Nodose Ganglion Neurons Research Articles

Role of the Acid-Sensing Ion Channel 3 in Blood Volume Control

The mechanically sensitive volume receptors, primarily located in the venoatrial junction area, are essential for blood volume homeostasis. However, the molecular basis of the volume receptors is still unknown. We hypothesized that the acid-sensing ion channel 3 (ASIC3) might be a candidate for the mechanically sensitive molecules expressed in the volume receptors. We examined the effect of Asic3 null mutation (Asic3(-/-)) on blood volume expansion (BVE)-induced urine flow, neural activation, and atrial natriuretic peptide (ANP) release in mice. BVE-induced urine flow was lower in Asic3(-/-) mice than in wild-type littermates. In addition, the stretch-activated channel blocker GdCl(3) further reduced the BVE-induced urine flow in Asic3(-/-) mice. BVE increased phosphorylated extracellular signal-related kinase (pERK) immunoreactivity in nodose ganglia and many segments of dorsal root ganglia (DRG) in all mice, but pERK-positive neurons were fewer in Asic3(-/-) mice or mice pretreated with GdCl(3) than in wild-type mice. Asic3 knockout selectively decreased BVE-induced pERK-immunoreactive neurons in nodose ganglia, and in C8 and T2 DRG. Moreover, BVE increased the circulating ANP level, which was abolished in Asic3(-/-) mice and wild-type mice treated with GdCl(3). Asic3 knockout reduced the BVE-induced plasma ANP elevation in a GdCl(3)-independent manner. ASIC3 is a molecular substrate involved in detecting the vessel stretch caused by BVE.

Inhibition of gastric motility by hyperglycemia is mediated by nodose ganglia KATP channels

The inhibitory action of hyperglycemia is mediated by vagal afferent fibers innervating the stomach and duodenum. Our in vitro studies showed that a subset of nodose ganglia neurons is excited by rising ambient glucose, involving inactivation of ATP-sensitive K(+) (K(ATP)) channels and leading to membrane depolarization and neuronal firing. To investigate whether nodose ganglia K(ATP) channels mediate gastric relaxation induced by hyperglycemia, we performed in vivo gastric motility studies to examine the effects of K(ATP) channel activators and inactivators. Intravenous infusion of 20% dextrose induced gastric relaxation in a dose-dependent manner. This inhibitory effect of hyperglycemia was blocked by diazoxide, a K(ATP) channel activator. Conversely, tolbutamide, a K(ATP) channel inactivator, induced dose-dependent gastric relaxation, an effect similar to hyperglycemia. Vagotomy, perivagal capsaicin treatment, and hexamethonium each prevented the inhibitory action of tolbutamide. Similarly, N(G)-nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase, also blocked tolbutamide's inhibitory effect. To show that K(ATP) channel inactivation at the level of the nodose ganglia induces gastric relaxation, we performed electroporation of the nodose ganglia with small interfering RNA of Kir6.2 (a subunit of K(ATP)) and plasmid pEGFP-N1 carrying the green fluorescent protein gene. The gastric responses to hyperglycemia and tolbutamide were not observed in rats with Kir6.2 small interfering RNA-treated nodose ganglia. However, these rats responded to secretin, which acts via the vagal afferent pathway, independently of K(ATP) channels. These studies provide in vivo evidence that hyperglycemia induces gastric relaxation via the vagal afferent pathway. This action is mediated through inactivation of nodose ganglia K(ATP) channels.

