GABA and the enteric nervous system. A neurotransmitter function?

GABA and GABA-related properties in the enteric nervous system of the gastrointestinal tract, the third and most complex division of the vertebrate autonomic nervous system, have been the subject of relatively few studies. This chapter aims at being a comprehensive review of these investigations. With respect to GABA the enteric nervous system shows in some respects similarities with, and in others, notable differences from other parts of the peripheral nervous system. Like the cell bodies of other autonomic and sensory neurons, the cell bodies of enteric neurons possess bicuculline and picrotoxin sensitive GABA receptors, the activation of which leads to depolarization, probably mediated by increase in Cl- conductance. Further, in common with other peripheral glia, the cell membrane of the enteric glial cells appears to contain beta-alanine sensitive high affinity transport sites by which they can accumulate exogenous GABA. However, the present evidence, although not completely conclusive, suggests that unlike other parts of the peripheral nervous system, the enteric ganglia may contain a population of GABA-ergic neurons; in vertebrates such neurons have hitherto been thought to be present in the brain and spinal cord only. At present the mst important single strand of evidence for this notion is the demonstration of a population of enteric neurons possessing high affinity transport sites for GABA, while it is supported by studies of GAD and GABA content, the effects of GABA receptors blockade on gut motility and GABA release.