PubMed Health⌕ Search

Biomedical subjects

D F Mettrick

Publications and source records attributed to D F Mettrick.

At least 37 records · Page 2Linked to original sources
PubMed1984

Ultrastructural morphology of the nerve cells in the cerebral ganglion of the Acanthocephalan Moniliformis moniliformis.

The morphology of the cerebral ganglion of the Acanthocephalan Moniliformis moniliformis was studied in serial sections using electron microscopy. The organization of the cerebral ganglion was typical of other invertebrates with the cell bodies forming a rind, 1 cell thick, and their processes forming the central core of the neuropile. The ganglion was surrounded by a connective tissue capsule composed of collagen-like fibrils. Externally, the free surface of the cell bodies was covered by an electron-dense extracellular lamina. Seventy-six cells were identified in every ganglion examined and, on the basis of their cellular characteristics, they were divided into 5 distinct cell types, classified as type A, B, C, D and E cells. The characteristic morphological features of each cell type have been described, and the distribution of the different cell types in the cerebral ganglion was mapped.

Acanthocephala↗
PubMed1983

Aminergic neurons in the anterior nervous system of the rat acanthocephalan Moniliformis dubius.

The cerebral ganglion and nerve tracts of Moniliformis dubius show intense, specific, green fluorescence that is also associated with the lateral and apical sensory bulbs. Radioenzymatic assays showed that high levels of dopamine were present but only small amounts of the catecholamines norepinephrine and epinephrine were identified. Incubations of the proboscis sac in dilute solutions of dopamine increased fluorescence while incubations in reserpine resulted in loss of fluorescence. Nonfluorogenic amine octopamine was also detected radioenzymatically. Neutral red vitally stained a number of cells in the cerebral ganglion and the nerve tracts extending from the ganglion. Electron microscopy showed that many neurons contained electron-dense vesicles. The close association of the fluorescing, amine-containing nerve tracts with the sensory bulbs suggests that they may play a functional role in sensory reception and transmission in M. dubius. This is the first report on the presence of biogenic amines in the Acanthocephala.

Acanthocephala↗
PubMed1983

Effects of 5-hydroxytryptamine on carbohydrate metabolism in Hymenolepis diminuta (Cestoda).

Under in vitro anaerobic and aerobic incubations the presence of 5-hydroxytryptamine (5-HT) resulted in an accelerated rate of carbon transfer through the carbohydrate metabolic pathways of Hymenolepis diminuta resulting in an increase in worm tissue total carbon pools. Under aerobic incubation, levels of phosphoglycerates, phosphoenolpyruvate (PEP), and pyruvate were significantly increased over the corresponding levels under anaerobic incubation. Excreted end products of carbohydrate metabolism also differed significantly depending on the gas phase and the presence of 5-HT. Under atmospheric (21%) oxygen concentrations excreted levels of lactate, succinate, and acetate were all significantly elevated; under a 95% O2-5% CO2 gas phase only lactate excretion was increased, and under a 95% N2-5% CO2 gas phase only succinate and acetate excretion increased. The presence of oxygen reduced acetate excretion by up to 55% and under the 95% O2-5% CO2 gas phase succinate excretion was reduced 48%. Irrespective of gas phase or the presence of 5-HT, adenine nucleotide pool sizes and the adenylate energy charge remained constant. The addition of 5-HT had no significant effect in increasing the specific activity of phosphofructokinase (PFK). In the presence of ATP the addition of cAMP increased PFK activity by up to 48%; AMP enhanced the enzyme activity by up to 69%, irrespective of the presence or absence of 5-HT. These results are discussed in terms of the effects of 5-HT, gas phase, and nucleotide pools on the motility, metabolism, and control of H. diminuta, and of other parasites which respond to 5-HT.

Adenosine Triphosphate↗
PubMed1982

5-hydroxytryptamine, glucose uptake, glycogen utilization and carbon dioxide fixation in Hymenolepis microstoma (Cestoda).

