Muscarinic M2 acetylcholine receptor distribution in the guinea-pig gastrointestinal tract

In the enteric nervous system, acetylcholine is the most common neurotransmitter to induce gastrointestinal smooth muscle contractions. Cholinergic signaling is mediated by muscarinic acetylcholine receptors on the surface of smooth muscle cells. Five different muscarinic receptor subtypes (M1–M5) have been identified and characterized, all of which belong to the superfamily of the G-protein-coupled receptor. The muscarinic M2 acetylcholine receptor is the major muscarinic receptor subtype expressed by smooth muscle tissues in the gastrointestinal tract, where it is coexpressed with a smaller population of M3 receptor. In this study, we examined the immunohistochemical distribution of the M2 receptor using a specific antibody in the guinea-pig gastrointestinal tract. M2 receptor-like immunoreactivity was mainly observed as associated with smooth muscle cells in the gastrointestinal tract. M2 receptor-like immunoreactivity in smooth muscle cells was distributed throughout the cell membrane associated with caveolae. In the proximal colon, M2 receptor-like immunoreactivity in the smooth muscle cells was weak. In the small intestine, interstitial cells of Cajal that possessed neurokinin 1 receptor-like immunoreactivity had intense M2 receptor-like immunoreactivity. In the proximal colon, intramuscular and myenteric interstitial cells of Cajal exhibited M2 receptor-like immunoreactivity. These findings indicate that, in the gastrointestinal musculature, M2 receptors are distributed both in the smooth muscle cells and interstitial cells of Cajal, suggesting that the M2 receptor elicits smooth muscle cell contraction and the interstitial cells of Cajal are the sites of innervation by enteric cholinergic neurons

A part of cholinergic fibers in mouse superior cervical ganglia contain GABA or glutamate

The localizations and functions of glutamate and GABA, the major amino acid neurotransmitters in the central nervous system, are still unclear in the peripheral nervous system. We immunohistochemically double-stained mouse superior cervical ganglia with antibodies for the vesicular acetylcholine transporter (VAchT), GAD65, the vesicular glutamate transporters 1-3 (VGluTs1-3), the marker of the sympathetic preganglionic neuron (SPN), GABAergic, and glutamatergic terminals, respectively. All GAD65-positive terminals showed VAchT-immunoreactivity, indicating that GABAergic fibers originate from SPNs. VGluT2-immunoreactive terminals showing colocalization with VAchT were observed, but VGluT1 and 3 immunoreactive terminals were not. Colocalization of GAD65 and VGluT2 was rarely found. All VGluT2-immunopositive terminals were also immunopositive for neuronal nitric oxide synthase (nNOS), a marker for the subpopulation of the SPNs, while about half of the GABA-immunopositive fibers were immunopositive for nNOS. The origin of these fibers was discussed

Expression of Hex mRNA in early murine postimplantation embryo development

AbstractThe onset of Hex expression and its role in early murine development was analyzed using in situ hybridization. Hex mRNA was first detected in the chorion of the ectoplacental cavity and weakly at the visceral endoderm of the future yolk sac at embryonic age (E) 7.5. Expression in embryonic tissues was detected exclusively in the hepatic anlage and thyroid primordium at E 9.5. At E 12.5 and E 15.5, Hex expression persisted in the fetal liver and thyroid, and was also detected in the fetal lung. These results suggest that Hex has its role in differentiation and/or organogenesis of several embryonic tissues

GABA-containing sympathetic preganglionic neurons in rat thoracic spinal cord send their axons to the superior cervical ganglion.

GABA-containing fibers have been observed in the rat superior cervical ganglion (SCG) and, to a lesser extent, in the stellate ganglion (STG). The aim of present study is to clarify the source of these fibers. No cell body showed mRNAs for glutamic acid decarboxylases (GADs) or immunoreactivity for GAD of 67 kDa (GAD67) in the cervical sympathetic chain. Thus, GABA-containing fibers in the ganglia are suggested to be of extraganglionic origin. Since GAD67-immunoreactive fibers were found not in the dorsal roots or ganglia, but in the ventral roots, GABA-containing fibers in the sympathetic ganglia were considered to originate from the spinal cord. Furthermore, almost all GAD67-immunoreactive fibers in the sympathetic ganglia showed immunoreactivity for vesicular acetylcholine transporter, suggesting that GABA was utilized by some cholinergic preganglionic neurons. This was confirmed by the following results: 1) after injection of Sindbis/palGFP virus into the intermediolateral nucleus, some anterogradely labeled fibers in the SCG were immunopositive for GAD67, and 2) after injection of fluorogold into the SCG, some retrogradely labeled neurons in the thoracic spinal cord were positive for GAD67 mRNA. Finally, when the ventral roots of the eighth cervical to the fourth thoracic segments were cut, almost all GAD67- and GABA-immunoreactive fibers disappeared from the ipsilateral SCG and STG, suggesting that the vast majority of GABA-containing fibers in those ganglia were of spinal origin. Thus, the present findings strongly indicate that some sympathetic preganglionic neurons are not only cholinergic, but also GABAegi