A comparison of sensory nerve function in human, guinea-pig, rabbit and marmoset airways.

We have investigated the role of sensory nerves in regulating airway smooth muscle function in the guinea-pig, marmoset, rabbit and man. Tissue levels of the sensory neuropeptides CGRP and substance P in the airways of the guinea-pig were significantly greater compared with the rabbit and marmoset. The relative order of tissue content was guinea-pig >>> rabbit = marmoset. Marmoset bronchial and tracheal preparations responded weakly to exogenously administered substance P and neurokinin A but contracted to methacholine and demonstrated atropine-sensitive cholinergic responses. In marmoset, rabbit and human airway preparations, capsaicin mediated weak contractile responses to exogenously administered capsaicin. However, high concentrations of capsaicin elicited a relaxation response that was epithelium-independent, cyclo-oxygenase-insensitive, not involving nitric oxide and not dependent on the activation of capsaicin-sensitive afferents. These results suggest that rabbit and marmoset airways respond functionally in a similar way to human airway preparations and maybe more relevant than guinea-pig airways with regard to understanding the role of sensory neuropeptides in airways.

Selective stimulation of jugular ganglion afferent neurons in guinea pig airways by hypertonic saline.

We evaluated the ability of hyperosmolar stimuli to activate afferent nerves in the guinea pig trachea and main bronchi and investigated the neural pathways involved. By using electrophysiological techniques, studies in vitro examined the effect of hyperosmolar solutions of sodium chloride (hypertonic saline) on guinea pig airway afferent nerve endings arising from either vagal nodose or jugular ganglia. The data reveal a differential sensitivity of airway afferent neurons to activation with hypertonic saline. Afferent fibers (both A delta and C fibers) with cell bodies located in jugular ganglia were much more sensitive to stimulation with hypertonic saline, compared with afferent neurons with cell bodies located in nodose ganglia. Additional studies in vivo demonstrated that inhalation of aerosols of hypertonic saline induced plasma extravasation in guinea pig trachea that was mediated via tachykinin NK1 receptors. Identification of a differential sensitivity of guinea pig airway afferent nerves to hypertonic saline leads to the speculation that airway responses to hyperosmolar stimuli may result from activation of afferent neurons originating predominantly from the jugular ganglion.

The effect of 15-HPETE on airway responsiveness and pulmonary cell recruitment in rabbits.

1. In the present study we have investigated the effect of 15-hydroperoxyeicosatetraenoic acid (15-HPETE) and 15-hydroxyeicosatetraenoic acid (15-HETE) on airway responsiveness to inhaled histamine in rabbits in vivo. 2. 15-HPETE increased airway responsiveness to histamine 24 h after tracheal instillation and this was associated with a cellular infiltration consisting mainly of neutrophils, as measured by bronchoalveolar lavage. The airway hyperresponsiveness induced by 15-HPETE was still present 72 h after tracheal instillation of 15-HPETE, but had returned to baseline values one week post challenge. The number of neutrophils in bronchoalveolar lavage remained significantly elevated compared to pre-challenge levels. In contrast to 15-HPETE, the major metabolite 15-HETE, failed to alter airway hyperresponsiveness to histamine despite the recruitment of neutrophils into the lung, suggesting that the effect of 15-HPETE was not secondary to the generation of this metabolite nor dependent on the influx of neutrophils. 3. Both capsaicin and atropine but not the peripherally acting mu-opioid receptor agonist, BW443C (H-Tyr-D-Arg-Gly-Phe(4-NO2)-Pro-NH4), attenuated 15-HPETE-induced hyperresponsiveness. The increased cellular infiltration induced by 15-HPETE was only attenuated by capsaicin. 4. The results of the present study suggest that the release of 15-HPETE into the airways could contribute to sensitization of afferent nerve endings analogous to the hyperalgesia induced by this mediator in skin.

Effect of nedocromil sodium on neurogenic mechanisms in vitro.

We have developed a guinea pig model that allows monitoring of single afferent nerve fiber activity after stimulation of tracheal nerve endings with various stimuli. Action potentials from nodose or jugular neurons are recorded extracellularly. Previous experiments have shown that the excitability of the nerve endings to, for example, mechanical stimuli can be increased by antigen challenge of presensitized guinea pigs. Nedocromil sodium 10(-4) mol/L significantly reduced by more than 50% the generation of action potentials in C fibers in response to stimulation by capsaicin. The precise mechanism is not known, although the membrane depolarization induced by capsaicin was reduced in the presence of nedocromil sodium. This agent did not have a generalized inhibitory effect on afferent excitability because it had no effect on sensitivity to electrical or mechanical stimuli. Nedocromil sodium did not affect the generation of action potentials in A delta and C fibers in the presence of hypertonic saline solution.

