Genetic stress-reactivity, sex, and conditioning intensity affect stress-enhanced fear learning.

The Stress-Enhanced Fear Learning (SEFL) model of posttraumatic stress disorder (PTSD) reveals increased fear memory in animals exposed to stress prior to contextual fear conditioning (CFC), similar to the increased likelihood of developing PTSD in humans after prior stress. The present study utilized the SEFL model by exposing animals to restraint stress as the first stressor, followed by CFC using foot-shocks with 0.6 mA or 0.8 mA intensity. Adult males and females from the two nearly isogenic rat strains, the genetically more stress-reactive Wistar Kyoto (WKY) More Immobile (WMI), and the less stress-reactive WKY Less Immobile (WLI) were employed. Percent time spent freezing at acquisition and at recall differed between these strains in both prior stress and no stress conditions. The significant correlations between percent freezing at acquisition and at recall suggest that fear memory differences represent a true phenotype related to the stress-reactivity differences between the strains. This assumption is further substantiated by the lack of effect of either conditioning intensity on percent freezing in WLI males, while WMI males were affected by both intensities albeit with opposite directional changes after prior stress. Differences between the sexes in sensitivity to the two conditioning intensities became apparent by the opposite directional and inverse relationship between fear memory and the intensity of conditioning in WMI males and females. The present data also illustrate that although corticosterone (CORT) responses to prior stress are known to be necessary for SEFL, plasma CORT and percent freezing were positively correlated only in the stress less-reactive WLI strain. These differences in baseline fear acquisition, fear memory, and the percent freezing responses to the SEFL paradigm in the two genetically close inbred WMI and WLI strains provide a unique opportunity to study the genetic contribution to the variation in these phenotypes.

Hippocampus-dependent memory and allele-specific gene expression in adult offspring of alcohol-consuming dams after neonatal treatment with thyroxin or metformin.

Fetal alcohol spectrum disorder (FASD), the result of fetal alcohol exposure (FAE), affects 2-11% of children worldwide, with no effective treatments. Hippocampus-based learning and memory deficits are key symptoms of FASD. Our previous studies show hypothyroxinemia and hyperglycemia of the alcohol-consuming pregnant rat, which likely affects fetal neurodevelopment. We administered vehicle, thyroxine (T4) or metformin to neonatal rats post FAE and rats were tested in the hippocampus-dependent contextual fear-conditioning paradigm in adulthood. Both T4 and metformin alleviated contextual fear memory deficit induced by FAE, and reversed the hippocampal expression changes in the thyroid hormone-inactivating enzyme, deiodinase-III (Dio3) and insulin-like growth factor 2 (Igf2), genes that are known to modulate memory processes. Neonatal T4 restored maternal allelic expressions of the imprinted Dio3 and Igf2 in the adult male hippocampus, while metformin restored FAE-caused changes in Igf2 expression only. The decreased hippocampal expression of DNA methyltransferase 1 (Dnmt1) that maintains the imprinting of Dio3 and Igf2 during development was normalized by both treatments. Administering Dnmt1 inhibitor to control neonates resulted in FAE-like deficits in fear memory and hippocampal allele-specific expression of Igf2, which were reversed by metformin. We propose that neonatal administration of T4 and metformin post FAE affect memory via elevating Dnmt1 and consequently normalizing hippocampal Dio3 and Igf2 expressions in the adult offspring. The present results indicate that T4 and metformin, administered during the neonatal period that is equivalent to the third trimester of human pregnancy, are potential treatments for FASD and conceivably for other neurodevelopmental disorders with cognitive deficits.

Gene expression patterns in the hippocampus and amygdala of endogenous depression and chronic stress models.

