5.9 Influence of Drugs on Neurotransmission

Agonists vs. Antagonists

Psychoactive drugs alter brain function by affecting neurotransmission. Agonists mimic or enhance a neurotransmitter's effect (e.g., binding to its receptor or increasing its release). Antagonists block or reduce a neurotransmitter's effect (e.g., blocking receptors so the neurotransmitter can't bind). Some drugs also block reuptake, keeping neurotransmitters in the synapse longer, intensifying their effect.

Depressants, Stimulants, and Hallucinogens

Depressants (alcohol, benzodiazepines) slow neural activity, often by enhancing GABA. Stimulants (caffeine, cocaine, amphetamines) increase neural activity, often boosting dopamine and norepinephrine. Hallucinogens/psychedelics (LSD) distort perception, often affecting serotonin. Opioids (morphine, heroin) relieve pain and produce euphoria by binding endorphin receptors.

Tolerance, Dependence, and Addiction

Repeated drug use can cause tolerance (needing more for the same effect) as the brain reduces natural neurotransmitter production or receptor sensitivity. Withdrawal produces unpleasant symptoms when use stops. Physical dependence and addiction (compulsive use despite harm) often develop, driven by the brain's reward pathway involving dopamine.

Key terms

Agonist

A drug that enhances or mimics a neurotransmitter's effect at the synapse.

Antagonist

A drug that blocks or reduces a neurotransmitter's normal effect.

Reuptake inhibitor

A drug that blocks reabsorption of a neurotransmitter, prolonging its effect in the synapse (e.g., cocaine, SSRIs).

Tolerance

The need for increasing amounts of a drug to produce the same effect, due to brain adaptation.

Withdrawal

Unpleasant symptoms that occur when a person stops using a drug they've become dependent on.

Try an AP-style question

Cocaine produces euphoria by…

1. blocking dopamine reuptake
2. mimicking GABA
3. destroying dopamine
4. blocking dopamine receptors