A 34-year-old woman with bipolar II disorder stabilized on olanzapine 10 mg nightly has gained 30 pounds over 6 months. She also reports excessive daytime sedation despite adequate sleep. Her PMHNP reviews the receptor binding profile of olanzapine to identify which pharmacological actions are driving these side effects. Which of the following best explains the neurobiological basis of olanzapine's sedation and weight gain?