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D B Morton

Publications and source records attributed to D B Morton.

At least 55 records · Page 3Linked to original sources
PubMed1995

Effect of cycloheximide on eclosion hormone sensitivity and the developmental appearance of the eclosion hormone and cGMP regulated phosphoproteins in the CNS of the tobacco hornworm, Manduca sexta.

The neuropeptide, eclosion hormone (EH), triggers ecdysis behavior at the end of each molt in Manduca sexta. Previous studies have shown that the action of EH is mediated by an increase in cGMP and is associated with the phosphorylation of two proteins, named the EGPs. The ability of insects to respond to EH is developmentally regulated with sensitivity being first seen at about 8 hr prior to the normal time of ecdysis. The EGPs are also first detectable in the CNS at 8 hr prior to ecdysis, suggesting that it is their synthesis which determines EH sensitivity. The protein synthesis inhibitor, cycloheximide was used to study the development of the events leading to pupal ecdysis in Manduca. The results of these experiments suggest that protein synthesis is necessary about 10 hr before ecdysis for both the development of EH sensitivity and for the appearance of the EGPs.

Animals↗
PubMed1994

Spatiotemporal pattern of expression of tenascin-like molecules in a developing insect olfactory system.

During the development of the olfactory (antennal) lobe of the moth Manduca sexta, olfactory sensory axons induce glomerular branching patterns in their target neurons. Glial cells, by surrounding the developing glomerular template, are thought to mediate the developmental influence of olfactory axons on these branching patterns. Previous studies have demonstrated that, in the absence of glia, neurons in the antennal lobe branch in an aglomerular fashion, even in the presence of competent antennal axons (Oland and Tolbert, 1988, J. Comp. Neurol. 278:377-387; Oland et al., 1988, J. Neurosci. 8:353-367). We have begun to explore the molecular basis by which glial cells could influence patterns of neurite branching. For this work, we have utilized immunocytochemical techniques and a partial biochemical analysis to demonstrate that molecules antigenically similar and comparable in size to mammalian tenascin are localized on the neuropil-associated glial cells that form borders around glomeruli in the developing antennal lobe. These tenascin-like molecules associated with neuropilar glia are present at critical stages of glomerulus development; tenascin-like immunoreactivity declines after glomeruli form and become stabilized. Neither the arrival nor the absence of antennal axons in the lobe induces changes in either the molecular forms or the amounts of tenascin-like molecules. The spatiotemporal pattern of expression of tenascin-like molecules suggests that they are in a position to participate in the formation of a glomerular neuropil and could form a molecular barrier that constrains neurite outgrowth strictly to glomeruli.

Animals↗
PubMed1994

Isolation and partial characterization of a gene from trachea of Manduca sexta that requires and is negatively regulated by ecdysteroids.

The molting cycle in insects is regulated by the fluctuating levels of ecdysteroids. Twenty-four hours prior to the pupal molt in Manduca sexta steroid titers are relatively high and they fall to very low levels at 4 hr before the molt. Several physiological events accompanying molts have been shown to require the rise and then the subsequent decline of ecdysteroid levels. These events also require the expression of a new set of genes. We used subtractive hybridization to isolate genes that are expressed 4 hr, but not 24 hr, prior to the pupal molt in the nervous system of Manduca. These genes are expected to play a role either in ecdysis behavior or in the development of pupal/adult structures. The first such gene we have identified, esr20 (EcdySteroid Regulated) encodes a 20-kDa protein. The deduced amino acid sequence of the protein shows similarity to acidic domains in three urelated proteins, chick nucleolin, rat heavy-molecular-weight neurofilament, and the Drosophila steroid orphan receptor, knirps-related. The similarity among the four proteins appears to be in regions implicated in protein-protein interactions. The accumulation of esr20 mRNA starts 16 hr prior to the pupal molt and abruptly stops at ecdysis. Expression of esr20 was localized to tracheal epithelial cells within all tissue types, and the transcript was present prior to the larval, pupal, and adult molts only after the molting peak of ecdysteroids had declined. Its expression was inhibited in the presence of ecdysteroids in vitro and required protein synthesis.

Amino Acid Sequence↗
PubMed1992

Pancreatic function following partial pancreatectomy and anastomosis of the pancreatic duct to the stomach or duodenum in dogs.

The effects of pancreatic duct anastomosis to stomach (stomach group) or duodenum (duodenal group) on pancreatic function were examined in dogs following two thirds pancreatectomy. Normal fasting blood glucose concentrations were maintained in both groups despite significant reductions in glucose tolerance in the stomach group, and reductions in fasting insulin and insulin peak response in both groups. Pancreatic exocrine function was significantly decreased in both groups, though plasma p-aminobenzoic acid (PABA) concentrations were generally higher in the duodenal group. A correlation was found between plasma trypsin-like immunoreactivity (TLI) and pancreatic weight. These results indicate that anastomosis of the pancreas to bowel can be undertaken with minimal postoperative complications and that the site of the anastomosis influences pancreatic function. They suggest that preservation of more than one third of the pancreas is required for optimal function. The complementary information provided by the PABA and TLI tests suggests their dual application will be clinically useful for the detection and characterisation of naturally occurring pancreatic diseases.