Synergistic Role of TRPV1 and TRPA1 in Pancreatic Pain and Inflammation

The transient receptor potential (TRP) channels TRPV1 and TRPA1 have each been associated with regulation of efferent properties of primary afferent neurons that initiate neurogenic inflammation and are required for the development of inflammatory hyperalgesia. To evaluate the role of these channels in producing pain during pancreatic inflammation, we studied pancreatic nodose ganglion (NG) and dorsal root ganglion (DRG) sensory neurons (identified by content of retrograde tracer) and behavioral outcomes in a mouse model of acute pancreatitis. Pancreatic inflammation was induced by 8 hourly injections of cerulein (50 μg/kg). The extent of inflammation, pancreatic neuron TRP channel expression and function and excitability, and pain-related behaviors were evaluated over the course of the following week. Histology and myeloperoxidase activity confirmed pancreatic inflammation that was associated with increased excitability and messenger RNA expression of the TRP channels in NG and DRG pancreatic neurons. Calcium imaging of pancreatic NG and DRG neurons from mice given cerulein revealed increased responses to TRP agonists. TRPV1 and TRPA1 antagonists attenuated cerulein-induced pain behaviors and pancreatic inflammation; they had a synergistic effect. Pancreatic inflammation significantly increased the expression and functional properties of TRPV1 and TRPA1, as well as the excitability of pancreatic sensory neurons in vagal and spinal pathways. TRP channel antagonists acted synergistically to reverse pancreatic inflammation and associated pain behaviors; reagents that target interactions between these channels might be developed to reduce pain in patients with acute pancreatitis.

The influence of exercise on morphological and neurochemical properties of neurons in rat nodose ganglia

Physical exercise can induce immunohistochemical changes and cell proliferation in the hippocampus. One of the main effects of prolonged exercise is resting bradycardia, most probably caused by enhanced vagal activity. To investigate whether physical exercise can cause neurochemical and morphological changes in vagal afferent neurons, we performed immunohistochemical studies of nodose neurons using isolectin B4 (IB4), 200-kDa neurofilament protein (N52) and calretinin in adult female rats. To distinguish subpopulations of neurons projecting to the left ventricle, we applied a Fast Blue patch to the epicardial surface of the left ventricle. Treadmill running for 8 weeks significantly increased the size of N52-positive cardiac projecting neurons. Furthermore, the proportion of IB4-positive neurons among all nodose ganglia neurons was significantly higher in trained animals. These data indicate that exercise leads to plastic changes in nodose ganglia neurons that may initiate changes of vagal activity caused by prolonged exercise.

Adenosine-induced activation of esophageal nociceptors

Clinical studies implicate adenosine acting on esophageal nociceptive pathways in the pathogenesis of noncardiac chest pain originating from the esophagus. However, the effect of adenosine on esophageal afferent nerve subtypes is incompletely understood. We addressed the hypothesis that adenosine selectively activates esophageal nociceptors. Whole cell perforated patch-clamp recordings and single-cell RT-PCR analysis were performed on the primary afferent neurons retrogradely labeled from the esophagus in the guinea pig. Extracellular recordings were made from the isolated innervated esophagus. In patch-clamp studies, adenosine evoked activation (inward current) in a majority of putative nociceptive (capsaicin-sensitive) vagal nodose, vagal jugular, and spinal dorsal root ganglia (DRG) neurons innervating the esophagus. Single-cell RT-PCR analysis indicated that the majority of the putative nociceptive (transient receptor potential V1-positive) neurons innervating the esophagus express the adenosine receptors. The neural crest-derived (spinal DRG and vagal jugular) esophageal nociceptors expressed predominantly the adenosine A(1) receptor while the placodes-derived vagal nodose nociceptors expressed the adenosine A(1) and/or A(2A) receptors. Consistent with the studies in the cell bodies, adenosine evoked activation (overt action potential discharge) in esophageal nociceptive nerve terminals. Furthermore, the neural crest-derived jugular nociceptors were activated by the selective A(1) receptor agonist CCPA, and the placodes-derived nodose nociceptors were activated by CCPA and/or the selective adenosine A(2A) receptor CGS-21680. In contrast to esophageal nociceptors, adenosine failed to stimulate the vagal esophageal low-threshold (tension) mechanosensors. We conclude that adenosine selectively activates esophageal nociceptors. Our data indicate that the esophageal neural crest-derived nociceptors can be activated via the adenosine A(1) receptor while the placodes-derived esophageal nociceptors can be activated via A(1) and/or A(2A) receptors. Direct activation of esophageal nociceptors via adenosine receptors may contribute to the symptoms in esophageal diseases.

