AGE-DEPENDENT CHANGES IN THE EXPRESSION OF DOPAMINE-RECEPTOR SUBTYPESIN HUMAN PERIPHERAL-BLOOD LYMPHOCYTES

The pharmacological profile and the density of dopamine D-3 and D-5 re ceptor subtypes expressed by human peripheral blood lymphocytes of sub jects of different ages (ranging from 20 to 75 years) were assessed us ing radioligand binding techniques. Dopamine D, receptor was assayed w ith [H-3]7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([H-3]7-OH-DPAT) a s a ligand. Dopamine D-5 receptor was assayed using etrahydro-5-phenyl -1H-3-benzazepin-al-hemimaleate) ([H-3]SCH 23390) as a ligand. The aff inity and the pharmacological profile of [3H]7-OH-DPAT and [3H]SCH 233 90 at dopamine D-3 and D-5 receptor, respectively, were similar in sub jects 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 w as then found between 40 and 49 years of age in comparison with younge r 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 sta bilized after 60 years of age. The density of dopamine D-5 receptor bi nding sites did not show age-dependent changes. The above findings ind icate the occurrence of a decline in the density of lymphocyte dopamin e D-3 but not D-5 receptor between adult and mature subjects, The poss ibility that dopamine D-3 receptor assay in peripheral blood lymphocyt es may represent a tool for investigating dopamine receptor function i n aging and age-related neurological disorders is discussed.