The most important neurotransmitters are: acetylcholine, dopamine, serotonin, noradrenaline, endorphin, glutamate, and gamma aminobutyric acid. Neurotransmitter are broken down once it reaches the post-synaptic cell to avoid further excitatory or inhibitory signal transduction. Acetylcholine, which is an excitatory neurotransmitter, is broken down by acetylcholinesterase. Choline is taken up and recycled by the pre-synaptic neuron to synthesize more acetylcholine. Other neurotransmitters, such as dopamine, diffuse away from their targeted synaptic junctions and are eliminated from the body via the kidneys, or destroyed in the liver.