Professor murphy is studying neurons that release a particular small-molecule neurotransmitter. in these many of these neurons, the professor should expect to see​ ​no other types of neurotransmitters. ​at least one type of neuropeptide neurotransmitter. ​at least one other type of small-molecule neurotransmitter and multiple types of neuropeptides neurotransmitters. ​a second type of small-molecule neurotransmitter.