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Biomedical subjects

R Dawson

Publications and source records attributed to R Dawson.

At least 145 records · Page 8Linked to original sources
PubMed1984

Manipulation of mobile phase parameters for the HPLC separation of endogenous monoamines in rat brain tissue.

Multi-component mobile phases are common in ion pair reverse phase high performance liquid chromatography for the analysis of endogenous monoamines in rat brain tissue. By examining the effects of each component of a mobile phase on the separation of a number of monoamines and their metabolites, we show how optimization of parameters can achieve and/or maintain a separation both within and between different octadecyl columns. The assay itself is rapid, sensitive, demands minimal sample preparation, and results in complete resolution of the amines. More importantly, the basis for the manipulation of mobile phase components is discussed with regard to practical utilization in selective amine separation. We conclude that knowledge of mobile phase parameters, their mechanism, and manipulation is as important as the assay itself.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1984

Optic neuritis.

Explore the source record for details and available documents.

Adrenal Cortex Hormones↗
PubMed1984

High-performance liquid chromatographic (HPLC) separation and quantitation of endogenous glucocorticoids after solid-phase extraction from plasma.

This study describes a method for the extraction and simultaneous measurement of cortisone, cortisol and corticosterone using dexamethasone as an internal standard. Solid-phase extraction of plasma steroids with C18 columns allows the samples to be extracted, washed and concentrated in a single step with minimal sample handling and without the use of large volumes of organic solvents. HPLC separation of the steroids is accomplished within 10 min and the individual steroid peaks are quantitated by UV detection at 239 nm. This assay was examined for linearity, extraction efficiency, precision and potential interference by commonly used drugs. Plasma values of glucocorticoids are reported for samples obtained from human subjects as well as from rats. HPLC was also compared to RIA for the determination of plasma levels of corticosterone in the rat. Solid-phase extraction and assay by HPLC provides a rapid and specific method for the simultaneous determination of plasma glucocorticoids.

Animals↗
PubMed1983

Acute and long lasting neurochemical effects of monosodium glutamate administration to mice.

Acute administration of excitatory amino acids alters the release of anterior pituitary hormones. The neurochemical effects of monosodium glutamate (MSG) administration to adult mice were examined 30 minutes and 60 days after an acute injection (4 mg/g). The permanent effects of an acute injection of MSG were limited to a slight loss of neurons in the ventral arcuate nucleus and a 21% reduction in hypothalamic 5-HIAA levels. Thirty minutes after MSG administration hypothalamic DA and DOPAC levels were increased 27% and 25%, respectively and MOPEG levels were increased 75% in the hypothalamus and 34% in the remaining whole brain. These findings show that the acute administration of MSG results in alterations in hypothalamic monoamine metabolism which may be related to the neuroendocrine consequences of excitatory amino acid administration.

Animals↗
PubMed1982

Changes in the collagen of rat heart in copper-deficiency-induced cardiac hypertrophy.

Groups of rats were maintained from weaning on copper-supplemented or copper-deficient diets. After 2, 4, 6, 8 or 12 weeks animals were killed, their hearts were removed and the solubility and phenotype composition of the collagen of the hearts was studied. In the hearts from the copper-supplemented animals 35 to 45% of the collagen could be extracted after two treatments with pepsin but up to 74% could be extracted from the hypertrophied copper-deficient hearts. Almost all of the increase in the soluble material was found in the first pepsin extract. Electrophoretic analysis of the extracts showed that in the copper-supplemented hearts the ratio of Type III/Type I collagen increased about threefold between 2 and 6 weeks after weaning but by 8 weeks it had returned to about the level found at 2 weeks and was maintained at this level to the end of the experimental period. In the copper-deficient hearts the ratio of Type III/Type I collagen had increased about fivefold by 6 weeks after weaning and from 8 weeks to the end of the experimental period it remained at two to three times the value found in the copper-supplemented hearts. There was an indication that the relative proportion of Type V collagen was reduced in the copper-deficient hearts. The possible significance of these results in relation to the known pathological effects of copper deficiency on the cardiovascular system is discussed.