The etiology of depression is still poorly understood, but two major causative hypotheses have been put forth: the monoamine deficiency and the stress hypotheses of depression. We evaluate these hypotheses using animal models of endogenous depression and chronic stress. The endogenously depressed rat and its control strain were developed by bidirectional selective breeding from the Wistar-Kyoto (WKY) rat, an accepted model of major depressive disorder (MDD). The WKY More Immobile (WMI) substrain shows high immobility/despair-like behavior in the forced swim test (FST), while the control substrain, WKY Less Immobile (WLI), shows no depressive behavior in the FST. Chronic stress responses were investigated by using Brown Norway, Fischer 344, Lewis and WKY, genetically and behaviorally distinct strains of rats. Animals were either not stressed (NS) or exposed to chronic restraint stress (CRS). Genome-wide microarray analyses identified differentially expressed genes in hippocampi and amygdalae of the endogenous depression and the chronic stress models. No significant difference was observed in the expression of monoaminergic transmission-related genes in either model. Furthermore, very few genes showed overlapping changes in the WMI vs WLI and CRS vs NS comparisons, strongly suggesting divergence between endogenous depressive behavior- and chronic stress-related molecular mechanisms. Taken together, these results posit that although chronic stress may induce depressive behavior, its molecular underpinnings differ from those of endogenous depression in animals and possibly in humans, suggesting the need for different treatments. The identification of novel endogenous depression-related and chronic stress response genes suggests that unexplored molecular mechanisms could be targeted for the development of novel therapeutic agents.

Pilot validation of blood-based biomarkers during pregnancy and postpartum in women with prior or current depression.

Major depressive disorder (MDD) is more common in women than in men, and evidence of gender-related subtypes of depression is emerging. Previously identified blood-based transcriptomic biomarkers distinguished male and female subjects with MDD from those without the disorder. In the present pilot study, we investigated the performance of these biomarkers in pregnant and postpartum women with prior major depressive episodes, some of whom had current symptomatology. The symptom scores of 13 pregnant and 15 postpartum women were identified by the Inventory of Depressive Symptoms (IDS-SR-30) at the time of blood sampling. Blood levels of the 20 transcriptomic biomarkers and that of estrogen receptor 2 (ESR2), membrane progesterone receptor alpha and beta (mPRα, mPRß) were measured. In pregnant women, transcript levels of ADCY3, ASAH1, ATP11C, CDR2, ESR2, FAM46A, mPRß, NAGA, RAPH1, TLR7, and ZNF291/SCAPER showed significant association with IDS-SR-30 scores, of which ADCY3, FAM46A, RAPH1, and TLR7 were identified in previous studies for their diagnostic potential for major depression. ASAH1 and ATP11C were previously also identified as potential markers of treatment efficacy. In postpartum women, transcript levels of CAT, CD59, and RAPH1 demonstrated a trend of association with IDS-SR-30 scores. Transcript levels of ADCY3, ATP11C, FAM46A, RAPH1, and ZNF291/SCAPER correlated with ESR2 and mPRß expressions in pregnant women, whereas these associations only existed for mPRß in postpartum women. These results suggest that a blood biomarker panel can identify depression symptomatology in pregnant women and that expression of these biomarker genes are affected by estrogen and/or progesterone binding differently during pregnancy and postpartum.

Blood and affective markers of stress in Elite Airmen during a preparatory training course: A pilot study.

In highly stressful environments, individuals with diverging stress-reactivity can perform differently. Identification of blood markers of stress-reactivity is of major significance to help human performance during stress. Candidate transcripts were identified between stressed and non-stressed strains of rats' blood and brain, and overlapping significant differentially expressed genes were selected. Serum levels of human orthologues of these proteins, in lieu of blood RNA, in addition to classic stress and general clinical markers, were measured in 33 Battlefield Airmen undergoing a 52 day long preparatory training course before their course of initial entry (COIE). Blood samples and factors of affective state, negative valence "Threat" and positive valence "Challenge", were obtained five times across different days of training which included either routine physical exercise or prolonged and intense physical and mental training. During training, levels of chloride (Cl), dehydroepiandrosterone-sulfate (DHEA-S), creatinine kinase (CK), and total carbon dioxide (TCO2) differed between airmen who subsequently graduated from their COIE and those who did not. Time dependent changes of serum TCO2 and neuropeptide Y (NPY), as well as the affective factor Challenge differed by future graduation status throughout the training. Serum levels of parvin beta (PARVB) correlated with the affective factor Threat, while those of NPY, testosterone, coactosin like F-actin binding protein 1 (COTL1) and C-reactive protein (CRP) correlated with factor Challenge during the extended, intensive periods of training, consistently. These pilot data suggest that the identified panel of blood markers can measure stress responsiveness, which has the potential to advance individualized stress-management strategies.

Heterogeneous stock rats: a model to study the genetics of despair-like behavior in adolescence.

