dopamine: excitatory; involved in mood, sleep, learning
serotonin: inhibitory; involved in mood, sleep
norepinephrine: excitatory; involved in heart, intestines, alertness
histamine: involved in GI, allergic response, cardiac stimulation
GABA: inhibitory; involved in brain function, sleep
glutamate: excitatory; involved in memory, learning
acetylcholine: inhibitory and excitatory; involved in muscle action, memory