Localization of thiamine in cholinergic nerve terminals: a histofluorescence study in the electric organ ofTorpedo

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Abstract
Thiamine (vitamin B1) and its phosphoric acid esters were found at a surprisingly high level in the electric organ of the fishTorpedo marmorata. The localization of the vitamin was investigated by a sensitive reaction in which the thiamine molecule was converted into a blue fluorescent thiochrome by treatment with an alkaline potassium ferricyanide solution. Whereas only slight fluorescence occurred in the electroplaque cells, a strong fluorescent reaction took place in their nerve supply. Intense fluorescence was observed not only in the myelinated nerve fibres but also at the nodes of Ranvier; moreover, preterminal branches and nerve endings, which are nonmyelinated, were also strongly stained. The emission spectrum of this fluorescent material was found to be nearly identical to that of standard thiochrome. These findings substantiate the hypothesis that vitamin B1 plays an important role in acetylcholine metabolism and release.