Natural neuroactive substance

A natural neuroactive substance (NAS) is a chemical synthesized by neurons that affects the actions of other neurons or muscle cells. Natural neuroactive substances include neurotransmitters, neurohormones, and neuromodulators.^[1] Neurotransmitters work only between adjacent neurons through synapses. Neurohormones are released into the blood and work at a distance. Some natural neuroactive substances act as both transmitters and as hormones.