Activation of a nerve injury transcriptional signature in airway-innervating sensory neurons after lipopolysaccharide-induced lung inflammation.

The lungs and the immune and nervous systems functionally interact to respond to respiratory environmental exposures and infections. The lungs are innervated by vagal sensory neurons of the jugular and nodose ganglia, fused together in smaller mammals as the jugular-nodose complex (JNC). Whereas the JNC shares properties with the other sensory ganglia, the trigeminal (TG) and dorsal root ganglia (DRG), these sensory structures express differential sets of genes that reflect their unique functionalities. Here, we used RNA sequencing (RNA-seq) in mice to identify the differential transcriptomes of the three sensory ganglia types. Using a fluorescent retrograde tracer and fluorescence-activated cell sorting, we isolated a defined population of airway-innervating JNC neurons and determined their differential transcriptional map after pulmonary exposure to lipopolysaccharide (LPS), a major mediator of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) after infection with gram-negative bacteria or inhalation of organic dust. JNC neurons activated an injury response program, leading to increased expression of gene products such as the G protein-coupled receptor Cckbr, inducing functional changes in neuronal sensitivity to peptides, and Gpr151, also rapidly induced upon neuropathic nerve injury in pain models. Unique JNC-specific transcripts, present at only minimal levels in TG, DRG, and other organs, were identified. These included TMC3, encoding for a putative mechanosensor, and urotensin 2B, a hypertensive peptide. These findings highlight the unique properties of the JNC and reveal that ALI/ARDS rapidly induces a nerve injury-related state, changing vagal excitability.

Decreased Migration of Dendritic Cells into the Jugular-Nodose Ganglia by the CXCL12 Neutraligand Chalcone 4 in Ovalbumin-Sensitized Asthmatic Mice.

OBJECTIVE: The chemokine CXCL12 interacting with the CXC receptor 4 (CXCR4) has been reported to play a role in the development and progression of bronchial asthma, but its mechanism of action is still unknown. The objective of this study was to assess the effect of the CXCL12 neutraligand chalcone 4 on the migration of dendritic cells (DCs) in a murine model of allergic airway inflammation. METHODS: A 21-day ovalbumin (OVA)-induced allergic-airway TH2 inflammation model in BALB/c mice was used. Four groups were sensitized with OVA adsorbed on alum and challenged either with OVA or saline for 4 days. Mice were treated intranasally with chalcone 4 (300 nmol/kg body weight) or solvent 2 h before each OVA or saline challenge; 24 h after the last challenge, CD11c+F4/80- DCs were counted in the bronchoalveolar lavage. Jugular-nodose ganglion complex (JNC) sections were sampled, and for immunofluorescence staining, cryocut sections were prepared. MHC II+F4/80- DCs as well as calcitonin gene-related peptide (CGRP)- and substance P (SP)-positive neuronal cell bodies were analyzed. RESULTS: In OVA-challenged mice, chalcone 4 caused a significantly decreased DC/neuron ratio in the JNC from 51.7% in solvent-treated to 32.6% in chalcone 4-treated mice. In parallel, chalcone 4 also decreased the DC population in BALF from 11.5 × 103 cells in solvent to 4.5 × 103 cells in chalcone 4-treated mice. By contrast, chalcone 4 had no effect on the expression of the neuropeptides CGRP and SP in JNC. CONCLUSION: This study reported the CXCL12 neutraligand chalcone 4 to affect DC infiltration into the airways and airway ganglia as well as to decrease airway eosinophilic inflammation and, therefore, validated CXCL12 as a new target in allergic disease models of asthma.

Parainfluenza 3-Induced Cough Hypersensitivity in the Guinea Pig Airways.

