Neurotransmitters are chemicals in the brain and nerves (neuro) that transmit (send) signals from one nerve cell to another.
There are more than 100 such chemicals, but one of the best known ones is dopamine. A dopamine deficiency may result in hyperactivity, attention deficit disorder, depression, Parkinson’s Disease or restless legs syndrome. (http://www.medikidz.com/medipedia/dopamine#BPkfFD4VW85y1Oi6.99) On the positive side, healthy levels of dopamine result in happiness, positiveness and motivation to achieve goals. (http://www.news.cornell.edu/chronicle/96/10.24.96/dopamine.html)
Another well known neurotransmitter is serotonin. Serotonin affects sleep, appetite, and mood and is thought to result in a feeling of well-being and happiness. A deficiency of serotonin may cause depression and anxiety.
Both of these neurotransmitters have been found to be increased when low (and decreased when too high) by the remarkable new supplement stemFit.
My wife and I have personally been taking it and have noticed better sleep (deeper, more relaxing and easier and faster to fall asleep) and increased feeling of happiness and well-being.