Search PubMed⌕ Search

Biomedical subjects

J Christensen

Publications and source records attributed to J Christensen.

At least 199 records · Page 11Linked to original sources
PubMed1985

Nerve cell density in submucous plexus throughout the gut of cat and opossum.

Quantitative differences in submucous plexus density were sought in cat and opossum gut by examining full-thickness whole mounts of the submucosa stained with silver, and counting ganglia per square centimeter and nerve cell bodies per ganglion in order to compute density of innervation (nerve cell bodies per square centimeter). In the cat, the nerve cell bodies per square centimeter in the 12 named regions were as follows: proximal esophagus, 0; mid-esophagus, 0; distal esophagus, 0; fundus, 84; gastric antrum, 18; duodenum, 5831; jejunum, 4632; ileum, 3191; proximal colon, 1275; mid-colon, 689; distal colon, 359; rectum, 144. In the opossum, values were as follows: proximal esophagus, 37; mid-esophagus, 52; distal esophagus, 84; duodenum, 1812; jejunum, 2234; ileum, 1488; proximal colon, 206; mid-colon, 197; distal colon, 121; rectum, 61. Adequate specimens could not be obtained from opossum stomach. Differences were due more to variations in distribution density of ganglia than in ganglionic size. The relatively dense submucous plexus of the intestine probably is related to the capacity of the intestinal mucosa for peptide secretion as well as to its absorptive function.

Animals↗
PubMed1985

Antibiotic depression of evoked and spontaneous responses of opossum distal colonic muscularis mucosae in vitro: a factor in antibiotic-associated colitis?

Certain antibiotics depress both skeletal neuromuscular transmission and intestinal neuroeffector transmission. Impaired intestinal motility may facilitate the proliferation of the bacterium Clostridium difficle and thus lead to the development of antibiotic-associated pseudomembranous colitis. Many antibiotics accumulate in the colonic lumen at concentrations several times their associated blood levels. This study examined whether certain of these could interfere with colonic muscularis mucosal movement in vitro, using tissue from opossum distal colon as a model. At concentrations approximating those in the colonic lumen, ampicillin, clindamycin, erythromycin, and lincomycin depressed tone and spontaneous contractions of the muscularis mucosae. Clindamycin, gentamicin, kanamycin, and lincomycin abolished electrically evoked contractions but only gentamicin and kanamycin could abolish the ensuing relaxation. Vancomycin potentiated the response of the muscularis mucosae to acetylcholine; erythromycin and clindamycin depressed it. Antibiotic-induced depression of colonic muscularis mucosal movement may contribute to the development of antibiotic-associated pseudomembranous colitis.

Animals↗
PubMed1985

Shunt fascicles in the gastric myenteric plexus in five species.

Thick nerve bundles, called shunt fascicles, lie in the myenteric plexus of the stomach in guinea pig, rabbit, cat, opossum, and cynomolgus monkey. They enter the stomach at the cardia, either as extensions of the esophageal myenteric plexus or of vagal branches to the caudal esophagus, and radiate toward the greater curvature. They bypass ganglia in the orad part of the stomach but give off branches to ganglia in more caudad parts. They are more abundant in the gastric fundus and body than in the antrum; they are infrequent along the greater curvature of the antrum. About 4% of the fibers they contain are myelinated. Arterioles and venules follow shunt fascicles and give rise to perifascicular capillary networks. Shunt fascicles are prominent in the cat, opossum, and monkey; they are short, thin, and sparse in the rabbit and guinea pig. They do not appear to be extensions of the direct vagal branches to the stomach but may be special nerve pathways from the esophagus to parts of the stomach.

Animals↗
PubMed1985

The response of the colon to eating.

Much evidence indicates that there is an increased motor activity in the colon from eating in several species of animals. Though some of this effect may be cephalic in origin, the greater part of the response results from the arrival of food in the stomach and proximal intestine. Chemoreceptor stimulation appears to be more important than mechanoreceptor stimulation in bringing about this effect. The means by which this effect comes about could be either hormonal or neural. Several polypeptide hormones released from the proximal gut by eating are candidates. Neural pathways through both parasympathetic and sympathetic systems could be responsible. The exact nature of the change in colonic motility that is produced is unknown. It could involve changes in the pacemakers for colonic contractions (the electrical slow waves of the colon and the migrating spike burst of the colon), changes in the excitability of the colonic musculature or changes in colonic mucosal function.