Low-affinity CCK-A receptors are coexpressed with leptin receptors in rat nodose ganglia: implications for leptin as a regulator of short-term satiety.

The paradigm for the control of feeding behavior has changed significantly. Research has shown that leptin, in the presence of CCK, may mediate the control of short-term food intake. This interaction between CCK and leptin occurs at the vagus nerve. In the present study, we aimed to characterize the interaction between CCK and leptin in the vagal primary afferent neurons. Single neuronal discharges of vagal primary afferent neurons innervating the gastrointestinal tract were recorded from rat nodose ganglia. Three groups of nodose ganglia neurons were identified: group 1 responded to CCK-8 but not leptin; group 2 responded to leptin but not CCK-8; group 3 responded to high-dose CCK-8 and leptin. In fact, the neurons in group 3 showed CCK-8 and leptin potentiation, and they responded to gastric distention. To identify the CCK-A receptor (CCKAR) affinity states that colocalize with the leptin receptor OB-Rb, we used CCK-JMV-180, a high-affinity CCKAR agonist and low-affinity CCKAR antagonist. As expected, immunohistochemical studies showed that CCK-8 administration significantly potentiated the increase in the number of c-Fos-positive neurons stimulated by leptin in vagal nodose ganglia. Administration of CCK-JMV-180 eliminated the synergistic interaction between CCK-8 and leptin. We conclude that both low- and high-affinity CCKAR are expressed in nodose ganglia. Many nodose neurons bearing low-affinity CCKAR express OB-Rb. These neurons also respond to mechanical distention. An interaction between CCKAR and OB-Rb in these neurons likely facilitates leptin mediation of short-term satiety.

Visualising vagal afferent neurons and their terminals whilst silencing TRPV1

Visualising vagal afferent neurons and their terminals whilst silencing TRPV1

The effect of Δ 9-tetrahydrocannabinol on 5-HT 3 receptors depends on the current density

The effects of Δ 9-tetrahydrocannabinol (THC), the psychoactive component of cannabis, on the function of 5-HT type 3 (5-HT 3) receptors were investigated using a two-electrode voltage clamp technique in Xenopus oocytes, and a whole-cell patch clamp technique in rat nodose ganglion neurons. In oocytes injected with 3 ng cRNA of 5-HT 3A receptor, THC reversibly inhibited currents evoked with 5-HT (1 μM) in a concentration-dependent manner (IC 50=1.2 μM). The extent of THC inhibition was inversely correlated with the amount of cRNA injected and the mean 5-HT 3A receptor current densities. Pretreatment with actinomycin D, which inhibits transcription, decreased the mean 5-HT 3 receptor current density and increased the extent of THC inhibition on 5-HT 3 receptor-mediated currents. The IC 50 values for THC increased from 285 nM to 1.2 μM in oocytes injected with 1 and 3 ng of 5-HT 3A cRNA, respectively. In radioligand binding studies on membrane preparations of oocytes expressing 5-HT 3A receptors, THC did not alter the specific binding of a 5-HT 3A receptor antagonist, [ 3H]GR65630. In the presence of 1 μM THC, the maximum 5-HT-induced response was also inhibited without a significant change in 5-HT potency, indicating that THC acts as a noncompetitive antagonist on 5-HT 3 receptors. In adult rat nodose ganglion neurons, application of 1 μM THC caused a significant inhibition of 5-HT 3 receptors, extent of which correlated with the density of 5-HT-induced currents, indicating that the observed THC effects occur in mammalian neurons. The inhibition of 5-HT 3 receptors by THC may contribute to its pharmacological actions in nociception and emesis.

