Beyond these areas, the strength and timing of c-Fos induction showed stressor specificity in olfactory and septal region, basal ganglia, hypothalamus, hippocampal formation, amygdala and brainstem. Handled rats displayed a lower number of c-Fos-positive cell nuclei and weaker staining intensity than non-handled controls in the hypothalamic paraventricular nucleus, bed nucleus of stria terminalis, central nucleus of amygdala, hippocampus, piriform cortex and posterior division of the cingulum. Significant differences were revealed in timing of c-Fos induction as a function of stressor and early life experience. Together, these data provide functional anatomical evidence that environmental enrichment in the early postnatal period attenuates the reactivity of stress-related neuronal circuitries in the adult rat brain.

Maternal care, hippocampal synaptogenesis and cognitive development in rats

We report that variations in maternal care in the rat promote hippocampal synaptogenesis and spatial learning and memory through systems known to mediate experience-dependent neural development. Thus, the offspring of mothers that show high levels of pup licking and grooming and arched-back nursing showed increased expression of NMDA receptor subunit and brain-derived neurotrophic factor (BDNF) mRNA, increased cholinergic innervation of the hippocampus and enhanced spatial learning and memory. A cross-fostering study provided evidence for a direct relationship between maternal behavior and hippocampal development, although not all neonates were equally sensitive to variations in maternal care.

The importance of neurobiological research to the prevention of psychopathology

There is both a biological and environmental component to the neural substrates for various forms of psychopathology. Brain dysfunction itself not only constitutes a formidable liability to psychopathology, but also has an impact on environmental and social responses to the individual, compounding the risk for an adverse outcome. Environmental conditions, such as social and physical stimulus deprivation, poverty, traumatic stress, and prenatal drug exposure, can further compromise brain function in the context of existing liabilities. The relationship between genetic and environmental processes is interactive, fluid, and cumulative in their ability to influence an individual's developmental trajectory and alter subsequent behavioral outcomes. Given the codependent relationship between these processes, brain function is now believed to be malleable via manipulations of the environment in ways that may decrease liability for psychopathology. Research that explores these relationships and ways in which interventions can redirect this developmental track may substantially advance both the science and practice of prevention. Studies attempting to isolate the neurobiological effects of socioenvironmental factors are reviewed, implications for intervention strategies are discussed, and a future research agenda is proposed to provide greater insight into specific brain-environment relationships. Armed with this knowledge, prevention scientists may eventually design programs that directly target these effects to reverse or attenuate negative outcomes.

Dysthymia: a review of pharmacological and behavioral factors

Although dysthymia, a chronic, low-grade form of depression, has a morbidity rate as high as that of major depression, and increases the risk for major depressive disorder, limited information is available concerning the etiology of this illness. In the present report we review literature concerning the biological and characterological features of dysthymia, the effectiveness of antidepressant treatments, the influence of stressors in the precipitation and maintenance of the disorder, and both quality of life and psychosocial correlates of the illness. We also provisionally suggest that dysthymia may stem from disturbances of neuroendocrine and neurotransmitter functioning (eg, corticotropin releasing hormone and arginine vasopressin within the hypothalamus, or alternatively monoamine variations within several extrahypothalamic sites), and may also involve cytokine activation. The central disturbances may reflect phenotypic variations of neuroendocrine processes or sensitization of such mechanisms. It is suggested that chronic stressor experiences or stressors encountered early in life lead to the phenotypic neurochemical alterations, which then favor the development of the dysthymic state. Owing to the persistence of the neurochemical disturbances, vulnerability to double depression is increased, and in this instance treatment with antidepressants may attenuate the symptoms of major depression but not those of the basal dysthymic state. Moreover, the residual features of depression following treatment may be indicative of underlying neurochemical disturbances, and may also serve to increase the probability of illness recurrence or relapse.

Different effects of acute neonatal stressors and long-term postnatal handling on stress-induced changes in behavior and in ornithine decarboxylase activity of adult rats

A transient increase in brain polyamine (PA) metabolism, termed the PA-stress-response (PSR), is a common response to stressful stimuli. Previous studies have implicated the PSR as a component of the adaptive and/or maladaptive brain response to stressful events. Ample evidence indicates that stressful experiences during early life can alter normal developmental processes and may result in pathophysiological and behavioral changes in the adult. The aim of the present study, therefore, was to determine whether strong acute neonatal stressors (3 mg/kg dexamethasone, or 2 h restraint stress at day 7), as compared to mild long-term intermittent maternal separation and handling (15 min, twice a day between postnatal days 2 and 25), would lead in adult Wistar rats to different PSR and behavioral reactivity to novelty stress. Changes in ornithine decarboxylase (ODC) activity and in tissue PA concentrations served as markers of the PSR, and behavioral alterations in an open-field arena indicated the reactivity to novelty stress. Animals subjected to acute neonatal stressors, showed reduced behavioral reactivity in the open-field test, indicative of increased emotional reactivity to novelty. In these animals, the increase in ODC activity after dexamethasone challenge was attenuated in the brain, but exaggerated in the liver. In the thymus and adrenal gland of these animals, the basal enzyme activity was significantly increased, but a similar reduction was observed after dexamethasone challenge. In contrast, long-term postnatal handling led in adults to novelty-induced changes indicative of reduced emotional behavior, yet the alterations in ODC activity after dexamethasone challenge in these animals were similar to those in animals after acute stressors. The concentrations of tissue polyamines in adults were not affected by any of the postnatal stressors. The results justify the following conclusions: (1) Strong acute neonatal stressors can lead to increased emotional behavior in adults, while mild long-term intermittent handling, may result in adaptation and reduced emotionality. (2) Attenuated stress-induced increase of ODC activity in the brain, but exaggerated increased activity in the liver, may be implicated in altered emotional behavior reactivity to stressors.

