Dural mast cells: source of contaminating histamine in analyses of mouse brain histamine levels

Histamine levels were determined in mouse brains from WBB6F1-+/+ (mast cell normal) and WBB6F1-W/Wv (mast cell-deficient) mice whose brains were dissected immediately after decapitation or after freezing the severed heads in liquid nitrogen for 10 s. In WBB6F1-+/+ mice, brains obtained from frozen heads contained significantly higher levels of histamine than those obtained from unfrozen heads. The converse was found in brains obtained from the WBB6F1-W/Wv mice. When CF-1 mice (which also contain brain-associated mast cells) were treated as described above, results very similar to those found with the WBB6F1-+/+ mice were obtained. Further, the high levels of histamine found in CF-1 mice whose brains had been frozen in situ were accompanied by an extensive degranulation of mast cells in the dura mater of these mice. Because of this degranulation of mast cells, and the fact that increased levels of brain histamine were not found in mast cell-deficient mice, it is concluded that dural mast cells are the likely source of the artifactually higher levels of histamine seen in brains frozen in situ.