Major depressive disorder (MDD) is a complex illness caused by both genetic and environmental factors. Antidepressant resistance also has a genetic component. To date, however, very few genes have been identified for major depression or antidepressant resistance. In this study, we investigated whether outbred heterogeneous stock (HS) rats would be a suitable model to uncover the genetics of depression and its connection to antidepressant resistance. The Wistar Kyoto (WKY) rat, one of the eight founders of the HS, is a recognized animal model of juvenile depression and is resistant to fluoxetine antidepressant treatment. We therefore hypothesized that adolescent HS rats would exhibit variation in both despair-like behavior and response to fluoxetine treatment. We assessed heritability of despair-like behavior and response to sub-acute fluoxetine using a modified forced swim test (FST) in 4-week-old HS rats. We also tested whether blood transcript levels previously identified as depression biomarkers in adolescent human subjects are differentially expressed in HS rats with high vs. low FST immobility. We demonstrate heritability of despair-like behavior in 4-week-old HS rats and show that many HS rats are resistant to fluoxetine treatment. In addition, blood transcript levels of Amfr, Cdr2 and Kiaa1539, genes previously identified in human adolescents with MDD, are differentially expressed between HS rats with high vs. low immobility. These data demonstrate that FST despair-like behavior will be amenable to genetic fine-mapping in adolescent HS rats. The overlap between human and HS blood biomarkers suggest that these studies may translate to depression in humans.

A support vector machine model provides an accurate transcript-level-based diagnostic for major depressive disorder.

Major depressive disorder (MDD) is a critical cause of morbidity and disability with an economic cost of hundreds of billions of dollars each year, necessitating more effective treatment strategies and novel approaches to translational research. A notable barrier in addressing this public health threat involves reliable identification of the disorder, as many affected individuals remain undiagnosed or misdiagnosed. An objective blood-based diagnostic test using transcript levels of a panel of markers would provide an invaluable tool for MDD as the infrastructure-including equipment, trained personnel, billing, and governmental approval-for similar tests is well established in clinics worldwide. Here we present a supervised classification model utilizing support vector machines (SVMs) for the analysis of transcriptomic data readily obtained from a peripheral blood specimen. The model was trained on data from subjects with MDD (n=32) and age- and gender-matched controls (n=32). This SVM model provides a cross-validated sensitivity and specificity of 90.6% for the diagnosis of MDD using a panel of 10 transcripts. We applied a logistic equation on the SVM model and quantified a likelihood of depression score. This score gives the probability of a MDD diagnosis and allows the tuning of specificity and sensitivity for individual patients to bring personalized medicine closer in psychiatry.

Nature and nurture: environmental influences on a genetic rat model of depression.

In this study, we sought to learn whether adverse events such as chronic restraint stress (CRS), or 'nurture' in the form of environmental enrichment (EE), could modify depression-like behavior and blood biomarker transcript levels in a genetic rat model of depression. The Wistar Kyoto More Immobile (WMI) is a genetic model of depression that aided in the identification of blood transcriptomic markers, which successfully distinguished adolescent and adult subjects with major depressive disorders from their matched no-disorder controls. Here, we followed the effects of CRS and EE in adult male WMIs and their genetically similar control strain, the Wistar Kyoto Less Immobile (WLI), that does not show depression-like behavior, by measuring the levels of these transcripts in the blood and hippocampus. In WLIs, increased depression-like behavior and transcriptomic changes were present in response to CRS, but in WMIs no behavioral or additive transcriptomic changes occurred. Environmental enrichment decreased both the inherent depression-like behavior in the WMIs and the behavioral difference between WMIs and WLIs, but did not reverse basal transcript level differences between the strains. The inverse behavioral change induced by CRS and EE in the WLIs did not result in parallel inverse expression changes of the transcriptomic markers, suggesting that these behavioral responses to the environment work via separate molecular pathways. In contrast, 'trait' transcriptomic markers with expression differences inherent and unchanging between the strains regardless of the environment suggest that in our model, environmental and genetic etiologies of depression work through independent molecular mechanisms.

Corticotropin release inhibiting factor is encoded within prepro-TRH.

