The population firing rate in the presence of GABAergic tonic inhibition in single neurons and application to general anaesthesia

Tonic inhibition has been found experimentally in single neurons and affects the activity of neural populations. This kind of inhibition is supposed to set the background or resting level of neural activity and plays a role in the brains arousal system, e.g. during general anaesthesia. The work shows how to involve tonic inhibition in population rate-coding models by deriving a novel transfer function. The analytical and numerical study of the novel transfer function reveals the impact of tonic inhibition on the population firing rate. Finally, a first application to a recent neural field model for general anaesthesia discusses the origin of the loss of consciousness during anaesthesia.     

Investigations into the chirality of the metabolic sulfoxidation of cimetidine

The individual enantiomers of cimetidine sulfoxide were resolved by preparative chromatography using a Chiralcel OC stationary phase and were characterized by the determination of optical rotation and circular dichroism spectra. Cimetidine sulfoxide was isolated from the urine of two healthy male volunteers following oral administration of cimetidine (400 mg). Urine was collected every 2 h for 12 h postdosing, after which time HPLC analysis indicated negligible recovery of the drug as the sulfoxide. Some 7% of the dose was recovered as cimetidine sulfoxide over this period. The enantiomeric composition of cimetidine sulfoxide was determined by sequential achiral—chiral chromatography using the OC phase. Over the collection period the enantiomeric ratio was found to be constant in all samples at (+/?) of 71 ± 2.5:29 ± 2.5. The enantiomeric composition of cimetidine sulfoxide was also determined in rat urine (24 h) following the administration of cimetidine (30 mg/kg po) to male Wistar rats (n = 7). The enantiomeric ratio in this case was found to be (+/?) 57 ± 2.3:43 ± 2.3. These preliminary data indicate that sulfoxidation of cimetidine is stereoselective with respect to the (+)-enantiomer and that species variation in enantiomeric composition occurs. © 1994 Wiley-Liss, Inc.     

Species variability in the stereoselective N-oxidation of pargyline

The monoamine oxidase inhibitor pargyline (N-benzyl-N-methyl-2-propynylamine) is known to undergo extensive in vitro microsomal N-oxidation, thought to be mediated predominantly by the flavin-containing monooxygenase (FMO) enzyme system. Formation of the pargyline N-oxide (PNO) metabolite creates a chiral nitrogen centre and thus asymmetric oxidation is possible. This study describes a reverse-phase high-performance liquid chromatographic (HPLC) method for the quantitation of PNO and a chiral-phase HPLC method for the determination of the enantiomeric ratio of PNO. In vitro microsomal N-oxidation of pargyline was found to be highly steroselective in a number of species, with the (+)-enantiomer being formed preferentially. This metabolic transformation was stereospecific when purified porcine hepatic FMO was used as the enzyme source. © 1994 Wiley-Liss, Inc.     

Toward intrinsically fluorescent proteomimetics: fluorescent probe response to alpha helix structure of poly-gamma-benzyl-L-glutamate

A fluorescent probe (1), developed for recognition of alpha helical secondary structure, shows a large fluorescence change upon titration with the synthetic protein PBLG. Compared to fluorophores of similar size and shape, 1 displayed the smallest dissociation constant (K(D)=80microM) when titrated with PBLG. These preliminary studies are directed toward developing small molecule proteomimetics that have intrinsic fluorescence and are specific for helical-protein binding-sites.     

The Histone Deacetylase Inhibitor,Vorinostat, Represses Hypoxia Inducible Factor 1 Alpha Expression through Translational Inhibition

Hypoxia inducible factor 1α (HIF-1α) is a master regulator of tumor angiogenesis being one of the major targets for cancer therapy. Previous studies have shown that Histone Deacetylase Inhibitors (HDACi) block tumor angiogenesis through the inhibition of HIF-1α expression. As such, Vorinostat (Suberoylanilide Hydroxamic Acid/SAHA) and Romidepsin, two HDACis, were recently approved by the Food and Drug Administration (FDA) for the treatment of cutaneous T cell lymphoma. Although HDACis have been shown to affect HIF-1α expression by modulating its interactions with the Hsp70/Hsp90 chaperone axis or its acetylation status, the molecular mechanisms by which HDACis inhibit HIF-1α expression need to be further characterized. Here, we report that the FDA-approved HDACi Vorinostat/SAHA inhibits HIF-1α expression in liver cancer-derived cell lines, by a new mechanism independent of p53, prolyl-hydroxylases, autophagy and proteasome degradation. We found that SAHA or silencing of HDAC9 mechanism of action is due to inhibition of HIF-1α translation, which in turn, is mediated by the eukaryotic translation initiation factor - eIF3G. We also highlighted that HIF-1α translation is dramatically inhibited when SAHA is combined with eIF3H silencing. Taken together, we show that HDAC activity regulates HIF-1α translation, with HDACis such as SAHA representing a potential novel approach for the treatment of hepatocellular carcinoma.     

