Degranulation of brain mast cells in young albino rats

Quantitative measurements were made of brain mast cell (MC) degranulation in juvenile albino rats. Neither acute nor chronic intraperitoneal injections of Compound 48/80 (C 48/80) evoked any clear degranulation. Fifteen to thirty minutes after the injection of either C 48/80 or physiological saline into the right anterior thalamus, frank degranulation in the leptomeninges and some degranulation in the parenchyma were evident. The injected sides contained about twice as much degranulated cells as the noninjected sides. In a second experiment, animals were killed 10, 100, 1000, and 10,000 min after a single 10-microliters injection of C 48/80 into the anterior thalamus. Although about 40% of the leptomeningeal and 20% of the parenchymal MCs were degranulated within 10 min, more than 50% of the MCs in both areas were degranulated within 100 min after the injection. More extensive degranulation was evident at both times within the parenchyma of the injected sides. Degranulated MCs were not obvious after this period although nuclei surrounded by sparse granules (in the parenchyma) or by fused, globular metachromatic material (in the leptomeninges or their ventricular processes) were still discernable 7 days later. The implications of brain mast cell degranulation for psychoneuroimmunology are considered.