Distribution of GABA, glutamate decarboxylase 67 (GAD67), Vesicular GABA transporter (VGAT) and GABA B -receptor Immunoreactivities in the Rat Esophagus

We investigated the distributions of gamma-aminobutyric acid (GABA), vesicular GABA transporter (VGAT), GABA _B -receptor (GABA _B -R) and glutamate decarboxylase 67 (GAD67), immunoreactivities in the rat esophagus. GABA immunoreactivity was found in the nerve fibers of the esophagus, but not in the neurons. A few GABA-immunoreactive nerve fibers ran along the muscularis mucosae and some GABA-immunoreactive nerve bundles and fibers ran along and contacted clusters of myenteric neurons. Numerous GABA-immunoreactive nerve terminals ran along the striated muscles and formed motor endplates on the muscles while GABA-immunoreactive nerve fibers contacted nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d)-positive or choline acetyltransferase (ChAT)-immunopositive neurons in the myenteric plexus. NADPH-d-positive nerve fibers often intermingled with GABA-immunoreactive motor endplates in the striated muscles. The GABA-immunoreactive nerve fibers contacting the myenteric neurons were also ChAT-immunopositive. The GABA-immunoreactive nerve fibers that formed motor endplates corresponding to α-bungarotoxin (BTX)-positive areas on the striated muscles were also ChAT-immunopositive. The average percentage of GABA-immunoreactive motor endplates to total ChAT-immunoreactive motor endplates in the upper, middle, and lower portions of the esophagus was 24.8%. VGAT immunoreactivity was seen in almost all motor endplates on the esophageal striated muscles, but not in the neurons of the myenteric plexus. Some VGAT-immunoreactive nerve terminals contacted clusters of myenteric neurons. GABA _B -R immunoreactivity was observed in numerous myenteric ganglia and in the proximal-to-distal part of the axons of the ganglia, but not in the striated and smooth muscles. GABA _B -R-immunoreactive neurons were brain nitric oxide synthase (bNOS)- or ChAT-immunopositive. The present study suggests that GABA and GABA _B -R may be present in the neuronal elements of the striated muscle of the rat esophagus and may play an important role in the local inhibitory system of rat esophageal motility. No GAD67 immunoreactivity was found in the nerve fibers and neurons of the esophagus. In the nucleus ambiguus and in the dorsal motor nucleus of the vagal nerves, GAD67 and VGAT immunoreactivities were shown in numerous nerve fibers on the surface of the cell bodies, but not in the cell bodies of the vesicular acetylcholine transporter-immunoreactive neurons. The present study suggests that GABA may be taken up and accumulated in the synaptic vesicles by VGAT in the nerve terminals, but not in the cell bodies of the neurons of the brainstem.