1. In vitro glucose uptake and glycogen utilization by Hymenolepis microstoma decreased under high oxygen concentrations. 2. 5-Hydroxytryptamine did not stimulate in vitro glucose uptake but did increase glycogen utilizations by H. microstoma. 3. The reduced glucose uptake under high oxygen concentrations (21 and 95%) resulted in a reduction in excretory products. 4. 14CO2-incorporation studies confirmed that, under both 95% O2:5% CO2 and air-minus-CO2 (identical to 21% O2). CO2-fixation by phosphoenolpyruvate carboxykinase (EC 4.1.1.32) was inhibited. 5. The specific activity of hexokinase (EC 2.7.1.1), phosphofructokinase (EC 2.7.1.11) and pyruvate kinase (EC 2.7.1.40) was not stimulated by 5-HT. 6. The concentration of ATP required for optimal stimulation of phosphofructokinase activity was 0.67 mM. Activity was further significantly increased by the addition of cAMP and even greater by AMP.

Animals↗
PubMed1982

Circadian variation in the distribution of Hymenolepis diminuta (Cestoda) and 5-hydroxytryptamine levels in the gastro-intestinal tract of the laboratory rat.

The circadian migration of Hymenolepis diminuta in the small intestine of the rat may be correlated with a circadian variation in 5-hydroxytryptamine levels present in worm tissue, in the intestinal lumen, in the intestinal mucosa, with the amount of fold present in the small intestine and in arterial blood. 5-HT and food levels in uninfected animals were also determined. The 16.00 h stage in the circadian cycle marks both the commencement of host feeding, followed by rising 5-HT levels in both worm and host tissues, and initiation of an anteriad migration of worm biomass. It was found that 5-HT levels in the intestine of parasitized animals were significantly higher than in the intestine of uninfected controls. This is the first report of circadian variation in mucosal and luminal 5-HT levels. The similarity in the circadian patterns of worm migration and worm luminal, mucosal and blood 5-HT levels were striking. Fasting eliminated the circadian rise in intestinal 5-HT levels and the worms did not migrate. Luminal 5-HT levels were significantly lower in fasted animals than in the comparable rats fed ad libitum. When the intestine was ligatured at the pyloric sphincter, worm anteriad migration still occurred after feeding, indicating that the presence of exogenous food in the intestine is not a factor in the initial migration of the worms.

Animals↗
PubMed1981

Effect of 5-hydroxytryptamine (5-HT; serotonin) on in vitro glucose uptake and glycogen reserves in Hymenolepis diminuta.

Glucose uptake by Hymenolepis diminuta was linear for up to 60 min following in vitro incubation in 10 mM glucose. Following the addition of 1 mM 5-HT, with a 95% O2/5% CO2, gas phase, glucose uptake by H. diminuta was significantly (P less than 0.001) enhanced, remaining linear and parallel to that of control groups between 15 and 60 min incubation. Under air, the rates of glucose uptake were higher, but were only significantly increased by 5-HT during the first 30 min of incubation. In further experiments, in the absence of glucose in the incubation media worm glycogen reserves decreased by over 50% after 60 min. With the addition of 1 mM 5-HT, the reduction in glycogen content was significantly (P less than 0.025) greater, exceeding 65% after 60min. When glucose was added to the incubation media, worm glycogen reserves were not significantly depleted irrespective of the presence or absence of 5-HT. Incubations under a 95% O2/5% CO2 gas phase did not significantly influence glycogen content compared to corresponding groups incubated in air. The results suggest that 5-HT stimulates glycolysis in H. diminuta through increased glucose uptake by the worm or by a reduction in glycogen reserves in the absence of external glucose.

Animals↗
PubMed1981

A study of phosphoenolpyruvate carboxykinase from Moniliformis dubius (Acanthocephala).

Procedures have been developed for the extraction and subsequent purification of the enzyme phosphoenolpyruvate carboxykinase (GTP) (PEPCK) from Moniliformis dubius (Acanthocephala), a parasite of the rat small intestine. This is believed to be the first purification of PEPCK from an invertebrate animal. The enzyme, when purified to homogeneity as indicated by electrophoretic criteria, has a molecular weight of 73 700. Kinetic studies indicated that the enzyme had a pH optimum of 5.5 and required Mn2+ as the divalent cation. The apparent Km values determined for the substrates of the carboxylation reaction were low compared with the published values for purified PEPCK from vertebrate sources. Several competitive inhibitors were found and their Ki values determined. The possible regulation of PEPCK activity in M. dubius is discussed with reference to the observed kinetic parameters.

