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

Cortisol and Major Depressive Disorder-Translating Findings From Humans to Animal Models and Back

Major depressive disorder (MDD) is a global problem for which current pharmacotherapies are not completely effective. Hypothalamic-pituitary-adrenal (HPA) axis dysfunction has long been associated with MDD; however, the value of assessing cortisol as a biological benchmark of the pathophysiology or treatment of MDD is still debated. In this review, we critically evaluate the relationship between HPA axis dysfunction and cortisol level in relation to MDD subtype, stress, gender and treatment regime, as well as in rodent models. We find that an elevated cortisol response to stress is associated with acute and severe, but not mild or atypical, forms of MDD. Furthermore, the increased incidence of MDD in females is associated with greater cortisol response variability rather than higher baseline levels of cortisol. Despite almost all current MDD treatments influencing cortisol levels, we could find no convincing relationship between cortisol level and therapeutic response in either a clinical or preclinical setting. Thus, we argue that the absolute level of cortisol is unreliable for predicting the efficacy of antidepressant treatment. We propose that future preclinical models should reliably produce exaggerated HPA axis responses to acute or chronic stress a priori, which may, or may not, alter baseline cortisol levels, while also modelling the core symptoms of MDD that can be targeted for reversal. Combining genetic and environmental risk factors in such a model, together with the interrogation of the resultant molecular, cellular, and behavioral changes, promises a new mechanistic understanding of MDD and focused therapeutic strategies.

Brain Systems Underlying Susceptibility to Helplessness and Depression

There has been a relative lack of research into the neurobiological predispositions that confer vulnerability to depression. This article reviews functional brain mappings from a genetic animal model, the congenitally helpless rat, which is predisposed to develop learned helplessness. Neurometabolic findings from this model are integrated with the neuroscientific literature from other animal models of depression as well as depressed humans. Changes in four major brain systems are suggested to underlie susceptibility to helplessness and possibly depression: (a) an unbalanced prefrontal-cingulate cortical system, (b) a dissociated hypothalamic-pituitary-adrenal axis, (c) a dissociated septal-hippocampal system, and (d) a hypoactive brain reward system, as exemplified by a hypermetabolic habenula-interpeduncular nucleus pathway and a hypometabolic ventral tegmental area-striatum pathway. Functional interconnections and causal relationships among these systems are considered and further experiments are suggested, with theoretical attention to how an abnormality in any one system could affect the others.

Individual differences in novelty-seeking behavior in rats as a model for psychosocial stress-related mood disorders

Most neuropsychiatric disorders, including stress-related mood disorders, are complex multi-parametric syndromes. Diagnoses are therefore hard to establish and current therapeutic strategies suffer from significant variability in effectiveness, making the understanding of inter-individual variations crucial to unveiling effective new treatments. In rats, such individual differences are observed during exposure to a novel environment, where individuals will exhibit either high or low locomotor activity and can thus be separated into high (HR) and low (LR) responders, respectively. In rodents, a long-lasting, psychosocial, stress-induced depressive state can be triggered by exposure to a social defeat procedure. We therefore analyzed the respective vulnerabilities of HR and LR animals to long-lasting, social defeat-induced behavioral alterations relevant to mood disorders. Two weeks after four daily consecutive social defeat exposures, HR animals exhibit higher anxiety levels, reduced body weight gain, sucrose preference, and a marked social avoidance. LR animals, however, remain unaffected. Moreover, while repeated social defeat exposure induces long-lasting contextual fear memory in both HR and LR animals, only HR individuals exhibit marked freezing behavior four weeks after a single social defeat. Combined, these findings highlight the critical involvement of inter-individual variations in novelty-seeking behavior in the vulnerability to stress-related mood disorders, and uncover a promising model for posttraumatic stress disorder.

Novelty-evoked activity in open field predicts susceptibility to helpless behavior

Learned helplessness in animals has been used to model disorders such as depression and post-traumatic stress disorder (PTSD), but there is a lack of knowledge concerning which individual behavioral characteristics at baseline can predict helpless behavior after exposure to inescapable stress. The first aim of this study was to determine behavioral predictors of helplessness using the novel and familiar open-field tests, sucrose consumption, and passive harm-avoidance tasks before learned helplessness training and testing. Individual differences in physiologic responses to restraint stress were also assessed. A cluster analysis of escape latencies from helplessness testing supported the division of the sample population of Holtzman rats into approximately 50% helpless and 50% non-helpless. Linear regression analyses further revealed that increased reactivity to the novel environment, but not general activity or habituation, predicted susceptibility to learned helplessness. During restraint stress there were no mean differences in heart rate, heart rate variability, and plasma corticosterone between helpless and non-helpless rats; however, a lower heart rate during stress was associated with higher activity levels during exploration. Our most important finding was that by using an innocuous screening tool such as the novel and familiar open-field tests, it was possible to identify subjects that were susceptible to learned helplessness.

