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Bradykinin (BK) and its receptors, B 1 and B 2 , in trigeminal ganglion (TG) neurons are involved in the regulation of pain. Recent studies have revealed that B 1 receptors are expressed in neonatal rat TG neurons; however, the intracellular signaling pathway following B 1 receptor activation remains to be elucidated. To investigate the mechanism by which B 1 receptor activation leads to intracellular Ca 2+ mobilization, we measured the intracellular free Ca 2+ concentration ([Ca 2+ ] i ) in primary-cultured TG neurons. The application of Lys-[Des-Arg 9 ]BK (B 1 receptor agonist) increased the [Ca 2+ ] i in these TG neurons even in the absence of extracellular Ca 2+ . Pretreatment with inhibitors of ryanodine receptors or sarco/endoplasmic reticulum Ca 2+ -ATPase suppressed the increase in Lys-[Des-Arg 9 ]BK-induced [Ca 2+ ] i . The Lys-[Des-Arg 9 ]BK-induced [Ca 2+ ] i increase was unaffected by phospholipase-C inhibitor. B 1 receptor activation-induced [Ca 2+ ] i increase was suppressed by phosphodiesterase inhibitor and enhanced by adenylyl cyclase inhibitor. These results suggest that B 1 receptor activation suppresses intracellular cAMP production via adenylyl cyclase inhibition and mobilizes intracellular Ca 2+ via ryanodine receptors that access intracellular Ca 2+ stores.

Purinergic receptors play key signaling roles in neuropathic pain in the orofacial region, which is innervated by trigeminal ganglion (TG) neurons. The neuropathology of purinergic P2Y12 receptors is well characterized in glia; however, their physiological role in TG neurons remains to be fully elucidated. The present study investigated the expression and function of P2Y12 receptors in rat TG neurons. P2Y12 receptor immunoreactivity was intense in the soma, dendrites, and axons, and colocalized with a pan-neuronal marker, neurofilament H, isolectin B4, and substance P. In the presence of extracellular Ca(2+), 2-methylthio-ADP (an agonist of P2Y1, 12, 13 receptors) transiently increased intracellular free Ca(2+) concentrations ([Ca(2+)]i), an effect that was abolished by P2Y12 receptor antagonists. In the absence of extracellular Ca(2+), ryanodine receptor/channel inhibitors diminished the 2-methylthio-ADP-induced increases in [Ca(2+)]i. A sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibitor gradually increased [Ca(2+)]i, and after a plateau, application of 2-MeS-ADP induced a rapid and transient, but additive increase in [Ca(2+)]i. An adenylate cyclase inhibitor transiently increased [Ca(2+)]i, while a phosphodiesterase inhibitor prevented the 2-methylthio-ADP-induced increase in [Ca(2+)]i. Our study shows that P2Y12 receptors are expressed in TG neurons, and act via a cAMP-dependent pathway to release intracellular Ca(2+) from ryanodine-sensitive Ca(2+) stores., (Copyright © 2015 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

Extracellular ATP, an essential pain mediator, is received by cell-surface ionotropic P2X and/or metabotropic P2Y receptors. Although the contribution of P2X₃ and/or P2X(2/3) receptors toward the pain mechanism is well described in trigeminal ganglion neurons, the expression of other subtypes of P2X receptor remains to be clarified. We examined expression of P2X receptor mRNA and measured intracellular free Ca²⁺ concentration ([Ca²⁺]i) by the activation of these receptors by fura-2 fluorescence in primary cultured rat trigeminal ganglion neurons. Real-time reverse transcription-PCR analysis revealed mRNA expression of P2X receptor subtype P2X₁, P2X₃, and P2X₄ in trigeminal ganglion neurons. In the presence of extracellular Ca²⁺, the application of P2X receptors agonists, ATP, α,β-methylene ATP or β,γ-methylene ATP induced Ca²⁺ influx significantly. The ATP-induced increase in [Ca²⁺]i was inhibited by a series of selective antagonists for P2X₁, P2X₃, or P2X₄ receptors. These results indicate that trigeminal ganglion neurons functionally express P2X₁, P2X₃, and P2X₄ receptors and that these receptors are involved in the mediation of not only nociceptive but also neuropathic pain in the orofacial area.

It is established that neuropeptide Y (NPY) is a transmitter of parasympathetic secretory impulses in submandibular gland. The neuropeptides substance P, vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) are likely mediators of secretory parasympathetic responses of the gland. Previously, we have shown that substance P, VIP and CGRP modulate voltage-dependent Ca(2+) channels (VDCCs) in hamster submandibular ganglion (SMG) neurons. In this study, we attempt to characterize the effect of NPY on VDCCs current using Ba(2+) (I(Ba)) in SMG neurons. Application of NPY caused both facilitation and inhibition of L-type and N/P/Q-type I(Ba), respectively. Intracellular dialysis of the Gα(s)-protein antibody attenuated the NPY-induced facilitation of I(Ba). The adenylate cyclase (AC) inhibitor, as well as protein kinase A (PKA) inhibitor attenuated the NPY-induced facilitation of I(Ba). Intracellular dialysis of the Gα(i)-protein antibody attenuated the NPY-induced inhibition of I(Ba). Application of a strong depolarizing voltage prepulse attenuated the NPY-induced inhibition of I(Ba). These results indicate that NPY facilitates L-type VDCCs via Gα(s)-protein involving AC and PKA. On the other hand, NPY also inhibits N/P/Q-type VDCCs via Gα(i)-protein βγ subunits in the SMG neurons., (Copyright © 2012 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

