Cocaine Increases Dopamine Release by Mobilization of a Synapsin-Dependent Reserve Pool

• Published in: The Journal of neuroscience Vol. 26; no. 12; pp. 3206 - 3209
• Main Authors: Venton, B. Jill, Seipel, Andrew T, Phillips, Paul E. M, Wetsel, William C, Gitler, Daniel, Greengard, Paul, Augustine, George J, Wightman, R. Mark
• Format: Journal Article
• Language: English
• Published: United States Soc Neuroscience 22.03.2006; Society for Neuroscience
• Subjects: alpha-Methyltyrosine - pharmacology; Animals; Brain - drug effects; Brain - metabolism; Brain - physiopathology; Brief Communications; Cocaine - pharmacology; Cocaine-Related Disorders - metabolism; Cocaine-Related Disorders - physiopathology; Disease Models, Animal; Dopamine - metabolism; Dopamine Uptake Inhibitors - pharmacology; Electric Stimulation; Enzyme Inhibitors - pharmacology; Medial Forebrain Bundle - drug effects; Medial Forebrain Bundle - metabolism; Mice; Mice, Knockout; Neostriatum - drug effects; Neostriatum - metabolism; Presynaptic Terminals - drug effects; Presynaptic Terminals - metabolism; Reward; Synapsins - genetics; Synaptic Transmission - drug effects; Synaptic Transmission - physiology; Synaptic Vesicles - drug effects; Synaptic Vesicles - metabolism; Up-Regulation - drug effects; Up-Regulation - physiology; Ventral Tegmental Area - drug effects; Ventral Tegmental Area - metabolism
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.4901-04.2006

Cocaine primarily exerts its behavioral effects by enhancing dopaminergic neurotransmission, amplifying dopamine-encoded sensorimotor integration. The presumed mechanism for this effect is inhibition of the dopamine transporter, which blocks dopamine uptake and prolongs the duration of dopamine in the extracellular space. However, there is growing evidence that cocaine can also augment dopamine release. Here, we directly monitored the actions of cocaine on dopamine release by using electrochemical detection to measure extracellular dopamine in the striatum of anesthetized mice. Cocaine enhanced the levels of striatal dopamine produced by electrical stimulation of dopaminergic neurons. Even after pretreatment with alpha-methyl-p-tyrosine, which depletes the readily releasable pool of dopamine, cocaine was still capable of elevating dopamine levels. This suggests that cocaine enhances dopamine release by mobilizing a reserve pool of dopamine-containing synaptic vesicles. To test this hypothesis, we examined electrically evoked dopamine release in synapsin I/II/III triple knock-out mice, which have impaired synaptic vesicle reserve pools. Knock-out of synapsins greatly reduced the ability of cocaine to enhance dopamine release with long stimulus trains or after depletion of the newly synthesized pool. We therefore conclude that cocaine enhances dopamine release and does so by mobilizing a synapsin-dependent reserve pool of dopamine-containing synaptic vesicles. This capacity to enhance exocytotic release of dopamine may be important for the psychostimulant actions of cocaine.