Synapses and Drugs

 

 

Psychoactive drugs alter behavior, thinking, and mood by acting on the brain. Most psychoactive drugs affect the brain's activity by changing synaptic transmission of a particular neurotransmitter(s). Within seconds of entering the body, drugs cause dramatic changes to synapses in the brain. Drugs modify synaptic transmission, changing the way neurons communicate with each other. A drug that affects dopamine synaptic transmission can increase the dopamine that reaches the receiving neuron by bypassing the five senses and directly activating the brain's reward circuitry fast and hard. This can cause a jolt of intense pleasure. Drugs either facilitate or inhibit transmission at synapses. A drug that blocks a neurotransmitter is an antagonist, whereas a drug that mimics or increases the effects is an agonist.

 

Drugs of abuse affect the brain in such a dramatic way that the brain must try to adapt. One way the brain compensates is to reduce the number of dopamine receptors at the synapse. As a result, after the user has "come down," they will need more of the drug next time they want to get high. This response is commonly referred to as tolerance. As the brain continues to adapt to the presence of the drug, regions outside of the reward pathway are also affected. Brain regions responsible for judgment, learning and memory begin to physically change or become "hard-wired." Once this happens, drug-seeking behavior is driven by habit, almost reflex. This is how a drug user becomes transformed into a drug addict. When a person uses drugs, the brain learns to function in the presence of those drugs. When the person quits using drugs, the brain doesn't immediately start to function the way it did before the drug use.