You have been tasked with testing pharmacological agents derived from plants and animals that could be used to study the electical properties of neurons. You are making simultaneous recordings from presynatic and postsynatic terminals in vitro (i. e., you can stimulate the giant axon by injecting a current and record the postsynaptic responses). The traces depicted above show the responses of the postsynaptic axon upon presynaptic stimulation before (A) and after bathing the postsynaptic axon in a solution containing pharmacological agents. After testing dozens of compunds you finally get a hit: one animal compound alters the postsynaptic axon responses. The observed postsynaptic response (B) suggests that your compound: