This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Physiology
[{'content': 'Melatonin is \nSelect and explain. \nA. Serotonergic, B. Dopaminergic, C. Adrenergic, D. Estrogenic', 'role': 'user'}, {'content': 'Answer: A \nExplanation: (A) Serotonergic # Melatonin is synthesized by pineal parenchymal cells and secreted by them into the blood and CSF.> It is synthesized from serotonin by N-acetylation and O-methylation.> Formation and metabolism of Melatonin: Tryptophan; 5-Hydroxytryptophan 5-Hydroxytryptamine (Serotonin) N-Acetyl -5-methoxytryptamine < (Melatonin) N-Acetyl-Serotonin metabolism 6-Hydroxymelatonin (in Liver) & other metabolites (in brain)', 'role': 'assistant'}]