Just as a rat will stimulate itself with a small electrical jolt (into the reward pathway), it will also press a bar to receive heroin. In this image, the rat is self-administering heroin through a small needle placed directly into the nuclues accumbens. The rat keeps pressing the bar to get more heroin because the drug makes the rat feel good. The heroin is positively reinforcing and serves as a reward. If the injection needle is placed in an area nearby the nucleus accumbens, the rat won't self-administer the heroin. Scientists have found that dopamine release is increased within the reward pathway of rats self-administering heroin. So, since more dopamine is present in the synaptic space, dopamine-dependent neurotransmission is augmented, causing the activation of the reward pathway.
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NIDA (2007). The Neurobiology of Drug Addiction. Retrieved , from https://www.drugabuse.gov/publications/teaching-packets/neurobiology-drug-addiction
Explores the consequences of drug abuse on the brain and body and introduces the topics of prevention, and treatment.