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) 04/2011; 81(1):22-7. DOI:10.1016/j.bioelechem.2011.01.001 · 3.87 Impact Factor
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ABSTRACT: The effect of short-term lower esophageal distension on intragastric pressure (IGP) and the related neural pathways involved were investigated in urethane-anesthetized rats in which enteric nervous system connections were interrupted by ligations of the pylorus and the gastroesophageal junction while keeping the gastric vagus nerve trunks intact. Under these conditions, lower esophageal distension with a bolus of 0.2 to 0.5 ml saline in 0.1 ml step increments, raised the inside esophagus balloon pressure from 1.89 +/- 0.17 to 4.21 +/- 0.13 cm H2O and reduced IGP from -0.42 +/- 0.08 to -0.77 +/- 0.12 cm H2O, respectively. Bilateral cervical vagotomy partly blocked the gastric relaxation induced by 0.5 ml esophageal distension from -0.77 +/- 0.12 to -0.34 +/- 0.02 cm H2O; in contrast, a further bilateral splanchnectomy partly rebounded the effect of 0.5 ml esophageal distension from -0.34 +/- 0.02 to -0.46 +/- 0.05 cm H2O. These results suggest that the enteric nervous system may not play a prominent role in acute esophageal distension induced-gastric relaxation. However, more than 50% of this effect is central nervous system mediated (via the long vago-vagal reflex). The other 40% can be maintained without central and enteric nervous systems involvement, probably via a proposed gastric vagal afferent-esophageal collateral reflex.Journal of the Autonomic Nervous System 04/1997; 63(1-2):12-8. DOI:10.1016/S0165-1838(96)00126-9
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ABSTRACT: Smooth muscles are complex tissues containing a variety of cells in addition to muscle cells. Interstitial cells of mesenchymal origin interact with and form electrical connectivity with smooth muscle cells in many organs, and these cells provide important regulatory functions. For example, in the gastrointestinal tract, interstitial cells of Cajal (ICC) and PDGFRα(+) cells have been described, in detail, and represent distinct classes of cells with unique ultrastructure, molecular phenotypes, and functions. Smooth muscle cells are electrically coupled to ICC and PDGFRα(+) cells, forming an integrated unit called the SIP syncytium. SIP cells express a variety of receptors and ion channels, and conductance changes in any type of SIP cell affect the excitability and responses of the syncytium. SIP cells are known to provide pacemaker activity, propagation pathways for slow waves, transduction of inputs from motor neurons, and mechanosensitivity. Loss of interstitial cells has been associated with motor disorders of the gut. Interstitial cells are also found in a variety of other smooth muscles; however, in most cases, the physiological and pathophysiological roles for these cells have not been clearly defined. This review describes structural, functional, and molecular features of interstitial cells and discusses their contributions in determining the behaviors of smooth muscle tissues.Physiological Reviews 07/2014; 94(3):859-907. DOI:10.1152/physrev.00037.2013 · 29.04 Impact Factor