Effect of PEA on λ-carrageenin-induced mast cell activation. " A" shows the effect of PEA on λ-carrageenin-induced mast cell (MC) activation. MC degranulation was evaluated by microscopy. Connective MCs stained with 0.05% (w/v) toluidine blue and counterstained with 0.1% (w/v) nuclear fast red (magnification 100×). A differentiation between non degranulated (deep blue) and degranulated (light blue) MC was evaluable (a; b; c). In d) is shown the percentage of MC degranulation (ratio between degranulated and non degranulated MC). Results are expressed as mean ± SEM of 3 experiments. ***p < 0.001, °°p < 0.01. "B" shows high magnification of a representative histological analysis of granulomatous tissues stained with toluidine blue in which the presence of degranulated MCs is clearly visible close to blood vessels and nerves.