Phenylbiguanide is primarily used in pharmacological research as a selective agonist for the 5-HT3 receptor, a subtype of serotonin receptor. It is often employed in experimental studies to investigate the role of 5-HT3 receptors in the nervous system, particularly in relation to neurotransmitter release, neuronal excitability, and pain pathways. Its ability to activate these receptors makes it a valuable tool for studying conditions such as nausea, vomiting, and certain psychiatric disorders. Additionally, phenylbiguanide is used in in vitro and in vivo models to explore potential therapeutic agents targeting the 5-HT3 receptor. Its application extends to electrophysiological studies, where it helps in understanding the mechanisms of receptor activation and ion channel function.