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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The accumulation, metabolism and stimulated-induced release of 5-HT in the nervous system of the snail was studied. When nervous tissue was incubated at 24°C in a medium containing [14C]5-HT or [3H]tryptophan, tissue: medium ratios of about 25:1 and 4:1 respectively were obtained after 45 min incubation.The process responsible for [14C]5-HT accumulation showed properties of an active transport system: it was temperature sensitive and was greatly inhibited by dinitrophenol and ouabain. Furthermore, the accumulation process was inhibited by imipramine and desipramine.Of a number of analogues of indole, N-acetyl-5-HT and 5-hydroxytryptophan were the most potent in the inhibition of the accumulation of [14C]5-HT. The presence of a large molar excess of amino acids had little effect.A small amount (less than 14 per cent) of the accumulated [14C]5-HT was metabolized to form 5-hydroxyindole acetic acid, even after long periods (2 h) of incubation. The accumulated [3H]tryptophan was metabolized to form 5-hydroxytryptophan and 5-HT; the content of formed [3H]5-HT increased with incubation time whilst the [3H]5-hydroxytryptophan remained more or less constant.The presence of p-chlorophenylalanine in the incubation medium did not interfere with the accumulation of [3H]tryptophan, though it inhibited the formation of [3H]5-hydroxytryptophan and to a greater extent [3H]5-HT.A rapid efflux of the accumulated [14C]5-HT from snail nervous tissue was observed on electrical stimulation. Slower release resulted when the Ca2+ ion content of the incubation medium was replaced by Mg2+ ions. There is also a slight efflux of radioactive substances following electrical stimulation in tissues previously incubated in [3H]tryptophan. Most of this radioactivity was attributed to the formed [3H]5-HT.The data support the idea that 5-HT is a transmitter-substance in the snail Helix pomatia, and that re-uptake of the substance is a method of inactivating the released amine.
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