The distribution of mast cells in the human area postrema

Abstract

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 (r(2) = 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.

Fig. 1

(a) Transverse section of the caudal medulla showing the separation of the right and left parts of the area postrema (arrows) as a result of the interposition of the caudal extremity of the IV ventricle floor (azan-Mallory, ×1). (b) Higher magnification of the medullary tegmentum shown in (a), demonstrating the relationship of the area postrema with the dorsal part of the nucleus of the tractus solitarius (azan-Mallory, ×2.5) (ST: solitary tract; Sol: nucleus of the tractus solitarius). (c) Schematic diagram of the subdivision of the area postrema (higher magnification of b) in the three subregions (subependymal, central and close to the nucleus of the tractus solitarius). The dotted line represents the main axis of the area postrema in the transverse section; the perpendicular lines have been subdivided into three segments of the same length corresponding to the extension of the three subregions. (d) Topography of mast cells in the area postrema, showing the possible superficial and deep (near nucleus of the tractus solitarius) location (anti-tryptase, ×4). (e) Detail of (d), showing the perivascular location of four mast cells in subependymal subregion (anti-tryptase, ×20). (f) Section stained immunohistochemically for CD31, showing positive reaction at the level of endothelial cells of small vessels in the area postrema (anti-CD31, ×40). (g) Perivascular location of mast cells along the course of small arterioles (anti-tryptase, ×10).

Fig. 2

(a) Coexistence of alcian-blue-(low-sulphated glycosaminoglycans) and safranin-positive (high-sulphated glycosaminoglycans) granules giving a dark violet colour to the mast cell cytoplasm. Note the proximity with a small pale-blue stained vessel on the left (alcian blue/safranin, ×100). (b) Intense anti-tryptase reactivity of mast cell cytoplasmic granules (anti-tryptase, ×100).

Fig. 3

Diagram showing the mean mast cell density and microvessel density in the single cases. Analysis of linear correlation revealed no statistical significance (r² = 0.19, P = 0.09).

Fig. 4

Diagram showing the topographic distribution of mast cells with reference to vascular relationships, i.e. close to arterioles (Art), venules (Ven) or with no vascular relationships (No Rel), and with reference to subregional division – subependymal (Subep), central (Cen) and close to the nucleus of the tractus solitarius (Deep). Values are expressed as mean ± SD.