In vivo brain calcium homeostasis during aging.

Since in vitro experiments suggest that brain calcium metabolism is altered with aging, the estimated rate of calcium uptake by the brain in vivo was determined with senescence. Calcium-45 incorporation into cortex, striatum, hippocampus, cerebellum, forebrain, midbrain and brainstem was determined in 3-, 10- and 30-month-old mice at 5 h after either an intravenous or intraperitoneal injection. Calcium uptake (brain dpm/mg protein divided by blood specific activity at 5 h) into these regions declined 19-33% at 10 months and 41-51% at 30 months. Subcellular fractionation of the cortex revealed that the decrease was similar in P1 (myelin, nuclei and tissue debris), P2 (synaptosomes, mitochondria and myelin) and S2 (microsomes, ribosomes and cytosol). Brain calcium concentrations declined with age in brain stem (-62%) and midbrain (-48%) but did not significantly vary with age in the other regions. These results support the suggestion that alterations in calcium homeostasis may underlie age-related changes in neurotransmitter metabolism.