Molecular and Functional Diversity of GABA-A Receptors in the Enteric Nervous System of the Mouse Colon

Abstract

The enteric nervous system (ENS) provides the intrinsic neural control of the gastrointestinal tract (GIT) and regulates virtually all GI functions. Altered neuronal activity within the ENS underlies various GI disorders with stress being a key contributing factor. Thus, elucidating the expression and function of the neurotransmitter systems, which determine neuronal excitability within the ENS, such as the GABA-GABA A receptor (GABA A R) system, could reveal novel therapeutic targets for such GI disorders. Molecular and functionally diverse GABA A Rs modulate rapid GABAergic-mediated regulation of neuronal excitability throughout the nervous system. However, the cellular and subcellular GABA A R subunit expression patterns within neurochemically defined cellular circuits of the mouse ENS, together with the functional contribution of GABA A R subtypes to GI contractility remains to be determined. Immunohistochemical analyses revealed that immunoreactivity for the GABA A R gamma (␥) 2 and alphas (␣) 1, 2, 3 subunits was located on somatodendritic surfaces of neurochemically distinct myenteric plexus neurons, while being on axonal compartments of submucosal plexus neurons. In contrast, immunoreactivity for the ␣4 -5 subunits was only detected in myenteric plexus neurons. Furthermore, ␣-␥2 subunit immunoreactivity was located on non-neuronal interstitial cells of Cajal. In organ bath studies, GABA A R subtype-specific ligands had contrasting effects on the force and frequency of spontaneous colonic longitudinal smooth muscle contractions. Finally, enhancement of ␥2-GABA A R function with alprazolam reversed the stress-induced increase in the force of spontaneous colonic contractions. The study demonstrates the molecular and functional diversity of the GABA A R system within the mouse colon providing a framework for developing GABA A R-based therapeutics in GI disorders.

Peripheral GABA receptors regulate colonic afferent excitability and visceral nociception

“…Like GABA B receptors, GABA A receptors are also present on a number of additional cell types in the colon (Seifi et al . ), including a number of types of neurons in the enteric nervous system (Minocha & Galligan, ; Krantis et al . ).…”

Immunolocalization of AMPA receptor subunits within the enteric nervous system of the mouse colon and the effect of their activation on spontaneous colonic contractions

“…Mice were anesthetized with isoflurane and pentobarbitone (1.25 mg/kg of bodyweight; i.p.). The animals were transcardially perfused using a fixative containing 1% w/v paraformaldehyde and 15% v/v saturated picric acid in 0.1 M phosphate buffer (pH, 7.4) according to previously described protocols . After perfusion, the brains and colons were removed and postfixed in the same fixative over night at 4 °C.…”

“…The animals were transcardially perfused using a fixative containing 1% w/v paraformaldehyde and 15% v/v saturated picric acid in 0.1 M phosphate buffer (pH, 7.4) according to previously described protocols. 31 After perfusion, the brains and colons were removed and postfixed in the same fixative over night at 4°C. The next day, tissue was washed in 0.1 M phosphate buffer until it was clear of the fixative.…”

Rhynchophylline, One of Major Constituents ofUncariae Ramulus et UncusEnhances Pentobarbital-induced Sleep Behaviors and Rapid Eye Movement Sleep in Rodents

“…2,3 Basic subunits are composed to α (1~6), β (1~3) and γ (1~3). 4 These binding sites trigger the chloride channel's opening with resulting membrane hyperpolarization 5 . GABA A -ergic drugs have induced sedative-hypnotic effects in animals and humans.…”