Chronic corticosterone manipulations in mice affect brain cell proliferation rates, but only partly affect BDNF protein levels.

We investigated whether the effects of corticosterone (CORT) on brain cell proliferation are mediated via its detrimental effect on brain-derived neurotrophic factor (BDNF). Using a [3H]thymidine tracer study, it was demonstrated that the cell proliferation rate in the neurogenic hippocampus and subventricular zone was increased in placebo-treated adrenalectomized (ADX) mice with low plasma corticosterone levels when compared with chronically CORT-treated ADX animals (25mg or 100mg sustained-release pellet). The cell proliferation rate of SHAM animals was in between the ADX-placebo group and ADX CORT-treated groups. BDNF protein contents in the hippocampus and subventricular zone were not different between the SHAM group and ADX-placebo group, although BDNF contents were decreased in the chronically CORT-treated ADX animals. Thus, other factors besides BDNF are involved in mediating CORT-induced changes in cell proliferation. Further, CORT manipulations did not affect caspase-3-like activity in any of the brain regions investigated, suggesting that caspase-3 is not involved in possible CORT-induced cellular losses.

Gene expression profiles highlight adaptive brain mechanisms in corticotropin releasing factor overexpressing mice.

Corticotropin-releasing factor (CRF) plays an important role in mediating central and peripheral responses to stress. Alterations in CRF system activity have been linked to a number of psychiatric disorders, including anxiety and depression. Aim of this study was to elucidate homeostatic mechanisms induced by lifelong elevated CRF levels in the brain. We therefore profiled gene expression in several brain areas of transgenic mice overexpressing CRF (CRF-OE), a model for chronic stress. Several genes showed altered expression levels in CRF-OE mice when compared to their wild type littermates and were confirmed by quantitative PCR. Differences in gene expression profiles revealed the presence of previously unrecognized homeostatic mechanisms in CRF-OE animals. These included changes in glucocorticoid signaling, as exemplified by changes in 11beta-hydroxysteroid dehydrogenase type 1, FK506 binding protein 5 and serum/glucocorticoid kinase. Alterations in expression of genes involved in myelination (myelin, myelin-associated glycoprotein), cell proliferation and extracellular matrix formation (Edg2, Fgfr2, decorin, brevican) suggest changes in the dynamics of neurogenesis in CRF-OE. Pronounced changes in neurotensin (NT) receptors 1 and 2 mRNA were identified. Overall downregulation of NT receptors in CRF-OE animal was substantiated by receptor binding studies. Pronounced neurotensin receptor downregulation was observed for NT type 1 receptors in limbic brain areas, suggesting that NT could be implicated in some of the effects attributed to CRF overexpression. These data show that lifelong exposure to excessive CRF leads to adaptive changes in the brain which could play a role in some of the behavioral and physiological alterations seen in these animals.

Molecular characterization of the high-affinity [3H]neuropeptide Y-binding component from the venom of Conus anemone.

The venom of the marine snail Conus anemone contains the 'ANPY toxin' which binds neuropeptide Y (NPY) and related insect peptides with nanomolar affinity. This toxin has initially been proposed to be a major 18.5 kDa component of the venom. Here we demonstrate that the 18.5 kDa proteins of venom produce at least five different bands in native electrophoresis and that none of them binds [3H]NPY. Instead, the ANPY toxin migrates as a distinct band on native electrophoresis and is only present as a minor component in the venom. Its approximate molecular weight is 17.5 kDa and its [3H]NPY binding activity is extremely stable below 37 degrees C, even in the absence of protease inhibitors.

Distinct binding properties of the AT(1) receptor antagonist [(3)H]candesartan to intact cells and membrane preparations.

[(3)H]-2-Ethoxy-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]-1H-benzimidazoline-7-carboxylic acid ([(3)H]candesartan), a non-peptide angiotensin II type 1 receptor (AT(1) receptor) antagonist bound with high affinity and specificity to intact adherent human AT(1) receptor transfected Chinese hamster ovary cells. The binding characteristics were preserved when cells were suspended, but the dissociation was 3-4-fold faster and the affinity 2-fold lower, while examining [(3)H]candesartan binding to cell membranes. These data suggested the role of the intracellular organisation of living CHO-hAT(1) cells in antagonist-AT(1) receptor interactions. Yet, a specific role of microtubule or actin filaments of the cytoskeleton, receptor phosphorylation by Protein Kinase C, membrane polarity, cytoplasmic components like ATP and the need of an intact cell membrane could be excluded. The potential effect of protease degradation or receptor oxidation during the membrane preparation was also unlikely. The dissociation rate and the equilibrium dissociation constant of [(3)H]candesartan increased with the temperature for both intact cells and membranes. Thermodynamic studies suggested that the bonds between candesartan and the hAT(1) receptor may be of different nature in intact CHO-hAT(1) cells and membranes thereof. Whereas the binding was almost completely enthalpy-driven on intact cells, there was a mixed contribution of both enthalpy and entropy on membranes.