Aging and sex differences in striatal dopaminergic function.

In this report the potassium- (30 mM) and amphetamine- (10 microM) stimulated responses of dopamine (DA) and 3,4-dihydroxy phenylacetic acid (DOPAC) from superfused striatal tissue of female and male mice as sampled at 2, 6, 18 and 24 months of age were compared. When assessed relative to responses obtained from 2-month-old female mice, potassium-stimulated DA output of female mice was significantly decreased at 18 months of age and significantly increased at 24 months of age. In male mice, the only statistically significant change was an increase in potassium-stimulated DA in the 24 versus 2-month-old mice. In response to amphetamine-stimulation, DA responses from striatal tissue of 18-month-old females were significantly decreased and that of 24-month-old mice significantly increased relative to that of the 2-month-old females. In the case of male mice, amphetamine-stimulated DA responses of 6- and 18-month-old mice were significantly decreased compared with responses observed in the 2-month-old males. In addition, amphetamine-stimulated DA responses of the 24-month-old females were significantly greater than the 24-month-old males. In general, the response profiles for DOPAC to potassium and amphetamine stimulation were similar to that of DA for male, but not female, mice. These results demonstrate that sex differences in striatal dopaminergic function are differentially affected by age. Overall, striatal DA responsiveness of female mice shows more extreme age-related changes, particularly between the 2- and 6-month versus the 18- and 24-month-old mice and a discord between DA and DOPAC responses. Such extreme changes may be related to the presence (at 2 and 6 months) versus absence (at 18 and 24 months) of estrous cycles/gonadal steroid hormonal functions in female mice.