Age-related decreases in dopamine receptors in the caudate nucleus and putamen of the rhesus monkey (Macaca mulatta).

Specific binding of the dopamine receptor ligand 3H-spiroperidol to cell membranes prepared from the caudate nuclei and putamens of 29 rhesus monkeys (M. mulatta), ranging in age from 2 to 22 years, was investigated. Receptor concentration (Bmax) decreased in the caudate nucleus and putamen with age at mean rates of 2.1 and 1.7% per year, respectively, whereas binding affinity (Kd) did not change significantly with age. The rate of decline in Bmax appeared to be more rapid before adulthood and in old age than during young adulthood and middle age. These data are compared with the results from similar studies of other animal species including human, rabbit, rat, and mouse. The rate of decline in striatal dopamine receptors is closely related to the rate of aging and maximal life span of the species. It may reflect both maturational and senescent processes modifying the behavior of animals as they age.