ABSTRACT
The sympathetic and parasympathetic divisions of the autonomic nervous system have been shown to exert control over the function of the target organs and tissues by the release of noradrenaline and Ach, respectively. These are the primary neurotransmitters of the efferent pathways of these divisions of the autonomic nervous system, however, it has been shown in previous chapters that other transmitters co-exist in the nerve terminals and their release may accompany that of the principal transmitters. This chapter considers the role of the non-adrenergic non-cholinergic (NANC) 446transmitters of autonomic nerves. They are generally co-transmitters, which by definition are two or more transmitters released from the same neurone by the invading action potential and which influence the activity of an effector cell, being the target cell or the neurone itself. In general, the NANC transmitters co-exist with either noradrenaline or Ach. Noradrenaline and Ach do not usually serve as co-transmitters from the same neurone. In a very few instances, namely certain enteric neurones of the gastrointestinal tract, release of only NANC peptide transmitters may occur. The main types of co-transmitters of the autonomic nerves are peptides, purines and nitric oxide (NO), and the locations and pharmacology of these will be considered in this chapter.
