It is under tight feedback control and is modulated by afferent connection from multiple brain areas,

including the amygdala and hippocampus. In the hypothalamus, arginine vasopressin and corticotrophin-releasing hormone (CRH) are synthesized by parvocellular neurones of the paraventricular nuclei which project widely to the limbic system, brain stem and spinal cord and to the median eminence. Secretion into the hypothalamo-pituitary portal system of these two peptides regulates the secretion from the Inhibitors,research,lifescience,medical anterior lobe of the pituitary gland into the systemic circulation of adrenocorticotropic hormone (ACTH). ACTH, a polypeptide derived from the pro-opiomelanocortin precursor molecule, acts at the adrenal cortex to rapidly stimulate the biosynthesis of corticosteroid hormones such as cortisol from cholesterol. Circulating cortisol acts at two types of receptor – type

1 mineralocorticoid receptors (MRs) and type 2 glucocorticoid Inhibitors,research,lifescience,medical receptors (GRs) [Herman et al. 1989a]. GRs have high affinity for dexamethasone. Regions of high GR mRNA levels include CA1, CA2 and dentate subregions of the hippocampus, paraventricular Inhibitors,research,lifescience,medical hypothalamus, lateral geniculate, lateral and medial amygdala, and cerebellum. Regions of high MR mRNA levels include all hippocampal pyramidal cell fields, dentate gyrus granule cell layer, lateral septum, medial and lateral amygdala, and to a lesser extent, RAD001 research buy cerebellum [Patel et al. 2000]. Cortisol diffuses through the cell membrane, binds to intracellular Inhibitors,research,lifescience,medical GRs and MRs and promotes their translocation to the nucleus. In response to stress, glucocorticoid levels rise, MR saturate and GR becomes the primary mediator of feedback inhibition of CRH (and the HPA

axis) (Pariante and Miller, 2001, De Kloet et al., 1998). GR acts as a transcription factor to both positively and negatively regulate target genes. A decrease in glucocorticoid bioavailability might stem from decreased production of upstream glucocorticoid Adenylyl cyclase secretagogues including CRH and Inhibitors,research,lifescience,medical ACTH, this mechanism has been implicated in the pathogenesis of a range of neuropsychiatric diseases including atypical depression (Geracioti et al., 1997). Reduced glucocorticoid bioavailability may also be caused by a primary deficit in adrenal hormone production and/or release. Decreased glucocorticoid bioavailability might also result from alterations in 1) binding proteins, which have been identified for both cortisol and CRH (Rosner, 1991), 2) enzymes such as 11-β-hydroxysteroid dehydrogenase, which metabolize endogenous glucocorticoid hormones upon entry into the cell (Seckl and Walker, 2001), and 3) the multidrug resistance pump, which extrudes cortisol but not corticosterone from the cell (Karssen et al., 2001).