Paradoxical nature of mineralocorticoid receptor antagonism by progestins

Progesterone, but not the synthetic progestagen R-5020, was as good as aldosterone in displacing the mineralocorticoid from its specific receptor in rat kidney both in classical competition studies and in aldosterone binding to MR₁ and MR₂ components of MR during physical separation. Paradoxically, at equimolar (10^?8 M) concentrations, both gestagens (progesterone = 1, R-5020 = 20) were preferentially bound to the MR₄ component which coeluted with serum bound ¹⁴C-corticosterone (or ¹⁴C-progesterone), which could not be labelled with aldosterone in the kidney, and which could not be detected in the liver and the serum under any condition. The MR₁ entity, at 10^?8 M, was saturated as: aldosterone = 2, R-5020 = 1 = progesterone. Thus, the agonist and the antagonist function in mineralocorticoid action may be expressed by two or more distinct and different sites.     

Androgen receptor mRNA expression in Xenopus laevis CNS: Sexual dimorphism and regulation in laryngeal motor nucleus

Using Northern analysis, in situ hybridization, and nuclease protection assays, the expression and regulation of androgen receptor messenger RNA (AR mRNA) was examined in the CNS of juvenile Xenopus laevis. Only one of the AR mRNA isoforms expressed in X. laevis is transcribed in the CNS as shown by Northern blot analysis. Nuclease protection assays demonstrate that the expression of AR mRNA is higher in the brain stem than in the telencephalon and diencephalon. Although expression of AR mRNA is widespread throughout the CNS, cells of cranial nerve nucleus IX-X (N. IX-X) and spinal cord display the highest in situ hybridization signals in their cytoplasm. Double labeling using horseradish peroxidase and digoxigenin labeled AR probes reveals that laryngeal and anterior spinal cord motor neurons express AR mRNA. More cells express AR mRNA in N. IX-X of males than of females. The number of AR expressing cells in N. IX-X decreases following gonadectomy in both sexes, and dihydrotestosterone (DHT) treatment for 1 month reverses this effect. Increased expression of AR mRNA in the brain of DHT treated animals is also apparent in nuclease protection assays. Sex differences in number of AR expressing cells and hormone regulation of AR mRNA expression in motor nuclei may influence neuromuscular systems devoted to sexually differentiated behaviors. © 1996 John Wiley & Sons, Inc.     

mRNA transport,translation, and decay in adult mammalian central nervous system axons

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Comparison of opioid receptor distributions in the rat central nervous system

The opioid receptors, mu, delta and kappa, conduct the major pharmacological effects of opioid drugs, and exhibit intriguing functional relationships and interactions in the CNS. Previously established hypotheses regarding the mechanisms underlying these phenomena specify theoretical patterns of relative cellular localisation for the different receptor types. In this study, we have used double-label immunohistochemistry to compare the cellular distributions of delta and kappa receptors with those of mu receptors in the rat CNS. Regions of established significance in opioid addiction were examined. Extensive mu/delta co-localisation was observed in neuron-like cells in several regions. mu and kappa receptors were also often co-localised in neuron-like cell bodies in several regions. However, intense kappa immunoreactivity (ir) also appeared in a separate, morphologically distinct population of cells that did not express mu receptors. These small, ovoid cells were often closely apposed against the larger, mu-ir cell bodies. Such cellular appositions were seen in several regions, but were particularly common in the medial thalamus, the periaqueductal grey and brainstem regions. These findings support proposals that functional similarities, synergy and cooperativity between mu and delta receptors arise from widespread co-expression by cells and intracellular molecular interactions. Although co-expression of mu and kappa receptors was also detected, the appearance of a separate population of kappa-expressing cells supports proposals that the contrasting and functionally antagonistic properties of mu and kappa receptors are due to expression in physiologically distinct cell types. Greater understanding of opioid receptor interaction mechanisms may provide possibilities for therapeutic intervention in opioid addiction and other conditions.     

A nuclear action of the eukaryotic cochaperone RAP46 in downregulation of glucocorticoid receptor activity.

RAP46 is a eukaryotic cochaperone that associates with several proteins, including the heat shock protein hsp70/hsc70 and the glucocorticoid receptor (GR). Here we show a downregulation of GR-mediated transactivation by RAP46 via a mechanism independent of a cytoplasmic action of this cochaperone. We demonstrate a specific cytoplasmic-nuclear recruitment of RAP46 by the liganded GR that results in inhibition of the transactivation function of the receptor. A repeated sequence motif [EEX(4)](8) at the NH(2) terminus of RAP46 or BAG-1L, a larger isoform of RAP46, is responsible for this downregulation of GR activity. BAG-1, a shorter isoform with only a duplication of the [EEX(4)] sequence, does not inhibit GR activity. The [EEX(4)](8) motif, when linked to an otherwise unrelated protein, abrogated the inhibitory action of endogenous RAP46 on GR-mediated transactivation. The nuclear effects of RAP46 and BAG-1L are specific since GR-mediated inhibition of AP-1 activity was not affected. These studies identify the [EEX(4)](8) sequence as a signature motif for inhibition of GR-mediated transactivation and demonstrate a specific nuclear action of a eukaryotic cochaperone in the regulation of GR activity.     

