definition of brain neurotransmitters
Neurotransmitter. A chemical in the brain that transmits messages between neurons, or nerve cells. Changes in the levels of certain neurotransmitters, such as serotonin, norepinephrine, and dopamine, are thought to be related to bipolar disorder. substance (e.g. norepinephrine, acetylcholine, dopamine) that is released from the axon terminal of a presynaptic neuron on excitation, and which travels across the synaptic cleft to either excite or inhibit the target cell.