Sympathetic input into the enteric nervous system.

Introduction The basic concepts of the autonomic nervous system of organs and tissues were formulated around the turn of the century and summarised in a classical monograph by Langley (1921). The detailed distribution of the sympathetic nerves was, however, not elucidated until it became possible to stain sympathetic neurones specifically using the FalckHillarp technique. When this technique was applied to the gastrointestinal tract the picture seen was in some respects surprising. At the time it was generally believed that most organs and tissues had a dual innervation (sympathetic and parasympathetic) with opposite eVects on function. It seemed, therefore, puzzling when the Falck-Hillarp technique revealed that innervation of a major part of the gastrointestinal wall, the smooth muscle layers, was very scarce. Instead it was found that most adrenergic fibres make contact with one of the two major plexuses in the alimentary canal. Adrenergic innervation is seen in the mucosa, in particular around the crypt epithelium. The functional consequences of this distribution are discussed below. This brief review of the interplay between the sympathetic and enteric nervous systems will discuss the control of blood vessels, epithelial transport, motility, and endocrine cells (the enterochromaYn cells in particular).