Plasma homovanillic acid and performance on motor and cognitive tasks in community-dwelling elderly: Macarthur studies of successful aging

To investigate the dopaminergic correlates of the aging- related motor and cognitive deficits, the dopamine metabolite homovanillic acid (HVA) in plasma was studied in a community-dwelling elderly cohort (n = 141). The results showed that hand-signature time (HST), a measure of bradykinesia, correlated negatively with plasma HVA (r = -0.24, p <.007). Similarities task performance showed a trend-level positive correlation with plasma HVA (r = 0.15, p =.08). Because plasma HVA is derived from several sources including central dopaminergic neurons and both central and peripheral noradrenergic neurons, the noradrenergic metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) in plasma was also measured to indirectly estimate the relationships, with HVA originating from noradrenergic metabolism. Plasma MHPG significantly correlated with similarities scores (r = 0.34, p <.001) but not with HST. The results suggested that the association of HVA with prolonged HST may be related to central dopamine metabolism, but its association with similarities scores may be due to noradrenergic metabolism. The results raise the possibility that prolonged HST may be an indicator of preclinical brain dopamine loss in the elderly.