S-12-01

Stress system regulation, glucocorticoid receptors and traumatic early life events

M. Oitzl, E. Leo, d. K. Ron. University Hospital Div. Med. Pharmacogy, Leiden, Netherlands

Objective: Traumatic events in early life are considered to increase the susceptibility for psychiatric disorders. In animal models, manipulations of mother-pup interaction have been shown to produce long lasting changes in emotional, cognitive and neuroendocrine reactivity. Evidence accumulates that the mechanisms underlying these long-term effects of early adversity are to be found in the glucocorticoid-related stress system (hypothalamic-pituitary-adrenal (HPA) axis). Glucocorticoid effects in the brain are mediated by the high affinity mineralocorticoid receptor -MR, and the low affinity glucocorticoid receptor -GR. MR and GR control the basal and stressinduced secretion of the hormone, determine neuronal excitability and distinct behavioural domains.

Methods: Rat/mice pups were separated from their mother for a certain period (once or repeatedly for 8 or 24 hours) at different postnatal days. We studied both, the immediate and long-term effects of this early life trauma, measuring a series of neurochemical markers of stress-system (re)activity and behaviour.

Results: During the postnatal period, when glucocorticoid concentrations are kept actively low by maternal care, separation of mother and pup severely disrupts the developmental pattern of the stress system. Frequency and duration of deprivation differentially affect the stress sensitivity and individual response characteristics.

Conclusion: Maternal deprivation disrupts the normal development of the brain and stress system. As a consequence, the animal is exposed to oscillating high and low levels of glucocorticoids, while negative feedback regulation seems to be dysfunctional and cognitive performance impaired in later life.

S-12-02

Glucocorticoid receptor transgenic mice as models of depression

P. Gass. Zentralinstitut Psychiatry, Mannheim, Germany

Objective: Impaired ghicocorticoid receptor (GR) signaling is a postulated mechanism for the pathogenesis of affective disorders, such as major depression and posttraumatic stress disorder. Since in vivo expression and functional studies of GR are not feasible in humans, we have generated different mouse strains that over- or underexpress GR. This presentation will summarize neuroendocrinological and behavioral findings that have been obtained in several mouse strains that turned out to be highly interesting for depression research:

Methods: Using transgenic techniques we generated i) mice that lack GR specifically in the brain; ii) mice with a 50% GR gene dose reduction (GR heterozygous mice); iii) mice with a 100% GR gene dose elevation (GR transgenic mice).

Results: i) mice that lack GR selectively in the CNS show a disinhibition of the hypothalamic-pituitary-adrenal (HPA) system similar to depressed patients, but reduced anxiety and despair behavior. Due to the lack of GR in the brain, they represent a behavioural model for a depression-resistant mouse strain, ii) heterozygous mice that underexpress GR exhibit normal baseline behaviors, but after stress exposure they demonstrate helplessness and despair. Similar to depressed patients they show a disinhibition of the HPA system and a pathological DEX/CRH test. Thus they represent a murine depression model with good face and construct validity, iii) mice that overexpress GR by a yeast artificial chromosome (YGR) are more resistant to develop helplessness and despair following stress exposure, i.e. they show the opposite phenotype as mice that underexpress GR. They same is true for their HPA system, which is more resistant to stress, and the DEX/ CRH test, where they are oversuppressors. Thus they represent a model for a stress-resistant mouse strain.

Conclusion: These mouse strains can be used to study longterm plasticity changes underlying the pathogenesis of depressive episodes. Using modern genomic or proteomic techniques they may turn out to be valuable tools to detect new molecular targets for antidepressive therapy, and thus open new therapeutic avenues for faster and better treatment with less side-effects.

S-12-03

Genetic factors have an impact on cortisol and ACTH responses to psychosocial stress

S. Wiast, I. Federenko, E. F. C. Van Rossum, J. W. Koper, R. Kumsta, S. Entringer, D. H. Hellhammer. Department of Psychobiology, U, Trier, Germany

Objective: In the present study the impact of genetic factors on hypothalamus-pituitary-adrenal axis responses to psychosocial stress was investigated.

