An increase of sigma 1 receptors in the aged monkey brain

Abstract

We evaluated in vivo the effect of aging on the sigma 1 receptors in the monkey brain by the quantitative analysis of the binding of [ 11 C ]SA4503 to sigma 1 receptors with positron emission tomography. Based on a three-compartment model, the influx rate constant K 1 of [ 11 C ]SA4503 from plasma to brain across the blood–brain barrier in all 10 regions investigated became smaller in the aged monkeys (20–28 years old, n=5) than in the young adult monkeys (4–8 years old, n=5), but the reduction was not significant due to the individual differences. On the other hand, the binding potential, which was calculated as the ratio of the association rate constant k 3 to the dissociation rate constant k 4 for the binding of [ 11 C ]SA4503 to sigma 1 receptors in the brain, significantly increased in nine of the brain regions of the aged monkeys to the 160–210% levels of the young monkeys. We concluded that the sigma 1 receptor binding sites increased in the aging process of the monkey brain.