The effect of respiratory tract viral infection on evoked cough in guinea pigs was evaluated. Guinea pigs were inoculated intranasally with either parainfluenza type 3 (PIV3) and cough was quantified in conscious animals. The guinea pigs infected with PIV3 (day 4) coughed nearly three times more than those treated with the viral growth medium in response to capsaicin, citric acid, and bradykinin. Since capsaicin, citric acid, and bradykinin evoked coughing in guinea pigs can be inhibited by drugs that antagonize the transient receptor potential cation channel, subfamily V, member 1 (TRPV1), it was reasoned that the virally-induced hypertussive state may involve alterations in TPRV1 activity. PIV3 infection caused a phenotypic switch in tracheal nodose Aδ "cough receptors" such that nearly 50% of neurons began to express, de novo, TRPV1 mRNA. There was also an increase TRPV1 expression in jugular C-fiber neurons as determined by qPCR. It has previously been reported that tracheal-specific nodose neurons express the BDNF receptor TrkB and jugular neurons express the NGF receptor TrkA. Jugular neurons also express the artemin receptor GFRα3. All these neurotrophic factors have been associated with increases in TRPV1 expression. In an ex vivo perfused guinea pig tracheal preparation, we demonstrated that within 8 h of PIV3 infusion there was no change in NGF mRNA expression, but there was nearly a 10-fold increase in BDNF mRNA in the tissue, and a small but significant elevation in the expression of artemin mRNA. In summary, PIV3 infection leads to elevations in TRPV1 expression in the two key cough evoking nerve subtypes in the guinea pig trachea, and this is associated with a hypertussive state with respect to various TRPV1 activating stimuli.

One-day high-fat diet induces inflammation in the nodose ganglion and hypothalamus of mice.

A high-fat diet (HFD) induces inflammation in systemic organs including the hypothalamus, resulting in obesity and diabetes. The vagus nerve connects the visceral organs and central nervous system, and the gastric-derived orexigenic peptide ghrelin transmits its starvation signals to the hypothalamus via the vagal afferent nerve. Here we investigated the inflammatory response in vagal afferent neurons and the hypothalamus in mice following one day of HFD feeding. This treatment increased the number of macrophages/microglia in the nodose ganglion and hypothalamus. Furthermore, one-day HFD induced expression of Toll-like receptor 4 in the goblet cells of the colon and upregulated mRNA expressions of the proinflammatory biomarkers Emr1, Iba1, Il6, and Tnfα in the nodose ganglion and hypothalamus. Both subcutaneous administration of ghrelin and celiac vagotomy reduced HFD-induced inflammation in these tissues. HFD intake triggered inflammatory responses in the gut, nodose ganglion, and subsequently in the hypothalamus within 24 h. These findings suggest that the vagal afferent nerve may transfer gut-derived inflammatory signals to the hypothalamus via the nodose ganglion, and that ghrelin may protect against HFD-induced inflammation.

Allergen challenge sensitizes TRPA1 in vagal sensory neurons and afferent C-fiber subtypes in guinea pig esophagus.

Transient receptor potential A1 (TRPA1) is a newly defined cationic ion channel, which selectively expresses in primary sensory afferent nerve, and is essential in mediating inflammatory nociception. Our previous study demonstrated that TRPA1 plays an important role in tissue mast cell activation-induced increase in the excitability of esophageal vagal nodose C fibers. The present study aims to determine whether prolonged antigen exposure in vivo sensitizes TRPA1 in a guinea pig model of eosinophilic esophagitis (EoE). Antigen challenge-induced responses in esophageal mucosa were first assessed by histological stains and Ussing chamber studies. TRPA1 function in vagal sensory neurons was then studied by calcium imaging and by whole cell patch-clamp recordings in 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-labeled esophageal vagal nodose and jugular neurons. Extracellular single-unit recordings were performed in vagal nodose and jugular C-fiber neuron subtypes using ex vivo esophageal-vagal preparations with intact nerve endings in the esophagus. Antigen challenge significantly increased infiltrations of eosinophils and mast cells in the esophagus. TRPA1 agonist allyl isothiocyanate (AITC)-induced calcium influx in nodose and jugular neurons was significantly increased, and current densities in esophageal DiI-labeled nodose and jugular neurons were also significantly increased in antigen-challenged animals. Prolonged antigen challenge decreased esophageal epithelial barrier resistance, which allowed intraesophageal-infused AITC-activating nodose and jugular C fibers at their nerve endings. Collectively, these results demonstrated that prolonged antigen challenge sensitized TRPA1 in esophageal sensory neurons and afferent C fibers. This novel finding will help us to better understand the molecular mechanism underlying esophageal sensory and motor dysfunctions in EoE.

