Growth differentiation factor 15 (GDF-15) is a member of the transforming growth factor-β superfamily. It is widely distributed in the central and peripheral nervous systems. Whether and how GDF-15 modulates nociceptive signaling remains unclear. Behaviorally, we found that peripheral GDF-15 significantly elevated nociceptive response thresholds to mechanical and thermal stimuli in naïve and arthritic rats. Electrophysiologically, we demonstrated that GDF-15 decreased the excitability of small-diameter dorsal root ganglia (DRG) neurons. Furthermore, GDF-15 concentration-dependently suppressed tetrodotoxin-resistant sodium channel Nav1.8 currents, and shifted the steady-state inactivation curves of Nav1.8 in a hyperpolarizing direction. GDF-15 also reduced window currents and slowed down the recovery rate of Nav1.8 channels, suggesting that GDF-15 accelerated inactivation and slowed recovery of the channel. Immunohistochemistry results showed that activin receptor-like kinase-2 (ALK2) was widely expressed in DRG medium- and small-diameter neurons, and some of them were Nav1.8-positive. Blockade of ALK2 prevented the GDF-15-induced inhibition of Nav1.8 currents and nociceptive behaviors. Inhibition of PKA and ERK, but not PKC, blocked the inhibitory effect of GDF-15 on Nav1.8 currents. These results suggest a functional link between GDF-15 and Nav1.8 in DRG neurons via ALK2 receptors and PKA associated with MEK/ERK, which mediate the peripheral analgesia of GDF-15.
Analgesia ; Animals ; Ganglia, Spinal ; Growth Differentiation Factor 15 ; NAV1.8 Voltage-Gated Sodium Channel ; Rats ; Sensory Receptor Cells ; Sodium Channels ; Tetrodotoxin/pharmacology*

BACKGROUND/AIMS: Although bisacodyl is a widely administered laxative, its underlying mechanism of action remains generally unknown. This study focuses on investigating the effects of bisacodyl on the human colon muscle contraction, and elucidating its mechanism of action. METHODS: Sigmoid colon muscle strips (20 longitudinal and 18 circular muscles) were obtained from 20 subjects who underwent colectomy for colon cancer. Isometric force measurements were calculated in response to electrical field stimulation (EFS, 0.3 milliseconds in trains of 10 Hz for 20 seconds, 150 V). Peak and nadir (tone) during and after EFS, were measured in a controlled state, and after sequential addition of bisacodyl (1 μM), atropine (1 μM), N-nitro-L-arginine (L-NNA, 100 μM), MRS2500 (1 μM), and tetrodotoxin (TTX, 1 μM) to the organ bath. RESULTS: Transient phasic contractions were observed during EFS, and after cessation of EFS. In the longitudinal muscles, nadir during EFS, and tone after EFS, significantly increased after addition of bisacodyl, and persisted after sequential addition of atropine, L-NNA, MRS2500, and TTX, indicating a direct action of bisacodyl on the smooth muscle. In the second experiment, pretreatment of TTX abolished EFS-induced phasic contractions. Although no phasic contraction was produced after perfusion of bisacodyl, tone was increased, thereby supporting evidence of a direct mechanism of action of bisacodyl on the colon smooth muscle. CONCLUSIONS: Bisacodyl increases the tone of longitudinal muscle in the human sigmoid colon through a direct action on the smooth muscle. Further study is warranted to investigate the neural mechanism of action of bisacodyl.
Atropine ; Baths ; Bisacodyl ; Colectomy ; Colon ; Colon, Sigmoid ; Colonic Neoplasms ; Humans ; In Vitro Techniques ; Muscle Contraction ; Muscle, Smooth ; Muscles ; Perfusion ; Physiology ; Tetrodotoxin

