A 26-year-old woman with schizophrenia stabilized on risperidone 4 mg daily presents with amenorrhea, galactorrhea, and decreased libido for the past 3 months. Laboratory testing reveals a prolactin level of 85 ng/mL (normal < 25 ng/mL). The PMHNP evaluates whether these symptoms are related to her antipsychotic medication and considers the neuroanatomical basis. Which of the following best explains the mechanism of antipsychotic-induced hyperprolactinemia?