Ventral subicular interaction with the hypothalamic paraventricular nucleus: Evidence for a relay in the bed nucleus of the stria terminalis

The axonal projections of the ventral subiculum to the bed nucleus of the stria terminalis (BST) were examined in the rat with the anterograde neuronal tracer Phaseolus vulgaris - leucoagglutinin (PHA-L). Axons originating in the ventral subiculum coursed to the BST through either the fimbria-fornix, or a pathway involving the stria terminalis via the amygdala. Ventral subicular axons gave rise to dense terminal networks that were preferentially distributed in medial and ventral subregions of the BST. The distribution of subicular fibers and terminals was examined in relation to BST neurons that project to the hypothalamic paraventricular nucleus (PVN). In these cases, discrete iontophoretic injections of the retrograde tracer Fluoro-gold were made in the PVN, with PHA-L delivered to the ipsilateral ventral subiculum. An immunocytochemical double-labeling protocol was then employed for the simultaneous detection of PHA-L and Fluoro-gold, and provided light microscopic evidence for subicular input to PVN-projecting cells located within the BST. In a second series of experiments, the Γ-amino butyric acid (GABA)ergic nature of the BST was examined by in situ hybridization histochemistry for detection of transcripts encoding GAD 67 mRNA. The studies revealed that a high proportion of BST neurons express GAD 67 transcripts. Also, experiments combining Fluoro-gold tracing with GAD 67 in situ hybridization suggested that a proportion of PVN-projecting neurons in the BST are GABAergic. Taken together, the results of these sets of studies suggest that the inhibitory influences of the hippocampus on the PVN might be relayed through specific portions of the BST. These findings may have important implications for our understanding of the neural regulation of the hypothalamic-pituitary-adrenal axis. © 1993 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50057/1/903320102_ftp.pd

Mechanism for modulation of gating of connexin26-containing channels by taurine

The mechanisms of action of endogenous modulatory ligands of connexin channels are largely unknown. Previous work showed that protonated aminosulfonates (AS), notably taurine, directly and reversibly inhibit homomeric and heteromeric channels that contain Cx26, a widely distributed connexin, but not homomeric Cx32 channels. The present study investigated the molecular mechanisms of connexin channel modulation by taurine, using hemichannels and junctional channels composed of Cx26 (homomeric) and Cx26/Cx32 (heteromeric). The addition of a 28–amino acid “tag” to the carboxyl-terminal domain (CT) of Cx26 (Cx26T) eliminated taurine sensitivity of homomeric and heteromeric hemichannels in cells and liposomes. Cleavage of all but four residues of the tag (Cx26Tc) resulted in taurine-induced pore narrowing in homomeric hemichannels, and restored taurine inhibition of heteromeric hemichannels (Cx26Tc/Cx32). Taurine actions on junctional channels were fully consistent with those on hemichannels. Taurine-induced inhibition of Cx26/Cx32T and nontagged Cx26 junctional channels was blocked by extracellular HEPES, a blocker of the taurine transporter, confirming that the taurine-sensitive site of Cx26 is cytoplasmic. Nuclear magnetic resonance of peptides corresponding to Cx26 cytoplasmic domains showed that taurine binds to the cytoplasmic loop (CL) and not the CT, and that the CT and CL directly interact. ELISA showed that taurine disrupts a pH-dependent interaction between the CT and the CT-proximal half of the CL. These studies reveal that AS disrupt a pH-driven cytoplasmic interdomain interaction in Cx26-containing channels, causing closure, and that the Cx26CT has a modulatory role in Cx26 function

Sex-dependent changes in neuroactive steroid concentrations in the rat brain following acute swim stress

Sex differences in hypothalamo-pituitary-adrenal (HPA) axis activity are well established in rodents. In addition to glucocorticoids, stress also stimulates secretion of progesterone and deoxycorticosterone (DOC) from the adrenal gland. Neuroactive steroid metabolites of these precursors can modulate HPA axis function; however it is not known whether levels of these steroids differ between male and females following stress. Here we aimed to establish whether neuroactive steroid concentrations in the brain display sex- and/or region-specific differences under basal conditions and following exposure to acute stress. Brains were collected from male and female rats killed under non-stress conditions or following exposure to forced swimming. Liquid chromatography-mass spectrometry was used to quantify 8 steroids: corticosterone, DOC, dihydrodeoxycorticosterone (DHDOC), pregnenolone, progesterone, dihydroprogesterone (DHP), allopregnanolone and testosterone in plasma and 5 brain regions (frontal cortex, hypothalamus, hippocampus, amygdala and brainstem). Corticosterone, DOC and progesterone concentrations were significantly greater in the plasma and brain of both sexes following stress; however the responses in plasma were greater in females compared to males. This sex difference was also observed in the majority of brain regions for DOC and progesterone, but not for corticosterone. Despite observing no stress-induced changes in circulating concentrations of pregnenolone, DHDOC or DHP, concentrations were significantly greater in the brain, and this effect was more pronounced in females than males. Basal plasma and brain concentrations of allopregnanolone were significantly higher in females; moreover, stress had a greater impact on central allopregnanolone concentrations in females. Stress had no effect on circulating or brain concentrations of testosterone in males. These data indicate sex and regional differences in the generation of neuroactive steroids in the brain following acute stress, especially for the 5α-reduced steroids, and further suggest sex-specific expression of steroidogenic enzymes in the brain. Thus, differential neurosteroidogenesis may contribute to sex differences in HPA axis responses to stress

