Psychoactive drugs alter brain function by acting at synapses in the brain, where they may mimic, enhance, or block the effects of natural signaling molecules (neurotransmitters). The neurotransmitter dopamine plays a particularly important role in creating the dependency aspect of both drug and behavioral addictions. Natural behaviors which enhance survival and/or reproduction, such as eating or engaging in sex, result in a surge of dopamine. Normally, this response helps individuals learn to repeat beneficial behaviors. However, when an addict uses a drug or behavior to cause dopamine release, they are using this learning pathway to teach themselves that this behavior is essential to their well-being. These circuits become a lifelong plague which makes the addict more prone to relapse.
Brain imaging studies from drug-addicted individuals show physical changes in areas of the brain that are critical to judgment, decision-making, learning and memory, and behavior control. Psychoactive drugs affect signal transmission in the brain by encouraging or inhibiting release of a neurotransmitter, blocking or mimicking its action, or affecting its reuptake. The effect of a particular neurotransmitter on a postsynaptic cell depends on the type of neurotransmitter and the type of receptor it binds to. The neurotransmitter ACh affects alertness and plays a role in memory. Norepinephrine and epinephrine (adrenaline) prepare the body to respond to stress or excitement. Dopamine influences reward-based learning and acts in fine motor control. Serotonin influences mood and memory. Glutamate is the main excitatory signal in the central nervous system. Endorphins are the body’s natural pain relievers.
Important Concepts from Chapter 13:
Section 13.3: How Neurons Communicate The region where an axon terminal sends chemical signals to a neuron, a muscle fiber, or a gland cell is a chemical synapse. Axon terminals have synaptic vesicles filled with neurotransmitter, a signaling molecule that relays messages between cells at a synapse. The plasma membrane of a postsynaptic cell has receptor proteins that reversibly bind neurotransmitter. How a receiving cell responds depends on the type and amount of the neurotransmitter, the kinds of receptors, and other factors. Certain drugs can block reuptake of neurotransmitters.
Section 13.13: The Brain on Mind Altering Drugs Drugs such as morphine and heroin mimic a neurotransmitter’s effect on a postsynaptic cell; they bind to receptors for endorphins (natural pain relievers), and elicit pain relief and feelings of well-being. Caffeine binds and inactivates receptors for adenosine, a neurotransmitter that causes drowsiness. Alcohol encourages drowsiness by releasing adenosine. Other drugs interfere with reuptake of neurotransmitter from the synaptic cleft. For example, cocaine slows reuptake of several neurotransmitters, including dopamine.
- 1. Visit the NIH National Institute on Drug Abuse and read the article Drugs, Brains and Behavior: The Science of Drug Addiction.
- 2. Go to Indiana University and read an article on Addictive Behaviors.
Prompt : – Using the sources provided, briefly describe one factor that can increase the risk of drug addiction, and one protective factor that can reduce the risk of drug addiction. – Why do you think Americans use so many legal drugs (e.g., alcohol, tobacco, and OTC drugs)?