Detecting signals of weakly first-order phase transitions in two-dimensional Potts models

We investigate the first-order phase transitions of the $q$-state Potts models with $q = 5, 6, 7$, and $8$ on the two-dimensional square lattice, using Monte Carlo simulations. At the very weakly first-order transition of the $q=5$ system, the standard data-collapse procedure for the order parameter, carried out with results for a broad range of system sizes, works deceptively well and produces non-trivial critical exponents different from the trivial values expected for first-order transitions. However, a more systematic study reveals significant drifts in the `pseudo-critical' exponents as a function of the system size. For this purpose, we employ two methods of analysis: the data-collapse procedure with narrow range of the system size, and the Binder-cumulant crossing technique for pairs of system sizes. In both methods, the estimates start to drift toward the trivial values as the system size used in the analysis exceeds a certain `cross-over' length scale. This length scale is remarkably smaller than the correlation length at the transition point for weakly first-order transitions, e.g., less than one tenth for $q=5$, in contrast to the naive expectation that the system size has to be comparable to or larger than the correlation length to observe the correct behavior. The results overall show that proper care is indispensable to diagnose the nature of a phase transition with limited system sizes.Comment: 10 pages, 7 figures. One figure has been replaced to make our claim cleare

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

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

Serotonin Augments Gut Pacemaker Activity via 5-HT3 Receptors

Serotonin (5-hydroxytryptamine: 5-HT) affects numerous functions in the gut, such as secretion, muscle contraction, and enteric nervous activity, and therefore to clarify details of 5-HT's actions leads to good therapeutic strategies for gut functional disorders. The role of interstitial cells of Cajal (ICC), as pacemaker cells, has been recognised relatively recently. We thus investigated 5-HT actions on ICC pacemaker activity. Muscle preparations with myenteric plexus were isolated from the murine ileum. Spatio-temporal measurements of intracellular Ca2+ and electric activities in ICC were performed by employing fluorescent Ca2+ imaging and microelectrode array (MEA) systems, respectively. Dihydropyridine (DHP) Ca2+ antagonists and tetrodotoxin (TTX) were applied to suppress smooth muscle and nerve activities, respectively. 5-HT significantly enhanced spontaneous Ca2+ oscillations that are considered to underlie electric pacemaker activity in ICC. LY-278584, a 5-HT3 receptor antagonist suppressed spontaneous Ca2+ activity in ICC, while 2-methylserotonin (2-Me-5-HT), a 5-HT3 receptor agonist, restored it. GR113808, a selective antagonist for 5-HT4, and O-methyl-5-HT (O-Me-5-HT), a non-selective 5-HT receptor agonist lacking affinity for 5-HT3 receptors, had little effect on ICC Ca2+ activity. In MEA measurements of ICC electric activity, 5-HT and 2-Me-5-HT caused excitatory effects. RT-PCR and immunostaining confirmed expression of 5-HT3 receptors in ICC. The results indicate that 5-HT augments ICC pacemaker activity via 5-HT3 receptors. ICC appear to be a promising target for treatment of functional motility disorders of the gut, for example, irritable bowel syndrome