Antenatal glucocorticoids and programming of the developing CNS

Glucocorticoids (GCs) are essential for many aspects of normal brain development. However, there is growing evidence from a number of species that exposure of the fetal brain to excess GC, at critical stages of development, can have life-long effects on behavior and neuroendocrine function. The hypothalamo-pituitary-adrenal axis, which is central to the integration of the individual's endocrine and behavioral response to stress, appears highly sensitive to excess GC exposure during development. A number of animal studies have shown that exposure to synthetic GCs in utero results in adult offspring that exhibit hyperactivity of the hypothalamo-pituitary-adrenal axis. This will have a long-term impact on health, inasmuch as increased life-long exposure to endogenous GC has been linked to the premature onset of diseases associated with aging. The mechanisms involved in the permanent programming of hypothalamo-pituitary-adrenal function and behavior are not well understood. Synthetic GCs are used extensively to promote pulmonary maturation in fetuses at risk of being delivered before term. Therefore, it is important that we understand the potential long-term consequences of prenatal GC exposure on brain development as well as the underlying mechanisms involved. This review will explore the current state of knowledge in this rapidly expanding field.

Environmental risk factors for multifactorial epilepsy in EL mice

PURPOSE

The epileptic EL mouse has been studied extensively as a model of multifactorial epilepsy. Although EL mice have a seizure occasionally during routine handling associated with cage changing, most studies have used vigorous tossing or shaking procedures for seizure induction. A new seizure testing procedure was developed that involved gentle handling and simulated situations associated with emotional stress in rodents. This new testing procedure was used to identify and characterize several environmental risk factors that influence seizure predisposition in EL mice.

METHODS

Ten adult EL mice were monitored for 7 days under 24-h light/dark video surveillance to assess the frequency of spontaneous seizures. The development of handling-induced seizures also was studied in EL mice, in nonepileptic ABP and DDY mice, and in reciprocal ABP x EL F1 hybrids from ages 30-180 days.

RESULTS

Seizure induction was necessary in EL mice, as spontaneous clinical seizures were not observed. Handling-induced seizure susceptibility was strongly age and gender dependent in naive EL mice (not previously handled) and peaked approximately 90 days, with males significantly more susceptible than females. No seizures were induced by handling in the nonepileptic mouse strains (ABP and DDY) over the testing period. Handling and seizures at young ages in EL and EL x ABP F1 hybrid mice significantly enhanced their seizure susceptibility when they were tested again 1 month later. A significant "Gowers effect" was seen also in EL mice. Furthermore, susceptibility was higher in ABP x EL F1 hybrids than in their reciprocal EL x ABP F1 hybrids at 90-150 days.

CONCLUSIONS

Seizure susceptibility in EL mice was significantly influenced by a number of environmental factors including age, gender, maternal/paternal effects, prior handling, and seizure history. The emotional stress/fear response is the likely trigger for seizure induction in EL mice. An early life experience stress-diathesis model, similar to that proposed for major depression in humans, was applicable to the development of seizure susceptibility in EL mice. The new seizure test will be useful for defining gene-environment interactions and in identifying susceptibility genes for multifactorial epilepsy.

The influence of postnatal handling on adult neuroendocrine and behavioural stress reactivity

Environmental stimuli during early stages of life can influence the development of an organism and may result in permanent changes in adult behaviour and physiology. In the present study we investigated the influence of early postnatal handling on adult neuroendocrine and behavioural stress reactivity in Wistar rats. Pups were subjected to handling from postnatal day 1-21. The young were taken from the nest every day for 15 min and each of the pups was handled separately. Control nests were left undisturbed. When the animals had reached an adult age of 3-4 months they were individually housed and subjected to a series of tests to measure their stress reactivity. In the first experiment we established adult behavioural coping with stressors and anxiety in the following series of tests: open field test, shock prod defensive burying test, elevated plus maze and conditioned fear test. Collectively, the data clearly indicate that handled animals are characterized by a lower stress-induced anxiety. Yet, handled and control animals do not differ in their general way of coping with stressors. Although the lower anxiety in handled animals is often reflected in a higher activity, they are not more active per se. In a second experiment, animals were provided with a permanent jugular vein canula for repeated blood sampling to determine stress hormones: noradrenaline, adrenaline, prolactin and corticosterone. Animals were subjected to a novelty test and a conditioned fear test. The neuroendocrine response profile is consistent with the conclusion that handled animals are less anxious than controls but are not different in their general strategy of coping with stressors. The handled animals showed an attenuated adrenaline, prolactin and corticosterone response. Yet, in neither of the two tests there was a difference in noradrenaline response, a typical marker for an active coping strategy. Interestingly, the differences in neuroendocrine reactivity already appeared in response to a mild novelty challenge when there were no clear behavioural differences yet. The neuroendocrine measures are in line with the behavioural data but more sensitively reflect the differences between handled and control animals.

