The molecular neurobiology of stress--evidence from genetic and epigenetic models

Genetic and Targeted eQTL Mapping Reveals Strong Candidate Genes Modulating the Stress Response During Chicken Domestication

The stress response has been largely modified in all domesticated animals, offering a strong tool for genetic mapping. In chickens, ancestral Red Junglefowl react stronger both in terms of physiology and behavior to a brief restraint stress than domesticated White Leghorn, demonstrating modified functions of the hypothalamic–pituitary–adrenal (HPA) axis. We mapped quantitative trait loci (QTL) underlying variations in stress-induced hormone levels using 232 birds from the 12th generation of an advanced intercross between White Leghorn and Red Junglefowl, genotyped for 739 genetic markers. Plasma levels of corticosterone, dehydroepiandrosterone (DHEA), and pregnenolone (PREG) were measured using LC-MS/MS in all genotyped birds. Transcription levels of the candidate genes were measured in the adrenal glands or hypothalamus of 88 out of the 232 birds used for hormone assessment. Genes were targeted for expression analysis when they were located in a hormone QTL region and were differentially expressed in the pure breed birds. One genome-wide significant QTL on chromosome 5 and two suggestive QTL together explained 20% of the variance in corticosterone response. Two significant QTL for aldosterone on chromosome 2 and 5 (explaining 19% of the variance), and one QTL for DHEA on chromosome 4 (explaining 5% of the variance), were detected. Orthologous DNA regions to the significant corticosterone QTL have been previously associated with the physiological stress response in other species but, to our knowledge, the underlying gene(s) have not been identified. SERPINA10 had an expression QTL (eQTL) colocalized with the corticosterone QTL on chromosome 5 and PDE1C had an eQTL colocalized with the aldosterone QTL on chromosome 2. Furthermore, in both cases, the expression levels of the genes were correlated with the plasma levels of the hormones. Hence, both these genes are strong putative candidates for the domestication-induced modifications of the stress response in chickens. Improved understanding of the genes associated with HPA-axis reactivity can provide insights into the pathways and mechanisms causing stress-related pathologies.

Involvement of Nitric Oxide, Neurotrophins and HPA Axis in Neurobehavioural Alterations Induced by Prenatal Stress

Several studies suggest that negative emotions during pregnancy generate adverse effects on the cognitive, behavioural and emotional development of the descendants. The psychoneuroendocrine pathways involve the transplacentary passage of maternal glucocorticoids in order to influence directly on fetal growth and brain development.Nitric oxide is a gaseous neurotransmitter that plays an important role in the control of neural activity by diffusing into neurons and participates in learning and memory processes. It has been demonstrated that nitric oxide is involved in the regulation of corticosterone secretion. Thus, it has been found that the neuronal isoform of nitric oxide synthase (nNOS) is an endogenous inhibitor of glucocorticoid receptor (GR) in the hippocampus and that nNOS in the hippocampus may participate in the modulation of hypothalamic-pituitary-adrenal axis activity via GR.Neurotrophins are a family of secreted growth factors consisting of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT3) and NT4. Although initially described in the nervous system, they regulate processes such as cell survival, proliferation and differentiation in several other compartments. It has been demonstrated that the NO-citrulline cycle acts together with BDNF in maintaining the progress of neural differentiation.In the present chapter, we explore the interrelation between nitric oxide, glucocorticoids and neurotrophins in brain areas that are key structures in learning and memory processes. The participation of this interrelation in the behavioural and cognitive alterations induced in the offspring by maternal stress is also addressed.

A substitution in the ligand binding domain of the porcine glucocorticoid receptor affects activity of the adrenal gland