Corticotropin synthesis and secretion is under negative feedback regulation by glucocorticoids. In addition a hypothalamic factor inhibiting ACTH synthesis and secretion, named corticotropin release inhibiting factor (CRIF), has been postulated but not identified. Here we report that transient transfection of a rat prepro-TRH cDNA into the mouse anterior pituitary tumor cell line AtT-20 inhibits the synthesis and secretion of both basal and CRH-stimulated ACTH. Thus, CRIF appears to be encoded by the same precursor as TRH, suggesting a coordinated regulation of pituitary-adrenal and pituitary-thyroid functions.

Corticotropin release-inhibiting factor is preprothyrotropin-releasing hormone-(178-199).

ACTH is the major regulator of the body's adaptive response to stress and the physiological stimulus for glucocorticoid secretion. In addition to the known negative feedback regulation of ACTH by glucocorticoids, a hypothalamic corticotropin release-inhibiting factor (CRIF) that inhibits ACTH synthesis and secretion has been postulated, but not identified. We previously reported that transfection of prepro-TRH complementary DNA into the mouse anterior pituitary tumor cell line AtT-20 results in inhibition of basal and corticotropin-releasing hormone (CRH)-stimulated ACTH synthesis and secretion, suggesting that one or more of the cryptic peptides encoded within the prepro-TRH precursor has CRIF activity. To narrow the choice of peptides responsible for CRIF activity, we first deleted specific sequences within the prepro-TRH complementary DNA and transfected these constructs into AtT-20 cells. Deletion of sequences encoding amino acids 119-229 resulted in the loss of CRIF activity. Of the peptides encoded within this region, prepro-TRH-(178-199), a 22-amino acid peptide, inhibited basal and CRH-stimulated ACTH synthesis and secretion in cultured primary anterior pituitary cells. As this peptide is processed from prepro-TRH in vivo, is found in the external zone of the median eminence, and is secreted from hypothalamic slices in vitro, prepro-TRH-(178-199) fulfills the criteria for a physiological CRIF. The significance of TRH and CRIF sharing a common precursor opens new areas of research in the integrated regulation of pituitary-adrenal and pituitary-thyroid functions.

Corticotropin-releasing hormone and proopiomelanocortin gene expression is altered selectively in the male rat fetal thymus by maternal alcohol consumption.

The present study was carried out to investigate how hormonal changes caused by chronic alcohol exposure of rats during the late period of gestation are coordinated with neuroendocrine functions of the fetal thymus, namely thymic expression of CRH and POMC genes. Alcohol consumption by pregnant dams led to a 5-fold elevation of plasma corticosterone (CORT) levels and significantly decreased fetal CORT levels. This generally inverse correlation between maternal and fetal CORT was absent in alcohol-consuming dams and their male fetuses on day 19 of gestation. These day 19 fetuses also had an attenuated plasma testosterone surge that occurred in the male control (pair-fed) fetus on day 19 of embryonic life. Furthermore, fetal alcohol exposure (FAE) resulted in a significant increase in thymic CRH and a decrease in thymic POMC expression in the male fetuses only, specifically on embryonic day 19. Thus, the strong positive correlation between CRH and POMC gene expression in the thymus of pair-fed male and female FAE fetuses was abolished in the FAE males. However, regardless of embryonic age or treatment, a strong positive correlation between thymic POMC gene expression and plasma testosterone levels in the male fetuses was detected. These data suggest that the sexually dimorphic effect of FAE on the fetal thymic POMC and CRH expression in males is driven by testosterone and may be related, therefore, to the presence of alcohol at the time of the prenatal testosterone surge in the male fetuses.

Thyroxine administration prevents streptococcal cell wall-induced inflammatory responses.