Calcium transient evoked by TRPV1 activators is enhanced by tumor necrosis factor-α in rat pulmonary sensory neurons

TNFα, a proinflammatory cytokine known to be involved in the pathogenesis of allergic asthma, has been shown to induce hyperalgesia in somatic tissue via a sensitizing effect on dorsal root ganglion neurons expressing transient receptor potential vanilloid type 1 receptor (TRPV1). Because TRPV1-expressing pulmonary sensory neurons play an important role in regulating airway function, this study was carried out to determine whether TNFα alters the sensitivity of these neurons to chemical activators. Responses of isolated nodose and jugular ganglion neurons innervating the rat lungs were determined by measuring the transient increase in intracellular Ca(2+) concentration ([Ca(2+)](i)). Our results showed the following. 1) A pretreatment with TNFα (50 ng/ml) for ∼24 h increased significantly the peak Δ[Ca(2+)](i) evoked by capsaicin (Cap) in these neurons. A pretreatment with the same concentration of TNFα for a longer duration (∼48 h) did not further increase the response, but pretreatment for a shorter duration (1 h) or with a lower concentration (25 ng/ml, 24 h) failed to enhance the Cap sensitivity. 2) The same TNFα pretreatment also induced similar but less pronounced and less uniform increases in the responses to acid (pH 6.5-5.5), 2-aminoethoxydiphenyl borate (2-APB), a common activator of TRPV1, V2, and V3 channels, and allyl isothiocyanate (AITC), a selective activator of TRPA1 channel. 3) In sharp contrast, the responses to ATP, ACh, and KCl were not affected by TNFα. 4) The TNFα-induced hypersensitivity to Cap was not prevented by pretreatment with indomethacin (30 μM). 5) The immunoreactivity to both TNF receptor types 1 and 2 were detected in rat vagal pulmonary sensory neurons. In conclusion, prolonged treatment with TNFα induces a pronounced potentiating effect on the responses of isolated pulmonary sensory neurons to TRPV1 activators. This action of TNFα may contribute in part to the airway hyperresponsiveness induced by this cytokine.

P2X 2/3 receptor activity of rat nodose ganglion neurons contributing to myocardial ischemic nociceptive signaling

Myocardial ischemia causes the production of a variety of chemical substances, which act on the cardiac afferent nerve to cause pain. Myocardial damage can affect cardiac vagal afferent activity. Survivors of myocardial infarction are often left with impaired activity of cardiac vagal sensory fibres. The nodose ganglia (NG) are lower ganglia of cardiac vagus nerve, which are chiefly visceral afferent in the sensation of heart. ATP as a possible damage signal may activate nociceptive sensory neurons. Activation of P2X 3, P2X 2/3 receptors by endogenous ATP contributes to the development of hyperalgesia. The present results have shown that the sensitivity of P2X 2/3 receptor in nodose ganglion neurons was increased after myocardial ischemic injury under electrophysiological observation. The inhibitive role of P2X 2/3 antagonist A-317491 on ATP-activated currents in myocardial ischemic rats was significantly increased, compared with that in control group at the same concentration of A-317491. The staining of P2X 2 and P2X 3 receptors in myocardial ischemic injury group appeared to be more intense than those in naive rats and myocardial ischemic rats treated with A-317491 with immunofluorescence double labeling methods. Therefore, the activity of P2X 2/3 receptors in NG neurons was involved in the transmission of myocardial ischemic nociceptive signal.

Excitation of primary afferent neurons by near-infrared light in vitro

Near-infrared light therapy is an emerging neurostimulation technology, but its cellular mechanism of action remains unresolved. Using standard intracellular recording techniques, we observed that 5-10 ms pulses of 1889 nm light depolarized the membrane potential for hundreds of milliseconds in more than 85% of dorsal root ganglion and nodose ganglion neurons tested. The laser-evoked depolarizations (LEDs) exhibited complex, multiphasic kinetics comprising fast and slow components. There was no discernable difference in the LEDs in intact ganglion neurons and in acutely isolated neurons. Thus, the LED sensor seems to reside within the neuronal membrane. The near-uniform distribution of responsive neurons increased membrane conductance, and the negative reversal potential value (-41+/-2.9 mV) suggests that LED is unrelated to the activation of heat-sensitive transient receptor potential cation channel subfamily V member 1 channels. The long duration of LEDs favors an involvement of second messengers.

