Neuroscientists have been able to pinpoint the exact parts of the brain involved, with the help of the rats.
This part of the brain is called the reward system. Explain that there is actually a part of the brain that is activated by natural rewards and by artificial rewards such as addictive drugs. Animals and people will continue to exhibit a behavior that is rewarding, and they will cease that behavior when the reward is no longer present. Natural rewards include food, water, and sex - each is required to maintain survival of our species. This is called positive reinforcement, or reward. The rat keeps pressing to get more cocaine or heroin because the drugs make the rat feel so good. Explain that rats will press a lever to self-administer an injection of cocaine or heroin that is inserted into either the peripheral bloodstream (left image) or into specific brain regions (right image). Introduce the concept of positive reinforcement or reward.
Dopamine and the production of cyclic AMP The endorphins are destroyed by enzymes rather than removed by uptake pumps. Endorphins bind to opioid receptors (in green) which reside on the post-synaptic cell or in some cases on the terminals of other neurons (this is not shown so it must be pointed out). In this case it is an "endorphin" (blue flying saucers). Also point out that there is a neighboring neuron, which releases another compound called a neuromodulator. This process is important so that not too much dopamine is left in the synaptic cleft at any one time. After the dopamine binds, it comes off the receptor and is removed from the synaptic cleft by uptake pumps (also proteins) (in red) that reside on the terminal. The dopamine molecules can then bind to a dopamine receptor (in blue). Show how the vesicle fuses with the membrane and releases dopamine. Reiterate the steps in neurotransmission. Explain that it is synthesized in the nerve terminal and packaged in vesicles. Using the close-up of a synapse, continue using dopamine for your example of synaptic function.