It has been reported that Korean red ginseng (KRG), a valuable and important traditional medicine, has varied effects on the central nervous system, suggesting its activities are complicated. The paraventricular nucleus (PVN) neurons of the hypothalamus has a critical role in stress responses and hormone secretions. Although the action mechanisms of KRG on various cells and systems have been reported, the direct membrane effects of KRG on PVN neurons have not been fully described. In this study, the direct membrane effects of KRG on PVN neuronal activity were investigated by using a perforated patch-clamp in ICR mice. In gramicidin perforated patch-clamp mode, KRG extract (KRGE) induced repeatable depolarization followed by hyperpolarization of PVN neurons. The KRGE-induced responses were concentration-dependent and persisted in the presence of tetrodotoxin, a voltage sensitive Na+ channel blocker. The KRGE-induced responses were suppressed by 6-cyano-7-nitroquinoxaline-2,3-dione (10 µM), a non-N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, but not by picrotoxin, a type A gamma-aminobutyric acid receptor antagonist. The results indicate that KRG activates non-NMDA glutamate receptors of PVN neurons in mice, suggesting that KRG may be a candidate for use in regulation of stress responses by controlling autonomic nervous system and hormone secretion.
6-Cyano-7-nitroquinoxaline-2,3-dione ; Animals ; Autonomic Nervous System ; Central Nervous System ; Glutamic Acid ; Gramicidin ; Hypothalamus ; Medicine, Traditional ; Membranes ; Mice ; Mice, Inbred ICR ; Neurons ; Panax ; Paraventricular Hypothalamic Nucleus ; Patch-Clamp Techniques ; Picrotoxin ; Receptors, GABA ; Receptors, Glutamate ; Tetrodotoxin

The ventral pallidum (VP) is a crucial component of the limbic loop of the basal ganglia and participates in the regulation of reward, motivation, and emotion. Although the VP receives afferent inputs from the central histaminergic system, little is known about the effect of histamine on the VP and the underlying receptor mechanism. Here, we showed that histamine, a hypothalamic-derived neuromodulator, directly depolarized and excited the GABAergic VP neurons which comprise a major cell type in the VP and are responsible for encoding cues of incentive salience and reward hedonics. Both postsynaptic histamine H1 and H2 receptors were found to be expressed in the GABAergic VP neurons and co-mediate the excitatory effect of histamine. These results suggested that the central histaminergic system may actively participate in VP-mediated motivational and emotional behaviors via direct modulation of the GABAergic VP neurons. Our findings also have implications for the role of histamine and the central histaminergic system in psychiatric disorders.
Action Potentials ; drug effects ; Animals ; Basal Forebrain ; cytology ; Dimaprit ; pharmacology ; Dose-Response Relationship, Drug ; Electric Stimulation ; Female ; GABAergic Neurons ; drug effects ; Histamine ; pharmacology ; Histamine Agonists ; pharmacology ; Lysine ; analogs & derivatives ; metabolism ; Male ; Patch-Clamp Techniques ; Pyridines ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Histamine H1 ; metabolism ; Receptors, Histamine H2 ; metabolism ; Sodium Channel Blockers ; pharmacology ; Tetrodotoxin ; pharmacology ; gamma-Aminobutyric Acid ; metabolism

Botulinum toxin type A (BoNT/A) has been used therapeutically for various conditions including dystonia, cerebral palsy, wrinkle, hyperhidrosis and pain control. The substantia gelatinosa (SG) neurons of the trigeminal subnucleus caudalis (Vc) receive orofacial nociceptive information from primary afferents and transmit the information to higher brain center. Although many studies have shown the analgesic effects of BoNT/A, the effects of BoNT/A at the central nervous system and the action mechanism are not well understood. Therefore, the effects of BoNT/A on the spontaneous postsynaptic currents (sPSCs) in the SG neurons were investigated. In whole cell voltage clamp mode, the frequency of sPSCs was increased in 18 (37.5%) neurons, decreased in 5 (10.4%) neurons and not affected in 25 (52.1%) of 48 neurons tested by BoNT/A (3 nM). Similar proportions of frequency variation of sPSCs were observed in 1 and 10 nM BoNT/A and no significant differences were observed in the relative mean frequencies of sPSCs among 1–10 nM BoNT/A. BoNT/A-induced frequency increase of sPSCs was not affected by pretreated tetrodotoxin (0.5 µM). In addition, the frequency of sIPSCs in the presence of CNQX (10 µM) and AP5 (20 µM) was increased in 10 (53%) neurons, decreased in 1 (5%) neuron and not affected in 8 (42%) of 19 neurons tested by BoNT/A (3 nM). These results demonstrate that BoNT/A increases the frequency of sIPSCs on SG neurons of the Vc at least partly and can provide an evidence for rapid action of BoNT/A at the central nervous system.
6-Cyano-7-nitroquinoxaline-2,3-dione ; Animals ; Botulinum Toxins* ; Botulinum Toxins, Type A* ; Brain ; Central Nervous System ; Cerebral Palsy ; Dystonia ; Hyperhidrosis ; Mice* ; Neurons* ; Substantia Gelatinosa* ; Synaptic Potentials* ; Tetrodotoxin