4-Aminobenzoic Acid↗
PubMed1992

Eclosion hormone stimulates cyclic GMP levels in Manduca sexta nervous tissue via arachidonic acid metabolism with little or no contribution from the production of nitric oxide.

The neuropeptide eclosion hormone acts directly on the nervous system of the tobacco hornworm, Manduca sexta, to trigger ecdysis behavior at the end of each molt. Previous studies have shown that the action of eclosion hormone is mediated via the intracellular messenger cyclic GMP. In the present study we have investigated the mechanisms involved in the eclosion hormone-stimulated increases in cyclic GMP. No stimulation of guanylate cyclase was seen in homogenized nervous tissue, suggesting that eclosion hormone does not directly stimulate a membrane-bound form of guanylate cyclase. Nitric oxide synthase inhibitors, N-methylarginine and nitroarginine, had no effect on eclosion hormone-stimulated cyclic GMP levels. By contrast, 4-bromophenacyl bromide, an inhibitor of arachidonic acid release, and nordihydroguaiaretic acid, an inhibitor of arachidonic acid metabolism, almost completely abolished the eclosion hormone-stimulated cyclic GMP increase. We hypothesize that eclosion hormone receptors are coupled to a lipase, activation of which causes the release of arachidonic acid. Either the arachidonic acid directly stimulates the soluble guanylate cyclase or further metabolism of arachidonic acid yields compounds that activate guanylate cyclase.

Animals↗
PubMed1992

The HID50 (hypothermia-inducing dose 50): an alternative to the LD50 for measurement of bacterial virulence.

A group of 40 mice involved in bacterial LD50 estimations was monitored over a period of 4 days by two teams of observers. One team measured the colonic temperature of the mice, the other assessed them clinically and killed those they judged terminally ill. The temperatures of all mice considered terminally ill dropped before this judgement was made. Measurement of such infection-induced hypothermia provides a more objective, reproducible, and earlier endpoint than that used in conventional LD50 estimation.

Animals↗
PubMed1991

Effect of pancreatectomy on plasma activities of amylase, isoamylase, lipase and trypsin-like immunoreactivity in dogs.

The contribution of the pancreas to the plasma activities of amylase, isoamylase, lipase and the concentration of trypsin-like immunoreactivity (TLI) in the dog was examined by measuring the activities of these enzymes before and after total pancreatectomy. Pancreatectomy was followed by a decrease in the concentration of TLI (from 6.2 +/- 0.3 micrograms litre-1 to 1.2 +/- 0.3 micrograms litre-1; P less than 0.001) and activity of isoamylase peak 4 (from 1257 +/- 105 iu litre-1 to 894 +/- 171 iu litre-1; P less than 0.05). Though significantly reduced, the activities of peak 4 isoamylase were still within the normal range for control dogs. Pancreatectomy did not significantly alter the activities of amylase, lipase or isoamylase peaks 1, 2 and 3. These findings provide strong evidence that the pancreas is not the sole source of circulating amylase, isoamylase and lipase activities. In contrast the marked reductions in TLI to values close to the limits of assay sensitivity suggest that TLI is derived from the pancreas alone. The results indicate that assay of circulating TLI provides a more sensitive and specific indicator of pancreatic exocrine mass than plasma amylase, lipase or isoamylase activities.

Amylases↗
PubMed1990

Homoeopathy.

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Animals↗
PubMed1990

Effects of exocrine pancreatic insufficiency and replacement therapy on the bacterial flora of the duodenum in dogs.

The influence of pancreatic secretions on the bacterial flora of the small intestine in 6 dogs was investigated by determining effects of exocrine pancreatic insufficiency on numbers and types of bacteria in duodenal juice, and by examining the subsequent response to dietary supplementation with bovine pancreatic extract. Exocrine pancreatic insufficiency was induced by ligation of pancreatic ducts and was confirmed by indirect assessment of exocrine pancreatic function. Duct ligation was followed by large increases (P less than 0.01) in total numbers of bacteria, reflecting increased numbers particularly of Lactobacillus spp and Streptococcus spp, in 3 dogs accompanied by obligate anaerobes. Total numbers of aerobes and anaerobes decreased markedly (P less than 0.05) after supplementation with bovine pancreatic extract to values that were not significantly different from those determined before duct ligation. Exocrine pancreatic insufficiency therefore resulted in small intestinal bacterial overgrowth that was reversed by pancreatic replacement therapy, indicating that pancreatic secretions can have an important influence on the small intestinal bacterial flora of dogs.

Animals↗
PubMed1989

The use of a biological adhesive to achieve sutureless epikeratophakia.

An adhesive made of concentrated human fibrinogen produced from samples of single donor blood by a simple cryoprecipitation method was tested for its ability to bond lamellar corneal buttons in vitro and found to have a bond strength of 140 gm/cm2. The adhesive was successfully used to attach experimental epikeratophakia grafts in a rabbit model. The results were similar to those reported from an earlier trial using a commercially available adhesive prepared from pooled multi-donor human plasma. This experimental trial of single-donor adhesive demonstrates the possibility of successful use of autologous fibrinogen adhesive in human epikeratophakia. Autologous adhesive would remove the possible threat of transmitted disease posed by multi-donor adhesive and avoid immune reactions to foreign proteins.

Animals↗