Administration of streptococcal cell wall (SCW) preparation induces an inflammatory response in susceptible animals that is a model frequently used for rheumatoid arthritis. The degree of inflammation produced by SCW is greatly enhanced by low endogenous levels of glucocorticoids due to diminished hypothalamic-pituitary-adrenal activity. Because decreased glucocorticoid production is known to occur in the hypothyroid state, we tested whether hypothyroidism would increase, and conversely, whether hyperthyroidism would decrease, the inflammatory responses to SCW. Adult female Sprague Dawley rats were fed a regular diet (control), L-T4 (T4; hyperthyroid), or 6-propyl-thiouracil (hypothyroid) in drinking water for 7 weeks. Hypothyroidism resulted in elevated plasma levels of TSH and hypothalamic preproTRH messenger RNA (mRNA) while reducing anterior pituitary POMC mRNA and plasma ACTH and corticosterone levels. In contrast, hyperthyroid rats produced opposite results: decreased measures of central thyroid function but increased pituitary-adrenal function. Three days after administration of SCW, macrophage inflammatory protein-1alpha and interleukin-1beta mRNA expression increased dramatically in controls and even further in hypothyroid animals, as measured by Northern blot analysis. In contrast, T4-treated rats showed significant inhibition of these inflammatory markers. Thus, the hyperthyroid state combined with increased endogenous glucocorticoid levels is protective against inflammatory challenges. The inverse relationship between preproTRH expression and pituitary-adrenal function suggests the possibility of a direct inhibitory link connecting the hypothalamic-pituitary-adrenal and thyroid axes, and suggests alternative sites of therapeutic intervention for rheumatoid arthritis and other inflammatory associated disorders.

Maternal adrenalectomy alters the immune and endocrine functions of fetal alcohol-exposed male offspring.

Exposure to ethanol in utero compromises the offspring's developing immune and endocrine systems. Persistent functional changes, particularly in T-cell-dependent aspects of immunity and in hypothalamic-pituitary-adrenal activity, are commonly seen. The present study examined the degree to which fetal alcohol exposure (FAE) during development suppressed the lymphocyte proliferative response to Concanavalin-A (Con A). We also examined the effect of maternal adrenalectomy on the expression of glucocorticoid-regulated genes and the response to Con A in FAE offspring. Con A-stimulated lymphocyte proliferation was stably suppressed (between 28-46%) in FAE males compared to isocalorically pair-fed offspring at 7, 21, 40, and 60 days of age. In contrast, lymphocyte proliferation in the immature or peripubertal FAE female was totally unaffected. In 60-day- old male rats, maternal adrenalectomy reversed the FAE-induced suppression of Con A-stimulated proliferation, but had no effect on lymphocyte proliferation. FAE increased anterior pituitary POMC (the precursor of ACTH) mRNA levels dramatically in males, and this increase was also reversed by maternal adrenalectomy. In both sexes, anterior pituitary glucocorticoid receptor mRNA levels were unaffected by prenatal alcohol exposure alone, but were significantly decreased in male and increased in female offspring of adrenalectomized dams ingesting alcohol. Furthermore, in male, but not female, offspring, hypothalamic levels of glucocorticoid receptor and CRF mRNA were increased significantly by FAE alone or in combination with maternal adrenalectomy. In female, but not male, offspring, maternal adrenalectomy with concomitant alcohol exposure increased anterior pituitary POMC mRNA levels compared to that in sham/pair-fed offspring. In summary, FAE induced a gender-specific impairment of Con A-stimulated lymphocyte proliferation. This deficit is present both before and after puberty, demonstrating its stability into adulthood. Furthermore, in males, maternal adrenalectomy reversed these FAE-induced deficits in T-cell function as well as the effect of FAE on anterior pituitary POMC expression. This supports the hypothesis that maternal adrenal hormones participate in the immunosuppressive "imprinting" of the FAE fetus and are, therefore, causally implicated in the sexually dimorphic T-cell dysfunction found in FAE offspring.

Effects of ethanol on CRF release in vitro.

