Neurotransmitter

Neurotransmitters and the related neuromodulators are the chemical side of cell-to-cell communication in the nervous system [1]. They take part in processes including growth, reproduction, memory and behavior [1].

A neuromodulator changes the state of whole networks of neurons and how they respond to inputs; a 2012 review in Neuron describes acetylcholine as a classic example [2]. Two other examples show the range: in the cortex, glutamate is the main excitatory neurotransmitter and GABA the main inhibitory one [3]. Some molecules work as a neurotransmitter in the brain and as a hormone elsewhere in the body, and serotonin is one of them [4].

A neurotransmitter is a mechanism term. When a nootropic is described in terms of one, four questions help:

• Does the compound reach the brain? Serotonin made in the body, for example, cannot readily cross the blood-brain barrier [4].
• Was the change measured in people, or in cells or animals?
• Was a measured outcome, such as memory or reaction time, compared with a placebo?
• Is the claim about the molecule itself or about a precursor, a building block the body uses to make it? Tyrosine, for example, is the precursor of dopamine and norepinephrine [5].

A change in a neurotransmitter is not an outcome by itself. Grades on our compound pages attach only to outcomes measured in people, and neurotransmitter findings are labeled as mechanism.

• Acetylcholine
• Dopamine
• Serotonin
• GABA
• Glutamate