A biochemical and immunohistochemical study of central serotonin nerves in rats with chronic thiamine deficiency.

An immunohistochemical and neurochemical investigation of central serotonin (5-HT) nerves was made in rats deprived of dietary thiamine at various stages of development. The classical symptoms of severe thiamine deficiency were produced in adult rats which had been maintained on a synthetic thiamine-free diet for 5-8 weeks and in young rats reared from birth to weaning by thiamine-deficient mothers. Offspring of rats which had been thiamine-deficient throughout pregnancy were also studied; there were no visible symptoms of thiamine deficiency in these rats after weaning. The number and distribution of 5-HT nerve cell bodies in the brainstem were compared in control and thiamine-deficient rats after visualizing the cells by immunofluorescence of endogenous 5-HT. 5-HT nerve terminals and axons were also compared in normal and deficient rats by immunofluorescence after loading with 5,7-dihydroxytryptamine. The immunohistochemical examination showed that central 5-HT nerves were not affected in any of the groups of thiamine-deficient rats studied. This was confirmed by measurements of tryptophan hydroxylase activity and 5-HT concentration in several brain regions. These results do not support earlier reports of a selective impairment of central 5-HT nerves in chronic diet-induced thiamine deficiency.