Mechanisms of Amphetamine Action Revealed in Mice Lacking the Dopamine Transporter

Abstract

Amphetamine (AMPH) inhibits uptake and causes release of dopamine (DA) from presynaptic terminals. AMPH can act on both vesicular storage of DA and directly on the dopamine transporter (DAT). To assess the relative importance of these two processes, we have examined the releasing actions of AMPH in mice with a genetic deletion of the DAT. The sequence of actions of AMPH has been determined by following the real time changes of DA in the extracellular fluid of intact tissue with fast scan cyclic voltammetry. In striatal slices from wild-type mice, AMPH causes a gradual (approximately 30 min) increase in extracellular DA, with a concomitant disappearance of the pool of DA available for depolarization-evoked release. Conversely, in slices from mice lacking the DAT, although a similar disappearance of electrically stimulated DA release occurs, extracellular DA does not increase. Similarly, microdialysis measurements of DA after AMPH in freely moving animals show no change in mice lacking the DAT, whereas it increases 10-fold in wild-type mice. In contrast, redistribution of DA from vesicles to the cytoplasm by the use of a reserpine-like compound, Ro4-1284, does not increase extracellular DA in slices from wild-type animals; however, subsequent addition of AMPH induces rapid (<5 min) release of DA. Thus, the DAT is required for the releasing action, but not the vesicle-depleting action, of AMPH on DA neurons, and the latter represents the rate-limiting step in the effects of AMPH. Furthermore, these findings suggest that in the absence of pharmacological manipulation, such as the use of amphetamine, endogenous cytoplasmic DA normally does not reach sufficient concentrations to reverse the DAT.

D-Amphetamine Stimulates D2Dopamine Receptor-Mediated Brain Signaling Involving Arachidonic Acid in Unanesthetized Rats

“…In addition to increasing the synaptic concentration of DA to activate D 2 -like receptors (see Introduction) (Butcher et al, 1988;Creese and Iversen, 1975;Fuller and Hemrick-Luecke, 1980;Houston et al, 2004;Jones et al, 1998;Kuczenski and Segal, 1989;Laruelle et al, 1997;Segal et al, 1980;Sharp et al, 1987), D-amphetamine can increase extracellular serotonin and epinephrine to indirectly stimulate serotonergic 5-HT 2A/2C and b 2 -adrenergic receptors, respectively. These receptors, like D 2 -like receptors, can be coupled to PLA 2 activation and AA release (Berg et al, 1998;Garcia and Kim, 1997;KurraschOrbaugh et al, 2003;Pavoine et al, 2003;Qu et al, 2003).…”

“…Such behavioral effects have been ascribed to its ability to increase synaptic dopamine (DA) and indirectly activate brain DA receptors (Butcher et al, 1988;Houston et al, 2004;Kuczenski and Segal, 1989;Laruelle et al, 1997;Sharp et al, 1987). D-Amphetamine does this by causing vesicular DA to enter the cytoplasm of presynaptic DA terminals, and by changing the direction of DA transport by the presynaptic DA reuptake transporter (DAT) (Creese and Iversen, 1975;Fuller and Hemrick-Luecke, 1980;Jones et al, 1998;Segal et al, 1980). D-Amphetamine also can activate adrenergic and serotonergic receptors by increasing extracellular synaptic concentrations of norepinephrine and serotonin, respectively (Berridge and Stalnaker, 2002;Kuczenski and Segal, 1989;Pascoli et al, 2005;Vanderschuren et al, 2003).…”

Genetic NMDA Receptor Deficiency Disrupts Acute and Chronic Effects of Cocaine but not Amphetamine

“…Cocaine elevates dopamine by preventing the reuptake and clearance of the stimulated release of dopamine, whereas amphetamine elevates dopamine not only by acting as a dopamine transporter substrate and competitively inhibiting dopamine transport, but also by dissipating the vesicular storage and reversing plasma membrane monoamine transporters, thus releasing the vesicular pool of stored dopamine into the synapse (Amara and Kuhar, 1993;Jones et al, 1998;Sulzer et al, 2005).…”

Quantitative Changes in Gαolf Protein Levels, but not D1 Receptor, Alter Specifically Acute Responses to Psychostimulants

“…Acute stimulant effects of cocaine and D-amph result primarily from the enhancement of extracellular dopamine levels in limbic regions (Di Chiara and Imperato, 1988;Giros et al, 1996;Jones et al, 1998). This increase in extracellular dopamine is also essential for reinforcing properties of psychostimulants (for a review see Berke and Hyman (2000)).…”