Biomedical subjects

W A Weems

Publications and source records attributed to W A Weems.

21 records · Page 2Linked to original sources

PubMed1977

Modulation of colonic motility by peripheral neural inputs to neurons of the inferior mesenteric ganglion.

Colonic motility is known to be regulated, in part, by postganglionic sympathetic neurons whose cell bodies are located in the inferior mesenteric ganglion (IMG). Several studies have demonstrated that the neural activity of postganglionic neurons located in the IMG results from the synaptic integration of neural input received not only from the central nervous system via the inferior splanchnic nerves but also from sensory receptors located in the periphery and received via the lumbar colonic, intermesenteric, and hypogastric nerves. To investigate some of the interactions among colonic motility, peripheral neural input to the IMG, and postganglionic neural activity, intracellular recordings were made from single neurons located in the IMG of in vitro IMG-colon preparations obtained from guinea pigs. Recordings of colonic intraluminal pressures were simultaneously obtained with these neurophysiological recordings. Gross afferent input to the IMG from colonic mechanoreceptors was found to be nonadapting, to the correlated with physiological levels of intraluminal pressure, and to vary with propulsive motor activity. Both peripheral and central preganglionic inputs to the IMG reduced or abolished colonic motiligy, but with varying degrees of effectiveness. It is concluded that the firing patterns of sympathetic postganglionic neurons affecting motility of the terminal colon result primarily from the synaptic integration of inputs from preganglionic fibers of both central and peripheral origin.

Animals↗

PubMed1976

A study of peripheral input to and its control by post-ganglionic neurones of the inferior mesenteric ganglion.

1. Intracellular recordings were made, in vitro, from neurones of guinea-pig inferior mesenteric ganglia (IMG) attached, via the lumbar colonic nerves, to segments of distal colon. 2. 'Spontaneous' synaptic input from colonic afferent fibres was observed in 79% of the neurones tested. In any given preparation, the level and pattern of this synaptic input to different neurones varied considerably. 3. Superfusion of colonic segments with drugs (papaverine, isoprenaline, and adenosine triphosphate) which reduce colonic motility decreased colonic afferent input to IMG neurones. 4. Superfusion of colonic segments with acetylcholine or stimulation of pelvic nerves, both of which increase colonic motility, increased colonic afferent input to IMG neurones. 5. Superfusion of colonic segments with either atropine or tubocurarine reduced the level of 'spontaneous', colonic afferent input. However, distension of these relaxed segments increased the colonic afferent input. 6. Repetitive stimulation of preganglionic inputs to the IMG inhibited afferent input from drug relaxed segments of colon that were moderately distended by the injection of air into the lumen. Superfusion of the colon with phentolamine blocked this inhibition. 7. The results of this study suggest that IMG neurones receive afferent input from mechanoreceptors located in the distal colon and that the mechanosensitivity of this afferent pathway is in part controlled by efferent noradrenergic neurones of the IMG. The IMG-colon neural circuitry can therefore be considered to form a feed-back control system which participates in the regulation of colonic motility.

Acetylcholine↗

PubMed1974

A study of pace-maker activity in intestinal smooth muscle.

1. Electrical activity of longitudinal muscle from cat intestine was recorded in the double sucrose gap.2. Approximately 20% of the preparations demonstrated slow, spontaneous fluctuations of membrane voltage, slow waves. This activity, although quite uniform in a given preparation, showed considerable inter-preparation variation with respect to amplitude, frequency and wave form.3. Application of steady hyperpolarizing current decreased slow-wave frequency and increased slow-wave amplitude while depolarizing currents increased frequency and decreased amplitude.4. Some preparations with no spontaneous slow-wave activity developed slow waves when the membrane was hyperpolarized into a given range which, depending on the preparation, varied in size from 10 to 40 mV. Step or ramp depolarization of the membrane from hyperpolarized levels triggered slow waves in some preparations.5. When the membrane potential of a slow-wave generating preparation was clamped at the resting potential, spontaneous inward-directed current transients were observed.6. No changes in membrane conductance were observed during the course of a slow wave.7. The slow-wave pattern was simulated for individual preparations by applying the membrane current measured under voltage clamp to the passive membrane resistance and capacitance measured independently under current clamp.8. In addition to the defined slow-wave activity, voltage-dependent oscillations in membrane potential were sometimes observed.9. Application of 10(-5)M ouabain irreversibly blocked slow waves and produced a membrane depolarization equal to or slightly greater than the slow wave crest. Repolarization of the membrane to the resting potential, or hyperpolarization, failed to restore slow-wave activity.10. Removal of external potassium produced a reversible sequence of events almost identical to those following ouabain application.11. Replacement of 50% of the external sodium chloride with sucrose produced no changes in slow-wave activity with respect to rates of rise or fall, maximum amplitude or frequency. Sucrose replacement of all external sodium chloride eliminated slow waves after 5 min; however, activity could be restored by a slight hyperpolarization. Longer exposures to the modified bath abolished activity.12. Following a conditioning exposure to potassium-free Krebs solution, readmission of potassium at normal concentration produced a mean hyperpolarization of 20.5 mV and in spontaneous preparations an arrest of activity.13. Pump current in sodium-loaded, non-spontaneously active preparations was measured by voltage clamp and was observed to be voltage-dependent.14. The results of this study indicate that an electrogenic pump is present in longitudinal muscle of cat duodenum, and that oscillations in the level of pump current produce slow waves.

Action Potentials↗