What Is the Term for a Neurotransmitter That Merely Indirectly

Multiple Choice

What is the term for a neurotransmitter that merely indirectly modifies the effect of another neurotransmitter (e.g. increases the effect that glutamate has when it binds) , as opposed to more directly producing an excitatory or inhibitory effect as a direct consequence of binding to a receptor itself?

A) neuroregulator
B) agonist
C) neuromodulator
D) antagonist
E) microtransmitter