Glutamate- and GABA-mediated neuron–satellite cell interaction in nodose ganglia as revealed by intracellular calcium imaging

In the sensory ganglia, neurons are devoid of synaptic contacts, and ganglion neurons surrounded by one of glial cells, satellite cells. Recent studies suggest that neurons and satellite cells interact through neurotransmitters. In the present study, intracellular Ca(2+) ([Ca(2+)](i)) dynamics of neurons and satellite cells from one of viscerosensory ganglia, nodose ganglion (NG), were investigated by stimulation with glutamate and its agonist and/or the antagonist of the GABA(A) receptor bicuculline. In the specimens containing neurons with satellite cells, glutamate and a metabotropic glutamate receptor (mGluR) agonist t-ACPD evoked [Ca(2+)](i) increases in both neurons and surrounding satellite cells. Moreover, bicuculline also induced [Ca(2+)](i) increases in neurons and satellite cells. However, in the isolated neurons, bicuculline did not cause an increase in [Ca(2+)](i), suggesting that satellite cells are equipped with the ability to release GABA. In the neurons associated with satellite cells, the delay time until the onset of a response was shorter in the case of glutamate stimulation with bicuculline than that without bicuculline (107.3 +/- 93.4 vs. 231.8 +/- 97.0 s, p < 0.01). Furthermore, immunoreactivities for glutamate transporter, GLAST, and GABA transporter, GAT-3, were observed in both neurons and satellite cells of NG. In conclusion, the levels of [Ca(2+)](i) of NG neurons and surrounding satellite cells are increased by glutamate through at least mGluRs, and endogenous GABA modulates these responses; GABA inhibition is dependent on a close association between neurons and satellite cells. Such neuron-glia interaction in the nodose ganglion may regulate sensory information from visceral organs.

W1361 Colon Electrical Stimulation: A Potential Treatment for Obesity

In Vitro extracellular recordings were performed from jejunal afferents. Nodose ganglion neurons (NGNs) were dissociated and plated onto coverslips. Whole cell patch clamp recordings or Fura-2AM calcium imaging experiments on NGNs were performed 18-24 h post-dissociation. Results: In recordings from jejunal afferents, responses to 100nM CCK (11.5 ± 3.2 vs. 3.35 ± 1.0 spikes/s n=10, p<0.05) and 10μM 5-HT (4.85 ± 1.4 vs. 1.75 ± 0.25, n=10, p<0.05) were decreased in HFF mice compared to LFF controls. However responses to non satiety related compounds such as nicotine, and baseline firing rate were also decreased, suggesting a global decrease in excitability. Current clamp experiments were performed on NGNs to assess the membrane properties in LFF and HFF neurons. Resting membrane potentials were similar -46.6 ± 3.5 mV (LFF, n=5) and -43.1 ± 2.5mV (HFF, n=5). Rheobase was significantly increased (34.0 ± 9.3 vs. 128.0 ± 24.6 pA, n=5, P < 0.05) and the number of action potentials at 2X rheobase was decreased (3.0 ± 0.8 vs. 1 ± 0, n= 5 p<0.05) in HFF compared to LFF, and there was a large, but non statistically significant reduction in input resistance (LFF, 725.6 ± 266.9 MΩ vs. HFF, 141 ± 15.6 MΩ). In Calcium imaging studies on HFF neurons, 0.5% (1/21) and 9.5% (2/21) of the neurons responded to 100nM CCK-8s and 1μM 5-HT respectively. The number of responsive neurons was higher in LFF mice CCK; 18.9 % (7/37), 5-HT; 21.6% (8/37). Conclusions: Responses to the satiety mediators CCK and 5-HT are significantly attenuated in gut vagal afferents. This reduction in response appears to be due at least in part to a global reduction in excitability of vagal afferents in diet induced obese mice, raising the possibility that high fat diet can cause vagal hyposensitivity, impairing normal satiety signals from the GI tract.