Acute ethanol exposure produces activation of the brain-pituitary-adrenal (BPA) axis, resulting in the release of ACTH, beta-endorphin, and glucocorticoids. While elevated levels of plasma glucocorticoids are also found after chronic ethanol administration, plasma ACTH and beta-endorphin are normal or reduced. It is also unclear whether chronic ethanol exposure results in tolerance to the stimulatory effect of ethanol on BPA activity. To determine the site and mechanism of ethanol action on the BPA axis we studied the CRF secretory profile in a superfused rat hypothalamic preparation after chronic ethanol administration in vivo and the CRF responses after acute ethanol exposure in vitro. Superfused hypothalami from normal and pair-fed control rats released CRF-like immunoreactive material (CRF-LI) in a pulsatile manner, with a mean (+/- SE) frequency of 5.1 +/- 0.7 pulses/h. In contrast, the pulse frequency of CRF-LI release from hypothalami of rats receiving chronic ethanol treatment (fed an alcohol-containing liquid diet for 2 weeks) increased dramatically; the basal mean CRF level, pulse amplitude, and pulse duration remained unchanged. Hypothalamic CRF content was decreased. This chronic ethanol exposure also altered the dose-response characteristics of CRF release when ethanol was introduced acutely, as a pulse, into the in vitro preparation. Acute exposure to 20 mg/100 ml ethanol produced greater release of CRF-LI from control hypothalami than from chronic ethanol-exposed hypothalami. A further elevation above basal levels was produced by 200 mg/100 ml ethanol in control, but not ethanol-exposed, hypothalami. Secretion of CRF from ethanol-exposed hypothalami in response to depolarizing concentrations of potassium chloride was suppressed. Chronic ethanol treatment had no effect on CRF-LI and CRF bioactivity responses to stimulation with acetylcholine. These findings suggest the presence of a high frequency pulse-generating mechanism for CRF release in the hypothalamus. This pulsatile secretory mechanism is altered by chronic ethanol exposure of the animals in vivo. Chronic intoxication resulted in tolerance to the stimulatory effect of ethanol on CRF release in vitro.

Maternal adrenalectomy eliminates a surge of plasma dehydroepiandrosterone in the mother and attenuates the prenatal testosterone surge in the male fetus.

Previous work has established a number of sex-related deficits in immune function, behavior, and endocrine responses to stress in the offspring of dams exposed to ethanol. To examine the potential role of maternal glucocorticoids as a mediator of these sexually dimorphic effects in the fetus, we examined the influence of prenatal alcohol exposure in the presence or absence of maternal glucocorticoids on fetal plasma corticosterone (CORT) production. An additional question to be addressed by these studies was whether maternal adrenalectomy could eliminate the known inhibition by ethanol of the prenatal surge of plasma testosterone in male fetuses. Pregnant dams were adrenalectomized (ADX) or sham-adrenalectomized on gestational day (G) 7 and placed on a liquid diet containing 35% ethanol-derived calories or pair-fed an isocaloric control diet throughout the experiment. On G18, G19, and G21, plasma levels of CORT, testosterone, and dehydroepiandrosterone (DHEA) were measured in male and female fetuses and their mothers. Ethanol administration consistently increased maternal plasma CORT levels but did not significantly alter CORT levels in the fetus. Maternal ADX resulted in compensatory increases in fetal CORT levels that were lower in fetuses of ADX dams on alcohol, suggesting a direct effect of ethanol on fetal pituitary-adrenal activity. There were no significant sex differences in fetal plasma CORT levels in response to any of these manipulations. A novel surge of maternal plasma DHEA was found on G19 that was absent in plasma from ADX dams. In spite of the absence of a surge on G19, plasma DHEA levels of ADX dams rose from very low levels at G18 to levels on G21 that were significantly higher than in Sham dams. A normal testosterone surge was observed in male fetuses on G18 and G19 from sham-adrenalectomized dams administered the pair-fed diet. However, this surge was greatly attenuated in males administered ethanol and also in male fetuses from ADX dams. These results reveal a direct inhibitory influence of ethanol on fetal CORT secretion as well as on the prenatal testosterone surge in males. Furthermore, these studies demonstrate the presence of a surge of DHEA in the pregnant rat. Overall, these data suggest that there is a critical adrenal factor in the rat that regulates the maternal surge of DHEA on G19 and the prenatal testosterone surge of male fetuses on G18-19.

Dehydroepiandrosterone sulfate and psychiatric measures in a frail, elderly residential care population.

BACKGROUND: Previous reports have found low levels of dehydroepiandrosterone sulfate (DHEA-S) in association with physical illness, and with frailty in the elderly. In a preliminary study, we also found low DHEA-S associated with increased disability and number of pain sites. However, we found the opposite relationship between DHEA-S and cognitive impairment. Therefore, we conducted a study of a second sample to confirm this unexpected finding and the expected inverse correlations between DHEA-S levels and increased disability and number of pain sites. METHODS: Psychiatric symptoms and disorders were correlated with DHEA-S and related steroid levels in a second convenience sample in the nursing home population. RESULTS: This sample confirmed the previous finding of a positive association of cognitive impairment with higher DHEA-S levels but the inverse association of DHEA-S levels with the numbers of pain sensations did not reach statistical significance. Cognitive impairment was also positively associated with higher dehydroepiandrosterone (DHEA) and estradiol levels (women only). Cortisol levels were inversely associated with depressive symptoms. CONCLUSIONS: The anomalous positive correlation between cognitive dysfunction and DHEA-S levels, and the inverse correlation between cortisol levels and depressive symptoms, suggests that the relationships between psychiatric symptomatology and levels of steroids that are part of the hypothalamic-pituitary adrenal axis are different in the frail elderly population from that of younger and heartier populations.

