GABA A receptor subunit messenger RNA expression in the enteric nervous system of the rat: implications for functional diversity of enteric GABA A receptors

Abstract

GABAergic neurons occur in the myenteric plexus and submucosa and their innervations of the gut, where GABA stimulates motor neurons, and non-neural cells via “central type” GABA A receptors. These receptors occur on half of the neurons in the rat intestine. The GABA A receptor is a ligand-gated chloride channel constructed from different subunit families (α, β, γ, δ, ϵ). In rat these exist as subtypes, α 1–6, β 1–3, γ 1–3 and δ, defining the clinically relevant pharmacological features of GABA A receptors. However, the identity, distribution, and abundance of enteric GABA A receptor subunits are unknown. To identify and map the regional expression of GABA A receptor subunit messenger RNAs in the enteric nervous system, we assayed enteric RNA from the ileum of Sprague–Dawley rats by reverse transcription–polymerase chain reaction for α 1–6, β 1–3, γ 1–3, and δ subunit messenger RNAs. Subunit messenger RNA localization, was probed by in situ hybridization. Reverse transcription–polymerase chain reaction analysis of RNA from myenteric and submucosal nerve layers revealed the expression α 1, α 3, α 5, β 2, β 3, γ 1 and γ 3 subunit messenger RNAs. Little α 4 and α 6 and no α 2, β 1, γ 2 or δ subunit messenger RNA were detected. In situ hybridization revealed that transcripts for α 1, α 3, α 5 and β 2 subunits occur in both myenteric and submucous ganglia. However, β 3 messenger RNA was found only in myenteric plexus. The γ 1 subunit messenger RNA was also restricted to the cells in the myenteric plexus while γ 3 was found in cells of both nerve layers. In this study of the subunit messenger RNA expression profile of GABA A receptors within the enteric nerve layers we show an abundant, diverse and widespread distribution that is unique in comparison to the CNS. The distinctive and heterogeneous distribution of enteric GABA A subunits may be important in the integration of neural control of gut function.