GABA and Endocrine Cells of the Gastro-entero-pancreatic System: A Review

γ-Aminobutyric acid (GABA) is not only a major inhibitory neurotransmitter in the central nervous system of vertebrates, but it is also a peripheral neuromodulator, as in the enteric nervous system [49]. A few years ago, the presence of GABA was thought to be restricted to nerve cells only. However, recent studies have revealed its presence in various non-neural organs such as the ovary, adenohypophysis, adrenal medulla, liver, digestive tract, and pancreas. In these organs, several categories of (neuro)endocrine cells display both morphological and physiological indications of direct interaction with GABA, i.e., prolactin-secreting cells [4, 5, 60, 69] and adrenal chromaffin cells [11, 16, 51, 52]. GABA has also been involved in the regulation of hormonal secretion in the gastro-entero-pancreatic (GEP) system, but its precise localization and mechanisms of action remain unclea