What is the primary mechanism of action of first-generation antipsychotics?

What is the primary mechanism of action of first-generation antipsychotics?

• A. They block dopamine D2 receptors and reduce positive symptoms.
• B. They block serotonin 5-HT2A receptors.
• C. They increase norepinephrine release.
• D. They enhance glutamate transmission at NMDA receptors.

Answer: (A)

Dopamine D2 receptor antagonism in the brain, especially in the mesolimbic pathway, is the primary action of first-generation antipsychotics. Blocking these receptors reduces dopaminergic signaling that drives positive psychotic symptoms like hallucinations and delusions, which is why these drugs are effective for such symptoms. This same D2 blockade in other pathways explains common side effects: in the nigrostriatal pathway it can cause extrapyramidal symptoms, and in the tuberoinfundibular pathway it can raise prolactin levels, leading to issues like galactorrhea. These agents typically have limited impact on negative symptoms and cognitive deficits, which is part of why atypical antipsychotics that also target serotonin receptors were developed. The other options describe mechanisms that are not how these drugs work: serotonin 5-HT2A blockade is more characteristic of later-generation antipsychotics; increasing norepinephrine release or enhancing NMDA receptor activity isn’t the mechanism behind first-generation agents.

Dopamine D2 receptor antagonism in the brain, especially in the mesolimbic pathway, is the primary action of first-generation antipsychotics. Blocking these receptors reduces dopaminergic signaling that drives positive psychotic symptoms like hallucinations and delusions, which is why these drugs are effective for such symptoms.

This same D2 blockade in other pathways explains common side effects: in the nigrostriatal pathway it can cause extrapyramidal symptoms, and in the tuberoinfundibular pathway it can raise prolactin levels, leading to issues like galactorrhea. These agents typically have limited impact on negative symptoms and cognitive deficits, which is part of why atypical antipsychotics that also target serotonin receptors were developed.

The other options describe mechanisms that are not how these drugs work: serotonin 5-HT2A blockade is more characteristic of later-generation antipsychotics; increasing norepinephrine release or enhancing NMDA receptor activity isn’t the mechanism behind first-generation agents.