The role of corticotropin-releasing factor--norepinephrine systems in mediating the effects of early experience on the development of behavioral and endocrine responses to stress

Naturally occurring variations in maternal care in early postnatal life are associated with the development of individual differences in behavioral and hypothalamic-pituitary-adrenal responses to stress in the rat. These effects appear to be mediated by the influence of maternal licking and grooming on the development of central corticotropin-releasing factor (CRF) systems, which regulate the expression of behavioral, endocrine, and autonomic responses to stress through activation of forebrain noradrenergic systems. These findings provide a neurobiologic basis for the observed relationship between early life events and health in adulthood. In more recent studies, we explored the behavioral transmission of individual differences in stress reactivity, and thus, vulnerability to stress-induced illness, across generations.

Short- and long-periods of neonatal maternal separation differentially affect anxiety and feeding in adult rats: gender-dependent effects

Environmental manipulations during early development can induce permanent alterations in hypothalamic-pituitary-adrenal (HPA) and behavioral responses to stressors. However, little is known about the impact of early life experiences on appetitive responses. The present investigation assessed the effects of brief handling/separation or protracted separation from the dams, on feeding and anxiety responses during development. During the first 3 weeks post-partum, Sprague-Dawley rat pups were exposed daily to either brief (15 min) handling/isolation (H), a more protracted (3 h) period of maternal separation (MS), or were not handled (NH). When tested on the elevated plus-maze (at 5-6 weeks) H groups displayed less anxiety than NH gender-matched controls. Surprisingly, so did the MS females. At weaning (Day 22), the MS rats weighed significantly less than both the H and NH animals; the difference between the H and MS was more robust and persisted throughout the experiment (D 62). The H animals of both genders, and the females of the MS group, consumed more of the palatable 'snack' than their NH counterparts. The feeding suppressant response to the various satiety peptides (bombesin, cholecystokinin, and amylin) was not affected by the early life experience, with exception of cholecystokinin (CCK) effects, which were more pronounced in H and MS males. These results suggest that early life events may contribute to anxiety and/or ingestive disorders such as anorexia nervosa, bulimia and obesity.

Maternal care and the development of stress responses

Studies dating from the 1950s have documented the impact of early life events on the development of behavioral and endocrine responses to stress. Recent findings suggest that these effects are mediated through changes in mother-offspring interactions and have identified central corticotropin-releasing factor systems as a critical target for the effects of variations in maternal care.

Developmental regulation of the brain polyamine-stress-response

A transient increase in brain polyamine metabolism, termed the polyamine-stress-response is a common response to stressful stimuli. Previous studies have implicated an over-reactive polyamine response as a component of the maladaptive brain response to stressful events, and as a novel molecular mechanism involved in the pathophysiology of affective disorders. Ample evidence indicates that stressful experiences during early life can alter normal developmental processes and may result in pathophysiological and behavioral changes in the adult. Additionally, an important characteristic of affective disorders is their age dependency, a phenomenon that may be correlated with a maladaptive regulation of the hypothalamic-pituitary-adrenocortical (HPA) neuroendocrine system. In the present study we measured the activities of the enzymes ornithine decarboxylase and S-adenosylmethionine decarboxylase as markers of polyamine synthesis and found that unlike adults, immature rats do not show the characteristic brain polyamine-stress-response. Instead of the characteristic increase observed in adults, ornithine decarboxylase activity in immature animals was reduced or remained unchanged (for up to 16 days of age) after a dexamethasone injection or restraint stress application. The ontogenesis of this ornithine decarboxylase response was brain region-specific, indicating its dependence on the stage of neuronal maturation. Animals treated with dexamethasone at 7 days of age, showed increased behavioral reactivity in the open-field test as adults and an attenuated increase in ornithine decarboxylase activity after a re-challenge with dexamethasone at age 60 days. The results indicate that: (1) the brain polyamine-stress-response is developmentally regulated and its ontogenesis is brain region-specific, indicating dependence on the stage of neuronal maturation; (2) the switch to a mature polyamine-stress-response pattern coincides with the cessation of the stress hyporesponsive period in the HPA system: (3) activation of the polyamine-stress-response, as in the mature brain, appears to be a constructive reaction, while its down-regulation, as in the developing brain, may be implicated in neuronal cell death; (4) an attenuated dexamethasone-induced increase in ornithine decarboxylase activity implicates an altered polyamine-stress-response in the maladaptive response of the brain to stressful events.