W1360 Effects of Rimonabant on Gastrointestinal Transit in Dogs

In Vitro extracellular recordings were performed from jejunal afferents. Nodose ganglion neurons (NGNs) were dissociated and plated onto coverslips. Whole cell patch clamp recordings or Fura-2AM calcium imaging experiments on NGNs were performed 18-24 h post-dissociation. Results: In recordings from jejunal afferents, responses to 100nM CCK (11.5 ± 3.2 vs. 3.35 ± 1.0 spikes/s n=10, p<0.05) and 10μM 5-HT (4.85 ± 1.4 vs. 1.75 ± 0.25, n=10, p<0.05) were decreased in HFF mice compared to LFF controls. However responses to non satiety related compounds such as nicotine, and baseline firing rate were also decreased, suggesting a global decrease in excitability. Current clamp experiments were performed on NGNs to assess the membrane properties in LFF and HFF neurons. Resting membrane potentials were similar -46.6 ± 3.5 mV (LFF, n=5) and -43.1 ± 2.5mV (HFF, n=5). Rheobase was significantly increased (34.0 ± 9.3 vs. 128.0 ± 24.6 pA, n=5, P < 0.05) and the number of action potentials at 2X rheobase was decreased (3.0 ± 0.8 vs. 1 ± 0, n= 5 p<0.05) in HFF compared to LFF, and there was a large, but non statistically significant reduction in input resistance (LFF, 725.6 ± 266.9 MΩ vs. HFF, 141 ± 15.6 MΩ). In Calcium imaging studies on HFF neurons, 0.5% (1/21) and 9.5% (2/21) of the neurons responded to 100nM CCK-8s and 1μM 5-HT respectively. The number of responsive neurons was higher in LFF mice CCK; 18.9 % (7/37), 5-HT; 21.6% (8/37). Conclusions: Responses to the satiety mediators CCK and 5-HT are significantly attenuated in gut vagal afferents. This reduction in response appears to be due at least in part to a global reduction in excitability of vagal afferents in diet induced obese mice, raising the possibility that high fat diet can cause vagal hyposensitivity, impairing normal satiety signals from the GI tract.

S1802 Upregulation of N-Methyl-D-Aspartate Subunit Phosphorylation in Nodose Ganglia Neurons Following Acid-Induced Esophagitis in Cats

S1802 Upregulation of N-Methyl-D-Aspartate Subunit Phosphorylation in Nodose Ganglia Neurons Following Acid-Induced Esophagitis in Cats

PP-014 Control of receptor expression in vagal afferent neurons by activation of cannabinoid 1 receptors