Paradoxical hormonal and behavioral responses to hypothyroid and hyperthyroid states in the Wistar-Kyoto rat.

Wistar-Kyoto (WKY) rats show endogenous depressive behavior that can be reversed by antidepressants. Given that WKYs exhibit decreased sensitivity to some antidepressants and treatment-resistant depressed patients often show hypothalamic-pituitary-thyroid (HPT) dysregulation, we examined the behavioral and HPT hormonal responses of WKYs to altered thyroid status. "Euthyroid" WKYs had elevated basal plasma TSH and T(3) levels as compared to Wistars. Hypothyroidism increased TSH levels more in WKYs than in Wistars and increased response latency in the open field test (OFT) of WKYs only. Administration of T(4) and T(3) suppressed plasma TSH equally in both strains. Wistars responded to increased T(3) levels with decreased response latency and increased activity in the OFT, but increased immobility in the forced swim test. In contrast, WKYs responded only to the high T(3) levels with decreased response latency in the OFT. These results suggest the existence of a decreased central nervous system sensitivity to thyroid hormones in WKYs that could be related to their depressive behavior.

Prepro-thyrotropin-releasing hormone 178-199 increases sensitivity of AtT-20 cells to dexamethasone.

The prepro-thyrotropin-releasing hormone (ppTRH)-derived peptide, ppTRH178-199, has been proposed to inhibit ACTH release at the level of the pituitary and attenuate prolactin and behavioral responses to stress as well. The objective of this study was to elucidate a possible link between the effects of ppTRH178-199 and glucocorticoids on the inhibition of ACTH release in corticotrophs. Compared with mock-transfected cells, AtT-20 cells that were stably transfected with full-length ppTRH cDNA showed significantly increased sensitivity to dexamethasone, as measured by inhibition of ACTH release. In a group of control cells, expressing a mutated form of ppTRH cDNA lacking the ppTRH178-199 region, sensitivity to dexamethasone was not different from mock-transfected controls. Exogenous ppTRH178-199 also increased the inhibitory effect of dexamethasone in wild-type AtT-20 cells. The combined effect of dexamethasone and ppTRH cDNA in cells that express the latter was not due to increased endogenous secretion of ppTRH178-199 in response to dexamethasone, as dexamethasone was independently found to inhibit secretion of ppTRH178-199. Taken together, these data suggest that ppTRH178-199 can interact with the glucocorticoid negative feedback inhibition to regulate ACTH secretion.

Decreased in vitro sensitivity to dexamethasone in corticotropes from middle-age rats.

A disregulation of the hypothalamic-pituitary-adrenal (HPA) axis due to a decline of negative feedback regulation is a consistent feature of the aging process. Hippocampus has been proposed to be a primary site responsible for this alteration in the HPA axis in aging in rat. In this study an alternative hypothesis that the decreased sensitivity of the HPA axis to glucocorticoids in aging occurs directly in pituitary corticotropes has been tested. The sensitivity of corticotropes isolated from 2- and 13-month old male Sprague-Dawley rats to dexamethasone (DEX) in vitro was examined using a modification of the combined DEX/CRH challenge test that was originally designed for investigation of relative glucocorticoid resistance in vivo. No significant difference in basal ACTH production by corticotropes from the two age groups was detected. Corticotropes from middle-aged rats showed a diminished response of ACTH to CRH stimulation. DEX treatment did not cause a significant inhibition of either basal or CRH-stimulated ACTH release in corticotropes from middle-aged rats. These findings demonstrate an age-related decrease in the sensitivity of corticotropes to glucocorticoids in vitro suggesting that there is a direct, pituitary-mediated dysregulation of the HPA axis in rat starting as early as middle age.