Acanthocephala↗
PubMed1981

Migration of Hymenolepis diminuta (Cestoda) and changes in 5-HT (serotonin) levels in the rat host following parenteral and oral 5-HT administration.

Changes in the distribution of the tapeworm Hymenolepis diminuta in the rat small intestine were studied for up to 3 h following intraperitoneal, intramuscular, subcutaneous, and oral administration of 5-HT. Changes in 5-HT levels in the arterial circulation, intestinal lumen, and in worm tissue were also monitored. In all cases following 5-HT administration there was an anteriad migration by H. diminuta. The extent of the migration was dose dependent, the higher the dose the more marked the migration response. Normal 5-HT levels in the parasitized gut are higher than those in uninfected animals. The pattern of increasing levels of 5-HT in worm tissue directly followed the increases in the intestinal lumen, suggesting that worm 5-HT was of host origin. Blood 5-HT level similarly followed luminal increases. It is suggested that the pharmacological action of 5-HT on H. diminuta resulting in worm migration is implemented through the regulation of helminth neuromuscular activity and the carbohydrate metabolism, as has been demonstrated in other parasitic worms.

Animals↗
PubMed1981

Effect of electrical vagal stimulation on migration of hymenolepis diminuta.

Stimulation of the left efferent vagal nerve (2 msec, 5 V, 10 Hz), for up to 60 min in rats infected with 11-day-old Hymenolepis diminuta induced anteriad migration of worm scolex and biomass in the small intestine. Ligation at the pyloric sphincter prior to vagal stimulation shortened the length of time before significant relocation occurred and increased the migrational response. The results support the hypothesis that work migration is mediated via vagal stimulation of gastrointestinal function, and is unrelated to actual feeding.

Animals↗
PubMed1981

Purification and properties of phosphoenolpyruvate carboxykinase from Hymenolepis diminuta (Cestoda).

A method is described for the purification of the enzyme phosphoenolpyruvate carboxykinase (PEPCK) from the cestode Hymenolepis diminuta. When purified to electrophoretic homogeneity, the enzyme had a molecular weight of 70,600 and an isoelectric point of 7.5. Kinetic studies indicated that the pH 5.6 was optimal for the carboxylation reaction and that Mn++ was the preferred divalent cation; there was no activity of the enzyme in the presence of Mg++. Apparent Km values for the carboxylation reaction were determined; those for GDP (20.6 muM) and PEP (38.9 muM) were lower than the values previously reported. GTP, GMP, ITP, IMP, fumarate, succinate and alpha-ketoglutarate were found to be competitive inhibitors and their Ki values determined.

Animals↗
PubMed1979

Vitamin absorption in the in vivo intestine of normal and infected (Hymenolepis diminuta: Cestoda) rats.

Uptake and serosal transfer of the vitamins thiamine, riboflavin and folic acid have been studied in vivo in normal and parasitized rats infected with Hymenolepis diminuta (Cestoda). Regional differences in intestinal uptake of all three vitamins in both uninfected and parasitized animals were not satistically significant. In the parasitized intestine mucosal uptake and serosal transfer of thiamine were significantly inhibited, with increased mucosal accumulation of the vitamin as luminal thiamine concentration increased. Apparent increased riboflavin mucosal uptake in parasitized animals, was not matched by the reduced serosal transfer, suggesting adsorption of the vitamin in the unstirred aqueous layers. Mucosal uptake of folic acid increased in the parasitized gut; serosal transfer and mucosal accumulation were not affected. These results, indicating vitamin malabsorption associated with infection by H. diminuta, are consistent with the parasite inhibiting mucosal passive transport mechanisms. This conclusion is supported by the changes in net water fluxes associated with vitamin uptake in the parasitized intestine.

Animals↗