KIT/KIT ligand in mammalian oogenesis and folliculogenesis: roles in rabbit and murine ovarian follicle activation and oocyte growth

In rodent ovaries Kit ligand (KITL) and its receptor KIT have diverse roles, including the promotion of primordial follicle activation, oocyte growth, and follicle survival. Studies were undertaken to determine whether KITL and KIT carry out similar activities in rabbits.KitlandKitmRNA and protein were localized to oocytes and granulosa cells, respectively, in the rabbit ovary. Ovarian cortical explants from juvenile rabbits and neonatal mouse ovaries were subsequently cultured with recombinant mouse KITL and/or KITL neutralizing antibody. Indices of follicle growth initiation were compared with controls and between treatment groups for each species. Recombinant mouse KITL had no stimulatory effect on primordial follicle recruitment in cultured rabbit ovarian explants. However, the mean diameter of oocytes from primordial, early primary, primary, and growing primary follicles increased significantly in recombinant mouse KITL-treated explants compared with untreated tissues. In contrast, recombinant mouse KITL promoted both primordial follicle activation and an increase in the diameter of oocytes from primordial and early primary follicles in the mouse, and these effects were inhibited by coculture with KITL-neutralizing antibody. Recombinant mouse KITL had no effect on follicle survival for either species. These data demonstrate that KITL promotes the growth of rabbit and mouse oocytes and stimulates primordial follicle activation in the mouse but not in the rabbit. We propose that the physiologic roles of KITL and KIT may differ between species, and this has important implications for the design of in vitro culture systems for folliculogenesis in mammals, including the human.     

CCAAT/enhancer-binding protein delta regulates mammary epithelial cell G0 growth arrest and apoptosis.

CCAAT/enhancer-binding proteins (C/EBPs) are a highly conserved family of DNA-binding proteins that regulate cell-specific growth, differentiation, and apoptosis. Here, we show that induction of C/EBPdelta gene expression during G0 growth arrest is a general property of mammary-derived cell lines. C/EBPdelta is not induced during G0 growth arrest in 3T3 or IEC18 cells. C/EBPdelta induction is G0-specific in mouse mammary epithelial cells; C/EBPdelta gene expression is not induced by growth arrest in the G1, S, or G2 phase of the cell cycle. C/EBPdelta antisense-expressing cells (AS1 cells) maintain elevated cyclin D1 and phosphorylated retinoblastoma protein levels and exhibit delayed G0 growth arrest and apoptosis in response to serum and growth factor withdrawal. Conversely, C/EBPdelta-overexpressing cells exhibited a rapid decline in cyclin D1 and phosphorylated retinoblastoma protein levels, a rapid increase in the cyclin-dependent kinase inhibitor p27, and accelerated G0 growth arrest and apoptosis in response to serum and growth factor withdrawal. When C/EBPdelta levels were rescued in AS1 cells by transfection with a C/EBPdelta "sense" construct, normal G0 growth arrest and apoptosis were restored. These results demonstrate that C/EBPdelta plays a key role in the regulation of G0 growth arrest and apoptosis in mammary epithelial cells.     

Nxf1 Natural Variant E610G Is a Semi-dominant Suppressor of IAP-Induced RNA Processing Defects

Endogenous retroviruses and retrotransposons contribute functional genetic variation in animal genomes. In mice, Intracisternal A Particles (IAPs) are a frequent source of both new mutations and polymorphism across laboratory strains. Intronic IAPs can induce alternative RNA processing choices, including alternative splicing. We previously showed IAP I∆1 subfamily insertional mutations are suppressed by a wild-derived allele of the major mRNA export factor, Nxf1. Here we show that a wider diversity of IAP insertions present in the mouse reference sequence induce insertion-dependent alternative processing that is suppressed by Nxf1^CAST alleles. These insertions typically show more modest gene expression changes than de novo mutations, suggesting selection or attenuation. Genome-wide splicing-sensitive microarrays and gene-focused assays confirm specificity of Nxf1 genetic modifier activity for IAP insertion alleles. Strikingly, CRISPR/Cas9-mediated genome editing demonstrates that a single amino acid substitution in Nxf1, E610G, is sufficient to recreate a quantitative genetic modifier in a co-isogenic background.