Animals↗
PubMed1982

High-affinity uptake of hypothalamic neurotransmitters in mice treated neonatally with monosodium glutamate.

Monosodium glutamate (MSG) administration to neonatal mice results in destruction of the arcuate nucleus (AN) of the hypothalamus and numerous behavioral, endocrine and neurochemical sequelae. the present study assessed high-affinity neurotransmitter uptake into hypothalamic synaptosomes isolated from adult mice which were treated on postnatal day 4 with either MSG (4 mg/g) or saline. MSG treatment produced a significant reduction in synaptosomal uptake of dopamine (DA), choline (Ch) and GABA when expressed in terms of hypothalamic wet weight. However, MSG treatment resulted in a significant loss (70%) of synaptosomal protein and consequent increases in synaptosomal uptake of these neurochemicals when expressed per unit of synaptosomal protein. The results indicate that MSG treatment produced an overall reduction in net hypothalamic uptake, with surviving neuronal elements exhibiting an increased uptake which may reflect compensatory changes in these nerve terminals. MSG may this disrupt pituitary and intrahypothalamic functions via its effects on neuronal systems of the AN.

Animals↗
PubMed1981

Behavioral and neurochemical effects of neonatal administration of monosodium L-glutamate in mice.

Feeding behavior, activity level, and thermoregulatory ability of mice made obese by neonatal administration of monosodium L-glutamate (MSG) were studied. The degree of obesity and other characteristics of the syndrome were found to depend on age, diet, and housing condition. Carcass fat determinations demonstrated the presence of obesity in all MSG animals; however, body weight was elevated over control levels only in adult mice caged in groups. Group-housed MSG animals also failed to increase food intake in response to food deprivation and were both hypoactive and hypothermic. INdividually caged MSG mice showed normal activity levels and body temperature, an attenuated response to food deprivation, and an enhanced response to a high-fat diet. Since MSG obesity may be the consequence of damage to the dopamine-rich arcuate nucleus of the hypothalamus, a second goal of the study was to measure central catecholamines and examined any changes in the MSG animal's behavioral responses to catecholaminergic drugs. Animals treated with MSG sustained some loss of hypothalamic dopamine, but no systematic relation between central catecholamines and behavioral aspects of the syndrome could be discerned.

Animals↗
PubMed1980

Depletion of central catecholamines alters amphetamine- and fenfluramine-induced taste aversions in the rat.

Conditioned taste aversions induced by pairing the consumption of saccharin with an amphetamine injection are attenuated in rats with depletion of central catecholamines caused by intraventricular administration of 6-hydroxydopamine (6-OHDA). The hypothesis that dopamine (DA) depletion is responsible for this effect was tested. The reduction in conditioning caused by intraventricular 6-OHDA could not be duplicated either with injections of 6-OHDA into the substantia nigra (Experiment 1) or with intraventricular 6-OHDA injections in animals pretreated with desmethylimipramine (Experiment 2). Both treatments, however, produced large depletions of telencephalic DA. 6-Hydroxydopa infusions caused a preferential loss of telencephalic norepinephrine (NE) but also failed to alter taste aversion learning. It is concluded that the effect of intraventricular 6-OHDA on amphetamine-induced aversions was the result of depletion of both NE and DA. In a third experiment the generality of the effect was examined by pairing saccharin consumption with injections of the amphetamine congener fenfluramine. Depletion of both NE and DA failed to alter fenfluramine-induced aversions. Infusion of 6-OHDA into the substantia nigra, however, retarded the extinction of such an aversion. Evidence is discussed for a peripheral site of action for fenfluramine in the conditioned aversion paradigm.

Animals↗
PubMed1980

Interrelationships between microbiological and chemical parameters of sandy beach sediments, a summer aspect.