Osmoadaptation cellulaire cérébrale en situation d'hypertonicité systémique chez le rat (expession des gènes osmoprotecteurs et de leur facteur de transcription transactivateur)

Les observations cliniques suggèrent que les cellules du cerveau possèdent une capacité d'osmoadaptation. Dans un modèle animal d'hypertonicité systémique, nous avons étudié, au niveau du cerveau par immunocytochimie et hybridation in situ, l'expression cellulaire des gènes osmoprotecteurs aldose réductase (AR) et transporteur du myo-inositol (SMIT) et celle de leur facteur de transcription transactivateur (TonEBP). L'expression osmo-induite de TonEBP est restreinte aux neurones, celle de AR et de SMIT à certaines sous-populations respectivement neuronales et non-neuronales. Cette divergence d'expression cellulaire suggère l'implication d'autres gènes. Par biopuce, nous avons identifié quatre gènes précoces codant des facteurs de transcription et un transporteur des acides aminés neutres dont l'expression est osmo-induite dans le tissu cérébral et qui sont potentiellement impliqués dans l'osmoadaptation celluaire cérébraleClinical observations suggest that brain cells possess osmoadaptation ability. Using an animal model of systemic hypertonicity, we have studied by immunocytochemistry and in situ hybridization cellular expression of osmoprotective genes, aldose reductase (AR) and myo-inositol transporter (SMIT) and their transactivator transcription factor (TonEBP). TonEBP is expressed and tonicity-induced in neurons only. Tonicity-induced expression of AR and SMIT is restricted to respectively some neuronal and non-neuronal cell subsets. These large discrepancies in cellular expression suggest the involvement of other genes. Using microarray analysis, we have identified four immediate early genes encoding transcription factors and one neutral aminoacid transporter whose tissular expression is tonicity-induced in brain and which might be involved in brain cellular osmoadaptationLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Gabaergic regulation of melanocyte-stimulating hormone-secretion from the pars-intermedia of xenopus-laevis - immunocytochemical and physiological evidence

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Differential cellular distribution of tonicity-induced expression of transcription factor TonEBP in the rat brain following prolonged systemic hypertonicity

n a previous work performed on cerebral cortex and hippocampus we reported that tonicity-responsive enhancer binding protein (TonEBP), originally identified as a transactivator of osmoprotective genes involved in osmoadaptation of renal cells, was induced in neurons only, but to varying levels, following acute systemic hypertonicity. Whether or not this cellular specificity reflected a unique ability of neurons or a differential time course among brain cells for tonicity-induction of TonEBP was investigated throughout the brain in this study by subjecting the animals to prolonged systemic hypertonicity. In normal rats, TonEBP immunolabeling and TonEBP-mRNA in situ hybridization labeling showed a widespread, uneven and parallel distribution. TonEBP was expressed primarily in the cell nuclei of neurons, where it was heterogeneously distributed in a nucleoplasmic and a granular pool. In rats subjected to prolonged systemic hypertonicity, TonEBP labeling increased in the cell nuclei of neurons only. The tonicity-induced expression of TonEBP for a given cell group of neurons was rather uniform but varied greatly among neuronal cell groups and was positively correlated with the average size of the cell nuclei, as determined by quantitative analysis of digitized images. The detailed distribution of tonicity-induced expression of TonEBP is reported throughout the brain. In normal rats, a very minor proportion of non-neuronal cells, identified as a subset of astrocytes and possibly oligodendrocytes, showed faint nuclear immunolabeling, which however did not increase in hypertonic animals. Ependymocytes, capillary endothelial cells, and microglial cells showed no TonEBP labeling, even in hypertonic animals. Altogether our data indicate that neurons, albeit possibly to a varying extent, are the only brain cells able to use TonEBP-mediated processes for adaptation to a systemic hyperosmotic unbalance.close161