Exogenous Tryptophan Increases Synthesis, Storage, and Intraneuronal Metabolism of 5-Hydroxytryptamine in the Rat Hypothalamus

The effects of tryptophan administration on neurochemical estimates of synthesis [5-hydroxytryptophan (5-HTP) accumulation following administration of a decarboxylase inhibitor], storage [5-hydroxytryptamine (5-HT) concentrations], and metabolism [5-hydroxyindoleacetic acid (5-HIAA) concentrations] of 5-HT in selected regions of the hypothalamus were determined using HPLC coupled to an electrochemical detector. Tryptophan methyl ester HCl (30-300 mg/kg i.p.) produced a dose-dependent increase in the rate of 5-HTP accumulation throughout the hypothalamus but had no effect on the rate of accumulation of 3,4-dihydroxyphenylalanine. Peak 5-HTP levels were attained by 30 min following administration of tryptophan (100 mg/kg i.p.) and were maintained for an additional 60 min. Tryptophan also produced concomitant dose-dependent increases in 5-HT and 5-HIAA concentrations in these same regions without changes in the 5-HIAA/5-HT ratio. These results indicate that exogenous tryptophan administration selectively increases the synthesis, storage, and metabolism of 5-HT in the hypothalamus without altering the synthesis of catecholamines. Inhibition of 5-HT uptake with chlorimipramine or fluoxetine produced modest (10-40%) reductions in 5-HIAA concentrations throughout the hypothalamus, revealing that only a minor portion of 5-HIAA is derived from released and recaptured 5-HT, whereas the major portion of this metabolite reflects intraneuronal metabolism of unreleased 5-HT. In both chlorimipramine- and fluoxetine-treated rats, 5-HIAA concentrations were significantly increased by tryptophan administration, indicating that the increase in synthesis of 5-HT following precursor loading is accompanied by an increase in the intraneuronal metabolism of 5-HT.     

5,5-Diphenylhydantoin Antagonizes Neurochemical and Behavioral Effects of p, p'-DDT but Not of Chlordecone

Abstract: Rats were given 75 mg/kg of 5,5-diphenylhydantoin (phenytoin) or vehicle 30 min prior to 75 mg/kg of 1, 1, 1-trichloro-bis( p -chlorophenyl)ethane ( p, p' -DDT) (p.o.) or chlordecone (i.p.) and tremor was measured 12 h later. Rats were then killed, and regional brain levels of biogenie amines and their acid metabolites and amino acids were determined. Pretreatment with phenytoin significantly attenuated the tremor produced by p, p' -DDT but enhanced that produced by chlordecone. p, p' -DDT had significant effects on the levels of asparate, glutamate, 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), whereas chlordecone increased glycine, 5-HIAA, and MHPG levels. Pretreatment with phenytoin blocked p.p' -DDT-induced increases of aspartate in the brainstem and spinal cord, 5-HIAA in the hippocampus, and MHPG in the brainstem and hypothalamus. Phenytoin significantly enhanced chlordecone-induced increases of MHPG in the brainstem. These data indicate that organo-chlorine-induced increases in noradrenergic activity in the brainstem and spinal cord may be directly related to the tremorigenic effects of these chemicals.     

Binding of the Novel Serotonin Agonist 8-Hydroxy-2-(Di-n-Propylamino) Tetralin in Normal and Alzheimer Brain

Binding of [3H]8-hydroxy-2-(di-n-propylamino) tetralin, a putative ligand for the 5-hydroxytryptamine (5-HT, serotonin) 1A recognition site, was measured in neocortex from postmortem human brain. The substance was found to bind to a saturable site with a KD value and pharmacological profile similar to that of rat. Binding to membranes from normal human temporal cortex was found to significantly correlate (inversely) with age. A significant reduction in binding, reflecting decreased density of recognition sites, was observed in the frontal cortex of patients with Alzheimer's disease (48% loss). This region in the dement brains showed unaltered presynaptic 5-HT function (5-HT and 5-hydroxyindoleacetic acid content) whereas 5-HT concentration was reduced in the temporal cortex.     

Increased 5-Hydroxytryptamine and Norepinephrine Release from Rat Brain Slices by the Red Sea Flatfish

The effect of the Red Sea flatfish toxin pardaxin was examined on K+-evoked and on basal release of either [3H]norepinephrine or [3H]5-hydroxytryptamine from preloaded rat cortical slices. The K+-induced release of the neurotransmitters was stimulated in a dose-related manner at concentrations ranging from 0.5 to 4 micrograms/ml. Basal release of the two transmitters was elevated to a lesser extent. Although the stimulation of evoked release was approximately equivalent for the two neurotransmitters, the response to 5-hydroxytryptamine was reversible whereas that of norepinephrine was not washed by 20 min of superfusion. The mechanisms involved in producing these actions of pardaxin are not known; however, they may be mediated by changes in electrolyte fluxes across the neuronal membranes.     