Introduction The intestinal hormone cholecystokinin (CCK) inhibits food intake via stimulation of vagal afferent neurons (VAN). In fasted rats, there is increased synthesis of the endocannabinoid anandamide (AEA) in the small intestine, and of its receptor (CB1) in VAN. Peripheral AEA stimulates food intake via VAN and endogenous CCK inhibits expression of CB1. The aim of the present studies was to characterise CB1 expression in VAN and to determine the functional significance of stimulation of these receptors. Methods Nodose ganglion neurons expressing CB1 were detected by immunohistochemistry or in situ hybridisation in rats following dietary manipulation or administration of drugs and hormones ip. Similar approaches were used for MCH1 and Y2 receptor expression. Results Expression of CB1 in rat VAN was detectable within 6 h and increased to a maximum after 24 h of fasting when approximately 50% of neurons in the mid- and caudal regions expressed the receptor. In contrast, MCH1R, which is also associated with orexigenic signalling, showed a delayed increase in expression compared with CB1 while Y2R, associated with satiety signalling, exhibited decreased expression with fasting. Administration of CCK8s (10 nmol) to fasted rats decreased expression of CB1 and MCH-1 but the t1/2 for loss of CB1 was approximately 1 h compared with 3 h for MCH-1. The action of CCK was inhibited by ghrelin and orexin-A. The CB1 agonist AEA (10 mg) had ghrelin-like actions in reversing the effect of CCK on CB1, MCH1 and Y2 receptor expression. In contrast, in rats fasted for 18 h, administration of a CB1 antagonist/inverse agonist (AM281, 0.25 mg) downregulated CB1 expression and increased Y2 receptor expression. Conclusion Activation of CB1 on vagal afferent neurons determines the pattern of expression of receptors in these neurons indicating a new and hitherto unrecognised role for endocannabinoids in gut-brain signalling.

Plasticity of nodose ganglion neurons after capsaicin- and vagotomy-induced nerve damage in adult rats

Previous reports show that vagal afferent innervation of the stomach eventually regenerates from surviving nodose ganglion (NG) neurons after subdiaphragmatic vagotomy. Systemic capsaicin treatment destroys gastric vagal afferent neurons expressing vanilloid receptor 1 (VR1). However, it is not known whether gastric innervation lost after neuronal destruction can be restored. Here, we report that capsaicin-induced damage of NG neurons innervating the stomach in adult rats is followed by restoration of vagal afferent projections. Specifically, we compared measures of neuronal plasticity in NG and vagi after subdiaphragmatic vagotomy or capsaicin treatment. The numbers of VR1-immunoreactive neurons projecting to the stomach were significantly reduced 10 days after either capsaicin treatment or vagotomy. However, the VR1-immunoreactive afferent innervation of the stomach was restored to levels exceeding those of vagotomized rats by 37 days after capsaicin, whereas neither total afferent innervation nor VR1-immunoreactive innervation reached control levels, even by 67 days after vagotomy. Capsaicin treatment significantly increased NG neuronal nitric oxide synthase (nNOS) immunoreactivity at 10 days after capsaicin, and this increase was sustained for the duration of the study, indicating higher nNOS demand in restoration of vagal projections. Vagotomy was associated with a much smaller increase in the number of nNOS-immunoreactive NG neurons, detectable only at 10 days after surgery. The number of nNOS-immunopositive gastric-projecting neurons was dramatically reduced 10 days after either capsaicin treatment or vagotomy but returned to the control level in both groups at 67 days. We found a significantly higher number of growth cones in capsaicin-treated animals compared with controls. Capsaicin significantly increased the number of nNOS-immunopositive and nNOS-immunonegative growth cones in NG at all time points. Vagotomy did not increase the number of nNOS− growth cones in NG. We conclude that capsaicin treatment may result in more significant restorative capacities than vagotomy, mainly because of sprouting of capsaicin-insensitive nerve fibers.

Electrophysiological identification of glucose-sensing neurons in rat nodose ganglia