Neurogenic airway inflammation induced by repeated intra-esophageal instillation of HCl in guinea pigs.

This study was conducted to investigate if repeated intra-esophageal acid administrations may induce neurogenic inflammation in the airways and nodose ganglion in a guinea pig model. Guinea pigs were sedated and perfused with 0.1 N HCl in the distal esophagus via a nasoesophageal catheter for 14 consecutive days. Substance P (SP), neurokinin A (NKA), neurokinin B (NKB), and calcitonin gene-related peptide concentration were measured by ELISA or radioimmunoassay. Neuropeptide expression in the airways and nodose ganglion was detected by immunohistochemistry and assessed semi-quantitatively. Inflammation was found in the trachea and bronchi. There was a threefold increase in substance P concentration in the trachea, main bronchi, and lung homogenate and a twofold increase in NKA and NKB concentration in the main bronchi, lung homogenate, and bronchial alveolus lavage fluid, respectively. The SP and NKA expressions in the airways and nodose ganglion were also significantly increased. Chronic intra-esophageal acid instillation induces significant neurogenic inflammation in the airways and nodose ganglion in the vagus nerve in guinea pigs.

TRPV1 induction in airway vagal low-threshold mechanosensory neurons by allergen challenge and neurotrophic factors.

We addressed the hypothesis that allergic inflammation in guinea pig airways leads to a phenotypic switch in vagal tracheal cough-causing, low-threshold mechanosensitive Aδ neurons, such that they begin expressing functional transient receptor potential vanilloid (TRPV1) channels. Guinea pigs were actively sensitized to ovalbumin (OVA) and beginning 21 days later exposed via aerosol to OVA daily for 3 days. Tracheal-specific neurons were identified in the nodose ganglion using retrograde tracing techniques. Tracheal specific neurons were isolated, and mRNA expression was evaluated at the single-neuron level using RT-PCR analysis. Electrophysiological studies have revealed that the vast majority of vagal nodose afferent nerves innervating the trachea are capsaicin-insensitive Aδ-fibers. Consistent with this, we found <20% of these neurons express TRPV1 mRNA or respond to capsaicin in a calcium assay. Allergen exposure induced de novo TRPV1 mRNA in a majority of the tracheal-specific nodose neurons (P < 0.05). The allergen-induced TRPV1 induction was mimicked by applying either brain-derived neurotrophic factor (BDNF) or glial-derived neurotrophic factor (GDNF) to the tracheal lumen. The BDNF-induced phenotypic change observed at the level of mRNA expression was mimicked using a calcium assay to assess functional TRPV1 ion channels. Finally, OVA exposure induced BDNF and GDNF production in the tracheal epithelium, the immediate vicinity of the nodose Aδ -fibers terminations. The induction of TRPV1 in nodose tracheal Aδ -fibers would substantively expand the nature of stimuli capable of activating these cough-causing nerves.

House dust mite potentiates capsaicin-evoked Ca2+ transients in mouse pulmonary sensory neurons via activation of protease-activated receptor-2.

House dust mite (HDM) is a major source of allergen in house dust and has been suggested to be involved in the pathogenesis of asthma. In this study, we aimed to investigate whether HDM can modulate the sensitivity of pulmonary sensory neurons and, if so, to elucidate the underlying mechanism. Fura-2-based ratiometric Ca(2+) imaging was carried out to determine the effect of HDM extract on the capsaicin-evoked Ca(2+) transient in mouse vagal pulmonary sensory neurons. Pretreatment with HDM (50 µg ml(-1), 5 min) significantly enhanced the Ca(2+) transient evoked by capsaicin in these neurons isolated from wild-type mice. This potentiating effect of HDM was not antagonized by E-64, a selective cysteine protease inhibitor, but was completely prevented by AEBSF, a specific serine protease inhibitor. In addition, the potentiating effect of HDM on capsaicin-evoked Ca(2+) transient was absent in the pulmonary sensory neurons isolated from protease-activated receptor-2 (PAR(2)) knockout mice. Furthermore, the sensitizing effect of HDM was completely abolished by U73122, a phosholipase C inhibitor, or chelerythrine, a protein kinase C inhibitor. In summary, our results demonstrate that HDM, mainly through its serine protease activity, potentiates capsaicin-evoked Ca(2+) transient in mouse pulmonary sensory neurons via the activation of PAR(2) and the phosholipase C-protein kinase C intracellular transduction cascade.