Inhibition of glycine N-methyltransferase activity by folate derivatives: implications for regulation of methyl group metabolism

Glycine N-methyltransferase, an enzyme that uses S-adenosylmethionine to methylate glycine with the production of sarcosine, was recently shown to be identical with a major folate binding protein of rat liver (Cook, R.J. and Wagner, C. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 3631-3634). We now present evidence that 5-methyltetrahydropteroylpentaglutamate (5-CH3-H4PteGlu5) is bound with high specificity, and is a powerful inhibitor of the enzyme. It is proposed that this information may be used to modify the "methyl trap" hypothesis which describes how the availability of one-carbon units is regulated by folate, vitamin B12 and methionine.     

Cyclic AMP inhibits platelet activation independently of its effect on cytosolic free calcium

Stimulation of platelets with the ionophore A23187, thrombin, ADP or PAF-acether resulted in a rapid increase of cytosolic free Ca2+, as measured with Quin-2, and in aggregation, 5HT secretion and - in the case of the first two agonists - thromboxane generation. PGI2 and dibutyryl cyclic AMP inhibited all these responses, except in the case of A23187, in response to which the increase in Ca2+ was unaffected, although the other responses were inhibited. The inhibition of aggregation and secretion in response to the combination of thrombin and A23187 was indistinguishable from that in response to thrombin alone. It thus appears that cAMP inhibits these responses independently of its effect in lowering cytosolic free Ca2+.     

5S and 5.8S ribosomal RNA evolution in the suborder tetrahymenina (Ciliophora: Hymenostomatida)

Summary The nucleotide sequences of the 5S and 5.8S rRNAs of eight strains of tetrahymenine ciliates have been determined. The sequences indicate a clear distinction betweenTetrahymena paravorax and its suggested conspecificT. vorax, but leave the taxonomic distinction betweenT. vorax andT. leucophrys in doubt. The rRNA sequences of sixTetrahymena species and of three other species of the suborder Tetrahymenina have been used to deduce evolutionary schemes in which ancestral rRNA sequences and changes are proposed. These schemes suggest the predominant acceptance of GA and CT transitions in the 5S rDNA during the evolution of the suborder.     

Phylogeny of the 5S ribosomal RNA fromSynechococcus lividus II: The cyanobacterial/chloroplast 5S RNAs form a common structural class

Summary The complete nucleotide sequence of the 5S ribosomal RNA from the cyanobacteriumSynechococcus lividus II has been determined. The sequence is 5-UGCCUAGUGUUUAUGGCGCG-GUGGAACCACGCUGAUCCAUCCCGAACUC-AGAGGUGAAACAUCGCAGCGGUGAAGAU-AGUUGGAGGGUAGCCUCCUGCAAAAAUA-GCUCAAUGCUAGGCA_OH-3. This 5S RNA has the cyanobacterial- and chloroplast-specific nucleotide insertion between positions 30 and 31 (using the numbering system of the generalized eubacterial 5S RNA) and the chloroplast-specific nucleotide-deletion signature between positions 34 and 39. The 5S RNA ofS. lividus II has 27 base differences compared with the 5S RNA of the related strainS. lividus III. This large difference may reflect an ancient divergence between these two organisms. The electrophoretic mobilities on nondenaturing polyacrylamide gels of renatured 5S RNAs fromS. lividus II,S. lividus III, and spinach chloroplasts are identical, but differ considerably from that ofEscherichia coli 5S RNA. This most likely reflects differences in higher-order structure between the 5S RNA ofE. coli and these cyanobacterial and chloroplast 5S RNAs.     

Regulation of resynthesis of the CO2-acceptor in photosynthesis. Feedback inhibition of transketolase

The presence of ribulose-5-phosphate epimerase (EC 5.1.3.1, epimerase) in samples of ribose-5-phosphate isomerase (EC 5.3.1.6, isomerase) obtained from spinach ( Spinacea aleracea L. cv. Bloomsdale Long Standing) was determined using (i) a sampling procedure which measured the quantity of xylulose-5-phosphate formed in the reaction mixture and (ii) a coupled enzyme assay in which the rate of oxidation of NADH was measured after establishing steady-state concentrations of xylulose-5-phosphate, dihydroxacetonephosphate and glyceraldehyde-3-phosphate by the action of epimerase, transketolase (EC 2.2.1.1), triosephosphate isomerase (EC 5.3.1.1) and glycerol-3-phosphate dehydrogenase (EC 1.1.1.8). In preparations where the ratio of isomerase to epimerase activities was less than 100, both assay procedures yielded valid indications of epimerase activity. The steady-state assay system was found, however, to seriously underestimate epimerase activity in enzyme preparations which were enriched in isomerase. Cross plots of epimerase activity determined by the sampling and steady-state procedures demonstrated that an inhibitor of the coupling enzyme mixture was formed in the presence of high relative concentrations of the isomerase. The inhibited coupling enzyme mixture was fully active with glycer-aldehyde-3-phosphate. Inhibition of the coupling enzyme mixture was attributed to transketolase. Feedback inhibition of transketolase is proposed to be of physiological significance in the photosynthesis cycle, operating to restrict resynthesis of CO₂-acceptor under conditions where high steady-state concentrations of the intermediates of the photosynthesis cycle are maintained.