This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Pharmacology
Activation of the following type of receptors present on myenteric neurons by metoclopramide is primarily responsible for the enhanced acetylcholine release and improving gastric motility: 
Select and explain. 
A. Muscarine M1, B. Serotonergic 5-HT3, C. Serotonergic 5-HT4, D. Dopaminergic D2
C: Serotonergic 5-HT4
Answer: C: Serotonergic 5-HT4 
Explanation: (Ref: KDT 6/e p646, 647) Gastric motility is increased by ACh. Release of this neurotransmitter is enhanced by 5HT4 receptor stimulation and 5HT3 and D2 receptor antagonism.