Synergistic role of TRPV1 and TRPA1 in pancreatic pain and inflammation.

BACKGROUND & AIMS: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Airway hyper-responsiveness in allergic asthma in guinea-pigs is mediated by nerve growth factor via the induction of substance P: a potential role for trkA.

BACKGROUND: The neurotrophin nerve growth factor (NGF) has been implicated as a mediator in allergic asthma. Direct evidence that inhibition of NGF-induced activation of neurotrophin receptors leads to improvement of airway symptoms is lacking. We therefore studied the effects of inhibitors of NGF signal transduction on the development of airway hyper-responsiveness (AHR) and pulmonary inflammation in a guinea-pig model for allergic asthma. METHODS: Airway responsiveness to the contractile agonist histamine was measured in vivo in guinea-pigs that were sensitized and challenged with ovalbumin (OVA). Inflammatory cell influx and NGF levels were determined in bronchoalveolar lavage fluid (BALF). Substance P, a key mediator of inflammation, was measured in lung tissue by radioimmunoassay, while substance P immunoreactive neurons in nodose ganglia were measured by immunohistochemistry. RESULTS: OVA challenge induced an AHR after 24 h in OVA-sensitized guinea-pigs. This coincided with an increase in the amount of NGF in BALF. Simultaneously, an increase in the percentage of substance P immunoreactive neurons in the nodose ganglia and an increase in the amount of substance P in lung tissue were found. We used tyrosine kinase inhibitors to block the signal transduction of the high-affinity NGF receptor, tyrosine kinase A (trkA). Treatment with the tyrosine kinase inhibitors (K252a or tyrphostin AG879) both inhibited the development of AHR, and prevented the increase in substance P in the nodose ganglia and lung tissue completely whereas both inhibitors had no effect on baseline airway resistance. Neither treatment with K252a or tyrphostin AG879 changed the influx of inflammatory cells in the BALF due to allergen challenge. CONCLUSIONS: We conclude that substance P plays a role in the induction of AHR in our model for allergic asthma which is most likely mediated by NGF. As both tyrosine kinase inhibitors AG879 and K252a show a similar inhibitory effect on airway function after allergen challenge, although both tyrosine kinase inhibitors exhibit different non-specific inhibitory effects on targets other than trkA tyrosine kinases, it is likely that the induction of substance P derived from sensory nerves is mediated by NGF via its high-affinity receptor trkA.

Nerve growth factor-induced substance P in capsaicin-insensitive vagal neurons innervating the lower mouse airway.

BACKGROUND: Nerve growth factor (NGF) is elevated in allergic diseases such as bronchial asthma and can lead to an induction of substance P (SP) and related neuropeptides in guinea-pigs large-diameter, neurofilament-positive airway neurons. OBJECTIVE: In the present study, the effect of NGF on tyrosine kinase receptor trkA and the capsaicin receptor TRPV1 expression in airway-specific vagal sensory neurons located in the jugular-nodose ganglia complex (JNC) of mice was investigated. METHODS: Using retrograde neuronal tracing in combination with double-labelling immunohistochemistry, SP, trkA- and TRPV1-receptor expression was examined in airway-specific sensory neurons of BALB/c mice before and after NGF treatment. RESULTS: NGF injected into the lower airway was able to induce SP (13.0+/-2.03% vs. 5.9+/-0.33%) and trkA expression (78+/-2.66% vs. 60+/-2.11%) in larger diameter (>25 microm), capsaicin-insensitive and trkA-positive vagal sensory neurons that were retrograde-labelled with Fast Blue dye from the main stem bronchi. CONCLUSION: Based on the extent of SP and trkA co-expression in airway-specific neurons by NGF treatment, the present study suggests that, following a peripheral activation of trkA receptor on SP afferent by NGF which is elevated in allergic inflammation, there may be trkA-mediated SP induction to mediate neurogenic airway inflammation.