Glucocorticoids produced in the adrenal cortex under the control of the hypothalamic-pituitary axis play a vital role in the maintenance of basal and stress-related homeostasis and influence health and well-being. To identify loci affecting regulation of the hypothalamic-pituitary-adrenal (HPA) axis in the pig we performed a genome-wide association study for two parameters of acute and long-term adrenal activity: plasma cortisol level and adrenal weight. We detected a major quantitative trait locus at the position of the glucocorticoid receptor gene (NR3C1) – a key regulator of HPA axis activity. To determine the causal variant(s), we resequenced the coding region of NR3C1 and found three missense single nucleotide polymorphisms (SNPs). SNP c.1829C>T, leading to a p.Ala610Val substitution in the ligand binding domain, showed large (about 0.6× and 1.2× phenotypic standard deviations for cortisol level and adrenal weight, respectively), and highly significant (2.1E-39≤log10(1/p)≤1.7E+0) negative effects on both traits. We were able to replicate the association in three commercial pig populations with different breed origins. We analyzed effects of the p.Ala610Val substitution on glucocorticoid-induced transcriptional activity of porcine glucocorticoid receptor (GR) in vitro and determined that the substitution introduced by SNP c.1829C>T increased sensitivity of GR by about two-fold. Finally, we found that non-coding polymorphisms in linkage disequilibrium with SNP c.1829C>T have only a minor effect on the expression of NR3C1 in tissues related to the HPA axis. Our findings provide compelling evidence that SNP c.1829C>T in porcine NR3C1 is a gain-of-function mutation with a major effect on the activity of the adrenal gland. Pigs carrying this SNP could provide a new animal model to study neurobiological and physiological consequences of genetically based GR hypersensitivity and adrenal hypofunction.

Effects of chronic light/dark cycle on iron zinc and copper levels in different brain regions of rats

In this study, we aimed to investigate whether chronic shift in light/dark cycle alters brain trace element concentrations. For this purpose, 20 male Wistar albino adult rats were weighed and randomly divided into three groups. The first group (n = 6) was the control and had been subjected to 12/12-h light/dark cycle for 30 days. The second group (n = 7) was subjected to 6/18-h light/dark cycle for 15 days, and the third group (n = 7) was also subjected to 6/18-h light/dark cycle for 15 days and then returned to normal 12/12-h light/dark cycle for 15 days. When light/dark cycle protocols were completed, tissue specimens of the frontal lobe, temporal lobe, and brain stem were collected. Iron (Fe), zinc (Zn), and copper (Cu) concentrations of the frontal lobe, temporal lobe, and brain stem were determined by an atomic absorption spectrophotometer. When compared with controls, Fe levels of the temporal lobe significantly increased in 6/18-h light/dark cycle group (p < 0.05), whereas it was statistically unchanged in rats which were exposed to 6/18-h light/dark cycle then returned to the normal 12/12-h light/dark cycle period. Our results show that chronic shift in light/dark cycle affects trace element concentrations of the brain, especially Fe level in the temporal lobe, and these changes are reversible.

Central CRH administration changes formalin pain responses in male and female rats

Corticotropin-releasing hormone (CRH) is suggested to be involved in the regulation of pain. To better evaluate the CRH-mediated behavioral alterations in the formalin inflammatory pain test, we administered CRH or the CRH receptor antagonist α-helical CRH(9-41) (ahCRH) intracerebroventricularly to male and female rats and compared the effects with those of saline control. Nociceptive stimulation was carried out through a subcutaneous injection of dilute formalin (50μL, 10%) in the plantar surface of the hind paw. In both sexes, formalin-induced responses, recorded for 60min, were affected by CRH but not by ahCRH treatment. Paw flexing duration was decreased in both sexes during the formalin interphase period in the CRH-treated group compared to saline control groups; however, licking of the injected paw was markedly increased by the same treatment at other time periods. Treatments induced only a few changes in spontaneous non-pain behaviors, which do not account for the effects on pain response. In conclusion, these data demonstrate the ability of CRH to affect the behavioral responses to an inflammatory nociceptive stimulus, and that the effects can be in opposite directions depending on the behavioral response considered.

Epidemiology of stress and asthma: from constricting communities and fragile families to epigenetics

Several epidemiologic frameworks, exemplified through extant research examples, provide insight into the role of stress in the expression of asthma and other allergic disorders. Biologic, psychological, and social processes interact throughout the life course to influence disease expression. Studies exploiting a child development framework focus on critical periods of exposure, including the in utero environment, to examine the influence of stress on disease onset. Early stress effects that alter the normal course of morphogenesis and maturation that affect both structure and function of key organ systems (eg, immune, respiratory) may persist into adult life underscoring the importance of a life course perspective. Other evidence suggests that maternal stress influences programming of integrated physiologic systems in their offspring (eg, neuroendocrine, autonomic, immune function) starting in pregnancy; consequently stress effects may be transgenerational. A multilevel approach that includes an ecological perspective may help to explain heterogeneities in asthma expression across socioeconomic and geographic boundaries that to date remain largely unexplained. Evolving studies incorporating psychological, behavioral, and physiologic correlates of stress more specifically inform underlying mechanisms operating in these critical periods of development. The role of genetics, gene by environment interactions, and epigenetic mechanisms of gene expression have been sparsely examined in epidemiologic studies on stress and asthma although overlapping evidence provides proof of concept for such studies in the future.