Social stress, therapeutics and drug abuse: preclinical models of escalated and depressed intake

The impact of ostensibly aversive social stresses on triggering, amplifying and prolonging intensely rewarding drug taking is an apparent contradiction in need of resolution. Social stress encompasses various types of significant life events ranging from maternal separation stress, brief episodes of social confrontations in adolescence and adulthood, to continuous subordination stress, each with its own behavioral and physiological profile. The neural circuit comprising the VTA-accumbens-PFC-amygdala is activated by brief episodes of social stress, which is critical for the DA-mediated behavioral sensitization and increased stimulant consumption. A second neural circuit comprising the raphe-PFC-hippocampus is activated by continuous subordination stress and other types of uncontrollable stress. In terms of the development of therapeutics, brief maternal separation stress has proven useful in characterizing compounds acting on subtypes of GABA, glutamate, serotonin and opioid receptors with anxiolytic potential. While large increases in alcohol and cocaine intake during adulthood have been seen after prolonged maternal separation experiences during the first two weeks of rodent life, these effects may be modulated by additional yet to be identified factors. Brief episodes of defeat stress can engender behavioral sensitization that is relevant to escalated and prolonged self-administration of stimulants and possibly opioids, whereas continuous subordination stress leads to anhedonia-like effects. Understanding the intracellular cascade of events for the transition from episodic to continuous social stress in infancy and adulthood may provide insight into the modulation of basic reward processes that are critical for addictive and affective disorders.

Experiential and genetic contributions to depressive- and anxiety-like disorders: clinical and experimental studies

Stressful events have been implicated in the precipitation of depression and anxiety. These disorders may evolve owing to one or more of an array of neuronal changes that occur in several brain regions. It seems likely that these stressor-provoked neurochemical alterations are moderated by genetic determinants, as well as by a constellation of experiential and environmental factors. Indeed, animal studies have shown that vulnerability to depressive-like behaviors involve mechanisms similar to those associated with human depression (e.g., altered serotonin, corticotropin releasing hormone and their receptors, growth factors), and that the effects of stressors are influenced by previous stressor experiences, particularly those encountered early in life. These stressor effects might reflect sensitization of neuronal functioning, phenotypic changes of processes that lead to neurochemical release or receptor sensitivity, or epigenetic processes that modify expression of specific genes associated with stressor reactivity. It is suggested that depression is a life-long disorder, which even after effective treatment, has a high rate of re-occurrence owing to sensitized processes or epigenetic factors that promote persistent alterations of gene expression.

Inflammation-Susceptible Lewis Rats Show Less Sensitivity Than Resistant Fischer Rats in the Formalin Inflammatory Pain Test and With Repeated Thermal Testing

Comparisons between Lewis and Fischer inbred strains of rats are used frequently to study the effect of inherent differences in function of the hypothalamic-pituitary-adrenal axis on pain-relevant traits, including differential susceptibility to chronic inflammatory disease and differential responsiveness to analgesic drugs. Increasing use of genetic models including transgenic knockout mice and inbred strains of rodents has raised our awareness of, and the importance of, thorough characterization (or phenotyping) of the strains of rodents being compared. Furthermore, genetic variability in analgesic sensitivity is correlated with, and may be caused by, genetically determined baseline sensitivity. Thus in this study, baseline inflammatory and thermal nociceptive sensitivities were measured in awake male and female Lewis and Fischer rats to examine whether the results could explain relevant strain differences reported in the literature. The effect of maternal separation was also examined and no effect was found on nociceptive sensitivity, corticosterone responses, or the development of adjuvant-induced arthritis, a model of rheumatoid arthritis. Lewis rats and female rats were more sensitive to thermal nociception in the tail withdrawal test (mean of 3 trials) than Fischer rats and male rats, respectively. Unexpectedly, the more inflammation-susceptible Lewis rats were less sensitive in the formalin inflammatory nociception test, and showed a significant decrease in sensitivity with repeated thermal nociceptive testing, whereas Fischer rats did not. These results affect the interpretation of previously observed results. Further study of the underlying mechanisms and the relevance to differential susceptibility to chronic inflammation is warranted.