BACKGROUND/AIMS: Bile acid is an important luminal factor that affects gastrointestinal motility and secretion. We investigated the effect of bile acid on secretion in the proximal and distal rat colon and coordination of bowel movements in the guinea pig colon. METHODS: The short-circuit current from the mucosal strip of the proximal and distal rat colon was compared under control conditions after induction of secretion with deoxycholic acid (DCA) as well as after inhibition of secretion with indomethacin, 1,2-bis (o-aminophenoxy) ethane-N,N,N′,N′-tetra-acetic acid (an intracellular calcium chelator; BAPTA), and tetrodotoxin (TTX) using an Ussing chamber. Colonic pressure patterns were also evaluated in the extracted guinea pig colon during resting, DCA stimulation, and inhibition by TTX using a newly developed pressure-sensing artificial stool. RESULTS: The secretory response in the distal colon was proportionate to the concentration of DCA. Also, indomethacin, BAPTA, and TTX inhibited chloride secretion in response to DCA significantly (P < 0.05). However, these changes were not detected in the proximal colon. When we evaluated motility, we found that DCA induced an increase in luminal pressure at the proximal, middle, and distal sensors of an artificial stool simultaneously during the non-peristaltic period (P < 0.05). In contrast, during peristalsis, DCA induced an increase in luminal pressure at the proximal sensor and a decrease in pressure at the middle and distal sensors of the artificial stool (P < 0.05). CONCLUSIONS: DCA induced a clear segmental difference in electrogenic secretion. Also, DCA induced a more powerful peristaltic contraction only during the peristaltic period.
Animals ; Bile ; Calcium ; Colon ; Deoxycholic Acid* ; Gastrointestinal Motility ; Guinea Pigs* ; Guinea* ; Indomethacin ; Intestine, Large* ; Peristalsis ; Phenobarbital ; Rats* ; Tetrodotoxin

Recent studies indicate that mitochondria are an important source of reactive oxygen species (ROS) in the spinal dorsal horn. In our previous study, application of malate, a mitochondrial electron transport complex I substrate, induced a membrane depolarization, which was inhibited by pretreatment with ROS scavengers. In the present study, we used patch clamp recording in the substantia geletinosa (SG) neurons of spinal slices, to investigate the cellular mechanism of mitochondrial ROS on neuronal excitability. DNQX (an AMPA receptor antagonist) and AP5 (an NMDA receptor antagonist) decreased the malate-induced depolarization. In an external calcium free solution and addition of tetrodotoxin (TTX) for blockade of synaptic transmission, the malateinduced depolarization remained unchanged. In the presence of DNQX, AP5 and AP3 (a group I metabotropic glutamate receptor (mGluR) antagonist), glutamate depolarized the membrane potential, which was suppressed by PBN. However, oligomycin (a mitochondrial ATP synthase inhibitor) or PPADS (a P2 receptor inhibitor) did not affect the substrates-induced depolarization. These results suggest that mitochondrial substrate-induced ROS in SG neuron directly acts on the postsynaptic neuron, therefore increasing the ion influx via glutamate receptors.
Animals ; Calcium ; Electron Transport Complex I ; Glutamic Acid ; Membrane Potentials ; Membranes ; Mitochondria ; Mitochondrial Proton-Translocating ATPases ; N-Methylaspartate ; Neurons* ; Oligomycins ; Rats* ; Reactive Oxygen Species ; Receptors, AMPA ; Receptors, Glutamate ; Receptors, Metabotropic Glutamate ; Spinal Cord Dorsal Horn ; Substantia Gelatinosa* ; Synaptic Transmission ; Tetrodotoxin

BACKGROUND/AIMS: Myenteric plexus interstitial cells of Cajal (ICC-MY) are involved in the generation of gut pacemaker activity and neuronal communication. We performed patch clamp on ICC-MY in situ to observe the changes of pacemaker activity in response to neural modulations. METHODS: A fresh longitudinal muscle with myenteric plexus (LMMP) from mouse jejunum was prepared. ICC-MY and ganglion neurons embedded in the layer of longitudinal muscles were targeted by patch clamping in whole-cell configuration in a model of current or voltage clamp. Neurogenic modulators were applied to evaluate their effects on ICC pacemaker activity. RESULTS: In situ ICC-MY showed spontaneous and rhythmical voltage oscillations with a frequency of 27.2 ± 3.9 cycles/min, amplitude of 32.6 ± 6.3 mV, and resting membrane potential of −62.2 ± 2.8 mV. In situ neurons showed electrically evocable action potential in single or multiple spikes. Pacemaker activity was modulated by neuronal activators through receiving a neuronal input. Application of tetrodotoxin depolarized pacemaker potentials in a dose dependent manner, and decreased the amplitude at tetrodotoxin 0.3 μM for about 40 ± 10%; capsaicin (1 μM) ameliorated ICC-MY K+ current for about 49 ± 14.8%; and, nitric oxide hyperpolarized pacemaker potential and decreased the amplitude and frequency. CONCLUSIONS: The in situ preparation patch clamp study further demonstrates that the pacemaker activity is an intrinsic property of ICC. The neurogenic activators change and shape pacemaker potential and activity in situ. LMMP preparation in situ patch clamp provides an ideal platform to study the functional innervation of the ICC and the enteric neural system, thereby, for evaluating the neural regulation of pacemaker activity, especially in disorder models.
Action Potentials ; Animals ; Capsaicin ; Constriction ; Enteric Nervous System ; Ganglion Cysts ; Interstitial Cells of Cajal ; Jejunum* ; Membrane Potentials ; Mice* ; Muscles ; Myenteric Plexus* ; Neurons ; Nitric Oxide ; Tetrodotoxin

