The distribution of mast cells in the human area postrema

The topography and phenotype of mast cells in the human area postrema, together with correlation between mast‐cell density and microvessel density (MVD), were analysed in 16 brains. Transverse serial sections of formalin‐fixed, paraffin‐embedded brainstems were stained with toluidine blue and alcian blue/safranin stainings, and with anti‐tryptase and anti‐CD31 monoclonal antibodies. The mean (± SD) numbers of mast cells per section were 1.3 ± 0.8 and 1.2 ± 0.7 with toluidine blue and alcian blue/safranin, respectively, whereas anti‐tryptase monoclonal antibody showed a mean of 5.1 ± 2.4 cells. Mast cells were alcian blue‐ and safranin‐positive in 56%, because of the coexistence of low‐sulphated (blue‐staining) and high‐sulphated (red‐staining) granules. No significant linear correlation between mast‐cell density (4.9 mm−2) and MVD (114.5 mm−2) was found (r2 = 0.19, P = 0.09). Mast cells were frequently located close to blood vessels (55%) (33% to venules, 22% to arterioles), indicating that their products play a role in the regulation of blood flow and in vessel permeability in the area postrema. Mast cells were located subependymally in 44% and close to the dorsal aspect of the nucleus of the tractus solitarius in 31%, suggesting a subregional distribution.