Association of HPA axis-related genetic variation with stress reactivity and aggressive behaviour in pigs

Background

Stress, elicited for example by aggressive interactions, has negative effects on various biological functions including immune defence, reproduction, growth, and, in livestock, on product quality. Stress response and aggressiveness are mutually interrelated and show large interindividual variation, partly attributable to genetic factors. In the pig little is known about the molecular-genetic background of the variation in stress responsiveness and aggressiveness. To identify candidate genes we analyzed association of DNA markers in each of ten genes (CRH g.233C>T, CRHR1 c.*866_867insA, CRHBP c.51G>A, POMC c.293_298del, MC2R c.306T>G, NR3C1 c.*2122A>G, AVP c.207A>G, AVPR1B c.1084A>G, UCN g.1329T>C, CRHR2 c.*13T>C) related to the hypothalamic-pituitary-adrenocortical (HPA) axis, one of the main stress-response systems, with various stress- and aggression-related parameters at slaughter. These parameters were: physiological measures of the stress response (plasma concentrations of cortisol, creatine kinase, glucose, and lactate), adrenal weight (which is a parameter reflecting activity of the central branch of the HPA axis over time) and aggressive behaviour (measured by means of lesion scoring) in the context of psychosocial stress of mixing individuals with different aggressive temperament.

Results

The SNP NR3C1 c.*2122A>G showed association with cortisol concentration (p = 0.024), adrenal weight (p = 0.003) and aggressive behaviour (front lesion score, p = 0.012; total lesion score p = 0.045). The SNP AVPR1B c.1084A>G showed a highly significant association with aggressive behaviour (middle lesion score, p = 0.007; total lesion score p = 0.003). The SNP UCN g.1329T>C showed association with adrenal weight (p = 0.019) and aggressive behaviour (front lesion score, p = 0.029). The SNP CRH g.233C>T showed a significant association with glucose concentration (p = 0.002), and the polymorphisms POMC c.293_298del and MC2R c.306T>G with adrenal weight (p = 0.027 and p < 0.0001 respectively).

Conclusions

The multiple and consistent associations shown by SNP in NR3C1 and AVPR1B provide convincing evidence for genuine effects of their DNA sequence variation on stress responsiveness and aggressive behaviour. Identification of the causal functional molecular polymorphisms would not only provide markers useful for pig breeding but also insight into the molecular bases of the stress response and aggressive behaviour in general.

Expression quantitative trait loci and genetic regulatory network analysis reveals that Gabra2 is involved in stress responses in the mouse

Previous studies have revealed that the subunit alpha 2 (Gabra2) of the gamma-aminobutyric acid receptor plays a critical role in the stress response. However, little is known about the gentetic regulatory network for Gabra2 and the stress response. We combined gene expression microarray analysis and quantitative trait loci (QTL) mapping to characterize the genetic regulatory network for Gabra2 expression in the hippocampus of BXD recombinant inbred (RI) mice. Our analysis found that the expression level of Gabra2 exhibited much variation in the hippocampus across the BXD RI strains and between the parental strains, C57BL/6J, and DBA/2J. Expression QTL (eQTL) mapping showed three microarray probe sets of Gabra2 to have highly significant linkage likelihood ratio statistic (LRS) scores. Gene co-regulatory network analysis showed that 10 genes, including Gria3, Chka, Drd3, Homer1, Grik2, Odz4, Prkag2, Grm5, Gabrb1, and Nlgn1 are directly or indirectly associated with stress responses. Eleven genes were implicated as Gabra2 downstream genes through mapping joint modulation. The genetical genomics approach demonstrates the importance and the potential power of the eQTL studies in identifying genetic regulatory networks that contribute to complex traits, such as stress responses.

