tetrodotoxin and Ileitis

We investigated the responses of morphologically identified myenteric neurons of the guinea-pig ileum to inflammation that was induced by the intraluminal injection of trinitrobenzene sulphonate, 6 or 7 days previously. Electrophysiological properties were examined with intracellular microelectrodes using in vitro preparations from the inflamed or control ileum. The neurons were injected with marker dyes during recording and later they were recovered for morphological examination. A proportion of neurons with Dogiel type I morphology, 45% (32/71), from the inflamed ileum had a changed phenotype. These neurons exhibited an action potential with a tetrodotoxin-resistant component, and a prolonged after-hyperpolarizing potential followed the action potential. Of the other 39 Dogiel type I neurons, no changes were observed in 36 and 3 had increased excitability. The afterhyperpolarizing potential (AHP) in Dogiel type I neurons was blocked by the intermediate conductance, Ca(2+)-dependent K(+) channel blocker TRAM-34. Neurons which showed these phenotypic changes had anally directed axonal projections. Neither a tetrodotoxin-resistant action potential nor an AHP was seen in Dogiel type I neurons from control preparations. Dogiel type II neurons retained their distinguishing AH phenotype, including an inflection on the falling phase of the action potential, an AHP and, in over 90% of neurons, an absence of fast excitatory transmission. However, they became hyperexcitable and exhibited anodal break action potentials, which, unlike control Dogiel type II neurons, were not all blocked by the h current (I(h)) antagonist Cs(+). It is concluded that inflammation selectively affects different classes of myenteric neurons and causes specific changes in their electrophysiological properties.

Topics: Action Potentials; Animals; Disease Models, Animal; Guinea Pigs; Ileitis; Ileum; Intermediate-Conductance Calcium-Activated Potassium Channels; Myenteric Plexus; Neurons; Phenotype; Potassium Channel Blockers; Pyrazoles; Synaptic Transmission; Tetrodotoxin; Time Factors; Trinitrobenzenesulfonic Acid

Intestinal inflammation induces hyperexcitability of dorsal root ganglia sensory neurons, which has been implicated in increased pain sensation. This study examined whether alteration of sodium (Na+) and/or potassium (K+) currents underlies this hyperexcitability. Ileitis was induced in guinea pig ileum with trinitrobenzene sulphonic acid (TBNS) and dorsal root ganglion neurons innervating the site of inflammation were identified by Fast Blue or DiI fluorescence labelling. Whole cell recordings were made from acutely dissociated small-sized neurons at 7-10 days. Neurons exhibited transient A-type and sustained outward rectifier K+ currents. Compared to control, both A-type and sustained K+ current densities were significantly reduced (42 and 34%, respectively; P < 0.05) in labelled neurons from the inflamed intestine but not in non-labelled neurons. A-type current voltage dependence of inactivation was negatively shifted in labelled inflamed intestine neurons. Neurons also exhibited tetrodotoxin-sensitive and resistant Na+ currents. Tetrodotoxin-resistant sodium currents were increased by 37% in labelled neurons from the inflamed intestine compared to control (P < 0.01), whereas unlabelled neurons were unaffected. The activation and inactivation curves of these currents were unchanged by inflammation. These data suggest ileitis increases excitability of intestinal sensory neurons by modulating multiple ionic channels. The lack of effect in non-labelled neurons suggests signalling originated at the nerve terminal rather than through circulating mediators and, given that Na+ currents are enhanced whereas K+ currents are suppressed, one or more signalling pathways may be involved.

Topics: Animals; Drug Resistance; Electric Conductivity; Female; Ganglia, Spinal; Guinea Pigs; Ileitis; Ion Channel Gating; Male; Models, Biological; Neurons, Afferent; Potassium Channels; Potassium Channels, Voltage-Gated; Sodium Channels; Tetrodotoxin; Trinitrobenzenesulfonic Acid

The efferent secretomotor activity of capsaicin-sensitive nerves was monitored during the evolution of 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced ileitis in the guinea pig by recording changes in short-circuit current (DeltaI(sc)) in response to capsaicin, substance P (SP), and carbachol. Submucosal-mucosal preparations mounted in standard Ussing chambers were studied at time 0, at 8 h, and 1, 3, 5, 7, 14, and 30 days following the intraluminal instillation of TNBS or saline. Maximal DeltaI(sc) responses to capsaicin were dramatically attenuated (54%) by 24 h. By day 7, SP- and TTX-insensitive carbachol-stimulated DeltaI(sc) were also significantly reduced. Similar attenuation in capsaicin and carbachol responses was observed in jejunal tissue 20 cm proximal to the inflamed site at day 7. These studies demonstrate that efferent secretomotor function of capsaicin-sensitive nerves is maintained early in TNBS ileitis but significantly reduced by 24 h. By day 7, defects in enterocyte secretory function at inflamed and noninflamed sites also occurred, an effect that may be mediated by circulating cytokines.

Topics: Anesthetics, Local; Animals; Biological Transport; Capsaicin; Carbachol; Cholinergic Agonists; Electric Stimulation; Electrolytes; Epithelial Cells; Guinea Pigs; Ileitis; Ileum; Intestinal Mucosa; Submucous Plexus; Substance P; Tetrodotoxin; Time Factors; Trinitrobenzenesulfonic Acid

Spontaneous in vivo phasic contractions are suppressed during ileal inflammation. The aim of this study was to test the hypothesis that modulation of the contractile response to muscarinic receptor activation contributes to this inhibition.. Muscarine, methacholine, and arecaidine propargyl ester were infused close-intra-arterially in the normal and inflamed ileum of conscious dogs. Concurrent studies were performed on in vitro muscle strips.. Prior close-intra-arterial infusions of tetrodotoxin or hexamethonium had no significant effect on the contractile response to any agonist, indicating that they acted primarily on smooth muscle muscarinic receptors. The contractile response to each agonist was suppressed significantly during inflammation. The median inhibitory dose of 4-diphenylacetoxy-N-methyl-piperidine methiodide (4-DAMP) was 57-244-fold smaller than that of pirenzepine, methoctramine, and tropicamide to inhibit the contractile response to muscarine. Inflammation induced a significant leftward shift in the inhibitory dose-response curve to methoctramine but not to 4-DAMP, pirenzepine, or tropicamide. The data from in vitro muscle strips were similar to those in conscious dogs.. Inflammation suppresses the phasic contractile response to muscarinic receptor activation in circular smooth muscle cells. The spontaneous and muscarinic agonist-stimulated in vivo phasic contractions of ileal circular smooth muscle cells are mediated primarily by M3 receptors.

Topics: Animals; Dogs; Female; Ileitis; In Vitro Techniques; Male; Muscarinic Agonists; Muscle Contraction; Muscle, Smooth; Myoelectric Complex, Migrating; Receptors, Muscarinic; Tetrodotoxin