Mapping of chemical trigger zones for reward.

Addictive drugs are thought to activate brain circuitry that normally mediates more natural rewards such as food or water. Drugs activate this circuitry at synaptic junctions within the brain; identifying the junctions at which this occurs provides clues to the neurochemical and anatomical characteristics of the circuitry. One approach to identifying the junctions at which drugs interact with this circuitry is to determine if animals will lever-press for site-specific microinjections of addictive drugs. This approach has identified GABAergic, dopaminergic, glutamatergic, and cholinergic trigger zones within meso-corticolimbic circuitry important for natural reward function.