A trans-dimensional approach to the behavioral aspects of depression

Depression, a complex mood disorder, displays high comorbidity with anxiety and cognitive disorders. To establish the extent of inter-dependence between these behavioral domains, we here undertook a systematic analysis to establish interactions between mood [assessed with the forced-swimming (FST) and sucrose consumption tests (SCT)], anxiety [elevated-plus maze (EPM) and novelty suppressed feeding (NSF) tests] and cognition (spatial memory and behavioral flexibility tests) in rats exposed to unpredictable chronic-mild-stress (uCMS). Expectedly, uCMS induced depressive-like behavior, a hyperanxious phenotype and cognitive impairment; with the exception of the measure of anxiety in the EPM, these effects were attenuated by antidepressants (imipramine, fluoxetine). Measures of mood by the FST and SCT were strongly correlated, whereas no significant correlations were found between the different measures of anxiety (EPM and NSF); likewise, measures of cognition by spatial memory and behavioral flexibility tests were poorly correlated. Inter-domain analysis revealed significant correlations between mood (FST and SCT) and anxiety-like behavior (NSF, but not EPM). Furthermore, significant correlations were found between cognitive performance (reverse learning task) and mood (FST and SCT) and anxiety-like behavior (NSF). These results demonstrate interactions between different behavioral domains that crosscut the disciplines of psychiatry and neurology.

Analysis of chloroethane toxicity and carcinogenicity including a comparison with bromoethane

Chloroethane (CE) gas carcinogenicity is analyzed and determined from a National Toxicology Program (NTP) bioassay where an inhalation concentration of 15,000 ppm CE gas in air produced the highest incidence of an uncommon-to-rare tumor ever observed by the NTP. Persistently inhaled CE produces endometrial cancers in female mice. The first-tumor-corrected uterine endometrial incidence (I) in B6C3F1 mice is 90%, but no significant tumors occurred in F344 rats. The endometrial cancers dispersed by 1) migrating locally to the adjacent myometrium, 2) then migrating to the bloodstream by intravasation, 3) entering 17 distal organs by extravasation and adapting to the new tissue environment. Distal cancers retained sufficient endometrial cell features to be recognized at each metastatic site. CE produced one of the highest metastasis rates ever observed by NTP of 79%. Comparing CE with bromoethane (BE), a structural analogue, it was found that BE too produced rare murine endometrial cancers yielding the second highest NTP incidence rate of I = 58% with a similar high malignancy rate of 56%. Because of the historical rarity of endometrial tumors in the B6C3F1 mouse, both of these SAR haloethanes seem to be evoking a strong, related carcinogenic potential in B6C3F1 mice, but not in F344 rats. The question of whether humans are similar to mice or to rats is addressed here and in Gargas, et al., 2008. The powerful carcinogenesis caused by these halohydrocarbons may have been caused by excessive and metabolically unresolved acetaldehyde (AC) which is directly generated by Cyp2E1 in the oxidative elimination of CE. With >95% AC metabolic production, as predicted from pharmacokinetic (PK) studies depending on CE exposure, AC is the main elimination intermediate. AC is a known animal carcinogen and a strongly suspected human carcinogen. Also, CE causes incipient decreases of tissue essential glutathione pools [GSH] by Phase II conjugation metabolic elimination of CE (and BE), by glutantione transferase (GST), in most organs (except brain) exposed to high circulating CE and it metabolites. In three laboratories, an excessive stress reaction of hyperkinesis was observed only during 15,000 ppm gas exposure but not when the exposure ceased or when exposure was presented at 150 ppm. Test rodents other than the female mice did not exhibit a pattern of visible stress nor did they have a carcinogenic response to CE gas. Unremitting stress has been documented to contribute a feedback to the hypothalamus which stimulates the hypothalamic-pituitary-axis (HPA), which in turn, induces the adrenal glands. Because estrus and estrogen and progesterone levels were unaltered by CE gas, the adrenal over stimulation, causing high steroid output, may be the penultimate step in this extraordinary carcinogenic response. High adrenal production of corticosteroids could adversely promote endometrial cells to cancers in mice − a mechanism that has already been observed in humans.

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.

Timing of stress and testing influence the long-lasting behavioral performance in rats

Three exposures (Days 1, 2 and 3) of rats to immobilization or immobilization combined with cold induced an alteration of exploratory behavior in an open space arena. When tested 1h after both stressors exposure, rats displayed a decrease in locomotor and rearing score. The deficit disappeared when rats were tested five days later and the performance remained unchanged in trials performed on days 9, 10, 15, 22 and 29 of the study. When testing was postponed five days after the third stressor exposure, a gradual reduction of the performance developed and the deficit persisted until the last trial on Day 29. Amphetamine, in a dose of 0.3 mg/kg revealed a sensitized response to the drug in the stressed animals. The results showed short- and long-lasting behavioral consequences of the used stressors, the long-term manifestation of the sequelae being dependent on the sequence and timing of stressor exposure and open space testing.

