Function of Catecholamine-containing Neurones in Mammalian Central Nervous System

SEVERAL chemical substances are involved in synaptic transmission in the mammalian central nervous system^1–3. The Falck-Hillarp technique⁴ has demonstrated noradrenaline, dopamine and 5-hydroxytryptamine within nerve cell bodies and terminals^5,6 and the belief that these amines act as neurohumours is strengthened by observations that nerve fibre activation leads to their release from the terminals^7,8. Histo-chemical evidence suggests that discrete systems of neurones can be identified by their content of particular amines and it seems possible that such neurohumorally homogeneous systems have a functional as well as a chemical identity. Before the anatomical distribution of amine-containing neurones had been described, Brodie and Shore⁹ proposed that noradrenaline functions as the central neurohumour of the sympathetic and 5-hydroxytryptamine of the parasympathetic system. This suggestion has not been supported by anatomical evidence; the amine-containing neurones form systems of small diameter fibres of very diffuse terminal distribution, which do not correspond to recognized ascending or descending pathways^5,6, although amine-containing neurones in invertebrates have been identified as sensory systems¹⁰.