Dual sensory innervation of pulmonary neuroepithelial bodies.

The characteristics of the different populations of sensory nerve terminals that selectively contact pulmonary neuroepithelial bodies (NEBs) in rat lungs were investigated after chemical denervation with capsaicin and compared with control lungs. Vagal calbindin D28k and P2X(3) purinoceptor immunoreactive (IR) afferent nerve terminals contacting NEBs appeared to have their origin in the nodose ganglion. Thick CB/P2X(3)-IR nerve fibers were seen to be myelinated and to lose their myelin sheaths just before branching and protruding intraepithelially between the NEB cells. This vagal sensory component of the innervation of NEBs was not affected by capsaicin nor expressed capsaicin receptors (vanilloid receptor subtype 1). A second sensory nerve fiber population that selectively innervates pulmonary NEBs in the rat lung consists of thin unmyelinated nonvagal substance P/calcitonin gene-related peptide IR nerve fibers, contacting mainly the basal pole of pulmonary NEBs, and having their origin in dorsal root ganglia. In concordance with vanilloid receptor 1 expression on these nerve terminals, the spinal sensory substance P/calcitionin gene-related peptide-IR component of the innervation of NEBs was depleted by systemic capsaicin treatment. The complex sensory innervation pattern of pulmonary NEBs characterized in the present study strongly suggests that, physiologically, pulmonary NEBs represent a group of intraepithelial receptors that may be able to accommodate various local and central reflex actions, in relation to both chemo- and mechanosensory stimuli.

5-HT(3) receptors mediate inflammation-induced unmasking of functional tachykinin responses in vitro.

Exogenously applied tachykinins produce no measurable electrophysiological responses in the somata of vagal afferent neurons [nodose ganglion neurons (NGNs)] isolated from naive guinea pigs. By contrast, after in vitro antigen challenge of nodose ganglia from guinea pigs immunized with chick ovalbumin, approximately 60% (53 of 89) of NGNs were depolarized an average of 13 +/- 1.2 mV by substance P (SP; 100 nM; n = 53). Receptor antagonists and enzyme inhibitors were utilized to screen a number of mast cell-derived mediators for their role in the uncovering or "unmasking" of functional tachykinin receptors after antigen challenge. Two chemically distinct 5-hydroxytryptamine-3-receptor antagonists significantly reduced the percentage of NGNs displaying depolarizing SP responses. Treatment with Y-25130 (1 or 10 microM) or tropisetron (1 microM) 15 min before and during antigen challenge reduced the percentage of SP-responsive neurons to approximately 20 and approximately 15% respectively. These results suggest that activation of 5-hydroxytryptamine-3 receptors plays an integral role in the unmasking of functional tachykinin receptors after specific antigen challenge of nodose ganglia. The mediator(s) underlying tachykinin-receptor unmasking in the remainder of the NGNs has yet to be characterized. However, it does not appear to be histamine, prostanoids, or peptidoleukotrienes.

Intraepithelial vagal sensory nerve terminals in rat pulmonary neuroepithelial bodies express P2X(3) receptors.