Activation of the hypothalamic-pituitary-adrenal axis and autonomic nervous system during inflammation and altered programming of the neuroendocrine-immune axis during fetal and neonatal development: lessons learned from the model inflammagen, lipopolysaccharide

The hypothalamic-pituitary-adrenal axis (HPAA) and autonomic nervous system (ANS) are both activated during inflammation as an elaborate multi-directional communication pathway designed to restore homeostasis, in part, by regulating the inflammatory and subsequent immune response. During fetal and neonatal development programming of the HPAA, ANS and possibly the immune system is influenced by signals from the surrounding environment, as part of an adaptive mechanism to enhance the survival of the offspring. It is currently hypothesized that if this programming is either misguided, or the individual's environment is drastically altered such that neuroendocrine programming becomes maladaptive, it may contribute to the pathogenesis of certain diseases. Current research, suggests that exposure to inflammatory signals during critical windows of early life development may influence the programming of various genes within the neuroendocrine-immune axis. This review will provide, (1) an overview of the HPAA and ANS pathways that are activated during inflammation, highlighting studies that have used lipopolysaccharide as a model inflammagen and, (2) evidence to support the hypothesis that inflammatory stress during fetal and neonatal development can alter programming of the neuroendocrine-immune axis, influencing stress and immune responsiveness, and possibly disease resistance later in life.

Maternal and environmental factors influence the hypothalamic–pituitary–adrenal axis response to corticotropin-releasing hormone infusion in offspring of mothers with or without mood disorders

Individuals with melancholic major depression exhibit basal hypercortisolism and an attenuated ACTH response to exogenous corticotropin-releasing hormone (CRH) infusion. Given the greater incidence of depression in children of depressed parents, we examined the ACTH and cortisol responses to ovine CRH (oCRH) infusion in 63 adolescent offspring of mothers with major depression, bipolar illness, or no psychiatric illness. Psychiatric and observational assessments of these families had been conducted over the course of 10 years preceding this study. We examined the children's responses to CRH in relation to maternal characteristics and family environment and found the following: (a) cortisol responses were negatively related to chronic family stress and (b) offspring of depressed mothers with an avoidant personality disorder showed an exaggerated ACTH response. In addition, adolescents in late puberty (Tanner 4 and 5) had lower ACTH and cortisol responses to oCRH infusion than those in early puberty. Further, offspring with early histories of mood problems, and those who developed major depressive disorder as young adults, did not exhibit basal hypercortisolism but did show an attenuated ACTH response to CRH. Our results add to the growing body of literature showing the influence of maternal characteristics and environmental factors on hypothalamic-pituitary-adrenal axis patterns in children.

Corticotropin-releasing factor receptor subtype 1 and somatostatin modulating hypoxia-caused downregulated mRNA of pituitary growth hormone and upregulated mRNA of hepatic insulin-like growth factor-I of rats

The study aims to examine the effects of restraint, cold, and in combination of hypoxia on pituitary GH mRNA and hepatic IGF-I mRNA and its protein in rats, and the potential involvement of corticotropin-releasing factor receptor subtype 1 (CRFR1) and SS in mediating the effects of continual hypoxia. Continual or intermittent hypoxia of 5 km (10.8% O2) was simulated in a hypobaric chamber. The mRNAs and peptides were determined using RT-PCR and Elisa or histochemistry. Continual hypoxia of 5 km markedly enhanced immunostaining pituitary GH and hepatic IGF-I for 1 and 2 days restoring afterward. The hypoxia for 5 days significantly reduced the pituitary GH mRNA and increased the hepatic IGF-I mRNA. Intermittent hypoxia of 5 km 4 h/day for 2 days, cold (4 degrees C) 4h/day for 2 days, and restraint 4 h/day for 2 days alone or in combination significantly enhanced immunostaining pituitary GH and hepatic IGF-I (except cold). The combined stresses had greater effects than single stresses alone. CRFR1 antagonist (CP154526) or SS antagonist (cysteamine) markedly blocked hypoxia-reduced pituitary GH mRNA and hypoxia-activated hepatic IGF-I mRNA, and further reduced hypoxia-reduced plasma IGF. In conclusion, hypoxia (continually or intermittently), restraint, cold alone or in combination modulate pituitary GH and hepatic IGF-I. The pituitary GH/GH mRNA and hepatic IGF-I/IGF-I mRNA, and plasma IGF-I are modified by hypoxia through SS and CRFR1 mediation.

Mood and hormone responses to psychological challenge in adolescent males with conduct problems

BACKGROUND

Relations between stress hormones and antisocial behavior are understudied.