The vagal afferent system is strategically positioned to mediate rapid changes in motility and satiety in response to systemic glucose levels. In the present study we aimed to identify glucose-excited and glucose-inhibited neurons in nodose ganglia and characterize their glucose-sensing properties. Whole-cell patch-clamp recordings in vagal afferent neurons isolated from rat nodose ganglia demonstrated that 31/118 (26%) neurons were depolarized after increasing extracellular glucose from 5 to 15 mm; 19/118 (16%) were hyperpolarized, and 68/118 were non-responsive. A higher incidence of excitatory response to glucose occurred in gastric- than in portal vein-projecting neurons, the latter having a higher incidence of inhibitory response. In glucose-excited neurons, elevated glucose evoked membrane depolarization (11 mV) and an increase in membrane input resistance (361 to 437 M). Current reversed at 99 mV. In glucose-inhibited neurons, membrane hyperpolarization (13 mV) was associated with decreased membrane input resistance (383 to 293 M). Current reversed at 97 mV. Superfusion of tolbutamide, a K(ATP) channel sulfonylurea receptor blocker, elicited identical glucose-excitatory but not glucose-inhibitory responses. Kir6.2 shRNA transfection abolished glucose-excited but not glucose-inhibited responses. Phosphatidylinositol bisphosphate (PIP(2)) depletion using wortmannin increased the fraction of glucose-excited neurons from 26% to 80%. These results show that rat nodose ganglia have glucose-excited and glucose-inhibited neurons, differentially distributed among gastric- and portal vein-projecting nodose neurons. In glucose-excited neurons, glucose metabolism leads to K(ATP) channel closure, triggering membrane depolarization, whereas in glucose-inhibited neurons, the inhibitory effect of elevated glucose is mediated by an ATP-independent K(+) channel. The results also show that PIP(2) can determine the excitability of glucose-excited neurons.

Immunohistochemical characteristics of neurons in nodose ganglia projecting to the different chambers of the rat heart

Despite the contribution of nodose ganglia neurons to the innervation of the heart being the subject of several studies, specific neuronal subpopulations innervating the four different chambers of the heart have not been distinguished. In our study, the application of Fast Blue-loaded patch to the epicardial surface of different chambers of the rat heart (the right or left atrium or the right or left ventricle) resulted in labeling of discrete populations of immunohistochemically diverse neurons. About one half (55%) of these neurons showed immunoreactivity for the 200-kDa neurofilament protein (marker of myelinated neurons), with a higher proportion of positive staining among neurons projecting to the left than to the right ventricle. Isolectin B4 immunoreactivity (characteristic for a subset of nonmyelinated non-peptidergic neurons) was more abundant among neurons projecting to the right side of the heart (right atria and right ventricles) compared to the left side (23% vs. 16%). Calretinin immunoreactivity (possible marker of mechanosensitive neurons) was significantly higher among neurons projecting to the ventricles than among those projecting to atria (36% vs. 11%). These findings reveal that chambers of the rat heart are innervated with immunohistochemically different subpopulations of neurons from the nodose ganglia.

Distinct expression of cold receptors (TRPM8 and TRPA1) in the rat nodose–petrosal ganglion complex

TRPM8 and TRPA1 are cold-activated transient receptor potential (TRP) cation channels. TRPM8 is activated by moderate cooling, while TRPA1 is activated by extreme, noxious cold temperatures. These cold receptors are expressed in different subpopulations of primary afferent neurons. TRPA1 is co-expressed in a subpopulation of somatosensory neurons expressing TRPV1, which is activated by heat. However, the distribution and co-expression of these channels in the nodose–petrosal ganglion complex, which contains the jugular (JG), petrosal (PG), and nodose ganglia (NG) (mainly involved in putative somatic, chemo- and somato-sensation, and somato and visceral sensation, respectively), remain unknown. Here, we conducted in situ hybridization analysis of the rat nodose–petrosal ganglion complex using specific riboprobes for TRPM8, TRPA1, and TRPV1 to compare the features of the cranial sensory ganglia. Hybridization signals for TRPA1 were diffusely observed throughout these ganglia, whereas TRPM8 transcripts were seen in the JG and PG but not in the NG. We retrogradely labeled cranial nerve X with Fast Blue (fluorescent dye) and found TRPM8 transcripts in the jugular-vagal ganglion but not the NG neurons. TRPA1 transcripts were not detected in TRPM8-expressing neurons but were present in the subpopulation of TRPV1-expressing visceral sensory neurons. Taken together, these findings support that in the vagal system the expression of cold-activated TRP channels differs between nodose- and jugular-ganglion neurons suggesting different mechanisms of cold-transduction and that the TRPA1 distribution is consistent with its proposed function as a cold-sensing receptor in the visceral system.