Animals↗
PubMed1985

Control mechanism of spontaneous in vitro contractions of the opossum sphincter of Oddi.

We evaluated the control mechanism of peristaltic contractions in the opossum sphincter of Oddi (SO) by means of an in vitro preparation. At each of four sites spaced uniformly along the sphincter segment, a force transducer recorded contractions while a monopolar electrode recorded myoelectric activity. Spontaneous myoelectric and contractile activity occurred in 15 of the 20 intact SO specimens studied. Electrical recordings showed characteristic control waves and response activity. Each control wave was invariably accompanied by a phasic contraction, irrespective of whether or not response activity was superimposed on the control wave. The predominant motor activity of the SO was antegrade peristalsis. Retrograde peristalsis occurred when antegrade peristalsis failed to traverse the entire sphincter. Spontaneous SO phasic contractions were not antagonized by tetrodotoxin. Muscle rings sectioned from the SO exhibited spontaneous phasic contractions with a proximal-to-distal gradient of intrinsic contraction frequencies. We conclude that a) the frequency of SO phasic contractions is determined by control wave frequency, b) spontaneous SO peristalsis is myogenic in origin and may be modeled by a linear array of bidirectionally coupled relaxation oscillators, c) the predominance of antegrade peristalsis may be explained by a high-frequency oscillator in the proximal SO that drives the slower, more distal oscillators, d) retrograde peristalsis is initiated by an ectopic oscillator in the distal SO when antegrade contractions fail to propagate the entire length of the SO, and e) ectopic SO contractions can propagate retrograde when the more proximal oscillators are not in their absolutely refractory state.

Ampulla of Vater↗
PubMed1984

A pharmacological study of oesophageal muscularis mucosae from the cat, dog and American opossum (Didelphis virginiana).

Strips of muscularis mucosae from the oesophagi of cat, dog and opossum have been studied to determine their responses to drugs to electrical field stimulation. All tissues were contracted by acetylcholine, histamine and, with the exception of strips of muscularis mucosae from the opossum proximal oesophagus, noradrenaline. The effects of acetylcholine and histamine were competitively antagonized by atropine (50 nM) and mepyramine (50 nM) and were abolished by atropine (1 microM) and mepyramine (1 microM) respectively. Contractile responses to noradrenaline were competitively antagonized by phentolamine (50 nM) but were converted to propranolol (50 nM)-sensitive relaxations by phentolamine (1 microM). Relaxations were abolished by propranolol (1 microM). Cholecystokinin octapeptide, gastrin 1 and vasoactive intestinal polypeptide were ineffective on any of the tissues examined. Substance P caused contractions in tissue from all three species. These effects were atropine and tetrodotoxin insensitive. All tissues gave atropine (50 nM)- and tetrodotoxin (100 nM)-sensitive contractions in response to electrical field stimulation. Contractions were not followed by relaxations and spontaneous mechanical activity was not suppressed between periods of stimulation. No evidence was obtained for the presence of non-adrenergic, non-cholinergic inhibitory innervation of the oesophageal muscularis mucosae in any species. During electrical field stimulation noradrenaline always reduced the amplitude of evoked contractions and, with the exception of tissue from proximal opossum oesophagus, increased resting tension. In opossum distal oesophageal muscularis mucosae, the effects of noradrenaline during electrical field stimulation were abolished by a 30 min pretreatment of the tissue with phentolamine (1 microM) and propranolol (1 microM). To Achieve this in all other tissues, it was also necessary to use yohimbine (1 microM). 7 In all tissues where noradrenaline caused a phentolamine (1 microM)-and propranolol (1 microM)- resistant depression of electrically evoked responses, clonidine produced a yohimbine (1 microM)- sensitive depression. 8 Evidence was obtained for the presence of excitatory alpha 1-and inhibitory alpha 2- and beta-adrenoceptors. Inter-species differences in their distribution are discussed.

Acetylcholine↗
PubMed1984

Origin of sensation in the esophagus.

