Autonomic control of gut motility: a comparative view

Gut motility is regulated to optimize food transport and processing. The autonomic innervation of the gut generally includes extrinsic cranial and spinal autonomic nerves. It also comprises the nerves contained entirely within the gut wall, i.e. the enteric nervous system. The extrinsic and enteric nervous control follows a similar pattern throughout the vertebrate groups. However, differences are common and may occur between groups and families as well as between closely related species. In this review, we give an overview of the distribution and effects of common neurotransmitters in the vertebrate gut. While the focus is on birds, reptiles, amphibians and fish, mammalian data are included to form the background for comparisons. While some transmitters, like acetylcholine and nitric oxide, show similar distribution patterns and effects in most species investigated, the role of others is more varying. The significance for these differences is not yet fully understood, emphasizing the need for continued comparative studies of autonomic control.