Why Don't More Affective Neuroscientists Study the Neurotransmitters Underlying Emotions

Why don't more affective neuroscientists study the neurotransmitters underlying emotions?

A) Most work on neurotransmitters is done in animal models, and it is sometimes difficult to translate to human behavior
B) Neurotransmitters have widespread effects in the brain, making specific behavioral correlates challenging to pinpoint
C) The blood-brain barrier makes it difficult to experimentally manipulate the amount of particular neurotransmitters in the brain
D) All of the above reasons make the neurochemical basis of emotions challenging to study