PURPOSE: We conducted this study in order to determine clinical features and prognostic factors in adults with acute tetrodotoxin (TTX) poisoning caused by ingestion of puffer fish. METHODS: In this retrospective study, 107 patients were diagnosed with TTX poisoning. The subjects were divided into two groups according to duration of treatment; Group I, patients were discharged within 48 hours (n=76, 71.0%), Group II patients were discharged after more than 48 hours (n=31, 29.0%). Group II was subsequently divided into two subgroups [IIa (n=12, 11.2%), IIb (n=19, 17.8%)] according to the need for mechanical ventilation support. RESULTS: In multivariable logistic regression analysis, the predictors of the need for treatment over 48 hours were dizziness (odds ratio [OR], 4.72; 95% confidence intervals [CI], 1.59-12.83), time interval between onset of symptom and ingestion (OR, 0.56; 95% CI, 0.16-0.97), PaCO2<35 mmHg (OR, 8.37; 95% CI, 2.37-23.59). In addition, predictors of the need for mechanical ventilation were a time interval between onset of symptoms and ingestion (OR, 0.54; 95% CI, 0.11-0.96) and PaCO2<35 mmHg (OR, 5.65; 95% CI, 1.96-18.66). CONCLUSION: Overall, dizziness, time interval between onset of symptoms and ingestion, DeltaDBP and PaCO2<35 mmHg predict the need for treatment over 48 hours, time interval between onset of symptoms and ingestion and PaCO2<35 mmHg predict the need for mechanical ventilation support after acute TTX poisoning.
Adult* ; Dizziness ; Eating ; Humans ; Logistic Models ; Poisoning* ; Respiration, Artificial ; Retrospective Studies ; Tetraodontiformes* ; Tetrodotoxin

BACKGROUND/AIMS: DA-9701 significantly improved gastric accommodation by increasing the postprandial gastric volume. In this study, we investigated how DA-9701 affects the rat gastric fundus relaxation. METHODS: Gastric fundus muscle strips (9 longitudinal and 7 circular muscles) were obtained from rats. Electrical field stimulation (EFS) was performed at various frequencies (1, 5, 10 and 20 Hz) and train durations (1, 5, 10 and 20 seconds) to select optimal condition for experiments. Isometric force measurements were performed in response to EFS. Peak and nadir were observed during the first 1 minute after initiation of EFS in control state and after sequential addition of atropine (1 microM), DA-9701 (0.5, 5, 25 and 50 microg), N-nitro-L-arginine (L-NNA, 100 microM), MRS2500 (1 microM) and tetrodotoxin (TTX, 1 microM) to the organ bath. RESULTS: The optimal frequency and duration of EFS to evoke nerve-mediated relaxation was determined as 5 Hz for 10 seconds. Addition of L-NNA in the presence of atropine and DA-9701 (50 microg) decreased nadir by inhibiting relaxation from -0.054 +/- 0.021 g to -0.022 +/- 0.015 g (P = 0.026) in longitudinal muscles. However, subsequent application of MRS2500 in the presence of atropine, DA-9701 (50 microg) and L-NNA did not affect nadir. In circular muscles, subsequent addition of L-NNA and MRS2500 in the presence of atropine and DA-9701 (50 microg) did not show significant change of nadir. CONCLUSIONS: Our data suggest that the effect of DA-9701 on the rat gastric fundus relaxation is mainly mediated by nitrergic rather than purinergic pathway.
Animals ; Atropine ; Baths ; Gastric Fundus* ; Muscles ; Rats* ; Relaxation* ; Tetrodotoxin