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The Brain and Addiction
Images and text for this gallery courtesy of The National Institute on Drug Abuse (NIDA) http://165.112.78.61/NIDAHome.html.

<< 7/12 < > Using dopamine for an example of synaptic function, it is synthesized in the nerve terminal and packaged in vesicles. The vesicle fuses with the membrane and releases dopamine. The dopamine molecules can then bind to a dopamine receptor (in pink). After the dopamine binds, it comes off the receptor and is removed from the synaptic cleft by uptake pumps (also proteins) that reside on the terminal (arrows show the direction of movement). This process is important because it ensures that not too much dopamine remains in the synaptic cleft at any one time. There are neighboring neurons that release another compound called a neuromodulator. Neuromodulators help to enhance or inhibit neurotransmission that is controlled by neurotransmitters such as dopamine. In this case, the neuromodulator is an "endorphin" (in red). Endorphins bind to opiate receptors (in yellow) which can reside on the post-synaptic cell (shown here) or, in some cases, on the terminals of other neurons. The endorphins are destroyed by enzymes rather than removed by uptake pumps.

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