Silvia Helena Cardoso, PhD and
Renato M. E. Sabbatini, PhD
André Luis Malavazzi (art and animation)
Neurons communicate among themselves in the brain by mean of contacts between the cells named synapses. The animation shows a travelling zoom towards the axon of a neuron contacting the dendrites of another neuron (the synapse). The postsynaptic element of this neuron shows its ordered molecular structure (membrane) and special features in its surface called receptors, which attach themselves to the neurotransmitters to mediate their action. Two types of receptors, one for each kind of neurotransmitter, are shown.
Normal Function of Dopamine in the Brain
When Cocaine Arrives in the Brain
See the animation (290 K)
When cocaine arrives at the brain reward system, it blocks the dopamine transport sites, which are responsible for the reuptake of dopamine 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.
See also the paper Cocaine. In: Drug Abuse
Complete Animation Sequence
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