Evidence that enhanced nasal reactivity to bradykinin in patients with symptomatic allergy is mediated by neural reflexes.

OBJECTIVE: The aim of this study was to determine whether allergic inflammation induces nasal hyperreactivity to bradykinin by enhancing neuronal responsiveness. METHODS: We compared the response to localized, unilateral nasal challenge with bradykinin in patients with perennial allergic rhinitis and nonallergic subjects, and in patients with seasonal allergic rhinitis challenged in and out of season. Weights of secretions from each nostril were recorded, and levels of albumin and lactoferrin in secretions recovered from each nostril were assayed. Contralateral administration of atropine (0.32 mg) was used to evaluate the role of cholinergic reflexes in nasal hyperresponsiveness to bradykinin. RESULTS: In patients with symptomatic allergy, bradykinin induced greater symptom scores than in asymptomatic atopic or nonallergic control subjects. Moreover, bradykinin caused sneezing in a majority of patients with symptomatic allergy but in none of the asymptomatic atopic or nonallergic control subjects. Only patients with symptomatic allergy showed dose-dependent bilateral increases in secretion weights and levels of the serous glandular marker, lactoferrin. In contrast, bradykinin induced similar increases in ipsilateral, but not contralateral, levels of albumin in all patient populations. Atropine inhibited contralateral secretion and lactoferrin production (p < 0.05) in patients with symptomatic allergy. CONCLUSION: The induction of sneezing and of atropine-inhibitable contralateral glandular secretion demonstrates that allergic inflammation causes nasal hyperreactivity to bradykinin, at least in part, by enhancing neuronal responsiveness.

Immunomodulation of afferent neurons in guinea-pig isolated airway.

1. The trachea, larynx and main bronchi with the right vagus nerve and nodose ganglion were isolated from guinea-pigs passively immunized 24 h previously with serum containing anti-ovalbumin antibody. 2. The airways were placed in one compartment of a Perspex chamber for recording of isometric tension while the nodose ganglion and attached vagus nerve were pulled into another compartment. Action potentials arriving from single airway afferent nerve endings were monitored extracellularly using a glass microelectrode positioned near neuronal cell bodies in the ganglion. Mechanosensitivity of the nerve endings was quantified using calibrated von Frey filaments immediately before and after exposure to antigen (10 micrograms ml-1 ovalbumin). 3. Ten endings responded to the force exerted by the lowest filament (0.078 mN) and were not further investigated. In airways from thirteen immunized guinea-pigs, the mechanical sensitivity of A delta afferent fibres (conduction velocity = 4.3 +/- 0.6 m s-1) was enhanced 4.1 +/- 0.9-fold following airway exposure to antigen (P < 0.005). Mechanical sensitivities of afferent fibres (conduction velocity = 4.3 +/- 0.6 m s-1) from non-immunized control guinea-pig airways were unaffected by antigen (n = 13). 4. Antigen did not overtly cause action potential generation except in one instance when the receptive field was located over the smooth muscle. This ending also responded to methacholine suggesting that spatial changes in the receptive field, induced by muscle contraction, were responsible for the activation. 5. The mediators responsible for these effects are unknown, although histamine, prostaglandins, leukotrienes and tachykinins do not appear to be essential. The increase in mechanical responsiveness was not associated with the smooth muscle contraction since leukotriene C4, histamine and tachykinins, which all caused a similar contraction to antigen, did not affect mechanical thresholds. Moreover, the antigen-induced increases in excitability persisted beyond the duration of the smooth muscle contraction. 6. These results demonstrate that antigen-antibody-mediated inflammatory processes may enhance the excitability of vagal afferent nerve terminals projecting from the airway and thus may contribute to the pathophysiology of allergic airway diseases.

Effects of intranasal administration of endothelin-1 to allergic and nonallergic individuals.

Endothelin-1 (ET-1), a 21 amino acid peptide, and its receptors are distributed in the mammalian respiratory tract. To examine the responses of human upper airways to ET-1, we investigated the effects of intranasal administration of ET-1 to nine symptomatic allergic and nine nonallergic volunteers. Paper discs were used to administer ET-1 or diluent to one side of the nasal mucosa, and to collect secretions from the ipsilateral (challenged) and contralateral (opposite) nostrils. ET-1 (0.3-10 micrograms), but not diluent, induced dose-dependent bilateral increases in secretion weights, lysozyme secretion, symptoms of rhinorrhea and itch, and sneezing in both populations. ET-1 did not induce albumin secretion, histamine release, or symptoms of nasal congestion. Compared with the nonallergic subjects, allergic individuals sneezed more and had significantly higher bilateral secretion weights, contralateral lysozyme secretion, and symptoms of rhinorrhea following ET-1 provocation. In summary, ET-1 induced symptoms relevant to inflammatory upper airway diseases in allergic and nonallergic subjects. However, responses of allergic subjects were more pronounced, particularly with respect to symptoms associated with neural reflex responses, such as sneezing and contralateral secretion. Therefore, allergic inflammation enhances responsiveness of the nasal mucosa to ET-1.