METHODS

A subsample (n = 335) of at-risk males recruited in first grade for a longitudinal study were recruited at approximately 16 years of age for a laboratory study, including two psychological challenges: describing their worst experience on videotape, and a task in which a loud tone could be avoided. Measures of affect, urine, and saliva were collected multiple times before and after challenges.

RESULTS

Negative affect increased following the worst-event challenge and decreased following the avoidance challenge. Mean conduct problems (CP) across ages 7-17 years were positively related to negative affect and inversely related to positive affect. CP were inversely related to post-challenge urinary epinephrine (E) levels when baseline E and potential confounds were controlled. Cortisol concentrations in saliva collected soon after the first challenge were positively related to CP in a post hoc subset of youths with extreme CP.

CONCLUSIONS

Key findings A) associated persistent CP with more negative affectivity and less positive affectivity, B) replicated and extended prior findings of an inverse association of CP and urinary E, and C) suggested provocative hypotheses for future study relating CP, trauma history, trauma recall, and cortisol reactivity.

Stress models of depression: Forming genetically vulnerable strains

Among the most useful models for depressive disorders are those, which involve a stress induced change in behaviour. Learned helplessness is one such model and is induced through exposure to uncontrollable and unpredictable aversive events. Learned helplessness as induced in rats using foot shock is well characterized and has good face validity and predictive validity as a model of depression, including alterations in HPA axis activity and REM sleep characteristic of depression. The data concerning the validity will be briefly reviewed. The model can also be used to look at the role of genetics through selective breeding. These studies will be reviewed and the utility of the genetic strains for understanding the interaction of stress and affect will be examined. A second model of depression using exposure to chronic stress also has high face and predictive validity. A new form of this approach, recently described, also is suitable for the examination of genetic factors leading to depressive like behaviour and this will be presented.

Brain differences in newborn rats predisposed to helpless and depressive behavior

Inborn brain differences in metabolic capacity were mapped in congenitally helpless rats, a genetically selected strain predisposed to show helpless and depressive behavior. There are a number of brain regions showing abnormal metabolism in adult congenitally helpless rats. Some of these alterations may be innate while others may be due to environmental factors, such as maternal care and postnatal stress. To identify which brain structures show innate differences, brains of newborn rats from congenitally helpless and non-helpless strains were compared using cytochrome oxidase histochemistry, an endogenous marker of regional metabolic capacity. A smaller subset of regions affected in adults showed significantly less metabolic activity in the newborn brains, including paraventricular hypothalamus, habenula, hippocampus, subiculum, lateral septal nucleus, anterior cingulate cortex, infralimbic cortex, and medial orbitofrontal cortex. A covariance analysis further revealed a striking reduction of functional connectivity in the congenitally helpless brain, including a complete decoupling of limbic forebrain regions from midbrain/diencephalic regions. This pattern of brain metabolism suggests that helplessness vulnerability is linked to altered functioning of limbic networks that are key to controlling the hypothalamic-pituitary-adrenal axis. This implies that vulnerable animals have innate deficits in brain systems that would normally allow them to cope with stress, predisposing them in this manner to more readily develop helpless and depressive behaviors.

Glucose metabolism and insulin receptor signal transduction in Alzheimer disease

Nosologically, Alzheimer disease is not a single disorder in spite of a common clinical phenotype. Etiologically, two different types or even more exist. (1) In a minority of about 5% or less of all cases, Alzheimer disease is due to mutations of three genes, resulting in the permanent generation of betaA4. (2) The great majority (95% or more) of cases of Alzheimer disease are sporadic in origin, with old age as main risk factor, supporting the view that susceptibility genes and aging contribute to age-related sporadic Alzheimer disease. However, disturbances in the neuronal insulin signal transduction pathway may be of central pathophysiological significance. In early-onset familial Alzheimer disease, the inhibition of neuronal insulin receptor function may be due to competitive binding of amyloid beta (Abeta) to the insulin receptor. In late-onset sporadic Alzheimer disease, the neuronal insulin receptor may be desensitized by inhibition of receptor function at different sites by noradrenaline and/or cortisol, the levels of which both increase with increasing age. The consequences of the inhibition of neuronal insulin signal transduction may be largely identical to those of disturbances of oxidative energy metabolism and related metabolism, and of hyperphosphorylation of tau-protein. As far as the metabolism of amyloid precursor protein (APP) in late-onset sporadic Alzheimer disease is concerned, neuronal insulin receptor dysfunction may result in the intracellular accumulation of Abeta and in subsequent cellular damage. In this context, the desensitization of the neuronal insulin receptor in late-onset sporadic Alzheimer disease is different from that occurring in normal aging and early-onset familial Alzheimer disease. In late-onset sporadic Alzheimer disease changes in the brain are similar to those caused by non-insulin-dependent diabetes mellitus.

