FIGURE 7.

An amphetamine challenge on WD 50 promotes a paradoxical presynaptic potentiation at high-frequency stimulation. (a) Average half-times of FM1-43 release in slices from amphetamine-treated mice on WD 50 before and following an amphetamine (10 μM) challenge in vitro. An amphetamine challenge has no effect on FM1-43 destaining during cortical stimulation at 1 Hz and 10 Hz. Amphetamine produced a frequency-dependent increase in FM1-43 release (lower t_1/2) at 20 Hz. For all panels, ^!!p<0.01, ^!!!p<0.001, Mann-Whitney. ^&p<0.05, 2-way ANOVA for interaction between frequency and treatment. The number of puncta (n) is indicated in parenthesis. (b) In slices from amphetamine-treated mice on WD 50, the half-time responses of individual boutons are compared with and without an amphetamine challenge at 1 Hz, (c) 10 Hz, and (d) 20 Hz. At 20 Hz, amphetamine increases exocytosis (decreased t_1/2) from boutons with a low probability of release. (e) Summary graph compares the half-times of FM1-43 release in saline-treated and amphetamine-treated mice on WD 50 in response to low-frequency (1 Hz) stimulation of the PFC. Compared to saline-treated controls, exposure to repeated amphetamine increases presynaptic release on WD 50. An amphetamine challenge has little effect on the average half-time of FM1-43 release in saline-treated or amphetamine-treated mice on WD 50. Veh, vehicle. (f) Summary graph compares the half-times of FM1-43 release in saline-treated and amphetamine-treated mice on WD 50 in response to high-frequency (20 Hz) stimulation of the PFC. Compared to saline-treated controls, withdrawal from repeated amphetamine decreases release from presynaptic corticoaccumbal boutons. Acute amphetamine in vitro reduces the average release of FM1-43 in slices from saline-treated mice but boosts FM1-43 release in slices from amphetamine-treated mice on WD 50.