The neurotransmitters/modulators involved in the interaction between pulmonary neuroepithelial bodies (NEBs) and the vagal sensory component of their innervation have not yet been elucidated. Because P2X(3) purinoreceptors are known to be strongly expressed in peripheral sensory neurons, the aim of the present study was to examine the localization of nerve endings expressing P2X(3) purinoreceptors in the rat lung in general and those contacting pulmonary NEBs in particular. Most striking were intraepithelial arborizations of P2X(3) purinoceptor-immunoreactive (IR) nerve terminals, which in all cases appeared to ramify between calcitonin gene-related peptide (CGRP)- or calbindin D28k (CB)-labeled NEB cells. However, not all NEBs received nerve endings expressing P2X(3) receptors. Using CGRP and CB staining as markers for two different sensory components of the innervation of NEBs, it was revealed that P2X(3) receptor and CB immunoreactivity were colocalized, whereas CGRP-IR fibers clearly formed a different population. The disappearance of characteristic P2X(3) receptor-positive nerve fibers in contact with NEBs after infranodosal vagal crush and colocalization of tracer and P2X(3) receptor immunoreactivity in vagal nodose neuronal cell bodies in retrograde tracing experiments further supports our hypothesis that the P2X(3) receptor-IR nerve fibers contacting NEBs have their origin in the vagal sensory nodose ganglia. Combination of quinacrine accumulation in NEBs, suggestive of the presence of high concentrations of adenosine triphosphate (ATP) in their secretory vesicles, and P2X(3) receptor staining showed that the branching intraepithelial P2X(3) receptor-IR nerve terminals in rat lungs were exclusively associated with quinacrine-stained NEBs. We conclude that ATP might act as a neurotransmitter/neuromodulator in the vagal sensory innervation of NEBs via a P2X(3) receptor-mediated pathway. Further studies are necessary to determine whether the P2X(3) receptor-expressing neurons, specifically innervating NEBs in the rat lung, belong to a population of P2X(3) receptor-IR nociceptive vagal nodose neurons.

GABA- and glutamate-immunoreactivity in sensory ganglia of cat: a quantitative analysis.

Several amino acids may function as neurotransmitters in the nervous system. The potential role of glutamate (Glu) and aspartate in excitatory responses was demonstrated and it was established that GABA and glycine act as inhibitory agents. The present study aimed at investigating the availability of Glu and GABA in certain feline sensory ganglia, i.e. the trigeminal (TrG), nodose and dorsal root ganglia (DRG). A significant part of the neurons were GABA-positive (19.5% to 23.5%). These were large-sized neurons as well as small- to medium-sized ones. The intensity of immunostaining varied from weak to strong. GABA-containing neuronal fibres were seen in the neuropil and some of them surrounded unstained ganglionic cells. The Glu-immunoreactive (IR) neuronal perikarya in all the investigated ganglia were 63.6% to 66.4%. The majority of positive cells were small- to medium-sized, but large primary sensory neurons were also seen. There was no difference between the intensity of the reaction in the primary sensory and small neurons. Glu-IR neuronal fibres were seen in close apposition to immunopositive as well as immunonegative neurons. In conclusion, in the TrG, nodose and DRG, GABA and glutamate are involved in neurotransmission. There is a significant number of GABAergic neurons in the investigated sensory ganglia of the cat. The difference in the expression of these amino acids suggests that they can act not only as neurotransmitters but also as modulators of sensory information.

Nitric oxide synthase-immunoreactive vagal afferent fibers in rat superior cervical ganglia.

Chronic (5-14 days) preganglionic denervation of the rat superior cervical ganglia by sectioning the cervical sympathetic trunk resulted in a time-related partial or complete loss of nitric oxide synthase (isoform I)-immunoreactive fibers and terminals surrounding many sympathetic ganglionic neurons. Unexpectedly, denervation unmasked many varicose nitric oxide synthase-immunoreactive fibers, some of which could be traced the entire length of the superior cervical ganglia. Injection of the retrograde tracer Fluorogold into the superior cervical ganglia labeled a population of nodose ganglion cells and of dorsal root ganglion cells from C8 to T3 segments. When the same sections were processed for nitric oxide synthase-immunoreactivity, 40% of the Fluorogold-containing nodose ganglion cells also expressed nitric oxide synthase-immunoreactivity, whereas colocalization was observed in only a few dorsal root ganglion cells. Similarly, injection of Fluorogold into denervated superior cervical ganglia labeled a population of nodose ganglion cells. Sectioning of all nerve trunks associated with the superior cervical ganglion prior to injection of Fluorogold, except the cervical sympathetic trunk, resulted in no detectable labeling of Fluorogold in the ipsilateral nodose ganglion cells. These results indicate that a population of rat nodose ganglion cells contain nitric oxide synthase and that some of these neurons project their axons through the superior cervical ganglion and terminate in the peripheral target tissues. The possibility that nitric oxide synthase-immunoreactive vagal afferent fibers may participate in nociception is considered.