Neurophysiology of mast cell-nerve interactions in the airways.

The sensitized guinea pig was employed as a model to study the effect of immunological activation of resident mast cells on neuronal activity in the airways. The trachea was isolated with the vagus nerves and vagal sensory ganglia intact. Using conventional electrophysiological recording techniques, we noted that antigenic stimulation led to an increase in the sensitivity of sensory nerve endings located in the airway wall. Moreover, previous work has revealed that antigen challenge potentiates action-potential-driven tachykinin release from afferent fibers in the guinea pig isolated airway. Anatomical and electrophysiological studies indicate that tachykinin-containing sensory fibers directly innervate the local parasympathetic ganglion neurons in the airway. Therefore, antigen-induced increases in the excitability of sensory fibers in the airways can increase parasympathetic tone in the airway by increasing central and peripheral reflex arcs. In addition, we have found that antigen stimulation has direct effects on the excitability of the parasympathetic ganglion neurons. Considered together, the data demonstrate that increased vagal sensory and parasympathetic activity may be a consequence of the allergic reaction in the airways.

A novel animal model for investigating persistent airway hyperresponsiveness.

The present study investigates the development and maintenance of airway hyperresponsiveness in neonatally immunized rabbits. Rabbits were immunized within 24 hr of birth with the antigen Alternaria tenuis together with aluminum hydroxide as an adjuvant, followed by repeated antigen and adjuvant administration up to 3 months of age. Anesthetized, spontaneously breathing rabbits immunized according to this protocol exhibited a 3.7- (p < 0.01) and 1.8-fold (p < 0.05) increase in airway responsiveness to inhaled histamine when compared with groups of naive or sham-immunized rabbits, respectively. In the absence of further antigen challenge, these changes in airway responsiveness to histamine in a subpopulation of antigen-immunized rabbits persisted for up to 12 months of age. This hyperresponsiveness was not associated with an alteration in either total or differential inflammatory cell numbers as assessed by bronchoalveolar lavage (BAL), and no significant differences in isolated bronchial smooth muscle responsiveness to methacholine, histamine, theophylline, or electrical field stimulation were observed. These results demonstrate that neonatal immunization of rabbits with Alternaria tenuis can lead to the development of persistent airway hyperresponsiveness, and that the maintenance of this state is unrelated to either a detectable alteration in cellular infiltration within the airway lumen or changes in bronchial smooth muscle responsiveness. It is suggested that neonatal exposure to antigen and adjuvant may be important determinants for the development of persistent airway hyperresponsiveness. This animal model may provide a useful way to investigate the effects of drugs on airway hyperresponsiveness.

The effect of neonatal capsaicin on the development of bronchial hyperresponsiveness in allergic rabbits.

We have investigated the effects of neonatal capsaicin treatment of rabbits on the development of bronchial hyperresponsiveness following allergen exposure from birth. In vivo airways responsiveness was assessed as the concentrations of histamine to cause a 35% decrease in compliance (PC35) and a 50% increase in resistance (PC50). Rabbits treated with vehicle capsaicin (10% ethanol, 10% tween 80 and 80% saline) and then immunised with Altenaria tenius (40,000 protein nitrogen units (PNU)/ml + AL(OH)3 + saline in a ratio 2:1:1) were more responsive to aerosol histamine in vivo at three months of age when compared to sham-immunised (AL(OH)3 + saline 1:3) or saline-treated rabbits for compliance measurements (P < 0.05). However, immunised rabbits although not significantly different to sham-immunised (P > 0.05) were significantly more responsive than saline-treated rabbits for resistance measurements (P < 0.05). Neonatal capsaicin treatment significantly attenuated the increased responsiveness seen in immunised rabbits for both compliance and resistance measurements (P < 0.05). The bronchial hyperresponsiveness is unlikely to be due to cellular infiltration per se as cell numbers assessed by bronchoalveolar lavage were not significantly different between groups (P > 0.05). Exogenous in vitro functional bronchial responses to capsaicin were increased in vehicle-immunised rabbits, an effect attenuated by neonatal capsaicin treatment (P < 0.05) whereas responses to methacholine, histamine or electrical field stimulation remained similar between groups (P > 0.05). Bronchial levels of calcitonin gene-related peptide- and substance P-like immunoreactivity were unaffected by any treatment (P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)