Genetic analysis of the stress-responsive adrenocortical axis

The underlying genetic components contributing to individual variability in functions of the stress-responsive hypothalamic-pituitary-adrenal (HPA) axis are poorly understood. To determine genetic loci mediating three aspects of the adrenocortical function, we conducted a quantitative trait locus (QTL) analysis in the segregating F2 generation of a Wistar Kyoto (WKY) x Fischer 344 (F344) cross, two inbred rat strains that differ in several HPA axis measures. The following three components of adrenocortical function are known to be regulated by different mechanisms that are mediated via suprahypothalamic, hypothalamic, pituitary, and intra-adrenal influences: basal plasma corticosterone (Cort) levels, plasma Cort response to a 10-min restraint stress, and adrenal weight. Genome scans identified a complex genetic architecture for the basal Cort phenotype, including sex and maternal lineage effects. Pairwise interactions were also identified for this trait. We identified three significant and two suggestive QTLs for stress Cort, along with two pairs of interacting loci for this trait. Four highly significant and two suggestive loci were identified for adrenal weight, with no interacting loci. In contrast to basal Cort, no sex- or lineage-dependent QTL were identified for stress Cort or adrenal weight, despite the large sex differences in these phenotypes. We identified three nucleotide alterations in an obvious candidate gene mapped to the most significant QTL for stress Cort, Cort-binding globulin (CBG), one of which is known to alter CBG binding. This analysis confirms that three separate traits regulated by the HPA axis are controlled by multiple, but mainly nonoverlapping, QTLs.

QTL mapping for traits associated with stress neuroendocrine reactivity in rats

In the present study we searched for quantitative trait loci (QTLs) that affect neuroendocrine stress responses in a 20-min restraint stress paradigm using Brown-Norway (BN) and Wistar-Kyoto-Hyperactive (WKHA) rats. These strains differed in their hypothalamic-pituitary-adrenal axis (plasma ACTH and corticosterone levels, thymus, and adrenal weights) and in their renin-angiotensin-aldosterone system reactivity (plasma renin activity, aldosterone concentration). We performed a whole-genome scan on a F2 progeny derived from a WKHA x BN intercross, which led to the identification of several QTLs linked to plasma renin activity (Sr6, Sr8, Sr11, and Sr12 on chromosomes RNO2, 3, 19, and 8, respectively), plasma aldosterone concentration (Sr7 and Sr9 on RNO2 and 5, respectively), and thymus weight (Sr10, Sr13, and Srl4 on RNO5, 10, and 16, respectively). The type 1b angiotensin II receptor gene (Agtrlb) maps within the confidence intervals of QTLs on RNO2 linked to plasma renin activity (Sr6, highly significant; LOD = 5.0) and to plasma aldosterone level (Sr7, suggestive; LOD = 2.0). In vitro studies of angiotensin II-induced release of aldosterone by adrenal glomerulosa cells revealed a lower receptor potency (log EC50 = -8.16 +/- 0.11 M) and efficiency (Emax = 453.3 +/- 25.9 pg/3 x 10(4) cells/24 h) in BN than in WKHA (log EC50 = -10.66 +/- 0.18 M; Emax = 573.1 +/- 15.3 pg/3 x 10(4) cells/24 h). Moreover, differences in Agtr1b mRNA abundance and sequence reinforce the putative role of the Agtr1b gene in the differential plasma renin stress reactivity between the two rat strains.

The impact of stress on the development and expression of atopy

PURPOSE OF REVIEW

Biological hypersensitivity to environmental stimuli is a fundamental feature of atopy predisposing to a number of clinically expressed disorders including allergic rhinitis, atopic dermatitis or eczema, and allergic asthma. There is provocative evidence that psychological stress constitutes an increased risk for atopy. This risk is thought to be mediated by the effects of stress on neuroimmunoregulation which in turn modulates the hypersensitivity response. The primary objective is to review recent evidence updating our understanding of the role for psychological stress in atopy.

