Age-dependent changes in the expression of dopamine receptor subtypes in human peripheral blood lymphocytes

The pharmacological profile and the density of dopamine D-3 and D-5 receptor subtypes expressed by human peripheral blood lymphocytes of subjects of different ages (ranging from 20 to 75 years) were assessed using radioligand binding techniques. Dopamine D, receptor was assayed with [H-3]7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([H-3]7-OH-DPAT) as a ligand. Dopamine D-5 receptor was assayed using [H-3][R]-(+)-(-chloro-2,3,4,5,tetrahydro-5-phenyl-1H-3-benzazepin-al-hemimaleate) ([H-3]SCH 23390) as a ligand. The affinity and the pharmacological profile of [3H]7-OH-DPAT and [3H]SCH 23390 at dopamine D-3 and D-5 receptor, respectively, were similar in subjects of different ages, The density of dopamine D-3 receptor binding sites was slightly decreased in subjects of 30-39 years in comparison with younger individuals. A remarkable loss of dopamine D-3 receptor was then found between 40 and 49 years of age in comparison with younger subjects. A further slight decrease was noticeable between 50 and 59 years of age. The number of [H-3]7-OH-DPAT binding sites was then stabilized after 60 years of age. The density of dopamine D-5 receptor binding sites did not show age-dependent changes. The above findings indicate the occurrence of a decline in the density of lymphocyte dopamine D-3 but not D-5 receptor between adult and mature subjects, The possibility that dopamine D-3 receptor assay in peripheral blood lymphocytes may represent a tool for investigating dopamine receptor function in aging and age-related neurological disorders is discussed.