Action of cocaine involves depletion of dopaminergic and serotonergic storage vesicles

Cocaine is known to increase the extracellular levels of dopamine (DA) and serotonin (5-HT) by inhibiting the neuronal reuptake of these monoamines. However, individuals with reduced monoamine reuptake transporter expression do not display a reduction in cocaine intake, suggesting that a mechanism other than inhibition of monoamine reuptake contributes to the rewarding and addictive effects of the psychostimulant. Here we report that cocaine depletes the dopaminergic and serotonergic storage vesicles of the rat nucleus accumbens. This cocaine-induced vesicle depletion gave rise to acute increases in the extracellular levels of DA and 5-HT, which in turn correlated with monoamine-type-specific changes in behavior. Both the neurochemical and behavioral responses to cocaine varied among individual animals, which was not due to individual differences in the reuptake of DA and 5-HT, but rather to individual differences in their vesicular release. Furthermore, we found that reserpine-induced depletion of storage vesicles reduced both short and long access cocaine self-administration, and the degree of reduction was linked to the vesicular storage capacity of the animals. In conclusion, we demonstrate a novel mechanism by which cocaine increases the extracellular concentrations of accumbal DA and 5-HT, namely via release from storage vesicles. Furthermore, individual differences in cocaine-induced vesicular monoamine release shape individual differences in not only the acute behavioral and neurochemical effects of the stimulant, but also in its intake. Thus, intracellular storage vesicles represent an attractive novel drug target to combat psychostimulant addiction.