Developmental Exposure to Fluoxetine Modulates the Serotonin System in Hypothalamus

The selective serotonin reuptake inhibitor (SSRI) fluoxetine (FLU, Prozac®) is commonly prescribed for depression in pregnant women. This results in SSRI exposure of the developing fetus. However, there are knowledge gaps regarding the impact of SSRI exposure during development. Given the role of serotonin in brain development and its cross-talk with sex hormone function, we investigated effects of developmental exposure to pharmacologically relevant concentrations of FLU (3 and 30 nM (measured)) on brain neurotransmitter levels, gonadal differentiation, aromatase activity in brain and gonads, and the thyroid system, using the Xenopus tropicalis model. Tadpoles were chronically exposed (8 weeks) until metamorphosis. At metamorphosis brains were cryosectioned and levels of serotonin, dopamine, norepinephrine, and their metabolites 5-hydroxyindoleacetic acid, 3,4-dihydroxyphenylacetic acid, and homovanillic acid were measured in discrete regions (telencephalon, hypothalamus and the reticular formation) of the cryosections using high-performance liquid chromatography. Exposure to 30 nM FLU increased the concentration of 5-hydroxyindoleacetic acid in hypothalamus compared with controls. FLU exposure did not affect survival, time to metamorphosis, thyroid histology, gonadal sex differentiation, or aromatase activity implying that the effect on the serotonergic neurotransmitter system in the hypothalamus region was specific. The FLU concentration that impacted the serotonin system is lower than the concentration measured in umbilical cord serum, suggesting that the serotonin system of the developing brain is highly sensitive to in utero exposure to FLU. To our knowledge this is the first study showing effects of developmental FLU exposure on brain neurochemistry. Given that SSRIs are present in the aquatic environment the current results warrant further investigation into the neurobehavioral effects of SSRIs in aquatic wildlife.     

Turnover of Brain Monoamine Oxidase Measured In Vivo by Positron Emission Tomography Using l-[11C]Deprenyl

The distribution of carbon-11-labeled L-deprenyl, an irreversible inhibitor of monoamine oxidase type B (MAO-B), was determined in the baboon brain by positron emission tomography. The irreversible blood-to-brain transfer constant (influx constant, K_i) was measured using a complete metabolite-corrected arterial plasma concentration curve. This influx constant was used as a measure of functional enzyme activity for sequential determinations of MAO-B recovery following a single high dose of unlabeled l -deprenyl. The half-life for turnover of MAO-B was thus determined to be 30 days. Using appropriate irreversible inhibitors, this procedure should be generally useful for determining enzyme turnover rates in any organ in vivo and can be applied to some human studies as well.     

Large Alterations in Ganglioside and Neutral Glycosphingolipid Patterns in Brains from Cases with Infantile Neuronal Ceroid Lipofuscinosis/Polyunsaturated Fatty Acid Lipidosis

Lipid composition was studied on cerebral tissue from nine children who had died of a progressive encephalopathy called the infantile form of neuronal ceroid lipofuscinosis (INCL) or polyunsaturated fatty acid lipidosis (PFAL). In the terminal stage of the disease, the concentrations of all lipid classes were found to be significantly reduced in the cerebral and cerebellar cortex and white matter. The concentration of gangliosides of the cerebral cortex was 15% and that of cerebrosides (galactosylceramide) in white matter 0.2-5% of the normal values for the children's ages. The reduction of gangliosides mainly affected those of the gangliotetraose series, particularly GD1a. The fatty acids of the linolenic acid series were strongly reduced in ethanolamine and serine phosphoglycerides. A very large increase up to 100-fold of oligoglycosphingolipids of the globo series and two fucose-containing lipids of the neolacto series was found in the forebrain of the three advanced cases examined. The brain tissue also contained very high concentrations of mono-, di-, and trisialogangliosides of the lacto and neolacto series, gangliosides with type 1 chain dominating. The structures of the gangliosides were tentatively identified by gas chromatography-mass spectrometry and monoclonal antibodies with carefully determined epitope specificity. The gangliosides and neutral glycosphingolipids had very similar fatty acid composition, consisting of about 40% stearic acid and 40% C24-acids.     

Cloning and expression of the gene for a fibronectin-binding protein from Staphylococcus aureus.