Calcitonin gene-related peptide immunoreactivity in the nucleus of the tractus solitarius and the carotid receptors of the cat originates from peripheral afferents.

The presence and distribution of the calcitonin gene-related peptide was studied, using immunohistochemical techniques, in carotid receptors, in the nodose and glossopharyngeal ganglia and in the nucleus tractus solitarii of the cat. Seventy-seven per cent of the 42% of the nodose ganglion cells were labeled. Fine, sparsely branched immunoreactive terminal axonal arborizations were found in the carotid body; they disappeared after petrosal ganglionectomy. The intense immunoreactivity present in fibers in the commissural, medial, interstitial, gelatinosus, dorsal, intermediate and rostral gustatory subnuclei of the nucleus tractus solitarius was drastically reduced after removal of the ipsilateral nodose and petrosal ganglia. The central distribution of the immunoreactive axons, the morphology of the terminals in the carotid receptors and their dependence on an intact peripheral innervation are consistent with the idea that in the cat the calcitonin gene-related peptide is present in a high proportion of the primary visceral afferents, most of them unmyelinated.

A new monoclonal antibody against the GABA-protein conjugate shows immunoreactivity in sensory neurons of the rat.

A monoclonal antibody, 115AD5, was raised against GABA coupled to bovine serum albumin. The monoclonal antibody 115AD5 also reacted with other GABA-protein conjugates. The specificity of the monoclonal antibody was corroborated by enzyme-linked immunoassay, dot-immunobinding experiments and immunostaining of rat cerebellum sections. The monoclonal antibody 115AD5 could successfully be applied on Vibratome and cryostat sections using either indirect immunofluorescence or peroxidase techniques. In rat cerebellar cortex the monoclonal antibody 115AD5 gave an intense immunoreaction in stellate cells, in Golgi neurons, and in basket cells and their processes around Purkinje cell bodies. Purkinje cell dendrites showed GABA immunoreactivity while the cell bodies were non-reactive or only weakly reactive. There was labelling in some nuclei of Purkinje cells. GABA immunoreactivity was also found in dot-like structures in the granular layer. A large population of sensory neurons in rat thoracic and lumbar spinal dorsal root ganglia presented an intense immunoreactivity for the monoclonal antibody 115AD5. Nerve bundles immunoreactive for GABA were also seen in these ganglia. In the trigeminal ganglion, a major population of sensory neurons and some of their processes presented immunoreactivity for GABA. In the sensory nodose ganglion of the vagus nerve, many neuronal cell bodies and some fibres were immunoreactive for GABA. Ligation of the vagus nerve caudal to the ganglion resulted in an increased GABA immunoreactivity in neuronal somata of the ganglion, as well as in nerve fibres on the ganglionic side of the ligature. The present results suggest that in the rat, a population of sensory neurons in thoracic and lumbar spinal dorsal root ganglia, as well as in the trigeminal and nodose ganglia contain GABA. The presence of GABA immunoreactivity in these neurons raises the possibility of a neurotransmitter or modulator role.

Differential uptake of peroxidase (HRP) and peroxidase-lectin (HRP-WGA) conjugate injected in the nodose ganglion of the cat.

A comparison was made of the uptake and consequent axonal transport of peroxidase and peroxidase-lectin conjugate injected in low concentrations (0.167%) in the nodose ganglion of cats. At the light microscopic level horseradish peroxidase (HRP)-wheat germ agglutinin (WGA) intensely labeled only central terminal fields of vagal afferents (anterograde), while free HRP only labeled perikarya in vagal motor nuclei (passing retrograde). Low concentrations of these proteins, in addition to normal diffusion equilibria, permit a differential distribution of those species demonstrating some affinity for cell membranes. We attribute these differences in the uptake of HRP and HRP-WGA to the selective affinity of WGA for cell surface receptors (n-acetyl glucosamine) on the plasma membrane. This results in a greater number of WGA molecules coupled to HRP being internalized in any given endocytotic event compared to free HRP. The fractionation of efferent and passing fiber populations within a nodosal injection site can be discriminated with these different preparations.