Age-related changes in rat brain dopaminergic receptors

The number (Bmax) and affinity (Kd) of [3H] spiroperidol binding sites in the cerebral cortex, striatum and hypothalamus of 2-, 10- and 22-month old male Wistar rats (20 rats per group) injected i. p. for 10 days with saline, L-DOPA (250 mg/kg) or haloperidol (1 mg/kg) were determined in the presence of 10(-6) M unlabelled haloperidol. The Bmax values in the three brain structures studied decreased with aging in both controls and L-DOPA- or haloperidol-treated rats. The Kd values increased with age. That specific [3H] spiroperidol binding was determined through displacement of the labelled ligand by haloperidol suggested that an age-related loss of dopamine receptors occurred in the brain structures studied. However, considering the fact that in the cerebral cortex [3H] spiroperidol labels a subclass of serotonin receptors (5-HT2) rather than DA receptors, the present results, particularly those concerning the cerebral cortex, suggest an age-related decrease also in the number of 5-HT receptors in this cerebral structure.