The influence of alpha-fluoromethylhistidine on the regional brain histamine and plasma corticosterone levels in aging

alpha-Fluoromethylhistidine, a histidine decarboxylase inhibitor, induced a significant depletion in the hypothalamic, midbrain, and cortical brain histamine amounts in 12- and 3-month-old rats. In all three brain regions the most evident depletion occurred 2 h after treatment. In both groups of rats midbrain histamine levels returned to control values 6 h after treatment; however, hypothalamic histamine depletion was still significant and more evident in the old than in the young animals. Cortical brain histamine also remained significantly depleted in old rats, but returned to control values in young animals 6 h after alpha-fluoromethylhistidine treatment. These results suggest that old rats show a slower rate of new histamine synthesis in the cortex and hypothalamus. Regional brain histamine depletion was associated with a very significant decrease in plasma corticosterone levels, which indicates that brain histamine-corticosterone interactions do occur.