Tissue Kallikrein in Rat and Mouse Neurons

1. The distribution of tissue kallikrein in the rat brain was investigated by an immunohistochemical technique using antiserum against rat urinary kallikrein. The kallikrein-immunoreactive cells were widespread and scattered in both the cerebral cortex and brain stem, and the immunoreactive substance appeared to be preferentially localized around the neuronal cell body and their processes. 2. Furthermore, in order to define whether brain kallikrein levels vary in the aging process, the hydrolyzing activity in the cerebrum L-prolyl-L-phenylalanyl-L-arginine-4-methyl-coumaryl-7-amide (Pro-Phe-Arg-MCA) was measured in young (7-week old) and old (36-week old) female senescence accelerated mice (SAM-P/8 and SAM-R/1). The brain kallikrein levels of 7- as well as 36-week old SAM-P/8 were found to be lower than those of 7-week old SAM-R/1 (a control strain). Also, the brain kallikrein level of 36-week old SAM-R/1 animals was markedly reduced when compared with the 7-week old mice, suggesting that the reduced amount of cerebral kallikrein reflects the aging of the brain.