The brain scans in this figure show a lower level of dopamine receptors (dimmer colors and less red) in the brain of the methamphetamine abusers (Volkow, 2001).

GABA
What is GABA and How Does in Work in Your Brain?
GABA is called an inhibitory neurotransmitter because it tends to make nerve cells less excitable. Drugs that increase GABA levels in the brain or which attach to GABA receptors are used to treat epileptic seizures (brain attacks characterized by excessive activity) and other conditions thought to be related to excessive brain activity (Mody, 2005). The major GABAergic pathways in the brain are shown in Figure 8, but it is important to remember that GABA exerts its “calming” effects in virtually all parts of the brain (Mody, 2005).