The gene encoding the fibronectin-binding protein (FNBP) from Staphylococcus aureus strain 8325-4 was isolated from a gene bank in pBR322. The original clone, containing a 6.5-kb insert, gave a functional product present in the periplasm of Escherichia coli. Analysis of polypeptides isolated after affinity chromatography on fibronectin-Sepharose followed by ion-exchange chromatography revealed two gene products, 87 and 165 kd in mol. wt. The amino acid compositions of these two polypeptides and a native FNBP from S. aureus strain Newman were very similar. Antibodies raised against the native FNBP from strain Newman precipitated the 125I-labelled 165-kd polypeptide, and unlabeled 165- and 87-kd polypeptides as well as native FNBP inhibited the immunoprecipitation reactions. The region of the fnbp-gene encoding the fibronectin-binding activity has been identified and subcloned in an expression vector based on the staphylococcal protein A gene. The resulting product in E. coli is an extracellular fusion protein consisting of two IgG-binding domains of protein A followed by a fibronectin-binding region. The fusion protein binds to fibronectin and completely inhibits the binding of fibronectin to intact cells of S. aureus.     

Identification of the carbohydrate receptor for Shiga toxin produced by Shigella dysenteriae type 1

The binding of Shiga toxin isolated from the bacterium Shigella dysenteriae type 1 to a series of glycolipids and to cells or cell homogenates has been studied. Bound toxin was detected using either 125I-labeled toxin or specific monoclonal antibody and 125I-labeled anti-antibody. Overlay of toxin on thin-layer chromatograms with separated glycolipids and binding to glycolipids coated in microtiter wells established that the toxin specifically bound to Gal alpha 1-4Gal beta (galabiose) placed terminally or internally in the oligosaccharide chain. No glycolipid shown to lack this sequence binds the toxin. Most of the glycolipids with internally placed galabiose were not active, indicating a sterical hindrance for toxin access to the binding epitope. Binding of toxin to HeLa cells in monolayers could be inhibited by preincubation of the toxin with galabiose covalently linked to bovine serum albumin (BSA), but not with free oligosaccharides containing galabiose or with lactose coupled to BSA. This demonstrated that the inhibition is specifically dependent on galabiose and requires multivalency of the disaccharide to be efficient. The inhibitory effect was successively enhanced by increasing the substitution on BSA (7, 18, and 25 mol of galabiose/mol of BSA). The BSA-coupled galabiose could also prevent the cytotoxic effect on HeLa cells (detachment of killed cells). There are cell lines with a dense number of receptor sites, but which are resistant to toxin action (uptake and inhibition of protein synthesis) which may suggest two types of receptor substances which are functionally different and unevenly expressed. In analogy with the mechanism earlier formulated for cholera toxin, we propose glycolipid-bound, bilayer-close galabiose as the functional receptor for membrane penetration of the toxin, while galabiose bound in glycoproteins affords binding sites but is not able to mediate penetration.     

N-Deacetylation of 2-acetamido-2-deoxy-hexosecontaining oligosaccharides and polysaccharides by calcium in liquid ammonia

N-Deacetylation of 2-acetamido-2-deoxy-hexose residues is accomplished in liquid ammonia containing calcium. Oligosaccharides, lacto-N-fucopentaose II and lacto-N-difucohexaose I, containing 3,4-disubstitutedN-acetylhexosamine residues are quantitativelyN-deacetylated. When applied to polysaccharides, however, only partialN-deacetylation was achieved.Author for correspondence. AXRD     

Mouse steroid 15 alpha-hydroxylase gene family: identification of type II P-450(15)alpha as coumarin 7-hydroxylase

We identified type II P-450(15)alpha as mouse coumarin 7-hydroxylase (P-450coh). Unlike type I P-450(15)alpha, the other member within the mouse steroid 15 alpha-hydroxylase gene family, type II catalyzed little steroid 15 alpha-hydroxylase activity, yet structurally there were only 11 substitutions between type I and type II P-450(15)alphaS within their 494 amino acid residues (Lindberg et al., 1989), and the N-terminal sequence (21 residues) of P-450coh was identical with that of both P-450(15)alphaS. Induction by pyrazole of coumarin 7-hydroxylase activity correlated well with the increase of type II P-450(15)alpha mRNA in 129/J male and female mice. Pyrazole, on the other hand, was less in males or not effective in females in inducing the 15 alpha-hydroxylase activity and type I P-450(15)alpha mRNA. Expression of type I and II in COS-1 cells revealed that the latter catalyzed coumarin 7-hydroxylase activity at 10 to approximately 14 pmol min-1 (mg of cellular protein)-1. The former, on the other hand, had a high testosterone 15 alpha-hydroxylase but little coumarin 7-hydroxylase activity. It was concluded, therefore, that type II P-450(15)alpha is the mouse coumarin 7-hydroxylase. Identification of type II as the P-450 specific to coumarin 7-hydroxylase activity and characterization of its cDNA and gene, therefore, were significant advances toward understanding the basis of genetic regulation of this activity in mice (known as Coh locus).