Long-term influence of an initial exposure to alcohol on the rat hypothalamic-pituitary axis

OBJECTIVE

We have previously shown that adult male rats injected with alcohol daily for 3 consecutive days displayed a significantly blunted ACTH to a second alcohol injection, given 3 to 7 days later. The purpose of the present work was to determine the maximum duration over which the ACTH response remained blunted after an initial alcohol treatment.

METHODS

Male rats were exposed to alcohol (intragastrically or via vapors for 4 hr) on three consecutive days, starting when they were 22 (group A), 34 (group B), or 50 days old (group C). Control animals were injected with the vehicle intragastrically or kept in chambers through which normal air was circulated. At 60 days of age, the animals were injected with the vehicle or alcohol (4.5 g/kg intragastrically) to determine whether the initial treatment had long-term consequences on the ACTH response to a second alcohol challenge.

RESULTS

Rats of group C, pretreated with alcohol via intragastric injections or vapors, all exhibited a blunted ACTH response to the second acute alcohol challenge. In contrast, the second alcohol challenge only attenuated ACTH responses in rats of group B that had received intragastric injections, but not vapors. Group A showed a comparable response to acute intragastric alcohol injection at 60 days of age regardless of whether they had been preexposed to the drug. This was not due to a lack of neuroendocrine response because alcohol vapors significantly increased plasma ACTH levels and up-regulated paraventricular nucleus neuronal activity regardless of the age at which it was initially administered.

CONCLUSIONS

Repeated (daily for 3 consecutive days) administration of alcohol by the gastric route induces a long-lasting (up to 24 days) but not permanent blunting of the ACTH response to a second (acute) alcohol challenge. The fact that alcohol delivered by inhalation only caused a relatively brief (</=8 days) decrease in the ability of a second intragastric alcohol challenge to release ACTH suggests that the mode of alcohol delivery influences its long-term consequences.

Corticotropin-releasing factor receptor type 1 and 2 mRNA expression in the rat anterior pituitary is modulated by intermittent hypoxia, cold and restraint

We had previously demonstrated that continual-hypoxia stimulated corticotropin-releasing factor (CRF)mRNA in hypothalamus, and release of CRF, as well as enhancing plasma adrenocorticotropic-hormone and corticosterone of rats. The present study demonstrates using in situ autoradiography that CRF receptor 1 (CRFR1) and CRF receptor 2 (CRFR2) mRNA in the rat anterior pituitary is changed by intermittent hypoxia, cold, restraint, alone and in combination. Rats were exposed to intermittent hypoxia for 4 h/day during various periods in a hypobaric chamber. Hypoxia equivalent to an altitude of around 2 km (16.0% O2) or 5 km (10.8% O2) caused a biphasic change in both CRFR1 and R2 mRNA, there being an initial significant decline on day 1 and then an enhancement by day 2. The increase of both receptor subtypes mRNA was relatively well maintained up to 15 days in rats exposed to 2 km intermittently. CRFR2 mRNA in rats exposed to 5 km, after peaking at day 2 therefore declined and was not different to controls at 15 days. Five kilometer hypoxia markedly reduced body weight gain. The increased CRFR1 mRNA was also induced by restraint alone, hypoxia+restraint and hypoxia+cold but not by cold alone. The CRFR2 mRNA was significantly increased by all the stresses except for hypoxia+restraint. These results show that the acute response to intermittent hypoxia is a decrease in the CRF receptor mRNA whereas longer exposure to the three environmental stressors hypoxia, cold and restraint is needed to provoke an increase. This may have important consequences for adaptation to high altitude. The significant differences between the expression of CRFR1 mRNA and CRFR2 mRNA in response to the different stimuli might suggest that the two receptors in the pituitary play different roles in behavior.

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.

