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Carlsson A, Bédard P, Lindqvist M, Magnussen T. 
“The Influence of Nerve Impulse- Flow on the Synthesis and Metabolism of 5-Hydroxytryptamine in the Central Nervous System”. 
Biochem.Soc.Symp.. 1972;36:17-32.
Two inhibitors of L-5-hydroxytryptophan/L-3,4-dihydroxyphenylalanine decarboxylase were injected intraperitoneally into mice and rats. The subsequent accumulation of the normally undetectable 5-hydroxytryptophan and dopa (3,4dihydroxyphenylalanine) in the central nervous system was investigated. The distribution of the two amino acids in rat brain was found to be similar to that of endogenous 5-hydroxytryptamine and catecholamines [noradrenaline+ dopamine (3,4-dihydroxyphenethylamine)] respectively. The time-course of the accumulation was linear for the first 30min. The rate of 5-hydroxytryptophan formation was increased by c-tryptophan administration. Section of the axons of monoamine fibre systems led to immediate changes in hydroxylation rates. The hydroxylation of tryptophan was decreased by about 50 0n rat spinal cord, but much less in the brain. The hydroxylation of L tyrosine was accelerated in the forebrain, where the striatal dopamine system predominates. In a cortical area, where noradrenaline is the predominating catecholanine, axotomy did not significantly influence r-tyrosine hydroxylation. The hydroxylation of t-tryptophan was retarded by the monoamine oxidase inhibitor nialamide and by the hallucinogenic agents compound LSD-25 (lysergic acid diethylamide) and NN-dimethyltryptamine. The results obtained indicate that monoamine synthesis is not regulated by one single mechanism. For 5-hydroxytryptamine both the -tryptophan hydroxylase and the intraneuronal portion of the monoamine oxidase are probably involved in the regulation of metabolism according to physiological needs.
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