The sensory innervation of the esophagus is important both to physicians, for whom esophageal sensation can cause clinical confusion, and to physiologists, who wish to understand the regulation of esophageal motion. Sensory mechanisms in the gut in general are not well understood. Mechanoreceptive reflexes and their pathways, both parasympathetic and sympathetic, have been studied in the esophagus, and thermoreceptive reflex pathways that are parasympathetic have recently been described. The terminal sensory innervation of the esophagus contains several structures that may be receptors to such stimuli. Esophageal striated muscle contains muscle spindles like those of somatic muscle. Within the myenteric plexus, the bodies of certain ganglion cells themselves may be mechanoreceptive. Also, complex subcapsular laminar arborizations that arise from cells of the nodose ganglion have been described in ganglia of the esophageal myenteric plexus. Similar laminar arborizations have been found on vessels of the submucosa in the midesophagus. In the esophageal mucosa, the terminal innervation ends in structures of diverse form located both superficially and deep in the squamous epithelium. Thus, a variety of specific neural structures that seem to represent the terminals of sensory nerves exist in the esophagus and may serve the mechanoreceptive and thermoreceptive reflexes that modify esophageal motility.

Animals↗
PubMed1984

Differences in cytochrome c oxidase capacity in smooth muscle of opossum esophagus and lower esophageal sphincter.

The tonic contraction that defines the lower esophageal sphincter is exclusively aerobic, whereas the rhythmic contractions that characterize the smooth muscle of the esophageal body can be partially sustained anaerobically. Also, relative mitochondrial mass is greater in the sphincter than it is in the body of the esophagus. Full-thickness strips of the muscularis propria of the opossum esophagus were examined as to cytochrome c oxidase capacity to test the hypothesis that differences in oxidative metabolism exist among different levels of the smooth-muscled esophagus. Homogenates were examined as to rate of cytochrome c oxidation, deoxyribonucleic acid content, and protein content. The rate of cytochrome c oxidation was greatest at the top of the smooth muscle segment and declined distally to reach the lowest value in the lower esophageal sphincter. Deoxyribonucleic acid content did not differ among levels examined. Protein/deoxyribonucleic acid ratios were lower in the sphincter than at other levels of the smooth-muscled esophagus. The results indicate that the sphincter muscle has a lower capacity for oxidative metabolism than does the body, that a gradient exists along the esophageal body in oxidative capacity, and that smooth muscle cells in the sphincter are likely to be smaller than are those of the esophageal body. The gradient in oxidative capacity along the esophageal body may be related to other gradients that have been described in this region.

Animals↗
PubMed1984

Comparative anatomy of the myenteric plexus of the distal colon in eight mammals.

The behavior of the most distal part of the colon in a variety of species suggests that the innervation of this part may differ from that of more proximal parts. Silver impregnation was used to demonstrate the arrangement of the myenteric plexus of the distal colon in eight species (rat, guinea pig, rabbit, Australian possum, American opossum, cat, dog, and monkey). A distal zone, approximately 5%-20% of the total length of the colon above the anal verge in the nonrodents, was characterized by a plexus of very irregularly disposed intersecting nerve bundles of highly variable size with few and small ganglia; this zone was absent in the three rodent species. A next most distal zone, approximately 10%-65% of the total colonic length, contained a stellate plexus of large, regularly disposed ganglia interconnected by small nerve fiber bundles upon which were superimposed large dark-staining nerve bundles; these bundles began to be seen at the level of the irregular rectal plexus and ran cephalad, bypassing some ganglia but giving off branches to others. These, called shunt fascicles, contained many myelinated nerve fibers. Above this zone, the plexus was a stellate plexus throughout the remainder of the colon.

Animals↗
PubMed1983

The stability of the tibio-fibular syndesmosis following rigid internal fixation for type C malleolar fractures: an experimental and clinical study.

In 5 cadavers, type C malleolar fractures of the pronation-eversion rotation type, were produced. The stability of the ankle mortice under stress was tested before and after rigid internal fixation of the fracture in the fibula. The intact interosseous membrane above the fracture in combination with the internal fixation of the fibula was sufficient to keep the lateral malleolus in place. A clinical series of 8 equivalent fractures treated with rigid internal fixation without suture of the syndesmodesis was collected and evaluated clinically and radiologically 3 years after the injury. None of the patients had significant complaints and all ankle joints were stable.

Adult↗