Long-term effects of neonatal methamphetamine exposure in rats on spatial learning in the Barnes maze and on cliff avoidance, corticosterone release, and neurotoxicity in adulthood

Methamphetamine (MA) is a commonly abused stimulant and because of its addictive properties, abusers may not cease use during pregnancy, thereby exposing the fetus to the drug. The consequences of such exposure remain largely unknown however data from animal models show that long-term deficits in spatial learning and memory in the Morris water maze (MWM) occur. In this study we explored the spatial learning ability of rats treated four times daily with MA (5 mg/kg/dose) during the sensitive period for induction of MWM deficits, postnatal days (P) 11-20, using a different maze. In adulthood the animals were tested in a non-swimming spatial task, the Barnes maze, using either aversive (bright light) or appetitive (food reward) motivation. Approximately 30 days after behavioral testing, the pituitary and adrenal response to forced swim was assessed and susceptibility to MA-induced neurotoxicity measured. MA-treated animals tested in the aversive, but not the appetitive, version of the Barnes maze demonstrated spatial learning deficits. An attenuated corticosterone response in MA-treated animals was observed following forced swimming, however no differences in ACTH were found. Following acute MA administration in adulthood to all animals, the neonatally MA-treated animals displayed longer latencies to fall from a cliff than neonatally saline-treated rats given the same acute MA dose. This effect supports previous data showing hypoactivity in neonatally MA-treated animals. Acute MA treatment caused comparable striatal monoamine depletions in all groups, although females treated with MA as neonates displayed increased basal levels of corticosterone three days after the acute dose. These data demonstrate that MA administration during the neonatal period impairs spatial learning in an aversive non-swimming task and alters the adrenal response to a forced swim stressor, suggesting that the adrenal output during learning may contribute to the spatial learning deficits.

Selectively bred Wistar-Kyoto rats: an animal model of depression and hyper-responsiveness to antidepressants

The Wistar-Kyoto (WKY) rat strain demonstrates endogenous hormonal and behavioral abnormalities that emulate many of those found in symptom-presenting depressive patients. Evidence suggests that the WKY strain may harbor heterogeneity not found in other inbred strains, including greater behavioral and genetic variability. We took advantage of this variability and selectively bred WKY for 'depressive' behavior using immobility in the forced swim test (FST) as a functional selector. Successive generations of selective breeding resulted in rats that exhibited the extremes of immobility in the FST: 'WKY most immobile' (WMI) and 'WKY least immobile' (WLI). Male WMI rats also showed significantly decreased activity in the open field test (OFT). Plasma corticosterone (CORT) response to restraint stress was significantly lower and less variable in WMI compared to WLI males. Subacute treatment of males with several classes of antidepressant had different effects on FST behavior in the two substrains. Both desipramine (10 mg/kg body weight), a tricyclic antidepressant, and phenelzine (7.5 mg/kg), a monoamine oxidase inhibitor, significantly and drastically decreased FST immobility in WMI. In contrast, WLI showed a limited response to these antidepressants. Neither substrain responded to fluoxetine (10 mg/kg), a selective serotonin reuptake inhibitor. These data show that selective breeding of WKY rats has resulted in two substrains with reduced variability and differing responsiveness to antidepressants, which represent a novel means to dissect the molecular mechanisms underlying depressive behavior.

Congenitally learned helpless rats show abnormalities in intracellular signaling

BACKGROUND

Affective disorders and the drugs used to treat them lead to changes in intracellular signaling. We used a genetic animal model to investigate to what extent changes in intracellular signal transduction confer a vulnerability to mood or anxiety disorders.

METHODS

Levels of gene expression in a selectively bred strain of rats with a high vulnerability to develop congenitally learned helplessness (cLH), a strain highly resistant to the same behavior (cNLH) and outbred Sprague-Dawley (SD) control animals were compared using quantitative reverse transcription polymerase chain reaction.

RESULTS

Congenitally learned helpless animals had a 24%-30% reduced expression of the cyclic adenosine monophosphate response element binding protein messenger ribonucleic acid (mRNA) in the hippocampus and a 40%-41% increased level of the antiapoptotic protein bcl-2 mRNA in the prefrontal cortex compared to cNLH and SD rats. Other significant changes included changes in the expression levels of the alpha catalytic subunit of protein kinase A, glycogen synthase kinase 3beta, and protein kinase C epsilon.

CONCLUSIONS

Congenitally learned helpless animals show evidence of altered signal transduction and regulation of apoptosis compared to cNLH and SD control animals.

Opposite metabolic changes in the habenula and ventral tegmental area of a genetic model of helpless behavior

Congenitally helpless rats have been selectively bred to display an immediate helpless response to stress in order to model hereditary brain differences that contribute to depression vulnerability. Differences in regional brain metabolism between congenitally helpless and non-helpless rats were investigated using quantitative cytochrome oxidase histochemistry. The results indicated that congenitally helpless rats had 64-71% elevated metabolism in the habenula and a 25% elevation in the related interpeduncular nucleus. In contrast, helpless rats had 28% reduced metabolism in the ventral tegmental area (VTA) and 14-16% reductions in the basal ganglia and basolateral and central amygdala. The opposite metabolic changes in the habenula and ventral tegmental area may be especially important for determining the congenitally helpless rat's global pattern of brain activity, which resembles the metabolic activity pattern produced by dopamine antagonism.