At 12 stations located in sandy beach sediments of the brackish water Kiel Fjord and Kiel Bight (Baltic Sea, FRG), variations and interrelationships of microbiological, chemical, and physicochemical parameters were monitored. Depending upon location, wide variations of a number of parameters reflecting dissolved organic and inorganic nutrients, chlorophyll a, microbial number, and uptake activity of glucose were measured. Whereas most of the parameters generally showed the tendency to decrease from the inner to the outer Kiel Fjord, individual parameters (oxygen, particulate nitrogen, ribose, chlorophyll a, glucose/fructose ratio) increased with increasing distance from the inner Kiel Fjord. Similarities in the local variation pattern demonstrated various relationships between individual parameters. Among those, dissolved organic nutrients on the one hand and inorganic nutrients on the other hand were closely linked together. Variations of organic and inorganic nutrients corresponded to variations of microbial activity and physicochemical parameters. By comparing standing stock carbon with carbon production, a microbial biomass turnover time of about 100 h was calculated. Approximately 50% of the microphytobenthos primary production was fixed by microorganisms. Daily microbial carbon production (43 mg of C per m) was in the range of meiofauna carbon (35 mg of C per m).

Journal Article↗
PubMed1979

Organochlorine insecticides and PCB in the sediments of Lake Huron (1969) and Georgian Bay and North Channel (1973).

Surficial and core sediments were collected from the main body of Lake Huron in 1969 and Georgian Bay and North Channel in 1973. These were analysed for organochlorine insecticides and PCB. Residues of organochlorines were higher in the twelve depositional basins in Lake Huron and Georgian Bay than in sediment in the non-depositional zones. PCB was present at similar concentrations to sigma DDT; with mean levels of 13 and 10 ng/g for PCB and sigma DDT in the main body of Lake Huron and 11 and 5 ng/g for PCB and sibma DDT in Georgian Bay. Residues of PCB varied from 9--33 ng/g in the 12 basins. With respect to sigma DDT, both parent DDT and its two metabolites were present in sediment at a mean residue of 7.8 ng/g for the whole lake. The main lake had residues of 10.2 ng/g while Georgian Bay had 5.8 ng/g and North Channel 4.1 ng/g in keeping with use pattenrs since 1943. HEOD was present in only 5.7% of sediment samples from main Lake Huron, 30% from Georgian Bay and 15% from North Channel. The highest residues 1.7 ng/g occurred in the North Channel. No chlordane was detected, however, heptachlor epoxide was identified in 8.5% of sediments collected in Lake Huron, 23% from Georgian Bay and 14% in North Channel. Endosulfan appeared in 4% of samples from both Georgian Bay and North Channel.

Canada↗
PubMed1979

Evaluation of the non-specific effects of catecholamine and serotonin neurotoxins by injection into the medial forebrain bundle of the rat.

Low doses of 6-hydroxydopamine (6-OHDA), 5,6-dihydroxytryptamine (5,6-DHT) and 5,7-dihydroxytryptamine (5,7-DHT) that have previously been shown to produce behavioral change following intracerebral infusion were injected into the medial forebrain bundle of the rat. This site contains serotonin (5-HT), norepinephrine (NE), and dopamine (DA) fibers whose anatomical locations have been described. Damage to these fiber systems was quantified by measuring depletion of telencephalic 5-HT, NE and DA. The effects of infusions of 6-OHDA, 5,6-DHT and 5,7-DHT were compared to the effects of unequivocally non-specific electrolytic lesions and copper sulfate infusions. Survival time was varied to evaluate the amount of regeneration that could be expected over periods from 8 to 60 days. Amine levels were found to be stable over the time period examined. With the doses used, evidence was found to support the position that non-specific damage caused by general cytotoxic effects of 6-OHDA and 5,7-DHT is minimized sufficiently to permit the acquisition of useful data on the function of central catecholamine and indoleamine systems.

5,6-Dihydroxytryptamine↗
PubMed1979

Effects of goldthioglucose lesions on central catecholamine levels in the mouse.

Male and female C57 B1/6J mice were injected with goldthioglucose (GTG) to induce an obesity syndrome. Significant increases in body weight were inversely correlated with pituitary dopamine (DA) levels. Significant reductions in hypothalamic norepinephrine (NE) and DA were also noted; however, these reductions did not appear to be related to body weight gain. The GTG injections did not produce any significant alterations in telencephalic NE or DA. The damage to catecholamine neurons is discussed in relation to the endocrine abnormalities of the GTG mouse and some current hypotheses on the control of food intake.

Animals↗