Regulation of cadherin expression in nervous system development

This review addresses our current understanding of the regulatory mechanisms for classical cadherin expression during development of the vertebrate nervous system. The complexity of the spatial and temporal expression patterns is linked to morphogenic and functional roles in the developing nervous system. While the regulatory networks controlling cadherin expression are not well understood, it is likely that the multiple signaling pathways active in the development of particular domains also regulate the specific cadherins expressed at that time and location. With the growing understanding of the broader roles of cadherins in cell–cell adhesion and non-adhesion processes, it is important to understand both the upstream regulation of cadherin expression and the downstream effects of specific cadherins within their cellular context.     

Regulation of cadherin expression in nervous system development

This review addresses our current understanding of the regulatory mechanisms for classical cadherin expression during development of the vertebrate nervous system. The complexity of the spatial and temporal expression patterns is linked to morphogenic and functional roles in the developing nervous system. While the regulatory networks controlling cadherin expression are not well understood, it is likely that the multiple signaling pathways active in the development of particular domains also regulate the specific cadherins expressed at that time and location. With the growing understanding of the broader roles of cadherins in cell–cell adhesion and non-adhesion processes, it is important to understand both the upstream regulation of cadherin expression and the downstream effects of specific cadherins within their cellular context.     

Cloning and expression of ligand-gated ion-channel receptor L2 in central nervous system

An orphan receptor of ligand-gated ion-channel type (L2, also termed ZAC according to the presence of zinc ion for channel activation) was identified by computer-assisted search programs on human genome database. The L2 protein shares partial homology with serotonin receptors 5HT3A and 5HT3B. We have cloned L2 cDNA derived from human caudate nucleus and characterized the exon-intron structure as follows: (1) The L2 protein has four transmembrane regions (M1-M4) and a long cytoplasmic loop between M3 and M4. (2) The sequence is conserved in species including chimpanzee, dog, cow, and opossum. (3) Nine exons form its protein-coding region and especially exon 5 corresponds to a disulfide bond region on the amino-terminal side. Our analysis using multiple tissue cDNA panels revealed that at least two splicing variants of L2 mRNA are present. The cDNA PCR amplification study revealed that L2 mRNA is expressed in tissues including brain, pancreas, liver, lung, heart, kidney, and skeletal muscle while 5HT3A mRNA could be detected in brain, heart, placenta, lung, kidney, pancreas, and skeletal muscle, and 5HT3B mRNA in brain, kidney, and skeletal muscle, suggesting different significance in tissue expression of these receptors. Regional expression of L2 mRNA and protein was examined in brain. The RT-PCR studies confirmed L2 mRNA expression in hippocampus, striatum, amygdala, and thalamus in adult brain. The L2 protein was immunolocalized by using antipeptide antibodies. Immunostained tissue sections revealed that L2-like immunoreactivity was dominantly expressed in the hippocampal CA3 pyramidal cells and in the polymorphic layer of the dentate gyrus. We analyzed the expression of L2 protein in HEK293 cells using GFP fusion protein reporter system. Western blots revealed that L2 protein confers sugar chains on the extracellular side. In transfected HEK293 cells, cellular membranes and intracellular puncta were densely labeled with GFP, suggesting selective dispatch to the final destination.     

Individual variability in the stress response of C57BL/6J male mice correlates with trait anxiety

Stress strongly alters the physiology and behavior of some individuals, while others are little or not affected. The causes of this individual variability have remained unknown. Here, we hypothesize that epigenetically induced levels of trait anxiety predict the stress response of individual mice in a genetically homogeneous population. Inbred C57BL/6 male mice were selected for their latency to freely enter from their home cage into an unfamiliar arena and classified as having high or low levels of trait anxiety. Mice were then exposed to acute stress (1-h olfactory contact with a rat) or control conditions. After 24 h, acute stress enhanced state anxiety measured in the elevated-plus maze test only in mice previously classified as having high levels of trait anxiety. This anxiogenic effect of acute stress was paralleled by enhanced novelty-induced plasma corticosterone secretion and increased messenger RNA (mRNA) expression for glucocorticoid and mineralocorticoid receptors in the hippocampus. No effects of acute stress were observed in mice classified as having low levels of trait anxiety. Under unstressed control conditions, mice only differed in basal levels of hippocampal mRNA for the glucocorticoid receptor, which were higher in mice with high trait anxiety than in mice with low trait anxiety. In summary, inbred C57BL/6 mice display a remarkably high interindividual variability in their trait anxiety that predicts the behavioral and neuroendocrine response to an acute stressor, indicating that expression of extremely different coping strategies can develop also between genetically identical individuals.     

Glucocorticoid‐mediated modulation of morphological changes associated with aging in microglia

Microglia dynamically adapt their morphology and function during increasing age. However, the mechanisms behind these changes are to date poorly understood. Glucocorticoids (GCs) are long known and utilized for their immunomodulatory actions and endogenous GC levels are described to alter with advancing age. We here tested the hypothesis that age‐associated elevations in GC levels implicate microglia function and morphology. Our data indicate a decrease in microglial complexity and a concomitant increase in GC levels during aging. Interestingly, enhancing GC levels in young mice enhanced microglial ramifications, while the knockdown of the glucocorticoid receptor expression in old mice aggravated age‐associated microglial amoebification. These data suggest that GCs increase ramification of hippocampal microglia and may modulate age‐associated changes in microglial morphology.     

Speculations on the role of the microtubule network in glucocorticoid receptor signaling

The glucocorticoid receptor (GR) is an important player in the life of a cell. This is underlined by a cohort of protein and nucleic acid structures interacting with the GR. Among many issues surrounding GR activity that are under active investigation, the role of microtubules (MTs) is still unclear. This article aims to evaluate the ayes and noes in favor of microtubule importance and then form a hypothesis on their function in GR activity.