Subcellular localization of brain mast cell histamine in developing rat

The intracerebroventricular administration of compound 48/80 or polymixin B to rats 0 to 60 days old, produced a decrease both in the histamine which sediments in the crude nuclear fraction, as well as in the number of mast cells in the brain. In contrast, the histamine-releasers did not affect histamine levels in subcellular fractions where neuronal histamine is found. Once released, histamine disappeared rapidly (t 1/2 = 3.8 min). In untreated animals and in those treated with histamine releasers, the number of mast cells/g in the whole brains of developing rats and in the cerebral regions of adult rats showed a close correlation with the histamine levels in the crude nuclear fraction. The content of histamine per mast cell in adult rat brain was estimated to be about 13 pg/cell. Histologic examination of the subcellular fractions revealed the presence of intact mast cells in the crude nuclear fraction obtained from untreated animals, and of degranulated mast cells in the same fraction obtained from animals treated with histamine releasers. The mast cell contribution to adult rat brain histamine levels was about 22%. Our results strongly support that most of the histamine which sediments in the crude nuclear fraction of the rat brain is located in mast cells. Determination of histamine in the crude nuclear fraction and in the supernatant of this fraction is proposed as an easy way for identifying the cellular pool altered by any treatment affecting brain histamine levels.