(p. 168) Neurotransmitters and signalling 

By the end of the 19th century it was recognized that signalling from one neurone to the next occurs at specialized contacts – Sherrington coined the term ‘synapse’. It took another 50 years for scientists to accept that information passes between neurones principally through the movement across synapses of chemicals and not electrical current. Today changes in chemical transmission at brain synapses are accepted as being key to the successful drug treatment, and cause, of many forms of psychiatric illness. This article focuses on general aspects of chemical transmission and describes some recent advances relevant to psychiatry that point the direction of future research. Otto Loewi identified the first chemical neurotransmitter, acetylcholine, in 1921. Today evidence suggests that there are many tens if not hundreds of molecules in the brain that have neurotransmitter properties. These molecules include not only the three major classes of neurotransmitters—amines, amino acids and neuropeptides—but also specific purines, trophic factors, inflammatory mediators (chemokines and cytokines), lipids, and even gases. Examples of molecules that serve neurotransmitter functions in the brain are listed in Table 2.3.4.1. This list is not exhaustive and more are likely to be discovered.