Objective: The control of saliva secretion is mainly under parasympathetic control. The submandibular ganglion (SMG) is a parasympathetic ganglion which receives inputs from preganglionic cholinergic neurons, and innervates the submandibular salivary gland to control saliva secretion. The aim of this study was to investigate if adrenomedullin (ADM) and/or calcitonin gene-related peptide (CGRP) modulate voltage-dependent calcium channel (VDCCs) current (I(Ca)) in SMG., Design: The profile of CGRP and ADM actions in SMG was studied using the whole-cell configuration of the patch-clamp technique., Results: Both ADM and CGRP facilitated I(Ca). These facilitations were attenuated by intracellular dialysis of the anti-Gα(s)-protein and pretreatment of SQ22536 (an adenylate cyclase inhibitor)., Conclusions: ADM and CGRP facilitates VDCCs mediated by Gα(s)-protein and adenylate cyclase in SMG., (Copyright © 2010. Published by Elsevier Ltd.)

Bradykinin (BK) and its receptors, B.sub.1 and B.sub.2, in trigeminal ganglion (TG) neurons are involved in the regulation of pain. Recent studies have revealed that B.sub.1 receptors are expressed in neonatal rat TG neurons; however, the intracellular signaling pathway following B.sub.1 receptor activation remains to be elucidated. To investigate the mechanism by which B.sub.1 receptor activation leads to intracellular Ca.sup.2+ mobilization, we measured the intracellular free Ca.sup.2+ concentration ([Ca.sup.2+].sub.i) in primary-cultured TG neurons. The application of Lys-[Des-Arg.sup.9]BK (B.sub.1 receptor agonist) increased the [Ca.sup.2+].sub.i in these TG neurons even in the absence of extracellular Ca.sup.2+. Pretreatment with inhibitors of ryanodine receptors or sarco/endoplasmic reticulum Ca.sup.2+-ATPase suppressed the increase in Lys-[Des-Arg.sup.9]BK-induced [Ca.sup.2+].sub.i. The Lys-[Des-Arg.sup.9]BK-induced [Ca.sup.2+].sub.i increase was unaffected by phospholipase-C inhibitor. B.sub.1 receptor activation-induced [Ca.sup.2+].sub.i increase was suppressed by phosphodiesterase inhibitor and enhanced by adenylyl cyclase inhibitor. These results suggest that B.sub.1 receptor activation suppresses intracellular cAMP production via adenylyl cyclase inhibition and mobilizes intracellular Ca.sup.2+ via ryanodine receptors that access intracellular Ca.sup.2+ stores. Keywords: Adenylyl cyclase, Ca.sup.2+ mobilization, Cyclic AMP, G protein, Ryanodine receptors, Trigeminal ganglion neuron, Author(s): Reiko Terashima[sup.1,2], Maki Kimura[sup.2], Asuka Higashikawa[sup.2], Yuki Kojima[sup.2], Tatsuya Ichinohe[sup.1], Masakazu Tazaki[sup.2] and Yoshiyuki Shibukawa[sup.2] Introduction Bradykinin (BK) and related peptides play important roles in the modulation of physiological [...]

Background: Noxious stimulation and nerve injury induce an increase in intracellular Ca2+ concentration ([Ca2+]i) via various receptors or ionic channels. While an increase in [Ca2+]i excites neurons, [Ca2+]i overload elicits cytotoxicity, resulting in cell death. Intracellular C2+ is essential for many signal transduction mechanisms, and its level is precisely regulated by the Ca2+ extrusion system in the plasma membrane, which includes the Na+-Ca2+ exchanger (NCX). It has been demonstrated that Ca2+-ATPase is the primary mechanism for removing [Ca2+]i following excitatory activity in trigeminal ganglion (TG) neurons; however, the role of NCXs in this process has yet to be clarified. The goal of this study was to examine the expression/localization of NCXs in TG neurons and to evaluate their functional properties. Results: NCX isoforms (NCX1, NCX2, and NCX3) were expressed in primary cultured rat TG neurons. All the NCX isoforms were also expressed in A-, peptidergic C-, and non-peptidergic C-neurons, and located not only in the somata, dendrites, axons and perinuclear region, but also in axons innervating the dental pulp. Reverse NCX activity was clearly observed in TG neurons. The inactivation kinetics of voltage-dependent Na+ channels were prolonged by NCX inhibitors when [Ca2+]i in TG neurons was elevated beyond physiological levels. Conclusions: Our results suggest that NCXs in TG neurons play an important role in regulating Ca2+-homeostasis and somatosensory information processing by functionally coupling with voltage-dependent Na+ channels. [ABSTRACT FROM AUTHOR]

The topography of the insula and operculum responses to electrical stimulation, applied to the first and third transverse palatine ridge and mucosa of foramen palatinum majus of normal volunteers, was analyzed using a 306-channel, whole-head DC-superconducting quantum interference device (SQUID) magnetoencephalography (MEG). The following order of a location of equivalent current dipoles (ECD) was found: third transverse palatine ridge—Insula, Parietal operculum, SI-Frontal operculum, Parietal operculum-SI or SI. It has been reported that the primary gustatory area is the transition area between the operculum and insula in macaque monkeys and humans, and the neurons in the insular cortex of rats are mechanoreceptive. Stimulus to the oral mucosa, therefore, has the possibility to influence the sense of taste. [Copyright &y& Elsevier]