RECENT FINDINGS

The Th1-Th2 paradigm has been central to interpreting quantitative differences in cytokine expression in response to environmental stimuli like stress. Here we argue that examination of other mechanisms (e.g. oxidative stress pathways, glucocorticoid resistance, nerve-mast cell interactions, intestinal dysbiosis) and a broader range of cytokines and neuropeptides produced by cells both within and outside the immune system may better delineate the true complexity of the underlying mechanisms linking stress to allergic sensitization and asthma. The role of genetics and gene by environment interactions - based on evolving knowledge of candidate genes that may be relevant to both the stress response in general and pathways linked specifically to atopy - is also discussed.

SUMMARY

Psychological stress may be conceptualized as a social pollutant that, when 'breathed' into the body, may disrupt biological systems related to inflammation through mechanisms potentially overlapping with those altered by physical pollutants and toxicants.

Mechanisms of action of antidepressants: from neurotransmitter systems to signaling pathways

Antidepressants are commonly used in the treatment of anxiety and depression, medical conditions that affect approximately 17-20% of the population. The clinical effects of antidepressants take several weeks to manifest, suggesting that these drugs induce adaptive changes in brain structures affected by anxiety and depression. In order to develop shorter-acting and more effective drugs for the treatment of anxiety and depression, it is important to understand how antidepressants bring about their beneficial effects. Recent reports suggest that antidepressants can induce neurogenesis in the adult brain, although the mechanisms involved are not clearly understood. In this review, we describe the different neurotransmitter systems that are affected by anxiety and depression and how they are modulated by antidepressant treatment with a focus on signaling molecules and pathways that are activated during neurotransmitter receptor induced neurogenesis.

Acute social defeat reduces neurotrophin expression in brain cortical and subcortical areas in mice

Acute social defeat in mice activates the hypothalamic-pituitary-adrenal axis (HPA) and induces long-term behavioral changes, including exaggerated fear responses and inhibition of territorial behavior. Stress-induced hormonal and neurotransmitter release may contribute to disruption of expression of genes important for cell survival, neuronal plasticity, and neuronal remodeling. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor associated with structural cellular changes that occur during nervous system development and contributes to neural plasticity in the adult brain. In rats, acute (1-2 h) restraint stress transiently reduces BDNF mRNA expression in the hippocampus, a region important in the memory and in HPA regulation; restraint stress also decreases BDNF expression in the basolateral amygdala (BLA), a region important for fear consolidation and emotional memory. We hypothesized that a brief (10 min) exposure to intense social stress, a more naturalistic stressor than restraint stress, would also reduce BDNF mRNA in the hippocampus and BLA of mice. In the present study, we examined the time course of expression of BDNF mRNA expression in the hippocampus and amygdala, as well as other subcortical and cortical brain regions, following acute social stress. In situ hybridization analysis for BDNF mRNA expression showed that there was a significant decrease in BDNF mRNA expression in all regions studied in mice 24 h after social defeat when compared to control (naive) mice (P<0.05). These findings support our hypothesis that BDNF mRNA levels are reduced by social stress, and may have implications for brain plasticity and behavioral changes following social stress.

Transcriptional response to corticotropin-releasing factor in AtT-20 cells

Corticotropin-releasing factor (CRF) plays a central role in the regulation of the hypothalamic-pituitary-adrenal axis, mediating endocrine and behavioral responses to various stressors. Two high-affinity receptors for CRF have been described. Although many of the intracellular signaling pathways activated by CRF have been studied extensively, our knowledge of transcriptional responses downstream of the CRF receptor 1 (CRFR1) is still limited. To elucidate gene networks regulated by CRF and CRFR1, we applied microarray technology to explore transcriptional response to CRF stimulation. Therefore, mouse pituitary-derived AtT-20 cells were exposed continuously to CRF either in the presence or absence of the specific CRFR1 antagonist R121919. Transcriptional responses to different treatments were studied in a time course ranging from 0.5 to 24 h. Microarray data were analyzed using classic microarray data analysis tools such as correspondence factor analysis, cluster analysis, and fold-change filtering. Furthermore, spectral map analysis was applied, a recently introduced unsupervised multivariate analysis method. A broad and transient transcriptional response to CRF was identified that could be blocked by the antagonist. This way, several known CRF-induced target genes and novel CRF responsive genes were identified. These include transcription factors such as cAMP-responsive element modulator (7x increased), secreted peptides such as cholecystokinin (1.5x), and proteins involved in modulating intracellular signaling, such as regulator of G-protein signaling 2 (11x). Up-regulation of many of these genes can be explained as negative feedback, attenuating CRF-activated pathways. In addition, spectral map analysis proved to be a promising new tool for microarray data analysis.