Centrifugal gastric vagal afferent unit activities: another source of gastric "efferent" control.
ABSTRACT Our previous studies indicated that in rats about 10% of ventral gastric vagal efferent discharges do not originate from supracervical neural elements. To determine the origin of these efferent activities, an in vitro subdiaphragmatic vagus nerve-esophagus preparation was used. Action potentials with the same amplitude and waveform, and behaving 'all or none' characteristic are considered to be recorded from a nerve fiber and defined as an unit activity. Because these centrifugal unit activities were recorded from the proximal cut end of the ventral gastric vagal strands, they are ostensibly considered to be efferent activities. However, about 50% of unit action potential samples (21 out of 40) behave like unit activities recorded from mechanoreceptive afferent fibers. They have spot-like or diffuse mechanoreceptive fields on the subdiaphragmatic esophagus. When these receptive fields were stimulated the sensory nerve terminals in the fields generate afferent unit action potentials. These afferent potentials not only propagate orthodromically to the central nerve system, but also can be transmitted centrifugally to the gastric branches of the same vagal afferent neuron. Together with the efferent discharges of gastric vagal motor neurons, these centrifugal sensory potentials can be intercepted from the proximal cut end of gastric vagal nerve strands at gastroesophageal junction. Three types of mechanoresponsive centrifugal afferent unit activities were observed: rapidly adapting (n = 8), with or without after-discharge; slowly adapting (n = 8), with or without after-discharge, and initial high frequency followed by a plateau, with long-lasting after-discharge (n = 5). Of the tested units (n = 24), 25% were either activated or inhibited by esophageal inflation and 23% (n = 22) by esophageal deflation. It is evident that not all centrifugal unit action potentials recorded from the proximal cut end of gastric vagal nerve strands are generated from the vagal motor neurons, the recorded centrifugal unit activities may contain antidromic unit action potentials generated from the esophageal collateral branches of the gastric vagal afferent nerve fibers. These results suggest that gastric vagal afferent neurons possess collateral branches innervating the esophagus, activation of esophageal terminals may exert an effect on the gastric terminals via collateral reflex, analogous to the 'axon reflex' mechanism.
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ABSTRACT: A method for assessing the performance of microbial fuel cells (MFCs) is the polarisation sweep where different external resistances are applied at set intervals (sample rates). The resulting power curves often exhibit an overshoot where both power and current decrease concomitantly. To investigate these phenomena, small-scale (1 mL volume) MFCs operated in continuous flow were subjected to polarisation sweeps under various conditions. At shorter sample rates the overshoot was more exaggerated and power generation was overestimated; sampling at 30 s produced 23% higher maximum power than at 3 min. MFCs with an immature anodic biofilm (5 days) exhibited a double overshoot effect, which disappeared after a sufficient adjustment period (5 weeks). Mature MFCs were subject to overshoot when the anode was fed weak (1 mM acetate) feedstock with low conductivity (<100 μS) but not when fed with a higher concentration (20 mM acetate) feedstock with high conductivity (>1500 μS). MFCs developed in a pH neutral environment produced overshoot after the anode had been exposed to acidic (pH 3) conditions for 24 h. In contrast, changes to the cathode both in terms of pH and varying catholyte conductivity, although affecting power output did not result in overshoot suggesting that this is an anodic phenomenon.Bioelectrochemistry (Amsterdam, Netherlands) 01/2011; 81(1):22-7. · 2.65 Impact Factor
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ABSTRACT: • Colonic afferent fibres were recorded using a novel in vitro preparation. Fibres with endings in the colonic mucosa are described, along with those in muscle and serosa, and their responses to a range of mechanical and chemical luminal stimuli. • Mechanical stimuli were applied to the tissue, which included stretch, blunt probing of the mucosa and stroking of the mucosa with von Frey hairs (10-1000 mg). Chemical stimuli were applied into a ring that was placed over the mechanoreceptive field of the fibre; these were distilled water, 154 and 308 mM NaCl, 100 M capsaicin, 50 mM HCl, and undiluted and 50 % ferret bile. • Recordings were made from 52 fibres, 12 of which showed characteristics of having endings in the mucosa. Mucosal afferents were sensitive to a 10 mg von Frey hair and were generally chemosensitive to ≥ 1 chemical stimulus. • Ten fibres showed characteristics of having receptive fields in the muscular layer. These fibres responded readily to circumferential stretch, as well as to blunt probing. • Twenty-seven fibres showed characteristics of having endings in the serosal layer. They adapted rapidly to circumferential stretch and responded to blunt probing of the serosa. Fifteen of 19 serosal fibres tested also responded to luminal chemicals. • Three fibres were unresponsive to all mechanical stimuli but were recruited by chemical stimuli. • This is the first characterization of colonic afferent fibres using an in vitro method and the first documentation of afferent fibres with their endings in the mucosa of the colon. These fibres are likely to be important in aspects of colonic sensation and reflex control.The Journal of Physiology 09/2004; 518(1):271 - 282. · 4.38 Impact Factor
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ABSTRACT: Intramuscular arrays (IMAs), vagal mechanoreceptors that innervate gastrointestinal smooth muscle, have not been completely described structurally or functionally. To delineate more fully the architecture of IMAs and to consider the structure-function implications of the observations, the present experiment examined the organization of the IMA terminal arbors and the accessory tissue elements of those arbors. IMA terminal fields, labeled by injection of biotinylated dextran into the nodose ganglia, were examined in whole mounts of rat gastric smooth muscle double-labeled with immunohistochemistry for interstitial cells of Cajal (ICCs; c-Kit) and/or inputs of different neuronal efferent transmitter (markers: tyrosine hydroxylase (TH), vesicular acetylcholine transporter (VAChT), and nitric oxide synthase (NOS)) or afferent neuropeptidergic (calcitonin gene-related peptide (CGRP)) phenotypes. IMAs make extensive varicose and lamellar contacts with ICCs. In addition, axons of the multiple efferent and afferent phenotypes examined converge and articulate with IMA terminal arbors innervating ICCs. This architecture is consistent with the hypothesis that IMAs, or the multiply innervated IMA-ICC complexes they form, can function as stretch receptors. The tissue organization is also consonant with the proposal that those units can operate as functional analogues of muscle spindle organs. For electrophysiological assessments of IMA functions, experiments will need protocols that preserve both the complex architecture and the dynamic operations of IMA-ICC complexes.Neuroscience 07/2011; 186:188-200. · 3.12 Impact Factor