1.5 Influence of Drugs on Neural Firing

Agonists vs. Antagonists

Psychoactive drugs change neurotransmission by mimicking or blocking chemical messages. Agonists bind to receptors and increase or mimic a neurotransmitter's effect (e.g., opioids mimic endorphins). Antagonists block receptors or reduce neurotransmitter activity, preventing normal signals (e.g., certain drugs block dopamine receptors). Both alter the brain's normal chemical balance.

Reuptake and Release Effects

Some drugs interfere with reuptake, the process where neurotransmitters are reabsorbed into the sending neuron. Reuptake inhibitors (like some antidepressants and cocaine) keep neurotransmitters in the synapse longer, intensifying their effect. Other drugs stimulate excess release of neurotransmitters, flooding synapses (e.g., amphetamines boost dopamine release), leading to heightened neural activity.

Why It Matters

Understanding agonists, antagonists, and reuptake inhibitors explains how drugs, medications, and toxins alter mood, perception, and behavior. This same framework explains addiction, tolerance, and withdrawal — repeated agonist use can downregulate natural receptor sensitivity, requiring more drug for the same effect.

Key terms

Agonist

A drug that binds to a receptor and mimics or increases a neurotransmitter's normal effect.

Antagonist

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

Reuptake

The reabsorption of neurotransmitters by the sending (presynaptic) neuron, ending the signal.

Reuptake inhibitor

A drug that blocks reuptake, leaving more neurotransmitter in the synapse and prolonging its effect (e.g., cocaine, some antidepressants).

Tolerance (from agonist use)

A reduced response to a drug over time as receptors downregulate, requiring higher doses for the same effect.

Try an AP-style question

A drug that mimics a neurotransmitter and activates its receptors is an…

1. depressant only
2. antagonist
3. reuptake inhibitor
4. agonist