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.

5-HT(1B) mrna regulation in two animal models of altered stress reactivity

BACKGROUND

Acute stress has profound effects on serotonergic activity, but it is not known whether alterations in the serotonin system can predispose individuals to exaggerated stress responses. We examined the regulation of 5-HT(1B) and 5-HT(1A) mRNA in two rodent models of differential sensitivity to stress: congenital learned helplessness (cLH) and handling and maternal separation (HMS).

METHODS

5-HT(1B) and 5-HT(1A) mRNAs in brain tissue sections were quantitated by in situ hybridization from control, stress-sensitive, and stress-resistant male rats in the HMS model and stress-sensitive and stress-resistant rats (both males and females) in the cLH model. Dorsal raphe nucleus, striatum, and hippocampus were examined.

RESULTS

The main result was that dorsal raphe 5-HT(1B) mRNA was substantially elevated (63-73%) in male rats in the stress-resistant group of both models compared with stress-sensitive animals. 5-HT(1B) mRNA in female rats did not differ between groups in the cLH model. There were no differences in 5-HT(1A) mRNA between HMS groups.

CONCLUSIONS

These findings suggest that 5-HT(1B) autoreceptor regulation is altered in animals with diminished stress reactivity. These results suggest that 5-HT(1B) autoreceptors in unstressed and acutely stressed animals differ, indicating the importance of state versus trait changes in serotonin function in animal models of anxiety and depression.

The validity of animal models of predisposition to depression

Some animal models of depression, including the majority of the more recently introduced models, are better characterized as models of predisposition to depression. In the first part of this paper, we show that the basis for such a model could be either a procedure that increases the ease with which an analogue of major depression may be evoked, or a presentation analogous to dysthymia (chronic mild depression). We then consider how the concepts of predictive, face, and construct validity apply to such models. Next, we review the validity of the available models of predisposition to depression, which derive from genetics, genomics, developmental manipulations, and brain lesioning. Finally, we compare the performance of the different models, using a novel scoring system that formalizes the evaluation of animal models against each of the three sets of validation criteria.

In vivo models of interstitial cystitis

PURPOSE

We systematically identified and evaluated various animal models that have been studied to help identify the underlying mechanisms of and possible treatment options for interstitial cystitis.

MATERIALS AND METHODS

Models of interstitial cystitis published between 1983 and 2001 were obtained by searching MEDLINE and other Internet databases using cystitis and model as the primary key words. Models with characteristics of interstitial cystitis similar to those defined by National Institutes of Arthritis, Diabetes, Digestive and Kidney Diseases criteria were reviewed. Some articles describing animal models with similar pathological conditions in other organs were also included to enlarge the base of potentially relevant material.

RESULTS

We identified and evaluated some 16 animal models of interstitial cystitis, which we categorized as bladder inflammation induced by intravesical administration of an irritant or immune stimulant, systemic and environmentally induced inflammation, and a naturally occurring model of interstitial cystitis that occurs in cats. Some abnormalities identified in humans and cats with interstitial cystitis can be reproduced in healthy animals using luminal, systemic or environmental stimuli. At the level of the bladder the source of stimulation cannot be discriminated. Variability in the extent of bladder distention complicated the interpretation of some studies. In addition, the noxious stimuli used can affect many epithelial surfaces as well as the urothelium, suggesting they are nonspecific responses to injury rather than specific to interstitial cystitis.

CONCLUSIONS

No model in bladder injury in healthy animals currently reproduces as many features of interstitial cystitis as the naturally occurring disease in cats. While induced models of relative injury may help to provide insight into the bladder response to injury, feline interstitial cystitis follows a similar chronic waxing and waning time course as does interstitial cystitis in humans, which may be more suitable for studying the effects of stressors on the severity of clinical signs as well as newly proposed therapies.

Genetic predisposition and the development of posttraumatic stress disorder in an animal model

BACKGROUND

Exposure to extremely stressful events can lead to Posttraumatic stress disorder (PTSD). Due to the complexity of PTSD, animal models have been designed and advanced to address the role of psychosocial stressors in the etiology; however, the apparent role of genetics in susceptibility to PTSD-like behaviors in animals remains unexplored.

METHODS

An animal model of congenital learned helpless (cLH) behavior has been used to study the effects of genetic disposition as a risk factor for the development of PTSD-like behaviors. Animals were monitored for changes in pain tolerance, spatial memory and hypothalamic-pituitary-adrenal functioning after re-exposure to intermittent stress in the presence and absence of situational cues.

