The Effects of Cocaine in the Brain
Graphical Animations

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.

The Normal Function of Dopamine in the Brain

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Dopamine (shown in red) is a neurotransmitter, a substance synthesized by certain neurons in parts of the brain which are responsible, among others, for motivation and pleasure. After being synthesized, it is stored inside special little bags, named synaptic vesicles (in green). When an electric impulse arrives at the tip of the nerve terminal, these vesicles move into the presynaptic membrane of the neuron and discharge their contents of dopamine into the synaptic gap. The dopamine molecules traverse this gap and attach themselves to specific receptors (dopaminergic receptors) situated in the outer surface of the cell membrane of the following neuron (post-synaptic neuron). This provokes a series of reactions in the neuron, such as the inflow and outflow of some ions, and the release or inhibition of some enzymes. After being released from the dopaminergic receptors, the free dopamine molecules are taken up again by the presynaptic button, by means of so-called dopamine transport sites.

When Cocaine Arrives in the Brain

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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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Brain & Mind Magazine 3(8), Jan/March 1999
An Initiative of the Center for Biomedical Informatics
Copyright (c) 1998 State University of Campinas, Brazil
Published on 18/Jan/1998
URL: http://www.epub.org.br/cm/n08/doencas/drugs/anim1_i.htm
brain@nib.unicamp.br