Serotonin release from rat brain mast cells in vitro

Mast cells are primarily localized in connective tissues, where they secrete numerous mediators. They have also been identified in the mammalian central nervous system on the basis of their histochemical and morphological properties, but their role there remains unknown. A perfusion system was used to investigate in vitro mediator release from rat brain mast cells. Compound 48/80, the classic mast cell secretagogue of connective tissue mast cells, induced dose-dependent and non-cytotoxic release of serotonin, histamine and β-hexosaminidase from mast cells in the rat thalamus and hypothalamus, but not in the cerebellum which was used as a negative control. Detailed studies were performed on thalamic mast cells, which were identified on the basis of metachromasia with Toluidine Blue and Safranin-positive staining with the Alcian Blue/Safranin technique. Their secretion was characterized by: (a) parallel release of serotonin, histamine and β-hexosaminidase; (b) lack of dependence on extracellular calcium; (c) susceptibility to inhibition by disodium cromoglycate; and (d) lack of lactate dehydrogenase release. These results indicate that the morphology and secretory characteristics of thalamic mast cells resemble those of connective tissue mast cells. The ability of brain mast cells to secrete their mediators is discussed in the context of their possible involvement in brain pathophysiology.