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Biomedical subjects

J S Davison

Publications and source records attributed to J S Davison.

At least 19 recordsLinked to original sources
PubMed1979

The role of intrinsic, non-adrenergic, non-cholinergic inhibitory nerves in the regulation of distensibility of the guinea-pig colon.

1. The lengthening responses of segments of distal colon of guinea-pigs to applied weights were measured. 2. Distensibility was reduced by tetrodotoxin and quinidine; increased by atropine and hyoscine, and unaffected by guanethidine and phentolamine. 3. Tension changes produced by controlled stretches were increased by tetrodotoxin. 4. These results suggest that there is a net, inhibitory, non-adrenergic, non-cholinergic influence acting on the muscle during stretch against a background of cholinergic excitatory tone. This inhibitory activity may be activated reflexly by stretch.

Animals↗
PubMed1978

Mucosal receptors in the gastric antrum and small intestine of the rat with afferent fibres in the cervical vagus.

1. Electrical stimulation of the abdominal vagi revealed that abdominal vagal fibres are distributed throughout the cervical vagal trunk. Conduction velocities of the main group of abdominal fibres ranged from 0.4 to 1.5 m.sec-1. 2. Thirty-seven single afferent fibres, with endings in the gastric and intestinal mucosa, were isolated from the cervical vagus of adult rats. Conduction velocities of eighteen of these endings ranged from 0.5 to 2.5 m.sec-1. 3. Light mechanical stimulation, such as stroking the mucosa, evoked a rapidly adapting response from these endings. Sustained pressure or distension with fluid or air did not excite these endings although excessive stretching of the mucosa excited three units. Balloon distension usually evoked an 'on-off' response due to phasic stimulation of the mucosa by the balloon during inflation and deflation. 4. These same endings also functioned as non-specific, slowly adapting chemoreceptors responding to various organic and inorganic acids, tap water and distilled water, alcohol, hypertonic saline, NaOH, NH4Cl, CuSO4, casein hydrolysate, mustard powder and cayenne pepper. Hypertonic glucose and guinea-pig bile were ineffective as stimuli. 5. In the presence of an excess of chloride ions the effectiveness of acids in stimulating these endings was in part determined by the pK of the acid. However pH per se was not the basic determining factor but rather the molecular size of the acid.

Acids↗
PubMed1978

Modulation of single vagal efferent fibre discharge by gastrointestinal afferents in the rat.

1. A single fibre dissection technique was used to record activity from efferent fibres in the left cervical vagus nerve of urethane anaesthetized rats. 2. The efferent discharge, in all units, was modulated by gastric inflation, gastric contractions or compression of the stomach wall. The receptors mediating these effects are the slowly adapting 'in-series' tension receptors in the gastric musculature with afferent fibres in the vagus nerves. 3. Efferent units were classified according to their response to passive gastric distension and active gastric contractions. 4. Four distinct types of efferent unit were isolated. Type I units were excited and Type II units were inhibited by gastric distension and contraction. Type III units were excited at low or moderate levels of inflation and inhibited at high levels of inflation or during gastric contractions. Type IV units were inhibited by low levels of inflation but excited at higher levels. 5. Since there is clearly a reciprocal organization at least of some neurones in the vagal nucleus the possibility of reciprocal control of antagonist, cholinergic and 'purinergic' vagal pathways is discussed.

Action Potentials↗
PubMed1977

Relaxation of the lower-oesophageal sphincter during swallowing.

A rapid-pull through technique was used to measure lower oesophageal sphincter pressure before and immediately after swallowing. Often no high pressure zone could be detected after a swallow although sometimes an attenuated pressure profile persisted, associated with weakly developed peristalsis. The persistence of normal sphincter profiles was associated with failure of peristalsis or weak peristaltic pressure waves. Overall, there was a significant drop in mean sphincter pressure after swallowing.

Adult↗