Mast cell degranulation is increased 3 hours after capsaicin. Mast cells are present in the lumbar dura and can be visualized with toluidine blue staining as mostly granulated with some being degranulated after vehicle treatment (A) or intensively degranulated after Compound 48/80 (B). C-fiber stimulation with capsaicin induces a significant increase in percent mast cell degranulation at 3 hours post-injection in the lumbar dura mater as compared to vehicle (C), but not in the thoracic dura mater (D) (* = P < 0.05). I.p. Compound 48/80 administration induces a significant increased in percent degranulation in both lumbar and thoracic dura mater (* = P < 0.05) (C, D). There are no significant changes in granulated, degranulated, or total mast cell density in neither the lumbar (E), nor the thoracic dura mater (F) after Compound 48/80 or capsaicin administration.