RESULTS

Exposure to stress resulted in an increase in pain tolerance in the cLH animals. In the spatial memory test 80% of the cLH animals manifested a decrease in performance after exposure to stress. These animals also had a blunted poststress corticosterone response.

CONCLUSIONS

The genetic learned helpless animal model exhibited physiologic symptoms of analgesia, cognitive deficits and hyporesponsivity of the hypothalamic-pituitary-adrenal axis similar to those observed in human subjects with PTSD. It is proposed that the cLH model may be a valuable tool for exploring the role of genetic predisposition in the etiology of PTSD.

Brain-derived-neurotrophic-factor (BDNF) stress response in rats bred for learned helplessness

Stress-induced elevation of glucocorticoids is accompanied by structural changes and neuronal damage in certain brain areas. This includes reduced expression of brain-derived neurotrophic factor (BDNF) in the hippocampus which can be prevented by chronic electroconvulsive seizures and antidepressant drug treatment. In the last years we have bred two strains of rats, one which reacts with congenital helplessness to stress (cLH), and one which congenitally does not acquire helplessness when stressed (cNLH). After being selectively bred for more than 40 generations these strains have lost their behavioural plasticity including their sensitivity to antidepressant treatment. We show here that in cLH rats, acute immobilization stress does not induce a reduction of BDNF expression in the hippocampus which is observed in Sprague--Dawley and cNLH rats. All animals tested exhibited elevated corticosterone levels when stressed, an indication, that in cLH rats regulation of BDNF expression in the hippocampal formation is uncoupled from corticosterone increase induced through stress. This may explain the lack of adaptive responses in this strain.

Antidepressants during pregnancy and lactation: defining exposure and treatment issues

The majority of psychiatric illness onsets early in an individual's life, typically before or during the reproductive years. The increased incidence of major depression, dysthymia, and panic disorder in women compared with men underscores the likelihood that the clinician will encounter the clinical dilemma of medication use during pregnancy and lactation. The emergence of specialized clinics at several academic centers specifically to investigate and address issues in Perinatal psychiatry illustrates this conundrum best. The extant literature derived from human studies suggests that maternal mental illness and stress may have an adverse impact on obstetrical outcome. These clinical investigations are complemented by a burgeoning series of laboratory studies in rodents and nonhuman primates, showing the profound deleterious impact of maternal stress during the perinatal and neonatal periods on the development of the offspring. Data obtained from pharmaceutical registries, cohort studies, toxicology centers, and case series have consistently failed to show an adverse effect associated with in utero antidepressant exposure. Despite these advances and treatment guidelines proposed by the various academic leaders, investigations describing the extent of fetal/neonatal exposure, clinical methods for minimizing such exposure, and clinical treatment guidelines that include the physiological impact of pregnancy are sparse. The available literature shows distinct pharmacokinetic profiles of the selective serotonin reuptake inhibitors in placental passage and breast milk. Preliminary animal studies have shown higher than expected central nervous system concentrations associated with exposure during pregnancy and mathematical modelling for calculating infant exposure when nursing. The clinical import of these data will require further investigations of central nervous system bioavailability in the fetus and neonate.

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.

Preweaning treatment with methamphetamine induces increases in both corticosterone and ACTH in rats

Treatment with methamphetamine (MA) on postnatal days P11-20 induces adult spatial learning and memory deficits without affecting monoamine levels in various brain regions. In this study, we examined the pituitary and adrenal response of animals administered MA four times daily on P11, P11-15, or from P11 to P20. Corticosterone (CORT) and adrenocorticotropin hormone (ACTH) levels were assessed over a 1-hour period following MA exposure. On P11, MA produced marked elevations of both CORT and ACTH; this is during the stress hyporesponsive period (SHRP). On P15 and P20, the maximal effect of MA on CORT titers was observed at 30 min, with lower, but still significantly increased, levels at 60 min compared to controls. Males receiving MA on P15 had higher levels of ACTH than did control males, while no differences were noted among females. On P20, MA treatment resulted in higher levels of ACTH relative to vehicle-injected controls, but levels were not different from controls that were only weighed at each drug administration. MA treatment inhibited body, but not brain weight gain, resulting in hippocampal weights that were heavier in the MA-treated animals when expressed as a percent of body weight. The elevations of adrenal steroids by MA, during late phases of hippocampal neurogenesis, may contribute to neuronal alterations that are later manifested in deficits of learning and memory.