Previous studies have indicated that thiamine deficiency is associated with clearly elevated histamine concentrations in the rat hypothalamus, whereas other brain regions contain normal amounts of the amine. The purpose of this study was to find out if the increased hypothalamic histamine concentrations are due to increased numbers of mast cells or changes in neuronal histamine stores.
Thiamine-deficiency was induced by daily injections of pyrithiamine until the animals lost the righting reflex. Control animals were pair-fed with either thiamine-deficient or normal thiamine-supplemented food. A significant increase in histamine concentration was observed in the hypothalamus and pons-medulla of the pyrithiamine-treated rats, but not in the cerebellum, thalamus, cerebral cortex or pituitary gland. Immunohistochemically, no histamine-containing mast cells were found in the hypothalami of the pyrithiamine-treated rats or control animals. The histaminergic tuberomammillary neurons were very intensely immunofluorescent, and the density of histamine-immunoreactive nerve fibers in the hypothalamus was also increased in the pyrithiamine-treated animals.
The results indicate that in the brains of thiamine deficient rats increasing amounts of histamine accumulate in hypothalamic neurons.