In this review, we have described the function of MR and GR in hippocampal neurons. The balance in actions mediated by the two corticosteroid receptor types in these neurons appears critical for neuronal excitability, stress responsiveness, and behavioral adaptation. Dysregulation of this MR/GR balance brings neurons in a vulnerable state with consequences for regulation of the stress response and enhanced vulnerability to disease in genetically predisposed individuals. The following specific inferences can be made on the basis of the currently available facts. 1. Corticosterone binds with high affinity to MRs predominantly localized in limbic brain (hippocampus) and with a 10-fold lower affinity to GRs that are widely distributed in brain. MRs are close to saturated with low basal concentrations of corticosterone, while high corticosterone concentrations during stress occupy both MRs and GRs. 2. The neuronal effects of corticosterone, mediated by MRs and GRs, are long-lasting, site-specific, and conditional. The action depends on cellular context, which is in part determined by other signals that can activate their own transcription factors interacting with MR and GR. These interactions provide an impressive diversity and complexity to corticosteroid modulation of gene expression. 3. Conditions of predominant MR activation, i.e., at the circadian trough at rest, are associated with the maintenance of excitability so that steady excitatory inputs to the hippocampal CA1 area result in considerable excitatory hippocampal output. By contrast, additional GR activation, e.g., after acute stress, generally depresses the CA1 hippocampal output. A similar effect is seen after adrenalectomy, indicating a U-shaped dose-response dependency of these cellular responses after the exposure to corticosterone. 4. Corticosterone through GR blocks the stress-induced HPA activation in hypothalamic CRH neurons and modulates the activity of the excitatory and inhibitory neural inputs to these neurons. Limbic (e.g., hippocampal) MRs mediate the effect of corticosterone on the maintenance of basal HPA activity and are of relevance for the sensitivity or threshold of the central stress response system. How this control occurs is not known, but it probably involves a steady excitatory hippocampal output, which regulates a GABA-ergic inhibitory tone on PVN neurons. Colocalized hippocampal GRs mediate a counteracting (i.e., disinhibitory) influence. Through GRs in ascending aminergic pathways, corticosterone potentiates the effect of stressors and arousal on HPA activation. The functional interaction between these corticosteroid-responsive inputs at the level of the PVN is probably the key to understanding HPA dysregulation associated with stress-related brain disorders. 5. Fine-tuning of HPA regulation occurs through MR- and GR-mediated effects on the processing of information in higher brain structures. Under healthy conditions, hippocampal MRs are involved in processes underlying integration of sensory information, interpretation of envi...

The hippocampal expression profiles of wild-type mice and mice transgenic for δC-doublecortin-like kinase were compared with Solexa/Illumina deep sequencing technology and five different microarray platforms. With Illumina's digital gene expression assay, we obtained ∼2.4 million sequence tags per sample, their abundance spanning four orders of magnitude. Results were highly reproducible, even across laboratories. With a dedicated Bayesian model, we found differential expression of 3179 transcripts with an estimated false-discovery rate of 8.5%. This is a much higher figure than found for microarrays. The overlap in differentially expressed transcripts found with deep sequencing and microarrays was most significant for Affymetrix. The changes in expression observed by deep sequencing were larger than observed by microarrays or quantitative PCR. Relevant processes such as calmodulin-dependent protein kinase activity and vesicle transport along microtubules were found affected by deep sequencing but not by microarrays. While undetectable by microarrays, antisense transcription was found for 51% of all genes and alternative polyadenylation for 47%. We conclude that deep sequencing provides a major advance in robustness, comparability and richness of expression profiling data and is expected to boost collaborative, comparative and integrative genomics studies.

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Glucocorticoids (GCs) exert profound effects on a variety of physiological processes, including adaptation to stress, metabolism, immunity, and neuronal development. Cellular responsiveness to GCs depends on numerous factors, including the amount of the glucocorticoid receptor (GR) protein. We tested the hypothesis that micro-RNAs (miRs), a recently discovered group of noncoding RNAs involved in mRNA translation, might control GR activity by reducing GR protein levels in neuronal tissues. We tested a panel of five miRs consisting of 124aa, 328, 524, 22, and 18. We found that miRs 18 and 124a reduced GR-mediated events in addition to decreasing GR protein levels. miR reporter assays revealed binding of miR-124a to the 3' untranslated region of GR. In correspondence, the activation of the GR-responsive gene glucocorticoid-induced leucine zipper was strongly impaired by miR-124a and -18 overexpression. Although miR-18 is expressed widely throughout the body, expression of miR-124a is restricted to the brain. Endogenous miR-124a up-regulation during neuronal differentiation of P19 cells was associated with a decreasing amount of GR protein levels and reduced activity of luciferase reporter constructs bearing GR 3' untranslated regions. Furthermore, we show that miR-124a expression varies over time during the stress hyporesponsive period, a neonatal period when GC signaling is modulated. Our findings demonstrate a potential role for miRs in the regulation of cell type-specific responsiveness to GCs, as may occur during critical periods of neuronal development. Ultimately, our results may provide a better understanding of the etiology of stress-related diseases as well as the efficacy of GC therapy.

The adrenal steroid corticosterone has profound effect on the structure and function of the hippocampus. Probably as a result of that, it modulates memory formation. In this review, the question is addressed if the corticosterone effects on memory processes are mediated by alterations in the expression of the neurotrophin Brain-Derived Neurotrophic Factor (BDNF) in the hippocampus. First, studies are described investigating the effect of corticosterone on BDNF expression in the rat hippocampus. It appears that corticosterone suppresses the BDNF expression at the mRNA and protein level in a subfield-specific way. Second, a model for the mechanism of action is proposed. In this model, activated mineralocorticoid and glucocorticoid receptors repress transcriptional activity of the BDNF promoter site-specifically via interaction with other transcription factors. Third, the implications for learning and memory are discussed. Studies show that during water maze training, corticosterone levels rise significantly, but the BDNF expression is not suppressed in any hippocampal subfield. Furthermore, high BDNF expression levels in specific subfields correlate with a good memory performance. Therefore, we suggest that the resistance of the hippocampal BDNF expression to suppression by corticosterone, as seen after water maze training, may contribute to an optimal memory performance.