Action of Cocaine
When cocaine (in white) arrives at the brain reward system, it blocks the dopamine transport sites, which are responsible for the reuptake of dopamine (in red) in dopaminergic synapeses in this region. Therefore, dopamine is not removed from the synaptic gap, and it remains free there, in ever increasing amounts, because successive nervous stimuli continue to arrive and to release dopamine. The effect remains until cocaine is removed from the presynaptic terminals. It is believed that the abnormally long presence of dopamine in the brain is responsible for the pleasure effects associated to the use of cocaine. The prolonged use of cocaine makes the brain to adapt to it, and the overall synthesis of dopamine by the neurons is decreased. Between cocaine doses, or when the use of cocaine is interrupted, the drug user experiences the opposite of pleasure, due to the low levels of dopamine: fatigue, depression and altered moods.
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