The neurotransmitter that is released by the axon of a sympathetic preganglionic neuron to communicate with the sympathetic postganglionic neuron is Acetylcholine. Acetycholine is the neurotransmitters released by the postganglionic neuron in sympathetic division. Acetycholine is responsible for the stimulation of muscles, including the muscle of the gastro-intestinal system. It is also found in sensory neurons and in the autonomic nervous system and has a part in scheduling REM sleep.
