Changes in dopamine release in vitro from the corpus striatum of young versus aged rats as a function of infusion modes of L-dopa, potassium, and amphetamine.

In the present experiments we examined the effects of two different modes of infusion (two separate 10 min versus continuous infusions) of a depolarizing concentration of potassium (K+, 30 mM), amphetamine (AMPH, 10 microM), or L-DOPA (5 microM) upon dopamine (DA) release in vitro from superfused corpus striatal (CS) tissue fragments of young (2-4 months) and aged (18-24 months) male rats. The relative changes in DA release to two infusions of K+ and AMPH (R2/R1) were virtually identical for CS from both young and aged rats. In the case of L-DOPA, DA release from CS of young rats was markedly increased in response to the second compared to the first L-DOPA infusion (R2/R1 = 2.48 +/- 0.33, N = 7) and significantly greater than that of aged rats (R2/R1 = 1.24 +/- 0.17, N = 6). A continuous infusion of K+ and AMPH resulted in an overall greater amount of DA release from the CS of young versus aged rats. In contrast, DA release from CS of aged rats showed an overall more rapid and greater amount of DA release to continuous L-DOPA infusion than that from the CS of young rats. These results demonstrate age-dependent differences in DA release from the CS as a function of the infusion mode of specific secretagogues. Particularly interesting were the responses to L-DOPA where a pulsatile administration resulted in an overall greater amount of DA release from the CS of young rats while a continuous infusion produced a greater amount of DA release from the CS of aged rats.