Methods: Three times at one week intervals 33 monozygotic (MZ) and 25 dizygotic (DZ) male twin pairs were exposed to a laboratory stressor including a flee speech and mental arithmetic tasks in front of an audience ('Trier Social Stress Test, TSST'). Salivary cortisol, total plasma cortisol and ACTH responses were assessed and intrapair correlations for the areas under the curves (AUC) were computed. Furthermore, the impact of two polymorphisms of the glucocorticoid receptor gene on TSST responses was studied. The 'N363S' polymorphism is located in exon 2 and the 'BclI' polymorphism is sited 646 nucleotides downstream from the 3'-end of exon 2.

Results: AUC heritabilities increased across sessions for all measures (free cortisol: TSSTI: rMZ=.38/rDZ=.34, T2: .70/.42, T3: .78/.27; total cortisol: TI: .51/.35, T2: .58/.40, T3: .66/.17; ACTH: TI: .17/.15., T2: .63/.04, T3: .66/.13). Regarding the BclI polymorphism allelic discrimination identified 48 CC subjects, 18 GG subjects, and 46 heterozygotes. Ten CC carriers were additionally either heterozygous (AG, n=8) or homozygous (GG, n=2) N363S carriers. Salivary cortisol responses to the TSST exposures differed significantly between genotypes (all p<.05). Compared to participants with the rather common genotype? BclI CC & N363S AA?, carriers of the N363S G allele showed an enhanced cortisol response while the response in Bcll GG subjects was diminished. ACTH responses to the first TSST as well showed a trend towards higher values in N363S carriers compared to BclI GG subjects.

Conclusion: The observed rise of heritabilities across sessions suggests that situational variables are initially dominant and might mask existing genetic factors. This is the first investigation that documents an impact of GR polymorphisms on adrenocortical responses to psychosocial stress.

S-12-04

I. Heuser. Psychiatrische Klinik, Freie U, Berlin, Germany

S-12-05

Using cellular systems to understand glucocorticoid resistance in depression

C. Pariante. Institute of Psychiatry, London, United Kingdom

Objective: Depression is characterised by an over activity of the hypothalamic-pituitary-adrenal (I-IPA) axis and by increased concentrations of circulating cortisol. The picture is further complicated by the fact that increased cortisol levels in the bloodstream do not necessarily translate into increased effects of cortisol on the brain. In fact, brain sensitivity to cortisol is also regulated by the function of the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR), the receptors that mediates the effects of the cortisol on target tissues, as well as by effiux systems for cortisol at the blood-brain barrier. Nevertheless, the "glucocorticoid resistance" model is supported by the evidence, in cellular systems, that GR function is reduced in the lymphocytes of depressed patients, and that antidepressants enhance cortisol action in the brain by increasing the expression and the function of the GR and the MR.

Methods: I will summarise our work on the effects of antidepressants on the HPA axis in "in vitro" cellular models and in healthy controls.

Results: Antidepressants enhance GR function in vitro by inhibiting the multidrug resistance p-glycoprotein, a steroid transporter that regulate the intracellular concentration of glucocorticoids. These transporters also regulate GR function in lymphocytes, and the access of glucocorticoids to the brain. Furthermore, antidepressants enhance ghicocorticoid-mediated negative feedback on the HPA axis in humans after as little as 4 days of treatment.

Conclusion: Taken together, these findings further support the notion that one of the mechanisms by which antidepressants exert their therapeutic effects is by inhibiting steroid transporters localised on the blood-brain barrier, in lymphocytes and in neurones, like the multidmg resistance p-glycoprotein, and thus by increasing the access of cortisol to the brain and the glucocorticoid-mediated negative feedback on the HPA axis. These molecular mechanisms can be studied in humans using in vitro cellular systems. Acknowledgements: My research is funded by the UK Medical Research Council (MRC), the NARSAD, and the GENDEP project from the European Commission's Framework 6 Programme.