Differential effects of intragastric acid and capsaicin on gastric emptying and afferent input to the rat spinal cord and brainstem

BACKGROUND: Hydrochloric acid (HCl) is a potential threat to the integrity of the gastric mucosa and is known to contribute to upper abdominal pain. We have previously found that gastric mucosal challenge with excess HCl is signalled to the rat brainstem, but not spinal cord, as visualized by expression of c-fos messenger ribonucleic acid (mRNA), a surrogate marker of neuronal excitation. This study examined whether gastric mucosal exposure to capsaicin, a stimulant of nociceptive afferents that does not damage the gastric mucosa, is signalled to both brainstem and spinal cord and whether differences in the afferent signalling of gastric HCl and capsaicin challenge are related to different effects on gastric emptying. RESULTS: Rats were treated intragastrically with vehicle, HCl or capsaicin, activation of neurons in the brainstem and spinal cord was visualized by in situ hybridization autoradiography for c-fos mRNA, and gastric emptying deduced from the retention of intragastrically administered fluid. Relative to vehicle, HCl (0.5 M) and capsaicin (3.2 mM) increased c-fos transcription in the nucleus tractus solitarii by factors of 7.0 and 2.1, respectively. Capsaicin also caused a 5.2-fold rise of c-fos mRNA expression in lamina I of the caudal thoracic spinal cord, although the number of c-fos mRNA-positive cells in this lamina was very small. Thus, on average only 0.13 and 0.68 c-fos mRNA-positive cells were counted in 0.01 mm sections of the unilateral lamina I following intragastric administration of vehicle and capsaicin, respectively. In contrast, intragastric HCl failed to induce c-fos mRNA in the spinal cord. Measurement of gastric fluid retention revealed that HCl suppressed gastric emptying while capsaicin did not. CONCLUSION: The findings of this study show that gastric mucosal exposure to HCl and capsaicin is differentially transmitted to the brainstem and spinal cord. Since only HCl blocks gastric emptying, it is hypothesized that the two stimuli are transduced by different afferent pathways. We infer that HCl is exclusively signalled by gastric vagal afferents whereas capsaicin is processed both by gastric vagal and intestinal spinal afferents

Neuroantibodies: Ectopic expression of a recombinant anti-substance P antibody in the central nervous system of transgenic mice

AbstractRecombinant antibodies are efficiently secreted by cells of the nervous system. Thus, their local expression in the CNS of transgenic mice could be used to perturb the function of the corresponding antigen. As a first application of this approach, we have generated transgenic mice that express antibodies against the neuropeptide substance P, under the transcriptional control of the promoter of the neuronal gene vgf. The transgenic antibodies are expressed in a tissue-specific and developmentally regulated manner and are effective in competing with the endogenous substance P, as demonstrated by a marked Inhibition of neurogenic inflammation and by motor deficits. This phenotypic knockout approach may provide a complementary alternative to gene knockout by homologous recombination

EP4 receptor stimulation down-regulates human eosinophil function

Accumulation of eosinophils in tissue is a hallmark of allergic inflammation. Here we observed that a selective agonist of the PGE2 receptor EP4, ONO AE1-329, potently attenuated the chemotaxis of human peripheral blood eosinophils, upregulation of the adhesion molecule CD11b and the production of reactive oxygen species. These effects were accompanied by the inhibition of cytoskeletal rearrangement and Ca2+ mobilization. The involvement of the EP4 receptor was substantiated by a selective EP4 antagonist, which reversed the inhibitory effects of PGE2 and the EP4 agonist. Selective kinase inhibitors revealed that the inhibitory effect of EP4 stimulation on eosinophil migration depended upon activation of PI 3-kinase and PKC, but not cAMP. Finally, we found that EP4 receptors are expressed by human eosinophils, and are also present on infiltrating leukocytes in inflamed human nasal mucosa. These data indicate that EP4 agonists might be a novel therapeutic option in eosinophilic diseases

Activated prostaglandin D2 receptors on macrophages enhance neutrophil recruitment into the lung

BackgroundProstaglandin (PG) D2 is an early-phase mediator in inflammation, but its action and the roles of the 2 D-type prostanoid receptors (DPs) DP1 and DP2 (also called chemoattractant receptor–homologous molecule expressed on TH2 cells) in regulating macrophages have not been elucidated to date.ObjectiveWe investigated the role of PGD2 receptors on primary human macrophages, as well as primary murine lung macrophages, and their ability to influence neutrophil action in vitro and in vivo.MethodsIn vitro studies, including migration, Ca2+ flux, and cytokine secretion, were conducted with primary human monocyte-derived macrophages and neutrophils and freshly isolated murine alveolar and pulmonary interstitial macrophages. In vivo pulmonary inflammation was assessed in male BALB/c mice.ResultsActivation of DP1, DP2, or both receptors on human macrophages induced strong intracellular Ca2+ flux, cytokine release, and migration of macrophages. In a murine model of LPS-induced pulmonary inflammation, activation of each PGD2 receptor resulted in aggravated airway neutrophilia, tissue myeloperoxidase activity, cytokine contents, and decreased lung compliance. Selective depletion of alveolar macrophages abolished the PGD2-enhanced inflammatory response. Activation of PGD2 receptors on human macrophages enhanced the migratory capacity and prolonged the survival of neutrophils in vitro. In human lung tissue specimens both DP1 and DP2 receptors were located on alveolar macrophages along with hematopoietic PGD synthase, the rate-limiting enzyme of PGD2 synthesis.ConclusionFor the first time, our results show that PGD2 markedly augments disease activity through its ability to enhance the proinflammatory actions of macrophages and subsequent neutrophil activation